From 34cac6ea59f20b08cb9f74cd9b2d1f304e209659 Mon Sep 17 00:00:00 2001 From: James Briggs Date: Fri, 20 May 2022 10:51:18 +0200 Subject: [PATCH] adding final content/tweaks from Cohere + Pinecone demo --- .../03_filtering.ipynb | 345 - .../README.md | 2 +- .../askscience.tsv | 22929 ++++++++++++++++ 3 files changed, 22930 insertions(+), 346 deletions(-) delete mode 100644 integrations/cohere/webinar_classification_and_search/03_filtering.ipynb create mode 100644 integrations/cohere/webinar_classification_and_search/askscience.tsv diff --git a/integrations/cohere/webinar_classification_and_search/03_filtering.ipynb b/integrations/cohere/webinar_classification_and_search/03_filtering.ipynb deleted file mode 100644 index cff4d02..0000000 --- a/integrations/cohere/webinar_classification_and_search/03_filtering.ipynb +++ /dev/null @@ -1,345 +0,0 @@ -{ - "cells": [ - { - "cell_type": "markdown", - "metadata": { - "id": "view-in-github", - "colab_type": "text" - }, - "source": [ - "\"Open" - ] - }, - { - "cell_type": "markdown", - "source": [ - "# Searching and Filtering" - ], - "metadata": { - "id": "7jef4UKJwpdC" - } - }, - { - "cell_type": "code", - "source": [ - "!pip install cohere pinecone-client" - ], - "metadata": { - "colab": { - "base_uri": "https://localhost:8080/" - }, - "id": "Qia-LzrBwpvB", - "outputId": "dd0b612d-5c58-40ac-d172-69201d6a7407" - }, - "execution_count": 1, - "outputs": [ - { - "output_type": "stream", - "name": "stdout", - "text": [ - "Collecting cohere\n", - " Downloading cohere-1.3.9-cp37-cp37m-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (18.0 MB)\n", - "\u001b[K |████████████████████████████████| 18.0 MB 180 kB/s \n", - "\u001b[?25hCollecting pinecone-client\n", - " Downloading pinecone_client-2.0.10-py3-none-any.whl (159 kB)\n", - "\u001b[K |████████████████████████████████| 159 kB 58.5 MB/s \n", - "\u001b[?25hRequirement already satisfied: requests in /usr/local/lib/python3.7/dist-packages (from cohere) (2.23.0)\n", - "Collecting pyyaml>=5.4\n", - " Downloading PyYAML-6.0-cp37-cp37m-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl (596 kB)\n", - "\u001b[K |████████████████████████████████| 596 kB 36.8 MB/s \n", - "\u001b[?25hRequirement already satisfied: urllib3>=1.21.1 in /usr/local/lib/python3.7/dist-packages (from pinecone-client) (1.24.3)\n", - "Collecting loguru>=0.5.0\n", - " Downloading loguru-0.6.0-py3-none-any.whl (58 kB)\n", - "\u001b[K |████████████████████████████████| 58 kB 6.3 MB/s \n", - "\u001b[?25hRequirement already satisfied: python-dateutil>=2.5.3 in /usr/local/lib/python3.7/dist-packages (from pinecone-client) (2.8.2)\n", - "Collecting dnspython>=2.0.0\n", - " Downloading dnspython-2.2.1-py3-none-any.whl (269 kB)\n", - "\u001b[K |████████████████████████████████| 269 kB 37.2 MB/s \n", - "\u001b[?25hRequirement already satisfied: typing-extensions>=3.7.4 in /usr/local/lib/python3.7/dist-packages (from pinecone-client) (4.2.0)\n", - "Requirement already satisfied: six>=1.5 in /usr/local/lib/python3.7/dist-packages (from python-dateutil>=2.5.3->pinecone-client) (1.15.0)\n", - "Requirement already satisfied: idna<3,>=2.5 in /usr/local/lib/python3.7/dist-packages (from requests->cohere) (2.10)\n", - "Requirement already satisfied: certifi>=2017.4.17 in /usr/local/lib/python3.7/dist-packages (from requests->cohere) (2021.10.8)\n", - "Requirement already satisfied: chardet<4,>=3.0.2 in /usr/local/lib/python3.7/dist-packages (from requests->cohere) (3.0.4)\n", - "Installing collected packages: pyyaml, loguru, dnspython, pinecone-client, cohere\n", - " Attempting uninstall: pyyaml\n", - " Found existing installation: PyYAML 3.13\n", - " Uninstalling PyYAML-3.13:\n", - " Successfully uninstalled PyYAML-3.13\n", - "Successfully installed cohere-1.3.9 dnspython-2.2.1 loguru-0.6.0 pinecone-client-2.0.10 pyyaml-6.0\n" - ] - } - ] - }, - { - "cell_type": "markdown", - "metadata": { - "id": "uQomGiK3wDbJ" - }, - "source": [ - "\n", - "\n", - "Taking our search one step further, we can add filtering to specify our search scope, while still maintaining fast search times using Pinecone's single stage filtering.\n", - "\n", - "We can start by initializing Cohere + Pinecone." - ] - }, - { - "cell_type": "code", - "execution_count": 2, - "metadata": { - "id": "29JYnPS0wDbM" - }, - "outputs": [], - "source": [ - "COHERE_KEY = \"<>\"\n", - "PINECONE_KEY = \"<>\" # app.pinecone.io" - ] - }, - { - "cell_type": "code", - "execution_count": 3, - "metadata": { - "id": "XK1E7xhdwDbN" - }, - "outputs": [], - "source": [ - "import cohere\n", - "import pinecone\n", - "\n", - "co = cohere.Client(COHERE_KEY)\n", - "\n", - "pinecone.init(PINECONE_KEY, environment='us-west1-gcp')\n", - "\n", - "index_name = 'cohere-pinecone-askscience'\n", - "# connect to index\n", - "index = pinecone.Index(index_name)" - ] - }, - { - "cell_type": "markdown", - "metadata": { - "id": "VgXYr2RKwDbN" - }, - "source": [ - "For the filters we will use *four* categories, each of which includes many flairs used by users in **r/askscience**." - ] - }, - { - "cell_type": "code", - "execution_count": 4, - "metadata": { - "id": "y7XktfVpwDbN" - }, - "outputs": [], - "source": [ - "all_tags = ['Physics', 'Biology', 'Engineering', 'Unknown', 'Earth Sciences',\n", - " 'Astronomy', 'Anthropology', 'Human Body', 'Social Science',\n", - " 'Medicine', 'Computing', 'Psychology', 'Chemistry', 'Linguistics',\n", - " 'Mathematics', 'Planetary Sci.', 'Neuroscience', 'Paleontology',\n", - " 'COVID-19', 'Archaeology', 'Earth Sciences and Biology', 'Meta',\n", - " 'Economics', 'CERN AMA', 'Dog Cognition AMA',\n", - " 'Cancer Treatment AMA', 'Psychology AMA', 'Archaeology AMA',\n", - " 'Alzheimer’s disease AMA', 'Oceanography AMA', 'Biology AMA',\n", - " 'Biology/Agriculture', 'Neuroscience AMA', 'Climate History AMA',\n", - " 'Climate Science AMA', 'Food Safety AMA', 'Ecology and Evolution']\n", - "\n", - "chats = {\n", - " \"#general\": all_tags,\n", - " \"#medical\": [\n", - " 'Human Body', 'Medicine', 'COVID-19', 'Cancer Treatment AMA', 'Food Safety AMA'\n", - " ],\n", - " \"#natural-sciences\": [\n", - " 'Physics', 'Biology', 'Earth Sciences', 'Astronomy', 'Anthropology'\n", - " 'Human Body', 'Chemistry', 'Mathematics', 'Planetry Sci.', 'Neuroscience',\n", - " 'Earth Sciences and Biology', 'CERN AMA', 'Oceanography AMA',\n", - " 'Biology AMA', 'Biology/Argiculture', 'Neuroscience AMA', 'Climate History AMA',\n", - " 'Climate Science AMA', 'Ecology and Evolution'\n", - " ],\n", - " \"#social-sciences\": [\n", - " 'Anthropology', 'Social Science', 'Psychology', 'Linguistics', 'Economics',\n", - " 'Psychology AMA'\n", - " ]\n", - "}" - ] - }, - { - "cell_type": "code", - "execution_count": 5, - "metadata": { - "colab": { - "base_uri": "https://localhost:8080/" - }, - "id": "zWyxkxZKwDbO", - "outputId": "0d60b392-1d38-425e-80f8-ae661544078b" - }, - "outputs": [ - { - "output_type": "stream", - "name": "stdout", - "text": [ - "0.48: Are there any positive effects of climate change? (Earth Sciences)\n", - "0.42: AskScience AMA Series: We mapped human transformation of Earth over the past 10,000 years and the results will surprise you! Ask us anything! (Unknown)\n", - "0.36: Has human society and culture fundamentally altered our own biological evolution? (Ecology and Evolution)\n", - "0.36: What environmental impacts would a border wall between the United States and Mexico cause? (Earth Sciences)\n", - "0.36: How different was this world ecologically, about 2000 to 2500 yrs ago? (Earth Sciences)\n" - ] - } - ], - "source": [ - "query = \"what are the effects of the anthropocene?\"\n", - "\n", - "# create embedding with cohere\n", - "xq = co.embed(\n", - " texts=[query],\n", - " model='large',\n", - " truncate='LEFT'\n", - ").embeddings\n", - "\n", - "# query, returning the top 5 most similar results\n", - "res = index.query(xq, top_k=5, include_metadata=True)\n", - "\n", - "for match in res['results'][0]['matches']:\n", - " print(f\"{match['score']:.2f}: {match['metadata']['title']} ({match['metadata']['link_flair_text']})\")" - ] - }, - { - "cell_type": "markdown", - "metadata": { - "id": "tu9MmgYzwDbP" - }, - "source": [ - "Naturally there's some overlap between topics (and this example may be pretty inaccurate), but these will build the filters we will use.\n", - "\n", - "Filtering in Pinecone is pretty simple, we pass our conditions to the `filter` parameter using operators like equal to `$eq`, in `$in`, greater than `$gt`, etc. So if we want to return `Paleontology` specific results we can like so:" - ] - }, - { - "cell_type": "code", - "execution_count": 7, - "metadata": { - "colab": { - "base_uri": "https://localhost:8080/" - }, - "id": "fDv2PR_9wDbS", - "outputId": "74cec566-f64e-4767-96ce-6c1b28b23a4a" - }, - "outputs": [ - { - "output_type": "stream", - "name": "stdout", - "text": [ - "0.25: What exactly would the landscape of the British Isles have looked like prior to human cultivation? (Paleontology)\n", - "0.17: AskScience AMA Series: I am paleontologist Hans Sues, I study late Paleozoic and Mesozoic vertebrates. Ask Me Anything! (Paleontology)\n", - "0.16: Given the way the Indian subcontinent was once a very large island, is it possible to find the fossils of coastal animals in the Himalayas? (Paleontology)\n", - "0.15: If I went back to the Cretacious era to go fishing, what would I catch? How big would they be? What eon would be most interesting to fish in? (Paleontology)\n", - "0.13: We are paleontologists who study fossils from an incredible site in Texas called the Arlington Archosaur Site. Ask us anything! (Paleontology)\n" - ] - } - ], - "source": [ - "query = \"what are the effects of the anthropocene?\"\n", - "\n", - "# create embedding with cohere\n", - "xq = co.embed(\n", - " texts=[query],\n", - " model='large',\n", - " truncate='LEFT'\n", - ").embeddings\n", - "\n", - "# then query pinecone w/ a filter\n", - "res = index.query(\n", - " xq, top_k=5, include_metadata=True,\n", - " filter={\n", - " 'link_flair_text': {'$eq': 'Paleontology'}\n", - " })\n", - "\n", - "for match in res['results'][0]['matches']:\n", - " print(f\"{match['score']:.2f}: {match['metadata']['title']} ({match['metadata']['link_flair_text']})\")" - ] - }, - { - "cell_type": "markdown", - "source": [ - "Or as with our demo, we might group flair labels together and use `$in`." - ], - "metadata": { - "id": "kytGzOZDxGHS" - } - }, - { - "cell_type": "code", - "source": [ - "query = \"what are the effects of the anthropocene?\"\n", - "\n", - "# create embedding with cohere\n", - "xq = co.embed(\n", - " texts=[query],\n", - " model='large',\n", - " truncate='LEFT'\n", - ").embeddings\n", - "\n", - "# then query pinecone w/ a filter\n", - "res = index.query(\n", - " xq, top_k=5, include_metadata=True,\n", - " filter={\n", - " 'link_flair_text': {'$in': chats['#social-sciences']}\n", - " })\n", - "\n", - "for match in res['results'][0]['matches']:\n", - " print(f\"{match['score']:.2f}: {match['metadata']['title']} ({match['metadata']['link_flair_text']})\")" - ], - "metadata": { - "colab": { - "base_uri": "https://localhost:8080/" - }, - "id": "ft1YCgctxDNz", - "outputId": "d331409c-a209-45b4-d5a9-2525e61d7835" - }, - "execution_count": 8, - "outputs": [ - { - "output_type": "stream", - "name": "stdout", - "text": [ - "0.23: Why has Europe's population remained relatively constant whereas other continents have shown clear increase? (Social Science)\n", - "0.22: AskScience AMA Series: I’m Stephan Lewandowsky, here with Klaus Oberauer, we will be responding to your questions about the conflict between our brains and our globe: How will we meet the challenges of the 21st century despite our cognitive limitations? AMA! (Psychology)\n", - "0.20: Has the growing % of the population avoiding meat consumption had any impact on meat production? (Anthropology)\n", - "0.20: What will happen to us if the birth replacement rate keeps falling? (Social Science)\n", - "0.19: If modern man came into existence 200k years ago, but modern day societies began about 10k years ago with the discoveries of agriculture and livestock, what the hell where they doing the other 190k years?? (Anthropology)\n" - ] - } - ] - } - ], - "metadata": { - "interpreter": { - "hash": "52a41a0d6b6e16f4b56c5995d2d276cfef8bcc0e6d8203d15fa60c631f3e9c76" - }, - "kernelspec": { - "display_name": "Python 3.8.12 ('streamlit')", - "language": "python", - "name": "python3" - }, - "language_info": { - "codemirror_mode": { - "name": "ipython", - "version": 3 - }, - "file_extension": ".py", - "mimetype": "text/x-python", - "name": "python", - "nbconvert_exporter": "python", - "pygments_lexer": "ipython3", - "version": "3.8.12" - }, - "orig_nbformat": 4, - "colab": { - "name": "03_filtering.ipynb", - "provenance": [], - "collapsed_sections": [], - "include_colab_link": true - } - }, - "nbformat": 4, - "nbformat_minor": 0 -} \ No newline at end of file diff --git a/integrations/cohere/webinar_classification_and_search/README.md b/integrations/cohere/webinar_classification_and_search/README.md index a6d8295..5c388aa 100644 --- a/integrations/cohere/webinar_classification_and_search/README.md +++ b/integrations/cohere/webinar_classification_and_search/README.md @@ -1 +1 @@ -Here are notebooks and data for the Cohere x Pinecone webinar in May 2022. +Here are notebooks and data for the Cohere x Pinecone webinar in May 2022. Find the [demo here](https://share.streamlit.io/pinecone-io/playground/not_slack_chatbot/src/server.py) and for a recording of the workshop [see here](). diff --git a/integrations/cohere/webinar_classification_and_search/askscience.tsv b/integrations/cohere/webinar_classification_and_search/askscience.tsv new file mode 100644 index 0000000..d27bd49 --- /dev/null +++ b/integrations/cohere/webinar_classification_and_search/askscience.tsv @@ -0,0 +1,22929 @@ +Unnamed: 0 title score url body created_utc id link_flair_text time comment_1 comment_2 +899 Stephen Hawking megathread 65836 https://www.reddit.com/r/askscience/comments/84auzr/stephen_hawking_megathread/ 1521003828 84auzr Physics 2018-03-14 8:03:48 Many large threads on reddit are known for containing many jokes which AskScience moderators try to limit in the first place. However, out of respect, we ask that you please do not joke about Stephen Hawking's passing. "Do we know what helped Hawking survive the disease for so long? As far as I know, he was given no more than 2-3 years to live when he was first diagnosed. + +Is there anything we have learned from his case that could eventually lead to a cure? + +  + +(Rest in peace. A Brief History of Time was the book that first sparked my interest in astronomy and physics.)" +600 Do giraffes get struck by lightning more often than other animals? 31843 https://www.reddit.com/r/askscience/comments/627akk/do_giraffes_get_struck_by_lightning_more_often/ 1490801125 627akk Biology 2017-03-29 18:25:25 Thanks for all of the info, guys. I posted this after waking up from a dream in which giraffes were being struck by lightning, of all things. "So this is not my area of expertise and I hope other more qualified people chime in but I have found some informations (some of it even peer reviewed!). + +[This article [1]](https://link.springer.com/article/10.1007/s00484-011-0515-5) talks about how four legged animals are more vulnerable to lightning strikes because ground current has high chances to go through vital organs. It also describes how large animals such as giraffes and elephants have higher chances of deadly strikes. There is the obvious thing about the fact that they are tall so even under a tree there is a non-negligeable chance that lighting could [jump directly to their head](http://i.imgur.com/iYzL85H.png). The other less obvious one is that even if they are not directly hit, the large distance their legs span increased the voltage (and potentially the current) going though them (as described in[ this figure](http://i.imgur.com/JkPWM1K.png)). Sadly the article lacks hard numbers on strike frequency depending on the species. + +This [blog post](http://scienceblogs.com/tetrapodzoology/2009/07/15/mammal-deaths-by-lightning/) seems to suggest that giraffes getting killed by lightning is not that uncommon. + +> Between 1996 and 1999 the Rhino and Lion Reserve near Krugersdorp, South Africa, had two of its three giraffes killed by lightning – the third animal (a juvenile) was also struck but survived. Betsy the giraffe was killed by lightning at Walt Disney World in Florida in 2003 (in front of lots of witnesses). + +... + +> A juvenile giraffe at Louisiana’s Global Wildlife Center, named Dusty, was killed after lightning struck a nearby tree. + +[1] Gomes, Chandima. ""Lightning safety of animals."" International journal of biometeorology 56.6 (2012): 1011-1023." +799 What % of my weight am I actually lifting when doing a push-up? 31671 https://www.reddit.com/r/askscience/comments/78xinz/what_of_my_weight_am_i_actually_lifting_when/ 1509042346 78xinz Physics 2017-10-26 21:25:46 "Your question made me curious and a quick search yielded the study linked below, which looked at exactly this question.^1 The researchers found that the answer depends both on the variant of the exercise as well as the stage of the exercise. For example, in a traditional push-up the number is about 69% in the up position (at the top of the movement) and 75% in the down position (bottom of the movement). + +It's also worth mentioning that the study also looked at a ""modified push-up."" This modification [as shown here](https://i.imgur.com/2PagQIv.png) is essentially just an ~~lazier~~ easier version of the exercise where the knees stay on the floor. Surprisingly (to me at least), even in this simpler version you still lift quite a bit of your body mass (54% in the up position and 62% in the down position). + +edit: I corrected ""going up/down"" to ""up/down position"" to reflect the fact the body was kept stationary when the force was recorded in this study. + +^(**1**) Suprak, et al. **The effect of position on the percentage of body mass supported during traditional and modified push-up variants.** 2011: 25 (2) pp 497-503 *J. Strength Cond. Res.* [Link](https://www.ncbi.nlm.nih.gov/pubmed/20179649)" To measure yourself: Put a bathroom scale under one of your hands while doing a push up. Double the maximum value the scale lists and divide that by your total weight (and multiple by 100) to calculate the percentage. +699 What is the point of using screws with a Phillips head, flathead, allen, hex, etc. instead of just having one universal screw type? 30971 https://www.reddit.com/r/askscience/comments/6dpog2/what_is_the_point_of_using_screws_with_a_phillips/ 1495915189 6dpog2 Engineering 2017-05-27 22:59:49 You've got some good answers here already, but they're all leaving out an important aspect, which is how the screw and screwdriver deal with fouling. Dirt, oil, weld slag, multiple layers of paint, whatever. If you're in an environment where you don't have to worry about that, a complex geometry is fine. But on a factory floor, Phillips or torx can get irreversibly fouled. Allen head screws can be relatively easily cleaned, but the master of this is the shittiest of all screw heads, the flat head. The *only* tool you need to clear the slot of a flat head screw is the screwdriver you're going to use to unscrew it. No other screw type has that ability. "The reason for the different styles is cost and torque. The slotted head screws are cheap and easy to make. But they're completely useless for powered screwdrivers and you can't put much torque on the screw without it either slipping out or stripping the head (and maring the surface of whatever you're screwing). Phillips screws are self-centering, making powered screwdrivers possible. They're somewhat more expensive to produce than slotted-head. They tend to 'cam-out' easily under torque, making it hard to apply much torque. I've heard they were designed that way to prevent overtightning. However, it's not good for exposed fasteners to look stripped. Robertson-head and allen-head fasteners can handle more torque than phillips-head fasteners, but are more expensive. Because the bottom of the hole is flat (unlike the pointed end of the phillips), there's more contact area and so it's less likely to cam-out. The robertson-head is cheaper than the allen-head, but the allen-head has six points of contact rather than 4, making it less prone to rounding out the hole. The Torx-head fasteners solve the problem of rounding/stripping by having the flat bottom of the robertson/allen that reduces cam-out, but it has much better contact with the driving bit to prevent stripping the head. The points of the 'star' on the driving bit engage the recesses on the screw at nearly right angles, so it has a very positive contact. Torx is becoming more and more popular because of that, particularly in assembly-line work. Because they're less likely than a phillips to be damaged when tightening, the allen (internal hex) heads are often used for exposed ('decorative') fasteners on 'some assembly required' furniture. It's also very cheap to make the allen keys, so they usually include one with the fasteners. +" +800 If hand sanitizer kills 99.99% of germs, then won't the surviving 0.01% make hand sanitizer resistant strains? 28019 https://www.reddit.com/r/askscience/comments/75p8dn/if_hand_sanitizer_kills_9999_of_germs_then_wont/ 1507730421 75p8dn Biology 2017-10-11 17:00:21 Most hand sanitizers use alcohol, which kills indiscriminately. It would kill us if we didn't have livers to filter it, and in high enough doses will kill anyway. Some germs survive due to randomly being out of contact, in nooks and crannies and such, not due to any mechanism that might be selected for. "Sanitizers almost always use alcohol, which bacterial cells don’t really have any cellular means of developing resistance against. You may as well worry about developing resistance to having a nuke dropped directly on your face. Alcohol essentially saps bacterial cells of all moisture instantaneously, and to combat that they would need to develop characteristics which would essentially make them not even bacteria anymore (like a plant-like cell wall or a eukaryote-like complex cell membrane) + +EDIT: I got a few things wrong, thanks for pointing them out everyone! (no sarcasm intended). + +- Alcohol doesn’t work mainly by sapping moisture, it actually causes the bacterial cell membrane (and eukaryotic cell membranes also) to basically dissolve. We can put it on our hands because of our epidermal outer layer of already-dead cells which basically doesn’t give a fuck about alcohol. + +- Some bacteria actually can develop resistance to low to moderate concentrations of alcohol, by devoting more resources to a thickened cell membrane. + +- Look up bacterial endospores. These can survive highly concentrated alcohol solutions and cause surfaces to be re-colonized under the right conditions." +999 "Why do we have to ""fall"" asleep? Why can't we just decide to be asleep?" 27014 https://www.reddit.com/r/askscience/comments/8zlzuy/why_do_we_have_to_fall_asleep_why_cant_we_just/ 1531840647 8zlzuy 2018-07-17 18:17:27 "This post has attracted a large number of personal and medical anecdotes as well as request for medical advice. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." "Sleeping literally changes our very physiology. Our core body temperature drops which allows certain proteins to work differently than they do during our ""waking temp,"" as a broad example. It's not something we'd want easy control over. + +Most importantly the process of getting sleepy is highly regulated by not only our Circadian rhythm but also by other hormone systems. + +We need to burn energy to feel fatigued (when we use ATP and make Adenosine as a byproduct, which signals fatigue in humans). + +We need a lack of blue-wavelength light to initiate the process of releasing melatonin at night, which makes us sleepy and helps initiate the sleeping-end of our Circadian processes. + +We don't have voluntary control over sleep because it's chemically regulated. Adenosine, melatonin, hypercretin (Orexin), etc.. + +It's not something we can flex like a muscle. It's essentially hormonal in nature and therefore requires us to use drugs (meaning ligands that bind to targets in our body) to control it. + +" +700 "Does the size of a creature, or the size of its eye, affect what can be seen by the ""naked eye""? for example, can ants see things we consider microscopic? are ants microscopic to elephants?" 27010 https://www.reddit.com/r/askscience/comments/6idvam/does_the_size_of_a_creature_or_the_size_of_its/ 1497963652 6idvam Biology 2017-06-20 16:00:52 "in terms of optics and photoreceptor density, which are the principal factors in a creature's visual resolution (""details per degree of visual angle""), there probably isn't much real difference between the *angular* visual resolution of e.g. a jumping spider and a house cat - both can see, at best, about ~10 details per degree. so if you shrank a cat down to spider size (or vice versa), they'd both have similar limits to the smallest things they could see. + +but since they're different sizes, the sizes of the things they can see will also scale; since the eye is getting smaller, its ~~*near point*~~ (i think i meant 'depth of field' here) is getting proportionally shorter. so if a jumping spider's eye is a thousand times smaller than a cat's eye, it can potentially resolve details that are a thousand times smaller than what a cat's can resolve. a cat can never get optically close enough to a grain of sand to make it a degree wide, so that it could see 'ten details' on its surface, while this optical distance is easily available to the spider. + +the caveat to this general scalability of vision is in the ""noisiness"" of light, i.e. factors like diffraction (limitation in how small of a point can be focused) or chromatic aberration (the difference in focal distance for different light wavelengths) - for a big eye with a big pupil, this noisiness is insignificant, but for a spider's eye it is getting significant, since all of us are looking at more-or-less the same light bandwidth. jumping spiders, for example, deal with this by having retinas at different focal depths to try to account for chromatic aberration. + +but this stuff gets complicated, especially considering that the range in optical quality and photoreceptor density across species washes out most of these limitations. i think you could safely suppose that, in the range of terrestrial creature sizes, vision basically scales with size. + +*edit* the important thing is that things scale, but my concepts are confused re ""near point"" etc, see /u/craigdubyah for better/more detailed info--- + +*edit edit* sorry i didn't keep up with this, was busy all day; but let me excuse the rough edges of my answer by saying it was a lot of well-informed hand waving and of course i didn't try to go into detail about diffraction and lens power and etc etc; i just wanted to get the basic gist across that vision should more-or-less scale with the size of the eye, receptor sampling being equal (as in the cat/spider comparison). field of view, pupil sizes, etc, all very important but another time and place, ok?" "Okay, so in terms of physical optics, and not taking into account the limits of biology, a smaller aperture means less resolution. There are simply not as many photons coming in to tell you about the world, and there are limits to how far a given aperture size can zoom in before diffraction starts to make things blurry. + +Optically speaking, an ant would have lower limits on its visual acuity than an elephant. + +Biologically speaking, since we can't focus at arbitrarily close distances, ants would be able to see small things better, and elephants could probably only see ants in small groups, the same way we can see groups of blood cells, but not individual ones. + +The pinhole effect mentioned elsewhere is only relevant to the lens of the eye, it's the aperture that determines maximum angular resolution, and the retina that determines how much of that resolution a creature can make use of." +900 Do heavily forested regions of the world like the eastern United States experience a noticeable difference in oxygen levels/air quality during the winter months when the trees lose all of their leaves? 26417 https://www.reddit.com/r/askscience/comments/7xvk9r/do_heavily_forested_regions_of_the_world_like_the/ 1518747060 7xvk9r Earth Sciences 2018-02-16 5:11:00 "Yes. [Here](https://m.youtube.com/watch?v=x1SgmFa0r04) is an excellent map showing accurately modeled atmospheric levels of CO2 from satellite and ground measurements taken during a year, for example. You can easily see humans emitting it, and then forested regions sucking it up. Unless it’s winter in that hemisphere, in which case it just swirls around until spring. Other gas levels show similar seasonal patterns. + +(Edit: changed to specify that it is a model based on continuous samples. They obviously can’t sample the entire atmosphere at once every day. And CO2 isn’t bright red. Among other points people apparently felt necessary to clarify.) + +(Edit again: wow, I was not really expecting so much karma and a double-gold for this. The question just reminded me of this cool map I once saw. I bet it's even a repost!)" "According to *Measuring Metabolic Rates* by Dr. John RB Lighton, atmospheric levels of oxygen are incredibly stable worldwide at 20.94%. That is all locations, all altitudes and all year. + +Of course barometric pressure will play a role due to Dalton’s Law of Partial Pressures, but when compensated for you’ll get such a stable reading that you can calibrate a sensor against it. + +The only time oxygen is much different is when measuring essentially exhaled breath. But if you get outside a confined space and away from creatures, you’re at 20.94%. " +1395 Why do nearsighted people need a prescription and a $300 pair of glasses, while farsighted people can buy their glasses at the dollar store? 25754 https://www.reddit.com/r/askscience/comments/d26nwr/why_do_nearsighted_people_need_a_prescription_and/ 1568117527 d26nwr 2019-09-10 15:12:07 "Because the dollar store readers are not made to correct hyperopia (“farsightedness”); they are made to correct presbyopia (the loss of focusing flexibility that hits all of us in our early 40s). Presbyopia occurs in all of us in a relatively equal way, so making a standardized power for presbyopia is easy. + +Basically, the cheater readers are making the assumption that the wearer has perfect distance vision, and simply brings the focal point forward to a comfortable reading distance. + +Now, plus power lenses that correct for presbyopia also happen to help with hyperopia. However, unless your hyperopia just coincidentally happens to be equal between your eyes, free of astigmatism, and of a small enough amount, the readers are only partially correcting it. It may be better than nothing, or even good enough for practical use in many cases, but they do not usually fully or adequately correct the hyperope’s vision. + +As far as myopia (“nearsightedness”) goes, its generally too unique to the individual to standardize in a “drug store reader” kind of way. Plus if people are self-diagnosing/correcting myopia, they almost always tend to overcorrect it, making them prone to eyestrain, headaches, and if they are young enough, a worsening of their prescription. In fact a huge part of the refraction procedure (“one or two?”) is making sure the patient hasn’t overcorrected themselves. + +Source: I’m an optometrist" "Nearsightedness needs to be corrected precisely so that objects at infinity are in focus. Each eye may need a different correction and there may be astigmatism as well. Farsightedness just needs to be corrected for a comfortable reading distance. A limited analogy is that it is like buying and using magnifying glass vs a camera or projector lens. + +Edit: An optometrist's explanation is here + +https://www.reddit.com/r/askscience/comments/d26nwr/why_do_nearsighted_people_need_a_prescription_and/ezt656x/" +901 For humans, sea water is not drinkable due to its high salt content. How do whales, manatees, seals, and other sea faring mammals stay hydrated? 23316 https://www.reddit.com/r/askscience/comments/7nuedz/for_humans_sea_water_is_not_drinkable_due_to_its/ 1514983322 7nuedz Biology 2018-01-03 15:42:02 "The short answer is: + +A. They get water from their food, and avoid salty food + +B. They may have modification to their kidneys to allow them to excrete more salt + +C. There a lot we don't know, marine animals are hard to study + + + +[Source and more details](https://www.scientificamerican.com/article/how-can-sea-mammals-drink/)" "I have not seen a very comprehensive answer here, so allow me to copy from ""Marine Mammals Evolutionary Biology"" by Annalisa Berta et al. I worked closely with her and she is one of the foremost experts on evolution and systematics of marine mammals. I will add personal clarifying results in [brackets]. + +>Most marine mammals are hypoosmotic; their body fluids have a lower ionic [salt] content than their surrounding seawater environment, and they are constantly losing some water to the hyperosmotic seawater in which they live. + +>Marine mammals obtain the water they need from the food they eat: preformed water in their diet [as previously mentioned in this thread] and subsequent metabolically derived water [not previously mentioned]. Most fish and invertebrate prey consists of 60-80% water, and the metabolism of fat, protein, and carbohydrates provide metabolic water during the digestion of food. It has been shown experimentally that seals [also referred to as phocids] can obtain all the water they need from the food they eat. If seawater is given to seals, the stomach becomes upset and the excess salts have to be eliminated using body water. + +>Despite this, seals occupying warm climates have been observed drinking seawater (King, 1983), a practice called mariposia. It has been suggested that intermittently consume small amounts of seawater at intervals that would not be enough to cause digestive problems, but would be sufficient for facilitating nitrogen excretion [peeing]. Mariposia is especially common among adult male otariids [sea lions and fur seals] (Riedman, 1990) + +>Why do pinnipeds [seals, sea lions, fur seals, and walruses] drink seawater? Gentry (1981) noted that most of the otariids observed ingesting seawater live in warmer climate and lose water by urination, panting, and sweating. He suggested such water loss , along with prolonged fasting by territorial males, may be severe enough to promote the drinking of seawater. The behavior may play a role in nitrogen excretion by supplementing water produced oxidatively from metabolized fat reserves. Mariposia has also been reported for Atlantic bottlenose dolphins, common dolphins, and harbor porpoises. +I'm getting tired of typing, but theres about one more page to go. I'll type it up if anyone wants to read more + + +TL;DR +1. Eat high water content food +2. Metabolically produce water from digestion and fat reserves +3. Kidneys stronger than desert animals" +1396 If we return to the moon, is there a telescope on earth today strong enough to watch astronauts walking around on the surface? 23035 https://www.reddit.com/r/askscience/comments/d7qi0y/if_we_return_to_the_moon_is_there_a_telescope_on/ 1569159378 d7qi0y Astronomy 2019-09-22 16:36:18 "No, I don't think any telescope could come close. + +For instance, Hubble has an angular resolution of about 1/10 of an arcsecond. It is approximately 384,000km from the moon. 1/10 arcsecond is 1/36000 of a degree, and a circle is 360 degrees. + +1/10 arcsecond on a circle with radius 384000 km is: + +2 * 384000 * pi / 360 / 36000 = 0.18617 + +So the resolution of Hubble would be 186m, much too large to make out a single human. To achieve the sub-1m resolution needed to discern a person on the moon, a telescope would need a resolution over 100 times better, which does not exist." "I'm an astrophysicist, and I believe the answer is: ~~yes~~ maybe. + +First we need to calculate the angular size of a \~2 meter astronaut on the moon. We can do this easily on [Wolfram Alpha](https://www.wolframalpha.com/input/?i=%28%282+meters%29+%2F+%28distance+to+the+moon%29%29+radians+to+milliarcseconds): we find that the astronaut is about 1.04 milliarcseconds. + +As other users have pointed out, no single telescope is large enough to have this kind of angular resolution. Hubble is about a 100x too small. Typically, to resolve an object, you need the resolution to be at most half of the object's size. So you'd need a resolution of < 0.5 milliarcseconds. + +But you don't need a telescope 100x bigger than Hubble to have 100x Hubble's resolution. An interferometer is an array of telescopes that have the light-gathering power of their total mirror areas, but the effective angular resolution is determined by their most-separated elements. + +The most powerful optical interferometer in the world is the [CHARA array](http://www.chara.gsu.edu/public/instrumentation/31-the-chara-array), located on Mt. Wilson. It's a series of six, 1-meter telescopes that are about 330 meters apart (at longest separation). This means it has the resolution of a 330 meter telescope! CHARA has an angular resolution of 0.2 milliarcseconds, which should be plenty to detect our astronauts. + +UPDATE (7 hours later): Someone asked a question that led me to think of an obvious concern: while the astronaut be bright enough to be visible by a small telescope array like CHARA? + +The moon reflects [\~12% of the light](https://www.universetoday.com/19981/moon-albedo/) that hits it. Let's assume an astronaut is wearing a classic white spacesuit. That reflects [\~80% of the light](https://space.stackexchange.com/questions/29901/why-were-eva-suits-never-silver) that hits it. Let's say then, that for equal angular sizes, astronauts are 6x brighter than the moon's surface. The moon has a surface brightness of [\~4](https://www.ee.ryerson.ca/~phiscock/astronomy/light-pollution/moon-brightness.pdf) [mag](https://en.wikipedia.org/wiki/Apparent_magnitude)/arcsecond^(2). If an astronaut has an angular size of \~1 mas, then let's say they have a solid angle of \~1 mas^(2). Then they are [6 x 1 mas^(2) / 1 arcsecond^(2) = 6E-6](https://www.wolframalpha.com/input/?i=6+*+%281+square+milliarcsecond+%2F+1+square+arcsecond%29+) times fainter than a square arcsecond of the moon. Which means their apparent magnitude is \~[13](https://www.vcalc.com/wiki/sspickle/Difference+in+magnitudes+from+Flux+Ratio)\+4 = 17. + +What sort of exposure time is needed to see a 17th mag object? Well, on the [Kitt Peak National Observatory 0.9 m telescope](https://www.noao.edu/gateway/ccdtime/), it looks like to get a signal-to-noise ratio of 10, we need a an exposure time of 0.7 seconds. But CHARA has 6 telescopes that are a bit bigger at 1.0 meters, so lets call this (0.7/6) \* (1.0/0.9)\^2 = \~0.1 seconds. But I'm going to assume that optical interferometry is more lossy than a simple imager, like in the KPNO example. So let's just arbitrarily bump this up to 0.2 seconds. + +I'm not certain what sort of exposure time is necessary for a ground-based telescope like CHARA to work well is. But their [user's manual has an example](http://chara.gsu.edu/wiki/doku.php?id=chara:pavo_user_manual&s[]=exposure) where they use an exposure time of 8 ms. Now, is this fast exposure time needed in order to be smaller than the timescale of atmospheric variations? If so, then it's hopeless for our astronaut project. + +But, if it's instead the case that CHARA had a rapid exposure time in this example because their target is very bright, then we may still be in business. CHARA might be observing bright targets because they are **big** (because they are close, which is also why they are bright), rather than because they can only see bright things. In this case, CHARA could afford to take slightly longer exposure times of \~0.2 seconds for our astronaut, even if that's a bit slower than the atmospheric coherence timescale (which is usually taken to be 0.01 to 0.1 seconds or so, depending on lots of stuff). + +So, because I don't know CHARA's upper limit for exposure time (if there is one), I must offer an unsatisfying conclusion of ""Maybe."" + +EDIT: had the wrong link for CHARA initially. Fixed now." +701 The recent fire in London was traced to an electrical fault in a fridge freezer. How can you trace with such accuracy what was the single appliance that caused it? 22236 https://www.reddit.com/r/askscience/comments/6j0tg2/the_recent_fire_in_london_was_traced_to_an/ 1498220172 6j0tg2 Physics 2017-06-23 15:16:12 My father is a fire investigator. I asked him the same question. He showed me photos of the last one he determined the cause. All the knobs on the stove were off besides one. It melted obviously being on. The people had left the stove on. They start at the area that has the most fire damage then look for something that isn't how it should be. "In this case, it was easy - the fire was seen when it started, reported, firefighters attended and extinguished the fire in that flat - but not before the fire spread to the outside of the building. The questions to be answered here are engineering ones - why a cladding material that would have been designed and tested as safe proved to be so unsafe in practice. + +But even in less obvious cases, the source of the ignition is often obvious. When ignition happens, there is lots of oxygen there, so things burn completely. When the fire gets going, there's less oxygen available, so things burn partially. Fire generally burns up - so the source of a fire is often the only thing on the floor that is badly burned. + +Edit: Lots of good replies to my comment - including some fire investigators that state that the source of the fire is usually less combusted than the surroundings, as they burn cooler before the fire gets going." +902 Why do we use pillows now when we sleep? Did we need this during the prehistoric/ancient age? What changed? 21978 https://www.reddit.com/r/askscience/comments/85kaz5/why_do_we_use_pillows_now_when_we_sleep_did_we/ 1521473220 85kaz5 Anthropology 2018-03-19 18:27:00 "The answer, as far as I can tell, is that we don’t know for certain. What we know about the development of pillows and bedding, however, suggests a few options. + +I found this site which details the history of the pillow. + +http://hankeringforhistory.com/pillows-throughout-the-ages-guest-post/ + +The oldest known pillows date back around 9,000 years and are made of carved stone. The shape suggests suggests an attempt at providing comfort...a smooth surface is much better for laying your head on, after all, than a rough one. It’s also been suggested by historians that pillows like this protected people from bugs. It’s possible, therefore, that cavemen used nearby rocks to keep their heads elevated. + + +This is not, however, the oldest known bedding. That dates back 77,000 years and consists of compressed grass, leaves, and plant stems found at archaeological site called the Sidubu Cave. Interestingly, the specific plants they found in the bedding served as natural insecticides, suggesting that protection from bugs was at the front of mind due cavemen as it was for ancient Egyptians. It’s possible a mound of this material was used on top of the bedding as a makeshift pillow. Here is the study. + +http://www.sciencemag.org/news/2011/12/earliest-human-beds-found-south-africa + +Lastly, the Japanese Geisha have used wooden blocks with cushioning on top to serve as a pillow. These blocks allowed them to protect their elaborate hair styles while sleeping. A log or other piece of wood, therefore, is a potential third option for cavemen pillows. + +In the case of rocks and pillows, there’s no reason grass and leaves couldn’t have been used as a softer barrier to increase comfort. We wouldn’t know that, however, since such technology wouldn’t necessarily register with archaeologists if it wasn’t shaped or processed on some way such as to distinguish it from other debris. + +Edit: the rocks are no longer imprisoned. TIL proofreading matters. " "Kind of relevant; a really fascinating thing in Nelson Mandela’s biography is when he describes sleeping on a mattress and experiencing pillows for the first time when he was a boy. The way he talks about it is so insane to me because I have always had such luxuries. + +Edit* It’s from his book: A Long walk to freedom + +Can’t be bothered with finding the part where he describes sleeping with pillows but here is a passage that alludes to it + +https://ibb.co/egDt5H +" +801 When a person gets a cut, is it better to wipe off the blood or let the blood coagulate to protect the cut? 21143 https://www.reddit.com/r/askscience/comments/7hmh2c/when_a_person_gets_a_cut_is_it_better_to_wipe_off/ 1512439921 7hmh2c Human Body 2017-12-05 5:12:01 This thread have been locked due to the high number of anecdotes and medical advice requests. Some good answers have already been provided. "Hi, medic here! It depends. For the sake of the conversation, I'm going to assume you mean something like a run-of-the-mill, basic cut. You nicked yourself shaving, or your knife slipped a little when you were cutting veggies. Nothing that would require sutures. + +Typically, its best to wash the cut with antibacterial soap (like Dial) and warm water, that probably constitutes ""wiping it away"", but only to get any dirt/nasties out of the cut. You do this because when you DO hold pressure to stop the bleeding, you don't want to keep the trapped nasties in there. So technically, it's better to take a little of column a, a little of column b. After your cut has been wiped clean, put steady pressure on it until it clots, then put a layer of protectant (neosporin or the like) and a bandage/bandaid/gauze over it to help it heal. + +Now, if you're talking about a trauma situation, it's a little different. Say, for example, you're first responding to a motorcycle accident and this dude's calf is just wrecked to hell, blood everywhere, gravel everywhere inside the laceration- your best bet isn't to keep wiping the gash continuously, you need to apply direct pressure first and foremost to stop the bleeding. Wiping it will do nothing and not allow the blood to clot properly. Pop a tourniquet on too. (This includes keeping the nasties and gravel and all, unfortunately, the hospital will properly clean and suture when they arrive. Motorcycle dude has bigger issues than a little dirt and gravel right now.) You don't want to be exsanguinated just because you kept wiping blood. Wiping continuously doesn't really promote clotting factors, nor allows platelets to form to stop the blood. It's why you are always taught ""direct pressure"" any time there is blood leaking from a wound that shouldn't be there. + +TL;DR: when in doubt, keep pressure on it. + +I hope this makes sense and answers your question, I'm on maternity leave, pregnant AF, insomnia and heartburn have kept me up for over a day. (: + +Edit: holy shit RIP inbox, I wake up because my son decided to falcon punch my bladder after I could finally go to sleep (weird sensation from the inside out) and I have 100+ comments, replies, and messages. Obligatory thank you for the gold! Now, a few clarity points: + +For my first basic scenario, I used a common example of what might happen at home/what people have at home to use. Water and really any kind of soap is fine, Dial soap is just what I've been taught to use if I have it, and many of my colleagues do too. (I HATE it though, but I'm also allergic to a lot of other cleansing agents and have to stick with it.) Personally, I don't think water temperature is a difference/makes a difference in the basic cut situation. I cut myself in the shower shaving the other day (big 'ol 32w pregnant belly over here) and I just let it run in the shower, cleaned with soap, but it didn't clot until after I got out and put pressure. EVERY PERSON'S CLOTTING FACTOR IS DIFFERENT, your mileage may vary from others. It takes me 20 minutes to stop a simple little cut like that, whereas my husband just washes and slaps a bandaid on it and forgets about it in three minutes. + +On using alcohol/sticking your finger in your mouth- as long as it's rubbing alcohol or peroxide, I don't see why you couldn't dab a bit on. We carry it in the ambulance in situations like this. (Since we don't exactly have a sink with soap and water.) If the drinking alcohol (high proof) you want to use is fresh/unopened, or ensure that nobody has drank from the bottle directly. I've never used drinking alcohol as a sanitizer, so I couldn't tell you. As for sticking your finger or cut in your mouth- I'm completely guilty of doing this too, but just keep in mind that human mouths are NASTY AF! We treat human bites wayyyy more aggressively than dog or animal bites (save for snakes, because venom). Human mouths are just... filthy. I learned how gross our mouths are and made a conscious effort to stop sticking my cut up hands/arms in my mouth. Google some human bites, and look at when they get infected. They aren't pleasant. After seeing some in the field and looking at the infections they harbor, I wouldn't ever consciously do it again- but I mean, you do you. Like I said, I'm guilty of it too, and I think it's a bit of a reflex if I'm honest. (So many people do it!) I'm too tired to do any link adding, so if someone wants to add it, I'll put it here. (: + +ON TOURNIQUETS: + +A little background for those that don't know me: before I got off the truck due to my little parasite I have affectionately decided to raise, I work in a huge metropolitan area with a combo critical care/911 system. I'm mainly on the CCT (critical care transport) side, meaning we transferred people from hospital to hospital, higher level of care, etc. Got to see some gnarly stuff. We also backflowed our 911 areas when they got busy, so I've seen some crap there too. + +Tourniquets are coming back into the mainstream. Using a tourniquet is simple, easy, and (in my opinion) should be part of a public safety course/first aid/CPR for civilians. You have HOURS (if tourniquet applied correctly) before you risk ANY harm to the limb. (And remember! Life > limb, regardless. So that argument is out.) + +You do not need to loosen it every fifteen minutes. That's the exact opposite of what you're trying to do. You do need to check for pulses in the extremity very frequently- if you feel one, readjust till there isn't one. Double tourniquets are a thing, I've had to do it on people before. You are restricting blood flow. A pulse means that the person has blood flow and they will continue to bleed out. Once you apply it, hospital staff need to be the ones removing it, not you. In my trauma scenario, I pictured a free flowing bloody calf that got ripped to shreds by a gravel road and is squirting blood that you can't stop with direct pressure alone. (Guess I should've said femoral, I wasn't thinking straight. Either way.) Put the tourniquet on the femoral artery, as high as you can, and cinch it tight. If that doesn't help, double tourniquet it. + +Tourniquets are a very underrated emergency medical device, in my opinion. We carry several on the ambulance. They're good use for GSWs, deep cuts, lacerations, arterial bleeding from pretty much anywhere. It's easier to remove a tourniquet than remove a limb. We might use them more than you think. Open fractures that are bleeding and you can't put pressure on because bone is protruding, etc. They're very useful and can be used for several situations. + +Another local EMS company near me actually does civilian first aid training, and they are doing a good job in removing public stigma around tourniquets in our huge metropolitan area. ""Stop the Bleed!"" is really great too. + +As for in-field debridement: if I have the chance to squirt some saline and remove the dirt from a wound (and the bleeding IS CONTROLLED) I do en route to the hospital. If they're so messed up that I got called because of a GSW or severe accident, I'm going to be a little too busy maintaining airway, keeping BP up, etc to do much. We'll be at the facility that can take their time to clean it properly versus my crude knock-up job when I really need to focus on doing other things. If I have an extra hand or some firefighters, I might ask them to help me if I have everything else under control. (S/O to my fire guys, you rock!) + +I hope I answered all the questions and cleared some stuff up in the edit. I will totally try to get back to all that commented! Baby boy is craving some tacos, now I gotta go make some tacos at 7am... my husband will be very confused when he wakes up, lol. " +702 If each day is only 23h56m4s, over the course of 4 years, we accumulate 95.7 hours of unaccounted time when approximating each day to 24 hours. We give ourselves one extra day in February, which accounts for only 24 hours of that extra time, but where does that extra 71.7 hours go? 21128 https://www.reddit.com/r/askscience/comments/6c3t0s/if_each_day_is_only_23h56m4s_over_the_course_of_4/ 1495202494 6c3t0s Astronomy 2017-05-19 17:01:34 "It sounds like you're confusing [sidereal time](https://en.wikipedia.org/wiki/Sidereal_time) with [solar time](https://en.wikipedia.org/wiki/Solar_time). A sidereal day is the amount of time it takes for the Earth to rotate by 360°, and is indeed 23h56m4s. A solar day is the interval between two successive instances of the Sun crossing the [local meridian](https://en.wikipedia.org/wiki/Meridian_\(astronomy\)). Since the Earth moves by roughly 1° around the Sun each day, the Earth has to rotate by roughly 361° for the Sun to cross the local meridian. In [this image](https://en.wikipedia.org/wiki/File:Sidereal_day_\(prograde\).png), sidereal time is the difference between the blue circles labelled ""1"" and ""2"", where solar time is the difference between the blue circles labelled ""1"" and ""3""." "That's how long it takes for a 360° rotation of the earth. Since it's also revolving around the sun it requires more than a 360° turn for the same point to be facing the sun again. Therefore, a ""day"" as we know it is more than 360° and a lot closer to 24 hours than your estimate." +802 If light can travel freely through space, why isn’t the Earth perfectly lit all the time? Where does all the light from all the stars get lost? 20834 https://www.reddit.com/r/askscience/comments/7ft65h/if_light_can_travel_freely_through_space_why_isnt/ 1511763721 7ft65h Astronomy 2017-11-27 9:22:01 "Excellent Minutephysics video explaining exactly this. [Why is the sky dark at night?](https://www.youtube.com/watch?v=gxJ4M7tyLRE) + +Summary: + +* Universe had a beginning so there aren't necessarily stars in every direction +* Some of the far away stars light hasn't reached us yet +* The really far away stars light is red-shifted towards infrared (not visible to the naked eye) because of the expansion of the universe. + +Edit: To add in some points from the comments. + +* Yes some of the light from distant stars is blocked by dust and other objects in the way. The dust tends to absorb visible wavelengths and re-emit in the IR range which we can’t see but that wasn’t in the video so I didn’t include it in my summary. + +* Inverse-square law for light intensity. Intensity reduces massively over interstellar distances but that doesn’t really help answer the question because every star does this. Multiplied by an infinite number of stars in every direction, suddenly that tiny bit of light from each star adds up and the night sky should be far brighter than it is. For why it isn’t, I refer you back to the video and my original 3 points." "The existing top comment correctly realises the OP is asking an age old question, that of Olber's paradox. The top comment though goes on to make some mistakes, the first is the solution of the paradox and the second is crossing the CMBR with the paradox which are not related. + +The paradox is: If the universe is infinite then in every direction there must be a star. In such a scenario the whole sky would be a uniform brightness, the same brightness as the surface of a star in fact. + +The paradox was first resolved long before we knew about the expansion of space, with a finite speed of light and a finite life time for stars there is only so much of the universe that each star can be illuminating at once. Imagine a shell that has a thickness equal to a stars lifetime propagating through the universe at c. + +We later learned that not only would an infinite universe not be bright that our universe is not infinite, there is a observation horizon due to it's expansion and a start point 13.7bn years ago. This defeats the entire premise of the paradox where every single line of sight direction intersects with a star. + +While you can explain the lack of light from distant stars as being due to redshift, it is answering a question already answered and is being a bit dishonest anyway since, you are going to be caught out in several other aspects of the more classical solution on your way to a more complicated unnecessary solution. For example, if you were to work out the average redshift of each unit solid angle in the sky you would find the sky would be much brighter than it is, and much MUCH brighter than the 2.7K you rattled off. + +This 2.7K is where the mistake really lies is in equating the redshift from distant stars to the CMBR. The CMBR was not emitted by stars (which are the subject of the OP and Olber's paradox) but by a global distribution of hot gas circa 380,000 years after the big bang. + +The biggest difference here is that the CMBR was in every direction, unlike stellar light which is only where a star is, it was also initially much cooler (<3000K) and importantly this was emitted long before - and therefore much more heavily redshifted - than the light from even the earliest, most distant stars." +903 Similar to increasing wealth gap, are we experiencing an increasing educational gap? Are well-educated getting more educated and under-educated staying under-educated? 20401 https://www.reddit.com/r/askscience/comments/7v0z9e/similar_to_increasing_wealth_gap_are_we/ 1517681683 7v0z9e Social Science 2018-02-03 21:14:43 "Re most comments in this thread that have been removed: /r/askscience is not the right place for speculation / personal take on the matter. + +A good answer will provide a reference showing stats that can address this question. ""We don't know at the moment / those stats don't exist"" is also a perfectly reasonable answer. " "TLDR: Yes and no. There is no direct connection between having and education and then getting more education as a result. However, education leads to more money and more money leads to more opportunities for education and more success in obtaining education, both for an individual and for that individual's children. It would be perfectly correct to say that the Wealth Gap has created an Education Gap because the American education system is so dependent upon local economies. + +----- + +Sociology professor here. + +It can be stated as a scientific fact that [wealth inequality exists in America.](https://books.google.com/books?hl=en&lr=&id=FpkMaxCWUsMC&oi=fnd&pg=PP11&dq=america+wealth+disparity&ots=mfq68ureXx&sig=3pdwpch0YiMTgCa2g2QS8eoRVJU#v=onepage&q=america%20wealth%20disparity&f=false). It can also be stated as a scientific fact that [wealthy individuals are more likely to graduate high school, graduate college, and obtain advanced degrees](https://books.google.com/books?hl=en&lr=&id=-EiLBQAAQBAJ&oi=fnd&pg=PP1&dq=america+wealth+disparity&ots=UUSV9oWRtc&sig=uN3VqNhDi4H_TaB14KEdeIzlRXI#v=onepage&q&f=false). Therefore, the wider the inequality in wealth the wider the inequality in education. + +However, there is a worse problem that's hidden in that statement. Education attainment is not a perfect indicator of how educated a person is. That's sort of counter intuitive, so here is an example: + +Group A) A poor section of town has low property values which means less taxes that fund schools. This then means that the school cannot hire the best teachers because it cannot pay very well. This means that the education being received by students is delivered by average or below average teachers, that textbooks and campus facilities are more likely to be outdated, and that after-school activities and extra curriculars are more likely to utilize sub-par equipment. + +Group B) A wealthy neighborhood has high property values which means plenty of funding for schools. They can afford high salaries, so many teachers apply to work here, meaning the school can select the best of the best. They also have money to keep their facilities and extra curricular activities up to date. + +Now if both Group A and Group B have a perfect 100% graduation rate, can we say that the students that graduate have the same education? Yes and no. They passed 12th grade, but in one situation the academics were more rigorous and the education included more than just the bare minimum. So on one hand we can point to statistics that say America's graduation rates are increasing, so we must be smarter. On the other hand, our schools are getting less funding and in some neighborhoods the curriculum are more lax, therefore the graduation rates increasing may be showing that our schools are getting easier to pass. + +Some studies have shown that [private schools emphasize critical thought and leadership, while public schools are more likely to emphasize discipline, cooperation, and obedience](http://archive.wilsonquarterly.com/sites/default/files/articles/WQ_VOL11_W_1987_Research.pdf). Is this a disparity? In a way. Leadership and critical thought are skills needed in management and entrepreneurial jobs, while cooperation and obedience are more useful in menial labor. This isn't specifically tied to school funding, but it is worth noting that education quality will affect job prospects and success. + +Lawmakers and policy makers are well aware of these trends. To correct for this, America has the ""No Child Left Behind"" law which forces all public schools to meet at least a minimum standard of education. The problem is that some schools barely meet it, while other (well funded) schools exceed it by leaps and bounds. + +Some states also have a ""Robinhood"" law which takes excess money from wealthy neighborhoods and redistributes it to poor neighborhoods to keep schools from becoming too polarized. These are effective, but not perfect, and I'm not an expert on this area so I'll leave it at that. + +However, all of this just says that the wealth gap creates an education gap. So the next question is, does higher education create more education? + +For an individual, no. Most people seek a particular degree, and then stop seeking education. If education snowballed like the OP implies that then we'd have individuals who obtain dozens of Ph.D's, and that's pretty rare. + +It is common, though, that [educated parents are more likely to raise educated children](http://psycnet.apa.org/buy/2005-06518-016) (pay wall). There's a lot of different factors here, mostly having to do with parent's higher education meaning more income and more free time. At the same time, this social fact is why colleges have programs set aside to specifically help first generation college students. People who go to college when their parent's hadn't gone to college are [half as likely to graduate](https://education.cu-portland.edu/blog/classroom-resources/first-generation-college-students-graduation-rates/) as students whose parents do have a degree. + +In summary, the answer is a soft yes. There is an education gap in america and it is growing, but it has more to do with the wealth gap and school funding than with education specifically." +904 Why are Primates incapable of Human speech, while lesser animals such as Parrots can emulate Human speech? 19980 https://www.reddit.com/r/askscience/comments/7omaq1/why_are_primates_incapable_of_human_speech_while/ 1515276018 7omaq1 Biology 2018-01-07 1:00:18 "Non-human primates lack the neurological regions responsible for producing speech as well as the musculature in the throat. There are several theories of how language and learned vocalizations evolved in humans, songbirds, parrots, bats, and cetaceans (whales, dolphins), but a general consensus is that it arose independently several times. Some of my favorite neuroscientists who write about this are Erich Jarvis and Johan Bolhuis. Both are songbird researchers. Jarvis has a three part series on [YouTube](https://youtu.be/E0MtW9URFhg) about this if you want to learn more. I haven't watched it but have seen him lecture a few times and he does a great job explaining it. + +Also, I wouldn't refer to parrots as lesser animals in terms of intelligence. Corvids and parrots have exhibited a wide range of intelligent behaviors that was once considered only available to humans and some other apes such as tool use and recursive learning. A recent [study](http://m.pnas.org/content/113/26/7255.full) has shown that the density of neurons in birds' brains, especially parrots and songbirds, are comparable to humans and primates." Parrots evolved to emulate the sounds of their surroundings to survive, to confuse the competition or predators. Monkeys' environment so far has demanded that they use their voice only for advance warning or intracommunal communication. +905 "The video game ""Subnautica"" depicts an alien planet with many exotic underwater ecosystems. One of these is a ""lava zone"" where molten lava stays in liquid form under the sea. Is this possible?" 19800 https://www.reddit.com/r/askscience/comments/7vgwdg/the_video_game_subnautica_depicts_an_alien_planet/ 1517856231 7vgwdg Earth Sciences 2018-02-05 21:43:51 "Oh shoot! As a geoscientist and a huge Subnautica fan, I'm sorry to come in late on this. + +**No**, the lava depicted in the lava zone is completely unrealistic (but *so* cool.) Let me comment on the pieces of the answer that people have already given: + +As /u/Little_Mouse points out, real underwater volcanism on Earth doesn't have much glow to it: the water cools the lava so fast that it's almost all dark except for a few glints of red. Their video was taken at shallow depth by a scuba diver: here's a video from 1 km deep, similar to the lava zone in Subnautica: + +https://www.youtube.com/watch?v=hmMlspNoZMs + +No glowing pools, no red lava falls. Water is a fantastic reservoir for heat, and the fact that warm water rises lets it carry away heat by convection really *really* well. + +/u/PresidentRex has a great analysis of pressures and the phase diagram of water, but there's one thing they didn't realize: **hot supercritical water is always less dense than cold**, as shown in the graphs [here](http://www1.lsbu.ac.uk/water/water_density.html). Thus, there will be no ""stable layer of supercritical water"": it would be buoyant, rise, and be replaced by cool water, carrying away heat by convection. + +What if the layer of water near the lava surface had a ton of salts dissolved in it, so it was denser? As /u/Bassmanbiff points out, the thermal radiation law applies to *everything*, not just rock: the supercritical water layer *itself* would glow. But that's clearly not what we see in Subnautica, and in any case the water above this layer would still convect, rapidly cooling it just as if it were lava itself. + +Finally, as /u/UniqueUserTheSecond points out, there's a thermometer in the game, and it reads 70 degrees C in the active lava zone. That's probably a reasonable temperature, actually -- note that in the video I linked to, the submersible isn't damaged by the volcano's heat, and /u/Little_Mouse 's video was taken by a scuba diver swimming just a few feet from the lava! But this is nowhere near the temperature at which stuff starts to glow -- no matter what stuff. + +As a side note, several people are commenting on air pressure and O2. One thing's for sure: the way Subnautica handles air and breathing at depth is completely wrong, and trying to dive the way you can in Subnautica would kill you dead. Nobody in the real world has done a dive on pressurized gas to a depth greater than 700 meters, the people who've done it to a depth below 100 meters only do so with hours of preparation, a special gas mixture, and slow cautious pressure changes, and even then many people who've tried to dive below 300 meters have died. The vehicles and seabases behave as if they are at sea-level pressure (if they weren't, they wouldn't implode if you take them too deep), but you can't just hop from 800 meters of pressure into your sea-level pressure vehicle without dying immediately. And let's not even talk about how moonpools work.... + +Of course, a realistic approach to lava and air pressure wouldn't make for nearly as fun a game!" "I can't speak directly to lava coexisting next to saltwater at depth, but there's some other misinformation thrown about this thread that I wanted to clear up: + +**Lava temperature** + +Lava glows because of [thermal radiation](https://en.wikipedia.org/wiki/Black-body_radiation). This is linked with the concept of blackbody radiation, where matter emits electromagnetic radiation based on its temperature. All matter emits this radiation above absolute zero, but the color becomes visible to humans around 800 K (980 °F/526 °C) as a dull red. As temperature increases further, objects appear yellow and then white hot (possibly with a tinge of blue). + +The in-game lava is a deep red, so it's likely on the lower end of visible thermal radiation (800 - 1000 K). So while it's possible the lava doesn't have the same composition as typical earth-like lavas, it can't have a temperature much lower (e.g. lead melts at 600 K, but you can melt lead without it emitting a red glow). + + +**Atmospheric composition and air pressure** + +The planet in Subnautica could have an atmosphere of anywhere between about 0.4 to maybe 5 atm of pressure. The partial pressures (pp) of various gases in the atmosphere are the important part for humans. [Partial pressure](https://en.wikipedia.org/wiki/Partial_pressure) is neat because if you take out the percentage of each gas in a gas mixture, the partial pressure would be equal to that percentage. Earth's atmosphere is (currently) 21% oxygen and basically 1 atm at sea level; that means that the oxygen has a partial pressure of 0.21 atm. On Mount Everest with a pressure around 0.33 atm, that's 0.07 atm of oxygen partial pressure. We need about 0.15 atm of partial pressure to breathe over the long term, but we can survive in less for brief periods (minutes/hours). + +On the other extreme, our bodies would suffer if the [composition in a high-pressure environment was not just right](http://www.physiology.org/doi/abs/10.1152/jappl.1970.29.1.23). Non-noble gases start having detrimental effects at high partial pressures - including oxygen. Oxygen-related problems can start at 0.3 atm pp (aside from a risk of fire, this is one reason why we don't use 100% oxygen atmospheres at earth-like pressures in spacecraft), but up to 2 atm can be used [for short periods](https://en.wikipedia.org/wiki/Breathing_gas#Oxygen). Carbon dioxide starts negatively affecting us around 0.06 atm of pp. Nitrogen narcosis is also well known in diving circles. The only somewhat safe options are neon and helium, and they can even start affecting our cell structures at extreme pressures. This really only applies to a human on the surface breathing air, though. + + +**Pressure at depth** + +(Tiny edit: I should note that these pressure calculations are based on normal earth gravity. Higher gravity means more pressure for equivalent depth; lighter gravity means less pressure for equivalent depth.) + +Atmospheric pressure ends up being of little concern once you get deeper. The water pressure exerted at 1300 m of depth is about 130 atm. Adding 0.5 or 4 atm on top of that is miniscule. Water at normal temperatures is still just a normal liquid at this pressure (as we can experience here on earth diving into deep ocean trenches). Nobody is really going to dive that deep on a regulator though; you'd need a pressurized tank to breathe (otherwise the water pressure would collapse your lungs) and the gases will do unpleasant things to your blood and body once you start breathing gases at those pressures. There are reasons the current free dive record is 214 m and the scuba record is 333 m. + +As an explanation for the [phase diagram for water](http://www1.lsbu.ac.uk/water/water_phase_diagram.html): Temperature is the horizontal axis (in Kelvin); pressure is the vertical axis (usually in Pa and/or bar). The basic ice/water transition is the vertical line around 273 K (0 °C, naturally). In the big graph on that page, E is basically normal earth conditions (293 K or 20 °C and about 1 atm or 1 bar of pressure). Pressure in water (like any fluid) increases with depth. The rule of thumb is 10 m of water = 1 atm of pressure (technically it's 10.33 m = 1 bar, but everything else I wrote is in atm and 1 bar is just about 1 atm). This means you increase pressure by 1 atm each time you go another 10 m down. + + +**Phase state at pressure and temperature** + +Water is a normal liquid at 130 atm at standard temperature. Water is a supercritical fluid at 130 atm at 800+ K. (I wouldn't recommend swimming in it; it'll do unpleasant things to your body other than just burning you). This means it will be stable and won't turn into steam because it's already a weird mixture of steam and water. Unfortunately, my chemistry isn't good enough to tell you how salt is going to affect this in detail (other than to say that solids tend to dissolve better at higher temperatures and pressures so it could be denser). + +So, at the very least, it's at least plausible for the lava to sit there covered in a layer of supercritical, denser saltwater. +" +703 What affect does the quantity of injuries have on healing time? For example, would a paper cut take longer to heal if I had a broken Jaw at the same time? 19529 https://www.reddit.com/r/askscience/comments/6uc2os/what_affect_does_the_quantity_of_injuries_have_on/ 1502995456 6uc2os Medicine 2017-08-17 21:44:16 "A distal injury won't affect another injury until it begins needing more resources than the body has to distribute - take burns for example. + +If you had a burn on your hand all sorts of plasma and proteins and immune related cells would be rushing to the site (some already there) causing both local inflammation and an immune response that ultimately results in a blister - the blister is full of immune cells that help to repair the damaged tissues by providing an ideal micro environment for healing. Now let's say there's a burn to a large portion of your body; depending on the degree and the inflammation response (3rd degree burns have a different response as many of the biological channels of cell repair are completely destroyed) while your body will send out all its required immune cells that it has it might simply not be enough - in this case bacterial infections can take hold in the blisters as they provide an ideal environment for certain infections to grow, this results in sepsis and eventually septic shock. Imagine that the bodies immune repair system is spread too thin to repair both burns - it doesn't have a very good system at establishing where it should send immune cells with regard to controlling sepsis beyond directing blood away from the extremities and towards critical organs as septic shock progresses. + +Ultimately it depends on the nature of the two injuries but yes they could affect one another." "A fun bit of trivia: + +In polytrauma injuries involving a traumatic brain injury and bone fracture, the fracture may actually heal at a faster rate than the same fracture alone. The mechanism is currently not well understood, but some researchers speculate it's related to enhanced macrophage mobilization. + +EDIT: For some more formal reading, check out some of work being performed in small animal models: [here](https://www.ncbi.nlm.nih.gov/pubmed/25682315), [here](https://www.ncbi.nlm.nih.gov/pubmed/26636276), [and here](http://globalprojects.ucsf.edu/project/murine-model-polytrauma-understanding-molecular-basis-accelerated-bone-repair-concomitant). Then, even more exciting, check out [this study](https://www.ncbi.nlm.nih.gov/pubmed/22323691) that looked at human patients with combined TBI + fracture injuries. Finally, to try to sum it up as best as we can, check out these lit reviews: [here](https://www.ncbi.nlm.nih.gov/pubmed/25873754) and [here](https://www.ncbi.nlm.nih.gov/pubmed/15710151)" +704 Why is the human nose the shape it is? Why isn't it just two holes in our face? 19208 https://www.reddit.com/r/askscience/comments/6qaduo/why_is_the_human_nose_the_shape_it_is_why_isnt_it/ 1501325982 6qaduo Biology 2017-07-29 13:59:42 In addition to what everyone else said there is one point that no one brought up: The shape of a human nose helps infants breathe while suckling. Other primates have protruding jaws that allow them to breathe while suckling. If we didn't have our noses we could be more prone to smothering. "The nose is actually an organ that performs many functions aside from just being a conduit to the respiratory and olfactory system. The nose warms up and moistens air before it enters the trachea in the winter and has an air conditioning effect in the summer. The nose is the first line of defense before foreign particles can be inhaled into the respiratory tract – large particles are captured by hairs and smaller ones get caught in mucus. In that way, it can be thought of as an organ of the immune system, since it is responsible for draining the sinuses. The endings of the olfactory nerves go through the roof of the nasal cavity; if there was no protection and just open orifices on the front of the face, you would basically have very little between raw exposed cranial nerve endings and the outside world. Lastly, the shape of the nose changes vocal resonance and affects your voice. + +Edit: Wow, leaving for a few hours, you wouldn't expect a little comment about the nose to blow up like this, or else I would've elaborated more. I did a little lower down, going into more detail on theories of racial/climate-related differences in nose shape and comparative anatomy of other animal noses (carotid rete). I also agree that noses are not usually classified as immune system organs, but I just meant that it has functions with innate immunity. And good point on helping to keep liquids out of the respiratory tract!" +803 Why do computers and game consoles need to restart in order to install software updates? 19011 https://www.reddit.com/r/askscience/comments/7mmz8i/why_do_computers_and_game_consoles_need_to/ 1514472415 7mmz8i Computing 2017-12-28 17:46:55 "Hey all, + +Please remember that in /r/askscience we require _accurate, in-depth explanations_ to our questions and their concerns. Please refrain from posting analogies and ""ELI5"" explanations which don't directly answer the question." "A CPU can only work on stuff in its cache and the RAM of the device (be it PC / Mac / console / mobile / etc). However, such memory is volatile, and loses all its data if it is not powered. To solve this problem, secondary storage exists: hard disk drives, DVD drives, USB disks, flash memory, etc. They hold persistent data that is then transferred to the RAM as and when needed, to be worked on by the CPU. + +Now, when a computer boots up, a lot of its core processes and functions are pre loaded into RAM and kept there permanently, for regular usage. (The first of this stuff that loads is known as the *kernel*.) They are also heavily dependent on each other; eg, the input manager talks to the process scheduler and the graphics and memory controllers when you press a button. Because these are so interconnected, shutting one down to update it is not usually possible without breaking the rest of the OS' functionality*. + +So how do we update them? By replacing the files *on disk*, not touching anything already in memory, and then rebooting, so that the computer uses the new, updated files from the start. + +*In fact, Linux's OS architecture and process handling tackles this modularity so well that it can largely update without a restart." +705 How will the waters actually recede from Harvey, and how do storms like these change the landscape? Will permanent rivers or lakes be made? 18960 https://www.reddit.com/r/askscience/comments/6wzxql/how_will_the_waters_actually_recede_from_harvey/ 1504107367 6wzxql Earth Sciences 2017-08-30 18:36:07 "As a flood engineer i wish i came here sooner to answer a few questions. + +But the main thing is that a number of vectors will remove the water due to gravity. Namely sewers, ground drains, good old evaporation, lay of the land, local ground geology, tidal differences to name a few. Once the hurricane has passed though then levels will drop fairly quickly. + +The biggest problem will be both the environmental (mobilised sewage etc...) and physical property damage that has occured. + +Lots of standing water means mozzies and vermin. Contaminated waters means polluted ground water sources, damaged agriculture infrastructure, dead livestock, crops wiped out and quarantined/destroyed (certain crops absorb harmful nasties). + +Infrastructure wise lots of work gutting out the drainage system and clearing hurricane damage will take place. Damaged electricity/phone/gas infrastructure will need checking too. + +Now let's talk about the houses that are damaged. + +There are typical damage assessments that can be done but there are 2 typical factors that ultimately determine damage costs and severity - the depth of water and the time water stays around (ok and type of building materials used) + +Anything typically above 400mm for a day or 2 means that the lower floor needs gutting and requires a complete rework. + +Now think of this in terms of demands locally. Every homeless person will need rehousing, every house will require skilled trades to repair them(and they WILL be in demand). It will take years for all affected properties to be repaired by all trades. + +But as a starter for then why not google what happened during hurricane katrina or the 2005 flooding carlisle in the UK. Some of the stats are just mindblowing and heartbreaking. + +Ps also google the lake levels rises during hurricane Katrina due to the low air pressure alone. It makes for amazing reading. + +Source : i am really a flood engineer 😊 + +Edit: Thank you for my first ever gold(s!!!) and all your messages." "I'm a semester away from graduating with a degree in soil science, so I'll answer this as it pertains to soil. + +The most important concept to understand before I delve into this is that everything moves through soil via water. This includes nutrients, pollutants, minerals, etc. + +The large scale scope of a flood like this is pollution and soil erosion. When soil is flooded to the point that water can no longer infiltrate, it begins transporting the top 2 layers of soil. This is the organic layer (such as leaf litter) and the surface layer (topsoil). These are the two most nutrient rich layers of soil, and often the most polluted (by pesticides, foreign chemicals, or trash). This is not good for a few reasons: + +1. The main source of nutrients have now been stripped from the plants. + +2. The sub-surface layers are exposed, and from what I understand about Texan soil, this is mostly clay. + +3. Pollutants are now being transported and dumped into waterways or varying soil environments. + +Some of the nutrients will be returned to soil elsewhere, but most of these nutrients will flow to waterways and into the ocean. This will not be good for the Gulf, as it is already hypoxic (lack of dissolved oxygen due to nutrient runoff. Essentially, the large amount of nutrients results in algae blooms which deprives the water of oxygen). The reduction of plant matter will also reduce the stability of the soil, meaning it will be more likely to erode in the future. + +The second portion of this is that clay now becomes the surface layer. Because clay is so small, it takes water significantly longer to move through the soil profile, thus lowering the hydraulic conductivity. This means water runoff will now become a large problem in the affected areas for months or years to come. + +The third portion is pollutants. Chemicals and trash are now being transported to different soils and waterways. Not good. + +As for the smaller scope impacts, soil horizons will become disrupted. Soil stability will be negatively impacted. Nutrients will be forced through the horizons quicker, leaving a deprived soil. Many soil microbes (the most important indicator of soil health, depending on who you ask) will be killed off. + +So, yeah. It's disastrous for soil and the overall environmental health of the area. + +EDIT: Also, as for plants, many can survive being submerged for up to a weekish. Many cannot. The flooding will inhibit root nutrient uptake, which will result in decay. Water-logged roots are also more susceptible to organisms that specialize in root-rot. + +EDIT2: /u/BadBadger42 asked a question about highly expansive clays. These are what we call shrink-swell soils. The clay fraction is expanded in area when water-logged, which causes extra stress on infrastructure. This is the leading cause of flooding basements, and why many buildings in Texas do not have basements. Taking a look at [this soil map of Texas](https://www.nrcs.usda.gov/Internet/FSE_MEDIA/nrcs144p2_000979.jpg), most of the area effected is Vertisol. I'm sure you've all noticed a vertisol before, when it dries it looks like [this](http://geotechfoundation.com/wp-content/uploads/2013/04/cracked-soil-texas.jpg). The ""swell"" of the soil is caused by the micropores between the clay particles becoming over-saturated - and when it dries (""shrinks"") those cracks are left behind. Vertisol is the shrink-swell classification of soil. I would imagine that the effects of shrink-swell on infrastructure will be exacerbated by the flooding. " +500 If we could drain the ocean, could we breath or live on the deepest parts or would pressures, temperatures, and oxygen levels be too extreme for us to live such as high altitudes? 18789 https://www.reddit.com/r/askscience/comments/5l7nj4/if_we_could_drain_the_ocean_could_we_breath_or/ 1483154684 5l7nj4 Human Body 2016-12-31 6:24:44 "The Mariana trench is about 11,000 meters below sea level. If you built a cofferdam down to that depth, as u/SirHerald suggests, the pressure would be about 3.2 atm. Divers experience a similar pressure at a depth of around 22 meters, so humans can survive these pressures in the short term. In the long term, I found [this chart](http://www.hq.nasa.gov/pao/History/conghand/fig15d3.gif) from NASA suggesting you would have to worry about mild [nitrogen narcosis](https://en.wikipedia.org/wiki/Nitrogen_narcosis), making you feel slightly drunk, and mild [oxygen toxicity](https://en.wikipedia.org/wiki/Oxygen_toxicity). So you probably wouldn't want to live at that pressure, but a short trip down wouldn't be any worse than diving. + +But, your question was about draining the oceans. The oceans cover 72% of the surface of the earth, and the average depth of the ocean is about 3700 meters. That means a large portion of the atmosphere will sink into the ocean, resetting 1 atm of pressure to a depth of something like 2600 meters below sea level. So that would make the Mariana trench a bit more tolerable at around 2.5 atm, but it would also mean some high altitude cities would become nearly uninhabitable. + +**edit** Fixed the bracket on the link. Wish I had caught it before I left this morning - wasn't expecting this to blow up so much." The oxygen would re-distribute, and as such some of the higher elevation places would see a dramatic decrease in air thickness. Think akin to how on higher elevation mountain the air is thinner which affects blood flow and your brain. Hypoxia occurs when not enough oxygen is distributed among the body, it can be general (throughout) or localized to a specific part. Since the Oxygen re-distribution would re-scale altitude, people would suffer Altitude Sickness. We know the extreme baseline for this is 6000m, at which and beyond, human sustained life is not possible. Essentially those effects would now be on higher elevated cities. So anything currently exceeding 1000m would, under the new distribution be at the threshold where our current 6000m altitude sickness baseline is. BASICALLY we'd just have to move to more coastal situated cities. +601 "The all-green picture with ""red"" strawberries picture. Do I see red because I know ripe strawberries are red?" 18522 https://www.reddit.com/r/askscience/comments/5x3wr2/the_allgreen_picture_with_red_strawberries/ 1488469368 5x3wr2 Psychology 2017-03-02 18:42:48 "Even though the ""red"" in the altered image is literally just gray, it is still *more* red than green is on the hue scale. If we break the colors into the RGB components, the green will be something like R:0 G:200 B:50, and the grey will be R:100 G:100 G:100, that is, much more red component and much less green component. + +The eye/brain's color processing is super complex, but the most simple version is that we take a lot of cues from the *differences* between shades, and not their absolute values." Your brain will compensate away the green tint, similar to automatic color balance in a camera, and the gray will then look red in comparison. Knowing anything about strawberries is not necessary. The brain guesses that the background is meant to be white, which helps this compensation happen. +706 What is the reason for our irrational disgust of insects and arachnids? Were humans often poisoned-killed by them while we evolved? 17990 https://www.reddit.com/r/askscience/comments/6jepka/what_is_the_reason_for_our_irrational_disgust_of/ 1498402453 6jepka Human Body 2017-06-25 17:54:13 "I'm surprised nobody has mentioned the fact that humans are predisposed to feel more affectionate towards ""cute"" animals, and feel disgust for those that look alien. https://www.wikiwand.com/en/Cuteness + +Not only have scientists identified the specific facial traits that trigger ""caretaking behavior""--big eyes, bulging craniums, retreating chins--dogs and cats have evolved to elicit it. For example, cats purposefully utilize the frequency range of a baby's cry when attempting to solicit care. http://www.cell.com/current-biology/abstract/S0960-9822(09)01168-3 And over time dogs have evolved to appear more like human babies over years of humans preferring dogs with paedomorphic facial expressions. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0082686 + +The examples of preferential treatment by humans for ""cute"" animals is extensive. You can simply look at the types of animals on the endangered creature list, or which animals get funding for research. https://www.cambridge.org/core/journals/oryx/article/trends-and-biases-in-the-listing-and-recovery-planning-for-threatened-species-an-australian-case-study/DC0D198D842AE8963787297094B8C263 + +Furthermore, it has been shown that this bias isn't learned, but is hard-wired into our brains. The following study found that kids ages 3-6 showed the same preference for animals with infantile features, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4019884/ + +At the same time that dogs and cats have evolved to ingratiate themselves to humans, humans have evolved to utilize dogs and cats to fulfill social and psychological needs. This study of the human-animal bond focuses on neuroendocrine regulation--primarily oxytocin secretions--and the considerable health benefits that result. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4782005/ + +" "A swedish scientist named Arne Ohman conducted an experiment to understand fear of spiders, snakes, and other things by exposing a subject alongside an electric shock. + +What he found was that one shock was enough to create an ongoing fear response for future exposures. This fear persisted for spiders and snakes, but eased over time for other stimuli. + +He concluded that there is a hereditary predisposition to fear of spiders and snakes not present for several other common, learned phobias." +906 Ethiopia is building the largest hydroelectric power plant in Africa, Egypt opposes the dam which it believes will reduce the amount of water that it gets, Ethiopia asserts that the dam will in fact increase water flow to Egypt by reducing evaporation on Egypt's Lake Nasser, How so? 17625 https://www.reddit.com/r/askscience/comments/7s57t6/ethiopia_is_building_the_largest_hydroelectric/ 1516621369 7s57t6 Earth Sciences 2018-01-22 14:42:49 "Due to the nature of the topic discussed, this post has spawned several political arguments. The mod team would like to remind you that /r/askscience is a place dedicated to science questions. Off topic comments will be removed. We also have a zero tolerance policy on racist content. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." "There is a fixed amount of water available in the basin that varies only slowly over decade time scales. So if Ethiopia builds a dam close to the source of the water and stores it there this will have results downstream. A minor effect would be the evaporation from the lake which would be lost to the region (the recycling factor in the Ethiopian highlands is small). A major effect would be a quick fill which would temporarily cut off water supply to the downstream areas. A long term effect would be that in times of drought Ethiopia has control over the distribution and can keep more water for itself. All of these are negative effects for Egypt's water security. As for the claim that Egypt's waterflow is increased by reducing Lake Nasser evaporation, this is really a wry statement. It means that they might reduce the level of Lake Nasser by siphoning of more water upstream thereby decreasing the volume of the lake and the area from which it can evaporate. That might slightly reduce evaporation in Egypt which is what they could mean by ""increased water flow"" but I don't see how Egypt's total water budget would increase because of this. + +That said, if Ethiopia's dam is properly managed it might increase the overall water security of the region, something that would also benefit Egypt. It all depends on the amount of irrigation Ethiopia is going to develop with this dam." +602 Is it possible to Yo-Yo in space? 17296 https://www.reddit.com/r/askscience/comments/5vs989/is_it_possible_to_yoyo_in_space/ 1487875946 5vs989 Physics 2017-02-23 21:52:26 "It is indeed possible to yo-yo in space. The only thing is that if you ""free wheel it"" (sorry not a yo-yo expert) it tends to float around. It will however try to keep its orientation due to gyroscopic effects. This is sometime used on spacecraft to either stabilise them or to turn them (with moment gyros). [Here is a great video](https://www.youtube.com/watch?v=ni4j5K4Lz3o) of my favorite astronaut Dr Don Pettit inventing new yoyo tricks on board the international space station." "You don't need gravity to yoyo. Think of how you can throw a yoyo out perpendicular to the ground and have it return. + +The way a yoyo works is this: the string isn't tight to the bearing which is how you can walk the dog etc. If you cause enough snap, it starts to wind, then due to the spinning, causes it to wind back on the string itself. Gravity plays no real part in basic yoyoing, only in certain tricks" +804 If my 60 GB phone is full or empty, is there any difference in weight at the nano level? 17188 https://www.reddit.com/r/askscience/comments/74rboo/if_my_60_gb_phone_is_full_or_empty_is_there_any/ 1507331423 74rboo Physics 2017-10-07 2:10:23 "Yes, if my understanding of this article is correct: +http://www.nytimes.com/2011/10/25/science/25qna.html +(I hope nytimes is an acceptable source, even if not academic) + +In the linked article, John D. Kubiatowicz, a professor of computer science at the University of California, Berkeley says that for a kindle with 4 Gigabyte memory, this would mean a rough increase in weight of 10^–18 grams. + +For your situation of a 60GB phone, this would mean +(60Gb/4Gb) * (10^-18 grams) = 1.5 × 10^-17 grams. So certainly less than what you would be able to feel. + +While I originally thought this would be because the storage would use extra electrons, the article/Prof. Kubiatowicz say otherwise: + +""Although the total number of electrons in the memory does not change as the stored data changes,” Dr. Kubiatowicz said, the trapped ones have a higher energy than the untrapped ones. A conservative estimate of the difference would be 10^–15 joules per bit. + +""As the equation E=mc2 makes clear, this energy is equivalent to mass and will have weight."" + +It is my understanding that most/all mobile phones use flash memory for storage so the linked article about flash memory in Kindles would be applicable here. Please let me know (or just delete this outright) if I am mistaken. + +*edited to fix exponent formatting + + +" "Most comments here are assuming that ""empty"" space on the phone is occupied by 0 bits, and that new data will switch some to 1. In reality, there's no guarantee that those bits are 0, since most operating systems have clever bookkeeping to allow regions of memory to be marked as empty without having to overwrite that entire section with 0 bits. + +Your meta question appears to be: does data have mass? And the answer to that question, and in my mind one of the cool things about data, is that it does not. + +A knit quilt with intricate, colorful patterns weighs the same as a gray, featureless one. A book filled with random scribblings weighs the same as an equivalent dictionary. We're a species that evolved to match patterns; data is just patterns: human-interpretable arrangements of things. " +707 Does sipping water vs 'chugging' water impact how the body processes water? 17058 https://www.reddit.com/r/askscience/comments/6uijoe/does_sipping_water_vs_chugging_water_impact_how/ 1503069938 6uijoe Human Body 2017-08-18 18:25:38 "Ok, this will likely get buried, but I'll give an explanation. + +After you ingest (swallow) water, it goes to your stomach. There, it is slowly released to your small intestine to be absorbed and pass to your bloodstream. +It takes water between 10 and 40 minutes to pass to your small intestine and be absorbed. The speed of this depends on how much water, the temperature (cold water will be released slower), if there is something else in the stomach, etc. +But, in general, it doesn't matter whether you chug a bottle of water down in 10 seconds or slowly sip it in 10 minutes. It will all end up in your bloodstream in about the same time. + +The only thing that can make a difference is whether you vomit the water that you are ingesting. You stomach vomits its contents in response to a series of things (whether it senses that something you ate may be rotten or dangerous, whether there is a bad smell, etc), and one of those things that the stomach takes into account is how full it is. So ingesting water in small sips can help avoid vomiting, and that is what's recommended when for example children have gastroenteritis. But if you don't vomit the water that you swallow, it doesn't matter whether you swallowed it in 10 seconds or 10 minutes. + +Edit: Wow, thanks for all the upvotes. Turns out it didn't get buried after all! This is 1/4 of my total karma right there! Glad you liked it! + +Edit2: it's actually not clear whether cold water will be released (and thus absorbed) slower. As someone pointed out below, studies on this seem to be contradictory. +" [deleted] +805 If you put a Garden in the ISS, Could you have infinite oxygen? 16899 https://www.reddit.com/r/askscience/comments/75ggm6/if_you_put_a_garden_in_the_iss_could_you_have/ 1507635631 75ggm6 Astronomy 2017-10-10 14:40:31 "This is called bioregenerative life support, and in falls in the broader category of Environmental Control and Life Support Systems (ECLSS). Short answer is yes, but not infinite and not without disadvantages. + +Note that plants aren't the only way to recycle oxygen. Currently they use water electrolysis to inject oxygen into their atmosphere, and use the resulting hydrogen to apply the Sabatier reaction with CO2. This yields methane as a waste product, and captures oxygen from CO2 in the form of water, so they can later apply electrolysis again and recycle oxygen. + +A clear advantage of using plants would be trapping carbon into edible forms, so you'd be recycling not only oxygen but also food. However, not all plants have a 100% edible mass, and those who do usually offer very few calories if not negligible (e.g. lettuce). + +A problem with plants is that they could die under some conditions, so this system isn't 100% reliable. And in any case, whether bioregenerative or artificially regenerative, you can never achieve a 100% reuse of ECLSS resources. But it's ok, you can get close enough and have them for a long time relying on very little supplies. + +They are actively researching on this topic. Recently they've been able to grow lettuce in the ISS. +" "Whoa something I can answer - I worked on the Lunar Greenhouse Module at the University of Arizona! + +Bioregenerative Life Support Systems could continually produce oxygen and some amount of food (our goal was always atmospheric conditioning with food production as a windfall of that). In fact, you kind of have to decide if you'd like the plants to focus on growing leaves for oxygen production or fruits for food production. Either way, there are a lot of challenges in feeding those plants. We proposed using composters to recycle human waste to make the system fully sustainable, as plants ""breathe"" pure water out which could then be utilized as drinking water as well. I don't know all the details about that part of it, as that wasn't my section. We also intended to use Fresnel lenses with fiber optic cables to deliver sunlight directly to the plants, with blue and red LEDs as a backup (it'd be placed underground because the moon lacks an atmosphere to burn up space debris). + +Unfortunately, hydroponics would have difficulty in a low gravity environment like the ISS without some real specialized design, which the plants may not like. The moon would give us an environment that is a little more familiar to us and the plants. + +Edit: the guys in charge of it did an AMA a couple years ago if anyone wants to look around for more info without leaving Reddit: [Link](https://www.reddit.com/r/IAmA/comments/3npxoj/move_over_hollywood_we_are_roberto_furfaro_and/?st=J8LQQOVW&sh=91652fb3) " +708 We encounter static electricity all the time and it's not shocking (sorry) because we know what's going on, but what on earth did people think was happening before we understood electricity? 16767 https://www.reddit.com/r/askscience/comments/6gwffm/we_encounter_static_electricity_all_the_time_and/ 1497314460 6gwffm Physics 2017-06-13 3:41:00 "Electricity has been known for a long time. Egyptians noted the similarity between electric eel shocks and lightning. + +Pliny the elder (and many others) noted that these shocks could be transferred, that objects when rubbed often attracted things, that so did magnets, and that the three phenomena were connected. Thales of Miletus came up with the theory that when Amber underwent friction, it became a lodestone, and if rubbed further produced lightning proving it was a magnetic force behind lightnng. Both though in terms of ""Gods"" or ""Souls"", which in terms of philosophy might be better thought of as a ""motive force without a clear origin"". + +Which is a pretty solid conclusion if you discount Thales mixed up electric fields and magnetic ones. And, you know, thought everything was water (not as stupid as it sounds.)" I hope I'm not breaking any rules here, but r/askhistorians gets this question from time to time. [They have an FAQ section about it here](https://www.reddit.com/r/AskHistorians/wiki/science#wiki_ancients.27_views_of_static_electricity). +907 The universe is said to be around 23% dark matter, 72% dark energy and 5% ordinary matter. If we don't know what dark matter and dark energy are, where do the percentages come from? 16620 https://www.reddit.com/r/askscience/comments/82rhw8/the_universe_is_said_to_be_around_23_dark_matter/ 1520454426 82rhw8 Astronomy 2018-03-07 23:27:06 "We can calculate things like gravity and energy density of the universe base on how the galaxies behave on a cosmic scale. We can also calculate how much stuff is out there by direct observation. When we look at the cosmos and look at how the galaxies behave, there is not enough material to generate the gravity (even when accounting for all the gas and dust that may obscuring it). So there's some matter that doesn't emit light but still generates that gravity we see. We call it dark matter, because that's what it is: dark. + +There's also an expansion to the universe that suggests that the energy density is not what we can directly measure. There's a bunch of stuff out there causing the universe to expand at an accelerated rate. We call it dark energy, because, hey, we have dark matter already--why not call it ""Dark Energy""; that way it sounds cool. + +So there's like 5 times as much matter as what we can see, and like 3 times as much energy density as what can be explained by that matter. So that's where the percentages come from: just add up all the stuff we know about that makes up the universe even if we don't yet know what that stuff is." "In layman's terms: dark matter is *something that generates gravity that we can't see*. + +We can calculate the gravitational forces that impact everything we can see - stars, planets, black holes, dust, etc. We can calculate how much gravity the things we observe is generating. The problem is, they don't add up. There's way more gravity affecting everything than what is being generated. All of that unexplained gravity is just generalized as dark matter until a better explanation comes along. Same kinda deal with dark energy." +806 "How ""green"" is the life cycle of a solar panel end-to-end compared to traditional energy sources?" 16472 https://www.reddit.com/r/askscience/comments/7g6eyb/how_green_is_the_life_cycle_of_a_solar_panel/ 1511895048 7g6eyb Engineering 2017-11-28 21:50:48 [deleted] "Finally something I can help out with! Source: I'm a lecturer in the UK (roughly equiv. to assistant professor in the USA) specialising in life cycle assessment, particularly energy sources. + +I wrote a paper that's open access, which you can find here: http://www.sciencedirect.com/science/article/pii/S0306261914008745 + +The TLDR is that solar is good in terms of climate change but generally less good in terms of other impacts. Overall it's typically not as good as wind or nuclear power. However, bear in mind two things: + +1. Impacts are very dependent on location. E.g. solar installed here in the UK is worse than in Nevada or Spain because the impacts are all up-front but you get much more energy output in sunny countries, therefore better impacts per kWh. +2. Solar technology is moving fast. I actually have some updated figures that I'd love to share with you but they're not published yet, so they're not peer-reviewed. Reductions in impacts in the past few years have been considerable: about 50% reduction between 2005 and 2015. So for instance I now estimate a carbon footprint of about 45 g CO2-eq./kWh for a UK installation or 27 g in Spain. This contrasts with the figure of 89g you'll see in the paper I linked." +1000 What is the “pins and needles” feeling that happens when you cut off circulation to a part of your body? 16402 https://www.reddit.com/r/askscience/comments/908y52/what_is_the_pins_and_needles_feeling_that_happens/ 1532028443 908y52 Human Body 2018-07-19 22:27:23 This post has attracted a large number of low quality answers. The moderation team would like to remind you that answers on r/askscience are expected to be accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating. "Its not actually circulation of BLOOD (if it was, those limbs or body parts would die off) +, its nerves being compressed and cut off . When ever you sit in a position or are in a position for a while that can COMPRESS nerves, they will stop transmitting. The nerve cells themselves will TRY to transmit at first, but when they don't receive feedback, they stop. This is the ""numbness"" or ""this body part fell asleep"" that we all experience. When the compression ends, the nerves can sense this and all at once begin a chain of ""testing"" aka sending out signals to all cells affected down the line, to make sure they are still there. Its like the electrical grid firing back up. It feels painful because our nerves use pain a response. The sensory organs in our brain after about 30 seconds to 120 seconds will shut this test firing pattern off and resume normal operations. But that time in between is pretty painful. It feels like Pins and needles because each sensation is a nerve "" thread ending "" being tested. (source [USC Berkeley's neuroscience center ](http://neuroscience.berkeley.edu/research/) +Edit well this blew up overnight! Thanks for the gold, kind stranger! " +1001 What happened to acid rain? I remember hearing lots about it in the early 90s but nothing since. 16188 https://www.reddit.com/r/askscience/comments/8ozzuy/what_happened_to_acid_rain_i_remember_hearing/ 1528286164 8ozzuy 2018-06-06 14:56:04 "Acid rain was caused by SO2 emissions from coal plants, **which have been cut by >90% since 1990**. + +The 1990 Clean Air Act Amendments kicked off a cap-and-trade scheme that incentivized coal plants to install scrubbers and/or switch to low-sulfur coal, then low-cost natural gas took ~50% of coal's market share since 2008. + +Bottom line: coal is somewhat cleaner than it used to be, and we're burning far less of it. + +[SOURCE](https://www3.epa.gov/airmarkets/progress/reports/index.html)" "The reduction in the prevalence of acid rain in the US is largely been attributed to the success of the EPAs Acid Rain Program. + +All rain is somewhat acidic from rainwater forming carbonic acid from rainwater reacting with carbon dioxide, but acid rain is particularly lower in pH. This is due to the reaction of rainwater with nitrogen and sulfur oxides to form the much stronger nitric and sulfuric acids, respectively. The primary source of these nitrogen and sulfur oxides is power plant emissions, particularly those burning coal. The Ohio River Valley contains a large concentration of these power plants, and acid rain issues in the US were largely concentrated around this region and points downwind (the Atlantic Coast). + +The Acid Rain Program was begun in 1990 based under the Clean Air Act. It established a market-based (cap and trade) system of regulation upon which emitters of sulfur and nitrogen oxides were granted pollution allowances. Polluters were incentivized to voluntary undertake measures to reduce the volume of their emissions as they could sell unused allowances for profit. + +By most estimates, the Acid Rain Program has been largely successful. The Pacific Research Institute has estimated that this program has reduced total acid rain levels by 65% from 1976 levels while the EPA estimates the program cost businesses only a quarter of what was originally estimated. Savings in property damage and human health costs, such as lowered incidences of heart and lung problems exacerbated by acid rain, most likely have resulted in the Acid Rain Program actually saving money, overall." +807 If you placed wood in a very hot environment with no oxygen, would it be possible to melt wood? 16176 https://www.reddit.com/r/askscience/comments/751o3a/if_you_placed_wood_in_a_very_hot_environment_with/ 1507469273 751o3a Chemistry 2017-10-08 16:27:53 "It is pretty much impossible to melt wood. The reason is that as you start heading the wood up, its constituent building blocks tend to break up before the material can melt. This behavior is due to the fact that wood is made up of a strong network of cellulose fibers connected by a lignin mesh. You would need to add *a lot* of energy to allow the cellulose fibers to be able to easily slide past each other in order to create a molten state. On the other hand, there are plenty of other reactions that can kick in first as you transfer heat to the material. + +If you have oxygen around you one key reactions is of course combustion. But even in the absence of oxygen there are plenty of reactions that will break up the material at the molecular level. The umbrella term for all of these messy reactions driven by heat is called [pyrolysis.](https://en.wikipedia.org/wiki/Pyrolysis) + +**Reference:** + +1. Schroeter, J., et al. Melting Cellulose. *Cellulose* 2005: 12, pg 159-165. ([link](https://link.springer.com/article/10.1007%2Fs10570-004-0344-3))" "No. In fact the process you are describing is exactly [how you make charcoal](https://en.wikipedia.org/wiki/Charcoal). + +""Charcoal is usually produced by slow [pyrolysis](https://en.wikipedia.org/wiki/Pyrolysis) — the heating of wood or other substances in the absence of oxygen"" + +Water and other volatile organic compounds (such as methanol) are basically boiled off and what remains is a large lump of carbon- a.k.a charcoal. + +Can you melt carbon? No- not at [atmospheric pressure](https://en.wikipedia.org/wiki/Carbon#Characteristics) + +""At atmospheric pressure it has no melting point as its triple point is at 10.8 ± 0.2 MPa and 4,600 ± 300 K (~4,330 °C or 7,820 °F), so it sublimes at about 3,900 K.""" +908 Ages 1 to 4 are very important for brain development but yet most people can't recall anything from that time period. Why don't we remember our earliest memories? 16142 https://www.reddit.com/r/askscience/comments/7qbgxo/ages_1_to_4_are_very_important_for_brain/ 1515930781 7qbgxo Human Body 2018-01-14 14:53:01 "This post has attracted a large number of anecdotes. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. In particular **this is not the right place to share what your earliest memory is**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating. + +" "It’s not that we forget our earliest years, it’s that we don’t form memories in the first place. The term for this is infantile “amnesia”, but this is not actually a form of amnesia — that would require forgetting. As infants grow into toddlers, their brains grow fantastically quickly. So much so, that any pathways that are deemed unimportant/weak are “pruned”. Pruning is the technical term actually. By age three, pruning calms down to the point where toddlers can start forming the memories they’ll remember for possibly the rest of their lives. However, usually the very earliest memories are traumatic or notable in some way. Pruning continues for some time into childhood. Maybe age 4. + +Edit: this has gotten more traction than I anticipated, and I have to clarify: when I say “we don’t form memories in the first place” what I’m saying is that we form memories that we will NOT be able to RECALL after our brains grow and pruning occurs. Toddlers can remember things, but, as we’ve all experienced, they forget an exceptional amount of their day-to-day experiences. As another user pointed out, toddlers actually are learning a metric ton of stuff (motor, language, etc.). + +Edit 2: another user pointed out that it is the delayed development of the hippocampus (learning/memory/encoding center) that contributes to infantile amnesia. " +709 Why does my shower curtain seem to gravitate towards me when I take a shower? 16135 https://www.reddit.com/r/askscience/comments/6cmj7m/why_does_my_shower_curtain_seem_to_gravitate/ 1495450410 6cmj7m Physics 2017-05-22 13:53:30 "Just a gentle reminder that /r/AskScience aims to provide in-depth answers that are accurate, up to date, and on topic. You should only answer questions if you have expertise in the topic and can provide sources for your answer if asked. For more details please refer to our [guidelines.](https://www.reddit.com/r/askscience/wiki/index#wiki_askscience_user_help_page) + +In particular anecdotes are not permitted, especially as a top level comment. This is not the right subreddit to discuss your special technique of stacking shampoo bottles or using magnets to block your shower curtain. So far we have had to remove about 60% of the comments in this thread. Please refrain from speculations, personal theories and joke comments." "I recall reading an analysis of this phenomenon many years ago in scientific american. The shower head does generate airflow, but also in a hot shower the warm air goes out over the top, sucking in cold air at floor level, causing the curtain to blow in. + +I tried to find it again, but failed. Instead, [here](https://www.scientificamerican.com/article/why-does-the-shower-curta/) is a modern equivalent analysis of the airflow using a finite element simulation - it seems comprehensive enough. +" +808 With all this fuss about net neutrality, exactly how much are we relying on America for our regular global use of the internet? 16065 https://www.reddit.com/r/askscience/comments/7ez85x/with_all_this_fuss_about_net_neutrality_exactly/ 1511438792 7ez85x Computing 2017-11-23 15:06:32 "Canadian checking in here. + +**This comment has been updated with better info and links for the sake of clarity, see below for new info** + +Original Comment: + +>As far as I can tell from my research into how this affects Canada, there is only one undersea fiber cable linking Canada's internet to the rest of the world that doesnt go through the US first. That link goes to Greenland and reportedly has had frequent issues since it was built due to poor construction. Aside from this Greenland link, all other wired Canadian internet traffic goes through the US first before going to the rest of the world. The US could effectively cut Canada off from the internet if it wanted to. + +>However, there is a proposal to built a new, modern fiber link through the Canadian arctic that would link London, UK with Tokyo, Japan. This would significantly reduce latency between Western Europe and East Asia while also bypassing the mainland US. It would also provide gigabit internet access to thousands of remote Inuit communities in the Canadian Arctic, which could have life changing effects on their economies. + +**UPDATES** + +Thanks to /u/RcNorth and /u/markszpak for highlighting [this more detailed map](https://www.submarinecablemap.com/#/submarine-cable/gtt-atlantic) than the ones I based the previous version of this comment on. This more detailed map clearly shows that there are 3 fiber links from Halifax to the UK in addition to a fiber link up to Greenland that I mentioned previously. + +However as described by /u/SoontobeSam: + +>As a former network operations technician for a Canadian ISP, this is correct, telegreenland's cable is the only subsea fiber I am aware of that does not enter the US before Canada, our other main access routes are in Toronto and Vancouver, but both connect to the US to access international networks. +I can also confirm that their network uptime is mostly ok, but when they do have issues it takes forever to get any progress and dealing with ongoing non outage issues is difficult, also Newfies and Scots have a serious language barrier even though they're both speaking ""English"". + +So while my initial remarks regarding the US basically being the gatekeeper for Canada's access to the wider Internet may be more or less correct, I was incorrect in saying that the Greenland fiber link is the ONLY fiber link Canada has to the rest of the world. While the Toronto, Halifax, and Vancouver links /u/SoontobeSam mentioned appear to all go through the US in some way first which technically restricts Canada's direct access through those links. + +**Arctic Fiber** + +By popular request here is [the link to the site](http://qexpressnet.com/system/) for the fiber link through the Canadian Arctic that I mentioned previously. The project was formerly known as Arctic Fiber, but has been re-branded as the Quintillion Cable System after the name of the company task with installing the cable. Yes, you read that right, this project has gotten the green light since I last checked up on it (I didn't have time to check on my way to work when I commented originally). They just completed Phase 1 which covers Alaska, and will be starting the Phase 2 to expand through Asia to Tokyo soon. Quintillion has also built a terrestrial link through Alaska and down to the mainland US in order to provide connection to existing connection hubs on the west coast. + +*UPDATE 2: Just have to highlight these two awesome users comments:* + +User /u/KrazyTrumpeter05 posted [an awesome comment](https://www.reddit.com/r/askscience/comments/7ez85x/with_all_this_fuss_about_net_neutrality_exactly/dq9ir7v/) with more info about Canadian Fiber connections, and also linked to [this 293 report](http://subtelforum.com/products/submarine-cable-almanac/) they claim to have played a major role in writing about Internet Fiber connections around the world. Thanks for the fascinating info! + +User /u/Fochang1 posted [this fascinating comment](https://www.reddit.com/r/askscience/comments/7ez85x/with_all_this_fuss_about_net_neutrality_exactly/dq9ic13/) about how South American/Caribbean nations have a similar issue with the US acting as their Internet gatekeepers. They linked to [this insane Internet Exchange Point](https://en.m.wikipedia.org/wiki/NAP_of_the_Americas) in Miami that routes most of South/Central America's internet traffic. Thanks for sharing this incredible perspective that Canadians like myself would otherwise be oblivious to! + +**Some thoughts on the impact of Arctic Fiber** +The fact that this project is actually being built is incredible, because it will mean a huge boost in connection for remote arctic communities that open up massive new economic and information exchange opportunities to these historically very isolated regions. I can't wait to see what the Inuit peoples of Canada's arctic will do with this new link to the outside world. Reconciliation between Canada's indigenous and non-indigenous peoples has become a major focus for Canada in recent years, with the Canadian government [set to fully implement into law](http://www.cbc.ca/news/politics/wilson-raybould-backs-undrip-bill-1.4412037) a 2007 [UN declaration on the rights of Indigenous peoples](https://www.un.org/development/desa/indigenouspeoples/declaration-on-the-rights-of-indigenous-peoples.html). There is a long way to go for reconciliation, and it has been a very rocky road so far, but I hope that this new Fiber link will open up new ways for a large portion of Canada's indigenous population to showcase their own culture to the world and make new economic opportunities for their communities in the digital marketplace. + +If you for some reason read through everything to this point, thanks for reading :)" I would like to know what the ISPs are thinking of Elon Musk's (and others) notion of covering the planet with satellite based service, and how would they compete with that? It seems inevitable that this is in some form the future of internet. And then as an aside, will the competition be companies throwing up MORE satellites? +809 What determines the lifespan of a species? Why do humans have such a long lifespan compared to say a housecat? 15908 https://www.reddit.com/r/askscience/comments/7kq5r4/what_determines_the_lifespan_of_a_species_why_do/ 1513649920 7kq5r4 Biology 2017-12-19 5:18:40 "Other responses have gone into what makes an individual long-lived. This post will address the question as OP phrased it: what determines the lifespan *of a species*? And what's the deal with human longevity? + +Many people have a concept of aging that could be described as the ""wear-and-tear"" model. Basically, the notion is that as you go through life, you accumulate nicks and dings from macroscopic scars and stretch marks to accumulating microscopic injury and DNA damage. Eventually it's just too much and you run down. *It turns out this concept is markedly untrue, at least at the species level*. + +Drosophila melanogaster, the fruit fly, has been the workhorse of many experiments, including those studying longevity, life-history theory, and evolution. Many years ago, researchers working with flies did an evolution experiment. They selectively bred fruit flies for longevity, and in a remarkably short time they had flies with dramatically longer life-spans than is the norm. These flies weren't evolving novel genes in just a few generations, rather, they had recombined existing alleles in ways that lead to longevity. The important thing to note is what happened when these long-lived flies were re-introduced into a 'normal' population. Did these super-long-lived flies thrive? No, quite the contrary. Within a few short generations, any sign of longevity had disappeared. In competition with their 'normal' counterparts, they were immediately outcompeted. (I tried finding the original papers, here's a [modern replication](http://www.pnas.org/content/97/7/3309.full) of these sorts of studies, with more precision.) + +What these researchers discovered was that while longevity is perfectly possible, and within the realm of already-existing genes in most populations, this potential isn't realized *because of trade-offs*. Increased longevity is exchanged for decreased fitness in other areas. Perhaps these long-lived flies in nature would be less likely to evade predators, have more difficulty finding food, or are less likely to find a mate. Everything has a cost. Note that this is different than the 'programmed' idea of death, that your genes have predetermined a time of death for you. In the life-history model of aging, it's not that DNA 'wants' an organism to die, far from it - it's just that other traits (that hurt longevity) are more directly advantageous to the propagation of genes, and so combinations of genes with these traits out-survive and out-reproduce the combinations that lead to longevity. + +The immune system gets interesting. Unless something else kills it first, it's all but inevitable that an animal will die of cancer. The ticking clock of mutations accumulate, eventually leading cells to proliferate out of control, breaking internal apoptosis mechanisms, evading the immune system, and eventually killing the host organism by hogging the lion's share of nutrients and energy. + +What exactly is a 'cancer resistance gene' or a 'cancer susceptibility gene'? Why would anything evolve a 'cancer susceptibility gene'? That doesn't make sense, and they don't. Rather, it's a gene that is perilously close to breaking something important, if it mutates. *Redundancy* is an important concept. If you have 3 copies of something important, you're more or less ok if 2 of them break. If you only have 1 copy, you will be in trouble quickly. Animals that tend to be long-lived, such as elephants and whales, tend to have many, multiply redundant copies of genes involved in important functions like apoptosis and immune regulation - the sorts of genes that when they break ~~tend to cause~~ are no longer able to stop cancer. + +Humans don't seem to have nearly enough multiply-redundant copies of these sorts of genes to explain all of our longevity, while it might contribute somewhat. We don't look like elephants or whales in this respect. This sort of evolution towards longevity would reasonably be expected to take a relatively long time to evolve, as many duplication events would have to happen, and then spread through the population. + +It seems humans are probably like the flies that were selectively bred specifically for longevity. In humans, the [grandmother hypothesis](https://www.nature.com/articles/428128a) conceives of human longevity as something that is directly advantageous to gene propagation ([wikipedia](https://en.wikipedia.org/wiki/Grandmother_hypothesis) introduces the concept well). It's a sort of grandiose kin selection, where elderly humans in prehistoric times were still able to contribute to the survival and reproductive fitness of their children, grandchildren, and extended relatives. Unlike other species that experience a rapid deterioration after their own ability to reproduce goes into decline (such as salmon after spawning), humans *could* contribute into their later years, and so longevity was selected for. Maybe we're not so unlike our experimental flies after all." "Evolutionary biologist here, a lot of the posts here are accurately describing the mechanisms by which we are better protected from aging, but behind each of those is a genetic prerogative for longer life. + +The first principle is that the fitness of an organism is defined as its ability to produce offspring which in turn survive to reproduce. + +If humans live longer that a comparable species, it must be because of an increase in fitness. Some of the leading theories are longer term parental care or multi generational families. Think about it this way: why should women ever go through menopause? It's because having non reproductive women in the social group increases the fitness of her offspring. " +810 Does a burnt piece of toast have the same number of calories as a regular piece of toast? 15854 https://www.reddit.com/r/askscience/comments/7jpnjl/does_a_burnt_piece_of_toast_have_the_same_number/ 1513230491 7jpnjl Chemistry 2017-12-14 8:48:11 "The easy answer is no. If you mean combustion (or burning) of the bread, then there would be less calories because once combustion occurs (even partial) the byproducts are either indigestible or barely so. + +If you mean dark toast, the kind you might get at 6 on the toaster, it has the same calories. The Maillard reaction is what drives browning and it is a complex process where proteins denature and bind to other proteins as well as carbohydrates and so forth created an amalgam of mixed molecules. Essentially this is what leads to that caramel/nuttiness you get when things are browned. However, this conformational change and denaturation does not decrease the calories because the overall building blocks are the same and still digestible. + +However, if let’s say a byproduct of a Maillard reaction is an indigestible molecule that was previously digestible, you could argue that it is now lower in caloric value because it is no longer bioavailable energy. + +Side note, a lot of people are talking about measuring calories by using a bomb calorimeter aka burning the item. This is no longer the method used for finding caloric value of food. Instead they find the net average of Atwater bioavailable nutrients and then use standardized values (e.g. 4 Kcal/g for Carbohydrates) to calculate the assumed caloric value. Again, this is obviously dependent on bioavailable sources of energy, not overall stored energy. + +A perfect example of how a bomb calorimeter is not a feasible option, is Lettuce. Excluding the water (which is 95% of the material) lettuce is primarily fiber. Insoluble fiber in this case or in other words fiber we cannot breakdown (Cellulose). This material has no caloric value to us because it is not bioavailable (aside from small amounts created by gut fermentation thanks to helpful bacteria). So a piece of lettuce has a net caloric value of basically 0 in the Atwater system. In a bomb calorimeter however, it might have a much higher value because inside each of those cellulose walled cells is stored sugars, proteins, and so forth. Additionally, cellulose is essentially a starch made up of Beta-Glucose, however Beta-glucose is in a different conformation than Alpha-Glucose in starches we digest which means it is incompatible with our enzymes. However, combustion wise, cellulose and amylose (Alpha-glucose polysaccharide aka starch to most people) are equivalent in “Calories” in the context of a bomb calorimeter. + +Again, this is not the case in bioavailability. The only animals that can actually get the full caloric potential from plant material are foregut fermenters and hindgut fermenters, aka Cows and Horses. This is why they need multiple stomachs or a large cecum, in order to host helpful microorganisms to breakdown cellulose. Even Termites are not able to digest cellulose, but usually carry symbiotic organisms that can. + +https://www.scientificamerican.com/article/how-do-food-manufacturers/ + +Addl. Note: /u/chuggsipas pointed out the fact that to be totally accurate about this discussion we have to really highlight that a Calorie at its base definition is the amount of energy required in order to raise one gram of water, by one degree Celsius. It’s important to distinguish this because while I do mention that a bomb calorimeter is not used for nutritional labeling values, it is the correct way to calculate calories in its true context. Another thing chugg brought up, and I absolutely agree with, is the fact that nutritional calories are a terrible measure of how our body uses energy. We do not just ingest and combust whatever is bioavailable, there are a multitude of processes that are dedicated to metabolism, storage, availability, etc that are not taken into account by flat caloric values. In fact evidence builds every year that quality of foods and caloric sources are more important than the overall calorie value. However, on some very basic level you can get a vague idea of your energy intake with the Atwater calorie system. + +Edit: Added some clarification in regards to glucose in Cellulose. + +Edit2: Fucked up and did L/D-Glucose instead of Alpha/Beta. Corrected that :X + +Edit 3: Just wanted to say thank you to anyone who challenged or questioned anything I wrote. I definitely needed to add some information and make changes here and there. I appreciate it, especially since that’s what healthy discussion is about, and no one can be 100% correct, 100% of the time without some input from others! " To go along with this question, as a banana goes from green to yellow to brown it gets sweeter because of I assume sugar. Does a yellow banana have more calories than green-yellow banana? I've always wondered. +710 Do animals have blood types like we do? 15543 https://www.reddit.com/r/askscience/comments/6mtsdg/do_animals_have_blood_types_like_we_do/ 1499864654 6mtsdg Biology 2017-07-12 16:04:14 "Apes and old-world monkeys have ABO blood types like us. + +Other animals have blood types, but not the same ones as us. There are thirteen different dog blood types, but cats are categorised as A, B, or AB. Not the same as human A and B. " [deleted] +909 Is there any reason for the alphabet being in the order its in? 15498 https://www.reddit.com/r/askscience/comments/7xmrjn/is_there_any_reason_for_the_alphabet_being_in_the/ 1518655291 7xmrjn Linguistics 2018-02-15 3:41:31 "Short answer: maybe, maybe not. No one is sure. + +Longer answer: The alphabet we use today is something that evolved over ~3,000 years, through 4 iterations minimum: + +Phoenician ⇒ Greek ⇒ Latin ⇒ modern languages with letters like J, W, and ß, as well as diacriticals like å and diphthongs like œ. + +As a result, there’s no one answer for where the order for a given modern language comes from. The alphabet for English is different from that of French, or Swedish, or Polish. Consider the Hungarian alphabet, which looks like this: + +a, á, b, c, cs, d, dz, dzs, e, é, f, g, gy, h, i, í, j, k, l, ly, m, n, ny, o, ó, ö, ő, p, q, r, s, sz, t, ty, u, ú, ü, û, v, w, x, y, z, zs + +Now, we can look at that and see that the basic order of the Latin alphabet remains. The additions are just stuck in after the related letters whose sounds they modify. As with English, we have the Latin alphabetical order, plus the later medieval insertions of j and w. The insertions are obvious and easy, because they simply follow the letters they were invented to modify/clarify. + +But for the Latin order, it’s trickier. Latin is a blend of Etruscan and Greek, and they adopted neither wholesale. For example, Etruscan had 3 letters for what we would think of a ‘k’ sounds today: C, Q, and K (probably ‘kay’, ‘qoo’ and ‘ka’ but this is a guess since Etruscan remains untranslated). G was a lesser-used sound in Etruscan, but /k/ was very important, so they invented C from G, swapped kappa and gamma in the order, then inserted the ‘other’ k sound further down the line from Ϙ or qoppa , a pre-standardized Greek letter used in some cities. + +Long story short, there’s some interesting linguistics research that suggests certain groupings of letters were created intentionally by different groups at different times, and then just kept out of habit by adopters. + +So for example, the Beth Gimel Dat sequencing mentioned in a number of other posts was adopted directly into Greek as Beta Gamma Delta, but then the Gamma was replaced with C in Latin. + +EDIT: Thanks for the gold, kind stranger!" "Semiotician W. C. Watt, after much research, concluded that the alphabet ordering descended from an early organization that grouped the letters by their sounds, which might have been used as a teaching tool for language (although that original organization/artifact is now lost). He called it the ""[Ras Shamra Matrix](https://www.degruyter.com/view/j/semi.1989.74.issue-1-2/semi.1989.74.1-2.61/semi.1989.74.1-2.61.xml)."" + +Apparently he hadn't really even considered the question until a student asked him, and he realized he didn't know. However, he thought about the alphabet (A-B-C-D), realized that earlier organizations, like in Hebrew, had Bet-Gimel-Daleth (B-G-D), which are phonetically related, and so it might not be arbitrary. This sent him off on a research quest trying to figure it out." +603 Are humans closer in relative size to the planck length or the entire observable universe? 15373 https://www.reddit.com/r/askscience/comments/5s7ago/are_humans_closer_in_relative_size_to_the_planck/ 1486300307 5s7ago Astronomy 2017-02-05 16:11:47 " + +Object | Size +---|--- +size of observable universe | 8.8×10^26 meters +average height of human | 1.7 meters +Plank length | 1.6×10^-35 meters + +_____________________ + +Universe / Human ratio = 5.16×10^26 + +Human / Planck length ratio = 1.1×10^35 + + +result : Humans are closer to the size of the universe than the Planck length is to the size of a human + +" Definitely the latter; the comoving radius of the observable Universe is on the order of 10^(26) m, while the Planck length sits at about 10^(-35) m. The metre is closer to the cosmological scale than the Planck scale. +604 So atmospheric CO2 levels just reached 410 ppm, first time in 3 million years it's been that high. What happened 3 million years ago? 15360 https://www.reddit.com/r/askscience/comments/6792ez/so_atmospheric_co2_levels_just_reached_410_ppm/ 1493040930 6792ez Earth Sciences 2017-04-24 16:35:30 "Geology PhD here, I will add citations and extra info if this comment gets interest, I'm just about to get on a plane so that'll be in several hours but a lot happened 3 Ma, during that period the Earth transitioned from a ""greenhouse"" earth to an ""ice house"" Earth as the Northern hemisphere glaciated. This was due to the closure of the Isthmus of Panama which altered ocean currents and allowed the Atlantic meridional overturning circulation to form (it may have existed in a weakened state before however). This cooled the northern hemisphere allowing ice sheets to form. The ice sheets of Antarctica had already formed at this point however around 34 Ma. + +In short the CO2 levels were higher due to a number of reasons but one was the planet was still in a warm ""phase"" with high levels of atmospheric CO2 because there was less area of ice sheet to store CO2 and cool the planet allowing more CO2 to be stored in the oceans + +Disclaimer: this is all I can remember off the top of my head, please correct me if any of it is wrong :-) + +Edit: My flight is delayed! Good news for you all but bad news for me haha, anyway, promised citations from a presentation I did on the topic recently: + +• Bartoli, G. et al. 2005: Final closure of Panama and the onset of Northern hemisphere glaciation. Earth and Planetary science letters. V. 237, 1-2, p. 33-44. http://dx.doi.org/10.1016/j.epsl.2005.06.020 + +• Filippelli, G. M. and Flores, J-A. 2009: From the warm Pliocene to the cold Pleistocene: A tale of two oceans. Geology. V. 37, no. 10, p. 959 – 960. doi: 10.1130/focus102009.1 + +• Grotzinger, J. P. and Jordan, T. H., 2014: Understanding the Earth. W.H. Freeman and Co. (seventh ed.) + +• Haug, G. H., and Tiedemann, R. 1998: Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation. Nature. V. 393, p. 673 – 676. doi: 10.1038/31447 + +• Schneider, B. and Schmittner A. 2006: Simulating the impact of the Panamanian seaway closure on ocean circulation, marine productivity and nutrient cycling. Earth and Planetary science letters. V. 246, p. 367 – 380. http://dx.doi.org/10.1016/j.epsl.2006.04.028 + +• Linthout, K., Helmers, H. and Sopaheluwakan, J. 1997: Late Miocene obduction and microplate migration around the Banda sea and the closure of the Indonesian Seaway. Tectonophysics. V. 281, no. 1, pp. 17 – 30. + +• Lisiecki, L. E., and Raymo, M. E., 2005: A Pliocene-Pleistocene stack of 57 globally distributed benthic 18O records. Palaeoceanography. V. 20. doi:10.1029/2004PA001071 + +Edit 2: If you thought the Pleistocene had high CO2 then google the paleocene eocene thermal maximum, I'm happy to add info about that after my flight (once I can access my computer) + +Edit 3: thanks for the gold! My first :-D boarding now (delay was minimal) I'll be back in a few hours with more cool palaeo stuff." "This question has attracted a number of joke answers, speculation, and low quality responses by non-experts, as well as a number of questions about the removed comments, all of which have been removed. If you are unqualified to give a thorough response, please consider refraining. + +Edit: Additionally, many responses are making arguments about CO2 levels over the past 500+ million years as well as general arguments for or against climate change. The question asks about the causes of levels 3 mya, please keep responses on topic." +711 How do women astronauts deal with periods in antigravity? 15152 https://www.reddit.com/r/askscience/comments/6o9rki/how_do_women_astronauts_deal_with_periods_in/ 1500483016 6o9rki Human Body 2017-07-19 19:50:16 "Due to the time currently and the influx of comments that are still violating the rules this thread is locked. + +~~If you are going to comment please read our [subreddit rules](/r/askscience/wiki/rules) because we have strict comment moderation. If you are starting off with a personal experience or a statement like ""I think"" without citations to back up your stance, your comment will be removed.~~" "You mean ""micro gravity"" as ""anti-gravity"" is more of a science fiction term ([micro-gravity is NASA's term](https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-microgravity-58.html) about living and working in/on spacecraft). Or more likely just ""weightlessness"". + +Female astronauts have the option of carrying their preferred pads or tampons while in space ([Popular Science 2016](http://www.popsci.com/brief-history-menstruating-in-space)). If they choose to not get their periods they can medically induce amenorrhea, or stop their periods from happening ([The Atlantic 2016](https://www.theatlantic.com/health/archive/2016/04/menstruating-in-space/479229/)). There was [a scientific paper](https://www.nature.com/articles/npjmgrav20168) written on medically induced amenorrhea in female astronauts in 2016. + +There are several ways to induce amenorrhea, through hormonal pills, injections or intrauterine device (IUDs). While it is safe to have your period in space, it may not be all that convenient to switch pads or tampons and deal with disposal. The water treatment is also set up to recycle water from urine, but not menstrual blood so that is also an issue ([American Chemical Society 2014](https://www.acs.org/content/acs/en/pressroom/presspacs/2014/acs-presspac-april-9-2014/recycling-astronaut-urine-for-energy-and-drinking-water.html)). + +According to National Geographic (link below) if a woman spent three years in space she would need about 1,100 pills, which adds some weight to a mission but is less unwieldy than many tampons. Alternatively, three years worth of tampons (or pads) still weighs more than three years worth of pills. + +Female astronauts' periods have a long history. National Geographic has a great opening paragraph in one of [their articles](http://phenomena.nationalgeographic.com/2016/04/22/how-do-women-deal-with-having-a-period-in-space/) on the subject: + +>Sally Ride’s tampons might be the most-discussed tampons in the world. Before Ride became the first American woman in space, scientists pondered her tampons, weighed them, and NASA’s professional sniffer smelled them—better to take deodorized or non-deodorized?—to make sure they wouldn’t smell too strongly in a confined space capsule. Engineers considered exactly how many she might need for a week in space. (Is 100 the right number?, they famously asked her. No, Ride said. That is not the right number.)" +1593 Why do we hear about breakthroughs in cancer treatment only to never see them again? 14987 https://www.reddit.com/r/askscience/comments/gzb3gy/why_do_we_hear_about_breakthroughs_in_cancer/ 1591659316 gzb3gy Medicine 2020-06-09 2:35:16 "Several things. + +There HAVE been many advances in cancer prevention, detection and treatment. (Though obviously there is tremendous work yet to be done.) + +Often, new treatment technologies, while genuinely promising, fail to fully live up to that initial promise. + +Pop science and medical news reporting often exaggerates or overstates the potential of emerging technologies. Even responsible journalism is often sensationalized to bolster reader interest. + +Finally, there are MANY different forms of cancer with wildly different causes, characteristics and disease processes. It is pretty unlikely that we will ever see any single ""cure"" for all types of cancers." "Pointing at just one of them: +https://www.cancerresearch.org/blog/december-2013/cancer-immunotherapy-named-2013-breakthrough-of-the-year + +Checkpoint inhibitors which that article talks about have had a massive impact on a wide variety of cancers. They don't always work, but for some types of cancer they improved survival 20% or more. That is massive for what probably averages a 1-2% per year increase in survival normally. + +I work in the cancer field and a decent percent of doctors still talk a bit in awe of checkpoint inhibitors and how big of an impact they have had. + +Likewise you have CAR-T linked as well. That also for the folks it works on is revolutionary. It took some cancers with an average survival measured in months and gave them a chance. Again it is for a limited number of cancers mostly blood cancers (work is ongoing for solid tumors, but proving difficult though recently there has been some promise), but for the cancer types it works on it certainly is life changing for those folks (namely that they will have a life)." +712 Why can't we just inject a ton of power into a phone at once to instantly charge it? Is that just too dangerous, or just not possible? 14983 https://www.reddit.com/r/askscience/comments/6efd2k/why_cant_we_just_inject_a_ton_of_power_into_a/ 1496241511 6efd2k Engineering 2017-05-31 17:38:31 "To understand why not, you have to understand how a battery works. It's not a tank of electrons, exactly. A battery is a chemical reaction between an anode (-), cathode (+), and an electrolyte (or some form of conduit) which facilitates the exchange of electrons. + +When you discharge (use) a battery, a chemical reaction is occurring, moving electrons between the two chemicals (anode and cathode). So, don't think of a battery as a vessel which just holds a pile of electricity. It's a specific transfer of energy between two chemicals. + +Now, in a rechargeable battery, this reaction can be reversed by applying electricity using a charger. But, again, it's not adding anything, really. It's reversing the chemical reaction which is putting the chemicals back to their original state. + +When charging, it takes time for the reaction to reverse and at the same time, heat is created because the electrons are moving back across the conduit they travelled across originally. Electrons moving over a conductor meet resistance which creates heat, no matter which direction. Much like the battery heating up when you use the phone, the battery will heat up while charging for the same reason. If you were to throw a bunch of current at the battery, it could easily cause a thermal issue. Nickel-cadmium (NiCd: pronounced Nye-Cad) batteries had a problem called thermal runaway where the battery, if charged too quickly, the heat generated could induce a self-feeding loop where the battery could heat to a point of ignition or explosion. But that's not an issue with Lead-Acid batteries (like sealed lead acid batteries like in your car, which use a liquid electrolyte, also known as a wet cell [thanks to u/gilescoreywasframed for the correction below]). Also prone are Lithium Ion (LiOn, like in your cell phone) or Lithium-Polymer (Li-PO) batteries (credit to u/incrediboy729 for the correction here), but these usually incorporate circuitry to prevent this situation. + +tl;dr - it is dangerous, and modern cell phone chargers and batteries have circuitry to prevent too fast/overcharging which could lead to heat damage or fire." "This is what we're hoping to be able to do with [graphene batteries](https://www.google.ca/amp/s/phys.org/news/2016-07-fast-charging-everlasting-battery-power-graphene.amp) + +They are an example of a supercapacitor, a battery able to physically hold onto electrons. You'd be able to plug it in, fill it up and go on with your life in a matter of seconds. + +This is very different from our current technologies, all of which use an electrical current to reverse a chemical reaction. As everyone is saying this process necessarily takes a while and is fairly inefficient, hence battery chargers getting hot, heat production=wasted energy. This is essentially the same difference between lightbulb types. Incandescents are very inefficient, so they get very hot, CFLs are fairly efficient so they only get warm and LEDs are very efficient so they barely produce heat at all." +1002 Humans are known to help out an animal if it's stuck, injured or in problems in the wild. Are there any animals that are known to help other animals or humans in distress? 14882 https://www.reddit.com/r/askscience/comments/98vg89/humans_are_known_to_help_out_an_animal_if_its/ 1534785090 98vg89 Biology 2018-08-20 20:11:30 [In 2003 a group of elephants released a bunch of captive antelope.](https://www.telegraph.co.uk/news/worldnews/africaandindianocean/1427058/Elephants-free-captive-antelope.html) Conservationists thought the elephants were coming to take some of the food but instead, they circled the compound and one opened the latch to the gate. The antelope left, followed by the elephants, who never touched the food. "Elephants have been reported many times to help humans and animals, although the case is more often than not ""helping by simply avoiding to crush someone under their enormous weight"". The [Wikipedia article](https://en.wikipedia.org/wiki/Elephant_cognition#Elephant_altruism) gives several examples of elephant helpfulness. In general, elephants have very strong feelings of mourning, compassion and empathy both towards their kin and other creatures, and it seems they're very aware of how fragile most things are compared to themselves. + +Elephants are the best." +713 Why does electricity always hum at a B-flat pitch? 14795 https://www.reddit.com/r/askscience/comments/6wdnnw/why_does_electricity_always_hum_at_a_bflat_pitch/ 1503856850 6wdnnw Physics 2017-08-27 21:00:50 Electricity is run on an alternating current (AC) which reverses voltage in the pattern of a sine wave. In the US, the frequency of this alternating is 60 Hz, which is a B flat (more of a flat B or sharp B flat, really). Sometimes interactions with surroundings, especially at high voltages like in transformers, can cause a hum at the frequency the grid is run on. In most of Europe, as an example, it's run at 50 Hz not 60 Hz, so you would hear a G (a little sharp) instead of a B flat. "In the US, alternating current (AC) oscillates at 60Hz and the buzzing you hear is generated by the second harmonic, so 120Hz. The nearest B-flat is at 116.54Hz, so it's pretty close! The next B is at 123.47Hz, so really you're hearing something that is very much in the middle of B and B-flat. If you were in Europe, where the standard is 50Hz, you'd be hearing something between G (98Hz) and G-sharp (103.83Hz). + +Also, excellent ear, are you a musician?" +1003 Does washing off fruits and vegetables before eating them actually remove much of the residual preservatives and/or pesticides? 14654 https://www.reddit.com/r/askscience/comments/8mwi0l/does_washing_off_fruits_and_vegetables_before/ 1527570421 8mwi0l Biology 2018-05-29 8:07:01 "For a big part, yes. It mainly works for residues, which are on the outer layer of the vegetable skin, where normally the biggest part of pesticides is located. A lot of studies show further, that a acidic washing solution, eg acetic or citric acid, is way more powerful, especially for organophosphorus and organochlorines. +Also, peeling and cooking also have a strong effect on reducing pesticide concentration. + +Anyway, normally fruits and vegetables are washed in the factory before selling and shouldn‘t have residues above critical limits, theres no need to be scared, at least if you‘re in a country with proper food safety regulations. + + +Some Papers about the topic (there are much more): + +https://www.sciencedirect.com/science/article/pii/S0278691501000163 + +https://www.sciencedirect.com/science/article/pii/S0308814698002313 + +https://www.sciencedirect.com/science/article/pii/S0308814610005984 + +https://www.sciencedirect.com/science/article/pii/S0278691500001770 + +Edit: spelling" "This question interested me. So I looked it up. Yes. It significantly removes pesticides. Washing with baking soda removes more. + +I also learned that after harvest produce gets washed for two minutes with a bleach based sanitizer to remove dirt and germs. + +https://cen.acs.org/articles/95/web/2017/10/Baking-soda-washes-pesticides-apples.html" +1004 Is it possible for a deck of cards to be shuffled accidentally into perfect order? 14495 https://www.reddit.com/r/askscience/comments/8spnd7/is_it_possible_for_a_deck_of_cards_to_be_shuffled/ 1529562939 8spnd7 Mathematics 2018-06-21 9:35:39 "u/Rannasha gives the ""proper"" answer, but I'm going to add a few twists to this question that can significantly reduce the probability immensely. + +The answer u/Rannasha gives makes two assumptions: one that there is a singular entity that we can call a ""perfect order"", and secondly that the ""shuffling"" is perfectly random. + +I'll tackle ""perfect order"" first. What is ""perfect order""? If we assume it's the order the cards were in when you first open the box, or that it has a single definition (such that the suits and values have to be of a fixed ordering), then there is only 1 out of 52! ways to achieve a ""perfect order"". + +But what if we don't care about the order of the suits? Maybe SPADES, HEARTS, DIAMONDS, CLUBS is just as valid as HEARTS, DIAMONDS, CLUBS, SPADES. You can reduce the ~~probability~~ permutations by a factor of 24 if the suit order doesn't matter. And what about the ace? Is it before the two or after the king? If it can be either, you can reduce the probability by another factor of 2. Combine both together, and you've reduced the ~~probability~~ permutations by a factor of 48. That reduces the ~~probability~~ permutations from 1 in ~8 * 10^67 down to ~1.6 * 10^66. That will still take you forever, but it _is_ a slight improvement. + +But what if I told you I could *guarantee* you can do it in only eight shuffles? + +""Shuffling"" is usually thought of conceptually as ""randomization"", and while that's the intent, the mechanical principals of how cards are actually shuffled aren't purely random events. Take the standard riffle shuffle for example. You split the deck into two nearly even halves, and than alternately drop a few cards from each pile into a new pile. This isn't a purely random series of events: the bottom card of the pile that has the first drop will always be on the bottom of the shuffled deck, for example. + +Indeed, if you're so very skilled in shuffling that you *always* split the deck into two perfect 26-card sub-decks, and then *always* start the shuffle with a card drop from the same sub-deck, AND *always* perfectly interleave the cards one at a time, you can ""shuffle"" the deck in a completely predictable way (this actually has a name, and is known as an [out shuffle](https://en.wikipedia.org/wiki/Out_shuffle)). And if you do that, after only 8 shuffles you'll have your original deck layout again! + +I suspect this isn't what you meant by ""shuffle"", ""accidentally"", or ""perfect order"", but if you're somewhat flexible with these definitions, you can get the probability down to something you can achieve in less than 5 minutes. + +EDIT: Added mention of (and link to) ""out shuffle"". +EDIT 2: Thanks to /u/unspeakableadvice for noticing I had substituted ""probability"" when I really meant ""permutations"". That's what I get for typing up replies at 0300 when I should be sleeping. Also, thanks for the gold, kind stranger!" "The number of possible shuffles of a standard deck of cards (52 cards) is 52 * 51 * 50 * ... * 1, or otherwise written as 52!. This number is approximately 8 * 10^(67) (an 8 followed by 67 0's). + +To get an idea of how unimaginably large that number is, lets assume that we can create a billion different deck-orderings every second. That's 3.6 trillion per hour or 86.4 trillion per day. At this rate, it would take about 10^(54) days to exhaust all possible orderings. Or about 3 * 10^(50) years. For reference, our universe is about 1.5 * 10^(10) years old. + +The chance of shuffling a deck of cards into one specific order is so incredibly small, that it is effectively impossible. You stand a better chance at trying to win the jackpot in the lottery multiple times in a row. + +edit: To anyone with the urge to reply ""So you’re telling me there’s a chance?"": This joke has already been made (repeatedly). Find some new material :)" +811 If doctors can fit babies with prescription eye ware when they can't talk, why do they need feedback from me to do the same thing? 14494 https://www.reddit.com/r/askscience/comments/73q2um/if_doctors_can_fit_babies_with_prescription_eye/ 1506910840 73q2um Human Body 2017-10-02 5:20:40 "Pediatric patients are fitted with eyewear based on prescriptions from mostly just the autofractors as jaimemaidana pointed out. This gives a really good estimation of the corrective lens prescription. A ballpark or rough estimation of the prescription. + +Once someone learns his/her abc’s or sometimes shapes a phoropter may be used. The device that sits in front of your face, and you are asked if one or two, or a or b looks better as you are looking at an eye chart. This allows for an even better prescription to be determined. The phoropter may be used by itself or it may be used to fine tune the prescription that the autorefractor read, so you get the best possible vision. + +It’s not that an adult’s autorefratcor generated prescription couldn’t be used, but your doctor wants your eyewear to have the best chance for giving you the best possible sight." "Streak retinoscopy is an objective way to get a prescription. [Here is a video showing it in action](https://youtu.be/kAreDffuVCQ). In short, you put lenses up until you perfectly focus a light beam on the eye. That gives the objective prescription. + +When the doctor is asking you ""1 or 2"" they are doing a subjective way of finding your prescription. It is you saying what you like better. + +A doctor can use streak retinoscopy to get any ones prescriptions. However, if the patient is able to speak, it is good to confirm, and tweak, if needed, the prescription. A subjective prescription may not give the best vision, but it is what the patient likes the most." +605 When a nuclear device detonates, the shockwave trends to clear overhead clouds, exposing the sky above. If it was raining, does that mean a nuclear device would stop the rain? 14491 https://www.reddit.com/r/askscience/comments/603u8z/when_a_nuclear_device_detonates_the_shockwave/ 1489839780 603u8z Physics 2017-03-18 15:23:00 "It is also known to cause precipitation as well. About 30-40 minutes after detonation in both Hiroshima and Nagasaki, survivors experienced an irradiated ""black rain."" While this may have also been attributed to heat gathering from city-wide fires, still a weird and terrifying phenomenon. + +http://atomicbombmuseum.org/3_radioactivity.shtml + +[John Hersey also did an article from the perspective of six survivors, amazing read ](https://www.google.com/amp/www.newyorker.com/magazine/1946/08/31/hiroshima/amp) " "I'm not a meteorologist so it's hard to answer this sort of thing. There doesn't seem to be much published on the question. It is just worth noting that thunderstorms are typically quite large — 15 miles in diameter or so. Even very large nuclear explosions have relatively small fireballs compared to that (the 100 Mt Tsar Bomba would have had a 10 mile diameter fireball; whereas a 10 Mt weapon fireball is only 4 miles in diameter — both of those are extremely large weapons). There are going to be complicated relationships with the clouds above; blast waves can reflect off of clouds and temperature inversions, which can under some circumstances increase their range on the ground, in some cases reduce them. Under some circumstances you can [actually create a thunderstorm with a nuclear blast](http://blog.nuclearsecrecy.com/2012/11/15/how-to-make-an-atomic-thunderstorm/) (and it's been done). + +So this isn't an answer — it's more of a ""it's complicated, it probably would require serious study"" sort of thing. I'm not sure it _has_ been studied. The effects of nuclear weapons on very large storm systems (e.g. hurricanes) would be negligible — the systems are just too large relative to the size of the bomb that would interact with them. For smaller systems, it's definitely the case that the detonations can affect the local weather, but I'm not sure how easy it is to predict what would happen in any given situation." +812 Can an insect be “fat”? How do they store energy? 14484 https://www.reddit.com/r/askscience/comments/78jrjn/can_an_insect_be_fat_how_do_they_store_energy/ 1508887847 78jrjn Biology 2017-10-25 2:30:47 "Bloodsucking insects will become engorged after feeding. Mosquitos, bed bugs, lice, ticks, fleas, ticks (arachnid), are visibly larger after feeding. + +Perhaps more relevant is the Fat Body. + +Insects have an organ called the Fat Body. Lipids (fats) are stored here in adipocytes in the form of triglycerides (same way mammals store fat, essentially). These lipids are consumed during periods of high energy demand (like when flying), and are replenished in periods of food abundance. + +Some insects have been shown to increase the size of the Fat Body in the winter, as a mechanism to enhance survival. Other insects (like house flies) don't seem to be able to store extra fat. + +edited to add some sources: + +Study on fat storage in Culex pipiens: https://www.ncbi.nlm.nih.gov/pubmed/2769712/ + +review paper on the insect Fat Body:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3075550/" "It depends a lot on the insect in question. + +The most extreme example I can think of is the [honeypot ant](https://en.wikipedia.org/wiki/Honeypot_ant). Some members of these colonies become living food storage for the rest, hanging in place and taking in or giving out their stored reserves as needed. " +910 "Can the ancient magnetic field surrounding Mars be ""revived"" in any way?" 14415 https://www.reddit.com/r/askscience/comments/878898/can_the_ancient_magnetic_field_surrounding_mars/ 1522061937 878898 Planetary Sci. 2018-03-26 13:58:57 "Here's a link to an article covering the idea. NASA proposed that placing a surprisingly small magnet at the L1 Lagrange point between Mars and the Sun could shield the planet from solar radiation. This could bea first step toward terraforming. The magnet would only need to be 1 or 2 Tesla (the unit, not the car) which is no bigger than the magnet in a common MRI machine. [EDIT] A subsequent post states that this idea is based on old science, and possibly would not be as effective as once thought. Read on below. + +https://m.phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html" "It's not mentioned here, but critics of this idea have said this does nothing to block gamma rays which come from every direction unlike the sun. While this is true the fact is this would solve immediate problems that make Mars uninhabitable. +It's also been suggested that once a large colony is established on Mars one of the first industries could be manufacturing a large quantity of these magnetic dipole shields (or something similar) and creating a global shield to reduce gamma rays. + +But the main reason that criticism isn't compelling is that once the atmosphere grows and becomes denser it will also act as a barrier to reduce gamma rays. + +We have the technological ability today to see Mars's atmosphere grow in our lifetime. That's very cool." +1295 In HBO's Chernobyl, radiation sickness is depicted as highly contagious, able to be transmitted by brief skin-to-skin contact with a contaminated person. Is this actually how radiation works? 14379 https://www.reddit.com/r/askscience/comments/c36ubu/in_hbos_chernobyl_radiation_sickness_is_depicted/ 1561096472 c36ubu 2019-06-21 8:54:32 "Radiation isn't ""contagious"" so much as you just have to keep in mind that radioactive material is constantly giving off radiation. At Chernobyl, that material was everywhere- not only on the ground in huge chunks, but also in the air, in fumes, ash, and dust. + +​ + +The firefighters who responded were covered in this material when they arrived at the hospital. It's why it was critical to remove their uniforms and store them in the basement where they are still radioactive today. I don't know if the time it took for a nurse to carry them downstairs would have been enough time to give the ""sunburn"" effect on her hand, but they're still moderately dangerous today, and would have been much more so at the time. + +​ + +The other thing to remember is that radioactive material can become trapped in the body. Those firefighters weren't just covered with the ash and dust, (which can mostly be removed with a shower and change of clothes), they breathed it in as well, where it gathered in their lungs and blood and ate them apart from the inside. The gamma rays emitted by those internal particles would have shot right through them and hit anything around them, making their bodies minorly radioactive. + +​ + +This is played up *slightly* on the show. While the radioactivity they admitted would be an issue, the main reason for keeping the patients separated from visitors is that your immune system is one of the first things to go from radioactivity, and so any visitors could pass on all manner of diseases to them." "Hi, I’m a radiation biologist. I’m currently halfway through the series and I’m not sure I’ve seen the scene you’re referring to, but the show is otherwise VERY realistic with regards to the physiological responses to radiation. + +Uranium decays into many unstable isotopes, one of the main ones the show discusses is Cesium 137, which is one of the main decay products from uranium, so for our purpose let’s talk about it’s contamination. Cesium undergoes beta decay, meaning it’s nucleus ‘spits out’ a beta particle and becomes Barium 137. Beta particles on the skin aren’t a huge deal in theory, because they don’t carry enough energy to breach the skin. You could have a chance of skin cancer depending on the contamination level. The issue becomes, that you can’t see it. In the best case scenario, you would wash your hands immediately after contamination, but you’ve touched the faucet, washed your hands and touched the faucet again. Guess what? These aren’t microbes. You will at one point touch food with your bare hands, and ingest it. Now you have radioactive decay trapped in your body for a long, long time, and you don’t have the protection of your skin anymore. The incidence of colon, lung, stomach cancers and leukemia are now massive. + +We’re talking about just one decay product of uranium here. There are many many others with different decay properties that will produce other qualities of radiation poisoning. Overall however, we’re concerned with cumulative dose. There are two main classifications of radiation poisoning: acute radiation syndrome (which occurs after a 4-8 Gy exposure within typically a few days) and Chronic radiation syndrome (which occurs after a .5-1.5 Gy exposure at a rate >.1 Gy/hr) + +-acute radiation syndrome- symptoms are present within a few hours, sometimes sooner. Early symptoms are malaise, and severe vomiting/dehydration. Sometimes seizures occur. Recovery at lower doses is possible, with high cancer risks. A dose of 8 Gy or higher is a death sentence. The cause of death is intestinal sepsis. + +-chronic radiation syndrome- you can go months without showing symptoms, however once they show up they are similar to those of the acute exposures. The symptoms in this form can be treated, but carcinogenesis is high. + +As for Chernobyl, basically anybody within close proximity to the plant including all workers at the time for sure got acute radiation syndrome, which the show did a great job of with symptoms and timing. As for the population of the city, it really depends on where they were relative to the wind, how long they were outside, and how much contact they had with contaminated surfaces. There certainly were a lot of suspected cases of acute radiation syndrome-about 237, with 169 confirmed. The average dose estimate is on the order of 6.5 Gy, though doctors at the time suspected bone marrow failure rather than sepsis, and the diagnostic practice along with any relevant political pressure, brings to question the true number of cases. + +There is of course a high cancer incidence in the exposed population, with an estimated death toll from 4,000 to over 90,000 so far. Again the estimates are highly politically charged. + +Edit: thank you so much for the silver, and my first gold, whoever you are! + +Update: got around to watching the scene in question. It’s not the scenario I describe above and I don’t know if lethal contamination could occur that way. My guess is no" +813 If the Niagara falls is frozen where does all the water go behind it? Does it just spill over and flood surrounding land 14377 https://www.reddit.com/r/askscience/comments/7n81em/if_the_niagara_falls_is_frozen_where_does_all_the/ 1514719404 7n81em Earth Sciences 2017-12-31 14:23:24 "“Niagara Falls” is actually three waterfalls, the “American”, the “Bridal veil”, and the “Horseshoe” falls. Never in recorded history have all three of them completely frozen, but the smaller two (American and Bridal Veil”) have frozen a few times. When it happens, most of the water on the surfaces of Lake Erie and the Niagara river is already frozen so the volume of water going over the falls is reduced anyway. The rest of the moving water goes over the unfrozen parts of the Horseshoe falls. Besides this, two big hydroelectric power plants, one American and one Canadian, divert water away from the falls to generate electricity. This means the river and the falls have less water than they can handle anyway. + +Source: grew up in the city of Niagara Falls. This stuff is local legend and drilled into our heads as kids. " "As mentioned in previous posts, much of the water gets diverted to hydro electric plants. In the summer, during the day, there is an agreement that states the water cannot he diverted as much. This is so that tourists can see the falls “in all their glory”. At nighttime and during the winter, much more is diverted for energy production. + +As for your question. Historically speaking, ice bridges have formed, even to the point where people would play on the bridges, set up a market, and walk across to the other country’s side. This has been illegal since 1912, but even while this happened, water still flowed over the falls. Although the ice bridge was thick and sturdy, the fast flowing water runs beneath the ice, so it can look like the falls have frozen, but there is still water flowing over them, along and behind the ice. Think of it like an icy covering that’s hiding the real flow of water. + +There is only one instance of the falls completely freezing over, about 150 years ago, however all the other water had completely frozen as well, so the side effects were minimal. + +tl;dr +If Niagara Falls ever did completely freeze over, the rest of Lake Erie probably did to, so there would be no concern for flooding or anything of the sort. " +714 How does a computer network like HBO's handle the massive output of data for short bursts of time, like a GoT episode? 14369 https://www.reddit.com/r/askscience/comments/6tut5w/how_does_a_computer_network_like_hbos_handle_the/ 1502810723 6tut5w Engineering 2017-08-15 18:25:23 Content Delivery Networks (CDN). Multiple servers around the country cache the content, closest geographical or fastest is the one that serves you so not everyone is pulling from the same server. It's not hard to forecast bandwidth usage since it is just simple data and in general most CDNs are not run near capacity so there is room for these spikes. Many people are mentioning CDNs and that is the correct answer. However, to address your question, it is possible for a site to spin up their own servers from a cloud service company to handle sharp increases in load. CDNs are very good at delivering static content but they wouldn't be able to help if the spike were due to a huge influx of user registrations or ticket purchases. +1005 Does a heart need to beat? Would we be able to replace the heart with something that continuously moves blood around with no pulse (using a pump/compressor of sorts)? Would there be complications by making the flow constant rather than pulsed/beats? 14353 https://www.reddit.com/r/askscience/comments/8jkbm1/does_a_heart_need_to_beat_would_we_be_able_to/ 1526377637 8jkbm1 2018-05-15 12:47:17 "There is already a device out there that does what you are saying. A lot of people with severe heart damage will get put on a device called an LVAD (Left Ventricular Assist Device) which can either assist a damaged heart or just replace it entirely. These devices have a rotor that circulates blood continuously instead of making it pump. It connects to a battery pack outside the body. These people will often have no pulse and by extension no measurable blood pressure because there is no pulsitile motion to measure. These devices are usually used as a temporary measure until a heart donor can be found, but it's getting more common to be used in those that cannot undergo a heart transplant as well. +Here's some more info if you want to read about it. + +https://stanfordhealthcare.org/medical-treatments/l/lvad.html + +I am an ED nurse at an LVAD center hospital so I see these fairly often." "This already exists - it's called a left ventricular assist device (LVAD). It is implanted in people who's heart is too weak to effectively pump blood at a sufficient perfusion pressure. + +Basically it consists of a pipe with a motor in the middle. One end of the LVAD is hooked up to the heart (left ventricle), the other end is hooked up to the aorta (largest artery carrying blood to the rest of the body), and in the middle there is a motor which generates a negative pressure which sucks the blood out from the heart (assists the heart) and into the aorta. The motor speeds are adjusted to optimize the pressures in the heart. It is powered by a battery that is worn outside the body, but connects to the LVAD through the abdomen. + +It is used in those who are waiting for a heart transplant but would otherwise die waiting. In some it’s also used as destination therapy (they are not candidates for a heart transplant but this will keep them alive longer than if they didn’t have an LVAD). + +Complications include hemolysis (shredding of red blood cells) due to the motor. There is also a high risk of infection and also clotting. + +Regarding pulsatile vs continuous flow - no one knows for sure. However, it has been shown that continuous flow can lead to more stiffening of blood vessels which is one theory behind why so many patients with LVADs have kidney failure later (but of course, the alternative is death relatively sooner). + +LVAD simulation: https://youtu.be/mOZIYoq32SQ + +LVAD review article: https://ccforum.biomedcentral.com/articles/10.1186/s13054-016-1328-z + +LVAD Kidney: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4464048/ + + + +" +814 What are the main complications stopping us from using nuclear fusion? 14205 https://www.reddit.com/r/askscience/comments/744w7q/what_are_the_main_complications_stopping_us_from/ 1507079676 744w7q Physics 2017-10-04 4:14:36 "(Edit: Wow, thank you for the gold, stranger. I didn't even think this was one of my better answers. Also, I have edited the post to clarify and correct some things based off some very good comments I received. Thank you all.) + +-------------- + +Fusion involves taking charged particles and ramming them together until they fuse. This releases a ton of energy, but it's like trying to push the same pole of two magnets together. You need to overcome the resistance first to get them to ""touch."" + +This requires an enormous amount of energy. The only way to really confine and squeeze the gas tightly enough to do this is via electromagnetic fields. More specifically, confining it inside a magnetic coil, like a cylinder. Most commonly, we then twist the cylinder back on itself to form a torus, and have the gas zoom around in circles inside the coil. + +But now you get into the problems: + +1) The amount of energy needed to drive the magnetic field is enormous, and the current will melt any standard conducting cable or metal. The only thing that won't heat up when that amount of current goes through it is a superconductor. There are no known room temperature superconductors, only those operating at very cold temperatures. So you have to keep the entire thing constantly cooled with liquid helium, and it's prone to break a lot. The Large Hadron Collider has the same issue and has suffered some high profile breakages this way. + +2) As the gas starts to collide and fuse, a plasma is formed. This is a good thing. It's what you want. But plasmas are highly conductive. As the plasma zooms around, it starts to form its own electromagnetic current and fields, which start to mess with the fields you're using to try and contain it. This is extremely difficult to detect or model and very hard to adjust in the split-second time frames needed to keep it stable. We're still figuring out the exact shape required to get the plasma's currents to self-contain in a nice stable way with the others. So far we can only keep the plasma going for about 100 seconds at the very longest recorded. + +3) Energy extraction. We still haven't quite figured this part out yet. All that energy in the plasma is ""real,"" but how do you get it out? The only simple and practical way we really know right now is using the heat to boil water and use the steam to drive turbines. (This is also how fission nuclear plants work.) This part is taken as a ""we'll do it easily once we get to that point,"" but we still aren't even to the point of stable long-standing plasmas so nobody's really invested much into it. The good news is, we have gotten very close to getting more energy out of the reaction than we put in at this point. The JET reactor hit 70% efficiency -- 97% efficiency if you don't count the initial startup spike. ITER is gunning for 1000%. We are confident it's doable at scale, now. + +4) Fusion is much safer than fission, and does not leave as many crazy exotic radioactive isotopes everywhere. This is because most of the radioactivity is confined within the plasma and does not ionize the surrounding material the same way. The ""fuel"" also does not naturally break down into dozens of exotic, long-lasting radioactive isotopes. However, fusion does produce neutron radiation, which by having no charge, can't be contained via electromagnetic field. These neutrons bombard the vessel walls and slowly irradiate and break it down over time. It's currently unknown how exactly we will avoid having to replace the entire reactor semi-frequently due to this, but like the above problem, it's considered a ""cross that bridge when we get to it"" issue that will be solved by some kind of new material or exotic layer of shielding like beryllium. The trick is making whatever shielding we use also compatible with energy extraction, because those neutrons are a good chunk of the energy that comes out." "Right now we have a few major issues: + +1. First Wall Problem: The fusion plasma needs a high product of density-temperature-confinement. Practical solutions almost always involve plasma at millions of degrees C. The plasma will also emit a lot of neutrons, assuming the mainstream D-T fuel approach. The layer of the reactor that faces the plasma is called the first wall, and in most fusion schemes it needs to have some pretty intense properties to survive. + +2. Simulation: Simulating a plasma is really hard. It has both fluid dynamics and electro-mechanics. This is called Magneto Hydro Dynamics (MHD), and it is a fairly good approximation of certain regimes of plasma operation. It is quite difficult to solve and simulate due to the nasty nature of the underlying equations. Fluid dynamics is very non-linear and chaotic, which is why it is hard to predict weather far into the future. There are many different code bases used to simulate MHD but as far as I know they all have their own major tradeoffs and there is no clear winner. + +3. Exotic hardware: most fusion schemes require expensive power supplies, since there is almost always a large amount of power involved in the process. The National Ignition Facility is a major fusion project and has 330MJ of capacitors that pulse into flash lamps which fire massive lasers at a tiny pellet of DT fuel. This capacitor bank is billions of dollars, and takes up several football fields. ITER is a tokamak fusion experiment that is wrapped in massive superconducting magnets and those are surrounded in a huge cryostat. The balance of plant required to make these kinds of machines function is truly massive." +911 When did scientists realize that Jupiter had no solid ground? 14116 https://www.reddit.com/r/askscience/comments/80cpqc/when_did_scientists_realize_that_jupiter_had_no/ 1519648610 80cpqc Planetary Sci. 2018-02-26 15:36:50 "As several people have pointed out, the question is not [""what is Jupiter's structure""](https://www.reddit.com/r/askscience/comments/80cpqc/when_did_scientists_realize_that_jupiter_had_no/duunoak/?utm_content=permalink&utm_medium=front&utm_source=reddit&utm_name=askscience) or [""When did scientists realize that Jupiter had an atmosphere""](https://www.reddit.com/r/askscience/comments/80cpqc/when_did_scientists_realize_that_jupiter_had_no/duupzwm/?utm_content=permalink&utm_medium=front&utm_source=reddit&utm_name=askscience), it's ""when did scientists realize it had no solid ground?"". It's about the *history* of knowledge of the interior composition. Since, [recent spacecraft results](https://www.reddit.com/r/askscience/comments/80cpqc/when_did_scientists_realize_that_jupiter_had_no/duuorz9/?utm_content=permalink&utm_medium=front&utm_source=reddit&utm_name=askscience) suggest it may gradually transition into something like a small solid core, let's interpret the question as, ""When did we first realize that Jupiter wasn't a rocky planet""? + +To solve this problem, you need to calculate the mass of Jupiter and its size, so you can find its *density*. The mass of Jupiter can be calculated using Newtonian orbital mechanics, provided you know the orbital period and orbital diameter of its moons. Period is easy, but a major historical problem in solar system studies was finding the relative scale of *everything*: it's easy to measure angles and relative sizes with a telescope, but we need the actual length dimensions. You need a baseline distance to start with, such as the distance from the Earth to the Sun: this was worked out [in the late 1600s](https://en.wikipedia.org/wiki/Astronomical_unit#History): from that, the size of Jupiter, the size of its moons' orbits, and thus its mass and density could be found. + +So even before 1700, astronomers realized that Jupiter was 300 times the mass of Earth, but with a density much less than that of rock. Since the density known today is about 1.4 times that of water, I suppose that without knowledge of high-pressure physics they couldn't rule out a liquid water or ice planet, but scientists have known for over 300 years that Jupiter is definitely not a rocky world. H. G. Wells was a fantastic writer, but he maybe wasn't so meticulous about doing his library research. + +The story is laid out by Reta Beebe in [*Jupiter: The Giant Planet*](https://www.amazon.com/JUPITER-Smithsonian-Library-Solar-System/dp/1560986859) (1997). +" Giovanni Cassini observed the different latitudes of Jupiter rotated at different rates in 1690. He concluded the planet could not be solid - ie was liquid or gas because a solid planet would not allow differential rotation +912 How do scientists know we've only discovered 14% of all living species? 13927 https://www.reddit.com/r/askscience/comments/87pqpx/how_do_scientists_know_weve_only_discovered_14_of/ 1522218755 87pqpx Biology 2018-03-28 9:32:35 "There have been many different estimates given for the total number of species on planet Earth. Some estimates are mere educated guesses by experts, while others are more grounded in statistics. A famous estimate was provided by Terry Erwin, an entomologist working for the Smithsonian Institute. He sampled beetles from the Amazon basin by pumping insecticides into large rainforest trees and catching the dead insects that rained down into nets (this method is now called 'fogging'). Using these samples, he observed that many species of beetles were only found within a single species of tree. By sampling lots of different species of tree, he found that on average, each species of canopy tree had roughly 160 species of beetle that were only found on a single tree species. So then, estimating that there are about 50,000 species of canopy trees, he simply multiplied 160 x 50,000 to come up with 8 million. Since it is relatively well known that beetles make up approximately 25% of all described species on Earth, he then multiplied 8 million x 4 to come up with 32 million. This estimate received a lot of attention because of how large it was. It also received quite a lot of criticism, given the extrapolations that he used. For example, his estimate of 50,000 Amazon tree species is likely too high, and the number of endemic beetles per tree species is also highly variables from one tree species to the next. Today, most scientists think the Erwin estimate is probably too high. + +There have thus been many other estimates provided by different groups over the years. A good one that comes to mind is described in a paper by Mora et al. 2011 in PlosONE (http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1001127). The authors identify an important relationship that helped them to derive an accurate estimation of global species diversity. That is, there tends to be a linear relationship between the log number of taxonomic units found within different taxonomic hierarchies (i.e., from species, to genus, to family, to order, etc.). While we have a poor idea of the total number of species on Earth, we do have very good estimates for the total number of genera and families, etc. So, using these numbers, the authors simply plotted the number of taxonomic units found within all hierarchies above the species level (i.e., from genera to phylum). Using the linear model obtained from this procedure, they extrapolated their data to the species level and found the model to land on the number 8.7 million. Given the fact that about 1.2 million species have been described, 1.2/8.7 = 14%, bringing us to your original question. + +This number is widely regarding as being a fairly accurate estimation of global species richness. Most biologists expect this number to be somewhere between 6 and 12 million now. However, it is important to point out that these estimates ignore microbes! We really don't have a clue what the diversity of prokaryotes looks like, so they are largely left out of these types of estimations. Advances in genomic sequencing will hopefully help us get closer to an answer, but we are still in the very early stages of developing techniques for describing microbial diversity. + +" It's basically extrapolating from data. One way of finding new species is (nowadays, less invasive methods are preferred) to go to the Amazon (or any other biodiverse ecosystem) and find a large tree (which shouldn't prove much of a challenge), spread a large sheet beneath the tree and then gas the whole tree to send every (formerly) living thing flying down onto your nice big sheet. You can then easily classify every animal. Scientists would then find that a large percentage of the animals collected were previously unknown species. This process would be repeated on several other trees in the area, with similar results. From this, we can tell that there are a whole lot of species we don't know about yet +715 Why don't humans have mating seasons? 13898 https://www.reddit.com/r/askscience/comments/6fcxo1/why_dont_humans_have_mating_seasons/ 1496651309 6fcxo1 Biology 2017-06-05 11:28:29 "Lets talk first about why many animals _do_ have mating seasons. The reason is usually quite simple: offspring born at certain times of the year have a better chance at survival. For example, deer mate in the fall and give birth in late spring, ensuring they have plenty of food and time to grow before the harsh winter season. Many tropical fish spawn when the rains come at the end of the dry season, providing their offspring with access to shelter and food in the newly flooded forests along the banks of their home rivers. + +In species where offspring survival isn't seasonal, breeding seasons don't tend to exist. This holds for many (but not all) tropical species, including all the great apes. And it holds for humans. + +So to get to specifics, below are some reasons it doesn't necessarily make sense for humans to have breeding seasons: + +A) none of our related species have them, so neither did our ancestors. + +B) Humans are fundamentally tropical (having originated in tropical regions), and thus our ""native climate"" didn't have the harsh winters that a breeding season is often timed to avoid + +C) Humans live in groups and use technology, and this insulates us from the variability of our environment, meaning our infants are less vulnerable to external environmental conditions + +D) Humans have very long infancies, meaning no matter when they are born they are going to be experiencing a full year's worth of climate variation as a baby." "Like all other organisms, our mating strategy is part and parcel of our overall survival strategy. + +In our case, we are extreme ""K-specialists"". We devote a *huge* amount of investment and resources in our offspring, compared to, say, willows who just scatter their seed to the wind by the millions. + +Our females have developped a strategy of concealed ovulation. Current thinking is that by concealing her ovulation and maintaining a perpetual state of potential sexual readiness, the human female makes it difficult for males to know whether her offpring are theirs. The male counter-strategy is to be at hand as often as possible to prevent cuckoldry. Together, this strategy and counter-strategy promote pair-bonding, monogamy and dual parental investment, thus maximising parental investment in offspring. + +see: + +[Benshoof, L., & Thornhill, R. (1979). The evolution of monogamy and concealed ovulation in humans. Journal of Social and Biological Structures, 2(2), 95-106.](https://www.researchgate.net/profile/Randy_Thornhill/publication/222051156_The_Evolution_of_Monogamy_and_Concealed_Ovulation_in_Humans/links/0f31752fa378bb0d42000000.pdf) + +[Strassmann, B. I. (1981). Sexual selection, paternal care, and concealed ovulation in humans. Ethology and Sociobiology, 2(1), 31-40.](http://sites.lsa.umich.edu/bis/wp-content/uploads/sites/171/2014/10/Strassmann-1981-Ethol-Sociobiol.pdf) + +[Buss, D. M., & Schmitt, D. P. (1993). Sexual strategies theory: an evolutionary perspective on human mating. Psychological review, 100(2), 204.](https://www.researchgate.net/profile/David_Buss/publication/14715297_Sexual_Strategies_Theory_An_Evolutionary_Perspective_on_Human_Mating/links/0deec5181791b73d35000000/Sexual-Strategies-Theory-An-Evolutionary-Perspective-on-Human-Mating.pdf) + +EDIT: Thanks for /u/ardent-muses (et *alia*) for correcting the -r/-K screwup. " +815 Would a boat with its hull sprayed by a hydrophobic coating have an advantage over an otherwise identical boat in a race? 13892 https://www.reddit.com/r/askscience/comments/7aba1z/would_a_boat_with_its_hull_sprayed_by_a/ 1509627112 7aba1z Physics 2017-11-02 15:51:52 This is actually an active area of research in ship engineering. One of the big sources of drag is hull-water friction, so there's research into making the hulls more hydrophobic so they slide through the water more easily. It's not feasible to spray or micropattern an entire boat, so other methods are being investigated to keep their surfaces in a [Cassie, not Wenzel, state](http://www.ramehart.com/cassie_wenzel.jpg). So to answer your question, yes. "Kayakers, rowers and canoists have been experimenting with this idea for about 30 years now. The conclusion they came to was that it didn't sufficiently improve performance over the standard gel coat on a composite boat. What apparently does improve performance is a slime that slowly dissolves in the water and reduces the water's viscosity for a minute or so, or applying directional riblet films such as these: + +http://news.3m.com/press-release/company/3m-reveals-successful-collaboration-bmw-oracle-racing-33rd-americas-cup-match" +1296 Is there really no better way to diagnose mental illness than by the person's description of what they're experiencing? 13872 https://www.reddit.com/r/askscience/comments/cr6fq9/is_there_really_no_better_way_to_diagnose_mental/ 1565962451 cr6fq9 Medicine 2019-08-16 16:34:11 "There has been tremendous interest among psychiatrists in coming up with objective tests for mental illness. There is a large group of researchers as part of the [ENIGMA](http://enigma.ini.usc.edu/) study to try to tease this out. The issue is that there is tremendous variation between normal people so abnormalities are not specific to people with mental illness. Additionally, similar to pain, mental illness is literally ""all in your head."" You can't objectively measure pain, sadness, and suicidal ideation with the techniques we have right now; I doubt we ever well. For example, what is an acceptable level of apathy? That may differ tremendously between people based on their jobs, family lives, culture, and general life views. That's why we have psychiatrists, to tease these issues out and adjust the plan appropriately. A good psychiatrist is really listening to what you say, how you look, etc to really gain a sense of how you're doing and where she wants you to go with your illness. She's not just sitting there and randomly throwing out meds. + +Right now, the field of neuropsychiatry is in its infancy, trying to understand changes in the brain to better map out the pathways involved. If we understand the pathways, we could maybe treat better." One of the criteria for something to be classified as a mental disorder is that the issue must cause significant distress to the individual or those around them. Often times the best way to determine if this criteria has been met is to take into account the patients' subjective experience of the phenomenon, as they're the ones experiencing the fallout of the disorder (or lack thereof). Source: DSM +716 How can we hear the voice in our head and how is it produced? 13858 https://www.reddit.com/r/askscience/comments/6w956o/how_can_we_hear_the_voice_in_our_head_and_how_is/ 1503792774 6w956o Human Body 2017-08-27 3:12:54 "The ability for an internal monologue is a fascinating, not well studied feature of the human mind. The current hypothesis for what causes it lies within that of corollary discharge (efferent copy). + +Whenever neurons within the primary motor cortex of the brain ""fire"" to do a specific action, this information flows in different ways. One signal goes directly to the muscle in which the brain is trying to manipulate, and instantly causes a reaction. However, at the same time, a ""copy"" of this signal goes to the cerebellum and parietal lobes. Information from the sensory receptors at the muscle also feed back to the parietal lobes and cerebellum. So, whenever movement is initiated, the signal immediately goes to the muscle, it moves, and then a signal from those sensory neurons heads back to the cerebellum and parietal lobes. This allows them to compare the input signal and the actual action of the muscle, where they send near instantaneous corrective signals to make the movement more refined in what is called a servo-loop. + +At the same time as the original firing, however, a signal is sent into a different region of the parietal lobe from the primary motor cortex of the movement about to take place. There, the signal is interpreted, and neurons responsible for the comprehension of one's self and its whereabouts in space form a ""simulation"" of the movement of the muscle in what is known as corollary discharge so that the action is understood by the brain, and no response occurs in the brain that would end up inhibiting the action trying to take place. + +One can ""see"" corollary discharge by closing his/her eyes and waving his/her hand in front of his/her face. Even though there is no real visual input of the action taking place, one can clearly imagine a ""ghost"" like limb performing the action in front of themselves. The corollary discharge is able to simulate the action taking place, and is thus able to predict the other sensory results of that action, too. + +In an internal monologue, it appears that the effects of corollary discharge, that is the simulation of the sensory affects of one's actions, is able to occur independently, without the original motor signal. The exact mechanism for how this works is not completely understood, but, it has been hypothesized that it has something to do with internally projecting mirror neurons. Therefore, this imagined speech is from a mere prediction of resultant sensory input from a simulation within the right parietal lobe's proprioceptive (whereabouts in space) regions of the brain. + +If I were to take a guess, the actual voice one hears is not processed within the auditory regions of the brain. Rather, the complex planning that occurs in the prefrontal cortex connects with wernicke's area (a language center in the temporal lobe of the brain), which assigns language to the thoughts. Then, this would most likely get sent to internally projecting mirror neurons in the frontal lobe in Broca's Area (another language center in the brain, is responsible for syntax and controlling the movements within the mouth to produce speech), where the corollary discharge simulation would take place. This, would produce the ""sounds"" of internal speech. Since the meaning of the internal speech would already be known, then, audial processing and interpretation would not need to occur. Thus, the corollary discharge would only be used to produce the recognizable interpretations of speech that allows for more complex thought. + +I hope that this explains it in a clear, understandable fashion! + +Also, [here](https://psychlopedia.wikispaces.com/file/view/cerebral_cortex_lobes.gif/94009736/cerebral_cortex_lobes.gif) is a diagram of the lobes of the cerebral cortex. [Here](https://en.m.wikipedia.org/wiki/Wernicke's_area#/media/File%3ABrocasAreaSmall.png) is a diagram pointing out Broca's Area and Wernicke's Area. [Here](https://en.m.wikipedia.org/wiki/Cerebellum#/media/File%3ACerebellum_animation_small.gif) is where the cerebellum is. + +References: +-https://www.sciencedaily.com/releases/2013/07/130716080028.htm +-https://en.m.wikipedia.org/wiki/Efference_copy +-https://en.m.wikipedia.org/wiki/Cerebellum +-https://en.m.wikipedia.org/wiki/Parietal_lobe +-My own internal knowledge of studying neuroscience for years + +Edit: From popular demand, I broke up the text to make it easier to understand! Also, thanks for the gold!" What I would like to ask towards this question, is the voice we are talking about usually the voice of the person, or someone else? As far as I can tell, the voice I listen to isn't from anyone in particular I know, but isn't my own either. +717 When our brain begins to lose its memory, is it losing the memories themselves or the ability to recall those memories? 13835 https://www.reddit.com/r/askscience/comments/6jot46/when_our_brain_begins_to_lose_its_memory_is_it/ 1498519415 6jot46 Neuroscience 2017-06-27 2:23:35 "I hate to give an unsatisfying answer, but... we aren't really sure. + +Every time we remember something we ""corrupt"" it just a little bit by reviewing it through our mind's eye. Each time you remember a car accident, we distort it a little bit at a time. Scientifically speaking, humans don't really ""remember"" things. We encode what we perceive, and while you might consider that a semantic distinction, it isn't. Human's have very limited attention spans that forced our brain to learn shortcuts to to maximize what we can perceive and cutting out as much 'noise' as possible. My previous sentence had a redundant 'to' that probably went unnoticed because you aren't really *reading*, you're basically engaging in pattern recognition. This extends to other aspects of memory as well. We encode what we think is important, distorting that information in the process, and we can't ever tell it's happening without an outside informant. + +Often you aren't able to recall much at all, but if you sit in a familiar place, or hear a song all these memories associated with that setting can come flooding back to you, even decades later. Scientists aren't even sure how things are forgotten or if they're just integrating into the subconscious personality, just testing these kinds of things is incredibly difficult, but we have some accurate research that points to the depths of human memory... + +Here's a [piece of research](http://www.sciencedirect.com/science/article/pii/S0010945208703423?via%3Dihub) (I can't find any without the paywall, so apologies to those without a university account) done on synthesia. + +It was essentially a test to see if there were any correlation between colors associated with letters among synthetics (people whose sensory inputs get scrambled, taste color, hear textures etc.), and there wasn't any correlation among any group except one... + +Among synaesthetics born in the 1970's there was a massive portion of people that had identical colors associated with their letters. This generation had all grown up with Fisher Price [refrigerator magnets](https://i.imgur.com/LwTMkET.png) as infants. + +So how deep does memory go? Where does memory end and personality begin? When do we really ""forget"" things, if we forget at all? + +Our brains are constantly building and rewiring and re-associating with all of our experiences, and it makes memory so *so* complicated that we simply don't have accurate answers to these questions right now. " "Simple question, not a simple answer. And it's not an either/or like you posit. + +First, background. There are different types of memory. + +1. Declarative (explicit) - these are factual memories we can explicitly recall. Further broken down into semantic (facts) and episodic (events) + +2. Nondeclarative (implicit) - what we remember only in our actions. This is broken into 4 groups: procedural skills (motor, perceptual, cognitive), priming (perceptual, semantic), conditioning, and nonassociative (habituation, sensitization). + +ok, next step. There's the natural decay of memory due to aging. Then there is losing memory due to physical trauma (bonked on the head) and then there is losing memory due to disease (alzheimers). These later two are legit lost and never to be retrieved b/c the part of the brain required for that type of memory is gone b/c of surgery or other means. + +For the natural decay of memory, it's also complicated. I think you're talking about memory retention and retrieval, rather than encoding and storage of memory. Is this right? Because how memories are converted from working memory into long-term memory does have an impact on retention & retrieval. For example, if someone is in a heightened emotional state it can make it easier to encode the memory and also make it easier to recall if the person is primed. + +Good times, right? + +And then there are times our brain weirds out and we get deja vu and jamais vu situations. Something corrupts the retrieval of those memories and you get a sensation that ""this has happened before"" (deja vu) or in a familiar situation (like standing in your living room) you get the sensation of ""this doesn't feel familiar"". + +So, yeah, these are just some weird ways memory works or doesn't. " +718 If you throw a waterproof speaker under water, and then dive under water yourself, can you hear the sound? 13742 https://www.reddit.com/r/askscience/comments/6cwkwj/if_you_throw_a_waterproof_speaker_under_water_and/ 1495564521 6cwkwj Physics 2017-05-23 21:35:21 "Yes. Basically sound has a huge problem crossing a barrier where there is a large ""Impedance mismatch"" like between water and air. When sound hits that ""soft release"" (because the air's impedance is much less than the water impedance) it gets reflected back into the water and doesn't radiate out efficiently. You have a similar problem of sound starting in the air and moving to the water. + +However, for sound created in water, you should be able to hear it in the water." "Yes, you can. In fact, there are purpose made speakers you can buy for your pool. It's pretty trippy the first time you hear a song underwater. +The Broadmoor Hotel and Resort had them in their main pool back in the 90's. Not sure common they are. " +913 How deep or shallow can the sand be in a desert? 13725 https://www.reddit.com/r/askscience/comments/8eu5ua/how_deep_or_shallow_can_the_sand_be_in_a_desert/ 1524668046 8eu5ua Earth Sciences 2018-04-25 17:54:06 "How deep can it be? + +Very deep. Over half a mile, perhaps as much as mile under very special circumstances. + +The thickness of sand under the dunes is going to depend on the length of time that deposition was greater than erosion. In a desert, deposition = sand being blown in, and erosion=sand being blown out. If you were to measure these rates in (thickness)/(time), you can imagine that it is possible to get a lot of sand built up in short times relatively speaking. However, the rate of erosion will increase if you build sand ""up""-- so what you need is accommodation space where sand can accumulate. + +And there are thick sandstones, such as those that form the ancient geology of the American west, which you can see at parks such as [Arches](https://www.nps.gov/arch/index.htm) in Utah. When you see all the rocks at Arches, you are seeing a HUGE pile of what remains of thousands and thousands of sand dunes that were partially buried in accommodation space provided by evacuating salt. + +[The Navajo Sandstone](https://en.wikipedia.org/wiki/Navajo_Sandstone) is up to 2,300 ft thick, but it's been compressed--it would have been thicker before it was buried and re-exposed. And, there is some additional amount of material that would have been on top that has eroded. So, at *least* half a mile. + +But also very cool--the Navajo sandstone was being deposited over a period of 15 million years, so the net rate of addition might have been around 2,300 ft/15 million years = 1/10000 ft/year. That's a tiny net amount, and we know that accumulation happened in fits and starts--there are packages that are the ""base"" of sand dunes that are 30' thick that show all their original structure, which means that 30' thick sand dune was laid down millions of years ago and never reactivated. So it was a lot of boring time and then *boom*, your sand dune gets buried and stays. + +Why was there so much sand accumulation there? The answer is [salt tectonics](https://en.wikipedia.org/wiki/Salt_tectonics). If you fill up a basin with sea water and keep evaporating, you can end up with salt a mile thick. Then, if you blow sand over it, you end up with a sandy desert dune on top of your mile thick salt. And here's the cool thing: sand dunes are denser than salt *so they start sinking into it*. That's where the accommodation space comes from! + +One last thing: these thick sands are great places to hold oil, and have been important targets of exploration all across the world. + +" "Top answer is totally correct, but from your wording, it sounded like you were asking about unconsolidated (loose) material. Sandstones, by definition, are not so loose as to be dune-forming. They might be buried dunes that have subsequently lithified, but they are not necessarily associated with desert environments—they’re buried beaches, or other sandy environments—which brings us to dunes. + +Dunes are loose sand (or other grain sizes) that pile up in a sub aerial (ie on land) environment. They form by the same process as ripples on a beach, that is, they scale to the energy of the body that moves them. Ripples scale to the waves over top of them, and dunes scale to the air masses that move them. That means that some dunes scale to the troposphere! That isn’t to say that we have Everest-sized sand dunes on Earth, but rather, that sand dunes may be up to kilometers thick, depending on the strength of the wind that pushes them, among other factors. Those might include the amount of source material available, and the qualities of the source material itself (rounded vs angular grains, etc.) + +Good luck, and I hope this answers your question!" +719 Who feels the umbilical cord being cut? Mother, child or both? 13656 https://www.reddit.com/r/askscience/comments/6p1gug/who_feels_the_umbilical_cord_being_cut_mother/ 1500818920 6p1gug Human Body 2017-07-23 17:08:40 Please remember, if you are going to comment, that AskScience has very strict [comment rules](/r/askscience/wiki/rules). If you are commenting on a personal experience or personal opinion it does not belong in this subreddit. "Neither, actually. + +The parenchyma of the umbilical cord is made up of something called [Wharton's jelly](https://en.wikipedia.org/wiki/Wharton%27s_jelly), it's basically a very thick, mucous-ey substance that provides structural support to the important stuff inside (umbilical arteries and vein). There are no nerves in Wharton's jelly, so no one feels the umbilical cord being cut." +1196 "If gold is a worse electrical conductor than silver and copper, why are gold plated contacts considered ""better"" by the market?" 13647 https://www.reddit.com/r/askscience/comments/b0onxw/if_gold_is_a_worse_electrical_conductor_than/ 1552497986 b0onxw 2019-03-13 20:26:26 "100% its corrosion. Copper and even silver corrode when exposed to air. This becomes a problem, it adds a highly resistive layer and adds a worse fit. If you've ever had actual ""silver-ware"" it usually needs to be polished on a semi regular basis.. Gold is pretty much the most inert conductor out there and the gold used can be so little that that its cost is very low." Gold doesn't oxidize like silver and so on. So the electrical conduction is optimal from gold contact to gold contact as there is no resistance generated due to corrosion. As soon as the electrical current has passed this gold/gold contact then of course the other metals are a better choice. +1098 How many people can one tree sufficiently make oxygen for? 13609 https://www.reddit.com/r/askscience/comments/9jyde2/how_many_people_can_one_tree_sufficiently_make/ 1538238919 9jyde2 2018-09-29 19:35:19 "The exact number will depend of course on the location, size, species, and maturity of the trees, etc. However, I found one study^(1) where researchers estimated the number of trees needed to offset the average oxygen consumption of a single person in various North American cities. [Here is the full table](https://i.imgur.com/5rKHPCO.png), where you can see that in an average city (e.g. Philadelphia) you need about 20 trees to provide enough oxygen for one person. + +That may sound like a lot of trees, but fortunately the oxygen we breathe doesn't need to be produced locally. Forests all over the world continuously pump oxygen that is mixed into the atmosphere and spreads across the globe. Moreover, trees are not even the biggest source of oxygen on Earth. That honor goes to [phytoplankton in our oceans, which collectively are responsible for the majority of the world's oxygen supply](https://en.wikipedia.org/wiki/Phytoplankton#Oxygen_production). + +1. Nowak, D., et al. Oxygen Production by Urban Trees in the United States. Arboriculture & Urban Forestry 2007. 33(3):220–226. [link](https://www.nrs.fs.fed.us/pubs/jrnl/2007/nrs_2007_nowak_001.pdf) " "I find it's better not to think of oxygen and CO2 as being consumed and produced. Instead, think of carbon as existing either in biomass or in atmosphere. + +If a plant isn't growing (because, say, it has reached its mature size), it turns CO2 to O2 during the day as it photosynthesizes, then turns it back at night as it lives off of stored energy. It isn't making any oxygen. + +But if you cut it down, it would get eaten by a fungus or burned by a fire and all (or most) of its carbon would be converted back into CO2. + +We convert O2 into CO2 at the exact amount that we consume biomass. If I grow a potato (or an edible tree), it converts CO2 into O2 and stores that carbon in a potato. If I eat that potato, I break up that carbon and bind it to O2, and use the energy from that to drill for more fossil fuels. + +So if you had a potato farm, fertilized it with your poop, and only ate those potatoes, you would be carbon-neutral. No trees needed. + +--- + +Now think back to the Carboniferous period. Trees develop lignin, and no microbes have figured out how to eat it yet. So they grow, eventually fall over (because early trees had [weak root systems](https://www.nationalgeographic.com/science/phenomena/2016/01/07/the-fantastically-strange-origin-of-most-coal-on-earth/)), and then just pile on top of each other. Biomass increases, atmospheric carbon levels fall, and we get giant insects because there's (relatively) more O2. + +Many of those trees turn to coal. If microbes hadn't evolved the ability to eat trees, then this would have kept happening until the CO2 levels were so low that plants were competing for it. Instead, fungi started eating trees, CO2 levels rose again, but not as high as they were before -- because many of those trees had turned to coal. So there's this phenomenon where old biomass now has a mineral form. + +Fungi evolve how to eat tree, CO2 levels rose, and the atmosphere changed significantly and many species went extinct. Including, I imagine, many fungi who had previously thrived on the massive volume of tree-based food available to them. + +--- + +So flash forward. Now a new organism has evolved a way to take the energy out of that old biomass: coal and oil. It's us. We're tapping into biomass from the Carboniferous and burning it. We can't replace old biomass, so unless we make new biomass at an equal rate, we'll change the temperature. Instead, though, we're also destroying new biomass. + +A gallon of gasoline [creates](https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle) 8.8kg (20 lbs) of CO2, with most of that mass coming from atmospheric O2. A kg of tree soaks up 1.6kg of CO2. So you would need to make 5.5kg (12 lbs) of tree per gallon of gasoline you use. + +General Sherman, an enormous sequoia in Sequoia National Park, weighs 1.2 million kg, and is the largest tree in the world. In the US, people use a total of 391 million gallons of gasoline per day. So to counterbalance that, we would need to grow 1780 General Shermans *every day*. There are about 8000 giant sequoias in Sequoia National Park, and all of them are smaller than General Sherman. So every week, we would need to grow another one and a half Sequoia National Parks. + +Incidentally, General Sherman is 2,300-2,700 years old. + +Sequoia National Park is [about](https://en.wikipedia.org/wiki/Sequoia_National_Park) 400,000 acres. We're growing one Sequoia National Park per week. Let's step out of California for a moment, because California has a lot of biomass, especially northern California. Let's step next door to Nevada. To keep up with USA gasoline consumption, you would need to grow one Nevada of Sequoia National Park every 2 years and 2 months. + +In other words, since Obama was first elected (remember that?), you would need to have covered all of Texas, Oklahoma, Arkansas, and Arizona with Sequoia National Park (without removing the existing biomass) in order to offset human carbon consumption in the US from gasoline alone. + +Not counting diesel. Not counting coal. Not counting natural gas. Not counting industrial use. Not counting airline use. Not counting the fuel used to ship goods to the US. + +--- + +I guess what I'm saying here, is that it's not like there's a number of trees at which we'll be all set. + +--- + +EDITS: more sources, and more contiguous states. Here's the maths. Links provided separately because Reddit doesn't like links with parenthesis in it. I also fixed some of the numbers above. They're worse now. + +Thanks for the gold! + +[[[(142.98 billion gallons gasoline/year)x(8887 grams CO2/gallon gasoline)x(1 kg of tree /1.63 kg of CO2)]/(1.2 million kg of tree x 8000 trees/400000 acres)]x(time since noon, Jan 20, 2009)]/(area of Texas + Oklahoma + Arkansas + Arizona) = 0.97 + +Gallons consumed in 2017: https://www.eia.gov/tools/faqs/faq.php?id=23&t=10 -- I didn't check how gallons/year changed since 2009, so consider this only a commentary on current usage. + +CO2 emitted per gallon of gasoline: https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle -- it's more than 1:1 because the CO2 mass includes the mass of the O2 consumed in burning it. + +CO2-to-tree ratio: https://www.quora.com/How-many-trees-does-it-take-to-transform-one-ton-of-CO2-into-oxygen-over-the-time-of-one-year-Are-there-any-statistics-for-different-trees-leaf-trees-conifers-or-even-other-plants -- this one's a weak point in my maths, because it was somebody else's napkin-maths. I'm open to better sources. They were also thinking of oak, not Sequoia. + +Stats for Sequoia National Park and General Sherman from Wikipedia. + +Monster Wolfram Alpha link: http://www.wolframalpha.com/input/?i=%5B%5B%5B(142.98+billion+gallons%2Fyear)*(8887+grams%2Fgallon)*(1%2F1.63)%5D%2F(1.2+million+kg+*+8000%2F(400000+acres))%5D*(time+since+noon,+Jan+20,+2009)%5D%2F(area+of+Texas+%2B+Oklahoma+%2B+Arkansas+%2B+Arizona) + +--- + +Okay, one more edit: there are a lot of non-Sequoia trees in Sequoia National Park. It's about one sequoia per thirty football fields. Typical temperate forest sequesters 5.6kg of carbon per square meter, in both its tree mass and in its soil ([source](http://www.fao.org/docrep/004/y1997e/y1997e07.htm) -- that's 59 gigatons/10.4 million square kilometers.) So using that instead, we get: + +[(142.98 billion gallons/year)x(8887 grams/gallon)x(12 g C/44 g CO2)]/[5.6 kg/(square meter)] + +That means we need about 1,960 m^2 per *second* of temperate forest growth (that's a FIFA soccer field every four seconds), to keep up with gasoline use. + +How long would that take to cover Texas? Almost exactly as long as it has been since the iPhone was released, in June 2007. + +(The fact that these numbers aren't *that* different is a testament to how much carbon General Sherman has sequestered.) + +http://www.wolframalpha.com/input/?i=%5B(%5B(142.98+billion+gallons%2Fyear)*(8887+grams%2Fgallon)*(12%2F44)%5D%2F%5B5.6+kg%2F(square+meter)%5D)*(time+since+noon+June+29,+2007)%5D%2F(surface+area+of+texas)" +606 Are there ocean deserts? Are there parts of the ocean that never or rarely receive rain? 13596 https://www.reddit.com/r/askscience/comments/5v1f3j/are_there_ocean_deserts_are_there_parts_of_the/ 1487549928 5v1f3j Earth Sciences 2017-02-20 3:18:48 [deleted] Yes. If you look at a map of annual precipitation, a few of the recognisable land deserts look like they stretch well out to sea. Mainly off the western edge of continents, eg. off Western and Southern Africa (Sahara and Namib deserts). +1297 Can fish live (or at least breathe) in liquids that are not water? For example milk 13528 https://www.reddit.com/r/askscience/comments/bmzivx/can_fish_live_or_at_least_breathe_in_liquids_that/ 1557501373 bmzivx 2019-05-10 18:16:13 "If a fish was in milk or another liquid with the correct oxygen concentration, yes, it could *respire*. That's not a dig on your vocabulary, that's all I think a fish could really get out of another liquid: just enough oxygen to technically be able to do body processes like exchanging CO2. + +Fish also experience osmotic stress, ph stress, turbidity stress, viscosity stress, chemical (ammonia, nitrite, nitrate, and other) mineral/hardness stress, heavy metal stress, etc. Putting a fish in milk for more than a few seconds would likely put strain on its gills because of all the fats, proteins, minerals etc, that the gills have to filter out. You couldn't survive in air that had oxygen, but was also filled with ash or small particles, either. + +Long term, fish also rely on their environment to not be too salty or not salty enough, and not too acidic or alkaline. Over time, this fish in oxygenated milk would experience stress because the milk didn't have the correct amount of salt, or was too acidic. You couldn't survive in air that had oxygen, but was also part damaging chlorine gas. + +Fish are whole animals and have more requirements other than just not suffocating or desiccating out of water. They rely on their environment that completely surrounds them to take care of the same body processes that we have. It just happens to be water for them, and air for us. You would need to find another liquid that didn't have anything else suspended in it that would strain the gills, was the correct ph, salinity, and be free of chemicals or minerals that might poison it.Source: graduating tomorrow with a fisheries degree + +TL;DR: yes, if you forget every technicality. + + +Edit: multiple people have pointed out milk is actually slightly acidic (close to ph=6.6) I originally wrote it was too alkaline for fish. My bad! I will point out fora the sake of technicality that some fish do thrive below a ph of 6.6 (fish that prefer blackwater like some rasbora sometimes like water with a ph as low as 5.0!) but it was merely an error. I learned something today!" No. Fish can’t even live in water that has the wrong amount of salt or dissolved oxygen in it. Putting a fish in a liquid other than the correct water would be like putting a human in the Venus atmosphere. Sure it’s “air” but the concentration of oxygen, nitrogen, CO2, etc are all wrong. Every animal, especially fish, are evolved to very specific environments, and putting them in something they are not adapted to survive in will kill them +720 How do third party headphones with volume control and play/pause buttons send a signal to my phone through a headphone jack? 13525 https://www.reddit.com/r/askscience/comments/696mv5/how_do_third_party_headphones_with_volume_control/ 1493892704 696mv5 Engineering 2017-05-04 13:11:44 "[Here's a diagram of a TRRS audio jack](http://www.circuitbasics.com/wp-content/uploads/2015/03/TRRS-Wiring-Diagram-300x224.png). You'll see that the connector is divided (separated by insulators into distinct conducting strips). The reason this is called a TRRS audio jack is that it's broken into 4 different conducting strips, called Tip, Ring, Ring, Sleeve. There are also TRRRS jacks which have an extra ring and thus 5 conducting strips in total. + +To do mono audio, you need 2 conducting strips (audio + ground). To do stereo audio, you need 3 conducting strips (left audio + right audio + ground). If you have 4 or more conducting strips, then you can have stereo audio plus some other form of communication. The diagram I linked to you has the 4th strip be a microphone, but some smartphones will use the 4th conducting strip to send control information such as ""pause"" and ""play"" commands. + +Unfortunately there's no one standard for how TRRS and TRRRS jacks are used. Different devices and different headphones will make different (incompatible) decisions on what to do with the extra strips. If you're going to buy headphones with a TRRS or TRRRS connector, you just have to check beforehand whether it's coincidentally going to be compatible with your phone. + +The most common protocol used by phones is called CTIA~~or OMTP~~. (Edit: upon further research, CTIA and OMTP are 2 different standards, but seem to be largely compatible in this area). It's defined by the Cellular Telecommunications Industry Association. Note that other audio and video equipment will use the same jacks but be electrically incompatible in the higher rings of the jack." "https://source.android.com/devices/accessories/headset/plug-headset-spec + +Here's a link to the Android headset spec, scroll down to the diagram and you'll see that it's simply a series of pulldown resistors, one for each button. + +Given the tolerance of the resistors you can quickly hand-calc the expected voltage on the Mic pin for each button press (voltage divider with Rbias)." +721 When a banana gets bruised, does the nutritional content of the bruised area change? 13498 https://www.reddit.com/r/askscience/comments/6ryps7/when_a_banana_gets_bruised_does_the_nutritional/ 1502030843 6ryps7 Chemistry 2017-08-06 17:47:23 "Once a banana starts to over ripen - be it from time or from some sort of damage to the peel - the starches start to break down into sugars. That's what makes brown, or bruised, bananas taste sweeter. You can eat a brown or bruised banana so long as you enjoy a sweet banana, but when they start to get darkened or blackened then they usually reserved for baking pies or something like that. + +Does the nutritional content change? Yes, starches break down into sugars as the fruit gets bruised or ripens." Yes, likely. The enzymes in the banana that were compartimalised before can come into contact with the vitamine C and break it down. Its a highschool biology experiment where you measure mashed bananas vitamine c concentration over time. +722 There are thousands of seemingly isolated bodies of water all throughout the planet which happen to have fish in them. How did they get there if truly isolated? 13449 https://www.reddit.com/r/askscience/comments/6khe99/there_are_thousands_of_seemingly_isolated_bodies/ 1498843672 6khe99 Biology 2017-06-30 20:27:52 [Massive floods](http://www.huffingtonpost.ca/2013/06/29/calgary-flood-from-space-chris-hadfield_n_3523233.html), [changes in river flows](http://www.tribuneindia.com/news/science-technology/canadian-river-changes-course-in-4-days-as-glacier-retreats/394334.html), [freak weather events](http://www.bbc.com/news/world-asia-27298939), [historically very different climate](https://en.wikipedia.org/wiki/Lake_Lahontan) with larger or interconnected lakes. "In Wyoming we have granite mountains with no springs or streams, a thousand feet above the dry prairie floor. They are almost solid rock with very little dirt, large rounded massive structures. When it rains, small depressions in the rock fill up with water and I often find what looks like tiny shrimp swimming around in the water. They can't be full of water for more than a few weeks at a time. Independence Rock, a tourist spot, is an example where you can find small shrimp in puddles on top, the higher mountains around it have them too. + +Sometimes I'll also see a small basin in the prairie floor fill up with water and there will be tiny fish fry swimming around in them, after only having rained a few weeks ago at the most. They look like little guppy babies or something, very tiny. + +It doesn't seem like the top answer would explain either of these. Anyone familiar with Wyoming or similar environments know how these happen?" +816 Does running a mile in 10 minutes burn the same number of calories as walking a mile in 20 minutes? 13391 https://www.reddit.com/r/askscience/comments/73webg/does_running_a_mile_in_10_minutes_burn_the_same/ 1506984714 73webg Biology 2017-10-03 1:51:54 "No, this has been proven. + +Per Stanford study:[ Running elicited a significantly greater total energy expenditure than walking on both the treadmill and the track (P < 0.001) for both genders (Fig. 1a). On the treadmill, the males expended 520.6 ± 27.6 kJ for 1600 m; this was significantly higher (P < 0.05) than the energy expenditure by the females (441.1 ± 25.6 kJ). For the walk, the males expended 370.4 ± 17.7 kJ, and the females expended 309.6 ± 17.2 kJ for 1600 m (P < 0.05 between genders). When energy expenditure was adjusted for fat-free mass, the gender effect disappeared, but running exercise still required more energy than walking (P < 0.01; Fig. 1b).](https://web.stanford.edu/~clint/Run_Walk2004a.rtf)" "There's a u-shaped sort of curve for walking. It's more biomechanically efficient at slower speeds (becoming less efficient at very low speeds as basal metabolism becomes significant given the amount of time). [This](http://fellrnr.com/wiki/Calories_burned_running_and_walking) has a whole bunch of info, and takes slope into account. Pretty cool. According to their data, a 14 min/mile is roughly the crossover point where running starts to be more efficient, but that depends on the person a bit (different sized legs). + +Any running motion is pretty much steady-state as far as energy expenditure/distance." +817 Is a single Elephant's skin cell bigger than a human's skin cell? 13312 https://www.reddit.com/r/askscience/comments/6xvhkc/is_a_single_elephants_skin_cell_bigger_than_a/ 1504469709 6xvhkc Biology 2017-09-03 23:15:09 [deleted] Time for one of my favorite scientific articles: http://www.bmj.com/content/347/bmj.f6833 +818 What is the gold and silver foil they put on satellites and why is it important? 13294 https://www.reddit.com/r/askscience/comments/70mzcp/what_is_the_gold_and_silver_foil_they_put_on/ 1505647976 70mzcp Engineering 2017-09-17 14:32:56 "Despite the common knowledge that space is ""cold,"" it's actually difficult to get rid of heat in a vacuum. Spacecraft without a highly reflective surface tend to absorb the sun's energy and heat up to the point of failure. Putting ""foil"" (which is actually a more advanced insulation) around satellites makes sure they can maintain a good operating temperature. + +https://www.nesdis.noaa.gov/content/good-gold-are-satellites-covered-gold-foil" "It's thin insulating foil. It's made from a very thin and lightweight but strong mylar film, sprayed with vaporised aluminium which is very reflective but again very lightweight. All these properties make it very suitable for use as insulation round spacecraft to stop radiant heat from the sun building up and damaging them. + +Also known as space blankets..." +819 Do humans have a vestigial tail wagging response? Is it detectable? 13220 https://www.reddit.com/r/askscience/comments/72za7r/do_humans_have_a_vestigial_tail_wagging_response/ 1506595628 72za7r Human Body 2017-09-28 13:47:08 "Not really, no. Animals wag their tails for a variety of reasons, but the happy=tail wagging response in dogs is unique to them. (Interestingly, foxes that were domesticated as part of an experiment also began [wagging their tails in greeting](https://en.wikipedia.org/wiki/Russian_Domesticated_Red_Fox#Genetic_experimentation) after several generations of breeding for tameness. So the potential for tail-wagging in excitement and happiness when bred for juvenile traits is present through a lot of the canine family tree.) A cat wagging its tail is most likely annoyed or agitated, or at least overstimulated. There is no hardwired environmental or behavioral reason for tail wagging that all animals share. (EDIT: And yes, a dog can also wag its tail when it isn't happy; I was specifically referring to the common, stereotypical behavior of the happy tail-wagging doggo.) + +Apes 'lost' their tails at least 14 million years ago, well before the human branch of the family tree had even begun to split. Human responses that involve butt-wiggling (for lack of a more specific term) like dancing or squirming are coming from a different behavioral source that has nothing to do with tails." No, but Humans have other limbic reactions that signify happiness pretty much across the board. Watch someone's feet next time they are very excited or happy; it's where the phrase 'happy feet' comes from. Closest thing I can think of to tail wagging +723 Why do we have to kill a horse when it broke its leg? What is the difference in biological processes between man and horse in bone mending? 13194 https://www.reddit.com/r/askscience/comments/6bv9tk/why_do_we_have_to_kill_a_horse_when_it_broke_its/ 1495102328 6bv9tk Biology 2017-05-18 13:12:08 "Hi there. + +The biological processes of bone healing are the same in both horses and humans. The problem is in their weight and behavior. And it depends on the location of the fracture whether or not the horse may need to be euthanized. + +When humans break bones, they can take weight off by sitting down, using crutches, etc. Horses don't have this option. If they take the weight off of the leg by themselves by favoring the leg, especially if they are young, the other limb may become deformed due to the increased burden. Even if they do lie down, the act of standing back up can cause the fracture to break again. Smaller horses may heal from fractures better, and a few cases may do well with amputation, but these cases are few and far between. + +Even if the leg is stabilized, it takes a very long time to heal. During this long time of inflammation, the horse may develop [laminitis](https://en.wikipedia.org/wiki/Laminitis), which causes, in a word, the hooves to fall off. This is similar to having your fingernails pulled off, and for an animal that relies on supporting all of its weight on its ""fingernails"" this is incredibly painful and debilitating. (This is actually what happened to [Barbaro](https://en.wikipedia.org/wiki/Barbaro)). Here is a look at [Barbaro's radiographs](http://www.two-views.com/celebrity/barbaro-leg-xray.html#sthash.uUMadT8t.dpbs) and how they attempted to stabilize his distal limb. + +Also, practically, many horses have jobs (racers like thoroughbreds/standardbreds, work-horses like draft horses, etc), and their lives are sometimes seen as an investment. If the owner cannot afford to keep them on pasture, if it isn't a financially viable option, they may elect to euthanize. + +Edit: added links and clarified" "And another point: horse physiology is designed so that blood flow to the foot and leg is partially accomplished through pressure to an area on the sole of the foot called the frog. When horses don't move regularly and put pressure on this surface, it can damage circulation in the hoof wall and cause reduced circulation in the entire injured leg. + +What's more, the additional weight on the non- injured feet frequently causes a condition in the weight-bearing feet called laminitis, where circulation is damaged and the hoof wall begins to detach. This is a condition that is frequently the cause of permanent and severe lameness and often requires the horse to be put down. + +So ultimately it is not the broken leg that is the problem, but the cascade of other problems that results in the horse being euthanized." +1197 Why don't we just boil seawater to get freshwater? I've wondered about this for years. 13090 https://www.reddit.com/r/askscience/comments/axqtel/why_dont_we_just_boil_seawater_to_get_freshwater/ 1551823099 axqtel Earth Sciences 2019-03-06 0:58:19 "You can do this, and we do. It's call desalination. The process you describe is called distillation desalination, and historically was the only way to turn salt water into drinking water. However, this is getting less and less common these days. Now it is mainly done by ""reverse osmosis"" where pressure is applied to sea water to drive it through a special filter that separates the salt from the water. + +​ + +The reason these technologies are not more widely used is because they are expensive. Obviously distillation desalination requires you to boil water, when we're talking gigalitres of water a year, this means a lot of electricity is needed. Reverse osmosis isn't cheap either. You have to pump the water to develop pressure, and the reverse osmosis membranes are always getting fouled and damaged. Roughly speaking, the highest efficiency desalination plants make water at about 10x the price of rain water collection. That is why desalination is somewhat rare (though more common than a lot of people think) and is only used in large amounts in very dry places. Australia, for instance, is extremely dependent on desalination for drinking water, and the large desalination plant in the world operates in Saudi Arabia. + +EDIT: I'm having lots of complaints from Australian. If your city's backup supply of water is desalination, you are dependent on it. Australia has some of the highest desalination capacity per capita in the world. The are huge plants in three states. I never said they supply your daily drinking water." "Israel actually does a lot of desalination, 55% of their water now comes from the sea. 70% of their drinking water is from desalination (from a different article). + +https://www.scientificamerican.com/article/israel-proves-the-desalination-era-is-here/ + +However, difficulties are now beginning to crop up: + +https://www.haaretz.com/israel-news/.premium-desalination-problems-begin-to-rise-to-the-surface-in-israel-1.5494726" +1006 Why is it that when you feel mildly sick from dehydration, within merely the time it takes to drink water, you almost instantly feel better? Is it a psychosomatic case, or is the body that effective at taking in water? 13070 https://www.reddit.com/r/askscience/comments/8n7zt2/why_is_it_that_when_you_feel_mildly_sick_from/ 1527681684 8n7zt2 Human Body 2018-05-30 15:01:24 There are receptors in your throat that can detect the cold fluid, and these down-regulate the release of thirst/stress hormones (such as vasopressin) almost immediately. These hormones work to conserve water in the kidney as well; once you drink the water your body is already anticipating its effects! "Yes . The body doesnt actually hydrate that fast, BUT the body can tell when you are drinking fluids, and will anticipate the body responses in ADVANCE of actual processing! Like getting a call that you inlaws are coming , you automatically pick up the house and clean it, even before they get there so that WHEN they do actually get there, your house is fantastic. +" +1198 AskScience AMA Series: We are scientists here to discuss our breakthrough results from the Event Horizon Telescope. AUA! 13026 https://www.reddit.com/r/askscience/comments/bbknik/askscience_ama_series_we_are_scientists_here_to/ 1554894059 bbknik 2019-04-10 14:00:59 Just a reminder, if you know stuff about black holes but are not an AMA guest, please hold off on answering until after the AMA guests have finished. They will start answering 20:00 CEST (14:00 EDT, 18:00 UTC). It was mentioned that physical hard drives had to be shipped to carry all the data from the various telescopes since it was too big for the Internet. How much data is that? Where is the 'cut off' point for something still requiring physical media? +1007 What is the white stuff inside pimples? What it's made out of, why we have it, and why does it exit in this way? 13022 https://www.reddit.com/r/askscience/comments/8u97lg/what_is_the_white_stuff_inside_pimples_what_its/ 1530102627 8u97lg 2018-06-27 15:30:27 "This post has attracted a large number of medical anecdotes. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. Providing specific medical advice is also against our rules. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." "A pimple is an infection. Bacterial infections begin with a bacterial pathogen and an inflammatory response to the pathogen. For pimples, anaerobic bacteria colonize a hair follicle and consume the sebum produced by sebaceous glands. This forms lipid byproducts which irritate the surrounding area. This inflammatory reaction recruits immune cells called neutrophils (a type of WBC). Neutrophils come in and dump bleach on the bacteria. As neutrophils die, they accumulate and form what we call pus or the “white stuff”. It only has one immediate way out; through the hair follicle to the skin surface. That’s why it exits that way. + +Edit: correction about sebaceous glands (not sweat glands) + +Edit2: I’m getting a lot of questions about the one way out. Added that exit to the skin surface is the only immediate way out. After a few days the pimple will resolve following absorption back into the body. " +1199 Can you kill bacteria just by pressing fingers against each other? How does daily life's mechanical forces interact with microorganisms? 12977 https://www.reddit.com/r/askscience/comments/b423nu/can_you_kill_bacteria_just_by_pressing_fingers/ 1553240003 b423nu Biology 2019-03-22 10:33:23 "In theory yes, bacteria can be crushed just like anything. When using microscope slides it's possible to crush them if you don't do it properly. But those are incredibly smooth surfaces. Your fingers are not. There are visible grooves and grooves and imperfections so small you can't see them. Your fingers also have a fair bit of give to them as do the cells that make them up. So most, if not all, of the bacteria present will not experience much force. Not to say it couldn't happen in the right circumstances though. + +To have a good chance of crushing them you need a material that is rigid and so flat that they won't just be pushed into grooves or holes. + +" I think the other comments address your first question well, but I wanted to add that it is possible to use mechanical forces to kill bacteria. It's been discovered relatively recently that some insects use a purely mechanical system of nanostructures to kill surface bacteria without having to rely on chemicals or other methods ([article](https://www.nature.com/news/insect-wings-shred-bacteria-to-pieces-1.12533), and original [source](https://www.cell.com/action/showPdf?pii=S0006-3495%2813%2900003-9)). +820 How much does drinking a cold drink really affect your body temperature? 12864 https://www.reddit.com/r/askscience/comments/6xeuh3/how_much_does_drinking_a_cold_drink_really_affect/ 1504275850 6xeuh3 Biology 2017-09-01 17:24:10 "I'm an anesthesiologist. We monitor body temperature during surgery because anesthesia inhibits your ability to autoregulate temperature. Essentially you are turned into a poikilotherm like a snake, and lose heat to the cold operating room. An inability to contract your muscles prevents you from generating heat. We have a rule of thumb that 1 liter of room temperature intravenous fluids will reduce a patient's body temperature by 0.25 degrees Celsius. We used forced air warming blankets and heated IV fluids to maintain a normal body temperature, which helps the body to metabolize medications predictably and the blood to clot properly. + +After reading comments I want to add that the reason I brought up anesthesia here is that only when you remove the body's ability to generate heat can you actually measure a reduction in temperature, unless you infuse the fluid very quickly. When we drink cold fluids, the body generates heat to correct the drop in temperature before an appreciable difference can be measured. + +Furthermore, there are some interesting studies out there on this. Many involve rapidly administering cold IV fluids in attempt to show that hypothermia is protective against neurologic injury in situations such as cardiac arrest. + +Here is one study: + +Ann Emerg Med. 2008 Feb;51(2):153-9. Epub 2007 Nov 28. + +They infuse cold and room temperature fluids rapidly in non anesthetized patients and measure a temperature change before compensatory mechanisms (shivering) can restore the body to normal temp. This is better than my rule of thumb as it uses weight-based dosing for IV fluids. Interesting, 30ml/kg of room temp fluid reduced the body core temp by 0.5 Celsius degrees. That would be 3 liters of fluid for a 100kg (220lb) person. Cold fluid reduced the body temp by a full degree Celsius. " "You can check this article on popsci: http://www.popsci.com/does-drinking-hot-liquids-cool-you-off#page-3 + +Long story in short: There are some heat receptors in stomach helping your body determine sweating and drinking hot beverages may freshen you since you sweat more (and if the place is windy so that your sweat would vaporize, unless you just feel hotter) and drinking cold beverages lessen your sweating after an instant cooling so it depends on the environment. If the place is chilly/windy like in front of a fan, hot drinks better. But most of the time cool beverages are the best." +1298 Some flying insects such as butterflies have very erratic and disorienting looking flight paths. Are they in complete control of their movements or do they really struggle to get around? 12798 https://www.reddit.com/r/askscience/comments/cfzexj/some_flying_insects_such_as_butterflies_have_very/ 1563718418 cfzexj Biology 2019-07-21 17:13:38 "The erratic flight is thought to help them avoid predators, and more toxic butterflies tend to fly more smoothly. As for control, well, they can land on a flower. + +https://www.sciencefocus.com/nature/why-dont-butterflies-fly-in-straight-lines/" [deleted] +1200 Theoretically the efficiency of a solar panel can’t pass 31 % of output power, why ?? 12766 https://www.reddit.com/r/askscience/comments/arkttl/theoretically_the_efficiency_of_a_solar_panel/ 1550412412 arkttl 2019-02-17 17:06:52 "That theoretical limit is called the shockley-queisser limit. https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit + +It has to do with the fact that photons that are absorbed by a semiconductor (silicon most commonly for solar cells) with a specific band gap. For silicon that band gap is 1.1 electron volts. when light is shined on a solar cell, an electron is excited in the semiconductor material by the energy of the photon. If that energy is high enough, the electron is excited to the conduction band, and it leaves behind a mobile, positively charged energy state called a hole. Electrons and holes migrate to opposite electrodes in a solar cell to generate power based on their voltage difference. + + Photons with energy lower than the band gap do not excite electrons enough to get over the band gap, and thus don't produce power, and photons with energy higher than the band gap will be absorbed, but relax back to the band gap energy before being transported to the electrode. This relaxation process is complicated and has to do with the continuum of energy states accessible to electrons in the conduction band. Those nearby energy states allow for nonradiative relaxation back to the band gap energy. + +So, the sun shines with a certain spectrum, and only a fraction of the photons will be high enough energy to be absorbed productively, and those above that energy will relax back to the band gap as well. + +With this in mind, even a perfectly efficient cell at converting photons to electrons is limited in its overall efficiency because semiconductors have a specific band gap, and only a certain fraction of the incident radiation from the sun can supply that amount of energy. The specific % limit will be different for semiconductors with different band gaps (CIGS, CdTe, perovskite, GaAs, organics etc), and would also theoretically be different if we had a different sun." "It's called the [Shockley-Queisser Limit](https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit). + +Caveat: This limit is for ideal single np-junction solar cells. + +The main problem lies in the band gap (the energy difference between the conductive band and the valence band of the materials). + +Very briefly, you face two main problems: + +If the energy of the incoming photon is below the band gap, then the photon won't be absorbed by the solar cell. The photon has not enough energy to pump an electron from the valence to the conductive band. + +If the incoming photon has an energy above the band gap you lose energy due to band edge relaxation. In short, while the photon will excite the electron, the excess energy above the band gap is converted to heat and therefore lost for our purpose. + +This band gap problem alone imposes a maximal efficiency of about 48 % for sunlight. + +Then there are some thermodynamical considerations, limited mobilities of the charge carriers, non-radiative recombinations, etc... that cost you another 12 to 15 %. + +Therefore, the highest possible efficiency value for a single pn-junction solar cell is about 33 %. + +Theoretically, if you can produce a multilayer cell with several band gaps that cover the whole energy spectrum of sunlight (and therefore mitigate the band gap problem from above), you could go up to 77 % efficiency. + +So, there still is room for gains." +724 When and why did the English accent in early America fade away, and the American accents come about? 12765 https://www.reddit.com/r/askscience/comments/6n1f28/when_and_why_did_the_english_accent_in_early/ 1499950456 6n1f28 Linguistics 2017-07-13 15:54:16 "English as it was spoken during colonial times isn't the same as it is spoken now in either Britain or America. Both populations have had their pronunciation drift over time. So Americans never lost their British accent, because they never had what we would now call a British accent to begin with. + +You can look up ""Original Pronunciation"" (Called OP English) to get an idea of how pronunciation has changed over time since the early 17th century. There are people who do Shakespeare productions using reconstructed OP to recreate what Shakespeare's plays would have originally sounded like. + +P.S. I should have linked [this](https://www.youtube.com/watch?v=k7tZFqg2PqU) from the beginning. + +P.P.S. [Here](https://www.youtube.com/watch?v=AIZgw09CG9E) is another video talking about a modern accent that many think is close to what colonial-era English sounded like." "Here's an article that discusses English in Colonial America and the roots of American Standard English. + +https://daily.jstor.org/colonial-america-gain-linguistic-independence + +Basically, people arrived from many different places (not just Britain) and developed a common mode of speech fairly quickly." +1397 We hear all about endangered animals, but are endangered trees a thing? Do trees go extinct as often as animals? 12749 https://www.reddit.com/r/askscience/comments/d8fggx/we_hear_all_about_endangered_animals_but_are/ 1569284572 d8fggx Earth Sciences 2019-09-24 3:22:52 "In the eastern USA the most prominent example of a tree that is extinct (or functionally so) is the American Chestnut (*Castanea dentata*)which was killed off due to the Chestnut blight, there are continuing efforts to breed resistance into the handful of surviving trees and their offspring, with varying success. + +We're currently losing all of the Ash trees in the USA today due to the Emerald Ash Borer. Growing up they were all through our woods and we had a half dozen or so throughout our yard, including one giant tree. Now they're all dead or dying. + +The American Elm (*Ulmus americana*) has been suffering from Dutch Elm disease for decades and as a result mature, healthy American Elm trees are also quite rare today. + +Those are the 3 that I am most familiar with from my part of the world (Ohio), though I'm sure there are plenty of other examples from around the world." "Yes, absolutely there are endangered trees! And they go extinct very similarly to animals, but not exactly the same since trees generally live a lot longer and are less... Hidden. Like, if you spot a tree in the wild, you know exactly where it is always going to be. But beyond that, its almost exactly the same. + +Especially in the sense that some cultivation programs keep certain trees alive even as they're extinct or almost-extinct in the wild. + +[This tree](http://nzpcn.org.nz/flora_images_large/Pennantia-baylisiana-2.jpg) for example is the last wild tree of its kind. And its been the last one since at least the 1940s. It grows on an island off the coast of New Zealand. The rest of them went extinct when goats or sheep were introduced to the island and the little buggars ate them all. + +There are more of those trees being cultivated in nurseries, but they haven't been introduced because researchers are concerned about potential contamination. The trees grew in complete isolation naturally; they don't want to introduce disease and pathogens to the island by planting a bunch of trees from nurseries, especially at the expense of the last one. + +Edit: u/polypeptide147 has some more up-to-date [info](https://www.reddit.com/r/askscience/comments/d8fggx/we_hear_all_about_endangered_animals_but_are/f1akby0/)." +607 How are we able to perform a body transplant when we can't repair spinal injuries? 12491 https://www.reddit.com/r/askscience/comments/620y9t/how_are_we_able_to_perform_a_body_transplant_when/ 1490723444 620y9t Medicine 2017-03-28 20:50:44 "https://en.m.wikipedia.org/wiki/Head_transplant + +In real terms, we have no way of knowing if the spinal nerves will re-fuse and if signals will flow again. Present medical knowledge is that once there is a catastrophic cord injury and severance, then it is pretty much over from a neurological point of view. + +The issue here is that the brain stem deals with and controls all autonomous functions of the body (heart beat, breathing, etc) - which presumably will be above the incision point. It is unknown whether the brain stem will be able to send signals down the new spinal nerves, thus there is a very real risk that the ""head"" will not be able to breathe or function without life support. Combined with that, it is unknown whether the donor body's other functions (digestion, excretion etc) can be maintained by the donor brain, especially if the spinal fusion fails. + +It appears that the head donor is terminally ill and has agreed to take part in a ""last ditch"" attempt at furthering of his life. He already has a terminal neurological condition which affects his body, therefore the logic is that if his head and brain ""survive"" the operation but there is no cord fusion giving movement or any quality of life, he hasn't ""lost"" anything as his brain is still in a crippled body and will likely die in due course. + +From a medical science point of view, it will be fascinating to see what happens and he should be thanked for his courage and generously in effectively donating his body for the advancement of medical science and understanding. However, I fear that the outcome will not be successful, and for that, I wish him a safe and peaceful trip. " "The surgeon claims that this will all be possible because he plans on using a super-sharp knife to cut the spinal cord cleanly. + +That's all well and good...but, axonal injury is still axonal injury. Wallerian degeneration (in which the nerve cell dies all the way back to the nerve body) will still occur. Nerves can regenerate after Wallerian degeneration, but they do so at a very slow rate. + +I can't imagine a way this would work out such that the patient wouldn't have to be on life support for at least 6 months, likely longer, *in the best case scenario*...notwithstanding the secondary infections he'd likely get which might kill him before anything good happens. + +Of course, the whole goal of this is to prove us naysayers wrong, and I, for one, would be amazingly excited to be proved wrong. " +1398 Do bees that get lost (f.e.riding a bus) get adopted by local colonies ? 12458 https://www.reddit.com/r/askscience/comments/dholl7/do_bees_that_get_lost_feriding_a_bus_get_adopted/ 1571048359 dholl7 Biology 2019-10-14 13:19:19 "This can actually be a real problem if you set up your bee yard with all of the hives in straight line with all entrances facing the same way. Foragers loaded with nectar and pollen will generally be accepted by the guard bees into a hive. Honeybees tend to prefer the hives on the end which can weaken the center colonies. Generally hives are set up in a horseshoe or some other pattern to reduce this drifting. + +However the average lost honey bee is probably not going to find a colony as wild colonies are very rare now due to imported pests and disease. In positive news most bees you see in nature are likely not honey bees and are native solitary bees." "In most instances, bees carry unique chemical identifiers that are associated with the queen from their home colony. Often, though not always, during a peak, heavy nectar flow, when bees are extreemly busy, the occasional bee from another hive can become adopted into a new hive. However, under normal condition, the guards that greet the returning bees will reject bees that do not carry the chemical markers of their unique colony. In the case of persistent foreign bees, the guards may resort to killing the foreign bee. This can be a good thing if the outsider bee is from a deceased colony and could be carrying that infection. Such bees can spread these deseases. + +Often, man-made behives look very similar to each other, and are in close proximity to each other. This condition can promote bees becoming confused, which can increase the likelyhood that bees will try to enter a foreign hive. As an aid for the bees, some beekeepers will mark the front of hives with unique markings that bees learn to recognize, which helps bees return to their own home hive. + +Under another cerconstance, if a bee becomes lost while forging, it is likely they will die in the field." +608 "Later this year, Cassini will crash into Saturn after its ""Grand Finale"" mission as to not contaminate Enceladus or Titan with Earth life. However, how will we overcome contamination once we send probes specifically for those moons?" 12451 https://www.reddit.com/r/askscience/comments/673bvk/later_this_year_cassini_will_crash_into_saturn/ 1492967047 673bvk Planetary Sci. 2017-04-23 20:04:07 "The goal is not to avoid any possible contamination - if we would do that, we wouldn't send probes at all. Possible contamination should be as unlikely as reasonably possible. If we can let a spacecraft burn up in the atmosphere of the gas giant, that is done. + +A lander cannot do that, of course, so it will get sterilized as good as reasonably possible. + +The Mars rovers avoid regions where liquid water temporarily could exist underground today, for example." "It's difficult to do. We build all our spacecraft in sterile conditions , but can't do anything about contamination during launch. Most bacteria die in space, but there is always a chance some will survive. + +Randall Monroe has done a good article discussing this a bit: https://what-if.xkcd.com/117/ " +914 When we extract energy from tides, what loses energy? Do we slow down the Earth or the Moon? 12393 https://www.reddit.com/r/askscience/comments/81xc2f/when_we_extract_energy_from_tides_what_loses/ 1520165474 81xc2f Physics 2018-03-04 15:11:14 "It is exactly the same process as restrictions in the tidal flow caused by the continents being in the way. It adds more ""friction"" to the system (tidal dissipation) and will result in the tidal bulge being dragged further round (since the Earth spins faster than the Moon orbits). This means we would get an increased slowing of the Earths rotation due to increased tidal dissipation and more energy transferred to the Moon increasing its orbital distance. Of course this effect would be so negligible as to be immeasurable over even a few thousand years even if we increased our tidal energy production significantly. + +  + +edit* I REALLY want to add anything humans do would be completely negligible! The tidal dissipation in the Earth naturally is so small that the Earth-Moon system will not reach tidal equilibrium for many billions of years. Humans do not have the capability of building structures to increase this by any real measurable amount. + +  + +edit2* +Given some of the response about ""we made small changes before and look at climate change"" lets consider the tidal system and how realistic it would be for humans to change the orbital evolution of the Earth-Moon system significantly. + +The easiest thing to look at is what the natural rate of evolution is. The day on Earth lengthens by about 1.7 milliseconds per 100 years. What is more while the Earth slows the Moon moves away from us. This further slows the rate at which the Earths rotation slows. In fact the transfer of energy from the Earth to the moon is proportional to 1/r^6 where r is the orbital distance of the Moon. So basically the Moons moving away from us slows down (as does the slow down of the Earth). + +Now if we consider that the transfer of energy in the system is dominated by seabed surface area and think to ourselves, ""How much could we increase the surface area by?"". The oceans cover 71% of the surface of the Earth but this is a near uniform level. So in order to have a significant effect this is what we are competing against. + +Now couple these two things together. You have a natural process that acts on timescales of millions/billions of years (unlike the climate which acts on timescales of years) where we can only hope to increase its effect by an immeasurable amount (literally due to it being so small that the natural variation in length of day due to super-rotation of the Earths core being larger than the increase we could impart)." "This post goes into a lot of depth, and also answers the question of whether tidal energy could be an answer to our clean energy concerns (Answer: No. Currently natural barriers extract 0.1TW of energy from tides, and global human energy use is about to 16.5 TW currently) + +https://dothemath.ucsd.edu/2011/12/can-tides-turn-the-tide/ +" +1201 CPUs have billions of transistors in them. Can a single transistor fail and kill the CPU? Or does one dead transistor not affect the CPU? 12353 https://www.reddit.com/r/askscience/comments/bew9ft/cpus_have_billions_of_transistors_in_them_can_a/ 1555657477 bew9ft 2019-04-19 10:04:37 "I actually work for AMD and work on the test team, so I might be able to provide some insight!! As a lot of people said before, there are different bins, or SKUs you see, like the i7, i5, i3, they are in fact the same exact silicon, just with things disabled because they may not have worked. For example, if one of the cores doesn’t work, they can just disable another one, and instead of having an 8-core processor, they can sell it as a 6-core. Aside from disabling cores, another common place you see faulty transistors, are within fast internal memory called cache. Processors usually have a few Mb of cache, it’s common for some of the cache cells to be dead upon manufacturing, so manufacturers build some backup cache cells. And when running tests, we can find those dead cells, and reroute those dead cells to the new ones. So when a processor tries to write to a cache address that is dead, there is some microcode internally that reroutes it to the newly assigned back up cache cell. It is possible too that there is enough cache cells that are dead that they end up having to drop the bin from an i7 to an i5 for example. + +Also, there are a lot of transistors, and full circuits that are used simply for testing, and will never ever be used once the processor is on the shelf ready for someone to buy. These are called Design For Test features, or DFT. An example of one of these are some structures called ring oscillators, which are basically really fast operating clocks, and their frequency can be affected by a lot of things, like heat and the health of the silicon. These are scattered all around the silicon at different points, and the frequency can be measured as another metric to heat at various parts of the silicon, as well as the health of the silicon at various parts, and they can also be averaged as another metric to gauge the overall health and possible operating frequency of the entire processor. However, they will never have any use once the processor is ready to be sold, and it’ll actually be impossible to access them. + +So really to answer your question, a lot a lot a lot of testing goes in to making sure your processor is ready to go for all of your gaming or workstation needs. It would be rare for a transistor to die, it probably wouldn’t affect you much though unless it was a very very critical part, and it could take a long time for that dead transistor to mess up your computer. + +EDIT: Thanks for my first silver!! + +EDIT 2: 2x Gold??? Thank you!!! + +EDIT 3: Amazed at how interested people are about this. I have been trying to answer as many questions as possible, but im currently at work! Happy to see people are genuinely interested in very low level details of processors. I am happy to share my knowledge because I dont really talk about any of this with my friends or family!" "There are multiple factors there. + +First, chips are made out of a single large wafer. Usually, each wafer (currently most famous ones are 300mm in diameter) will make tens to hundreds of chips depending on the die size. The smaller the die, the more chips you can make. + +So a large die like a big GPU will need a lot of space on the wafer, the whole wafer which cost can be anything between $3K to $12K depending on quality and the target process required will have much fewer chips than a small die chip like a mobile SoC. for GPU's you might get something like 150\~170 320mm² high-end GPU's out of a single wafer, but smaller low-end GPUs are designed to be small, so you can get hundreds of them on a single wafer. A typical low-end GPU might be 77mm² which will give you roughly 810 dies. So this is one reason why a high-end product which tends to be large as it much more expensive to make, here you can see almost 5 folds the number of chips per the same wafer for just different die size. + +Then you have things called yields and defects. But let's start with defects as it's just a sad part, while they always make these chips in very clean rooms, small defects particle will still find it's way into those wafer while in the making. So let's assume that 30-40 small dust particles stuck on the wafer, on the large dies, the high-end ones, this will basically make at most 40 dies not working properly, so out of those 150 dies, you can get only 100\~110 working chips. While on the smaller dies, you already have 810 chips, so you might get away with 760 chip already. + +​ + +That's why, while making chips, especially large ones, the designers will make the design flexible, they can completely disable parts of it and still make use of the chip, this can work like magic for things that contain a lot of similarly designed blocks, like GPU's, or Multi core CPU's, as when a defect is affecting a part of the GPU cores/shaders, or the CPU cores you can just disable that part and things will work. But if the defect happens to a crucial part that the GPU/CPU can't just work without it (like the scheduler) then that chip will be dead. + +​ + +Some times, the chip designer will intentionally make extra logic just to increase the working chip yields, or they will just assume having less than the actual hardware logics so they can increase the yields of qualified chips. For example the PS3 Cell processor actually have 8 logics called SPE, but the requirement for the PS3 is just 7 SPE's, so and chip with at least 7 SPE's working is qualified to to be tested (other factors includes clocks, power, temps, etc..). This made chips that have either 7 or 8 working SPE's are qualified which will be much better yields than only 8 working SPE's. + +​ + +For other consumer grade products, partially defective chips can also be sold under other product segments. for example GeForce 1080, 1070 & some 1060 are all based on the same die called GP104, while the larger die called GP102 is used to make the 1080Ti, Titan X, and Xp. The GP104 is the same chip here, just the 1070 is using a partially defective chip, so NV just disabled some shaders and other logics and re-used the chip as 1070. If the chip contains more defect, it can be disabled also and used as 1060 as well. + +​ + +The same can be applied to CPU's, now CPU's have many cores, and we have many segments also, so if a CPU die have one or two Cores not working properly then it can be used for a lower segmented CPU. Both Intel and AMD do this actually, some i5's are using a partially defective i7 die actually. + +​ + +But some times the die might not be defective, it might be working, but it's of a low quality one, this is called binning, usually on the wafer, the dies closer to the center have better quality or to say characteristics than the ones which are on the edge, these qualities are like ability to work faster using lower voltage/power/temps, better overclockability. etc.. This what make it different for products like an i7 8700K and a regular i7 8700, or like Ryzen 7 1800X and Ryzen 7 1700X or Core i5 9600K and Core i5 9400, Both are the exact same chips but the former can be clocked higher on stock while maintaining the required voltages, temps and power consumption, or it can also overclock better too, some differences can be small like Ryzen case but some differences can be big like the i5 case where the product is marketed with a different name. + +Edit: small corrections (including the main typo: the wafer diameters 300mm not 300m), and the Ryzen example. + + +Hell thanks alot for those Silver, Gold & Platinum !! all are my first ever !." +915 If iron loses it's magnetism around 800 degrees C, how can the earth's core, at ~6000 degrees C, be magnetic? 12270 https://www.reddit.com/r/askscience/comments/7vo4ir/if_iron_loses_its_magnetism_around_800_degrees_c/ 1517931540 7vo4ir Earth Sciences 2018-02-06 18:39:00 "[Dynamo Theory](http://abyss.uoregon.edu/~js/glossary/dynamo_effect.html). Quote: + +_""In this dynamo mechanism, fluid motion in the Earth's outer core moves conducting material (liquid iron) across an already existing, weak magnetic field and generates an electric current. The electric current, in turn, produces a magnetic field that also interacts with the fluid motion to create a secondary magnetic field.""_ + +So, to paraphrase, while the iron itself is not magnetic, it produces an electric current, which generates an electo-magnetic effect." "There are two different magnetic effects there. + +The inherent ""magnetism"" of ferrous magnets (""permanent magnets""), like you might find on your fridge, is due to a magnetic field being aligned in the metal (frozen, quite literally). As you heat the metal, the field ""melts"" and becomes misaligned. + +The magnetic field generated by the core is due to the material being in motion. Electric and magnetic fields are generated by charged particles in motion. A classic example of this is an electromagnet where you coil conductive wire and run electricity through it to generate a magnet (electricity is just electrons, charged particles, in motion). The liquid iron at the core of earth has sufficient charge that it acts in a similar manner, and generates a magnetic field. If the earth's core would cool fairly quickly, and we had an external magnetic field that was strong enough - the earth could become a permanent magnet as well." +821 How much of sleep is actual maintenance downtime, and how much is just time-killing energy conservation? 12206 https://www.reddit.com/r/askscience/comments/76w48s/how_much_of_sleep_is_actual_maintenance_downtime/ 1508213244 76w48s Biology 2017-10-17 7:07:24 "The problem here, as far as I'm aware, is that we're still not even entirely sure what sleep is *for*. It's noted that it has a lot of very unique benefits, and is essential to our health and well-being, but this question is made even more complicated when you consider that [we've recently discovered that even brainless creatures have need of sleep!](https://www.scientificamerican.com/article/jellyfish-caught-snoozing-give-clues-to-origin-of-sleep/) + +Needless to say, this is going to be a very important avenue of research, because why would a brainless creature need to sleep? Why would its cognitive ability be impaired if it has no brain to speak of? This is one of those magical areas where science doesn't quite have all of the answers just yet." "Virtually every question on sleep should be answered with ""nobody knows"". This is one of those. Keep in mind that some mammals, like horses, sleep 3 hours a day while others, like bats, sleep 21 hours a day. Your question will most likely have different answers depending on the animal we are talking about" +1202 Why can cannabis be detected in urine weeks after use while other drug traces dissipate after days? What properties set it apart in that regard? 12176 https://www.reddit.com/r/askscience/comments/bgf7am/why_can_cannabis_be_detected_in_urine_weeks_after/ 1556018596 bgf7am 2019-04-23 14:23:16 "Cannabis doesn't actually have a trace profile significantly longer than any other substance, it's a bit of myth cooked up by adverse parties. + +[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763020/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763020/) + +THC is broken down quickly and excreted in comparable rates to other common substances, but 11-nor-9-carboxy-Δ9-Tetrahydrocannabinol (THCCOOH), formed by the breakdown of THC, lasts significantly longer. Most urine tests are for THCCOOH. + +The industry standard for THCCOOH is 50 ng/ml, which occasional smokers (1-2X a week) can achieve in a little under three days. + +The long detection times you are referring to occur in chronic users because, as the other guy said, THC is fat soluble. The body clears THC at a more or less constant rate, but ingesting THC at a higher rate than it can be cleared results in THC being saturated more fully over your fat cells. + +Even with that in mind, studies show that the average chronic user, with a low BMI, can clear out THC stores and return to the under 50 ng/ml limit in just over a week. Though there are many who may retain THC in their urine for close to a month." "So I'm seeing replies about the fat soluble nature of THC metabolites and the clearing speed of average BMI individuals. + +Does this mean that higher BMIs clear slower? + +Also does that mean if I take a fat soluble drug, is it less effective because of obesity?" +1008 Why does hitting the top of a bottle of beer with another bottle of beer create that much froth? 12152 https://www.reddit.com/r/askscience/comments/8q1uc8/why_does_hitting_the_top_of_a_bottle_of_beer_with/ 1528647433 8q1uc8 Physics 2018-06-10 19:17:13 it momentarily cause the bottom of the bottle to move away from the beer faster than the beer can move. this creates lots of tiny vacuum bubbles. the beer then rushes into this gap. each of those becomes a nucleation site for the dissolved carbon dioxide to form dozens of small bubbles. this basically turns all the beer contacting the bottle into foam. fun fact if the original hit is just right the vacuum pressure can cause the beer to slam back into to bottom of the bottle so hard it blows out the bottom. "the impact of a weight against the mouth of a bottle triggers a compression wave, which hits the bottom of the bottle and bounces off as an expansion wave. Then the expansion wave hits the free surface of the liquid and bounces back as a compression wave, and so on and so on until the waves are damped out. Because the free surface is relatively close to the bottom of the bottle, we get a train of expansion and compression waves, driving the rapid cavitation of the air bubbles in the beer. + +The air bubbles collapse due to the train of expansion-compression waves, forming clouds of much smaller daughter bubbles. These daughter bubbles have a larger surface to volume ratio than their parent bubbles, and therefore expand much more quickly. This turns the liquid to foam and results in buoyant clusters of expanding air bubbles that rise to the surface—and swiftly make their way to the mouth of the beer bottle. + +source: I am a physicist and engineer who wrote my thesis on Fluid Mechanics, also a master brewer. " +1099 As we begin covering the planet with solar panels, some energy that would normally bounce back into the atmosphere is now being absorbed. Are their any potential consequences of this? 12112 https://www.reddit.com/r/askscience/comments/9gajto/as_we_begin_covering_the_planet_with_solar_panels/ 1537104644 9gajto 2018-09-16 16:30:44 "While not the most definitive source, [this](https://blogs.scientificamerican.com/solar-at-home/the-albedo-effect/) Scientific American post did some quick math on the effects of albedo (""reflectivity"") change from solar panels with the reduction in carbon dioxide from traditional fuel sources and found it's result in a net heat reduction after about 3 years" Albedo is the proportion of of light that is reflected off a surface. It’s low for things like pavement, and high for things like snow. Albedo has the ability to affect climatic systems (do a quick search on albedo feedbacks in the arctic). An example off the top of my head is how permafrost thaws more quickly with an absence of snow. The vegetation beneath the snow is able to absorb solar radiation that would normally be reflected by snow (high albedo). I would argue that there are possible consequences to covering our surface with solar panels (low albedo I suspect), yet it is most likely negligible at our current land use. Good question, sorry my answer isn’t more insightful +822 Keep hearing that we are running out of lithium, so how close are we to combining protons and electrons to form elements from the periodic table? 12073 https://www.reddit.com/r/askscience/comments/7h9ymc/keep_hearing_that_we_are_running_out_of_lithium/ 1512312054 7h9ymc Chemistry 2017-12-03 17:40:54 I work for one the largest lithium producers and refiners. We certainly don’t think lithium is running out. We get a lot of ours by drying brine combined with earth in old volcanic zones. The left over salts have a decent concentration of lithium. This helps avoid so much mining too, but there are a couple lithium mines in America and a big one in Australia. We can and do use nuclear reactions to produce specific isotopes of specific elements, however it's very expensive, and generally not commercially viable except to produce radioactive nuclides which can't be found in nature (for medical purposes, experiments, etc.). +823 If you were to randomly find a playing card on the floor every day, how many days would it take to find a full deck? 11900 https://www.reddit.com/r/askscience/comments/6y93j8/if_you_were_to_randomly_find_a_playing_card_on/ 1504628725 6y93j8 Mathematics 2017-09-05 19:25:25 This is a rephrased version of the [coupon collector's problem](https://en.wikipedia.org/wiki/Coupon_collector's_problem), where an item is chosen at random, with replacement, from a collection of n distinct items, and we want to know how many tries you would expect to take before you drew every item at least once. The answer turns out to be, for n items, n\*H*_n_*, where H*_n_* is the nth [harmonic number](https://en.wikipedia.org/wiki/Harmonic_number) (i.e. H*_n_* = 1 + 1/2 + 1/3 + 1/4 + ... + 1/n). For n = 52, this gives an average result of [almost 236 days](http://www.wolframalpha.com/input/?i=52+*+H_52). "I wrote a quick R script to compute how long this would take by simulation. + + num.simulations = 10000 + deck <- 1:52 + full.deck <- function(collected) all(deck %in% collected) + lengths = vector(,num.simulations) + + for (i in 1:num.simulations) + { + collected <- c() + + while(!full.deck(collected)) + { + collected <- c(collected, sample(52,1)) + } + lengths[i] = length(collected) + } + +From running this simulation I get a mean number of days to collect a whole deck of approximately 236 in agreement with /u/Redingold, providing a nice sanity check. + +The five number summary of the simulation results (min, 1st quartile, median, 3rd quartile, max) is 100, 191, 224, 268, 670, indicating a pretty significantly right-skewed distribution. " +1009 Why do we lose the desire to eat while we are sick? (Ex. when having a cold, I lose the desire to eat) 11859 https://www.reddit.com/r/askscience/comments/90jdxq/why_do_we_lose_the_desire_to_eat_while_we_are/ 1532117846 90jdxq Human Body 2018-07-20 23:17:26 Something no one's really mentioned yet is that when you get sick your immune system releases cytokines. One of these, TNF-a, makes you lose your appetite. It's the main cytokine that causes cancer patients to get skinny and have very little appetite. "This is actually a very interesting question and still not clearly understood. I work in Critical Care / ICU and we know that if you force a patient to have calories early in their critical illness with intravenous nutrition they have worse outcomes. + +We do know that mitochondria - the key subcellular generators of energy - essentially hibernate during critical illness from sepsis / systemic infection. Overloading them with substrate results in free radical generation which causes harm. + +When you're very sick your body enters a catabolic state. That is, it utilises all the body's resources to fight the infection as well as putting the brakes on the human inflammatory response. The key feature is protein loss. The result of high levels of adrenaline, pro-inflammatory cytokines, and other inflammatory mediators, cause insulin levels to drop and energy to be released from stores. + +An area of research I'm interested in is whether we can use indicators of hunger to determine whether a patient is improving and use that to guide when we start feeding the patient. + +*edit: I should say that I was writing this with a 5 year old demanding attention at the same time, so isn't quite as expansive as I'd intended!*" +1010 The freezing point of carbon dioxide is -78.5C, while the coldest recorded air temperature on Earth has been as low as -92C, does this mean that it can/would snow carbon dioxide at these temperatures? 11840 https://www.reddit.com/r/askscience/comments/98b7jf/the_freezing_point_of_carbon_dioxide_is_785c/ 1534593793 98b7jf Planetary Sci. 2018-08-18 15:03:13 "Yes and No. + +Hypothetically yes, a container of CO2 would freeze in those conditions, in a practical sense though, CO2 only makes up 0.04% of the atmosphere, and, unlike water nucleating into raindrops, won't gather into single places, so you wouldn't actually get dry ice snow. " Interestingly, even at -90C, a pile of dry ice will still sublime away, since the partial pressure of CO2 in the atmosphere is so low. +1299 Why can hormone therapy make a clitoris grow but can't make a penis grow? 11750 https://www.reddit.com/r/askscience/comments/c0w2xv/why_can_hormone_therapy_make_a_clitoris_grow_but/ 1560596001 c0w2xv Medicine 2019-06-15 13:53:21 "A penis and a clitoris come from the same embryological tissue. Testosterone therapy makes a clitoris grow because it begins signaling the body to change the clitoris into a penis. Of course, that change is far more complex than simply ""growing"" into a penis, but it still causes hyperplasia of the clitoral tissue. + +It won't make a penis grow larger because the body has already signaled the growth of a penis; there is no conversion to occur. + +We can see the same change in men transitioning to female; estrogen therapy and testosterone blockers will cause a penis to lessen in size. + +I hope that helps." "[This](https://pedclerk.bsd.uchicago.edu/sites/pedclerk.uchicago.edu/files/uploads/UTD_0.png) image is our genitals before they form. Notice that it's the same tissue. + +[This](https://ars.els-cdn.com/content/image/3-s2.0-B9780123821843000052-f05-09-9780123821843.jpg) is an example where stuff can go wrong. Notice how the genitals are always impacted by the presence of hormones. + +Edit: thanks for the silver!!!! + +Edit 2: thanks for the gold!! Y'all are too sweet. Thank you. :)" +501 If we detonated large enough of a nuclear bomb on Jupiter, could we initialize a nuclear chain reaction and create a second sun? 11690 https://www.reddit.com/r/askscience/comments/5bm4cv/if_we_detonated_large_enough_of_a_nuclear_bomb_on/ 1478525225 5bm4cv Physics 2016-11-07 16:27:05 "No. + +Jupiter is not nearly heavy enough to sustain a fusion reaction. Fusion only takes place under extreme circumstances (temperature, pressure). It happens in stars, because they are so big that their own gravity compresses the core sufficiently to create these circumstances. Detonating a bomb on/in Jupiter won't do anything to change its mass or density. + +Furthermore, hydrogen fusion isn't a chain reaction process in the way that nuclear fission is. Nuclear fission (as used by humans anyway) relies on energetic neutrons striking the atoms of the fissionable material (e.g. uranium), causing it to break apart and emit more energetic neutrons, which will cause fission in other atoms, etc... a chain reaction. + +Hydrogen fusion doesn't need an external input, such as neutrons, like fission does. Simply crank up the temperature and pressure of a hydrogen gas and eventually fusion will take place. This means that starting the process isn't a matter of ""kickstarting"" it." In 1992 comet Shoemaker-Levy 9 broke up and collided with Jupiter, the largest of the 21 impacts was estimated at around 6 million megatons of TNT, or around 600 times the world's nuclear arsenal. Big bomb, no sun. +916 What elements are at genuine risk of running out and what are the implications of them running out? 11648 https://www.reddit.com/r/askscience/comments/7znpil/what_elements_are_at_genuine_risk_of_running_out/ 1519389185 7znpil Earth Sciences 2018-02-23 15:33:05 "Phosphorus. high quality phosphate ores to be specific. They play a huge role in industrial scale agriculture as fertilizer. The amount of readily available phosphates for fertilizers is worryingly low, and might lead to a drop in global farming output in the near future (1 or 2 generations), and food shortages. + +http://web.mit.edu/12.000/www/m2016/finalwebsite/solutions/phosphorus.html" [Cobalt](https://en.wikipedia.org/wiki/Lithium_cobalt_oxide). Contrary to what is said here in this tread, it is not Lithium that we will run out of, but cobalt, one of the main elements in high energy density [cathodes](https://journalofeconomicstructures.springeropen.com/articles/10.1186/s40008-016-0035-x). Many researchers are trying to find new electrode chemistries made from abundant materials to avoid this problem. +1011 Why can't we perform a Pancreas transplant for those with Diabetes? 11631 https://www.reddit.com/r/askscience/comments/8nhhi7/why_cant_we_perform_a_pancreas_transplant_for/ 1527764431 8nhhi7 2018-05-31 14:00:31 "Hey, I work in pancreas development so this is a topic I know fairly well, but don't directly study. + +Anyways, pancreas transplants. First an important note- to treat diabetes, you don't need a whole new pancreas. In fact, you only need two percent of one! The pancreas is comprised of two tissue types- exocrine tissue, which aids in digestion, and endocrine tissue, which secretes hormones to regulate blood sugar levels. The vast majority of the pancreas is exocrine tissue, while the endocrine portion, comprised of approximately one million micro-organs called ""islets of Langerhans"", is the only part that secretes the hormones you need to ""cure"" diabetes (including most notably insulin). The two components function largely independently, and it is rare that patients with diabetes have exocrine dysfunction, so actually you only need those darn islets and not the whole pancreas. + +So, what then are the barriers to islet transplantation? The major issues are two-fold. First is getting (enough) islets. It is a non-trivial task to harvest intact and functional islets even in laboratory animals (mice), to say less of a much larger and rarer human pancreas. Remember how the vast majority of the pancreas aids in digestion? Well it does that by making digestive enzymes, and you can imagine what happens when a potential donor passes away- those enzymes get released willy-nilly and start breaking up anything nearby, including our precious islets. It's estimated by the NIH that [only slightly more than half of decedent donors, which are rare enough already, are viable for islet transplantation](https://www.niddk.nih.gov/health-information/diabetes/overview/insulin-medicines-treatments/pancreatic-islet-transplantation). Even if you get a good donor, islet recovery rates aren't perfect and you usually get maybe half of the islets available, sometimes far less. This then necessitates pooling of islets from multiple pancreata (the fancy scientific plural of pancreas), which currently averages out to I believe two good donor pancreata per recipient. It also makes living donation of islets sub-optimal, since again a single donor is unlikely to provide enough viable islets. + +The other major issue is engraftment. To start with there are the usual complications with allo-transplantation- potential rejection, a need for immunosuppressants, etc. By contrast, one pro with islet transplants is that you don't have to connect a bunch of complicated blood vessels like you do with whole organ transplant- we've injected islets into the liver, kidneys, under the skin, even under the capsule of the eye, and had them engraft successfully. However, a great number of the transplants fail, and we don't know completely why- this is one of the hot topics of pancreas research. Perhaps it's poor islet [re-vascularization](https://www.ncbi.nlm.nih.gov/pubmed/24106517). Perhaps it's [islet inflammation destroying islets](https://www.ncbi.nlm.nih.gov/pubmed/25777058). Or a thousand other things acting in concert- I study a molecule called Hmgb1, [which is elevated in islets that engraft poorly](https://www.ncbi.nlm.nih.gov/pubmed/25058889). The current debate is whether this is causational- do transplanted islets secrete Hmgb1, causing islet failure, or are islets secreting Hmgb1 because they are injured? Research seems to be leaning toward the former. + +So to summarize- you don't need the whole pancreas, just the islets. However, it's hard to get enough islets for transplantation, and it's hard to get the islets to function properly/not die in the recipient. On a final note, this is why xenotransplantation (islets from other animals, usually pigs) and stem-cell derived islets are such hot topics in the field. They circumvent the first problem and in the case of stem-cell derived islets, a lot of the second. + +edit: Several posters have astutely pointed out that getting new islets would likely not circumvent the autoimmune disorder that underlies most Type-1 diabetes cases, and would eventually result in transplant failure in that subset of cases. I didn't discuss that issue because 1) it's far outside my specific expertise, and 2) I didn't think of it. /u/SPACE_CHUPACABRA has a great comment below [addressing some of these issues](https://www.reddit.com/r/askscience/comments/8nhhi7/why_cant_we_perform_a_pancreas_transplant_for/dzvynnk/). + +edit 2: Another common question is why not just transplant the whole pancreas then, if it's so difficult to extract islets. Whole pancreas transplant as you can imagine is a major surgery with major risks. Often patients suffering from advanced stages of diabetes or other pancreatic diseases are in bad shape, which increases the risks for complications even further. By contrast, islet transplantation is usually done through catheterization, sticking a long tube into your liver, which doesn't even require general anesthesia. " "Type 1 diabetes has been treated with transplants of the pancreas islet cells which produce insulin. Interestingly, the cells are injected into the liver where they happily produce insulin. The problem is rejection and limited supply of donors. It is still experimental, but has helped people who had very unstable blood sugar levels. + +>[If the cells are not from a genetically identical donor the patient's body will recognize them as foreign and the immune system will begin to attack them as with any transplant rejection. To prevent this immunosuppressant drugs are used. Recent studies have shown that islet transplantation has progressed to the point that 58% of the patients in one study were insulin independent one year after the operation.](https://en.wikipedia.org/wiki/Islet_cell_transplantation) + + " +725 If a bottle is completely filled with water and I shake it. Does the water still move inside? 11550 https://www.reddit.com/r/askscience/comments/6pw57i/if_a_bottle_is_completely_filled_with_water_and_i/ 1501164421 6pw57i Physics 2017-07-27 17:07:01 I actually have a lot of experience with a practical application of this very problem. I teach a chemistry lab where we do the Winkler method test for dissolved oxygen in water. Part of that process involved vigorously shaking a completely full glass bottle to break up and dissolve a precipitate that forms during one of the steps. If you shake the bottle straight up and down (like a shake weight), very little happens. If you hold the bottle at arms length and rapidly rotate your wrist back and forth (your tricep or underarm fat should be flapping away) you will create a vortex inside the bottle and will rapidly mix the contents. [deleted] +917 "Why do cognitive abilities progressively go down the more tired you are, sometimes to the point of having your mind go ""blank""?" 11550 https://www.reddit.com/r/askscience/comments/8cl1vt/why_do_cognitive_abilities_progressively_go_down/ 1523853802 8cl1vt Human Body 2018-04-16 7:43:22 "tl;dr: We don't know but it could have something to do with reduced energy supplies, a build-up of waste metabolites and reduced synaptic pruning (impairing removal of old connections to make room for new ones). + + +We know that people need sleep as all animals do it or at least have some equivalent of sleep. For example, insects don't have REM and dolphins sleep by turning off one brain hemisphere (since they breathe voluntarily, one hemisphere must be active at all times to avoid drowning). The thing is, we know a lot about what happens during sleep, in terms of the electrophysiological, biochemical and psychological markers, but not an awful lot as to why we actually need it. There is no single theory that explains why exactly we need it, but the most popular ones tend to revolve around fighting infections, reducing energy consumption and clearance of waste products from the brain. + +Off the top of my head I can think of three pieces of evidence for this (I'm sure there's more). The first two are pretty obvious. Firstly, we fight off infections best when we are asleep and we consume less energy while asleep. In terms of clearing waste products, changes in neuroglial behaviour suggest that they clear waste products from the brain while sleeping, as many regulate cerberopinal fluid; the main mechanism of removing waste metabolites from the brain (as this organ requires different conditions from the rest of the body). It's perfectly possible that all these theories are correct and we need to sleep for all three reasons. + +Another more recent theory suggests that synaptic pruning occurs during sleep, whereby unwanted connections are removed from the brain (this also happens in babies: they are born with something like 10 times the amount of neurons they and only the strongest neurons and connections between them survive into adulthood). So for example, it may not be necessary for me to remember a certain conversation I had with a friend that day, so the synapses conveying that information may be pruned during sleep. + +So I can think of two reasons as to why cognitive performance declines when sleep deprived. The brain could be working inefficiently when sleep deprived due to an energy deficiency and build up of waste metabolites which screw up the carefully designed molecular machinery that keeps your brain functioning. It could also (or additionally) be due the reduced synaptic pruning consequent of sleep deprivation: the unnessecary synapses don't just create clutter, they take up space and this may make it harder for new synaptic connections to form. This would impair cognition as a large chunk is dependent on synaptic plasticity." Daniel Kahneman’s book “Thinking Fast and Slow” answers this question from a psychology standpoint. Essentially, cognition is hard for our brains, so whenever possible we avoid it. Most of our decision making is done in System 1 thinking, which is quick but often lazy. It’s where many of our biases reside. When we actually think hard about something we enter System 2, which requires more of your body and brain. Kahneman and his partner Amos Tversky did a whole bunch of experiments where they watched the subjects’ eyes while they were engaged in the Add-3 task and found that our pupils dilate when we enter System 2 thinking. System 2 thinking requires a lot of effort, which is why we mostly avoid it unless we have to. In addition, the more we enter into System 2, the less likely we are to go back into System 2 for the next task, since our brains are tired and don’t want to work hard again, which is why we often make poor decisions at the end of a long day or when mentally or physically tired. +609 Why are car antennas so small now, when 10 years ago they were 2-3 feet tall? 11464 https://www.reddit.com/r/askscience/comments/686ygh/why_are_car_antennas_so_small_now_when_10_years/ 1493431528 686ygh Engineering 2017-04-29 5:05:28 "There are two main factors. Most antennas people notice are for xm radio that works at 2.3 ghz instead of 100 mhz that standard fm radio operates. The wavelength is directly related to the antenna size and the wavelength of 100mhz is roughly 10 feet were 2.3ghz is 5inches. + +Secondly electromagnetic modelling software has made amazing jumps in the ability to model complex structures, like HFSS and Feko. So designers can embed antennas in places they never could before, like most cars have the fm antenna in the wind screen. + +There has been a lot of talk about impedance matching, although helpful not really that important in this case. Just because I can impedance match a beer can to 50 ohms doesn't mean it propagates worth a damn. + +Source: I've been rf and antenna designer for 15 years" The length of the old antennas approximately matched the wave length of the band and were placed on the fender to get a good ground plane. Newer digital circuitry in the radio actively matches the impedance so the length or placement of the antenna is less crucial. The antenna can be incorporated into stripes printed on the windows. [A more technical explanation here.](https://www.engr.sjsu.edu/rkwok/Engr297/Val_Impedance%20Matching%20and%20Matching%20Networks.pdf) +1203 How large does building has to be so the curvature of the earth has to be considered in its design? 11368 https://www.reddit.com/r/askscience/comments/avckgw/how_large_does_building_has_to_be_so_the/ 1551267629 avckgw Engineering 2019-02-27 14:40:29 "Definitely for the Large Hadron Collider and similar insanely large particle accelerators or that laser-bouncing tunnel for detecting gravity waves. Not just because they are huge but because their operation relies on incredible precision. + +IIRC the LHC had to account for how the moon's gravitational pull moves Switzerland/France and if the bedrock under the east side moves slightly more than the bedrock under the west side then the beam will be out of alignment." "The Humber suspension bridge has a main span a little less then a mile long (4,626 ft). Due to the Earth's curvature the two main supporting towers (510 feet tall) are 1.4 inches further apart at the top than the bottom. + +[https://en.wikipedia.org/wiki/Humber\_Bridge](https://en.wikipedia.org/wiki/Humber_Bridge)" +1012 Of all the nuclear tests completed on American soil, in the Nevada desert, what were the effects on citizens living nearby and why have we not experienced a fallout type scenario with so many tests making the entire region uninhabitable? 11343 https://www.reddit.com/r/askscience/comments/96yqay/of_all_the_nuclear_tests_completed_on_american/ 1534170375 96yqay 2018-08-13 17:26:15 [deleted] "Strictly you can walk around at any of the above ground detonation sites today and suffer no real or obvious ill effects. You'll get a slight dose but no worse than flying over the poles or living in Telluride (12K feet). + +Most fallout has relatively short half-life and that is also the most intense radiologically. So the greatest risk is short-lived - after 3-6 months, the radiation dose from high radiation sources is 1% of peak; and within 2 years it's a a tiny fraction of that. + +Longer half-life materials last longer but have far lower radiation dose so are low risk anyway. The long half-life sources come to dominate within a few years but are nearly at a background dose rate. + +On top of all of this, there is still weather including rain, snow and wind even in the Nevada desert so what was left on top of the soil has long ago been washed away and diluted to low concentrations. That further reduces any direct risk. + +This is why you can walk on the detonation sites. How do I **really, really** know? I've been to these sites - I used to hold a Q-clearance and participated in ""UGTs for radiation effects on electronics"" back when testing was still being done. Wore a film badge and all that. Total radiological dose reports listed nearly zero dose from my visits. I still have the paperwork for it. + +In general, there's a lot of misinformation about radiation. People are still stupid enough to confuse non-ionizing cell phones with ionizing gamma rays. It's almost like we no longer teach science in schools!!" +918 Is lab grown meat chemically identical to the real thing? How does it differ? 11322 https://www.reddit.com/r/askscience/comments/82zdve/is_lab_grown_meat_chemically_identical_to_the/ 1520531213 82zdve Chemistry 2018-03-08 20:46:53 "Lab grown meat is just muscle. By contrast, conventional meat is muscle plus connective tissues, fats, blood, salts, etc. Those other components are really important to the experience of eating meat. Blood supplies nutrients like iron which contributes colour and flavour. Connective tissues get converted to collagen during cooking and make meat gelatinous and rich. Fats lubricate meat when its chewed and also provide important flavours and nutrients. + +Lab grown meat can be supplemented with some of these things to compensate for what it lacks. Those could be grown or synthesized in a lab separately. The science still has a long way to go. As I understand, there isn't really a way to scale the cell production yet, they just make lots and lots of small petri-dish sized cell cultures and mash them together to make a burger. That takes a lot petri dishes, waste, and money. As a result, I'd also expect the texture of lab grown meat to be very short. Muscles in animals are long strings of cells that can span the entire muscle. Lab grown meats are made up of much smaller subunits that don't string together in the same way. It'll work for burgers which are restructured meat products but it's going to be a lot harder to simulate a tenderloin. + +Lab grown meat would arguably be cleaner than some conventional meat on the market which, like most food, can contain environmental contaminants like dioxins or heavy metals. The lab gives a lot more control than the feedlot. Nutritionally they could be identical. I think the high cost of lab grown meat is probably making digestion studies prohibitive but I would doubt there'd be much of a difference between conventional meat protein and lab grown protein. There could be significant differences in iron digestibility however as the structure of iron in muscle tissue is very important for its digestion. Depending on how lab grown meat iron is structured, there could be different absorption kinetics. + +Edit: To add and address some questions below: + +1) Lab grown meat would probably be microbiologically sterile. It would however be very easy to contaminate in packaging, prep, and storage. I don't see any reason why you couldn't eat it raw but the technology is still a long way from producing anything more sophisticate than a hamburger. Without a lot of the minor components that are present in true meat, uncooked and unseasoned lab grown meat will likely be quite bland. + +2) It is still going to be mostly water by weight, as most things are. + +3) If you want to learn more about lab grown meat you can check out: + +Lab Grown meat company: http://www.memphismeats.com/ +Lab grown animal products support organization: http://www.new-harvest.org/ +Lab grown meat organization (Affiliated with Mark Post, fairly famous scientist on this field): https://culturedbeef.org/ + +Edit 2: Something else interesting! There is some debate about the kosher status of lab grown meat and [here's](https://ohr.edu/5518) a fairly lengthy halachic discussion for the stronghearted. If the initial cell comes from a kosher animal, the meat should be kosher too. Moreover, the opinion seems to be that it would be considered pareve meaning it's neither meat nor dairy. This opens the possibility for a kosher cheeseburger, just with a very large price tag." "Working on meat production as an undergraduate research analysis thing. +Muscular stem cells are used to grow fibers and a company called Memphis meats has made a somewhat cheap (when compared to the first lab to produce one) edible product. +The first product produced was edible but it wasn't tasty and it's texture was all off. A key obstacle to this is that muscular cells have a distinct meshwork and the in-vitro meats were not able to produce this. Also, much of the meat flavor and tenderness comes from reactions that occur after death. A series of enzymes break down the tissues yielding a more flavorful and tender meat than simply adding fat to lab produced meat. +You will get to experience for yourself within the near future as a lab will have a product comparable in price ($30-$50) a pound within 20 years!" +919 How did we first find out there was no oxygen in space? 11301 https://www.reddit.com/r/askscience/comments/8cefwo/how_did_we_first_find_out_there_was_no_oxygen_in/ 1523789735 8cefwo Astronomy 2018-04-15 13:55:35 "The earliest record I could find was 1648, where Blaise Pascal convinced his brother-in-law Florin Perier to take a barometer up the mountain Puy de Dome, where they gathered the first data showing decreasing air pressure with altitude. By the mid 19th century, we had ballonists up to 10km, which is 6.2 miles; I'm not sure how they did that without oxygen supplementation that air would be very thin. + +AFAICT, this knowledge was incrementally acquired over a period of time through various observations like the above. Also during this period (1662-1834), you had Boyle''s Law, Charles's Law, Avogadro;s Law, Ideal Gas Law all get articulated. These laws addressed volume & pressure, volume & temperature, volume & #molecules, pressure & volume & #molecules & temperature, etc." "When you say no oxygen what you mean is no air, right? + +The first Western scientist to conclude that there is a vacuum between Earth and Moon was apparently Otto von Guericke in 1650. He concluded this because he was able to construct a vacuum pump. A vacuum pump can suck the air out of a container such that there is a vacuum in the container. For a long time people thought it was impossible to create a vacuum. They thought there must always be something. And it is indeed not easy to create a vacuum but it's possible. + +Now how did von Guericke conclude that there must be a vacuum in space from his vacuum pump? Well at this point people already knew about gravitation and they knew that air has some weight. If you combine these two facts you come to the conclusion that the air that is higher up puts pressure on the air below, because the air high above weighs something. This means that the air is denser near the ground because it is pressed tight. And this also means the air becomes less dense higher up. + +In 1648, Florin Périer had investigated whether air is less dense up on a mountain. For that he used the recently invented barometer (from around 1640). And he found that indeed air is less dense up on a mountain. + +So, combining the knowledge that vacuums are possible and the knowledge that air is thinner higher up, von Guericke concluded in 1650 that there is most likely a vacuum between Earth and Moon." +824 If the sea level rises, does the altitude of everything decreases ? 11286 https://www.reddit.com/r/askscience/comments/73f39q/if_the_sea_level_rises_does_the_altitude_of/ 1506780577 73f39q Earth Sciences 2017-09-30 17:09:37 "Depends on what you mean. Two different forms of your question: + +**1)** If you were to start walking from mean sea level (as defined as the average position of sea level at a given point over a several year period to account for tidal and storm variability) at a specific point to a specific mountain peak now vs 100 years from now, would the total vertical distance you travel be different? + +Generally, yes. Because the total mass of water in the ocean is increasing and the volume is also increasing via thermal expansion, mean sea level is rising (in most places, there are important local variations due to variations in gravity, bathymetry, and isostatic rebound in response to melting of glaciers/ice sheets) the total vertical distance between mean sea level and mountain peaks will decrease between now and 100 years from now. + +**2)** Will the elevation on maps of mountain peaks change between now and 100 years because of sea level rise? + +No (with a caveat). While conversationally people refer to topographic height as a value above 'mean sea level', unless you're referencing an old map, this is not really the case in that these elevations are not referenced directly to measurements of sea level. When describing a position, whether that's a horizontal or vertical position, this position needs to be referenced to something. This is equivalent to simple plotting in cartesian coordinates where everything is referenced to the origin. When talking about geographic/topographic coordinates, the reference points are called the [datum](https://en.wikipedia.org/wiki/Geodetic_datum). For heights, a [vertical datum](http://gisgeography.com/vertical-datum/) is what we're concerned with and you can see from that link that we can kind of think of three broad categories, 'tidal datums', 'ellipsoidal datums', and 'geodetic datums' (also sometimes called 'orthometric datums'). While a tidal datum is tied to actual measurements of mean sea level height in several areas, a geodetic datum is tied to a specific point, that may or may not coincide with a place where we have measured mean tidal heights. For a geodetic datum, heights are essentially [orthometric heights](https://en.wikipedia.org/wiki/Orthometric_height), so heights above the [geoid](https://en.wikipedia.org/wiki/Geoid), which is an equipotential gravitational surface which represents what sea level would be if only influenced by gravity and earth's rotation, then referenced to our zero coordinate which is specific to that datum. Ellispoidal datums are reference heights to an ellipsoid, so a mathematical approximation of the shape of the earth without topography. There are [lots](https://community.esri.com/groups/coordinate-reference-systems/blog/2014/08/14/mean-sealevel) of different vertical datums that vary by place, for the US we currently use [North American Vertical Datum of 1988](https://www.ngs.noaa.gov/datums/vertical/) which is a geodetic datum. Because elevations are referenced to the height of a specific point (with corrections for the height of the geoid as a function of location) changes in sea level have no influence on the vertical datum. Now, the caveat would be that NOAA or the equivalent body for another country could decide in the future that they want to update their geodetic datum so that they choose a new zero point based on the new sea level height in some location, but there's not really a reason to do this. Vertical datums do get updated (though not incrementally, a vertical or horizontal datum is not changed once it's established, but a new one can be introduced, an example as described on several of those pages is the switch from the tidal datum of 1929 to the geodetic datum of 1988) but this is driven by better and more precise measurements of the gravitational field of the Earth and not changes in sea level, and in fact the US vertical datum [is set to be replaced in 2022](https://www.ngs.noaa.gov/datums/newdatums/index.shtml)." "What about from a barometric pressure point of view? If you’re running at 10,000’ ASL you feel the lack of pressure/less available oxygen - if the sea level somehow rose by 6,000’ would it then feel as if you’re running at 4,000’? + +For example: if the world somehow went Water World enough and only the top of Mount Everest was sticking out above the waves it would feel like sea level today, right? " +726 Has the growing % of the population avoiding meat consumption had any impact on meat production? 11276 https://www.reddit.com/r/askscience/comments/6ntzq1/has_the_growing_of_the_population_avoiding_meat/ 1500307399 6ntzq1 Anthropology 2017-07-17 19:03:19 "[This site](http://www.fao.org/faostat/en/#data/CL) has the answer. + +It's just throwing numbers at you, so I just glanced at it, but meat consumption seems to be growing everywhere. World meat consumption is increasing like crazy, European meat consumption a little less, but still growing. + +Is anyone from /r/dataisbeautiful around?" "What ""growing % of the population avoiding meat consumption"" ? + +Worldwide, the largest reason why people don't eat meat has always been (and still is) being too poor to afford it. As large parts of global population are getting out of poverty, they're starting to consume large amounts of meat - for example, the per capita (so, ignoring population growth) meat consumption in China has doubled in the last 25 years. + +If anything, today the global % of meat-eaters is larger than ever before, simply because more people than ever can afford to eat it and not just the cheap staple crops." +1013 "Can plants be ""fat""?" 11253 https://www.reddit.com/r/askscience/comments/8hxlx6/can_plants_be_fat/ 1525793639 8hxlx6 2018-05-08 18:33:59 "I think there are a few ways this question can be answered. The short answer is ""no"" but the long answer is ""not exactly."" + +Chloroplasts are plant organelles that can undergo dramatic changes as they develop from proplastids. When developed in the dark, proplastids develop into amyloplasts: chloroplast derivatives that stockpile starches in huge quantities. These amyloplasts are abundant in starchy roots known as *tubers* (think potatoes) which are (in simple terms) swollen roots that store energy. This is roughly analogous to fat reserves on an animal. + +Very well-fertilized and watered plants have more succulent tissues than plants grown under more limited conditions. In gardens and fields, this can result in plants that are more susceptible to pathogens, as their tissue is rich in nutrients and water. This is roughly analogous to the propensity of the obese to suffer from health complications. + +TL:DR: plants will not get ""fat"" but there are some aspects of plant physiology that could be considered similar to obesity/fat storage." "Yup. We activated the seed oil synthesis and accumulation pathways in leaves. They make enormous amounts of oil which is basically liquid fat. We're now up to seed levels of 40% by dry weight in leaf. + +https://onlinelibrary.wiley.com/doi/full/10.1111/pbi.12131" +610 If my speed is 100 km/h and my destination is 100 km away and then I move 90 km/h if it's 90 km away. 80 km/h if it's 80 km away. Keep on slowing to match the distance. When will I arrive? 11251 https://www.reddit.com/r/askscience/comments/66wqc9/if_my_speed_is_100_kmh_and_my_destination_is_100/ 1492877249 66wqc9 Mathematics 2017-04-22 19:07:29 "I know that you've gotten some great answers so far, but I wanted to give you a bit of the calculus explanation and how beautiful this question really is. If you don't have a calculus background, don't worry, I'll try to explain this intuitively. + +Generally, we think of **velocity** (speed with a direction component) as how far we've gone in a given amount of time, change in x divided by change in t, if x is how far we travel, and t is how long it took us to travel that distance. + +So if I travel x = 10km in t=2 hr, 10/2 = 5km/hr, and that would be my velocity. + +But here we're focusing on velocity at an instant. **Velocity at any instant** is actually defined to be the instantaneous change in position, which we can denote with dx, divided by the instantaneous change in time, which can be denoted with dt. This is where the calculus comes in. It's just describing what your velocity is at any instant in time, kinda like the speedometer on your car shows you at a certain moment how fast you're traveling. This is actually called a derivative in calculus. + +We can then set up a differential equation which describes your motion. This is an equation that can relate a rate of change in a quantity with the actual quantity. + +Velocity at any point in time = (how far I am from my destination at any point in time) + +If we start at 0m, at any distance x we've traveled, how far I am from the destination is just 100-x. For example, at x=25km from where you started, you are moving at 75km/hr. And our instantaneous velocity at any time is just dx/dt, as I explained above. + +So we can write this as: + +dx/dt = 100-x + +This is our differential equation, and I'm not going to get into how to solve it, but I'll tell you that the solution in this particular example is: + +x(t)=-100e^(-t)+100 + +""e"" is Euler's number, around 2.71828. + +x(.632) is 50m, so you'd be halfway there in .693 hours, or about 42 minutes. If you plug in t=10 hours, for example, + +x(10) = -100e^-(10) + 100 + +which, if you calculate, is about 99.995m to our destination after traveling for 10 hours. + +As t gets infinitely large (as an infinite amount of time passes), x(t) gets extremely close to 100km, but never reaches it, and so it's consistent with the other explanations. But if you're curious what the graph of position vs. time looks like, check [this](https://www.desmos.com/calculator/h1icybh65l) out. + +Bonus: if you're still curious about this, /u/3blue1brown is going to release an ""essence of calculus"" series on YouTube soon. He explains all this super well and how beautiful all this is." If you get within 0.5 nm (in ~200K years) you'll probably just get sucked the final distance by intermolecular forces, so you have that to look forward to. +1014 Supposing I have an unfair coin (not 50/50), but don't know the probability of it landing on heads or tails, is there a standard formula/method for how many flips I should make before assuming that the distribution is about right? 11191 https://www.reddit.com/r/askscience/comments/90s854/supposing_i_have_an_unfair_coin_not_5050_but_dont/ 1532204545 90s854 Mathematics 2018-07-21 23:22:25 "Yes, there is a more or less standard way of solving this problem, but there is a lot of latitude. For instance, it's well possible that your biased coin gives you results that look perfectly unbiased for any arbitrary number of flips. So you can never know *for sure* whether your coin is biased or unbiased. + +Suppose we have the following, significantly *easier* problem. We have two coins, X and Y, one of which has probability of heads *p* and the other has probability of heads *q*. But we don't know which is which. We randomly choose one coin and our goal is to determine whether our coin has chance *p* or *q* of showing heads. Note that we *know* the values of *p* and *q* *a priori*; we just don't know which coin is which. + +For the solution to this problem, [you can read this post on StackExchange](https://math.stackexchange.com/questions/2033370/how-to-determine-the-number-of-coin-tosses-to-identify-one-biased-coin-from-anot/2033739#2033739). The idea is that you need to flip the coin enough times so that you are confident that both you have X and that you don't have Y. The punchline is that if the coins have *p* and 0.5 as their chance for getting heads (so we are trying to distinguish a biased coin from an unbiased coin), then the minimum number of flips needed for a 5% error is roughly N = 2.71/(p - 0.5)^(2). Note that the closer the biased coin is to being fair, the more flips we need. If the biased coin is known to have, say, p = 0.51, then we need about 27,100 flips to distinguish between the two coins. + +[**edit:** Another user discovered a missing factor of 4 on the formula in the StackExchange post. I have since corrected the formula and the calculated value of n.] + +However, the problem posed in the title is much different since we do not know the bias of the coin *a priori*. This means that will not be able to write down the number of required flips once and for all. It depends on how biased the coin can be. As the calculation linked above shows, we may very well require arbitrarily many flips if the bias (deviation from fair) is allowed to be arbitrarily small. If the bias is bounded away from 0, then the above analysis can be applied to give an upper bound for the minimum number of flips. + +The best you can arguably really do in the general case is flip the coin with unknown bias many times and then consider a certain desired confidence interval. So let *p* be the unknown chance of getting heads on your coin. The procedure to distinguish this coin from fair would be as follows: + +1. Flip the coin *n* times and record the results. Let *h* = observed proportion of heads. +2. Find the *Z*-value corresponding to a confidence level of γ. (There are plenty of calculators that can do this for you.) +3. Calculate W = Z/(2n^(1/2)). This expression comes from the fact that the standard error for *n* Bernoulli trials with probability *p* is (p(1-p)/n)^(1/2), and this expression is maximized when p = 1/2. (Remember we don't know the value of p, so that's the best we can do.) +4. The confidence interval for *p* is thus (h-W, h+W). + +Please note carefully what this confidence interval means. This means that if you were to repeat this experiment many times (or have many different experimenters all performing it independently of each other), then the proportion of experiments for which the confidence interval would actually contain the true value of *p* tends toward γ. It does *not* mean that there is a probability of γ that the true value of *p* lies in this particular interval (h-W, h+W), although that is a common misinterpretation. + +[**edit:** I've changed the description of a CI to be more intuitive and more correct! Thank the various followup comments for pointing this out to me.] + +As a particular example, suppose you flipped the coin 10,000 times and got 4,000 heads. You want a 99.99% confidence level. So h = 0.4 and γ = 0.9999. A confidence level calculator gives Z = 3.891, and hence W = 0.019455. Hence your confidence interval is (0.381, 0.419). So if many other people performed the same experiment and you collected all of the results, roughly 99.99% of the calculated confidence intervals would contain the true value of *p*, *and* they would all have the same length. So it's probably safe to say the coin is biased. Can't know for sure though based on just one CI. But if you repeat this process and get, say, 5100 heads, then your confidence interval is (0.491, 0.529). So it's probably not safe to say the coin is biased in that case. + +In general, for this method, the number of trials required depends only on the desired confidence level. Whether you decide the coin is biased is a different question really. At the very least, you would want your confidence interval not to include p = 0.5. But this doesn't mean that can't be true. Confidence intervals are notoriously misinterpreted. + +Wikipedia has an article on this very problem. The method of using confidence intervals is described. Another method based on posterior distributions is also considered, and you can read the details [here](https://en.wikipedia.org/wiki/Checking_whether_a_coin_is_fair#Posterior_probability_density_function)." "*EDIT: I've slightly modified what I originally wrote to more directly answer OP's question (previously I considered Chernoff bounds with multiplicative error, but I've changed it to use additive error so that the number of required flips is independent of the coin's bias).* + +*EDIT 2: for a different explanation of what I've written below, see [this wikipedia article on Hoeffding's inequality](https://en.wikipedia.org/wiki/Hoeffding%27s_inequality) which is very closely related to the Chernoff bound. This article derives the same final answer I've written below. The nice thing about this solution is that it rigorously answers OP's question, in the sense that it tells you exactly how many coin flips you should do to obtain a specified precision on the true bias of the coin. One issue with the current top answer is that it relies on the central limit theorem and z-values. This is actually not necessary for this problem - the approach below is simpler and more rigorous, but perhaps less intuitive than the z-value approach.* + +================================= + +One simple approach for studying this problem is to use the *Chernoff bound*, a very powerful bound which applies to situations where you have a sum (or average) of independent random variables. See for example [these notes](http://math.mit.edu/~goemans/18310S15/chernoff-notes.pdf), or [wikipedia](https://en.wikipedia.org/wiki/Chernoff_bound#Additive_form_(absolute_error)). + +Here is one form of the Chernoff bound which we can use on this problem. Say you perform *n* coin flips. Let *X* denote the total number of heads you got. Let *p* denote the coin's probability of ""heads"". Then the Chernoff bound implies + +Pr[|X/n - p| >= δ] <= 2*exp[-2nδ^2] + +That is, the probability that the observed average number of heads (X/n) differs from the expected average number of heads (p) by more than δ is upper bounded by the quantity on the right hand side. + +Now, say we are willing to tolerate a probability of ε of being wrong. How many coin flips do we need to estimate p to within δ, and have a probability of no more than ε of being wrong? To calculate this, set the right hand side of the inequality to ε and solve for n: + +2*exp[-2nδ^2] = ε +==> n = 1/(2δ^2) * ln(2/ε) + +Now let's plug in some actual numbers. Let δ=0.1 and ε=0.01. Plugging this into the above expression, we find that **265 flips are sufficient to determine p to within an accuracy of ±0.1, with 99% probability of success**. + +Let's do another one. Now set δ=0.01 and ε=0.001. Plugging this into the above expression, we find that **38005 flips are sufficient to determine p to within an accuracy of ±0.01, with 99.9% probability of success**. + +Here's an interesting feature of the above result. Note that the dependence of the number of required flips with δ scales like 1/δ^2. So, for example, decreasing δ by a factor of 1/100 corresponds to multiplying the required number of flips by 10000. But the dependence with ε goes like ln(1/ε). This function increases very slowly as ε gets smaller and smaller, meaning that not too many additional flips are required to drastically decrease our probability of failure, for a given fixed confidence interval δ. + +So, to answer OP's question, **1/(2δ^2 ) * ln(2/ε) flips are sufficient to deduce the true probability of heads, up to precision ±δ, and with probability of error given by ε.**" +1793 Why do Giraffes only live for 25 years but Elephants live upto 70 years even though they both share similar diets, size and live in the same parts of the world? 11189 https://www.reddit.com/r/askscience/comments/lsdn7i/why_do_giraffes_only_live_for_25_years_but/ 1614278696 lsdn7i Biology 2021-02-25 21:44:56 "Okay, let me introduce you to r vs K selection. + +All living creatures have to have babies, to pass their traits on to the next generation, ensure that their species survive. But there's 2 general strategies, r and K + +r selection are the creatures that have many offspring at once. Think of insects or fish. They have lots of babies, and most of these babies will die. They put very little effort into raising these young. Basically they reach sexual maturity early, have a hundred or more babies at a time, and sometimes die soon after, leaving room for their offspring to take their place. Think of salmon spawning in a river then dying. Think of insects, which typically have one large clutch of eggs then die soon after. These species are short lived, but just spew out their offspring, most of whom will die. If ever there's a favorable change in the environment more of their offspring will survive and can very quickly take over. If the environment changes for the worst, well they had hundreds of offspring, one or two might make it. + +K selected have fewer offspring. They devote a lot of attention to these offspring, investing a lot of time and effort into teaching them how to survive. Their plan is to have fewer offspring, but invest a lot of effort into protecting and teaching their offspring so that most will survive. Because the parent(s) need to invest so much effort into raising their young, the parents have to be long-lived to allow time for them to pass on their knowledge and provide protection. Think of humans who's offspring are completely helpless for the first 2 years or so, and are not ready to take care of themselves until they are teenagers (or in the case of my nephew, 30+ years old). + +Elephants are highly K selected. It takes a lot of effort to raise a young elephant, so they don't reach sexual maturity before they are teenagers. When they become pregnant it's 22 months, almost 2 years, before they give birth. They only give birth to a single offspring. This offspring is dependent on it's mother for at least 5 years, and up to 10 years. A baby elephant nurses for at least 2 years, it can't survive without it's mother's milk, and if orphaned before this will die of starvation. After giving birth the mother will not be able to get pregnant again for at least 4 years, so their first child will be almost 6 years old before there is a chance at a brother or sister. An elephant can become pregnant well into their 50's or even 60's, although fertility drops after age 30. All of this mothering gives baby elephants a high chance of survival. 70% of elephants will live to the age of sexual maturity. + +For all of these reasons, an elephant has to be long-lived. It, like humans, invests so heavily in raising their offspring that they have to be able to stick around for years. + +Now giraffes, on the other hand, are kind of in between r and K. They reach sexual maturity at around age 7, half the age of an elephant. They are pregnant for 15 months, and give birth to a single offspring (usually). The offspring are weaned off their mothers milk at age 1, although they can begin to eat solid food at around age 4 months. Baby giraffes are reliant on their mothers for less than 2 years, generally becoming independent at 15-18 months. Meanwhile the mother giraffe can become pregnant again almost immediately after giving birth, so she can be nursing one young while pregnant with it's sibling. Sadly, only about 50% of giraffes will survive infancy. + +For a mammal that's even more r selected than a giraffe, look at a dog. Dogs are pregnant for 63 days, and give birth to multiple offspring. They can get pregnant at 10 months, and the puppies are weaned at about 30 days. And dogs only live about half as long as giraffes. + +Clarification: I stated that elephants have to live a long time because they are highly K selected. In actuality it's more of a ""there's a genetic push for an elephant to live longer lives. A long lived elephant, since they remain fertile right up almost to the point of death, will have more offspring. These offspring will in turn inherit their parent's long life, so there is a selective pressure for longer lives in elephants, which allows them to devote more effort into raising their young.""" "Genetics. They process that food differently, they have different behaviors, and ultimately, it wasn't selected for by evolution. + +Elephants are very social and are matrilineal. Matriaches lead their groups based on knowledge they've learned throughout their life. This is then passed down. Additionally, by living longer, there are more older adults to care for young. + +I don't know enough about giraffes to contrast their behavior, but ~~I thought it was similar to horses where males fight for control of groups of breeding females. IF I'm right on that, then~~ there isn't the social network there to reinforce long life. (Edit: don't really know how to phrase it... but, This is about evolutionary selection and the role society and group behavior influences the prevalence of certain genes in a population of animals [and the other way around, can't form a society if everyone dies too fast. *Looking at you, MAYFLY*] In this case, genes that would help giraffes live longer such as promoting a stronger heart and circulatory system) + +Lastly, brains. Elephants are smart and learn a lot. They're problem solvers, they remember stuff, etc. Giraffes, I don't think they're at elephant level intelligence. So, a giraffe is gonna learn everything it needs to (or can learn) much faster than an elephant, so the longer lifespan of the elephant accounts for this as well. + +Everything I've said about elephants is magnified in humans if that helps conceptualize it. + +EDIT: +My most popular post is actually in my area of expertise and not one of my random back-asswards comments. I feel lucky. ⭐ + +There are lots of additions that could be made to this! This was just an unemployed microbiologist's remembrance of Zoology class and all those nature documentaries. Thanks to everyone for the replies!" +920 Am I using muscles to keep my eyelids open or to keep them closed or both? 11188 https://www.reddit.com/r/askscience/comments/83f7nj/am_i_using_muscles_to_keep_my_eyelids_open_or_to/ 1520689397 83f7nj Human Body 2018-03-10 16:43:17 "You have 3 sets of eye lid muscles, and when all of them are relaxed your eyelids will find a nice balance of being a bit open (think of how it looks when you're tired). + +One set is circular and goes around the whole eye, when it contracts your eyelids close (you can flex it by squeezing your eyes shut). It's the orbicularis occuli. + +The second set is inside the upper eye lid and it's the one you use to open your eyes wide. It's the levator palpebrae superioris. + +The third set is an odd one - it controls the upper eyelids too, but only when you're surprised. You don't have any direct control over this muscle, it'll fire off when you need to open your eyes very quickly. It's the superior tarsal muscle." "Both. Pretty much every every muscle in your body works in pairs, an agonist and antagonist. What the agonist does, the antagonist does the opposite of. That way neither can pull too far and no muscle ever gets stuck in one plane or position. Every skeletal muscle in the body can only ""pull"",even when you think you are ""pushing"". So the agonist pulls one direction and the antagonist pulls the other 😊" +1204 Considering that the internet is a web of multiple systems, can there be a single event that completely brings it down? 11159 https://www.reddit.com/r/askscience/comments/azd4qp/considering_that_the_internet_is_a_web_of/ 1552200294 azd4qp Computing 2019-03-10 9:44:54 "One that no one is mentioning is potentially the most likely and damaging. BGP is the protocol that handles routing on the internet and is what enables the internet to be decentralized. BGP is largely trust based, and there have been cases of companies saying they “own” IPs that they do not. There have been several instances of countries trying to censor sites like YouTube. Generally this is done by “black holing” IP subnets. So for example, in that country, all traffic destined to You Tube would simply be discarded and your request would never make it to YouTube. Since BGP propogates routes automatically and is latgely trust based, there have been times where these “null routes” escape from the country they are meant for, and impact global traffic. + +There are of course many mitigations to this, but its conceivable that a specially crafted BGP hijack could significantly disrupt global traffic (as has already happened several times over the years). I would definitely say BGP is right now the achilles hell of the internet, much more so than DNS (its just that many non-networking folks have likely never heard of it, while many people are aware of DNS) + +Speaking of DNS, another risk to worry about is a DNS hijack(which are generally much less impactful than BGP hijacks), discussed in some other posts. We are starting to see more of these schemes (sometimes in conjunction with a BGP hijack to point endusers DNS traffic to nefarious servers), and sometimes these schemes are designed to steal cryptocurrency. As there is money in this, I would expect to see more and more of these types of attacks, especially if crypto prices go back up. + +See more [here](https://en.m.wikipedia.org/wiki/BGP_hijacking) " A very large Coronal Mass Ejection during a period of low magnetic field could conseivably knock out most or all of the internet. Similarly, large scale coordinated EMP attack could do a similar thing. Those are my best ideas, obviously both are hardware focussed I'm not sure if there are possible software solutions that could take down the entire internet, but it seems like it would be extremely challenging to achieve that. +1300 [Neuroscience] Why can't we use adrenaline or some kind of stimulant to wake people out of comas? Is there something physically stopping it, or is it just too dangerous? 11154 https://www.reddit.com/r/askscience/comments/cs0win/neuroscience_why_cant_we_use_adrenaline_or_some/ 1566133317 cs0win Neuroscience 2019-08-18 16:01:57 "Comas aren't just a form of deep sleep. In fact, sleep is a complex and specific pattern of brain activity that requires a healthy brain to perform it (and just happens to produce unconsciousness as a side effect). Your brain just temporarily switches off consciousness - and various stimuli can make your brain switch it back on. A sufficiently loud noise, a certain amount of physical touch or movement of the body in space, a shot of adrenaline as in your question, etc. will all send signals to that switch and flip it back to the ""on"" position. + +A coma is a *lack* of activity. The consciousness switch (parts of the ascending reticular activating system) is broken, or the wires leading it to the machinery of consciousness (other parts of the ARAS) are not working, or the machinery itself (cerebral cortex) is hopelessly damaged. This damage can be due to lack of oxygen (suffocation, drowning, opioid overdose, stroke) or due to mechanical injury, but in all cases, the neurons are severely damaged or dead. In some cases a signal can't even get to the ARAS. Even if it can, the ARAS and/or the cortex can't respond like it should. That's the entire reason the coma is happening, and it's the reason that playing Justin Bieber at full blast or jostling the person won't wake them up either. + +Tl;dr: a coma is what happens when your on/off switch is broken or disconnected. Trying to hit the on/off switch won't solve the problem." "Adrenaline, cortisol, and other stimulants are like an alarm. They're a chemical signal that can quickly travel around the body. + +People fall into comas for many reasons, but generally increasing the 'wake up' signal won't do anything. It's like a ringing alarm clock for a deaf person. + +Most comas are caused by drug overdose of one kind or another. This tends to cause coma through damage to a region of the brain stem called the Ascending Reticular Activating System (ARAS). In particular, synaptic function is impaired. Basically the neurons that form the 'wake up' button lose the ability to talk to each other. Pressing the button harder won't make a difference. + +Other times, there's systemic damage to the brain. The 'wake up' button may work, but the stuff it's connected to can't sync up correctly. This is particularly true for damage to the outer layer of the brain - the cerebral cortex - which is where consciousness seems to happen." +921 What does unplugging your electronics when not in use do for the environment/electricity bill? 11153 https://www.reddit.com/r/askscience/comments/7zwhvz/what_does_unplugging_your_electronics_when_not_in/ 1519477927 7zwhvz Physics 2018-02-24 16:12:07 "Nowadays not a lot. + +Modern electronic equipment has a negligible standby power consumption but it's not zero so there will be a micro saving. But boiling too much water in an electric kettle or letting warmed air leak from a leaky building will cause far higher power wastage than leaving your TV or PVR plugged in and on standby. + +Switching off when not in use is a good policy so don't switch on the games console, satellite receiver, PVR, and the Bluray/DVD at the same time. + +Unplugging has no environmental effect on its own in so far as you can switch off the mains power at the socket in some cases, or use remote switchable adaptors to disconnect power supplies when not in use. + +Edit: a word" "If you're interested in how much electricity your devices use when not in use, I'd recommend a Kill-A-Watt device. It'll give you realtime information on watt consumption. The term for this is standby power, or I've always heard it called ghost load: https://en.m.wikipedia.org/wiki/Standby_power + +In short, it depends on the device. Some are better than others. In aggregate, all our devices do have some meaningful effect on the minimum amount of electricity the grid needs to produce as a baseline. Peak electricity usage - for instance at times when air conditioning use is high - may be a more significant factor in terms of environmental impact. If you're looking to make a personal contribution, consider looking into weatherproofing (insulation, weatherstripping, finding leaky windows or doors) your home to save energy on heating and cooling, or planting a tree outside your home where it will provide summer shade. These energy sources are typically much higher than your average consumer electrronic in standby. + +I'm a firm believer that every little bit helps. + +Sorry for the rambling message with probably lots of typos (on my phone)." +727 Why do you not feel hungry after not eating for a long time? 11076 https://www.reddit.com/r/askscience/comments/6mbbr6/why_do_you_not_feel_hungry_after_not_eating_for_a/ 1499649480 6mbbr6 Biology 2017-07-10 4:18:00 "In short, adrenaline and cortisol. If you haven't eaten in a long time, your body doesn't relax, it instead increases stress hormones which induce the metabolism of energy stores (ie, fat tissue, glycogen) and help mobilize you so that you can find food or fight for it. + +Once you eat, stress hormones decrease, blood flow to the intestines and visceral organs is restored, and you feel hungry again (this is why appetizers induce appetite). " "I'll try and answer, but it's been many years (10+) since I've done this study. + +One of the most predominant reasons is gluconeogensis, when you do not eat for a period of time your body detects the fall in serum (bloodstream) glucose (This and your stomach being physically empty will trigger a hunger mechanism) and eventually it begins to increase the gluconeogenesis pathway. + +This is a process by which your body begins to increase glucagon production (Hormone that tells your body to raise glucose levels) and maintain your blood glucose level, conversely it will decrease insulin production (Most easily explained as: insulin is necessary to transport glucose for use at the cellular level and therefore decreases serum glucose levels). + +As you enter gluconeogenesis, your body is now breaking down predominantly proteins and fats rather than utilising the glucose as it is entering your bloodstream from the food absorbed in your (predominantly small) intestines. +Initially these proteins and fats will be from intramuscular/lipid/cellular stores and then finally, provided by directly catabolising your own body tissue and organs. +Throughout this process, essential for life neurotransmitters: phosphates, magnesium and potassium continue to be utilized to maintain fluid balance, electroconduction and intracellular movements (which includes the glucose we're 'producing' and using). + +Once a stasis level is achieved (stomach has collapsed, intestinal peristaltic motion has slowed considerably, serum glucose is stable) you no longer feel hungry as there are no rapid changes occurring, essentially your body is being supplied the necessary fuel it currently requires to keep going. +(And from a perhaps historic standpoint: There was probably no point tormenting you that you're hungry while you're trying to hunt for food). + +If you maintain this fasting for long enough, there is a risk of potential serious medical compromise (Cardiac Arrest, Seizure etc) predominantly due to neurotransmitter depletion and in some cases due to direct catabolism of the vital organs to provide glucose (such as the heart). + +There is a further risk if you enter in to this state and that's resuming eating, this is called 'refeeding syndrome'. +In refeeding syndrome, where the body is already in an elevated state of glucagon production, the sudden increase in blood glucose results in a sudden increase in insulin and thus consequently your body's overall metabolism spikes which continues to include proteins and fats (Elevated Glucgaon). With this, neuotransmitters (Potassium and Phosphate predominantly) which the bodies stores have already depleted to maintain serum levels, have a sudden intracellular shift and serum levels can decrease to fatal levels. " +611 How do animals like whales not get the bends when breaching at high speeds from the depths? 11063 https://www.reddit.com/r/askscience/comments/68d1zk/how_do_animals_like_whales_not_get_the_bends_when/ 1493516792 68d1zk Biology 2017-04-30 4:46:32 "http://news.nationalgeographic.com/2015/08/150819-whales-dolphins-bends-decompression-sickness/ + +>Researchers from the University of North Carolina Wilmington investigated how marine mammals’ tissues—specifically, fat deposits in the jaws of toothed whales that are used in echolocation—absorb nitrogen gas, one of the gases that contributes to the bends. They found that the makeup of the fat affected how much nitrogen gas dissolves in it—and that different species had different fat compositions. + + >Once, scientists thought that diving sea creatures like the elusive, deep-diving Cuvier’s beaked whale were resistant to the bends, but mounting evidence suggests that this may not be entirely true. + +>In 2002, international navy sonar exercises were linked to a mass stranding of 14 whales in the Canary islands. The whales had gas bubbles in their tissues, a sign of decompression sickness." I've always been told that free divers (divers without SCUBA gear) aren't subject to the bends. What I've always heard is that they don't get the bends because since they only go down with the air in their lungs, there isn't an excess of nitrogen to go into their blood to form bubbles. Basically, the nitrogen in their lungs just comes back out of their bloodstream into their lungs instead of being trapped since they aren't constantly breathing in new air leading to an excess of nitrogen to be dissolved in their blood. Seems like the same logic would apply to whales and dolphins. They only go down with their lungs worth of air so it just comes out of their blood back into their lungs. +825 From my kid: Can you put a marshmallow on a stick out into space and roast it with the sun? 11026 https://www.reddit.com/r/askscience/comments/7engan/from_my_kid_can_you_put_a_marshmallow_on_a_stick/ 1511317914 7engan Physics 2017-11-22 5:31:54 "I actually did a calculation just like this for my physics course last week. The result was that a spherical object orbiting the sun at the same distance as Earth eventually assumes a temperature of roughly five degrees Celsius (slightly above freezing) + +This is in a very simplified model though. However, I can check whether I can find or reconstruct the formula to see how close to the sun you have to get. + +Does anyone know how hot a marshmallow needs to be to melt? + +**EDIT:** + +Okay so the formula is + +Distance to sun = radius sun * (T sun)^2 /(2 * (T marshmallow)^2 ) + +assuming the following values: + +radius sun = 696342 km + +T (sun) = 5776K + +marshmallow melting point = 50 degrees C = 323K + +We get the result of 63 370 834 km which is roughly 160 times the radius of the sun, roughly two fifth the distance between the sun and earth, and lies between the orbits of Venus and Mercury. + + +So good news, if you are in a spaceship near Mercury and push a marshmallow out the door it will indeed melt. + + +If you want to see how I got to the equation, [here](https://www.reddit.com/r/askscience/comments/7engan/from_my_kid_can_you_put_a_marshmallow_on_a_stick/dq6tw8b/) is a rough outline of my approach. + +**SECOND EDIT:** + +To alleviate some confusion, my calculation assumes a spherical body that receives heat radiation on the side facing the sun and radiates heat off to all sides equally. This is only the case when the entire surface has roughly the same temperature. + +For a small object like a marshmallow (that possibly even rotates) that is not a bad assumption but for large bodies like the moon it doesn't quite work that way. For those objects you can regard the 5°C as a very rough approximation of the average surface temperature (take this with a grain of salt, I'd have to do some calculations to be sure) but since heat traverses from one side to the other very badly the side facing the sun will be way hotter and the side facing away from the sun will be way colder. + +Earth has a greenhouse effect that traps heat inside the atmosphere which is why it is way hotter than 5°C even on average. + +Also, regarding astronauts and spaceships, unlike the marshmallow those produce heat internally which is very hard to get rid of without an atmosphere, so without a cooling system they will overheat regardless of the sun." "Near earth? No. The amount of heat from the sun just outside Earth's atmosphere isn't that much higher than what hits the surface--the atmosphere is mostly transparent. + +There is some distance at which you'd be close enough; I'm not in a position to do the math, but expect it to be close than Mercury. Perhaps try making a request on /r/theydidthemath if you don't get specific numbers here. + +At that distance it would be difficult but possible to shield a spacecraft, allowing it to be crewed. + +The main reactions that go into caramelization don't depend on oxygen, so I see no reason why the marshmallow wouldn't caramelize. It wouldn't catch fire if you're doing this in the vacuum of space. + +One notable effect of the vacuum of space is that the marshmallow would expand *substantially* as you removed it from the atmosphere. You can look up YouTube videos of marshmallows in vacuum chambers to get an idea of this. + +**** + +Edit, since everyone feels the need to make the same comments: + +Space can be very hot. Thermodynamics in space are quite different from on the ground, and I didn't intend to imply that *temperature achieved* would be similar just above Earth's atmosphere as it is on the ground. + +In space the thermodynamics of an object are almost entirely governed by radiation. Solar radiation is about 1 kW per m^2 on the surface, or about 1.3 kW just above the atmosphere; those are the same order of magnitude, hence my opening statement. + +~~Ultimately I would expect a marshmallow to be fairly similar thermodynamically to the moon; both are fairly white and fairly spherical. Temperatures on the moon are not hot enough to toast a marshmallow, though they can be very hot (as much as 100 C in sunlight). + +Its important to note that the moon sees extreme temperature differences because there's no effective way for heat to transfer from the sunlit side to the dark side; it's too big for conduction to be relevant. On a marshmallow scale conduction would be very relevant and would allow the entire marshmallow to be a more moderate temperature than areas of the moon see.~~ + +I rescind any comparison to the moon. On the scale of a marshmallow conduction dominates. The side facing the sun would be quite hot and the side facing away would be quite cold, but exactly how hot and cold depend significantly on internal conduction. Regardless, no toasting could occur as that would require near perfect black body absorption and near perfect insulation. + +My initial estimate of ""closer than Mercury"" is probably closer than you need, but I stand by my claim that it's not hot enough near earth. " +922 If you cut entirely through the base of a tree but somehow managed to keep the tree itself perfectly balanced on the stump, would the tree “re-bond” to the stump or is this a tree death penalty? 11012 https://www.reddit.com/r/askscience/comments/83xrp8/if_you_cut_entirely_through_the_base_of_a_tree/ 1520883161 83xrp8 Biology 2018-03-12 22:32:41 "TL;DR Yes it is possible. There are grafting techniques which can be reliably used to save the tree. usually in the case of rodent damage. Source, Am nursery owner, work with trees/grafting regularly. + +Edit: Both the xylem and phloem would be reconnected with a bridge graft as long as you line the scion up properly. + + + +As a Nursery owner Ill throw my two cents in. + +Yes it is possible, but unlikely if the two parts were simply balanced together. However there are grafting techniques which can reliably save the tree. + +It is highly dependent on tree species, age, health, local weather, time of year, and a huge number of other factors. You would need the tree to be cut so thinly that there is zero diameter change between the two halves of the tree. This is nearly impossibly and is why wedge or vernier grafting exist. + +You actually only need some of the vascular tissue (cambium, phloem, xylem) to be lined up for success. Obviously more is better but close to half is good enough for survival. There would be damage but the top would live. + +That being said there is a technique which would greatly improve the chances of survival. You could bridge the gap. A bridge graft is where you take stems from younger trees of the same species and use them to connect the two separated pieces. + +https://imgur.com/a/HNJBu + +This can even be done in a way where the old wood from the original tree is removed so you have a large void instead of dead wood there. This technique is rarely practiced but is used to save heritage trees which have been damaged by rodents or mechanical damage usually from people mowing the lawn. " "The phloem and cambium tissues could potentially form callous tissue and rebond but the xylem (being already dead) would not resulting in an extreme interruption in water flow. More than likely the tree would die. + +Edit: cause auto correct + +Edit 2: look, I'm not saying grafting is impossible. We wouldn't have desirable apple cultivars and greenhouse tomatoes if it wasn't. All of those are performed on juvenile plants with care and precision. I am saying that if you cut a large adult tree through and through the odds of it healing and carrying on are slim." +923 Since light stops penetrating water at 1000 meters deep and the deepest freshwater lake is 1642 meters deep(both according to Google), is there an equivalent to deep sea creatures for freshwater? 10985 https://www.reddit.com/r/askscience/comments/7sewfa/since_light_stops_penetrating_water_at_1000/ 1516719282 7sewfa Biology 2018-01-23 17:54:42 "[Lake Baikal](http://www.irkutsk.org/baikal/animals.htm) (deepest freshwater lake) appears to have complex life forms at it's greatest depths. + +""Baikal is also home to the world's most abyssal freshwater fish. These fish have managed to preserve eyesight even at the greatest depths, although they see only in black and white."" + +Also the golomyanka (oil fish) ""can endure most pressure in the depths of the Baikal water. At night it rises to the water surface, and at daytime it swims down to great depths. Limnologists have had a chance to observe the golomynka's behaviour in the water depths. At a depth of 1,000-1,400 metres and more, the golomyanka moves freely both horizontally and vertically, whereas at such a depth even a cannon cannot shoot because of the enormous pressure.""" "There are organisms that live at the bottom of the world's deepest lakes such as [amphipods](http://onlinelibrary.wiley.com/doi/10.1111/j.1463-6409.2011.00490.x/full), [bacteria](https://www.researchgate.net/profile/Natalia_Belkova/publication/12725338_Diversity_of_bacteria_at_various_depths_in_the_southern_part_of_lake_Baikal_as_detected_by_16S_rRNA_sequencing/links/00b49528d5fcc08ddc000000.pdf), and fishes like *Trematocara* and Abyssocottids, but not very many for several reasons. + +The biggest reason is that the abyssal zone of the ocean is truly enormous and has existed for billions of years. Evolution has been able to have its heyday down there, which has led to a diverse assemblage of fishes, crustaceans, cephalopods, and other invertebrates. + +On top of this, there are only two freshwater lakes on earth that are over 1000 m deep, Baikal and Tanganyika. The latter is about ten million years old, the former perhaps 30 million years old. Compared to the age of the ocean, that is a tiny fraction of time. They have also been isolated from other water bodies due to topography, so there aren't many immigrants that can later evolve into new species. + +In addition, Tanganyika has spent a significant proportion of its history as a much shallower lake than this (it was actually multiple lakes, which is [reflected in the diversity of cichlid fish there](http://kops.uni-konstanz.de/bitstream/handle/123456789/7087/Mitochondrial_Phylogeography_of_Rock_Dwelling_1996.pdf?sequence=1&isAllowed=y)). So the abyssal zone in Tanganyika is relatively young and unstable. + +Baikal is older and larger and the abyssal zone was more stable (including never scoured by ice like most similar lakes), but it is still in a cold climate (less biodiversity to begin with) and isolated from other bodies of water. Because of the depth of ice coverage, the entire Baikal ecosystem has occasionally [collapsed](https://www.sciencedirect.com/science/article/pii/S0031018204001099), effectively re-starting the evolutionary race. + +So the two lakes on earth that are deep enough to be completely devoid of light just haven't had the evolutionary chances of the ocean." +728 How come, when we rub our eyes hard enough we see those weird colors and patterns? 10945 https://www.reddit.com/r/askscience/comments/6a4tbb/how_come_when_we_rub_our_eyes_hard_enough_we_see/ 1494329405 6a4tbb Human Body 2017-05-09 14:30:05 "This thread is trending high on the subreddit and has attracted a lot of attention. While we all have eyes and visual experiences, that does not make us all experts on the science of sight and visual perception. + +We have had to remove an abnormal number of anecdotes (particularly about visual 'floaters', a phenomenon which if you're interested in, you should submit a separate question). Also removed are non-expert opinions, speculation, medical advice, other anecdotes, jokes, low-quality posts containing only links to questionable sources, and comments asking about the removed comments. All of the above are against our rules. + +In short, please refrain from commenting unless you are an expert in visual perception or procession, ocular physiology, or the human body. If you are unsure if you are an expert, ask yourself if you can provide sources for assertions in your post and adequately respond to follow up questions. If not, your comment is likely inappropriate for AskScience and will be removed." "Last time someone asked this one of the answers said it had to do with physical stimulus to the optical nerves, and the nerves sending the information the only way they know how. I'll see if I can find it hold on + +Edit: /u/kgluds with the answer, link to comment: https://www.reddit.com/r/askscience/comments/29d26x/what_is_the_circle_that_sometimes_forms_when/cik0num + +Edit 2: or for the lazy, + +""These are called phosophenes. This happens when you touch or rub your closed eyes, or even squeeze them tightly closed, because the pressure stimulates your retina and makes your brain perceive light. Your retina has tiny cells in it that are used to collect light. When it takes in a light stimulus, the sensation crosses over to the other side of the eyeball which is why you see the light form opposite of the side of the eye that pressure was added. Phosophenes are different from hallucinations because they are caused by a physical pressure to the eyeball that creates the sensation of ""seeing light"" whereas hallucinations are generated solely in the occipital lobe."" + +Edit 3: I am not an opthalmologist, I just remembered someone asked a similar question. I know nothing of Opthalmology aside from that iritis sucks a whole hell of a lot." +826 Was the super massive black hole at the center of the Milkyway ever anything else? 10932 https://www.reddit.com/r/askscience/comments/7b4t7j/was_the_super_massive_black_hole_at_the_center_of/ 1509971179 7b4t7j Astronomy 2017-11-06 15:26:19 "The origin of the super-massive black hole at the centre of the Milky Way (and most but not all other galaxies) is still a bit of a mystery. + +Clearly, the general ingredients are there: typically galaxies are much denser in the middle (even without the supermassive black hole), and if you have enough stuff in the middle, then it makes sense that you might find a giant black hole there. But the question is how exactly does it form? + +There are several scenarios. One is that you basically have a big concentration of gas in the centre of the galaxy, and it just all collapses together into a giant black hole. Another is that the galaxy forms a whole bunch of stars in the middle of the galaxy, which eventually go supernova and turn into neutron stars and black holes, which all merge into a single supermassive black hole. There are numerous other ideas, but it really is unknown. We know why there's a lot of ""fuel"" there to form a supermassive black hole, but we don't know exactly which way all this stuff combined to form the supermassive black hole. + +Additionally, it looks like galaxies collide with each other all the time. The most commonly accepted theory for the evolution of galaxies on a big scale is that they basically build up from small galaxies to big galaxies through a lot of mergers over a long period of time. These galaxies can have their own supermassive black holes. After a merger, the new supermassive black hole will ""sink"" to the centre of a galaxy, where it will merge with the existing supermassive black hole. This isn't the origin of the supermassive black hole, but it could be an important part of how it grows. They can grow in other ways as well, by slowly accreting gas and tearing apart stars that come too close. + +**tl;dr:** It makes sense why a bunch of mass in the middle of a galaxy, but we have too many ideas about how this could collapse into a supermassive black hole, and we're not sure which idea is correct." "There is lots of speculation in this thread! + +The details of SMBH formation are not well understood. ([See here for a comprehensive review](https://arxiv.org/pdf/1003.4404.pdf)). + +Supermassive black holes *probably* have to start as ""seed"" black holes. **Maybe** these can come from the first population of stars that had only hydrogen and helium in them. These first generation stars could have been very massive and lost less mass at the end of their lives because of the opacity differences between hydrogen/helium and heavier elements, which ultimately means forming (potentially) larger black holes at the end of their lives (maybe this also explains the [larger black hole masses that LIGO has been detecting](https://www.ligo.caltech.edu/system/avm_image_sqls/binaries/91/original/Mass_plot_black_no_gap.jpg?1508029040), but that's only one possible explanation for the LIGO events). + +Another possible source of seed black holes is that star formation is suppressed and direct gas accretion into smaller black holes through instabilities in an accretion disk. Another is that star formation *isn't* suppressed, but that the star cluster that forms from the gas cloud collapsing is dense and leads to trees of merging black holes, forming the larger seeds that build to a SMBH. + +The common theme to all of these mechanisms is that smaller seed black holes form first, and then somehow grow into a larger black hole. + +These seed black holes have to then grow *extremely* rapidly, within the first billion years (since we can see them at that time period, we know that they have to be able to form by then). + +This is one of the major problems of modern astrophysics, and there is no definite answer at this point for how we got from the Big Bang to having a SMBH at the center of our galaxy. +" +1301 Megalodon is often depicted as an enlarged Great a White Shark (both in holleywood and in scientific media). But is this at all accurate? What did It most likely look like? 10913 https://www.reddit.com/r/askscience/comments/coxtdp/megalodon_is_often_depicted_as_an_enlarged_great/ 1565536051 coxtdp Paleontology 2019-08-11 18:07:31 "We of course have no idea what a Megalodon actually looked like. However, there are some significant reasons to think that Megalodon looked very similar to a Great White. + +1) Megalodon was likely, like the Great White and Mako sharks (among others) a [semi-warm blooded shark \(endotherm\)](https://www.enchantedlearning.com/subjects/sharks/anatomy/Blood.shtml). This has to do with the [position of the muscles within the body](https://youtu.be/aHKcxyCbWu8?t=264) as well as other parts of the anatomy. This ability to raise their body temperature allows them to perform necessary hunting feats for sharks of that size. Without this advantage, it's unlikely a shark as large as a Megalodon would have been able to support it's bulk. + +2) The coloring of large sharks like the Mako and Great White are very similar. The reason for this is simple; it makes them blend in with the deep blue depths when [seen from above](http://www.oceanwideimages.com/images/5916/large/great-white-shark-24M2655-05.jpg), and makes them blend in with the white surface when [seen from below](https://www.naturepl.com/cache/pcache2/01544394.jpg). + +3) The [tooth shape](https://i.imgur.com/zW7ycqK.jpg) and vertebrae of the Megalodon, the only fossil records we have, indicate that it's closely related to the Great White, suggesting they likely looked very similar. + +[This](https://www.britannica.com/animal/megalodon) is a pretty good rundown about what we know about Megalodons, and why we believe them to look like Great Whites. You're correct, however, to be skeptical. For all we know Megalodons just had ridiculously oversized teeth for their size." "It is extremely accurate according to the information we have, Megalodon is a species of shark from only 23-3.6 million years ago, Mackeral Sharks(which it descends from) on the other hand are ~~425~~ \~120 million years old. We're able to guess its size [based on the teeth](https://cdn.britannica.com/s:700x450/46/200146-004-027139A0.jpg) we've found over the years. Thankfully evolution tends to be very slow and as a result you won't see a ton of differences over time which allow us to more or less accurately assess what a creature looks like based on the characteristics we see from members surrounding it. + + +**edit**, Lamniformes (Mackeral Sharks) appeared in the early cretaceous period around 120ish million years ago, my bad!" +827 Would 100 1dB speakers sound the same as one 100db speaker? 10872 https://www.reddit.com/r/askscience/comments/7h2mww/would_100_1db_speakers_sound_the_same_as_one/ 1512221537 7h2mww Engineering 2017-12-02 16:32:17 No decibel is measured on a log scale, so adding a second speaker (of 1 db, thus doubling the sound pressure) adds 3 dB, adding 9 speakers (10 fold increase) adds 10dB and adding 99 speakers (100 fold increase) adds 20 dB. The total would be 21 dB "No they would not since Decibel is a logarithmic scale. Sound itself is measured in energy and decibel is the log of that. + +Edit: For example look at [the wiki page of the Decibel](https://en.m.wikipedia.org/wiki/Decibel) and look at that table. The dB is the Decibel and the power ratio is the thing that you can add. From that table we can see one hunderd one Decibel speakers would be around twenty Decibell." +729 Do all organisms perceive the passage of time at the same rate? 10842 https://www.reddit.com/r/askscience/comments/6utsjy/do_all_organisms_perceive_the_passage_of_time_at/ 1503202683 6utsjy Neuroscience 2017-08-20 7:18:03 "No. + +Studies indicate that temporal perception is linked with metabolism and body size. + +[Metabolic rate and body size are linked with perception of temporal information](http://www.sciencedirect.com/science/article/pii/S0003347213003060),*Healy et al* compared body size and metabolism with the [critical flicker fusion](https://en.wikipedia.org/wiki/Flicker_fusion_threshold) and found that smaller body size with higher metabolism tended to also have a high CFF. + +What this can be understood to mean, is that these animals perceive their changing environment over a much finer timescale than larger animals with a lower metabolism. " "First you have to consider that not even a single organism experiences time in a consistent manner. + +For humans the difference can be dramatic. The classic example is a traumatic experience appears to be in ""slow-motion"", this is because as a novel experience while extremely physiologically arroused, we are creating more memory per second. More information crammed into the seconds make them appear longer, so they go by ""slower"". + +Consider how this concept could apply to completely different biology... " +1399 How do super storms like Hurricane Dorian affect marine life as the storm travels through the area? Do they affect deep sea creatures? 10831 https://www.reddit.com/r/askscience/comments/cyi0rj/how_do_super_storms_like_hurricane_dorian_affect/ 1567385147 cyi0rj Earth Sciences 2019-09-02 3:45:47 "I am writing a PhD thesis on the ocean response to tropical cyclones. Contrary to what some people have suggested here, the energy of cyclone (hurricane) winds powers ocean currents well over 100 meters below the ocean surface. This has been observed directly using autonomous ocean profilers that measure temperature, salinity and velocity at different depths: +https://journals.ametsoc.org/doi/full/10.1175/2010JPO4313.1 + +Now, the answer to your question varies according to what you consider ""deep sea."" However, a particular process does come to mind that can reach down hundreds of meters deep and impact marine organisms: hurricanes power vertical currents that lift up water towards the surface. + + If a hurricane's eye moves slowly (say 1m/s), water may be sucked up from 150 meters deep all the way up to the surface ([source]{https://journals.ametsoc.org/doi/full/10.1175/2009MWR2863.1}). + +However, if the hurricane moves much faster, it will create a large underwater wave: deep, cold water will be carried up and down by as much as 80 m and with a regular frequency in time. These are called near-inertial internal waves (NIWs) and they are an effect of the Earth's rotation. Across the global ocean, these waves help transport energy from the ocean surface towards deeper regions and thus play a role in shaping climate. + +Now... These effects are mostly localized along the hurricane track, and are likely to be very weak to the sides of the track. This explains why a submarine could navigate ""below"" a hurricane and not have much trouble. However, a submarine navigating right below a hurricane eye is about to get into A LOT of trouble, as it's going to lose (to some extent) the ability to control its depth." "Large storms like Dorian with high winds cause a mixing of the nutrient-poor surface layer with slightly deeper, nutrient-rich waters, bringing nitrogen, phosphorus and trace metals to the sunlit photic zone which can cause phytoplankton blooms and subsequent zooplankton blooms, which then attract larger predators like fish. + +As for deep sea creatures on the ocean bottom? They can’t feel the relatively shallow surface mixing caused by storms (disclaimer: does not apply to creatures in shallow coastal waters), the energy dissipates with depth and in any case the ocean is separated by density gradients between different layers of water that kind of act as barriers to mixing/energy transfer" +828 Does writing by hand have positive cognitive effects that cannot be replicated by typing? 10813 https://www.reddit.com/r/askscience/comments/6z2y0n/does_writing_by_hand_have_positive_cognitive/ 1504977827 6z2y0n Neuroscience 2017-09-09 20:23:47 "Two things that would be interesting to try: + +1. Find subjects who type very slow. As quickly as they hand write. Compare results typing vs writing? + +2. What about touchscreens and styluses? How closely to the paper experience do we have to go to completely model this difference? Can apps like OneNote's handwriting suffice?" "A huuuuuuuge one is being missed out on here. + +Pictograph languages. + +Chinese and Japanese are straight up being killed by typing. Young people can recognize and read the characters, but since writing them isn't a practiced skill, it is basically fading out. It is receptive only. Given a pen and paper, Japanese young people in particular will resort to phonetically writing out words, instead of using Kanji. Simply because they do not remember how to write them. + +Edit: I gather that most of the answers are talking about cognitive skills OUTSIDE of writing gained by handwriting, so I thought I'd take a different approach. I've found it interesting because it is something that utterly doesn't come up with English-centric thinking. The English character set is so small that there is little risk of losing it. Whereas Japanese/Chinese is tens of thousands of characters. Basically infinite, as no one really knows ALL of them, like you would expect in English. + +So the opposition to 'devices' in classrooms has a whole nother angle to it in these countries." +1205 Where in your body does your food turn brown? 10778 https://www.reddit.com/r/askscience/comments/b863wm/where_in_your_body_does_your_food_turn_brown/ 1554141598 b863wm Human Body 2019-04-01 20:59:58 "Your stool turns brown in the large intestine (colon). The brown color is NOT from bilirubin directly, but from a breakdown product of the bilirubin known as stercobilin. +Stercobilin is produced by bacteria in the gut once they have broken down bilirubin (which is broken down from the iron-containing part of your red blood cells that gets released when a red blood cell is destroyed, also known as heme). When red blood cells are injured, heme is released, and it gets absorbed by white blood cells (macrophages, basically these big dumb goons that float around eating whatever doesn't belong in the body) where it gets processed and then sent back into the blood to the liver. The liver will further process the Particle Formerly Known as Heme into bilirubin, which is then stored in bile and released into the duodenum (the part of your digestive system immediately after the stomach). +As the bilirubin progresses through the gut, it will be converted by bacteria into something called urobilinogen. Urobilinogen can be released in the blood or stay in the digestive system for excretion. The urobilinogen that remains in the gut will get eaten by bacteria in the colon; the waste product from these bacteria is stercobilin, and that's what gives poop its brown color. +Whether you have an iron deficiency or not doesn't affect the color of your stool very much, unless the bleeding is in your actual GI tract which can cause black or tarry stools (from the clotted blood). + +TLDR: Colon + +edit: Wikipedia is a surprisingly excellent resource for medical knowledge. Sometimes the explanations are difficult to understand without background knowledge, but usually they're pretty good + +https://en.wikipedia.org/wiki/Stercobilin + +Double edit: Thank you so much for my first-ever Reddit gold! I always knew it'd be for talking about poop. And the follow-up questions are awesome too, thanks guys" Brown color also comes from bilirubin which is a byproduct of hemoglobin from your red blood cells breaking down. Bilirubin is processed in the liver and excreted in bile. It's also filtered by your kidneys, making urine yellow. +1015 Chemically, why was the Fat Man more powerful than the Little Boy? (The nuclear bombs dropped on Hiroshima and Nagasaki) 10767 https://www.reddit.com/r/askscience/comments/8pb285/chemically_why_was_the_fat_man_more_powerful_than/ 1528384193 8pb285 Chemistry 2018-06-07 18:09:53 "There are mechanical differences as well as chemical differences that account for the difference in explosive power of the Fat Man and Little Boy: + +**Fat Man**: + +Used about 13.6 lbs. of plutonium in an implosion, caused by surrounding the plutonium in nearly 3 tons of conventional explosives. Plutonium releases about 210 MeV of energy per fission. Total explosive power of the Fat Man was about 21,000 tons of TNT, which is 5.48404 x 10^32 eV. + +**Little Boy**: + +Using a gun mechanism, a 85 lb. hollow ""bullet"" made of uranium is shot into a 55 lbs. mass of uranium, causing it to go critical. Uranium releases about 200 MeV of energy. Little Boy's explosive power was about 15,000 tons of TNT, which is 3.91717 x 10^32 eV. + +Most likely, the initiation mechanism for the Fat Man was just more efficient, causing more atoms to undergo fission. This would make sense if you think about an implosion vs a gun barrel mechanism. Doing the math, you'd find that 2.61144762 x 10^24 atoms of plutonium underwent fission. For the uranium, it was 1.958585 x 10^24 atoms. To calculate the efficiency of the bombs, you'd have to know their relative atomic densities, but I can't find that information. + +Edit: fixed notation and which mass of uranium was shot into which." "For the implied backup question: why did they go with one design over the other? + +The explosives needed to make Fat Man work had to be incredibly precise. If they all didn't go off in the exact correct shape at the exact right time, it would have shot the Plutonium out of the shell like a cannon instead of compressing it. Frankly, the explosives were possibly a greater engineering challenge than the nuclear part. + +Little Boy was much simpler, engineering-wise. They both took an astronomical amount of resources to build, but Little Boy they were almost positive would work. Fat Man was much more efficient, but required testing and had a higher potential failure rate. We went with Fat Man style bombs going forward, hence all the nuclear testing, but we had Little Boy as backup to make sure *something* went off." +1206 Does Acid Rain still happen in the United States? I haven’t heard anything about it in decades. 10678 https://www.reddit.com/r/askscience/comments/bd33fs/does_acid_rain_still_happen_in_the_united_states/ 1555250951 bd33fs Earth Sciences 2019-04-14 17:09:11 [deleted] "yes and no. The severity of the problem has been reduced a lot because of air emission rules limiting discharge of acid-forming gases (sulfur and nitrogen oxides are the main problem). Restrictions such as requiring the use of ""clean coal"" (low sulfur coal) or use of air scrubbers for discharge stacks have resulted in significant decreases in total discharges of acid-forming compounds, and thus the precipitation is less acidic. There is still some man-caused acidity that is mostly a problem in the northeast, but it is a lot less severe than it was only a couple decades ago. + +It isn't gone, just no longer really bad and getting worse. Unless you live in China. It is getting worse there." +1207 Why can we understand a language but not speak it? 10607 https://www.reddit.com/r/askscience/comments/aso35b/why_can_we_understand_a_language_but_not_speak_it/ 1550667830 aso35b Linguistics 2019-02-20 16:03:50 "We often call the process of ""speaking"" a language [language production](https://en.wikipedia.org/wiki/Language_production). It's way more than just speaking. + +The first thing to keep in mind is that using language keeps your brain very busy. If you ever thought that the whole ""10% of your brain"" thing had even conditional truth to it, go take a look at fMRIs of people doing simple linguistic tasks — real talking uses most parts of your brain, as you're generally engaging spatial, quantitative, emotional, and all sorts of other reasoning on the fly as you're conjuring up words and orchestrating your various meat-flaps to represent them. + +When you're understanding a language, the number of steps you have to do is cut down dramatically. Your ear picks up acoustic signal; you bucket into phonemes, which if you're proficient is going to be sensitive to the language you're listening for; you build those sound-idea strings into morphological segments, which you gradually slot into phrases and sentences; and then, in normal listening, as you *infer* enough, you're pretty much done—you get the idea and it's just refining. There's time in there to do some quick spot-translations, to do some on-the-fly word order swaps, and other touch-up work, especially if the speaker isn't going at all-out max speed at you. + +Contrast that to language production. Hoo boy. First you have an idea; Sapir-Wharf debates notwithstanding, the very early concepts of what you're trying to say are at least *unspecialized* to a language's specific quirks. From the idea, you have to create a sentence structure around it. Maybe you normally use SOV ordering but you're trying to make an SVO sentence. That's a cognitive overhead tax on you. Then you start trying to find the right words. More overhead. Now you're trying to recall the right sounds to go along with it; more tax. Finally, while you're generally still trying to juggle all of that, you're trying to orchestrate those meat-flaps to make the unfamiliar sounds. More tax. It adds up! Without practice, it's just too much to do at full speed. And practice, in the meaningful sense, is an extremely contextual thing; replying to the questions and answers fixed to a topic in your textbook is going to only have a small crossover with the highly-inferred, highly chaotic banter you get in a real, typical conversation. + +Interestingly enough, there's an extra sociolinguistic aspect that kicks in where the self-awareness of speaking ""indirectly"" levies yet more of a cognitive hit, which helps explain why some people will objectively speak a language better when they're a bit drunk. + +So, tl;Dr? ""Speaking"" is a whole lot more than speaking, and it's hard work until you've done a lot of it in very representative environments—listening has many fewer and much more predictable difficulty variables in the speed and complexity, while production is just way more nuanced and complicated. +" Another thing to keep in mind with language is that practice makes perfect. He isn't practicing his Arabic speaking, so it isn't getting any easier for his brain to process it, but he still practices listening. Doing this for a long enough time would create a gap between his and your speaking abilities. All he has to do is start speaking Arabic more and he'll quickly be able to speak it as well as you. +1208 If darker skin colors absorb more heat energy and have a higher resistance to cancer then why did humans who live in snowy/colder climates develop fare skin? 10603 https://www.reddit.com/r/askscience/comments/b3qjuo/if_darker_skin_colors_absorb_more_heat_energy_and/ 1553175042 b3qjuo Human Body 2019-03-21 16:30:42 Better translucency to UV rays, that are important for Vitamin D Production, that are significantly less frequent in colder regions because of the rotation of the earth to its axis. That's one possible reason. To maximize your vitamin D Production you need more UV rays-> lighter skin My understanding is that human skin is locked in an eternal battle to find a balance between creating vitamin D from sun exposure while protecting itself from UV exposure at the same time. If you're in a tropical area, darker skin is more appropriate--the amount of light exposure will still create vitamin D, but there is a need for enhanced UV protection. If you're in a northern area, darker skin would block vitamin D production while there is less UV exposure, so lighter skin is more appropriate. +730 Why do those with Down syndrome have similarly shaped faces? 10530 https://www.reddit.com/r/askscience/comments/6kugpz/why_do_those_with_down_syndrome_have_similarly/ 1499016829 6kugpz Human Body 2017-07-02 20:33:49 If you are not very familiar with our subreddit rules for comments, please familiarize yourself [here](/r/askscience/wiki/rules). We have very strict comment policies and we are enforcing the rules and banning users whos comments that are flagrant in their violations. "The best answer anybody can give is that some gene (or most likely genes) on chromosome 21 is responsible. We don't have a specific answer to the question yet. + +One known factor, however, that almost certainly plays a role is the [overexpression of a gene associated with collagen.](https://www.ncbi.nlm.nih.gov/pubmed/23452080) Collagen plays a major role in the development of many different structures in the body such as bone, muscle, tendons, and cartilage. Needless to say, anything that affects these is going to have a drastic affect on one's appearance. It's also likely that this is responsible for many of the other issues associated with Down's such as muscular deficiency, weak joints, and cardiovascular problems. There are many more factors involved but to my knowledge, this seems to be the one that's most responsible for many of Down's most identifiable traits. + +It's also worth looking at the genetics behind the disorder. First off, there is very little variation across typical humans: roughly 99.5% of genes will be the same when comparing one person to another. Down's syndrome, however, is the addition of an entire chromosome. Humans have 46 chromosomes so an additional chromosome equates to roughly a 2% difference from the norm. This means somebody with Down's is effectively 4x more different from you or me than we are from each other. Furthermore, since 99.5% of genetic material will be the same, virtually all of the differences due to Down's syndrome that are present in one person will also be present in the next. In short, instead of just having a few random individual variations from person to person you have a large set of common variations from a normal person to a person with Down's. Of course, this is a gross simplification but it illustrates the principles at hand. + +As you can see, it's really 3 different questions: + +1. What mechanisms are responsible for the typical Down's morphology? +(We're not entirely sure but differences in collagen probably play a major role) +2. Why do we see a similar morphology across different cases of Down's? +(Because it's a common set of genes that are affected) +3. Why do these differences stand out more than the typical differences across normal humans even when looking at diverse populations? +(The variation associated with Down's is much larger than the typical variation from one person to another) + +That's the best I can do to explain it, hopefully it tells you what you wanted to know. And of course, please correct me if I'm wrong on anything or add on if you see something important is missing." +1209 "For whales and dolphins can water ""Go down the wrong pipe"" and make them choke like with humans?" 10473 https://www.reddit.com/r/askscience/comments/b8yjtg/for_whales_and_dolphins_can_water_go_down_the/ 1554301165 b8yjtg Biology 2019-04-03 17:19:25 "At least for Blue whales they lunge feed and their mouth expands as it gets filled with water. Once their mouth is full they try to filter away as much water as possible by expelling it out back out of their mouth. Blue whale have baleen plates which kinda works like a sieve, keeping the food inside while letting the water pass through. They try to swallow as little water as possible so their kidneys have to work less dealing with the salt water. + +For breathing they have a completely separate system that doesn't really share anything with how they eat so they can breath independently from eating. However because they live underwater whales have evolved a different way of controlling their breathing. Humans have a central respiratory rhythm which controls our breathing, we can voluntarily choose to breath manually by suppressing the signal but if we don't breathe for a long time we have a primitive neural circuit that ignores higher brain areas and just tells your muscles to breathe even though you don't want to. This is why a person drowning will always end up swallowing water. + +Whales don't work this way. Whales are basically always breathing manually. They will swim to the surface and then decide they want to take a breath. I think it's technically possible for whales to inhale water if they forcefully inhale underwater. It's extremely rare because it's similar to a person choosing to drink bleach, it's not something someone would ever actually do on their own. Many whales have just suffocated underwater without even having tried to take a breath. " "Cetaceans in fact have a remarkable adaptation of the respiratory/digestive system to prevent this. + +[This](https://image.slidesharecdn.com/lp13respiratorysystem2008-130223235443-phpapp02/95/lp-13-respiratory-system-2008-12-638.jpg?cb\u003d1361663957) is a normal mammal. [Here's](https://c8.alamy.com/comp/RN74JB/anatomy-of-the-woodchuck-marmota-monax-woodchuck-mammals-chapter-6respiratory-system-101-fig-6-1-sagittal-section-of-the-head-medial-view-1-ventral-nasal-concha-2-dorsal-nasal-concha-3-middle-nasal-concha-2-5-ethmoid-conchae-6-hard-palate-7-nasopharynx-8-soft-palate-9-pharyngeal-opening-of-the-auditory-tube-10-pala-topharyngeal-arch-1-1-aryepiglottic-fold-12-lamina-of-the-cricoid-cartilage-13-epiglottis-14-trachea-15-vocal-fold-16-thyroid-cartilage-pharynx-the-pharynx-fig-6-1-connects-the-nasal-cavity-to-the-larynx-and-the-oral-cavity-to-the-esophagus-it-is-di-RN74JB.jpg) a more accurate and detailed picture that is not labeled. Note the trachea (air tube) lies underneath the esophagous (food tube) and opens into it through the larynx. Then, at the roof of the mouth, behind the soft palate, there's another opening connecting to the nasal sinuses and from there to the nostrils. Because of this, the paths of air and water cross through a region known as the pharynx..however in most animals this area is pretty small and the epiglottis is right next to the soft palate. Normally, food is prevented from going down the trachea by the epiglottis. But if this system fails, it's possible to choke on food going ""down the wrong pipe."" Now, this is actually quite rare in most mammals, not just dolphins and whales. Humans are much more likely to choke on their food than other species...why? Our larynx is [much lower](https://i.stack.imgur.com/h5MUV.jpg) in our throat than most [but not all](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1088793/) other mammals. In other mammals, the top of the larynx actually projects up toward the soft palate. All this can be moved around of course, it's not a solid or permanent connection (which is why the air can also be directed through the mouth) but it makes it much harder for animals to choke as opposed to people, who have the opening to the larynx way down in the throat where food can more easily fall down into it. Why do we have such a low larynx? [It lets us talk](https://www.cell.com/current-biology/pdf/S0960-9822(08\)00371-0.pdf). + +So what about dolphins? Well, they take things further, making a semi-permanent connection between larynx and nasal cavity through a structure called a goosebeak [good diagram here](http://medicalart.johnshopkins.edu/wp-content/uploads/BK_Dolphin.jpg) and another [here](https://ai2-s2-public.s3.amazonaws.com/figures/2017-08-08/030fc1231a2a1ab62c4bad53b9fbfb0d2f9e9c7e/8-Figure3-1.png). Instead of just being located high in the pharynx, like in most mammals, the structure actually sticks all the way up into the nasal cavity through the opening in the back of the soft palate, which seals around it with a sphincter. This basically seals off the air tube from the food tube, making it nigh impossible for water to go down the wrong pipe. + +But of course there are exceptions, like [this mouth breathing dolphin](https://www.hakaimagazine.com/news/scientists-discover-mouth-breathing-dolphin/). Humpback whales also seem to be able to move this structure and emit air into the mouth, allowing them to produce their famous bubblenets [link](https://www.ncbi.nlm.nih.gov/pubmed/17516445)." +1100 What's happening in our brains when we're trying to remember something? 10467 https://www.reddit.com/r/askscience/comments/9kb64i/whats_happening_in_our_brains_when_were_trying_to/ 1538350594 9kb64i Neuroscience 2018-10-01 2:36:34 "Nobody knows! We don't know how memory works really, but we have a few ideas. Memory is super complex and truly amazing. + +The hippocampus is involved in some way with memory making, and memory recall. We don't understand the mechanisms underlying this well enough though. + +Memory is *probably* stored across the brain but is not a single thing. Motion memory is stored in the motor cortex, visual memory is stored in the visual cortex etc + +It is not known where semantic memory is stored, there is a semantic hub theory worth looking at on Wikipedia. Semantic memory is like the meaning of an object. For example, remembering what a chair is, and what it is for. + +When you remember something simple, such as eating an apple, your brain is doing something so coordinated it is almost unbelievable. + Your motor cortex is procesing the motion of your hand/arm and mouth, your visual cortex is processing the colour and shape, some part of your brain is recalling that is is food and so on. They all come together to form the memory. + +What is amazing is that you can break down which bits of your brain are procesing in to smaller and smaller locations. For example, the location of the fingers area on the motor cortex and the mouth chomping bit are not the same place. The sensory input of taste, your mouths location relative to the apple, the feeling of the apple in your hand and mouth are all processed differently. Colour, size, shape are all processed in different places of the visual cortex. There is way more areas involved than these too, but you get the idea. + +Despite the vast array of brain regions needed to come together to form a memory, you experience the memory as a single and unified. That is mind-blowingly awesome! + + +As a side note, the way memories appear to be stored and processed goes some way to explaining how they change so much over time. Chances are that some of your memories are just plain wrong, you don't know which ones are a true representation of what happened, and which are not. + +Sorry for the poor grammar and format, typing on the phone." "The process is not completely understood, but it's thought to occur through the use of engrams or neuronal traces. Essentially these are encoded chemical changes in specific neuronal network pathways that make them more likely to fire in specific sequence, corresponding to the stimuli that triggered it. This is believed to be mediated by the hippocampus. When attempting recall, your hippocampus tries to reactivate this same pathway to reproduce part or all of the stimulus response, allowing you to remember the stimulus by basically re-experiencing it. Hence also why memories tied to strong stimuli like trauma can have such profound and real effects on people when recalled. + +*Edit - clarification" +731 Why isn't the human body comfortable at 98.6 degrees if that's our internal temperature? 10437 https://www.reddit.com/r/askscience/comments/6m1fpl/why_isnt_the_human_body_comfortable_at_986/ 1499526338 6m1fpl Human Body 2017-07-08 18:05:38 "Just a reminder that /r/AskScience aims to provide in-depth answers that are accurate, up to date, and on topic. + +In particular anecdotes are not permitted, especially as a top level comment. **This is not the right subreddit to discuss what is your preferred AC setting or how hot/cold local weather is.**" "Your body is a like a heater that is always on; it cannot be turned off because that heat is produced by and required to maintain a delicate environment for your life processes. + +Heat only flows from hot to cold. If temperatures are equal, there is no cold for the hot to flow to. + +If 98F is ambient temperature then the constantly-produced heat in your body has nowhere to flow to. The heat will build up in you and you will overheat. + +The rate of heat flow is proportional to the difference between the hot and the cold. Even if your internal temp reaches 105F+ and outside is 98F the heat flow would be small. + +We evolved sweating as a way to cheat this by using evaporation to pull away heat from our skin. When water evaporates, it actually cools down when doing so, because changing a liquid to a gas takes energy (heat). + +This works so long as the surrounding air isn't already full of water. Once it is full, sweat stops evaporating and you will overheat no matter what. This kills people." +612 Is the Earth attracted to the location of the sun now or the location it was 8 minutes ago? 10434 https://www.reddit.com/r/askscience/comments/649kh2/is_the_earth_attracted_to_the_location_of_the_sun/ 1491687701 649kh2 Physics 2017-04-09 0:41:41 "Even though changes in the gravitational field propagate at c, the Earth is attracted to where the sun is **now**, not 8 minutes ago. + +See [this paper](https://arxiv.org/abs/gr-qc/9909087)." "Ok, I'm wondering about this now too, and the explanation in the paper seems to be unhelpful since it just makes it sound like massive bodies are just somehow really good at math... + +So maybe someone can verify: it sounds like what they're saying is that since the affecting gravitational field is *in motion* it creates a vector to its current position, i.e. part of the orbital path is determined by momentum, which, assuming the velocity of the sun is constant, causes the movement to follow the true position of the sun. + +How far off am I?" +829 Can you determine the cause of a headache from the region of the head it is affecting? 10390 https://www.reddit.com/r/askscience/comments/777q8i/can_you_determine_the_cause_of_a_headache_from/ 1508344146 777q8i Human Body 2017-10-18 19:29:06 "This question has attracted a lot of speculation, anecdotes about personal medical problems, and lay explanations which have been removed. Please only provide a top level response if you are able to back up your comment with sources if asked and address follow up questions. + +In addition, please do not use this topic as an excuse to break our rules about asking for medical advice or giving unsolicited medical advice. " "migraines are often lateralized (on one side or the other), and this lateralization is correlated with physiological and prodrome/aura lateralization. for example, visual migraine aura are typically on one side or the other of the visual field; since each side of the field is processed on the opposite side of the brain, the aura side will predict the headache side, so if the aura is on the right side, the pain will be focused on the left. + +The basic hypothesis here is that the aura (which is a temporary disastrous malfunction in cortex) creates byproducts that drift down from the cortex (where there are no pain receptors) into subcortical structures where they directly irritate the trigeminal nerve (which innervates the face, superficially and deep) etc, producing localized pain in the face and head. Since most of the brain is lateralized into left and right structures, the offending stuff is more-or-less confined to the side where it originated - the aura was on the right side, so the bad stuff is happening in the left side of the brain, and the left trigeminal nerve (which doesn't cross over like the cortical maps do) is annoyed. + +here are two publicly available papers that touch on some of these issues (others I know are paywalled): + +http://www.nmr.mgh.harvard.edu/DOT/PDF/nm_csd.pdf + +http://www.mitchelleffect.com/pdfs/11a_CLUE_article_lauritzen1994.pdf + +*edited for wordage* + +*edit* + +I would like to recommend the following papers for those interested in migraine aura (I am a vision guy, not a migraine guy, btw): + +[Karl Lashley, more famous for his theory of memory, recorded and modeled his own aura for a great paper published in 1941] (https://jamanetwork.com/journals/archneurpsyc/article-abstract/648953) +(sorry i cannot find a non-paywalled version) + +[Peter Milner, husband of the even more famous psychologist Brenda Milner, figured out that Lashley's description of aura was a great fit with the then-rather-obscure phenomenon of ""cortical spreading depression""] (http://www.sciencedirect.com/science/article/pii/0013469458900737) - he realized that CSD across the visual cortex would produce a symptom exactly like that described by Lashley ... paywall again :( + +[And here is one of my all-time favorite papers] (https://pdfs.semanticscholar.org/9593/af950f3e72ccd692ec40bb11a172356b2fee.pdf) by the neuroscientist Otto Grusser. This one is free! + +*edit 2* + +to reiterate my above parenthetical and my mod tag: i am a vision scientist not a migraine scientist, my knowledge of headache is entirely a side effect of my study of migraine aura, so i cannot really answer your headache questions with any particular expertise!" +732 Does the human stomach digest food as a batch process, or in a continuous feed to the rest of the digestive tract? 10373 https://www.reddit.com/r/askscience/comments/6pl5wr/does_the_human_stomach_digest_food_as_a_batch/ 1501036529 6pl5wr Human Body 2017-07-26 5:35:29 "Kinda like a continous batch. + +The stomach doesn't digest the food though. The stomach has the essential enzymes for protein digestion (Pepsin, Kathepsin) which cracks the polypeptides in small digestable chains. Fat basically just passes through the stomach but get made more liquidous through peristaltic. Carbohydrates are also just passing the stomach since the enzymatic digestion of the alpha(1-4)glycosidbinding of amylose through alpha-Amylase gets inhibited through the low ph Value of the stomach. +Which is the next function of the stomach. It inhibits the growth of a lot of harmful microorganisms. + +The stomach passes the ""mash"" to the intestine. The pylorus takes care that everything stays long enough in the stomach so that it get ""worked up"" enough and supply the intestine slow and continously." "Lots of great posts about the pylorus in here. I'd like to add that the pylorus only allows passage of things smaller than 2 mm in diameter, meaning that food will be mostly homogenous when it hits the small instestine. + +The only exception to this is when the gastrointestinal tract makes so-called moving-motor-complexes, a sort of cleaning program for the tract. This happens in short intervals after fasting for approximately 8 hours. That is the only way to rid the stomach of small fragments of plastic that you might have eaten. If you never faste for 8 hours straight (some people like to eat small meals frequently), these fragments can back up in the stomach indefinitely, so remember to take a break from eating every now and again. These moving-motor-complexes are not well understood at all, so there may be more to them than just emptying large particles from the stomach. + + +Source: Baron and Boulpaep, ""Medical Physiology""" +1594 Is it possible that someone can have a weak enough immune system that the defective virus in a vaccine can turn into the full fledge virus? 10282 https://www.reddit.com/r/askscience/comments/gzw0ha/is_it_possible_that_someone_can_have_a_weak/ 1591736216 gzw0ha Biology 2020-06-09 23:56:56 "Live vaccine: measles, mumps, and rubella vaccine (MMR) and chickenpox vaccine. These are attenuated, meaning they are weakened but can still cause the disease. These are not given to immunocompromised people. Intranasal flu is live, but the shot is not. Normal flu shot is inactivated. + +Inactivated vaccine: these are killed, then injected, and create enough of a response to provide immunity. Example of this would be polio vaccine. You might need a few doses to become immune, but you can not get the disease from an inactivated vaccine. + +Toxoid Vaccine: this uses the toxin, just weakened, to create an immune response. Things like tetanus and diphtheria use this method. You might need boosters to continue with immunity. But these aren't even the bacteria, they are just the weakened toxin from the bacteria. So can't cause the disease. + +Subunit vaccine: basically a chopped up virus or bacteria. So enough parts in there that the body will mount an immune response. + +Conjugate vaccine: a little more complicated. These add little flags called antigens on the outside of a bacteria that usually has a sugar coating around it to disguise itself. So now the new flags help the body recognize and fight it. + +​ + +Ask questions if I wasn't clear and I will try my best to clarify or answer new questions. + +Edit: My post now makes fireballs and has helping hands on it, and I'd like to say that this is very cool. Thank you for this." "Yes: live vaccines can be a risk to elderly people and immunocompromised people. However, there are Inactivated Vaccines, that do not use pathogens that do not have this risk, because the pathogens are specially designed to be unable to reproduce. + +Sadly, these inactivated vaccines create a much reduced immune reaction from the body, which is why most people are recommended to get a live vaccine if they are low risk. While immunocompromised people get better odds from inactive vaccines, things like booster injections and herd immunity also helps keep them safe." +924 Why doesn't a dark chocolate bar break predictably, despite chocolate's homogeneity and deep grooves in the bar? 10231 https://www.reddit.com/r/askscience/comments/7pchkq/why_doesnt_a_dark_chocolate_bar_break_predictably/ 1515551765 7pchkq Physics 2018-01-10 5:36:05 "Materials engineer and here, so I'll weigh in. The answer stating it's an amorphous material is part of the answer. It's not a complete answer since the milk chocolate is also an amorphous material and doesn't exhibit the failure mode to the same level. Plus, both are not 100% amorphous since there is some recrystallization during cooling, I'm sure. The other key here is the dark chocolate is harder, and more brittle. This means when breaking the material, more energy is required (input to the equation) which leads to a brittle and catastrophic failure (more energy out in a shorter period of time), thus less controlled and more random. It's also why you'll see more sharp fragments in the break vs. softer/weaker materials such as the milk chocolate. + +The other note here is regarding the squares in the bar formed by the mold, and why the break doesn't always follow the pattern. This has to do with the sharpness at the bottom of the valley of the pattern as well as the break direction. A stress riser is formed (on the tension side) in the valley that is proportional to 1 / square of the radius of the groove. The sharper the groove, the higher the stress. Many of these squares have large radius grooves in them, for looks, but they don't concentrate the force very well to drive the cracking to happen at the groove; especially if you hold the bar with the grooves towards you and push away - the tensile force is now on the surface without grooves. Break the other way to have a higher chance of perfect squares." "Interestingly [this paper from Sheffield Uni](https://www.sheffield.ac.uk/polopoly_fs/1.649051!/file/FractureBehaviour.pdf) talks about the fracture behaviour of chocolate, and seems to find that an increase in cocoa solids (e.g. the darker the chocolate) the more brittle a chocolate bar becomes. + +It also talks about particle size of the chocolate bits, and how chocolate has a polymorphic, crystalline structure. " +925 How do we know what Ancient Egyptian (or any ancient language) sounded like? How accurate are names like “Osiris” and “Tutankhamen” to what they actually sounded like when spoken by Ancient Egyptians? 10204 https://www.reddit.com/r/askscience/comments/7trnof/how_do_we_know_what_ancient_egyptian_or_any/ 1517224916 7trnof Linguistics 2018-01-29 14:21:56 "Spoken languages change in predictable ways. Vowels shift, consonants are replaced, etc. Linguists have made evolutionary trees that map which languages arose from which. By comparing related languages that diverged a long time ago (eg Sanskrit and German), linguists can work out some features of the shared common ancestor language (proto-Indo European). P.I.E. hasn't been spoken for 7000+ years, but we have some idea of vocabulary and pronunciation. + +It's a really fascinating subject. Google ""archaeolinguistics"" for more. There's also a book called The Horse, the Wheel and Language that takes a deep dive into indoeuropean archaeology and linguistics. Finally, the game Far Cry: Primal is not an accurate depiction of ""cave man life"", but they did hire actual archaeolinguistic experts to create several spoken variations of indoeuropean that are used in the game." Its classical form is known as Middle Egyptian, the vernacular of the Middle Kingdom of Egypt which remained the literary language of Egypt until the Roman period. The spoken language evolved into Demotic by the time of Classical Antiquity, and finally into Coptic by the time of Christianisation. Spoken Coptic was almost extinct by the 17th century, but it remains in use as the liturgical language of the Coptic Orthodox Church of Alexandria. +613 Could an iPod ever successfully shuffle an album in the correct order? What are the odds of this? 10179 https://www.reddit.com/r/askscience/comments/5zx8xb/could_an_ipod_ever_successfully_shuffle_an_album/ 1489753211 5zx8xb Mathematics 2017-03-17 15:20:11 [deleted] It would be possible if the algorithm was truly random, but most randomization algorithms focus on purposefully avoiding noticeable patterns like that. It might still be possible, but less likely than if it were truly random. +614 What keeps wi-fi waves from traveling more than a few hundred feet or so, what stops them from going forever? 10129 https://www.reddit.com/r/askscience/comments/64bny5/what_keeps_wifi_waves_from_traveling_more_than_a/ 1491716620 64bny5 Physics 2017-04-09 8:43:40 "This is a fun one, because there's so many different answers that are correct + +So, the first one to deal with is simply fundamental to all wave propagation - [Inverse Square Law](https://en.wikipedia.org/wiki/Inverse-square_law). So lets say a wave leaves a point, with a power of X. Once it's travelled 1m in a given direction, it should also have a power of X. Except, it hasn't *just* travelled in that given direction. It's travelled in all possible directions, creating a sphere in space. That original power of X is now the total of the energy across the surface of that sphere, and the energy at a given point is a mere fraction of what it was only a meter ago. + +Picture an inflating balloon. When it has only just enough air in it to actually form its shape, it looks opaque. But as it starts to expand, it becomes more translucent - because you still have as much material as you started with, no more no less - but it's being stretched further. Inverse-Square law is the maths behind how this affects waves. + +(You can stretch this one with directional antenna, but you can't beat it.) + +The next thing we have to deal with is .. something I don't understand the science behind at all. Different wavelengths have different propagation characteristics. The most striking example of this, is the difference between visible light, and x-rays. Visible light can be blocked by a piece of fabric, while the x-rays will go straight through it. There's similar differences in the radio end of the spectrum. My house has heavy concrete construction - I have no problem receiving commercial FM statations (~100MHz), but it stops wifi (~2400MHz) in its tracks. + +So from this we're going to get considerable path loss. Microwaves are going to bounce and refract around a lot more than longer waves, so every molecule they meet, be it walls, air, cats, is going to give us signal attenuation. + +Now, we have why these two points matter - background noise. That hiss of 'static' you hear when you tune a radio to nothing, is the background noise of the universe. Even if you were the only person on earth, it'd still be there. So one of the characteristics we look for in a radio receiver, is 'sensitivity'. This is how much stronger a signal has to be over the 'noise floor' (that hiss) before the receiver can distinguish between them. If the difference between the signal and the noise, is greater than your receiver's sensitivity - you win! Once it goes below this line, it's frustrating, and once it goes below the noise floor .. it's gone. + +That bit's fun for me. This means your signal is actually travelling forever - it's just indistinguishable from every other signal that's travelling forever. When we talk about range, we're only talking about the part of the path where the signal betters the noise by enough to be useful. + +Final thing I'll touch on, is .. humans. They mess everything up. Humans introduce two new factors to this. First, they'll introduce more noise. Since you're not actually the only human on earth, you're competing with every other signal out there. Everyone around you, using the same band (microwave ovens, dect phones, bluetooth, wifi ..), is contributing to that background noise. + +The second thing humans add, is rules. So, there's 11-13 channels for wifi (in the 2.4GHz band, and depending on country). If your next-door neighbour is trying to use the same band as you, you'll find out quickly. It's hugely frustrating. So if we took the simple approach to boosting our wifi range, and tried to use 50W instead of 500mW .. so would our neighbours. And now, instead of trying to compete for those 11 channels within neighbourhood of 50-100meters, you'd be competing with the entire city. + +This last bit is the interesting bit. If wifi signals travelled forever, wifi would be useless. The 2.4GHz ISM band would have enough space for 13 sending stations, and the rest of us could only listen. +" "Lack of appropriate antennas and an upper limit on power severely limits range. + +Almost all wifi devices use an ~~isotropic~~ *omnidirectional* antenna, meaning they detect/emit waves in all directions equally well. This is a very desirable property because it means you don't have to point your device at the access point to get a signal through. Downside is if you double the physical distance between you and the base station the signal 'strength' reduces by a factor of 4. You very quickly end up in a situation where you can detect *something* but not actually send any real information; the received signal is just too weak. + +Wifi devices are also limited in power by FCC regulation in the US, other countries have similar restrictions. It's technically possible to build a device that could have a useful range much longer than normal by jacking up the power but you'd adversely affect everyone in the vicinity who view you as an extremely powerful source of noise. + +**** + +If you were to replace the antenna by something [like this](https://images-na.ssl-images-amazon.com/images/I/41knJU42aIL.jpg) the effective range can be much longer with the restriction that the antennas point directly at each other. A mile or more isn't uncommon for purpose-built point-to-point systems. + +If you want extreme range but realistic amount of coverage you pair such a point-to-point link with a general-purpose router to ""rebroadcast"" the signal in all directions around the destination. + +**** + +e: Meant omnidirectional, not isotropic. The description is also technically wrong because it's only equally-well in one plane and messes with the `r^2` distance but I think that detail needlessly complicates the answer." +1016 How far do you have to go beneath the ocean floor before the earth becomes dry again? 10094 https://www.reddit.com/r/askscience/comments/94d77s/how_far_do_you_have_to_go_beneath_the_ocean_floor/ 1533328603 94d77s 2018-08-03 23:36:43 "Based on OP's clarification, nobody has answered the question yet. All the answers so far basically state, ""There's water in the crust everywhere, so you'll never find crust without some sort of water."" That answers the title's question, but OP doesn't want to know where the crust is no longer wet. He or she appears to be asking where the ocean's influence ends downward from the ocean floor. Right?" "[Deepest water found 1,000km down, 1/3 the way to the Earth's core](https://www.newscientist.com/article/mg23231014-700-deepest-water-found-1000km-down-a-third-of-way-to-earths-core/) - to be fair though, this water isn't wet: + +>The diamond has an imperfection – a sealed-off inclusion – that contains minerals that became trapped during the diamond’s formation. When the researchers took a closer look at it with infrared microscopy, they saw unmistakable evidence of the presence of hydroxyl ions, which normally come from water. They were everywhere, says Jacobsen + +Also, the magma that comes bubbling out of volcanic vents is bubbling because of dissolved gasses *and steam* that's venting from the mantle. + +Who knows, maybe there's steam as deep as the core itself." +1210 What do swordfish use their sword for? 10054 https://www.reddit.com/r/askscience/comments/baf355/what_do_swordfish_use_their_sword_for/ 1554634136 baf355 Biology 2019-04-07 13:48:56 "There is some debate over how the sword is used to hunt. In a study on swordfish in 1981: + +> ... swordfish rise beneath a school of fish, striking to the right and left with their swords until they have killed a number of fish, which they then proceed to devour + +Swordfish are also different from other fish with spears on their heads, such as marlins and sailfish, since their ""swords"" are dorsoventrally compressed (i.e. horizontally flattened). This suggests that they use their swords not for stabbing but for slashing laterally. + +Source: Palko, Barbara Jayne, Grant L. Beardsley, and William Joseph Richards. ""Synopsis of the biology of the swordfish, Xiphias gladius Linnaeus."" (1981). " They will swing it through groups of smaller fish injuring or disabling some to create easier to catch prey. It's [also speculated](https://www.quora.com/How-do-swordfish-eat) though never observed that they use their bill to disturb bottom sediments, releasing deepwater crustaceans & other bottom dwelling creatures for food. +1211 Why does every human has a unqiue voice, and how come voice artists are able to replicate other's voice so authentically? 10028 https://www.reddit.com/r/askscience/comments/at5mvy/why_does_every_human_has_a_unqiue_voice_and_how/ 1550769183 at5mvy 2019-02-21 20:13:03 "Social species learn to differentiate between members of their own species. It's pretty rare when one species can do that with another species. Some animals may sound all the same to us but sound unique to individuals within that species. I'm willing to bet that, if we could talk to birds, humans would sound all the same to them. + +An interesting counter-example of that has been dubbed the ""Crow Paradox"". You can raise a crow from the time it's a baby until adult but as soon as you set it free and it joins a murder of crows, you won't be able to tell it apart from other crows. But, for some reason, crows are really good at telling humans apart. Like scary good. And no one really knows why. + +[https://www.npr.org/sections/krulwich/2009/07/27/106826971/the-crow-paradox](https://www.npr.org/sections/krulwich/2009/07/27/106826971/the-crow-paradox)" "As some other commenters have said, the shape of your vocal tract (respiratory tract, nose and mouth) influences the tone of your voice. This is a result of differences in how soundwaves bounce around in one person’s vocal tract vs. another’s. Scientific research shows that people can tell a speaker’s identity based on these differences. But it’s not only the anatomical shape of the vocal tract, but also how you use it. People can have different inflections, pronunciations, etc. (think of one accent vs another as one example) that can cue us into who is speaking. In fact, some research suggests that cell phones garble our voices so much that we rely on these inflection/pronunciation cues when recognizing someone over the phone. Actors have a very limited ability to change their anatomy, but they can control these cues and that is probably a large part of their ability to imitate. + +As for animals, research out of my own lab has shown that people can tell different monkeys apart based solely on their calls. Even though they had never heard these individual monkeys before. The thing is, they weren’t confident in their ability: they would say “I have no idea if I’m right,” but lo and behold they would be right more often than chance. So we might actually be better at this than we would think. + +As an aside, my lab is in the process of publishing a study showing that listeners can also tell different people apart by their screams alone, even without having met them! This makes sense evolutionarily since if you hear someone scream it would potentially be beneficial to be able to know who it is right off the bat. Monkeys can also tell which monkey is screaming (although researchers have only looked at this with individuals within a social group - we don’t know if monkeys can tell strangers apart). " +830 What is a birth mark and why do so many people have them? 10003 https://www.reddit.com/r/askscience/comments/72hrud/what_is_a_birth_mark_and_why_do_so_many_people/ 1506396827 72hrud Biology 2017-09-26 6:33:47 "Since so many comments are asking why everything is removed, I would like to remind you that /r/askscience has relatively strict [commenting guidelines.](https://www.reddit.com/r/AskScience/wiki/quickstart/commenting) + +In particular **we do not allow anecdotes**. This thread was filled by people describing their, or their relative's, birth marks." "Some are blood vessels near the skin (like a capillary hemangioma that grows for several months and then starts to recede). + +Some are just moles, but it makes people feel better to call them birthmarks. + +Some are basically large freckles that don't mean anything unless you have several of them over a certain size (for example in neurofibromatosis). + +Some, like the ""Mongolian spot"" near the butt areas of some babies, show up in a ton of babies and slowly fade with age like the ""stork bite"" redness behind the neck or the ""angel's kiss"" between the eyes/forehead. + +Why do people have all of these benign marks? In the absence of a more sinister condition... just plain ol' unexplained luck or genetics (Mongolian spots more in Asians for example). " +733 What happens if you let a chess AI play itself? Is it just 50-50? 9982 https://www.reddit.com/r/askscience/comments/6gbjny/what_happens_if_you_let_a_chess_ai_play_itself_is/ 1497045180 6gbjny Computing 2017-06-10 0:53:00 "Check out TCEC if you want to see the results of chess engines playing other engines. http://tcec.chessdom.com/archive.php + +Heres a general rating system for the engines. http://www.computerchess.org.uk/ccrl/4040/ + +At higher levels chess is largely considered a draw as there are many many ways to cause a draw, often in professional games like the world championship last year with Magnus Carlsen vs. Sergey Karjakin, Karjakin seemed to almost put Carlsen on tilt because he kept trading down pieces as if he was trying to cause a draw. + +You have to keep in mind that in Chess draws are possible, so absolutely perfect doesn't mean much unless whenever it's solved it's proved that one side has the advantage in which case that color would always win." "They actually do that, and they have tournaments for different engines. The games can get a little weird and hard to understand at times but it's just chess nonetheless. + +Current engine ratings: + +http://www.computerchess.org.uk/ccrl/4040/ + +https://en.wikipedia.org/wiki/Chess_engine#Ratings + +Here is an actual example of two chess engines playing each other if you want to know what it looks like: + +https://www.youtube.com/watch?v=iEEYRAy6HrU" +615 Why can our eyes precisely lock onto objects, but can't smoothly scroll across a landscape? 9896 https://www.reddit.com/r/askscience/comments/5wnt4v/why_can_our_eyes_precisely_lock_onto_objects_but/ 1488286475 5wnt4v Human Body 2017-02-28 15:54:35 "Eye movement is controlled by a couple different mechanisms that are essentially reflex mediated. The first is saccadic movement. This is the fast, voluntary movement you use to 'lock onto' an object. Saccades can rotate the eye up to 500^o per second. The movement of the eye is so fast that there is a phenomenon called saccadic masking where the brain ignores visual input during the saccade to avoid blurring of the vision during eye movement. Yes, you go temporarily blind when you move your eyes with saccadic motion. Saccades are controlled by the frontal eye fields and the superior colliculus allowing for fixation of the eyes on a point. + +The next type of reflex/eye movement is called smooth pursuit. The exact neuronal circuitry for this is still up for debate, but we do know that the cerebral cortex, cerebelleum, and superior colliculus are involved. This eye movement allows you to track a moving object without the need for saccades. This reflex also requires input from the pre-frontal cortex, and is often suppressed under the effects of alcohol. This is why a sobriety test involves tracking a finger across the visual field; under the influence of alcohol the brain cannot perform smooth pursuit so the brain resorts to saccades, resulting in what looks like nystagmus. + +The next type of eye reflex is the vestibular-occular reflex. This mechanism takes orientation/acceleration input from the inner ear and processes the data so that as your head moves, your eyes move in the opposite direction. This is why your vision doesn't jump around when you walk or move. You can try it by nodding your head up and down: your head moves, but your eyes move opposite, so the resulting visual image appears stationary. It even works with eyes closed. + +So in summary, there are three main control mechanisms for eye movement, saccades, smooth pursuit, and the vestibulo-occular reflex. Saccades allow for precise fixation, smooth pursuit allows for tracking a moving object, and the V-O reflex reduces signal noise from head movement. + +E: Thanks for the gold, really cool. I just got home and saw this, I'll try answer the unanswered questions. + +Just a couple points of clarification: saccadic masking takes the blur out and replaces it with the end image after the saccade. You don't actually go blind, your brain still 'sees something'. This is why if you saccade onto the second hand of a clock it can seem to pause longer than a second. Apologies for the unclear wording above. And to everyone asking about 'why' vs 'how' these reflexes work/exist I'll just leave you with the words of [Richard Feynman](https://m.youtube.com/watch?t=0h0m4s&v=MO0r930Sn_8). " You don't know how many times I have made my self motion sick trying to allow my eyes to smoothly scroll like this. Will not happen unless I relax my vision to the point of seeing double. I always wondered if other people thought about this. +1017 Is it a coincidence that all elements are present on Earth? 9893 https://www.reddit.com/r/askscience/comments/8gozuz/is_it_a_coincidence_that_all_elements_are_present/ 1525338389 8gozuz 2018-05-03 12:06:29 "Astrophysicist here - + + +1. past supernovae and kilonovae produced a lot of these elements. Just this past discovery of the colliding neutron stars that got a lot of news for its gravitational wave, it produced ~~solar~~ many earth masses of gold. + +2. The most important thing though is turbulent mixing in the interstellar medium. This process mixes heavy elements in a very short timescale. So effectively there's pretty much of the same relative abundance of the same periodic table elements everywhere. Astronomers routinely just used a term called metallicity Z to describe the content of heavy element relative to the sun. + +3. However, have we lived in an elliptical galaxy, or some region of the halo of a galaxy, there are chances that the relative pattern might be different for alpha elements. This is because of the population of stars that could be different. More type I vs type II supernovae could change this. + +Edit: See correction down comments below. Not solar masses. But you get the idea " "There's at least one element we never really discovered until we observed the decay of uranium + +Astatine is a highly unstable element and is thought to only have 30 grams in the entire earths crust. It's never been observed by the naked eye. + +With such small amounts available for study it unlikely we have confirmed all of it's chemical properties though we likely have a good model from what they are. + +https://www.sciencealert.com/meet-the-rarest-natural-element-on-earth + +Francium is also ridiculously rare +https://en.m.wikipedia.org/wiki/Francium + +I believe that as long as a planet has uranium on it it'll be guaranteed to have all decay elements between it and lead." +926 When octopus/squid/cuttlefish are out of the water in some videos, are they in pain from the air? Or does their skin keep them safe for a prolonged time? Is it closer to amphibian skin than fish skin? 9859 https://www.reddit.com/r/askscience/comments/7w632y/when_octopussquidcuttlefish_are_out_of_the_water/ 1518108034 7w632y Biology 2018-02-08 19:40:34 "Octopuses themselves depend on water to breathe, so in addition to being a cumbersome mode of transportation, the land crawl is a gamble. “If their skin stays moist they can get some gas exchange through it,” Wood notes. So in the salty spray of a coastal area they might be okay to crawl in the air for at least several minutes. But if faced with an expanse of dry rocks in the hot sun, they might not make it very far. + +Source: https://blogs.scientificamerican.com/octopus-chronicles/land-walking-octopus-explained-video/" "The problem with pain is that it not universal for all organisms. For molluscs there is some behaviours when introduced to a stressful environment that react in a way that suggests they do feel pain. +https://www.ncbi.nlm.nih.gov/pubmed/21709311 + +There are a lot of guidelines on how cephlapods are to be handled, minimising the amount of time that they should be exposed to air, developing systems to identify signs of distress https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3938841/ + + + +" +1302 If a pregnant woman has cancer, is it possible for the cancer to spread to the fetus? 9845 https://www.reddit.com/r/askscience/comments/bkt1tz/if_a_pregnant_woman_has_cancer_is_it_possible_for/ 1557024987 bkt1tz Human Body 2019-05-05 5:56:27 "It’s exceptionally rare. Metastatic disease is usually caused by seeding through the blood supply, or, invasive growth into new organs. + +Because mums and bubs don’t actually share a blood supply (their supplies run very close together in the placenta, facilitating transfer of nutrients etc, it’s very hard to seed from one to the another, and invasive growth is pretty damn hard through amniotic fluid. + +There’s a couple of dozen of “proven” cases, mostly leukaemia and melanoma (while melanoma is a solid tumour, it’s insanely invasive), and leukaemia is a liquid tumour which would facilitate the transfer from mum to bubs blood." Rarely. https://www.cancer.ca/en/cancer-information/diagnosis-and-treatment/cancer-during-pregnancy/?region=ab +927 How does a master key work? 9800 https://www.reddit.com/r/askscience/comments/8e2ir3/how_does_a_master_key_work/ 1524393955 8e2ir3 Engineering 2018-04-22 13:45:55 "The master key itself is nothing special, the trick is in the locks set up to accept the master key. Most locks have a set of metal bars called pins, that prevent the lock from turning. A regular key pushes these pins to a precise height, moving them out of the way and allowing the lock to turn. Locks set up for a master key have two sets of these pins on top of each other. One set is properly aligned when the normal key is inserted, the other set is properly aligned when the master key is inserted. + +For a more in depth explanation, check out https://unitedlocksmith.net/blog/how-master-key-systems-work" "Master-keyed systems have locks that are specially set up to accept more than one key. You can actually even set up multi-tiered systems, for example, with a ""grand master"" key that opens every door in the system, then a ""sub-master"" key for each individual building, and then ""change"" keys for each individual lock. + +There are some great diagrams of pin and tumbler locks on the [pin tumbler lock Wikipedia page](https://en.wikipedia.org/wiki/Pin_tumbler_lock). Basically: a normal lock has two ""pins"" in each stack. The key moves the pins up just the right amount such that all of the ""shear points"" - where one pin ends and the next begins - line up at the right place. + +In a master-key system, at least one position has at least one small, extra pin (sometimes these are called ""master wafers"", because they are so thin, and because they are only used for master-keyed systems) between the two normal pins. This means that there are two different shear points for that pin stack, and therefore two different keys that can make all the shear points line up. To create a master-key system, you make a ton of locks with unique keys, but also add master wafers of the correct size to allow the lock to be opened by both its own unique key, and by the chosen master key. + +This can be done by anyone who buys re-keyable cylinders and all the right sizes of pins for their chosen lock, you can keep track of everything in a notebook and assemble a master-keyed system yourself. However, the professionals have computer systems that can track and manage all the details of a key system, including multiple levels of master keys and other stuff. + +This does add some vulnerabilities to the system. For example, you might imagine that it's easier to pick a lock that is designed to be opened by multiple keys, and it's true. But, if you have access to one key and one lock in your system, and a small supply of key blanks, [it's possible to create a master key](http://www.crypto.com/papers/mk.pdf). In some systems, if you have access to a large number of normal keys, it's possible to discover the master key without ever trying a key in a lock because of some constraints that master-keying places on a system. (This is also discussed somewhat in the paper - look for ""TPP"" and ""MACS"", the sections that introduce those explain the limitations that we exploit.)" +928 How do scientists studying antimatter MAKE the antimatter they study if all their tools are composed of regular matter? 9792 https://www.reddit.com/r/askscience/comments/7qxdy6/how_do_scientists_studying_antimatter_make_the/ 1516152278 7qxdy6 Physics 2018-01-17 4:24:38 It comes from collisions in particle accelerators. After that, the antimatter they make exists for only a very brief moment before annihilating again. Progress has been made in containing the antimatter in a magnetic field, though this is extremely difficult. I believe the record so far was achieved a few years back at CERN. Something along the lines of about 16 minutes. Most antimatter though is in existence for fractions of a second. In my undergrad program, we had a professor that studied [Positron Annihilation Spectroscopy.](https://en.wikipedia.org/wiki/Positron_annihilation_spectroscopy) There are naturally occurring radioactive materials that will create positrons when they go through Beta decay (Na-22 for example). We were from a fairly small school and department, so it is fairly easy to get your hands on these types of naturally occurring materials. +616 "Why do ""campfire smells"" (or other wood-burning smells) seem to stick to clothing/skin longer than other smells?" 9781 https://www.reddit.com/r/askscience/comments/5uqlow/why_do_campfire_smells_or_other_woodburning/ 1487389123 5uqlow Chemistry 2017-02-18 6:38:43 "Wood is made of very large molecules that are very closely packed together. While they are combusting, they are not all completely converted to small gaseous molecules like CO2, but rather you get ""volatilization"" of some larger organic molecules that can collect when they cool down - like on your clothes. These molecules and particles are what you see in smoke, and in fact you can collect smoke by making a small distillery and that is how you get ""liquid smoke"". You are literally getting smoke to stick to your clothes. When you collect them, they are sticky and greasy, which makes them hard to wash out." "Burning any organic matter releases something called **P**olycyclic **A**romatic **H**ydrocarbons, or PAHs for short. You probably know all about these as it is colloquially known as tar. As I'm sure you know, tar is ""sticky"" and it will cling to surfaces more readily than your favorite perfume for example. + +The unfortunate part is tar is carcinogenic. Yes, breathing in wood smoke from a campfire *can* give you cancer. " +734 If humans have evolved to have hair on their head, then why do we get bald? And why does this occur mostly to men, and don't we lose the rest of our hair over time, such as our eyebrows? 9758 https://www.reddit.com/r/askscience/comments/6qmjd3/if_humans_have_evolved_to_have_hair_on_their_head/ 1501480658 6qmjd3 Biology 2017-07-31 8:57:38 "Edit: My answer below covers the mechanistic reasons for baldness (because I'm biochemist and that's the portion I know about) and why it occurs mostly to men. I'm not aware of definitive research on the evolutionary reasons for baldness so I've stayed away from speculating on that and tried to stick to what biochemistry/physiology does know. You are free to speculate about the why as much as you'd like, hopefully someone with a good understanding of hominin anthropology can likely fill in such details. Note that not all traits are positively selected so Male Patterned Baldness may just be a non-deleterious side-effect of sexual maturation. + +Hair follicles are mostly switched on by the presence of androgens (i.e. testosterone and dihydrotestosterone) and the follicles have two important reaction parameters; a testosterone sensitivity threshold and a kind of response strength. The sensitivity threshold level sets how much testosterone must be circulating before a follicle switches over to producing mature hairs. Head and eyebrow hairs are examples of follicles with exceptionally high sensitivity. Very, very, very little testosterone/DHT is required for the follicle to switch on, mature and start producing hair. And this is why male and female infants quickly start producing mature head hairs. On the other hand pubic, underarm and beards hairs have low androgen sensitivity and this is why they do not switch on until the increases in testosterone/DHT levels seen at puberty. + +Alongside this follicles have a response strength that dictates how vigorously the follicle produces hair once they are activated. Beards hairs have high response levels, eyebrow and arms hairs not so much. So beard hairs come in fast and thick. Scalp follicles also have a very strong testosterone/DHT response but they don't undergo significant changes at puberty as they are already fully mature when puberty arrives. + +If just so happens that there is a loose correlation between this response strength and testosterone/DHT toxicity. Essentially the more strongly a follicle reacts to testosterone the more likely it is to die off after chronic DHT exposure. I guess you could think of it like the follicle being ""overworked"" but it is a little more sophisticated than that (see first link). As men produce the most testosterone their most sensitive and strongly reacting follicles are at higher risk of this toxicity, and these happen to be the ones on the scalp. And this appears to be the driver for Male Pattern Baldnss. The mechanism for this are not completely understood but this is a nice easy to read summary + +http://www.medicalnewstoday.com/articles/68082.php + +As I recall this is also a great review of the effects of androgens on hair development and it covers a lot of detail on the biochemical science of follicle maturation. +http://onlinelibrary.wiley.com/doi/10.1111/j.1529-8019.2008.00214.x/full" "I'll avoid biochemical explanations (biochemist here) and share my observations from a population genetics perspective (a 2nd year uni course I once taught) + +From a purely adaptive standpoint, head hair is selected for to protect against cuts and perhaps sunburn. This is helpful, but one can clearly survive without hair. Head hair is not a requirement for survival, but almost everyone has head hair, at least through early life, and survival benefits are understood. The classic Darwinian survival benefit of hair is clear enough. + +The maintenance of male pattern baldness genes within the population appears to be more complicated. It seems to be partly a secondary sexual characteristic, perhaps mixed with a male dominance trait. These things are indeed connected. + +Traits used in sexual selection need not improve (individual) survival. There are examples where the opposite is true. eg Deer antlers are a survival penalty. However, antlers cannot be faked. Only a truly healthy male of sufficient age will have impressive antlers. This is the handicap principal of sexual selection, and it can help to explain the existence of traits that do not (directly) improve survival. + +In modern times, an expensive car is a huge financial penalty, but since it cannot be faked, an expensive car does provided a prospective mate with an authentic indicator of wealth. + +Male pattern baldness occurs in sexual maturity (often early 20's) and coincides with increases in muscular strength and sexual desire/aggression. This is analogous to the morphological changes seen in a male silverback gorillas. An alpha silverback will dominate the troop, and have distinctive secondary sexual characteristics (which include a silver back). Maturing males developing similar characteristics, which pose a challenge to the alpha's dominance. So others with these emerging traits become targets of aggression. Young males may be driven-off or become subordinate. Subordinate behavior has been shown to decrease testosterone, while dominant behavior increases testosterone. This may explain how submissive make gorillas suppress silver-back traits, and may become a dominant silverback later in life. + +Successfully displaying silverback traits is a handicap, since one must endure constant challenges to dominance. Similarly, deer with impressive antlers must endure challenges from other dominant deer for mating rights. + +In modern humans the significance of male pattern baldness may be far less significant than it was in our violent, evolutionary past. However, the trait does have many similarities to male dominance traits seen in primates, such as gorillas. It is a male trait seen in sexual-maturity and it is testosterone correlated. While western society seems to value youth, and hair is a symbol of youth, most western men treat baldness almost like a disease.... something that needs a cure. I find it interesting to note a significant number of women find male baldness to be sexy. There are also cultural examples (east asia comes to mind. monks?) where youth and adolescents are seen to shave their foreheads in an apparent attempt to appear more mature. + +My advice for balding men is to embrace it. Society may subtly judge you to be more mature, dominant and sexually capable. Nothing to be ashamed of. Embrace your inner silverback! (but try not to get into fights)" +831 Do caterpillars need to become butterflies? Could one go it's entire life as a caterpillar without changing? 9734 https://www.reddit.com/r/askscience/comments/7dp1a1/do_caterpillars_need_to_become_butterflies_could/ 1510962682 7dp1a1 Biology 2017-11-18 2:51:22 "Insects go through stages culminating in the final “imago”, the adult insect that is distinguished by its precursor stages in that only it can reproduce. +So caterpillars can totally live a long, full life of caterpillary wholesomeness, but they can’t have descendants until they transform into a butterfly or moth. + +Realistically speaking, in most species the vast majority of larvae get eaten by something bigger long before they reach adulthood, and those who make it are the rare exception. So in a way, many caterpillars actually do live their whole life in the larva stage, never growing up... but probably not in the way you imagined. " "I'm not aware of any caterpillar examples, but there are insects in which the female doesn't really turn into (on the outside) into an adult looking insect, called [Larviform](https://en.wikipedia.org/wiki/Larviform_female). They'll have reproductive organs and by definition be an adult, but they still look like the larval stages mostly. + +There are unnatural ways of keeping them in the larval stage. Manipulating their hormones can cause them to stay in the larval stage longer than normal and get a lot bigger." +735 Is there a difference between hitting a concrete wall at 100mph and being hit by a concrete wall at 100mph? 9700 https://www.reddit.com/r/askscience/comments/6dtz3i/is_there_a_difference_between_hitting_a_concrete/ 1495980752 6dtz3i Physics 2017-05-28 17:12:32 "In an idealised case no. In reality there will be small differences due to things which aren't really mentioned in your question. + +For instance if you drive into a wall at 100mph the fact that your wheels are spinning (for example) makes the situation different from if the wall is launched towards the car at 100mph. " "If you're in outer space, then there is no difference. But here on the ground there's a huge difference. In case #1 you'll hit the wall, rebound a bit, and come to rest with respect to the Earth. You might crack the wall a little, but for the most part, you won't affect it much. + +In case #2, though, the wall will continue to drag you across the ground until you both come to rest. + +It is the introduction of the Earth into the problem that creates a huge asymmetry. (And that means event #2 will get far more views on Youtube.)" +1212 How many lines of code does new PC games take? 9700 https://www.reddit.com/r/askscience/comments/au9lj2/how_many_lines_of_code_does_new_pc_games_take/ 1551026145 au9lj2 Engineering 2019-02-24 19:35:45 "Unreal Engine has more than 2 million lines of code alone, and custom code on top of that will be at least 100,000-500,000 by the time it ships. Some could easily double that figure, especially if you include associated tools for the games. + + +A modern game is probably 1.5-5 million lines of code, if written in a C-like language. Contrast with a game from the mid-90's at around 3-500,000 of mixed assembly language and higher-level code. Quake shipped with about 310,000 lines of code. + + +[1] http://blog.klocwork.com/static-analysis/analysis-of-unreal-engine-4/ + +[2] https://www.gamedev.net/forums/topic/530022-how-many-lines-of-code-are-in-the-quake-engine/ + +addition source: years of writing game code + +EDIT: One additional note - the first games I shipped included the Operating System in it's code line count, modern games run on top of an existing operating system with substantially more lines of code than the game that runs on it. This is independent of third-party libraries used in either one." "Our FPS game Diabotical, which is coming out soon, is 350,000 lines of code after doing my best to exclude dependencies from the count, but that may still include small dependencies like liberally licensed headers that I copy-pasted into the code base. +That's 300,000 of C++, 30,000 of HLSL. JS adds about 20,000 used for UI and server stuff. (I reckon only about 250,000 are actually written by me). + +Cheers. + +Edit: Corrected some numbers." +929 If the great pacific garbage patch WAS compacted together, approximately how big would it be? 9684 https://www.reddit.com/r/askscience/comments/8emto6/if_the_great_pacific_garbage_patch_was_compacted/ 1524595291 8emto6 Earth Sciences 2018-04-24 21:41:31 "[According to Wikipedia](https://en.wikipedia.org/wiki/Great_Pacific_garbage_patch), the plastic density of the patch is about 5kg/km^2 and it covers the region between 135°W to 155°W and 35°N to 42°N. That region is about 1.3 M km^2 since a degree of lattitude is about 111 km and a degree of longitude, at 40°N, is about 85 km. So the total plastic mass is about 7 million kg or 7 thousand tons. The [typical density of compactified recycled plastic](http://www.wrap.org.uk/sites/files/wrap/Bulk%20Density%20Summary%20Report%20-%20Jan2010.pdf) ranges from 20 to 200 kg/m^3, depending on the method of compactification, so if all the plastic was compacted together it would work out to a sphere between 40 and 80 meter in diameter, i.e., a bit smaller than a football field. + +It would definitely not be visible on Google Earth if you were zoomed out enough to see the ocean." "Reposting my comments from the last time this came up +---- + +I did a breakdown below to help people with the scale and context: https://www.reddit.com/r/science/comments/86bthl/great_pacific_garbage_patch_is_16_times_bigger/dw4kdwg/ + +In short, **if you cleaned up every spec of plastic in the entire 1.6 million square kilometers, and dumped it all into a Walmart, it would fill the Walmart 1 foot deep**. + +That's it? Yep, that's it. + +Still awful, and half of it is made from fishing nets, but, context is important to avoid sensationalizing things. + +Some interesting tidbits because I hear about this all the time but never get a chance to grasp the scale: + +- **92% of the plastic mass is large chunks**, baseball or bigger, but it will all eventually break down into tiny pieces. + +- 1.8 trillion pieces of plastic currently. That's 250 pieces per person on the planet they say. That's sensationalist rhetoric. Most of the pieces are miniscule. **They know the reader will think about every person throwing 250 water bottles or toothbrushes into the ocean every year as a ""piece"", but, in reality a single water bottle might break down into 4000 micro pieces that they're counting**. While 92% of the mass is huge, 94% of the piece-count is rice-sized. This number is completely meaningless because if you took each piece and broke it in half and in half again, you'd have 7.2 Trillion pieces. Is that any worse? It's the same mass. The number of pieces is interesting maybe, but doesn't mean anything other than perhaps the degree to which the plastic is broken down. + +- **46% of the mass of the plastic is fishing nets**. I'd never heard that before. HALF the mass is just fishing nets. That's where it's coming from. Nets are shitty for entanglement reasons too, obviously. + +- There's ""only"" 80,000 tons of it in total. That sounds like a big number, but let me frame that in context. **That's only half of what an average landfill ads in a year**. An average landfill in the USA ads 150,000 tons a year, and they're usually around for 50+ years. The page says it's 500 jumbo jets. Well 500 jumbo jets is actually shockingly small, that's one jet, then a 2 hour drive to find the next closest one. **Or, think of a giant redwood tree, it's only 40 of those for the entire mass of the patch**. Think of seeing a giant tree, then driving 8 hours to the next nearest. To me, it's a shockingly small amount of garbage. This relatively small amount of garbage is dusted over an area half the size of the entire USA. + +- Broken down (by me), while there's 250 pieces per person on earth, by mass, **there's 10 grams of plastic in the ocean per person on earth. Your share of that is about 2 plastic bottlecaps worth**. That actually seems like a lot. + +- Volume-wise, **the size of all the plastic in the entire Great Pacific Garbage Patch, is about 3% the size of a single Walmart**. Think about one cube of plastic, 129 feet (43m) square. That's it. That's the entire patch. **If you ""cleaned up"" every scrap of plastic in the entire 1.6 million square km of the patch and threw it on the floor of a Walmart to house it, it would only reach half way to your knee**. It's really just, not that much plastic. + +... + +My concern is, **can it ever completely break down, or, what's the end-game of it?** I've heard that it will become microscopic in size, continue to poison or bioaccumulate in fish. But then what? Will sunlight/abrasion ever completely break it down like ocean water does to everything else, atomizing it? + +Scooping it up while it's large definitely makes sense, as does not putting the stuff there in the first place, but, if half of it is fishing nets, presumably they just tear off on their own. + +Overall I think this story is generally overblown because the dramatic name ""Giant Pacific Garbage Patch"" leads you to think of a country-sized landfill floating in the ocean. Still something worth addressing though." +736 Askscience Megathread: Climate Change 9679 https://www.reddit.com/r/askscience/comments/6ertms/askscience_megathread_climate_change/ 1496372665 6ertms Earth Sciences 2017-06-02 6:04:25 "Please remember AskScience is strictly moderated. Please read our [comment rules](https://www.reddit.com/r/askscience/wiki/rules) if you have questions on what is acceptable. Since the top level post is not a question, feel free to ask your questions as a top level comment. + +" "I have a simple question. + +What is the worst case scenario for climate change? In other words, what happens if we cannot stop or inhibit the process of climate change? + +Alternatively, what are the most likely effects of climate change? " +930 What would happen if the oxygen content in the atmosphere was slightly higher (within 1 or 2%) would animals be bigger? Would things be more flammable? 9655 https://www.reddit.com/r/askscience/comments/83m5sp/what_would_happen_if_the_oxygen_content_in_the/ 1520766944 83m5sp Planetary Sci. 2018-03-11 14:15:44 "On the Isle of Arran in Scotland there is a trace fossil left by a ~1 m long 46-legged myriapod, from the Carboniferous period when oxygen levels were significantly higher. + + +Just imagine a 1 m long bug, you could probably ride it! + + +Source https://www.palass.org/publications/palaeontology-journal/archive/22/2/article_pp273-291" Yes, things would be more combustible. With higher oxygen concentrations, the limits of flammability of combustible gasses/liquids/solids would increase and the auto-ignition temperature would decrease. In other words, fires would be easier to start and burn at a wider range of fuel to air ratios. Forest fires would be more common and harder to put out. Source: Combustion Engineer; Bureau of Mines Limits of Flammability of Gasses and Vapors +1400 Why do we use steel from ships made before 1945 atomic bombings for radiological instruments? Is it just cheaper or are we totally unable to purify steel with today's processes? 9590 https://www.reddit.com/r/askscience/comments/d78kek/why_do_we_use_steel_from_ships_made_before_1945/ 1569059833 d78kek 2019-09-21 12:57:13 The story about how this was discovered is well documented. The government tried to build a lab and could not get the base numbers for background radiation. It caused a rift in the scientific community for a while. Many scientists didn’t believe it. In the end, it was discovered that all steel since the 40s is slightly radioactive. "Once it's in there there's really no simple way to get it out, also steel production uses a lot of air, filtering that air to remove the contaminants would be tricky to do and expensive. + +These days the electronics used are sophisticated enough that we can compensate for the background radiation in most cases as far as I know." +1101 Do dogs understand pictures of their owners? 9569 https://www.reddit.com/r/askscience/comments/9jas4g/do_dogs_understand_pictures_of_their_owners/ 1538033400 9jas4g Psychology 2018-09-27 10:30:00 "Hello everybody, + +Please be mindful of our guidelines. Anecdotes that do not contribute to an answer will be deleted. +" "From this article I found, the answer is [sometimes](http://www.animalplanet.com/pets/would-my-dog-recognize-me-in-a-picture/). They're kind of bad at it, as dogs rely much more heavily on smell/hearing than sight, so they may or may not recognize *particular* photos. Some are easily confused by things like haircuts and camera angles. + +The study was pretty small with only 12 dogs and 12 cats. When given the option of a handler picture vs. non-handler picture. The dogs chose their handler 88% of the time, while cats choose their handler only 54% of the time. + +The most interesting thing though, is when they tested animals' abilities to recognize other animals in photos. Dogs were able to identify familiar dogs 85% of the time, while cats chose familiar cats a whopping 91% of times. + +EDIT: Dropped the part where I referred to sight as a ""tertiary sense"", I picked that up from elsewhere on reddit, so I can't define the term and shouldn't use it." +1018 When it rains, do flies or other flying bugs dodge raindrops? And if not, is each impact like being hit by a gigantic missile of water? 9564 https://www.reddit.com/r/askscience/comments/8o3na7/when_it_rains_do_flies_or_other_flying_bugs_dodge/ 1527973982 8o3na7 2018-06-03 0:13:02 "Andrew K. Dickerson, Peter G. Shankles, and David L. Hu of Georgia Tech among others have done a few preliminary papers taking high speed video of mosquitoes and other insects being hit by droplets of water. + +The basic findings are that sufficiently small raindrops will bounce off, larger ones that hit off center can rotate the insect in air, and larger ones making ""direct hits"" can cause the insect to drop, but even then quick recovery is possible. The mosquitoes studied appear to survive the impacts well due to their ""strong exoskeleton and low mass... [causing] raindrops to lose little momentum upon impact and so [imparting] correspondingly low forces to the mosquitoes"". + +* [ +Mosquitoes survive raindrop collisions by virtue of their low mass]( +http://www.pnas.org/content/109/25/9822/tab-figures-data) +* [Raindrops push and splash flying insects](https://aip.scitation.org/doi/abs/10.1063/1.4865819) " "[My answer from when a similar question as asked in October 2017](https://www.reddit.com/r/explainlikeimfive/comments/75w44z/eli5how_do_small_animals_not_get_hurt_by_rain/do9i4x6/). + +The short answer is that rain is not really much of a problem for insects. It's fog that is the bigger problem. + +Here's my old comment in full: +>Lots of talk of arthropods and such, with some good references, but that's kind of missing several important factors. It's easy to intuitively think of raindrops hitting small organisms as being equivalent to cinder blocks falling from the sky and hitting us, but that's not how it plays out. + +>[Raindrops are not moving very fast, nor are they heavy](http://wxguys.ssec.wisc.edu/2013/09/10/how-fast-do-raindrops-fall/). For a raindrop to be considered a raindrop it has to be between roughly .5mm - 6mm (about the size of a fly at the largest). A big raindrop has a terminal velocity of about 10 m/s (20 mph), with smaller drops down closer to 0.9 m/s (2 mph). That's basically to say that there isn't much energy in any given raindrop to do a lot of damage with. + +>Another part is that smaller creatures are quite strong and tough as a result of the [Square-cube Law](https://en.wikipedia.org/wiki/Square%E2%80%93cube_law). This is why an ant or a spider is proportionally so strong and an element of this is why a mouse generally won't fall fast enough to get seriously injured whereas a horse or an elephant will splash from a long fall. Also why a raindrop falling on a shrew or a butterfly isn't the equivalent of a cinder-block falling on a human. + +>Raindrops can certainly hinder small organisms, but that tends to be more an issue of surface tension, heat loss, splashing and water flow, and things like that rather than the actual impact of the water droplet. + +>For many flying organisms *fog* (and, to a certain degree, drizzle) is actually much more difficult thing to deal with as the tiny water droplets are suspended in the air and they accumulate on the surface of the flying organism, adding a lot of weight. This is why you usually don't get mosquitoes buzzing about when it's foggy. + + +EDIT: + +And before anyone says the mouse/elephant thing is taken from a youtube video, it's not. It's from ""*[On Being the Right Size](https://irl.cs.ucla.edu/papers/right-size.pdf)*,” by J.B.S. Haldane published in 1926." +1213 Should I trust the spedometer of my car or the speed stated by my GPS? Which one is correct and even more important, which one do the cops use? 9543 https://www.reddit.com/r/askscience/comments/bimebt/should_i_trust_the_spedometer_of_my_car_or_the/ 1556520202 bimebt 2019-04-29 9:43:22 "Laws and practices vary by country, the following applies in the UK. + +The UK (and the EU) has largely adopted United Nations Economic Commision for Europe (UNECE) regulations, which state that if the true speed is *x* km/h then the indicated speed must be between *x* and *(1.1x + 4)*. This is usually tested at 40, 80, and 120 km/h. This means that if your speedometer reads, for example, 50 mph, then your true speed might be slower but should not be faster. However if your vehicle is faulty or improperly modified this may no longer be the case. + +http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2018/R039r2e.pdf + +These rules mean that vehicle speedometers will in general have a systematic error, with some being more accurate than others. + +GPS is subject to no such rules and will be more accurate. Others have answered this in more detail. + +Onto the police. In the UK, speed cameras use a time-and-distance method. The camera must take *two* photos of your vehicle, both showing the vehicle and a known position and time, and the speed calculated from the distance the vehicle moves. The photos may be a couple of seconds apart as with a GATSO camera, or taken by ""average speed cameras"" several miles apart. Radar or laser speed measurement is used to trigger speed cameras but in the UK a radar measurement by itself is not enough for a fine or conviction. + +If you are pulled over by a police officer for speeding, the police car will have been following your vehicle for some time. Traffic police cars have their speedometers calibrated regularly to ensure accuracy. By the police office maintaining a reasonably constant distance, the speedo reading on their own car indicates the speed you are doing, and the whole thing will be recorded on video. Again, a police officer may use a radar gun to detect speeders, but must follow the speeding car to get sufficient evidence. + +CORRECTION: As per /u/SynAck_Fin, radar is not approved but *laser* devices operated by an office *are* valid evidence, meaning following the car isn't needed. + +One police force giving info: https://www.westyorkshire.police.uk/sites/default/files/files/disclosure-logs/2014_87_foi20132340754_vascar.pdf" A LOT of car manufacturers add about 5-7% of your real speed to speedometer value snown to you. Tested on VW Polo, Hyundai Solaris / Creta, Kia Rio / Soul, Skoda Rapid / Octavia, some Renault, Smart, BMW and even Mercedes. Everytime their speedometer showed 80 km/h, my (and not only mine) GPS showed 75 km/h. Straight line, no acceleration, good GPS satellites signal. So car speedometer may be more accurate in some cases, but as far as I know, it is designed to show a bit more speed for some purposes. (I can say only about cars in Russia and showing speed in km/h, this may be not true for some other countries and speed units) +737 What does it feel like walking in areas with high radiation? Does it feel hot or something? Does it smell? Harder to breathe? Or is the only way you will figure it out (w/out a Geiger meter) is when you start to get sick? 9499 https://www.reddit.com/r/askscience/comments/6cgdnn/what_does_it_feel_like_walking_in_areas_with_high/ 1495371314 6cgdnn Medicine 2017-05-21 15:55:14 "I work in a radiation therapy clinic. Patients generally don't feel a thing, in fact some even ask us after a treatment if we remembered to turn the machine on. The consequential damage radiation does is mostly at a genetic level, so it doesn't have a noticeable effect until cells try to use their DNA to divide or make some more proteins, or the cell inspects the DNA and finds damage. + +A sufficiently high dose could in principle increase someone's temperature noticeably, but the dose needed for that would be way above the lethal threshold. A lethal dose only adds as much heat to a body as drinking a ~~cup~~ sip of coffee. + +Some patients receiving high-dose therapy to their brains report some sensations during treatment. Unclear if real or imagined. + +In the early days of accelerator-based radiotherapy there were some accidents where a machine accidentally delivered a dose ~100× higher and faster than intended, and the patients reported a feeling like an electrical shock. That may have actually been an electrical shock though, as the electron radiation carries a charge with it. (Machines are now built with physical interlocks to prevent that type of accident from ever happening again)." "[Louis Slotin](https://web.archive.org/web/20080516101332/http://www.mphpa.org/classic/FH/LA/Louis_Slotin_1.htm) + +Interestingly, Louis Slotin reported that he experienced a sour taste in his mouth and a burning sensation after he was exposed to a lethal dose of radiation. There isn't really a well understood neurological reason for this, and it's kind of hard to confirm since he's one of the few people to receive a lethal dose. We would need a double-blind study where we irradiate people, with and without their knowledge, to definably answer this question. That might be a tad unethical though." +1019 How do our hairs know when to stop growing? 9470 https://www.reddit.com/r/askscience/comments/8kcnci/how_do_our_hairs_know_when_to_stop_growing/ 1526645212 8kcnci 2018-05-18 15:06:52 "Hair does not know how long they have to grow. + +But they have a finite lifetime. After that they stop growing and they fall out. Also new hair is allways growing. The equilibrium is the terminal length where you think hair is no longer growing. + +Bodyhair has a much lower liftetime than head hair, thats why eyebrowns are shorter. + +If you don't cut your hair it will also reach a terminal length and it will look like its not growing anymore." Hair length is predetermined and follows a schedule called active and regressive phases. Your body will continually grow hair during the active phase and when it turns regressive, it stops and falls out, not allowing the hair to grow any further. +1020 Why do we experience no sort of gag reflex when we are swallowing food or a drink? 9448 https://www.reddit.com/r/askscience/comments/91iglq/why_do_we_experience_no_sort_of_gag_reflex_when/ 1532446673 91iglq Human Body 2018-07-24 18:37:53 "There's a voluntary and an involuntary aspect to swallowing. Generally you start by pushing your tongue back, it triggers a cascade of reflex movements that close the nasal passage at the posterior end of the palate with the soft palate and close the trachea opening with the epiglottis. +Once the reflexes start, your body presumably disables the gag reflex as further sensation from the Vagus nerve in the area is unnecessary to complete the action of swallowing. + +EDIT: Nomenclature mistake" "The gag reflex is a protective response of the body to prevent the passing of food, drink, or other substances from the oral cavity (the mouth) into the pharynx (the throat). The primary role of this reflex is to protect the airway from invasion, thus reducing the risk of aspiration or choking. + +When we swallow, however, a different reflex is triggered: the swallow reflex. This occurs when the tongue voluntarily pushes food or drink (called a bolus) toward the back of the oral cavity. The bolus activates some combination of nerves in the back of the tongue, the pharyngeal arches, uvula, and posterior pharyngeal wall to initiate the swallow reflex, which enacts a series of involuntary muscle movements designed to close off the trachea (windpipe) and direct the bolus into the esophagus. + +When swallowing foods and liquids the swallow reflex typically activates instead of the gag reflex, thus allowing people who have a gag reflex (about 1/3 of the population do not) to swallow easily. Some people have an atypically sensitive gag reflex that can preclude swallowing as it activates prior to the swallow reflex when a bolus is propelled toward the back of the oral cavity. These people are treated by a team that often includes an otolaryngologist (ENT) and speech-language pathologist to minimize the sensitivity of the reflex to allow for more effective swallowing. + +I would also like to clarify on some points I have seen so far in this thread. + +First, the swallow reflex can still be activated even if the food is not sufficiently masticated (chewed) into small enough pieces to pass safely through the pharynx and esophagus. The gag reflex is designed to decrease the risk of this happening, but it is not always activated in these circumstances and (again) not all people have one. + +Second, the larynx does not open up during the gag reflex. Instead, the vocal folds (vocal cords) close and often the aryepiglottic folds (false vocal cords) close as well. This protects the airway from invasion in case the gag reflex is not successful in clearing the material from the pharynx back into the oral cavity. + +Third, the absence of the gag reflex has been shown to be associated with dysphagia (disordered swallowing) [source](https://dx.doi.org/10.1007/s00455-017-9826-y). However, the loss of a gag reflex is only one reason among many that increase a person's risk for dysphagia with advancing age. More common reasons speech-language pathologists see older individuals for dysphagia evaluation and treatment include: decreased muscle tone or control of the tongue, larynx, or pharynx; decreased pharyngeal or laryngeal sensation; anatomical changes (e.g. cancer, surgery); and changes in cognitive abilities. Many of these are secondary to diseases and conditions that become more likely with advanced age such as dementia and Parkinson's disease. + +Edit: deleted ""overrides"" in favor of ""activates instead of"" in first sentence of third paragraph as a more accurate, clear description + +Edit 2: 1st sentence - replaced ""designed"" with ""a protective response of the body""" +832 What happens to fish that die near the poles? 9442 https://www.reddit.com/r/askscience/comments/7m9i7u/what_happens_to_fish_that_die_near_the_poles/ 1514314247 7m9i7u Biology 2017-12-26 21:50:47 It is not actually freezing at the ocean floor, so they would not be preserved like you're thinking. The temperature down there is 0-3 °C (https://en.wikipedia.org/wiki/Deep_ocean_water). Metabolism slows down at that temperature, but there are various micro- and macro-creatures there to break down the carcass. "Interesting factoid. On the ocean floor where the Titanic sank, there are no bodies, there are no bones. The biomass was quickly consumed by fish in microbes. + +What didn't decompose is the shoes. When you see interior pictures of the Titanic on the ocean floor you will see lots of shoes. Every one of those pairs of shoes was likely attached to a body that went down with the ship" +833 I’ve read that when caterpillars are in their cocoons, they dissolve completely into goo; no original parts survive in the butterfly. How is the butterfly made from the goo? Is there an embryo that grows and uses the goo like a yolk sac? Or does the goo somehow arrange itself into new body parts? 9426 https://www.reddit.com/r/askscience/comments/7f4htq/ive_read_that_when_caterpillars_are_in_their/ 1511491957 7f4htq Biology 2017-11-24 5:52:37 """Certain highly organized groups of cells known as imaginal discs survive the digestive process. Before hatching, when a caterpillar is still developing inside its egg, it grows an imaginal disc for each of the adult body parts it will need as a mature butterfly or moth—discs for its eyes, for its wings, its legs and so on. In some species, these imaginal discs remain dormant throughout the caterpillar's life; in other species, the discs begin to take the shape of adult body parts even before the caterpillar forms a chrysalis or cocoon. Some caterpillars walk around with tiny rudimentary wings tucked inside their bodies, though you would never know it by looking at them."" +https://www.scientificamerican.com/article/caterpillar-butterfly-metamorphosis-explainer/ + +There's a great radiolab show where they address this: +http://www.radiolab.org/story/goo-and-you/" "By the way, ""cocoon"" is probably not the word you're looking for. + +[This is a pupa](https://upload.wikimedia.org/wikipedia/commons/1/1a/Nymphalidae_-_Danaus_plexippus_Chrysalis.JPG) (also known as a chrysalis). It's the stage a holometabolous insect passes through before adulthood. So it's not a shell or container or anything; it *is* the insect. That green stuff is the skin of the animal. For comparison, [here's a ladybug pupa](https://upload.wikimedia.org/wikipedia/commons/f/fd/Multicolored_Asian_Lady_Beetle_Pupa_%2814401873284%29.jpg), and [these are bee pupae](https://upload.wikimedia.org/wikipedia/commons/6/62/Drohnenpuppen_79d.jpg). + +[These are cocoons](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Cocoon_-_Bombyx_mori_-_Kolkata_2013-06-04_8545.JPG/1280px-Cocoon_-_Bombyx_mori_-_Kolkata_2013-06-04_8545.JPG). As you can see, they're made of silk, which is produced glands on the caterpillar's face. Some insects (but rarely butterflies) make cocoons before pupating. If you cut open a cocoon, you'll usually find a pupa inside it." +1102 When sign language users are medically confused, have dementia, or have mental illnesses, is sign language communication affected in a similar way speech can be? I’m wondering about things like “word salad” or “clanging”. 9416 https://www.reddit.com/r/askscience/comments/9cgr4m/when_sign_language_users_are_medically_confused/ 1535932802 9cgr4m Neuroscience 2018-09-03 3:00:02 "Anything that affects the ""language"" part of your brain will also affect sign language users. Sign languages operate/reside in the same part of the brain as a spoken languages -- even though the method of reception (visual) is different, language is language as far as that part of the brain is concerned. Obviously, some disorders that may relate directly to speech/sound vs sight/movement would be different. Clanging, and the aphasias you mentioned, I believe manifest themselves in sign language users (albeit the modality is different but the underlying effect is the same). + +As for muttering: yes, folks mutter to themselves in sign language in much the same way as spoken language users do: diminished or minimal moments or partially formed signs. " "American Sign Language interpreter here: I haven't worked with patients (it requires particular certification and licensure in my state to work professionally in medical settings), but from my observational hours, internship experience and time with mentors (these hours are 200+ hours and mentorship is heavily encouraged in the interpreting field to prepare budding interpreters) the short answer is yes. Patients produce word salad and other symptoms as would a hearing person. Hearing voices is a strange one that hearing people often will play up in movies, etc but those symptoms manifest in deaf people as well. They might not refer to them as voices but as confusion or distortions in their thinking. + +Again, I do practice professionally as an American Sign Language interpreter but have little experience in mental health interpreting. If you have further questions, I'll try my best to answer them from the interpreter perspective. + +Thanks for asking this question. Glad to see discussion about American sign language and deaf people. + +Cheers." +1401 Why have CPU clock speeds stopped going up? 9385 https://www.reddit.com/r/askscience/comments/davjoi/why_have_cpu_clock_speeds_stopped_going_up/ 1569765988 davjoi 2019-09-29 17:06:28 "tl;dr increasing CPU frequency is kind of like increasing RPMs on a car engine - it's one unit of how much power a car's engine is producing, but it's not so good for comparing multiple types of cars in terms of how fast they can go or how much they can tow. If one person is driving a Toyota Corolla at 2000 RPM and another is driving a Ford F150 at 2000 RPM, that tells you very little about which is carrying more weight (IPC\*) or going faster (CPU benchmarks) or has more room (cache?\*). + +You can push a car's RPMs higher to go faster, but then you produce **more heat** and it's harder on the engine; generally, there'll be a range of RPMs where it's most efficient and is designed to run stably - *frequencies are largely the same sort of thing.* + +You can think of CPUs as having basically five metrics that improve performance: + +1. Manufacturing tech - how small can pieces of the CPU be built? +2. CPU Frequency - number of times the core clock 'ticks' per second. 3, 4 GHz, etc. +3. CPU Instructions Per Clock (IPC\*) - number of instructions the CPU can execute during a core clock cycle +4. CPU memory\* cache/cache speed - amount and speed of memory that the CPU can use to store instructions/results +5. Design/layout of the chip itself + +The implication being: + +1. Make the manufacturing tech smaller and everything else constant = lower power requirements, less heat, faster on/off switching of transistors +2. Make the CPU frequency faster = more power requirements, less stability +3. Make the IPC higher = faster (more work done) at the same CPU frequency +4. More memory/faster memory speed = real-world improvements irrespective of CPU frequency +5. Design/layout = real-world improvements in cost, etc + +A 4 GHz CPU in 2019 is actually much faster than a 4 GHz CPU in 2009, because the IPC (roughly the amount of work that gets done per Hz) is higher. The 2019 CPU would also use much less power per calculation than the 2009 CPU, because the manufacturing tech is much smaller. And it would feel faster because more of the work can be loaded into very fast memory very close to the actual CPU cores (instead of running back-and-forth to RAM). + +Basically, they discovered about 10 years ago that they were hitting diminishing returns on increasing CPU core clock speed. So they looked to other areas where they could improve efficiency and/or speed: more cores, better cores (higher IPC), more on-chip memory, smaller tech = less power draw, etc. + +For a real example: In 2008, a Pentium 4 at 2.8GHz had a per-thread PassMark score of 633; in 2017, an i9-7960X at 2.8 GHz had a per-thread passMark score of 2337. Same frequency, drastically different amount of work getting done." "I don't think it's the main explanation (power dissipation is probably the biggest factor as mentionned above), but you also have to consider that at this frequency the distance that an electric signal can travel in one clock cycle can be comparable or smaller than the physical size of the processor. +Let's consider a 5GHz processor, one clock cycle is 200ps. The velocity of light in silicon is v=c/sqrt(epsilon) where epsilon is the relative permittivity of silicon and c the speed of light in vacuum. taking epsilon=12, you get v=8.7e7m/s. In 200ps this means that the distance traveled by the signal in **straight line** is 17mm. + +That being said, [superconducting processors](https://en.wikipedia.org/wiki/Superconducting_computing) have been operated at frequencies above serveral dozens of GHz. But as far as I know, those processors have simpler architecture that makes it easier to manage. In the end it is a design constraint that has to be taken care of. + +EDIT : As a few of you already mentioned, it is not unfeasible to have a processor that is larger than the distance that the signal travel in a single clock cycle. But it is still a serious design consideration that has to be considered when you are looking for solutions to improve your processor. I never meant that it was a no-go, just that it makes the things harder and harder as you increase the clock frequency." +617 If an astronaut travel in a spaceship near the speed of light for one year. Because of the speed, the time inside the ship has only been one hour. How much cosmic radiation has the astronaut and the ship been bombarded? Is it one year or one hour? 9343 https://www.reddit.com/r/askscience/comments/5rlx9p/if_an_astronaut_travel_in_a_spaceship_near_the/ 1486029626 5rlx9p Physics 2017-02-02 13:00:26 "You get the full year's worth of radiation. + +From an outside point of view, we see that time is dilated and the astronaut is moving very slowly inside their spaceship. But we see the spaceship take a full year to reach its destination, and gets hit by all this radiation along the way. + +From the astronaut's point of view, there is another effect - length contraction. From their point of view, the reason it only takes an hour to reach the destination is because the distance has shrunk down by a huge amount. So, from the astronaut's point of view, they still have to move through the same amount of ""stuff"" - interstellar gas, radiation, whatever - it's just that this ""stuff"" is packed really close together, and the astronaut hits it all really quickly. + +Of course, it's not all that simple - you have to deal with redshift and all that - but it does often work out that length contraction and time dilation basically cancel out, and that can allow different reference frames to not contradict each other." "You get the radiation (particles) from the distance traveled. Think of it as a scoop. Whether the stuff is moving or standing still does not matter, the scoop comes through that almost 1 light year and gets it all. +" +738 Why does removing a battery and replacing the same battery (in a wireless mouse for example) work? 9336 https://www.reddit.com/r/askscience/comments/6d9lah/why_does_removing_a_battery_and_replacing_the/ 1495718734 6d9lah Engineering 2017-05-25 16:25:34 The contacts on the battery and your device can develop a layer of corrosion as they're exposed to oxygen. This layer does not conduct well. By replacing it you're scraping the contacts clean allowing better conductivity. When the batteries get low, this can make the difference between a usable amount of current and not. "One little nitpick for the pretty good explanations above. Unless you are using a car battery, the cells you are using don't have acid in them, they have the opposite, a base. Hens the name ""alkaline"" battery for the disposable versions." +1303 Did the plague doctor masks actually work? 9319 https://www.reddit.com/r/askscience/comments/bvg55i/did_the_plague_doctor_masks_actually_work/ 1559356719 bvg55i Human Body 2019-06-01 5:38:39 "Ah yes finally a question that my obsession with plague doctor's can contribute to. + +Short answer: yes but actually no (but mostly no) + +Long answer: they wouldn't work for the reasons expected. The theory at the time was called the miasma theory of disease, and that is that disease travels through the air and are present in bad smells. The beak was full of strong smelling herbs and the the entire garb was waxed to prevent bodily fluids from seaping through. Obviously the miasma theory isn't true, but the masks *were* a physical and water resistant barrier so they did *something* to prevent spread of disease to the ""doctor"" from fluids. It should be added; however, that the bubonic plague that caused the black death is largely believed to be transmitted by fleas, but (as several people have let me know in replies) the later plague outbreaks when the plague doctor garb was actually used were mostly transmitted through the air and fluids. Furthermore, at the time, the more bloody your uniform was, the better the doctor you were considered. So yeah... I'm sure the masks and garb as a whole would have been great for the time if only they were actually cleaned. + +Edit: [here](https://i.pinimg.com/originals/b6/6a/10/b66a10f3e1fccf4ac74fe84010eddae4.jpg) is i believe the only preserved actual plague doctor mask. [It is currently in a museum in Germany](http://www.dmm-ingolstadt.de/aktuell/objektgeschichten/april-2011.html)." "The masks weren't just a long flute for air to flow through. They were filled with potpourri and other scented stuff. Before germs and bacteria were known, it was believed that disease was spread by foul odours, which can be counteracted or blocked with good odours. They did also believe that disease was spread by touch, which is correct in some cases, so the doctors also used special wands so they didn't have to touch their patients directly. + + +For example during a severe cholera outbreak in London in 1854, authorities burned barrels of tar in the streets to cover up the foul odours which they thought were spreading the illness. [It was during this outbreak that a doctor discovered that the disease wasn't being spread by odours, but by contaminated drinking water.](https://en.wikipedia.org/wiki/John_Snow) When he investigated further is when germs were discovered." +931 If Potassium acts as a counter-agent to sodium in the body, is there a scientific reason we're not simply adding potassium to high sodium foods (i.e. processed frozen food) to lower the overall sodium level? 9313 https://www.reddit.com/r/askscience/comments/8b0ngb/if_potassium_acts_as_a_counteragent_to_sodium_in/ 1523297906 8b0ngb Chemistry 2018-04-09 21:18:26 "Mechanistically while yes they offset each other in terms of electrochemical gradient for depolarization vs repolarization, they are not regulated by the same mechanisms. Raising one does not change the other or vice versa medically. There are various ion channels and other transports by which these electrolytes pass in and out of cells. + +To clarify: They oppose each other in terms of electrochemical gradient BUT sodium or potassium intake do not affect/antagonize each other significantly on a clinical basis. " "In what systems does it act as a counter agent? + +With regard to neuronal employment of sodium and potassium, both these ions need to be kept at very specific concentrations (both in intracellular and extracellular environments) for proper signalling function. In which case, simply substituting one for the other could lead to serious problems. Beyond that, I'm not familiar with any counter-function of these ions. " +502 How do you optimally place two or more Hot Pockets in a Microwave? 9308 https://www.reddit.com/r/askscience/comments/5ce8no/how_do_you_optimally_place_two_or_more_hot/ 1478867433 5ce8no Physics 2016-11-11 15:30:33 "Provided your microwave has a turntable, place food you want cooked evenly toward the outside so that it travels through more of the microwave and thus consistently passes through hot/cold areas. If you put food in the very middle it could more or less be stuck in a single... hot pocket? (or cold pocket). + +Toward the outside of the turntable, not touching." "Others have mentioned that optimally you place them evenly spaced around the edge of the turntable; if you'd like an interesting experiment, take the turntable out of your microwave, and replace it with a glass dish with a layer of marshmallows in it. Microwave it for 2-3 minutes on low until you see evenly spaced lines of the marshmallows melting, with un-melted lines in between them. If you measure the distance between two melted lines in cm and double it, you've found the wavelength; if you convert to meters and multiply by the frequency of your microwave (listed on the inside of the door usually), you'll get the speed of light as a result, around 2.99e8 m/s. + +More relevant to your question, you'll also see that there are ""hot"" and ""cold"" bands in your microwave, rather than arbitrary spots. It also shows why you'd rather have food at the outside edge of the turntable (so that these bands fully pass over the entire food item as it rotates) rather than at the center (which, if you placed the food on a ""cold"" band, could leave a cold spot in the middle)." +503 In terms of a percentage, how much oil is left in the ground compared to how much there was when we first started using it as a fuel? 9305 https://www.reddit.com/r/askscience/comments/5dypa2/in_terms_of_a_percentage_how_much_oil_is_left_in/ 1479658721 5dypa2 Earth Sciences 2016-11-20 19:18:41 Estimates vary wildly, especially for [how much we've used so far](https://www.sciencedaily.com/releases/2009/05/090507072830.htm), but they say we've used up to 1 trillion barrels and have 1.5 trillion left that we think we can get to with current technology. [Here's a video](https://www.youtube.com/watch?v=ynaOH7OmMcM) with some additional sources in the description. "> An example of the answer I'm looking for would be something like ""50% of Earth's oil remains"" or ""5% of Earth's oil remains"". + +Almost all of oil is still in the ground. The vast majority of the oil hasn't even been discovered and most of the oil isn't recoverable with current technology. + +What we have used up are the accessible lowest hanging fruit. The readily available and accessible cheap oil. Like in east texas, saudi arabia or baku. + +Just in terms of shale oil, there are nearly 5 trillion barrels of it. + +""A 2008 estimate set the total world resources of oil shale at 689 gigatons — equivalent to yield of 4.8 trillion barrels (760 billion cubic metres) of shale oil"" + +https://en.wikipedia.org/wiki/Oil_shale_reserves + +But that's just discovered shale oil and most of it 3.7 trillion barrels are in the US. There are tons of other shale oil deposits all around the world that hasn't been discovered or hasn't been assessed. + +Add to that the amount of oil in harsh environments like arctic or antarctica or deep sea regions like south china seas, humanity has only just tap a tiny portion of oil in the world. There is a reason why britain, australia, US, russia, etc haven't abandoned their claim on antarctica. There is shitload of oil there. + + +But most of the oil is prohibitively expensive or technological difficult to extract currently. We have used up significant amounts of ""easy"" oil. But that's a tiny fraction of overall oil on earth. " +1021 AskScience AMA Series: We have made the first successful test of Einstein's General Relativity near a supermassive black hole. AUA! 9276 https://www.reddit.com/r/askscience/comments/921mov/askscience_ama_series_we_have_made_the_first/ 1532606421 921mov 2018-07-26 15:00:21 "Thank you so much for being here to answer our questions. It's very much appreciated. + +What are the most surprising findings after all these years of hard work? + +What effects are the black hole having on the Milky Way?" As a software developer, one of the things I love to see is software in science. What types of modeling software do you use and how much of it is stuff you’ve written yourself? +834 Megathread: 2017 Hurricane Season 9254 https://www.reddit.com/r/askscience/comments/6yje2n/megathread_2017_hurricane_season/ 1504740540 6yje2n Earth Sciences 2017-09-07 2:29:00 What effect (if any) could the current wildfires going off on the other side of the nation have on the hurricanes? Winds and pressure and thing of that sort What prevents hurricanes from reaching sustained winds in excess of 200+ mph? The highest sustained winds in recorded history are all in the 180-190 mph range which almost makes it seem like there is an imaginary cap of some sorts. +1022 Is there a certain priority list for a severely damaged human body to heal itself? 9248 https://www.reddit.com/r/askscience/comments/8i6844/is_there_a_certain_priority_list_for_a_severely/ 1525874693 8i6844 Human Body 2018-05-09 17:04:53 "Hematology MD here - good question! + +If you're thinking of the body like the Enterprise or something (damage control teams to E deck!) the short answer is no, there isn't a mechanism like that, with a set reserve of 'repair ability.' + +Since your question focuses on two different 'levels' of damage, e.g. at the DNA/cellular level, and in the trauma setting e.g. lacerated organs, internal bleeding, cuts/bruises etc, I'll answer them separately. + +On a cellular level, multiple DNA repair mechanisms exist - Dr Paul Modrich won the nobel prize in 2015 for exploring some of these. The individual cell has an incredible ability to reconstitute / repair DNA following damage; if damage is so great that I can't be repaired, the cell will self-destruct, so to speak; failure to do so is one mechanism by which cancer arises. However, the ability of individual cells to repair themselves is distinct from that of macroscopic injuries. + +In the trauma setting, the circulating coagulation factors / prothrombotic pathways become activated, to stop bleeding. It's not a specific process (e.g. bypass the cut on your arm to stop the bleeding in your spleen) but rather occurs wherever the pro-coagulant mediators see damage. That's part of the problem in conditions like sepsis/severe injury - a condition called DIC (disseminated intravascular coagulation) develops with massive activation of the pro-coagulant pathways in an effort to stop bleeding (or as an 'accidental activation' in the setting of inflammation, where you get similar procoagulant markers expressed). In DIC, you get concurrent bleeding/clotting, since the pro-coagulant factors that are meant to stop bleeding are being used up faster than the body can produce them, while concurrently, clots (thrombi) are forming, often inappropriately. + +It would actually be really helpful in the setting of DIC if something like a priority list did exist, so the less important injuries would be ignored and the more serious ones dealt with. + +I hope that's helpful! + +Edit: Thanks for the gold!! Glad folks found my reply informative!" "This is a really good question, one that comes up all the time in my profession as an ICU physician. As /u/SGDJ points out, blood flow is key to not only the bodily repair process, but also to its normal homeostatic function. One way to gain insight into what the body “prioritizes” as vital for function is to note what happens when the body is in a shock state. This occurs for example when there is massive blood loss (i.e. hemorrhagic shock). The body will attempt to compensate for diminished oxygen delivery to the tissues by shunting blood away from less essential organ systems to those that are ‘vital’ in the immediate sense. What we see in this scenario is that blood shunts *away* from skin, kidneys, liver, intestines and *towards* three main organs: **the brain, the heart, and the adrenal glands.** + + + +The reason for this priority is abundantly clear. The most important organ to ultimate survival is the brain. It is also the most sensitive to hypoxia injury. Therefore, the heart must be able to sustain cardiac output and oxygen delivery. And the adrenal glands that secrete vasogenic hormones like epinephrine and dopamine are necessary to regulate it all. + + + +There is constant debate regarding which organ systems should be deemed ‘vital,’ but in actuality, blood flow is preserved to those three organ systems in a shock state in an attempt to preserve immediate survival." +1023 Why do the boys rescued from the cave in Thailand need to be quarantined? 9248 https://www.reddit.com/r/askscience/comments/8y0uec/why_do_the_boys_rescued_from_the_cave_in_thailand/ 1531325048 8y0uec 2018-07-11 19:04:08 "From [here:](https://www.livescience.com/63018-thailand-boys-quarantined-cave-diseases.html) + +>...caves can be petri dishes for bacteria and viruses. ""The big worry that you get with caves is the presence of bats,"" said Dr. Amesh Adalja, a senior scholar at the John Hopkins Center for Health Security in Baltimore. ""We know that bats can transmit many different infectious diseases, including things like rabies.""....""Certain fungi can really thrive in bat droppings,"" Adalja said, and inhaling these fungal spores can lead to lung infections, including cryptococcosis or histoplasmosis, which is also known as ""caver's disease."" " "Bacteria and physical health reasons have been stated but there are psychological benefits as well. + +Long term isolation may not help (or may even hurt) the victims, but a monitored quarantine with limited family interactions would actually be beneficial immediately after such trauma + +These kids now have social identity. They will be known as the Cave Boys, media will want to get interviews and quotes and stories. +Placing them in quarantine gives them a chance to settle back into the world and not be bombarded with attention and reminders of their trauma, giving them better chance to heal mentally." +932 If extra wings seen on biplanes add more lift and maneuverability, why don’t we add them to modern planes or jets and have them built into the airframe like we do today? 9216 https://www.reddit.com/r/askscience/comments/8bymow/if_extra_wings_seen_on_biplanes_add_more_lift_and/ 1523621137 8bymow Engineering 2018-04-13 15:05:37 "Biplanes are really not advantageous. The only reason biplanes were used was because technology hadn't advanced far enough to allow any other options. Prior to WWII, plane engines mostly weren't powerful enough to provide the necessary lift with monoplanes, and aircraft structures weren't strong enough to support the forces of flight on a single set of wings. There were some monoplanes in service in WWI but they were far outnumbered and generally outperformed by biplanes. By the 30's technology improved to the point where monplanes became not only more feasible but actually better than biplanes at most things. Once this happened, biplanes pretty quickly went from the majority of planes being manufactured to limited numbers meant for niche roles. + +Biplanes can add lift and maneuverability, but this comes at the cost of a ton of extra drag (which means far less fuel efficiency and in may cases worse maneuverability and high-speed performance) and poor visibility. There's nothing a modern monoplane can do that it would do better as a bi-plane, and in fact, designing modern planes such as commercial airliners or fighters around biplane wing architecture would all around worse. + +" "The whole point of a biplane design is to achieve a given wing area with the lightest possible structure. In a monoplane, the wing roots (where the wings meet the fuselage) has to carry a large bending load, which means it has to be very stiff, which means it's heavy. In a biplane, the wings are interconnected by an array of compression members (struts) and tension members (wires), which is very light. + +The biplane design also keeps the wingspan small, which means the moment of inertia in the roll axis is small, which means it's very *maneuverable* and great for aerobatics. + +The downside is that all that external structure makes *drag*, and the faster you want to go, the worse it gets." +933 If you were to fly a drone in a moving car, would it start moving to the back of the car or remain stationary? 9202 https://www.reddit.com/r/askscience/comments/7ng2bh/if_you_were_to_fly_a_drone_in_a_moving_car_would/ 1514825439 7ng2bh Physics 2018-01-01 19:50:39 "It would move back as the car accelerated, but at steady velocity it would be stationary with respect to the car. + +edit: A guy tries this in [this video](https://youtu.be/XjTj-tGPSWE?t=199), you can see that the drone starts moving ""backwards"" as the car starts moving and ""fowards"" when it stops (at 4:12) even though the guy is trying to hover it in one place." Would this be any different than tossing a ball straight up and down in a school bus? You toss it up and it comes straight down. If the bus speeds up, slows down or turns, the ball veers off accordingly. I think the drone would behave the same way, lacking any influence from wind resistance. +618 If the universe is expanding in all directions how is it possible that the Andromeda Galaxy and the Milky Way will collide? 9193 https://www.reddit.com/r/askscience/comments/61mlxd/if_the_universe_is_expanding_in_all_directions/ 1490547934 61mlxd Physics 2017-03-26 20:05:34 "The expansion of the universe is easiest to understand at cosmic scales. In that case you can take all the matter and energy and treat it like a homogeneous sheet with some average densities. You then use Einstein's field equations to see how much this tarp will stretch, i.e. expand. + +However, locally the story is different. On smaller scales gravitational attraction can dominate, preventing objects from expanding away from each other. For example, that is the story in our [Local Group](https://en.wikipedia.org/wiki/Local_Group) that includes the Milky Way and Andromeda Galaxies. In fact, in our cosmic neighborhood, the gravitational attraction is strong enough that eventually these two galaxies will collide. Of course, it will take another 4 billion years for this drawn out merger to kick in." "Imagine you and a friend are standing on a floor that is slowly expanding so that each second, each foot of floor becomes 1.1 feet. + +If you are standing 10 feet apart, a second later each foot between you will become 1.1 and you'll be 11 feet apart. You separated at a rate of 1 foot per second. + +But if you were 100 feet apart, each of those became 1.1 foot and you would be 110 feet apart after 1 second. So by being 100 feet apart, you separated at a rate of 10 feet per second. And if you were 1000 feet apart at the start, you'd be separating at 100 feet per second and so on. + +So as you can see, if you're close together there is little growth between you and you could easily walk up to each other. But if you were far apart, even running top speed you couldn't get to your friend, they would just be getting farther and farther apart. + +This is an analogy to the expansion of the universe. Things that are close enough together can be pulled together because the expansion between them isn't fast enough to overcome gravity. As things get farther apart though, the expansion between them increases while the gravity between them decreases. So expansion doesn't pull apart solar systems, galaxies, or even galaxy clusters. But on larger scales expansion wins. +" +1103 Why are people’s palms never dark? 9191 https://www.reddit.com/r/askscience/comments/9i9ced/why_are_peoples_palms_never_dark/ 1537717759 9i9ced Human Body 2018-09-23 18:49:19 "“Skin contains the pigment melanin which is activated by exposure to light. The palms of your hands and the soles of your feet have much thicker layers of skin due to their regular contact and friction with other objects (the ground, tools, etc). Melanocytes exist in the dermal layers of your palms and soles, but are buried beneath the more callous layers and are rarely directed at the sun. You could in theory try to tan your hands but the results would be pretty minimal compared to the rest of your body.” + +[sauce](http://health.answers.com/mobile/Q/Why_cant_you_get_a_tan_on_your_palms) " "You gotten a lot of bad answers, and a lot of bad guesses, including the top voted one. + +The really answer is, some people do have dark palms, that match their overall skin tone, and some people have nearly white palms, regardless of skin tone. + +You skin (epidermis) comes in two varieties, simply named thick skin and thin skin. The thin skin has 4 layers (or strata), and the thick skin has 5. + +Thin skin has specialized cells in the base layer (stratum basale) called melanocytes. Melanocytes produce a certain amount of melanin, determined by your genetics, but are also UV reactive. When exposed to UV light they respond by producing more melanin. There are variations in the structure of melanin, but eumelanin (true melanin) is black. The melanin secreted by these cells is incorporated into the other layers of skin as they migrate towards the surface, and are eventually soughed off. This is why you get tan when you go out in the sun, and why it takes months to lose a tan completely. + +Thick skin only occurs in the palms of your hands, and soles of your feet. It has all the same layers as the thin skin, with an additional layer inserted just about the base layer. This additional layer (the stratum lucidum) is actually quite thin, and nearly transparent. It does **not** obscure the ability to see the melanin in the base layer. However, the base layer is also structurally different in the thick skin than in the thin skin. It has higher density of sensory cells (for touch, temperature, etc), is arranged in ridges that translate upward to fingerprints, and it generally has a lower density of melanocytes. How dense the melanocytes are in the thick skin is another genetic trait. Some people have the same density as the rest of their body, some people have little to none. How many active melanocytes are on the palms of the hands determines the level of pigmentation." +1304 "For species with very long life spans (everything from Johnathan, the 187-year-old tortoise, or Pando, the 80,000-year-old clonal tree system), are there observable evolutionary differences between old, still-living individuals and ""newborn"" individuals?" 9156 https://www.reddit.com/r/askscience/comments/cudmk7/for_species_with_very_long_life_spans_everything/ 1566565584 cudmk7 2019-08-23 16:06:24 [deleted] "I feel like nobody is actually answering the question here. + +The answer is: it depends. Sometimes, a noticeable mutation can occur over a single generation. Sometimes, there might actually be quite a few generations between those two specimens. + +In case of trees, it's quite possible that a tree can ""see"" the birth of its great times n grandchildren. If that's the case, some significant differences *can* occur." +1595 After the COVID vaccine is out will we still need to social distance and wear masks? 9131 https://www.reddit.com/r/askscience/comments/hvizj5/after_the_covid_vaccine_is_out_will_we_still_need/ 1595375972 hvizj5 COVID-19 2020-07-22 2:59:32 "First thing to note is that while we have phase 1 and 2 data for several of the early vaccine candidates we have no phase 3 data, which is where vaccines shows how effective they are. Some of the ones we hope will work may not prove to work or they could show bad adverse events in a larger population. Phase 1 and 2 have had less than 1000 people in most cases and in many cases less than 100. A vaccine that hurts 1:10,000 people is not going to be used in all probability. We won't know that until phase 3. + +When you can relax some restrictions within a population depends on 5 main factors: R0 of the pathogen, the length of immunity from natural infection, the population that has had it naturally, the effectiveness of the vaccine, the fraction of people who take it. + +Your goal is to get the total number of people in your population over the so called herd immunity threshold. That depends on R0 of the pathogen and also on the heterogeneity of your population (do old people only hang out with old people, or do people mix). From that society movement you can get an effective R0 which would tell you the basic effective level of immunity you need in the population to get R0\_effective < 1 which would prevent epidemics but not people getting sick still. + +Let's say the effective R0 requires 60% of the population to be immune to get under 1 for R0\_effective. Let's say you live in the US where in a lot of places about 10% of the population has already had COVID and let's assume that natural immunity is long-ish lasting based on T-Cell results from SARS-COV-1. In that case we need 50% more immune people. Let's say we get a vaccine with 80% effectiveness then we need about 62% of the population to take such a vaccine to get to the level we are targeting. (0.62\*0.8 \~= 0.5). For the US in total that means we would need 217 million doses. + +80% effective is rosy for how effective this vaccine might be. The FDA has indicated it would give a EUA for 50% effective. Clearly you can't get to 60% immune with a 50% effective vaccine. + +Don't get too too sad though, even if you don't get to R0\_effective < 1 everyone who does it a vaccine reduces the rate of spread. + +Ball park you will need 75% of your population to get a vaccine to really go back to normal. That will happen if the current candidates make it through phase 3 sometime in the middle of 2021 in rich western democracies. It will happen by 2022 for everyone. If every candidate works then maybe you get there by very late 2021, but I'm skeptical, you need 5-6 billion doses. If you thought testing for COVID was hard..." Yes. It will take a long time for the vaccine to deploy, especially to countries that have poorer economies and inadequate healthcare systems. In addition, if travel is less restricted, community transmission will continue to be a risk. Nobody really knows when the right time to open up will be. +1024 When an animal is eaten whole, how does it actually die? Suffocation? Digestive acid? 9123 https://www.reddit.com/r/askscience/comments/96oicv/when_an_animal_is_eaten_whole_how_does_it/ 1534072851 96oicv 2018-08-12 14:20:51 It varies depending on the species and what their specific eating mechanism is. But generally speaking if the animal is swallowed whole while still alive it will suffocate first and then be broken down by the digestive system. "On planet earth , a big pelican swallows a chick (forget the species) then flies back to its nest(1 hour flight) and regurgitated the chick back up *still alive* for the baby pelicans to tear apart. + +I felt kinda bad for the prey chick , it was alive for an hour inside a pelicans before it was eaten. + +EDIT : Life by BBC episode 5 , not Planet Earth series. + +UPDATE: The episode is available on canadian Netflix at least. " +504 Why do flames take a clearly defined form, rather than fire just being a glow of incandescent radiation? 9109 https://www.reddit.com/r/askscience/comments/5b80il/why_do_flames_take_a_clearly_defined_form_rather/ 1478315725 5b80il Physics 2016-11-05 6:15:25 "Fire works a little differently than people imagine. + +When you look at something like a campfire, the actual wood isn't on fire. (Well, it's 'on fire', but combustion isn't occurring much at all on the wood's surface.) And the flames themselves are not super-heated *gases* emitting blackbody radiation. + +Now, the gas particles are hot, and they *are* emitting red and even yellow light, but there's so little mass that the light from the gas is barely visible at all. + +Instead, when you look at a fire, what you're seeing are little soot particles that are being vaporized off of the wood from the intense heat, and being carried upwards by the convection. That glowing soot is what provides the flame with enough mass to emit enough visible light for us to see it. + +Now, this soot is plenty hot - well past its flash point. So as soon as it runs into enough oxygen it will burn. In a steady state flame, there is very little oxygen near the wood, so you have a lot more unburnt soot, so the flame is both redder (cooler) and brighter. As you go outwards (upwards due to gravity) the soot starts encountering more oxygen. So more soot burns and the flame gets hotter. So the flame is simultaneously more yellow - hotter, and dimmer - less soot, so less dense, so less overall light. As you get towards the tips of the flame, that's the boundary where there is basically more than enough oxygen that pretty much all the soot burns. So the flame is technically hottest there, but there's also no soot left - just gas - so the visible flame dies away. The heat being generated all the way up the flame, mostly towards the tip, radiates back down and continually heats the wood, freeing more soot particles and continuing the cycle. + +And if it's not hot enough, fewer soot particles are liberated, less oxygen is consumed, so the edges of the flame shrink, get closer to the wood, and thus heat the wood up more. So there's a feedback system involved that will tend to keep the flames at some roughly constant height based on hot much fuel and oxygen you have available. + +The reason that flame has so well-defined of edges is basically because if you consider diffusion of oxygen into oxygen-free gas, it's a pretty slow process. If I take a tank of oxygen and a tank of nitrogen of equal pressure and attach them by a hose, the two gases won't really mix all that quickly. An open flame is going to have a bit more active gas mixing, but it's a good first-order understanding on why there's such a well-defined, narrow barrier between *'not-enough'* and *'plenty-of'* oxygen for the soot to burn and thus for the flame to dissipate. + +This is also why you can do cool party tricks like [re-lighting a candle from its smoke trail](https://youtu.be/C5eTn5d0cvg?t=14s) Smoke is basically unburnt soot - unburnt fuel. This is why you can tell a smokey fire is too cold and inefficient - lots of smoke means that the fire doesn't keep the soot hot enough for it to ignite by time it gets access to oxygen. + +This is also why when you blow on a flame, the flames get smaller while the fire seems to get hotter - you're providing extra oxygen into the flames - where flames are basically the area of superheated soot suspended in gas too deprived of oxygen to burn. + +**TL;DR:** + +For a campfire, the wood is the fuel tank, the flames are the fuel line, and the tips of the flame are really the combustion chamber where most of the fuel gets burnt. What you see as 'flame' is actually the super-heated fuel in the line, which hasn't ignited because it's oxygen deprived, but is hot enough to glow from the heat radiating from the combustion chamber (flame tips). Once it gets far enough away that it has abundant oxygen, it all burns, heating up the fuel in the fuel line to keep it glowing, and signifying the edge of the flame, as there is no longer enough soot - enough mass - radiating blackbody emissions for you to see. + +***Edit*** - This is what I get from doing things from memory. Everything above is fine, but below in some of the responses, when talking about gas stoves I need to talk about where the blue color comes from - rather than blackbody radiation, the blue light comes specifically from chemical emission spectra as particular compounds gets Oxidized. In a number of comments I mention Carbon Monoxide, CO, being combusted into CO2 as the culprit. Wherever you see me say that, *please imagine instead I said ""C2, CH, and CO""* as C2 and CH combusting into CO2 *also* emit blue light, and are far more [responsible for the majority](https://upload.wikimedia.org/wikipedia/commons/thumb/2/28/Spectrum_of_blue_flame.svg/479px-Spectrum_of_blue_flame.svg.png) of the blue light emissions than CO. The general principle that a blue flame is a result of a hotter fire with excellent access to oxygen, and represents more complete combustion still holds. Special thanks to /u/esquesque for correcting me. + +Also I woke up today to discover that you guys all *really* love fire. Can't blame you - it's fascinating." "A flame of the type you're thinking of is incandescent soot particles (I.e. hot smoke). The soot is emitting something close to blackbody radiation, which causes the usual ""fire colour"". The intensity of the emitted radiation is proportional to the fourth power of the temperature, so relatively small variations in temperature can create large differences in brightness, hence the sharp edges. + +I believe most of the heat in e.g. a candle flame is being carried upwards by convection from the source, which leads to the predominantly vertical shape. " +739 If iron loses its magnetism at around 1400°F, how is the earths core magnetic? 9080 https://www.reddit.com/r/askscience/comments/69r3rt/if_iron_loses_its_magnetism_at_around_1400f_how/ 1494160962 69r3rt Earth Sciences 2017-05-07 15:42:42 Geochemist here, not geophysicist, but... remember that with the core, you have to consider pressure as well. Also, seismic studies have long shown that the outer core is liquid. Recently they showed that it spins at a different rate than the solid inner core. The spinning generates the magnetic field. It's a Dynamo, not a bar magnet. Good explanation: http://www.geomag.nrcan.gc.ca/mag_fld/fld-en.php "Iron loses its *ferromagnetic* properties at 1043 K (1400 F). That's the Curie Temperature, where the heat jiggles the magnetism about harder than the exchange, anisotropy, and demagnetizing fields can keep it in place. That doesn't mean it's non-magnetic, it can still be paramagnetic. + +As for the earth's core, the other posters here are spot on. The core is spinning, and that spinning means charges are being spun, which looks just like an electromagnet. And although the magnetic field does need to travel through the rest of the earth, and other magnetic materials on its way to the surface, the field it produces it *huge*. Much weaker than if the core was a uniformly magnetised permanent magnet, but it is still an enormous electromagnet. + +As for the moon, the core isn't hot enough or large enough to convect. So, it doesn't spin. So, it doesn't produce an electromagnetic effect." +1025 During a nuclear disaster, is it possible to increase your survival odds by applying sunscreen? 9079 https://www.reddit.com/r/askscience/comments/8toi99/during_a_nuclear_disaster_is_it_possible_to/ 1529910432 8toi99 Human Body 2018-06-25 10:07:12 "**Short answer:** Oh no. Oh God no. You're so dead. It's not even really the UV rays that do the damage. + +**Long answer:** The important thing to know up front about 'radiation' is that it's a bit of a catch all term, and many of the uses have almost nothing to do with each other. To 'radiate' just means to give off energy. Sometimes that energy is good- the sun is radiating electromagnetic radiation, like visible light and infrared and UV. Other times, nuclear fallout is radioactive and emits electrons and alpha particles, which are incredibly dangerous inside your body. So that's takeaway number one- there are different kinds of 'radiation' and it's a bit of an overused buzzword at this point. + + +Now let's go back to your question. I'm going to give you two answers, one about atomic bombs and one about a reactor meltdown. Bombs first though, because that's more fun. + +Nuclear explosions tend to kill in 3 ways, depending on your distance from ground zero. The first is the fireball itself. That's the central explosion part. If you're near that, you're incinerated. Full stop. Nothing except a bunker under meters and meters of concrete will save you. + +Going farther out, the next things to kill are the overpressure and thermal radiation. Out here, the shockwave from the nuclear blast can rupture organs, but more likely it'll make a building fall on you. And similar to the fireball, the thermal radiation zone is *hot.* Like, imagine the sunrise on the horizon got bigger until it occupied 100x more of the sky than it used to, getting hotter and hotter until everything is on fire. That's what a nuclear bomb is like. Here, it's photons of all wavelengths that are impinging on you, burning you to a crisp. Sunscreen just filters some of the UV rays from the sun- it'll do nothing to stop you from cooking in this. + + +Last, of course, is the nuclear radiation that you asked about. In fact, this part of the answer is the same for the bomb and for the meltdown, which is why I saved it for here. Nuclear fission, whether in a bomb or reactor, makes a lot of radioactive nuclei which will decay and emit electrons (beta) and high energy helium nuclei (alpha), which produce a lot of damage in biological tissues. Other sources of the 'radioactive' kind of radiation include spontaneous fission and neutron emission from other radioactive nuclei. After bombs and meltdowns this stuff spreads, and if you're inhaling this stuff in any considerably amount you're pretty much gonna die a horrible painful death. Sunscreen is a glorified Maginot line. + +And on a funny historical note, Edward Teller (physicist from the Manhattan project) actually brought sunscreen to his viewing of the first nuclear detonation, the Trinity test. Even in retrospect, that's pretty amusing. " Something people haven't mentioned yet is that if you were outside, when you go inside, you'll want to ditch your clothes ASAP and take a shower immediately. Thus is to wash off any of the radioactive dust that may have accumulated on your skin and clothes. Wash or dispose of the aforementioned clothes. Do not use conditioner when you shower, it can cause your hair to lock in the radioactive dust. This will prove more useful than sunscreen. +835 How do psychologists distinguish between a patient who suffers from Body Dysmorphic Disorder and someone who is simply depressed from being unattractive? 9078 https://www.reddit.com/r/askscience/comments/7fyx12/how_do_psychologists_distinguish_between_a/ 1511820325 7fyx12 Psychology 2017-11-28 1:05:25 "This post has attracted a large number of medical anecdotes. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." "To answer that question, you must know that Body Dysmorphic Disorder (BDD) is a compulsive disorder, in the same family as OCD. A diagnosis of BDD features a prominent obsession with appearance or perceived defects, and related compulsive behaviors such as excessive grooming/mirror-checking and seeking reassurance. Keep in mind, these behaviors occur at a clinical level, meaning it is not the same as simply posting a 'fishing' status on Facebook; it's markedly more frequent and severe behavior. + +The differential diagnosis between BDD and Major Depressive Disorder (MDD) focuses on the prominence of preoccupation with appearance and the presence of compulsive behaviors. While appearance can be a factor in MDD, an individual with BDD will be markedly more concerned with appearance and will exhibit the aforementioned compulsions. + +It should also be noted that MDD is commonly comorbid with BDD, meaning that they are often diagnosed together. BDD often causes individuals to develop depression. In these cases, however, the diagnostic criteria for *both* disorders are met. + +*Source: Diagnostic and Statistical Manual, 5th Edition (American Psychiatric Association, 2013)*" +740 How is personality formed? 9035 https://www.reddit.com/r/askscience/comments/6ftcdu/how_is_personality_formed/ 1496841335 6ftcdu Psychology 2017-06-07 16:15:35 "SometHing I can actually answer! I am on the train at the moment so references will be sparse, but most of the information will come from funder's 2001 paper. + +Okay so there are many different ideas, approaches and factors to take into account so I will try and outline some of the main approaches and what they believe. + +There is the behaviourist approach that believes our personality emerges from our experience and interactions with our environment.this occurs through mechanisms such as classical conditioning, which is where we learn to associate co-occuring stimuli. This can be seen with pavlovs dog experiment and watsons (1925) little albert experiment. Another mechanism is operant condition proposed by B F Skinner, this claims basically we will perform tasks we are rewarded for more often, and ones we are punished for less. + +Another approach is the biological approach that claims that our personality is determined by chemicals, hormones and neurotransmitters in the brain. Examples of this is seratonin, which amongst other things, has been linked to happiness, and has been effectively harnessed to create effective anti-depressant medications + +There is also the evolutionary approach that posits that we inherit our personality through genes and natural selection. Some evidence does exist for this such as Loehlin and Nicholas (1976) which displayed behavioural concordance between twins. + +There is also the socio-cognitive approach which believes that personality comes from thought processing styles and social experience. Evidence from this can be seen in Banduras (1977) bobo doll experiment where he taught aggressive behaviour to children through them observing aggressive behaviour. Other theories in this area also include Baldwins (1999) relational schemas that claim that our behaviour is determined by our relation to those around us + +Another, but contentious approach is Psychodynamics, which is widely known as Freud's area of psychology. This approach believes that personality is formed from developmental stages in early life, and the conflict between the ID (desires), ego (implementing reality onto desires) and superego (conscience) + +The humanist approach also has views on personality, but provides little in the way of testable theories. This approach claims that people can only be understood through their unique experience of reality, and has therefore brought into question the validity of many cross-cultural approaches to testing personality. Studies such as hofstede (1976, 2011) have attempted to examine the effects of culture in personality, and have found significant effects, but an important thing to note is that whilst means differ, all types of personality can be found everywhere. + +When we talk about measures of personality we often measure it with the big five measure (goldberg et al., 1980: Digman, 1989). This measure includes openness to new experience, conscientious, agreeableness, neuroticism, and extraversion. + +There is more to say but I cannot be too extensive currently, hope this helps. If people want more info just say and I can fill in more detail later + +Sources: +Funder. D. C (2001) Personality, annual reviews of psychology, 52, 197-221. +. +Other sources I cannot access on a train +. +Bsc, Psychology, university of sheffield" "[The MaTcH study](http://match.ctglab.nl/#/specific/plot1) is a meta-analysis of twin studies (Nature Genetics, 2015). The link is to their interactive webpage which is quite nice at allowing you to explore the 'nature vs nurture' proportion for various factors. Unsurprisingly, things like disease markers are very largely inherited. + +The study seems to suggest a roughly 50-50 split between genetic factors and environmental factors under the subchapter measure of 'Temperament and Personality Functions'. + +From my reading of personality psych papers over the last few years, it seems we have some reasonably consistent personality traits (like Extraversion and Neuroticism) that are likely related to inherited biological factors. However, early environment obviously plays a large role in how these biological markers are expressed in later life. For example, one could be born with a tendency to respond more strongly to negative stimuli, but those with this trait and an undesirable childhood may be much more likely to develop anxiety and depression issues overall. + +(did a PhD partly involving personality, and have spoken to a few professors about this very subject)" +1305 How is it known that everyone with blue eyes has one single ancestor, rather than this mutation occurring in multiple individuals at many different times? 9020 https://www.reddit.com/r/askscience/comments/cbsfw2/how_is_it_known_that_everyone_with_blue_eyes_has/ 1562827503 cbsfw2 2019-07-11 9:45:03 "So, the paper that originally found this was published in 2008 here: https://link.springer.com/article/10.1007%2Fs00439-007-0460-x + +It found that blue eye color in Europe and the Near East was due to a mutation in a region of DNA that regulates the OCA2 gene. Since the same mutation was present in all the blue-eyed people they studied, and since the surrounding DNA (""haplotype"") was also the same, this implies that the mutation occurred in a common ancestor. From the paper's abstract: + +>One single haplotype, represented by six polymorphic SNPs covering half of the 3′ end of the HERC2 gene, was found in 155 blue-eyed individuals from Denmark, and in 5 and 2 blue-eyed individuals from Turkey and Jordan, respectively. Hence, our data suggest a common founder mutation in an OCA2 inhibiting regulatory element as the cause of blue eye color in humans. + +Since 2008, more research has been done on eye color genetics, especially regarding non-European populations (which in general have different genetic variants, not just for eye color). I'll edit this post with a summary once I read some papers. + +EDIT: It seems that subsequent research has identified additional genetic variants that can result in blue eye color. SNPedia has a good overview (https://www.snpedia.com/index.php/Eye_color) and also this 2012 review article on OCA2 variants (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3325407/) + +>We report that the blue-eye associated alleles at all three haplotypes were found at high frequencies in Europe; however, one is restricted to Europe and surrounding regions, while the other two are found at moderate to high frequencies throughout the world. + +Basically, additional research has shown that there are not one but at least three different genetic variants that can cause blue eyes. This means that not every blue-eyed person is descended from the same ancestor (although within certain European populations it's still pretty likely)." "While this doesn't answer the question directly (/u/-Metacelsus- did that nicely) I'd like to adress the aspect of ""how can a single common ancestor be responsible for *all* the blue eyes in the world?"" + +That's because we are all related to each other. [This video](https://www.youtube.com/watch?v=Fm0hOex4psA) explains the math but essentially, if you go back far enough in history then everyone alive then is either related to everyone alive today or their family line died out completely. And the amazing thing is that you don't have to go that far back in history at all. If you're of European descent then with enough work you're pretty much guaranteed to be able to trace your family lineage back to [Charlemange](https://en.wikipedia.org/wiki/Charlemagne). And that's not because he was some kind of prolific breeder. You are probably related to pretty much everyone from that time (who's family line didn't die out). It's just a whole lot easier to find documents about Charlemagne than some no name farmer out in bumfuck nowhere. + +And this is a mere 1300 years ago. According to simulations based on migration patterns and population growths the corresponding generation that is related to everybody alive *in the world* today would be somewhere between 4000-7000 years ago. That is more than enough time for a gene that's considered to be 10k years old to account for every pair of blue eyes in the world today." +619 "What is a ""zip file"" or ""compressed file?"" How does formatting it that way compress it and what is compressing?" 8996 https://www.reddit.com/r/askscience/comments/64xl01/what_is_a_zip_file_or_compressed_file_how_does/ 1491996939 64xl01 Computing 2017-04-12 14:35:39 "Compression is a way to more efficiently store data. It's best explained with a simplified example. + +Suppose I have a file that contains the string ""aaaaaaaaaaaaaaaaaaaa"" (w/o quotes). This is 20 characters of data (or 20 bytes using basic ASCII encoding). If I know that files of this type rarely contain anything other than letters, I could replace this string by ""20a"" and program my software to read this as an instruction to create a string of 20 a's. + +But what happens if I want to use the same function for something that does contain a number? Well, I could decide that any number that is to be interpreted literally, rather than as part of an instruction is preceded by a \-symbol (and then add the special case of using \\ whenever I want to represent a single \). + +In certain cases, where the file doesn't contain many numbers or slashes, the size of the file can be reduced by this shorthand notation. In some special cases, the filesize actually increases due to the rules I introduced to properly represent numbers and slashes. + +Next up a compression tool might replace recurring pieces of data by a symbol that takes up considerably less space. Suppose a piece of text contains many instances of a certain word, then the software could replace that word by a single character/symbol. In order to ensure that the decompression software knows what's going on, the file format could be such that it first includes a list of these substitutions, followed by a specific symbol (or combination thereof) that marks the actual content. + +A practical example. Lets use both of the previous concepts (replacement of repeated data in a sequence by a number and a single instance of that data and replacement of freqeuntly occurring data by a special symbol and a ""dictionary"" at the start of the file). We use the format ""X=word"" at the start of the text to define a substitution of ""word"" by symbol ""X"", with the actual text starting with a !. We use the \ to indicate that the following character has no special meaning and should be interpreted literally. + +The text is: + +I'm going to write Reddit 5 times (RedditRedditRedditRedditReddit) and post it on Reddit. + +This line has 90 characters. Applying our compression algorithm, we get: + +$=Reddit!I'm going to write $ \5 times (5$) and post it on $. + +This line has 62 characters. A reduction of a third. Note that this algorithm is very simplistic and could still be improved. + +Another technique that can be used is reducing the size of the alphabet. Using standard ASCII encoding, 1 character uses 1 byte of space, but this 1 byte allows for 256 different characters to be expressed. If I know that a file only contains lowercase letters, I only need 26 different characters, which can be covered with just 5 out of the 8 bits that make up a byte. So for the first character, I don't use the full byte, but rather just the first 5 bits and for the next character, I use 3 remaining bits of the first byte and 2 bits from the next byte, etc... + +Now a file like this can only be interpreted correctly if the software on the other end knows it's dealing with a file that uses 5 bits to encode a lowercase letter. This is rather inflexible. So what I can do is to include a special header in the file, a small piece of data that contains the details of the encoding used, in this case it will mention that each character uses 5 bits and then has a list of all the characters that are used. This header takes up some space, so reduces the efficiency of the compression, but it allows the compression software to use any type of character-set that it likes, making it useable for any file. + +In reality, ZIP and other compression techniques are considerably more complex than the examples I've demonstrated above. But the basic concepts remains the same: Compression is achieved by storing existing data in a more efficient way using some form of shorthand notation. This shorthand notation is part of the official standard for the compression-system, so developers can create software to follow these rules and correctly decompress a compressed file, recreating the original data. + +Just like in my examples, compression works better on some files than on others. A simple text file with a lot of repetition will be very easy to compress, the reduction in file size can be quite large in these cases. On the other hand, a file that contains data that is apparently random in nature will benefit very little, if anything, from compression. + +A final remark. All of the above is about ""lossless"" compression. This form of compression means that the no information is lost during the compression/decompression process. If you compress a file and then decompress it using a lossless algorithm, then the two files will be exactly the same, bit by bit. + +Another form of compression is ""lossy"" compression. Where lossless compression tries to figure out how data can be stored more efficiently, lossy compression tries to figure out what data can be safely discarded without it affecting the purpose of the file. Well known examples of lossy compression are various file formats for images, sound or video. + +In the case of images, the JPEG format will try to discard nuances in the image that are not noticable by a regular human observer. For example, if two neighbouring pixels are almost exactly the same colour, you could set both to the same colour value. Most lossy formats have the option to set how aggressive this compression is, which is what the ""quality"" setting is for when saving JPEG files with any reasonably sophisticated image editor. The more aggressive the compression, the greater the reduction in filesize, but the more data that is discarded. And at some point, this can lead to visible degradation of the image. So-called ""JPEG artifacts"" are an example of image degradation due to the application of aggressive lossy compression (or the repeat application thereof, the image quality decreases every time a JPEG file is saved). + +edit: +For a more detailed overview of the compression often used in ZIP files, see [this comment](https://www.reddit.com/r/askscience/comments/64xl01/what_is_a_zip_file_or_compressed_file_how_does/dg60pjr/) by /u/ericGraves " "There are already some good explanations of compression. But that isn't the whole answer to, ""what is a zip file"". + +A zip file is an *archive file* that also supports compression. An archive file is a way of storing a collection of files (and directories, file names, and other data necessary to reproduce a subset of a file system) in a single file. It is a convenient way of packaging a bunch of files for archiving, sharing, etc. + +Compression is a common feature for archive file formats, but is not required. Nor is an archive format required for compression. Classic Unix 'tar' and '.a' files are examples of archive formats that didn't include compression. And there are a variety of tools in Unix/Linux environments for compressing a single file without any kind of archive file format. + +.zip files were the file format for a ""shareware"" DOS program from *1989* called pkzip, from a company named pkware. Because it was functional and effectively free (and maybe because of the catchy name) it quickly grew to be a defacto standard." +1026 How Precisely Are Satellites put into orbit? Is it to the meter? 8985 https://www.reddit.com/r/askscience/comments/8g77ag/how_precisely_are_satellites_put_into_orbit_is_it/ 1525167488 8g77ag Engineering 2018-05-01 12:38:08 "It depends on how the satellite is to be used, but most standard rockets deliver their payload to an accuracy of about 10 kilometers in altitude. If more precision is required, additional rocket burns can fine-tune the orbit. + + +http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf + +http://www.arianespace.com/wp-content/uploads/2011/07/Ariane5_Users-Manual_October2016.pdf + +And in many cases, you don't need to place the satellite very precisely. Even GPS satellites have orbital heights that vary by [a kilometer or two](https://www.colorado.edu/geography/gcraft/notes/gps/ephclock.html): it doesn't matter exactly where the satellite is, so much as the GPS sensor has the data to *know* where it is. +" "Hi, SatNav for the GOES constellation here. Others are talking about the precision that launch vehicles can insert a satellite, so I'm going to touch on the precision of keeping an orbit. + +Most satellites locations are known within a decent margin of uncertainty. There's a lot we can do to infer their location and velocity, like using radio signals, but those depend highly on our ability to calculate their orbit based on their ISV, or Initial State Vector, a six-element vector describing the satellites position in x, y, and z, and velocity in x, y, and z. + +Following the Orbit Determination, or OD, we create an Ephemeris file. Assuming the OD is good, the ephemeris file is the best way for us to let people know where we're going to be. It's a list of points given at a certain interval, so that others don't have to perform the OD themselves to figure out where we are. This ephemeris is as accurate as our initial OD is, though, so if the OD is flawed the ephemeris will be, too. + +Between all of this is also the fundamental uncertainty of n-body orbital mechanics. We have a pretty good idea of what things will do at a given time, but it's quite hard to calculate all the influences. To this end, satellites often have a ""covariance bubble"" around them that defines the area of uncertainty around their possible position. [Here's](http://aero.tamu.edu/sites/default/files/images/news/S4.1%20Sabol.pdf) some more reading on Covariance and Monte Carlo simulations, although it's pretty heavy stuff. Truthfully I'm not too solid on that particular concept. + +Anyway, in terms of *maintaining* the orbit, geostationary satellites perform regular maneuvers to maintain their Semi-Major axis (which affects the rate they drift East/West) and larger, less regular maneuvers to correct their Inclination (The higher the inclination, the more the ground trajectory becomes a figure-eight rather than a small dot). The regularity of these maneuvers is somewhat arbitrary. Our older satellites operate on a monthly-ish cadence for East-West/SMA maneuvers, and a yearly-ish cadence for North-South/Inclination maneuvers. Our newer satellites, GOES-16 and GOES-17, have been automated so much that they can perform one of each every week! I mentioned in another comment, this is much preferable because it keeps the location nice and tight and there's less room for error, but if I'm being completely honest it's a little less fun. + +Let me know if you have any questions!" +1214 Why do some birds hop while some of them walk? 8965 https://www.reddit.com/r/askscience/comments/biwo4e/why_do_some_birds_hop_while_some_of_them_walk/ 1556582731 biwo4e Biology 2019-04-30 3:05:31 [deleted] "To complement u/CopperSeaUrchin's reply, there is some evidence that the bird's structure lends itself to either hopping or walking as being more efficient. + +Geijtenbeek, van de Panne and van der Stappen devised a [computational model for simulating muscle based locomotion](https://www.cs.ubc.ca/~van/papers/2013-TOG-MuscleBasedBipeds/2013-TOG-MuscleBasedBipeds.pdf). More specifically, the model hard wires parameters for the ""shape"" of the entity, and the model figures out how best to use the muscles to move (via genetic algorithm). In their simulations, they observe both walking, running and hopping [emerge](https://www.youtube.com/watch?v=pgaEE27nsQw) as the best form of locomotion for different parameters." +1306 Given the way the Indian subcontinent was once a very large island, is it possible to find the fossils of coastal animals in the Himalayas? 8959 https://www.reddit.com/r/askscience/comments/c7e89k/given_the_way_the_indian_subcontinent_was_once_a/ 1561902917 c7e89k Paleontology 2019-06-30 16:55:17 "Yes. In fact, [the summit of Mt. Everest is limestone](http://www.montana.edu/everest/facts/summit-limestone.html), a ~~mineral~~ *rock* formed in the seabed. [Ammonites](https://www.thehindu.com/society/history-and-culture/aftermath-of-the-great-collision/article19882356.ece), fossilized sea critters, are found throughout the Himalayas. + +Edit: why does this post show 17 comments by I can only see 4?" Before the Himalayas formed, the area was the seafloor of the Tethys Sea. There are fossils which have been found there that are roughly 200 million years old. The Himalayas themselves began to form 70 million years ago. +1027 What happens to the 0.01% of bacteria that isnt killed by wipes/cleaners? Are they injured or disabled? 8958 https://www.reddit.com/r/askscience/comments/998qhf/what_happens_to_the_001_of_bacteria_that_isnt/ 1534898507 998qhf Biology 2018-08-22 3:41:47 Ok, so I work in the industry of antimicrobial testing, and no, it's not a legal disclaimer, we test and see how much of a log reduction a product gets and we literally scrub the shit out of the device or surface or whatever, so no, it's not a CYA claim, it is based on actual FDA or EPA regulated testing on very specific strains of bacteria, fungi or viruses, or appropriate surrogates. The remaining bacteria or other microbes not killed may very well develop resistance and there are even concerns that some previously non-pathogenic strains of E. faecium and faecalis have evolved to be resistant to alcohol based sanitizers. And yes, sterilants can kill even super bad spore strains, but the contact times are like 20 minutes for even the best, trendiest ones used on devices. And those sterilants are pretty nasty. Basically, don't overuse any antibacterial substance, and know that manual scrubbing of contaminated surfaces with any cleanser or disinfectant goes a long way, a product just works better when you scrub and use at the proper contact time. There's also the [minimum infective dose](https://en.wikipedia.org/wiki/Minimal_infective_dose) to take into consideration. Let's say you're about to eat a sandwich and you've just washed your hands. If it takes 40 E. coli to infect you and washing your hands killed all but 10, you're likely to not be infected. +1307 Why does putting a leaf between pages of a firmly closed book prevent the leaf from decaying? 8947 https://www.reddit.com/r/askscience/comments/cmd7nz/why_does_putting_a_leaf_between_pages_of_a_firmly/ 1565022577 cmd7nz Biology 2019-08-05 19:29:37 Dehydration; by applying pressure and absorbent layers you're accelerating the removal of water from the leaf. Once it gets below a certain threshold, microorganisms don't have enough free water to function and reproduce, and decay is prevented. Along with the dehydrating effect, you are also preventing most air from getting to the leaf, which some if not most bacteria need in order to grow and thrive. Although this is likely minor compared to the other factors. +620 How much radiation dose would you receive if you touched Chernobyl's Elephant's Foot? 8944 https://www.reddit.com/r/askscience/comments/5njtbq/how_much_radiation_dose_would_you_receive_if_you/ 1484233458 5njtbq Physics 2017-01-12 18:04:18 Related question: The Russian guy, Litvinenko, was poisoned with Polonium in his wine glass, and died quite a miserable death. If you increased the radiation you poisoned someone with, does there come a point where they would stay conscious for only a minute or two and then eventually die? What would the symptoms of that look like? "Dr. Derek Muller, host of the YouTube channel [Veritasium](https://www.youtube.com/user/1veritasium?app=desktop), goes over [The Most Radioactive Places on Earth](https://www.youtube.com/watch?v=TRL7o2kPqw0&feature=youtu.be) as well as the jobs and activities in our daily life which expose us to radiation by using the famous banana for scale for unit of radiation. + +edit: links" +621 "On average, and not including direct human intervention, how do ant colonies die? Will they continue indefinitely if left undisturbed? Do they continue to grow in size indefinitely? How old is the oldest known ant colony? If some colonies do ""age"" and die naturally, how and why does it happen?" 8941 https://www.reddit.com/r/askscience/comments/64gxzg/on_average_and_not_including_direct_human/ 1491790450 64gxzg Biology 2017-04-10 5:14:10 "Ant colonies can die off in a variety of ways. Mites, other forms of parasites, ant wars, death of the queen, lack of food or sugar or water, predators, disease, and so many more. A colony can usually grow proportionate to its amount of resources, and room to roam. I am not sure how old the oldest ant colony is, but many colonies in captivity have survived for many years. Most colonies with only a single queen only last until her death. This is due to the fact that queen alates(young queen ants and their male equivalents) participate in yearly nuptial flights when they leave to mate. Male alates die right after this, but female alates that do make begin an entirely new colony, with only a few eggs to start. There are some species of ants that can have several queens however, and if the acclamation of the new queen goes well each time theoretically a colony could live forever. + +-an ant enthusiast." "interesting fact: there are 2 huge ant colonies battling on the planet! In a way they can be continuing indefinitely :3 + +http://www.radiolab.org/story/226523-ants/ + +""David Holway, an ecologist and evolutionary biologist from UC San Diego, takes us to a driveway in Escondido, California where a grisly battle rages. In this quiet suburban spot, two groups of ants are putting on a chilling display of dismemberment and death. According to David, this battle line marks the edge of an enormous super-colony of Argentine ants. Think of that anthill in your backyard, and stretch it out across five continents.""" +934 When does a mushroom die? When it's picked? When it's packaged? Refrigerated? Sliced? Digested? 8928 https://www.reddit.com/r/askscience/comments/7yjhmb/when_does_a_mushroom_die_when_its_picked_when_its/ 1519008024 7yjhmb Biology 2018-02-19 5:40:24 "Like u/Aww_Topsy explained, the mushroom is not the whole organism. It's just the fruiting body. The organism itself is the mycelium network. The mycelium network lives for a lot longer than the mushroom. I suppose a mushroom fruit body starts to die after it releases spore. Once it has completed its reproductive function it is no longer needed. Picked mushrooms are not dead. You can take tissue clones from store bought mushrooms and cultivate them. Mycelium networks die when another fungus or bacteria out competes them, or when they exhaust their food source. + +EDIT: Potato grammar. Thanks u/AugurAuger" "Mushrooms are the fruiting bodies, the “roots” would be the mycelium which is the “plant”. So when you ask when it dies, it’s like you’re asking when does an apple die.. it just spoils. The spore is the reproductive organs which can be found in gills of Agaricus bisporus, which is commonly used in cooking. The spores from the mushroom will create mycelium in the ground which may produce fruiting bodies - mushrooms. + +Source - study Mycology" +1028 AskScience AMA Series: We're three experts on plastic pollution who have worked with Kurzgesagt on a new video, ask us anything! 8912 https://www.reddit.com/r/askscience/comments/8v9qa6/askscience_ama_series_were_three_experts_on/ 1530450052 8v9qa6 2018-07-01 16:00:52 "I just have 4 questions to try to simplify it both for myself and to explain to others + +1. What are the simplest things any normal citizen can do every day to help with the issue? +2. What are some things that people can do if they want to get more involved? +3. What is the worse-case scenario if things don't change? +4. What is the most likely scenario if things don't change? + +Thank you for doing this!" "Thanks for all your questions and the interesting discussion! + +I've seen lots of questions based around a similar theme of: what can we do as individuals; do we make a difference; is this a regional or global problem; what should corporations be doing; what should governments be doing? So I thought I’d try to kill many birds (Kurzgesagt birds, of course) with one stone and gather some collective thoughts which tackle them all. + +I’m a researcher on the [Our World in Data](https://ourworldindata.org/) team – there we publish interactive data visualisations and research on how the world is changing over a long-term perspective across a wide range of social, economic, environmental dimensions. Therefore I try to use data to inform my choices on how to tackle problems and what makes sense. The data visualisations linked to below might be helpful for you. + +These interactive maps are based on data published a 2015 [paper in Science](http://science.sciencemag.org/content/347/6223/768/) (the only global quantification of plastic reaching the oceans by country that I’ve seen). The data is for 2010 so not ideal, but I suspect this does not strongly affect the overall balance. + +Let’s work through this in steps: + +\- Per person, the amount of plastic waste we generate is mixed across the world, but typically higher in richer countries. Explore the map [here](https://ourworldindata.org/grapher/per-capita-plastic-waste-generation). + +\- But, plastic waste across the world is not managed in the same way and therefore does not have the same probability of ending up in the ocean. Most of the waste that is collected and formally managed in proper landfills does not reach the ocean. We can define ‘mismanaged waste’ as waste that is littered or not formally managed and includes disposal in dumps or open, uncontrolled landfills, where it is not fully contained. The authors note that this is the plastic waste which could enter waterways and move into the ocean. Per person, the global map changes significantly; richer countries tend to have much better waste management methods and therefore very low levels of ‘mismanaged waste’. Explore the map [here](https://ourworldindata.org/grapher/mismanaged-plastic-waste-per-person). + +\- Of course, in terms of plastic which could reach the ocean, we’re interested in the total (not the per capita) plastic waste. This is how [that map looks](https://ourworldindata.org/grapher/mismanaged-plastic-waste). Here we see that the largest quantities of mismanaged plastic waste are regionally focused in Asia and across North Africa. As noted in the video, it tends to be in countries which have industrialized very quickly in recent decades and have large coastal populations. If we [plot mismanaged plastic waste against GDP per capita](https://ourworldindata.org/grapher/per-capita-mismanaged-plastic-waste-vs-gdp-per-capita), it tends to be highest at middle incomes. + +So, what is the most effective way of addressing this? + +It’s true that the quantity of mismanaged plastic waste (that could enter the ocean) across rich countries is in balance, relatively small at the global scale. Europe as a whole, for example, probably sums to the order of 100s of thousands of tonnes per year (maybe up to a million). This compares to some countries in South-East Asia, in contrast, which produce the in the order of millions of tonnes in a single country. + +What can we do as **individuals**? There is the obvious at-home or local practices we can do: recycle as much as you can, don’t take plastic you don’t need, be conscious of how much you’re using and where you can reduce (but before of unintended consequences such as food waste). + +But these practices alone are not close to enough. Sure, we should still do them, but only if they are additional to broader, more impactful action that higher-income countries take. They should not be a substitute, or a “we’ve banned plastic straws, so we’ve done our bit for the planet” campaign. If rich countries (and their populations) are as concerned and committed to this problem as they say they are then one of the most effective actions is to invest in waste management infrastructure across lower-to-middle income countries. Countries which have industrialized quickly have been left with insufficient waste management systems. If these are systems are not implemented and upscaled, then we will be unable to address this global problem. We could end plastic waste across Europe and North America and we would still have a major global problem. + +Note that this is not a finger-pointing blame game. This has been a consequence of economic growth, industrialization and globalisation which we all share responsibility for. It needs to be a collaborative effort to find the interventions which have the largest impact. + +So, governments should be investing in waste management infrastructure. Companies and industry should be taking responsibility for the redesign of new products which mimimise wastage. And as individuals we should be pressuring both into take these steps. Do your bit locally, but attempt to push for the high-impact global solutions too." +1308 Why are batteries arrays made with cylindrical batteries rather than square prisms so they can pack even better? 8909 https://www.reddit.com/r/askscience/comments/cms57p/why_are_batteries_arrays_made_with_cylindrical/ 1565105884 cms57p Engineering 2019-08-06 18:38:04 "First of all, some packs are made with prismatic cells. The pros and cons of cylindrical vs prismatic cells themselves are more important than packing efficiency. Notably, cylindrical manufacturing is more mature, and cylindrical cells tend to be better (in energy density and cost per kWh) at lower capacities, which most packaged battery packs are. + +Here's an in-depth article on the cylindrical vs prismatic question: https://www.sciencedirect.com/science/article/pii/S0378775316315981" "Mostly historical now. + +Originally many mass-manufactured batteries were made by rolling flat sheets of material, inserting a rod, and filling the space with an electrolyte. It made for a fairly simple method of manufacture and was pretty reliable. By rolling a sheet around a tube you easily got a known size without needing spacers and rods were pretty simple to extrude. You could also cast or extrude the tube pretty easily. + +If you went with two flat sheets you'd need several spacers to make sure the sheet was evenly spaced all around and a flat item is less structurally-sound than a round one. Look at the strength of an arch vs the strength of a square opening. + +In addition, you have the highest ratio of volume to surface area with a round container. But if you go with a sphere you lose a lot of volume when you pack them. It turns out that a great balance of volume to surface area and packing units comes from cylinders instead of spheres or square prisms. + +So most battery manufacturers settled around making cylindrical batteries rather than any other shape. The exception is when you really need to maximize volume, then they go with whatever shape does that best - such as in a cell phone, you'll see that the batteries will often be a flat rectangle which uses every bit of space possible." +622 In light of the recent growth of sightings of Tasmanian Tigers and possibility of a species coming back from what we thought was extinction... Has this happened with any other species in the last ~500 years? 8905 https://www.reddit.com/r/askscience/comments/63ef3e/in_light_of_the_recent_growth_of_sightings_of/ 1491316040 63ef3e Biology 2017-04-04 17:27:20 Black footed ferrets from the US and Canada were declared extinct in 1979 due to farmers poisoning prairie dogs, their food supply. Lo and behold, a farmer's dog brought home a dead one 2 years later and they became endangered instead! "Yes, this happens quite often, although you will hear more news about animals like tigers since they are more popular. There is also the issue of deciding when to declare an animal extinct. Many birds are elusive and haven't been sighted in years. From a quick search here are some animals thought to be extinct but rediscovered: + +* Yangtze River dolphin http://www.npr.org/templates/story/story.php?storyId=14599250 + +* ""Tree lobster"" http://www.npr.org/sections/krulwich/2012/02/24/147367644/six-legged-giant-finds-secret-hideaway-hides-for-80-years + +* imperial woodpecker http://www.npr.org/2011/12/23/144190097/searching-for-a-ghost-bird + +" +1029 Why do the cameras inside the ISS have so many dead or stuck pixels? 8886 https://www.reddit.com/r/askscience/comments/8thuco/why_do_the_cameras_inside_the_iss_have_so_many/ 1529847496 8thuco Engineering 2018-06-24 16:38:16 "Long term radiation damage on the cameras. Astronauts, for example, when they close their eyes, will occasionally see flashes of light as a heavy ion or charged particle crashes through their skull and fires off a photo receptor cell in their eye despite their eyes being closed. Luckily when ~~we lose cells~~ cells are damaged they can regenerate, not so for a semiconductor matrix inside the CMOS/CCD sensor of the camera. + +https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena + +Edit: Dead nerves don't regenerate. + +Edit2: Added link." "The sensitive parts of the cameras are semiconductor arrays. Every now and then a bit of cosmic radiation will fly through the camera and cause a chemical reaction in one of the pixels which causes that pixel to malfunction. + +The effect is apparently temperature dependent so cameras inside will be more effected than cameras outside where its very cold. " +505 Carbon in all forests is 638 GtC. Annual carbon emissions by humans is 9.8 GtC (1.5% of 638). Would increasing forests by 1.5% effectively make us carbon-neutral? 8856 https://www.reddit.com/r/askscience/comments/5c82ui/carbon_in_all_forests_is_638_gtc_annual_carbon/ 1478788063 5c82ui Earth Sciences 2016-11-10 17:27:43 "Depends on what you mean by ""increasing forests."" Short answer is yes: trees are made from carbon and so increasing the total biomass of all Earth trees (through growth or new saplings) by 1.5% would capture last year's carbon emissions. + +Increasing the total number of trees, or the proportion of earth's surface covered by forests, by 1.5% is a different proposition than increasing biomass... think about the difference between watching a giant oak grow 1.5% dry weight (start with one tree, end with one tree, but meet the carbon target) as opposed to planting an equivalent mass of new saplings (start with one tree, now have fifteen trees, but no growth occurred so carbon target is not met). The difference here is time. For your new saplings to actually put a dent in carbon emissions requires them to grow, which requires time. + +Furthermore, we need to meet this target *each and every year* until our carbon emissions stabilize. 1.5% growth year over year is exponential and wouldn't take too long for us to literally run out of room to plant more forests. To be specific, that means doubling the biomass of all forests on earth every 45 years or so. The concerted effort required by humanity to do so would be a project on a scale never before seen in human history. If we planted two or three saplings for each and every tree already planted in the world, and passed an international resolution making it illegal to cut down any living tree, we would have a small chance at making our first 45 year target. + +A related but interesting thing is carbon capture through algae. If I recall correctly, algae is responsible for a huge amount of carbon processing on this planet. Not only does algae grow faster than trees, it takes up a lot less space and the growth/cultivation of algae can be industrialized fairly easily. It may be far more reasonable for humanity to domesticate algae on a large scale (my first thoughts go to growing algae-based foods, producing algae-based paper products, and using algae to make combustible fuels) than to increase forest coverage." "The processes of removing CO2 from the atmosphere and storing it are called ""capture"" & ""sequestration"". Growing more trees is one of the easiest ways to capture CO2, but even if you manage to increase the Earth's biomass by 1.5%, you then have to worry about maintaining biomass at that higher level. It's easy for a catastrophic event like a forest fire to release that carbon back into the atmosphere at a future date, so forests are a poor form of sequestration. + +There are proposals to store significant amounts of carbon underground through ""geological sequestration"" (dissolving CO2 into deep-underground salty brines or permanently incorporating it into carbonate rocks). That's a better form of sequestration, but the ""capture"" part is more difficult in that scenario." +836 Nuclear power plants, how long could they run by themselves after an epidemic that cripples humanity? 8840 https://www.reddit.com/r/askscience/comments/76jaue/nuclear_power_plants_how_long_could_they_run_by/ 1508078536 76jaue Engineering 2017-10-15 17:42:16 "Depends on the type of reactor. Most plants are so ridiculously automated it's not even funny. Even the older ones. + +As someone stated though the lack of load would cause the generators to trip and with that happening the reactor would trip because there's nothing to take the load. Nuke plants aren't great at varying loads so a sudden drop off in load usage would cause it all to shutdown for safety reasons automatically. When we had that big power outtage many years ago on the east coast the plants all went into shut down because the systems all tripped as there was a sudden lack of load as far as the generators were concerned and all the reactors went into safety ""OH shit our powers got nowhere to go"" mode and started shut down processes. Which sometimes causes problems as the back ups for some plants are primarily fed from the grid (backups used if not acailable) but because the whole grid went down some back ups didn't do what they should have. + +Source: Am Nuclear Operator + +Edit: +Few questions were asked. +1) Depending on the age of the plant, in a perfect world they should technically run without any human intervention for quite awhile. That said no plant runs perfectly so it could be as short as a day before lack of humans causes it to shut down or a few weeks. As someone said they have entire shifts of people for the reactors I'm at at all times and they're integral to making sure it runs smoothly but even without us it generally can run for awhile before issues arise and it shuts down, but it's also a much older so without us it'd fall apart. + +2) The simulated load is incredibly low as the plants can't really run if there's nothing to draw the load. It's hard to just have electricity go to nothing and it's hard to pretend there's a load that can use up the pure energy a nuclear reactor puts out. Nuclear reactors do not handle adjusting their power very well and at relatively high numbers begin to poison themselves out if the level is too low. Something like 60%, I think I can't remember, reactor power causes it to be overwhelmed by it's byproducts to the point where it can't keep going and has to basically be shut down restarted after x amount of hours so that it can decay enough to not cripple the reaction. The simulated load would have to be equal to a load above poisoning levels and that's obscenely high. Generally if the generator detects no load drawing from it, it has no choice but to basically be like ""Mr reactor you need to turn off or shit going to go Cray."" + +3)Most reactors built nowadays generally have a ton of safety features to hopefully power cool the reactor and poison it out to the point where the reactions stop. However... the fuel is still hot. Really fricken hot. Without the water circulating through it constantly there could be some huge issues. I work at a CANDU reactor. We use heavy water as our heat transfer medium. One of our in case of emergency cool and poison the reactor mediums is a large eater tower that gravity feeds normal light eater into the reactor as that cools and absorbs the reactor faster than the current heavy water in it. However.. It's designed for 1 reactor messing up hard and hoping people can shut the others down (all reactors are independent system wise so that faults on one isn't faults on all 4). Another feature they have assuming 100% lack of power (no back up generators for emergencies) the system is designed to go for as long as it can on a thermal flow option... like, the hot water will flow through the system cool and return back, which they got to test in real life by accident during the black out because the faults were so bad. However it only last so long. The systems probably would never breach containment if it got too hot honestly however the plant itself would be a terrible place to be with how their systems are set up. A meltdown on the levels of what has happened with 3 mile and fukushima are interesting edge cases of poor decision or poor design. Fukushima actually caused my plant to put safeties in place in case something were to happen here... Even though we are nowhere near fault lines. Meltdowns are honestly a hard thing to judge. It depends on how containment is built. It's such a plant by plant basis that it's impossible to say how every plant would react. + +Edit 2: + +First off sorry I don't have much for sources. It's mostly the courses we took in training and operating procedure and most of it's not really linkable. + +Most plants are designed yes to just shut down the reactor if a problem arises and no human interaction occurs. The rods at most meant for poisoning the reactor out and shutting it down are gravity held up by electronic means. If no power, rods drop and kill the reaction really fast. + +Also the reason the load matters isn't for the reactor itself. It's for the generators. If they aren't using the steam from the reactor to power anything there's almost no reason for the reactor to be running so it would begin to shut itself down. + +Also my plant will never be re-tubed if that helps. Too old. On her last legs. Which is why we have to be more involved with plant operations, older plant with lots more terrible manual valves and etc. + +Plants are designed to have as much automation in its processes as technologically available at the time of construction, and as such as time goes on newer plants have more sustainability assuming peak conditions. + +Side note: If you want to get into it go for it but be warned rotating 12 hour shifts which we have are absolutely the worst. Anyone who says it's okay is an edge case. + +Edit 3: I'm currently out, I'll try and have answers to what I can actually answer when I'm at a computer. + +Edit 4: + +Is CANDU the best: Eh. Depends. Its a system that works, its pretty safe, can run off not just enriched fuels, but its not necessarily the best or most efficient. It uses a Heavy Water Moderator for the heat transfer, as light water (normal ol' h20) tends to absorb a lot of the neutrons in the reaction, whereas Heavy Water does not. This is both good and bad, as the inventory of water for cooling has to be maintained and can't just be pumped from a lake (the water in most systems is never recycled back to the lakes, mind you) Edit edit: Biggest advantage of CANDU? Online refueling. We Refuel while she runs. Think of it like pushing the rods through a tube. Push one in, out comes one on other side. They very carefully balance the load with new/old fuel and which sides fueled for each tube to make sure there's no spikes in reactivity. Very neat stuff honestly. + +If the plant tripped and had the resources, could we restart?: Absolutely. Most plants are designed that way. If its been down long enough, though, it has to start up -really- slowly. Most reactors take hours / days to start up and get to full power due to the nature of nuclear reactions. It has to be super controlled (which nuclear is very controlled and safe in that matter) so as to not cause problems (or to detect problems and either fix them if possible, or power back down as happens from time to time). The biggest issue is most nuclear plants don't really start up without external power from the grid kind of keeping the systems going and jump-starting what needs to be before you're getting any real power from the Generators. I honestly don't know if we could cold start, with 0 external power. That said, there's still Natural Gas and or Coal depending on where you are (no coal here) to act in the interim, so the power companies could basically shunt the power to the plants to help them start up, which is what happened during the blackout as people mentioned (Some plants were able to keep 1 or more running and used those to basically restart the others) and then from there do what needs to be done, but without any real power source the plant would be unable to keep going, let alone start up. + +As for those who DO like shift work, honestly good on you. Legitimately. I found it tiring, staying concentrated for 12 hours isn't easy, and on a night shift on the last even 3 or so hours, you'll notice very few people doing anything that isn't urgent / mandatory outside of the control room. + +As for water getting contaminated: I can only vouch for CANDU, but we keep our steam flow separate from the other flows. We used heavy water as mentioned in its own flow, and it basically is used to heat up a boiler, which then heats up normal light water, which then turns the turbines. The heavy water, which flows through the reactor, never leaves containment. It's not allowed to unless there's a breach of some sort, or the vacuum building (a containment device) gets triggered, and at that point there is a lot of ""oh god, we got a lot of clean up to do"" going on.... But even that is a large, sealed, concrete building. It's a lot safer than people realize. They monitor any air going into and out, all water, etc. Some newer plants don't even let you near the core itself while in operation at all, where as some older ones kind of do but for obvious reasons you don't. Very safe. + +As for ""Melt downs"", it depends. Only if containment was breached (it takes a lot to breach containment under most circumstances) would there be risk to the outside, and if there was a breach, how big? There would be a lot of signs if there was, and you'd have plenty of warning. Radiation is fast, but linear in its motion. It would have to literally spill out and or explode everywhere, and exploding is something they're designed generally to not do. + +Oh this post got too long, had to cut two answer... I'll post as a comment." "Nuclear engineer and senior reactor operator here. + +Current day nuclear plants are not designed to go for more than 10-30 minutes post transient without human interaction. The logic and safety systems are only designed to respond to transients for immediate core protection and plant safety and do not bring the plant automatically to a cold shutdown condition. + +Generation 3+ plants (none in commercial operation yet), do have up to 1 week of walk away safety, but require operator actions to ensure long term core cooling. + +The bottom line is you can't leave a nuclear reactor. It takes a year or more before decay heat is low enough to prevent a zirconium fire and core melt or spent fuel pool fire. + +Operators like myself are licensed at the plant and we cannot leave our watch station until someone else with a license turns over with us. So every day I go in, I cannot leave until someone else who is licensed and qualified for my position takes over. I've done some long shifts due to people calling in sick. + +As for the plant side: you have to monitor and maintain equipment. Pumps need oil. Tanks need water filled (or drained). Systems need pressure vented. This stuff happens day to day, so without operators, equipment will fail and the plant will trip. + +Best case scenario, you cool the plant down to cold shutdown and leave it in shutdown cooling mode. If power trips off or anything malfunctions you'll lose core cooling again though, as shutdown cooling typically doesn't have auto restarts. + +Bottom line: you can't leave a nuclear reactor. And they won't be left unattended. " +1104 When staring into complete darkness do your eyes focus on infinity or are they unfocused? 8823 https://www.reddit.com/r/askscience/comments/9gkzp0/when_staring_into_complete_darkness_do_your_eyes/ 1537196062 9gkzp0 Biology 2018-09-17 17:54:22 "Optometrist here. + +In complete darkness the eyes almost fully relax their focus (accommodation). Some amount remains, known as tonic accommodation, which varies from person to person. This is inherent to the person's visual system and present unless they are dead! + +Note that focussing on infinity and fully relaxing the focus are, in terms of accommodation, the same thing. + +Accommodation is the system by which the eyes move their focal point closer to the body e.g. to read. At optical infinity no accommodation is required and the system is, in theory at least, fully relaxed. Is this the type of focus you meant? + +Vergence is the system by which the eyes move closer together to point at a near object. This works a bit differently, though the two, along with pupil dilation, are linked in terms of the nerve supply." "In flight training there is the idea of 'empty field myopia'. + + +If you are looking out into an empty sky, paying attention (looking out) but not focusing on anything in particular the eye will focus at around 1-2m. + + +This can be an issue so the training suggests looking at a cloud, a landmark, even the edge of the wings to avoid bringing focus in and hence missing another aircraft in the sky due to the short focus. + + +" +1215 Was there a scientific reason behind the decision to take a picture of this particular black hole instead of another one ? 8814 https://www.reddit.com/r/askscience/comments/bbwc8o/was_there_a_scientific_reason_behind_the_decision/ 1554962250 bbwc8o 2019-04-11 8:57:30 "Because it's really big. It's so big, that it looks bigger on the sky than closer black holes. + +We can talk about the ""angular diameter"" or ""apparent diameter"" of an object. This is how big it looks on the sky, rather than how big it really is. For instance, the Moon and the Sun have about the same angular diameter - half a degree - even though the Sun is much much bigger in actual size. This is of course because the Moon is much closer than the Sun. + +The super-massive black hole in M87 is about 3000 times bigger than the super-massive black hole in our own galaxy, and it's about 2000 times further away. So its apparent size is a little bit bigger than our own super-massive black hole. + +These two are the two black holes with the greatest apparent sizes. They're still working on releasing the image for our own supermassive black hole - Sag A* - but it's a bit trickier because there's more of our galaxy in the way." "Even with an 'Earth-sized telescope', the only black holes large enough to be viewed were the supermassive black holes at the center of Messier 87 and our galaxy (Sag A*). This is governed by an [equation](https://wikimedia.org/api/rest_v1/media/math/render/svg/680941f7a551ce5715e9e53fd55651b89be87daa), where a_r is the angular resolution, λ is the wavelength, and D is the diameter of the telescope. + +The angular size of this black hole is about 0.0000397"". The "" refers to seconds here, instead of inches. There are 3600 seconds in a single degree (°). Radio astronomy is usually done in the millimeter of wavelengths (1 mm to 1 cm), and at 1-2 mm range you get a necessary diameter of around 6300-12600 kilometers (Earth's diameter is 12700). + +Messier 87 was chosen because it was slightly larger in angular size than Sag A*, and because it was more stable. We didn't use another galaxy because none had a bigger supermassive black hole at its core. In order to account for the fact that the supermassive black holes at the core of other galaxies are thousands of times more distant than our galaxy's core, they must be thousands of times larger, like Messier 87. + +Why not a smaller black hole? Even if we had an active blackhole just 4 light years away (around Alpha Centauri) with an easily seen accretion disk, it would be smaller than Messier 87. A 50 solar mass black hole would only have an event horizon about 147 kilometers in size. That yields a .000000801"" angular size, which would require a telescope array 628,000 km in diameter. + +So basically, we needed a supermassive black hole. Our own galaxy's core was just barely big enough to see with a telescope the size of Earth at a 1-2 mm wavelength range, but there was one galaxy whose core had a bigger angular size." +741 In Earth travel, we use North, South, East, and West, plus altitude for three-dimensional travel. Since those are all relative to the Earth, what do they use for space travel? 8809 https://www.reddit.com/r/askscience/comments/6itmue/in_earth_travel_we_use_north_south_east_and_west/ 1498139798 6itmue Astronomy 2017-06-22 16:56:38 "Pretty much on every planet or moon it is possible to define North, South, East and West based on the body's rotation. Alternatively, they can be defined based on the Solar System's North and South (as the IAU did with Uranus, whose extreme axial tilt makes the rotational North opposite to the Solar System's North, but for all the other planets it's the same). + +However this isn't very precise to plan spacecraft trajectories. There are more precise reference frames based on longitude and latitude, so a prime meridian is defined pretty much arbitrarily as they did on Earth. It's also quite common to use Cartesian reference frames centered on a planet but with the axes based on far away celestial objects because they don't rotate with the planet, so you have an inertial reference frame. + +In deep space, far away from any planet, we use a reference frame centered on the Sun, with the X axis pointing along the ecliptic plane parallel to the vernal equinox (the intersection between Earth's equatorial plane and the ecliptic plane), the Z axis pointing North from the Sun, and the Y axis pointing 90° ahead of the X axis following the right hand rule. + +It is possible to define others, it depends on each particular trajectory. Basically you need a center (a planet, the Sun, etc), a fundamental plane (the ecliptic plane, the planet's equatorial plane, etc) and a direction for the X axis. +" Im a 6-DOF simulation engineer at NASA, so this is right up my alley. There are tons of different coordinate frames one can use to navigate 3D space, the key is know what kind of rotation matrix/quaternion you need to navigate from frame to frame. To name a few, there's topodetic, topocentric, PCI, PCR, J2K, M50, NED, DSL...the list goes on and on. I can give you more info tomorrow when I'm back at my desk if anyone is interested. +1309 "How did the ""right side up"" view of the Earth, aka North = up, become the norm for all globes and maps?" 8801 https://www.reddit.com/r/askscience/comments/cf0o48/how_did_the_right_side_up_view_of_the_earth_aka/ 1563496514 cf0o48 Planetary Sci. 2019-07-19 3:35:14 "This is a historical question, as Nowhere_Man_Forever points out. Generally, map makers oriented their maps towards what they thought was important. For example, some early maps were oriented east-west to aid navigation against the rising and setting sun. Later, North American explorers would make east-west oriented maps because those are the primary directions they traveled. + +But, people since antiquity have thought that the Earth rotated and knew that pole stars (i.e. the North Star for us today) would maintain an apparent fixed position in the night sky. This imparted special navigational importance to the north-south axis. + +Then, when the magnetic compass was invented that solidified the north-south axis as the primary axis for navigation. Since it makes a lot of technical sense to have all your maps use the same orientation, the north-south axis was the only orientation that made sense. + +There's not a clear technical reason to use north=top instead of south=top. One theory is that at the time of the explorers there was no comparable pole star in the southern hemisphere like there is Polaris (which is exceptionally bright) in the northern hemisphere. However, that's a pretty weak theory. + +It's probably just the case that the Europeans wanted to put Europe at the top of their maps, and their maps would end up having the largest sway over the future events to come. The other great powers in the world at the time didn't do as much exploration and weren't as imperial as the Europeans were, so their maps are the ones that stuck." "Globes have north at the top from that same convention that operates for maps; the convention is arbitrary (many early maps had east at the top, from which I believe is where the notion of 'orienting' a map stems). The choice of north at the top of the page or uppermost on a globe is not necessary in any sense - globes could be upside down or sideways (i.e. the axis horizontal), maps could have any direction to the top. + + +You may find the following article helpful: + +http://www.bbc.com/future/story/20160614-maps-have-north-at-the-top-but-it-couldve-been-different" +1030 How come when hot metal is placed in cold water, it does not shatter like glass? 8787 https://www.reddit.com/r/askscience/comments/8mjbk5/how_come_when_hot_metal_is_placed_in_cold_water/ 1527442602 8mjbk5 Physics 2018-05-27 20:36:42 "There are two main reasons. First, glasses are generally worse heat conductors than metals and second metals tend to be ductile while glasses are generally brittle. + +So let's step back a second. The reason that glass shatters when rapidly cooled is usually because of heat gradients in the material. These variations in temperature create stresses at different points in the material. If the stress is large enough it can then lead the glass to shatter. So what's different in metals? To start off metals are much better conductors so that such heat gradients can more quickly dissipate. + +But just as important is the fact that metals also tend to be much more ductile. The reason is twofold: 1) metals tend to be crystalline and 2) they are connected through metallic bonding. These properties allow metals to relieve stress through dislocations where planes of atoms slide past each other. As a result the material can easily deform in the presence of a stress without cracking, which is what makes crystalline metals rather soft. + +If you move away from these conditions you tend to reduce the ductility of the material. So for example if you move away from metallic bonding to ionic or covalent bonding the materials tend to become quite a bit more brittle. The reason is that now the directional bonding makes it much harder to slide atoms around in order to relax. It's for this reason that quartz (the crystalline form of common glass) is pretty brittle. Likewise if you move away [from a crystalline structure to an amorphous structure](https://i.imgur.com/RqBqCYW.gif) you again prevent atoms from being able to slide away from each other in an orderly way. As a result it's much likely for cracks to develop and propagate, which leads to materials shattering. For this reason, even metallic glasses can be quite brittle. + +As a final note, in some cases even crystalline metals can shatter. Certain metals exhibit [a ductile-to-brittle transition](https://en.wikipedia.org/wiki/Ductility#Ductile%E2%80%93brittle_transition_temperature) in a given temperature range. At those temperatures if you apply a strong enough stress the metal will also develop cracks like glass and shatter. + +edit: I added a more thorough discussion on the effect of the type of bonding per the point raised by /u/Narwhal_Jesus " It actually can shatter depending on the type of metal it is. Regular high carbon steel \(used for making knives\) is really susceptible to cracking and breaking if you quench if in water. It has to do with the metal crystals themselves during the quenching process. When you quench steel slowly i.e. in oil the metal cools slowly \(relatively\) and the crystals are larger and adhere to each other better. Fast quenching produces small, not very well bonded crystals that are brittle and susceptible to cracking and breaking. Metals ability to expand and shrink keeps if from shattering like glass. +1216 How do you grow seedless grapes of you don’t get any seeds from them ? 8771 https://www.reddit.com/r/askscience/comments/b4myyz/how_do_you_grow_seedless_grapes_of_you_dont_get/ 1553368382 b4myyz Biology 2019-03-23 22:13:02 You can propagate a lot of plants by grafting a branch from the desired plant onto the trunk of a hardier, similar variety. I have a Japanese Maple in the back yard that you can clearly see where it was grafted onto the trunk of another variety- it doesn’t produce seeds. "You can make a clone, which is taking any live part of a plant and planting that; from which is will start to regrow roots downwards and stalks upwards. + +Seeds just help with genetic diversity. You don't need them to regrow a plant. " +1794 If you dug a hole straight down to the other side of the earth, what would happen if you dropped something through it? 8769 https://www.reddit.com/r/askscience/comments/la1azg/if_you_dug_a_hole_straight_down_to_the_other_side/ 1612179897 la1azg Earth Sciences 2021-02-01 14:44:57 "The object would accelerate towards the core. Once at the core, there is no gravity, so the speed of the object doesn't change at the core. So the object will shoot straight through towards the other side. + +If there is no air resistance, the object will make it to approximately the same height that it was dropped from on the other side. At that point, it would finally come to a stop, before being pulled back down. The object would continue to oscillate between the two ends of the tunnel. + +With air resistance, the object gets slowed down gradually and would reach a lower height with each oscillation until it finally settles in the center of the Earth." "Simplest case: The hole is along the Earths axis of rotation (or the Earth isn't rotating), the Earth is a perfect sphere with uniform density, and there is no air. The object will fall straight down, accelerating as it falls. The acceleration will be proportional to how far from the center the object is (at the surface a=g, at the halfway point a=0.5\*g, at the center a=0). Once it passes the core, the objects inertia will keep it going, but now its slowing down. It will reach the surface level \~44 minutes after it is dropped, then fall back. The motion can be described by simple harmonic motion. + +If there is air in the hole: The object will quickly reach terminal velocity as it falls. It will still overshoot the center, but it won't leave the inner core. After a few oscillations, its motion will begin to resemble damped harmonic oscillation. + +If the Earth follows its real density profile: The objects acceleration will stop being proportional to its distance from the center. The acceleration will be relatively constant for most of the trip, only starting to drop around the outer core. You also need to account for the Earths lumpiness; dropping the object from one side might not make it to the surface of the other side, or it might make it overshoot (if we go back to the condition of no air). + +If you consider the Earths rotation: This can be described in therms of an inertial frame, or a non-inertial frame. The non-inertial answer is that the object will experience Coriolis acceleration, that has magnitude a=Wxv, where W is the vector of the Earths rotation (2\*pi/24hr, directed straight out of the north pole), v is the velocity vector of the object, and x is the cross product, meaning the more perpendicular the other two vectors are the larger the acceleration. The inertial answer is that the object has some lateral velocity when it is dropped anywhere but one of the poles, and the lateral velocity of the hole gets smaller as it gets closer to the center of the Earth. Either way, the object will keep bumping against the wall of the hole; the east wall as it falls toward the center, the west wall as it falls away from the center (with both actually being the same wall, since east and west are relative and will seem to swap when you pass the center). If the bumps are frictionless, this will not affect the motion in the direction of the fall." +742 If I shake hands with someone who just washed their hands, do I make their hand dirtier or do they make my hand cleaner? 8762 https://www.reddit.com/r/askscience/comments/6l0x5h/if_i_shake_hands_with_someone_who_just_washed/ 1499099229 6l0x5h Medicine 2017-07-03 19:27:09 "You transferred some bacteria to his hands, which were destroyed if the disinfectant was still present in sufficient quantity (i.e. not evaporated). + +There's no such thing as ""transferring cleanliness"" much like there's no such thing as ""transferring coldness."" Hot things transfer heat to cold objects, much like there was a net transfer of (temporarily) live bacteria from your hands to his. + +In reality, what probably happened was a transfer of some bacteria to his hands (which were killed if he still had disinfectant on them like you say), and you took some of the disinfectant onto your hands too, which killed bacteria on your hands as well. + +By the way, your body is crawling with bacteria like you wouldn't believe. They aren't bad—your skin exists to keep them out and to control. In most cases, there is no need to disinfect your kids' hands unless you or they have an active cold. And the immune system—especially in childhood—requires stimulation for proper development and function. There's been a slew of research that correlates insufficient exposure to ""germs"" and other foreign bodies with a higher rate of allergy development as well as autoimmune disorders. One reason for the recent FDA move to pull antibacterial soaps off the market is because they didn't actually do anything. +" "There's a very interesting RadioLab episode that goes over this very concept. They actually test it with Niel DeGrasse Tyson and one of the show hosts. + +http://www.radiolab.org/story/funky-hand-jive/ + +TL;DL: Some bacteria is stronger than others, and will ""win"" against other bacteria. If person A has a strong bacteria colony on their hand, and person B does not, some of person A's bacteria will try and set up a colony on person B's hand. To answer the question here. If the disinfectant was still present, likely a lot of bacteria would die. If not, some of the ""dirty hand"" bacteria would likely set up shop on the ""clean hand"". + +" +743 If quantim computers become a widespread stable technololgy will there be any way to protect our communications with encryption? Will we just have to resign ourselves to the fact that people would be listening in on us? 8751 https://www.reddit.com/r/askscience/comments/6dgpv8/if_quantim_computers_become_a_widespread_stable/ 1495802732 6dgpv8 Computing 2017-05-26 15:45:32 "The relevant fields are: + +* _post-quantum cryptography_, and it refers to cryptographic algorithms that are thought to be secure against an attack by a quantum computer. More specifically, the problem with the currently popular algorithms is when their security relies on one of three hard mathematical problems: the integer factorisation problem, the discrete logarithm problem, or the elliptic-curve discrete logarithm problem. All of these problems can be easily solved on a sufficiently powerful quantum computer running Shor's algorithm. + + PQC revolves around at least 6 [approaches](https://en.wikipedia.org/wiki/Post-quantum_cryptography#Algorithms). Note that some currently used symmetric key ciphers are resistant to attacks by quantum computers. + +* _quantum key distribution_, uses quantum mechanics to guarantee secure communication. It enables two parties to construct a shared secret, which can then be used to establish confidentiality in a communication channel. QKD has the unique property that it can detect tampering from a third party -- if a third party wants to observe a quantum system, it will thus collapse some qubits in a superposition, leading to detectable anomalies. QKD relies on the fundamental properties of quantum mechanics instead of the computational difficulty of certain mathematical problems + +Both these subfields are quite old. People were thinking about the coming of quantum computing since the early 1970s, and thus much progress has already been made in this area. It is unlikely that we'll have to give up communication privacy and confidentiality because of advances in quantum computation." "Certain algorithms (RSA, DSA, ECDSA) used for signing messages and assymetrically encrypting them (encrypting messages to someone without having to talk to them first to agree on a key) are badly broken by quantum computers. + +ECDH and regular DH (used for key exchange) are broken. + +The total loss of these first two classes would rule out most forms of practical cryptography. + + +All crypto algorithms are weakened, but not necessarily broken, by quantum Grover search. + +Symmetric encryption (AES, salsa20, etc.) should still be fine. You should use at least 256 bit keys on account of Grover search. + +Hashing algorithms (RIPE160, SHA2-3, etc.) should still be fine. RIPE and co are starting to look a little bit short on account of Grover. + +Certain signature algorithms (like merkel trees) should be fine. Unfortunately, these kind of suck compared to the assymetric algorithms broken by quantum computers. + +There is hope, in the form of several assymetric cryptosystems not known to be vulnerable to quantum computers. Lattice-based crypto is promising. + +" +744 Are there ways to find caves with no real entrances and how common are these caves? 8737 https://www.reddit.com/r/askscience/comments/6b82qe/are_there_ways_to_find_caves_with_no_real/ 1494818553 6b82qe Earth Sciences 2017-05-15 6:22:33 "There are, many of them former from trapped gas pockets during volcanic eruptions, or groundwater eroding softer stone and then changes in flow leave the chamber intact but unreachable. + +There are several ways to find such voids, we can detect them by drilling when the bit drops unexpectedly, if they are close enough to the surface using ground penetrating radar, from orbit if they are large enough by temperature variances where none should be there, or using a technique to measure electrical resistance across a given section of dirt in areas with the right soil type and moisture content (the void space doesn't conduct electricity so the value is lower than a solid chunk)" "This reminds me of this cave in Romania that was undisturbed for millions of years. + +When they stumbled upon it they found a bunch of insects and the like that had evolved differently - because there was no light they were blind and had little or no colour to them, but their antenna were longer and more sensitive. + +Edit: The [Movile Cave](http://www.bbc.com/earth/story/20150904-the-bizarre-beasts-living-in-romanias-poison-cave)" +1031 How does a compass work on my smartphone? 8723 https://www.reddit.com/r/askscience/comments/8ju1bq/how_does_a_compass_work_on_my_smartphone/ 1526468803 8ju1bq Earth Sciences 2018-05-16 14:06:43 "With a device called a Hall Effect magnetometer, which is a solid state device that produces a voltage proportional to the strength of a magnetic field (such as the Earth's) along a particular axis. + +By having two sensors at right angles, the phone can determine its heading/direction relative to the Earth's magnetic field." "People have already explained how, so hopefully you don't mind me explaining why not to for precise measurements due to the phones limitations. + +This is a common debate amongst Geologists. In the field we generally use Brunton Compasses (one of the geological transit models) for their incredible accuracy. + +Lately many have been using their phones with compass apps because it's... ""Close enough"". + +The issue is you can easily be off a few degrees if your compass or phone is not perfectly level. The Brunton solves this by using a planar level for measuring bearing. The phone however does not have a particularly accurate digital level, and the level they do have isn't necessarily on the compass apps. + +Another point which is more of a measure of convenience is that you can manually adjust your compass to the magnetic declination of wherever you are at. Most phone apps don't have this feature so you'll have to add or subtract the value accordingly for each measurement. " +935 Do insects have muscles? If so, are they structurally similar to ours, and why can some, like ants, carry so much more weight than us proportionally? If not, what to they have that acts as a muscle? 8686 https://www.reddit.com/r/askscience/comments/86zoq9/do_insects_have_muscles_if_so_are_they/ 1521969179 86zoq9 Biology 2018-03-25 12:12:59 "Hi PhD Student here, specializing in insect muscle physiology. + +1. Insect muscles are actually strikingly similar to vertebrate muscles! But some insects that have very fast wing beat frequencies ( think bees, flies, some beetles) have specialized ""myogenic"" muscles. The major difference between these muscles and our own is that normally one nerve signal corresponds to 1 muscular contraction. But these insects have evolved specialized muscles for which one nerve pulse can initiate multiple contractions thereby increasing the contraction speed. + +2. Insects do seem to have proportionally stronger muscles, this boils down to a fundamental constrain on the power of muscles as they get larger. Usually a muscle's contractile force is limited by the cross section area of the muscle (this has to do with the number of sarcomeres acting together). So as a muscle gets wider the cross section area is pi*radius^2 (note the square on the coefficient). But as muscles get larger the mass of the muscle scales with the volume of the muscle (mass ~ radius^3). So as muscles get bigger the power scales to the square of the radius and the mass is proportional to the cube of the radius. This means that a small insect like an ant has a lot of power per small amount of muscle compared to a relatively larger animal like a human + +" As a physicist I can only argue that all smaller animals are proportionally stronger, since muscle strength depends on the crossection of the muscle, which scales roughly with the square of the size of the animal, while weight scales roughly with the cube of the size. Hence the smaller the animal the easier it is to be stronger in relation to it's body wheight. As to how their muscles are structurally different I don't know. +623 How can my portable battery charger drain itself completely when charging my phone? Shouldn't the two batteries come to equilibrium? 8684 https://www.reddit.com/r/askscience/comments/63mm0h/how_can_my_portable_battery_charger_drain_itself/ 1491409715 63mm0h Physics 2017-04-05 19:28:35 "Portable chargers and phones are not directly connected batteries. The portable charger has a boost converter, that takes the voltage (between 3 and 4v) from the internal battery(ies), oscillates it to create an alternating current that can be boosted in voltage using a coil, capacitor or both, and then it gets rectified back to DC at 5v (USB standard). + +(edit: in a discussion below, I'm corrected: the current is not alternating, is in fact pulsating DC. And therefore doesn't get rectified to 5v, it gets smoothed to reduce ripple) + +The phone, on the other side, takes the 5v from the USB input and steps it down to the required voltage to charge the internal phone battery. That varies according to the technology of the battery, the charge remaining in it, the charge speed the phone wants, and so on. + +When you connect two batteries directly, yes, they more or less reach an equilibrium, because as the most charged one (higher voltage) recharges the empty one, its voltage decreases as the other one's increases. When there is not enough difference of potential (voltage, in other words) to make the charge flow from one battery to another, they reach the equilibrium. + +In the portable chargers, the boost circuitry makes sure the output voltage is 5v as long as possible, of course by drawing more current from the lower voltage internal cells, because in both sides of the conversion circuit the power should be almost equal [ P = I * V ] (ignoring losses in the conversion). So the charger extracts more current from cells to generate those 5v the phone needs, and the phone as long as it haves the right voltage, can charge the internal battery, so eliminating the ""equilibrium"". + +I'm sure a lot of people can give a more detailed and strict answer, but this is the way I get it. + +PD: sorry for any mistakes, english is not my main language. Regards!" I always find it easy to think of electricity like water. In this situation you have two pools, the portable charger and the phone battery. If your phone pool is low then the circuit board in the charger acts like a pump that takes water out of the charger pool and pumps it into the phone pool. This allows it to take all of the water out of the charger pool and put it in your phone pool. This fills up your phone pool even to the point of being fuller than the charger. +936 How did they beam back live images from the moon before the invention of the CCD or digital sensor?? What device turned the image into radio waves? 8668 https://www.reddit.com/r/askscience/comments/88ps5i/how_did_they_beam_back_live_images_from_the_moon/ 1522576195 88ps5i Engineering 2018-04-01 12:49:55 "Back then they used a video camera tube to capture images. +The signal from that would be amplified and then modulated onto a carrier wave. + +The camera tube worked in a similar way to the picture tubes that used be in televisions. + +https://en.wikipedia.org/wiki/Video_camera_tube" "The same way it was done with other video transmissions at that time. Scan row by row, and keep everything analog. + +The most notable step (and Apollo-specific) was probably the frame rate conversion: Show the original video on a screen on Earth, and film this screen with a different video camera. + +[Wikipedia has an article](https://en.wikipedia.org/wiki/Apollo_TV_camera)" +506 If my voice sounds different to me than it does in a recording, then how am I able to accurately match my singing voice to the key of a song? 8657 https://www.reddit.com/r/askscience/comments/5lbfz5/if_my_voice_sounds_different_to_me_than_it_does/ 1483215140 5lbfz5 Biology 2016-12-31 23:12:20 "Your voice sounds different due to hearing it through your skull and bones rather than , like everyone else, solely through your mouth. + +None of this, though, changes the NOTES you produce. It changes the character of the sound, but not the actual frequencies comprising the sounds. It's like if you were to put a blanket over a stereo - it sounds different, but everything would still be in the same key. " "Everyone is mentioning pitch vs timbre. For those who know what Fourier Transforms are, what is pitch defined as in the frequency domain? + +Is it simply the frequency with the most power? Is it the mean power frequency? Or is pitch something more complicated than that? + " +937 On an atomic level, what causes things to be shiny, dull, or reflective ? 8641 https://www.reddit.com/r/askscience/comments/8a8d1g/on_an_atomic_level_what_causes_things_to_be_shiny/ 1523009751 8a8d1g Physics 2018-04-06 13:15:51 "I teach electrodynamics, and this is one of the things that is covered. + +There are many things at play here. + +First of all, all things will do a combination of reflect, transmit, absorb, and disperse when light is incident on them. The amount of each depends on a lot of properties. + +Before getting into that, let's first address diffuse vs specular reflection. When a surface is rough, any light it reflects will be in random directions. Thus, light tends to spread out - reflections are not obvious, and the surface seems duller. This is not because it is less reflective, though, ~~per say~~ per se. Specular reflection is caused by smooth surfaces. When a smooth surface reflects, all of the rays typically follow the law of reflection, and remain collimated from their source. This allows you to see an image in the reflection, and thus the brain interprets this as more reflective. + +All material interfaces produce some reflection. From an electrodynamics perspective, light is an electromagnetic wave. When the EM field of the wave interacts with the electrons in the material it is entering, it produces an oscillating polarization. This, in turn, radiates the electrodynamic wave backwards (reflection) and produces the known ""slowing"" of light as it transmits in the material. (A naive look at this would be to claim it is ""boundary conditions"" that produce the reflection, but that is just a mathematical approach rather than the underlying physics.) + +The amount of reflection depends on a lot of different properties of the material: + +- The more mobile the electrons on, are the more the EM wave interacts with them. Conductive materials have a very high reflectance as a result, since they have much more mobile electrons. This is why silvering is used on the back of mirrors (it is not the glass that produces the reflection, the glass is simply used to make it easy to produce a smooth surface for specular reflection). + +- The higher the angle of incidence, relative to the normal to the surface, typically results in greater reflection. This is especially true if the index of refraction is lower in the transmitting material (hence total internal reflection). + +- Resonances with the material can influence all 4 behaviours of light at an interface. To a first approximation, all binding states can be treated as simple harmonic oscillators - the electrons are bound to the nuclei, and if we disturb them slightly (as with an incoming EM field), then they will oscillate. If they are oscillated at a natural frequency, the energy of the incoming EM wave will be absorbed at a higher rate (and converted to internal forms of energy, or radiated dispersively - in all directions rather than reflected/transmitted directions). + +If you have a grasp of the math involved in physics, check out Griffiths' Electrodynamics text. While not the most mathematically rigorous, or educationally helpful text, it does have decent descriptions and can help convince people that they understand (whether they do or not). Chapter 9 is all about electrodynamics waves. + +Edit: I don't use the phrase ""per se"" very often. My misspelling of it shouldn't detract from the rest of what I have said. I am a physicist who has never taken Latin." Metals are shiny because they have a layer of free or delocalized electrons on their surface. When light hits the surface of such a metal it causes these electrons to oscillate in phase with the light that is hitting it and thus causes the metal to appear shiny. +938 How did Voyager 1 send back images of earth? Film or digital?! lt always bothers me 8630 https://www.reddit.com/r/askscience/comments/804nbp/how_did_voyager_1_send_back_images_of_earth_film/ 1519567848 804nbp Engineering 2018-02-25 17:10:48 The Voyager spacecraft were equipped with Vidicon cameras. These cameras operated by scanning a photosensitive plate with a cathode ray tube and recording the differences in charge density. This is an analog technology, but the images could be stored on the spacecraft's tape memory and transmitted by radio. "Although Voyager 1 didn’t use this method, there was actually a US satellite program that did drop canisters of film back to earth. The Corona Program was a reconnaissance program which ejected film canisters from the satellite, which were then “caught” during re-entry by planes with special hooks. + +https://en.m.wikipedia.org/wiki/Corona_(satellite)" +1310 Are there any (currently) unsolved equations that can change the world or how we look at the universe? 8578 https://www.reddit.com/r/askscience/comments/clsjm0/are_there_any_currently_unsolved_equations_that/ 1564894658 clsjm0 Physics 2019-08-04 7:57:38 "We still don't know how big of a couch we can get around a corner. + + [https://en.wikipedia.org/wiki/Moving\_sofa\_problem](https://en.wikipedia.org/wiki/Moving_sofa_problem) + +Think of the possibilities if we found the sofa constant. We could have bigger sofas. And they'll probably be weird shapes." "What first comes to mind are the [millenium problems](https://en.wikipedia.org/wiki/Millennium_Prize_Problems): 7 problems formalized in 2000, each of which has very large consiquences and a 1 million dollar bounty for being solved. Only 1 has been solved. + + +Only one I'm remotely qualified to talk about is the Navier-Stokes equation. Basically it's a set of equations which describe how fluids (air, water, etc) move, that's it. The set of equations is incomplete. We currently have approximations for the equations and can brute force some good-enough solutions with computers, but fundamentally we don't have a complete model for how fluids move. It's part of why weather predictions can suck, and the field of aerodynamics is so complicated." +624 Discussion: Kurzgesagt's newest YouTube video on GMOs! 8555 https://www.reddit.com/r/askscience/comments/62e54o/discussion_kurzgesagts_newest_youtube_video_on/ 1490882750 62e54o Biology 2017-03-30 17:05:50 "There was a point about the American chestnut tree being great at carbon fixing, and how GMO trees could be used as a carbon dump. + +What sort of genetic modifications need to happen here, and have there been studies on how this could be deployed? Would these trees have to be grown from terminator seeds in order to prevent the GMO chestnut from wreaking havoc? + +And, as weird as this question may be, has the ecological impact of planting a fuckton of one tree been studied? Are there any field tests?" "At 7:55 he mentions that the world eats 11 million pounds of food every day. Is that a mistake? I haven't seen any other comments address this but surely the quantity would be much larger. + +Unless I'm mistaken that would mean each human eats only 0.0015 lb of food to sustain themselves per day." +745 Does what my mother ate while she was pregnant with me effect what I like/don't like to eat? 8543 https://www.reddit.com/r/askscience/comments/6n9s3m/does_what_my_mother_ate_while_she_was_pregnant/ 1500046514 6n9s3m Human Body 2017-07-14 18:35:14 "Just a reminder that /r/AskScience aims to provide in-depth answers that are accurate, up to date, and on topic. + +In particular anecdotes are not permitted, especially as a top level comment. **This is not the right subreddit to discuss what your mom ate when she was pregnant.** So far we have had to remove about 75% of the comments for being along the lines of ""I don't like oysters"" and ""my mom ate PB&J sandwiches"". + +You can help the moderation team by reporting anecdotal and other rule breaking comments. " "At least for infants, it's the opposite. + +Babies have shown preference to foods their mother ate while they were in utero and being breastfed. + +http://www.npr.org/2011/08/08/139033757/babys-palate-and-food-memories-shaped-before-birth + +However, how flavors taste to you may be partially controlled by genetics. So regardless of what your mother ate, if your father can't stand the taste of oysters, you may hate them as well. + +http://www.supermarketguru.com/articles/are-food-preferences-inherited-or-learned.html" +1402 Does a fully charged cell phone have enough charge to start a car? 8542 https://www.reddit.com/r/askscience/comments/d31uje/does_a_fully_charged_cell_phone_have_enough/ 1568257889 d31uje Engineering 2019-09-12 6:11:29 "Most phones have about a 3000mAh battery, Those charges are energized up 3.6 volts (give or take), which means the battery can supply 10.8 Watt hours. See as a Watt is Joules per second, and there are 3600 seconds per hour 10.8 joules/second \* hours \* (3600 seconds/hour) = 38,880 Joules of energy. Lets just call it 38 kJ of energy. + +​ + +So, how much energy does it take to start a car? Lets say you're car is nice and new, so you might need to run the starter motor for half a second. Your battery should be charge to 12.6 volts. But how much current will the starter draw? A hell of a lot is the answer. The inrush current to a starter motor might be 700 amps, and then settle to about 200 amps. But lets average it out at 400 Amps for half a second, at 12.6 volts. So 12.6 volts \* 400 Amps = 5 kW, for half a second is 2.5 kJ. + +Really? I'm shocked by that. So it seems your cellphone battery does have enough energy. + +However, you couldn't do it directly. Different batteries have different ""C"" ratings, which decide how much current they can pass without risking blowing up, and I expect the C rating on cell phone batteries is quite low. Which is to say, the cell phone battery can't supply the 200-700 Amps you need to spin the motor. Furthermore, and more fundamentally, your cellphone battery is too low a voltage to get the motor moving. So you would need to have a circuit that probably was composed of a DC/DC converter, that boosts the voltage of your phone battery, and then 6 or so super capacitors to store the energy that your phone battery trickle into them. I reckon your phone battery can probably supply about 1 amp of current max, \[totally guessing that number\] at 3.6 volts, which is 3.6 watts, or 3.6 joules per second. So in order to charge up this hypothetical device to 2.5 kJ of energy it would take 700 seconds, or 11 minutes. Give or take. And this is all assuming your car starts in half a second, and 100% efficiency. In reality, it might take a good second or two, and you'd be lucky to get 80% efficient. In which case it might take over an hour. + + +So, TLDR: Most modern cell phone batteries have enough energy to start a typical car motor, certainly at least a couple times, but they can't supply enough current at a high enough voltage to do it. You might be able to build a device that could allow your cellphone battery to start your car, but it would take a bare minimum of 11 minutes, and perhaps as long as an hour, for your phone battery to charge the device." "/u/NeuroBill seems to have it right, yes, a cellphone battery has enough *energy* to start the car. But the problem is that the cellphone battery is: + +a) The wrong voltage. + +b) The wrong 'C' rate. (IE, it can't put out 100's of Amps like a car battery can.) + +These things are possibly correctable via use of a DC-DC converter and a bank of super capacitors; but those are kind of specialty components, even today. + +... + +But if your question was, ""Can I rig this like MacGyver?"" the answer is, ""No, probably not.""" +837 How does boiling water clean it? What can it NOT clean? 8537 https://www.reddit.com/r/askscience/comments/6zfbtz/how_does_boiling_water_clean_it_what_can_it_not/ 1505135812 6zfbtz Chemistry 2017-09-11 16:16:52 "If you boil water, you'll kill most pathogens living in it. +Dissolved chemicals or particulates will remain, so if you boil brown water it'll still be brown. If whatever is making the water brown happens to be a toxin drinking the boiled water is still inadvisable. + +However, you can use boiling the water to clean it. Catch the steam, let it condense and have some clean water. + +We don't do that generally because it's a rather arduous process and it consumes a lot of energy." "Boiling water doesn't ""clean"" it. It does, however, kill certain harmful bacteria, which results in water that is safer to ingest." +838 What exactly does the cold virus do to me to make me so weak? 8522 https://www.reddit.com/r/askscience/comments/7innjm/what_exactly_does_the_cold_virus_do_to_me_to_make/ 1512836640 7innjm Human Body 2017-12-09 19:24:00 Specifically, the cause of the crummy feeling is due to your innate immune system cells, like macrophages, detecting foreign materials and releasing cytokines to call attention from more and more immune cells (this starts the inflammation response). Some types of cytokines are specifically responsible for triggering the brain to make you sleepy, sore, and have a fever. Here's a great little video with a little more detail: https://youtu.be/gVdY9KXF_Sg "The fatigue is likely caused by fever. In response to an infection with a cold-causing virus, your immune cells begin to secrete cytokines that cause both localized inflammation and a full-fledged immune response from the rest of the body. Chemokines like Interleukin-1 (IL-1) and IL-6 are considered major endogenous (meaning they are produced by your own body) pyrogens (molecules that cause fever). + +In addition, other endogenous molecules are also produced that aid in inducing a fever. IL-1 and IL-6 can both activate the [arachidonic acid pathway](http://www.cvphysiology.com/Blood%20Flow/BF013), which ends in the synthesis of Prostaglandin E2 (PGE2). PGE2 is a major regulator of the febrile response and acts on the hypothalamus and other areas of the brain, which induces shivering to create heat, constriction of blood vessels to prevent heat loss, and can also cause the release of adrenaline. + +The virus itself can cause tissue damage, which further exacerbates inflammation in the area of the infection. Not all viruses that cause colds replicate through the same mechanism: some are lytic and others are lysogenic. Lytic viruses like rhinoviruses rupture cells once the infected cell reaches its burst size. The insides of the cell can trigger inflammatory signals from neighboring cells as well, further exacerbating the immune response. Lysogenic viruses such as coronaviruses tend to bud or undergo exocytosis from cells, and the immune response to these is somewhat dampened by the lack of damage-associated molecular patterns (DAMPs) that would trigger inflammation from nearby cells. + +Unfortunately, from what I can find it's not totally clear what it is about fever or inflammation that causes lethargy, though I would speculate it likely has to do with the modulation of the [autonomic nervous system](https://en.wikipedia.org/wiki/Autonomic_nervous_system) by prostaglandins." +939 A tidally locked planet is one that turns to always face its parent star, but what's the term for a planet that doesn't turn at all? (i.e. with a day/night cycle that's equal to exactly one year) 8497 https://www.reddit.com/r/askscience/comments/7uu1qo/a_tidally_locked_planet_is_one_that_turns_to/ 1517601630 7uu1qo Astronomy 2018-02-02 23:00:30 "Non-rotating? + +We don't really discuss such things very often because it's not a stable situation--the orbit around the star will result in a tidal force that imparts a torque to the planet, causing it to start rotating. A planet that's rotating counter to the direction of its orbit, like Venus, can be expected to eventually have zero rotation (unless, as may be the case with Venus, tidal effects from other planets counteract this), but its rotational speed would only be exactly zero for an instant, as this would be a continuous process of angular acceleration." "There are no examples of this as far as I’m aware, every object in space rotates. + +You could examine the orbit of Uranus, which rotates on its side, producing a relatively similar effect. The poles get sunlight for half a year, and then no sunlight for the other half. " +746 Why do some people have good sense of direction while other don't? Do we know how the brain differs in such people? 8492 https://www.reddit.com/r/askscience/comments/6q31lw/why_do_some_people_have_good_sense_of_direction/ 1501239244 6q31lw Neuroscience 2017-07-28 13:54:04 "Hello, and welcome to askscience! + +Before you comment, please ask yourself, ""Can I back up what I'm about to type with peer reviewed science?"" + +If the answer is yes, then please do. If not, then you probably have an anecdote or speculation, which will be removed. +" "This article explains it pretty well. It's like language, we are born with the ability and the amount of time we spend on tasks that use sense of direction directly influences how developed or underdeveloped our directional awareness becomes. There's a lot of cool ethnographic research about sense of direction. We use egocentric coordinates that depend on where we are...but many cultures describe where they are and how to get places using fixed geographic locations....that requires them to basically have a compass updating constantly in their brain. I wouldn't quote me on the exactness of these details because I read this quite a while ago in a cultural anthropology textbook, but some cultures have such a highly developed sense of direction that anyone can be taken out into the woods blindfolded at night and spun around a bunch of times and still know exactly what direction they were facing when the blindfold came off....really cool stuff. +Hope that helps! + +https://www.brainscape.com/blog/2015/06/humans-innate-sense-of-direction/ + +UPDATE: This is the article that was in my textbook and the part about language and space is almost toward the middle of the page...right below the graphic with all the mouths + +http://www.nytimes.com/2010/08/29/magazine/29language-t.html" +625 What is the smallest amount of matter needed to create a black hole ? Could a poppy seed become a black hole if crushed to small enough space ? 8483 https://www.reddit.com/r/askscience/comments/5t7b51/what_is_the_smallest_amount_of_matter_needed_to/ 1486734039 5t7b51 Physics 2017-02-10 16:40:39 "black holes must be significantly heavier than the Planck mass M_P, which is about 22 μg. Anything quite heavier can form a (extremely short-lived unless it is really heavy) black hole, while anything quite lighter cannot. So yes, poppy seed is good, *E. coli* bacterium doesn't work. + +Imagine you have an object lighter than M_P and you're trying to compress it to inside its Schwarzschild radius, which is smaller than the Planck length l_P. In fact, ignoring some pesky numerical factors, you have the formula + + M / M_P ~ R / l_P + +where R is the Schwarzschild radius of the mass M, the radius in which you'd have to compress M to make it a black hole. Since at the length scale of l_P smooth classical spacetime stops existing to give way to a quantum foam, for R to be smaller than l_P sounds already fishy. + +But you try anyway. What you find is that well before your compressing mass even reaches the Planck length, in compressing it you have already given it a lot of energy, which increases its mass (through E = Mc^(2)). In the end, it turns out you have made it into a black hole with M >> M_P and R >> l_P. " If you condensed a poppy seed down to a black hole then took an open palm swat at it, what would happen? Could you move it, would it be so dense it goes through your hand? Would the mysterious forces of gravity make your hand explode? +1032 Why is it that some muscles «burn» while exercised hard, while in others you experience more of a fatigue-like feeling? 8478 https://www.reddit.com/r/askscience/comments/90ydcj/why_is_it_that_some_muscles_burn_while_exercised/ 1532272181 90ydcj Human Body 2018-07-22 18:09:41 "**On crunches and 'the burn':** + +Accumulation of metabolic waste product. When doing an exercise with a muscular metabolic demand similar to crunches (high rep pushups and squat jumps would be similar), the limiting factor is metabolic waste product buildup. The 'burn' you feel is the accumulation of metabolic waste (particularly lactic acid) from the chemical reactions making your muscles 'go'. At this exercise intensity, you are operating at a rate of power where your muscles are accumulating metabolic waste products faster than that waste can be pumped out and excreted or processed. Think of the burn you feel as a warning alarm, and the point where you can't do any more reps like your body hitting the emergency shut-off switch so you don't damage your muscles with excess waste buildup. + +*(Interesting anecdote: prey animals such as horses and rabbits have been known to 'run themselves to death,' as they seem to not have the same biophysiological safegaurds as humans in terms of the 'emergency stop' response to metabolic waste buildup. Only time I've heard of a human doing that was the first ancient Marathon.) + +**On pullups and acute fatigue at high-maximal power output:** + +Because each rep requires substantially more force and power than each rep of, for example, crunches, the limiting factor here is creatine-phosphate (CP) availability. You may have heard of 'creatine' in nutritional supplements; basically what creatine does is hold onto a phosphate, so when you break down adenosine-triphosphate (ATP) for energy, that creatine is waiting hooked up to a spare phosphate molecule to donate to spent adenosine-diphosphate (ADP), thus quickly and rapidly replenishing ATP for energy. + +However, creatine is limited within the muscle, so once you've used up all of the creatine-phosphate 'donations', you're just out and can't produce power at the same capacity anymore until you allow some recovery time for the now free creatine molecules to pick up free phosphate molecules so they're ready to be again donated to ADP. It takes roughly 10-20 seconds operating at maximum power to exhaust the vast majority (I don't remember the percentage off the top of my head) of your creatine-phosphate within a given muscle. Once this happens, you suddenly feel your muscles being unable to produce the required force for a movement, which is where the ""my arms just stop moving"" sort of feeling comes from. + +However! if you were to immediately jump off the pullup bar after a set and swap to a lower-resistance exercise using the same muscle groups (e.g. pulldowns, rows, etc.) you could continue operating with less force and power until you begin accumulating metabolic waste products in those muscle groups and get the 'burn'. + +**Source**: National Strength and Conditioning Association (NSCA) 'Essentials of Strength Training and Conditioning,' Third Edition; Editors: Thomas R. Baechle, Roger W. Earle + +**Personal Credentials**: B.S. Kinesiology; American College of Sports Medicine Certified Personal Trainer (ACSM CPT); National Strength and Conditioning Association Certified Strength and Conditioning Specialist (NSCA CSCS); 5 years work experience in the fields of fitness, strength and conditioning, and physical therapy. + +_______________________________________________________________________________ + +**EDIT**: Here's a further breakdown of metabolic physiology! + +**Immediate phophagen**: The previously mentioned creatine-phosphate donation system. Provides majority of power for the first 10-20 seconds of activity at high-maximal power output. Requires 3-5 min for recovery. *This reaction does not require oxygen. + +*Adaptaion mechanisms*: Increase in muscle cross-sectional area; shift of muscle fiber type towards faster-twitch glycolytic type (these fibers are actually whiter in color due to less blood demand) + +*Examples of activity with high phosphagen demand*: 40-100 yard dash, set of 5-15 reps of resistance training + +**Glycolytic system**: This system functions on the reaction of glycolysis within the cell cytoplasm. This chemical reaction replenishes ATP relatively quickly, but still more slowly than the phosphagen system. Glycolytic reactions create a byproduct of lactic acid (among other byproducts; citation needed), which can be cycled out and processed by the liver (if I recall correctly) or processed and used within the cell for aerobic respiration if the activity is at a low enough intensity. At high intensities, waste products from glycolysis accumulate and cause a burning sensation and eventual lack of muscular function until said waste products can be cycled out. *This reaction does not require oxygen. + +*Adaptation mechanisms*: Increased cytoplasmic glycolysis enzymes, shift of muscle fiber type towards faster-twitch glycolytic type (these fibers are actually whiter in color due to less blood demand) + +*Examples of activities primarily utilizing glycolysis*: 400 meter run; maximal set of pushups or other calisthenic exercise for trained individuals + +**Aerobic respiration**: Lastly, aerobic respiration. This is the process which is likely dominant right now as you're comfortably sitting at a computer screen operating at a low power output. If operating at a low enough power output, lactate from the aformentioned glycolysis reactions can be cycled to the mitochondria to be processed through the elector transport chain for ATP resynthesis. I'm not gonna get into the nitty gritty of all of these reactions, but aerobic respiration is more energy efficient than glycolysis, but a much slower process. Thus, aerobic respiration is the default mechanism used to supply energy at rest or at lower intensity/high duration activity (e.g. distance running) + +*Adaptaion protocol*: Increased capillary density, increased mitochondrial density, shift of muscle fiber proportion towards slower-twitch aerobic type (these fibers are more red in color due to increased capillary density.) + +*Examples of activity primarily utilizing aerobic respiration*: running >1 mile, hiking, average pace over the course of a workout, resting state + +**Disclaimer**: I work in the field; not academia. As such I do not remember every single reaction, its components, and its products and byproducts. This breakdown is intended for an audience of educated laymen outside the field of exercise physiology. Experts on exercise physiology, please feel free to elaborate on any of my points!" "Your body cheats its way out of uncomfortable situations when it can. Working a muscle so hard that it burns is one of those situations. + +When you do a compound movements like chin ups (more than 1 muscle group involved, biceps, lats etc) your body can switch between how hard it taxes each of those. If it feels your biceps are getting too tired during chin ups it just won’t rely on them that much. Also compound movements use different muscles to a different extent during different parts of the lift. The bottom part of the chin up might be the easiest for the biceps but hardest for the upper back muscles. In the top in might be the opposite, but you won’t get to the top if your lats are too tired so you won’t train your biceps as much that’s why they don’t burn. + +Crunches are ab isolation exercise. This means your body doesn’t have a choice but to use only your abs, and this makes it easier to overload it to a point when it burns. If you do a leg raise or something you probably won’t feel the same burn even though it’s also an ab exercise, but it is limited by hip flexor strength. +Alternatively if you do bicep curls you will feel the same burn in your biceps. If you do a lat isolation exercise you will feel the same burn in your lats etc. + +Experiences lifters will be able to force these ‘burns’ even in compound movements but it takes more mind muscles control. Otherwise the body will just pick the path of least resistance. " +1033 When the mars rover went to mars were they able to remove all bacteria and small life from it? If not could any of the bacteria be able to live in the harsh conditions of mars? And how do they obtain soil samples looking for bacteria if it could possibly be from the rover itself? 8456 https://www.reddit.com/r/askscience/comments/8gw1g2/when_the_mars_rover_went_to_mars_were_they_able/ 1525402133 8gw1g2 Astronomy 2018-05-04 5:48:53 "Anything that is sent to Mars is thoroughly inspected, cleaned, and sanitized {[marsmobile.jpl.nasa.gov](https://marsmobile.jpl.nasa.gov/msl/mission/technology/insituexploration/planetaryprotection/)}. There are some microorganisms that can still survive a trip to Mars, such as a well-known [Tardigrade (Wiki)](https://en.m.wikipedia.org/wiki/Tardigrade). That's the main reason rovers avoid parts of the planet that contain water or ice - they can still carry Earth's life and contaminate it {[sciencealert.com](https://www.sciencealert.com/here-s-why-nasa-s-mars-rovers-are-banned-from-investigating-that-liquid-water)}. + +So far all life-detecting tests done by rovers are interpreted as negative. If we find a sign of life on Mars, we will make sure it's not brought by us from Earth. + +**Edit: Answering a few questions that keep repeating.** + +> *Why do we refrain from contaminating Mars? Wouldn't that be an interesting experiment?* + +It would be, but before we do that, we want to make sure there is no native life on Mars that we might accidentally destroy (as we often do). If we find micro-organisms there, it would be nice to study them without our own organisms getting in the way wherever we go. + +> *Wouldn't a manned mission contaminate Mars?* + +It will. Before we can send humans to Mars we will have to modify the rules of the Outer Space Treaty. Hopefully we can find life there before we send humans. If not, hopefully the first humans will find life. If we don't, it's pretty clear there is no life there. But we will not be colonizing and terraforming Mars until this question is answered. + +> *Shouldn't we search for life in water-rich zones, instead of the opposite?* + +Yeah, ideally we should, but because our rovers are not 100% clean, letting invasive life forms flourish in Mars's potentially already living waters, before we have a chance to at least send a few of them back to us, is just not worth it. On top of that, we don't need to check water contents to determine if Mars has life - the atmosphere and soil can give us enough clues to answer that. + +> *Don't we have the technology to sterilize things to 100%? Or are we that neglectful?* + +We do have the technology, and we can use it with ease. The problem is that if you want to sterilize a circuit board, you end up frying it. One proposed idea is to build a rover on Mars with 3D printers, and sterilize all the necessary materials separately." "I actually wrote my thesis along these lines + I was studying Antarctic yeast species, which live in cold, dry environments and are exposed to incredible amounts of uv radiation. In other words, very similar conditions to space. Numerous studies have found that they in fact can survive in space, so it's entirely possible that other microbes could survive the trip to Mars. The yeast I studied ate rocks, do they may even be able to reproduce on Mars as well. We try to sanitize most stuff that gets sent to space, because on the off chance there is native alien life ( bacteria and what not) we don't want to accidently kill it off with an invasive species" +747 Can statisticians control for people lying on surveys? 8426 https://www.reddit.com/r/askscience/comments/6u2l13/can_statisticians_control_for_people_lying_on/ 1502895539 6u2l13 Mathematics 2017-08-16 17:58:59 "Some schools when giving out surveys like ""have you ever tried *random drug*"" or ""Do you know anybody that has self harmed"" will have a question like ""have you ever tried *fake drug*"" and if the answer to that one is yes, then your survey is thrown out. That reduces the results from people who don't want to to take the survey and are just messing around." "Yes. It's easier to do in a large (read: lots of questions) assessment. But we ask the same question a few different ways, and we have metrics that check that and we get a ""consistency score"" + +Low scores indicate that people either aren't reading the questions or they are forgetting how they answered similar questions (I.e., they're lying)." +626 "A bluish aurora-like streak informally called ""Steeve"" has been recurrently spotted int the night sky of the Canadian prairies - what might it be, and how could this phenomenon be investigated?" 8424 https://www.reddit.com/r/askscience/comments/67nvw2/a_bluish_auroralike_streak_informally_called/ 1493210809 67nvw2 Planetary Sci. 2017-04-26 15:46:49 "If I recall correctly, current working hypothesis is that it's a flow channel of gas that is moving much faster than the surrounding gas and is hot enough that it glows. I don't think we have a hypothesis for what causes the enhanced flow. I will see if I can talk to someone who would know and will report back. + +Source: was at Eric Donovan's talk at SWARM conference" "As /u/1976dave mentioned, SWARM might be a good way to study it. SWARM is a European Space Agency satellite constellation (3 separate satellites flying together) that measures the Earth's electric/magnetic field. + +Edit: the reason I say SWARM could elucidate this phenomenon is that it has actually already measured it. The article is missing the actual data plot but SWARM measured a big change in the field as it passed through Steve. + +http://m.esa.int/Our_Activities/Observing_the_Earth/Swarm/When_Swarm_met_Steve" +839 If I am made from star dust, how many stars do I come from? 8419 https://www.reddit.com/r/askscience/comments/79vir0/if_i_am_made_from_star_dust_how_many_stars_do_i/ 1509454404 79vir0 Astronomy 2017-10-31 15:53:24 "[;N\geq2;] + +The exact number is unknowable without knowing the entire history of this part of the galaxy, which we can't. Based on the recent LIGO/VIRGO discovery with the NS-NS collission creating the r-process elements we know that whatever molecular cloud gave birth to our system had to be enriched from such a collission to have the abundance of r-process elements we see. It's possible that we are the results of the supernova of those two stars and then their subsequent merger alone in which case you'd be the result of 2 stars. It's more likely that there are traces from multiple supernova and possible even multiple mergers. " Is there a minimum amount of stars though? From what little I understand, not all the elements come from same star types, and humans contain several elements. So what is the minimum amount of stars needed to create all the necessary elements? +1217 What actually is the dial up internet noise? 8395 https://www.reddit.com/r/askscience/comments/b4d2dd/what_actually_is_the_dial_up_internet_noise/ 1553303137 b4d2dd Computing 2019-03-23 4:05:37 "Everything you need to know about the acoustic modem handshake can be found here on this map: https://oona.windytan.com/posters/dialup-final.png + +Then you can listen to the actual handshake and follow along: +https://www.youtube.com/watch?v=abapFJN6glo + +Yes, this is what network engineers still do with packet sniffers and other protocol analyzers on various types of layer 2 networks like ethernet, PPP, MPLS.. etc." "Computers use electrical signals to establish connections. Phones take electrical signals and turn them into audible noise ( sure, when sending they also take audible noise and turn it into signals as well ) so what you HEAR is simply the audible representation of the signals sent to establish a connection. + +​ + +Computers still 'negotiate' the same sorts of details ( at heart ) when making connections today. Its just that we do not do this over phone lines so we would have to design and engineer a new device or system just to play noise as phone modems used to do. + +​ + +I say this to highlight that us hearing dial up modems at all was a convenient coincidence to provide live-feedback ( think audio progress bar ) of the process. Modems making noise was never a designed engineering goal, but more so taking advantage of a convenient opportunity to provide live-status of the establishment of the connection. + +​ + +Keep in mind we are spoiled now by solid stable reliable connections. Back in modem-days phone lines kinda really sucked, in comparison to what we have now. Outages and drops were, comparatively, extremely common. Having the modem play noise gave you immediate information on the quality of the connection too - almost diagnostic in a way. + +​ + +​" +1218 Can you use a regular compass on Mars? 8379 https://www.reddit.com/r/askscience/comments/b0d7in/can_you_use_a_regular_compass_on_mars/ 1552425347 b0d7in Planetary Sci. 2019-03-13 0:15:47 "I suppose you mean if a compass can be used to find geographic north? No, though your compass will be able to show the local direction of some of the strongest crustal fields, which are estimated to measure at most about 15,800-19,900 nT at the surface (/u/photonsource's value of 1500 nT was measured in orbit). + +Source: [Brain et al. (2003) Martian magnetic morphology: Contributions from the solar wind and crust, *Journal of Geophysical Research*, doi:10.1029/2002JA009482](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002JA009482). + +Outside of crustal fields, a more sensitive compass (science-grade magnetometer) might be able to sense the induced magnetosphere, which will change orientation depending on the upstream interplanetary magnetic field. Currently, we don't know if that's the case, but we're hoping to find out when the first results from the magnetometer on the InSight lander are released." Hm, this brings up some interesting spin-off questions, are there many planets that have a significant magnetic field/mineral deposits that would make a compass usable? Would the magnetic pole most likely be at the north or south pole, or could it be along the equator? Are us earthlings just lucky that we ended up with a magnetic north pole that's very close to the true north pole? +748 Hummingbirds flap their wings around 70 times per second during normal flight...what is the fastest natural movement that humans are capable of, either voluntary or involuntary? 8355 https://www.reddit.com/r/askscience/comments/6f7p0m/hummingbirds_flap_their_wings_around_70_times_per/ 1496587723 6f7p0m Biology 2017-06-04 17:48:43 The National Science foundation released an article on the fastest articulated motion a human can execute, which is throwing. When an arm is cocked back it can store a lot of energy which is then released during a throw. The finger tips can reach over 100mph. A hummingbird flapping at 70 times per second with wing chord of 40mm and assuming it flaps in half a circle would have an average speed if 8796mm per second or about 20mph. "[The Guinness world record for drumming is 1208 strokes in a minute, or just over 20 per second.](https://www.youtube.com/watch?v=Q9FrW-Wr-ds) + +[For guitar the record is faster, about 2000 notes per minute, or about 33 per second.](https://www.youtube.com/watch?v=CSaRWt4cxao) + +[The world record for tap dancing is 1163 taps in a minute, a bit over 19 per second.](http://www.guinnessworldrecords.com/world-records/tap-dancing-most-taps-in-a-minute/) + +[I was able to click a button on my keyboard 70 times in ten seconds, or about 7 times per second.](https://scratch.mit.edu/projects/27310194/) + +What about what humans can perceive? [We begin to lose the ability to distinguish sounds at around 10 sounds per second, and at around 20 the sounds blend together into a low-pitched noise.](https://www.youtube.com/watch?v=h3kqBX1j7f8) + +[24 frames per second is a pretty standard frame rate for video, and most people perceive such video as continuous motion.](https://en.wikipedia.org/wiki/Frame_rate)" +1311 What effect does Viagra have on a [biological] female? 8352 https://www.reddit.com/r/askscience/comments/c2tl67/what_effect_does_viagra_have_on_a_biological/ 1561020421 c2tl67 Human Body 2019-06-20 11:47:01 Due to a high volume of rule breaking comments, this thread is locked. "Viagra is prescribed to women all the time under its other common market name - ~~Rovatio~~ Revatio . It's mostly a semi-specific vasodilator so it's used to treat pulmonary hypertension and right heart failure. There is no special relationship between the penis and Viagra other than the penis has blood vessels. + +EDIT: Now that I have more time and a real keyboard. Viagra is also a fairly potent performance-enhancing substance for endurance sports. For one of my research rotations, we tested it in a group of athletes that included men and women. We eventually stopped calling it Viagra and just said sildenafil because the guys wouldn't stop making jokes and the women got freaked out and either dropped from the study or it affected the results. In both men and women, it improved performance about the same amount, they both felt accelerated heart rate over what they typically experience at those intensities, flushing in the face and neck, and lightheadedness after the tests. None of the subjects reported sexual side affects (we specifically asked)." +1034 If there was a bag of 10 balls, 9 white and 1 red and 10 people including you has to pick one randomly and who gets the red ball wins, does it matter what order you all pick, or is it better to go first or last with probability? 8322 https://www.reddit.com/r/askscience/comments/8qqp7v/if_there_was_a_bag_of_10_balls_9_white_and_1_red/ 1528877048 8qqp7v Mathematics 2018-06-13 11:04:08 "It doesn't matter. + +The first person to pick has a 1/10 (10%) chance to win. So he has a 9/10 (90%) chance to not win. That means that the second person to pick has a 9/10 (90%) chance to get his turn (which only happens if person 1 doesn't win), but if he gets his turn he has 1/9 (~11.11%) chance to win. That means his total chance to win is 9/10 * 1/9 = 1/10 (10%). + +Person 3 only gets his turn if both 1 and 2 don't win. That means that the chance that he gets his turn is equal to 1 minus the chance that either player 1 or player 2 wins. That means: 1 - (1/10 + 1/10) = 8/10 (80%). At that point, he has a chance of 1/8 to pick the correct ball, so his total chance of winning is 8/10 * 1/8 = 1/10 (10%). + +You can extend the same line of reasoning for the other players and find the same outcome, 10%, for each." "the probability of final result is the same regardless of what order you go in + +however it's _feels_ like the probabilities are different because _if_ you reveal the outcomes as you go, the likelihood of someone now pulling out the red ball _given that_ the last X were white _does_ change as you go along + +e.g. initial likelihood of anyone getting the red ball regardless of order = 10% + +but say _given that_ the first 8 people pulled out white, the 9th person to go now has a 50% chance of pulling red + +if they pull white, the final person now has 100% chance of pulling red + +however everyone had a 10% chance to start with regardless of order" +840 What have been the implications/significance of finding the Higgs Boson particle? 8312 https://www.reddit.com/r/askscience/comments/71uou2/what_have_been_the_implicationssignificance_of/ 1506121473 71uou2 Physics 2017-09-23 2:04:33 "The particle itself was never of any particular relevance, except for potential weeding out potential grand-unified theories. The importance of the discovery of the boson was that it confirmed that the Higgs FIELD was there, which was the important thing. For about the last 50 years, particle physics has constructed itself upon the un-verified assumption that there must be a Higgs field. However, you can't experimentally probe an empty field, so to prove it exists you must give it a sufficiently powerful ""smack"" to create an excitation of it (a particle). + +So the boson itself was pretty meaningless (after all, it was at a pretty stupid high energy). But it confirmed the existance of the Higgs field and thus provided a ""sanity check"" for 50 years of un-verified assumption. + +Which for particle physicists was something of a bittersweet sigh of relief. Bitter because it's written into the very mathematical fabric of the Standard Model that it must fail at SOME energy, and having the Higgs boson discovery falling nicely WITHIN the Standard Model means that they haven't seemingly learned anything new about that high energy limit. Sweet because, well, they've been out on an un-verified limb for a while and verification is nice." "It also wasn't the ""god"" particle, it was the ""god damn"" particle. Physicists were having such a difficult time proving it existed, it was that god damn particle but when people started getting excited about it, it obviously couldn't be printed/discussed with that moniker so it was shortened to the god particle. " +1219 Why are marine mammals able to keep their eyes open under water without the salt burning their eyes? 8293 https://www.reddit.com/r/askscience/comments/b1x6xr/why_are_marine_mammals_able_to_keep_their_eyes/ 1552769565 b1x6xr Biology 2019-03-16 23:52:45 "Somewhat related, human children can actually train their eyes to be able to see clearly underwater! This was first observed in the Moken people of Thailand who spend a large amount of time diving for shellfish, but was replicated in European children who underwent training. The ability to see clearly underwater was achieved by tightening the pupil and extended the accommodation of the lens. Humans lose this ability as the lens stiffens with age. + +The Moken children also did not seem to experience the same salt water irritation in their eyes as European children, but the researcher didn't study that particular effect. + +http://www.bbc.com/future/story/20160229-the-sea-nomad-children-who-see-like-dolphins" "In short, they produce a film that covers their eyes. + +For cetaceans, [Kremers, et al.](https://www.frontiersin.org/articles/10.3389/fevo.2016.00049/full) state: +> [A] secretion produced by the Harderian gland protects the eyes from the high concentration of salt in marine water (Dawson et al., 1972, 1987). + +As for their references, 1972 paper is not available online and the 1987 paper is [behind a paywall here](https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1748-7692.1987.tb00161.x). + + +[Here is a paper about the tears for pinnipeds.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3594129/) + +That is why when dolphins strand alive it looks like they are crying. Their eyes are producing the film but the seawater is not there to wash it away." +940 Does the language you speak affect the shape of your palate? 8256 https://www.reddit.com/r/askscience/comments/7wmirx/does_the_language_you_speak_affect_the_shape_of/ 1518281341 7wmirx Human Body 2018-02-10 19:49:01 "I don't believe there is any evidence to support that language affects palate morphology. However, vice versa it may be that morphology affected the development of (aspects of) languages. + +For example, see these two paragraphs from a [2015 conference paper by Moisik and Dediu](http://pubman.mpdl.mpg.de/pubman/faces/viewItemOverviewPage.jsp?itemId=escidoc:2166182): + +> It is an undeniable fact that human populations vary in certain systematic ways in their anatomy and physiology. This is true at both micro- and macroscopic levels, and advances in genetics will continue to elucidate the extent of these patterns of variation across populations. Early in the development of modern phonetic and phonological science, several proposals (e.g. [[24]](http://www.worldcat.org/title/reader-in-historical-and-comparative-linguistics/oclc/220270) and [[2]](https://trove.nla.gov.au/work/17928687?selectedversion=NBD4131403)) were made which held that some of the diversity observed in speech sound systems around the globe might be owing to systematic variation observed in the anatomy and physiology of the speakers of language, in addition to the other factors driving language change and diversification. These ideas were hastily dismissed as implausible, on the grounds that any human being can learn any human language. +> +> It is an incontrovertible fact that normal variation of the human vocal tract does not preclude an individual from acquiring any spoken language. However, the hypothesis that human vocal tract morphology exerts a bias on the way we speak seems plausible, and the possibility that such biases might have expressions at the level of populations of speakers has never been satisfactorily ruled out. It also seems to have resulted in the unfortunate side- effect that details of vocal tract shape are rarely if ever correlated to production variables in phonetic research. A relatively recent return to the question of whether normal vocal tract variation can indeed exert such biases reflects the unresolved nature of the problem. Many examples exist for such research examining the individual level (e.g. [[25]](https://www.researchgate.net/publication/261256855_Palatal_Morphology_Can_Influence_Speaker-Specific_Realizations_of_Phonemic_Contrasts), [[3]](https://www.ncbi.nlm.nih.gov/pubmed/19507976), and [[18]](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4492454/)), and these are laden with implications for impacts at broader levels, with some researchers even suggesting it may be a driver of change of certain aspects of entire phonological systems (e.g. [[1]](http://cogprints.org/3286/), [[5]](https://www.ncbi.nlm.nih.gov/pubmed/21615290), and [[17]](https://www.ncbi.nlm.nih.gov/pubmed/23811472)). + +Of course, this wouldn't help you identify which language someone spoke while alive." "SLP student here... +Sounds like a plot mover to me. The way the mouth and larynx are shaped isn't because of accent (plus there is no British accent...there are many, very different accents in the UK). There will be some difference between speakers but more of the accent you hear will come from formants and frequencies, and the way the speaker manipulates the air coming up the vocal tract. People with palate abnormalities such as cleft still have accents, so I doubt the palate was how they determined the person's nationality. " +749 Why is your mouth much more sensitive to cold water after brushing your teeth or chewing mint gum? 8252 https://www.reddit.com/r/askscience/comments/6saqlj/why_is_your_mouth_much_more_sensitive_to_cold/ 1502161384 6saqlj Human Body 2017-08-08 6:03:04 "the culprit is a protein called ""TRPM8"". It's ion channel is the main molecular transducer of cold sensations in your mouth. It can however also be activated by the presence of menthol which is found in mints and tooth paste for that ""cool & fresh"" feeling. So if you drink cold water after chewing mint gum you'll get the double sensation as the protein is activated by temperature and the menthol molecules." +627 Is there a reason all the planets orbit the sun in approximately the same plane and direction? 8250 https://www.reddit.com/r/askscience/comments/5lrjgz/is_there_a_reason_all_the_planets_orbit_the_sun/ 1483444368 5lrjgz Planetary Sci. 2017-01-03 14:52:48 Yes. Conservation of angular momentum. Our solar system started out as a rotating gas cloud. Over time, this cloud collapsed and denser regions formed the sun and the planets. But due to conservation of angular momentum, the rotation had to remain, which means that the solar system as a whole rotates around the same axis that the original gas cloud did. "The current nebular theory of solar system formation explains this feature of our solar system as the result of formation from the collapse of a large cloud of gas and dust (nebula). As the nebula collapses under its own gravity, any tiny initial rotation in the cloud is amplified as it shrinks in size, just like a figure skater pulling in their arms to increase their rate of spin (conservation of angular momentum). The nebula forms a disk as it collapses, because of the combination of gravity and centrifugal force: gravity points *towards* the **center** of the cloud, and centrifugal force points *away* from the **axis of rotation** of the cloud. This means that on the ""equator"" of the cloud, these two forces point in opposite directions and partially cancel each other, but on the ""poles"" of the cloud, they are at right angles to each other, and there's nothing stopping gravity from flattening the cloud into a disk. The sun forms in the middle of this disk, and the planets form around it, in the rotating disk, and so they all end up going in the same direction and in (nearly) the same plane. + +I'm on mobile, but I can add some links later if any of that isn't clear. " +1035 When Pangea divided, the seperate land masses gradually grew further apart. Does this mean that one day, they will again reunite on the opposite sides? Hypothetically, how long would that process take? 8246 https://www.reddit.com/r/askscience/comments/97f7y2/when_pangea_divided_the_seperate_land_masses/ 1534305706 97f7y2 Mathematics 2018-08-15 7:01:46 "Geologist graduate here: +Before Pangea, we had a supercontinent called Rodinia, and another prior to it (evidence gets weaker over time due to crust destruction). Depending on the direction and movement of plates, some continents will collide again, and some will tear apart (east Africa). +The process of moving the plates relies on how much the mid ocean ridges are pushing out new oceanic crust, how quickly the old oceanic crust is getting sucked under bouyant continental crust, and movements in the asthenosphere. +To be honest, i have no idea how long away the next supercontinent is. Pangea was approx 200mya, Rodinia approx 750mya. Rodinia also hung around for a longer period of time than Pangea. +I hope I helped answer some of your questions. + +Fun fact: they believe the initial move to break up Pangea was caused by insulation under the land mass, which heated up, allowing magma to melt above crust and swell and push the land masses apart. " "This cycle between a sole landmass (resulting from a great orogenic phase, like the hercynian orogenesis for example) and a phase were continental drift is dominant is called a ""Wilson Cycle"" and is known to take roughly 700Ma. Sometimes more, sometimes less. +" +507 With today's discovery that hydrogen and anti-hydrogen have the same spectra, should we start considering the possibility that many recorded galaxies may be made of anti-matter? 8227 https://www.reddit.com/r/askscience/comments/5jhfou/with_todays_discovery_that_hydrogen_and/ 1482286992 5jhfou Astronomy 2016-12-21 5:23:12 "No, that was never the premise on which ruling out large quantities of anti-matter in our Universe was based. + +The space between galaxies may seem empty, but all of it is chock full of matter, just at very low densities. However, intergalactic gas clouds do interact with each other from one galaxy or galaxy cluster to the next. Most of the time this is a very mild interaction because the gases are at very low densities and typically not traveling at any great tremendous speeds relative to each other. + +However, if one galaxy, or galaxy cluster, were made of anti-matter there would most definitely be an observable effect. At some boundary between the two oppositely composed regions there would be an interface where one side would be a gas cloud of matter and on the other side would be a gas cloud of anti-matter. And the properties of matter and anti-matter are such that these would continuously interact. And by ""interact"" I mean they would continuously annihilate, releasing vast quantities of energy in the process. + +Now, you might imagine that a super low density gas as surrounds a galaxy at hundreds of thousands of light years distance would not have many molecules per volume, and you'd be absolutely right. Such gases would be considered extremely good vacuums here on Earth. And that might lead you to think that the total quantity and rate of annihilation reactions would thus be small. But that's not thinking on astronomical scales. We're not talking about a boundary interface that is a few square meters or even square kilometers in area, nor even a few square light years. We're talking about areas that are on the scale of hundreds of thousands of light years on a side and thus many billions of square light years. Millions of trillions of *moles* of square meters in area. When you do the math you come to the conclusion that these interfaces, if they were to exist, would glow as brightly as any galaxy, and would be quite distinctive in their very specific gamma ray emissions (especially corresponding to the electron-positron annihilation energy) which would be detectable across the visible Universe. + +Simply put, we see absolutely nothing like that, which means that unless there is some bizarre unknown process keeping anti-matter and matter galaxies separate from one another then we can fairly conclusively rule out the existence of any anti-galaxies in our visible Universe. + +**Edit**: adding in some additional material to answer some common questions. + +First off, as mentioned galaxies / galaxy clusters are surrounded by gas (actually plasma) bubbles. These bubbles have a pressure and a temperature (from about 100 thousand Kelvin to 10 million Kelvin), and are mostly made up of ionized Hydrogen. Because they are under pressure if you take away material from some area the intergalactic medium will continuously fill it, just as any time you release a gas into a vacuum. And because of the high temperature of the IGM the matter is travelling fairly fast, on the order of 10s of km/s. Even though the density of the IGM is very low, a few atoms per cubic meter, that high speed means that a significant flux of atoms would be continuously hitting a boundary layer between galaxies. If that boundary layer is just another bubble of IGM plasma then the two will press against each other and find an equilibrium. If the other side of the boundary layer is anti-matter then the atoms and anti-atoms in the IGM/anti-IGM will rapidly attract one another and ionize, with a rate on the order of the density of matter and the molecular velocity of matter in the IGM due to its temperature. A simplistic ""napkin math"" calculation would be: 5 atoms / m^3 * (100000 light-years)^2 * 50 km/s, times 2, or roughly 4e47 Hydrogen/anti-Hydrogen annihilations per second, which corresponds to roughly 10^38 Watts, or about 250 billion times the Sun's luminosity. And keep in mind that this is a fairly low estimate. But it indicates how bright such an interface would typically be, which would be on the same scale as the luminosity of a galaxy. Additionally, as I alluded to, because of the very specific gamma-ray emissions of electron-positron annihilation (at 511 KeV) even if it was many orders of magnitude dimmer, it would leave incredibly distinctive ""spectral fingerprints"" in gamma ray emissions. + +Also, I should mention that the IGM is observable, so we know that these bubbles of plasma between galaxies do exist and we have measured some of their properties, it's not merely a matter of assuming they are real. + +Second, currently we have not conclusively demonstrated that anti-matter is affected by gravitation exactly the same way that normal matter is. However, that is the model that is consistent with our current best understanding of the laws of physics. So much so that if anti-matter and regular matter were to, say, repel each other gravitationally that would actually be a vastly more significant result even than the existence of huge swathes of the Universe that were made of anti-matter. And in general it falls under the ""extraordinary claims"" banner. It's not 100% ruled out as a possibility, but then again neither is the explanation of, say, aliens who are hiding the evidence of anti-galaxies from us using extremely advanced alien technologies. + +Additionally, I should address the fact that observing our entire visible Universe being made up almost entirely of matter (well, the non dark-energy / dark-matter part of it anyway) is itself a somewhat significant result, due to the fact that the laws of physics seem more or less symmetrical with respect to matter/anti-matter. Naively we would assume that matter and anti-matter should always be produced in equal quantities, so the Universe should be 50/50 even today. However, that's not entirely true. We do observe so-called CP-violations in particle physics experiments which show that some of the things we think are always 100% conserved are not and there is a slight bias to the laws of physics. We haven't been able to come up with the complete chain of events which connects the CP-violations we can observe to the net abundance of matter over anti-matter in the Universe but it is essentially a smoking gun in the case of the ""death"" of anti-matter." Can someone explain to me anti-matter and what is unique about particles that are opposite charges forming an opposite matter? Is a anti-hydrogen atom different from a normal hydrogen atom in terms of reactions and interactions with other elements? +750 Why is a frozen and thawed banana so much sweeter, and how does this change its nutritional value? 8206 https://www.reddit.com/r/askscience/comments/6i3ymg/why_is_a_frozen_and_thawed_banana_so_much_sweeter/ 1497842918 6i3ymg Biology 2017-06-19 6:28:38 "Putting together the information here + +One of the main processes in bananas (and all fruit) ripening is the amylase dependent conversion of savoury or flavourless starches in to sugar (specifically glucose). Amylase is a common enzyme (also present in your saliva) which converts starch to sugar and is an important part of your digestion. + +There are essentially 2 ways something will taste sweeter. + +1) There is more sugar present + +or + +2) Your tastebuds can access the sugar more rapidly + +Freezing and then defrosting fruit essentially lets both of these things happen. Freezing causes water in the fruit cells to crystallise and expand. This destroys the cell walls and is the principal reason defrosted fruit is soggy and limp. However it also means that the cell contents (all those sugars) are now in the juices that are running off the fruit and if you taste the juice you'll find it is very sweet. You can experience this at the most extreme if compare the difference in sensation between holding a mouthful of orange juice in your mouth or holding a slice of orange (without chewing). In the case of a banana there isn't much excess of liquid to run off so those exposed cell contents will largely stay within the fruit pulp/body rather than running off. + +The other thing that happens while the fruit is defrosting is that all the amylase and starches in the cells are now able to diffuse (a little) through the defrosting fruit pulp. The amylase is no longer confined to the cell it started in, where it may have completed its starch converting job, and is free to find any remaining starch that may have come out of other nearby cells. This means that some of the remain starches will be converted to some extra sugars." "**Why is a frozen and thawed banana so much sweeter?** + +Fruits like banana contain water. When you freeze them, the resulting ice crystals breaking the cellular structure of the fruit. The result is that thawed fruit is mushy. Subsequently as they warm up again, a lot of the juice leaks out and you're left with less flavor. + +Harold McGee pointed out in his book “On Food & Cooking” that in some cases frozen fruit is better in taste. Many fruits and vegetables never reach their optimal point for taste once they are harvested. If picked too early, fruits like pineapple, melon, most citrus, and most berries will not continue to ripen or reach an optimal quality and sweetness. + + +""In many instances, the food you take off the shelf in a grocery store has been harvested under ripe to avoid damage during travel time. This means that it hasn't yet reached its peak nutrition. Furthermore, the minute it was picked, its nutritional content began to deteriorate. The food is then loaded on a truck, boat or plane, travels for days and waits on a shelf for you to choose it. After, which it may sit in your fridge for a few more days before being eaten. Over this period of potentially weeks, the food may lose up to 50% of its nutritional value. + +Frozen foods on the other hand are picked when they're ripe and frozen immediately. And while the quick freeze process does affect some vitamin content, it essentially freezes, or locks most of the nutrients in place. Next to the fresh produce that has been sitting around for weeks, there's no doubt that frozen foods can contain more nutrition, particularly during the month that local produce is not in season and travelling far distances."" ([Source](https://www.youtube.com/watch?v=zjsOOT347cA)) + +**how does this change its nutritional value?** + +It depends on the water content of the fruit. When water freezes, it expands, so when the water in the cells of the fruit freezes, it breaks through the cell membranes. This can be seen when you freeze and then thaw a high water content food such as strawberries; you'll be left with a squishy mess when you defrost them. + +So the amount of damage depends on the water content. Melons will be affected more than strawberries which will be affected more than bananas, which are affected the least because they are only 75% water. As an example, nuts would hardly be affected at all. + +So you do diminish the nutrient content of the bananas used in banana ice cream, but not anywhere near as much as the bananas used in banana bread (cooking does far more damage than freezing, including the causation of autoimmune reactions). + +A way to get around this nutrient damage issue is to chill the bananas but not let them freeze, and then mash them into ice cream. Or just eat them cold as is! This would result in a cold fruity treat (but make sure they are ripe before chilling them). In practical terms, most people just throw frozen bananas through a Champion juicer (the best machine) or a Vitamix (which takes some muscle but it can be done, just be sure to run the Vitamix only as much as needed to turn the bananas into ice cream or you'll warm up the ice cream too much). + +Bananas are known for their high potassium. In fact, a large bananas has over 450 mg of potassium. Fresh bananas are a bit different than buying bananas frozen in the store. Because commercially frozen bananas are usually blanched before they are frozen, you lose a little bit of the potassium. Blanching is a process that takes the fruit and boils it for about a half of minute and then immediately cools it in ice. It is not the freezing of the banana, but rather the blanching process that is thought to reduce the potassium content. Interestingly enough, potassium is a mineral that is not affected by the freezing process. So if you are taking your own fresh bananas and freezing them to throw in a shake or smoothie you are all good. However, you may pull a brown banana out of your freezer, but the potassium will remain intact. + +If the only way you eat bananas is as ice cream, then you're obviously missing out on some nutrition. But if you eat most of your yearly banana intake unfrozen, and you're not cooking the other foods you eat, then you can probably afford to trade some nutrition for a tasty dessert if it helps you stay on your raw food diet. + +__________________________________________________________________________________________ + +[Source 1](http://www.micfood.com/blog/3-sweet-reasons-to-choose-frozen-fruit-over-fresh/) + +[Source 2](http://health101.org/banana) + +[Source 3](http://www.chicagonow.com/katalin-fitness-health-driven/2012/03/are-frozen-bananas-as-healthy-as-fresh/) + + +" +751 With solar sails being so thin, how do they avoid being punctured by tiny space debris? 8196 https://www.reddit.com/r/askscience/comments/6nzxct/with_solar_sails_being_so_thin_how_do_they_avoid/ 1500373999 6nzxct Engineering 2017-07-18 13:33:19 Answered for the Planetary Society's LightSail project at http://sail.planetary.org/faq.html. Their sails use rip-stop construction so that a pinhole doesn't develop into a large-scale tear, and they can accept several localized holes without losing mission effectiveness. "They don't. Depending on the environment (low Earth orbit, high Earth orbit, solar orbit...) there will be a flux of particles of various sizes, with a distribution of relative speeds. A thorough solar sail design would need to analyze the expected exposure over the mission lifetime and show that it can meet the mission requirements with that many holes :-) + +Any big space structure (ISS for sure, probably JWST) does that kind of analysis. We're still in the early days of solar sails (i.e. ""let's just get something up there and see how far we can get""), so there may be less emphasis on this level of analysis. +" +752 Why does it take multiple years to develop smaller transistors for CPUs and GPUs? Why can't a company just immediately start making 5 nm transistors? 8161 https://www.reddit.com/r/askscience/comments/6t7bdh/why_does_it_take_multiple_years_to_develop/ 1502525308 6t7bdh Engineering 2017-08-12 11:08:28 "Ex Intel process engineer here. Because it wouldn't work. Making chips that don't have killer defects takes an insanely finely-tuned process. When you shrink the transistor size (and everything else on the chip), pretty much everything stops working, and you've got to start finding and fixing problems as fast as you can. Shrinks are taken in relatively small steps to minimize the damage. Even as it is, it takes about two years to go from a new process/die shrink to manufacturable yields. In addition, at every step you inject technology changes (new transistor geometry, new materials, new process equipment) and that creates whole new hosts of issues that have to be fixed. The technology to make a 5nm chip reliably function needs to be proven out, understood, and carefully tweaked over time, and that's a slow process. You just can't make it all work if you ""shoot the moon"" and just go for the smallest transistor size right away." "Nanotechnologist here! + + Because when a transistor is very small, it has a number of side effects like quantum effects and short-channel effects. Also, transistors work by doping semiconductors, if the semiconductor is very small there are very few doping atoms. Also, a small imperfection results in a big effect when we're working in small scales. There are many ways to fix it but it's not evident. This is the tl;dr it's actually a very vast science. You can ask me for specific things or you can google these 3 things: Beyond CMOS, more Moore, more than Moore" +1220 How are the undersea internet cables protected against the elements? 8158 https://www.reddit.com/r/askscience/comments/bfes9r/how_are_the_undersea_internet_cables_protected/ 1555781638 bfes9r Engineering 2019-04-20 20:33:58 "The outside of the cable has two layers of Galvanized steel. Galvanized steel is very difficult to rust. + +​ + +[https://www.youtube.com/watch?v=M7stcJ65\_X4](https://www.youtube.com/watch?v=M7stcJ65_X4) + +[https://galvanizeit.org/hot-dip-galvanizing/why-specify-galvanizing/durability](https://galvanizeit.org/hot-dip-galvanizing/why-specify-galvanizing/durability)" This post made me curious where these cables come from and where they go. Behold! I found [an interactive map of submarine cables](https://www.submarinecablemap.com/). We've laid a lot of cables in our oceans. I can only imagine the nightmare it was going across the Pacific! +508 In this gif of white blood cells attacking a parasite, what exactly is happening from a chemical reaction perspective? 8155 https://www.reddit.com/r/askscience/comments/5fqb31/in_this_gif_of_white_blood_cells_attacking_a/ 1480521152 5fqb31 Chemistry 2016-11-30 18:52:32 "A quick, incomplete answer since I'm in class. What you're talking about is called chemotaxis, and describes how white blood cells ""call for reinforcements"", but also any movement of a cell due to a gradient in some stimulating chemical. When some types of WBCs encounter trouble, they'll release chemotactic chemicals such as chemokines. When these diffuse into the surrounding tissue it creates a gradient that other cells can use to tell the direction from and will begin moving in that direction. There's a lot more to it, but that's a start." "The chemicals you are asking about are chemokines and cytokines, which in this case is likely to be cytokine IL-5, which recruits eosinophils (a type of WBC) to kill the parasite. Cytokines are proteins which bind to receptors on the eosinophil. Once bound a lot of things go on inside the cell, including phosphorylation of proteins causing remodelling of the internal structure to make it move in a direction. I'm deducing a bit here as my knowledge is rather undergraduate, but I imagine higher concentrations = more transcription = more movement = goes in the right direction by biased random walk kind of deal (someone please feel free to correct me). +These cytokines are produced by other white blood cells (in this case T-helper cells), which are responding to either more white blood cells or due to the adverse effect that the parasite is having on the surrounding tissues such as epithelium, which causes the production of different cytokines. The cytokine that activates T-helper cells is IL-4 but no one is quite sure which cells produce it in this kind of response. + +Source: mainly Janeway's Immunolobiology 9th ed. +Edit: was a bit wrong" +1312 What are the tiny triangular creases on your skin called? 8151 https://www.reddit.com/r/askscience/comments/bxpbso/what_are_the_tiny_triangular_creases_on_your_skin/ 1559874619 bxpbso Human Body 2019-06-07 5:30:19 "The crease itself is called a sulcus cutis, and the square within the crease is a crista cutis! Great question, took me a while to track these terms down. + +[source](http://file.scirp.org/Html/3-1050102_25855.htm) and [source](https://www.derm-hokudai.jp/shimizu-dermatology/pdf/01-01.pdf)" +941 What exactly is happening to your (nerves?) when circulation gets cut off and you start to tingle? 8149 https://www.reddit.com/r/askscience/comments/7rxv4o/what_exactly_is_happening_to_your_nerves_when/ 1516543814 7rxv4o Human Body 2018-01-21 17:10:14 "What most people think of as cutting off their circulation is actually compression of the nerves which innervate that area (typically a limb). The blood supply is generally not compromised at all, it takes quite a while (hours) for ischaemia to present with neurological signs (tingling etc). + + +The compression of the nerves causes abnormal discharging of the the sensory neurones which is in turn perceived as tingling (parasthesia) or other abnormal sensations. This is usually reversible but if the nerve is compressed for a long time it can persist or become permanent. You can look up Saturday Night Syndrome if you are interested. + +Edit: spelling and a missed “signs” + +Edit 2: Thanks for all the comments, my apologies if I don’t reply to them all. + +I perhaps should have been slightly clearer in my language as some have rightly pointed out that direct compression of nerves leads to changes in the microvascular supply to that region of the nerve and this is implicated in the development of symptoms. I more meant my above comment to convey the fact that it is the compression of the nerve itself (and subsequent microvascular and other sequalae) not the arteries supplying a limb which leads to the parasthesia many people experience. + +This is worth a quick read if you are interested but is by no means exhaustive: https://www.ncbi.nlm.nih.gov/m/pubmed/12371026/" In simple terms, when a nerve is crushed, suppressed, destroyed it stops eliciting action potentials correctly. Action potentials are signals that cells of the nervous system create to send messages to other cells, tissues, organs, etc. in the body. Everything you feel, temp, pain, pressure is interpreted by your brain. When the action potentials that carry the temp, pain, pressure are interrupted by a suppressed or damaged nerve then the brain interprets it as you describe, a tingly sensation. +1105 "Have humans always had an all year round ""mating season"", or is there any research that suggests we could have been seasonal breeders? If so, what caused the change, or if not, why have we never been seasonal breeders?" 8146 https://www.reddit.com/r/askscience/comments/9j1us0/have_humans_always_had_an_all_year_round_mating/ 1537963278 9j1us0 2018-09-26 15:01:18 [deleted] "True seasonal breeding is actually pretty rare among the haplorhine primates (of which we are members) While certain species will show peaks in breeding seasonally, haplorhines typically follow a cyclical period of menses and are capable of reproduction during key points of that cycle. Such cycles are typically not seasonally linked and can occur multiple times through a year. It is also important to note that it’s not just about cycling as most females are typically not cycling at a given point. This is due to the fact that among wild primates females are typically at a nonfertile point during their overall reproductive (not menstrual) cycle — either they are pregnant or are currently lactating. Actually actual fertile parts of the cycle come fairly infrequently, especially among taxa which demonstrate prolonged offspring dependence (e.g., orangs, chimps, etc) which may last a period of years. + +This is not to say all primates are not seasonal breeders. Strepsirrhines (lemurs, lorises and galagos) demonstrate strict reproductive estrus in the primitive mammalian form (think along the lines of a cat or a dog — they essentially go into heat). This is often linked to breeding seasonality so that lactation occurs during high resource availability and/or it is linked to patterns of infant development and the ability of the kids to be weaned on seasonally available food resources. + +So long story short...not all primates are seasonal breeders, including our closest ansestors. However, some species with faster interbirth intervals and infant development are...Although these tend to be strepsirrhines to which we are only distantly related." +753 Does a steady or a blinking digital clock use more energy? 8138 https://www.reddit.com/r/askscience/comments/6ay4wa/does_a_steady_or_a_blinking_digital_clock_use/ 1494686222 6ay4wa Engineering 2017-05-13 17:37:02 "I think the question you're really asking is ""does the energy savings from having the LED off part of the time outweigh the energy used by the circuit doing the blinking?"" It's hard to answer this in the general case because there are so many variables. If we assume the clock circuitry is simple and well designed, which is probably a reasonable assumption, it's likely the blink circuitry is lower power than the LEDs so it should save power." "Steady. It looks ""steady"" to you but the circuitry has to send ON constantly to each of the 7 segments. If it's blinking if only sends ON a fraction of a second. + +Source: electrical engineer who had to play with LEDs for his courses." +754 If Mars at some point had oceans that were filled with life similar to our own, would there still be oil there despite the harsh Marian conditions and what we know about the planet? 8129 https://www.reddit.com/r/askscience/comments/6v2ox8/if_mars_at_some_point_had_oceans_that_were_filled/ 1503319909 6v2ox8 Astronomy 2017-08-21 15:51:49 "It is very unlikely. Oil forms when organic matter of the right composition (with as high a H:C ratio as possible so with as little cellulose as possible) is buried rapidly at a depth where the geothermal gradient will allow the chemical transformation to oil & gas. + +There are thus 2 problems with Mars: 1 - While there is still some (but less and less) controversy over whether martian oceans existed, whether they were intermittent and how long they lasted, there is little controversy over the fact that they must have been quite shallow. This is a terrible constraint on the preservation of organic matter, in that storms may agitate bottom sediments and expose them to scavengers, bacteria and oxygen. Sucks for preservation. 2 - No plate tectonics means that basin development was slow, if indeed it was a thing. This makes it hard for whatever organic matter there may have been there to get buried deep enough to reach critical temperatures for the right chemistry to occur." If Mars ever had life it was in the shadows and partially under ground. No magnetic field means no protection from cosmic radiation. The Martian Radiation Experiment, or MARIE was designed to measure the radiation environment of Mars using an energetic particle spectrometer as part of the science mission of the 2001 Mars Odyssey spacecraft (launched on April 7, 2001). It was killed by cosmic radiation from a solar flare. Outside of the Earth's magnetosphere is a dangerous place for a living organism to be. +942 How much of the Mariana Trench have we explored? 8101 https://www.reddit.com/r/askscience/comments/7uodcx/how_much_of_the_mariana_trench_have_we_explored/ 1517540641 7uodcx Earth Sciences 2018-02-02 6:04:01 [deleted] "Seeing as you have no answers so far i decided to do some reasearch. I found the following snippet at: https://marine-conservation.org/media/shining_sea/place_wpacific_mariana.htm + +""Imagine the deepest, darkest place on Earth—an underwater trench plummeting to a depth of 35,800 feet, nearly seven miles below the ocean surface. The Mariana Trench is one of the least explored places on Earth. Deep enough to swallow Mt. Everest, the Mariana Trench was first pinpointed in 1951 by the British Survey ship Challenger II. Known since as Challenger Deep, it was not visited for nearly ten years. Jacques Piccard and Don Walsh descended in asubmersible called the Trieste, which could withstand over 16,000 pounds of pressure per square inch. Their descent to the bottom in cramped quarters took five hours, but provided our first glimpses of the seafloor and life at the ocean’s greatest depths. The Mariana Trench represents just one small part of the Earth’s last, great frontier. Less than five percent of the entire ocean has been explored, yet scientists have found that even the deep sea has great numbers of species—and the discoveries have only just begun"" + +Interesting info from wikipedia: + +""As of February 2012, at least two other teams are planning piloted submarines to reach the bottom of the Mariana Trench. Triton Submarines, a Florida-based company that designs and manufactures private submarines, plans for a crew of three to take 120 minutes to reach the seabed.[28] DOER Marine, a marine technology company based near San Francisco and set up in 1992, plans for a crew of two or three to take 90 minutes to reach the seabed."" + +""In 2011, it was announced at the American Geophysical Union Fall Meeting that a US Navy hydrographic ship equipped with a multibeam echosounder conducted a survey which mapped the entire trench to 100 metres (330 ft) resolution.[2] The mapping revealed the existence of four rocky outcrops thought to be former seamounts."" + +So we have mapped it roughly but their appears to be plenty more to discover. + +Also a cool fact on the wiki: + +""The trench is not the part of the seafloor closest to the center of the Earth. This is because the Earth is not a perfect sphere; its radius is about 25 kilometres (16 mi) less at the poles than at the equator.[6] As a result, parts of the Arctic Ocean seabed are at least 13 kilometres (8.1 mi) closer to the Earth's center than the Challenger Deep seafloor."" + + + +" +509 If fire is a reaction limited to planets with oxygen in their atmosphere, what other reactions would you find on planets with different atmospheric composition? 8099 https://www.reddit.com/r/askscience/comments/5iexyv/if_fire_is_a_reaction_limited_to_planets_with/ 1481768912 5iexyv Planetary Sci. 2016-12-15 5:28:32 Fire merely requires a sufficiently strong oxidizer, which doesn't necessarily have to be oxygen. Oxidizers are molecules that take electrons away from something, and tend to be toward the right of the periodic table. Fluorine is even stronger than oxygen and can react with water. Chlorine triflouride is powerful enough to ignite some things that are not normally flammable. Most people focused on the fire part of your question, but there are a lot of other reactions that may occur. In most cases, a planet's sun is constantly dumping photons into the atmosphere, which can produce free radicals from otherwise inert materials. These are highly reactive materials. Likewise, lightning can promote some really interesting reactions with seemingly inert materials like nitrogen. (With oxygen and carbon containing molecules present, you can even make amino acids.) Then you have geological events, like volcanos, helping to facilitate reactions, particularly between dissimilar metals. The number of reactions are really limitless, even in an oxygen free environment. +628 Why is it matter in the Sun's core can undergo fusion at 15 million degrees but our fusion reactors need to be 100+ million degrees? 8058 https://www.reddit.com/r/askscience/comments/5xmkkp/why_is_it_matter_in_the_suns_core_can_undergo/ 1488716824 5xmkkp Physics 2017-03-05 15:27:04 "Fusion reactions are a slow/low probability process. In the sun, the time it would take for a nominated atom to undergo fusion would be significant, but this is offset by the sheer number of atoms present. + +In a lab based fusion system, the number of atoms in the pool is a lot smaller, so this is offset by increasing the pressure/temperature and increasing the chance of a nominated atom colliding with another and undergoing fusion. " "There's two components to your question. First is why fusion is possible in the Sun's core, second is why our fusion reactors need to run at much higher temperatures. + +The second question is easier to answer, so I'll go for that one first. + +The Sun actually produces so little power by volume that it would be completely impractical to reproduce the conditions of the Sun's core in a fusion reactor, *even if we could somehow do so* (we can't, because containing plasma at such pressures would be incredibly difficult and dangerous). The Sun is producing a lot of energy because it's so huge, but the actual power release per volume is only about a quarter of human resting metabolism. + +You would literally get four times more thermal power out of a regular, resting person, than you could out of a human-sized chunk of solar core material. + +So reproducing the Sun's core would make even a reactor of gargantuan size produce very little power. You'd quite literally need a star-sized reactor for a significant power output... and we already have that (albeit at 1 AU distance). What we need for practical fusion reactors is a significantly higher energy density, and for technical reasons, that involves a much higher temperature to get the fusion yield higher. + + +The explanation on why fusion can occur in the Sun and other stars requires a longer explanation, which has to go a bit deeper into those technical reasons. + + +Fusion is what happens when two light atomic nuclei collide hard enough that they overcome their electrical repulsion, come into ""contact"" with each other, and discover that forming one large nucleus is energetically more favourable than existing as separate nuclei. So they merge, and release some high energy photons, and sometimes some leftover particles are also ejected. For example, when tritium and deuterium nuclei come together like this, they form one helium nucleus, and one leftover neutron is ejected. + +The more detailed reason as to why this happens is that there is a force called strong interaction, which is incredibly powerful at short ranges and is the main thing responsible for holding together not only protons and neutrons within atomic nuclei, but actually it is the force that binds together the quarks that form the protons and neutrons themselves. When two nuclei approach each other, they are strongly repelled from each other by the electric force (often called the Coulomb barrier), *but* if they get close enough, then the incredibly strong nuclear force will overcome the repulsion and bind the nuclei together. And sometimes eject something. Depends on the reaction. + +This is actually also why the amount of neutrons increases along with the protons as you go up the periodic table of elements - with protons alone, the electric repulsion is not strong enough to hold the nucleus together, and you need neutrons to increase the strong interaction while not contributing to the electric force. So, the neutrons act as a glue that holds large nuclei together - but only up to a certain point. After the number of protons reaches a certain amount, the sheer size of the nucleus becomes so large that the strong interaction provided by the increased neutrons can no longer hold it together, and the nucleus becomes unstable. This means it will at some point eject something in order to reach a more stable configuration; this is called radioactive decay, and the ejected something are what radioactivity is. This is also the reason why, say, Uranium-238 is much less radioactive than Uranium-235; the three additional neutrons make the nucleus it more stable... But I digress. Back to fusion. + + +Obviously, fusion doesn't happen easily, as evidenced by our existence. There are two main barriers in the way of fusion reactions happening. The first one is obviously that atomic nuclei are normally bound with electrons around them, forming actual atoms. The first thing you need to do is to get rid of the electrons entirely, which is something called ionization. This is done by heating the gas so much that the atoms shed their electrons by collisions with each other, and the high heat keeps them from re-binding into atoms. + +So now you have a plasma with free atomic nuclei surrounded by a free electron soup, hopefully contained in some way because otherwise it's going to just expand and cool off almost immediately. + +But this alone is not enough. Since atomic nuclei consist of positively charged protons, and neutrons with no charge at all, they are strongly repelled from each other by the electric force. So getting them to come into ""contact"" with each other is very hard, and that means they have to collide very violently in order to defeat the energy barrier created by their electric fields. + +However, if you increase the collision energy high enough - over the Coulomb barrier - the collisions will eventually bring the two nuclei close enough that the attractive force of the strong interaction overcomes the repulsive force of positive electric charges, and fusion can occur. + +Actually it turns out that fusion occurs at significantly lower collision energies than expected simply by naïve analysis based only on the relative strengths of electric repulsion and strong nuclear attraction, but it is still a good basic summary of the problem. The reason for the lower energy requirement in reality is due to quantum physics: The nuclei basically have a certain probability of quantum tunneling through the energy barrier, achieving a closer proximity to each other than classical physics predicts, which means that *sometimes*, even at ""too low"" energies, fusion will still occur. And if that distance is small enough for the strong interaction to take the wheel... well, fusion happens. And it turns out that this process is actually significant enough to be a big deal for stellar fusion, as the temperature and pressure withing the cores of stars is just too low to break the Coulomb barrier. + +Regardless of the minutia of how the nuclear fusion is achieved, the important thing to realize here is that as far as particle collisions are concerned, pressure and temperature are kind of interchangeable. Increasing the temperature makes the collisions more high-energy, but increasing the pressure means there's more of them happening. More collisions happening means you'll get more quantum tunneling going on, and thus you start getting some fusion out of this mess even though you're too low to break the Coulomb barrier. + +At any rate, the Sun's core is compressed by the gravity of all the mass of the Sun itself around it. The density itself is actually surprisingly low, ""only"" about 160 times the density of water (160000 kg/m^3). It's still way more dense than any element we can handle in solid form - depleted uranium, for example, is about 19,050 kg/m^3 in density, which is only about 1/8th of the density of the Sun's core, but it's still a number we can understand well enough. A litre of the Sun's core would weigh 160 kg, though. This density, at 15 million degrees temperature, is enough to bring a great number of protons to a close proximity to each other, which increases the chances of the quantum tunneling happening through sheer statistical probability. And there was light. + +By contrast, the plasma densities we can achieve are pretty much limited by how strong a magnetic field we can produce, and compared to gravitationally compressed plasma, it's not actually all that high. We can achieve very high pressures in small scale, like with a diamond anvil (high enough to allegedly turn hydrogen into a metallic phase), but containing fully ionized plasma at such pressures and at large scales would quite likely be impossible. And like explained in the short explanation, even if we *could* do it, it would not actually help make a useful reactor, so increasing the temperature is probably the only way we can do it. + +Basically, if we want a high enough fusion yield out of the plasma to actually cover the expenses of running it, we simply cannot rely on the quantum tunneling, we *have* to break the Coulomb barrier. If we can do that consistently, and with a good fusion yield, then the thermal energy yield should be quite substantially more than it took to run the reactor (heating the plasma to fusion temperatures and containing it during the reaction), but so far it's proven to be rather an extreme technical challenge to get a net yield of energy out of it. Aside from thermonuclear bombs, of course, but those are not very practical for energy production..." +1036 Is there a spot where the big bang happened? do we know where it is? Is it the center of the universe? If you go there, is there a net force of zero acting on you in all directions ( gravity) 8034 https://www.reddit.com/r/askscience/comments/97l97s/is_there_a_spot_where_the_big_bang_happened_do_we/ 1534361435 97l97s 2018-08-15 22:30:35 "Please remember that /r/AskScience is for reading answers from experts. If you answer a question, please make sure your answer is supported by credible sources. Do not speculate if you do not know the answer to a question. + +We also ask that, before asking a follow-up question to a top-level comment, you read other child comments to see if your question has already been asked. This helps keep information readily accessible and readable for all users. + +Thank you." "The big bang happened *everywhere*, right where you're sitting now included. The universe doesn't have a center; instead, *everywhere* is equally the center. When we talk about the universe expanding, what we mean is that *space itself* is expanding, not that the universe is expanding into something or away from a center point. + +This is a difficult point to grasp, but it helps if you remember that the universe may well be infinite - it's only the *observable* universe that's finite, and that's because of two things: 1) light takes time to travel and 2) the universe hasn't always existed. There's more universe further out, ad infinitum, but the light from those parts hasn't had time to reach us yet. The stuff inside the universe is being carried away from the other stuff inside the universe as space itself expands, like a baking cake carrying raisins inside further away from other raisins as it rises. " +1221 "The Tsar Bomba had a yield of 50 megatons. According to Wikipedia ""the bomb would have had a yield in excess of 100 megatons if it had included a uranium-238 tamper"". Why does a U-238 tamper increase the yield as opposed to other materials or no tamper at all?" 8010 https://www.reddit.com/r/askscience/comments/b63mqv/the_tsar_bomba_had_a_yield_of_50_megatons/ 1553688186 b63mqv 2019-03-27 15:03:06 "A hydrogen bomb works by having at least two ""stages."" The first, the ""primary"" stage, is basically the same kind of ""atomic"" bomb dropped on Nagasaki: a fission bomb that works by splitting a _fissile_ isotope (like U-235 or Pu-239) and releasing a bunch of energy. Fissile isotopes are defined as isotopes that can sustain a nuclear chain reaction, and in practice that means that they are heavy atoms that can be easily split by neutrons of basically any energy level, including the same energy level as those that are produced by fission reactions. This is a tricky but core concept here: splitting U-235 or Pu-239 produces neutrons, and the same neutrons that are produced can split other atoms of U-235 and Pu-239, hence they can create self-sustaining reactions. + +The ""secondary"" stage in a hydrogen bomb takes the energy from the primary stage and uses it to compress and then heat a bunch of light atoms, the fusion fuel. The fusion fuel is usually lithium-deuteride, which undergoes reactions that turn it into isotopes of hydrogen that get fused together. This releases a _lot_ of energy. The tamper is the part of the secondary that helps squeeze the hydrogen atoms — it's something heavy that can be pushed, and will stay pushed for a few nanoseconds even when the fusion reactions start pushing back on the other direction. So for a design like the Tsar Bomba, you need a heavy tamper no matter what. + +Hydrogen fusion reactions release neutrons that are 10X more energetic than the ones released by fission reactions. Remember how I said that U-235 and Pu-239 were fissile, because they could be split by neutrons of basically any energy level? Well, there are some isotopes that are _fissionable_ but not _fissile_: they can be split by neutrons of certain energy levels, but they can't sustain a self-sustaining reaction because the energy levels of neutrons they need are higher than those that are released by their own splitting. U-238, for example, will split from high-energy neutrons, but not the lower-energy neutrons that come from fission. So if you had, say, a source of a massive number of neutrons that were, say, 10X the power of fission neutrons, you could split a LOT of U-238 atoms. + +So the trick the weapons designers of the world realized very immediately when thinking about H-bombs was this: you already need a heavy tamper, so why not make it out of U-238? If you do, then the high-energy neutrons from the fusion reactions will cause it to split, and you'll get a HUGE yield increase. And even better: U-238 is basically a ""waste"" product of the U-235 enrichment process, so it's extra explosive power for basically ""free."" You're taking something that you have large amounts of anyway and turning it into a way to multiply the power of your bomb very dramatically. Win-win... except that the splitting of heavy elements is the part of the nuclear explosion that creates most of the radioactive fallout problem. + +So the Tsar Bomba, as tested, had 97% of its energy from fusion. That means that 1.5 Mt came from fission (the primary and some other fission elements that are used to get the fusion working), and 48.5 Mt came from fusion. That's a very ""clean"" bomb for its yield: only 1.5 Mt of fission products, which is to say, about 10X less fissioning than the Castle Bravo bomb. They accomplished this by _not_ using U-238 in the tamper, and by using lead instead — and lead will not fission (it is an extremely stable element). They used the lead, rather than the U-238, to cut down on the fallout problem. + +If they had used U-238 as the tamper of the secondary of the weapon (or secondaries — there may have been multiple in this particular weapon), then the yield would have been around 100 Mt. So, again, 1.5 Mt would have been from the fissioning needed to start the fusion reaction, 48.5 Mt from the fusion reaction, and then another 50 Mt from the U-238 tamper fissioning. So the total fission products would have been 51.5 Mt... which is a _lot_ of radioactivity from a single test. + +To give you an idea of how much the fission product aspect of the radioactivity matters, you can use the [NUKEMAP](https://nuclearsecrecy.com/nukemap/). Here's [a chart](http://blog.nuclearsecrecy.com/wp-content/uploads/2013/08/Fallout-comparisons.jpg) showing three surface burst weapons: the top is Castle Bravo (15 Mt, 68% fission), then the Tsar Bomba as tested (50 Mt, 3% fission), and then the Tsar Bomba as designed (100 Mt, 52% fission). You can see that the Tsar Bomba as tested could have (if it was a surface burst) spread radioactivity over an area as large as Castle Bravo, but it would have been less intense. The Tsar Bomba as designed, however, would have spread intense radioactivity over a much larger area." One thing to add that I think was only touched on is what is a tamper. The tamper is some structure or mass or whatever that holds back the explosion. This is very important in what makes an explosion so powerful. Without a tamper on explosion will build up enough pressure in order to break whatever containing vessel it is and expands in every direction with the minimum needed pressure it takes to break that barrier. Add in a tamper that is able to contain the explosion to allow it to build to a higher pressure before releasing and you will create a bigger bomb which is clearly the objective of the atom bomb. There is no possible material or structure on Earth they could use to contain a hydrogen bomb so there is nothing we can build to fully surround a bomb to make it explode with the maximal force. What they've done is they've picked literally the heaviest element on Earth, which has the added bonus of being used as fuel itself, and used the property of inertia to build up as much pressure as possible before and while the bomb is exploding. because uranium is so heavy it takes more energy to push it away then a lighter material thus causing the bomb to build up a higher pressure when it explodes. +1403 AskScience AMA Series: We are researchers studying biological rhythms and we want to 'lock the clock' to permanently end daylight saving time - ask us anything! 8005 https://www.reddit.com/r/askscience/comments/dq2nv3/askscience_ama_series_we_are_researchers_studying/ 1572606040 dq2nv3 2019-11-01 14:00:40 "What test cases have you studied? I'm from Western Australia where it's been trialled a couple of times and rejected at referendum each time, but we're treated like Luddites by East-coasters. + +This makes me wonder: are there geographic arguments for and against? In Perth WA, the summer afternoons can be brutally hot through to 5 or 6pm standard time, I've always thought this played against implementing DST. Also possibly ~~lat~~longitude relative to the 'natural' timezone (not specific to Perth)?" "What's the best advice you can give someone to maintain a healthy circadian rhythm? What exactly is a good rhythm? + +Should one: +Use blue light blockers at a certain time? +Wake up at the same time? +Eat breakfast at the same time?" +1037 When dolphins open their eyes above water, are things blurry like when humans open their eyes below water? 7998 https://www.reddit.com/r/askscience/comments/8ha7d0/when_dolphins_open_their_eyes_above_water_are/ 1525552379 8ha7d0 2018-05-05 23:32:59 I know I'm late, but I'm in the unique position where I actually study corneas for a living and I've been consulted before regarding dolphin eyes. The real answer to this question is that dolphins rely on their echolocation almost exclusively. They have eyes, and they can see, but they are practically vestigial at this point. Many dolphins actually lose their eyes due to infection and trauma and it really doesn't affect their behavior much. So whether their vision is slightly blurry through air is kinda a moot point. "The refractive index of the lens in your eye as well as the fluid inside and on the surface of your eye all interact to give you a focused image. Air has a refractive index of 1, and water is higher at 1.333. This means that light passes through air differently than water. Human eyes are best adapted to see in air, while fish eyes (and dolphins etc.) are adapted to water, so while we can’t say for sure what that looks like to them since we don’t know what their normal vision looks like, it’s possible that they have some accommodation in their neural processing or eye anatomy that helps with the difference but most likely yes, it would be blurrier, or at least look differently, than underwater. + +Edit: turns out dolphins can’t see that well underwater or in air as they primarily use echolocation. So most likely it’s blurry everywhere. Thanks /u/MyDogHatesYou !" +1106 "If the gravitational pull of a planet is the same in all directions, why does Saturn, for example, have rings in only one plane? Shouldn't it be inside of a ""shell"" of debris instead of just having rings?" 7997 https://www.reddit.com/r/askscience/comments/9f78gn/if_the_gravitational_pull_of_a_planet_is_the_same/ 1536754789 9f78gn 2018-09-12 15:19:49 "A shell or ball is what you'd expect if the particles don't collide with each other. This is why you can get elliptical galaxies - stars almost never collide and don't even have close encounters very often, so once you get a ball of stars, the stars will just keep on buzzing around in a ball for a very long time. This is also supposed to be the case for dark matter. The dark matter particles don't really collide with each other, so they just stay in a big puffy ""halo"" around the galaxy. + +However, the dust and rocks and moonlets in a planetary ring *can* collide with each other. So if you some particles in a ""polar"" orbit, going up over the north pole and back around the south pole, and other particles in an ""equatorial orbit"", going in circles around the equator, then these particles will smash into each other. Unless all the particles are orbiting in the same plane, their orbits will cross and they'll collide. These collisions transfer momentum between the particles, and also get rid of kinetic energy. Eventually, through enough collisions, everything will settle down until you get a disc or a ring. Then all the particles can have nice circular orbits without bumping into each other. (Another way to think of it is this: you can get rid of energy, but you can't get rid of momentum. A ring or disc is the lowest energy system you can get while still conserving angular momentum). + +This is true for more than just planetary rings. Gas and plasma particles in space will bump into each other too. So when you get a lot of gas coming together to form a galaxy - or, on a smaller scale, a chunk of gas coming together to form a star - it will also collapse into a disc. For a galactic gas disc, this will collapse to form stars, so you get a disc of stars. For a stellar gas disc, this will collapse to form planets, so you get all the planets within the same plane. It's not that the stars or planets need to be in a disc - neither really is good at collisions - it's that the gas they formed from was in a disc." "It's basically the same reason all the objects in orbit end up going the same direction. The minority objects going in an opposing direction, or intersecting plane get eliminated. + +Check out this video of marbles on a stretchy table to visualize the process! + +https://www.youtube.com/watch?v=MTY1Kje0yLg" +755 How far does an insect (like a beetle or a fly) travel from the place they were born in? 7977 https://www.reddit.com/r/askscience/comments/6hejov/how_far_does_an_insect_like_a_beetle_or_a_fly/ 1497527907 6hejov Biology 2017-06-15 14:58:27 "African blue dragonflies travel from AUS>Africa>>aus>africa on a yearly cycle, 11,000 miles over the ocean. + +In the US you'll recognize them along Gulf coast states, as the Grey or Blue Darner (no studies have been done to track N.American migration patterns) + +both adults make the trip, and breed along the way for the next generation to follow - adults can live 3-5 YEARS, Nymphs can live for 3-5 years before they ever spread their wings, so the large dragonflies you see could be up to +10 years old. + +(its both a generational and a lifetime journey, they dont settle.) + +http://www.dailymail.co.uk/sciencetech/article-1200054/Longest-insect-migration-dragonflies-fly-11-000-mile-round-trip-ocean.html" "A British study was done on this using radar to track insects flying: + +https://arstechnica.com/science/2016/12/researchers-use-radar-to-track-3-5-trillion-insects-migrating-over-england/ + +""The travel speed of these larger insects indicated that they weren't simply passively riding the wind. They reached speeds of between 30 and 60 kilometers an hour, which suggested that they were actively flying along with the wind. The authors note that, in just a few hours, these insects would be able to cover over 200km."" + +Another big surprise of the study was the pure volume of insects, 3.5 trillion insects over the course of a year migrating. " +1404 Do deep sea creatures have a sleep schedule? 7970 https://www.reddit.com/r/askscience/comments/dkpg6x/do_deep_sea_creatures_have_a_sleep_schedule/ 1571603818 dkpg6x 2019-10-20 23:36:58 "That is an interesting question! I came across a very thorough review by [Beale et al. 2016](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090016/) which broadly discusses physiological rhythms in environments without clear daily cycling (of which the deep sea is obviously a prime example). As u/wrathchilde mentions, there are plenty of organisms from various taxonomic groups that move from deep waters to shallow and back again in daily cycles, which generally falls under the umbrella of [diel vertical migration](https://www.cell.com/current-biology/fulltext/S0960-9822(14)01067-7). However, for organisms that permanently live at depths of over a kilometre, there is no sunlight which might be used to measure daily cycles, nor are there any regular variations in temperature on the scale of days or even seasons. + +However, that doesn't mean that life in the deep sea is totally arrhythmic; Beale et al. cite several studies which have looked into this question. Examination of the stomach contents of crustaceans ([Maynou and Cartes 1998](https://www.int-res.com/articles/meps/171/m171p221.pdf)) and fish ([Modica et al. 2014](https://www.ncbi.nlm.nih.gov/pubmed/25052896)) from below 1000 m demonstrated mixed results, with some species showing apparent 24-hour cycles, but others having no clear pattern (though as the authors point out, it could also be the case that this cycling is actually a feature of the prey species being consumed, rather than their deep-sea predators). + +Another study, by [Wagner et al. 2007](https://www.sciencedirect.com/science/article/pii/S0967063707002002), looked at melatonin levels in fish collected from as deep as 4800 m, and found some not quite statistically significant evidence of correlation to lunar (i.e., tidal) cycles. And finally, yet another study by [Cuvelier et al. 2014](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0096924) went a step further and decided to actually just record video of some deep sea communities over a few weeks. They again found mixed results, with [12-hour cycles](https://journals.plos.org/plosone/article/figure/image?size=medium&id=info:doi/10.1371/journal.pone.0096924.g006) apparent in the behavioural patterns of tube worms, but not so much in the case of scale worms, sea spiders, or sea snails. + +So to summarize, I think it's fair to say that the answer is kind of variable for different organisms; some appear to demonstrate cycling of some kind (though I'm not sure we can definitely call it ""sleep"" per se), while others don't seem to have any clear schedule." "I don't know about ""sleep"", but the largest migration of animals on earth happens every day from the sea surface to the deep ocean. If you consider 1000m deep, that is. This certainly establishes a schedule, but who knows what the lanternfish are doing in their down time. + +​ + +Here is an interesting TED talk by Heidi Sosik on the Twilight Zone: [https://www.youtube.com/watch?v=rJmwZhy9Suk](https://www.youtube.com/watch?v=rJmwZhy9Suk)" +629 "Is there any validity to the claim that Epsom salts ""Increase the relaxing effects of a warm bath after strenuous exertion""? If so, what is the Underlying mechanism for this effect?" 7969 https://www.reddit.com/r/askscience/comments/65vy4z/is_there_any_validity_to_the_claim_that_epsom/ 1492440202 65vy4z Medicine 2017-04-17 17:43:22 [deleted] "Probably not the primary benefit that epsom salts claim, but dissolving salts in water (or solutes into any solvent) makes the solution denser. So you're going to float slightly easier in an epsom salt batch than a normal one. Whether this makes any difference physiologically I have no idea. + +edit: The amount of people that made it through school without learning what a salt is is depressing me. Yes, epsom salts are salts. They are primarily a salt of magnesium, magnesium sulfate, just like table salt is a salt of sodium, sodium chloride." +943 "How is it so that several (all?) mammals grow and lose a set of ""baby teeth"" before growing their final dentition? Why stop at two sets when other vertebrates such as sharks regenerate their teeth constantly?" 7963 https://www.reddit.com/r/askscience/comments/8e8kuh/how_is_it_so_that_several_all_mammals_grow_and/ 1524454580 8e8kuh Biology 2018-04-23 6:36:20 "There are a handful of mammal species that constantly replace lost teeth, but most don't. On the flip side, quite a few non-mammals continuously replace lost teeth. + +There's two factors that seem to be at play in mammal tooth growth patterns. First, early mammals were probably relatively short-lived little shrewlike insect - eating things like[this](https://en.wikipedia.org/wiki/Morganucodonta). You don't need to constantly replace teeth if you aren't wearing them out. + +But on the flip side, not constantly replacing teeth allows mammals to do things with their teeth that other groups can't. Even mammal ancestors like cynodonts were starting to get distinctive canines. Mammals take this further with an array of highly specialized teeth rather than just one or a few kinds of teeth like you see in other groups. And those teeth lock together in precise ways allowing mammals to process food effectively. Our jaws are simpler than the reptilian norm because some of the jawbones have been incorporated into the inner ear, but despite that our precision swiss army teeth let us eat efficiently and effectively. It's hard to have that kind of interlocking if teeth are constantly being shoved around as they get replaced" "From: [Origin and Evolution of the Human Dentition](https://books.google.nl/books?hl=nl&lr=&id=VIoRAwAAQBAJ&oi=fnd&pg=PA3&dq=evolution+of+temporary+dentition&ots=1U4yMlcBYW&sig=Rc_ui3dfoJZvQpilJI18o5BQuMQ#v=onepage&q=evolution%20of%20temporary%20dentition&f=false) + +By William King Gregory + +>It is known to all students of odontology that, in typical sharks, the skin all over the body is covered with shagreen denticles, and that the primitive dental lamina of sharks is merely a rolled-up fold of skin bearing the dermal denticles, and carried around onto the inner side of the mouth. The whole surface of the throat is also covered with this denticle-bearing skin, and it is for this reason that in later groups of fishes we often find teeth on the pharyngeal parts of the gill arches. + +To explain: sharks do not have sockets in their jaw bones for teeth. Rather, they grow out of the skin, which is why they are able to have so many cycles of teeth. In most other animals, the teeth are plugged into the jaw bone. This is not the case in sharks. This is probably because shark jaws are not entirely homologous, evolutionary seen, to our jaw bones. The jaws of sharks are developed from the first pharyngeal arch if I remember correctly, which is the same arch that our jaws are developed from. However, cartilaginous fish, also known as chondrichtyes, do not really develop as many bones as we do. Rather, a lot of their skeleton is made of cartilage. The rest of their skull develops very differently from bony fish (osteichtyes) and from tetrapods (amphibians, reptiles (including birds) and mammals). If I'm correct, although evolutionary development is a while ago for me, the feature of having dentition incorporated into the skeleton happened after the evolution of bony fish, which have jaws that are more similar to ours. Since sharks split off from bony fish before this happened, their jaws are different from ours. + +Disclaimer: if anyone can correct me, please do so, because I am not 100% sure if what I said is correct + +Edit from /u/TheMythof_Feminism: +>In humans at least, the teeth are not ""plugged into the bone"", there is a significant separation called the periodontal ligament. It doesn't sound like a big deal, but it is; The tooth and the bone are necessarily separated and when this is not the case, that's called anquilosis and a major hassle. +" +1222 Do mosquitoes have a preference on blood type? Do some people have more “attractive” blood? 7963 https://www.reddit.com/r/askscience/comments/bb31a5/do_mosquitoes_have_a_preference_on_blood_type_do/ 1554780000 bb31a5 Biology 2019-04-09 6:20:00 "[Harvard Article Summary on the Subject](http://sitn.hms.harvard.edu/flash/2018/why-mosquitoes-like-you-the-most/) + +Tl;dr It has been found that some mosquitos favor certain combinations of bacteria in our skin and our body. Scientists do not know what combinations are favored. This also does not remain constant until after puberty, so where you grow up and the bacteria you were exposed to when you were younger could play a role. It is also noted that body odor genetics could possibly be related to this and be involved as well. + +They also mention at the end that future research into this could lead to identifying the attractive bacteria to mosquitos and modifying them as a permanent repellant." "*Not surprisingly—since, after all, mosquitoes bite us to harvest proteins from our blood—research shows that they find certain blood types more appetizing than others. One study found that in a controlled setting, mosquitoes landed on people with Type O blood nearly twice as often as those with Type A. People with Type B blood fell somewhere in the middle of this itchy spectrum. Additionally, based on other genes, about 85 percent of people secrete a chemical signal through their skin that indicates which blood type they have, while 15 percent do not, and mosquitoes are also more attracted to secretors than nonsecretors regardless of which type they are.* + +https://www.smithsonianmag.com/science-nature/why-do-mosquitoes-bite-some-people-more-than-others-10255934/" +630 Trappist-1 Exoplanets Megathread! 7952 https://www.reddit.com/r/askscience/comments/5vm1i8/trappist1_exoplanets_megathread/ 1487803812 5vm1i8 Astronomy 2017-02-23 1:50:12 Can tidally locked planets have warm (> 0 °C) atmosphere? What kind of convection there would be between the sides? Will all water end as snow on the dark side? "supposedly the planets are close enough to be seen approximately the size of our moon with the naked eye from one another. Does this not significantly decrease their potential habitability? + +would these bodies not experience exceptional seismic forces? + +combined with their short orbital periods, wouldn't this mean that their orbits are in constant significant flux? + +how do we know that none of them are moons of the other?" +1313 If fevers are the immune system's response to viral/bacterial infection, why do with try to reduce them? Is there a benefit to letting a fever run its course vs medicinal treatment? 7914 https://www.reddit.com/r/askscience/comments/bnbnlp/if_fevers_are_the_immune_systems_response_to/ 1557578547 bnbnlp Medicine 2019-05-11 15:42:27 "Yep. It alleviates the symptoms when you reduce the fever. Also, in some cases, the fever can go ‘out of control’ and get way too high, which causes your own proteins to start unraveling. + +There are plenty of physicians who would agree that sometimes it’s best to just not take anything and let the cold run its course. Some will say that it does shorten the downtime In the case of viral infections because it allows a stronger immune response (so long as the fever is controlled and doesn’t get too high). Of course, the fever is unnecessary when antibiotics are available in microbial infections, so might as well relieve symptoms and fight the bugs. + +The concept is similar to inflammation. There we have another biological response that physicians work hard to suppress in order to relieve pain and facilitate healing because medicine has developed ‘better’ or alternative ways of healing. + +But obviously, fevers and inflammation kept us alive for hundreds of thousands of years- for the most part- and are interesting to talk about." "The effects of fever in the immune system are still debated and not completely understood. Some pathogens reproduce more slowly in a fever, but not all. Recent studies have highlighted some Heat Shock Proteins that trigger an immune response cascade. This study bolsters the argument to let a mild fever run it's course. + +[http://blogs.discovermagazine.com/d-brief/2019/01/15/fever-immune-system-heat-inflammation/](http://blogs.discovermagazine.com/d-brief/2019/01/15/fever-immune-system-heat-inflammation/)" +1038 What population density could t-rex realistically have had? 7899 https://www.reddit.com/r/askscience/comments/8kxme6/what_population_density_could_trex_realistically/ 1526870534 8kxme6 2018-05-21 5:42:14 "[Here's a paper from a time this was previously asked](http://earth.geology.yale.edu/~ajs/1993/11.1993.06Farlow.pdf). + +Short answer seems to be that they don't know. + +There are a number of factors (prey density, metabolism, hunting strategy) that are all pretty speculative, making it difficult to get something approaching a real answer. There's even [some evidence](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4108409/) of social behaviors - pack hunting remains a possibility. Hard to be very sure of specific animal behaviors from ~~150~~ 66 million years ago." "You know, I have always been a bit bothered by the ecology in Jurassic Park, especially as it's supposed to contain entire herds of sauropods. + +Anyway, your comparison of tigers to dinosaurs is based on the faulty assumption that they have similar metabolisms, and so require similar amounts of food. There is mounting evidence that dinosaurs had a higher metabolic rate and were more active to their reptilian ancestors, but that doesn't necessarily mean they were as active as modern mammals. T. rex is a bit of an odd example, because as Tyrannosaurs evolved and got bigger, rather than extending their growth period, they just grew faster over the same period; which implies that, at least through their adolescence, they had a fairly high metabolism compared to their ancestors. On the other hand, their sheer size at adulthood would have meant that they didn't have to spend as much energy on maintaining their body heat (if anything keeping themselves cool would have been more of an issue). + +There are also several ecological factors that could foul this comparison; the density of potential prey in the region, the amount that varies across the year, the difficulty in taking down the prey, competition from other predators, etc. + +As to finding mates, bear in mind that T. rex had its head pretty far off the ground, which would have made it easy for it to see and hear other individuals at a distance. Such a large animal could probably roar pretty loud if that's how they communicated, and I've read at least one paper suggesting that the need to be seen at a distance played a role in determining theropod cranial anatomy. + +So in terms of your question, I don't really know, and I'm not sure anyone can make a confident estimate without knowing a good deal more about T. rex and its ecosystem." +1039 How do we know the age of the universe, specifically with a margin of error of 59 million years? 7897 https://www.reddit.com/r/askscience/comments/8m9iof/how_do_we_know_the_age_of_the_universe/ 1527333466 8m9iof 2018-05-26 14:17:46 "There's a phenomena called the Cosmic Microwave Background, or CMB. If you point a radio telescope in any direction, you see radio waves from the CMB. Looking at radio waves from the CMB is kind of like looking at visible light from the sun. If you go far back enough in time, the universe was denser and hotter, so dense and so hot that hydrogen atoms filled all of space ~~and there was fusion happening everywhere~~. But as time went on, the universe became less dense and less hot, until ~~fusion stopped happening and~~ the light could travel freely through space. The light we see from the CMB is from the moment that light could freely travel. + +Interestingly enough, both light from the CMB and light from the sun follow a blackbody spectrum. In fact, anything with a temperature emits blackbody radiation. If you measure the intensity of the light at different frequencies, you can fit the temperature. Right now the CMB is in radio, which is cold (about 2.73 kelvin), but if you go back in time the CMB light was much hotter. The reason it's colder now is because light is a transverse wave. As the universe expanded, the peaks and troughs of the light waves expanded with the expanded space. This phenomena is known as red-shifting. + +Anyway, if you look in different directions, the original temperature of the CMB is almost exactly the same in every direction, to about one part in 100,000. But it's not exactly the same in every direction. If you look at different angles, the temperatures can be slightly different. If you look at temperature deviations as a function of different angles, you can calculate what's called a Power Spectrum. The Power Spectrum allows you to solve what are called the Boltzmann Equations. The Boltzmann Equations are thermodynamic equations which constrain many parameters of the universe, such as its age, the expansion rate, the density of normal matter, density of dark matter, etc. Solving the Boltzmann Equations constrains the age of the universe. + +As a side note, the Boltzmann Equations are perhaps the most compelling argument for dark matter, since it's impossible to fit the Power Spectrum without a dark matter component (but this argument is so technical that many people are not familiar it). + +edit: if anyone is interested in learning more, this is a good resource: https://arxiv.org/abs/1502.01589. It's the 2015 Planck results, an experiment to map the CMB super precisely. + +edit2: As others have mentioned, the period of fusion was between 10 seconds and 20 minutes after the big bang, and is known as big bang nucleosynthesis. The period when light could travel freely was much later, about 380,000 years after the big bang, and is known as the time of last scattering. + +Also I should mention there are easier, more intuitive ways of calculating the age of the universe, such as measuring the Hubble Constant directly from redshifts and distances and calculating T = 1/H. However, the current best margin of error of 59 million years comes from precise measurements of the CMB Power Spectrum." "There are many ways and clearly many answers. For those who do not want to read any lengthy answers, I will make a couple breif ones + +1) Edwin Hubble noticed that almost all galaxies when being looked at are ""redshifted"". Redshirting is like listening to a police siren going away from you, the sound waves are stretched, but in this case it's lightwaves. Not only that, but the further a galaxy was from us, the faster it was moving away. This can be witnessed in the perspective of nearly any Galaxy you put yourself in. This discovery leads to the idea of an expanding universe. Over time we asked ""wait, what if we wound the clock backwards?"" So we did, and realized, logically, everything was closer together back in the past, and with lots of math and computations, we calculated that all matter was concentrated to a single point which is the beginning of The Big Bang. We don't know what happened before then, so we just leave it at that + +2) The Cosmic Microwave Background (CMB) has been redshifted as well, but to a much larger degree, making their once visbile light waves stretch out so much that they are now radiowaves. Not visible to the human eye, but once were. When you look at the CMB, you notice that everything is uniform with very minor variations. This suggests that all of these points we look at that are billions and billions of light-years away were once all together. There is some fancy math to be done here but it essentially proof of concept of the big bang, some fancy math was done (Blotzman Equations as mentioned in other comments), and it gives you the general beginning of when the universe might have been" +841 Nutrition Facts: Why is sodium listed instead of salt? 7893 https://www.reddit.com/r/askscience/comments/7284qu/nutrition_facts_why_is_sodium_listed_instead_of/ 1506290296 7284qu Chemistry 2017-09-25 0:58:16 "Because sodium is the component of salt that has an effect on our health. Also, sodium is naturally occurring in foods when not in salt. So when a food has sodium but no salt it could be confusing since people would see 0% DV for salt but 60% or something for Sodium + +Edit: I guess this is one way to more than double your karma" "Sodium chloride is the major ingredient in what we know as ""table salt"". There are other sodium salts, such as sodium iodide, which is added in small amounts to table salt, and sodium bicarbonate, known as baking soda. There are also non-sodium salts, such as potassium chloride, that contribute to the ""salty"" taste of foods. The word ""salt"" is simply too vague to list as a nutrient. + +Here's an interesting salt product to consider: [Half Salt](http://windsorsalt.com/products/half-salt/) contains 50% sodium chloride, 50% potassium chloride, and a trace of potassium iodide. It tastes similar to salt, but only contains half of the normal sodium compared to the same amount of table salt. + +Edit: Half Salt is not for everyone. There are health warnings associated with it. Please consult your doctor before using this type of product. I brought it up as an example of a different salt product, but it is certainly not appropriate for everyone. + +Edit2: [Here is an image of the Nutrition Facts and Health Warning found on the bottle of Half Salt.](https://i.imgur.com/eFBseD9.jpg) ""For normal healthy people, not to be used by persons on sodium or potassium restricted diets unless approved by a physician.""" +1040 Wilderness can be a rough place, do wild animals commonly suffer from anything like PTSD or anxiety? 7865 https://www.reddit.com/r/askscience/comments/8o9f4j/wilderness_can_be_a_rough_place_do_wild_animals/ 1528041353 8o9f4j 2018-06-03 18:55:53 This question gets at one of the most challenging issues with studying psychiatric illness, which is that finding decently valid animal models for those diseases is somewhere between extremely difficult and impossible. I would be very hesitant to accept a claim that a wild animal is suffering from PTSD or generalized anxiety disorder just because of how difficult it is to demonstrate that those conditions exist even in a perfectly controlled laboratory animal. Not an expert- and this isnt answering the question directly but more adding onto better answers. In the book Sapiens, the author briefly mentions that humans were very much prey and the jump to predator was pretty quick by evolutionary standards. The theory is that we still have prey instincts that we havent fully dealt with. So its very possible that we share fear traits with most animals - but its possible that 'predators' like wolves, bears, lions dont feel that fear/anxiety. When these types of animals have never seen humans or only seen friendly humans they tend to not be very worried. The Selous safari park in Tanzania for example is split into two parts: a hunting section and no hunting section. The animals in the hunted section will all run away if they see a car/human - meanwhile the ones on the other side are used to seeing humans and are completely unfazed. I noticed the zebras/antelopes/grazers etc were way more skittish and suspicious of us- whilst the lions acted like we weren't there. I was 1 meter away from a lioness, my heat was beating fast and my adrenaline was going off even though I knew I was safe but that lion couldn't have been more chill. Makes me wonder if hierarchy plays a role in this. +1041 Theoretically if there were 6 black holes making a cube shape that blocked off all entrances and you went into the empty space between the black holes (without getting sucked in) what would happen to space and time around you and outside of the theoretical black hole cube? 7860 https://www.reddit.com/r/askscience/comments/8qxua7/theoretically_if_there_were_6_black_holes_making/ 1528939236 8qxua7 2018-06-14 4:20:36 "This is just a friendly reminder that users should consult our [guidelines](https://www.reddit.com/r/askscience/wiki/index#wiki_askscience_user_help_page) before commenting, particularly before making a top-level comment. Top-level comments are required to be accurate and, if requested, you should be able to provide peer-reviewed sources to support your claims. You should refrain from making top-level comments if you do not have the required expertise to answer the question. + +This post has attracted many top-level and child comments that violate our guidelines. So this post has been locked. Fortunately, there are already a few threads which contain accurate and high-quality discussions of the answer to the OP's question. + +Cheers." "So im a little late. All these answers here are not very satisfactory. You can in fact have a region of space that is blocked off from the rest of the universe due to a lattice of black holes surrounding the region. One of my friends phd thesis was on this exact topic. And heres one of the papers that describes this. The phenomenon is called ""piecewise silence"" https://arxiv.org/abs/1402.3201 + +Basically what you get is a region of space that is distinct from the outside universe, and evolves completely independently. Its as if there were a smaller isolated universe inside the lattice of black holes" +1042 Do obese people have more blood? 7848 https://www.reddit.com/r/askscience/comments/8hmmmh/do_obese_people_have_more_blood/ 1525690765 8hmmmh Biology 2018-05-07 13:59:25 [deleted] "Ahh! Finally one relevant to my expertise!! + +The respondents so far are essentially saying “yes”. They’re not wrong, since each body cell requires a blood supply- so the BIGGER you are, the more blood you have. But let me tackle another angle: No. + +Take two people who are both 90kg. Same weight. One of these two runs 4 times a week and body builds at the gym. He is filled with lean muscle mass, which requires a vast network of vasculature to deliver oxygen and nutrients. His 90kg counterpart is made up of adipose tissue (fat storage cells) which just deposits energy for future usage and does not require extensive vasculature. A kg of lean muscle mass has a ton more vascular volume than a kg of adipose tissue. Sure, while your weight goes up due to obesity, you have more vascular volume than before, but the rise of blood volume per kilogram is lower than previous. It makes (accurate) drug dosing of narrow therapeutic range drugs that are dosed per kilogram much more difficult. + +Therefore, obesity actually = LESS blood volume than comparators of the same weight. + +EDIT: unautocorrected autocorrect" +842 Is there a limit on how long a power cord can be? 7843 https://www.reddit.com/r/askscience/comments/7j9og9/is_there_a_limit_on_how_long_a_power_cord_can_be/ 1513071869 7j9og9 Physics 2017-12-12 12:44:29 Short answer: yes. The longer a given wire gets, the greater electrical resistance it has. Resistance causes a voltage drop. If the wire is long enough, that voltage drop would be sufficient that the device would fail to work. Since I haven’t seen anyone mention yet: even if you could run it, a hair dryer would be a very ineffectual form of heating in a vacuum. Hair dryers rely on convection heating, and blowing warm air over their target, which of course is not possible on the Moon. +756 Why do so many medicines require you to stop eating grapefruit? 7832 https://www.reddit.com/r/askscience/comments/6bk8hr/why_do_so_many_medicines_require_you_to_stop/ 1494968622 6bk8hr Medicine 2017-05-17 0:03:42 "In a nutshell, It's because grapefruit contains compounds called furanocoumarins that inhibit cytochrome P450 enzymes; (mainly CYP3A4) which are responsible for the metabolism of many drugs (statins, anti platelets, antihistamines etc). Generally this causes them to hang around longer in higher concentrations, thus increasing the risk of adverse effects occurring. For example with a statin it'll increase the risk of liver side effects, myalgia and myositis. Other citrus fruits (limes, Seville oranges) can also cause this grapefruit reaction, and there are other foods that also contain furanocoumarins. It's a minefield! + +EDIT: goodness me, this simple explanation really blew up. Bear in mind it is just that; an explanation kept deliberately easy to follow. If you're interested I'd suggest a good pharmacology textbook that can give you a footing in basic principles. I should also point out that CYP enzymes are pretty much contained in most tissues in the body, and whilst I was talking about liver inhibition of CYP3A4 it is located elsewhere. This is why it's not a simple linear explanation of inhibition will cause raised levels, or increased half lives. I've also tried to reply to comments individually but I've been at work all day and am only getting a chance now. Also thank you to other awesome redditors who have contributed to further fleshing out my barebones answer, and correcting errors in other answers. " "PSA: effectiveness of oral hormonal birth control (the pill) is inhibited by grapefruits and grapefruits juice. So do not eat grapefruits or consume grapefruit products if you are on the pill. I know this doesn't answer OP's question but many others have answered it and I thought this was an important point to bring up. + + + +Also, most commonly prescribed antibiotics inhibit the effectiveness of the pill as well so use a second method of birth control while taking antibiotics! " +510 Why are snowflakes flat? 7809 https://www.reddit.com/r/askscience/comments/5gae8u/why_are_snowflakes_flat/ 1480783763 5gae8u Chemistry 2016-12-03 19:49:23 "First of all, it's important to realize that snowflakes come in all shapes and sizes. For example, [this chart](http://i.imgur.com/GbkLZKQ.jpg) shows the different kinds of snowflakes that will form under different conditions. You can clearly see many of these shapes in [this series real images](http://i.imgur.com/CVnnAUU.jpg) taken at high magnification. Now it is true that most of the flakes on both sets of images consist of flat and highly branched structures. The reason for this typical shape is due to 1) the hexagonal crystal structure of ice and 2) the rate at which different facets grow as the flake is forming. + +Let's look at this process in more detail. Snowflake formation begins with the growth of a small hexagonal base, [as shown here](http://i.imgur.com/dcOAyDs.jpg). The reason for this hexagonal shape is due to the crystalline network that ice likes to take under conditions we are used to. What happens next is a mixture of atmospheric conditions and random chance. There are three main processes that will determine the final shape of the flake:^(1) + +1. **Faceting:** Different parts of a snowflake will naturally show edges with the same symmetry as the crystal structure of the ice. + +2. **Branching:** As the crystal grows, some faces can start to grow faster than others. As they grow, each bit of the crystal will develop its own facets. This process can then repeat again and again creating the fractal-like shape we associate with snowflakes. + +3. **Sharpening:** As snowflakes grow, their edges tend to become thinner. Again, this has to do with the fact that the edges tend to grow more quickly than the interior so that the flake tends to taper off. + +As the chart in the first paragraph implies, atmospheric conditions will have a big effect in shaping these processes. As a result, at a given temperature and humidity, certain structures will tend to dominate. However, the exact details of how each flake will form also depends very strongly on the *exact* conditions it experiences. The problem is that the system is chaotic. In other words, even small differences in the initial shape of the flake or the layers of air it tumbled through can have a big effect on its final shape. No wonder then that it is basically impossible to find two snowflakes that look exactly the same! + +**Sources:** + +1. Kenneth G. Libbrecht/CalTech ([link](http://www.snowcrystals.com/science/science.html)) + +2. Nelson, J. Origin of diversity in falling snow. Atmos. Chem. Phys., 8, 5669–5682, 2008. ([link](http://atmos-chem-phys.org/8/5669/2008/acp-8-5669-2008.pdf)) + +___ + +**Edit:** I see it may be useful to add a tl;dr here: Ice crystals are like a six-sided prism. This prism grows as more ice molecules stick to its faces. It turns out that under conditions found in common snowstorms, some facets in XY plane tend to grow much faster than the facets along the main axis of the crystal. As a result, snowflakes usually end up looking like flat pancakes with many finger-like branches. " "To add on a little bit to what u/crnaruka said, the growth of snowflakes originally starts with a small hexagonal ice crystal or ice nuclei. + +The best ice nuclei (IN) are ones that are in a very similar [geometry](http://openscience.org/~chrisfen/Pages/Research/iceImages/ice1h/1h001.png) to of [Ice Ih](https://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Phase_diagram_of_water.svg/725px-Phase_diagram_of_water.svg.png) which forms in our atmosphere. The best IN that we use in cloud seeding is Silver Iodide. Other good IN that are found in the atmosphere are Kaolinite, bacteria, and many others. Ice can grow off of IN in three ways: + +1. Deposition onto the IN directly (water vapor freezing onto the crystal) +2. Condensation on to the IN and then freezing. +3. Immersion of the IN into a water droplet and then reaching the temperature in which freezing will occur. +4. Contact of an IN with a supercooled water droplet + +Anyway, once this seed crystal is established, an ice crystal can continue to grow through diffusional growth or by riming. +Riming will create [graupel \(which look like dip n dots\) or hail](http://www.wmdt.com/image/view/-/39154854/medRes/1/-/maxh/360/maxw/640/-/hdusxfz/-/GraupelvHail-jpg.jpg) if the collection of supercooled water is high enough. + +However we care about growth of ice crystals, which is through diffusional growth. If the seed crystal is in a supersaturated environment the growth will be dominated by deposition. However, as soon as water vapor deposits onto ice, a large amount of latent heat is released due to the phase change. This heat will affect the supersaturation around that area, limiting the growth. So there is a balance between the diffusion of vapor toward the crystal and the diffusion of heat away from the crystal. + +The ""desired"" growth rate depends primarily on the potential gradient around the ice crystal. This potential is not electric, but rather tied to the diffusion. If there is some curvature (which happens at 6 points around the hexagon seed crystal) it will enhance the growth rate locally by curving the potential lines and [depositing water vapor there](http://cdn.iopscience.com/images/0034-4885/68/4/R03/Full/rpp131559fig09.jpg) due to the Mullins-Sekerka instability. + +Finally, there's still a lot we don't know, but as computing advances are being made, out ability to model this type of behavior is becoming more realistic. [This paper](https://www.math.ucdavis.edu/static/research/infovault/gravner/Phy_Rev_E-79-2009.pdf) from 2009 had incredible results, given some of the pretty hefty assumptions they made." +757 Do rainbows also have sections in the infrared and/or ultraviolet spectrum? 7804 https://www.reddit.com/r/askscience/comments/69mjxt/do_rainbows_also_have_sections_in_the_infrared/ 1494093533 69mjxt Earth Sciences 2017-05-06 20:58:53 "Yes, definitely! You can easily see that in [this series of images](http://i.imgur.com/NZjWfWT.jpg) taken in the ultraviolet (UV), visible, and infrared (IR) parts of the spectrum. As you can see there is a UV band below the violet edge and an IR band above the red edge, which you obviously can't see with the naked eye. + +This result is exactly what we would expect. The way rainbows work is that when sunlight strikes water droplets suspended in the air, part of the light is reflected at the air/water interface at the back of each droplet, [as shown in this diagram](http://i.imgur.com/tcLYm5o.png). Since water is dispersive (meaning that the rerfractive index varies by wavelength), each droplet effectively acts as a small prism spreading the white light into its spectral components. Now our eyes our only sensitive to the visible (by definition), which is why a rainbow looks like a colorful transition from violet to red. However, sunlight also contains [IR and UV components in addition to visible light](http://i.imgur.com/KbIrTzA.png). While the water droplets absorb some of this light, much of it ends up reflected, as part of this extended rainbow that you can see from the IR and UV images posted above." "They do, and this is how William Herschel discovered infrared radiation. + +He was conducting an experiment to see if the different colors of a rainbow (as produced by a prism) had different temperatures. He placed a series of thermometers in the different colors of the rainbow and another to the side, next to the red in the rainbow, as a control. When he discovered that his control thermometer indicated a higher temperature than any of the others, he correctly theorized that there was an invisible form of light that was being split off past the red component." +843 There is a video on the Front Page about the Navy's Railgun being developed. What kind of energy, damage would these sort of rounds do? 7798 https://www.reddit.com/r/askscience/comments/70wiw4/there_is_a_video_on_the_front_page_about_the/ 1505755524 70wiw4 Physics 2017-09-18 20:25:24 "Others have calculated the energies of the projectiles, though for u/SocomTedd: the Mark 7 gun fired explosive shells, whose *explosive* energies far exceeded the kinetic energy of the projectile (~6000 MJ explosive vs. ~40 MJ kinetic.) The kinetic energy of the projectile, while large, is insignificant compared to the actual payload. + +I actually wrote an executive-level summary of railgun physics and their operation for a high-level program manager working for the Navy. (None of this involved classified material.) One potential issue is that railguns tend to use very dense materials for their projectiles, which are liable to penetrate through targets rather than deliver energy to them. This is easily solved by modifying the projectile to *scatter many smaller projectiles* near the target. + +As u/jehan60188 says, 4 MJ/kg is the threshold for railgun superior effectiveness. Once the projectile is fast enough it is more effective to use the kinetic energy of the projectile rather than use (chemical) explosives. As kinetic energy scales essentially without limit with respect to velocity, railguns are inevitably more effective. They are not, *yet*, more effective, which is what motivates continuing naval research on the subject. + +Chemical explosives provide a fundamental limit on the effectiveness of traditional guns, either through explosive or kinetic payloads. (There is a similar limit to the effectiveness of chemical rockets.) Electromagnetic propulsion, on the other hand, suffers from no such limit. " [deleted] +1314 Scientists think the Earth had 2 periods of time when it was almost completely covered in ice. They only lasted a few million years. Do we have any way of knowing if Europa or Enceladus might be in similar temporary freezes? Or is theirs a clearly permanent state? 7777 https://www.reddit.com/r/askscience/comments/cnw61y/scientists_think_the_earth_had_2_periods_of_time/ 1565318634 cnw61y 2019-08-09 5:43:54 "Oh, man, is this question right up my alley. + +Europa and Enceladus are definitely in a permanent state. They get so little sunlight that even if you caused them to melt somehow, they'd just freeze right back up again. + +The ""two-state"" nature of Earth's climate comes about because of the ice albedo feedback: ice is white, and so it reflects away sunlight and keeps the planet cold; water is dark, so it absorbs sunlight and keeps the planet warm. + +The Earth gets the right amount of sunlight that when it's covered in water, it absorbs enough sunlight to stay above freezing, and when it's covered in ice, it absorbs little enough sunlight to stay frozen. But if it were closer to the Sun, even an ice-covered Earth would be too hot to be frozen, and so only the water-covered Earth is possible. If it were farther away, only the frozen Earth is possible. + +Aaaanyway, Europa's ice absorbs only 30% of the sunlight that strikes it, and its surface temperature is about 110 Kelvin (-300 Fahrenheit). The [simplest possible climate models](https://en.wikipedia.org/wiki/Climate_model#Zero-dimensional_models) predict that if the planet is in balance so energy in equals energy out, temperature (in Kelvin) should be proportional to albedo to the 1/4 power (square root of square root). + +Deep water oceans absorb about 95% of the sunlight that strikes them. And so we can predict that if something caused Europa to melt, its steady-state temperature would be (110) * (95% / 30%)^(1/4) = 147 Kelvin, or -200 Fahrenheit. + +A hefty warming, but definitely it's just going to freeze back up again. Enceladus is even worse." "Europa and Eceladus are almost certainly permanently encased in ice, for a couple reasons: + +First, their distance from the sun gives very little solar heating compared to the earth. As radiated energy flux scales as the distance to the radiator squared, and Jupiter averages just over five times farther from the sun than the earth, Europa gets about 25 times less solar energy per square meter than the earth. Saturn is about nine times further from the sun than the earth, so Enceladus gets somewhere around 80 times less solar energy per unit area than the earth does. + +Second, these moons have no significant atmosphere to speak of. Water has no stable liquid phase below about 0.6% of atmospheric pressure. Without a mechanism to generate an atmosphere, the water will always be ice or gas, or be on its way to one of these two phases. + +Third, in the snowball earth situation, runaway glaciers increased the albedo -- the amount of light the earth reflects back into space -- enough that glaciers completely covered the earth. Once this occurred, large amounts of CO2 from volcanism built up in the atmosphere as one of the primary ways CO2 is removed from the atmosphere is by the weathering of certain rocks, which is severely slowed in the absence of rain. Europa and Enceladus have minimal, if any, volcanism (maybe cryovolcanos?), and very little atmosphere, so we aren't likely to see any significant changes to the greenhouse effect there." +1043 Why do things get darker when wet? 7770 https://www.reddit.com/r/askscience/comments/8ouk73/why_do_things_get_darker_when_wet/ 1528232735 8ouk73 2018-06-06 0:05:35 "This is the simplest explanation I can make. + +A layer of water sits on top of the fibres. +This re-refracts the light that’s bouncing off the fibres back onto the fibres, instead of a single refraction like what would normally happen when the material is dry. + +This allows the material to absorb more light, making it appear darker. " "**Refractive index** of a material is the ratio between speed of light in vacuum and speed of light in that material. Light tends to bounce back when encountered with a sharp change in refractive index. Being wet means that there's a water film covering the material, mediating the change in refractive index, resulting in reduced reflection. + +**Edit** + +Part 2 of the story + +Apart from index mediation, the water film does something else. For rough/fibrous surfaces, the reflection will be **diffuse**, i.e. visible from all directions. When a water film is present, the surface becomes smooth, and the reflection will be **specular**, and only visible in one direction. So in most directions, the material will appear darker. + +Conductors are a completely different beast. The reflection off of metals are not solely dictated by the refractive index." +1223 Is there a reason that the majority of Earth's landmass is in the northern hemisphere? 7753 https://www.reddit.com/r/askscience/comments/b3imz9/is_there_a_reason_that_the_majority_of_earths/ 1553121872 b3imz9 Earth Sciences 2019-03-21 1:44:32 Geology student here. It's a coincidence. There were large portions of the past, such as [during the Cambrian](http://www.scotese.com/newpage12.htm) where the northern hemisphere was essentially a giant ocean, and all the land was concentrated in the southern hemisphere. "It is just due to where the landmass is now. It hasn't always been that way, nor has the amount of land stayed constant. Think of continents as ""giant Earth floaties"" of lighter bulk rock, that just slowly flow around the surface of a ""liquid in the very loosest sense of the word"" sphere of dense liquid (plastic) rock and metal. This is called plate tectonics. + +The position and characteristics of continents and oceans at any given point in time cause big changes in climate and weather on the scale of millions of years." +631 We are Professor Tim Lenton and Dr Damien Mansell from the University of Exeter and we're about to launch our free global climate change course. Ask us anything about Climate Change, from challenges to solutions! 7745 https://www.reddit.com/r/askscience/comments/5ow6eu/we_are_professor_tim_lenton_and_dr_damien_mansell/ 1484827241 5ow6eu Earth Sciences 2017-01-19 15:00:41 Really basic one here, what can I or my family do, that is free (financially) to help. I'm happy to invest time, effort and myself but just don't have enough spare capital to buy an electric car, solar electric system or solar heated water, what else is there that we can do ? Simply put: is it too late? +1315 Why do plants never get cancer? 7702 https://www.reddit.com/r/askscience/comments/c6pjr3/why_do_plants_never_get_cancer/ 1561755093 c6pjr3 Biology 2019-06-28 23:51:33 "Plants can absolutely have uncontrolled growth of cells, which is how cancer is usually defined. + +For example, trees can have burls. The way these form is distinct from mammalian cancers because they do not metastasize and travel to other “organs”. + +Usually burls make beautiful furniture and are not fatal to trees. But also, having numerous copies of chromosomes is not usually fatal to plants either. In fact, it can even be desirable (think “huge” strawberries) + +But plants are awesome and can live thousands of years (like the Bristlecone pine) and handle diseases differently than other organisms. + +You can usually pick up a cheap book on Dendrology at a used bookstore or on Amazon if you want some light reading!! (Disclaimer - “lightness” of the reading depends on your inner nerd and curiosity!) + +*Edit* -removed “knot” because as u/autoradiograph pointed out, these are different than burls (and galls)." """*Plant cells are anchored in place by the cell walls, so plant cancers never spread far or metastasise to other tissues.*"" + +​ + +Reference: + + [https://www.sciencefocus.com/science/can-plants-get-cancer/](https://www.sciencefocus.com/science/can-plants-get-cancer/) + +​ + +"" *“Plants don’t get cancer like animals do,” said Susan K. Pell, director of science at the Brooklyn Botanic Garden, “and the tumors they do get do not metastasize because plant cells don’t move around.” Rather, they are held in place by cell walls.* + +*Plant tumors — aggregates of cells that have multiplied excessively — are usually caused by a bacterium, virus or fungus, or may develop as a result of structural damage, Dr. Pell said.*"" + +​ + +Reference: + + [https://www.nytimes.com/2013/07/16/science/can-plants-get-cancer.html](https://www.nytimes.com/2013/07/16/science/can-plants-get-cancer.html)" +758 "Why does the electron just orbit the nucleus instead of colliding and ""gluing"" to it?" 7694 https://www.reddit.com/r/askscience/comments/6ju93t/why_does_the_electron_just_orbit_the_nucleus/ 1498584469 6ju93t Physics 2017-06-27 20:27:49 "This is one of the problems that led to the development of quantum theory. The [gold foil experiment](https://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment) showed that an atom's positive charges are concentrated in a small region (the nucleus) and its negative charges are spread around it in a much larger volume. It was immediately apparent that according to the classical laws of mechanics and electrodynamics, an atom's electrons should very quickly spiral into its nucleus. Obviously, these theories could not be used to understand the internal behavior of atoms. + +The solution to this conundrum was found in a reformulation of Hamiltonian mechanics. Hamiltonian mechanics uses the relationship between an object's energy and momentum to derive its motion through its environment. By combining this with the observation that atomic systems can only exist in discrete energy states (ie, 1 or 2 but not between them), it was discovered that the momentum states must also be discrete. In particular, the electrons' momentum is constrained in such a way that there is no pathway for them to travel into the nucleus." "Well they do in fact collide and glue together sometimes. This is [reverse beta decay](https://en.wikipedia.org/wiki/Electron_capture), which causes a proton to become a neutron. + +The trouble with this is that neutrons are heavier than the mass of a proton and electron combined, and so require even more energy to create than was available from the incoming electron. It also means that when there are too many neutrons in the nucleus, there is enough surplus energy to cause the nucleus to decay by [alpha](https://en.wikipedia.org/wiki/Alpha_decay) or beta emission and fire out particles that sort out the imbalance. + +Another simple explanation is the [bohr model](https://en.wikipedia.org/wiki/Bohr_model) of the atom, which assumes that an electron is a simple wave (pre schrodinger) and it needs to form whole wavelengths that are proportional to its momentum. If it fell into the atom, its wavelength would get longer, but there would not be enough space to contain a whole cycle of the wave, making it an impossible position." +1044 Is the brain of someone with a higher cognitive ability physically different from that of someone with lower cognitive ability? 7681 https://www.reddit.com/r/askscience/comments/8zckwc/is_the_brain_of_someone_with_a_higher_cognitive/ 1531760184 8zckwc Neuroscience 2018-07-16 19:56:24 "I think using the technical definition of ""physical"" would mean the answer *must* be yes. All cognitive phenomena are the result of *something* in the brain--chemical, structural, whatever, but it can't exist if it's not physically explainable. + +I realize you may have meant more like ""are the differences macroscopically visible,"" but worth all saying all the same. " "Yes there are differences, but the way that they differ and the scale at which they do are so vastly minuscule that we can't even begin to change or shape those differences to our benefit. + +Just as an example, we can treat certain brain disorders which we know stem from a deficiency or surplus of a specific neurotransmitter. Things like ADD or Parkinson's can be controlled with medication but primarily because we understand the disorders enough to have a working antagonist for them. + +Things like knowledge and cognitive function are multifaceted and cannot be affected by simply introducing a serotonin blocker, it requires a cocktail of medication that we have not discovered yet. This is mostly because we still have not discovered what ""causes"" people to be smarter than others. + +In considering the future, I can foresee a certain blend of ""mentally stimulating"" medication that can maybe facilitate learning and knowledge gaining to an extent by reducing noise and brain power to at least focus better at learning, but it would still require an active component from the learner to gain the knowledge themselves. + +If you want to talk centuries into the future, then maybe one day we really will be able to download information to the brain, but that's still a topic for sci-fi books for now." +511 If you had a pinhole camera with an aperture that only let one photon in at a time- what would its pictures look like? 7680 https://www.reddit.com/r/askscience/comments/5k90xr/if_you_had_a_pinhole_camera_with_an_aperture_that/ 1482684782 5k90xr Physics 2016-12-25 19:53:02 "My understanding is that diffraction becomes a limiting factor with smaller apertures. I believe a ""photon sized"" (aka wavelength sized?) pinhole with an ambient brightness source would result in a diffraction pattern of concentric rings with no capability to resolve any detail. + +The diffraction limit describes the absolute maximum angular resolution for optics. To resolve very fine details, you need a large aperture. This is one reason why telescopes and huge and why SLR camera will always have better image quality than mobile phones given the same technology in each. + +http://www.astro.cornell.edu/academics/courses/astro201/diff_limit.htm + +As the aperture approaches zero, the angular resolution approaches infinity, meaning you can't resolve the details of anything, no matter how large it is. " This depends on your pinhole size and light intensity. If you have a pulsed laser directly incident on the pinhole stopped down so only <<1 photon passes through the aperture per pulse, you'll form the appropriate diffraction pattern on the other side - that is, a single photon can interfere with itself to form a diffraction pattern. This is reminiscent of Youngs double slit with a single photon experiment. +1045 Why are there so many volcanic eruptions recently? Are they somehow connected or is it a coincidence? Or is it just new media coverage? 7652 https://www.reddit.com/r/askscience/comments/8ogln9/why_are_there_so_many_volcanic_eruptions_recently/ 1528112571 8ogln9 Earth Sciences 2018-06-04 14:42:51 The current level of activity is normal. On average, there are usually ~20 volcanoes in some stage of erupting at any given time. The recent news worthy eruptions (e.g. Hawaii and the recent one in Guatemala) are not connected. So the short answer it's just the coverage and/or the fact that these two eruptions are happening in populated places and that both are being filmed a lot by locals (mostly safely in the case of Hawaii and **really** unsafely in the case of the Guatemalan eruption, you should never be as close to a pyroclastic flow as some of the people shooting video are). As for the rates, couldn't find any particularly good plots, but you can check out [the smithsonian](http://volcano.si.edu/reports_weekly.cfm) weekly eruption report to 1) get a sense that there are lots of eruptions going on that aren't making the news and 2) if you go back into the archives, which span ~18 years, you can get a somewhat qualitative sense that this number of currently erupting volcanoes isn't particularly odd. As a side note, this is not quite real time, so this is the summary for last week so it doesn't yet include the eruption in Guatemala. "It is worth noting that the current eruptions at Kīlauea in Hawaii and Fuego in Guatemala are nothing new. Kīlauea has been in a constant state of eruption since Jan. 1983. More than 35 years. A few weeks ago a dike intruded further east into the Lower East Rift Zone, causing the fissure eruptions that have been so much in the news. It’s been a long time since Kīlauea burnt down any houses, but as soon as it does it suddenly gets media attention and a lot of people think it’s a new eruption when in fact it’s just another phase of the activity that started in 1983 - just at a new vent location. + +Volcan Fuego too has been in a frequent state of eruption for years now, with frequent Strombolian activity and often sending lava flows down the various arroyos descending around the summit. Only when it enters a more explosive phase, producing pyroclastic density currents that kill people, does it make the news. Thus further adding to the general impression that there has been an increase in volcanic activity world-wide, when in fact this is not true. " +1494 Can other animals be allergic to us? 7633 https://www.reddit.com/r/askscience/comments/g25krx/can_other_animals_be_allergic_to_us/ 1587001197 g25krx Biology 2020-04-16 4:39:57 "Yes! You can get your pet tested for human dander and even get them allergy immunotherapy shots for it. + +Info here: https://wagwalking.com/condition/human-dander-allergies + +Here is the veterinary catalog for Greer which makes allergen extracts. Human dander is on page 20 (item E18): https://www.stagrveterinaryallergy.com/wp-content/uploads/2019/12/Stallergenes-Greer-Veterinary-Product-and-Services-Catalog.pdf + +Source: work in the allergy immunotherapy market." "Yes. Cats and Dogs can be allergic to humans. For the same reasons humans can be allergic to them [""Dander"" or dry shed skin.](https://wagwalking.com/condition/human-dander-allergies) Dogs and Cats can also be allergic to one another. + +To my knowledge most if not all animals can have allergies and against most if not all shed skin it should be theoretically possible for any animal to allergic to another." +1316 What happens to your voice if you don't speak for a very long time? 7620 https://www.reddit.com/r/askscience/comments/bw78ym/what_happens_to_your_voice_if_you_dont_speak_for/ 1559541112 bw78ym Human Body 2019-06-03 8:51:52 There's a world of difference between being alive for 2000 years without using your voice, and being frozen for 2000 years. Assuming your story solves the issue of unfreezing without damage, and people's brains and hearts and systems work normally -- vocal cords should too. Sort of unrelated to OP's story, but the question got me curious - what happens in the real world if someone didn't talk for years (something like selective mutism)? Would your larynx be weak so that talking again would be an issue you'd have to have some form of physical therapy for? +844 How does the body decide where to store fat? 7616 https://www.reddit.com/r/askscience/comments/7lhjob/how_does_the_body_decide_where_to_store_fat/ 1513950752 7lhjob Biology 2017-12-22 16:52:32 Beyond the generalized sex differences, there are a number of hormones that affect where and how we store fat - for ex. estrogen encourages the more 'classically feminine' fat storage patterns (hips and thighs) whereas stuff like cortisol and insulin production lead more to belly fat. As the latter two, cortisol in particular, are highly stress-dependent, people may even notice different fat storage patterns at different stages of life, depending on things like diet and levels of stress or of sex hormones. "I'm a graduate student studying human nutrition, and I just finished a class on nutritional biochemistry where we studied the metabolism of carbohydrates, fats, and energy balance regulation in great detail. To answer your question, I'll need to start by explaining a couple of small details about fat digestion, and then I'll move on to answering your actual question. + +When you consume any amount of fat in your diet, the cells in your small intestine will package those fatty acids into things called chylomicrons. When you think of a chylomicron, think of the fat-equivalent of a water balloon, but at the molecular level. Chylomicrons have a number of different molecules, but you might say that their primary function in the body is to transfer any fat you ingest to wherever the body needs it to go, be it for energy use or energy storage. All the fat that's being transported via these chylomicrons is done so in the form of triglycerides, which are three fatty acids attached to a 3-carbon molecule called glycerol. + +After the small intestine cells package the fat into these chylomicrons, the chylomicrons are sent throughout the body by entering the lymphatic system, which then eventually pours into the blood stream via the subclavian vein. The blood takes these small packages of fatty acids throughout all tissues in the body. (Side note--this is oversimplified: fatty acids of different lengths have different pathways, but this will give you the basic idea without overloading you with too much detail that you don't care about.) + +The main way the body regulates where this fat is stored is by regulating the specific protein that these chylomicrons dock to that will cause the fatty acids to be transferred to whatever cells are in a given area. Keep in mind that these could be any cells in the body, including skeletal muscle cells (which would primarily metabolize the fatty acids for energy production), as well as adipocytes (the name for cells whose primary function is to store fat in the body for use during periods of fasting, starvation, or simply between meals in a given day). The name of the protein that is responsible for transferring these fatty acids from chylomicrons to neighboring cells is called lipoprotein lipase, and you'll see it commonly abbreviated as LPL. + +This protein is located in capillaries throughout the body. When a passing chylomicron encounters LPL, a receptor on the exterior of the chylomicron known as Apo-C allows for the chylomicron to dock to the LPL protein, and LPL begins to drain the chylomicron of the triglycerides it contains and hydrolyze them to make free fatty acids--they're not attached to a glycerol molecule anymore. These free fatty acids then float near cells that are found near that capillary where this is all taking place and are free to pass through the membrane of whatever cell is in the vicinity due to how similar they are to the general structure of cell membranes. Once inside the cells, these fatty acids are restructured into a triglyceride by using a glycerol molecule that was created within the cell, and the triglyceride is now able to be stored or used for energy. + +So now to your question: how does the body regulate where fat is stored? Why do we accumulate fat in our stomachs, butts, and thighs instead of our foreheads or the backs of our hands? This is primarily determined by where and to what degree LPL is expressed. I believe there are several ways LPL is genetically regulated, but they only ways I've learned about are hormonal regulations. For example, when you consume a diet containing both carbohydrate and fat molecules (which will be most any meal you eat, really), the insulin that's expressed will spread throughout the body and interact with all the cells it reaches in several different ways. One of those ways is going to be by inducing an upregulation of LPL in those parts of the body that the body desires fat to be stored or taken up. As others have mentioned, other hormones affect the body's fat distribution in several ways, and I admit I don't understand the specific mechanisms for how these hormones all work on LPL, but I know that insulin is one of the major hormones involved. + +Now, out of principle I try to admit there may be errors in my explanation, but I'm fairly confident in this description overall. If you have further questions--be it about this topic or any other in the field of nutritional science--feel free to PM me and I'll see if I can answer your questions." +759 During the winter, humans are known to track animals via their footprints in the snow, as we do not posses the same olfactory capabilities as say a wolf. Are there any other animals which have been observed tracking animals by means of visual cues? 7592 https://www.reddit.com/r/askscience/comments/6lvrth/during_the_winter_humans_are_known_to_track/ 1499453387 6lvrth Biology 2017-07-07 21:49:47 A Norwegian study found that kestrels at least seem to be able to track the paths of small animals. [They preferentially hunt over the established vole trails.](http://www.nytimes.com/1995/04/25/science/raptors-found-to-track-prey-s-ultraviolet-trail.html). Which if I'm reading your question right is what you're asking, basically using 'historical' sensory data to track prey as opposed to direct sight and chase style hunting. "Some falcons, which have poor senses of smell, are capable of tracking rodents and other small mammals by the UV signature emitted in their urine. + +http://www.nytimes.com/1995/04/25/science/raptors-found-to-track-prey-s-ultraviolet-trail.html" +944 Why did all the lithium end up in Chile? 7591 https://www.reddit.com/r/askscience/comments/89yh9m/why_did_all_the_lithium_end_up_in_chile/ 1522923024 89yh9m Earth Sciences 2018-04-05 13:10:24 It didn't. However, the combination of natural concentrations and the mechanics of salt flats has created the world's most cheaply-accessible lithium source. There are other deposits around the world, and there are other salt flat sources (Argentina and Bolivia both have some, as do Tibet and Nevada USA), but Chile's the biggest. "Lithium is a very interesting element which is actually ubiquitous in the earth's crust but occurs in very low concentrations in most terrestrial rocks. As a result of fractionating magma crystallization, lithium is most often concentrated in granites in the earth's crust. Furthermore, it occurs in higher concentrations in sea water than in rocks. As a result, we source the majority of our lithium from either pegmatites (highly fractionated granites) and sea water/groundwater brines and resulting evaporites (salt beds). + +There are pegmatite deposits all over the world since they occur in different geological terranes and they are actually a source many of our rare earth elements. The Li-bearing salts and brines (a brine being a fluid with high salt content) are not unique to Chile and they are exploited in other countries like the US and Australia... but Chile (and to an extent, Argentina and Bolivia) has the largest reserves in the world. + +A couple of key geological components are needed to contain and naturally concentrate lithium in order for it to be profitable to extract and refine. The geology of Chile is dominated by the Andean mountain range. This extensive orogeny has resulted in a large-scale subsidence adjacent to the mountains. This tectonic subsidence has become a drainage basin, collecting any sea/river/ground water running off the mountains and from surrounding areas. Since the extensive Andean mountain range in Chile also created the driest desert/region in the world (i.e. the Atacama), you now have a massive drainage basin that collects water and it evaporates incredibly fast, leaving behind salt flats and salt lakes. When you evaporate water with anything dissolved in it, the water will leave behind these dissolved constituents (primarily salts and carbonates/sulphates/borates). This process is how the Li is naturally concentrated in the salt flats - a constant recharge of Li-bearing water being added to the basin and then evaporation leaving the Li-bearing salts in the salty brines and ultimately salt beds. + +Like I mentioned above, this process isn't unique to Chile and the same hydrogeologic system feeds Li-bearing deposits in the adjacent countries of Argentina and Bolivia. But the massive scale of the Andean orogeny and the incredible evaporation rates in the related deserts probably results in an ideal environment to concentrate lithium. " +845 Did NASA nuke Saturn? 7580 https://www.reddit.com/r/askscience/comments/70g7k1/did_nasa_nuke_saturn/ 1505558138 70g7k1 Planetary Sci. 2017-09-16 13:35:38 The isotope of plutonium used in Cassini's RTG is not fissile. It just continues to emit alpha particles until it's all decayed away. "The plutonium will not cause an uncontrolled nuclear explosion, it is not designed to do so. + +The 'damage' done will be in the form of kinetic impact. + +Consider what 20 grams of steel travelling at 900km/h does to a human (aka a handgun bullet). + +Cassini was more than ten thousand times that mass, and hit Saturn at around fifty times that speed. + +That said, Saturn's upper atmosphere is hit by larger kinetic impactors quite regularly. Cassini would have flared up and burned just like a larger-than-usual meteor burning up in Earth's atmosphere. + +Picture the Chelyabinsk impactor from 2012. It was about 12 tons, and hit Earth's atmosphere at around 50000km/h. Cassini would have been less impactful than that. + +(Edit: Correction from /u/scifiguy95 below - the impactor was 12000 tons)" +760 Is gravity weaker on the equator just because the radius is larger, or also because of a centrifugal force? 7577 https://www.reddit.com/r/askscience/comments/6f3qee/is_gravity_weaker_on_the_equator_just_because_the/ 1496526575 6f3qee Physics 2017-06-04 0:49:35 "Both, and the radius is larger because of the centrifugal force. Both effects contribute about 0.3% each. + +[See here](https://www.physicsforums.com/insights/all-about-earths-gravity/)" "Yes. + +A person standing on the summit of Mt Chimborazo in Ecuador (furthest surface point from the center of the Earth, 6260 m ASL, 1.47° S.) would weigh about 0.7% less than they would at the North Pole. + +While I haven't done the math recently, I believe the two effects in play, gravitational and rotational, each contribute approximately equally to this result – between 0.3-0.4% each." +761 Does continental shift have any effect on man made structures like bridges and canals that connect them? 7576 https://www.reddit.com/r/askscience/comments/6vp34q/does_continental_shift_have_any_effect_on_man/ 1503556842 6vp34q Earth Sciences 2017-08-24 9:40:42 "Oh yes, they wreak havoc on man made structures! Plate boundaries are shifting on average around 5cm per year, some are much slower but some are much faster (I think they clocked one in at 18cm / year) so there are *huge* engineering efforts combating these perpetual forces of nature. + +The first thing they do is avoid these areas at all costs but if it's not avoidable (Think San Francisco, everywhere) then building things so they can either bend or have devices in the to let them either expand or contract is just the start. Now, overpasses and pipelines and sewers don't like to do these things so engineers either have to choose what the smaller cost is: to replace it after it is destroyed or to put in failsafes. + +A highway or water infrastructure system failure isn't nearly as catastrophic as a hydro-electric dam failure so planning accordingly is the biggest factor in it all. " The longest suspension bridge in the world, the [Akashi Kaikyo bridge](https://en.wikipedia.org/wiki/Akashi_Kaiky%C5%8D_Bridge), had both its two towers erected but none of the cabling when the Great Hanshin earthquake of 1995 struck. The slip beneath the bridge widened the gap by 1 meter (0.8 meters between the towers, and 0.3 between one tower and Awaji island). However the bridge was initially designed to withstand length changes of up to 2 meters *per day* due to temperature alone, so the lengthening of 1 meter only required very minor changes. +1405 Family members are posting on Facebook that there has been no warming in the US since 2005 based on a recent NOAA report, is this accurate? If so, is there some other nuance that this data is not accounting for? 7576 https://www.reddit.com/r/askscience/comments/d0gfhl/family_members_are_posting_on_facebook_that_there/ 1567775258 d0gfhl 2019-09-06 16:07:38 "**Edit:** As /u/joekercom points out, [the 2005 date is not arbitrary](https://www.reddit.com/r/askscience/comments/d0gfhl/family_members_are_posting_on_facebook_that_there/ez9ihup/). In 2005 NOAA began collecting climate data from a new network of weather stations due to criticisms about the validity of the existing weather station network. The data since 2005, from both the new and the old networks, does not show a significant warming trend. The misconception here is that this new network is more accurate than the existing network and that a lack of warming in the new network's data refutes the existing observations of warming in the USA. This is not the case. + +The whole purpose of the new network (called the US Climate Reference Network) was not to replace the existing network of weather stations, but to measure the validity of the existing network's data and determine whether there are baises in the data due to things such as urban development. We did not know whether the existing weather station network was accurate, but we do know that the USCRN is a ""pristine"" weather station network that should be free from bias. Here's the important point: [When researchers compared the results from the USCRN with the existing climate station network, they have found that the data from both networks largely agree with each other.](https://journals.ametsoc.org/doi/full/10.1175/BAMS-D-12-00170.1) What this means is that as far as we can tell, the existing climate data network that NOAA has been using for decades has not been strongly biased by external factors other than genuine climate change. + +Thus, while the 2005 date is not arbitrary, it is neither the beginning of a new era of climate data that rejects all previous observations. It's the opposite, the climate data collected since 2005 only supports the idea that the long-term warming trend we have seen here in the US and elsewhere is a genuine climatological phenomenon, and not due to unseen bias in the data collection methods. + +**Another Edit:** Just a nice source from /u/kilotesla showing how the new network (USCRN) compares to existing climate data networks used by NOAA: + +[New network USCRN vs old networks](https://www.ncdc.noaa.gov/temp-and-precip/national-temperature-index/time-series?datasets%5B%5D=uscrn&datasets%5B%5D=climdiv&datasets%5B%5D=cmbushcn¶meter=anom-tavg&time_scale=12mo&begyear=2000&endyear=2019&month=12) + +#End Edit / Original Post: + +They're right, but there are four things to keep in mind here: + +1. The year 2005 is an arbitrary date. [Over time there is a clear warming trend in the USA.](https://www.epa.gov/climate-indicators/climate-change-indicators-us-and-global-temperature) Go back to 1990 and there is a demonstrable warming trend, go back to 1980 and there is a very clear warming trend. + +2. US temperatures since 2005 have not been significantly rising, but they're already hot. All temperatures since 2005 have been above the historic average. If there was no warming trend, we would expect some years to be above the average and some years below. + +3. Changes in local weather patterns can dominate the warming trend in the short term, and the USA is a very temperate country. For example, El Nino vs. La Nina temperature conditions in the Pacific ocean can greatly influence the USA's temperature in any given year, with two of the hottest years in the last 15 being hot El Nino years. + +4. The years 2015-2018 are the four hottest years on record globally. The global warming trend is clear, and the local variations in weather that have stalled warming in the USA will not continue forever." "Everyone saying ""It's called global climate change, not US warming. The US could be getter colder"" is totally missing the point. The US is certainly getting warmer, and *even that cited NOAA data shows it.* + +The NOAA data that these Facebook posts are talking about comes from [here](https://www.ncdc.noaa.gov/temp-and-precip/national-temperature-index/time-series?datasets%5B%5D=uscrn¶meter=anom-tavg&time_scale=p12&begyear=2005&endyear=2019&month=7). (For example, [here's](https://www.realclearenergy.org/articles/2019/08/23/climate_alarmists_foiled_no_us_warming_since_2005_110470.html) an example of a page using that data to downplay global warming- written by a [Heartland Institute](https://www.nature.com/articles/475423b) lawyer.) *Even if you're only using this data*, it still shows a warming trend. You can find it in Excel yourself, or look at [this version that I made quickly](https://i.imgur.com/EUqU688.png). See how the black trendline slopes up, indicating a warming trend just in the last fifteen years? The main reason that the Facebook memes use this dataset is because it has monthly values with high variance, which makes that long-term trend harder to see. In contrast, [here's](https://i.imgur.com/mpl8sxH.png) the exact same data, but averaged over a 2-yr period, making the warming easier to see. But even though the month-to-month differences are much larger than the total warming, don't be tricked into thinking this warming doesn't matter. + +If you extrapolate that trendline, you get >5 degrees F of warming by the end of the century. 5 degrees might not seem like much, but it's about [double the warming](https://www.ipcc.ch/sr15/) that the IPCC sets as a relatively ""safe"" target, and about [half](https://xkcd.com/1379/) the temperature difference between the current climate and the cold of the last ice age. Remember, this is the chart that the Facebook memes and Exxon-funded lawyers are using to show that global warming isn't real. Imagine the charts they're not showing! In IPCC reports that *don't* cherrypick data from a specific place, time period, and single dataset, the total warming is predicted to be [twice as large](https://www.ipcc.ch/report/emissions-scenarios/) without serious interventions." +1046 How would having a fish in the ISS work? 7565 https://www.reddit.com/r/askscience/comments/8syf6g/how_would_having_a_fish_in_the_iss_work/ 1529640787 8syf6g Biology 2018-06-22 7:13:07 "Interestingly there has already been an experiment on the ISS involving fish. The [Medaka Osteoclast](https://www.nasa.gov/mission_pages/station/research/experiments/984.html) experiment was created by the Japanese Space Agency, and it tested the generation of osteoclasts in medaka fish. + +This was made possible due to the aquatic habitat - a facility specially designed to allow fish to live on ISS." "> Would the fish be able to get oxygen from the water? + +Yes, the gas exchange process only requires a sufficient amount of water passing over a large surface area of the gills. Gravity is not a significant part of the process (https://www.sciencedirect.com/science/article/pii/S1546509808601326), although it does affect the structure of the fish and the strength of their bones. (http://jeb.biologists.org/content/220/20/3605.2) + +> Would it be possible for the fish to flap its fins and create an air bubble around it? That would presumably kill it. + +Only because you specified a bowl. It would not really be an air bubble but the fish would push water away. Without gravity to keep the water in the bowl it would be pushed out, and the empty space would be filled in by the surrounding air. Eventually the fish would just be floating in the air flapping its fins uselessly, and the water would be floating all over the space station. + +Solution: sealed container. + +> And beyond all this, would the fish be able to even handle being in 0 gravity? + +They can live there, but they cannot navigate properly. The fish swim in loops instead of straight lines because they do not have Earth's gravity to orient them vertically. + +https://www.nasa.gov/audience/forstudents/9-12/features/F_Animals_in_Space_9-12.html" +1107 If a person is paralyzed from the neck down, does that paralyzed body still react to temperature changes? Sweat and goosebumps? 7535 https://www.reddit.com/r/askscience/comments/9frpsu/if_a_person_is_paralyzed_from_the_neck_down_does/ 1536929381 9frpsu 2018-09-14 15:49:41 "I’m a therapist in a neuro clinic. It depends on the involvement of their spinal cord injury or whatever condition has left them paralyzed. You can still have partial motor innervation or none at all depending the kind of injury/pathology. Tetra and paraplegic people have difficulties with regulation of body temperature for number of reasons but generally speaking they don’t sweat or have goosebumps. + +Most people still have some sort of autonomic warnings of when there “paralyzed” involved body is in trouble from an injury, infection, or a danger perceived scenario, its called autonomic dysreflexia. They develop a large change in blood pressure, feel sick, can develop uncontrolled muscle spasms. + +Edit: Grammarz and specifying I’m a physical therapist assistant, I help modify and execute plan of cares to rehabilitate spinal cord injuries, traumatic brain injuries, and other populations like orthopedics and amputees!" "I've been paralyzed from the chest down for 20 years. I was camping the other night and it was very warm and humid. I had blankets on my lower body and a fan blowing on my face/arms, and fell asleep, I woke up not feeling cold, but shivering terribly like I was cold (or had a fever). I took the blankets off and turned the fan off and equalized and was fine. If it rains and gets my pants wet, my face and upper body get really flushed and hot, presumably as my body warms up my wet legs. +But in the winter, my legs can get icy cold and I wont have any idea or indication, really, other than feeling uncomfortable/unsettled...then if I hit a certain point (presumably when my core temperature drops below a certain level), I feel terribly cold and it takes forever to get/feel warm (forever=an hour or more). Ive gotten better at equalizing, and depend 100% on my gerbing electric heated socks, which i recharge and reuse every single day once the temperature drops below 50° + +As for why i get flush from rain but not really cold... it seems to have to do with wetness/humidity/evaporation. Due to the nature of my spinal cord injury, I don't really sweat. A little in my armpits and a lot on my chest, but not on my head at all. Its bizarre and sucks. But again, if i'm in a humid environment, and especially when i'm wearing a hat, it seems to activate the sweating on my head. + +In the summer my legs get very hot; my body cant seem to cool them. Though if i put them up (i.e. Lay down) their temperature quickly evens out. (In the summer, hot legs equalize in like 15 minutes when i lay down, whereas in the winter, cold legs take over an hour to equalize)" +945 How common are illnesses such as the cold or the flu in other animals? and if they aren't common, why? 7517 https://www.reddit.com/r/askscience/comments/7ua3wr/how_common_are_illnesses_such_as_the_cold_or_the/ 1517407635 7ua3wr Biology 2018-01-31 17:07:15 "Flu is very common in waterfowl. It doesn’t make them sick, however. Generally people don’t get sick from the flu virus types that infect birds, but pigs can get both. And if a pig gets both, their cells can be infected by both viruses, both adding stuff into the cell’s DNA. Then a new virus emerges. This is why most epidemic versions of influenza have strain names of Asian cities. Asia is one place where ducks and pigs are often raised in close proximity. +" "Veterinarian here, the true flu H#N# viruses are pretty common in horses, birds and pigs (hence bird flu/swine flu) though they do not always cause significant disease in those species. There are currently multiple outbreaks of canine influenza (H3N8 and H3N2) around the US though this really isn’t very common in general. + +The flu virus mutates frequently and participates in genetic recombination. This means genes from multiple flu viruses can recombine into a virus with a unique/uncommon genetic make up. This is why they make a different flu vaccine every year and why that flu vaccine doesn’t always work (they have to predict what strains will be most common in any given year). It’s also what makes the flu virus able to cross species in all sorts of different directions. + +In general, however, our pets don’t have as much of a problem with viruses like the cold and flu. (With the exception of what I mentioned above regarding canine influenza). Both of those viruses rely strongly on many individuals of the same species having close contact with each other. That just doesn’t happen as much for dogs and cats as it does for humans. Diseases that are sort of in the same vein however include kennel cough in dogs and herpes and calicivirus in cats. They can all cause upper respiratory infections and are contagious. + +Other viral, infectious diseases that we really worry about are parvovirus and the feline equivalent, panleukopenia, as well as things like distemper and rabies. Good news is there are vaccines out there for those bad boys. +" +946 If presented with a Random Number Generator that was (for all intents and purposes) truly random, how long would it take for it to be judged as without pattern and truly random? 7504 https://www.reddit.com/r/askscience/comments/88ag93/if_presented_with_a_random_number_generator_that/ 1522417648 88ag93 Mathematics 2018-03-30 16:47:28 "The question you really want to ask is the opposite: how long would it take to determine that a random number generator has some structure, i.e. is NOT truly random? The most general answers to this question and specific ones like it are pretty advanced, and are the subject of considerable research in statistics. I will answer this with an example, and the reason you can never truly determine that there is no structure (your original question) will become clear by the end. + +Suppose I have a random number generator which picks an integer from 1-10 but it has a preference for the number 5. The probability that it picks 5 is 0.1+x, and the probability for it to pick each of the other nine choices is 0.1-x/9. This is a not-truly-random number generator, and we can choose x to be anything in the range [0, 0.9] to decide how strong its preference for the number 5 is. + +If we run this random number generator N times and count how many times we get the number 5, we should observe an excess over the expected value of N/10. The actual number of times I expect to get 5 is N/10 + N x, and the Gaussian uncertainty of this will be its squareroot: sqrt( N/10 + N x ). Google Poisson statistics if you'd like to know more about that. + +Now for simplicity let's just say x is small, so that the uncertainty is (approximately) simply the squareroot of N/10. If that uncertainty is much smaller than the excess I observe, then I can confidently say there is preference for the number 5. + +So the condition is that N*x is much larger than sqrt( N/10 ), which I can rewrite with some algebra as: + +N is much greater than 1 / ( 10 x^2 ) + +Let's look at each thing here to understand a bit more. First, the 10 comes from our specific example of choosing from 10 numbers. That could be anything in the general case. Second, the number of trials I need grows with 1 / x^2 which makes sense; if x is smaller, I need more trials. Third, in the limit as x goes to zero, N will get infinitely large! This is one way to understand why we can never truly say it is random, because there can always be arbitrarily small structure that we would need infinite trials to detect. + +Lastly, what do I mean by ""much greater""? That depends on how confident you want to be. For example, I could have a genuine random number generator and get 5 a hundred times in a row. I would then conclude with very high confidence that it is not random! But I would be wrong; that's because the probability to draw 5 a hundred times in a row by pure chance is extremely low. In practice, the confidence level that people use is generally between about 2 and 6 standard deviations. 2 corresponds to a confidence level of about 95%, and 6 corresponds to about 99.9999998%. + +So I will write for my final answer: + +N = k^2 / ( 10 x^2 ) + +Where you may choose any k from about 2-6, and any small x to determine a specific number for N. + +Here's another reason why you can never say that it's truly random: because to reach 100% confidence, k would have to be infinite, and therefore so would N. So to say for sure whether a number generator is random or has structure, we would need to have arbitrarily high confidence (k -> infinity), as well as a probe for arbitrarily small structure (x -> 0). Both of these make N explode to infinity, so it can never be done. But that's no fun, so let's at least plug in some numbers and get an answer. + +If x = 0.01, this represents an 11% chance to draw 5 and a 9.89% chance for each of the other numbers. I'll choose k = 3, which gives me a confidence of about 99.7%. + +N = 3^2 / ( 10 * 0.01 * 0.01 ) = 9 / 0.001 = 9000. + +So I would need, on average (since it's all probability after all), 9000 trials to determine with 99.7% confidence that my generator is not random." There is a Stanislaw Lem novel called [His Master's Voice](https://en.wikipedia.org/wiki/His_Master%27s_Voice_\(novel\)) - part of the premise is that an astronomical noise source is used to publish a table of random numbers, and the table author gets sued when the 2nd volume starts repeating the first - turns out it is a message (maybe) and that has a period of over a year. +846 How does a video game or software randomly decide something? 7503 https://www.reddit.com/r/askscience/comments/7law0k/how_does_a_video_game_or_software_randomly_decide/ 1513876902 7law0k Computing 2017-12-21 20:21:42 "Well that depends - are you asking what algorithm they use to determine a critical hit? Or how the random component of that works? + +Because the former is basically ""whatever teh programmer wants"". But how an RNG (Random Number Generator) works is much more interesting. + +As you've apparently surmised, computers are deterministic. They don't do things randomly - everything has defined inputs and defined outputs. So how do they generate a random number, right? That's why *this is actually a really good question*. + +They use what's called a ""pseudorandom number generator"" (PRNG) which is a program that *isn't* random. It's not. It's just a mathematical formula that's so crazy it *looks* random... but it is still deterministic. + +It can't pull the number from nowhere, so it needs an *input*. I put in a 1, I get 81. I put in a 2, I get 875. I put in a 3, I get 294. + +What's important is that, being deterministic, when I put in a 1 again, **I still get 81 back**. + +Now, to make it simple, they sometimes hide this input number so it loops on itself - so I only provide the *first* number, and then each subsequent run of the PRNG, it will just use the last number it generated. + +So I put in a 1, and I get 81, and then I don't have to put in something again - it will use 81 next time to get, say 788 for me. And then I'll ask it for another number, and it will use 788 as its input to generate... say... 294. + +What's important is that this is *still* deterministic. If I start up a new RNG, and I seed it with the number 1 again? It will still return 81, 788, 294, etc. in that order. + +This is called ""seeding"" a random number generator. If you play minecraft, that word sounds familiar - many procedurally-generated videogames will let you provide a ""seed"" - now you know what that means! The ""seed"" is the first number for the RNG, so if you use the same seed to run the procedurally-generated world twice, you get the same world twice, because it wen through the same pseudorandom numbers in the same order. + +Now, what if I don't provide a seed? Well then the computer needs to find a seed by itself. The clock works. The current date and time is always unique. You can get pretty good random numbers by seeding from the clock (note, a computer's ""clock"" includes the date). Seed from a number that is the total number of milliseconds that's passed since January 1st, 1970. + +The challenge is when you need to be really sure that nobody else can figure out your random number. It needs to be a secret. This is important for encryption. Everybody knows what time it is, and if they know your pseudorandom number generation algorithm, they can make the same numbers. + +That's when sources of ""entropy"" are important. Source of chaos that the computer can read to find something *truly* random it can use to seed the RNG. Fluctuations of the electrical power supply is a good source for this, for example. Reading this data is slow, so it's still just used as a seed - after that initial fetch from the truly random source, the computer still just calculates the next random number from the previous ones. + +edit: on Entropy, the most *extreme* source of randomness is quantum physics. Quantum physics are fundamentally random. And the easiest-to-detect form of quantum physics? **radioactivity**. + +[So here's a video of some guys using deadly radioactive Strontium-90 to generate random numbers](https://www.youtube.com/watch?v=SxP30euw3-0) + +Seriously, if you like computers and you like videos, if you have a question about computers look up Computerphile on Youtube. They do *fantastic* work. + +edit2: wow, this blew up like nothing I've ever written. Okay, I feel I should clarify something: these are toy examples. A real, proper PRNG is dealing with much larger numbers than 788 (a 32-bit integer has 4 billion values, and a 64-bit integer has 18 quintillion values) and then they're hammered into the range the programmer wants *after* the PRNG is done calculating them. Second, the ""input"" can be more than just the one previous value. For example, the Mersenne Twister is one of the most common PRNGs, and it stores *hundreds* of old random numbers and uses them all to help generate the next one." "Okay, now to answer the other half of the question: + +Once we've *got* a random number generator (see my other comment explaining how that works), the question is how we use it. + +The simplest case - let's say your design says that we should crit 20% of the time. + +In that case, the function for DoesAttackCrit will do the following: + +1. Get the global random number generator (it's already been seeded properly in your game's start-up code). +2. Generate a random number from 0 to 99. +3. Check if that random number is less than 20. +4. If it's less than 20, tell the system ""true"" which means that a crit happened. +5. If it's more than or exactly 20, tell the system ""false"" which means the crit did not happen. + +The system might have modifiers to ""nudge"" the random number - for example, in Team Fortress 2, there's a modifier - it keeps track of how much damage you've done in the last 20 seconds, and nudges the chance upwards with the amount of damage you've dealt. So if you're kicking ass, the normal 2% chance of a crit can go up to 10%. It also raises the likelihood of a crit if you use a mielee weapon. + +https://wiki.teamfortress.com/wiki/Critical_hits for details of TF2's crits. + +Every game will have its own logic for crits, but they'll all almost certainly use a pseudorandom number generator as part of the logic to make that decision." +1224 When animals leave their parents to establish their own lives, if they encounter the parents again in the wild, do they recognise each other and does this influence their behaviour? 7489 https://www.reddit.com/r/askscience/comments/belzgb/when_animals_leave_their_parents_to_establish/ 1555596535 belzgb Biology 2019-04-18 17:08:55 "In dogs the generally accepted explanation is that they have a ""scent memory"" and when a scent is matched they will feel safer and more comfortable with that other dog. This means that dogs will remember their parents and siblings but not in the same way as humans. Dogs just have a list of dog smells they like and get along with. You can read more about it here: + + [https://wagwalking.com/sense/can-dogs-remember-their-siblings](https://wagwalking.com/sense/can-dogs-remember-their-siblings) + +Not much research has been done in other animals but for the most part social animals will react the same way as dogs and non social animals have no concept of siblings or parents." Australian Magpies mate for life, and will help feed and care for their grandchildren. The male children eventually leave to forge territories of their own but usually stay close to the protection of their parents' territory. +1225 How do we know it rains diamonds on saturn? 7488 https://www.reddit.com/r/askscience/comments/bh1bdv/how_do_we_know_it_rains_diamonds_on_saturn/ 1556147048 bh1bdv Astronomy 2019-04-25 2:04:08 "Technically we don't ""know"" + +We know + +1) The chemical composition of the atmosphere contains a good chunk of methane based on light reflection analysis. + +2) We know the mass/volume/density of saturn based on lots of other math and observations. + +We put those together and realize that in certain areas of saturn there is enough pressure/temperature to form diamonds. These would form for a bit *sorta* like rain/drops and hail do in our atmosphere and then ""rain""" by diamonds scientists dont mean large rocks or even small stones. The pressures and composition of the atmosphere is such that nano crystals of diamonds OR graphite might be produced and rained down like a very fine glitter +1317 "We can't see beyond the observable universe because light from there hasn't reached us yet. But since light always moves, shouldn't that mean that ""new"" light is arriving at earth. This would mean that our observable universe is getting larger every day. Is this the case?" 7480 https://www.reddit.com/r/askscience/comments/c91kfq/we_cant_see_beyond_the_observable_universe/ 1562240214 c91kfq Astronomy 2019-07-04 14:36:54 Yes, the observable universe is getting larger every day, meaning the volume of space out to the farthest object we can see is increasing. However, because the expansion of the universe is accelerating due to dark energy (whatever it may be), there are objects in the sky that we can see today that we will not be able to see in the future. That is because these objects will be carried away from us faster than light can travel through the expanding space toward us. In fact, if we observe an object with a redshift of 1.8 or greater (meaning that the wavelength of the light has been stretched by the expanding space so it is 1.8 times longer by the time it reaches us), then we will *never* see the light it is emitting today. Well technically it is, but the issue is that due to Hubble's law, the very fabric of space is expanding, so even if we are able to view more galaxies (which gets harder due to redshift), we will end up seeing less and less extra galaxies as they accelerate to and past the speed of light. +847 If a nuclear bomb went off in Boston harbor could scientists tell after the fact who had manufactured it, do they leave distinct radioactive signatures? 7465 https://www.reddit.com/r/askscience/comments/719don/if_a_nuclear_bomb_went_off_in_boston_harbor_could/ 1505890789 719don Physics 2017-09-20 9:59:49 "Watched Sum of All Fears last night? + +You might want to look into the Monitoring Capabilities of the Comprehensive Test Ban Treaty (CTBT). You can read a bit about it here: + +https://www.nap.edu/read/10471/chapter/5 + +Basically, radiochemical analysis can tell you information about the bomb design and the metallurgical refinement techniques of the fissile material (which a lot of people don't know is the majority of the ""technology"" of a nuclear bomb). However, whether that can be mapped to a specific nation state, or even a specific manufacturing facility ultimately depends on how much we know about that nation state and its nuclear weapon manufacturing facilities." "Retired Nuclear Engineer here. + +When producing fissile material for weapons, there are multiple samples taken to determine the enrichment quality. There are also samples and pertinent data collected when inspecting the facilities for safety and efficiency. Because of variations in reactors, the specific facility can often be identified from records. And, in the case of agreements between countries, i.e. START, we have detailed records as well do the other countries of which facilities are capable of producing or do produce these materials for weapons. + +For reasons like cost and the fact no one can test these things due to international treaties(I'm not including DPRK in that) the only way we know if weapons work when they are upgraded or recycled is because we can do the math and know the chemical composition of the fissile material due to its byproducts. And every reactor has a byproduct footprint. This footprint can reveal what reactor, what year, what month, and which part of the vessel the material came from. + +We spend a massive amount of cash on maintaining the weapon stockpile in testing product chemistry and materials production. Not including maintenance on the delivery systems. And the delivery systems are much more complex than the payload. Once a country or organization learns how to make a bomb and gets the fuel right, it's actually a much (metaphorically)simpler mechanism than the wind up clock. Because for basics there are only two ways to go, (gun/implosion) and the more complex of the two (implosion) is 97% of the work for you to get to the one that makes the more predictable and scalable boom. + + + + + +Tl;dr: So yeah, most of the time they can tell you not only where, but what part of a reactor the enriched fuel came from because they keep records and because it's the only way to make sure they work." +1226 Will an Octopus Die If one or two of it hearts stop ? and Why ? 7463 https://www.reddit.com/r/askscience/comments/basfun/will_an_octopus_die_if_one_or_two_of_it_hearts/ 1554721661 basfun Biology 2019-04-08 14:07:41 "The three hearts aren't equal. + +It's got one main heart like other animals (the systemic heart), and two other minor hearts (branchial hearts), each pumping blood through one gill. If the main one stops it would have the same effect as if your heart stopped\*. *Maybe* it could live with one gill though (provided the stopped gill-heart didn't disrupt the circulatory system too much and it could survive on half the oxygen - but most animals can survive on one lung/gill until they get eaten) + +\*Apparently the systemic heart stops when it swims, hence they don't swim fast unless they have to." I think it would depend on which hearts fail because if the two bronchial hearts fail the octopus will likely die because the bronchial hearts control the gills, which are obviously very important to the octopuses survival. The third heart, the systematic one is less vital to the octopuses survival as it is inactive while the octopus is swimming (swimming for octopi is very energy consuming)but active while the octopus is crawling. So in conclusion survival without the two bronchial hearts is near impossible but survival without the systematic heart would be extremely tiring. +1318 "How does masturbating ""reduce the risk of prostate cancer""? Is it just a statistical correlation or is there a causal link?" 7448 https://www.reddit.com/r/askscience/comments/cusjqg/how_does_masturbating_reduce_the_risk_of_prostate/ 1566648044 cusjqg 2019-08-24 15:00:44 "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5040619/ + +>In addition to the prostate stagnation hypothesis [7], a number of mechanisms have been proposed to explain an inverse association between ejaculation frequency and PCa. More frequent ejaculation may influence the function of peripheral-zone epithelial cells, hindering the metabolic switch from citrate secretion to citrate oxidation known to occur early in prostate tumorigenesis [33]. Alternatively, more frequent ejaculation may reduce the development of prostatic intraluminal crystalloids, which have been associated with higher risk of PCa [34,35]. Higher ejaculatory frequency may be linked to lowering of psychological tension and central sympathetic nervous system suppression, which could dampen the stimulation of prostate epithelial cell division [36]. Given the lack of modifiable risk factors identified for PCa to date, the specific biological mechanisms underlying these associations are worthy of further investigation. + +(PCa = prostate cancer) + +Those are some of the main proposed explanations, if there is a causal link (which is unproven, but suggested by data so far). + +And yes, it is difficult to demonstrate a causal link." So the difficulty in answering that question is that medical studies such as these are very often conducted via measurement of correlations. Ethically, it's very difficult to ascertain the level and directionality of causal relationships in humans because in order to be definitive, there needs to be some amount of manipulation of variables. Since we're talking cancer, you can't manipulate people's behavior to see if cancer pops up, because if your hypothesis is correct, you just caused (or failed to prevent) a life-threatening illness. There are ways to get around this, such as statistical models (which appear to be fairly accurate in their predictions) and animal models. There's more to it, and there are always drawbacks to each method (hence testing and retesting being super important), but that's the basics. +1319 Since the small intestine is coiled up inside the body, are they all similar in shape? Or is it completely random? 7426 https://www.reddit.com/r/askscience/comments/cppyci/since_the_small_intestine_is_coiled_up_inside_the/ 1565683049 cppyci Human Body 2019-08-13 10:57:29 "When I was in medschool in wondered how they put back the small intestines in the right orientation. I expected it to matter a lot. + +What they actually do is lift the whole package a bit and then let it drop. The attachment via the mesentery will pull it into a coiling that is the most relaxed. + +Easy peasy." "The small intestine is attached to the body via the mesentery, through which vessels and nerves pass through. Otherwise they are completely mobile and move around as you move and in some cases can wrap around itself and cause ischemia requiring surgery. + +So yeah it’s both kinda random and ordered." +848 Is it possible to put my bare foot on the moon? 7425 https://www.reddit.com/r/askscience/comments/74vncq/is_it_possible_to_put_my_bare_foot_on_the_moon/ 1507391853 74vncq Planetary Sci. 2017-10-07 18:57:33 "3 issues come to my mind. The first is designing a spacesuit that lets you breathe normally while your bare foot is exposed. Your foot wouldn't suffer much from the vacuum exposure (see [this thread](https://www.reddit.com/r/askscience/comments/70s5om/what_would_happen_if_only_your_arm_and_nothing/) for details), I'm mostly wondering how you would prevent air from leaking. I'll just assume you have a solution for that. + +(Edit: there are several followup questions about swelling when your foot is exposed to a vacuum. See [this comment](https://www.reddit.com/r/askscience/comments/74vncq/is_it_possible_to_put_my_bare_foot_on_the_moon/do2h116/?context=3) for details and a source). + +Then you have the problem of temperature of the lunar surface, extremely hot during the day and extremely cold during the night. Let's assume you're stepping on it at sunrise or sunset when temperatures are milder. + +Finally, lunar dust is really harmful. It's because of the lack of weather erosion, grains aren't rounded and retain weird shapes with very sharp edges. Your scenario doesn't involve breathing lunar dust (except for what might penetrate into your suit's air, which isn't negligible), but your foot's skin certainly wouldn't be happy. + +https://en.wikipedia.org/wiki/Lunar_soil#Harmful_effects_of_lunar_dust +" "In my mind this is really two questions. 1) Can you expose your bare feet to the moon's environment? 2) Can you safely put your feet in lunar soil? + +As to 1, brief full body exposure (say, 5 seconds) [would not be a problem as long as someone was there to get you immediate and proper re-compression and to save you if you go unconscious (about 10 seconds.)](https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660005052.pdf) + +As to 2, there's a [whole article at Wikipedia about it.](https://en.wikipedia.org/wiki/Adverse_health_effects_from_lunar_dust_exposure) So long as you washed your feet after, I can't imagine you coming to any immediate harm. I imagine it would be something like walking in diatomaceous earth." +632 Why do they say not to put a car battery on a concrete floor? 7422 https://www.reddit.com/r/askscience/comments/5putlx/why_do_they_say_not_to_put_a_car_battery_on_a/ 1485242069 5putlx Chemistry 2017-01-24 10:14:29 Due to good answers being in this thread and a large number of anecdotal answers still being posted, this thread is locked. "Leaving a car battery on a concrete floor won't do anything abnormal to affect the charge. + +The belief stems from an outdated set of circumstances that no longer exist. Once upon a time, battery casings were made from more porous materials - tarred wood, [rubber](http://www.powerstream.com/1922/battery_1922_WITTE/batteryfiles/chapter03.htm), etc. - which were susceptible to degrading after exposure to the moisture coming from unsealed concrete. As the casing degraded, battery acid could leak out and water could enter the battery, causing the battery capacity to drop. + +With modern, plastic-encased batteries, the moisture-related degradation isn't really an issue on any meaningful time scales. + +(Incidentally, anecdotal proof is not actually proof.) + +edit: added source re: rubber enclosures" +1320 Historically, why did fevers used to kill so many people, but now they're a rarely fatal annoying symptom? 7413 https://www.reddit.com/r/askscience/comments/bsl7tm/historically_why_did_fevers_used_to_kill_so_many/ 1558726621 bsl7tm Medicine 2019-05-24 22:37:01 """Fever"" was just a colloquial term used to describe any illness that presented a raised temperature. Ebola will kill you, influenza may kill you, a common cold probably wont. All three of these illnesses were referred to by their symptoms aka. ""She died of a fever after visiting Africa"". We know now the underlying cause of the fever and can treat (and name) not only the illness, but the fever itself, much more successfully." Because fever isn’t an illness. It’s a way of your immune system to fight against these infections. The people died because of measles, flu, whooping cough, but the diagnose was fever, because you could detect a fever with the simple methods of that time. The illnesses that killed people are gone because of better treatment, vaccines, nutrition and hygiene. Only relatively harmless diseases like flu and colds etc. cause fevers today, so people don’t die and a fever is nothing more than disturbing. +947 Antarctica is defined as a desert, due to lack of precipitation. So where does all the 1-3 mile thick layers of ice and snow come from? 7373 https://www.reddit.com/r/askscience/comments/83atc3/antarctica_is_defined_as_a_desert_due_to_lack_of/ 1520635026 83atc3 Earth Sciences 2018-03-10 1:37:06 Precipitation in the center of Antarctica is small but not zero. Melting is almost totally zero, though, so there's a slow buildup of snow and ice. It's built up over hundreds of thousands of years. Because only a few centimeters of snow are deposited each year and become extremely hard during winter we can dig down into the ice with boring machines and extract ice core samples, which you can see physically have different layers in them depending on factors like the climate, atmospheric composition, CO2 levels, etc that were around when the snow was deposited. In fact, the trapped CO2 in the ice cores is one of the ways we study Earth's climate history and they can take us back many thousands of years with a great deal of accuracy. +1047 Why don't babies get stretch marks as they grow? 7340 https://www.reddit.com/r/askscience/comments/930c22/why_dont_babies_get_stretch_marks_as_they_grow/ 1532918223 930c22 2018-07-30 5:37:03 "This post has attracted a large number of personal and medical anecdotes as well as request for medical advice. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." "Along with other proteins,ELASTIN in your skin is the main component keeping your skin (you guessed it elastic) and its existence depends on 2 things. The rate at which you synthesize elastin and the rate at which the enzymes that break it down do so, this balance can be disturbed by decreasing synthetic function or increasing breakdown and is affected by different factors.. + +1. age: younger cells are better at making things than older cells due to factors like oxidative stress and accumulation of mutations over time. +2. Nutritional status: you need to have enough of the necessary ingredients to make elastin +3. Exercise: our bodies respond well to stimuli that tell it to work, exercise keeps your synthetic function going as you replace damaged muscle fibers and your body stays on top of its synthetic function as it has a constant stimulus to do so. +4. Stress: being under a lot of stress induces release of cortisol, the stress response hormone, one of the well known effects of high levels of circulating cortisol is skin atrophy aka getting thin bad skin due to decreased synthesis of all the proteins in your skin (elastin and co.) +5. UV radiation; this bad boy damages the skin cells that carry out that synthetic function, so keeping you skin protected is a way to preserve these cells, this is why some people that apply daily sunscreen to their faces look way younger for their age. UV leads to decreased elastin synthesis. +6. Smoking : terrible one right here, this bad boy directly damages proteins that slow down the rate at which you break down elastin, so if you damage the thing stopping the breakdown of the good stuff (elastin) then you break down more elastin and you’re left with once again.. less elastin +7. There’s other factors but i need to stop writing eventually so i don’t bore everyone to death. But i hope these helped. + +In a nutshell, as with most other things, eat well, exercise, don’t smoke, stay stress free ! + +hope this helps + +Edit: structure, grammar, spelling. " +1321 In 2024 if NASA do get to and land on the moon, will novice photographers or people with telescopes be able to see any of the mission? 7280 https://www.reddit.com/r/askscience/comments/bpnfd5/in_2024_if_nasa_do_get_to_and_land_on_the_moon/ 1558072181 bpnfd5 2019-05-17 8:49:41 "The spacecraft will be visible to the naked eye when it's in low Earth orbit, including just after the trans-lunar injection burn, just like satellites are. + +The TLI burn itself may well be seen with the naked eye, depending on the engines used and the lighting conditions. Rather than the exhaust's own glow, it tends to be the sunlight illuminating the plume that makes it visible. Venting of excess fuel, water, or other substances are also often quite visible. + +Out to geostationary distance, it should still be visible (and photographable) in amateur telescopes, just like geostationary sats are. + +With larger equipment, but still fairly small by professional standards, the spacecraft will be visible at lunar distances. In the case of Apollo, 2-metre class telescopes seem to have been commonly used. + +This article discusses amateur tracking of the Apollo missions: http://pages.astronomy.ua.edu/keel/space/apollo.html + +In all these cases, what's seen is just a point of light, or a cloud in the case of engine burns, fuel dumps, etc. The way it moves compared to the stars allows its trajectory to be calculated (so amateurs can confirm it's going to the Moon). Details on the spacecraft might be barely visible with a good amateur photography setup when it's in Low Earth Orbit, but any lunar ship is going to be a lot smaller than say the ISS. + +The actual landing is thus unlikely to be seen, because the spacecraft will not have any contrast against the bright lunar service. + +That's in the optical. As far as radio goes, transmissions from the spacecraft will not be difficult to recieve." "No one on earth would have the equipment to resolve something that small in visible wavelengths of light. The maximum resolution of a telescope (or your eye, for that matter) is set by the diameter. The bigger the diameter, the better the possible resolution. Even the largest telescopes on earth at around 30 feet is still an order of magnitude or two too small to see something that's landed on the moon. + +The one possible exception to this would be if they were to flash a bright light back at earth (which I don't think they'd do). It wouldn't be able to be resolved into a shape, but could be done so that it was bright enough to at least tell that it occurred." +512 Given recent developments in our understanding of water/ice bodies on Mars, is it possible that we could one day be surprised by Martian fossils? Or do we have reason to believe that Martian life would be limited to microorganisms? 7271 https://www.reddit.com/r/askscience/comments/5fjioz/given_recent_developments_in_our_understanding_of/ 1480436426 5fjioz Planetary Sci. 2016-11-29 19:20:26 "It's not _impossible_ (because that's a pretty high bar to clear) but I'd say it's very, very unlikely. + +The reason is time. Multicellular life didn't become common on Earth until 500-600 million years ago (EDIT: _Life_ showed up on Earth very early. But it consisted of microorganisms). There are a very few possible older fossils of very simple (think algae sheets) forms of multicellular life. This is also past the point where oxygen was common in the atmosphere. + +Mars never had that kind of time. When it dried out and froze, earth was still billions of years away from its first real multicellular life. For plants and animals to have shown up on Mars, they'd have had to appear much, much faster than they did on Earth. + +EDIT: Of course, stromatolites or other fossils resulting from single-celled organisms are more likely. I discussed the second part of the question, but fossils aren't limited to multicellular life. " "Short answer is, we don't know, but at least on Earth, where there is water we find life. [Here's](http://mail.everythingscience.co.za/emas/community/life-sciences-gr-10/diversity-change-and-continuity/lifes-history/historyoflife.gif) a simplified history of life on Earth from the 1996 Encyclopedia Britannica. [Here's](http://rstb.royalsocietypublishing.org/content/370/1684/20150036) a more detailed 2015 paper on the emergence of multi cellular life As you can see it took almost 4 Billion years for multi cellular organisms to evolve on Earth. [Here's](http://science.sciencemag.org/content/348/6231/218) an article on evidence of water on Mars 4.5 billion years ago. At this stage Mars and earth would have potentially been fairly similar! And if life on Mars mirrored the life appearing on earth, microbial life could have indeed evolved on Mars during this wet period. However this early wet period is [thought to](http://onlinelibrary.wiley.com/doi/10.1029/JB091iB13p0E139/abstract;jsessionid=C1FFA225B08E6091E9A1822529D38CB5.f02t01) only have lasted until 3.8 billion years ago, the end of the noacian era. This is old data based on early photographic evidence, Mars science is changing rapidly at the moment and new harder dates and evidence for water is rapidly being found, but the big picture of a wet Mars not lasting long persists. If Martians evolved like earthlings we don't expect to find multi cellular life. But here's the exciting part, we only have one datum at the moment and we have no idea how life could have (or not have) evolved to live in such a different planet. We won't know until new missions to look for direct evidence of life, such as fossils, set foot or wheel on the surface and start digging around. + +" +1227 "How do octopi kill sharks? Do they ""drown""/suffocate them? Do they snap their bones?" 7265 https://www.reddit.com/r/askscience/comments/ar96q2/how_do_octopi_kill_sharks_do_they_drownsuffocate/ 1550326957 ar96q2 Biology 2019-02-16 17:22:37 "They do drown the sharks. Unlike most fish, a good deal of species of sharks have rigid gills. This means that they can’t flap their gills to pass the water over them, so they need to maintain constant motion in order to breathe. This is called an “obligate ram ventilator”. As soon as no fresh water is able to pass over the gills, the oxygen in the water around the shark is depleted and they suffocate. There are some sharks who have spiracles, which are basically two little breathy holes right above their eyes. You can see these same holes on the backs or stomachs of rays, the shark’s close relatives. These can be used to pump air over the gills, so no constant motion must be maintained. Other sharks use the buccal method to respire, where they use their mouth as a pump. This is why you will see some sharks constantly opening and closing their mouths while stationary. +Anyway, the video you’re referring to happened at an aquarium. The shark was a spiny dogfish shark, which does have spiracles, but is a relatively small shark. The giant North Pacific octopus which attacked it is, well, giant. The people in the aquarium put up cameras to see what was happening, because multiple dogfish sharks were dying, which suggests this is a very successful hunting mechanism of the octopus. In the video, you can see that the octopus wraps their tentacles primarily around the head of the shark. Thus, the spiracles are covered, and the gills are stationary. Boom- suffocation. Don’t mess with a big boy octopus! +Aaaand here’s the [link](https://m.youtube.com/watch?v=p9A-oxUMAy8) + +EDIT: since there have been a ton of questions about this, I’ll tell you how sharks sleep while remaining in motion. The answer is that they, like dolphins and whales, sleep half of their brain at a time. One half sleeps, the other swims. Then switch. " In addition to targeting vulnerable body parts (like the gills) as other posters have stated, octopi also have a powerful beak that can slice through flesh, cartilage and bone with ease. They're very much capable of just chewing the shark open too. +633 Why does it take a million years for a photon moving at the speed of light to reach the sun's surface from its core? 7260 https://www.reddit.com/r/askscience/comments/5q79dy/why_does_it_take_a_million_years_for_a_photon/ 1485392410 5q79dy Physics 2017-01-26 4:00:10 [Thomson scattering](https://en.wikipedia.org/wiki/Thomson_scattering). The photon bounces around many thousands of times on average before it escapes the sun. The mean free path of a photon in the interior of the sun is about 2 centimeters. This is the average distance it travels in between bounces. If you compare this length to the radius of the sun, you see why it takes so long for the photons to escape. [deleted] +1228 Are we the only animal to predominantly use one arm/hand? 7246 https://www.reddit.com/r/askscience/comments/b2in4u/are_we_the_only_animal_to_predominantly_use_one/ 1552915128 b2in4u Biology 2019-03-18 16:18:48 "This post has attracted a large number of anecdotes. The mod team would like to remind you that **personal anecdotes are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. This is not the right place to share anecdotes about your pets." "Other animals definitely have laterality/handedness. I think for apes, one of the big researchers is William Hopkins - search laterality and his name and chimp and you’ll find a rabbit hole of scientific literature on handedness in non-human animals and its possible relation to hemispheric specialization in the brain. + +Edit: example https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2043156/ +Edit again: and here’s mice https://www.ncbi.nlm.nih.gov/m/pubmed/1881972/ +Also look up tree frogs that preferentially jump in one direction, etc." +849 If a person is allergic to domestic cats, would they also be allergic to wild cats (lions, bobcats, etc.)? 7223 https://www.reddit.com/r/askscience/comments/7cgdr2/if_a_person_is_allergic_to_domestic_cats_would/ 1510504727 7cgdr2 Biology 2017-11-12 19:38:47 "Please remember AskScience has strict comment rules. We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are unfamiliar with the rules you can [view them here](/r/askscience/wiki/rules). In particular we do not allow anecdotes or comments consisting of a single joke. + +There has already been hundred of comments removed along the lines of : + +> Yes. Source : I am allergic to cats and went to a zoo once. +" "Yes. It’s been studied (back in 1990). There is some cross reactivity with the major cat allergic protein (Fel d 1). But the extent of cross reactivity is variable. + +“They tested 11 cat-allergic patients against Fel d 1-like structures in eight members of the Felidae family: ocelot, puma, serval, siberian tiger, lion, jaguar, snow leopard, and caracal. Hair from the big cats were collected, extracted, and used in a RAST system and histamine test. The results showed that all patients had cross-reacting IgE antibodies to seven of the Felidae tested. No IgE antibodies were reactive with the caracal. Eight of the 10 patient with IgG4 antibodies directed to cat dander also had IgG4 antibodies directed to several Felidae species, including the caracal. + +In general, those with cat allergies also showed an allergic response to big-cat dander, but it wasn’t as strong. Your cat allergies should not deter you from visiting a zoo or sanctuary. You will be kept a safe distance from the big cats. The study found that this mild big-cat allergy doesn’t usually affect the patients’ lives. “ +Source/summary of original 1990 study - http://conservationcubclub.com/2016/02/allergic-to-cats-probably-allergic-to-lions-and-tigers-too/" +1229 AskScience AMA Series: I'm Matthias Hebrok, and my lab has just published a breakthrough in making insulin-producing cells in a dish. My team at UCSF hopes to one day cure type 1 diabetes with transplantable beta cells made from human stem cells. AMA! 7219 https://www.reddit.com/r/askscience/comments/avqbib/askscience_ama_series_im_matthias_hebrok_and_my/ 1551355250 avqbib 2019-02-28 15:00:50 Type 1 diabetic here! Thank you for your research. How does your team plan to prevent the immune system from attacking the new beta cells? Do you all plan to transplant the cells back into the pancreas or are there plans to place them in a pseudo pancreas, like a skin patch? No question. Just...thank you. For applying your brain, for caring. Thank you. +1693 Why exactly are overweight people at higher risk when they get infected with COVID-19? 7214 https://www.reddit.com/r/askscience/comments/juqulz/why_exactly_are_overweight_people_at_higher_risk/ 1605465555 juqulz COVID-19 2020-11-15 21:39:15 "Studies have shown it is likely several reasons: breathing (abdominal fat pushing on the diaphragm), weakened immune system (fat cells in the spleen, bone marrow and thymus leads to impaired function), clotting (obesity increases clotting, and covid triggers clots), inflammation, and delayed care-seeking (people with obesity tend to delay seeking care). + +This article in [Science](https://www.sciencemag.org/news/2020/09/why-covid-19-more-deadly-people-obesity-even-if-theyre-young) has a very good overview of the existing literature." "ICU doctor here. I can tell you that one of the biggest challenges is ventilation. You have to generate far higher pressures in order to ventilate the lungs due to the weight of the abdomen and chest wall. Also in general, obese patients are far more challenging to examine for new medical issues or complications. They are also more likely to develop severe bedsores. In the recovery phase (which really starts simultaneously on day 0), it is far more challenging to get them up and moving and working with physiotherapy. + +Just some extra things to mention on top of all the other ones mentioned." +513 How does radio stations transmit the name of the song currently broadcasted? 7198 https://www.reddit.com/r/askscience/comments/5eohiq/how_does_radio_stations_transmit_the_name_of_the/ 1480004490 5eohiq Physics 2016-11-24 19:21:30 "You can send any kind of informaton over radio waves (it's how WiFi, Bluetooth and RFID work), with FM Radio there's a specific protocol called the [Radio Data System](https://en.wikipedia.org/wiki/Radio_Data_System) which allows song names to show up, as well as other information such as the name of the staton, the show type, Traffic Alerts and some other stuff. + +How it's piggybacked onto the actual music signal is a little bit more complicated. Basically each station on FM is given a range of frequencies they can broadcast in (FM is Frequency Modulation after all, so they need some room to send their signal, though AM radio stations are also allocated a frequency range for other reasons). + +What happens with RDS is that a small amount of that frequency range (about 4kHz out of 57) is used to send additional data. The Data rate for this informaton is about 1kbps, but it's enough to send a short burst of data every couple of seconds, which is more than enough to keep you updated as to which track is playing." "The system is called RDS: + +https://en.wikipedia.org/wiki/Radio_Data_System + +It's a way to transmit a small digital information on the same frequency as the analog FM signal, without interfering with eachother.." +1406 Proxima Centauri, the closest star to the Sun is 4.85 billion years old, the Sun is 4.6 billion years old. If the sun will die in around 5 billion years, Proxima Centauri would be already dead by then or close to it? 7187 https://www.reddit.com/r/askscience/comments/dohc3f/proxima_centauri_the_closest_star_to_the_sun_is/ 1572305077 dohc3f 2019-10-29 2:24:37 Proxima will live much longer than the sun, because it is quite a bit smaller. Smaller stars last longer because they don't fuse through hydrogen as quickly (even compared to how much total hydrogen they have). "Interestingly, Proxima will become a type of star which cannot exist in the universe at the moment, but not until long, long after the Sun is but a cool stellar ember. + +Red dwarf stars, like Proxima, are frugal with their fuel and can also use far more of it, proportionally, than larger stars can. They aren't picky eaters, they're slow eaters. The Sun will be a planetary nebula in around 6-8 billion years, but Proxima will be unchanged from how it is today. It works on a completely different timescale, that of trillions, not billions, of years. At the upper edge of estimates, Proxima may get up to eight trillion years out of its hydrogen. + +Proxima will never fuse helium. As it ages, it contracts. Fusion rates try to decrease with declining hydrogen concentration, but the contracting star increases core pressure. Of course, being convective, Proxima doesn't have a core, and we don't think one will emerge even as the star contracts. This means its central pressure is ultimately limited by lower temperatures: Convection is an efficient way of moving heat to the surface. + +The star becomes a low mass blue dwarf, a spectral type of O or B, and very rich in helium. While more powerful, it is still quite feeble. To the spectroscope, it will appear to be a Wolf-Rayet star, but anyone who can measure its mass will realise it is much too small for this classification. + +It will remain like this for a few billion years before fusion begins to fade away completely. The star will cool through blue, white, yellow and back to red. Eventually it's just a really massive ball of helium, looking much like a gas giant planet, but for its lack of hydrogen and its very high mass. + +No grand event signals the end of its life, no great nebula nor mighty flash. It just fades and cools, becoming a helium ember." +514 Why do tires on cars when doing a burnout give white smoke, but a pile of tires burns black? 7182 https://www.reddit.com/r/askscience/comments/5ezbgw/why_do_tires_on_cars_when_doing_a_burnout_give/ 1480164429 5ezbgw Engineering 2016-11-26 15:47:09 "You're not actually setting the tire on fire when you do a burnout. You're superheating the rubber and it's vaporizing, then condensing in the cooler air, but not combusting. + +It would be more technically accurate, though less cool, to call it a steamout. ;)" "Because it's more like rubber vapor when you smoke tires, you're not actually burning anything. + +http://oppositelock.kinja.com/dear-dr-science-why-is-tire-smoke-white-1662701873" +1048 I heard that detergents, soaps, and surfactants have a polar end and a non-polar end, and are thus able to dissolve grease. But so do fatty acids; the carboxyl end (the acid part) is polar, and the long hydrocarbon tail is non-polar. So why don't fatty acids behave like soap? What's the difference? 7178 https://www.reddit.com/r/askscience/comments/8z57ep/i_heard_that_detergents_soaps_and_surfactants/ 1531690225 8z57ep Chemistry 2018-07-16 0:30:25 "You have heard correctly. Let me try to explain the differences. + + 'Fats' as we think of them (oils or tallow or some other such foody thing) are not just fatty acids, but are mostly fatty acids with the polar end stuck on to a somewhat non-polar molecule called glycerin. Usually three fatty acids will be stuck to one glycerin, making a triglyceride. This means that the fatty acids effectively stop having a 'polar' part, as the end of the fatty acid is now a somewhat non-polar glycerin with two other very non-polar fatty acid back ones sticking off of it. + +So the way soap works is by forming balls called micelles with polar part touching the water and the non-polar stuff touching the inside. All the grease can go on the inside of those balls, and that's how soap gets so much nonpolar stuff into water - by filling up these balls. + +Because triglycerides (read: fats) effectively lose the polar end, and because they have a bad packing geometry (which I won't get into), they can't form these fat-soaking micelles and so they sort of just clump together. + +As for your other question: surfactant is a big general word that basically means anything that aggregates at a surface. If you get technical, micelle formation falls into this category. Any ways, it's usually applied to things like fatty acids, which can form micelles and take up fats just like soap. And detergent is somewhat less general, usually applied to water-based molecules that form micelles, just like fatty acids. So to answer your question, fatty acids are just a single type of detergent, which is a type of surfactant. + +And to clarify: fatty acids are not necessarily the best type of detergent, but they should work as a kind of crappy soap as long as they're not stuck to glycerin! + +Hope that helps clarify. + +TLDR: Fatty acids are detergents. Fats are usually mostly triglycerides. Triglycerides are not detergents. + +EDIT: +Thanks for the gold, stranger! +" "This actually is quite a cool topic, your intuition of soap and fatty acids being similar is completely valid, it's because they are! + +To understand how similar they are I think it's worthy to mention [how soap is produced](https://en.wikipedia.org/wiki/Saponification). Soaps are produced by reacting fatty acids with a strong base, Sodium and ~~Kalium~~ *Potassium* Hydroxide are frequently used, which will steal a H^+ off of the COOH end of the fatty acid. This ""Locks"" the fatty acid in an ion state, which makes it way more effective as a partially polar partially apolar molecule, but also technically a [salt](https://images.duckduckgo.com/iu/?u=https%3A%2F%2Fwildearthapothecary.files.wordpress.com%2F2014%2F09%2Fchemistry-of-soap-goodness.png&f=1)! Another important thing to realize is that part of the reason soap is as stable as it is is due to the fact that the negative charge is [delocalized, as it is in all Carboxylates](https://en.wikipedia.org/wiki/Carboxylate). + + +As to the difference between surfactants and soaps let's look at the [definition of surfactans](https://en.wikipedia.org/wiki/Surfactant). Surfactants are compounds that lower the surface tension. Soaps are an example of surfactants as they lower the surface tension (in water), though not all surfactants are soaps per say. It's relatively easy to understand why soaps allow for the lowering of surface tension. For one, due to its polarity it can properly mix and thus get in between different water molecules, and lower the surface tension, [an example of which can be seen in this video](https://youtu.be/HNnFqve-Wgk?t=35s) +This lowering of surface tension is also the reason you need soap to make bubbles! You may at times have seen bubbles of water appear for brief moments in puddles while it's raining, but they never stick around for long. Due to the [high surface tension the internal pressure simply isn't high enough](https://www.exploratorium.edu/ronh/bubbles/soap.html) and therefore a bubble without soap collapses inward! + + +As a bonus soap fact: Back in High School whenever I asked what Bases tasted like (as acids had such a pronounced taste) I was always told they tasted 'soapy', which is only half the story. The reasons bases taste soapy is because it's converting the fat in your mouth INTO soap! I personally love how bases have such an indirect way of taste! + +Soap is exciting!" +1596 how do we know what the milkyway actually looks like? 7169 https://www.reddit.com/r/askscience/comments/htzqb9/how_do_we_know_what_the_milkyway_actually_looks/ 1595161714 htzqb9 Astronomy 2020-07-19 15:28:34 "By mapping the stars. We've gotten pretty good at measuring distances between us and other stars, and by putting those into some modeling software, we can then look at them from different angles. Kind of like how cartographers were able to make accurate maps before satellites or even aircraft were a thing. + +https://www.space.com/milky-way-3d-map-warped-shape.html" "It's not unfair to say that we don't. We know a great deal more than we did 10 years ago and 10 years ago we knew a great deal more than we did 10 year before... but our understanding of the shape of our galaxy is ultimately limited by our ability to know the locations of the stars and other matter in it. + +In a sense, we're just starting to expand our definition of what the Milky Way *is* in the sense that we've recently discovered much more of the structure of the ""halo"" region of the galaxy and begun to understand the interconnectedness of that halo to the rest of the Milky Way. + +What we know: + +* The locations and proper motion of most nearby stars over a certain brightness +* The locations and proper motion of a fraction of the stars over 10,000 light years (2/5 of the distance to the galactic center) +* That our galaxy has a substantial ""dark matter halo"" +* That there are multiple ""streams"" of stars around the central black hole, not all of which are within the galactic plane, and some of which may be remnants of ""recent"" galactic collisions. +* The general shape and extent of the part of the galaxy that we are within + +What we have only general ideas of: + +* The shape of the far side of the galaxy +* The structure of the halo +* The total number of dim stars in the galaxy +* The total mass of the Milky Way +* The amount of dark matter in our galaxy and its halo (we have what we think are reasonable constraints on the amount) + +##Sources + +### Our region of the galaxy + +* Hambly, Nigel C., et al. ""The solar neighborhood. VIII. Discovery of new high proper motion nearby stars using the SuperCOSMOS sky survey."" The Astronomical Journal 128.1 (2004): 437. + +### Mass of the galaxy + +* Kochanek, Christopher S. ""The mass of the Milky Way galaxy."" Arxiv preprint astro-ph/9505068 (1995). + +### Dark matter + +* Vera-Ciro, Carlos, and Amina Helmi. ""Constraints on the shape of the Milky Way dark matter halo from the Sagittarius stream."" The Astrophysical Journal Letters 773.1 (2013): L4. +* Ascasibar, Yago, et al. ""Constraints on dark matter and the shape of the Milky Way dark halo from the 511-keV line."" Monthly Notices of the Royal Astronomical Society 368.4 (2006): 1695-1705. + +### Galactic halo (not just dark matter) + +* Morrison, Heather L., et al. ""Mapping the Galactic halo. I. The “spaghetti” survey."" The Astronomical Journal 119.5 (2000): 2254. +* Youakim, K., et al. ""The Pristine Survey–VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime."" Monthly Notices of the Royal Astronomical Society 492.4 (2020): 4986-5002. +* Malhan, Khyati, and Rodrigo A. Ibata. ""Constraining the Milky Way halo potential with the GD-1 stellar stream."" Monthly Notices of the Royal Astronomical Society 486.3 (2019): 2995-3005." +850 Why do clothes feel crunchy when you air dry them, but soft out of the dryer? 7154 https://www.reddit.com/r/askscience/comments/6xpwcp/why_do_clothes_feel_crunchy_when_you_air_dry_them/ 1504396675 6xpwcp Chemistry 2017-09-03 2:57:55 Tap water has minerals dispersed in it in solution. When it dries on a line the fibers/threads stiffen because the clothing is not moving much, and the threads retain their shape as the water evaporates and leaves the minerals behind, while in a tumbling dryer the threads are constantly crunched and tugged and squeezed so they cannot stiffen in this way. "The dryer basically gently beats the ""crunchiness"" out of your clothes when it tumbles them. It causes excess wear and pilling, though. + +I fill the fabric softener cup in my washer with plain white vinegar, and my clothes come out soft and smelling great without perfume. The internet theory is that the rinse with a few tablespoons of vinegar gets the hard water minerals and the residual detergent much more thoroughly out of your clothes; IDK whether this is correct or not. + +I do know that soft water washed clothes are not as ""crunchy"" as regular hard water washed; my vinegar-treated, air-dried clothes are soft even with the hardest water; I don't use dryer sheets any more. The clothes come out of the washer with a vinegar smell, but acetic acid is quite volatile and is completely removed from your clothes by drying them. " +948 Why do certain flavours go well together? E.g. chicken/coleslaw, tomato/mozarella, spinach/garlic, walnuts/honey, tuna/mayonaise? 7139 https://www.reddit.com/r/askscience/comments/8bp089/why_do_certain_flavours_go_well_together_eg/ 1523527291 8bp089 Human Body 2018-04-12 13:01:31 "Good reference book: +On Food and Cooking, McGee (Alton Brown constantly references) +Awesome fact from the book: when you eat artichokes, they knock out your sweet taste receptor so whatever you eat next tastes sweet (great reason to eat with mayonnaise). Experiment with drinking glass of water after eating artichoke. Wow! +" "The IBM Watson team put together a set of recipes that were composed by the technology known as the Watson Discovery Advisor. The technology was designed to identify semantic concepts in a corpus of documents, then find patterns across all the documents. + +The system was loaded with corpora from three sources: 1) Recipes from Bon Appetit magazine, 2) Chemical definitions for cooking ingredients, and 3) linking it all together, a database of ""hedonic psychophysics"", a listing of how we experience different flavors from different ingredients. + +The machine was then asked to develop new recipes based on knowledge from these three sources. + +You can see some of the results here: [Chef Watson](https://www.ibmchefwatson.com/community). + +And a cookbook was published: [Cognitive Cooking with Chef Watson at Amazon](https://www.amazon.com/Cognitive-Cooking-Chef-Watson-Innovation/dp/149262571X/ref=sr_1_2?ie=UTF8&qid=1523540265&sr=8-2&keywords=chef+watson+cookbook) + + + +" +1322 How do cats know automatically how to use a litter box? 7131 https://www.reddit.com/r/askscience/comments/cqvgcn/how_do_cats_know_automatically_how_to_use_a/ 1565900692 cqvgcn 2019-08-15 23:24:52 "Please be mindful of: + +Rule 5 - Top level comments must be an answer to the question posed, or a follow-up question to the post. + +Rule 6 - Answers should be supported by reputable sources and scientific research. Do not cite yourself as a source. + +Anecdotes will be removed" ">[Lone feral cats](https://blog.petmeds.com/1800petmeds/how-do-cats-know-how-to-use-a-litter-box/) will naturally cover their waste without any training; they do so to cover the scent from predators and competitors. In groups of feral cats, dominant cats will often leave their feces uncovered as a way of marking their territory, while cats lower in the hierarchy are expected to cover their waste as a sign of subordination. **Since it’s easier to cover their droppings in soft dirt or sand, cats are naturally attracted to this material.** + +>[The act of meticulously](https://www.livescience.com/33147-why-do-cats-bury-their-poop.html) burying their waste stems from cats' long history of using urine and feces to mark their territory. Cat poop may all smell the same to us, but cats can tell their waste apart from another's thanks to unique chemical scent markers called pheromones, which are present in their urine and feces. + +>Wild cats will also hide their waste to avoid attracting unwanted attention from predators to themselves or their nest of kittens . Domesticated indoor cats (Felis catus) harbor the same strong, self-protecting instincts. Even though there are no predators in your home, your cat may not be so sure, and will bury its waste just in case. + +Basically, the litter box will be the only thing with soft, pliable material for them to dig in in your house. It's also why they sometimes target planters or other pots. After the first time they'll essentially have marked the litter box and make a habit out of it, since they're inherently territorial. Cats are borderline domesticated, so their wild instincts are still rough around the edges. And as posted, they're meticulous and fixated on staying clean. + +It's also why you should usually get 1 litter box per cat, and why cats won't simply shit on tiles when they have dirt nearby. Now there's the question of how crazy your own cat can be. Also, what the hell happened to all the posts? + +Edit: [Here's an extensive study covering various issues](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5059607/) cats might have to deal with. Note where it mentions cats who are able to go outside have significantly less troubles than purely indoor cats. Also spay and neuter them that's just basic + +Edit 2: Holy crap clean your cats litter boxes OFTEN + +>[Toxoplasmosis can be Deadly](https://www.healthline.com/health/toxoplasmosis) or cause serious birth defects for a fetus if the mother becomes infected. This is why doctors recommend against pregnant woman scooping or cleaning cat litter boxes. + +Edit 3: if your cat shits right outside the box it's crazy. Cats are crazy. They're just...[as crazy as people if not more](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/neurological-disorders). Also they're basically [psychopaths](https://www.smithsonianmag.com/smart-news/scientists-confirm-cats-are-pretty-smart-b-dont-really-care-what-you-want-180951194/)" +634 Why does the sound of cold water hitting steel sound different than hot water hitting steel? 7123 https://www.reddit.com/r/askscience/comments/5z4wer/why_does_the_sound_of_cold_water_hitting_steel/ 1489410906 5z4wer Physics 2017-03-13 16:15:06 "So your ears are not deceiving you, hot and cold water sound different. + +It doesn't have to be resigned to landing in your sink, pouring a mug of cold water versus boiling hot water sounds remarkably different. In fact, I can tell my shower at home has heated up when the sound changes. + +Despite how fascinating this is, the answer is unfortunately rather mundane. The viscosity of water changes as the temperature of the water changes, and this results in the change to the sound. + +Viscosity is how thick or ""gloopy"" the water is, while water is not very viscous at all the viscosity still drops by a factor of 4 or 5 between 0C and 100C. This is because the van der waal's, intermolecular forces become comparatively weaker as the random thermal motion of the water becomes stronger. + +[Here is a chart of the viscosity (and density) of water changing as it is heated](http://imgur.com/a/p11hx) " "I'm not a scientist but a video on Tom Scott's channel recently discussed this question too: + +https://www.youtube.com/watch?v=Ri_4dDvcZeM + +" +762 Is it possible to 'store' light so it can be used as a form of energy? 7120 https://www.reddit.com/r/askscience/comments/6dzrdm/is_it_possible_to_store_light_so_it_can_be_used/ 1496057347 6dzrdm Physics 2017-05-29 14:29:07 "What you are describing is basically an optical cavity. The most simple variation of cavity is just mirrors facing each other, but there are also ring resonators that basically do exactly what you are suggesting, which is keeping light on a circular trajectory by total internal reflection. + +Even the best cavities have a maximum lifetime of less than milliseconds (in vacuum). In order to get such lifetimes you need incredibly stable configurations and high finesse cavities are definitively delicate instruments that are susceptible to even small fluctuations in temperature and the like and need to be constantly locked to references and only very narrow-band light can be coupled inside. + +Fibers would be even worse for the task. Attenuation in silica fibers is at least 0.5 dB/km, meaning after 20km there is only 10% of your initial power. Light will travel this distance in 0.0000001s in fiber. + +So no, using them for energy storage is not reasonable. There are still tasks were we need to store light coherently (or more precisely store the information that is encoded in the light) as in my field which is quantum information. There we use effects as slow/stopped light or absorption by single atoms or collective excitation of several atoms. Just using fiber delays is not satisfying option for the reason that I mentioned above. Research on such so called quantum memories is a considerable field in experimental quantum info currently and I might even join a research group doing exactly this in autumn." "There are no superconductors for light yet. And fibres absorb quite a bit of light. So for now, not so much chance of getting there. + +Typical fibre loss rates are in the order of 1dB/km. Let's be generous and assume a super low loss of 0.01dB/km. + +Per second light travels 300000 km. This means that after a tenth of a second in a fibre loop the loss would already be 300dB which corresponds to an energy by a factor of 10^30 less than what was there in the beginning. + +To put that into perspective, if you were to come the entire output of the sun into the fibre, after a tenth of a second you'd hardly be able to detect a signal. + +Basically, any interaction with light causes losses so for now the better option is to store other forms of energy using light as an input, such as solar panels. + +Tiny edit: light is actually slower in fibres, but just by a factor of 1.5. It takes slightly longer to run through my fictional fibre but the rest of the math still stands. + " +949 Could I have a bag of neutrons? And if so, what would it look like, would they be reactive? 7114 https://www.reddit.com/r/askscience/comments/84wcpf/could_i_have_a_bag_of_neutrons_and_if_so_what/ 1521214811 84wcpf Chemistry 2018-03-16 18:40:11 "Depends on the density of the neutrons in question. If you're thinking standard every day densities regularly encountered in everyday life, then the answer is no. + +Neutrons cannot exist by themselves for extended periods of time. Outside the extreme gravity fields of a neutron star (we'll get to that in a minute), your average neutron will beta decay with a half life of about 10 minutes, spitting out an electron and a proton, with the leftover mass energy being released as an electron antineutrino. In somewhat rare cases, the decay event will also spit out a gamma ray. In extremely rare cases, the electron does not gain enough energy to escape the proton, and the decay event forms a hydrogen atom, with the antineutrino taking away much more energy than it normally would. + +In short, you'd have a fiercely radioactive (and potentially flammable due to the forming hydrogen) and glowing bag of neutrons in your possession. + +When a high mass star dies, depending on its composition and how much mass ends up in the core at T-0, it can form a stellar remnant known as a neutron star during the ensuing supernova. The inward force of gravity is no longer balanced by the outward force of thermonuclear fusion (fusion above nickel/iron consumes instead of produces energy), and the core is made of what is known as degenerate matter, where for each atom no 2 electrons can share an identical state (See: Pauli Exclusion Principle). Eventually, the weight of the iron ""ash"" as well as the rest of the star builds up to the point where electron degeneracy pressure can no longer withstand the pressure, and the electrons take the only way out left to them: by merging with the protons in the core. + +In the space of about a second, all of the electrons and protons in the core are consumed, and the resulting lump of matter screams inwards at a very significant fraction of the speed of light. Neutron stars run into another degenerate ""barrier"" and bounce off, rebounding outwards... right into the collapsing upper layers of star plasma crashing in. Unstoppable force (collapsing upper layers of star) meets immovable object (neutron star core), and you get a supernova as everything above the ball of neutrons goes boom. + +After the star has died and supernova faded, we have ourselves a neutron star, a couple-solar mass ball of neutrons and more exotic matter crammed into a space roughly the size of Manhattan Island. This ball of neutrons is *extremely* hot (600,000 kelvin is the typical surface temperature), very highly magnetized (many many millions of times stronger than Earth's field), is rotating at several hundred revolutions per second (with linear surface velocities pushing up to .24c), and dense enough to where a teaspoon of the stuff weighs more than Mt Everest. The star itself is so dense it generates its own gravitational lensing effect, allowing a viewer to potentially see more than half of the surface at any given time. But the neutrons would be stable. + +You still wouldn't want it though. A thimble-full of the stuff would still kill you, whether it be from the heat and radiation cooking you alive, the magnetism ripping all of the iron out of your blood, the attempt at extracting it, the tidal forces it would exert on you, or it exploding when it realizes its no longer being crushed together by several billion Gs of gravity. + +**tl;dr**: Free neutrons can and likely will kill you and will leave an expensive mess for the rest of us to clean up. + +Edit: Thanks for the gold, kind stranger!" "There are places where you can gather lots of slow neutrons and confine them into a region of space, for example the ultra cold neutron lab [here](http://lansce.lanl.gov/facilities/ultracold-neutrons/index.php). + +Neutrons undergo beta decay with a half-life on the order of 10 minutes, so you can’t hold onto them for very long." +635 Could a natural nuclear fission detonation ever occur? 7108 https://www.reddit.com/r/askscience/comments/60a3ox/could_a_natural_nuclear_fission_detonation_ever/ 1489931140 60a3ox Earth Sciences 2017-03-19 16:45:40 "Not quite, but close. + +For a detonation to occur, you need a nuclear bomb, which is a very complex and precise machine. This is probably too complex to be assembled by random natural processes. The closest which happens naturally is when Uranium ore deposits form, and then reach a supercritical concentration of fissile isotopes, which is rare. Then, you get a runaway fission reaction. It doesn't go ""Boom"", but it releases a lot of heat and radiation, as well as daughter isotopes. + +The best known examples occur in [Oklo](https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor), in Gabon. + +It has been discussed in previous posts: + +https://www.reddit.com/r/askscience/comments/2mup5t/what_would_the_oklo_natural_nuclear_reactor_in/ + +https://www.reddit.com/r/askscience/comments/rcprg/could_the_natural_nuclear_fission_reactor_in/ + +https://www.reddit.com/r/askscience/comments/z9533/could_a_nuclear_detonation_occur_on_a_planet_via/ + +https://www.reddit.com/r/askscience/comments/mc9hq/there_is_a_natural_nuclear_fission_reactor_in/ + +##UPDATE: + +We're getting a lot of posts in the thread along the lines of ""How is it possible that the formation of a nuclear bomb by natural processes is impossible when the formation by natural processes of complex intellects such as our own has occurred?"" + +This is a false equivalency. In simplest possible terms: both examples are not under the action of the same processes. The concentration or fissile material in ore deposits is under control of the laws of inorganic chemistry, while our own existence is the product of organic & inorganic chemistry, plus Evolution by natural selection. Different processes obtain different results; and different degrees of complexity ensue. + +That being said, the current discussion is about natural fission and whether it may or not achieve detonation by its own means. Any posts about the brain/bomb equivalency will be ruled off-topic and removed." "A detonation is not physically possible. Going critical and super critical, which is what happened at Oklo, yes but a detonation as a nuclear bomb, no. You may have a mechanical explosion caused by an expanding heated fluid due to the heat generated by a fission event and that is about it. + +The method of implosion, at our scale, is not a natural process, it is man made. + + + +" +1407 Why, after quick deceleration in most vehicles, is there a sudden lurch in the opposite direction to the initial direction of travel after the vehicle has come to a stop? 7087 https://www.reddit.com/r/askscience/comments/d0wzbr/why_after_quick_deceleration_in_most_vehicles_is/ 1567868261 d0wzbr Physics 2019-09-07 17:57:41 "Hi! Suspension engineer here! + +A few here have said suspension and they are correct, however I'd like to add on to their answers. There are several areas of elastic deformation which get compressed and suddenly spring back upon stopping. This is where this motion comes from, so I'll touch on the easy ones, then the lesser known ones. + +The first and most obvious thing is normal suspension compression. The center of gravity (COG) of a vehicle is the theoretical point at which the car could be suspended from a rope, and be perfectly balanced in any orientation. Very generally speaking, in most passenger cars, this is about where the gear selector lever is located on the center console. When you press the brake pedal, the front tires are effectively dragging (but still rotating) over the pavement. You can think of this as a rearward force acting on the tire precisely where the tire contacts the road. (We call this the contact-patch) + +Putting this all together, when a vehicle is slowing down there is a forward force at the vertically higher COG, and a rearward force at the tire contact patch which is on the ground. This difference in vertical height causes the vehicle to pitch forward, compressing the front suspension. The energy of deceleration is imparted into the front springs and shock absorbers. + +The second area that experiences elastic deformation is the tire. Engineers hate tires. I hate tires. People have spent lots of time worrying about the correct and best suspension geometry for the tire. But, at the end of the day, you're car rides on four floppy rubber bags with air in them. Even in the best test environments they can be somewhat unpredictable. When you brake (Not ""break""!!!, sorry. Pet peeve) the tire squishes around and acts like a spring. This moves the contact patch backwards with respect to the axle centerline. Upon braking, more stopping energy is pushed into the springy rubber tire. + +Seeing a trend, here? + +The third, and most fun thing, are the suspension bushings. A bushing is a flexible connection that allows for things to move and pivot more easily. In this case, your vehicles suspension is full of springy, rubber bushings. Much like the tire above, these bushings compress when you are stopping, turning, accelerating, or just going over bumps. + +There's one extra bushing that actually permits this action more than others called compliance bushings. Typically, the compliance bushings are located on the front axle assemblies, on the lower suspension arm. It's usually bigger than the others and farther forward or backward of the front axle centerline. The reason for this is because of wheel vibration. Wheels can vibrate due to many reasons, but usually it's because the rims and tires are not perfectly balanced. This is why you get new tires ""mounted and balanced"". When your front wheels are out of balance and vibrate, you get a wiggle in the car or steering. That sensation is the front wheels vibrating up and down AND front to back. The up and down vibration is usually handled by the spring and shock absorber, but what about the front to back vibration? Compliance bushing saves the day! It dampens (sometimes hydraulically) the vibration of the front tires in the longitudinal direction. They make your car vibrate less, with the drawback of being a springy thing in the front suspension. Slowing down in the car puts further energy into all of your springy bushings. + +To summarize, nothing in the world is perfectly rigid, and engineers spend a lot of time concerned with this fact. When you brake in your car, many non-rigid rubbery-springy-things absorb energy as they compress, then suddenly unload that energy just as you stop." "This is one of the occasions where you experience jerk (https://en.wikipedia.org/wiki/Jerk_%28physics%29?wprov=sfla1). It is the time derivative of acceleration, as acceleration is the time derivative of speed. + +It's a bit difficult to explain without some graphs, but I will try anyway: +If the car deaccelerates with a constant breaking force, the acceleration has a constant negative value. When coming to a standstill, the acceleration jumps to zero. This means a big, almost instant change of acceleration, which is also a very big value in the jerk. This has the effect that the car bounces back and forth a bit. + +You can prevent this by either releasing the break right when the car stopps or by driving immediately backwards after stopping (not really possible in a normal car, but often done in mechanical applications to prevent oscillation)" +1230 If you put a giant mirror on the floor of the earth and make a photo from a satelite, what would you be able to see? 7084 https://www.reddit.com/r/askscience/comments/ayo4xr/if_you_put_a_giant_mirror_on_the_floor_of_the/ 1552035424 ayo4xr Physics 2019-03-08 11:57:04 "I work for the Landsat program, and I can show you this! + +​ + +In the Novosibirsk region of Siberia, there is a gigantic greenhouse where they are able to grow vegetables all year round. The roof of that greenhouse is essentially a big mirror. Most of the year it just reflects the sky and appears somewhat dark. But during part of the year, the roof of that greenhouse reflects sunlight directly into the satellite's sensor. + +​ + +[This page has a small image of the greenhouse in various bands](https://landsat.gsfc.nasa.gov/keeping-cal/) (the satellite sees red, green, blue, and several infrared bands). There's a [better picture on page 19 of this journal article (PDF) (I'm a co-author)](https://www.mdpi.com/2072-4292/7/2/2208/pdf), if you want to take a look there. + +​ + +What happens is that the pixel appears very bright. But all sensors have a limit on how much brightness they can image. Most satellites will drive into saturation (full bright with no variance) and then oversaturation (the detectors fail and go dark temporarily, or roll over in integer space). The detectors normally recover after this; sometimes recovery takes a short period of time. + +​ + +So the answer to your question is #1 -- the color of the sky is reflected, and sometimes that color is dark blue (space with some refraction) but sometimes it's bright white when it looks at the sun." "That depends. If you look directly at the sun in the mirror, it would look red. + +The sky is blue, because the blue components are scattered in the atmosphere stronger than the red ones. + +If the light travels a long way through the atmosphere, fewer/no blue components are left in the ""original"" light ray coming directly from the sun. For that reason, sunrises and sunsets are red. The sun rays are propagating tangential to the ground and cover more distance through atmosphere. + +A mirror would cause the sunlight to pass the atmosphere twice. So the idealized reflection should show a red sun, as the problem is equivalent to a sunset. + +The tone of red may be different, but the underlaying principle is the same. + +Edit: If you just look at the scattered light, i would still use the same argument as before. The mirror shows you, how the light looks like after passing the atmosphere twice. So again, it would probably look like the sky at close to the horizon. + +As we know, the light scattered away fron the sun ray is blue. So the only light reaching the mirror is blue. This light gets reflected and passes the atmosphere again. + +On the way back, as to the way down, not all of the light is scattered. So the remaining light is blue, but less bright than on the ground. It would probably be hard to see in practice using only scattered light. + +Edit2: About the scattered part i am not sure, how the Ozone layer comes to effect, as it filters UV rays it also may filter blue slightly. + +Edit3: Thanks for the silver, i am glad i could help. + +Edit4: The sun would probably still look yellow. As some of you pointed out the atmosphere is not as thick as it would need to be to make the sun look red enough to see it with the bare eye. But it would probably be measurable using a spectrometer." +636 If we could use the Large Hadron Collider as a cannon pointed towards space, would the particle make it into orbit? 7080 https://www.reddit.com/r/askscience/comments/5o4dc5/if_we_could_use_the_large_hadron_collider_as_a/ 1484493270 5o4dc5 Physics 2017-01-15 18:14:30 As /u/RobusEtCeleritas said, they are going too fast for orbit. The relevant question then is how much would get through the atmosphere without being scattered. The opposite situation is something that actually occurs: high energy protons from space reaching Earth. While it is hard to find the exact information I'm looking for on this [the particle data group](http://pdg.lbl.gov/2011/reviews/rpp2011-rev-cosmic-rays.pdf) seems to indicate that most protons with TeV energies would be scattered long before they got through the atmosphere. [Artists's impression](http://www.space.com/images/i/000/034/337/original/cosmic-rays-nasa.jpg?interpolation=lanczos-none&downsize=*:600) The particles in the LHC are moving well above the escape speed of the Earth. They would not be able to form bound orbits. +1049 Is a patch of grass one singular organism? Or is multiple? How can you discern one specific organism of grass from another? 7078 https://www.reddit.com/r/askscience/comments/95cq43/is_a_patch_of_grass_one_singular_organism_or_is/ 1533656456 95cq43 Earth Sciences 2018-08-07 18:40:56 "A patch of grass can be a collection of individuals or, since grass is rhizomatous, a single individual can grow shoots from its root and become its own bunch. These are known as bunch grasses. So the answer to your question is sort of, ""it's both!""" "The concept of individual gets kind of fuzzy when talking about grass. The very word means ""not dividable""... but grass can often be easily divided, since many kinds of grass grow as clumps which send out runners that form new clumps. + +Some useful terms for dealing with this problem are ""genet"", which refer to the whole genetically identical plant that spread by asexual propagation from one original seed, and ""ramet"" which refers to one complete plant unit, eg a single clump of grass with roots and leaves. + +In your lawn you probably have a lot of genets..you could test by genetic testing...and each group of leaves emerging from a single cluster in the ground is a ramet" +1408 AskScience AMA Series: Experts are warning that measles are becoming a global public health crises. We are a vaccinologist, a pediatrician and a primary care physician. Ask us anything! 7078 https://www.reddit.com/r/askscience/comments/dinnrs/askscience_ama_series_experts_are_warning_that/ 1571223607 dinnrs 2019-10-16 14:00:07 The AMA will begin at 12pm EDT (16 UTC), please do not answer questions for the guests till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Keep questions and interactions professional and remember, asking for medical advice is not allowed. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). I’ve read (and heard on “This Podcast Will Kill You”) that measles is an immune memory wiper. Can you talk more about this and about why this isn’t blasting from the airwaves? I was stunned when I heard that. I would think that is a great message to get out to antivaxxers who believe their kids should just fight things with their natural immunity. +763 If telomers get shorter with every split of a cell, doesn't this mean we can pretty accurately calculate when someone will die of old age? 7057 https://www.reddit.com/r/askscience/comments/6sgjz4/if_telomers_get_shorter_with_every_split_of_a/ 1502226161 6sgjz4 Biology 2017-08-09 0:02:41 "The concept behind the question is an interesting one and the idea of predicting the lifespan of an individual based on biological indicators is indeed a popular research topic. + +Long story short specifically for telomeres, the answer is ""not really"". Different cells divide at different speeds. Also, many cells do not divide any further at all. If someone got even a minor injury or a mildly traumatic event or some weird habits, that would affect cell division as well. And then there are the individual differences in telomere lengths. Given all these, it will be virtually impossible to predict the ""endpoint"" of cell division in the real-time scale, let alone predicting one for an individual based on a few cells. + +Also, generally telomere length is not the limiting factor for humans. There's some evidence that it can be a contributing one, but it is not really a major factor (the correlation was not practically significant and causation is somewhat dubious). There are many other ways a person can die ""of old age"" depending on the definition, including cancer, neurological disorders (Alzheimer's etc.), osteoporosis, cardiovascular diseases, kidney failure, weak immune system etc. etc., all of which are very much age-related. There are even sayings that most people don't have Huntington's Disease because we die before we reach the age of developing one." "Short response because I'm on mobile. + +I believe more evidence is emerging (especially in the field of stem cells and iPSCs) that telomere length is a dynamic process. Cells contain proteins that can trim long telomeres (telomerase), protect short ones (TZAP and the shelterin complex), and lengthen critically short telomeres (thought to also be the telomerase). The whole thought that aging was directly attributed to telomere length was appealing. Although I think it is naive to assume a cell doesn't have a way to lengthen telomeres and just dies. Long telomeres are actually trimmed to a shorter length because it's considered a cancer risk. While I don't have telomere elongation articles right in front of me and some of the resources I'm finding suggest telomeres don't lengthen in somatic cells, the paper below does discuss the dynamic process. I'm starting to believe telomere length is a lot more dynamic than the previous notion that we lose some base pairs every replication cycle and then the cell dies. + + +Li JS, et al. TZAP: A telomere-associated protein involved in telomere length control. (2017) Science. 10.1126/science.aah6752 + +Edit: and I'll just quote this article to address your original question because there is a correlation. ""In addition, we find that telomere length inversely correlates with lifespan, while telomerase expression correlates with mass. The role of replicative aging as a tumor suppression mechanism is well accepted; however, its contribution to lifespan remains controversial."" +Gomes, Nuno M. V. et al. “Comparative Biology of Mammalian Telomeres: Hypotheses on Ancestral States and the Roles of Telomeres in Longevity Determination.” Aging Cell 10.5 (2011): 761–768. PMC." +764 On Jupiter, will more superstorms the size the Great Red Spot eventually form, or are the positions and types of storms relatively constant? 7037 https://www.reddit.com/r/askscience/comments/6exgpt/on_jupiter_will_more_superstorms_the_size_the/ 1496440609 6exgpt Planetary Sci. 2017-06-03 0:56:49 "The great red spot has been a standout feature of Jupiter for at least a couple hundred years, possibly a lot longer. Clearly it's not a short-lived feature like storms and hurricanes on Earth. + +But as for its evolution and the formation of other storms like it, that's all unknown AFAIK. Understanding our own atmosphere is hard enough, understanding Jupiter's very different atmosphere (with much more limited data) is very difficult. + +In recent years, the spot [has been shrinking](https://www.sciencedaily.com/releases/2014/05/140515103658.htm)." "The Juno probe is contributing data that will hopefully answer some of these questions - or at least get us closer to understanding how Jupiter's atmospheric system works. [This very recent video](https://youtu.be/6o9FiTf1vZE) outlines some of the latest discoveries from the probe - including the observation of many cyclone systems at the poles - which were not expected. + +If anything, this science poses more questions than it answers, however. Jupiter's atmosphere was assumed to be reasonably uniform; we now know that is not the case." +950 If someone becomes immunized, and you receive their blood, do you then become immunized? 7037 https://www.reddit.com/r/askscience/comments/89lb6r/if_someone_becomes_immunized_and_you_receive/ 1522807819 89lb6r Human Body 2018-04-04 5:10:19 "So for blood transfusions used in trauma, ~~the patient will receive what's called ""Washed"" blood, which is donated blood which has had its plasma components removed. This includes antibodies and another set of immunological proteins called complement proteins. So no, he wouldn't receive any antibodies in a normal situation.~~my apologies, I just glanced over some lecture materials and misinterpreted a slide, my mistake. + +However, I'm sure you're still interested in knowing what would happen and I'm happy to answer this. Transfusion of antibodies is already a medical technique called Intravenous Immunoglobulin transfusion. These are used for patients that unfortunately suffer from immune system disorders so they have diminished or absent immune response. These donated antibodies from vaccinated patients have the ability to bind to pathogens through their F-ab component while still being able to bind to F-c Receptors of immune cells by the F-c components. However, to answer your question, this would only be a transient protection and patients that need this procedure need them consistently. + +The reasoning for this is because B cells, the immune cells that produce the antibodies, have no process by which they could receive immunity from someone else's antibodies. Your B cells have to undergo a selection process in your bone marrow, like your T cells in your thymus. As a small background, your B cells provide practically all encompassing antigen binding because they undergo a controlled, mutagenic arms race in their selection process in order to be let out of the bone marrow. Once they're out of the bone marrow after successful selection, they have their own unique antigen binding trait and this would not be changed by the introduction of someone else's antibodies. The binding affinity of the antibody a B cell does change over time, however, once it encounters its match made in heaven antigen, it'll reignite its microbiological Cold War Era arms race in a process called somatic hypermutation to produce an improved antibody. + +tl;dr Your antibodies would only give a temporary immunity because there's no process that they could influence their own synthesis in your friend" In this situation no... When blood is donated its separated into it's components: red cell, plasma, and platlets. All your antibodies are in your plasma. And 2 units is not nearly enough. But what you are asking about is called a therapeutic plasma exchange. A machine pumps ur blood out goes through machine spins it down takes only the plasma out and then the donor plasma is then put back in your system( 2000-3000mls) for an adult. This process is used to treat the flu along with a host of other things. Doesn't last long few months or so it's called passive immunization. Source: me transfusion specialist +1323 Why is 18 the maximum amount of electrons an atomic shell can hold? 7019 https://www.reddit.com/r/askscience/comments/ck7l3x/why_is_18_the_maximum_amount_of_electrons_an/ 1564574636 ck7l3x Chemistry 2019-07-31 15:03:56 ">Why is 18 the maximum amount of electrons an atomic shell can hold? + +It's not. 18 is the maximum amount of electrons that the *third* shell can hold. Other shells have different maxima: the first shell can only hold 2 electrons; the second shell can hold 8, the third can hold 18, the fourth can hold 32, and so on. Each shell can hold 2n^(2) electrons. + +This formula arises because electrons are fermions (particles with half-integer spin) and fermions are required to occupy distinct quantum states. Electrons in atoms have four separate quantum numbers that can take different integer values, with the allowed ranges of some quantum numbers determined by the value of others. For example, the principle quantum number n denotes the shell number -- it starts at 1, counting up from there until that shell is filled with electrons; once it is full, additional electrons occupy the next shell with n=2, and so on. The azimuthal quantum number l (lowercase L) starts at 0 and increases up to a maximum of n-1 ... so when n=1, then l=0, but when n=2, l can have a value of either 0 or 1, and when n=3 then l can have a value of 0, 1, or 2. Then there's the magnetic quantum number m which has the same range as l except it can also take on negative values. So at n=2, m can be any of -1, 0, and 1. And at n=3, m can be -2, -1, 0, 1, or 2. And finally, for every unique pair of n, l, and m, each electron also has a spin projection of either +1/2 or -1/2 depending on whether it is spin-up or spin-down. So then, the first electron must have (n=1, l=0, m=0) and either possible value of s, and the second electron must have the same numbers but the opposite-signed value of s. Then the first shell is filled. The third and fourth electrons will have (n=2, l=0, m=0), the fifth and sixth will have (n=2, l=1, m=0), the seventh and eigth (n=2, l=1, m=1), ninth and tenth (n=2, l=1, m=-1), and then the second shell is filled, and so on. + +For a more detailed explanation why, you may want to read the [Wiki article on electron configurations](https://en.wikipedia.org/wiki/Electron_configuration)." "The 2, 8, 8, 18, 18 thing is really just an oversimplification of a far more complicated thing in the quantum model of the atom called electron orbitals. Crash course does a pretty decent video about it (The Electron: Crash Course Chemistry #5). I'll give it a shot assuming you're in early high school and just learning this stuff for the first time. + +Every time we get to a new noble gas, the periodic table starts to repeat its properties. In the early days, this was taken as evidence that we had reached a new valence shell which shielded the previous shells. The evidence came from the energy levels of the electrons that were added or taken away from the atoms. + +As scientists got better at studying the atom, a pattern emerged: in the first shell, both electrons had the same energy, but in the second and third ""shells"", two electrons had a lower energy than the other six. + +This led to subshell theory. There are 4 subshells, which can hold (in order) 2, 6, 10, and 14 electrons. There are further subshells (that pattern continues), but they are not commonly observed in everyday atoms or molecules. + +So where does 2, 8, 8, 18, 18 come from? Well the first shell can only have the first subshell (2 electrons), but the second can have the first and second (2 + 6 = 8). The third technically has all three subshells (2 + 6 + 10 = 18), but as you get higher in energy the shells start to get closer to each other so the first two electrons in the fourth shell kind of sneak in before the last ten in the third shell. + +Those first two electrons make a big spherical bubble around the atom, shielding the subshells beneath them, so that's where the periodic table restarts. That's why the third row of the table only has 8 elements. The other 10 electrons are only used in the 4th row (mind you, having those subshells available does change the chemistry of the atoms, making molecules like POCl3 possible). + +To answer your initial question, 18 is not the limit, even in the old school periodic table. The 6th and 7th row already contain 32 elements (2 + 6 + 10 + 14) and theoretically the next row would have 50!" +1409 Why doesn't our brain go haywire when magnetic flux is present around it? 7018 https://www.reddit.com/r/askscience/comments/d452qk/why_doesnt_our_brain_go_haywire_when_magnetic/ 1568467125 d452qk Biology 2019-09-14 16:18:45 The current produced would have to be strong enough to overcome our neuron's threshold for activation. All neurons have a base level of electric activity called a resting membrane potential, which is about -70 millivolts (mV). In order to cause that neuron to send an electrical impulse we must depolarize that same neuron to about -55 mV. This can either be done internally, with the release or intake of various electrically charged ions in and out of the neuron, or externally by inducing a current strong enough to penetrate the skull, depolarize the neuron, and be focused to be specific enough to hit just one neuron or a cluster of geographically associated neurons. This can be achieved with very strong and local electromagnetic transducers, such as with transcranial magnetic stimulation (TMS). Although an MRI produces a powerful electromagnetic field, the current it produces in the human body is not typically enough (strong enough, specific enough, or possibly even at the correct angle enough) to cause specific or generalized depolarization of the neurons resulting in activation. Electrical current doesn’t flow through nerves like it does in wires, where a magnetic field *would* induce a current. Instead, it’s an active process involving the movement of ions across the cell membrane that occurs in a moving gradient down the length of the nerve, which a magnetic field does not affect in the same way. +1495 Where do the photons go after the light is turned off in the room? 7009 https://www.reddit.com/r/askscience/comments/g1603c/where_do_the_photons_go_after_the_light_is_turned/ 1586872718 g1603c Physics 2020-04-14 16:58:38 "They get absorbed by the surroundings! Photons are electromagnetic waves, so when they come to matter, they ""wave"" the electrons in the matter around, so the photons lose their energy are are absorbed. This is why a wall in the sun feels hot! The light is being absorbed by the wall and all energy goes into the wall feeling hot. + +As a side note, this is a simplification. Like mirrors don't absorb light, they reflect it. For that matter, most materials reflect some amount of light, that's why we can see them. But all materials absorb light, even in small amounts, so eventually all the light would be absorbed by the material." "when the light is turned off the photons already in the room will eventually collide with a particle in the wall/air/furniture. That particle will absorb the photon. This particle's speed will now increase (vibration, rotation, linear, or combination off all 3). Now theres 2 options. either the particle will re-emit a photon and lose speed OR bounce into another particle and transfer some speed to it. Since the particles in your room are always bouncing and rubbing up against one another, after a few repititions of absorb->re emit->reabsorb, all the photon energy in the room will have eventually just been converted to speed energy. This happens super fast. Thats why it kinda looks like the light just disappeared instantly. + + +Another word for average speed energy of all the particles in a room is Temperature." +1050 mtDNA is passed down from females to all of their children; shouldn't there be people around who carry denisovan or neanderthal mtDNA because they had a great- great- (etc) grandmother who was denisovan or neanderthal? 7003 https://www.reddit.com/r/askscience/comments/99n9gy/mtdna_is_passed_down_from_females_to_all_of_their/ 1535029961 99n9gy 2018-08-23 16:12:41 "Yes - if there are surviving, female-line descendants of Denisovans or Neanderthals, and if the mitochondrial DNA of those populations was clearly distinct from H. sapiens sapiens. + +There are only a handful of mitochondrial genes, amounting to about 16,500 base pairs. There are only 200 variations for Neanderthals, and 400 for Denisovans. + +So we're not looking for much, and we haven't found it - there's no evidence of Neanderthal mitochondria in our cells. Interbreeding was rare, and mtDNA lines are too easily wiped out. " [I have an article you may find interesting.](https://blogs.plos.org/neuroanthropology/2010/10/26/the-neanderthal-romeo-and-human-juliet-hypothesis/) One thing to note is that the sex and species of the parents is relevant to the viability of the offspring; from what I've read in this paper and other articles, a male neanderthal is able to mate with a female human but a female neanderthal might not be able to carry a male human's child. It's an explanation of why we don't see neanderthal mtDNA in today's humans. +1051 Do dead insects “go bad” for other insects that eat them such as spiders? 7002 https://www.reddit.com/r/askscience/comments/8qipw2/do_dead_insects_go_bad_for_other_insects_that_eat/ 1528808287 8qipw2 Biology 2018-06-12 15:58:07 Yes, this could happen in theory. The reason that spoiled food makes us humans sick is because of the growth of harmful microorganisms and the subsequent release of toxins from those microbes. Many of the microorganisms that would grow on our human food would also grow on the soft tissue in insect bodies. However, due to our differing physiology, the things that make humans sick are seldom the same things that make animals sick, and so the insects that feed on other insects wouldn’t necessarily get sick from salmonella. It seems very likely that some of the microbes that grow on dead insects might produce toxins that could be harmful to scavengers but most animals that feed on dead things are adapted to handle the bacteria and fungi that grow on this refuse. "Soft bodied insects such as aphids tend to fully decay in the hours to days range, after that there really isn’t anything left. + +However hard bodied and/or dried insects such as beetles, some flies, spiders, etc. tend to stick arounds for a *very* long time. The Guiness Book of World Records shows the oldest known pinned insect from a natural collection at around 300 years old, which is far younger than the lice found on mummies and combs dating back thousands of years. Given the proper conditions dried dead insects could remain around for thousands of years without significant signs of decay. + +So really it just depends *what kind* of insect you’re talking about, but most tend to stay in pretty good condition and even the ones that dont will provide nutrition for microscopic organisms for a very long time." +765 Is it likely that dinosaurs walked like modern day pigeons, with a back and forth motion of their head? 6988 https://www.reddit.com/r/askscience/comments/6p71ia/is_it_likely_that_dinosaurs_walked_like_modern/ 1500884014 6p71ia Paleontology 2017-07-24 11:13:34 "It seems unlikely. Pigeons (and chickens) move that way to stabilize their vision. It's really only useful for creatures with a small head-and-neck mass capable of movement fast enough to blur vision otherwise; most other animals use other compensatory systems. (Humans, for example, have auto-tracking eyeballs.) + +Dinosaurs, with more body (and head) mass, and thus somewhat smoother movements, would be more likely to use vision stabilization systems common to larger animals." "Related note: There was actually a study on how dinosaurs walked. It won the Ig Nobel Prize. They glued a stick to a chicken's butt to transform it into a T-Rex and compared the walk of the chicken with and without the stick. +Source: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0088458" +766 Solar Eclipse Megathread 6983 https://www.reddit.com/r/askscience/comments/6sm5m7/solar_eclipse_megathread/ 1502291979 6sm5m7 Astronomy 2017-08-09 18:19:39 "# We cannot give you advice on whether you damaged you eyes or not. + +While the /r/askscience megathreads have more relaxed commenting rules than regular thread, this is still /r/askscience. **Top level comments should be scientific or technical questions.** Technical recommandations are fine if you have specific knowledge on eclipse observation. + +Please do not share personal anecdotes. This is not the right place to discuss travel plans, hotel reservations, or expected road traffic." [deleted] +1052 Why do your eyes physically hurt when they adjust to brighter light? 6981 https://www.reddit.com/r/askscience/comments/95quaj/why_do_your_eyes_physically_hurt_when_they_adjust/ 1533767936 95quaj Human Body 2018-08-09 1:38:56 "It's not entirely understood. We don't know if the pain comes from pain sensing nerves, or by the visual information carried by your optic nerve. + +The former is straight forward enough, the latter would mean the pain is a result of your brain detecting the signal is too strong and creating the feeling of pain to protect your eyes. Which would need a lot more study. + +Much better comment that I paraphrased: + +https://www.reddit.com/r/askscience/comments/hgzld/why_is_it_i_can_bear_the_sunlight_fine_with_one/c1vf7i9/" "eye doc here. In bright light your iris contracts which causes your pupil to get smaller. The iris and attached uveal tract is a relatively large radial muscle in the eye. Depending on other factors (such as your eye's size and any inflammation that may be present in the muscle) you may experience a tightening or even actual pain. This is called photophobia and may be a sign of inflammation in the eye called either iritis or uveitis. These can then be signs of broader systemic inflammatory conditions such as ankylosing spondylitis, Reiter syndrome, sarcoidosis, inflammatory bowel disease, psoriasis, etc. Typically though there should not be any physical pain associated with bright lights so if you have this, go get your eyes checked. I have diagnosed may people with systemic diseases through their eyes. +*edited spelling" +951 If camera lenses are circular, why do they produce a rectangular image? 6971 https://www.reddit.com/r/askscience/comments/7v6ayh/if_camera_lenses_are_circular_why_do_they_produce/ 1517744610 7v6ayh Engineering 2018-02-04 14:43:30 "The lens focuses light on an image sensor chip, which is what actually converts the light to an electronic signal. The chip is rectangular, and just covers a fraction of the focused image created by the lens. + +The image created by the lens -- the focused light -- doesn't have very abrupt edges. Far from the middle, the quality and intensity drop off. The sensor is positioned well within the good part. + +So why are the sensors rectangular? Partly it's just tradition, but it's also that many are made on a big silicon wafer and then cut apart, into rectangles. If the sensors were round, there would be wasted space in the corners of each square sensor chip. + +Edit: I've added [another comment with more details](https://www.reddit.com/r/askscience/comments/7v6ayh/if_camera_lenses_are_circular_why_do_they_produce/dtr5d8j/), including a sort of table of contents for some of the comments below that I think provide particularly good clarifications or explore interesting further aspects. + +My edit also rephrased the above explanation a little based on seeing what wrong impressions my original phrasing gave. I'm deliberately leaving it short and oversimplified because the original seemed to capture the key points and because more detail is in the linked comment." "The camera lens actually produces a circular image, but only a portion of it is captured. The images' shape comes from the sensor size rather than the lens. It's also more practical to have a digital image where all lines are of equal length. + +The ""Kodak No. 1"", an early comsumer-friendly camera, took circular photos. [Link](https://publicdomainreview.org/collections/kodak-no-1-circular-snapshots/)" +637 How can a Black Hole have rotation if the singularity is a 0-dimentional point and doesn't have an axis to rotate around? 6969 https://www.reddit.com/r/askscience/comments/5wgjys/how_can_a_black_hole_have_rotation_if_the/ 1488200019 5wgjys Physics 2017-02-27 15:53:39 "A few points: + +The angular momentum of a black hole is a property of the spacetime and needn't have anything to do with what is happening inside the horizon. + +The singularity is never a 0-dimensional point. In Schwarzschild it is an ""instant of time"". In Kerr it is a ring. I don't think the shape of the singularity in a real black hole is known. + +[Point-like objects can have angular momentum](https://en.wikipedia.org/wiki/Spin_\(physics\)) though this has nothing to do with black holes really (see the first point) " "1) the singularity is not a 0-dimensional point. That's true of non-rotating black holes. Rotating black holes probably don't even have a singularity (aka as ringularity since it would be a ring) even at a semi-classical level: the singularity lies in an interior region of the solution which we know cannot be trusted to model actual rotating black holes. + +2) the singularity does not ""carry"" or ""hold"" the properties of the black hole such as the mass, the linear and angular momentum, the charge... it will just lead to confusion to think in these terms. How/where exactly a black hole ""keeps"" these things is a subtle and counterintuitive matter. + +The technical answer is these properties are sort of ""delocalized"" in the case of a black hole and the black hole itself is essentially a type of topological defect. That would be a very agnostic, strictly classical answer. But that's close to impossible to explain for me. + +A simple, bizzarre and not really that wrong at all way to imagine a black hole is as a very thin 2-dimensional membrane lying above the horizon. This membrane is hot and has energy, so mass; when stuff falls in it gets burnt by the membrane and adds to its energy/mass. When charges fall onto the membrane, the membrane (which has a sort of electrical conductivity) absorbs and dissolves charges and become charged itself. And finally, it can acquire linear or angular momentum when it's provided by falling objects, and can start moving, or rotating (and become flattened). This is a quantum-gravity- (and string-theory-) inspired picture, but for what regards classical gravitation it gives the same answers as the ""standard"" one, and might help clarify a lot of the trickiness of black holes. " +638 Is my stomach ever completely empty? And about how much fluid is in there without and food or drink? 6942 https://www.reddit.com/r/askscience/comments/66t8f3/is_my_stomach_ever_completely_empty_and_about_how/ 1492822513 66t8f3 Human Body 2017-04-22 3:55:13 "I've seen the inside of thousands of stomachs while anesthetizing people for upper endoscopies. Most of them are mostly empty. All of these patients have had nothing to eat or drink for 8+ hours. + +The stomach collapses down when you haven't put anything into it. This is different than the heart and lungs, which keep a volume of blood and air in them, respectively, and need to do so to function properly. + +If there is still retained food in the stomach after a prolonged fast, it's frequently due a condition called gastroparesis, which means ""paralyzed stomach"". Gastroparesis is more common in diabetics, but non-diabetics can have it as well. + +I found [this study](https://www.ncbi.nlm.nih.gov/pubmed/25115349) which quantified the amount of water in the fasted stomach as 35 ± 7 mL, so about an ounce. When we put oro- or nasogastric tubes into patients having general anesthesia, we usually get about that much stomach juice back. In patients with bowel obstructions, we can get a liter or more out." "I'm an anesthesiologist, so supposedly my patients haven't had any food or drink since the night before. + +When I do anesthesia, I often drain stomachs with a tube in case they've eaten since unfortunately, people lie occasionally. However, I believe 99.9 percent tell me the truth. + +Anyhow, I'd say an average person has about 50 cc of stomach fluid. Diabetics, who often have a disorder called gastroparesis (basically slow emptying of the stomach), have between 100 and 250cc. + +Staying that, I pretty regularly find chunks of food. Most recently, a gentleman had green specks of something in his stomach. Upon closer inspection, it was chewed up dried seaweed. + + + +" +1053 Do firefighters have to tackle electric car fires differently? 6939 https://www.reddit.com/r/askscience/comments/8rqvu5/do_firefighters_have_to_tackle_electric_car_fires/ 1529240614 8rqvu5 2018-06-17 16:03:34 "[Understanding Why Electric Car Fires Pose a Unique Hazard](http://www.core77.com/posts/74535/Understanding-Why-Electric-Car-Fires-Pose-a-Unique-Hazard) + +Thus Tesla actually designed two ""first responder cut loops"" into their cars--one in the front trunk, one in the back--and each year releases Emergency Response Guides for first responders instructing them on how to fight a Tesla fire. + +Cutting either of the loops ""shuts down the high voltage system outside of the high voltage battery and disables the SRS and airbag components,"" reducing the risk of explosion. + +They also have to show firefighters where not to cut during rescue/firefighting efforts. + +Additionally, information is included in Tesla's guide warning of the toxic vapors released by a burning battery. + + +It should be noted that the battery packs in these cars are made up of thousands of smaller batteries. Not just one or 2 huge ass LI-Ion cells." [deleted] +1410 Liquids can't actually be incompressible, right? 6936 https://www.reddit.com/r/askscience/comments/dnmi9t/liquids_cant_actually_be_incompressible_right/ 1572137665 dnmi9t Physics 2019-10-27 3:54:25 Correct, they are just much harder to compress than gas. At the bottom of the ocean the water is compressed by a few percent compared to the top. Typically compressing a liquid enough turns it into a solid, water is a little weird in that regular ice is less dense, so if you compress water enough it'll form a less-common phase of ice. When you pressurize water to extreme #'s in a nuclear reactor you can see reactor power go up just a little bit as the molecules get just enough increase in density to cause more neutrons to reflect back into the core. (The increase in density of water causes more neutrons to bounce off moderator(water) and go back into the core to cause more reactions in the fuel.) We geeked out watching it happen while we were testing the piping in the reactor for our submarine, it was just a little increase but enough to make the nerds happy. +767 If all the polar ice caps melted, would the ocean become less salty? 6933 https://www.reddit.com/r/askscience/comments/6ikts6/if_all_the_polar_ice_caps_melted_would_the_ocean/ 1498038885 6ikts6 Earth Sciences 2017-06-21 12:54:45 "Physical oceanographer here. +There was an article published in Science 7 years ago answering this exact a question using Paleo oceanographic evidence from the last deglaciation (Synchronous deglacial overturning and water mass source changes by Natalie Roberts and others). + + +Deglaciation does, by simple math make the world's oceans less salty but not in the way you think it would. It takes gargantuan amounts of energy to mix water masses with different properties, so instead of the entire ocean reducing its spicyness (salt concentrations), you'd see certain currents take the biggest hits while others remain pretty much unchanged. + +Now, the ocean currents that have been shown to be most affected by current and past deglaciation are those feeding deep, cold water to the world's oceans (water can only sink to the bottom of the ocean near Antarctica and Greenland). In case of a total deglaciation, this supply would stop, meaning that: + + **The rates at which deep water resurfaces and that at which surface water sinks to abyssal levels would reduce drastically. Freshwater, the article finds, would remain in the upper ocean and drive overturning there.** + +In short, a deglaciation partially stops the exchange of energy, salt, and heat between the deep and upper ocean, leaving only topography-driven and tidally-aided sources for turbulence to cause 'communication' between these two layers. This is pretty much how lakes work (no tides though, but being smaller, lakes can have their bottom layers accelerated by wind under some special conditions), so oceans would become much more similar to them. This is by no means that currents would stop (wind and tides would remain stirring everything up), but it is only the deep/upper water exchange that would pretty much disappear." " +If you define ""saltiness"" as [salinity](https://www.google.com/?gws_rd=ssl#q=salinity&spf=1498068817254), then yes. It's actually a fairly big concern associated with the risk of glacial melt because it's widely believed that the [salinity influences ocean currents](https://en.wikipedia.org/wiki/Thermohaline_circulation). + + +One concern is that a massive influx in freshwater to the ocean could alter or even shut down major ocean currents, and ocean currents are what help keep the ocean oxygenated so that fish can live in them. We don't know for sure, but the concern is that global warming could cause serious disruption in the ocean food chain, and that would have ramifications for the food chain we're a part of too. +" +851 How are drill bits that make drill bits made? And the drill bits that make those drill bits? 6924 https://www.reddit.com/r/askscience/comments/7kd83x/how_are_drill_bits_that_make_drill_bits_made_and/ 1513507950 7kd83x Engineering 2017-12-17 13:52:30 "The ""paragon of cutting materials"", as it is known to some, is called tungsten carbide. It isn't necessarily the hardest material we know of but it is the cheapest/best material for cutting due to its abrasion and temperature resistance, and relatively easy processing. Tungsten carbide has an advantage to other materials in that it can be sintered,[Link 1] + (https://en.wikipedia.org/wiki/Sintering). This allows it to be formed into many useful shapes for cutting in a relatively cheap process. If you pause the video in your post, you can see the cutter being used has what appears to be triangle cutters with large holes. The holes are for mounting, so they are replaceable, and the triangle shape makes it so each insert has 3 cutting edges, increasing the life of the insert. [WC Insert](https://sc01.alicdn.com/kf/HTB1phgvKpXXXXaLXVXXq6xXFXXXZ/CNC-turning-inserts-tungsten-carbide-drill-bit.jpg_350x350.jpg) + [Insert Milling Cutter](http://img.directindustry.com/images_di/photo-m2/125441-7082491.jpg) This is how things are done nowadays, but I am unsure how it was done in the past. I hope this answers your question." "The hardness of drill bits is a result of an involved heat treatment process, not something that is normally present in the material. + + +Note that drilling items like steel plates, using too high a drill speed, will cause excessive heat from friction, and this rapidly softens the drill bit. + +The bits are usually milled from blank bars which have been carefully *Annealed* at the factor and thus have maximum softness. + +Annealed material can be milled, with some extra precautions, using tools of that very same material, that have been subsequently hardened by heat treatment. In the annealed state it is only slightly harder than normal structural steels. + +However it's industry standard these days to use milling tools made out of tungsten carbide which is an extremely hard, heat resistant ceramic material. These last much longer in nearly all metal cutting applications except drilling because of their extreme wear resistance, including the making of cutting tools. + +Generally the bit is started by carving the rough shape of the bit from round bar stock. + +The rough bit is then Heat Treated by soaking at red heat for an hour or more, then quenching in oil which rapidly cools the material, causing a chance in crystal grain structure. Then, the bit undergoes a careful tempering process at mild heat which optimizes it's hardness and toughness. + +Once the bit has been heat treated, it is precision ground and sharpened using diamond coated abrasives wheels. + + +" +1054 Why is green always used in special effects like green screens? Why not yellow or purple or red? 6919 https://www.reddit.com/r/askscience/comments/8lj266/why_is_green_always_used_in_special_effects_like/ 1527079536 8lj266 Engineering 2018-05-23 15:45:36 "In theory, any color screen could be used. However, there are a number of reasons why green is preferable over other colors. + +First is the nature of the subjects in front of the screen. In most scenes with a green screen (or the more technical term: chroma keying), humans are the main subjects in the scene. Humans tend to have very little green in their skin or their clothing, which makes it easier to replace the background without accidentally replacing part of the subject. + +Another reason is more technical in nature. Digital sensors don't record R, G and B with the same level of detail. This is by design. A pixel in a digital sensor can only capture the total light intensity. In order to capture color detail, each pixel is fitted with a filter that only lets a certain color through. So you'll have red pixels, green pixels and blue pixels. A full color image, where every pixel can have a full range of colors, is reconstructed using this limited information. Since human vision is more sensitive to green than to other colors, the commonly used approach is to divide the sensor into blocks of 2x2 pixels and giving 2 of them a green filter, and the other 2 are used for red and blue. This is called a Bayer filter. + +Because of this, the raw image data contains more green information than red or blue. That means that green features will have a higher resolution. Since the quality of chroma keying is very much affected by how accurate you can record the edge between the foreground subjects and the background screen, the increased resolution of the green channel allows for more accurate cutouts of the background. + +Note that in the time of analog film, blue screens were more common, since the chemical properties of analog film resulted in a higher level of detail (reduced grain) for blue elements. " "There are already some great comments. I just wanted to add a link to a recent Captain Disillusion episode that talked about this exact subject. I've included the timestamp for that particular topic, but really you should watch the whole thing as it's very informative while being entertaining. + +https://youtu.be/aO3JgPUJ6iQ?t=1m51s" +1893 The earth is about 4,5 billion years old, and the universe about 14,5 billion, if life isn't special, then shouldn't we have already been contacted? 6911 https://www.reddit.com/r/askscience/comments/nzh4j0/the_earth_is_about_45_billion_years_old_and_the/ 1623655039 nzh4j0 Astronomy 2021-06-14 10:17:19 "Let's say we have been contacted 1000 times in the history of the planet, so even one contact attempt every 4.5 Million years, how long were we listening for? + +How long would we have had the computing power to decode a message? On top of that, are we even looking in the right place? I saw a great cartoon once of a couple of ants saying they've scanned all known pheremone bands and can conclusively confirm they're alone in the universe." "This is a large part of the Fermi Paradox. The galaxy is only about 100,000 light years across, so even at 1% of the speed of light, it takes 10 million years to cross the galaxy. We evolved from small mammals to tool-using humans with space rockets over less than 100 million years. The invention of writing to the Apollo Program is maybe 10,000 years or less. All of these time-scales are much shorter than the age of the Earth, let alone the universe. This means that if life intelligent evolved anywhere else within the galaxy, it's unlikely that it appeared at the same time as us - it's almost certain that any intelligent life would be millions of years more advanced or millions of years less advanced. + +This tells us that galaxy-colonising advanced life must be rare, as if there is intelligent life that has the capability and intent to colonise the galaxy, anywhere within the galaxy, anywhere in the past X million or billion years, they should have reached Earth a very long time ago. + +Of course, there are multiple reasons why galaxy-colonising advanced life might be rare. + +- they lack the intent, i.e. they could colonise the galaxy, but they choose not to leave their home planet, or they do explore the galaxy but leave us alone (basically the Zoo hypothesis) + +- they lack the ability, i.e. even with millions of years of advancement it's not practical to leave a solar system in mass migrations, or a more advanced society generally becomes more at risk of destroying itself before it reaches that stage (""the great filter"") + +- *intelligent* life is rare. Life has thrived on Earth for billions of years before one species developed spaceflight. Evolution doesn't inevitably lead towards developing life that can invent advanced technology. There may be many planets out there full of animals and plants, or even just bacteria, but it's possible that humanity is a bit of a freak accident. + +- life is rare in general. We don't really know how common life is. We know the ingredients seem to be fairly abundant, but how often do these combine to make something we would reasonably call ""life""? + +- the conditions for life are rare. However, as we discover more and more exoplanets, it looks like there are quite a few planets that seem like they would be hospitable to life, so this is less of a factor than we used to think. + +So this isn't really a ""paradox"" in the common sense, because there are many ways to resolve it. But each of the resolutions involves stuff we just don't know - we don't know how frequently life evolves in the right conditions, we don't know how frequently life evolves to form intelligent space-faring species, and we don't know how often a space-faring space faring species would have the intent and capability to explore the galaxy. Any of these are plausible, and it could easily be a combination of everything." +1411 Why don't plants get sunburned or genetic damage/cancer being out in the sun all day? 6909 https://www.reddit.com/r/askscience/comments/do1fdw/why_dont_plants_get_sunburned_or_genetic/ 1572221872 do1fdw 2019-10-28 3:17:52 "It does and they do. Though as others here noted, many things help them defend against it. + +Leaves are disposable though, and the outer layers of bark are usually dead plant material that protects the rest. + +Most crucially, most plants don't have cells circulating like animals do, so they can't really get anything like metastatic cancer. They also lack vital organs that can become diseased and kill the whole plant. + +Plants get tumours of sorts for all kinds of reasons but they can't generally spread and kill the whole organism." "The UV damage repair enzyme, Photolyase, hasn't been covered yet. Mammals do not have functional Photolyase to repair pyrimidine dimers (the most common form of UV-induced damage), while many plants, fungi and bacteria do have Photolyase. Mammals rely on nucleotide excision repair (removing a chunk of DNA and re-writing it), instead. More efficient damage repair leads to less cancer. + +A review on Photolyase: https://www.nature.com/articles/1205958" +952 Why does fried food such as french fries start to float in the oil after a few minutes of cooking? 6891 https://www.reddit.com/r/askscience/comments/8ap3nn/why_does_fried_food_such_as_french_fries_start_to/ 1523182351 8ap3nn Chemistry 2018-04-08 13:12:31 "As the food heats the water inside starts boiling, forming steam. So first the steam enters the oil and evaporates from the top. + +Now a crust is formed, this makes it harder for the steam to leave the food. You'll often notice the food is a bit 'puffy': this is the steam pushing against the crust. This is when the food starts floating: the density of steam is very low. Once the average density of the food + steam is lower than the oil, it will start floating. + +You'll notice with some foods that the content has shrunken. Either the crust collapses with it, or it leaves a crusty shell. That's the steam that becomes water again, and the density of water is a lot higher, so it shrinks." "Food that you usually fry, contains a quantity of water in it. Water is heavier than oil. When you fry something, you are basically boiling it from the inside. So it does became less heavier than oil because it looses many of its water content while frying. Have you ever asked yourself why if you fry at low temp with little oil, food cames out oily, and when you use high temp with much oil, food came out almost dry? This is mainly for ebullition speed. Oil has quite high specific heat, so at 175°C degrees is not that difficult to heat up water to 100°C quickly, and water begins to became water vapor. From now on, the evaporation speed strongly depends on the calories given to water by oil, so another important fact is to keep the temperature stable while frying. This will lend many vapor steams to exit from the food, keeping out oil. After a while food begins to float, for the loosen weight due to loosen water and that's it. Volume doesn't change so much, so this density change is more a weight change related phenomena +EDIT: also, this doesn't involve chemistry at all folks! It's a Physics related phenomena" +768 What happens to water when it freezes and can't expand? 6887 https://www.reddit.com/r/askscience/comments/6jkg7l/what_happens_to_water_when_it_freezes_and_cant/ 1498475817 6jkg7l Chemistry 2017-06-26 14:16:57 "This is an interesting question, and it seems that no one has actually answered it as intended--what happens when you cool water in a container that allows no expansion? + +Looking at the [phase diagram of water](https://upload.wikimedia.org/wikipedia/commons/0/08/Phase_diagram_of_water.svg), my best guess is that ice VI would form. However, [ice VI has a higher density than water](http://www1.lsbu.ac.uk/water/ice_vi.html) at the pressure at which it forms, so it would not actually generate any pressure by forming in the first place. + +Perhaps what would actually happen in this thought experiment is that some amount of ""normal"" ice Ih would form, generating pressure in doing so, until the pressure generated was high enough that ice VI would form, which has the effect of relieving some of the pressure. In the end a mixture of ice Ih and ice VI is formed with the same density as water at that temperature." "Freezing and melting are both very dependent on temperature and pressure. Water can configure itself into around 17 different ways.* The ice we see is Ice I, and there's 2 forms of it. The type of ice will change with changes in pressure. So if you increase the pressure, you might get Ice II. The way we classify ice is in the order that we discovered it. Ice I was the first type we discovered, Ice II is the second and so on. + +*I say around 17 because there are some forms of ice that aren't considered ""real"" Ice, like amorphous ice, which is the most plentiful kind of ice(in the universe). This is because it doesn't have an orderly crystalline structure like the types of ice using the Roman numerals. " +852 From a cost stand point, would it not make sense to build duplicates of space probes and send them to different locations? 6884 https://www.reddit.com/r/askscience/comments/7c8ho4/from_a_cost_stand_point_would_it_not_make_sense/ 1510408483 7c8ho4 Astronomy 2017-11-11 16:54:43 "I presume you mean because the engineering required to build them can be directly reused. + +This is partially true, and why there are plenty of examples (especially in the earlier parts of the space program) of multiple copies of something being launched. + +E: [Note how many duplicate missions there are on this list](https://en.wikipedia.org/wiki/List_of_Solar_System_probes) + +However, at this point that doesn't really make too much sense. That's because launch cost is enormous. To LEO, depending on your contract, it costs on the order of $10-$50k/lb. Since there's that whole ""rocket equation tyranny"" thing, a deep space probe will have to bring a few times its mass in fuel beyond LEO in order to get the rest of the way out of Earth's gravity well. + +When you're talking possibly as much as $100k/lb, you want *exactly* the right instrumentation for exactly what you're trying to do. So yes, you reuse what you can, but if the mission is better suited by something a little different -- you make something different." "In most cases it does not make sense, most satellites have a limited number of instruments and the instruments that we put on the satellites are designed to study specific questions. For example a satellites designed to study the sun will have a different instruments than a satellite designed to study Jupiter. + +There are some ""cluster"" mission where we do send multiple copies of the same probe. Here the idea is that we want to get multiple simultaneous measurements of some at different locations in space." +1231 Are the nearby airplanes cleared of the sky when launching Falcon Heavy? I was checking Flightradar24 when launch occurred and didn't see any difference. Also, 3 boosters landed back successfully. I assume the sky has to be clear of airplanes to avoid any potential collision? 6866 https://www.reddit.com/r/askscience/comments/bcdk88/are_the_nearby_airplanes_cleared_of_the_sky_when/ 1555075669 bcdk88 Engineering 2019-04-12 16:27:49 "The Falcon Heavy (and Falcon 9) launch from Florida towards the east, flying over the Atlantic. This isn't a particularly busy part of the airspace, so the impact is limited. But even so, for launches like this, aviation authorities (the FAA in this case) clear a section of the airspace for some time, requiring airlines to fly around the section that is restricted. + +In the case of SpaceX launches, the restricted airspace is a thin, but long slice that starts at the launch site and extends far into the Atlantic Ocean. This restriction primarily affects flights from the US east coast towards the Caribbean and vice versa. + +Right now, the combination of low frequency of launches and launch sites that are away from busy airspace means that the impact on air travel is quite small. However, in a future where rocket launches become more frequent and with additional launch sites closer to population centers (for example for space tourism), the impact may increase. + +See also this [Washington Post article](https://www.washingtonpost.com/graphics/2018/business/spacex-falcon-heavy-launch-faa-air-traffic) for more on the impact of the Falcon Heavy launch (last year) and rocket launches in general on air travel." "Yes, there's an exclusion zone. This will be published in a NOTAM - Notice To Airmen. Pilots are expected to be aware of relevant NOTAMs before they fly. Should a pilot enter the exclusion zone, the launch will be delayed or cancelled (""scrubbed""). Though once the rocket is in flight, not much can be done. Similar applies at sea, for safety in case the rocket fails and crashes into the ocean. + +In 2014 an Antares rocket launch was scrubbed due to a boat in the exclusion zone, and the rocket failed during the next launch attempt the day after. In 2017 another Antares launch was scrubbed, 90 seconds before liftoff, due to an aircraft. + +http://spaceflight101.com/antares-launch-scrubbed-by-wayward-plane-liftoff-re-set-for-sunday/" +1324 Why was the number 299,792,458 chosen as the definiton of a metre instead of a more rounded off number like 300,000,000? 6852 https://www.reddit.com/r/askscience/comments/ctcsp6/why_was_the_number_299792458_chosen_as_the/ 1566368260 ctcsp6 Physics 2019-08-21 9:17:40 "The principle was to keep the definition consistent with previous measurements, within their uncertainty. We already had a definition for the metre, just not as precise as the current definition, and we want the new definition to be as consistent as possible, but just easier to measure precisely. Rounding to 300,000 km/s would change the definition of the metre by about 0.07%. That would just make life different for everybody: we'd have to specify if we're talking about the ""old"" metre or the ""new"" metre, because that 0.07% change is big enough to matter. It'd change the circumference of the Earth by about 30 km, for instance - a big enough difference that it's measurable, even if it's small. + +Rounding down to the nearest 1 m/s means that instead of a 0.07% change, the change is ~0.0000003% at most. So, that changes the circumference of the Earth by <10 cm at most. That's small enough that it would typically be within the measurement error, and it's close enough that we can treat the metre as unchanged without causing any problems." "The meter ~~is~~ was defined as 1/10,000,000 the distance from the equator to the North Pole at the longitude of Lyon. + +Then people figured out that this wasn't a great way of developing a precise unit of length due to difficulty measuring, and the fact that the value might even change due to Earthquakes, and it could only be referenced at one spot (the line through Lyon) and they searched for a definition that was a universal constant. Eventually the speed of light was chosen (there were electrum rod references in between), and it happened to be 299,792,458. It's a pure fluke that it's so close to 300,000,000" +639 If I'm in a car goong 25mph with 25mph sustained tailwinds, and i roll down the window, will i feel any breeze? 6844 https://www.reddit.com/r/askscience/comments/62x8p9/if_im_in_a_car_goong_25mph_with_25mph_sustained/ 1491099779 62x8p9 Physics 2017-04-02 5:22:59 "No, you'd feel very little. This is is actually a fairly common situation that is encountered when sailing. When running with the wind (ie the wind is to the back, and pushing the boat forward), the crew will feel very little breeze. + +In the sailing world, though, this is actually when a lot of things can go wrong. Crews become complacent because it feels like there is no wind, but the boat is actually under a lot of strain.. Gybes under that kind of power can seriously damage the rigging. + +Edit: Wow, my highest rated comment ever, and just about an observation from sailing. Thanks!" "Very little if any. I experience this often on my bike. + +Also, there is a range (determined by how strong a cyclists you are) where you can estimate the speed of the (tail)wind by matching your cycling speed until you feel no breeze. " +1232 How many tumours/would-be-cancers does the average person suppress/kill in their lifetime? 6843 https://www.reddit.com/r/askscience/comments/bg30ps/how_many_tumourswouldbecancers_does_the_average/ 1555944835 bg30ps 2019-04-22 17:53:55 "I don't think we can reliably estimate how many ""pre-cancers"" a healthy immune system can detect and destroy, but one of the major complications after a solid organ transplant is the risk for developing cancer due to the severe immune suppression needed to prevent transplant rejection. According to this article by Webster et al. (2007): ""Cancer is a major source of morbidity and mortality following solid organ transplantation. Overall risk of cancer is increased between two- and threefold compared with the general population of the same age and sex. Recipients of solid organ transplants typically experience cancer rates similar to nontransplanted people 20–30 years older, and risk is inversely related to age, with younger recipients experiencing a far greater relative increase in risk compared with older recipients (risk increased by 15–30 times for children, but twofold for those transplanted >65 years)"". So you can theorize that the immune system catches some in younger people (depending on the overall health of the person-some people have things that predispose them to developing cancer), with the immune system being unable to keep up as we age. Webster AC, Craig JC, Simpson JM, Jones MP, Chapman JR 2007. Identifying high risk groups and quantifying absolute risk of cancer after kidney transplantation: A cohort study of 15,183 recipients. Am J Transplant 7: 2140–2151" It's a big number. Good rule of thumb average mutation rate is about 1 in 1 million base pairs during DNA replication- almost all of those are immediately repaired or rectified. That sounds like a little but it adds up to a huge number. There is still so much we don't understand that appears to be related to oncogenesis, like telomeres +853 A 5 foot section of railroad rail does not seem very flexible but a 200 foot section appears to be as flexible as a noodle with bends under a foot. How does longer length make it more flexible? 6823 https://www.reddit.com/r/askscience/comments/7kj1br/a_5_foot_section_of_railroad_rail_does_not_seem/ 1513572556 7kj1br Engineering 2017-12-18 7:49:16 "You can bend the 5 foot section of railroad rail, but it's such a small amount you don't really notice it. When you have 200 feet of railroad rail that small bend is amplified by a factor of 40, because every 5 foot section of the rail is bending just a little bit. They likely bend nearly the same amount (same radius of curvature), but it isn't very noticeable until you have a long enough piece of rail to see the arc. + +EDIT: Yes, I understand that the weight of the rail itself also plays into this. I was assuming the rain was lying flat and you were just pushing on it while the other end was fixed, for simplicity. If it's hanging or in other scenarios you do still need to consider the additional weight and leverage of the rail causing additional bending. This simplification also assumed you could somehow apply the same force on each 5 foot section of rail, which is false as was pointed out by u/orangeman10987. The bend increases with the cube of the length in realistic scenarios." "First we must clear a misunderstanding up. The railroad rail’s flexibility is an intrinsic property, meaning that the actual amount of the material in question doesn’t affect the flexibility at all. + +In engineering applications, we calculate deflection of beams (we can consider the railroad rail as a beam for reference purposes) using pretty simple equations. For simplicity’s sake, I’ll reference a situation where the rail is fixed at one end and extends into space until it reaches the end (no support below). The maximum deflection, which as you noticed happens at the end of the beam, is equal to FL^4 /8EI. + +In this equation, F is the force per unit length (Newton per meter, for example), L is the length of track, E is the modulus of elasticity (that intrinsic property I talked about earlier), and I is the planar moment of inertia (a property of the shape of the object). + +Notice that for any two lengths of the same material, the only variable that will change is that L as the rest are intrinsic properties. On top of this, the L is to the fourth power and in the numerator, which causes it to really control the deflection in this equation. + +This equation does not hold true for a situation like a rail supported at only at both ends which sags in the middle, but I wanted to use it to mathematically show why length matters so greatly in deflection. + +Source: currently a mechanical engineering student. Anyone feel free to correct me if I’m wrong " +640 If we observe a star X light years away, does that mean theres nothing inbetween here and there obstructing our view? 6820 https://www.reddit.com/r/askscience/comments/60tniy/if_we_observe_a_star_x_light_years_away_does_that/ 1490175842 60tniy Astronomy 2017-03-22 12:44:02 "There can be stuff in between, it just can't be enough to completely block out the star. We will often see stars as being ""reddened"" because of the dust and gas in our line of sight that blocks out part of the light. Stars can also be partially eclipsed by a planet moving in front of them, but planets are much smaller than stars and only block out a small fraction of a stars' light. + +But yeah, generally space is very very empty, and you usually have a clean line of sight to most objects. The biggest issue is the dust and gas within the Milky Way - when we look straight along the plane of the Milky Way disc, we're looking through the thickest part of the disc, and all that dust and gas adds up and blocks out much of our own galaxy." There actually can be, it is called a [gravitational lens](https://en.wikipedia.org/wiki/Gravitational_lens). This is when an object bends the light around it, so we actually see the star in one place when it is in another, or [we see multiple copies of the same thing, but the light went in multiple directions around an object.](https://en.wikipedia.org/wiki/Gravitational_lens#/media/File:Einstein_cross.jpg) +300 Gravitational Wave Megathread 6778 https://www.reddit.com/r/askscience/comments/458vhd/gravitational_wave_megathread/ 1455199218 458vhd Astronomy 2016-02-11 17:00:18 Are there any currently accepted theories that will be eventually discarded as a result ? A wave is typically measured by frequency and amplitude. What aspects of gravity do these two properties affect, and are these aspects explainable/understandable to non-physicists? +515 Water is clear. Why is snow white? 6772 https://www.reddit.com/r/askscience/comments/5hdal8/water_is_clear_why_is_snow_white/ 1481283219 5hdal8 Chemistry 2016-12-09 14:33:39 "Water is clear, why are frothy waves white? + +Glass windows are clear, why is a pile of shattered safety glass white? + +All for the same essential reason. Something clear is clear because its structure is well aligned to allow light to pass through with**out** lots of refraction or absorption. Snow flakes (and bubbly water, and glass shards) provide millions of surfaces, all pointing different directions, sending light bouncing and bending and absorbing in all sorts of ways. The light gets diffused into what you see as white. " "The short answer is that in reality both liquid water and ice/snow have an intrinsic blue color. This color comes about because water and ice absorb the red part of the spectrum more strongly, leaving blue light to be reflected. However, in the case of ice/snow a second mechanism is at play, namely diffuse reflection caused by scattering and multiple reflection events. This diffuse reflection overwhelms intrinsic color of the ice and gives off a white appearance. +___ +To see that liquid water really looks blue, all you have to do is to look at a big clean body of water such as the ocean. You can make sense of this color by looking at its [absorption spectrum](http://i.imgur.com/WWn5L3Z.gif). As you can see in the graph, the absorption coefficient keeps rising as you move through the visible spectrum from blue to red. As a result, the red end of the spectrum gets absorbed more strongly, leaving mostly blue light to be reflected. Now this absorption coefficient is also very low, which is why a small volume of water looks clear and it is only once you have a sufficiently long optical path that the faint blue color becomes apparent. + +Now in the case of ice, the absorption spectrum changes a bit, but not that much in the visible part [as you can see here](http://i.imgur.com/cCqFZ5u.gif). As a result, you would once again expect ice to look clear for small bits and blue for sufficiently large chunks. Indeed that is true, but in many cases this color is hidden by a second factor: diffuse reflection. In the case of snow, part of this diffuse light comes from multiple reflection events [as light passes through the crystal](https://upload.wikimedia.org/wikipedia/commons/2/21/Diffuse_reflection.gif). Another somewhat related mechanism is scattering. Defects inside of the crystals as well as the air gap between the individual snowflakes can act as scattering centers. Moreover, because these spatial variations are on the length scale of visible light or larger, the mechanism at play will be [Mie scattering](https://en.wikipedia.org/wiki/Mie_scattering). This type of scattering is largely wavelength independent, which is why the scattered light looks white. The exact same effect explains why clouds are also white. More to the point, it also explains why ice cubes [can look clear in some parts and white in others.](http://i.imgur.com/E6PnR07.jpg) The white patches tend to be concentrated near the center where the crystals grew faster and with more defects. + + +edit: Elaborated on the importance of multiple reflection along scattering in causing the diffuse reflection." +1795 "Can years long chronic depression IRREVERSIBLY ""damage"" the brain/ reduce or eliminate the ability to viscerally feel emotions?" 6765 https://www.reddit.com/r/askscience/comments/ltp2hq/can_years_long_chronic_depression_irreversibly/ 1614435581 ltp2hq Neuroscience 2021-02-27 17:19:41 "Neurons aren’t firing or are misfiring, it’s not permanent damaged but more of a non- or low- active area of the brain. + +An easy way to understand what’s happening in the depressed brain is to look at recent studies done on various compounds (mostly psychedelics)/treatments and how they can stimulate neurons into firing again, often long term. + +This article is about the effects of ketamine on the brain, but there are other ways to stimulate the less active parts of the brain including transcranial magnetic stimulation, synthetic or natural substances, and on rare occasions a blunt trauma. However, without some form of stimulation those dormant neurons won’t just start firing correctly. At least that we know of yet. + +https://www.scientificamerican.com/article/behind-the-buzz-how-ketamine-changes-the-depressed-patients-brain/ + +Edit: readability, typos" Yes, but not necessarily irreversible. [Bipolar is similar in this too](https://www.sciencedaily.com/releases/2016/05/160531104421.htm#:~:text=of%20bipolar%20patients-,The%20blood%20of%20bipolar%20patients%20is%20toxic%20to%20brain%20cells,neurons%2C%20a%20new%20study%20shows&text=Summary%3A,the%20connectivity%20ability%20of%20neurons.). The extreme emotions, [including depression](https://sciencenordic.com/denmark-depression-evolution/depression-can-damage-the-brain/1392566) can negatively affect the brain, by atrophying parts, damaging cells, and [reducing white/gray matter](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6489983/). This in turn can cause the brain to be less able to process emotions and can make one more susceptible to those extreme emotions. They've found that by comparing images of the brain of those who suffer bipolar or depression early on to later in life pictures of the brain, there shows a clear progression of damage to the brain. +953 How does something as temporary as a human footprint get preserved for more than 10,000 years? 6758 https://www.reddit.com/r/askscience/comments/87zp23/how_does_something_as_temporary_as_a_human/ 1522312840 87zp23 Archaeology 2018-03-29 11:40:40 Mud retains its shape very well yet is still malleable. It also can harden under sun and be filled in by loose sediment, so that's where a lot of footprints come from. In this case the print was found at a prehistoric waterline of a lake so lots of clay. If you go to the paper you'll see the clay sequence in which the print was found in figure 13. On a related note, imprint fossils can be preserved for much longer. There are [fossil raindrop splashes in South Africa that are 2.7 billion years old](http://www.iflscience.com/environment/27-billion-year-old-fossilised-raindrops/). Similar fossils can be found in Glacier National Park in Montana and are around 1.2 billion years old. The crazy thing is we can use the splash diameter to estimate the density of the atmosphere from that time. +1233 How close would you have to get to the sun for the vacuum of space to be at room temperature? 6742 https://www.reddit.com/r/askscience/comments/ausel1/how_close_would_you_have_to_get_to_the_sun_for/ 1551139739 ausel1 Astronomy 2019-02-26 3:08:59 "The vacuum of space does not have a temperature, temperature is a property that materials have. For example, it's commonly said that deep space has a temperature of about 2.7 K, but that's misleading. 2.7 K is the equilibrium temperature that an ideal blackbody would reach in deep space due to cosmic microwave background radiation. + +So a better question would be, how close would you have to get to the sun for an ideal black body to be at room temperature? Spoiler alert: close to where the earth is. The answer is found by balancing incoming solar radiation with the outgoing blackbody radiation of the object, a common problem in introductory thermo classes. The derivation [here](https://en.wikipedia.org/wiki/Planetary_equilibrium_temperature), usually used to find the temperature of a hypothetical planet at a given distance, can be rearranged to solve for distance when given temperature, and the result is about 84 million miles, or 0.9 AU. This assumes the body is spherical, but an arbitrary shape would reach a similar temperature. + +The difference between our hypothetical blackbody and the earth comes down to albedo (reflection), emissivity, and various greenhouse effects; if the earth were a perfect blackbody it would be about ~~40~~ 10 °C colder. + +Edit: note, this only applies to something that isn't producing its own heat like a person or anything electronic. Any internal heat production means the body has to radiate more heat to reach equilibrium, resulting in a higher temperature. Additionally, it's hard to say how a person would *perceive* temperature in the vacuum of space (before dying, of course) since our perception of temperature is largely dependent on heat transfer and not necessarily absolute temperature." "On Earth the *air* has a temperature. (Which varies from place to place and time to time.) + +A total vacuum can't have a temperature - whether we're talking room temperature, colder than room temperature, warmer than room temperature, whatever. + +Other things that are *in* the vacuum - such as a rock or a spaceship - can have a temperature. + + + +" +954 Whats the usefulness of finding new bigger prime numbers? 6739 https://www.reddit.com/r/askscience/comments/7of8tf/whats_the_usefulness_of_finding_new_bigger_prime/ 1515194474 7of8tf Mathematics 2018-01-06 2:21:14 "Probably the most useful thing is the experience we gain in the hunt for the prime number. Writing programs to search for large primes is not trivial. Consider that the latest prime number is 23 million digits long. To store the number in its entirety takes about 10 Mb. People have to develop new algorithms to efficiently manipulate numbers this large. And once these algorithms have been developed they can be applied to other areas of research. + +I'll also point out that the search for prime numbers helps generate interest in math. People can take part in the search at home. Some of these programs are run on home computers when they are idle. When people sign up for the programs they often do some self research to understand what their doing. This outreach aspect should not be underestimated in value. + +Another point to make is the prime numbers are the building blocks of the integers. Every positive integer has a unique prime factorization. So studying the prime numbers is an important part of number theory. Every time we discover a new prime there's a chance that it will hint at something new pattern that we have yet recognized. + +At the same same time prime numbers have some interesting properties that were learning how to exploit. Encryption is often cited, but they can also be used for random number generation, and some other things. It's hard to imagine that a 23 million digit prime being useful today, but who knows what will happen in the future as computing continues to progress and people continue to test new ideas." "There's virtually no mathematical point to finding the actual primes. I say this as a number theorist. + +Finding new large primes is mostly a computer science pursuit. What may be of actual interest is any new methods for finding primes, new optimizations to existing algorithms, or just faster computer hardware. These may find other uses, but the actual prime numbers themselves are almost entirely useless. + +From a mathematician's point of view the discovery of the latest largest prime is not really any kind of breakthrough. It doesn't add anything significant to our mathematical knowledge. It's the same with digits of pi, for instance. + +I think such accomplishments get news coverage in lieu of actual mathematical discoveries because they are understandable by interested laymen. This is partly because, unlike in say theoretical physics, the important open questions of pure math are not really discussed outside academia." +1325 If ocean water had a higher viscosity, would wave size be affected? 6690 https://www.reddit.com/r/askscience/comments/bo734g/if_ocean_water_had_a_higher_viscosity_would_wave/ 1557771488 bo734g Physics 2019-05-13 21:18:08 "Yes because the viscosity changes the amount of energy needed to make the substance move, in this case you are asking about wave size so you are going to need more force to make the wave grow at least the actual size of waves right now. + +Imagine having a sea full of pancake syrup. If you throw a rock at the sea. The rings that are created on the impact would travel a little bit of space compared to what they normally do. + +Fun fact: you can “hear” the difference in viscosity based on the temperature of the water at the moment you are pouring it on a cup. Temperature changes the viscosity of the water so it sounds different. + + +I’m gonna add more knowledge: since temperature is energy being transferred to water particles “charging them” ( in this case ) energy transmission between particles it’s gonna be easier thats why it’s easier for hot water to flow. If seawater was hotter there would be bigger wavers + +At high temperatures the viscosity index lowers making it more fluid. + +Edit: since a lot of people are worried about global warming and the temperature of the sea I’m gonna answer it: yes the oceans are getting warmer but the increase in the temperature on the seas are really low to make a noticeable change (on the height of waves) +Ice caps melting would do more damage because sea level rises so more land is eaten by the sea. Temperature would affect somehow( in viscosity) but it’s too small to make an really extreme impact noticeable at first sight on the wave height ( in this case) we should be more worried about reefs bleaching and plastic destroying animal life." "It depends on how much you increase the viscosity. Making the oceans like jello would obviously change wave dynamics significantly, but it's possible that even a 10x increase in water viscosity wouldn't change wave physics very much. + +That might seem counterintuitive, because it seems obvious that waves would be in some kind of equilibrium, with energy being input by winds and energy being dissipated by viscosity. That intuition is misleading, because it leaves out an important process: the turbulent energy cascade. + +The turbulent cascade is the transfer of energy from large scales (where the energy is input by e.g. wind) to the small scales (where energy is dissipated by e.g. viscosity). Why doesn't viscosity just act directly at the large scales? Well, it does, but the effect is tiny. People who study fluids characterize the influence of viscosity using the Reynolds number, calculated as a length scale times a velocity scale, divided by viscosity. For an ocean wave with wavelength 10m, wavespeed 2m/s, and normal water viscosity of 10^-6 m^2 /s , the Reynolds number is 20,000,000. That means that the inertia of the wave is 20,000,000 times more important than viscosity at that scale, so there isn't much energy dissipation at that scale. + +What happens instead is that the energy is transferred from the largest scale to a slightly smaller scale, and then to a slightly smaller scale, and then to a slightly smaller scale, and so on, until it reaches a scale where the Reynolds number is roughly one. This transfer of energy can happen through waves breaking on the shore, internal waves breaking over seafloor topography, hard-to-visualize instabilities within the flow, or any number of other ways that are the subject of lots of research. + +So what does that mean for our hypothetical, ten-times-more-viscous ocean? Well, the wave Reynolds number is now 2,000,000, so viscosity still doesn't have much effect at that scale. The dissipation scale is now 10 times bigger, so there's maybe one less step in the energy cascade. That would probably cause an effect that scientists would notice with careful measurement, but it wouldn't be obvious to casual observers. + +What would be affected by increased ocean viscosity? Small ocean creatures like plankton often operate at Reynolds numbers of around 1, so viscosity has a direct effect on the forces they experience. A 10x increase in viscosity would cause a 10x increase in drag/thrust for those little guys. I don't know if they would like it or hate it, though." +1055 Do plants receive a measureable amount of energy from starlight other than the Sun, versus if they were in total darkness? 6684 https://www.reddit.com/r/askscience/comments/98k1wx/do_plants_receive_a_measureable_amount_of_energy/ 1534683474 98k1wx 2018-08-19 15:57:54 "According to [this paper](https://www.ncbi.nlm.nih.gov/pubmed/16916290), the answer is no. + +Plants need a certain minimum amount of photons per second per square meter for photosynthesis to work. This has to do with the intermediate products of the photosynthesis reaction ""slipping"" through the membranes before they can react and form molecules for long term storage of energy." "The light dependence of the key enzyme in photosythesis, Rubisco, is actually really interesting. The reaction it catalyses exists in an equilibrium between the carbon fixing we think of as photosythesis, and the energy consuming reverse reaction. As a result, plants have a number of mechanisms to stop this reverse reaction, most of which boil down to preventing photosynthesis in the dark. + +Because of these mechanisms, photosynthesis does not occur in low light such as starlight. Even if Rubisco were not inhibited in photosythesis, the reverse reaction would occur and actually consume the plants energy. + + +https://en.wikipedia.org/wiki/RuBisCO +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC17801/" +1108 Do (fighter) airplanes really have an onboard system that warns if someone is target locking it, as computer games and movies make us believe? And if so, how does it work? 6676 https://www.reddit.com/r/askscience/comments/9iwh3d/do_fighter_airplanes_really_have_an_onboard/ 1537912286 9iwh3d Engineering 2018-09-26 0:51:26 "The RWR (radar warning receiver) basically can ""see"" all radar that is being pointed at the aircraft. When the radar ""locks"" (switches from scan mode to tracking a single target), the RWR can tell and alerts the pilot. This does not work if someone has fired a heat seeking missile at the aircraft, because this missile type is not reliant on radar. However, some modern aircraft have additional sensors that detect the heat from the missile's rocket engine and can notify the pilot if a missile is fired nearby. " "Hey this is absolutely up my ally since I'm a subject matter expert on all this. + +What people have said in top-level replies is correct. What people have said after those replies is nonsense. + + +Let's pretend you're playing a game of hide and seek. The rules are simple - you hide in the woods at night, but you have to wear a big shiny reflective suit. The seeker is given a big powerful flashlight with varying brightness, and a friend called the 'finder' who has a smaller, weaker flashlight. The rules are that the seeker's friend has to be the one to 'find' people, but he has to accompany the seeker himself. + +So you stand out in the woods. You then see a flashlight beam through the dark. It's sweeping all over. Sometimes it passes over you. This is your RWR system picking up that something is out there and it's looking. It might not see you yet or it's just noticed you and done nothing else. We have a brevity code of 'nails'. It just means ""I see them"". Their radar system (the flashlight) is very bright and makes them very noticeable. + +The seeker gets closer to your position and he thinks he sees something. He shines the light in your direction and maybe turns the brightness up. This is called an RWR 'spike'. Because of the increase in power and the fact that that beam is focused in your direction, you're now alerted to the fact that he might be on to you. You can now take countermeasures of your own to throw him off. + +But maybe the seeker with the flashlight is smart and knows of tricks to prevent this. Maybe he notices you but just *pretends* to not notice. He passes the flashlight over in your direction while getting closer, but shines it off in other places too, pretending he's looking for others. But you're clever as well - you can tell that he's passing the flashlight over you too often. + +Now the seeker has a problem. He wants to tell the finder where to go to 'find' you, but the finder can't really see what the seeker can see, and the flashlight he has is too weak. Once the finder leaves and begins looking for you, he can't really keep up with what the seeker is able to see with his more powerful flashlight, so the seeker - for the highest chance of directing the finder to the right location, he has to crank the flashlight power up and shine it directly at you. Now the finder can rush in on you. Even if you manage to lose the seeker, the finder gets close enough that his little flashlight is now sufficient enough to let him track you down. + + +--- + + +This describes how radar and radar warning receiver function, and a active guided missile being fired. In real life, a lock or launch warning is detected by the presence of an extremely high-energy concentration of radar energy painting you. Most medium-ranged missiles don't have radar systems in them sufficient to guide themselves to the target the entire way (the tiny flashlight), so they need help tracking as they move in on the target to grab the kill. In the old days most of these missiles didn't even have their own transmitting systems (flashlight), they would have to rely on the firing aircraft (the seeker's flashlight) to track the hider the entire way. If the hider managed to break line of sight with the seeker, the finder would be lost. Modern missiles now have their own radar transmitting systems, though they still need help crossing the many miles to meet the target. They switch on their own radar systems as they get closer to help find a final guidance solution. + +Now there's a huge caveat to this - this is only true of radar-guided systems. There also exist other guidance systems. The first is MCLOS or SACLOS. This isn't used against aircraft anymore (too unreliable, too impossible to hit anything) but was common in the early Cold War when guidance systems were nonexistent. These are Manual or Semi-Autonomous Command Line of Sight. Basically it's someone manually steering the missile into you. These missiles generally emit no signal to indicate the target that they are being attacked. There are also laser-guided systems (again, not really used against aircraft, they're too far away and too fast, but they are used against ground targets). Targets can detect the laser beam hitting them and take action. Lastly, there's infrared or electro-optical guidance. These are ""sight"" driven missiles. They simply see the target and then chase after it. However, they only work within a few miles because too far away, their sensors aren't powerful enough to see anything. + +Like CLOS missiles, these emit no signals to be detected. In other words, if an enemy is behind you in a dogfight (which is where these missiles are intended to be used - the big radar guided systems are only for medium and long ranges, because it's too hard to keep a radar lock on a maneuvering target in close range) you *won't* get the ""missile lock"" tone. In Battlefield, the heatseeker missiles warning enemies that they're being targeted is nonsense. It *cannot* happen. + +There are systems now that try to sense the electromagnetic wavelength of a rocket motor firing in an attempt to detect these undetectable missiles, but obviously the missile technology is being designed to try to defeat those systems. + +--- + +Let's go back to our game of hide and seek. Right now the game isn't fair. You basically glow in the dark in your foil suit, and he has a huge spotlight. All he has to do is look for reflections in the night. + +Let's change it up a bit. Let's say we give you your own flashlight. We also give you glitter, mirrors, computer-controlled mirrors with flashlights, and black spraypaint. + +So you're hiding, and the seeker is coming in. You think he sees you, so you begin to mess with him. Since he's looking for shiny reflections in the night, what you do is set up the computer-controlled mirrors nearby. When he shines the light at you, the computer mirror picks up the flashlight and shines a reflective looking bright spot back at him. This is one form of electronic warfare jamming (the analogy is a little hard because using a light to see things is more effective than looking for a radar return signal). Basically, you make the shiny reflection look like it's coming from somewhere nearby. + + +Another form of electronic warfare jamming is ""barrage"" jamming. You have a flashlight that's not as powerful as his but it's still pretty strong. You wait for him to get close enough, and then you turn on your spotlight and blast him in the face. He's blinded, he can't see anything, and you can escape. However, he now knows you were in the area. + +Then there's the glitter. In real life it's called chaff. The guy is looking for you and you throw the glitter... except that didn't do anything. He can see the glitter and knows you're there. Where the glitter is useful is when the finder is sent out by the seeker and getting close. You whip the glitter in his face and it confuses and distracts him. It's very much a last-ditch move though. + +Lastly, there's the black spraypaint. This game isn't very fair because of your foil suit. So you spraypaint it black. Congratulations, you're now in stealth mode. He can still see you if he gets close enough but he no longer can spot you a mile away from your reflective suit. You can now maneuver in their dark to avoid him. + +--- + +Modern radars now use electronically steerable arrays. These make it more challenging to detect certain types of radar operation, because the fundamental ""flashlight of energy"" no longer exists. Instead, this is like giving the seeker ten thousand flashlights that he just randomly turns off and on a hundred times per second. It's now much harder to tell if he's looking at you or not because you can't track the beam of energy moving around. + + +**EDIT:** I love having to resubmit posts 40 times because of garbage word filters that make no sense." +1412 How do we know how to build large scale, but rare, civil engineering projects? (e.g. subways) 6675 https://www.reddit.com/r/askscience/comments/cy51mw/how_do_we_know_how_to_build_large_scale_but_rare/ 1567308171 cy51mw Engineering 2019-09-01 6:22:51 "Rarely will you find an expert in something like building a Subway. You'll find some engineers who specialize in designing tunnels, and some who design railroad systems, and people who design high-traffic spaces (like stations). They'll all work together, as well as with other people who have experience in the subparts of those tasks (electrical system design, HVAC, geologists, interior design, etc). + +All of these people can apply their skill sets to a variety of projects - it's all about gathering the right group of people." "There are a number of large scale infrastructure engineering design firms in the world. You can Google some of these companies to learn more about them - Jacobs, AECOM, Arcadis, China Com, Cardno, WSP, etc. + +I work for one of these global giants, so I can give you a little insight. + +A large scale infrastructure project such as an airport, major bridge, large interchange, tunnel, port, rail or subway system is planned for years, and sometimes even decades in advance. + +The projects often begin as identified needs, but also sometimes as political plays, and sometimes even the design firms themselves can 'create' the project out of thin air by convincing the governments and stakeholders in question that it would be a benefit to the town, city, or state as a whole. + +The projects float around for many years until finally they find some form of funding and begin to become a reality. + +The engineering firms have large numbers of specialised engineers, usually divided into teams, dedicated to all the different specialities needed to make a project a reality. + +For example, a subway system will need alternatives analysis - where engineers determine the most viable routes, vehicles etc., It will need Right of Way specialists to deal with all the impacted right of ways on the surface during the construction process. It will need environmental engineers to verify nothing will be illegally impacted. + +Geotechnical scientists and drainage engineers must study the geology and soils through borings and similar technologies. LiDAR specialists will image the ground. + +Utilities specialists will locate all the existing utilities (water lines, sewer, electric, gas) etc. They will identify what needs to be moved, removed, or replaced and they will also design the new utilities that will need to be in place. + +Architects will design the stations, platforms and entries and exits. + +Public involvement specialists will keep the public informed and as happy as possible during construction. + +Traffic engineers will design alternate routes for traffic on the surface so that construction can have the least impacts possible on the population. + +Tunnel boring specialists will design the methodologies that the tunnels will be excavated and figure out where the moved earth goes. + +Rail specialists will design the systems and procure the vehicles. + +The list goes on and on. I'm just skimming the surface here. For the most part, large infrastructure design firms have a lot of these specialists in house, but they will also often ""sub out"" certain tasks to smaller subconsultant firms. Sometimes they team with equally large firms to create a joint venture business entity just for the duration of the project. + +The organization chart for a project of this scale will often have hundreds of individuals from several firms. + +There will be one or two extremely experienced Project Managers at the top, assisted by more 'boots on the ground' Deputy Project Managers and Lead Engineers. There may be a dedicated 'Project Management Office' (PMO) set up. + + Below this upper management level is a whole heirarchy of engineers and other specialists, usually split into carefully thought out teams. For example, there may be a ""Rail engineering"" team, headed by an experienced rail project manager. Beneath him or her there might be specialists for such things as track design, lighting, electrics, stations, vehicle procurement etc. and each of those engineers will have small teams under them going down to the fairly new engineers doing simpler tasks on the bottom. + +When a project like this is finally funded and ready to begin being designed, the ""client"" (the city, government, or other agency requesting the project) puts out a 'request for proposals' (RFP). Then the engineering infrastructure firms will compete with each other for the job. They will each create detailed proposals about how they will approach turning the idea into a reality - how they'll keep costs down, how they meet the schedule, how they'll address technical problems, how they'll handle the public and the stakeholders, how they'll structure their team for optimum efficiency, etc. + +The client will receive all these proposals by a given deadline, then they will shortlist a few of the best ones and bring them in for interview. The winner of the interview wins the job. Then there's a process of negotiations and contracting before the design actually begins. + +Once the design is complete (or during the design process in the case of 'Design-Build' structured projects). Then the big contracting firms start bidding on the job. The contracter with the best experience and lowest/best value prices wins the right to build the project. The design project manager usually continues to oversee or work with the contracting form while the project is built to make sure everything goes according to plan. + +Some of the bigger contracting firms in the world are Skanska, Turner, Kiewit, Walsh. Sometimes the Design firms are so big that they double as contractors too -AECOM and China are examples of these megagiants. + +No project will ever go 100% according to plan. There will be scope changes, problems obtaining right of way, public and stakeholder backlash, technical issues, fluctuating material costs, inclement weather, political opposition etc., So all projects of this scale are 'living', 'organic', processes. They require deeply experienced people at the top who are capable of making quick decisions, solving unforeseen problems, and moving all the chess pieces just right. + +I'm super proud to be a tiny part of some of these projects. It's truly miraculous to watch so many complex moving pieces all come together to create a real physical thing like an interchange or a subway. + +Wow, that turned out really long, sorry. Hope it helps give you some insights into all the infrastructure around you and what it took to get it there." +1056 If someone gets a blood transfusion, wouldn’t they have a mishmash of genetic material appear in a DNA test? 6674 https://www.reddit.com/r/askscience/comments/8turi7/if_someone_gets_a_blood_transfusion_wouldnt_they/ 1529965450 8turi7 Biology 2018-06-26 1:24:10 "From a review of an article in *Scientific American*: + +Scientific American explains that when donor blood is mixed into the body with a transfusion, that person’s DNA will be present in your body for some days, “but its presence is unlikely to alter genetic tests significantly.” It is likely minimized because the majority of blood is red cells, which do not carry DNA — the white blood cells do. That publication notes studies have shown that highly sensitive equipment can pick up donor DNA from blood transfusions up to a week after the procedure, but with particularly large transfusions, donor white blood cells were present for up to a year and a half afterward. Still, even in those latter cases, the recipient’s DNA was clearly dominant over the donor DNA, which is easily identifiable as “a relatively inconsequential interloper.” + +==== + +This review raises a question for me. Suppose the white blood cells from the donor, that can persist for up to a year in the blood of the recipient, have a high risk of becoming cancerous. Is there any evidence of this occurring, that is, a recipient developing cancer of a type of white blood cell that came from a donor ? " "Many DNA tests do not require blood. Red blood cells do not contain DNA, but precursor cells to red blood cells and white blood cells do contain DNA. + +I would expect there to be an issue. A recent blood transfusion is a question that would be asked if the DNA test requires blood." +1057 Why do sunburns start to hurt after you get out of the sun? Why don’t we notice the pain while we are in the sunlight? 6669 https://www.reddit.com/r/askscience/comments/8y85ak/why_do_sunburns_start_to_hurt_after_you_get_out/ 1531386900 8y85ak Human Body 2018-07-12 12:15:00 It’s because the burn is caused by cells dying in response to DNA damage from the sun, but it takes time for the damage to be detected and apoptosis (programmed cell death) to begin. Once it does, the burn begins. A sunburn is not like a typical burn where you touch something hot and immediately feel pain. The damage is done more by UV radiation than by heat, so the temperature receptors in your skin aren't set off in the same way. The skin cells die from the damage, triggering inflammation (which is why your skin becomes warm, red, swollen, and painful). This is not an instantaneous process and can take hours to ramp up, which is why you don't notice it immediately. +1234 How do magnets get their magnetic fields? How do electrons get their electric fields? How do these even get their force fields in the first place? 6668 https://www.reddit.com/r/askscience/comments/bdrxjc/how_do_magnets_get_their_magnetic_fields_how_do/ 1555407356 bdrxjc Physics 2019-04-16 12:35:56 "Electrons have a fundamental property called the quantum mechanical spin. This spin can be understood and described as an intrinsic angular momentum. + +The spin creates a magnetic dipole moment with a certain magnitude. In non-interacting electrons, these dipole moments are randomly oriented such that in average all magnetic moments cancel each other and the net magnetization is vanishing. If the electrons are brought inside an external magnetic field, the spins partially align such that a rather small net dipole moment is created which is aligned in the same direction as the external field. This is called paramagnetism. As soon as the external magnetic field is removed, the electrons lose their alignment and the overall magnetization is zero again. + +If the distance between the electrons is reduced they start to interact with each other. Either through their direct magnetic interaction between the dipoles (dipole-dipole interaction) or through a quantum mechanical effect called exchange interaction. This causes the electrons to align with respect to their direct neighbor, either in a parallel or anti-parallel configuration. In the former case (ferromagnetism) the individual magnetic moments add up and a large net magnetization is maintained, even in the absence of an external magnetic field. In the anti-parallel case, it is called antiferromagnetism and the net magetization is cancelled even in the presence of an external magnetic field. + +In ferromagnets, the spins do align only within certain volumes, called the magnetic domains. Between these domains, these large net magnetizations may again be randomly oriented such that the overall magnetization of a piece of ferromagnetic metal is zero. If such a material is brought inside a sufficiently strong magnetic field, the domains rearrange such that all their magnetizations add up. The domains' orientations may be effectively ""locked-in"" so that when the external field is removed, the material maintains a significant amount of net magnetization and a magnet is obtained. This is called persistence." "I'm very curious to hear an answer to the second question, how do electrons get their electric fields? My version of the question is, why do electric fields/electric forces exist at all? Also, why are there two types of electric charges and not more or less? Do these questions even have meaning; is ""that's just the way the universe is"" the best we can do?" +1326 How do we measure the height of mountains on planets with no sea level? 6659 https://www.reddit.com/r/askscience/comments/c469e4/how_do_we_measure_the_height_of_mountains_on/ 1561303296 c469e4 2019-06-23 18:21:36 "I too saw this Reddit link. The Wikipedia page talks about this a bit; https://en.wikipedia.org/wiki/Olympus_Mons. This leads to a discussion of the Mars global datum, defined as (from https://en.wikipedia.org/wiki/Geography_of_Mars): + +> On Earth, the zero elevation datum is based on sea level. Since Mars has no oceans and hence no 'sea level', it is convenient to define an arbitrary zero-elevation level or ""datum"" for mapping the surface. The datum for Mars is arbitrarily defined in terms of a constant atmospheric pressure. +> +> From the Mariner 9 mission up until 2001, this was chosen as 610.5 Pa (6.105 mbar), on the basis that below this pressure liquid water can never be stable (i.e., the triple point of water is at this pressure). This value is only 0.6% of the pressure at sea level on Earth. Note that the choice of this value does not mean that liquid water does exist below this elevation, just that it could were the temperature to exceed 273.16 K (0.01 degrees C, 32.018 degrees F).[4] +> +> In 2001, Mars Orbiter Laser Altimeter data led to a new convention of zero elevation defined as the equipotential surface (gravitational plus rotational) whose average value at the equator is equal to the mean radius of the planet.[5] + +I hope others will comment and explain the last paragraph better for us all. Here is reference 5 from that article: + +Smith, D.; Zuber, M.; Frey, H.; Garvin, J.; Head, J.; et al. (25 October 2001). ""Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars"". Journal of Geophysical Research: Planets. 106 (E10): 23689–23722. + +A direct link. +https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2000JE001364" "1. First you need to define a zero altitude. Height is a relative value instead of an absolute value. + +2. If the planet has atomsphere, we can use the pressure deference between the mountain top and the defined zero altitude to find out the height of the mountain. You will also need to measure Temperature lapse rate, Standard temperature at zero altitude, Surface gravitational acceleration, Molar mass of dry air. + +3. We can also send satellites to do the job, if there is no atmosphere. The cheapest way to do so is to send one satellite with laser distance measuring tool. The satellite sends a laser to two places I mentioned above and calculates the difference of the time of the laser traveled. The time times the speed of light(assume it’s vacuum), you get the height." +854 Why is the Congo River so deep? 6642 https://www.reddit.com/r/askscience/comments/7j0adq/why_is_the_congo_river_so_deep/ 1512971537 7j0adq Earth Sciences 2017-12-11 8:52:17 "Well the short answer from the quoted paper where that measurement came from + + ""The channel is more like a high-gradient mountain stream with a very large discharge; which is consistent with the theory that a short mountain river eroded through the divide and reached Malebo Pool, forming the present Lower Congo River. "" + +This is the location where that measurement came from. + +However reading the rest of it, this is an anomalous depth and the majority of the river co forms to more normal standards and is around 10 to 80m on average." "Both [the height profile](https://i.imgur.com/GJWZEKs.png) and the sheer volume of water (42,000 cubic metres per second) give the river an insane amount of erosion power, carving a far deeper channel than, for example, the Amazon which has an [extremely shallow profile](https://media1.britannica.com/eb-media/55/103655-004-81742AE5.gif) over its lower course. (EDIT: In fact the amazon takes around 5000km to drop from 200 meters altitude to sea-level. The Congo does the same in just its final 100km.) + +The first European to explore [the Livingstone falls](https://en.wikipedia.org/wiki/Livingstone_Falls) (the long, steep stretch above Matadi), Henry Morton Stanley, said of them: + +*""..the wildest stretch of river that I have ever seen. Take a strip of sea blown over by a hurricane, four miles in length and half a mile in breadth, and a pretty accurate conception of its leaping waves may be obtained. Some of the troughs were 100 yards in length, and from one to the other the mad river plunged. There was first a rush down into the bottom of an immense trough, and then, by its sheer force, the enormous volume would lift itself upward steeply until, gathering itself into a ridge, it suddenly hurled itself 20 or 30 feet straight upward, before rolling down into another trough. If I looked up or down along this angry scene, every interval of 50 or 100 yards of it was marked by wave-towers - their collapse into foam and spray, the mad clash of watery hills, bounding mounds and heaving billows, while the base of either bank, consisting of a long line of piled boulders of massive size, was buried in the tempestuous surf. The roar was tremendous and deafening. I can only compare it to the thunder of an express train through a rock tunnel.""*" +1413 If the Earth was a giant eyeball, how far would it be able to see into space? Would it outperform modern telescopes? 6623 https://www.reddit.com/r/askscience/comments/druhb4/if_the_earth_was_a_giant_eyeball_how_far_would_it/ 1572929971 druhb4 Physics 2019-11-05 7:59:31 I think OP is talking about a scaled up human eye. Not radio telescopes or electronic cameras. "I did some math based on my own knowledge from Optometry school, and an [article](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3757906/). Don't nit pick numbers i'm doing fast math to get general magnitudes as a study break. Humans can resolve 1 minute of arc (1/60th of a degree). Based on an axial length of 22mm and a photoreceptor spacing of 6.5μm (0.0000065 meters). If we're blowing up an eyeball to have the same photoreceptor spacing, but the size of the earth (diameter 12741981.12 meters). This calculates out to 3x10\^-11 degrees of resolution. + +This would correspond to a resolution of 0.2mm on the moon (you'd be able to distinguish a grain of sand), 7.8cm on the sun, 4 meters on pluto, and 21 kilometers on the closest star Proxima Centauri. + +​ + +Yeah that looks better than modern telescopes. This is also assuming perfect optics (completely impossible and would degrade this system tremendously, but I'd bet it'd still be better than what we have). + +​ + +Anyways, back to finals." +1327 Why don’t starch and cellulose taste sweet like sugars, although they’re polymers of sugars? 6617 https://www.reddit.com/r/askscience/comments/bjw3uy/why_dont_starch_and_cellulose_taste_sweet_like/ 1556810082 bjw3uy Chemistry 2019-05-02 18:14:42 "Perception of taste and smell work on a ligand-receptor principle (falls under the classic ""lock and key"" analogy). A compound (sugar) binds to a receptor (taste bud) which then initiates a series of chemical and electrical events resulting in your perception of a sweet taste sensation. + +The binding of a compound to a receptor is highly dependent on a particular alignment of the two, in 3-dimension space (among several other factors that I won't bore you with). Polymerization of sugars blocks that 3-dimensional alignment. + +Returning to the lock and key analogy, imagine a regular key, versus a key that is welded to other keys on both ends (so including the grooved/toothed end). The former is a monomeric sugar, the latter is a polymer like cellulose which would not be immediately functional for purpose of opening the lock (binding to the receptor)." "u/Suta--Purachina is correct, but I'll add a bit of biochemistry to the answer. + +Evolutionarily, it makes sense for monomeric and dimeric sugars to taste ""sweet"" as we can utilize these for energy. You should want to consume these, and sweetness is the positive feedback for you to consume more. Cellulose, however, cannot really be broken down very well by human enzymes. It is necessary in the diet as fiber to help things move along through the digestive system, but it isn't providing energy to you. + +So how does this work from a mechanistic standpoint? Well, basically different receptors exist on your tongue which bind to different types of molecules. The different combinations and degrees of binding to different receptors contribute to the overall taste of a substance. The binding pocket in these receptors to which the sugars attach kind of compliments the structure of the sugar and binds favorably. This gets converted into a signal which eventually reaches your brain as sweetness. Cellulose is WAY too big to fit into these types of pockets and be recognized as sweet. Most other polymers larger than a couple units are similarly not sweet. + +That said, we can manufacture sugar alcohols that fit into these receptors even better than natural sugars (think artificial sweeteners like sucralose aka Splenda). At much lower concentrations these can bind these specific sweet receptors even better and come off as sweeter vs. sugar. However, they sometimes have strange aftertastes. As I mentioned a substance's interaction with all receptors and the degrees with which it interacts make up the taste. + +Sorry, got a little off track there at the end, but hopefully that answers the question a bit more." +955 What is happening when we randomly lose slight hearing in one ear and hear a loud ringing sound in it for a few seconds before the ringing fades away? 6604 https://www.reddit.com/r/askscience/comments/8bgawh/what_is_happening_when_we_randomly_lose_slight/ 1523445852 8bgawh Human Body 2018-04-11 14:24:12 "It's most likely from a muscle spasm near your inner ear, specifically the [tensor tympani](https://en.wikipedia.org/wiki/Tensor_tympani_muscle). This is the same muscle responsible for the roaring some people get when they yawn. Problems in that area of the ear/jaw can also cause tinnitus. + +It's not a well studied phenomenon, because it doesn't last long and isn't harmful. But you can read about it [more here] (https://www.tinnitusformula.com/library/sudden-brief-tinnitus/). + +EDIT: +And we're locked down. Since there were some unanswered questions related to the tensor tympani and tinnitus (with tinnitus being very unlike the roaring most people experience with tensor tympani action), please see [this paper](https://www.ncbi.nlm.nih.gov/pubmed/10753317). " +516 What has made solar energy so much more expensive in the past, and what developments are most important to further reduce the cost in the future? 6580 https://www.reddit.com/r/askscience/comments/5kggms/what_has_made_solar_energy_so_much_more_expensive/ 1482795040 5kggms Engineering 2016-12-27 2:30:40 "A large reduction in the cost came from the price of the active material used in the cells. The industry has traditionally been dominated by silicon panels and creating high quality crystalline silicon had been a pretty expensive process. What happened in recent years is summarized [in this chart](http://i.imgur.com/eHJPpcn.png). As the production volume spiked, the the price of panels based on c-Si eventually plummeted. This relationship is sometimes called [Swanson's Law](https://en.wikipedia.org/wiki/Swanson's_law). In fact, prices have dropped so much that now the silicon only accounts for less than half the price of typical modules. + + +As for what may reduce the price even further, that gets more speculative. A key short-term goal is to cut down on soft costs associated with installing and maintaining the cells. These costs are often lumped together as balance of system (BOS) costs. Here again, a key factor that can reduce these costs is the scale and maturity of the industry. For example, Germany which has been at this game longer already than the US has significantly lower BOS costs (e.g. see [this article](http://blog.rmi.org/blog_2013_12_05_can_usa_solar_cost_compete_with_germany)). + + +edit: To move further out in the long term, things get even more speculative. It is possible that eventually that a new kind of [thin film PV technology](https://en.wikipedia.org/wiki/Thin-film_solar_cell) will complement or supplant silicon PV. The advantage of such cells is that they could be flexible and more lightweight than silicon panels. These benefits in turn could potentially cut down on material and installation costs yet further. For example, so-called [perovskite PV cells](https://en.wikipedia.org/wiki/Perovskite_solar_cell) have shown promise in recent years in terms of efficiency, although stability remains a major concern. In addition to the active material itself, storage is still a huge stumbling block for solar energy to gain an increasingly larger share of the grid. Better and cheaper storage is key to deliver a steady supply to the grid in spite of daily and seasonal fluctuations in how much light we get from the Sun [e.g. shown here for Golden, Co.](http://i.imgur.com/ZLmlPZt.gif)" Power electronic advances in the last 20 years have also contributed to this. Using transistors vs linear power conversion allows over 90% conversion efficiency. Solar panels need to convert DC-DC-AC and do so with expensive modules. In the last 20 years these modules have become cheaper and better. +855 Does the long term use of antidepressants cause any change in brain chemistry or organization? 6549 https://www.reddit.com/r/askscience/comments/7c2urp/does_the_long_term_use_of_antidepressants_cause/ 1510337639 7c2urp Neuroscience 2017-11-10 21:13:59 "You might want to ask this is r/neuroscience. I'm an undergraduate student with a very limited understanding of this topic, but nobody else seems to be giving you a good answer, so I'll give it a shot. + +From what I understand, you have down-regulation of serotonin and norepinephrine receptors after chronic antidepressant use, but this isn't necessarily a negative thing, it's just evidence that those receptors have been particularly active lately. However, this increase in activation actually causes changes to happen in the cell that are hypothesized by some to treat the underlying cause of depression. The most important change is an upregulation of proteins in the cyclic-AMP pathway, including the transcription factor CREB, and its gene products such as BDNF, a cell-growth and synapse-stability-promoting protein, and it's receptor, TrkB. This is particularly important in the hippocampus, because it's implicated in increasing the number of synapses, the strength of synapses, and possibly promoting neurogenesis, and hippocampal volume reduction is associated with depression. The hippocampus does a lot of things, and is an important player in how your brain responds to stress. Basically, the hippocampus provides negative feedback to the stress circuit, but chronic stress can reduce hippocampal size and make it worse at its job. The stress circuit involves many other brain areas that contribute to depressive symptoms, such as the hypothalamus, which regulates sleep and hunger, for instance. Anyway, depression is really complicated and not perfectly understood, but if you want to learn more, I suggest looking up cAMP hypothesis of depression. " "https://www.ncbi.nlm.nih.gov/pubmed/15177061 + +Talks about tremor in patients receiving fluoxetine, a common antidepressant, which persisted in 11 of 21 patients for more than 450days after treatment had stopped. + +This is obviously a small sample size study but aligns with reports I got from colleagues who prescribed it to patients. " +956 Is there any part in the body that cannot get cancer? 6546 https://www.reddit.com/r/askscience/comments/8fqxwd/is_there_any_part_in_the_body_that_cannot_get/ 1525003394 8fqxwd Medicine 2018-04-29 15:03:14 "Cancer is unchecked cell growth that interferes with healthy function by changing or blocking blood flow, co-opting resources, and causing deterioration. + +Both body parts and cancer cells that are alive need circulation. Ostensibly, ""dead parts"" like hair and nails can't get cancer because they are not growing. But they can be affected by cancer, certainly. " "Great question! One thing you might find interesting is ""heart cancer"" - basically never happens / extremely rare. The reason we almost never find cancer in the heart is because the cells have terminally differentiated and mostly stopped dividing. This is also the reason recovering from heart attacks (myocardial infarction) where some heart muscle has died is not easy - we do not yet know how to repair the dead part of tissue, since the cells do not divide to do it by themselves. Cancer needs cells that are proliferating to gain traction, so these won't do!" +517 Why can online videos load multiple high definition images faster than some websites load single images? 6541 https://www.reddit.com/r/askscience/comments/5chr5g/why_can_online_videos_load_multiple_high/ 1478908408 5chr5g Computing 2016-11-12 2:53:28 "Two reasons mostly: + +First, still images are typically compressed much less than movie images even at the same resolution. This is because the viewer has more opportunity to scrutinize the still image (1/60th vs. several seconds or more) and may negatively perceive areas with less details. Less compression = more details = larger file size. + +Secondly, modern video codecs don't store movies as a series of still images, but as reference (full) images, followed by changes to that image. If the image hardly changes (which is the case most times except for panning/action scenes), those delta images will be really small." "Actually, the top comments in this thread are mostly wrong. Internet HTTP communications specialist here. + +The compression algorithm that's used to compress the video does a great job of reducing it's size and the overall bandwidth consumed but videos are too small for their size to matter on internet connection capable of streaming the video. Even if the video was 10 times bigger than it is, the frames would still arrive faster than they would need to be displayed, so compression really isn't relevant to why it's the same speed as imgur. I.E., your question is the video is way bigger... why does it load in the same amount of time? Answers about why the video is smaller than it could be otherwise are irrelevant, video is still way bigger than the image in question. + +Most display latency on modern websites is related to the ridiculously poor performance of the advertising networks, but that's not the deal with this particular case regarding imgur. + +TCP Handshake time + HTTP protocol overhead is what's up. + +TCP requires a round trip between you and the server to establish a connection. Then HTTP (Runs on top of TCP) requires another round trip to fetch the index page. Then at least one more round trip to fetch the image in question. After that the website will pretty much be streaming on a modern browser. Each round trip takes about 30-50ms. That's a minimum of about 100-150ms to set up depending on how low the latency on your internet connection is. + +Same thing happens on youtube. Takes about 100ms to get everything up and running and then the system is streaming and data is arriving faster than it's displayed. + +As a matter of fact, Google tunes their latencies hard... So in general that fat youtube video will actually load way faster than your average website." +1058 Why do ice cubes crack when liquid is poured over them? 6530 https://www.reddit.com/r/askscience/comments/8ivbep/why_do_ice_cubes_crack_when_liquid_is_poured_over/ 1526122613 8ivbep 2018-05-12 13:56:53 "[Rapid temperature change, which also leads to a change in density.](https://www.youtube.com/watch?time_continue=2&v=sPScqP3mFKQ) The density change pushes and pulls the molecules around it, applying mechanical force within and around the ice cube that breaks its crystal structure. Water is actually most dense at 4 deg C. It's very similar to you snapping a pretzel. + +LTP: Glass refrigerator shelves can do the same, and produce a lot of glass pebbles as a result." "Fun tidbit, the forces at play can, on rare occasion, cause the ice to crack with enough force to make a piece jump out of your drink. I’ve witnessed a grand total of one time in my life. It was spectacular. + +The forces at play are similar in some ways to the “prince rupert’s Drop”. Variable stress within the ice (or glass, in he case of the drop) pulling in multiple directions can sometimes cause explosive results." +1109 If numbers can be infinitely large, can they also be infinitely small? 6509 https://www.reddit.com/r/askscience/comments/9g0vnj/if_numbers_can_be_infinitely_large_can_they_also/ 1537012141 9g0vnj Mathematics 2018-09-15 14:49:01 "Why can't you go through these infinitely many ""halves"" in a finite amount of time? + +Let's say, for simplicity, that you're running to the bus stop at a constant speed, and you stop when you suddenly hit the sign, or something. So, you're running from position 1 to position 0 (note, I reversed this), say the units are meters. If you're running at, say, 1m/s, then the time it takes for you to go the first half, from 1 to 1/2, will be 1/2 a second. The time it takes for you to go the second chunk, from 1/2 to 1/4 is 1/4 of a second. The time it takes to get from 1/4 to 1/8 is 1/8 of a second. This pattern continues. The time it takes you to get from the chunk 1/2^(n) to 1/2^(n+1) is 1/2^(n+1) of a second. + +What, then, is the total time of the trip? You would have to sum up all the times together. The times for each chunk are 1/2, 1/4, 1/8, 1/16, 1/32, etc seconds each, so the total time will be + +* 1/2 + 1/4 + 1/8 + 1/16 + 1/32 +... + +where the sum goes on infinitely. This is a very classic [Geometric Series](https://en.wikipedia.org/wiki/Geometric_series), and adds up to a finite value. That finite value, in this case, is 1. So after 1 second, you will have gone through all of these infinitely many halfway points and gotten to the end (which makes sense, because you're going 1 m/s for 1 meter). So, even though there are infinitely many halves to go through, it takes a finite amount of time to get through them all. + +This situation is also known as [Zeno's Paradox](https://en.wikipedia.org/wiki/Zeno%27s_paradoxes)." "You might not know it, but you have stumbled onto one of the fundamental building blocks of calculus. The idea of a ""limit"". + +You are right that, as time passes on, the distance gets closer and closer to 0, but never actually reaches it, so we would say that the ""limit"" is equal to 0. + +Here is another example of a limit to think of. Say you have a sibling who is 3 years older than you, how many more *times* older than you are they? + +When you are 1, they are 4, and so they are 4/1 = 4 times older than you. + +When you are 2, they are 5, and so they are 5/2 = 2.5 times older than you. + +When you are 3, they are 6, and so they are 6/3 = 2 times older than you. + +Let's jump ahead. + +When you are 20, they are 23, and so they are 23/20 = 1.15 times older than you. + +When you are 50, they are 53, and so they are 53/50 = 1.06 times older than you. + +No matter how old you are, they will be 3 years older, and so this fraction will always be bigger than 1, but it will be getting closer and closer and closer to 1, so we say that ""limit"" is equal to 1." +957 Why can't we simulate gravity? 6486 https://www.reddit.com/r/askscience/comments/7wel50/why_cant_we_simulate_gravity/ 1518193788 7wel50 Physics 2018-02-09 19:29:48 "As a reminder to all readers, we ask that you please familiarize yourself with our [guidelines on commenting](https://www.reddit.com/r/AskScience/wiki/quickstart/answeringquestions). In particular, top-level comments should be substantive and supportable by current science. Please refrain from speculating, which includes suggestions that we do not understand gravity. + +Thank you." "In addition to using centrifugal force to simulate gravity you can also use linear acceleration. If your spacecraft can sustain accelerating at 9.8 m/s^2 for a long period of time the occupants inside the spacecraft would experience a force equivalent to gravity in the opposite direction to the acceleration. + +This is one of my favorite parts of the show ""The Expanse"". Often when they are travelling in space they have gravity and it was established early in the series that this is achieved by constantly accelerating toward the destination. Then when the spacecraft is halfway to its destination there is a warning followed by a brief moment of weightlessness as the craft flips around to point in the opposite direction. Then the deceleration burn begins and the simulated gravity is restored. That is a super neat detail in that show. " +1328 According to the last episode of Chernobyl, there is still a man buried inside reactor 4. Would his body have decomposed normally or would the excessive radiation not allow for any substantial bacterial activity? 6478 https://www.reddit.com/r/askscience/comments/bz886f/according_to_the_last_episode_of_chernobyl_there/ 1560229030 bz886f 2019-06-11 7:57:10 "Something very similar to this happened in the U.S. in 1960. He didn't decay. + +[SL-1 reactor incident](https://en.wikipedia.org/wiki/SL-1), three guys were on top of a small experimental reactor. For reasons unknown, one of them pulled out a control rod. This caused a [prompt criticality](https://medium.com/lessons-from-history/americas-fatal-nuclear-accident-you-ve-never-heard-of-16c621520792): + +>, it is known that in those four milliseconds enough heat was spontaneously generated in the water left in the reactor to instantly vaporize it. This, in turn, created an extremely concentrated “water hammer” that shot to the top of the reactor vessel at 109 mph, smashing the top of the vessel in a massive detonation that caused not just the entire 26,000-lb housing to jump vertically over nine feet, but for massive control rods, shield plugs and other pieces of the assembly to be blasted upwards with enough force to embed them into the steel and concrete ceiling 13 feet overhead. + +A plug over one of the control rods, propelled by the steam, effectively turned into a bullet. It pinned a guy named Richard C Legg to the ceiling of the reactor building. + +It took several days to [figure out](https://medium.com/lessons-from-history/americas-fatal-nuclear-accident-you-ve-never-heard-of-16c621520792) how to get him down. He was pinned up there pretty good, and the reactor room was obviously very hot indeed. They ended up doing a procedure similar to the Chernobyl liquidators--lots of men for 65 second shifts. + +When they got him down he hadn't decayed: + +> A post-mortem examination showed that his body had not decayed during the six days he was suspended from the ceiling, as the heavy radiation had effectively sterilized him. + +If you like salacious rumors, the story around this one is that it was a murder-suicide. The story goes that Byrnes pulled the rod on purpose, possibly because Legg (the guy who ended up pinned to the ceiling) was sleeping with his wife. Other versions have Byrnes being jealous because Legg got a promotion. + +The official (and likeliest) story is that the rod got stuck and Byrnes accidentally yanked it too hard." I haven't seen any of the chernobyl shows, but have read about [radiotropic fungus](https://en.wikipedia.org/wiki/Radiotrophic_fungus) growing in the reactor core areas of Chernobyl. These fungi literally feed on radiation. There is no information though about where they get the nutrients and mass needed to grow. Although radiation can drive ATP synthesis, the organisms still need a source of organic matter. It is entirely possible the body is being consumed by the radiotropic fungi species that are thriving in the high radiation enviornment +1329 How does Venus retain such a thick atmosphere despite having no magnetic field and being located so close to the sun? 6477 https://www.reddit.com/r/askscience/comments/c85rki/how_does_venus_retain_such_a_thick_atmosphere/ 1562048713 c85rki Planetary Sci. 2019-07-02 9:25:13 "You are right in observing Venus does not have an intrinsic magnetic field. [However, solar winds interacting in Venus's upper atmosphere ionize particles](https://link.springer.com/article/10.1007/s11214-017-0362-8) (an ionosphere). This ionosphere induces an external magnetic field around Venus which acts similarly to planets with magnetic fields and excludes solar winds. [Zhang et al.](https://science.sciencemag.org/content/336/6081/567) also provide evidence that Venus's externally induced magnetic field reconnects, which was previously thought not to occur. + +Despite this, Venus still does experience some atmospheric loss due to solar wind pressures. Perhaps there is some geological process that replenishes Venus's atmosphere, but this is outside the scope of my study so I will refrain from speculating more on it." "That's a great question and actually central to my own research. Mars is often considered to have lost its atmosphere due to the absence of an internal magnetic field, presumably allowing the solar wind to strip the planet's atmosphere over the age of the planet. So why does Venus still retain 92 bars of atmosphere? Well, the rate of solar wind driven atmospheric escape as measured by our orbiters is about the same for both Venus and Mars, and really slow, on the order of about 0.1-0.5 kg/s. + +[Kollmann, P., (2016), Properties of planetward ion flows in Venus' magnetotail, *Icarus*, **274**, 73–82, doi:10.1016/j.icarus.2016.02.053.](https://www.sciencedirect.com/science/article/pii/S0019103516001317?via%3Dihub) + +[Nilsson, H., et al. (2012), Ion distributions in the vicinity of Mars: Signatures of heating and acceleration processes, *Earth Planets Space*, **64**(2), 135–148, doi:10.5047/eps.2011.04.011](https://link.springer.com/article/10.5047%2Feps.2011.04.011), + +Both planets lack internal magnetic fields that would otherwise generate an Earth-like magnetosphere, but they are still both screened from the solar wind by the formation of induced magnetospheres. These induced magnetospheres form due to currents in the upper atmospheres induced by the solar wind's magnetic field, and they appear to be very efficient in protecting the bulk of the planetary atmospheres from the solar wind. + +[Ramstad et al., (2017) Global Mars-solar wind coupling and ion escape, *Journal of Geophysical Research*, **122**, 8, doi:10.1002/2017JA024306](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JA024306). + +In addition, Venus' gravity is too strong for other non-solar wind related escape processes to be active. + +Edit: /u/ResidentGift and /u/galendiettinger asked about how Mars, and not Venus, could have lost atmosphere without solar wind driven escape. The answers are somewhat buried, so I'll copy the permalinks here: + +https://www.reddit.com/r/askscience/comments/c85rki/how_does_venus_retain_such_a_thick_atmosphere/esks9kd/ + +https://www.reddit.com/r/askscience/comments/c85rki/how_does_venus_retain_such_a_thick_atmosphere/esmgm4c/" +856 "What is the velocity of the edge of a bubble as it is ""popping""?" 6468 https://www.reddit.com/r/askscience/comments/7ficf3/what_is_the_velocity_of_the_edge_of_a_bubble_as/ 1511647316 7ficf3 Physics 2017-11-26 1:01:56 "A rough approximation can be calculated: + +* Determine frame rate of the original video recording +* Determine size of bubble in video +* Measure time for bubble to pop +* Calculate speed: distance divided by time + +  + +Looking at the bubble at 1m43s: https://www.youtube.com/watch?v=ktvZ2Z_s4Bo&t=103s + +* video is recorded at 18,000 FPS. +* bubble size is about 15 cm. +* time to pop is about 13 seconds. +* 13s of video at 18,000 FPS is 0.72ms of real time. 0.15m/0.72ms = 208 m/s +* edit: MorRobots did the speed calculation for a spherical surface: 362.2 m/s + +  + +The bubble size and duration of the popping are just rough numbers and can be approximated better but it'll get you in the right ballpark. + +For homework, you can do the math for traversing a sphereical surface instead of the simpler calculation I'm using." "The link you provided for pressure differential includes an MS paint free body diagram. From this diagram we see that at any point on the bubbles surface, the forces due to surface tension are actually orthogonal to the forces due to the pressure differential. For this reason, forces due to pressure differential can be ignored in calculating how quickly the break will move along. + +Unless there is something else to be considered, I'd say that the upper bound of the material's speed of sound is a very reasonable approximation for the speed of propagation of the surface break." +857 Were cyclones more powerful when the Earth was covered in superoceans? 6468 https://www.reddit.com/r/askscience/comments/6z8b77/were_cyclones_more_powerful_when_the_earth_was/ 1505051242 6z8b77 Earth Sciences 2017-09-10 16:47:22 "TL;DR yes, but not by virtue of superoceans themselves. + +I am not sure of the effects of supercontinents on their own, but I can answer this question in the context of Earth's history, specifically the end [Permian](https://en.wikipedia.org/wiki/Permian) mass extinction event, which took place in the time of Pangaea. I am a graduate student in geology and currently studying mass extinction events. + +/u/Neolavitz is right in that the biggest limiting factor for tropical storm growth is ocean water temperature. To elaborate... + +When certain conditions are met, the oceans can become very warm. One such warming event (called a Hothouse state) took place at the end of the Permian, when the [Great Dying](https://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event) occurred. It is thought that this Hothouse state was triggered by a massive eruption at the [Siberian Traps](https://en.wikipedia.org/wiki/Siberian_Traps), which released enormous amounts of CO2 and other nasty compounds onto the surface of the planet. One of the consequences of this was dramatically slowed ocean circulation in a haline mode. A haline mode ""generates warm saline bottom water that heats the ocean"" (166), which transfers heat from the equator to the poles. This is in contrast to our present cycle, where deep ocean currents transport cold water to low latitudes, creating a gradient of heat and overall cooler oceans worldwide. + +In the Hothouse state, cyclones, which are restricted to about 40 degrees of latitude N or S in our current climatic regime, may traverse the entire globe (90N and 90S) thanks to worldwide elevated ocean temperatures. They would also create a positive feedback situation: +> As storms reached to higher latitudes, they would help deliver more heat to those regions. That would, in turn, further warm higher latitude surface waters, making it more likely that subsequent storms would have an ever-greater poleward reach. Polar storms would also lead to increased polar cloudiness, which would impede surface heat radiation to space, thus warming the poles even more. + +Magntitude of storms would increase. Modern cyclones are limited in their size by colder, deeper waters. The bases of their waves reach the colder deep waters and lose heat and energy. In a warmed ocean, this restraint would no longer exist. Kidder and Worsley specifically say, ""the cyclone-magnitude governor would be **completely removed** in a Hothouse..."" (emphasis mine). So to answer your third question, no, there are theoretically no limiting factors in a very warm, humid situation. To answer your fourth question, the vast, dry deserts of Pangaea were the most likely stopping zones for these storms, as they would be deprived of moisture in the deserts. + +Source: + +> Kidder, D.L., and Worsley, T.R., 2010, Phanerozoic Large Igneous Provinces (LIPs), HEATT (Haline Euxinic Acidic Thermal Transgression) episodes, and mass extinctions: Paleogeography, Paleoclimatology, Paleoecology, v. 295, p.162-191." "Unrelated to superoceans per se, but I have read a theory about 'hypercanes' proposed by a professor from MIT named Kerry Emanuel. Any analysis of that is beyond me as a layperson, but I believe the full text of his paper is available online if anyone was interested in confirming how reasonable or unlikely his ideas might be. + +EDIT: Here's a link to the paper for those interested! [Tropical Cyclones - Kerry Emanuel](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwiAnIOpoJvWAhUk5IMKHdw1DGYQFgg0MAI&url=ftp%3A%2F%2Ftexmex.mit.edu%2Fpub%2Femanuel%2FPAPERS%2Fannrevfinal.pdf&usg=AFQjCNHd1Xo28shD96bUX5CIDvl89Qv2nQ)" +1414 How many times has the average drop of water been through an animal kidney in the history of Earth? 6462 https://www.reddit.com/r/askscience/comments/dd5s24/how_many_times_has_the_average_drop_of_water_been/ 1570186696 dd5s24 Earth Sciences and Biology 2019-10-04 13:58:16 "Not the answer to the exact question, but this relevant [XKCD](https://what-if.xkcd.com/74/) has some usefull information. + +​ + +....The average ""residence time"" of water in the oceans—the amount of time a water molecule spends there before moving into another part of the water cycle—is about 3,000 years,\[14\] and no part of the water cycle traps water for more than a few hundred thousand years." "This is insanely complicated, but let's start with some simple concepts. + +**Population estimate:** All vertebrates have kidneys. Not all animals have kidneys. So you're really only looking at a subset of the animal population. Ants for example don't have kidneys, but there are 10,000 trillion alive at any one time. We need to estimate the number of vertebrates alive at any given moment. + +* Fish are about 5-10 trillion +* Mammals are about 100 billion to 1 trillion +* Birds are about 100 billion +* Reptiles somewhere between 1-10 trillion + +So an estimate of somewhere between **6.2-20.2 trillion** vertebrates alive on Earth right now. + +​ + +**GFR estimate:** A good [GFR](https://www.vetfolio.com/learn/article/glomerular-filtration-rate-in-general-small-animal-practice) estimate is \~3 mL/min/kg for small animals which are the majority of vertebrates, some larger some smaller but we have to get an average somehow. And a decent estimate of [body weight average for vertebrates](https://www.sciencedirect.com/science/article/pii/S0042698904001646) is around 0.572 kg. This leaves us with an estimate of **1.716 mL/min**. + +**Time estimate:** Next you have a time frame of around 500 million years for vertebrates. This population density hasn't been consistent over that period, so it's important to remember that as an estimate this is going to be the second biggest component of the error involved here because we also don't have super accurate counts for species and population density over that time frame. **500 million years** is the number we have though so we'll go with that period. + +​ + +**One year calculation:** We'll go with a middle number of 10 trillion vertebrates at an average weight of 0.572 kg. This would mean that each minute we have 10 trillion x 1.716 mL/min of fluid filtered. + +1.716 x 10^(13) mL/min (525,600 min/year) = 9.02 x 10^(18) mL/year + +​ + +**Total Vertebrate history GFR estimate = 4.5 x 10**^(27) **mL** + +**Water on Earth** = 1.26 x 10^(21) L = **1.26 x 10**^(24) **mL** + +​ + +# Rough Estimate: 3,000 times + +(now someone check my maths and let me know where I did wrongs) + +Edit: Thanks for the silver! +Edit: thanks for Gold! Wow, thanks." +1235 In snowy mountain areas, avalanches occur, we all know this, but does the same happen in the desert on high dunes? 6461 https://www.reddit.com/r/askscience/comments/awu3g9/in_snowy_mountain_areas_avalanches_occur_we_all/ 1551620724 awu3g9 2019-03-03 16:45:24 Yes, avalanches [are common and are a fundamental part of how dunes behave/evolve](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgrf.20130). Basically, grains roll and bounce along the windward, more gentle side of a dune and are deposited at the top of the leeward, steeper side of the dune (i.e. the slip face). These grains build up until they destabilize the slip face and avalanche down towards the base of the dune. This is a fundamental part of how a dune migrates. From the perspective of Jamming, or un-jamming in this case. Both same dunes and snow mountains un-jam at critical shear stress and then begin sliding downhill. However, this phenomenon is highly dependent on the material that is being jammed. Sand is a dry frictional poly-disperse material that un-jams at critical stress directly relate to its angle of repose and it well determined for different types of sand. Snow on the other hand is a potentially wet, mono-disperse material that has a highly variable critical shear stress dependent upon things like humidity, temperature, etc. So unlike sand, snow avalanches are less predictable and can sometimes build up much greater stresses leading to catastrophe. +1236 Does every man produce close to 50/50 X/Y sperm, or do some have a heavy bias? 6460 https://www.reddit.com/r/askscience/comments/az1p03/does_every_man_produce_close_to_5050_xy_sperm_or/ 1552123052 az1p03 2019-03-09 12:17:32 "There’s a really interesting 2008 study from Newcastle University suggesting that men actually inherit a genetic tendency to father more sons or daughters from their parents. That would make the X-Y sperm ratio different for each man. The study looked at 927 family trees in North America and Europe going back to 1600 to draw those conclusions. +Link: https://www.sciencedaily.com/releases/2008/12/081211121835.htm" "You might be interested in this [article from 2017](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5494181/) examining the Triviers-Willard Hypothesis (TWH) from 1973 for a specific population of chinese farmers. TWH states that socioeconomic status influences sex ratios. Its introduction section points out papers that have previously examined this in human as well as non-human populations. + +Other factors have been claimed to affect this (testicular temperature etc), though I have yet to see peer reviewed results substantiating such claims." +769 Do microwaves interfere with WiFi signals? If so, how? 6453 https://www.reddit.com/r/askscience/comments/6prkl4/do_microwaves_interfere_with_wifi_signals_if_so/ 1501107250 6prkl4 Physics 2017-07-27 1:14:10 Microwaves from microwave ovens do interfere with WiFi signals because physically they are the same thing. They are both electromagnetic waves with frequencies around 2.4GHz. Your microwave door should in principle block inside radiation from the magnetron from escaping but there can be some leaks. And since the amplitude of the these waves is much higher than the ones emitted by your router antennae, if you are near your functioning microwave oven, you may experience packet drop or total loss of WiFi connection. "There's a number of factors at work here. Microwave ovens are powered by a vacuum tube called a magnetron. It uses a magnetic field to cause electrons to excite cavities that resonate at a frequency near 2.4 ghz. They could be made to resonate at other frequencies, but that specific one is called an ISM band and is not supposed to be used for communication, but rather a trash space to place things that do what a microwave does, such as heating food using microwave energy. Over time it became a kind of free-for-all and data (and video, audio, remote controls, and so forth) transmitters appeared on the band as well because you did not require a license to transmit there. + +So the magnetron is a radio frequency generator, inside a box. If you do the math, the box doesn't ever have 100% isolation, even at -60 dB of isolation, 1 milliwatt still escapes the device and is radiated. This assumes a good seal, properly designed cavity, no damage to the unit or manufacturing defects. In fact, there was a phenomenon called ""Perytons"" and it was thought they came from outer space. Turns out that sensitive radio-telescopes could hear the burst of microwave energy as the door was opened on a microwave oven before the magnetron had stopped. For real! + +Wifi devices are limited in power output and sometimes cannot overcome the signal generated by the oven, and thus the access point cannot hear you. However, Wifi is built on ethernet and the OSI networking stack. Rather than fail instantly, the ""connection"" between you and the access point is fictional. Your devices will just try sending over and over again until the AP acknowledges receipt of the transmission. The AP doesn't really know if your phone is there or not, it can only wait for the acknowledging reply to its transmissions, and vice versa. There can be 99% packet loss but the few packets that get through are enough to convince the phone that the wireless network is still out there listening for it. + +As another poster commented, the magnetron isn't tightly controlled in frequency as a proper radio transmitter would be. It can drift in frequency to the limits of how the cavities in the devices will resonate. So, statistically it will output more power at 2.4 ghz than say at 2.3 or 2.5 ghz, but you never know where the peak of the output shall be. Early ovens took the 110v AC wave from the mains power and applied only a half-wave rectification, leading to the magnetron pulsing on and off at a 60hz rate. This was enough of a gap that clever wifi devices could expect the gap as the negative AC cycle approached, and attempt to slot their packet in that small window. This technique is only effective if there are gaps. Modern ovens run off an inverter which generates a constant DC high voltage to power the magnetron and thus there are no gaps to fit packets in." +1330 AskScience AMA Series: I'm Dr. Kaeli Swift, and I research corvid behavior, from funerals to grudges to other feats of intellect. Ask me anything! 6445 https://www.reddit.com/r/askscience/comments/cpatp3/askscience_ama_series_im_dr_kaeli_swift_and_i/ 1565607609 cpatp3 2019-08-12 14:00:09 I know a lot of corvids understand the concept of fun and engage in it themselves, like sledding and bothering each other and such - what's the funniest way you've ever seen a corvid amuse themselves? Also, thank you for doing this AMA, this is a very interesting topic to learn about! :) "When hiking this past May in Arizona there was some wind up-currents up on Wasson peak, and I think I saw a group of crows playing “pass and catch the feather “ as the winds kept the feather aloft. + +Am I anthropomorphizing this? Or does this fit in with known corvid behavior? + +I was so blown away by the display, I accidentally sat back in a cactus! + +/to be fair, that cactus totally snuck up on me" +1059 Are there stars so hot they would appear black to the human eye? 6438 https://www.reddit.com/r/askscience/comments/8ynjtj/are_there_stars_so_hot_they_would_appear_black_to/ 1531514196 8ynjtj Astronomy 2018-07-13 23:36:36 First of all, take a look at the emission spectrum in [this](https://upload.wikimedia.org/wikipedia/commons/1/19/Black_body.svg) diagram. Notice how as you increase the temperature, the amount of energy emitted increases for *all* wavelengths of light. For example, look at the line for 2 um wavelength: as you increase temperature from 3000->4000->5000 k, each time, the emission from this wavelength increases. This is *always* the case. For this reason, if you take the spectrum of the hottest stars in the universe, they emit massive amounts of UV- most of their energy could be in UV- but they will still emit more visible light than the sun. "No, it wouldn't be possible. [Look at this plot](https://upload.wikimedia.org/wikipedia/commons/thumb/1/19/Black_body.svg/600px-Black_body.svg.png), what you can see is that for increasing temperatures the peak of the distribution is indead shifted towards smaller wavelengths. For high temperatures the peak will eventually not be in the visible spectrum anymore. But notice how the rest of the curve increases. For higher temperatures, the curve will not go down, but keep increasing. + +Mathematically you can see this by taking the derivative of the planck function with respect to temperature. Since hc/(lambda\*kT)>0 for all possible lambda and T, the derivative will be greater than 0. Lambda and T can of course never be negative (excluding the special conditions when negative temperatures can occur). + +Edit: For all of you who don't know about negative temperatures, see [this](http://rantonels.github.io/capq/q/TD1.html)." +1331 Are there any trinary stars systems? 6437 https://www.reddit.com/r/askscience/comments/bk9xn1/are_there_any_trinary_stars_systems/ 1556898265 bk9xn1 Astronomy 2019-05-03 18:44:25 "Yes - they're what I research! + +It can be pretty difficult to tell, but we think that a few percent of stellar systems are triple. Since 3-body systems are generally unstable, they only last for significant times if two of the stars are close together, with one far away (think Earth-Moon-Sun)" Our closest neighboring star, Alpha Centauri, is actually a triple system-- Alpha Cen A, B, and Proxima, a red dwarf which orbits the other two in the system. If you want to see a cool multiple star system, check out Sigma Orionis. +770 What were the oceanic winds and currents like when the earth's continents were Pangea? 6414 https://www.reddit.com/r/askscience/comments/6lr5k5/what_were_the_oceanic_winds_and_currents_like/ 1499399380 6lr5k5 Earth Sciences 2017-07-07 6:49:40 "Here is a a picture of what scientists think the ocean currents likely looked like: http://imgur.com/geHb0nR + +I would imagine the wind patterns would be similar to what we see now days (westerlies and trade winds) but perhaps slightly shifted in latitude due to the warmer climate. + +I also believe at this time there was no deep water formation. Deep water formation occurs in two major regions in the ocean: + +1) In the North Atlantic where warm and very saline water moves north very quickly in the Gulf Stream and sinks as it cools at higher latitudes. The presence of the Gulf Stream is due to the ithsmus of Panama existing, not present in Pangea. + +2) In the Southern Ocean,during sea ice formation in the winter months a brine forms as salts in seawater does not fit well into the ice crystal lattice. This brine is heavier than surrounding non-frozen seawater, causing it to sink. This also was likely not happening in the warmer climates + +This result in an anoxic ocean at depth, zero oxygen below ~1000 - 500 m, high concentrations of hydrogen sulfide at depth. It is possible there was a small degree of deep water formation at the equator due to extremely high evaporation rates producing very saline waters of higher density. But there would likely not penetrate very deep, leaving a large portion of the ocean anoxic. + +Edit: Clarified my statement of #2 deepwater formation" "Thank you for this question! I'd never considered it before and the responses have been very informative and interesting. This topic got me looking at maps of Pangaea and how the continents eventually separated via the continental drift of the tectonic plates. Which got me thinking: If the continents keep moving around like this, will we get any supercontinents in the future? + +Did a quick wiki search and looks like there's already been a decent amount of research/speculation on [the matter](https://en.wikipedia.org/wiki/List_of_supercontinents#Future_.28speculative.29). Kind of neat to see where things might be headed millions of years from now. + +Kind of puts everything into prospective a little bit. No matter how much we pollute and destroy the planet, we're only doing it to ourselves (and our cohabitants). the Earth itself will be here long after we poison ourselves off of this rock. It's just going to keep doing its thing." +858 When a storm like Irma is at sea, what's happening below the surface? 6410 https://www.reddit.com/r/askscience/comments/6yd0zr/when_a_storm_like_irma_is_at_sea_whats_happening/ 1504667290 6yd0zr Earth Sciences 2017-09-06 6:08:10 "Chemical/biological oceanographer: + +The massive waves created churn up the water and cause the layers to mix. This redistributes nutrients evenly throghout the height of the water that is being mixed. This redistribution can be very beneficial to surface plankton communities who would otherwise have used up the nutrients in their waters. However, not all surface plankton are ""desirable"" (see: harmful algal blooms) and so the result of the higher nutrient waters can be ""good"" or ""bad"". The animal communities in the water have ways of dealig with the churning waters. Some will sink in the water column so the are below the churning waters, some are so small that they hardly notice it, others will migrate away from the area, and some don't really care. When the storm reaches shallower waters and the depth of the wabes created is larger than the depth of the waters, sediments from the bottom get churned into the waters. This increases the turbidity of the water. The sediment in the water will eventually settle out, but can be carried by currents for miles. This redistributes small amounts of sediment throughout the oceans, and can feed deeper organisms as it settles (as some sediments contain organic material). " "Meteorologist here. I cant speak much to biology but tropical systems like Irma cause significant mixing of the surface waters through localized upwelling and freshwater mixing from rainfall. They leave behind cold wakes where you can see the warm water has been mixed with deeper cooler water. I would imagine this impacts the thermocline and life in the lowest hundred feet of the ocean. + +Edit* top hundred feet of the ocean. Working overnight means my brain stops sometimes! + + +Edit edit* + + +For clarification the thermocline is a well defined mixed layer at the top of the ocean where temperature changes rapidly with depth. Its very similar to the boundary layer in earths atmosphere but reversed in that the sun heats the surface of the ocean and wave action and to a lesser extent convection mixes the top 100 meters or so of water. Tropical cyclones induce deeper mixing which brings even deeper cooler water up from below to alter this layer. Storm surge also plays a role in this. Because of the low minimum central pressure and the resulting strong winds inside tropical cyclones (916 mb as of 12z) the water is lifted up 10-20 feet like a giant straw and blown on shore (especially in the front quadrant relative to motion and wind direction.) This also induces mechanical mixing. + +There was a question about wave height as well. Wave height is proportional to wind speed. Irma right now has sustained maximum winds (this is a 1 minute average windspeed) 160 kts or 185 mph +(equivalent to a high end EF-4 tornado) +This can easily produce waves over 20 feet and probably higher. Right now some of the moored buoys are reporting seas of 17 feet. + + +edit edit edit* + + +Im trying to answer as many questions as I can but unfortunately I've got another night shift tonight so I need to call it for the day. Feel free to continue asking and I will try to answer what I can later. Hope this was helpful for some! I'm not a tropical weather expert but hurricanes are super cool and everyone should learn about them! " +771 What is the environmental impact of air conditioning? 6395 https://www.reddit.com/r/askscience/comments/6r4wux/what_is_the_environmental_impact_of_air/ 1501687559 6r4wux Earth Sciences 2017-08-02 18:25:59 "Air condition uses 18% of electricity in US homes, which is first on the list: +[www.eia.gov](https://www.eia.gov/tools/faqs/faq.php?id=96&t=3)." "People have mentioned that the amount of energy going to air condition is large, and that it is the primary driver of how much power plant capacity we need - peak power production, those are the two main power grid/engineering impacts that I know of. + +The escape of the refrigerants used in air conditioning which are strong green house gases themselves is another impact. + +Something I find interesting is due to cheap power and other priorities we have stopped designing our buildings to take advantage of local environment. For example Ancient Rome had the Justinian Code forbidding anyone from building tall enough to block their neighbors sunlight - something that we are having legal proceedings in the US today in regard to neighboring buildings and solar power production. + +Another cool ancient concept that i cant remember the name of is free air conditioning by using a chimney to draw air up from underground. +https://permies.com/t/9580/a/3102/Solarchimney.jpg + +Movements like Passive House are moving people back towards designing buildings to take advantage of free energy." +859 How did a population of landlocked seals manage to establish itself in lake Baikal, of all places, at an altitude of 450 m and several hundred kilometers from the Nearest coastline??? 6357 https://www.reddit.com/r/askscience/comments/7dxjzi/how_did_a_population_of_landlocked_seals_manage/ 1511057043 7dxjzi Biology 2017-11-19 5:04:03 "I once came across [this article](http://scienceblogs.com/tetrapodzoology/2010/06/15/most-inconvenient-seal/) that tackled this very question. Even though the article is written for a broader audience, its author is an expert in the field (and it's well sourced to boot). The gist is that at present (at least as of a few years ago) there was no clear consensus. Instead, there were two key hypotheses about where the Baikal seals came from. + +1. Seals from the [Paratethys](https://en.wikipedia.org/wiki/Paratethys), that huge ass sea in southern Eurasia tens of millions of years ago, could have wondered north reaching what is now Lake Baikal. Just how exactly that could have happened is quite spotty since it would have required the seals hopping through multiple rivers and lakes across a long distance. + +2. Alternatively, the seals could have moved north to south from the Arctic. Essentially the idea is that the seals would have moved down through the [Yensei/Angara Rivers.](https://upload.wikimedia.org/wikipedia/commons/d/d5/Yeniseirivermap.png) eventually reaching the waters that formed Lake Baikal. + +Since this is not my field I am not sure if there has been any new research on this topic that may give a more conclusive answer. But it sure is a fascinating question!" "Marine mammal paleontologist here: it's a subject of debate in the literature, and to be clear, my focus is typically on walruses (Odobenidae) and sea lions (Otariidae) but I have dabbled in true seal phylogeny/paleontology (Phocidae). + +Phocinae - specifically the Phocina tribe (Pusa + Phoca - Baikal/ringed/caspian seals + harbor/spotted seals, respectively) are a relatively recent, completely post-Paratethys diversification (likely during the Pliocene). The whole Paratethys idea is bunk and based on some rather antiquated Ukraine/USSR/eastern Bloc-centric ideas of seal evolution from the 60s/70s (Chapskii, Grigorescu, 'reanimated' by Koretsky). + +My own preferred hypothesis, and I hope this is covered in the literature (if not I've got an easy paper to write!), is that these seals colonized the Caspian Sea and Lake Baikal via the West Siberian Glacial Lake during the Pleistocene - a huge pond of meltwater at the edge of the Siberian ice sheet. This would have been semiconnected to the ocean by rivers of meltwater. Our own Great Lakes are the remnants of these lakes around the perimeter of the former Laurentide ice sheet (though the ground is depressed due to glacial isostasy - literally, the weight of the ice sheet compressed/depressed the earth's crust). Matter of fact, the Champlain Sea (now only lake Champlain) in New York/Vermont/Ontario/Quebec is now mostly dry but deposits of this glacial 'sea' are rich in now-Arctic marine mammals (beluga, ringed seal, walrus, etc.). + +So yes, technically a seal could swim up a river nowadays but during certain periods of the Pleistocene it was much easier owing to the vast lakes of meltwater along the edge of the ice sheet - just like the Champlain sea." +860 Is everything that we know about black holes theoretical? 6328 https://www.reddit.com/r/askscience/comments/6yuv1w/is_everything_that_we_know_about_black_holes/ 1504878448 6yuv1w Astronomy 2017-09-08 16:47:28 "I'm not sure what ""everything else"" you're thinking of here, if ""we understand their effect on matter"" is something you take as given. + +We have observed stars orbiting seemingly empty space as if there were a massive object there, and we don't have candidates for dark objects of the necessary mass apart from black holes. We have observed systems where gas is heated to extreme temperatures as it spirals into an otherwise invisible massive object, which again we have not been able to explain except as a black hole accretion disk. We have direct observations of stellar orbits around our galaxy's central mass, consistent with a supermassive black hole and pretty much nothing else (given the necessary density of the central object for the closest stellar orbits to avoid hitting it). + +We have gravitational wave observations from LIGO that quite precisely match theoretical and computational models of black holes spinning together to merge into a single larger (rotating) black hole; the fact that those observations are such a close match to the theory and its consequences is strong evidence that the details of our theories are quite accurate. + +So while I'd love to be able to take a spaceship out to a black hole and perform experiments right there in person, I feel like our understanding of black holes at this point has (very) roughly the same level of experimental evidence that our understanding of, say, neutron stars or red supergiant stars has. What else do you want to know about them that *isn't* covered by that? + +(One immediate possibility: ""What happens when you cross the event horizon and head inside?"" But I might claim that in that case, we don't ""know"" the answer theoretically/hypothetically, either. There's a guess, based on the equivalence principle, that for a big enough black hole you wouldn't even notice that you'd crossed that line, at least not until you discovered that you could no longer escape the central singularity. But 1) it's well-established theoretically that you wouldn't be able to report back on your experience anyway, so this is essentially impossible to check as far as we know, and 2) as far as I know, there's still active debate among quantum gravity/string theory researchers about whether there's some sort of ""firewall"" that would inevitably annihilate you the moment you reached the event horizon, due to quantum requirements that kinda seem to contradict the equivalence principle in this situation. So I don't think this question really fits what you're asking about, either.) + +Edit: A couple of people have pointed out that Hawking radiation counts quite nicely as something hypothetical/purely theoretical that we haven't been able to measure yet. That's a great point!" ">We know they exist and understand their effect on matter. But is everything else just hypothetical + +Your phrasing is still incorrect. Scientists will say that black holes exist because there is no better explanation for observations. ""Everything else"" we know about black holes is also determined in the same way. There aren't two categories of knowledge on black holes. It is a sliding scale of uncertainty. + +>Edit: The scientific community does not enjoy the use of the word theory. I can't change the title but it should say hypothetical rather than theoretical + +Actually, theoretical is a better term than hypothetical, scientifically, for this. The reason is that there is theory to explain things about a black hole other than that it exists. The problem is that your question implies that theory is the same as guessing. If you want to irritate a scientist, tell him that scientific theory is ""just a theory""." +518 What is the fastest beats per minute we can hear before it sounds like one continuous note? 6324 https://www.reddit.com/r/askscience/comments/5dpu0z/what_is_the_fastest_beats_per_minute_we_can_hear/ 1479514794 5dpu0z Neuroscience 2016-11-19 3:19:54 "Sound engineer here. + +What none of these post mention, and what you are looking for is something called the Haas-effect. Lots of people here mention Hz, and while that is certainly related you are still able to distinguish the individual beats at a low frequency. + +This is also known as the [Precedence effect](https://en.wikipedia.org/wiki/Precedence_effect): +>The ""precedence effect"" was described and named in 1949 by Wallach et al.[3] They showed that when two identical sounds are presented in close succession they will be heard as a single fused sound. In their experiments, fusion occurred when the lag between the two sounds was in the range 1 to 5 ms for clicks, and up to 40 ms for more complex sounds such as speech or piano music. When the lag was longer, the second sound was heard as an echo. + +So the real answer is, depending on your metronome sound it will range from 1 ms (60000 BPM) to around 40 ms (1500 BPM) between each click where you can no longer distinguish each hit. " "Steve Lehman in his [dissertation](https://slehman.s3.amazonaws.com/uploads/document/pdf/3/StephenHLehmanDissertation.pdf) talks about the highest perceivable tempo. + +>Parncutt also suggests a standard tempo range of 67-150 BPM, finding that listeners stop hearing durations as regular pulses below 33 BPM (1800 seconds) and start grouping individual pulses into larger units above 300 BPM (200 milliseconds). Parncutt’s proposed limits on the perception of tempo (200- +1800 milliseconds) can also be directly related to a listener’s physical ability to reproduce isochronous durations. Bruno Repp (2005) has cited 100 milliseconds as the shortest physically reproducible duration and 1800 milliseconds as the longest such duration. 1800 milliseconds (33 BPM) corresponds to Parncutt’s lower limit of tempo perception and the duration of 100 milliseconds, is half the value of Parcutt’s upper limit of 200 milliseconds. For many music theorists, the +very notion of tempo is contingent upon the ability to perceive symmetrical divisions of a regular pulse, usually in ratios of 2:1 or 3:1. Given our apparent inability to reproduce, and perceive regular sub-pulses shorter than 100 milliseconds, Parncutt’s upper limit of tempo perception (200 milliseconds) can be viewed as a logical threshold. + +For reference 16th notes around 150 bpm are approximately 100 ms. So 16th notes in [Radiohead's Weird Fishes](https://www.youtube.com/watch?v=TNRCvG9YtYI) are approximately 100ms long each. It's not exact, but it might give you a frame of reference for how long that duration is. + +It's not exactly what you asked about, but it does give you a place to start and should someone not come along with a full answer you could try looking through the sources. + +" +641 Is there anything the human body has three of? 6304 https://www.reddit.com/r/askscience/comments/5n2mi2/is_there_anything_the_human_body_has_three_of/ 1484019239 5n2mi2 Human Body 2017-01-10 6:33:59 This thread is being locked due to the excessive number of anecdotes. Please remember the rules on /r/AskScience before you post. "There are three cusps/leaflets to the tricuspid, pulmonary and aortic valves + +Slightly off topic but each kidney is created three times - the first two (pronephros and mesonephros) degenerate and the third (metanephros) becomes your kidney and urinary tract" +1237 When you get vaccinated, does your immunity last for a life-time? 6287 https://www.reddit.com/r/askscience/comments/bcyp8l/when_you_get_vaccinated_does_your_immunity_last/ 1555212047 bcyp8l 2019-04-14 6:20:47 "Everyone, + +Please remember when you are commenting on /r/askscience that we have very strict commenting guidelines in order to maintain the quality of conversation. + +Specifically, do not post anecdotes. Anecdotes are by their very nature unscientific. At best they are amusing, and at worst they are inaccurate and misleading. This includes posting personal medical information. Violations to this rule may result in a temporary ban. + +Have fun." "From [this website](http://www.immune.org.nz/vaccines/efficiency-effectiveness), here is a list of diseases and the estimated duration of protection from vaccine after receipt of all recommended doses: + +* Pertussis (whooping cough): 4-6 years +* Diphtheria: around 10 years +* Tetanus: 96% protected 13-14 years, 72% >25 years +* Polio: >99% protected for at least 18 years +* Haemophilus influenzae type B: >9 years to date +* Hepatitis B: >20 years to date +* Measles: Life-long in >96% vaccines +* Mumps: >10 years in 90%, waning slowly over time +* Rubella: Most vaccinees (>90%) protected >15-20 years +* Pneumococcal: >4-5 years so far for conjugate vaccines +* Human papillomavirus: >5-8 years to date +* Varicella: one dose - unknown; two doses >14 years to date" +861 Can satellites be in geostationary orbit at places other than the equator? Assuming it was feasible, could you have a space elevator hovering above NYC? 6280 https://www.reddit.com/r/askscience/comments/78rk06/can_satellites_be_in_geostationary_orbit_at/ 1508973139 78rk06 Physics 2017-10-26 2:12:19 "Hi! I work on the geostationary satellites for NOAA. Since you said you know very little about physics, here's a quick primer on orbits. + +Orbits occur when an object is falling sideways fast enough to ""miss"" the Earth. This might be hard to imagine, so imagine throwing a baseball. The baseball goes up and down, but moves sideways as well. The harder you throw it, the farther it goes. If you threw it hard enough (in a vacuum), it would miss the Earth and keep falling forever. + +Now, because gravity is exerted from the centers of mass (but the CoM of our satellite is relatively negligible), any orbit you travel in has to have the center of the Earth in its plane. This means you can't have a ""halo"" orbit over the North pole, or off to the sides of the Earth. In practical terms, we can say *any* orbit must cross the plane of the Equator at some point. + +So, as this relates to your question. A ""geostationary"" orbit is a geosynchonous orbit (one full orbit is one Earth day) that is in line with the equator. Since this matches the Earth's rotation,, you're always over the same location. Now imagine tilting the orbit so it was inclined. You still orbit in one day, but you are moving North and South as you pass the Ascending Node and Descending Node (The points where you cross the equator). Thus, your ground track is a figure-eight pattern, with the neck centered on the Equator. + +So, to answer the second part of your question, no, you couldn't have a space elevator over NYC. That would be in an orbit that doesn't cross the equator, which is not possible. Geostationary satellites (and, by extension, space elevators) are only possible at near-zero latitude. + +Let me know if you have any other questions!" Geostationary orbits can only occur along the equator. Any orbit occurs on a two dimensional plane that passes through the center of mass for the object it is orbiting. For a satellite orbiting earth anywhere north or south of the equator the position directly below the satellite would have to move north and south with the satellites orbit, not geostationary. This also means that a space elevator could only work at the equator but there is a simpler reason that is easier to visualize. In theory, a space elevator would use centrifugal force to cancel out the force of gravity trying to pull the structure down. Anywhere outside of the equator the centrifugal force would not be in line with gravity causing a sideways force on the elevator. +862 What did the SapceX Falcon 9 rocket launch look the way it did? 6276 https://www.reddit.com/r/askscience/comments/7lperb/what_did_the_sapcex_falcon_9_rocket_launch_look/ 1514045897 7lperb Engineering 2017-12-23 19:18:17 "A lot of folks noticed that the plume looked a lot like a contrail at first, then ballooned outwards later. + +As the rocket reached higher and higher altitude, there's less ambient air pressure to push against the rocket exhaust coming out of the engine, so the plume is able to expand much farther - this is what gives the plume its characteristic balloon shape. + +**EDIT:** Since a lot of folks are asking what the ""bright dot"" was on the inside of the balloon structure: + +That was the separation of the reusable primary stage. [In this high-res video](https://www.youtube.com/watch?v=tE5C3O71Xqo&t=2m18s) you can actually see the primary stage end (when the thrust goes dark), the secondary stage ignite (when the thrust goes bright again), and then the bright dot of the separated first stage lagging behind and dropping a bit. Note that it doesn't just drop like a rock, since it's also on a ballistic trajectory - it takes some time to lag behind and start falling. If you look closely, you can also see some spiral waves coming out from it, presumably because it's tumbling around while thrusting a bit to control its eventual descent. + +Eventually that first stage will land and be used again. [Here's a schematic](https://i.imgur.com/69PZxU9.jpg) of how all of the above actually works." You saw liftoff, stage one separation, stage two light off and leave great plume, sunlight reflection and then the fairing separation which many camera persons captured greatly trailing the stage two separation. Great view of Sunlight plume. Probably the best view people has ever seen of a rocket launch. You only see this when you launch at a late hour just after sunset or in the morning just before dawn. Try imagining where the sun is in the video and then you get why its only lighting up high flying objects or exhaust plumes in this scenario. When the earth rotates another hour, the sunlight would be blocked completely be earth and we would see only the fire from exhaust not the smoke light up like in the video. When rockets launch at daytime, the smoke plume gets illuminated just as in this video. But against an already bright sky it does not look super bright or glowing. +772 They say that to test String Theory, we need to build a particle accelerator as large as out galaxy. Is it a technical limitation or a fundamental one? 6265 https://www.reddit.com/r/askscience/comments/6bq1py/they_say_that_to_test_string_theory_we_need_to/ 1495040948 6bq1py Physics 2017-05-17 20:09:08 "It's a little of both. With how we currently probe high energy regimes, there is a fundamental limit to the energies we can obtain from collisions, related to accelerator designs (including size). But it is, pedantically, a technological limitation, because the science doesn't say ""the only way to test string theory is to use your current understanding of accelerator physics to build a very large accelerator,"" rather it says ""if you want to avoid building a very large accelerator, you need a breakthrough in how you probe very high energy regimes.""" "It's a ""technical"" limitation in the sense that there's no reason why we couldn't build one that big. + +But, although this is an often-made claim, it's really a quite misleading one. It's based on the idea that there's a certain ""characteristic"" energy scale associated with string theory, and in order to *directly* test string theory, we need to create particles of this energy, which requires a ridiculously large particle accelerator. These claims are true, but they are not the whole story. + +Think about it like this. Suppose you have a ruler. Let's say this ruler is only accurate to 1mm. That is, you can't use it to measure distances smaller than 1mm. Any measurement that falls between two different mm marks, you round to the closest mark. + +With this ruler, you can never measure something smaller than 1mm. Even if you try to do something clever, like make a lot of measurements and average them together to get a really accurate measurement, it won't work, because you always rounded to the closest 1mm mark. + +This means that, with this ruler, you can never *directly* measure distances smaller than 1mm. This does not mean, however, that you can not use the ruler to *indirectly* measure distances smaller than 1mm. + +For example, let's say you have a microscope that magnifies an image by a factor of 1000. You could then pick something that's smaller than 1mm, magnify it by 1000 using the microscope, measure the magnified image, and then divide that length by 1000. This allows the ruler to indirectly measure distances much smaller than it can directly measure. + +There are lots of other ways you can come up with to use this ruler to indirectly measure very small distances. + +Similarly, there are lots of indirect predictions of string theory that do not require enormous particle accelerators. In fact, there are so many of these predictions, and they are so structured, that pretty much all string theorists at this point are convinced in its correctness. (Mostly, the problem is in getting the theory to make predictions of the specific quantities you'd like to study, which is hard because the theory is complicated.)" +1332 Could you have a binary set of moons that orbit a planet together? Not 2 moons in separate orbits, but a pair or moons rotating around each other and orbiting a planet as well. 6265 https://www.reddit.com/r/askscience/comments/cdt2pm/could_you_have_a_binary_set_of_moons_that_orbit_a/ 1563256568 cdt2pm 2019-07-16 8:56:08 "These orbits are very difficult to get. The two moons would need to be quite far from the planet, the planet would need to be far from its star (the planet would need a very large Hill Sphere, like Neptune). + +In such a situation, a binary moon would be stable. + +How it would form is another matter. The angular momentum needed is way out of whack." There is something sort of similar going on already with Saturn's moons Janus and Epimetheus. They share the same orbit, but rather than orbiting around each other, they have a horseshoe orbit where their tugging on each other causes them to slightly change their orbital radius so that they switch who is closer, but never actually pass each other. +1238 How did scientists know the first astronauts’ spacesuits would withstand the pressure differences in space and fully protect the astronauts inside? 6257 https://www.reddit.com/r/askscience/comments/b9y8ct/how_did_scientists_know_the_first_astronauts/ 1554507191 b9y8ct Astronomy 2019-04-06 2:33:11 They built vacuum chambers on Earth large enough for people to fit inside. That way they could test the suits, with people inside them, in a hard vacuum before they actually sent anyone to space. If something went wrong during one of the tests the could open the door to the chamber and instantly repressurize it. "The actual pressure change is not really that significant. It’s just one atmosphere. In the negative direction but one atmosphere. + +A recreational diver experiences five times that, if he goes 50 meters underwater. A submarine can withstand 40 times that. + +Although these go in opposite directions, the engineering principles are essentially the same. The real challenge was in how to accomplish it without having everything inflate so much that it would excessively hinder the astronaut’s movements. " +1333 Are modern humans stronger or more athletic than our pre-agricultural counterparts? 6255 https://www.reddit.com/r/askscience/comments/bth9j7/are_modern_humans_stronger_or_more_athletic_than/ 1558928858 bth9j7 Anthropology 2019-05-27 6:47:38 "It depends on your viewpoint of the agricultural revolution and how you define stronger. Until very recently (within the last 200 years or so), the switch to agriculture had an overall negative impact on human health (Diamond 1987). Evidence for this can be seen in studies from western Ukraine on the Trypillia-Cucuteni(TC) culture (eneolithic, ~5 ka) (ka =calibrated c14 thousand years ago) which was the first farming community in that region. Previous archaeological cultures were mobile hunter-gatherers who subsisted on various plants and animals throughout the region. The TC had the common European domesticates such as wheat, barely, sheep, and goat. According to bioarchaeological studies on skeletons from Verteba cave, an archaeological site in western Ukraine with skeletons dating from both of the above mentioned groups, TC peoples are shorter, frequently have more dental carious lesions (cavities), and have more enamel hypoplasia. (Karsten et al. 2016). Enamel hypoplasia are used as proxies for poor health because they only develop during childhood and are markers of stress mainly due to starvation. Additionally, TC populations showed increased frequencies of violent trauma (~1/4 adults died violently!) and tuberculosis was common amongst the agricultural populations. + +Overall, I’d argue that prehistoric (pre-agg) hunter-gatherer populations were probably stronger because they were more mobile, had better diets (depending on region and temporal period), and lived in smaller groups which cut down on disease transmission. It is important to note however that the osteological paradox, the idea that skeletons could appear healthy because the disease that killed them worked so quickly that it didn’t leave a marker on the skeletal material, is a factor when comparing strength and health of two separate populations. Is what we see archaeologically representative of the entire population? Probably not but it’s a start. Finally, one of the greatest feats of strength (IMO) for pre-agricultural hunter-gatherer populations was the colonization of the south-central Andean highlands ~12.5 ka. One of the oldest archaeological sites in the new world is located at 4480 meters above sea level where only 60% of oxygen is available when compared to sea level (Rademaker et al. 2016). The populations that settled this area more than likely stayed up at these altitudes for extended periods of time (seasonally) which is downright incredible considering that when I when up there, the effects of hypoxia almost immediately took hold and I felt like death. I’m sure modern humans could settle high altitude and some still live in this area today but I think that it really speaks to the strength of pre-agg people who originally were colonizing these semi-harsh areas. + +Credentials: I participated in the excavation at Verteba cave in 2016 and 2017 and have a Masters degree in archaeology" "There is an argument using evolutionary theory that agriculture was only adopted to increase group fitness at the cost of indivual fitness. + +Lots of civilisation diseases started with the adoption of agriculture. + +So there is the argument that agriculture made civilisation possible but at the cost of pure indivual strength and physical prowess. + +There is lots of evidence that early agricultural societies had less than healthy members compared to hunter gatherers. + +When you think about it, the indivual skills of a warrior in a large army is less important than pure numbers, most armies in the past were farmers called to war once a year, and yet the prevailed most of the time against nomad societies whos way of life made them formidable indivual warriors like the steppe people, just by numbers alone. + +Edit: + +If someone is interested where these theories come from, I recommend these books: + +https://www.amazon.com/gp/aw/d/0452288193/ref=dbs_a_w_dp_0452288193 + +https://www.amazon.com/gp/aw/d/0996139516/ref=dbs_a_w_dp_0996139516 + + +https://www.amazon.com/Secret-Our-Success-Evolution-Domesticating/dp/0691178437/ref=mp_s_a_1_1?keywords=joseph+henrich&qid=1558984106&s=gateway&sprefix=joseph+henr&sr=8-1 + +https://www.amazon.com/Not-Genes-Alone-Transformed-Evolution/dp/0226712125/ref=mp_s_a_1_1?keywords=not+by+genes+alone&qid=1558984151&s=gateway&sprefix=Not+by+ge&sr=8-1" +1239 Do Tectonic plates ever change in size and or break apart? 6253 https://www.reddit.com/r/askscience/comments/b9bsc3/do_tectonic_plates_ever_change_in_size_and_or/ 1554379156 b9bsc3 Earth Sciences 2019-04-04 14:59:16 "Yes, they can break apart, join together, and be added to, as explained by u/cantab314 + +However, most continental tectonic plates (as opposed to oceanic ones) have very ancient, very stable cores, known as cratons. For example, the Laurentian Craton that makes up a large part of the North American continent has been relatively unchanged for billions of years, while the 'outer' parts of the North American plate are being continuously modified." "Yes. + +Plates breaking apart is known as *rifting*, and is the process that creates new oceans with their ridges. For example Africa and South America were once on one plate, that then rifted about 100 million years ago, forming the South Atlantic Ocean between. + +Plates can join together as a result of continental collisions. The join is known as a *suture*. An example is the Iapetus Suture which runs through eastern North America, Ireland, and Great Britain, marking where the Iapetus Ocean closed around 400 million years ago; England and Scotland were once on two seperate tectonic plates before they joined along that suture." +773 "Do bees or house flies have to individual trigger each wing beat or do they have more of an ""ON"" switch in their brain?" 6229 https://www.reddit.com/r/askscience/comments/6ldl7z/do_bees_or_house_flies_have_to_individual_trigger/ 1499256244 6ldl7z Biology 2017-07-05 15:04:04 "Many insects, and I believe flies and bees are in this group, use ""indirect"" flight muscles. Basically, the muscles that control the wings connect to the exoskeleton of the upper thorax, rather than the wings directly. When they contract, they cause the thorax to vibrate back and forth like a guitar string. Each vibration is beats the wings, but only the initial contraction requires an action potential. So the nervous system is operating many many times more slowly than the wings are beating. + +Disclaimer: Entomology was a long time ago, so that may be a bit off on on the specifics. I invite any entomologists around to correct me. " From a neuroscience perspective, most animals have Central Pattern Generators (CPGs) in the brain that allow for coordinated movement with minimal 'thinking' required. Think of riding a bicycle: you are not consciously moving every single muscle in your legs/feet/arms/balancing muscles, it just happens when you think - bike! Brains are so efficient! +642 when I shine a flashlight at Mars, does a small amount of the light actually reach it? 6220 https://www.reddit.com/r/askscience/comments/5xzt4s/when_i_shine_a_flashlight_at_mars_does_a_small/ 1488885628 5xzt4s Physics 2017-03-07 14:20:28 "Yes, you need to be careful with phrases like ""a small amount"". + +Mars is around 225 million km away at ~~closest approach~~ average distance. Lets say you have a 1W flashlight and aim it at Mars, the intensity very far away from this flashlight will drop off as the distance squared (also a little extra from absorption and scattering in the atmosphere). Without doing any exact calculations, if we assume scattering is negligible we can say the intensity that hits Mars will be larger than + +I > 1W / (2 pi * (225 million km)^2) ~ 3 × 10^-24 W /m^2 + +Mars has a surface area of 144.8 million km², so the power hitting Mars will be around + +I * A/4 ~ 2.3 × 10^-10 W + +This isn't a lot of power, but a single photon at optical wavelengths has an energy of around 3 × 10^-19 J, so this is still billions of photons a second hitting Mars. + +Edit: Lots of people are pointing out the beam divergence and scattering I ignored. Scattering I still don't think is very significant, [about a fraction 10^−5 of the light will be scattered for every meter of travel](https://en.wikipedia.org/wiki/Rayleigh_scattering), most of earths atmosphere is within 20 km of the surface so the intensity is reduced by a factor of around + +I/I_0 = exp(-20000*10^-5) ~ 0.8 + +which is a 20% loss and thus not significant. If you aimed the beam through more atmosphere or if you had a blue flashlight this gets worse, but never significant. + +The beam divergence depends heavily on how wide a flashlight you have to start with, if you had something which is quite compact the divergence is worse than something with a large output. Most of the power is actually in a spherical segment which is, say, 30 degrees in size, where as my calculation assumed this was closer to 90 degrees. To compensate the intensity on Mars would be bigger by a factor of (90/30)^2 = 9 ~ 10. " "Consider this: The [Voyager spacecraft](http://voyager.jpl.nasa.gov/news/pressrelease2.html), out there on the very edge of the heliosphere, is broadcasting with a 20W transmitter (a third of a regular light bulb's output). The amount of signal that reaches Earth (and is still recoverable!) is about 1/80,000,000,000^th the amount of power supplied by a digital watch battery! + +So, yeah, Mars is practically right next door. Your photons will get there. + +Edit: Precision of language. Also, adjusted figures based on the fact that the report is almost 20 years old. " +863 How catastrophic is an earthquake for deep sea creatures? 6220 https://www.reddit.com/r/askscience/comments/7aq2mc/how_catastrophic_is_an_earthquake_for_deep_sea/ 1509793959 7aq2mc Earth Sciences 2017-11-04 14:12:39 "I'm not aware of any studies or clear data on the effect of submarine earthquakes or associated tsunami on submarine creatures. In term of tsunami, it's important to understand the general characteristics of these [waves](http://www.bom.gov.au/tsunami/info/faq.shtml). They are unique in that they involve the entire water column (unlike normal wind driven surface waves), but in the open ocean they have very long wavelengths so for most creatures in the water column the passing of a tsunami wave would be barely noticeable. + +Earthquakes which generate tsunami do so by displacing water, which means there needs to be deformation of the ocean floor (i.e. a surface rupture of the fault that produced the earthquake). For example, in the Tohoku earthquake which caused the large tsunami in Japan in 2011, portions of the sea floor were [vertically displaced by ~10 meters](http://science.sciencemag.org/content/334/6060/1240). One could imagine if you happened to have misfortune of being some sort of benthic organism living right in that area, you may have been killed by debris from this scarp falling on top of you after the earthquake, but this would be limited to things living right at the rupture and again, we don't have any actual assessment of what this meant for deep sea creatures. + +At the surface, tsunamis can have pretty big effects on marine organisms. Lots of shallow marine organisms can be washed on land (and die) and there is also the influx of material from the near shore into the shallow marine environment that can disrupt things. [Here is a paper looking at the recovery of the shallow marine environment after the Tohoku quake](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168261). Tsunami can also do some pretty odd things to organisms, like this pretty wild example, again from the Tohoku tsunami of a [raft of (still living) marine organisms that floated across the pacific from Japan to the US west coast](http://science.sciencemag.org/content/357/6358/1402)." Follow up question: do underwater earthquakes move water around enough to damage something? And would an airplane or something flying above an earthquake feel alot of turbulence? +1060 What makes some people have a better memory than others? 6217 https://www.reddit.com/r/askscience/comments/8jdzxh/what_makes_some_people_have_a_better_memory_than/ 1526317926 8jdzxh Neuroscience 2018-05-14 20:12:06 Everything here people said is right. The thing you have the most control over is the technique which you employ to memorize details. However, genetics can play a role in this. This [study](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3889822/) suggests that hippocampus size, the part of your brain responsible for storing memory, can have a direct relationship with short and long term retention. People who engage in complex stimulus elaboration integrating new info with old remember better. The role of stimulus elaboration was shown clearly by Craik and Tulving way back in 1975 and numerous times since then. +864 Do you use muscles to open or close your eyes? 6206 https://www.reddit.com/r/askscience/comments/77j7lf/do_you_use_muscles_to_open_or_close_your_eyes/ 1508466040 77j7lf Biology 2017-10-20 5:20:40 "You actually have separate muscles that close and open your eyes. + +As others have said, the orbicularis occuli muscle closes your eyelid. It is innervated by cranial nerve 7 (facial nerve). + +The levator palpebrae superioris muscle opens your eyelid. It is innervated by cranial nerve 3 (occulomotor nerve). + +So in truth, at any given moment your eyelids are where they are because of a combination of those two muscles. If you close your eyes, you relax the levator palpebrae superioris muscle and contract the orbicularis occuli. If you open your eye, it’s the opposite. " "If you want to voluntarily close your eyes (think squint), you’d primarily be using your orbicularis oculi muscle. However, it would be very tiresome and inefficient to have to contract this muscle the entire time that you’re asleep. + +Instead there’s the superior tarsal and levator palpebrae muscle. These work together to keep your eyes open during wakefulness and are innervated by your autonomic sympathetics (you can’t consciously control them). When you sleep, these sympathetics are down-regulated and parasympathetic activity dominates. This causes your superior tarsal and levator palpebrae to relax, allowing the eyelid to close. + +Additionally, the levator palpebrae is responsible for voluntarily opening and closing your eye lid. +" +865 Was working at Jimmy John's today when I customer came in and was severely allergic to cucumbers but could eat pickles, how's that possible? 6204 https://www.reddit.com/r/askscience/comments/70rvds/was_working_at_jimmy_johns_today_when_i_customer/ 1505699198 70rvds Human Body 2017-09-18 4:46:38 "Food allergies are often caused by an allergic response to a protein. Proteins are very large molecules made out a long chain of chemical groups called ""amino acids."" These chains are ""crumpled up"" into a 3D shape, and the exact 3D shape is what the body recognizes as an allergen. If the protein is unfolded, then the body may no longer recognize it. If a protein is exposed to heat or to acidic conditions, like they would in the pickling process, it can unfold and lose its 3D shape." "There are three options for this. + +1) Allergic reactions are generally a response from our immune system to certain proteins. Proteins are 3D structures that living organism use for stability, to speed up chemical reactions, store energy, and a variety of other things. Some parts of that 3D structure is unique to certain proteins, and our body uses it to recognize proteins from organisms that could be dangerous to us (e.g. an aggressive bacteria. Sometimes the body misidentifies something innocuous as harmful, and the reaction triggers when it detects it. Those are allergies. But notice that the allergy is specific to the specific 3-D structure of the protein, which is what's detected. Now, heating or exposing proteins to acidic environments can change their structure, sometimes irreversibly. It's possible that this person had an allergy to one of the proteins in cucumbers that change conformation when you pickle them. So that specific conformation of a cucumber protein is not there in pickles. This, however, would be dangerous: it is hard to guarantee that all of the proteins they're allergic to would have changed conformation, so if their allergy is strong, they could still have a reaction if the pickling process was incomplete, for example with a thicker slice. + +2) A certain number of allergic reactions seem to be related to our interpretation of what we are eating. There are for example descriptions of people having allergic reactions when they knew that they were being exposed, but not when they didn't know. This does not mean that the reaction is ""fake"", though. This can be a very real allergic reaction, with very real symptoms (hives, inflammation, etc.). But it's triggered in combination with the knowledge of being exposed. It's possible that this is the type of allergy this person has, and it's only associated to cucumbers and not pickles. + +3) What I described before is the classical pathway for allergies (usually with skin symptoms or swelling). However, people often call ""allergies"" to basically any adverse reaction. This sometimes includes for example stomach upset. Now, that process is different, and is generally not based on an immune response. We have a way to detect what foods may be toxic using our smell. If we associate a certain smell with a stomach upset (e.g. because we ate a lot of something and then felt sick), we will then feel sick and want to vomit (take out the substance from our bodies) based on that smell, particularly if we eat it. If this is what this person has, and the smell of pickles and cucumbers is different enough to them that they associate cucumbers but not pickles, they may be able to eat pickles. This is the least likely explanation because this would not generate hives or skin reactions, which it seems this person has." +519 What environmental impacts would a border wall between the United States and Mexico cause? 6201 https://www.reddit.com/r/askscience/comments/5ej1av/what_environmental_impacts_would_a_border_wall/ 1479927625 5ej1av Earth Sciences 2016-11-23 22:00:25 "Please remember, /r/AskScience has strict comment policy. If you have any questions on the comment rules, you can read up on them [here](https://www.reddit.com/r/askscience/wiki/rules) + +-edit- **Due to repeat violations of the rules, any that are egregious violations will result in either a temp or permanent ban from this subreddit. This is not the subreddit for political arguments.**" [example: Great Wall of China altering gene flow ](https://www.ncbi.nlm.nih.gov/m/pubmed/12634804/) +1240 How do colorblind people perceive lasers at the wavelengths they cannot see? 6198 https://www.reddit.com/r/askscience/comments/bcookt/how_do_colorblind_people_perceive_lasers_at_the/ 1555146307 bcookt Human Body 2019-04-13 12:05:07 "the common forms of colorblindness (*protanopia* and *deuteranopia*) don't really reduce the range of visible wavelengths (at least, not significantly), they just reduce the discriminability of wavelength patterns. the 'missing' cone pigments (so-called Long and Medium pigments for protanopia/deuteranopia, respectively) are so similar that they mostly overlap in their spectral sensitivities. + +a protanope might report more difficulty seeing pure very-long-wavelength light, like a red LED or laser light. but they should be able to see it if it's strong enough. + +a rare form of colorblindness is *tritanopia* (lack of short-wavelength pigment), in that case short-wavelength light will be relatively invisible, so the visible spectrum really is significantly reduced (the short-λ pigment covers a really different range to the L/R pigments). but tritanopia is not what we typically refer to when we say 'colorblind'." The question shows a misunderstanding of what colour blindness is. It's not that there are colours the person cannot see: it's that there are colours they can't distinguish. A colourblind person can perceive the same range of wavelengths of light as someone with full colour vision. +774 What would happen if the Earth's oceans were replaced with fresh water? 6183 https://www.reddit.com/r/askscience/comments/6ce0l3/what_would_happen_if_the_earths_oceans_were/ 1495330057 6ce0l3 Earth Sciences 2017-05-21 4:27:37 "* Most macro sea life would die rather immediately. Land animals dependent on sea life could also face extinction + +* The heat capacity of fresh water is higher than that of salt water, which means the oceans could absorb more heat in the spring/summer and release in Autumn/winter while maintaining a more steady temp. themselves. + +* Fresh water freezes at a temperature 2°C warmer that saltwater. This would likely increase the extent, thickness, and duration of the polar caps. + +* Salinity driven ocean circulation patterns would cease — leading to a redistribution of the ocean heat content with resulting climate effects. + +* Oceanic mineral deposits in equalibrium with salt water will find that equalibrium disturbed +" Rather than replacing and getting a bunch of answers about how most everything in the oceans would die along with things dependent on that life, I wonder how life on Earth would have evolved differently if our oceans were fresh water. +1334 Since everything has a gravitational force, is it reasonable to theorize that over a long enough period of time the universe will all come together and form one big supermass? 6150 https://www.reddit.com/r/askscience/comments/bp5jt7/since_everything_has_a_gravitational_force_is_it/ 1557964586 bp5jt7 2019-05-16 2:56:26 Good question, but such a theory would be incorrect, for several reasons. First, the universe is expanding at an accelerating rate. This means that galaxies are generally moving away from us, and galaxies that are sufficiently far away are moving away from us faster than the speed of light. (Though their motion through local space is always less than *c*.) Second, if we ignore universal expansion, not all mechanical systems are gravitationally bound. The escape energy/velocity is obtained by integrating the gravitational force between two bodies until their distance is brought to infinity; because gravity scales as 1/r\^2, this energy is finite. For example, the sun has an escape velocity of about 43km/s, so anything traveling away from the sun faster than this speed will slow down over time due to gravity, but only to a finite (non-zero) speed, and will continue to travel away from the sun at that final speed forever. "Yes it is reasonable to think this. It was actually the leading theory for the end of the Universe for a long time. It's called the Big Crunch. + +However, it wasn't too long ago that we observed that the universe expansion isn't slowing down like it would do in the big crunch scenario. Instead the universe is rapidly expanding which is the opposite of what would happen in the big crunch. We do not know why the universe is rapidly expanding and we call the unknown cause dark energy. + +Nowadays the leading end time of the universe is the Big Freeze or the heat death of universe. They can go along with the theory called the Big Rip. When the big rip happens everything will disintegrate into elementary particles. However before that happens the Big Freeze could occur which will be when all the stars die and all the black holes disappear and spontaneous entropy decreases occur or the heat death could happen where max entropy is reached." +1335 When the sun becomes a red giant, what'll happen to earth in the time before it explodes? 6132 https://www.reddit.com/r/askscience/comments/c5ifx2/when_the_sun_becomes_a_red_giant_whatll_happen_to/ 1561509901 c5ifx2 Astronomy 2019-06-26 3:45:01 "The sun gets hotter over time so in about 600 to 700 million years the conditions on the planet won’t allow for photosynthesis and all the oceans will have boiled away a little while later. We’ll be a dead rock by the time the sun gets within a few billion years of turning into a red giant. Then we’ll be part of the sun. Only the ghosts will be bummed or maybe they’ll like the warmth. Also, Europa might be nice by then. + +EDIT: numerical clarification" "Astrophysicist here: When the sun reaches the red giant stage, its surface will reach up to the orbit if Venus, it's surface temperature will drop a bit, and it's luminosity will increase by a factor 100. This will undoubtedly be enough to kill of all lifeforms on earth. However, that's not the end of it. As the red giant ignites is core helium reserves, it will grow even more and it's surface will reach the orbit of earth. Once engulfed, the earth will spiral down into the stellar core, contaminating the mantle with 'exotic' elements as it dissolves/evaporates. Finally, the sun will begin losing its mantle via a intense dusty stellar wind, which eventually lays bare the stellar core. The intense uv radiation of the hot stellar core illuminates the escaping gas forming a beautiful planetary nebula. The stellar core then begins its slow cooling process as a white dwarf, while the expelled ~~had I~~ gas and dust is reprocessed into new stellar and planetary systems. So no explosions, really :) + +Edit: first gold!! Thanks for your appreciation, kind stranger :)" +643 How do lasers measure the temperature of stuff? 6112 https://www.reddit.com/r/askscience/comments/64muu5/how_do_lasers_measure_the_temperature_of_stuff/ 1491863237 64muu5 Engineering 2017-04-11 1:27:17 Usually they're used to just align an IR sensor, but in principle you could shine a laser on something and determine the ratio of Stokes to anti-Stokes scattering, which would be an indirect measure of the temperature. Do you mean in the case of a bolometer like [this](https://www.amazon.co.uk/Etekcity-Lasergrip-Non-contact-Infrared-Thermometer/dp/B01AT9TM3M/ref=sr_1_1?s=automotive&ie=UTF8&qid=1491865828&sr=1-1&keywords=heat+sensor+gun)? The laser does not measure the temperature, it is just used to align the IR sensor visually. +1241 Starfish Prime was the largest nuclear test conducted in outer space, by the US in 1962. What was its purpose and what did we learn from it? 6105 https://www.reddit.com/r/askscience/comments/ax74gq/starfish_prime_was_the_largest_nuclear_test/ 1551706084 ax74gq 2019-03-04 16:28:04 "Starfish Prime was part of a larger series of high-altitude tests called Operation Fishbowl (a subset of Operation Dominic). As the researcher Chuck Hansen puts it pithily in his _Swords of Armageddon_ (v2): + +> The purpose of the FISHBOWL program was to satisfy JCS requirements for weapons effects data about nuclear fireball transparency, growth and rise rates; intensity and duration of atmospheric ionization; missile RV structural response to thermal radiation; radiation flux measurements; electromagnetic pulse (EMP) effects and range; nuclear, thermal, and x-radiation output and effects; and radio and radar ""blackout"" effects (which would bear directly on antiballistic missile targeting and control). Knowledge of these effects was required to evaluate ICBM ""kill"" mechanisms and vulnerabilities; ABM effectiveness; communications and control; and the value of ICBM penetration aids. + +At the time, both the US and USSR were deploying anti-ballistic missile systems that would try to intercept incoming missiles at high altitudes with nuclear warheads, and used radio waves for communication and coordination of their forces. So understanding what would happen when a weapon went off very high above the atmosphere was important for this, especially since many of the effects of a nuclear weapon are somewhat different in versus outside of the atmosphere. And if you imagine lots of these things going off in the upper atmosphere, you get a picture of how ""messy"" it would be to try and detect incoming missiles and planes, and communicate outside of your home country, in the event of all-out war. + +To highlight two of the most important of the above: + +* The ""blackout"" effects pertain to the fact that a high-altitude nuclear weapon will interfere with radar and radio. That means that there is a period after a weapon has detonated at that height that the radars on the ground can no longer see any incoming weapons. Understanding this is crucial if you are really trying to field a nuclear-armed ABM system, because every ""hit"" makes it harder for you to see any further, incoming missiles, and makes it very easy to defeat (just send a lot). + +* The electromagnetic pulse (EMP) was somewhat understood prior to these tests but Starfish Prime in particular highlighted its effects. Because it ionized the upper atmosphere, it produced a massive EMP effect over a very large area. This was of interest for a lot of reasons relating to both defense and attack strategies — if you are able to interfere with electronics on a large scale, that can be useful; if you have electronics you don't want interfered with in that way, you have to design them to be able to resist it. + +Starfish was an ""effects"" test — the goal was to see ""what happened"" not to learn about whether it would work or not. This is different than, say, Frigate Bird, which was a ""systems"" test (does the whole system work?) or the other tests in the Dominic series that tried out new warhead ideas (""design"" tests)." "The main purpose was to test the effect of the electromagnetic pulse (EMP), which can affect much larger areas when the explosion takes place up in higher altitudes. The EMP was far larger than expected and affected Hawaiian islands more than 1000 km away from the launch point, damaging and destroying electrical objects like street lamps, which caused the public to become aware of this side effect of nuclear explosions. + +Many more details of course on the corresponding [wiki page](https://en.wikipedia.org/wiki/Starfish_Prime)." +644 Why doesn't the brain filter out Tinnitus? 6090 https://www.reddit.com/r/askscience/comments/65l79a/why_doesnt_the_brain_filter_out_tinnitus/ 1492287647 65l79a Neuroscience 2017-04-15 23:20:47 "This is not my field of expertise (otolaryngology), though, in 2014 a [comprehensive review and clinical guidelines](http://journals.sagepub.com/doi/full/10.1177/0194599814545325) were published in _Otolaryngology–Head and Neck Surgery_. + +It includes, amongst many other notable portions on the pathology, the current understanding of the disease, the treatment options, and further avenues of exploration and clinical management of patients with the disease. + +They classify Primary and Secondary tinitus as follows: + +>Primary tinnitus is used to describe tinnitus that is idiopathic and may or may not be associated with SNHL _[sensorineural hearing loss]_. Although there is currently no cure for primary tinnitus, a wide range of therapies has been used and studied in attempts to provide symptomatic relief. These therapies include education and counseling, auditory therapies that include hearing aids and specific forms of sound therapy, cognitive behavioral therapy (CBT), medications, dietary changes and supplements, acupuncture, and transcranial magnetic stimulation (TMS). + +>Secondary tinnitus is tinnitus that is associated with a specific underlying cause (other than SNHL) or an identifiable organic condition. It is a symptom of a range of auditory and nonauditory system disorders that include simple cerumen impaction of the external auditory canal, middle ear diseases such as otosclerosis or Eustachian tube dysfunction, cochlear abnormalities such as Ménière’s disease, and auditory nerve pathology such as VS. Nonauditory system disorders that can cause tinnitus include vascular anomalies, myoclonus, and intracranial hypertension. Management of secondary tinnitus is targeted toward identification and treatment of the specific underlying condition and is not the focus of this guideline. + +The paper is rather technical in looking into clinician practice and epidemiology, but it does give a very thorough breakdown of tinnitus as a physical malady. Understanding the specific pathology of the patient allows for more effective treatment. Unfortunately, this has the effect of splitting tinnitus into many subgroups of categories, though it may be a good place for OP to start to understand why this is a more difficult question to answer than he might've anticipated." "There are a number of treatment options for tinnitus, including [tinnitus retaining therapy] (http://www.nhs.uk/Conditions/Tinnitus/Pages/Treatment.aspx), which is to do exactly what you ask. + +Why don't we do this naturally? Well, tinnitus is often not a constant ringing, but can be [intermittent or changing](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2633109/). + +I myself have tinnitus, and I've had it for as long as I can remember. I find the pitch changes a lot throughout the day, but I've always been able to filter it out; although, if I concentrate on it, it becomes almost deafening, especially when it's quiet." +775 Are oceans necessary for a terrestrial planet to have sustained tectonic plate activity? Would a planet that was entirely covered by a single massive ocean have tectonic plate activity? 6085 https://www.reddit.com/r/askscience/comments/69yvla/are_oceans_necessary_for_a_terrestrial_planet_to/ 1494258237 69yvla Planetary Sci. 2017-05-08 18:43:57 "The key contribution of water in plate tectonics may seem to come from left field and be somewhat counter-intuitive, but it resides in the effect of water on the temperature at which partial melting of the mantle occurs. [For instance, the addition of about 15 wt% water to garnet peridotites will lower partial melting temperature requirements by 350°C](http://onlinelibrary.wiley.com/doi/10.1029/2011GC003942/full). In anhydrous settings, partial melting is much harder to achieve and the plate tectonic conveyor belt ""seizes up"", as rifting fails to give way to oceanic crust formation for lack of sufficient melt. the same problem occurs at the other end of the conveyor belt, as anhydrous lithospheric material will also require temperature a few hundred degrees higher to succefully initiate anatexis. Furthermore, the temperature increase for partial meltin of anhydrous rocks intensifies at higher pressures. ([See also](https://journals.lib.unb.ca/journalimages/GEOCAN/2006/Vol_33/No_04/geocan33_4ser01_fig8.jpg)) And just to be clear, it is not sufficient for the water to occur on the surface, the mantle has to be pervasively hydrated for the presence of water to matter. + +The case of Mars interesting, as [the martian mantle is understood to be water-poor, but chlorine-rich](http://geology.gsapubs.org/content/37/12/1087.full). So, even if there was water in Martian oceans, there does not appear to have been an efficient conveyor belt reintroducing that water back to the Martian mantle. And the Martian Lithosphere is much thicker that Earths, so the corresponding anhydrous melting temperatures are rather daunting. Yet, there was incipient rifting on Mars [see Valles Marineris], it just failed to open and produce oceanic crust. There is no evidance of incipient subduction to my understanding either. There was intense hotspot volcanism as witnessed by those spectacular shield volcanoes, however, so at least some degree of partial melting occured; just not enough at sustained rates enough to open up... + +That being said, I can't imagine how a global planetary ocean would interfere with an active plate system. Just gotta remember that over the course of geological time, plate tectonics tends to favor the progressive formation of continental crust which is much thicker and persistent, so just cause you start with a 100% oceanic crust and no emerging land in your system does not imply it will remain that way over geological time periods. In our Earths history, continental crust seems to have been much rarer and in smaller pieces in the Archean than today. + +TLDR: + +1 - No water - no significant plate tectonic activity + +2 - water sequestered at the surface without a way into the dry mantle: no significant plate tectonic activity + +3 - water at the surface in small or huge quantities and a wet mantle: plate tectonics all the way + +4 - No water at the surface, but a pervasively wet mantle: plate tectonics galore as long as the mantle remains wet. + +" "I interviewed Thomas Watters about this (sort of) last year for Smithsonian Magazine. He is a scientist who studied Mercury for years and published a paper about it's tectonic activity. No oceans there, so that might answer your question. + +http://www.smithsonianmag.com/smithsonian-institution/mercury-is-tectonically-active-making-uniquely-like-earth-180960636/ + +And if you want to get more geeky about what Watters had to say, I also posted a blog entry with a full transcript of my conversation with him. + +http://jacksonlanders.blogspot.com/2017/01/back-in-september-i-wrote-article-for.html" +958 When experiencing Sleep Paralysis some people feel like they can't move while others instead are met with a feeling of deep fear. What is the cause of that? 6082 https://www.reddit.com/r/askscience/comments/81d5z4/when_experiencing_sleep_paralysis_some_people/ 1519984280 81d5z4 Human Body 2018-03-02 12:51:20 "This thread has been locked. Over 80% of the comments had to be removed because they were personal anecdotes about sleep paralysis or requests for medical advice. + +A good answer is already present describing the phenomenon of hypnagogia and how it is related to sleep paralysis. +" "Sleep paralysis is an inaccurate label for the experience that has simply caught on as a broad descriptor in common language. ""Night terrors"" is another term sometimes used for this experience. + +The more accurate term for the overall phenomena is [hypnagogia](https://en.wikipedia.org/wiki/Hypnagogia), which is essentially the broad term for what happens to our consciousness and mental processes when transitioning from awake to asleep and vice versa (sometimes called ""threshold consciousness""). To be pedantic, hypnagogia is sometimes used only for the awake -> asleep transition, and hypnopompia for the asleep -> awake transition, but hypnagogia is typically accepted as a general term for both. + +Hypnagogia includes multiple things, including hallucinations, lucid dreaming, altered mental states, and sleep paralysis (i.e. the conscious awareness of REM atonia). + +So the different things people experience are potentially caused by very different mechanisms during this state. In the vernacular this entire state has picked up the label of ""sleep paralysis"", even though that is technically only one small subset of what could be happening during the transition and many hypnagogic episodes don't actually include sleep paralysis at all. + +As for what causes the various emotions and experiences, it's hard to say with certainty. The feeling of being unable to breathe, paralysis, or something ""heavy"" on the chest are all pretty clearly tied to the physical mechanisms of sleep paralysis. The overall sense of terror and fear are possibly a combination of sleep paralysis along with the general altered mental state of a sleep transition. The audiovisual hallucinations are probably being caused by the same mechanisms responsible for dreaming and may be effectively thought of as a lucid/waking dream. + +The fact that the nature of the hallucinations is relatively consistent across cultures/people is pretty interesting and has lead to a lot of common myth. Most full blown hypnagogic episodes include hallucinations of entities or presences in the room, sinister voices, and a general sense of dread/fear/terror. + +I don't know of any specific research that explains *why* these are the common hallucinatory experiences of this state, but it's easy to see how this would create the shared myths of demons, banshees, succubi, etc. and the modern shared myths of alien abduction. + +EDIT: Thread locked but I wanted to clarify a thing brought up in several replies here. I'm not saying sleep paralysis and night terrors are not well-defined things. I'm saying people inaccurately use these labels for a number of other hypnagogic episodes, which is why, as the OP describes, there are conflicting/differing reports of ""sleep paralysis"". Because essentially some reports are inaccurately calling their hypnagogic episode ""sleep paralysis"", when it was actually something else. This gets further muddied since hypnagogic episodes can share a lot of common aspects." +959 How can people sever entire legs and survive the blood loss, while other people bleed out from severing just one artery in their leg? 6073 https://www.reddit.com/r/askscience/comments/7qhoz3/how_can_people_sever_entire_legs_and_survive_the/ 1515995285 7qhoz3 Human Body 2018-01-15 8:48:05 Is some cases, when a limb is severed, the major arteries are pulled inside the muscle and the muscle squeezed the open end reducing or preventing blood loss. This only works with complete severing. A partial severing of the arteries will result in severe hemorrhagic blood loss and rapid decline to death. "Arteries have muscle in their walls. This muscle can clamp down and even large vessels can occlude themselves after trauma. There's a big problem with partial injuries though. Basically a partially cut artery bleeds more and can't close itself off by the muscle in its wall squeezing. A completely cut artery has a much better chance of doing so. + +Even so a big injury and a severed femoral artery in amputation through the thigh or big laceration is very likely fatal without immediate assistance. The black hawk down scene where the soldier dies after the leg wound showed this in a very accurate way. +A radial artery (wrist) will usually close itself off spontaneously after being transected." +1415 How could a body decompose in a sterilized room completely clean with no bacteria to break down the flesh? 6072 https://www.reddit.com/r/askscience/comments/dgqj48/how_could_a_body_decompose_in_a_sterilized_room/ 1570855413 dgqj48 Human Body 2019-10-12 7:43:33 "To add to the other commenter, [[edit: well now this is on top, so my comment is about *exceptions* to internal microbes leaving you with a only skeleton]] there are definitely different levels of decomposition that can happen. You won't always be left with a skeleton. Sometimes you may be left with a ""natural mummy"" that isn't very decomposed at all. Examples of conditions where you would find a natural mummy: + +Icy mountains - the body is frozen, such as in the Alps. See: Otzi the iceman. + +Also human sacrifices have been found in the Andes in even ""better"" condition. Here is a link but fair warning, it includes pictures of child mummies: https://www.penn.museum/sites/expedition/frozen-mummies-of-the-andes/ + +Dry sands - there were bodies buried in the ground in Egypt before the traditional mummification process was developed, I believe, and they were somewhat preserved by these conditions. This obviously dehydrates the body in a way that is different to ice mummies. + +And, bogs - they may have high moisture, and not quite freezing temperatures, but importantly, they do have low oxygen and an acidic environment, which prevents the microbes from decomposing the skin. + +Basically, various conditions can inhibit the decomposition process that microbes might otherwise cause. + +More reading here: +https://relay.nationalgeographic.com/proxy/distribution/public/amp/news/2016/01/160118-mummies-world-bog-egypt-science" "Depends on the type of 'sterile' environment you're in. Depending on temperature, there are several ways for a body to decompose. Normally, your mucous glands all along your intestines keep your digestive bacteria in check, so once you dies, and those mucous glands stop protecting your gut, those bacteria start digesting you. This happens at a fairly predictable rate just based off of body temperature when the body passes, but extremes in temperatures can greatly affect this rate. + +In a hot/humid 'sterile' environment, like a sealed room, a body will putrefy rapidly, turning into necrotic black soup. This is the fastest way to 'naturally' turn a body into a skeleton without outside factors like insects or foreign bacteria. + +In a hot/dry sterile environment, a body can still putrefy, but high temperatures might kill off the gut bacteria before the bloat the body and turn it to ooze, so in this case, it's possible for a body to become a dry mummy at which point other factors like sand erosion might break down and disperse the biomass. + +In tepid environments, humidity plays less of a factor, and a body will putrefy, bloat, and eventually turn to ooze on the inside, but the skin might remain recognizable for a fair amount of time. + +The interesting case, however, is in very cold environments. In particularly cold environments like the arctic and antarctic circles, as well as some mountain ranges, the low body temperature will cause a body to lose temperature at a rate fast enough that it can drop below the survivable threshold for bacteria long before putrefaction sets in too deeply. Once the bacteria are dead, the next thing that happens is that the moisture in the body will freeze, and ice has the odd ability to sublimate at low temperatures, so after a long enough period of time, the body will eventually dry out and leave a husk similar to a hot/dry decomposition." +1061 Do ozone holes (like the one above NZ) make solar power in that area more effective? 6066 https://www.reddit.com/r/askscience/comments/8k38qs/do_ozone_holes_like_the_one_above_nz_make_solar/ 1526553365 8k38qs 2018-05-17 13:36:05 "It wouldn't make a big difference. Firstly, the UV spectrum only makes a small portion of all sunlight (removing ozone makes red curve turn slightly more to be like yellow curve in UV range. You can even see the little dinky O^3 mark): + +https://en.wikipedia.org/wiki/File:Solar_spectrum_en.svg + +Secondly, based on how solar cells work, high energy photons give you the least ""bang for your buck"". Specifically, what you care about is total number of photons with energy greater than the bandgap. All energy a photon has above the bandgap energy is assumed thermally lost and provides no extra power. This leads to the Shockley-Quiessar limit where you basically just add up all photons above the cut-off and assume each one produces one electron-hole pair whose energy is the band-gap energy (i.e. all energy it had above that is lost). However, at smaller wavelengths/higher energies, for the same intensity you have less photons (i..e you have less photons, each carrying more energy). Thus: + +http://2012.igem.org/File:ETH_photoinduction_comparesun.png + +If you're going to go after anything outside the visible you want to go after IR not UV. Though, again, remember that all carriers are assumed to relax to the band-gap energy, so if you have a smaller band-gap you catch more photons, but each photon leaves the cell with less energy. Each one gives you less power if the band-gap is smaller. This is the trade-off of the Shockley-Quiessar limit: + +https://en.wikipedia.org/wiki/File:ShockleyQueisserFullCurve.svg + +And looky-there. Silicon, with its bandgap of 1.1 eV is pretty perfect." "In short, not really. + +Some thermal systems might see tiny gains, but most solar cells either cannot use the uv wavelength or extract only a tiny amount of the energy from a UV spectrum photon. + +Glass also absorbs a good bit of the UV radiation, preventing it from reaching the panels. + +Furthermore, UV causes degradation of the photovoltaic substrate, especially in thin film cells..... Shortening panel life and reducing output (but probably not by very much hole vs no-hole). + +So, no. No bonus energy from current solar infrastructure. Just cancer, poisoned beaches (from sunscreen), fading paint, and blisters." +776 [Physics] What makes the continuous stream of bubbles from a single spot when you pour champagne/highly carbonated beverages? 6061 https://www.reddit.com/r/askscience/comments/6np13a/physics_what_makes_the_continuous_stream_of/ 1500243064 6np13a Physics 2017-07-17 1:11:04 Dust or scratches in the glass provide what are referred to as nucleation sites where bubbles of dissolved gas can precipitate out of solution. It's hard for dissolved gases to escape a liquid without a nucleation site that allows bubbles to form. This is why boiling chips are used in a chemistry lab, to prevent liquids from becoming superheated and prone to explosion. The carbon dioxide prefers a nucleation point to form , usually a surface unevenness or a particle. If the rest of the glass is very clean and smooth, the few points where there is a nucleation point would give off an almost continuous stream of bubbles +777 Why do most objects in the night sky (stars and planets) look to be the same size relative to our naked eyes? 6053 https://www.reddit.com/r/askscience/comments/6h7fmo/why_do_most_objects_in_the_night_sky_stars_and/ 1497446360 6h7fmo Astronomy 2017-06-14 16:19:20 "To be able to tell the difference, by sight, that something is a disc rather than a dot, your eye needs to be able to detect the difference in angle between light leaving (say) the right and left edges of the disc. Planets and stars are so far away that our eye can't resolve this angle. It all just looks to our eye like it's coming from one place. + +Whether it's a huge sun at an extreme distance or a small planet at an extreme distance, either way our eye can't detect anything more than that there is light come from a particular spot. Our eye doesn't have the resolution to be able to detect that the light from the right and left edges of the body is coming from different places. + +Think about it this way; imagine you are looking at a really pixelated picture of a small very bright light against a pitch black background. All you can see in the photo to represent the light is a single big white pixel. Now imagine you are looking at a picture of a much smaller very bright light against a pitch black background. It will *still* look to you in the photo like a single white pixel. There isn't enough resolution to tell the difference " "This is because of the concept of angular resolution. Basically, any given aperture has a smallest possible angle that it can resolve, with the size of the angle being directly related to the size of the aperture. In our case the aperture is our eye, and it can see things of approximately an arcsecond or larger. Anything smaller than that, i.e. Stars, planets, etc. appears to be that size, regardless of how small it actually is because our eye simply can't bring it into focus on our retina at the true size. The light is blurred out to this minimum resolution, and thus most stars look the same size. + +Edit: The bigger the aperture, the smaller the size it can resolve as well. This is why we build telescopes with huge mirrors. On earth they are also limited by what is called seeing, but in space, telescopes can be made bigger and bigger and the image will become clearer and clearer. (In theory)" +866 Moon is in goldilocks zone but barren, what other criterions would declare a planet habitable? 6046 https://www.reddit.com/r/askscience/comments/7cvw2a/moon_is_in_goldilocks_zone_but_barren_what_other/ 1510669340 7cvw2a Planetary Sci. 2017-11-14 17:22:20 "Planet habitability is an active area of research, so there is a lot to say about it. But since your question specifically asks about planet atmospheres, I'm going to focus on that. + +An important factor to consider is the planet's escape velocity (how fast a particle of gas has to be moving to escape the planet's gravitational influence). Less massive objects (like the Moon and Mars) have lower escape velocities, so it is difficult for them to retain atmospheres. It's also important to remember that a strong magnetic field would only help prevent some forms of atmospheric escape (such as that involving solar winds). However, since there are multiple mechanisms by which a planet can lose it's atmosphere, the existence of a magnetic field is not always sufficient for atmospheric retention. + +So we know that planets with low masses have trouble retaining atmospheres, but what about planets with higher masses? It turns out that exoplanets with masses a few times greater than Earth's tend to have gaseous envelopes (sort of like a mini-Neptune). This is because the planet's gravitational force is so large that it can accrete a lot of gas when it's forming, and its escape velocity is so large that it's hard for the gas to escape. In these situations, the surface pressure of the planet would be too great for us to live on it (but who knows, maybe there are some aliens that can). + +The last thing to consider for habitability is atmospheric composition. Just because a planet has an atmosphere doesn't mean it's habitable (like Venus). To find out if a planet is truly Earth-like, we need to measure the composition of its atmosphere. + +So, in general, there are four things we need to determine to find out if a planet is habitable: its orbital period (to determine if it's in the habitable zone), its mass (to find out if it's massive enough to retain at atmosphere), its size (to find out if it has a thick gaseous envelope), and its atmospheric composition (to determine if it has an Earth-like atmosphere). Luckily, we can make all of these measurements today on both Solar System bodies and exoplanets, and our precision is only getting better with time. + +Edit: I forgot to mention one thing. Knowing the properties of the host star is also important when determining each of these properties. Specifically, we need to know the luminosity of the star to determine how far away its habitable zone is, we need to know the size of the star to determine the size of the planet, and we need to know the mass of the star to estimate the mass of the planet. Also, since the compositions of exoplanet atmosphere are determined by studying the light from the star that passes through or reflects off of the planet's atmosphere, it's important to characterize the star's spectrum. + +Edit 2: Also check out /u/Rekthor 's comment for some more great info about habitability!" "You're correct that the habitable zone is a flimsy concept, largely because there's such a wide variance in terms of converging conditions that have to be present to allow life (as we understand it) to form. Although, bear in mind that as we discuss this, we're understanding life *from an Earthlike perspective* (i.e. a carbon-based, homeostatic organism that can employ metabolic processes and reproduce), and since we're trying to draw a line with a single point, we're inevitably going to be hamstrung by that. + +/u/creamulum already has an excellent response breaking down the most important factors, but I'll try to focus on a few areas that are also (as we know) critical for the sustenance of those factors. These ones are particularly critical for Earth in particular, and we have reason to believe the same for other planets. + +1. **Geologic/geochemical activity.** A planet being able to grab an atmosphere is all well and good (in fact, it seems to be quite common, given that all planets in our solar system have them to one degree or another), but a planet being able to keep a stable atmospheric composition of elements that are conducive to is just as important for life to thrive. Atmospheric gases are (relatively) easy for a planet to get, whether by asteroid impacts or just simple gravity, but even if the planet has a magnetosphere to protect the gases from being blown away by the solar winds, the gases will eventually dissipate or condense or be ionized and vanish from the planet. **To keep those atmospheric gases**, one excellent way we know of is to have the planet be geologically active. Shifts in the planet's crust and heavy volcanism can release large amounts of gases (called ""outgassing"") into the planet's atmosphere, since the heavy pressure and temperatures in the mantle of the planet can break down, liquify and evaporate the solidified elements that originally formed the planet. Plate tectonics also plays a role by constantly moving around the surface of the planet, sucking volatile or toxic compounds back into the mantle and bringing up fresh rock (this is called ""crustal recycling""). These compounds can be anything (on Earth: water vapour, hydrogen, carbon, oxygen, silicon, sulfur, potassium, and especially nitrogen), but it's important to have them around *constantly* and *for long periods of time* to prompt life to arise. + +2. **Atmospheric patterns**. Another reason why the habitable zone is a flimsy concept is because even if a planet can keep an atmosphere composed of biogenic elements, that's no guarantee that it will be able to sustain a life-friendly climate (see: Venus and Mars). However, atmospheric weather patterns can help with this, because what kinds of patterns a planet has can make or break its potential for life, because the atmosphere can both redistribute cool or warm gases around a planet to make it a more stable temperature, or keep gases in one place for the same purpose. This is **very** complicated and I respect the shit out of planetary meteorologists who can wrap their minds around it, and there are many factors that influence this. Just one of them is planetary rotation: a planet spinning too slowly may not have enough motion in its atmosphere to properly distribute gases around the planet, but one spinning too fast may have significant storms or not maintain consistent-enough temperatures for life to for or thrive. Another factor is temperature: since hotter gases move faster and rise while cooler ones move slower and sink, planets that are too hot or cold (or who become as such due to an asteroid impact or catastrophic event) may have their atmospheres either—functionally—evaporate into space or literally freeze due to the extreme temperatures. + +3. **Stellar activity**. Another major factor we have to look at is what sort of star(s) the planet is orbiting around. Most of the exoplanets we've found so far orbit around red dwarfs: small, dim and relatively cool stars that make up more than 70% of the stars in the universe. However, red dwarves don't just have the problem of life-possessing planets needing to be so close to them that they'd be tidally locked (i.e. only one side faces the star at all times, due to gravitational tides), they're also extremely temperamental little stars. Red dwarfs regularly throw out solar flares that could ionize most of a nearby planet's atmosphere, and because they're so small, they can be covered in sunspots that hugely dim their radiation output, potentially freezing nearby planets as well. Conversely, any planets around high-mass stars would face similar troubles, and likely wouldn't be around long because high-mass stars generally live under one billion years before exploding as supernovae. Compare this to our Sun, for example: a G2-class star of medium size (that's still bigger than 90% of the stars in the universe) and middle-age, that only rarely undergoes significant solar events like sunspots, flares and Coronal Mass Ejections (CMEs). + +I could easily go into more factors (e.g. whether a planet is in a system with a lot of gravitational chaos that may cause it to be kicked out of its stellar orbit; a planet's neighbours that may ward off or increase the likelihood of suffering comet and asteroid impacts, etc.), but point being that there's a lot of them. We're building better telescopes all the time to investigate these factors though (especially atmospheric composition), and I suggest you check out the [James Webb Space Telescope](https://www.jwst.nasa.gov/)—set to launch next year—which will be specifically designed for that purpose if you're interested. + +EDIT: Link." +100 This coconut oil melted during a heat wave and later re-solidified. Why did it form this honeycomb structure? 6041 http://www.reddit.com/r/askscience/comments/3i1vd0/this_coconut_oil_melted_during_a_heat_wave_and/ 1440308013 3i1vd0 Chemistry 2015-08-23 8:33:33 "The images intrigued me, so I've looked into your query. It went a bit beyond chemistry, but science often does that, with phenomena crossing over between fields. + +First, it's important to note that this is not a crystalline solid, but rather an amorphous solid that you have: it's not a crystal structure / habit that's directing the structure that you have here! As coconut oil is [composed of a mixture of different fatty acids](https://en.wikipedia.org/wiki/Coconut_oil#Composition_and_comparison), it's highly unlikely that you would obtain a single crystal from it -- although sometimes single components may selectively crystallize: *e.g.* you can observe one component of olive oil precipitate when cooled. + +So we have a different process directing the structure here. It should be noted that hexagonal packing in 2D is the most efficient, hence it tends to be a natural default. But first let's look at why it's not just a continuous solid... + + +Typically (although water is not typical!) when a liquid solidifies, its density increases. [Lauric acid](https://en.wikipedia.org/wiki/Lauric_acid), the main component in coconut oil has a density of 1.007 g/cm^3 at 24 C, while at 50 C, it's density is 0.8679 g/cm^3 . That means as the liquid cools and solidifies, it is also contracting. When a material contracts due to temperature differences, it can create significant stress, as exemplified with [this hot Pyrex measuring cup being quickly cooled with cold water, and shattering](https://www.youtube.com/watch?v=OPetc9bpu5s) because of the stress induced quickly cooling. + +If we envision a surface contracting in 2D, there are two possible modes of contraction: either the whole sheet/surface can contract (essentially scaling down to a smaller version -- rare/unlikely), or the contraction can be localized (occurring at multiple points). Here's a [figure illustrating whole-sheet contraction vs localized contraction](http://www.gly.uga.edu/railsback/1121ColumnarJointing.jpeg). On average, the centres of contraction (when localized) will be [equally-spaced](http://www.nvcc.edu/home/cbentley/shenandoah/columnar_jointing.jpg), resulting in a [Voronoi diagram](https://en.wikipedia.org/wiki/Voronoi_diagram) which breaks the surface into polygons - if the centres are all equally spaced, the Voronoi diagram will be packed hexagons, such as in [these breath figure patterns](http://i.imgur.com/ESQqQTf.gif) (source doi: [10.1021/la035915g](http://www.doi.org/10.1021/la035915g)). + +The columnar shape is formed because there is a distinct direction of heat flow, with the material cooling from top to bottom, as shown in [this figure](http://www.engr.usask.ca/~reeves/prog/geoe118/images/joint4.gif). The result is that the joints (edges of the pologons; fissures; cracks) propagate downward as the (cooler) temperature front progresses toward the bottom of the jar. From the image posted, it appears that the joints are filled with higher-melting fatty acids. + +The result of this process of *cooling, contraction, and joint formation* can actually be observed in nature in the form of [columnar basalt](https://en.wikipedia.org/wiki/Basalt#Columnar_basalt) (also referred to as ""columnar jointing"" of basalt). Examples such as [Giant's Causeway](https://upload.wikimedia.org/wikipedia/commons/3/31/Drury_-_View_of_the_Giant%27s_Causeway.jpg) in Ireland or [Devil's Tower](https://upload.wikimedia.org/wikipedia/commons/4/46/Devils_Tower_CROP.jpg) in Wyoming. You can read up a bit about columnar basalt in [this post](http://blogs.agu.org/georneys/2012/11/18/geology-word-of-the-week-c-is-for-columnar-jointing/) by the American Geophysical Union, or [this good roundup from 2010](http://www.wired.com/2010/10/columns-not-just-for-basalt-anymore/) in Wired. Given the connection to columnar basalt, I think that we should actually get a specialist in geology to comment here... +" "It might be interesting to try to reproduce this effect. Are there any details you can share about what happened? It might be fun for a high school class to try out. + +Is this coconut oil from a particular brand? + +What kind of heat wave was it? How hot did it get, and how long did the heat wave last?" +778 Is there a reason we want more alcohol once we are buzzed? 6041 https://www.reddit.com/r/askscience/comments/6nketd/is_there_a_reason_we_want_more_alcohol_once_we/ 1500179217 6nketd Human Body 2017-07-16 7:26:57 "Without going into the neurochemical side of things (because others have somewhat covered it here, and it's exceptionally dirty when it comes to alcohol - multiple neurotransmitter systems are involved and even the metabolites of alcohol probably have their own effects)... there are significant expectancy effects associated with alcohol. That is, you expect to feel certain things, and therefore you do. The best example of this is when you start drinking you feel far more intoxicated at say 0.075 BAC than at the same level after you have stopped drinking. + +To directly answer your question, it'd be a combination of the euphoria produced by dopamine and endorphins reinforcing the behaviour of drinking, and the idea that more is going to be good. Then there's the positive social effects, relaxation of inhibition, conditioned cue responses, and lots more things telling you that it's a positive experience. This is all happening under your consciousness, so unless you kick in that prefrontal cortex and decide that anothery is a bad idea, off you go. + +The other thing is that alcohol is generally consumed over time more slowly than many other drugs. Also unlike other drugs, most of us can describe what overdosing feels like, which I'm guessing is the basis for your question. " "alcohol is a small molecule that interacts easily with many neurotransmitters compared to other drugs such as THC and cocaine. Drinking alcohol affects the gamma-Aminobutyric acid in your body producing an effect similar to valium which induces a feeling of relaxation and drowsiness. It also messes with your endorphins which gives you the ""I feel no pain"" mentality. All drugs which you can become addicted to affect the dopamine levels in your body which gives you a euphoric feeling as well as releasing Norepinephrine into your body which acts as a stimulant as well as depressant. Your adrenal glands also release adrenaline when you drink which contributes to the stimulant effect. Basically it feels good so you want more." +779 How do solar panels work? 6041 https://www.reddit.com/r/askscience/comments/6htaz5/how_do_solar_panels_work/ 1497704972 6htaz5 Engineering 2017-06-17 16:09:32 "Just as a warning this is a HIGHLY simplified version of how they work: + +(most) solar panels are made from two thin sheets of silicon. Silicon has a very regular crystal structure, but each layer has been mixed with a small amount of two other elements. What this accomplishes is that one layer has a crystal structure with some extra electrons and one has a crystal structure missing some electrons. + +When you connect both layers the extra electrons move over to fill the holes and it just sort of sits there. + +If you put this silicon sandwich in the sunshine, that sun has enough energy to knock an electron loose from one side, and then the electrons all shift places to fill in the new hole. If you hook a bunch of these small cells together into a big panel you can get the electrons to flow through a wire and you get electricity out of it. + +Keep combining more and more panels (made up of lots of tiny cells) and you can get a lot of energy. When the sun goes away all the electrons find all the holes and the whole things just sits there waiting for the sun to shine on it again. + +If you hook a battery into the mix you can charge that battery with the electrons (again very simplified) if you connect it to the grid you can power your home, or you can use it for anything else that you would use electricity for. + +EDIT: +A lot of people have asked about ""where the electrons come from"" or ""can the panel run out of them"" etc. As I stated above this is a VERY simplified explanation. The electrons don't actually move around, and again this is highly simplified, but think of it more like they bump into their neighbor which bumps into its neighbor, etc. They are not actually moving around the wire, or the panel. Hope that helps. + +Someone also asked why not one big panel instead of lots of little ones, and the answer to that is that no matter how big your panel is, it will always produce the same voltage. A little tiny solar cells pumps out about .5 volts so does a really big one. So if you want 12 volts, or 120 volts, etc you have to string the smaller panels together. In the same way you can take a whole bunch of AA batteries and get enough voltage to run something large, you can take a whole bunch of small solar cells and put them together in such a way that you can get the voltage you need. + +Different solar cells work with different efficiency in different wavelengths of light. Most commercial solar cells work best in full sun, but can still function in diffuse light. + +Solar cells seem to degrade a bit after about 25 years, and then slowly degrade after that, some very old solar panels from the 50's are still going strong with relatively minor degradation. With the current dramatic price drop in solar cells, it is very likely that the roof or the stand you have them affixed too will wear out before they do, and even then it will be nearly free to replace them in the future (assuming costs keep going down and efficiency keeps going up, which it can still do for a long time before we reach limits imposed by physics). + +Here is a cool chart of all the different solar cells being tracked by efficiency. (how much sun they turn into electricity). https://www.nrel.gov/pv/assets/images/efficiency-chart.png + +as you can see some cells are doing pretty good (46%), although they might be very expensive. + +Roughly 1000 watts of solar energy falls on 1 square meter of ground, so at 46% a meter of that solar cell would make (roughly) 460 watts of energy. + +As you can see as the price of the cells comes down, as does the price of battery and inverter tech, solar has a very real chance of powering just about the entire world. Combined with smart grids, grid energy storage, electric car energy storage, and increases in efficiency, solar and other renewables are clearly the energy supply we should be backing. +" "Solar cells are made out of semiconductors which absorb light at specific wavelengths. That absorbed light excites electrons, which ionize, leaving a net negative charge on one atom and positively charged ""hole"" where the electron used to be. A small applied voltage causes the electron and hole to move in opposite directions to electrodes where they become electric current." +1796 How has the flu been affected by the lack of people getting it? 6032 https://www.reddit.com/r/askscience/comments/lqnv37/how_has_the_flu_been_affected_by_the_lack_of/ 1614101254 lqnv37 Medicine 2021-02-23 20:27:34 "Based on info from one of the flu centers we work with having fewer people getting the flu means there's less data to understand the prevalence per strain and where they're appearing (since there are different vaccine formulations for different parts of the US). It adversely impacts our ability to design a vaccine formulation that's as effective as it might otherwise be. On one hand there are ""types"" of the virus against which we vaccinate that are effective against multiple strains that are always present in the vaccine. On the other hand we cannot vaccinate against all strains because the components of the formulation become mutually exclusive (thus we have to blend based on what we predict to be the hot-strains for a given year). + +In a sense, it's a modification on the saying ""a shot in the dark."" In this case the room's not pitch black, but it's definitely dimmer than it would otherwise be. Get your flu shot regardless! They have a cumulative effect." Three things. 1) The BASE mutational change rate, a function of time, will remain the same. Oxygen and nucleic acid interect to alter the bases at a known evolutionary rate. Flu has a substitution rate as a base that is known. You could argue that it does not radically change, but change my mind, it's relatively small. However 2) The IN-HOST mutation rate will be reduced overall as a function of the population, resulting in potentially fewer veriations in the virus pool, because there are fewer overall pathogen-host interactions. This is something like 10e-6 changes per nucelotide site infection cycle. Then, fewer infectious churn, result in fewer change. This is good!! It is known that being in a host accelerates the change of a virus somewhat. If you look at Marc Tompkins work in ferrets, you sequence a virus, put it in the host, incubate, and then get back out virus from a nasopharygeal swab in a week, what you get out is a slightly different sequence than what went in. I do not know how much, and for which host and segment combos you want to measure, sorry. But this phenomenon is because a host immune system selects differently against mixtures of virues because people have different antibody repertoires. The virus survivors move along, the ones that were proteolyzed do not. This is also known. Last 3) the REASSORTMENT will be radically reduced. I mean, a lot. So, because there are fewer infections, the chance of having two different strains from a pig and a person, or an avian passerine, or a dabbling duck, will be radically reduced. This goes down as a function of the two, or possbly the square. Two rare diseases do not usually mix. If you have fewer single infections, you have fewer double infections (different strains) required to mix segments of flu from one species to the next and thereby create a new reassortant like 2009 pandemic H1N1. Overall we are better off for having fewer flu infections, because it takes some of the novel variability off the table. We fight the newnes and variability with new vaccines each year. Fewer variations are out there because the disease transmission is less hot. We are better off for masks. There is a benefit to wearing them for corona. Source: 15 years of virus surveillance work under NIAID. Thanks +520 What causes the randomness of internet speeds, even on Ethernet? 6021 https://www.reddit.com/r/askscience/comments/5fbsab/what_causes_the_randomness_of_internet_speeds/ 1480341634 5fbsab Computing 2016-11-28 17:00:34 "There are many factors that come into play in internet connections, almost too many. The fact is, we have been studying the internet as long as it existed, and there are multiple papers published every year on traffic statistics, models, case studies on specific use cases, new protocols and protocol enhancements, census data, performance analyses, client characteristics, etc. Since our networks constantly change, their behaviour also does so. Characteristics of traffic of DSL users today may not be the same in 5-10 years, and has changed a lot in the last 10-15. + +Given the question is so broad, there is a lot of things to be said, so I'll stick with the most well-established ones. + +1. Typical DSL clients' web traffic has a few interesting characteristics: + * your upstream bandwidth limits your downstream throughput [Charzinski, 2000](https://pdfs.semanticscholar.org/45bb/4eda79f40960749ba4dd7386ffa661de965f.pdf) + * for some ISPs, there is an observed drop in performance early in the morning and late in the evening, performance variability increases for _all_ ISPs during peak hours [Sundaresan et al, 2011](http://conferences.sigcomm.org/sigcomm/2011/papers/sigcomm/p134.pdf) + * the _last-mile latency_ and jitter are lower than upstream, and losses are usually bursty - if you lose one packet, it's more likely you'll lose the next one, too + * excessive buffering tends to increase latency, just like insufficient buffering, but tends to increase jitter, contrary to insufficient buffering (a phenomenon aka ""bufferbloat"") + * there is no single best ISP for everyone + +2. The principal someone behind the ""randomness"", or to put it differently the exhibited negative impact, is _self-similarity_. Self-similarity is the property of a time series (in this case) to exhibit the same characteristics in varying scales. As an example, a series which exhibit bursty behaviour at a wide variety of scale. Surprisingly, this was shown for Ethernet as far back as 1995 by [Leland et al](http://ccr.sigcomm.org/archive/1995/jan95/ccr-9501-leland.pdf), and [Crovella & Bestavros](http://www.cs.bu.edu/~crovella/paper-archive/self-sim/journal-version.pdf) showed its adverse effects on HTTP traffic. + +I will stop here, as I realise I've spent about an hour trying to summarise this stuff in my head and only typed a handful about it, and I've left out huge amounts of literature on wireless & mobile networks, medium differences, caching, and network churn. If you have any specific questions ask away and I'll do my best to answer or at least point you to relevant literature." One factor is that when you are on the Internet you typically are using TCP. What TCP does is continually try to send more data. When the maximum is reached and the network is full a loss event will occur. When it does TCP will cut the amount of data it is trying to send, typically it will cut down to nothing and increase exponentially, or it will cut in half and increase linearly. This will continually happen and so the speed will always fluctuate. +1062 Why is it harder to send a spacecraft to the Sun than away from the Sun? 5997 https://www.reddit.com/r/askscience/comments/96f31o/why_is_it_harder_to_send_a_spacecraft_to_the_sun/ 1533975539 96f31o 2018-08-11 11:18:59 "on the scale of the solar system, the sun is small enough it can largely be considered a point source. Now since we are starting from earth, which is in orbit around the sun, any satellite launched will also be in orbit around the sun. as long as something is orbiting the sun, it wont actually crash into the sun, just move in a ellipse around it. in order to actually crash into the dot that is the sun, the spacecraft would need to basically stop being in orbit and instead be in free fall. This requires shedding ALL of the lateral velocity, which earth has a lot of. +" "Earth orbits the Sun with about 30 km/s. To reach the Sun (or get very close), you have to cancel all this speed - accelerate backwards by nearly 30 km/s. That is too much for rockets. In addition to a very powerful rocket you need tricks like fly-bys at the inner planets to reduce your tangential velocity. + +At the distance of Earth, the escape velocity from the Sun is 42 km/s (""exactly"" sqrt(2) times the orbital velocity). To escape, you can accelerate forwards by 12 km/s. That is something rockets can do." +101 "Why is it normal for children in practically all cultures to call parents ""Mother"" or ""Father"" rather than their real names?" 5995 http://www.reddit.com/r/askscience/comments/3g9y1t/why_is_it_normal_for_children_in_practically_all/ 1439063924 3g9y1t Anthropology 2015-08-08 22:58:44 "The answer is sort of backwards because it's really the parents' doing, not the children. The earliest sound shapes that infants tend to produce are usually a consonant followed by a vowel. The easiest consonants for a baby to produce are ones that don't require a lot of fine control of the tongue and lips, so sounds like /m/, /b/, /p/, /d/ tend to emerge first with a generic mid or back vowel sound, such as /a/. This results in early babbling and proto-words that often sound like /mama/, /dada/, or /papa/ across a large number of languages. Parents throughout history have likely assumed that the first sounds that their children were making were referring to them or seeking their attention, so these early proto-words became associated with or evolved into the words for 'mother', 'father', 'grandmother' and other caretakers. This also helps to explain why /mama/ is such a common word for 'mother' across many unrelated languages (Chinese, Swahili, English, Navajo...). + +Edit to add sources - + +For the development of speech sounds: + +>Sander, E.K. (1972). When are speech sounds learned? Journal of Speech and Hearing Disorders, 37, 55-63. + +>Smit, A.B. (1986). Ages of speech sound acquisition: Comparisons and critiques of several normative studies. Language, Speech, and Hearing Services in Schools, 17, 175-186. + +For the lexicalization of early words as a result of parent-child interactive routines: + +>Hollich, G.J., Hirsh-Pasek, K., Golinkoff, R. M. (2000). Breaking the language barrier: An emergentist coalition model for the origins of word learning. Monographs of the Society for Research in Child Development 265, 65(3). + +For 'mama' and 'papa' specifically: + +>Jakobson, R. (1962) ""Why 'mama' and 'papa'?"" In Jakobson, R. Selected Writings, Vol. I: Phonological Studies, pp. 538–545. The Hague: Mouton." "Humans use kinship terms as a way to show and make social meaning--across multiple cultures and languages parent-child relationships are immensely meaningful, and so what you call your parent means a lot. + +1. Using kinship terms of address is a *footing* move, reflecting and constructing social power. For example, among the Shona people, parents have the power to switch from affectionate kinship terms/nicknames to first name use, to show anger to reprove their children, but that power is one-sided: children can never do the same thing back. Similarly, in Japanese culture, personal names are only used by senior family members speaking to junior members--parents may call their children by their first name, but children may not call their parents back by their personal name. +2. Kinship address terms are variable and context-dependent. In America, children call their parents Father, Mother, Dad, Daddy, Pop, Mom, Ma, and so on. This variable between families--some children will use ""Pop/Ma"" to show intimacy, while others use Father/Mother to show respect. This is also situationally variable, as parents and children try to show closeness or distance based on what's happening at the moment. + +Some further reading: + +>Fischer, John L. ""Words for self and others in some Japanese families."" American Anthropologist 66, no. 6_PART2 (1964): 115-126. + + >Schneider, David M., and George C. Homans. ""Kinship terminology and the American kinship system."" American anthropologist 57, no. 6 (1955): 1194-1208. + +>Mashiri, Pedzisai. ""Terms of address in Shona: A sociolinguistic approach."" Zambezia 26, no. 1 (1999): 93-110. + +" +960 How do surgeons avoid air bubbles in the bloodstreams after an organ transplant? 5985 https://www.reddit.com/r/askscience/comments/7rbyim/how_do_surgeons_avoid_air_bubbles_in_the/ 1516301619 7rbyim Medicine 2018-01-18 21:53:39 "Air bubbles in the bloodstream (called air embolisms when they interfere with circulation) are a concern following organ transplantation because they can cause circulatory, and even neurological, problems. To preserve the organ during transportation, the blood in the organ is replaced with a solution designed to preserve tissue function following explantation. During the transplantation process, the organ must be connected to the circulatory system of the patient (individual blood vessels are connected through a process called anastomosis). Surgeons will connect arteries first (the inlets for the organ) before connecting the veins (the outlets for the organ), and thereby allow the patient's own blood flow to clear both the preservative solution and any air bubbles from the new organ. + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2845451/ + +Edit: Clarification on what qualifies as an air embolism thanks to /u/Tombomcfaren." "Awww nobody will see this since I'm late to the party... but I work in heart surgery and can tell you how we get air out of the heart after we open it. It's also important to know that air in the arterial system and left side of the heart is waaaaay more dangerous than heart in the venous system and right heart. This is because the air goes to the lungs before it goes to the left heart. Once in the aorta, air can enter the coronary arteries that supply blood to the heart and the brain. In the heart, air can cause ventricular fibrillation and in the brain it can cause a stroke. + +So to keep this from happening we utilize the clamp that is placed across the aorta (cross clamp) and vents that are inserted in the left ventricle (the chamber that pumps blood to the body) and the aortic root (where the aorta exits the heart). These vents are connected to pumps on the cardiopulmonary bypass pump (heart/lung machine). Before the cross clamp comes off the aorta, the perfusionist (person running the heart/lung machine) will fill the heart with blood. This causes the heart to contract and pushes blood out through the vents. If there is air, it hopefully exits the heart through the vents with the blood. At the same time, an anesthesiologist or cardiologist is looking at an echocardiogram, which allows them to see the air in the heart and aorta. The patient will be placed in a head up position so that the air will rise, and if there is a large amount of air, the surgeon may shake the patient. When this is done, the cross clamp can be taken off and the heart hopefully begins to resume normal function. + +Edit: a word + +Edit 2: obligatory thanks anonymous user for my first Reddit gold!" +1336 Why is gold used on connector ends, like on usb-connectors for gaming mice, when copper has lower electrical resistivity? 5970 https://www.reddit.com/r/askscience/comments/bs1nna/why_is_gold_used_on_connector_ends_like_on/ 1558610134 bs1nna Physics 2019-05-23 14:15:34 Gold doesn't tarnish as easily. "Gold does not tarnish or corrode, while copper corrodes very rapidly, and the actual conductivity of gold is not significantly lower than copper, but the kicker is that the coating is so thin that it does not increase the resistivity of the whole circuit by any relevant amount. + +​ + +There is absolutely no benefit gained by keeping the last 0.1mm of a cable copper, when the benefits of anti tarnish/corrosion are so important to the reliability and lifespan of a product," +867 Is there a limit to how many elements there can be? 5967 https://www.reddit.com/r/askscience/comments/6xl9qb/is_there_a_limit_to_how_many_elements_there_can_be/ 1504350585 6xl9qb Chemistry 2017-09-02 14:09:45 "Yes, probably. But we don't know what it is, and it's likely higher than what we're currently capable of producing experimentally. + +The IUPAC has strict criteria for what can be considered an ""element"". One of this criteria is that it has at least one isotope with a lifetime at least on the order of 10^(-14) seconds. + +As you go up in Z around the superheavy elements, they become very unstable to alpha decay and spontaneous fission. If you extrapolate the lifetimes to heavier species based on trends in nuclei that we know of, eventually you'll probably reach a point where no heavier species has a lifetime which meets that criterion in the definition of an element." [deleted] +1063 Do satellites, like the Hubble Telescope, get dirty? 5943 https://www.reddit.com/r/askscience/comments/9agylm/do_satellites_like_the_hubble_telescope_get_dirty/ 1535302174 9agylm 2018-08-26 19:49:34 "Yes. + +The space environment is pretty nasty. Atomic Oxygen, UV Radiation, Meteoroids/Orbital Debris all cause pretty severe surface degradation. + +Here's a video explaining the effects of atomic oxygen https://youtu.be/bjyv7bK9X74 + +Here's a video explaining the effects of radiation on spacecraft https://youtu.be/lL5JnfWA6CY + +And here's a video explaining the effects of charged particles https://youtu.be/GITtlkx2-Tw + +And here's a comprehensive NASA guide on the environmental effects of space https://www.nasa.gov/sites/default/files/files/NP-2015-03-015-JSC_Space_Environment-ISS-Mini-Book-2015-508.pdf + +Edit: and here's a good picture of the Russian Service Module on the ISS, that has been exposed to space for a long time. Look closely and you can see how dirty the once white surfaces are now. http://iss.jaxa.jp/spacerad/images/img_dos01_e.jpg" "The answer is.... sort of. However dust in space tends to be traveling freakishly fast, such that it turns into a plasma on impact. This creates microscopic pits in the outside of the craft. This is like an extreme form of sandblasting. Fortunately space is pretty empty and this damage occurs slowly. This fact makes the design of things like solar panels challenging, for example. It will also create a hazard to sensitive optics like mirrors or lenses. Optics need to be protected, as much as reasonably possible. + +The James Webb Space Telescope is a notable exception to this. The reason for the lack of shielding around it's primary mirror is due to it's sheer size and the need to fold and unfold it to fit inside the aerodynamic shroud of the launch vehicle. Shielding materials were considered too much of a weight penalty and could potentially cause mechanical jams during the unfolding process. + +Instead, digital image processing will be used to remove the effects of damage to the mirror, which can be tracked and accounted for. + + A second hazard, at least in low earth orbit, is that most of the ambient gas is reactive atomic oxygen. This can slowly degrade and erode carbon-based materials like plastics or paint over time. + +This is less of a problem in higher orbits. + +The third problem is high energy charged particles both from the sun and from deep space. Events like solar flares can bombard spacecraft with a storm of energized electrons. This could potentially cause a complete failure of electronic circuits, at least temporarily. Devices used in space need to be designed to be ""hardened"" against radiation. + +The most troublesome form of radiation is high energy Cosmic Rays. These consist of atomic nuclei with extreme kinetic energy and thus high penetrating power. Generally cosmic rays are bare protons or helium nuclei, however larger nuclei are also encountered. These are like atomic bullets and cause permanent microscopic damage to the structure of anything they pass through. Integrated circuits are most vulnerable to this radiation which is difficult to shield. Over time this can degrade IC chips to the point where they lose function. There is no simple solution to this problem. " +1337 Why are interplanetary slingshots using the sun impossible? 5940 https://www.reddit.com/r/askscience/comments/c6dj8l/why_are_interplanetary_slingshots_using_the_sun/ 1561683089 c6dj8l Astronomy 2019-06-28 3:51:29 "If you slingshot around the sun, you cannot gain any extra velocity from your maneuver (when you dive towards the Sun you gain kinetic energy and as you leave its gravity well, you gain back the gravitational energy) thus leaving you exactly the same as before; this is because within the Solar system the Sun isn’t moving. + +When you slingshot around the planet, because the planet is moving, you can go with the planet’s orbital motion around the Sun and use the planet to accelerate you as you move around it; essentially because the planet is moving ahead of you, its gravity pulls you along and accelerates you. And vice versa if you wish to slow down. + +The key takeaway is that the celestial object has to be in motion; that motion is where you take the energy from. + +You can slingshot around the Sun on an interstellar journey; you can also use the Sun as a sling and accelerate as you orbit it to save fuel that you would otherwise have to spend changing direction, using its gravity well to essentially change direction for free. + +You just can’t gain energy from it like you can from other planets in an interplanetary journey because it’s stationary and therefore doesnt move “ahead” of you and pull you along. + +Edit: wow, this blows up hard, thank you kind redditors for the platinum! I will try my best to answer your questions, but I know I missed some, so sorry about that, there were simply too many. If any of you are interested about this or still confused, I strongly recommend Kerbal Space Program; it is an educational game that will show you how orbital mechanics work. After enough Kerbals died you WILL understand interplanetary slingshots on an intuitive level. + +I will also take this opportunity to clear up some confusion: + +1) The Sun is moving, why is it consider stationary? + +Yes, the Sun is moving, but it is moving with the solar system as a whole; thus if you are only considering interplanetary travel (by definition, within the solar system), because everything already has the Sun's motion around the galactic centre we can discount this motion and treat the Sun (and the whole solar system) as stationary to simplify things. A simple analogy: if you are trying to calculate the route from Venice to Paris, because everything on Earth shares the Earth's rotational and orbital velocity, you can treat the Earth as stationary and discount its rotational and orbital velocity. + +2) Couldn't you switch your frame of reference so that the Sun is moving? Why wouldn't gravity assist work then? + +Someone can correct me if I'm wrong, but my understanding is that if you switch your frame of reference to say, Earth, the Sun will move in such a way that it will always cancel out any gravity assist; you will gain no net momentum or lose no net momentum to the Sun no matter what. This is still within the solar system as well. + +3) Can you slingshot around the Sun if you are travelling from outside the solar system? + +Yes, because in this case you have to switch your frame of reference to include your origin, which would mean the Sun can no longer be considered stationary. If the Sun is moving towards your destination in some way (ie, a component of its velocity is towards your destination) you can get a gravity assist from it. + +4) The Sun orbits around the barycenter (center of mass of the solar system); even if you are looking at the solar system only the Sun cannot be consider stationary because of this. + +The Sun accounts for 99.8% of the mass in the solar system; the barycenter of our solar system is actually within the Sun itself. So while technically correct, this orbital motion can effectively be discounted because it is so minute. + +5) Does this work in reverse? Can you slow down with gravity assist? + +Yes, you just have to go against the motion of the planet instead of with it. + +6) Can you alter the orbit of {insert planet name} by doing this many, many times, or with a very, very heavy spacecraft? + +Yes. Planets are really, really, really big though, so be prepare to do this many, many, many, many, many times, or just many, many, many times with a very, very heavy spacecraft. + +7) Is the slingshot maneuver in Interstellar anything like this? Why does it work then? + +Interstellar is, at the end of day, a movie. There are some physics it got right (the depiction of the supermassive black hole and time dilation for example), but many parts it got wrong. I don't think the slingshot maneuver at the end is one of the parts it got right. The film is necessarily vague on details when it comes to those part anyway (as it should be; it's not a scientific disposition on orbital mechanics), and I would not use it to think about physics in a realistic way. + +8) What about Star Trek slingshot time maneuver? + +Almost definitely complete fantasy. How would gravity even interact with superluminal objects? Does the addition of kinetic energy speed or slow a superluminal object? Why wouldn't every warp-capable civilizations just do this when they are losing a war?" The energy a spacecraft uses to slingshot comes from stealing the energy from a planet's rotational speed around the sun. Here's a [graphical version](https://i.stack.imgur.com/gSun7.jpg). Relative to the rest of the solar system the sun isn't moving. Thus there is no energy to 'steal'. +1338 Are micro black holes even dangerous? 5934 https://www.reddit.com/r/askscience/comments/cj9hfd/are_micro_black_holes_even_dangerous/ 1564396431 cj9hfd Physics 2019-07-29 13:33:51 "> as I understand it black holes interact only through gravity, so if there was a black hole with a mass of the Earth, the Moon wouldn't fall in it, cause gravitation will remain the same. + +This is correct. If you take a pebble and then compress it to such a density that it becomes a black hole, the gravitational attraction of the pebble-hole doesn't change. Any objects that were being pulled towards the pebble will still be pulled towards the pebble-hole, but any objects that weren't affected by the gravitational pull of the pebble still won't care about the pull of the pebble-hole. + +The range at which a micro black hole would be able to interact with other particles through its gravity in a meaningful way would be extremely small. In fact, if the micro black hole would be charged, it's likely that its electromagnetic interaction would be stronger than its gravitational pull, because electromagnetism is in general a stronger force than gravity. (EDIT: Maybe not, see [this comment](https://www.reddit.com/r/askscience/comments/cj9hfd/are_micro_black_holes_even_dangerous/evc77ru/)) + +In addition, it's commonly assumed that micro black holes evaporate very rapidly after being created through a process called Hawking radiation (although this process hasn't been observed experimentally yet, primarily due to the difficulties of detecting Hawking radiation). + +> If that's true - what was fear with micro black holes in CERN all about. + +Unfounded anxiety over things that have an ominous sounding name. + +> but hypothetically are micro black holes even dangerous? + +They were dangerous to one of the detectors at CERN, but not in a way you'd expect. Early versions of the processing software of the ATLAS detector had a small memory leak with each particle created in an event. Since the decay of a micro black hole would cause the creation (and detection) of a very large number of particles, the memory usage of the process would spike and it would crash. I've heard ATLAS researchers joke that such a software crash would be a good indication of the discovery of a micro black hole, but that they might have issues getting it published. To the best of my knowledge, this bug was resolved quite some time ago. Also, no micro black holes were detected. + +EDIT 17:30 UTC + +Multiple comments are discussing the gravitational pull of our ""pebble-hole"" and wondering if, assuming that such a micro black hole is stable, it could interact with nearby air particles (or other particles), swallow them up, grow, and eventually start to increase its gravitational pull. + +The short answer is ""No"". + +Gravity is a very weak force at those scales. For example, for a pebble of 1 kg (FYI: that's a rock, not a pebble at this point) you would obtain a pebble-hole with a Schwarzschild radius of 10^(-27) m. That means that anything that comes within 10^(-27) m from the pebble-hole would be definitely swallowed up, including light. + +How big is 10^(-27) m? Consider the radius of a hydrogen atom, the average distance between the proton and the electron making up this atom. This number is also known as the Bohr radius and is approximately 5.3 * 10^(-11) m. + +The space between matter, even solid matter, is extremely empty. The ratio of ""things"" to ""empty space"" at the microscopic level is much lower than it is at the macroscopic level (in star systems and galaxies). As such, the probability of a micro black hole interacting gravitationally with other matter is exceptionally small. + +And even if, in the case of some cosmic luck, a micro black hole were to swallow another particle, it wouldn't matter much. Lets take a medium-sized molecule, abundant in our atmosphere: nitrogen. 1 nitrogen molecule has a mass of approximately 4.6 * 10^(-23) gr. To double the mass (and gravitational force) of a pebble-hole of 1 gram, it would need to swallow up about 2 * 10^(22) nitrogen molecules. And considering a single interaction is already extremely unlikely, you can see what that means for the likelihood of the mass of a micro black hole ever increasing by any meaningful (or even measurable) amount." [deleted] +1064 What are the actual negative effects of Japan’s 2011 Fukushima Daiichi nuclear disaster today? 5902 https://www.reddit.com/r/askscience/comments/8yfpeh/what_are_the_actual_negative_effects_of_japans/ 1531445301 8yfpeh 2018-07-13 4:28:21 "The 2 events have been compared, of course. I refer you to: + +[Steinhauser, G., Brandl, A., & Johnson, T. E. (2014). Comparison of the Chernobyl and Fukushima nuclear accidents: a review of the environmental impacts. Science of the Total Environment, 470, 800-817.](http://www.fcav.unesp.br/Home/departamentos/morfologia/ELISABETHCRISCUOLOURBINATI/materialdidatico/07-comparison-of-the-chernobyl-and-fukushima-nuclear-accidents-2014.pdf) + +which have the following to say: ""*In almost every respect, the consequences of the Chernobyl accident clearly exceeded those of the Fukushima accident. ... the amount of refractory elements (including actinides) emitted in the course of the Chernobyl accident was approximately four orders of magnitude higher than during the Fukushima accident. ... In the course of the Fukushima accident, the majority of the radionuclides (more than 80%) was transported offshore and deposited in the Pacific Ocean. Monitoring campaigns after both accidents reveal that the environmental impact of the Chernobyl accident was much greater than of the Fukushima accident. Both the highly contaminated areas and the evacuated areas are smaller around Fukushima and the projected health effects in Japan are significantly lower than after the Chernobyl accident.*"" + +That being said, in the specific case of Fukushima, a large part of the radioactive emissions were carried out to the Pacific, away from inhabited territory. In the ocean, mixing and turbulence have been strong factors in diluting the contaminants to levels where they pose no threat to the food supply. In particular, see [Fisher, N. S., Beaugelin-Seiller, K., Hinton, T. G., Baumann, Z., Madigan, D. J., & Garnier-Laplace, J. (2013). Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood. Proceedings of the National Academy of Sciences, 110(26), 10670-10675.](http://www.pnas.org/content/pnas/early/2013/05/30/1221834110.full.pdf) whose frank and clear conclusion deserves to be quoted at length: + +""*This study shows that the committed effective dose received by humans based on a year’s average consumption of contaminated PBFT (pacific blue fin tuna) from the Fukushima accident is comparable to, or less than, the dose we routinely obtain from naturally occurring radionuclides in many food items, medical treatments, air travel, or other background sources. Although uncertainties remain regarding the effects of low levels of ionizing radiation on humans, it is clear that doses and resulting cancer risks associated with consumption of PBFT in eastern and western Pacific waters are low and below levels that should cause concern to even the most exposed segments of human populations. Fears regarding environmental radioactivity, often a legacy of Cold War activities and distrust of governmental and scientific authorities, have resulted in perception of risks by the public that are not commensurate with actual risks*"" + +I guess that one thing you have to keep in mind is that as radioactive elements disperse away from their source, they also dilute themselves until they hopefully reach concentrations which have an insignificant incidence on human health. In the case of Fukushima, this was reached sooner than in Chernobyl because the amount of radioactive elements produced was far less, and because much of it was deposited in that greatest of all dilution patches: the Pacific Ocean. It is also worth noting that these radionuclides will progressively ~~eliminate themselves though fission~~ reach stability through decay (EDIT: thanks to /u/Rishfee for the correction), thus bringing their concentrations even further down. + +You also bring up the question of the suitability of agricultural products. This was looked into by [Merz, S., Shozugawa, K., & Steinhauser, G. (2015). Analysis of Japanese radionuclide monitoring data of food before and after the Fukushima nuclear accident. Environmental science & technology, 49(5), 2875-2885.](https://pubs.acs.org/doi/full/10.1021/es5057648) They noted that maximum concentrations of radioactive caesium peaked successively, first in vegetables, then in mushrooms, followed by beef and boar. Maximum concentrations were reached within a few months of the accident, and then decreased rapidly. + +To put things into perspective, [the initial megathrust earthquake (9.0–9.1 (Mw)) and resulting tsunami](https://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami) were far more damaging. Those were thoroughly brutal and caused 15,896 deaths, 6,157 injured, and 2,537 people missing and an estimated economic cost of US$235 billion. Not that the area needed a nuclear disaster on top of things ... + +EDIT: thanks for the gold!" "I interviewed a man with a PhD in engineering from Waterloo, and also worked at NASA. During the meltdown, he was measuring levels of atmospheric pollution, mainly CO2 and Methane, but he also looked at the level of radiation released. He said that the level of atmospheric radiation peaked the day after the meltdown, and rapidly decreased for the next 10 days until it was indistinguishable from the background. If the peak atmospheric radiation had stayed the same for those 10 days, he said you would be exposed to less radiation than eating 1 extra banana. +Due to the radiation there were 0 deaths, and only 2 people exceeded the radiation exposure limit. https://www.google.ca/amp/s/amp.theguardian.com/world/2011/may/31/japan-nuclear-plant-explosion +The only deaths that he was aware of were from the evacuations and the massive oil spill (that also affected the nuclear plant)." +961 "Study ""Caffeine Caused a Widespread Increase of Resting Brain Entropy"" Well...what the heck is resting brain entropy? Is that good or bad? Google is not helping" 5888 https://www.reddit.com/r/askscience/comments/7xa638/study_caffeine_caused_a_widespread_increase_of/ 1518536053 7xa638 Biology 2018-02-13 18:34:13 **This post has been locked**. A few good answers are present and all the new comments are either talking about personal anecdotes with caffeine or are bad explanations of entropy. "Ph.D. in Psychology/neurophysiology here. It's hard to reduce this to an ELI 5 level, but I'll give it a shot. Say you're driving through a small, simple town with one street light at that town's rush hour: all the traffic will come up, pause, then go with a regular rhythm. That would be a high degree of order (the opposite of entropy). Not much communication or flexibility needed, and its the mental equivalent of a deep sleep. If you compare that to downtown tokyo, there are people everywhere, going in all directions on foot and in cars and bikes, etc. That's a lot of information flowing in many directions, and if we turn them in to brain cells they are busy, active, and adaptable. Chaotic systems have more energy and more going on than simple systems, and we measure this in terms of entropy (which is honestly a misnomer, it's all meaningful, but the math for entropy works as a best model). + + +All of this is fueled by blood flow to get oxygen to the cells, but it's not a 1:1 correlation. Having said that, the main measure they used is a measurement of where water/blood goes in the brain (fMRI). The study said that since caffine restricts blood flow, it should slow the brain down, but the chemical makes the cells all over the brain fire more easily, so lower blood flow but higher levels of cross-talk and entropy. + +So is it good or bad? Yes. It's good for the short term, making thinking more efficient and clear, but it's not good for the long term because you're making the cells work harder with less fuel. + +That also explain why withdrawal from caffine causes headaches, btw. Withdrawal from a chemical causes the opposite of the chemical's effect, so when you don't drink coffee after getting addicted, the blood flow in the head increases, causing higher pressure, which leads to pain." +1065 Why does rain fall as individual droplets and not sheets or continuous lines? 5876 https://www.reddit.com/r/askscience/comments/966gtm/why_does_rain_fall_as_individual_droplets_and_not/ 1533903822 966gtm Earth Sciences 2018-08-10 15:23:42 "Long streams and sheets simply are not stable and would break up into droplets, due to surface tension. Spheres are the least energy form for free floating water and that's what it goes to. + +Droplets form in the atmosphere when rising air cools to the dew point and starts forming droplets or ice crystals which start forming clouds. When droplets grow heavy enough, they fall and we get rain. + +Incidentally, the tear drop shapes used for taps and weather symbols and stuff is pretty much only seen when a drop hangs off something and drops off. Once falling the drop starts to pull toward spherical again." [deleted] +780 The existence of heavy elements on Earth implies our Solar System is from a star able to fuse them. What happened to all that mass when it went Supernova, given our Sun can only fuse light elements? 5867 https://www.reddit.com/r/askscience/comments/6hzc1u/the_existence_of_heavy_elements_on_earth_implies/ 1497787790 6hzc1u Astronomy 2017-06-18 15:09:50 "The solar system didn't emerge from a single larger star, rather it emerged from an ordinary molecular cloud, like any other star. The metals (heavy elements) originated from **many** star that went supernova and threw out their interior into interstellar space which mixed with the already existing gas clouds. + +New stars can't form from single supernova remnants because the gas is both hot and expanding, while stellar formation needs gas cold enough to contract. " "heavier elements were seeded through the universe by supernova. Specifically by Population III stars and the large examples of Population II stars. + +Supernova are unimaginably violent and energetic. The matter blown off by them from them isn't just flung out a little distance and then pulled back in, the shockwave is moving at thousands of kilometers per second. the Gravity of the solar system doesn't stand as chance. Given a bit of time, that matter gets spread and distributed over a very very large distance. + +And then another star goes supernova. And then another. And then a few million more. And so on. Each of them flinging those heavier elements out into their galaxies/protogalaxies. + +In the meantime star formation hasn't stopped. In the heart of giant molecular clouds throughout the galaxy, hydrogen is happily collapsing into new protostars, except instead of mostly pure hydrogen with bit of helium and a very little bit of lithium those first stars have spread heavier elements into the mix. This actually accelerates star formation in those molecular clouds since the higher density particles make it a bit easier for gravity to do it's thing. + +A few billion years of supernovae and there's now quite a lot of heavier elements out there. Relatively speaking anyways. The build of hydrogen in whatever molecular cloud are sun formed in collapsed in this ""modern"" era of star formation. Hence why we're here sitting on sitting on a rock mostly made up of those heavier elements talking about it. + +" +645 Why does a room go dark when you turn out the light - what happens to the light? 5850 https://www.reddit.com/r/askscience/comments/63ysfx/why_does_a_room_go_dark_when_you_turn_out_the/ 1491547082 63ysfx Physics 2017-04-07 9:38:02 "The light emitted by light sources such as lamps is absorbed by the objects in the room. We see these objects because they reflect part of the light that hits them, but every time they're hit a significant part of the incoming light is absorbed. If there's no active light source, it takes no more than a microsecond for almost all the light to be absorbed. + +The absorbed light is turned into heat, so the objects in the room are heated up very slightly by a light source." "Ask yourself why a room doesn't just grown infinitely bright over time after you turn the light on? + +Light is absorbed by everything in the room at some rate. It's also reflected at some rate as well. When you turn on the light there is an initial period of increasing brightness as the reflected light builds up, but then it reaches a state of equilibrium (much too fast to be perceptible, except in regard to the ramp up of the brightness of the light source itself). The light will have a characteristic number of average ""bounces"" in its lifetime before it is absorbed. Let's say you have a very ""bright"" room with 90% reflectivity (roughly mirror-bright). That means 10% of light is absorbed. After 131 bounces a given photon will have only a one in a million chance of having avoided being absorbed in such an environment. + +If you have, say, a 10m wide room, that's roughly 1310m of total distance traveled. Which a photon will travel in only 4.4 microseconds. So when you turn the lights off in a 10m wide mirror room the light will be one millionth as bright within 4 microseconds of the light going out. And 4 microseconds after that it will be one million times dimmer still, after only 12 microseconds the light will be a quintillion times dimmer than the start. In a very short amount of time even the vast number of photons produced by a light source will be completely absorbed on an instantaneous timescale for a human. A 100% efficient 100 Watt source of 2 eV red photons would produce 3e20 photons per second, which would be reduced to fewer than 1 photon in our hypothetical room in only 15 microseconds. + +**Edit:** I corrected some math mistakes! Sorry, I was tired last night." +646 Does pupil constriction only happen when your eye is exposed to light in the visible spectrum? 5838 https://www.reddit.com/r/askscience/comments/64r56s/does_pupil_constriction_only_happen_when_your_eye/ 1491920874 64r56s Human Body 2017-04-11 17:27:54 "Yes, it only reacts to light, if it is visible, which can be dangerous to your eyes, if you are exposed to strong UV or infrared light sources. +E.g. people who blow hot glass without protection often get eye problems later in life, due to the infrared exposure. Their pupils don't contract, because in the visible light, the hot glass only has a faint orange glow." Will a 100w 820nm IR LED floodlight damage your eyes? We use these a lot in security and I know a 100w visible light equivalent LED is like staring at the friggin sun. I do make an effort to not look at the LED when its powered but it happens. It has a dim red glow. +781 Do insects/arachnids get headaches? 5836 https://www.reddit.com/r/askscience/comments/6j7vpe/do_insectsarachnids_get_headaches/ 1498306914 6j7vpe Biology 2017-06-24 15:21:54 "Probably not. Not only do they not have a similar circulatory system to humans, there is good evidence that insects don't experience pain the way we do (some other arthropods may). + +Moreover, how would we even know. Pain is a subjective response, and there is no way they could communicate a headache to us. + +Edit: Thanks for all the karma, and the responses. There are so many responses now that they aren't even loading properly in the app when I click them. I've been trying to reply to all the responses to my explanation, but if I can't find it when I click on it, I'm not going to hunt for it. Have a great day everybody. + +Edit 2: Because so many people have asked, or in some cases tried to bring it up a counter point. Avoiding danger, and reacting to injury is not a sure indication or pain. It's possibly they have reflexes for damage avoidance that don't actually trigger anything like pain. Humans have many reflexes that help avoid injury, but we additionally interpret the stimulus as pain, but as a separate part of the process. + +The crossed extensor reflex is a great example. If you step on a sharp object (or an excessively hot object, or something that causes a chemical burn, etc.) your foot sends a signal to your spinal cord. In the spinal cord several synapses are triggered that connect to separate nerves. One causes an inhibition of the extensor muscles in the leg that has the injured foot, causing you to stop applying pressure with that foot. Another send a signal to your other leg, stimulating the extensor muscles, causing you to extend that leg, and catch your weight on the other foot. Another sends a signal to your brain, which then registers the injury and interprets it as pain. The interesting part is, the signals looping back to your legs fire at the same time as the signal going up to your brain, so your body is responding to the injury before your brain is even aware of it, and before you perceive the pain. + +For all we know, insects may have injury avoidance mechanisms like these, but may not actually experience anything akin to what we call pain. +" "Most likely no. + +Insects, at least some of them, cannot experience what we call pain. For instance, if you very carefully take the tip of the abdomen of a dragonfly that is eating and put it into its mouth, it will start eating its own abdomen. + +It really comes to the question what is pain in the first place. Pain is an unpleasant feeling - the most unpleasant one, by definition, - but WHY exactly is it unpleasant? + +It needs to be unpleasant for two reasons: first, to allow us to stop whatever causing pain (which roughly translates to damage) in a meaningful way, not just a knee-jerk reaction on a pure reflex; second, to allow us to remember the source of pain and avoid it later. + + +In other words, pain in the way we feel it is only needed (and possible) if you can learn from it and modify your future behaviour accordingly and/or if you can produce useful reactions beyond simple reflexes. Insects have nervous system just too primitive for either of those tasks. + +Edit: added immediate pain avoidance. " +521 Discussion: Veritasium's newest YouTube video on simulating quantum mechanics with oil droplets! 5820 https://www.reddit.com/r/askscience/comments/5aqdso/discussion_veritasiums_newest_youtube_video_on/ 1478099107 5aqdso Physics 2016-11-02 18:05:07 Are there any experiments that oppose the pilot wave theory to some degree, or is it just as possible as the standard theory of quantum mechanics? "The last video clip is absolutely stunning, where the droplet apparently retraces its path backward, ""erasing"" its previous wavetrain. Cannot this effect be thought of as a kind of spatial analog to the Feynman–Stueckelberg interpretation which states that antiparticles are simply regular particles traveling backward in time?" +1339 How does your phone gauge the WiFi strength? 5818 https://www.reddit.com/r/askscience/comments/caz0dq/how_does_your_phone_gauge_the_wifi_strength/ 1562667519 caz0dq 2019-07-09 13:18:39 "/u/baseball_mickey said how the phone’s hardware actually converts the raw data (I think), I’ll tell you what your phone is trying to actually measure. + +Measuring WiFi strength is the same as measuring phone signal. It’s done by measuring the actual wattage the phone is picking up. + +In the case of wireless signal and phone signal for that matter, it is measured in dbm (decibel milliwatt). Your phone will pick up how strong the wattage is and put it through the formula ‘10 x log10(P(w)) + 30’. Due to how logs work, wireless and phone signal strengths actually come out as negatives as the wattage is so small. (think of the log10 graph and sorta picture a really small x value. It’s going to be negative) + +Using this formula and a standard wireless signal strength (0.00000001w - this is how weak signal generally is lol) we can see that a signal strength with that wattage would be -50dbm. + +Because the conversion uses a log of base 10, just add an extra 0 for each ten dbm you go down (negative). And vice versa. + +For wireless anything more than -65dbm is going to give full bars (Definately for iPhone, I’m not sure about other models, should be about the same though). In the range of -65–>-80 is going to be 2 bars or middle. Then after -80dbm it’s looking bleak. + +Ultimately, it all varies on how sensitive your phone is I.e. how much power it can pick up. Some phones will have a stronger signal than others, while being in the same position. That’s just because they can pick up that wattage better. + +So yeah don’t have any knowledge on how the actual hardware in the phone measures watts, but my boy mickey gotchu on that part. + +P.s. on phone so sorry for shit grammar" "There is a whole class of circuits to measure signal strength. Likely they are using an [rms (root-mean square) detector](https://www.edn.com/electronics-products/electronic-product-reviews/other/4442820/RMS-detector-computes-real-power-of-an-RF-signal) of some type. You can also use a peak detector, but that tends to be inaccurate for high peak-to-average signals. There are other level detection circuits as well. + + +What do those measure against? There is another whole class of circuits that are built to utilize a physical property of silicon, the [bandgap voltage](https://en.m.wikipedia.org/wiki/Bandgap_voltage_reference). Most electronic components are built to 5-10% tolerance because they are really small, but bandgap circuits can be much more accurate. Often designers will use the bandgap and then a ratio of inaccurate components to maintain an accurate measurement - assuming the inaccuracies track, which is sometimes a safe assumption. Bandgaps are an old class of circuits and are incredibly useful for all types of measurements or just having reasonable values in your circuit. + + +Another point: there is a lot of variable gain in an RF receiver, so the signal detector either measures before the gain is adjusted, or it accounts for the gain adjustment. + + +I might have gone beyond what you were asking, but the circuits measure voltage levels inside the WiFi receiver integrated circuit." +1066 Vaginas contain lactobacillus, which are needed for healthy digestion. Do we know if performing oral sex in one can have health beneficts? 5801 https://www.reddit.com/r/askscience/comments/94l5pa/vaginas_contain_lactobacillus_which_are_needed/ 1533406318 94l5pa Human Body 2018-08-04 21:11:58 "Follow up question - is the bacteria in a birth canal related to gut bacteria in a healthy person? + +How much of a person's gut bacteria depends on vaginal birth and passing through their mother's bacterial cultures?" "Shirt answer: no. + +See my other reply for details. + +Tl;dr: lactobacillus in vagina and gut are different at species and strain level (in healthy women). + +Cunnilingus is no free probiotics treatment. + +Also, don’t try to make “vagina yoghurt”. (Please...). + +Source: I am an academic researcher on the human microbiome. + +Edit: These are some papers on this, as requested repeatedly. I posted them in a different reply before which was subsequently deleted. Some of these papers were published literally two weeks ago, but the results were known in the field for some time. + +https://www.ncbi.nlm.nih.gov/m/pubmed/30001516/ + +https://www.ncbi.nlm.nih.gov/m/pubmed/28144631/?i=2&from=/30001516/related + +https://www.ncbi.nlm.nih.gov/m/pubmed/30001517/?i=15&from=/30001516/related + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5880245/ https://www.ncbi.nlm.nih.gov/m/pubmed/29118049/?i=4&from=/30001516/related + +https://www.ncbi.nlm.nih.gov/m/pubmed/27503374/?i=5&from=/30001516/related + +https://www.ncbi.nlm.nih.gov/m/pubmed/28034306/?i=7&from=/30001516/related + +https://www.ncbi.nlm.nih.gov/m/pubmed/28073918/?i=8&from=/30001516/related + +https://www.ncbi.nlm.nih.gov/m/pubmed/29022384/?i=9&from=/30001516/related + +Edit2: these refs are on the much discussed sub-question below whether babies keep their mothers’ vaginal Flora after birth. Not directly on the question of oral sex and gut health..." +1242 "When you feel ""full"" or ""satisfied"" after a meal, is this due to the quantity of food eaten or the energy/nutritional value the meal gave?" 5796 https://www.reddit.com/r/askscience/comments/b24xty/when_you_feel_full_or_satisfied_after_a_meal_is/ 1552827733 b24xty Biology 2019-03-17 16:02:13 "Both! + +When the stomach is physically full, stretch receptors in the wall are activated, sending signals along parasympathetic (rest and digest) nerves to suppress the hunger centres in the brain. + +In addition, the composition of the food - its carbohydrate, protein and fat make up - will play an important role. Glucose levels are closely linked to hunger, as it is the main fuel used by most cells in the body. When glucose is high, insulin is released and glucose is driven into the cells; when it is low hormones like glucagon are released to drive glucose out of its stores in the liver. + +A hormone called cholecystokinin (CCK) is also released in response to amino acid and fat presence in the duodenum (first part of small intestine) and this delays the emptying of the stomach, resulting in you feeling fuller for longer. CCK also has effects on the central nervous system to reduce the feeling of hunger. + +" "Dietitian here: + +It's a lot more than 1 or 2 factors going into 'feeling full'. Ghrelin is an interesting hormone that plays a role in the feeling of hunger - mostly stimulated by protein and carbohydrate. But fat, on the other hand, slows gastric emptying giving a real physical sense of satiety. + +There is a difference between the physical sensation of being full, and being satiated, or not hungry. " +1340 Are a butterfly and a caterpillar the same animal genetically? 5792 https://www.reddit.com/r/askscience/comments/ccumae/are_a_butterfly_and_a_caterpillar_the_same_animal/ 1563052630 ccumae 2019-07-14 0:17:10 They have the same genome yes. And it shouldn't be that surprising, the same genome that produces your eye is the same genome which produces your kidneys, two very different organs. One of the biggest discoveries from the human genome project was that the absolute number of genes is not that high, it's the regulation of expression and splicing which allows for the huge amount of diversity in tissues. "Yes, they are the same organism and share the same genome. However, there are certainly major changes in gene expression that occur during metamorphosis as various developmental genes are activated or inactivated respectively. I recommend [this review article](http://www.biologiaevolutiva.org/xbelles/pdfs/2011-Belles-ELS.pdf) by Belles 2011, which is a good source of general information about insect metamorphosis. + +For several decades now, it's been know that this process is initially triggered by hormonal signals, the most important of which are [juvenile hormones](https://upload.wikimedia.org/wikipedia/commons/thumb/8/8e/AllJH.svg/1280px-AllJH.svg.png) (JH). As the name implies, juvenile hormone is present at high levels in larvae, and metamorphosis begins once levels of JH drop below a certain threshold; this also means that exposing insects to JH can indefinitely prevent them from maturing to adulthood ([source](https://www.sciencedirect.com/science/article/pii/S0022191008000267?via%3Dihub)). This property was somewhat unpleasantly discovered by Vincent Wigglesworth when he attached larvae of different stages together so they shared body fluids, which you can see in [figure 3](https://imgur.com/WMvyI0H) from the Belles 2011 article I already linked. + +So we know that the levels of hormones like this are responsible for *causing* metamorphosis, but the mechanics of how it happens on a genetic level are somewhat more complicated. The main group of genes associated with metamorphosis appears to be the ""Broad-Complex"" of genes, named after the [broad gene](https://www.wikigenes.org/e/gene/e/44505.html) in fruit flies. This family of genes encodes transcription factor proteins that go on to regulate the expression of over 100 other genes (including themselves), and some of those downstream genes regulated by the Broad-Complex are themselves transcription factors ([source](https://www.ncbi.nlm.nih.gov/pubmed/8076529)). There has been some work done to trace the labyrinthine web of relationships among these various developmental genes to figure out some of the finer details of how metamorphosis actually happens, but it's beyond the scope of my knowledge on this topic and this post is already long enough as it is. + +In summary then, caterpillars and butterflies do indeed share all the same genes, but the changes that occur during their life cycle are based on the selective activation and repression of different groups of genes at different times. From the outside, a freshly emerged butterfly may appear to be a completely different organism, but careful study has shown that there are clear anatomical connections between the larval and adult stages. For example, insect larvae have blobs called [imaginal discs](https://www.sdbonline.org/sites/fly/lewheld/fig11.jpg) composed of cells that already have specific preordained fates in the adult stage ([source](https://www.cell.com/current-biology/pdf/S0960-9822(10)00291-5.pdf)). And to reference another neat experiment, it's been shown that memories from the larval stages can be retained as adults, so there definitely isn't any kind of sneaky switcheroo going on in between ([source](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0001736))." +647 Why does sticking your fingers back your throat trigger your gag reflex, but swallowing food doesn't? 5786 https://www.reddit.com/r/askscience/comments/63132b/why_does_sticking_your_fingers_back_your_throat/ 1491155664 63132b Human Body 2017-04-02 20:54:24 "https://www.reddit.com/r/askscience/comments/171mp2/why_doesnt_eating_stimulate_our_gag_reflex/ + +Quote : "" I believe that swallowing is what's called a ""prepotent reflex."" This means that it is essential for survival or avoiding harm, and is therefore given the ability to override other competing reflexes, in this case the gag reflex. Gagging is also the result of receptors mainly located in the posterior 1/3 of your mouth, behind the palatoglossal folds therefore in the oropharynx. The boundaries of the pharynx itself are usually only breached upon the actual act of swallowing, so you are at a lower risk of gagging. Note that you will still gag if you accidentally try to swallow something without chewing it, as the area is not prepared and in the act of swallowing. "" + + -genuflect_before_zod, 4 years ago, slightly edited for better reading. + +" When a food/liquid bolus travels toward the back of the oral cavity, the swallow reflex is triggered. One of the muscle actions that happens during the swallow is that the velum (and uvula) elevate to close off the nasal cavity to prevent nasal regurgitation of the bolus. Along with what other people have said about sensation and reflexes, the uvula is mostly out of the way of the bolus. +782 Does the Doppler effect have any noticeable consequences on wireless Internet connection? 5780 https://www.reddit.com/r/askscience/comments/6x75kd/does_the_doppler_effect_have_any_noticeable/ 1504189355 6x75kd Physics 2017-08-31 17:22:35 "Yes it can actually have a pretty significant effect on communications. [In particular, if S(f) is the spectrum of your original signal, S(*a*f) will be the spectrum afterwards (PDF).](https://pdfs.semanticscholar.org/2aed/1ae6a8739069d3bc6f638758458425b079ca.pdf) Here *a* is relatively close^(1) to 1, basically 1 - v/c where c is the speed of light and v the velocity of the object. At most the shift will be a few Hz. + +The shift in Hz is not a problem, in fact [phase lock loop](https://en.wikipedia.org/wiki/Phase-locked_loop) are already usually applied so that the receiver can reap the gains of using coherent demodulators (PDF) [see here (PDF)](http://wireless.ece.ufl.edu/twong/Notes/Comm/ch2.pdf). Phase lock loops help to account for artifacts such as signal drift, and so on. The point being this is not where the problem comes in. + +The big problem is what occurs with multi-path communications. If your signal has multiple reflections (like, if you are in a room of some sort instead of in an open field). When moving now, there will be a different velocity shift depending on the angle of arrival of the wave. And because of this the signal, being the sum of the different waves, can experience a wide arrange of channels. ~~Some of these channels will begin to have different interference patterns.~~ This is problematic though as the capacity (maximum amount of bits/second that can be sent over it) basically defaults to the minimum rate achievable over all possible channels simultaneously (see [Theorem 1 (PDF)](http://www.ece.umd.edu/~prakash/papers/Csiszar_Narayan-IT_1991.pdf)). ~~Thus if one of those bands you pass over has a really bad channel, there goes your ability to connect in general.~~ While the variation due only to doppler shift will be small (about 80 Hz for 5 mph over 5GHz), it is just on the edge of what is considered to not be completely trivial.^(2) + +Anytime you transmit a code with a higher rate than the capacity of the channel, an error will occur. As a result a moving source does increase the probability of packet error, with the probability increase depending on the speed and strength of the reflections. + +The same principal applies to AM and FM radio. Although both of which are horribly inefficient in terms of transferring information, so it is unlikely that it would have a noticeable impact. To put it in perspective, a WiFi router is trying to transmit at the very edge of comprehension, while AM and FM require the signal to be easily understandable. Adding a little bit more noise to the WiFi signal will move it past the point of comprehension, while for AM and FM the added noise will still result in a large enough SNR for it to not make a difference. + +Edit-- + +1 - correction due to /u/devman0 + +2 - Added later, as was pointed out by /u/dirtyuncleron69 and /u/dayzstu. Crossed out what is not directly attributable to the doppler shift. + +Also, while on the edit, for a much more in depth discussion about how we model movement and the impact this has on communication, please see [Wireless Communications by Andrea Goldsmith](https://wsl.stanford.edu/~andrea/Wireless/SampleChapters.pdf). She is the most prominent authority on the subject. Chapter 3 in particular talks about this exact scenario in realistic environments, and chapter 5 the impact on capacity. " "The phase shift of the wireless data signals from the Malasian Airline MH370 aircraft was actually a significant piece of data that contributed toward determining approximately where it went. + +Modern equipment is designed to compensate for this effect where it is necessary, but the Inmarsat satellite logged all the correction factors it used when receiving the data from MH370, and those became the missing link in localizing the unknown transmission location." +1341 AskScience AMA Series: I'm Dr. Paul Knoepfler, stem cell and CRISPR researcher, here to talk about how you might build a real, fire-breathing dragon. AMA! 5777 https://www.reddit.com/r/askscience/comments/cvmi2d/askscience_ama_series_im_dr_paul_knoepfler_stem/ 1566817252 cvmi2d 2019-08-26 14:00:52 "Will CRISPR ever be able to make full changes towards an adult subject or will some other tool be required? + +Lets say you wanted to go crazy and give a person scales and such, would CRISPR be able to safely be used for such a modification or is it limited towards changes towards sperm/eggs when it comes to such an extreme modification?" "Overly simply stated, I understand that CRISPR can selectivly find/replace bits in a given genome, right? So wouldn't creating a ""New"" property like breathing fire require an existing and perfect model of both the original host ánd the property to be added? + +I can imagine that changing bits here n there would potentially have unintended or unforseeable outcomes." +962 As someone gets more obese, do their actual skin cells stretch or do they replicate fast enough to keep up with the increasing surface area? 5775 https://www.reddit.com/r/askscience/comments/7vvc1s/as_someone_gets_more_obese_do_their_actual_skin/ 1518001090 7vvc1s Biology 2018-02-07 13:58:10 "Their skin cells divide to increase surface area. Individual cells have limited elasticity and if they simply stretched to cover the increased fat tissue underneath, it would be like blowing up a balloon (e.g. getting thinner). In fact, more than just the skin cells help cover the area. Blood vessels, connective tissue, the fat cells themselves all have to accommodate the increased tissue volume. As a corollary, when someone has massive weight loss, you can see the large amount of loose and excess skin. The signals from the body to make the skin cells divide to cover the larger area can't just reverse instantaneously (you also have issues with looser connective tissue, loss of elasticity of various components, etc.) so now you have large folds of skin hanging around. + +EDIT: Forgot to respond to your follow-up. You can have issues with less touch sensitivity but it's hard to say that it's just because of less nerve endings (your nerves can make new connections so you still have touch sensations). More often, losing feeling in really any part of your body (bodybuilders with massive skeletal muscles, areas of fat deposits) is a combination of factors like poor blood flow to the cells rather than just not enough nerve endings." "Source: I'm a plastic surgeon. + +The phenomenon you are asking about is termed ""tissue expansion"" and is a phenomenon we use frequently in our practices to reconstruct defects such as after breast cancer. Patients will have their breast tissue removed (some skin, lots of subcutaneous fat, all of the breast parenchyma) and will have a smaller pocket than what they are looking for aesthetically speaking. We place basically inflatable balloons into the skin pocket and slowly expand the balloon over the next 5-6 weeks until the pocket will fit a more normal-appearing silicone or saline implant to reconstruct the breast. + +To answer your question more specifically, tissue expansion works by 2 main functions. Mechanical expansion, aka ""creep"" happens when you pull skin very tightly and occurs immediately. This occurs like others have said due to the elastin component of your skin microfragmenting, thins the skin out, and decreases the water content of the cells. It also causes your collagen fibrils to line up in parallel to the direction of force True tissue expansion over weeks or years or that occurs during pregnancy or obesity is known as ""biological expansion,"" which causes cell division, fibroblast proliferation, angiogenesis, and mitosis via transduction pathways. Thickness of the expanded skin IS less (with the exception of the epidermis, which thickens). It does not return to normal thickness until about 2 years. The one caveat to this is that pregnancy has a ton of hormonal influence on every cell in the body, so these changes will be markedly different. Obesity has endocrine abnormalities and metabolic disturbances as well, so there are some other slight differences. + +Stretch marks are areas of attenuated dermis. Dermis is the strength layer of the skin so areas with stretch marks are weaker components. + +In contrary to what many people are posting here, there is NO GOOD WAY TO TIGHTEN SKIN NONSURGICALLY. Regardless of how you lose your weight, you are decreasing the fat content (either by shrinking the cells or causing fat necrosis) but the skin will not change significantly. Some options do exist for VERY MODEST skin tightening, such as dermabrasion, lasers, chemical peels, etc; but these are much more relevant for wrinkles than significant skin tightening. This is why massive weight loss patients virtually always require surgery. It has nothing to do with the speed with which they lose weight you simply cannot get your skin to shrink without sharp excision. + +EDIT: in addition, lipo only removes fat. Does not tighten skin. Ultrasound assisted liposuction causes some thermal damage which again can cause a VERY MILD skin tightening. This is why fat people who get lipo don't get amazing results without concomitant skin resection. + +About the nerves. Don't forget that your 2-point discrimination or sensitivity to touch is different in different parts of your body (you can feel <1mm difference in your fingertips but it's not abnormal to have 5mm or more on your back). I can't comment directly on if stretched skin reduces 2-point discrimination as I have not read anything regarding that." +783 Why can't I remember a smell or taste the same way I can an image or a sound? 5767 https://www.reddit.com/r/askscience/comments/6gpy5h/why_cant_i_remember_a_smell_or_taste_the_same_way/ 1497240346 6gpy5h Psychology 2017-06-12 7:05:46 "This thread contains lots of answers with personal anecdotes and speculation; these will be removed. Please add [peer-reviewed sources](https://www.reddit.com/r/AskScience/wiki/quickstart/answeringquestions) to your answer. Note that magazine articles (printed or online) are typically *not* peer-reviewed and thus are not a suitable source (for more info, see [here](http://www.angelo.edu/services/library/handouts/peerrev.php)). + +If the answer boils down to ""we don't know (yet)"", or the question's premises/assumptions are not met, you may also provide: + +* research questions that encompass OP's question and are also unanswered, +* research questions that are tangentially related +* or more generally, publications that illustrate the difficulty of answering OP's question. +" "Perfumer here. +With training any person would be able to replicate smells inside their heads as well as any visual or auditory input. The main problem is cultural. Our western society does not value the sense of smell as highly as other senses: children are not taught to notice odors, our olfactory ""vocabulary"" is really limited, we are not used to rely on our sense of smell on a day-to-day basis etc. +The Jahai people in the Malayan peninsula is the best example I can remember of a culture that highly praises the sense of smell, having even specific vocabulary to describe odors: [an article on Cognitive magazine about that](http://www.sciencedirect.com/science/article/pii/S001002771300214X) +edit: formatting. +edit 2: removing link to non-scientific article. +edit 3: changed ""remembering"" to ""replicating inside the head""." +1342 Why is it if we stare at a bright light for too long we can still see a bright outline of said light when we close our eyes? 5755 https://www.reddit.com/r/askscience/comments/cd5ts6/why_is_it_if_we_stare_at_a_bright_light_for_too/ 1563126166 cd5ts6 Human Body 2019-07-14 20:42:46 "Basically you're overloading your eye receptors in that particular area of the receptor. + +It's called an [afterimage](https://en.m.wikipedia.org/wiki/Afterimage). Staring at a bright light for a long oeriod will eventually damage your eyes and you'll have a permanent afterimage called [visual snow](https://en.m.wikipedia.org/wiki/Visual_snow) and may take weeks, months, years or even not at all if damage is severe enough." "Optometrist here: Seems well covered already but it is due to the “bleaching” of retinal photoreceptors in any particular area. Each photo receptor has a stack of membrane disks which are covered in photopigments of different types called Rhodopsins. Each time a Rhodopsin molecule absorbs light it “flips” causing an electrical impulse down the membrane by way of a cascade it sends the signal down the rod/cone to a complicated chain of cells and cell processing which becomes quickly less relevant to this conversation. The disks are slowly “consumed” and moved Down the rod/cone until it can be shed and absorbed by the retinal pigment epithelium layer for reabsorption. When an area is bleached relative to another area the signal becomes muted as the cells regenerate (can take up to 5 seconds for most people longer if problems exist). The after image can last longer if a very intense stimulus (like a bright light) were to bleach the area. Sufficiently intense lights such as the sun simply burn a hole through the nerves causing permanent damage which you can not recover from. We refer to this as “solar retinopathy”. I have also seen cases where laser pointers have caused retinal burns. + +Edit: a letter" +963 Do animals that mate for life (eg. Penguins, beavers, etc.) sleep around a bit before mating for life or do they just spend the rest of their lives with the first one they mate with? 5747 https://www.reddit.com/r/askscience/comments/81r5h2/do_animals_that_mate_for_life_eg_penguins_beavers/ 1520094631 81r5h2 Biology 2018-03-03 19:30:31 Penguins aren’t entirely monogamous. Certain species are more likely to return to their same partners, but even in those cases, there will be years where they will pair up with another bird. I’ve even seen a male bounce back and forth between 2 females and try to maintain 2 separate nests for them. I’ve also seen 2 males continually nest together every year. There weren’t enough mature females in the colony and they grouped up, even though they never incubated any eggs. They were actually used to foster an abandoned egg one year and they succeeded in hatching and rearing the chick. Later on, they went their separate ways when more females became available. "A lot of animals that ""mate for life"" aren't completely monogamous. They'll raise young together for life, but they have extra pair copulations. This is called being socially monogamous. + +https://en.m.wikipedia.org/wiki/Social_monogamy_in_mammalian_species" +1343 When we take footage of the ocean floor that isn't reached by sunlight, are the lights used for filming harmful to the ocean life? 5747 https://www.reddit.com/r/askscience/comments/cmyw00/when_we_take_footage_of_the_ocean_floor_that_isnt/ 1565139009 cmyw00 Biology 2019-08-07 3:50:09 "Generally not. + +You might be drawing an analogy to 'if i sit in the dark for a while, a bright light is really bright - imagine if i lived in the dark!', but it isn't really like that. + +Most of the visible spectrum doesn't penetrate too far, with only the blue end of the visible spectrum penetrating to the depths. As a result many animals that far down are insensitive to light, and those that are tend to be sensitive to only blue light - It's why so many deep sea creatures appear to be red or pink when we film them with white light (since red light doesn't penetrate that far down, a red coloured object is functionally black). + +The only minor impact i can think of is in regards to a handful of species that have developed the ability to broadcast and sense red light. They are predators, and essentially have red 'headlights' under their eyes that cause the red/pink animals to light up like a christmas tree. Broadcasting white light down there would illuminate the subject to these predators...but it's a pretty niche thing, and not something to be concerned about." [deleted] +522 Why do some parrots live 30+ years, some 100+ and some animals like dogs only 10+? 5737 https://www.reddit.com/r/askscience/comments/5kku40/why_do_some_parrots_live_30_years_some_100_and/ 1482859512 5kku40 Biology 2016-12-27 20:25:12 "It depends on what you mean by ""why"". The mainstream big-picture answer is that animals die by old age at around the point that they'd probably end up dying anyway. + +Small animals that are heavily predated on (say, mice) have really short lifespans, because if they spent energy on hardening their systems so they could live longer it would be wasted; there is no point in a mouse that could live 20 years, because it would be eaten in a year or so anyway. + +Birds tend to live longer than mammals, because it's harder to prey on birds. Large seabirds, that live solitary lives away from dangerous things, live for a long time. Bats are as small as mice, but they can fly; they live much longer than mice do. + +There are other argument out there, but that's the general consensus. Again, this is the evolutionary-theory ""why"", not the mechanistic ""why""; the concept is that it takes more energy to live longer, but it doesn't say where that energy goes, specifically. + +A starting point for further reading: + +>The classical evolutionary theory of ageing, first proposed by the famous evolutionary biologist George C. Williams over 50 years ago, gives an answer. The theory predicts that high mortality rates in adult animals due to predation, exposure to parasites and other randomly occurring events will be associated with shorter maximum life-spans. This is because under high external mortality most individuals will already be dead (eaten or succumbed to disease) before natural selection can act on rare mutations that cause healthier ageing. The theory has since been further developed and tested in a number of experimental and comparative studies. + +--[Predators predict longevity of birds](https://www.mpg.de/8167842/predators-longevity-birds) + +>The classical evolutionary theory of ageing (ETA) predicts that exposure of adult individuals to high rates of mortality due to predation, parasites or other stochastic events will hinder the evolution of increased lifespans, because most individuals will already have died from these extrinsic causes before natural selection can act on reducing intrinsic causes of mortality that lead to longer lifespans (e.g. favoring mutations that lead to healthier ageing) + +--[Global gradients of avian longevity support the classic evolutionary theory of ageing](http://onlinelibrary.wiley.com/doi/10.1111/ecog.00929/full). There are multiple references, pro and con, in this article. + +It looks as if this is the first formal presentation of the theory: [Williams G. C. 1957. Pleiotropy, natural-selection, and the evolution of senescence. – Evolution 11: 398–411.](https://www.jstor.org/stable/2406060)" "I remember studying something like this a while ago. If you look up some terms such as ""life history trade-off"" ""iteroparous"", ""semelparous"" and ""K-strategist"" and ""r-strategist"", you'll get a feel for the answer you're looking for. + + +Basically, different organisms have evolved different strategies based on what worked best for their ancestors in their environments. Allocating resources to one factor of life such as reproduction comes at a cost to other aspects such as survival and longevity. Semelparous organisms, at one end of the spectrum, will reproduce only once in their lifetime and so there is no evolutionary benefit to them having long lifespans. Iteroparous organisms will reproduce several times throughout their lifetime and so can live longer lives. There is a balance to the amount of resources devoted to somatic effort and the amount devoted to reproductive effort. If I recall correctly, a ""K-strategist"" has a life history adapted to maximising its competitiveness and adult survival, and are usually found in environments which suit this life style. ""r-strategists"", on the other hand, are adapted to maximising their reproductive rate and usually are found in unstable environments where rapid development and early reproduction, and therefore shorter lifespans, are favoured by natural selection. + +So the differing lifespans of the different animals you mentioned will be due to the optimal life history strategy in the evolution of their respective phylogenetic lineages. + + +Hope this is helpful." +868 Does heat, humidity, and other atmospheric variables affect wi-fi and other signals? 5731 https://www.reddit.com/r/askscience/comments/71g8nl/does_heat_humidity_and_other_atmospheric/ 1505961417 71g8nl Physics 2017-09-21 5:36:57 "Water vapor does, but only slightly so to be unnoticeable. Water vapor (i.e., humidity) absorbs microwaves in the 3-5 GHz range only on the order of 0.001 dB per km. For a typical cell tower with 100 km range, this means humidity is only changing this range on the order of 1 to 10 meters or so. + +Rain or hail, on the other hand, can have huge effect, this is actually how our weather radar systems work. The US National Weather Service's 88Ds are 3 GHz radars, in the same frequency bands as wifi. The rain and hail won't appreciably absorb as much as it reflects the signal (this reflection is what shows up on the weather radar images). When you go to 5 GHz signal like wifi, hail cores in very strong thunderstorms can reflect all the signal over very short distances. + +Temperature gradients also affect the way directed microwaves travel. This can result in pulses from say, a radar, being bent back to the ground. + +If you want to experiment water's effect on microwaves you can place your phone in a water proof bag and submerge it in water and see your wifi signal drop. " "As a radio amateur who is active on microwave bands I can say that the answer is a big yes! What you need to read up is Tropospheric Ducting: + +https://en.wikipedia.org/wiki/Tropospheric_propagation + +Zones of temperature inversion in high pressure areas can offer propagation losses that are extremely small. The most pronounced effect is when the ducting occurs just above the surface of the sea or a lake. For example I once contacted Holland from the UK with only 1mW of power on 2,3 GHz ie about 100x less than WiFi." +523 Can a computer simulation create itself inside itself? 5728 https://www.reddit.com/r/askscience/comments/5cobkg/can_a_computer_simulation_create_itself_inside/ 1479010397 5cobkg Computing 2016-11-13 7:13:17 [deleted] "A cellular automaton can simulate the rules of its own world with some slowdown. [Here's an example with Conway's Game of Life](https://www.youtube.com/watch?v=QtJ77qsLrpw). (If you aren't familiar with Conway's Game of Life, you can read [this](http://www.math.cornell.edu/~lipa/mec/lesson6.html) for an intro.) + +A program written in a Turing-complete programming language like C is capable of interpreting itself. If you wrote a C program that implemented a C interpreter that interpreted its own source code, it would run forever with an ever-growing number of recursive levels." +524 What's the most powerful an earthquake could be? What would this look like? 5719 https://www.reddit.com/r/askscience/comments/5d2hc3/whats_the_most_powerful_an_earthquake_could_be/ 1479216376 5d2hc3 Earth Sciences 2016-11-15 16:26:16 "The most powerful earthquake that has been recorded was the [1960 M9.5 Valdivia](https://earthquake.usgs.gov/earthquakes/world/events/1960_05_22.php) earthquake in Chile that ruptured a length of about 1000 km. However the longest fault ruptured observed was during the [2004 M9.2 Sumatra-Andaman earthquake](https://earthquake.usgs.gov/learn/topics/sumatra9.php) that ruptured over a length of 1200 km. + +Fault length plays a key role in the most powerful earthquake that is theoretically possible, since rupture length will be limited to be less than the circumference of the Earth (40,075 km). To determine seismic moment or the amount of energy released in an earthquake, you would multiply the area of the fault that slipped (length x width), the distance it all slipped (usually in the tens of meters for great earthquakes like this), and the shear modulus of the fault (rigidity or how much the fault surface can resist breaking) [[Hanks and Kanamori, JGR, 1979](http://onlinelibrary.wiley.com/doi/10.1029/JB084iB05p02348/abstract)]. The width of a fault is also a limit, because beyond a certain depth the lithosphere no longer breaks brittlely but instead deforms ductilely. This limit varies, but the deepest known earthquakes tap out at ~700 km depth. Since the faults that the largest and deepest earthquakes occur on are subduction zone faults which dip into the earth at an angle, their width would technically be more than that 700 km depth limit but that is a huge width already so I am going to stick with that for this exercise. And since this is conjecture, I will stick with a generally accepted 3.0*10^10 N/m^2 for rigidity and 100 meters of slip as any more than that freaks me out. + +Putting that all together in our equations for moment M0 = (40075000 m * 700000 m) * (100 m) * 3.0*10^10 N/m^2, and subbing that into our equation for magnitude MW = (2/3) * log(M0) - 6.05, we would get a magnitude of 11.23 for an earthquake that basically breaks the full circumference of the earth like a plastic Easter egg to a depth of 700 km and twists it to shift everything by 100 m. + +Needless to say, that is far from what is expected to actually occur on Earth through plate tectonics in our lifetime. With current knowledge of the longest active faults a more reasonable limit on the most powerful earthquake would be a magnitude of about M9.6. It would be on a megathrust subduction zone fault probably on one of the faults in the Pacific, and it would likely have to rupture much of the shallow part towards the trench which would generate a significant tsunami impacting all countries with coastlines along that ocean with Hawai’i right in the middle of the fun. " "Maybe someone can answer a follow on question for me. + +The magnitude of an earthquake is a measure of the total energy released. The total energy released is going to be a function of the ground movement amplitude AND the length of time the shaking occurs. + +So, it's possible that a large amplitude short duration quake could release the exact same amount of energy has a low amplitude long duration quake...right? The effects of each on infrastructure would be drastically different. +" +525 "If I put a flashlight in space, would it propel itself forward by ""shooting out"" light?" 5714 https://www.reddit.com/r/askscience/comments/544ejw/if_i_put_a_flashlight_in_space_would_it_propel/ 1474633112 544ejw Physics 2016-09-23 15:18:32 "As an addendum to the information already provided here: + +Its not just visible light that'll produce a tangible thrust. Any wavelength of light will. This becomes a problem for space probes, because electronics and power supplies turning on and off create heat in the infrared spectrum, and these infrared photons cause a small thrust which over long periods of time will cause the probe to veer off course. + +There's actual computer simulation and modeling done at NASA to account for this infrared-thrust effect when setting probe trajectories and course corrections." "Yes, very slowly. + +Light has momentum, even though it is massless, so if you shoot a beam of light in one direction, conservation of momentum will push you in the opposite direction. + +A reasonably powerful LED flashlight will use about 1-3 Watt, lets say 3 W. The efficiency of a LED is somewhere between 25% and 40%, so for sake of ease of computation lets make that 33% and we get a net amount of light output of 1 W. + +The ratio between the momentum and energy of light is 299,792,458 (Which is also the speed of light). So in 1 second, the flashlight produces 1 J worth of light, which is equal to 0.33 * 10^-8 kg m/s. If the flashlight is not too heavy, say 100 gram or 0.1 kg, that means that 1 second of light would propel the flashlight to a velocity of 10^-7 m/s. This assumes that all light is directed in straight line. The more cone-shaped the bundle of light is, the lower the momentum transfer is. + +Leaving the light on for one day would propel the flashlight to about 0.009 m/s or almost 1 cm per second. Unfortunately, operating a 3 W LED for a day uses about 260 kJ of energy. Regular AA batteries have somewhere around 10 kJ of energy (depending on the type). And at a weight of 20-30 grams per battery, you can't carry put more than 2-3 in the device without violating our original assumption of a 100 gram device." +1243 Is there any seven-day periodicity in the global climate due to the industrial work-week? 5708 https://www.reddit.com/r/askscience/comments/bbegbx/is_there_any_sevenday_periodicity_in_the_global/ 1554849616 bbegbx 2019-04-10 1:40:16 "There is weekly variation due to human activity, but the details differ in different parts of the world. For example ""Parts of the United States have less rainfall on weekends, while Germany gets more rain at the end of the week."" + +https://www.nature.com/news/2008/080811/full/news.2008.1017.html" Wow this thread is a train wreck. Here's a straight forward answer from an atmospheric scientist. There aren't any global periodicities due to the work week simply because the Earth is big and a week is small. However, there absolutely are local periodicities due to the work week. Pretty much any pollutant (CO2, NOx, O3, etc.) is higher on weekdays than the weekends. Whether these variations in pollution affects other aspects of weather (rain and stuff), is contentious and probably unknowable. The problem is that there is already a very strong periodicity of 7-10 days that overwhelms whatever small affect we might have. +964 If the fusion reactions in stars don't go beyond Iron, how did the heavier elements come into being? And moreover, how did they end up on earth? 5678 https://www.reddit.com/r/askscience/comments/817aph/if_the_fusion_reactions_in_stars_dont_go_beyond/ 1519927698 817aph Astronomy 2018-03-01 21:08:18 "There are a couple of processes that create elements heavier than iron. The s-process (s for 'slow') happens in large stars, where atomic nuclei capture free neutrons, increasing their mass. Occasionally they'll undergo beta decay, increasing their atomic number. This takes a long time, but because there's just so much stuff inside stars, it works out, and is responsible for about half of the atomic nuclei heavier than iron. + +The other half are typically created by the r-process (r for 'rapid'). This occurs when there are a lot (and I mean a lot) of free neutrons around and nuclei just soak them up. Conditions like these tend to only happen in core-collapse supernovae, and so many of these elements are created during supernovae. + +EDIT: Others have pointed out that we now also have evidence that suggests many heavier elements are created within neutron star collisions. I figured I should add this here since it has become a popular answer." "Created in super and hyper novas and detonated out across cosmos. The remaining star dust then gets back together to form new stars and planets. + +Before the solar system, there was another star that detonated and from some of that material, the Sun, Earth and a bunch of other planets were formed. So we are like brother/sister with all the other planets and the sun. Earth wasn't formed ""by the sun"", we were both formed by the remains of some older, previous star." +1597 How do epidemiologists determine whether new Covid-19 cases are a just result of increased testing or actually a true increase in disease prevalence? 5678 https://www.reddit.com/r/askscience/comments/hw18jm/how_do_epidemiologists_determine_whether_new/ 1595449027 hw18jm COVID-19 2020-07-22 23:17:07 "One metric is the rate of positive tests. Let’s say you tested 100 people last week and found 10 cases. This week you tested 1000 people and got 200 cases. 10% to 20% shows an increase. That’s especially the case because you can assume testing was triaged last week to only the people most likely to have it while this week was more permissive and yet still had a higher rate. + +Another metric is hospitalizations which is less reliant on testing shortages because they get priority on the limited stock. If hospitalizations are going up, it’s likely that the real infection rate of the population is increasing." "As has been mentioned, testing postivity is used as an estimate for testing saturation. In normal circumstances, the percent positive tests should be <5% based on normally [circulating coronavirus trends](https://www.cdc.gov/surveillance/nrevss/coronavirus/natl-trends.html). + +[Hospital utilization](https://protect-public.hhs.gov/pages/hospital-capacity) is a potential estimate of burden based on known disease severity and local catchment populations and in reverse, we can [forecast hospital burden](https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/hospitalizations-forecasts.html) based on various assumptions and known population and disease parameters. + +The real silver bullet measure that epidemiologists are looking for are sero-prevalance studies, those let us know who has been infected so far. CDC [just released a large study](https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/commercial-labs-interactive-serology-dashboard.html) based on a convenience sampling of blood banks, not the greatest, nor even really representative sample but you use what you got in public health. India also did a [similar study](https://www.bbc.com/news/world-asia-india-53485039). + +This is just a very basic overview, if you're more interested, CDC has [their methodology](https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covidview/purpose-methods.html) available." +965 Are wild gorillas afraid of spiders? 5662 https://www.reddit.com/r/askscience/comments/8f6wzw/are_wild_gorillas_afraid_of_spiders/ 1524783045 8f6wzw Biology 2018-04-27 1:50:45 "The simple answer is: **it depends, but probably, yes**. + +Problem is, no lab experiments of gorillas + spiders show up. + +Our next best bet is by inference: evidence of similar 'fears' +Carel Van Shaik (a famous primatologist) argues that [having 'fears' like arachnophobia and ophidiophobia would be adaptive](https://books.google.com/books?id=3oCbCgAAQBAJ&lpg=PR13&ots=2r7lXEmesn&dq=%20gorilla%20arachnophobia%20evolution&lr&pg=PA28#v=onepage&q=arachnophobia&f=false) (e.g., you avoid, you live and make babies vs the fearless dead). In the period 50 [MYA](https://en.wikipedia.org/wiki/Year#Mya) to 1MYA, were spiders enough of a threat that fearing them would benefit you? Some researchers argue ""yes."" + +**But how do we fear such threats?** +I think this is the more interesting question. I noticed that in certain parts of Europe and the Galapagos, birds that are elsewhere skittish are shamelessly tame. Regarding most ""ancient fears,"" It seems we are **hard-wired to respond to templates and certain movements**. [Babies and Rhesus monkeys shown videos of snakes recognize them much much quicker than other objects](http://www.psy.cmu.edu/~rakison/Infant_Cognition_Lab/publications/LoBue,%20Rakison,%20&%20DeLoache%20\(2010\).pdf). This ultra-rapid recognition is important as it suggests the recognition machinery resides somewhere in our lower, ""[lizard brain](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4406946/)"". Patterns in our lower brain are more immediate and we learn from them faster than patterns we store in our cerebral cortex (I'm oversimplifying here to keep this explanation from being 10 pages). + +So this suggests we are not programmed to fear, but are programmed from deep in our 'lizard brains' to react quickly to certain movements (darting, slithering, jumping) and to certain templates (lots of legs or no legs) very fast. For gorillas, this would suggest **gorillas that didn't see spiders growing up would not fear them, but could quickly learn to fear them if some big bad spider creeped up to them**." [Yes, they can be](https://www.reddit.com/r/askscience/comments/16xgl9/are_our_closest_primate_relatives_as_scared_of/) +648 Why is it advised to keep using the same antiseptic to treat an open wound? 5651 https://www.reddit.com/r/askscience/comments/6183ly/why_is_it_advised_to_keep_using_the_same/ 1490350484 6183ly Medicine 2017-03-24 13:14:44 You don't need to use any antiseptic more than once anyway, and really you don't even need to do that. I'm an ER doc. We just irrigate with saline. Studies show tap water is just as good. Antiseptic solutions like chlorhexidine or betadine have been shown to both irritate the subcutaneous tissue and inhibit wound healing, so we don't use them except around the wound edges. "Everyone is right, but nobody is giving you a particularly relatable answer. + +Take 3 of the most common antiseptics, hydrogen peroxide, isopropyl alcohol, and iodine. + +On their own they work great. But hydrogen peroxide is a strong ""oxidizer"", a term in chemistry that means it has free oxygen that reacts with other chemicals. (It's H2O2, meaning one oxygen splits off to create h2o and o and the o is reactive). + +The Hydrogen peroxide will oxidize the alcohol, making it less effective, and it will oxidize the iodine and create a different chemical all together. + +Edit: just tried this so I wasn't a hypocrite in case it didn't work. If you have dry hands, pour alcohol on them. It will burn. Now pour peroxide on your hand, it will fizz. Now mix equal parts alcohol and peroxide in a bottle or cup and shake it vigorously for a few seconds, then let stand for a few seconds. Now pour it on your hand. It won't fizz, and it won't burn, and it won't smell that strongly of alcohol either. And oddly enough, it'll feel a little slippery." +1067 Why does a wound itch before it's healed? 5647 https://www.reddit.com/r/askscience/comments/8j8uml/why_does_a_wound_itch_before_its_healed/ 1526263764 8j8uml 2018-05-14 5:09:24 "There are a number of possible explanations for why itching occurs during wound healing. One or more of these explanations may be correct. + +Chemicals required for the wound healing process may also cause wound itching. Histamine is one of these potential for [early wound itching](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2519061/) and [plays a pivotal role in wound healing](https://www.ncbi.nlm.nih.gov/pubmed/1791057), and is released in response to cellular injury. + +Neuropeptides like [Substance P are also released during the wound healing process,](https://www.ncbi.nlm.nih.gov/m/pubmed/15792949/). While [Substance P has been proven to cause mast cells to degranulate, releasing histamine as well as other chemicals responsible for The immunoinflammatory response](https://www.ncbi.nlm.nih.gov/m/pubmed/8745057/) there are [other non-histamine controlled pathways activated by substance P have also been shown to cause itching,](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5546940/) which may show Substance P is partially independently responsible for transmitting pain and itch sensations to the brain. Mast cell degranulation and release of histamine is the primary accepted method that substance P triggers an itch sensation, but there is a possibility that there are other pathways involved in the itch sensation independent of histamine. + +There is also a potential mechanical explanation for wound itching. There are nerves in the skin that transmit pain and itch signals to the brain. As the wound closes, the edges of the wound constrict as collagen and connective tissue grow, potentially activating these nerves. " Histamine is released at the wound site during healing, which promotes vascularization (angiogenesis) and production of growth factors which accelerate skin cell growth and differentiation at the wound site. A side effect of this increased histamine is itching. +1344 Could solar flares realistically disable all electronics on earth? 5637 https://www.reddit.com/r/askscience/comments/boin2b/could_solar_flares_realistically_disable_all/ 1557838914 boin2b Astronomy 2019-05-14 16:01:54 "A solar flare, no. Maybe you're thinking of [coronal mass ejections](https://en.wikipedia.org/wiki/Coronal_mass_ejection) (CMEs), which can be troublesome. + +But even with CMEs, NASA says chill out: + +https://www.nasa.gov/mission_pages/sunearth/news/flare-impacts.html + +> But it is a problem the same way hurricanes are a problem. One can protect oneself with advance information and proper precautions. During a hurricane watch, a homeowner can stay put … or he can seal up the house, turn off the electronics and get out of the way. Similarly, scientists at NASA and NOAA give warnings to electric companies, spacecraft operators and airline pilots before a CME comes to Earth so that these groups can take proper precautions + +If you're not too prone to anxiety, read about the Carrington Event: + +https://en.wikipedia.org/wiki/Solar_storm_of_1859 + +The Earth's Aurora extended as far south as Columbia. It was so bright people got up in the middle of the night thinking it was morning. Some telegraph operators were able to send/receive messages with their batteries unhooked. Others had to fight fires caused by sparks leaping from their equipment. + +Oh btw a lot of people think NASA is downplaying the CME fears, [for example](https://www.sciencealert.com/here-s-what-would-happen-if-solar-storm-wiped-out-technology-geomagnetic-carrington-event-coronal-mass-ejection). + +****" "Read up on the Carrington Event of 1859. An event like this, were it to occur today, would likely cause widespread electric grid damage and result in electrical outages. These outages could be lengthy in duration due to the availability of replacement components. Satellites including communication and GPS would be affected. Astronauts and possibly humans at higher altitudes would be most affected by intense solar radiation and the duration of a solar storm would also make things worse. + + +No, it would not damage every terrestrial electronic device. You may be thinking of and EMP." +784 We often see ship hull breaches in space movies, but do they accurately depict the vacuum's pull? 5633 https://www.reddit.com/r/askscience/comments/6l5wni/we_often_see_ship_hull_breaches_in_space_movies/ 1499157723 6l5wni Physics 2017-07-04 11:42:03 "The vacuum ""pull"" is nothing but the internal pressure pushing against a lack of external pressure. So the force is given by a pressure differential of about one atmosphere acting on the area of the breach. For a small hole this is not a lot at all: Atmospheric pressure is 1 bar = 10^5 Pa = 100000 N/m^2 . If you have a breach with a cross section of 1 m^2 , the force would be 100000 N, i.e. roughly the equivalent of of 10 tonnes of weight distributed over that area. A hole with 100 cm^2 area (a fist sized hole in the hull) would only have 1000 N force, roughly 100 kg worth. Enough to lose air, but if you want to plug such a hole by putting e.g. a body part or a book on it it will hold. + +If you have access to a vacuum pump (e.g. in a science lab) put your finger over the tube and you will feel a slight pull - this is exactly what would happen with the space scenario. + +Movies rarely let science get in the way of a good story. + +" "The series 'The Expanse' on the SyFy network handles this smarter than any science fiction I've seen. + +Essentially the crew all [dons space suits and they depressurize the ship prior to combat. It makes for a cool effect as bits of shrapnel fly straight through the ship.](https://youtu.be/XhKWeGXduzs)" +966 How do scientists make sure that the light they are getting is from that particular heavenly body and not a nearby star, like the Sun? 5633 https://www.reddit.com/r/askscience/comments/7osvex/how_do_scientists_make_sure_that_the_light_they/ 1515354926 7osvex Astronomy 2018-01-07 22:55:26 "This question is extremely broad. Your question will most likely be interpreted as: + +--- + +""How do Astronomers get spectra of specific objects when there are other objects nearby?"" + +The answer to that is, we just block out the other light. Here's an example of an SDSS plate that takes a bunch of spectra from one ""Image"". Keep in mind SDSS is a specific survey, but plates are relatively common in the Astronomy world. I'm just using SDSS plates as an example. There's a few other methods, but this one is the most obvious and a very commonly used one. + +[SDSS plate visualization](http://blog.sdss.org/wp-content/uploads/2014/09/platez.png) + +[Actual sdss plate](http://shine.wp.st-andrews.ac.uk/files/2015/09/plate6612_small.jpg) + +Basically SDSS people know exactly where each object is, and hook up a bunch of fiber optic cables to the back of each hole in the plate. Then you can take 100 spectra in one image because you're only getting the light from one object in each cable. This is just a large scale use of this method. + +Also keep in mind that spectra for different objects are vastly different. + +[spectra of O-type star](http://hyperphysics.phy-astr.gsu.edu/hbase/Starlog/imgsta/otype.gif) + +[spectra of M-type star](http://www.martin-nicholson.info/sloan/m3.jpg) + +[spectra of super-massive-distant quasar object](https://ned.ipac.caltech.edu/level5/Charlton/Figures/figure1.jpeg) + +So it's pretty hard to mistake what exactly you're looking at if you've got spectra. If you have a field of stars they're usually separated enough to isolate their light, and their spectra are unique enough to clearly distinguish them. Galaxies are equally unique, as are any other of the objects in the sky. If you have a spectra of a galaxy it's pretty clear when a star shows up in it because of the giant peak of light, usually at specific wavelengths for specific elements that are emitting in that spectra. + +--- + +""When taking images of objects in space, how do you tell that you have the right object?"" + +Scales are pretty vastly different. [This isn't a spectra, just a color filter. The Stars in this image are all the bright points of light with little crosses. There are a lot of methods to pretty easily filter out unwanted light from stars in the way.] (http://www.astrophoto.net/images/uncalibrated_frame.jpg) If you're trying to take images or spectra of galaxies, you'll notice at one point your data is super bright and screwed up. You can either ignore it or filter it out. To filter it out you can take a lot of images from all the unwanted stuff, images of the wanted stuff, subtract the two, and you're left with the wanted stuff. + +edit: +When you have a star field and you're attempting to take images through a filter, [look at this post](https://www.reddit.com/r/askscience/comments/7osvex/how_do_scientists_make_sure_that_the_light_they/dscdtb8/)" "There is a fair bit of noise associated with any astronomical observation. There will be a base level of random photons being received from the sky that have to be subtracted at any given point before you can measure the source you are interested in. These could be scattered in the atmosphere or simply be from other faraway sources in the line of sight. + +However perhaps the real answer to the question is that all things being equal light travels in a straight line, so we know that nearly all the light we receive must have come from the very direction we are pointing the telescope. " +1068 What is happening in my body when I rest in between sets at the gym? Why does resting longer allow me to lift more the next set? 5623 https://www.reddit.com/r/askscience/comments/92sz4l/what_is_happening_in_my_body_when_i_rest_in/ 1532846778 92sz4l 2018-07-29 9:46:18 Read the basics about the ATP-CP pathway [here](https://en.m.wikipedia.org/wiki/Bioenergetic_systems). In short, heavy lifting exhausts the available ATP and a short rest replenishes a lot of it. Lifters often load creatine because they believe it will get them a couple of extra sets. "Taken from the book ""Recovering From Training"" by Drs. Israetel and Hoffman: + +**Section 3: The Pathways of Fatigue** + +As aforementioned, fatigue can be separated into acute fatigue, which dissipates within a single training session or very shortly thereafter, and cumulative fatigue which can take days, weeks or longer to resolve. For our current purposes, recovery from the latter type of fatigue (though not from the former) is critical, so we will go briefly over the acute pathways of fatigue and focus more heavily on potential pathways for its accumulation. + +Acute Fatigue Pathways: + +* ⠂  ATP Depletion +* ⠂  Creatine Phosphate Depletion +* ⠂  Nervous System Disruption +* ⠂  Oxygen Depletion +* ⠂  Blood Sugar Depletion +* ⠂  Metabolite Summation +**ATP Depletion** +Adenosine triphosphate (or ATP) is the transporter of chemical energy within cells and therefore the rate­limiting aspect of energy output. Insufficient ATP generates acute fatigue in high intensity exertions. The average muscle cell only stores enough ATP for about 1 second of maximum force production (explaining why plyometric movements are so depleting). Consequently, stored ATP is quickly exhausted during the first few seconds of exercise, forcing the body to regenerate ATP through the breakdown of other energy substrates. +**Creatine Phosphate Depletion** +When ATP is broken down into adenosine diphosphate (ADP) and inorganic phosphate as energy is used in the muscles, creatine phosphate (CP) can rapidly replenish ATP by donating its phosphate group to adenosine diphosphate (ADP). While this process doesn’t quite fully restore ATP levels, it comes close, and there is enough CP in the average skeletal muscle cell to power around 10 seconds of near­maximum muscle contractions. This is why 100 meter sprinters can run about the same speed toward the end of the race as they did about one quarter of the way through: not quite as fast as they did at the start, but pretty close. +Creatine phosphate is depleted during high­intensity efforts, and needs several minutes to recover to complete or near­complete levels. This is the reason that taking a 1­-3 minute rests between sets in weight training is a good idea. CP is regenerated to its full capacity within about 5 minutes of rest, which makes it a valuable energy substrate during intermittent, high intensity efforts. +**Nervous System Disruption** +It is generally accepted that decreased motor neuron output resulting from prolonged or intense exertion plays a role in fatigue generation, but the exact mechanisms remain unclear. Contributing factors may include negative feedback mechanisms via inhibitory neurons in the spinal cord, decreased or disorganized signaling from the motor cortex in the brain, and local + +11 + +neuronal firing issues (though these likely originate with biochemical changes in the muscle fibers that affect neuron signal propagation). + +These acute nervous system effects curb performance within the session, but sufficient rest should restore them to normal states. + +**Oxygen Depletion** + +Oxygen consumption in the muscle tissue can get so extreme that it exceeds the rate at which the body can deliver fresh oxygen to that area. In exercise physiology this is termed the “Oxygen Deficit”, where the oxygen already present in the muscle tissue is metabolized rapidly during exercise, but the cardiovascular and pulmonary systems have not yet adjusted to the increased energy demand on the body. This creates a “deficit” or gradient of oxygen concentration between the muscle tissue and the bloodstream. Within a few minutes of rest, however, oxygen levels can be replenished and homeostasis restored. + +**Blood Sugar Depletion** + +When we consume carbohydrates, whether as complex carbs from bread and pasta or as simple sugars from candy or juice, they are broken down into simple glucose molecules and released into our bloodstream to be used or stored for later. If you train for long enough without eating, especially under low carbohydrate conditions, you can run short on blood sugar. Because the nervous system prefers blood glucose over any other kind of fuel, when this preferred energy source is low, physical performance levels will begin to predictably drop. The good news is that a simple carb shake can quickly remedy this. Unused blood glucose can be combined into huge polysaccharides composed of many glucose molecules, called glycogen and stored in the liver or muscles. The liver releases its stored glycogen to replenish blood glucose levels. Even if liver stores are totally depleted, a couple of high carbohydrate meals after training can fully restock this supply. When liver glycogen stores are full, they can provide adequate blood glucose to fuel the demands of hours of training. Muscles also store carbohydrate as glycogen, but use it as a local energy source within the muscle rather than releasing it into the bloodstream. Due to its location within active muscles in need of energy, muscle glycogen is used preferentially during exercise and is more rapidly depleted. + +**Metabolite Summation** + +Muscles use a variety of reactions to produce the energy needed for contraction and these processes come with the creation of byproducts called metabolites. These molecules, including hydrogen ions, CO2, inorganic phosphate, and lactate are not all innocent bystanders. The accumulation of high levels of metabolites can result in interference with neuromuscular signaling and the mechanisms of muscle contraction itself. Metabolites can also significantly lower local pH, which results in the familiar “burn” experienced during training. Luckily, most of these metabolites are cleared within seconds after training. The notion that lactic acid from a previous day’s training remains uncleared from the body for an extended period of time is a common misconception, as lactate concentrations typically return to resting conditions within a few hours after exercise." +649 If a black hole created from matter, and a black hole created from antimatter collide, is the result a bigger black hole or would something else happen? 5616 https://www.reddit.com/r/askscience/comments/5tf5q6/if_a_black_hole_created_from_matter_and_a_black/ 1486824850 5tf5q6 Physics 2017-02-11 17:54:10 "A black hole built from antimatter or one built from matter with the same mass are identical. + +The quantity that distinguishes matter from antimatter is the baryon number. It is the total number of baryons (like protons and neutrons) minus the number of antibaryons. Baryon number is conserved in the standard model and that is what you would recognize as ""conservation of matter"" in some sense, and the reason for which the proton is stable in the SM: it is the lightest baryon and so it cannot decay to anything else because it needs to preserve its baryon number of +1. So the proton can only release its mass in energy for lighter particles if it meets an antibaryon carrying -1 baryon number, so they total to 0 and they can produce lighter non-baryon particles such as photons or mesons. That's why matter & antimatter annihilate. + +(A similar argument works with leptons, with a thing called lepton number). + +These, baryon and lepton #, however, are not conservation laws with any specific deep or fundamental justification behind, they are just accidental symmetries of the standard model. (Unlike, for example, charge). As soon as you step out of the SM, these are violated. Black holes are well outside the SM and do not care in the slightest about baryon number. Black holes don't have a well-defined baryon number and throwing a proton or an anti-proton\* into a black hole produces the same final black hole, whose only macroscopic distinguishing properties are mass, charge and angular momentum. After a lot of time the black hole has evaporated into Hawking radiation which is made of standard model particles, and the final baryon number of the radiation does not have any discernible relation with the baryon number of all the stuff that fell in. + + +\* woops forgot: except for charge, charge is conserved even by BHs. So maybe you can throw a hydrogen atom (baryon # 1, charge 0) or an anti-hydrogen atom (baryon # -1, charge 0). Or neutron/antineutron. " Even if the matter and antimatter inside of the now-merged black holes annihilate, the total energy of both is still contained inside of the black hole and cannot go anywhere anyways. Given that there is an equivalence between mass and energy, which does apply to particles with a mass of zero according to the full mass-energy equation (E^2 = (mc^(2))^2 + (pc)^(2), from which the famous E = mc^2 is derived), and that the only path available once inside the event horizon is towards the center of it, the mass of the resulting black hole would simply be the sum of the masses of the two colliding black holes. +102 A message to our users 5612 http://www.reddit.com/r/askscience/comments/3by2nk/a_message_to_our_users/ 1435891427 3by2nk Meta 2015-07-03 5:43:47 "For those that are out of the loop, here's what going on: +https://www.reddit.com/r/OutOfTheLoop/comments/3bxduw/why_was_riama_along_with_a_number_of_other_large/ + +Edit: To keep a little bit of science in every AskScience post, here's a neat color photograph of Pluto and Charon taken by the New Horizons spacecraft: +http://pluto.jhuapl.edu/Multimedia/Science-Photos/image.php?gallery_id=2&image_id=191" Here's to hoping r/funny joins in the solidarity. +967 Is extra muscle as hard on the heart as extra fat? 5608 https://www.reddit.com/r/askscience/comments/7tkb60/is_extra_muscle_as_hard_on_the_heart_as_extra_fat/ 1517147183 7tkb60 Human Body 2018-01-28 16:46:23 "Medical doctor. Short answer, for the average person, no. + +Your heart gets stronger through 2 methods: hypertrophy and **contractility**. Typically through exercise the latter happens - your heart doesn't get more muscular so much as it gets better at squeezing out the blood that's there. This is why elite athletes heart rates slow down, to even the 30s-50s when you look at cyclists - their **stroke volume** (how much blood the heart moves with each pump) improves. + +In normal exercise conditions your body mass and cardiac health increase 1:1 (ish). This becomes untrue if you build muscle through anabolic steroid use, which also has its own independent negative effects on the heart, hence why increasing muscle mass rapidly through non physiologic methods is unhealthy. + +In obesity, your heart undergoes hypertrophy to compensate for the added work. However, this works against the heart because not only does it have to pump blood, it has to *relax* to let blood fill. Imagine you have a cup that suddenly becomes 2 inches thicker on the outside *and* inside - suddenly the cup holds less volume, and the heart actually has to pump faster to put out the same volume as before. Again, typically the way you gain bodily muscle mass involves exercise, so the exercise has its own effects that puts people on a better path. + +The things other commenters are talking about - hypertrophic cardiomyopathy (sudden death from heart muscle that is too thick) - are unrelated to your total body mass, these are typically genetic conditions that affect both athletes and non-athletes (it just tends to kill you at moments when your heart is working harder). + +Edit: here's an excellent diagram of the different types of cardiac hypertrophy. Notice that in the athlete's heart the muscle gets thicker *and* the chamber size widens. In the obese and diseased person the muscle just gets thicker without that compensatory dilatation. https://www.msdnews.com/wp-content/uploads/2016/08/Sudden-death-in-hypertrophic-cardiomyopathy-rarely-associated-with-exercise-Science.jpg" "I would actually think up to a point of muscle building the heart can compensate-in many athletes there is natural hypertrophy (“thickening/enlargement”) of the heart muscle that is compensatory to account for the activity the person is posing and is good. The thicker the walls the stronger the heart can push blood. However, there’s a point where that compensation can fail leading to cardiomyopathies. I would think this “point” would be hard to reach in athletes though. It’s also very common in race horses to skip beats or have natural hypertrophy as they are essentially running machines. + +However, with that being said I know many body builders die of cardiomyopathies and cardiac-related deaths- I never thought of this as a possible cause but it makes sense- muscle requires a lot more vasculatization and blood flow to operate and if you have too much muscle your blood volume may not be able to equilibrate for that much mass. + +Really interesting question- I’ll do more research and let you know if I find anything too! + +Edit: Here’s and article on athletic hypertrophy: http://www.acc.org/latest-in-cardiology/articles/2014/10/14/11/02/the-athlete-grey-zone-distinguishing-pathologic-from-physiologic-left-ventricular-hypertrophy + +Also, from what I’m reading it’s because of steroid use (anabolic steroids) that body builders have hypertrophic cardiomyopathy. " +1345 "How should I imagine a Jurassic prairie, in terms of the common plants, without major grasses or flowering plants? What would have been the default ""ground cover"" for such an environ?" 5602 https://www.reddit.com/r/askscience/comments/coc8hr/how_should_i_imagine_a_jurassic_prairie_in_terms/ 1565403916 coc8hr 2019-08-10 5:25:16 "[This](https://en.wikipedia.org/wiki/Morrison_Formation#Fossil_content) section of the Wikipedia page on the Morrison Formation (late Jurassic) may be most constructive: + +>Though many of the Morrison Formation fossils are fragmentary, they are sufficient to provide a good picture of the flora and fauna in the Morrison Basin during the Kimmeridgian. Overall, the climate was dry, similar to a savanna but, since there were no angiosperms (grasses, flowers, and some trees), the flora was quite different. Conifers, the dominant plants of the time, were to be found with ginkgos, cycads, tree ferns, and horsetail rushes. Much of the fossilized vegetation was riparian, living along the river flood plains. Insects were very similar to modern species, with termites building 30-meter-tall (98 ft) nests. Along the rivers, there were fish, frogs, salamanders, lizards, crocodiles, turtles, pterosaurs, crayfish, clams, and mammaliforms. + +Of course, no angiosperms, and since grasses [didn't appear until 55-66 MYA](https://en.wikipedia.org/wiki/Poaceae#Evolutionary_history) (depending upon what you want to call a ""grass""), no ground cover, at least not as we know them. + +Depending upon moisture levels, there may have been algae, lichens, bryophytes, and ferns; even here in the desert, we get ferns like [Selaginella](https://en.wikipedia.org/wiki/Selaginella) that do well in drought, and [cryptogamic soil](https://en.wikipedia.org/wiki/Biological_soil_crust). + +Areas with more moisture might have had some mosses like sphagnum, and in the shade under conifers there could have been [lycopods.](https://en.wikipedia.org/wiki/Lycopodiophyta)" "For prairie-like ecosystems we have a number of lines of evidence that indicate that ferns occupied a similar niche to grassland type ecosystems in the present day. Essentially low-growing ferns instead of grasses in many areas. Possibly also with certain types of hardy mosses and lycopodium as well. Likely a number of small flowering plants later on as flowering plants evolved more than 145 million years ago. + +> The Mesozoic era might also have had large, open areas with low-growing vegetation, including savannas or fern prairie with dry, nutrient poor soil populated by herbaceous plants, such as ferns of the families Matoniaceae and Gleicheniaceae. +https://ucmp.berkeley.edu/mesozoic/triassic/triassic.php + + +> The vegetational dominants of the “fern prairies” at BCR belonged to non-polypod orders, which together comprised two-thirds of pteridophyte diversity. Polypodiales, in contrast, were significant in diversity (one-third of species) but minor in biomass. +[Dominance and diversity in a Late Cretaceous fern prairie at Big Cedar Ridge, Wyoming.](http://2013.botanyconference.org/engine/search/index.php?func=detail&aid=354)" +1069 When do deep-ocean thermal vent animals sleep, if at all? 5584 https://www.reddit.com/r/askscience/comments/8xvckh/when_do_deepocean_thermal_vent_animals_sleep_if/ 1531272813 8xvckh Biology 2018-07-11 4:33:33 "Ooh, this is a really interesting thought! What you're asking is whether deep sea critters have something known as a circadian rhythm, or a 'body clock', that regulates their behaviour - in this case, sleep. Most multicellular organisms have one, and it's usually regulated by exposure to daylight and nighttime. So what of creatures that can't detect this shift in light levels, or photoperiod? + +Alas, there are no published studies as far as I'm aware that have investigated circadian rhythms, or lack thereof, in deep sea fish. Not really surprising, as they're awfully difficult beasties to find and study anyway, let alone in the lab! + +What you might find interesting however is that we've done a buncha' studies on sleep in cave fish. [Mexican blind cave fish](https://en.wikipedia.org/wiki/Mexican_tetra) have two forms - a surface-dwelling sighted form that lives outside, and a blind cave form that lives in perpetual darkness. What's interesting is that the blind form has completely shut down it's circadian rhythm, and therefore saves about 30% more energy by default, compared to it's sighted form which 'gears up' every day in response to daytime. + +In the absence of light, the blind fish therefore don't have a 24-hour cycle and don't need to 'tell' whether it's day or night. Living in perpetual darkness, it's also disadvantageous to conform to a day-night sleep cycle anyway. Given food is scarce, it makes sense to try and remain awake and alert as much as possible - just in case a tasty morsel floats by. They therefore rarely sleep, and do so only in very short bursts, throughout a 24 hour period. + +I expect what applies to these cave fish applies equally well to deep sea fish. They don't care what time it is up on the surface, and sleep in quick snatches whenever and wherever. + +If that helps answer your question? +____ + +^**Sources:** + +[^(Duboué, E.R., Keene, A.C. & Borowsky, R.L. (2011)^) ^(Evolutionary Convergence on Sleep Loss in Cavefish Populations. *Current Biology*. 21 (8)^), ^671-676](https://www.cell.com/current-biology/abstract/S0960-9822%2811%2900292-2). ^Press ^release ^[here](https://www.nyu.edu/about/news-publications/news/2011/april/fishes-that-dont-sleep-point-to-genetic-basis-for-slumber-nyu-biologists-find.html). + +[^(Moran, D., Softley, R. & Warrant, E.J. (2014)^) ^(Eyeless Mexican Cavefish Save Energy by Eliminating the Circadian Rhythm in Metabolism. *PLoS One*. 9 (9)^) ](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0107877)" "A bit tangential, but fun! + + +Giulio Tononi's theory about sleep is that it is the price we play for neuroplasticity. There's loads of evidence to support this. In the simplest possible terms, neurons that fire together wire together. Throughout the day, perceptual inputs cause changes that we call learning. Sleeping does two things, it shuts off the perceptual systems (otherwise the systematic firing together would necessarily continue), and it actively resets the system by pruning connections based upon how strongly they fired together during the day (this is why you completely forget things like the color of your professor's tie, but you retain the things you focused heavily on like the contents of the lecture). + + +Different animals have lives that require different amounts of learning about their environment. Humans have very complex lives, so learning is outrageously important. Presumably, crustaceans near an ocean vent don't have to learn very much on a daily basis. They aren't facing novel problems technological problems, they likely aren't navigating to new locations very frequently, they probably don't have much need to communicate, etc. The less learning you require, the less sleep you need. Sleep, after all, is quite a risky thing to do. + + +If I recall correctly, Tononi reports that he has yet to find a living organism that contains neurons of any sort that does not have some sort of activity state that is at least analogous to sleep. Some don't have slow-wave REM sleep, for example, but they all have some sort of sleep-state during which the system can be reset. He has tried. He was actually contracted by the DoD to find a way to defer the need for sleep, through drugs or whatnot, so that soldiers could last for 4-5 days without sleeping. It simply can't be done." +968 Why do joints ache so much when you get the cold/flu? 5559 https://www.reddit.com/r/askscience/comments/7r6z4a/why_do_joints_ache_so_much_when_you_get_the/ 1516247251 7r6z4a Human Body 2018-01-18 6:47:31 "Inflammation, specifically chemical signal molecules called cytokines. + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2785020/ + +When you get infected with the cold or flu viruses you get replicating virus that likes to infect lots of cells. As a response, infected cells begin to alert nearby cells by sending out molecular signals called cytokines. These signals alert neighboring cells to up their defenses and tell the immune system something is going down. These cytokines include interleukins and TNFa. Activated immune cells in turn pump out more (and different) cytokines to recruit more immune cells and signal to various parts of the immune system to perform their functions. + +Neurons interestingly have receptors for many cytokines, linking the immune system to the nervous system. This can cause neuronal activation and signal pain. Additionally, inflammatory cytokines can trigger the production of prostaglandins, which are lipid messenger molecules. They have known roles in lowering the threshold of neuron activation. Meaning that elevated prostaglandins can lead to easier triggering of neurons that signal pain. + +On cytokines and neurons: https://www.ncbi.nlm.nih.gov/pubmed/8485449 +On prostaglandins: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2430679/ + +And as a side note for more localized pain: chest pain can occur due to tissue damage by the virus as well as increased fluid/cells that influx as a result of the mounting immune response. This swelling causes pain." "Cytokines is correct but what may be a more fitting answer to ""why"" is that the cytokine induced myalgia (muscle soreness) causes breakdown of skeletal muscle cells which frees up proteins and amino acids to be converted to antibodies etc by the liver. + +Here is an excerpt from ""Understanding the symptoms of the common cold and influenza."" (a review from The Lancet, Infectious Diseases) which is a very interesting review which covers why we go through all the symptoms during a URTI (upper respiratory tract infection). + +""Muscle aches and pains (myalgia) are a common symptom of URTIs, with around 50% of patients with common cold experiencing these symptoms.49 Myalgia isa symptom of the acute phase response to infection and there is evidence that the symptom is caused by the effects of cytokines on skeletal muscle.63 Proinflammatory cytokines have been implicated as inducing the breakdown of muscle proteins, and tumour necrosis factor was initially referred to as cachetin because of its role in causing muscle wasting or cachexia.64 The breakdown of muscle protein in response to URTI can be viewed as beneficial because it mobilises proteins and amino acids that can be converted in the liver to opsonins and other components of the immune response.64 Fever associated with URTIs is usually accompanied by other systemic symptoms such as myalgia and there is much evidence that indicates that both these symptoms are caused by the production of prostaglandin E2 in response to circulating cytokines.63The cytokine-induced generation of prostaglandin E2and the breakdown of skeletal muscle in vitro is inhibited by indomethacin,63 and similarly myalgia associated with URTIs is relieved with acetylsalicylicacid.49 Prostaglandin E2 is a mediator of pain by its effects on peripheral pain receptors.65 The cytokine stimulation of prostaglandin E2 production in skeletal muscle, and the effects of prostaglandin E2 on sensory nerves in muscle, may explain the myalgia associated with URTIs."" + +Edit: got rid of all the line breaks in the copied text " +1346 AskScience AMA Series: I'm Dr. Allison Kirkpatrick, an expert on supermassive black holes, and discoverer of the newly defined Cold Quasars. Ask Me Anything! 5557 https://www.reddit.com/r/askscience/comments/c20ujb/askscience_ama_series_im_dr_allison_kirkpatrick/ 1560855608 c20ujb 2019-06-18 14:00:08 "Hi Dr. Kirkpatrick, and congratulations on your impressive work! I was wondering, how do your newly discovered cold quasars fit within the taxonomy of quasars? Can previously documented subsets of quasars be re-characterized as ""cold"" in light of your new findings, or rather are cold quasars an entirely new discovery that requires adding a new branch to the taxonomic quasar tree? + +​ + +Thanks!" Is there a theoretical size limit to how massive a black hole can get? +1347 Why do people say that when light passes through another object, like glass or water, it slows down and continues at a different angle, but scientists say light always moves at a constant speed no matter what? 5549 https://www.reddit.com/r/askscience/comments/bv5044/why_do_people_say_that_when_light_passes_through/ 1559291607 bv5044 Physics 2019-05-31 11:33:27 "We're just speaking loosely. + +The speed of light *in a vacuum* is a universal constant. It is also ""invariant"", which means it doesn't change depending on your reference frame - i.e. it doesn't depend on your speed or location. + +The actual speed of light through a medium - not just the abstract theoretical limit of ""speed of light in a vacuum"" - can change depending on the medium, and isn't a universal constant. + +Edit: To clarify further, it might seem a bit odd that so much of physics depends on light, which is after all just one type of specific phenomenon. But really that's backwards. ""c"" is a special universal constant that tells us about the relationship between space and time, the propagation rate of information and so on. It just so happens that some phenomena - such as electromagnetic waves - will travel at *c*, under idealised circumstances. That is, relativity isn't really about light itself, it's just that light is strongly affected by relativity so it provides a useful way to work out what relativity does." "scientist say its a constant speed in a vacuum, not no matter what. + +why light slows down + +[https://www.youtube.com/watch?v=CUjt36SD3h8&list=PLpJPkyPx-rk6BKqQYev3lXeStMngVf5Mx&index=6&t=0s](https://www.youtube.com/watch?v=CUjt36SD3h8&list=PLpJPkyPx-rk6BKqQYev3lXeStMngVf5Mx&index=6&t=0s) + +​ + +why light bends + +[https://www.youtube.com/watch?v=NLmpNM0sgYk&list=PLpJPkyPx-rk6BKqQYev3lXeStMngVf5Mx&index=3](https://www.youtube.com/watch?v=NLmpNM0sgYk&list=PLpJPkyPx-rk6BKqQYev3lXeStMngVf5Mx&index=3)" +1244 Do primates have mental disorders like humans? 5547 https://www.reddit.com/r/askscience/comments/b8q58d/do_primates_have_mental_disorders_like_humans/ 1554245386 b8q58d Biology 2019-04-03 1:49:46 Animals, including primares, can show behavioral issues relating to anxiety, depression, and neuroses. I'm not sure if one could diagnose a primate, unless all the criteria for the diagnosis were observable behavior patterns. If the gorilla was compulsively and frequently tearing off scabbed flesh, I would assume the gorilla is anxious or bored, possibly due to the zoo environment. "I can't speak to gorillas, but yes, primates can suffer from behavioral conditions that could be described as psychological disorders. + +Back in the 50s and 60s, Harry Harlow did experiments on Rhesus monkeys that could be considered unethical by today's standards. These experiments included giving infant monkeys a choice between surrogate mothers; one was made of wire but had food, and the other was made of cloth but had no food; the infants preferred the cloth mother, who was soft like a real mother would be, despite the lack of nourishment. + +He did another version of the experiment in which the monkeys did not have a choice, and those raised with the wire mother behaved differently from those raised with the cloth one. +Harlow also put infant monkeys in ""the pit of despair,"" where they would spend their first years in almost complete isolation. The monkeys who underwent this emerged ""disturbed"". + +[The Nature of Love](https://psychclassics.yorku.ca/Harlow/love.htm) + +[Total social isolation in monkeys.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC285801)" +969 In the last 5-10 years, there’s been tremendous efforts made by many of the first world countries to curb carbon emissions. Have we made a dent? 5532 https://www.reddit.com/r/askscience/comments/8dk08m/in_the_last_510_years_theres_been_tremendous/ 1524188456 8dk08m Earth Sciences 2018-04-20 4:40:56 "Carbon emissions data is a really tricky subject and you have to be really careful with the graphs and data you read. + +For example many countries are not reducing their absolute carbon emissions, but reducing emissions per GDP. In essence as Long as their GDP grows faster than their emissions they look like they are reducing their emissions. Some countries have really stepped up their game with Australia pledging 5% reductions regardless of the rest of the world. However, with increasing protectionism in large global players like USA, the global agreement and action is unlikely to take effect. Also, climate change is a really Long term problem with effects happening in 50-100 years. Most governments are only interested in maybe the next 20 years and reelection’s so to them it isn’t a big priority. + +The IPCC AR5 report shows us that the danger of inaction now is likely to to cost magnitudes more than taking action now. But without global cooperation, CO2 is likely to exceed the 450ppm threshold that will allow us the time to adapt to climate change. + +However it is a good to note that even if all emissions were to stop now, the temperature would continue to rise due to the delayed action of our carbon sinks. Also there are a bunch of cool geoengineering projects that people believe we can “innovate” our way out of global warming like aerosol spraying and biosequestration using micro algae. So not all is lost, but much needs to be done. Whatever we are doing now is too little and too slow to avoid the deadliest impacts. We are on course for a more than 2 degree rise when the target is 1.5 degrees. There is a huge difference between them. " "Perhaps this is semantics. But I'm really not sure there has been ""tremendous efforts by first world countries."" There have certainly been tremendous efforts by individuals and NGOs. But most governments have not even come close to implementing the kinds of efforts consensus scientists have said would be necessary to deal with the problem. + +I feel like this is worth saying. The reason impacts have been underwhelming is not because scientists were wrong about what measures would be necessary or what the outcomes of those measures would be. It is because most governments have not been willing to do what scientists said we had to do. Even ""pro climate change"" agreements don't come close to implementing what the climate scientists proscribe as necessary." +1348 As the ISS grew over time, it’s center of mass must have changed location. How did their thrusters change their behavior or were they literally moved to a new location? 5532 https://www.reddit.com/r/askscience/comments/bl13hh/as_the_iss_grew_over_time_its_center_of_mass_must/ 1557080516 bl13hh Physics 2019-05-05 21:21:56 [deleted] "The ISS maintains orientation primarily through the use of gyroscopes, which can be used to counter any torque applied during thruster firings. + +Edit: As pointed out in the lower comments, the ISS actually uses a related technology called Control Movement Gyroscopes, the explanation given below is still an accurate representation of the situation, but the actual specifics of implementation are more complex than I've described as a result. + +A gyroscope is basically a heavy (and very well balanced) wheel. When you spin it clockwise, the motor spinning it has an equal and opposite force pushing it counterclockwise. So if you hook up a little DC motor to a battery and a wheel then drop it at the same time you turn it on, the wheel will turn one direction and the motor the opposite. + +So if the ISS is spinning about its X axis in one direction, then you can use the gyroscope to cancel it out, ""storing"" the rotational energy in the wheel. If you reduce the power to the motor then the momentum of the wheel is going to drop, dumping that energy back into the ISS. So you always have to keep the wheels spinning. + +Over time the gyroscopes become ""saturated"" which means that the motor cannot spin the wheel any faster, and so any additional spin on the ISS cannot be taken away by the wheel. In these cases they do a ""desaturation burn"" where a thruster is fired to cause the ISS to spin in the direction that cancels out the spin caused by the wheels slowing down. + +Fuel has mass and mass is precious in space, so you only burn thrusters when you really have to or if you happen to have some extra fuel, as was the case sometimes when the Space Shuttle would dock with the ISS. The SS always launched with a small extra fuel margin, just as a backup in case something went a bit wrong on the ascent, and once docked with the ISS the extra fuel didn't have any purpose, so they used it to save on the fuel the ISS had to use. [Here's a good video showing how quickly the ISS accelerated during these events.](https://youtu.be/sI8ldDyr3G0?t=202) Thrusters also are not terribly precise beasts in the grand scheme of things and burns are planned with an understanding of the error margins. Any given second of thruster firing is going to be ALMOST as the same as any other second, but not exactly. The gyroscopes on the other hand, just use electricity which the ISS generates in abundance and are very precise when it comes to the momentum they impart. + +So usually what they do, as I understand it, is that if the station tends to build up a clockwise rotation about say the X axis, then they will 'overburn' on the desaturation, so that way instead of the gyroscope slowly spinning faster and faster after the reset, it starts spinning slower and slower...eventually stops...then spins faster in the other direction. + +Edit: Check out /u/GNCengineer's post for better specifics." +1110 AskScience AMA Series: I'm Alex Marson and I'm an immunologist at UCSF. My lab is building more efficient CRISPR-based gene editing tools to supercharge the human immune system to fight cancer, infectious disease, and autoimmunity. AMA! 5519 https://www.reddit.com/r/askscience/comments/9igycc/askscience_ama_series_im_alex_marson_and_im_an/ 1537786818 9igycc 2018-09-24 14:00:18 If CRISPR is used, is there a chance for children to inherit that modified DNA? For example, if two parents are given boosted immune systems, will the child have a chance gain a boosted immune system? What is your opinion of the biohacker movement and the people who sell and buy crispr kits with the obvious intent of selfexperementation? +1349 How did the planetary cool-down of Mars make it lose its magnetic field? 5507 https://www.reddit.com/r/askscience/comments/cjpf7h/how_did_the_planetary_cooldown_of_mars_make_it/ 1564479710 cjpf7h Planetary Sci. 2019-07-30 12:41:50 "Mars' magnetic field is thought to have a very similar origin as Earth's magnetic field. It is created by [dynamo action](https://en.wikipedia.org/wiki/Dynamo_theory) in the molten core. +For this dynamo to occur several conditions need to be met. + +* You need a conductive fluid, i.e. molten iron. + +* Kinetic Energy (provided by the planetary rotation) + +* An internal heat source that causes convection in the liquid conductor to occur (heat from the formation of the planet, radioactive decay, differentiation of the planets interior, etc.) + +It is thought that Mars' internal heat source is too weak to drive the convection needed for the dynamo action to occur. We don't know for sure yet. But now we have a very accurate seismometer on Mars onboard of the Mars Insight lander. We will get more accurate data about the planetary interior. It will be an important part to get some certainty about Mars' magnetic field." "As a simple explanation of planetary magnetic fields for terrestrial (rocky) planets. + +If you take a big hot molten mass, particularly one high in metals, and you spin it around it will generate a magnetic field. We've simulated this by filling a giant spherical coil with molten ~~cesium~~ sodium and spinning it around, observing the magnetic field. There are two components, speed of spin and temperature. If you want to maintain the same magnetic strength while raising one of these components, the other must lower. IE: If you increase the temperature you must slow the spin. + +As that core of molten material starts to cool it will inevitably start to slow, relative to the rest of the planetary mass anyway. That will result in a small drop in the strength of the magnetic field, but in particular the drop in temperature is what decreases the strength of the field. Since one/both of the components are lowering in value, the overall strength decreases." +526 If you point your phone camera at an IR LED (like in a TV remote) it is visible but why does it show up as blue/purple rather than red? 5502 https://www.reddit.com/r/askscience/comments/5eut75/if_you_point_your_phone_camera_at_an_ir_led_like/ 1480096470 5eut75 Engineering 2016-11-25 20:54:30 "The explanation has to do with how digital cameras try to determine the color of an object. Cameras usually use a sheet of silicon sensors to detect the intensity of incoming light. However all the intensity tells you is how much total light falls on a given pixel (weighted by how responsive the sensor is in that spectral region). In other words, the best you could do at this point was to build up a grayscale image. In order to get information about the color, you need some way to separate light by wavelength. One way to do this is by adding a grid with color filters, e.g. a [Bayer filter](https://en.wikipedia.org/wiki/Bayer_filter) on top of the sensor layer, [as shown here](http://i.imgur.com/Gkv5a3M.jpg). + +Now this set of filters is the only know the camera can distinguish between different colors. Because there are only three color filters, there is only so much spectral information you can get. However, that is fine, since our eyes also only have three types of biological censors, called cone cells, [that can distinguish colors](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Cones_SMJ2_E.svg/1016px-Cones_SMJ2_E.svg.png). As a result, a camera can detect more or less as much spectral information as our eyes can see. A display can then use three color sources (e.g. RGB or red, green, and blue lights) to mimic the same color our eyes can see. + + +That intro was a bit long, but we finally we can get to the heart of the question. The actual efficiency of the red, green and blue pixels of a camera is shown in [this graph](http://imgur.com/a/QsrMo). Notice that above 650nm, a filter is said to block off most of the near infrared (IR) light. Of course, a bit of it will leak in. In the case of things like an IR remote, the light will usually have a wavelength of ~900nm. In that wavelength range, the green, red, and blue detectors are triggered about equally strongly. Now when the camera tries to map this response on the RGB color space, it looks for the closest mixture of visible colors that would have given the same reading. It turns out that you can mimic a similar response by shining white light with a bit of extra blue/violet light mixed in. As a result, the camera decides that this was the light that must have hit it and records the infrared light as having a violet hue. " "The best answer I've ever had to this question came from a Quora article: + +https://www.quora.com/Sensors-Why-does-infrared-appear-purple-in-digital-cameras + +This is a response curve for a typical digital camera sensor: + +http://i.imgur.com/xXa8prP.png + +So you'll notice that when the light is blue (wavelength of 400 to 500nm), the red and green sensors on the CCD/CMOS mostly ignore it, but the blue sensor picks it up. Same for red - between 600 and 650, which is where red light is, only the red sensor picks it up, mostly. + +But infrared is often defined as between 750nm and 1000nm. And you'll notice that for most of the infrared section of the graph, all 3 color sensors on the chip pick it up almost equally. Your TV remote is probably emitting infrared light at about 825nm, where it is mostly just the red and blue sensors that react to it, but less the green sensor, which is why it appears purple. A little higher, and it's closer to blue than purple. Even higher than that, and all 3 sensors pick it up equally, which should make it appear white on the camera's display. + +So to sum up, it's because the blue/red sensors on your camera's sensor don't just react to blue and red light respectively, they also both react to infrared light almost equally. It isn't easy to manufacture sensors that *don't* have this issue, so even the most expensive digital cameras typically just put a glass infrared blocking filter in front of the sensor, or somewhere in the lens. " +1070 People subjected to high amounts of radiation tend to report seeing bright flashes of color, a pins and needles sensation, and a metallic taste. What does the radiation do to the body to cause these sensations? 5491 https://www.reddit.com/r/askscience/comments/92huvg/people_subjected_to_high_amounts_of_radiation/ 1532737210 92huvg 2018-07-28 3:20:10 "Some wonderful people volunteered to have radiation shot at their head to see if they could replicate these light flashes. https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena#Ground_experiments_in_the_1970s + +There basically seem to be two plausible hypotheses. One is that very high energy particles could generated Chernenkov radiation within the eyeball. This would be seen as a flash of blue light. It's not confirmed, but it's plausible. + +The ground-based experiments showed that even particles incapable of generating these literal flashes of light still caused people to *see* flashes of light just fine. Since radiation shot at the brain doesn't seem to register anything, it further seemed reasonable to conclude that direct activation of neurons in the visual processing centers of the brain is not the cause. + +Instead, it is thought that most radiation that causes visual phenomena does so through directly activating photoreceptor cells in the eye. + +Now, one of the curious things about the way the eye works, is that even when you are ""dark adapted"", that is, you have not seen a bright source of light in about half an hour, it takes the activation of more than one photoreceptor cell to register a visual phenomenon. It's thought it actually takes around 10 cells to do so in the dark adapted state. + +A way this can happen with radiation is through what is called a ""particle shower"". Basically, a high energy particle interacts with an atom, and liberates an electron. But that liberated electron has so much energy it can actually bump into another atom, and liberate another electron. It's like a chain reaction, except it's less energy every time, so it doesn't go on forever. + +Anyway, a particle shower like this can cause a small region of cells to all get hit by ionizing radiation, and that could cause you to see a flash. + +So all that aside, your question asked about people who were subjected to ""high amounts of radiation"". It's known that victims of criticality accidents report seeing very bright light, even in well lit areas. One also reported feeling as if he was ""burning up"". Since everything I told you was based on the study of astronauts and test subjects, these were people exposed to high energy, but low doses, of radiation. There could be something more going on with someone who is exposed to a really tremendous, even deadly amount of high energy radiation." "The metallic taste is probably because of radiation damaging or at least irritating the chorda tympani nerve which communicates taste to the brain. It is part of an actually pretty complicated feedback loop where each nerve *inhibit* the signal of other nerves! This particular nerve seem to have a particularly strong (inhibitory) influence upon the others. + +Hard to tell about metallicity in paritcular. I think it is just by ""accident"" that if you damage this nerve, now more uninhibited signals from others just happen to result in a sour or metallic taste. + +Sources: + +1. [“Electric Taste” after Section of the Chorda Tympani](https://www.nature.com/articles/2141113a0) +2. [Chorda tympani nerve function after middle ear surgery](https://www.ncbi.nlm.nih.gov/pubmed/17195771) + +You can also read more about radiation and phantom metallic taste here: + +[http://optimalprediction.com/radiation-and-the-metallic-taste-phantom/](http://optimalprediction.com/radiation-and-the-metallic-taste-phantom/) + +Some report that following consistent exposure of this metallic taste, they have subsequent reduced/lost taste altogether, so this doesn't seem like something you want to sense for long periods of time... + +\--- + +I have no special sources on this but I would guess that pins and needles and bright flashes are radiation activated nerves and photoreceptors. I *d*o know that bright spots/flashes in digital camera sensors can happen from activated photoreceptors by radiation (you can sometimes see that in photography from e.g. the IIS or the Moon), and since we have a biological counterpart there... + +Source: [The Effects of Space Radiation on Flight Film](https://ston.jsc.nasa.gov/collections/trs/_techrep/CR188427.pdf) \[PDF\]" +869 Why aren't there any orbitals after s, p, d and f? 5489 https://www.reddit.com/r/askscience/comments/713bvh/why_arent_there_any_orbitals_after_s_p_d_and_f/ 1505831362 713bvh Physics 2017-09-19 17:29:22 "There are. The orbital angular momentum quantum number can be anything from 0 to (n - 1), and n can be anything from 1 to infinity. The naming convention goes (starting from zero and increasing by 1 unit each time) like s, p, d, f, g, h, i, j, k, etc. + +The problem is that we've only discovered 118 elements so far. We haven't got high enough in the ground state electron configurations to reach the g-orbital. + +In nuclei, g, h, and i orbitals are easy to reach. The shell model even has a j-orbital at 168 protons or neutrons. + +>Anything to do with energylevels? + +Yes, it's completely to do with the energies of the orbitals. Particles fill the orbitals in order of increasing energy. Atomic electrons fill all of the lowest-energy orbitals before they ever reach a g-orbital." Anyone have a good link to the shape of orbitals after f? +103 This is not a 'cicada year,' but I hear one buzzing outside right now. Is there a small set of cicadas out of sync with the main population, or do a few mistakenly mature early every year? Or is this a different species entirely? 5487 http://www.reddit.com/r/askscience/comments/3gzgyj/this_is_not_a_cicada_year_but_i_hear_one_buzzing/ 1439565564 3gzgyj Biology 2015-08-14 18:19:24 [deleted] "There are several (hundreds?) of species of annual cicadas, and even the 13 and 17 year periodic cicadas (genus Magicicada) have different broods such that some will be emerging in most years. Each brood has a slightly different geographical range. This year, brood 5 was scheduled, with a range that covers NY, OH, PA, VA, and WV. + +In addition, you're correct- there are both stragglers _and_ early bloomers that can appear from the periodic species. + +This late in the year however, you're almost certainly not hearing or seeing the Magicicadas. Their adult, above-ground lifespan is only ~4 weeks. Their emergence is dependent on soil temperature, and they are usually above ground by May or June and dead before the middle of July." +527 My 5-year-old wants to know: What would happen if a giant ball of water even bigger than the sun ran into the sun? 5487 https://www.reddit.com/r/askscience/comments/5kbn1h/my_5yearold_wants_to_know_what_would_happen_if_a/ 1482720964 5kbn1h Astronomy 2016-12-26 5:56:04 "I don't have a source right now but if I remember correctly adding a massive amount of water to the sun would actually make it burn hotter. The reason is that at these scales we can't think of water as something that extinguishes fire. What's going on in a star is a nuclear fusion reaction triggered by the massive amount of energy coming from the combined gravitational pull of all the components of the star. So by adding a massive amount of water to the star you're adding a lot of weight which means more gravitational energy meaning more fusion. You're also adding fuel that can be fused in the form of water molecules. + +Soeone please correct me if I'm wrong, I'm by no means an authority on the subject but I remember seeing something like this on a PBS spacetime video a while ago. " "Not sure if this is appropriate for a top-level comment, but all the answers so far are basically ""the ball of water wouldn't remain a ball of water"". If we change the question to ""What would happen if a huge amount of water, with total mass greater than the sun, were sprayed onto the sun?"" (so, basically the same question but eliminate the ""ball problem""), what's the answer?" +1993 Do individuals who appear older or younger than their biological age live a shorter or longer lifespan, respectively? 5482 https://www.reddit.com/r/askscience/comments/rb1zd9/do_individuals_who_appear_older_or_younger_than/ 1638891813 rb1zd9 Human Body 2021-12-07 18:43:33 This study from Christensen et al in 2009 found a relationship: https://www.bmj.com/content/339/bmj.b5262 "This article and the study it refers to think a younger appearance does indicate a longer lifespan! + +https://www.independent.co.uk/life-style/health-and-families/health-news/if-you-look-young-you-ll-live-longer-1839883.html" +970 In this pic of Mercury, what is the giant flat plain? This is the only picture of Mercury showing this plain and I cannot find any information on it. 5476 https://www.reddit.com/r/askscience/comments/886i3k/in_this_pic_of_mercury_what_is_the_giant_flat/ 1522371076 886i3k Planetary Sci. 2018-03-30 3:51:16 "As others have mentioned, your map of Mercury was built by assembling lots of pictures taken by Mariner 10, and the ""flat plain"" is an area where data is missing. But the missing data problem is worse than it looks! Your map shows the *good* side of Mercury. Here's a rectangular map that shows everything we knew about Mercury until a few years ago: + +https://www.nasa.gov/images/content/285929main_img5.1.jpg + +Your strip of missing data shows up, but **one whole side of the planet is blank!** We had no idea what this side looked like until the Messenger spacecraft arrived 40 years later in 2011. + +The reason is kind of interesting: Mercury rotates on its axis 3 times for every 2 times it goes around the sun. The Mariner 10 spacecraft flew by Mercury once every 2 times Mercury went around the sun... and so each time it flew by, the same side of Mercury was facing away from the sun, in darkness and impossible to photograph. + +NASA knew about this, of course, but there wasn't enough fuel to get Mariner 10 into a better orbit." "According to [this site](https://www.space.com/4839-enduring-mysteries-mercury.html) there has only been one mission to mercury. It said only 45% of it has been mapped. I'm assuming that the blank is not a giant plaine, but the 5% of that side of the planet that was not mapped. + +Edit: The source is outdated. There has been a more recent mission to mercury that took better pictures. Read other comments for more details. " +650 If elephants had gone extinct before humans came about, and we had never found mammoth remains with soft tissue intact, would we have known that they had trunks through their skeletons alone? 5467 https://www.reddit.com/r/askscience/comments/5o87y2/if_elephants_had_gone_extinct_before_humans_came/ 1484534170 5o87y2 Paleontology 2017-01-16 5:36:10 "Trunks do leave visible attachment marks for muscles, ligaments, & such on the skull. However, from osteological correlates alone, it would be impossible to infer exactly what the trunk looks like. In what is perhaps a ""reverse-application"" of this line of reasoning, [trunks can be rejected for sauropod dinosaurs](http://scienceblogs.com/tetrapodzoology/2009/03/20/junk-in-the-trunk/). + +EDIT: [Another discussion of osteological correlates of trunks](http://markwitton-com.blogspot.ca/2016/08/trunk-or-no-trunk-short-or-giant-ears.html), this time applied to the giant rhinoceratid *Paraceratherium*." [deleted] +1071 "Are certain people deep or light sleepers or is a person's sleep ""depth"" primarily dependent on conditions?" 5467 https://www.reddit.com/r/askscience/comments/92ly2i/are_certain_people_deep_or_light_sleepers_or_is_a/ 1532782836 92ly2i 2018-07-28 16:00:36 "One element of this is that the brain emits ""sleep spindles""(""a brief 11–15 Hz oscillation"") which cover over noises which might disrupt sleep. So a person who is sensitive to noises, probably produces less ""spindles"". +https://www.sciencedirect.com/science/article/pii/S0960982210007785" "Taking melatonin before bedtime improves over all sleep quality. This study looked at subjective change in sleep quality when people started taking melatonin and also measured sleep fragmentation to assess the effect of melatonin. Fragmented sleep is an indicator of how much of a light sleeper you are. Because melatonin reduced fragmentation, it probably made people sleep more ""deeply"". + +Edit: I should add that this study was conducted on breast cancer patients undergoing chemotherapy. Obviously this is an extremely physically/mentally stressed out population which increases the relevance of results to the average stressed and overworked adult employee. + +[https://www.ncbi.nlm.nih.gov/pubmed/26260726](https://www.ncbi.nlm.nih.gov/pubmed/26260726) + +Edit 2: I also realized I didn't answer the question. As [olafminesaw](https://www.reddit.com/user/olafminesaw) said, sleep spindles are a vital factor to falling and staying asleep. A recent study found a strong genetic component for sleep spindle traits and EEG patterns during sleep which explains why some people may be lighter sleepers. [https://www.nature.com/articles/ncomms15930](https://www.nature.com/articles/ncomms15930)" +1072 I get that bees are essential to an ecosystem, but do wasps/hornets do literally anything useful in that sense? 5452 https://www.reddit.com/r/askscience/comments/8h71x1/i_get_that_bees_are_essential_to_an_ecosystem_but/ 1525521116 8h71x1 2018-05-05 14:51:56 "Assuming that we're not talking about an invasive species, wasps are absolutely essential to an ecosystem. The same applies to hornets, which are actually a type of wasp in the family Vespidae. Here are some of the many ecological roles they play: + +**Pollination.** Many species of wasps are pollinators that are absolutely vital for flowering plants. Many plants have symbiotic relationships with wasps, and some even depend on wasps for their existence. Probably the most famous examples are fig wasps in the family Agaonidae, which coevolved with certain kinds of fig trees. So without wasps, we would lose many species of plants. + +**Predation.** Many kinds of wasps (such as hornets, yellowjackets, and spider wasps) are predators that eat other insects/arachnids like spiders, beetles, and caterpillars. Since a lot of these destroy plants and other organisms, this predation serves as an important control that helps balance their numbers in order keep an ecosystem healthy and diverse. Some wasps even eat other wasps, which helps keep their own numbers in control. + +**Parasitism**. In addition to being predators, some wasps are also parasites that feed on other insects. As described above, this has all of the same benefits for keeping the levels of other insects in balance. (For example, *Encarsia formosa* is used as pest control on tomato plants). + +So if we destroyed all wasps in their native habitat, we would see a rise in many insect populations, a decrease in many plant populations, and things would not be looking so good for the ecosystem as a whole. Wasps can be annoying, but they're absolutely vital to our ecosystems." "Aside from also being pollinators, they are (were?) essential to the beer/wine/bread industries. + +[Here](http://www.pnas.org/content/early/2012/07/26/1208362109) is an interesting paper about it. + +Apparently wasps are responsible for keeping strains of yeast in their stomachs over winter as they hibernate, which are essential for making beer wine and bread! Maybe these days that doesnt matter as much but up until a hundred years ago, it was pretty important." +1073 How is meth different from ADHD meds? 5450 https://www.reddit.com/r/askscience/comments/94rk1a/how_is_meth_different_from_adhd_meds/ 1533472544 94rk1a Chemistry 2018-08-05 15:35:44 "This post has attracted a large number of medical anecdotes. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating. + +You can also help by reporting comments that do not obey the rules of r/askscience. " "Ok so apparently I am the first medicinal chemist to discover this post! I have some things that I could shed some light on that nobody else has seemed to cover! + +So, yes, amphetamine, the main ingredient in adderall, is extremely similar to methamphetamine. In fact, meth is simply amphetamine with an added methyl group at the N-position. The addition of this methyl group has two consequences that make methamphetamine a more powerful drug than amphetamine. + +1. The methyl group makes the molecule overall more lipophillic (fat-soluable). As such, fat soluble compounds diffuse across the blood brain barrier much more quickly and in higher concentrations. This in tern elicits a more powerful rush and euphoric high, because that drug rushes into the brain much quicker. This effect is enhanced by quicker routes of administration such as smoking or injecting that already send a large amount of the drug directly to the blood stream. +2. The methyl group has effects on metabolism. Methamphetamine is active on it's own, but as soon as it enters the body, the methyl group is slowly being cleaved, as the molecule is metabolized into amphetamine. This increases the duration of the drugs effects by a large percentage, because not only does methamphetamine have to go through it's elimination halflife before it is cleared from the body, but the methamphetamine that is metabolized into amphetamine, is active on it's own, and must go through it's own halflife just as if someone were to have taken the amphetamine alone. + +So yea, Meth is innately a stronger and more euphoric/addictive drug than amphetamine because of these medicinal chemistry properties, but I would argue that this isn't what makes street meth so much more dangerous than prescription meth, the other answers reflect this a lot better. The purity of the drug is a huge danger as you don't know exact ingredients like you would pharm grade drugs. The lack of accurately measured dosages is a big danger, especially since even 10mg of meth may be cut with 5mg or more of inactive or different ingredients with unknown effects. Also, people redose and redose for days on end because you can buy tons of meth in powder form, this is when amphetamine psychosis kicks in and people start doing stereotypical meth head shit. Amphetamine psychosis can happen to people on ADD meds too, I saw it happen to my GF in college as she picked bugs out of her face even when she knew they were not there. + +And yea the worst thing about street meth/amphetamines vs ADD meds is route of administration. Just as I said the pharmacological differences of meth are enhanced by more direct method of administration such as smoking or injecting, these are the methods that most often are associated with the most danger. There isn't really a way to achieve the same type of rush from prepared ADHD medications, as one does from smoking or injecting straight crystalline forms of the drug. Now in the UK, speed is popular, which is a clandestine amphetamine preparation, and I am sure you see all of the same shit you see from meth in the US, despite the fact that amphetamine is the same chemical in adderall. Preparation and method of administration and dosage measurement are the main differences between street and Adhd stimulants." +1245 Storing Nuclear Waste: Why not dilute and put it back where it came from? 5436 https://www.reddit.com/r/askscience/comments/be9bpk/storing_nuclear_waste_why_not_dilute_and_put_it/ 1555515881 be9bpk Physics 2019-04-17 18:44:41 "This idea is actually similar to some forms of nuclear waste disposal that have been proposed and some forms that are being done for nuclear weapons waste disposal. There are a couple of problems with it though. Also it is important to remember that ""nuclear waste"" is a broad term that covers way too much stuff. A lot of radioactive waste from research and medicine is already disposed of in a similar (although not taken back to a mine) sort of [way](https://www.nrc.gov/reading-rm/doc-collections/maps/radioactive-waste-sites.html) + +. + +The primary concern with nuclear waste it two parts: Firstly (and most importantly), the radio-toxicity of the material. When uranium is fissioned a bunch of different radioactive fission products can be generated. Over the course of the fuel lifetime all of these various products will be generated in different concentrations. Some of them have very short half-lives and will decay so fast that they are not a problem. Others have longer half-lives which makes them annoying. Among these longer half-lived fission products, some of them can easily dissolve in water and then concentrate in a human body if consumed (cesium and iodine being great examples). Those are the ones we are concerned about and want to trap. That is why current nuclear waste plants seal these fission products into very tough forms and then bury [them](https://www.edf.fr/en/edf/radioactive-waste). This prevents the bad stuff from (which wasn't in the uranium ore BTW) from finding its way into our water supply. + + +The second big concern is fissile material. Nuclear reactors do not burn all of their fuel and actually breed some more fuel in the form of plutonium. We do not want this stuff to get into the wrong hands, so we either trap in in waste forms and bury it, reprocess the good stuff and use it [again](http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/fuel-recycling/processing-of-used-nuclear-fuel.aspx), or dilute it and bury [it](https://www.gao.gov/products/GAO-17-390) similar to what your boss proposed. This stuff is also toxic and we don't want it to get out into the environment, but the fission products are far worse. A third concern with dilution and burial is we then cannot easily get at the waste to pull more fuel out. The USA currently does not recycle our nuclear fuel and we have decades worth of usable fuel as ""waste"". It would be stupid to bury that in a way that we couldn't easily get at it again. + + +Sources for all of this are provided, plus I am an actual licensed nuclear engineer." "He is now wrong and it has been explored, but not in the way you would imagine. +The idea has been proposed to bury nuclear wast at the edge of tectonic plates where they are being pushed under another plate to be recycled into the mantle and effectively dissolved down to harmless levels. Obviously this is a plan that needs million of years to go to fruition." +1350 How long did it take dinosaurs to go fully extinct? 5430 https://www.reddit.com/r/askscience/comments/c72upy/how_long_did_it_take_dinosaurs_to_go_fully_extinct/ 1561833243 c72upy 2019-06-29 21:34:03 "~~It looks like the dinosaurs were in decline for several million years before the impact event at Chixulub~~. As best we can tell the extinction of the large therapod and sauropod dinosaurs happened instantaneously, geologically speaking. That might mean days, months or even decades or more in reality; rock preservation in most places does not work at human timescale resolutions. + +Ir could be as long as centuries or millennia. I would personally put my money on decade to century scale; with only pockets surviving the first year, and perhaps some isolated pockets lasting over 1000 years (similar to mammoth post ice age). + +Edit: turns out my dinosaur knowledge was a few years out of date. Strike out the first sentence. + +Edit2: Following the OP edit, /u/stringoflights adds the following and asked me to add it here for reference: +Birds didn’t just evolve from dinosaurs, they are dinosaurs, and dinosaurs did not go extinct. We have more dinosaur species alive today than mammal species. It’s fine to pose a question about non-avian dinosaurs, but the fact that birds are dinosaurs is important when we are studying patterns of extinction. + +The bird “evolving back” from extinction that is mentioned in the edit is an example of iterative evolution. It is absolutely not a reason to ignore an entire radiation of dinosaurs, and it’s pretty important that that misconception is corrected. + +Iterative evolution means that the same or similar structures arose from the same source population at different times. It doesn’t mean the wholesale evolution of the same species twice. In the case of the Aldabra rail, which is what the edit mentions, the white-throated rail has colonized the island from nearby and evolved flightlessness more than once." "For a large number of them, just a matter of minutes or hours depending on location. When the meteor hit the earth, it threw debris high enough that on reentry it turned into burning rain. This lit the world on fire, and the soot added to the dust in the air. The ones that didn't get killed in the initial event lived only as long as they has food. Plants were devastated and herbivores starved, and then when carnivores finished off those corpses they starved as well. It was likely a couple weeks, more or less depending on metabolic rates. + +BBC has a great writeup on the event: +http://www.bbc.com/earth/story/20160415-what-really-happened-when-the-dino-killer-asteroid-struck" +104 New Horizons flies by Pluto in 33 Minutes! - NASA Live Stream 5419 https://www.nasa.gov/multimedia/nasatv/ 1436872766 3d8puo Planetary Sci. 2015-07-14 14:19:26 I remember watching the launch 10 years ago... and it's always stuck with me since then. So happy to see the final result... "#July 15th Events + +* ""Charon is [geo] active"" - Alan Stern + +* Image of Hydra! http://i.imgur.com/FN4BLu7.png + +* Methane on Pluto! http://i.imgur.com/fkQELTJ.png + +* Charon close up! http://i.imgur.com/SVhOSjj.png + +* ***CLOSE UP PLUTO***: http://i.imgur.com/meaqdRP.png (no craters!?) + +* Pluto's surface is less than 100 million years old. Young surface! + +* Pluto has water ice ""in great abundance"" + +* Pluto is geologically active to explain surface features. + +* ""No significant exchange of tidal energy anymore"" between Pluto and Charon. Why Pluto and Charon are geologically active is a mystery. + +________ + +#July 14th Events + +***UPDATE: New Horizons is completely operational and data is coming in from the fly by!*** + +#""We have a healthy spacecraft."" + +This post has the official NASA live stream, feel free to post images as they are released by NASA in this thread. It is worth noting that messages from Pluto take four and a half hours to reach us from the space craft so images posted by NASA today will always have some time lag. + +This will be updated as NASA releases more images of pluto. Updates will occur throughout the next few days with some special stuff happening on July 15th: + +* Main website: https://www.nasa.gov/mission_pages/newhorizons/main/index.html + +* **APL** website: http://pluto.jhuapl.edu/ + +* Twitter: https://twitter.com/nasanewhorizons + +* NASA Instagram: https://instagram.com/nasa/ + +* NASA TV: https://www.youtube.com/watch?v=OX9I1KyNa8M + +* Alternate Live Stream link: http://www.ustream.tv/NASAHDTV + +* NASA TV Schedule: https://www.nasa.gov/multimedia/nasatv/schedule.html + +* Reddit Live Feed: https://www.reddit.com/live/v8j2tqin01cf/ +_______ + +The new images from today! + +* **Highest quality image so far!** https://instagram.com/p/5HTXKMoaFL/ + +* **LORRI Images:** http://pluto.jhuapl.edu/soc/Pluto-Encounter/ + +* **Other LORRI Images:** https://www.nasa.gov/newhorizons/lorri-gallery + +* Older images: https://www.nasa.gov/mission_pages/newhorizons/images/index.html + +_______ + +Some extras: + +* [**How do we know Pluto is Red?**](http://photojournal.jpl.nasa.gov/catalog/PIA19697) + +* [**What experiments/cameras/equipment does Hew Horizons have?**](http://pluto.jhuapl.edu/Mission/Spacecraft/Payload.php) + +* [**Emily Lakdawalla of the Planetary Society's New Horizon's picture timeline.**](http://www.planetary.org/blogs/emily-lakdawalla/2015/06240556-what-to-expect-new-horizons-pluto.html) + +_______ + +#[Megathread Ask Your Pluto Questions here!](http://redd.it/3d9bof)" +785 "Are there any other animals known to ""work out"", or do an activity for the sole purpose of muscle growth?" 5417 https://www.reddit.com/r/askscience/comments/6kpsa9/are_there_any_other_animals_known_to_work_out_or/ 1498946814 6kpsa9 Biology 2017-07-02 1:06:54 "Apart from the one answer about engaging in ""play which builds muscle and muscle memory"" the answer is most likely ""no"". Exercise for the sake of exercise burns up a lot of calories which in other animals is best preserved for acquiring food and reproducing etc. That humans engage in muscle building is a result of our societal evolution from that of hunter gatherers where we were just like other animals to today where division of labor has made food acquisition the least of our worries. So, we now have plenty of time and resources to waste working out to impress people (or most likely ourselves). When you look at the very few truly tribal societies still in existence today, you won't find too many people working out for the sake of it. + " "1. Any animal engages in behaviors to increase the size and responsiveness of their muscles. + +2. If you're looking for the human definition, that's tied to social displays, you could certainly look at male kangaroos and try to determine how much of their mass comes from behaviors they share with females, and those they engage in excess. + +3. Birds. Birds practice their mating dances. They develop and practice a range of moves that requires a range of muscles. They practice those moves to build their muscles for a display quite similar in intent to many humans who work out. + +4. If you're trying to determine the ""classes"" of animals that do a particular behavior, you're going to have a lot of trouble observing nature. + +Even amoebas gotta stretch their sacks, holmes." +870 Does the force of gravity travel at c? 5414 https://www.reddit.com/r/askscience/comments/7lvevd/does_the_force_of_gravity_travel_at_c/ 1514126148 7lvevd Physics 2017-12-24 17:35:48 "Yes. According to general relativity, changes in the gravitational field propagate at the speed of light. + +The best experimental verification of this so far (as far as I know) is the temporal coincidence between gravitational waves and gamma rays from the recent neutron star merger event, which set limits on the difference in propagation speed." "Yes, it does (according to general relativity). There have been numerous observations. + +The most recent and most accurate was from LIGO, when gravity waves were detected and correlated with a gamma ray burst (light waves) from a pair of neutron stars merging. The light waves and gravity waves traveled for 130 million years and arrived within a few seconds of each other. + +Prior to that we were able to make observations by watching the orbits of pairs of pulsars decaying; the rate at which energy is lost is related to the speed of gravity. + +So I would say that the theory (general relativity) proposes that gravity travels at the speed of light, and all observations/experiments so far are consistent with that. " +871 How do wireless chargers work? 5411 https://www.reddit.com/r/askscience/comments/7gr4x8/how_do_wireless_chargers_work/ 1512088755 7gr4x8 Engineering 2017-12-01 3:39:15 "Electrical current through a wire creates a magnetic field directed in a circular motion around the circumference of the wire. So, when you coil the wire into a circle, this creates a magnetic field in the direction perpendicular to the circular cross-section of this coil (think of a donut of wire sitting on a table, the magnetic field would be directed upward or downward through the hole of the donut). + +Now, if you take a second coil of wire and place it on top of the first coil, the magnetic field from the first coil will cause a flow of current in the second coil. This is due to the reverse of how you generated the magnetic field. + +The ""first coil"" is your wireless charger, and the ""second coil"" is inside your phone, connected to the battery. The current generated in the second coil charges your phone's battery. + +Edit: It should be noted that this was an extremely simplified explanation. An important aspect that I left off was that it is the *change* in magnetic field, called magnetic flux, through the second coil that induces a current. This means the coils must use alternating current (the type of power coming out of your wall socket), then the second coil's AC current must be converted to DC current (type of current a battery produces/charges on) in order to charge the battery. + +Edit: fixed wording to make less ambiguous" "Awesome! I think I can help. +https://upload.wikimedia.org/wikipedia/commons/b/b4/Wireless_power_system_-_inductive_coupling_de.svg + +This picture here illustrates well what is happening. The left side is your wireless charging pad, the right side is your phone. + +First, we need two coils, then we need alternating current and that's pretty much it. The purpose of the coils is to intensify and guide the magnetic field so we have lower power losses. + +In the picture above, ""B"" is the magnetic field created by the left coil. A magnetic field is created when you send AC through a coil. +As you can see, a lot of the magnetic field is ""lost"" on the left side of the transmitter coil, that's why magnetic charging is so inefficient and it takes a long time to charge the phone! + +On the right side, we have the receiver coil. A ""changing"" magnetic field induces a Voltage and thus a current flow in the coil, which can then be rectified to charge your battery (since the battery is often charged with 4.2V DC) + +And now the even cooler part: Wireless charging isn't scratching the surface of what kind of power we can deliver that way! +If you step up the power a litte bit, you can melt metal with a coil. +http://littleserver.spdns.org/imagetxt.php?datei=/ZVS_IH/P1010189.JPG + +In the middle of the coil is a red-hot glowing M20-nut. + + +" +872 Are Sociopaths aware of their lack of empathy and other human emotions due to environmental observation of other people? 5410 https://www.reddit.com/r/askscience/comments/759huj/are_sociopaths_aware_of_their_lack_of_empathy_and/ 1507560211 759huj Social Science 2017-10-09 17:43:31 "It may be better to describe the traits you are looking at in particular rather than using terms that people may confuse with another. I like this question in general because it asks whether or not people are self aware when they have a social mindset that is different from their peers. More importantly do they use it to their advantage or does it just hinder their ability to connect? + +I look through the posts and I see psychopath mentioned quite a bit but that wasn't what you asked about specifically, but people assumed. So as long as we are speaking about traits of a personality disorder, sociopaths and psychopaths get lumped together and I have read a book on Psychopathy that gave me a whole different appreciation for the very wide range of affects it can have on people. + +Dr. Kevin Dutton's book The Wisdom of Psychopaths was the book that really opened me up to at least understanding some core concepts behind the diagnosis and history of the disorder. I would say that yes, they can understand what makes them different. At the very least that they are different from other people. Another thing to point out is that while the disorders do breed bad apples, it's still the upbringing that holds the most weight. So the awareness in this scenario would come from childhood parenting. In the book one of the psychiatrists/psychologists that he talked to became aware of his own psychopath diagnosis while looking for others. It was his family that read his research and went back to him and told him to get tested for the warrior gene. + +The core question for me here was, are people with these disorders capable of becoming aware of their differences? Yes, I think they are capable." "This is a great question and I appreciate this being asked in r/askscience. To begin, sociopathy is not really a thing, per se. The construct you are referencing is almost certainly psychopathy, which has some relationship to antisocial personality disorder. However, many people with antisocial personality disorder do not exhibit traits of psychopathy. For example, if I steal from other people, con others, cheat, and lie, but do so for reasons that are based on my survival (regardless of whether this causes distress or impairment), one could argue that such a person does not exhibit traits of psychopathy. + +Additionally, it is certainly possible to be high in traits of psychopathy and not meet criteria for antisocial personality disorder. One example of this is sometimes referred to as the successful psychopath (think Wall Street executives, etc.). + +Antisocial personality disorder is a disorder that is largely behavioral. As such, many people who have been incarcerated may meet criteria for antisocial personality disorder. However, that does not mean that they would be a ""psychopath."" The vast majority of people who are high in psychopathy do not commit murder. While this is a common stereotype of psychopathy, it is overly shallow. + +People who are high in traits of psychopathy exhibit superficial charm, manipulativeness, empathy differences, and impulsivity. It gets confusing when we try to disentangle the lines of delineation between psychopathy, machiavellianism, and narcissism, however. For example, some people who are otherwise high in psychopathy, exhibit traits of grandiosity and intense planning/politic playing. As grandiosity is a hallmark of narcissism, and careful premeditated planning is a hallmark of machiavellianism, we will sometimes refer to these three constructs as the dark triad. The dark triad has certainly been the center of much research, and a simple Google Scholar search will yield some interesting results for you. + +Now on to your question. The short answer is that we don't actually really know yet. One major finding that comes to mind is from Meffert et al.'s (2013) publication in the journal Brain. They found that, when asked, ""psychopathic offenders"" could mediate their internal response to observed pain in others, much like a switch. + +I have a professional opinion based off of my own experience in this area as a fourth-year Clinical Psychology PhD student. I believe that individuals who exhibit traits of psychopathy develop strategies in response to a harsh childhood environment to protect themselves from experiencing the emotional pain induced by empathy. The funny thing is, we all do this just to a much smaller degree. Take for example my sister who savagely wails on my arm when watching a horror movie, until ultimately saying ""Oh my God, screw this bleep, she's stupid for even going in there. I don't care what happens to her. I hope she dies."" It is protective to deidentify with the other in pain. However, when one learns that they can circumnavigate the rules of society in a way that others can't, who can blame them, they might think. Life is so much easier this way, and it's not my fault that other people are so stupid as to play by the rules. + +I could talk about this a lot more but I hope this helped! I would just encourage anyone reading this to know that psychology is very much a science, and many of these questions become answered with all kinds of novel techniques, such as factor analysis and fMRI. Sometimes within the psychology community personality disorders and personality constructs tend to get a bad rap. This is primarily due to the fields origins in Freudian psychodynamic theory, but I just want to say that most personality research today has moved far from that realm. " +651 How can animals emerge from months long hibernation and run about without any signs of muscle degeneration? 5408 https://www.reddit.com/r/askscience/comments/68gik2/how_can_animals_emerge_from_months_long/ 1493571867 68gik2 Biology 2017-04-30 20:04:27 "In some animals, fasting inhibits the action of myostatin. Myostatin is the hormone that break down muscle tissue. When you eat enough nutrients your muscles will always want to grow. It's their natural state. They're prevented from constantly growing by the presence of myostatin. + +Google images of myostatin dogs and cows. Those animals are jacked, but it's not like they're hitting the gym or getting supplemental testoerone. They've genetically mutated to have more expression of myostatin inhibitor genes. + +In humans, fasting also increases the levels of human growth hormone, which is also muscle sparing." [deleted] +873 If two identical twins produced an offspring (gross), would the offspring be some kind of genetic clone? 5405 https://www.reddit.com/r/askscience/comments/7mflcz/if_two_identical_twins_produced_an_offspring/ 1514388093 7mflcz Biology 2017-12-27 18:21:33 "If this was possible (other people have mentioned the same-sex thing) then the child would not be a clone of the parent(s). + +Any genes where the parent was homozygous would still be homozygous. However, only 50% of the genes where there is heterozygosity would still be heterozygous. The others would become homozygous. + +It’s this increase in homozygosity which causes the negative effects of inbreeding." No. Imagine each identical parent has a dominant trait, but they also carry the recessive gene for that trait, Dd. D being the dominant gene, and d being recessive. A child gets only one copy of each gene from each parent, so it could be that said child would get dd, and display the recessive trait. +400 Is the earth pulled toward where the sun is now, or where the sun was 8 minutes ago? 5403 https://www.reddit.com/r/askscience/comments/4zwl8e/is_the_earth_pulled_toward_where_the_sun_is_now/ 1472337132 4zwl8e Physics 2016-08-28 1:32:12 "Even though changes in the gravitational field propagate at finite speed (c), and it takes about 8 minutes for signals from the sun to reach Earth, the Earth accelerates toward where the sun is **now** rather than where it was 8 minutes ago. + +[Here](http://arxiv.org/abs/gr-qc/9909087) is a paper explaining why." "I'll try to explain the paper in easier terms. + +So, gravity and electromagnetism are used in the paper to help explain it. Objects with constant acceleration will telegraph their future position. An analogy made in the paper is to solve the same issue but for a charge in an em field. We know speed of light is not infinite, so the analogy extends to gravitational radiation. EM radiation is dipole though, so constant velocity telegraphs charge's future position. Gravitational radiation is quadrupole, so constant acceleration telegraphs the future position of the ""charged"" object. + +Think of derivatives when you go from position to velocity to acceleration. Moving charge derivation tells you future position for its dipole. Moving mass derivation tells you the new speed as well as the new position due to its quadrupole nature. + +This wouldn't work if the sun magically started gaining jerk. That is a level above acceleration and that information would be received at c which is the 8 minute figure. For stable orbits, you have to have com be current and not delayed by light. Newtonian mechanics can explain basic orbits without needing or mentioning information speed behaviors. + +As the earth and sun orbit their com, the sun is telegraphing its future position and velocity. Some mass comes zipping by and disturbs the sun's orbit and earth wouldn't respond for 8 mins roughly. + +We're absolutely sure that current position is what orbits use. If you google the paper, some people might have broken it down better than I. Don't take this analogy past its use an oversimplified example. I was loose with some terms. " +1111 How many average modern nuclear weapons (~1Mt) would it require to initiate a nuclear winter? 5400 https://www.reddit.com/r/askscience/comments/9c25cz/how_many_average_modern_nuclear_weapons_1mt_would/ 1535798419 9c25cz Physics 2018-09-01 13:40:19 "It depends. Nuclear winter is currently still a guess, which is centered around how much soot would be injected into the stratosphere. If enough is sent up, we could end up with a scenario like the dinosaurs experienced. Soot of that magnitude would require a significant event - like continuous firestorms, with perhaps the entire nuclear arsenal detonated as ground bursts. If the entire nuclear arsenal was detonated subterranean, or as airbursts we would likely be fine. As a note, 1megaton warheads are not as common - Missiles are generally geared to carry ~300kiloton warheads, and multiples of them as MIRVs, as that is more efficient in terms of destructive capability. [Here's some info](https://en.wikipedia.org/wiki/Nuclear_winter) + +Edit: +I initially wanted to keep my answer short-ish, but I'll throw some more fuel on the firestorm, and discuss a few points that have been brought up - My comparison of the effects of nuclear winter to the [K/T extinction event](https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event) might be fairly contentious. I won't steal the fire of posters below, but it is still being discussed in scientific circles - here's a wikipedia excerpt: + +>The global firestorm winter, however, has been questioned in more recent years (2003–2013) by Claire Belcher, Tamara Goldin and Melosh, who had initially supported the hypothesis, with this re-evaluation being dubbed the ""Cretaceous-Palaeogene firestorm debate"" by Belcher. + +and: + +>A paper in 2013 by a prominent modeler of nuclear winter suggested that, based on the amount of soot in the global debris layer, the entire terrestrial biosphere might have burned, implying a global soot-cloud blocking out the sun and creating a nuclear winter effect. This is debated, however, with opponents arguing that local ferocious fires, probably limited to North America, fall short of global firestorms. This is the ""Cretaceous-Palaeogene firestorm debate"". + +To give an idea of scale, it is estimated that the Chicxulub impact generated 100,000,000megatons of TNT equivalent energy, which makes the entire modern nuclear arsenal look like firecrackers. Something else that may cast some doubt on nuclear winter theory - the oil fires following the 1991 gulf war that were lit by the retreating Iraqi army burned for months, and it was theorized that they might produce a similar cooling effect. The soot and clouds were massive, but didn't end up making it to the stratosphere. Another excerpt: + +>In a 1992 follow-up, Peter Hobbs and others had observed no appreciable evidence for the nuclear winter team's predicted massive ""self-lofting"" effect and the oil-fire smoke clouds contained less soot than the nuclear winter modelling team had assumed. +The atmospheric scientist tasked with studying the atmospheric effect of the Kuwaiti fires by the National Science Foundation, Peter Hobbs, stated that the fires' modest impact suggested that ""some numbers [used to support the Nuclear Winter hypothesis]... were probably a little overblown. + +I feel I should address my offhand comment on nuclear yield as well. The largest operational nuke in the American arsenal is the [B83 nuclear, free fall bomb](https://en.wikipedia.org/wiki/B83_nuclear_bomb). It has a variable yield warhead up to 1.2megatons. The largest device used by the U.S. was in the [Castle Bravo](https://i.imgur.com/y1E6vyu.png) test, which had a yield of 15megatons(incidentally, 2.5 times the expected 6) - note the height of the cloud compared to Hiroshima. The most prolific warhead currently in the American arsenal [is the W76](https://en.wikipedia.org/wiki/W76), having a yield of 100kilotons. The newest warhead being deployed [is the W88](https://en.wikipedia.org/wiki/W88), having a yield of 475kilotons - to replace the W76(primarily on submarines). The most common warhead for land based missiles [is currently the W87](https://en.wikipedia.org/wiki/W87), at 300kilotons(basis for original generalization). Something overall to keep in mind - the U.S. has conducted over 1000 nuclear detonations, many in the same year, with no signs of atmospheric change resulting. + +So, next question - what common event CAN change the weather outside of nukes and asteroids? Volcanoes. Volcano relative power is measured on a logarithmic scale, called the [Volcano Explosivity Index](https://en.wikipedia.org/wiki/Volcanic_Explosivity_Index), or VEI. As a reference, Mt. St Helens is considered a VEI5 event. Krakatoa(1883) is considered VEI6, with an estimated thermal energy release of 200megatons. The last VEI7 event occurred in 1815, and it was nicknamed 'the year without summer' - global temperatures dropped 1.5C for that event(attributed mostly to the SO2 ejected). Yellowstone's last major eruption occurred in 630,000 BC, and is considered a VEI8 event. VEI8 events are thought to occur every 50,000 -100,000 years, but it's been a while since the last one.... +(If you are are still reading this day old edit, pm me with 'Neeeeeerd')" "The entire concept of nuclear winter has a rather questionable foundation in science. + +The core concept is that nuclear bombs will set off raging infernos, and that the soot they release will block out the sun and destroy the world. + +There are two issues with that theory: +First, cities are unlikely to firestorm. Even Japan's notoriously combustible construction in WW2 didn't burn in one of the two blasts. Modern construction is even less likely to, as evidenced by the lack of fire on 9/11, which included two jumbo jets full of fuel. If all the burnable material in a city is covered in concrete and steel rubble, it's not going to burn. + +Second: the cooling effects of soot are likely extremely exaggerated in these scenarios. During the first gulf war the retreating Iraqis set almost all the oil wells in Kuwait on fire. They burned for months, spewing thick black smoke the entire time. This wasn't enough to have any significant local effect on temperature, let alone a global one. + +So if the bombs don't start firestorms, and firestorms don't have significant climate impact, then nuclear winter isn't a concern. Ultimate, we'll probably never know for sure though." +1074 In babies and small kids what is the reason of timing vaccines with age? Why can't all vaccines be given at the same age? 5397 https://www.reddit.com/r/askscience/comments/8u0fhc/in_babies_and_small_kids_what_is_the_reason_of/ 1530023183 8u0fhc Medicine 2018-06-26 17:26:23 "Babies survive initially on their mother's natural antibodies (shared through the placenta and then through breastmilk) until the baby itself has developed an immune system capable of protecting itself. The thymus in particular is an organ that needs to develop for a while before it can handle any vaccines. Otherwise, without a functional immune system, the vaccine can just make the baby sick and won't result in the development of any immunity. + +It then comes down to A) whether the vaccine is attenuated, dead, or a toxin vaccine, which each require the developing body to be a certain age/immune strength to be effective. B) The age of administration of the vaccine is also relevant to the diseases the baby will encounter at that age. Many are given at 6, 12, 18 months etc because babies are very prone to whooping cough, measels, pertussis, polio, with lethal outcomes. On the other hand, the gardasil vaccine isn't really necessary until the child is much older (I think the current age is 12, may soon be 10), because it is unlikely that a 12mo baby will encounter a sexually transmitted virus. + +The vaccine scheduled has been refined to make sure the greatest amount of immunity can be achieved at the earliest time possible." "A baby mammal receives a certain amount of antibodies in the colostrum. Those antibodies provide resistance to certain illnesses, but they run out after a certain time. Vaccines are given in a series based on when that resistance begins running out. + +So to use puppies as an example, 25% of the puppies will no longer be protected by maternal antibodies at 6 weeks and 100% will no longer be protected at 15 weeks. We give vaccines every three weeks between those two ages because we want to minimize the amount of time they are unprotected by either maternal antibodies or their own generated in response to the vaccine." +786 For people in areas with no access to clean water, do they live with constant parasite/bacterial infestations or do their immune systems become adept at clearing them? 5396 https://www.reddit.com/r/askscience/comments/6flqfr/for_people_in_areas_with_no_access_to_clean_water/ 1496755460 6flqfr Biology 2017-06-06 16:24:20 "Here is some data compiled by the WHO on the burden of water borne and sanitation related diseases worldwide (in 2012, I haven't found anything more recent that is as thourough as this). + +http://www.who.int/gho/phe/water_sanitation/burden/en/ + +So, to answer your question, in countries with poor access to clean water, a lot of people suffer from water borne diseases, and this leads to substantial morbidity and mortality, especially in young children. + +That being said, healthy adults in these countries have higher resistance to some pathogens compared to people who grew up in countries that have easy access to clean water (hence traveller's diarrhea)." " There's a bacteria called Campylobacter jejuni, it causes 'Traveller's diarrhoea' and is the most common cause of a bout of the poops for travellers. Most locals wouldn't be affected as they've developed an immunity to it. But immunity to things like this take time and although diarrhoeal illness of children is considered 'normal' it is also a major killer of children under five. +So there is an immunity developed to certain bacteria (not so much parasites) but diarrhoeal illness is pretty common place when there is no clean water. Also this is compounded by issues like HIV and malnutrition as to have an immunity you need an immune system. + + +For people asking why locals don't boil the water, it takes a kilo of firewood to boil a litre of water. When resources are limited they would rather use the wood to cook. + +I did my PhD on using Sunlight to disinfect water in developing countries. +" +105 "I've heard that one of the purposes of the ""fresh cut grass"" smell is a type of distress signal that warns nearby plants to start moving nutrients to the roots before they get cut down. Is there any truth to this?" 5395 http://www.reddit.com/r/askscience/comments/3gsfzg/ive_heard_that_one_of_the_purposes_of_the_fresh/ 1439425237 3gsfzg Earth Sciences 2015-08-13 3:20:37 "The smell is indeed a type of distress signal. This has been studied and confirmed. However, the signal is not for other plants, it is for insects. One job of the secreted compounds that give out the smell is to act as an insecticidal against the plant eating insect and the other effect is to attract other insects - parasitic wasps to come to the rescue and lay eggs in the herbivorous insect eating the plant. + +*I doubt that these secreted compounds can be detected by other plants* + +Source: http://www.sciencedaily.com/releases/2014/09/140922145805.htm" A similar system exists in [tobacco plants](https://www.newscientist.com/article/dn19371-tobacco-plants-outsmart-hungry-caterpillars/). When attacked by their predator, caterpillar, the tobacco plant sends out a signal which attracts the predator of the caterpillar. The predator arrives, eats the caterpillar and the tobacco plant survives. +787 If there used to be a lot of water on Mars, what happened to it? Did it leave the planet and atmosphere? 5387 https://www.reddit.com/r/askscience/comments/6gffh7/if_there_used_to_be_a_lot_of_water_on_mars_what/ 1497104008 6gffh7 Astronomy 2017-06-10 17:13:28 "Mars almost certainly had an ocean worth of water early in the life of the Solar System. However, the planet's low mass means it also has a relatively low escape velocity, and all sorts of escape processes can cause atmosphere to leak out to space. + +Water vapor on its own is just a bit too heavy to easily escape Mars (heavier molecules have slower speeds, and thus a harder time reaching escaping velocity). However, Mars has no form of ultraviolet shielding the way that Earth has an ozone layer. Gaseous water vapor that evaporated from the oceans could push high into the atmosphere and be exposed to ultraviolet photons. These are energetic enough to split water into its constituent hydrogen and oxygen atoms. + +Hydrogen is a very light atom, and can very readily escape Mars out to space. On an early Mars, this would primarily occur through two processes: + +- Just being warm enough, the fastest moving hydrogen atoms can reach escape velocity. + +- Early in the Solar System's there were a lot more impacts from asteroids, and Mars happens to be located very close to the asteroid belt. From our estimates of impact frequency at that time and location, there were more than enough to blow off most of the Martian atmosphere in just the first 100 million years. + +(A lot of folks might mention the fact that Mars currently doesn't have a magnetic field and thus exposes it to the full force of the solar wind. While that's an important process now, it's likely Mars did have a magnetic field early in its history.) + +So that's what happened to the hydrogen that was in all that water...but what about the oxygen? Well, an oxygen atom is 16 times heavier than a hydrogen atom, so it's considerably more difficult for it to reach escape velocity. + +However, free oxygen is also very reactive, so most of it likely reacted with surface minerals before it had a chance to escape. After all, the Martian surface was originally black like lava rock; only by getting massively oxidized did it turn red. + +If you want to know more about atmospheric escape processes on all the planets, I'd highly recommend [this PDF](http://faculty.washington.edu/dcatling/Catling2009_SciAm.pdf) - great layman-level reading material. + +**TL;DR**: Water vapor in the atmosphere was split up by ultraviolet light. The hydrogen was light enough to escape into space, while the oxygen got locked up in rocks on the surface." "Rocky planets with a molten iron core can *make and keep* their own water. Rocky planets without a molten iron core 'dry out' in space. The hydrogen floats away as solar radiation separates the oxygen and hydrogen. + +Mars is a rocky planet that used to have a molten iron core. However because Mars is so small, that molten core cooled quicker than Earth's. Once the molten iron solidified and stopped swirling, Mars began to 'dry out'." +200 My textbook says electricity is faster than light? 5383 https://www.reddit.com/r/askscience/comments/3sm2jj/my_textbook_says_electricity_is_faster_than_light/ 1447380616 3sm2jj Physics 2015-11-13 5:10:16 " You are right to be dubious of your textbook, because the statements made are false. Not ""false but only because we are making an approximation"" or ""false but it's only an apparent effect and not real"", but ""egregiously and totally false"", to the point that it's rather embarrassing that this paragraph made it into that text. + +Let's take a look at each of these statements. + +> In a DC circuit, the impulse of electricity... + +Just for the record, I have never in my life heard the term ""impulse of electricity"". An impulse is momentum and the term is typically used for describing the change in momentum due to a force that acts for only a very short time (e.g., the impulse of a tennis racket on an incoming tennis ball). We do have a term ""electromotive force"" which is abbreviated ""emf"" since it's not actually a force, but an electric potential. So maybe this author has defined ""impulse of electricity"" analogously, which would make ""impulse of electricity"" an electric potential per unit time. Those units strongly suggest that the author means ""impulse of electricity"" to mean that the dV/dt (where V is the voltage across the battery) is a unit impulse function. Not only is that impossible anyway, the term is still just not used, or used so exceedingly rare for my never to have heard it in my entire academic career. + +**edit:** *On further examination, however, it seems the author is using ""impulse of electricity"" to refer to (what he thinks to be a correct) fact that all electrons start moving at the same time once the switch is closed. So he is probably using ""electricity"" to mean electric current or the electron speed, and the ""impulse"" refers to the (incorrect) fact that the electrons begin at 0 speed and then all instantly being moving at some non-zero speed. Again, the term ""impulse of electricity"" is not used and it is extremely difficult to figure out what he means by it precisely because his entire explanation is wrong.* + +> Assume for a moment that a pipe has been filled with table-tennis balls. If a ball is forced into the end of the pipe, the ball at the other end will be forced out. Each time a ball enters one end of the pipe, the ball at the other end will be forced out. + +Yes... but it's not instantaneous as the author wants us to infer. In fact, this very consideration is what leads to one of the most commonly asked questions on this sub (""if I push a rod longer than one light-year, doesn't the end move faster than light?"" or something similar). When you push on the first ball, you create a pressure wave which propagates through the other balls and eventually pushes the last ball out. The speed of this wave is not infinite: it is finite and equal to the speed of sound in whatever material the balls are made of. + +> This principle is also true for electrons in a wire. + +No. The tennis balls in the pipe provide only a very rough analogy. In reality, when there is no electric field in the wire, the electrons are still moving. But they move randomly, and so, on average, they are at rest. If there is an electric field, the electrons still move randomly, but with some average drift in the direction of the higher potential. (Brownian motion with non-zero drift is a closer analogy than balls in a pipe.) + +> There are billions of electrons in a wire. If an electron enters one end of a wire, another electron is forced out the other end. + +Yes... but again, not instantaneously. If the electric field is already present in the wire, the drift velocity of the electrons is, in fact, very slow, literally a snail's pace in many common applications. + +> Assume that a wire is long enough to be wound around the earth 10 times. If a power source and switch were connected at one end of the wire and a light at the other end, the light would turn on the moment the switch was closed. But it would take light approximately 1.3 seconds to travel around the earth 10 times. + +No. Absolutely not. Period. This is certainly the most egregious error in this entire paragraph. **The light does not turn on instantaneously.** When the switch is closed, the change in the electric field in the wire propagates at a *finite* speed, less than the speed of light. (This signal is analogous to the pressure wave in the tennis balls.) The actual speed of this signal is determined by many factors, including the composition of the wire and its surroundings, and in copper wires in your home is typically on the order of 50-99% the speed of light. + +The author of your textbook is demonstrating a very fundamental misunderstanding of physics. I would say that I am horrified, but I have seen worse. + +--- +**Various followups to some common responses and questions** +--- + +* The author's first statement is that the electricity *appears* to travel faster than light. The word appear does not necessarily mean ""looks as if this happens, but it doesn't"". The word can mean ""this happens because this is what we see"". Regardless, the author very clearly states in at least 3 places (""instantaneously"", ""instantly"", ""the same moment"") that the propagation of the EM wave in the wire is instantaneous. + +* Some have commented that according to the second figure, the light bulb is actually connected via a very short wire to the battery, and the EM wave does not have to travel all around the world to reach it. First of all, I think it's rather odd to think that that specific part of the figure is drawn to scale but not anything else (or else the bulb is as large as Earth). Secondly, and more important, the light would *still* not turn on instantaneously. ""Nearly instant"", ""so quickly as to be imperceptible to humans"", ""effectively instant"", etc. are *not the same as* ""instantly"", which is what the author claims. + +* The text is written for electricians in a high school or community college trade program. It is not written for physicists. The errors are rather egregious, and I do understand that the correctness of this particular paragraph is likely not relevant to most using the book. (There are applications in signal processing where the signal speed in the wire does matter though.) However, I believe that a book that purports to be an educational tool, a textbook no less, should not be incorrect in anything it claims (barring new discoveries that make statements outdated). Yes, electricians probably don't need to know the details of copper wires and electricity to the atomic level, but the claim that common electricity allows for FTL communication is outrageous. I sincerely believe that many students would doubt the veracity of that statement, just as the OP has. Would you not then be cautious in trusting anything else in the book? Regardless, there are other mistakes in the text which are very relevant to the audience. + +* For those asking what I have seen that is worse, well, just your standard fare of creationism biology textbooks was what I had in mind. In terms of physics, I have seen new-ish fluid dynamics texts explain airplane lift incorrectly (i.e., that streamlines split and must meet up again at the other edge). I have also seen many incorrect explanations of why light does not travel at *c* in media. But IMO those last two are not as bad as an implication of FTL communication via a long wire and a light bulb. + + + + + + + + + +" Grace Hopper [famously gave a lecture](https://www.youtube.com/watch?v=JEpsKnWZrJ8) in which she presented a foot-long length of wire, and explained that it represented a nanosecond -- the approximate distance that electricity, travelling near the speed of light, travels in one billionth of a second. +1351 When people forge metal and parts flake off, what's actually happening to the metal? 5383 https://www.reddit.com/r/askscience/comments/bvvdjr/when_people_forge_metal_and_parts_flake_off_whats/ 1559464736 bvvdjr 2019-06-02 11:38:56 "I'm just an amateur blacksmith, not a materials scientist, but it is my understanding that scale -- what we call the ""flakes"" you're talking about that come off when you hammer a piece -- is a layer of rapidly oxidizing iron on the surface layer of the piece that you shatter and flake off when you hit it with the hammer." "Because the metal is at a high temperature oxygen diffuses rapidly into the metal, which forms various iron oxides (FeO, Fe2O3, etc.; You can look at the phase diagram to see which phases form). This layer is not that strong and little pieces fall off during forging. + +TL;DR It's rust/lost material + +Source: Chemistry student" +301 How did the Great Wall of China affect the region's animal populations? Were there measures in place to allow migration of animals from one side to another? 5379 https://www.reddit.com/r/askscience/comments/4bd0yr/how_did_the_great_wall_of_china_affect_the/ 1458578319 4bd0yr Biology 2016-03-21 19:38:39 "You may be interested in this: [""Deep in the Forest, Bambi Remains the Cold War's Last Prisoner""](http://www.wsj.com/articles/SB125729481234926717) + +During the Cold War the West German-Czechoslovakian border was divided by 3 electrical fences. Now that the fences are down, researchers following German and Czech deer found that the German deer stay on the German side of the border and the Czech deer stay on the Czech side of the border. + +Only 2 male deer have crossed and 1 male German deer visits the Czech Republic once a year." "I'm not sure about animals but I read an article a while ago about plants that were dependent on wind to spread their seeds and how the Great Wall actually did prevent these plants from interacting and therefore it created subspecies who were of the same plant, but up to half the genetic make up was different that it's counter part on the other side of the wall. + + + +I'm at work, but I'll try to get the article and find it when I get home. I can't remember specifics. + +Edit: See crnaruka's link below. Thanks crnaruka! " +1352 AskScience AMA Series: We're the team sending NASA's Dragonfly drone mission to Saturn's moon Titan. Ask us anything! 5372 https://www.reddit.com/r/askscience/comments/c7r6a0/askscience_ama_series_were_the_team_sending_nasas/ 1561978807 c7r6a0 2019-07-01 14:00:07 The AMA will begin at 3pm Eastern Time, please do not answer questions for the guest till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Please keep questions and your interactions professional. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). After googling I found out, that the temperature on Titan ist -179 °C. How difficult was it, to build a drone that can withstand such extreme temperatures? +1246 During timeperiods with more oxygen in the atmosphere, did fires burn faster/hotter? 5367 https://www.reddit.com/r/askscience/comments/bi1cxp/during_timeperiods_with_more_oxygen_in_the/ 1556385884 bi1cxp Physics 2019-04-27 20:24:44 Yes. And during periods with lower oxygen levels, fires burned more slowly or not at all. Some natural fuels will burn at high oxygen concentrations but not low. [This article](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3012516/) examines these relationships. Wildfires may actually act to stabilize atmospheric oxygen levels. If the concentration increases, fires will burn faster and consume the excess. If the concentration decreases, fires slow down and consume less oxygen, allowing the concentration to rise again. Check out [this excellent paper(PDF)](https://www.google.com/url?sa=t&source=web&rct=j&url=https://iopscience.iop.org/article/10.1088/1748-9326/aa9ead/pdf&ved=2ahUKEwjUtOaI7vDhAhVQcq0KHTalCjAQFjADegQIAhAB&usg=AOvVaw3QXcy76BSRYJO06lp9ikW0&cshid=1556388642646) to learn more about this and other relationships between fire and climate, ecology, evolution, etc. "Absolutely - we actually have a ton of fossil evidence for fires during the Carboniferous era, when both biomass and atmospheric oxygen content were high. If you look at the coal deposits from that time, there's a high percentage of charcoal in it. Some of the evidence actually suggests that wildfires may have been a regular feature of Carboniferous forests. + +Meanwhile at the end of the Permian, we had a decrease in atmospheric oxygen which contributed to the ""coal gap"" along with the decreased biomass from the end-Permian extinction." +1075 Why is the brain divided? 5365 https://www.reddit.com/r/askscience/comments/8nqm8y/why_is_the_brain_divided/ 1527845991 8nqm8y 2018-06-01 12:39:51 "Trying to explain this from a human-centered perspective won't work, as paired ganglia forming a cord is a common feature of bilateria. And no, it isn't just your brain, your ENTIRE nervous system has a left and right side that are mirror images. + +And don't believe the forebrain was a single mass that was selected to split. Remember, the chordate nervous system originates as a hollow tube which closes at the tips (if it doesn't close, you get Spina Bifida or anacephaly), then the walls keep growing in thickness. [And this is the embryonic brain](https://www.quizover.com/ocw/mirror/col11496/m46535/1302_Brain_Vesicle_DevN.jpg) + +However, remember, the tip of the neural tube is not the frontal lobe of the brain, but the lamina terminalis, which is pretty much in the center of the head, just above the optic chiasm. The hemispheres are LATERAL outgrowths, they are the left and right side of the tube, which grow on their own to the point they cover the remaining parts (in birds and mammals pretty much tho). But lateralization IS the ancestral condition. The longitudinal fissure wasn't selected for, it was a remainder of when worms had left and right ganglia. The thing that was selected for was the Corpum Callossum." "A lot of people have answered the bilateral aspect of body development, so I'll answer the last question. Yes, all animals with brains have bilateral structures. Even animals like worms and insects that we don't necessarily refer to as having ""brains"" but rather collections of neurons known as ganglia have bilaterality of their neurons. + +Look up images of comparisons of brains across the different animal groups. There are clear differences, but overall a lot of similarities in the overall structures present. " +1353 How fast did the extinct giant insects like Meganeura flap their wings to accomplish flight? Were the mechanics more like of modern birds or modern small insects? 5362 https://www.reddit.com/r/askscience/comments/c04f1i/how_fast_did_the_extinct_giant_insects_like/ 1560423857 c04f1i 2019-06-13 14:04:17 Interesting question! I found [this recent paper](https://jeb.biologists.org/content/jexbio/221/19/jeb185405.full.pdf), which estimated a variety of factors related to flight in these animals. Table 3 in particular is relevant here; it extrapolates wingbeat frequency with two different methods. In either case though, there's clearly a negative relationship between body mass and flapping frequency, and so *Meganeura* is reported to have had a wingbeat frequency of between 3 and 8 Hz. This is much lower than any living dragonflies (for which even the largest species flap their wings at around 30 Hz), and is instead comfortably within the range of birds (e.g., see table 3 of [this study](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.530.7390&rep=rep1&type=pdf) for wingbeat frequencies from a selection of bird species). However, the flight dynamics obviously still would have differed from birds significantly due to the presence of four wings, differing wing shape, etc. "I wonder if we have an accurate estimate for how ""thick"" the air was back then. Thicker air would give them quite a bit more lift and create a slower flap need. Thinner air would have a faster need. Also altitude may have had enough variance that the air could be significantly thinner at a couple thousand feet of altitude above sea level." +1354 How do we know the Mariana Trench is the deepest point in the ocean? 5360 https://www.reddit.com/r/askscience/comments/c9no6y/how_do_we_know_the_mariana_trench_is_the_deepest/ 1562375109 c9no6y 2019-07-06 4:05:09 "You often hear things like ""We've only explored X% of the ocean"" but this is very misleading because it depends on what you mean by ""explored"". It certainly doesn't mean that we know absolutely nothing about the majority of the ocean, because we do. Whilst it's true that only a very small proportion of the ocean has been observed *visually* by humans, the entire ocean floor has been mapped to a resolution of [at least 1km](https://topex.ucsd.edu/WWW_html/srtm30_plus.html) through a combination of satellite-derived gravity measurements and measurements from ship-borne instruments. Whilst it's technically true that we cannot entirely discount the existence of some extraordinarily steep and deep fissure that has evaded our remote sensing techniques, we can confidently say that the Mariana Trench is the deepest significant point in the ocean." "While we haven't been to the deepest parts of the ocean in person, we are able to measure them from a distance. + +By using technology like sonar, we can map out the sea floor, determining things like the depth. Map out the whole thing (even if on fairly poor quality) and it is simple enough to pick the deepest point. + +If you are referencing the comment of 'we have only explored x% of the ocean', what that is typically saying is that while we have basic knowledge of the whole area, we have not visited it in person and explored it in detail. + +Imagine flying over a mountain in a plane - it is easy to look out the window, spot the highest point and get a basic idea of what sort of landscape of is and how many trees there are. At the same time, from that height you won't have a clue what sort of animals live there, how the plant life has adapted to the area and so on, which you will only ever learn by landing and having a closer look." +1355 If I focused on my heart hard enough, could I control my heartbeat? 5359 https://www.reddit.com/r/askscience/comments/cfn0df/if_i_focused_on_my_heart_hard_enough_could_i/ 1563636420 cfn0df Neuroscience 2019-07-20 18:27:00 "Sort of! + +There are studies that have shown that meditation can slow a heartbeat. This is the result of the 'relaxing' mindset lowering the amount of cortisol being produced. Here's a link: [Effect of Buddhist Meditation](https://www.sciencedirect.com/science/article/abs/pii/003193849190543W) + +I've also read some articles about monks that claim to be able to do this at will; they can force themselves into the meditative mindset almost instantly. Can't find the links ATM, but will update when I do. + +HOWEVER, that does not mean you can *control* the heartbeat. Your heart does not have the correct nerve connections for this; you'll never be able to control it like your arm muscles, you can only influence it." "Absolutely yes. + +The actual heartbeat is involuntary and locally generated by the heart itself, but the heart rate is modulated by the vagus nerve and circulating neuroactive hormones, both of which can be controlled by the subconscious brain. + +But it takes much more than simply meditating or concentrating on your heart. You would have to reinforce neural pathways that are necessarily obscure and involuntary. Simple biofeedback with an EKG and meditation techniques would make that possible." +401 "In 1899 ""Mile-a-Minute"" Charles Murphy set a bicycle world record of 60 mph by riding behind a train to reduce drag, would this approach work for human runners as well to break the elusive 30 mph threshold?" 5358 https://www.reddit.com/r/askscience/comments/5057fv/in_1899_mileaminute_charles_murphy_set_a_bicycle/ 1472480105 5057fv Physics 2016-08-29 17:15:05 Interesting question. Typically the rule of thumb is that drafting in cycling lets you go the same speed as the leader using 30% less power. In running however, a much smaller portion of the overall drag is due to air resistance. [This article](http://www.ncbi.nlm.nih.gov/pubmed/7380693) estimates it at about 8% of the total power for sprinting (at 22 mph), meaning that if that were *totally* eliminated then the same athlete (let's call him Usain) could go about 2.5% faster (because power consumption is proportional to the cube of velocity). [Usain's top average speed](http://klotza.blogspot.com/2015/10/an-empirical-look-at-scaling-of-world.html) is about 23.5 mph, while his peak speed is about 27.3 mph. With this estimate, extreme drafting would still only bring him up to 28 mph. With a bicycle you can change the gearing so that your legs can keep pedalling at the same cadence. In running your legs have to move faster, and I suppose that is where the limit actually lies. Even in a vacuum your legs would probably not be able to move much quicker than they do at 1 atmosphere. +788 Do black holes swallow dark matter? 5358 https://www.reddit.com/r/askscience/comments/6k0sr6/do_black_holes_swallow_dark_matter/ 1498659281 6k0sr6 Astronomy 2017-06-28 17:14:41 "We don't really know what dark matter is. + +The prevailing hypothesis is that it's some kind of particle that only interacts gravitationally (well, for the most part). If that's the case, then yes, black holes should definitely be able to swallow that stuff up. + +Under that same assumption, it should be noted that dark matter will probably not form an accretion disk, nor would it care about an existing accretion disk. So dark matter particles would just describe conic curves around the black hole. If the curves happen to intersect the event horizon, the particles will be captured. Otherwise no capture will occur. (with some corrections to those trajectories due to general relativity) + +--- + +If it turns out that dark matter is not particulate stuff, then all of the above does not apply." "Black holes don't respond to dark matter the way that we might think apparently. Thanks to /u/WhyYaGottaBeADick for the find: + +https://www.universetoday.com/60422/astronomers-find-black-holes-do-not-absorb-dark-matter/ + +https://arxiv.org/abs/1002.0553 + +""**An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes**"" +*X. Hernandez and William H. Lee* +" +302 Is it possible to recreate a smell from a basic list of smells? in other words, is there an RGB equivalent for smells? 5356 https://www.reddit.com/r/askscience/comments/3zbp8j/is_it_possible_to_recreate_a_smell_from_a_basic/ 1451858222 3zbp8j Human Body 2016-01-04 0:57:02 "This is actually an area of heated debate right now. Short answer: we're not sure. There's a [few](https://en.wikipedia.org/wiki/Shape_theory_of_olfaction) [competing](https://en.wikipedia.org/wiki/Vibration_theory_of_olfaction) [models](https://en.wikipedia.org/wiki/Odotope_theory) (with varying degrees of support) for how exactly molecular recognition for smell works. Our understanding of how much the ""smell space"" can be reduced and quantized will be influenced heavily by which of these models most closely reflects reality. + +A paper from 2014 claimed that we could distinguish upwards of a trillion smells. This was refuted last year, with a paper claiming the original one was flawed. It's hard to know at this point if we might reduce the ""smell space"" to a small subset of base smells or not, there just isn't clear enough data yet. + +One important point is that our genome has about ~~10~~ 3% of our genes devoted to smell receptors - about ~~3000~~ 1000 genes. At least 400 of these are functional. This means that there are at least 400 different permutations of responses that could happen, and [different receptors could react to different molecules in different ways](http://superhelical.com/2015/11/30/how-spicy-would-you-like-that-chemotherapy/), so the complexity is already huge. Combine multiple receptors simultaneously, it gets even more complex. + +At the same time, that could be a lot of overkill and we might only use a subset of those receptors well, and there might be a much greatly reduced pool of ""dimensions of odour space"". + +In short, we're not sure, it's a bit of a tangled mess, but we'll know a lot more in a few years. + +Links: + +[Humans Can Discriminate More than 1 Trillion Olfactory Stimuli](https://www.sciencemag.org/content/343/6177/1370) + +[The number of olfactory stimuli that humans can discriminate is still unknown](http://lens.elifesciences.org/08127/index.html) + +[On the dimensionality of odor space](http://lens.elifesciences.org/07865/index.html) + +**Edit**: Whoops, remembered incorrectly, [there are ~1000 receptors, not 3000](https://en.wikipedia.org/wiki/Olfactory_receptor). But the point still stands. We've got a lot of receptors, and it's hard to make sense of them at this point." I have a question for you regarding naturally occurring flavor chemicals that mimic other food types. Are they the same? For example, there's an aromatic compound in an ethiopian coffee cultivar that tastes exactly like blueberry, and there's also a terpene in a marijuana strain that smells like blueberry. Are these the exact same chemical found in a ripe blueberry? +106 Windows 10 says pins are safer than passwords how can this be when passwords have more combinations? 5352 http://www.reddit.com/r/askscience/comments/3gd6ut/windows_10_says_pins_are_safer_than_passwords_how/ 1439140347 3gd6ut Computing 2015-08-09 20:12:27 "Pins aren't to increase the security of your machine, they are to increase the security of your microsoft account. + +Pins are for logging into the particular machine/account combination, and passwords CAN be for this, but also can be (and what microsofts wants) be multiplatform/cloud based (microsoft account) wide. + +Therefore, using your microsoft account to log into the computer creates a point of vulnerability for something much larger than just that computer. If that password is compromised, a person has access to all of your platforms, and a vast amount of data. + +If your pin is compromised, they only have access to that one computer, and perhaps your one drive. + +There are also procedure issues. Because people want to log on convienently, they may make easy password. But because microsoft accounts are online and always vulnerable, AND worthwhile targets, it should never have a simple password. Pins relieve this conflict, and so increase security of microsoft accounts this way as well. + +EDIT: Reading some posts made me realize that a lot of people missed a basic feature of the PIN. The login PIN is only enterable by someone who is physically present. + +The PIN, like biometrics (the other login feature added to win10) requires the operator to be physically in possession of the device, and manually interface with it. So, brute forcing your PIN is a slow and bloody fingers affair, and the PIN can complement other features like a security camera. So, the PIN is highly secure by design. + +by that same note if you make it so that only your PIN, and not your microsoft account, worked to logon to the machine, then switching to a PIN would make your machine more secure. But, as it stands, if your microsoft account is compromised, then the attacker can access your machine without knowing your PIN. This, coupled with the PIN being technically (though not meaningfully,) easier to guess manually, is why your PIN does not increase the security of the machine. PINs increase the security of your microsoft account, which, defacto, increases the security of the machine. + +If you want no exposure to microsoft account vulnerability, I believe you have to setup the PC with only a locally stored login. That local only login/password would be more secure than a PIN. + +IF you hear of someone logging in with a PIN remotely, then PINs become a huge liability until patched, and you should immediately disable it. no human enterable number is going to be secure against a brute force attack. + +" "People are forgetting that this PIN only logs you into the machine LOCALLY. This isn't the same thing as having your password be your PIN. + +So in theory, they're correct as no one is going to be at the machine long enough to try 10000 combinations. The Microsoft account's password can still be HolyCrapThisPasswordiSreaLLyLongandSECURE and be pretty safe." +1598 What the hell did I see? 5351 https://www.reddit.com/r/askscience/comments/h0aye6/what_the_hell_did_i_see/ 1591795689 h0aye6 Astronomy 2020-06-10 16:28:09 "Those would probably be the [Starlink satellite constellation](https://www.space.com/spacex-starlink-satellite-megaconstellation-launch-photos.html). They will get dimmer and more spread out as they reach their final higher orbit. + +They are somewhat controversial right now, because they have been interfering with [certain types of astronomical observations](https://www.theverge.com/2020/3/24/21190273/spacex-starlink-satellite-internet-constellation-astronomy-coating)." "This is the best space tracker website I have ever found. Gives times and what objects are visible, but also has a Google Street view of outside your house with a rough direction of where to look. [https://james.darpinian.com/satellites/](https://james.darpinian.com/satellites/) + +Edit: Thanks to the kind redditor for gold, and everyone else who has left a comment or going to try it out." +1076 Do we innately conceal our genitals? 5348 https://www.reddit.com/r/askscience/comments/8urjaq/do_we_innately_conceal_our_genitals/ 1530260868 8urjaq 2018-06-29 11:27:48 "You might be wondering why so many comments (about 90%!) have been removed. On /r/askscience we expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. **If you are not an expert in the domain please refrain from speculating.** + +You can find [AskScience's rules here](/r/askscience/wiki/rules)." Try /r/AskAnthropology those scientists have access to huge databases of cultures and customs +303 Planet IX Megathread 5340 https://www.reddit.com/r/askscience/comments/41wzn4/planet_ix_megathread/ 1453332172 41wzn4 Planetary Sci. 2016-01-21 2:22:52 If true, could this be the first of many such planets that we find? "It sounds like we have some circumstantial data and solid math supporting its existence, but no actual observations of the planet: + +> “We have pretty good constraints on its orbit,” Dr. Brown said. “What we don’t know is where it is in its orbit, which is too bad.” + +Is our next step to actually figure out where it is? Given its extremely large orbit, what are some observation techniques applicable for the kinds of distances we're talking about? + +If that's not our next step, what is? " +874 When a baby is in the womb, what is the biological signal that lets the mother know the baby has reached full development, and what goes wrong with this signal when a child is born premature or late? 5338 https://www.reddit.com/r/askscience/comments/72bvg8/when_a_baby_is_in_the_womb_what_is_the_biological/ 1506339859 72bvg8 Biology 2017-09-25 14:44:19 "EDIT: Oh boy this got big... So I've gone through this and corrected my terminology to better explain myself. + +Oh man I did a thesis on this! + +Premature labour is in a bad place. No one is really sure what triggers it and medical science as a result can only be reactive, which is far from ideal. The term for the initiation of labour is partuition. + +Now this is pretty much controlled by hormones. To condense a lot and keep it simple, the utureus begins to contract rhythmically in the process of partition. But you definitely do not want that happening before it's ready, so uterine contractions are suppressed by the hormonal action of pregnanolone and estradiol. + +My study examined the RNA editing of a certain receptor called the GABA^A Receptor (Specifically GABRA3-- the α3 subunit, and even more specifically the GABA^A that is expressed in uterine tissues, which contains the π subunit (GABRP, that is expressed basically nowhere else in appreciatable quantities that I'm aware of) over the course of mouse pregnancy. The study itself was crude (bachelor thesis, can't expect miracles!) but definitely implied that the editing changed definitively over the course of the pregnancy. The edit was present throughout the pregnancy until the final couple stages, where it seemed to vanish or at least dip below the detection of basic PCR. + +So our working hypothesis was that RNA editing was at least part of the mechanism that inhibited partuition-- GABA^A has a suppressive role when interacted with (In the brain it inhibits action potentials in neurons but can also inhibit the *contraction of smooth muscle*) and the edit occured within a portion of the protein that was within the membrane of the cell. So, an edit (or in this case the ceasation of an edit!) could destabilise this receptor, causing it to be taken into the cell faster and lowering the number of receptors that pregnanolone can reach. The result? Less inhibition of uterine contractions. The fact that the edit occurs in the π subunit acts to prevent such deregulation in other GABA^A Receptor rich areas-- the most notable of course being the brain. + +Do note that unless further research has been done recently that this is all a hypothesis we came to. Our study was preliminary and a lot more work was needed when I graduated. + +The biochemistry and endocrinology of preterm labor is absolutely an area of active research right now. GABA^A Receptors are mostly studied in terms of neuroscience and the π-subunit DOESNT occur in the brain so it frankly gets almost no attention. The fact that it occurs in the uterine walls though is perhaps a big hint. We basically know nothing about what the π-subunit *does*. + +This may be a tiny portion of the biochecmical regulation of labour, but in such situations when you have lots of little changes piling up, big things can happen... + + As a side note, the project taught me something else about studies-- people are a lot more likely to pour money into Alzheimer's than a very common issue that few people realise is a medical conundrum. It taught me to REALLY drive home the impact of a disease. The current treatment for preterm birth is either to hope for the best or tocolytic drugs to essentially freeze the birth like sticking a plug up there. They can have utterly horrendous side effects and are becoming more and more frowned upon. Understanding the chemical basis of preterm birth is essential then-- we can only design safer and specific drugs and more importantly a way to detect it occuring early if we understand the mechanism causing the issue. + +Sources- + +Preterm birth and complications: + +http://www.sciencedirect.com/science/article/pii/S0140673608600744 + +http://www.sciencedirect.com/science/article/pii/S0002937809004207 + +http://jamanetwork.com/journals/jama/fullarticle/197711 + +http://contemporaryobgyn.modernmedicine.com/contemporary-obgyn/news/modernmedicine/modern-medicine-now/management-preterm-labor?page=full + +GABRA Editing, and in pregnancy, and GABRP: + +http://www.jbc.org/content/286/3/2031.short + +https://academic.oup.com/endo/article/142/5/1770/2988868/Regulation-of-Uterine-Aminobutyric-AcidA-Receptor + +http://www.jbc.org/content/272/24/15346.short (Honestly the presense of GABRP is potentially more interesting than the RNA editing to me! Such a potential drug target!) + +Unfortunately theres a derth of detailed or even *recent* study. Fujii there provided a lot of background for my paper. + +A point of clarification: the study was more sold as a potential *biomarker* of preterm labor. Drugs are a lofty goal indeed, but one of the reasons preterm labor is so nasty is that once it's started its already too late. Finding a biochemical change that can be monitored would be a huge boon." "Preface: nursing student that took OB about 8 months ago on a cell phone. So excuse the lack of formatting and grammar and possible autocorrect sabotage. + +There isn't a prefect, defined signal. There are a lot of things happening at the end of gestation that can cause a baby to come early or late or on time. One of these is the growth and development of the fetus and when things are developed and it's just growing. If i rememeber correctly this is around 37 or 38 weeks. + +Another is the placenta, where the nutrients are exchanged between mom and fetus. Around 42 weeks the placenta will start to decline in function because it's done it's job and isn't programmed to last much longer. This is one reason they don't want people to go past 42 weeks. + +Mother's health and any chronic conditions also play into it. If she has been having high blood pressure or gestational diabetes that can change when things ""go"" or how big the fetus gets at certain points in time. This can cause her to carry longer or shorter depending on how her body handles things + +There is also moms body being triggered to go into labor when the fetus settles into the pelvis and pushes on the cervix, along with stretching of the lower uterus, etc. Fetus knows when it's ready the majority of the time (Not a conscious ""let's do this"" but more of a hormone and cell signal type thing) and starts to move into position. + +It's really a concert of hormones and receptors and signals that all work together to determine the right time. Sometimes those things trigger at the wrong time, or something happens to mom and that triggers it (trauma, drugs, disease, poor cervical tone, etc). Sometimes it's the anatomy of mom and her cervix can't hold shut well enough so when there's too much it decides it's labor time, or often this can cause miscarriages earlier in the pregnancy. There are a variety of other things that can cause those as well. + +And of course, emergencies can cause mom to need to go into labor or have a c-section earlier than they want because of risk of death to either mom or fetus. I know someone who had a baby at 28 weeks because her blood pressure was dangerously high and she was going blind (preeclampsia). Both of them are great now, but he had to spend a few weeks in the NICU since he was so small. + +I hope that helps. There's so many thing but I tried to cover some of the big ones we learned about. If i made a mistake please let me know. " +1356 AskScience AMA Series: We're the New Horizons team that flew past Pluto and are studying some of the oldest, farthest objects in the Solar System. Ask us anything! 5328 https://www.reddit.com/r/askscience/comments/cebbbz/askscience_ama_series_were_the_new_horizons_team/ 1563361240 cebbbz 2019-07-17 14:00:40 The AMA will begin at 5pm Eastern Time, please do not answer questions for the guests till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Please keep questions and your interactions professional. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). What's the plan after Ultima Thule? Is there enough power/fuel left for a flyby of another Kuiper Belt Object? +528 South Korea just got hit with a 5.4 magnitude earthquake. 3 days ago, North Korea carried out a nuclear weapons test that caused a 5.3 magnitude seismic event. Is it possible that today's earthquake is a result of the nuclear testing several days ago? 5322 https://www.reddit.com/r/askscience/comments/52ex23/south_korea_just_got_hit_with_a_54_magnitude/ 1473694435 52ex23 Earth Sciences 2016-09-12 18:33:55 "Just adding a bit to the answer given by /u/brandonsmash. If you are asking if the test explosion in North Korea physically triggered this earthquake in South Korea, you can think of it in the same terms of natural earthquake triggering. There are two physical mechanisms where earthquakes can trigger one another. One of these is static stress triggering and one is dynamic stress triggering. + +Earthquakes have triggered other earthquakes across long distances (1000+ km) through dynamic stress triggering. This occurs when an already stressed fault is near the breaking point, then the surface waves of a large earthquake pass by and throw that last straw on top to make the fault rupture. Remember that there are earthquakes much, much larger than these tests that do not seem to trigger any seismicity. Some do, and you can read about those in this recent paper published in Science [[summary article](https://scripps.ucsd.edu/news/study-finds-earthquakes-can-trigger-near-instantaneous-aftershocks-different-faults) / [Fan and Shearer, Science, 2016](http://science.sciencemag.org/content/353/6304/1133)]. + +There is also static triggering which is more like a domino effect. That's where one bit of fault ruptures and puts added stress on an adjacent fault, pushing it over the brink and causing it to rupture. This is only relevant over distances of about one fault length, so over a few hundred kilometers for a big M8 or 9 but a much smaller distance (~10 kilometers) for an M6 or less. + +So because the North Korean test was relatively small and about 500 km from the South Korean earthquake the strain transfer would be too localized for static triggering, and because the earthquake occurred days after the test the timing is too late for dynamic triggering. " "We're able to pinpoint the hypocenter of the earthquakes in South Korea. They're located near Gyeongju, which is an inland area. The North Koreans would have had to tunnel for several hundred kilometers to plant explosives underneath Gyeongju or somehow smuggle them across the eastern coastline inland and then detonate them underground, which would have been tremendously obvious. It seems safe to say that the South Korean earthquakes were not, in fact, seismic events triggered by nuclear detonations. + +According to the USGS, while a subterranean nuclear test can trigger localized seismic events due to a release of tectonic pressure, this effect is limited to a few tens of kilometers and doesn't extend down the fault line across days or larger geographical distances (https://www2.usgs.gov/faq/node/3339). + +There is substantial evidence indicating that a nuclear test conducted underground, no matter how strong, is not strong enough to trigger down-fault tectonic activity. " +529 How much more dangerous would lightning strikes have been 300 million years ago when atmospheric oxygen levels peaked at 35%? 5319 https://www.reddit.com/r/askscience/comments/58mqdp/how_much_more_dangerous_would_lightning_strikes/ 1477049668 58mqdp Earth Sciences 2016-10-21 14:34:28 "Lightning was far more damaging back then. The Carboniferous period is associated with the formation of large deposits of charcoal, which have been linked to massive wildfires. Part of the reason is that this period had ideal conditions for fires to start. Not only was the oxygen concentration at a record high, but there were also huge deposits of wood that could serve as fuel. Lightning then often acted to close the fire triangle by providing the spark needed to ignite the fuel. Quoting the introduction to [this paper](http://www.sciencedirect.com/science/article/pii/0031018294900051): + +>Fusain occurs widely in Carboniferous coals and sediments. It is now recognised to represent charcoal and be the product of wildfire. The occurrence of fire is partly constrained by atmospheric oxygen levels, availability and nature of fuel and by aspects of climate (rainfall and seasonability in particular). The majority of fires in the Carboniferous were probably started by lightning strikes or by volcanic activity. + +edit: Removed a sentence that was off topic" "Others have pointed out that lightning was probably more likely to cause wildfires in a more oxygen-rich atmosphere. + +However I take your question to be more about whether lightning would be on average more *energetic* with greater oxygen saturation. The [breakdown voltage](https://en.wikipedia.org/wiki/Dielectric_gas) of oxygen is lower than that of nitrogen, so it's possible this would lead to more frequent and powerful lightning. " +1247 In light of the recent first Marsquake recorded, what causes Marsquakes? Does Mars have tectonic plates like Earth? 5316 https://www.reddit.com/r/askscience/comments/bhwo9g/in_light_of_the_recent_first_marsquake_recorded/ 1556349536 bhwo9g Planetary Sci. 2019-04-27 10:18:56 "Mars does not have tectonic plates, it began to form them at some point in the past, but this ground to a halt. + +On Earth, volcanoes form in two main ways, at plate boundaries (think pacific ring of fire, the italian volcanoes), and secondly at hotspots, where a plume of hot magma melts through the crust (think Yellowstone, Hawaii or Iceland (but Iceland is a hotspot on a plate boundary)). + +The Martian volcanoes are all formed by hotspots. The reason they are so large is that the crust stays still relative to the plume, so the volcano just keeps growing, whereas on Earth, such as at Hawaii, the crust moves over the hotspot, leading to a chain. All the Martian volcanoes are now dormant or extinct, as Mars, being small, cooled down quicker than Earth, so the Martian crust is far thicker than Earth's crust, and its mantle is believed to have largely solidified. + +Marsquakes today are believed to be from a couple of main reasons: + +As things cool, they shrink. This shrinking inside Mars causes stress and fractures which are released as Marsquakes. + +Secondly, impacts cause shockwaves which travel throughout the planet. These quakes are easier to verify by looking at satellite imagery to check for new craters. + +Edit: obligatory thanks to the kind stranger for silver +Edit 2: wow gold" According to a talk by the NASA Chief Scientist Jim Green, which I attended yesterday, it's because Mars is still cooling. As (most) material cools, it contracts. This global contraction causes stress as it can't be done continually and smoothly, so sometimes things will snap/fracture/break and cause a marsquake. +652 "My six year old daughter asked after clapping her hands, ""How does the sound come out?""" 5302 https://www.reddit.com/r/askscience/comments/5ml0gf/my_six_year_old_daughter_asked_after_clapping_her/ 1483803638 5ml0gf Physics 2017-01-07 18:40:38 "There's actually [a paper about that](https://www.acoustics.asn.au/journal/2013/2013_41_2_Fletcher_paper.pdf). The sound is produced by the air escaping from between the palms as they come rapidly together. It's like a little explosion. + +You'll notice you can clap very softly with your fingers, but the loudest clap is palm to palm. The palms are slightly cupped, and the compression of these two cup shapes together encloses a larger volume of air, which then has to explode out of the space as the clap progresses. + +If you clasp your hands palm to palm and then squeeze, you can hear the air coming out. Clapping is like that, but faster, so the sound is more explosive." Get her to slap still water in a bathtub with the palm of her hand and point out the waves that form, then tell her that when she claps her hands, she's making waves like those but in the air. What might also help is putting a very low frequency sound (~1-2Hz) on a speaker cone, so she can see and then feel the cone vibrating, then increasing the frequency slowly so she can see and feel the cone vibrating faster. +653 What would happen if you shine a green flashlight in a spaceship going 0.5c? 5296 https://www.reddit.com/r/askscience/comments/5xssy0/what_would_happen_if_you_shine_a_green_flashlight/ 1488800908 5xssy0 Physics 2017-03-06 14:48:28 "From your point of view, the guy on the spaceship shining the torch, nothing would change. It would look exactly like it would if you shone it when you weren't moving at all. One of the fundamental axioms of relativity is that nothing changes when you move, we phrase this as 'all inertial frames are equivalent'. This means if an experiment, such as measuring the colour of a flashlight, has a result when you are stationary, it has the same result when moving. + +The interesting results from relativity come from other observers who do not share your speed. + +Someone who was in front of you would see the flashlight be blueshifted whereas someone behind you would see the light from the flashlight redshifted." "Probably late to the party, but here are the actual numbers. + +Like people said before, in the spaceship nothing would change. So let's shine the light outside the ship. + +This is what's known as the Relativistic Doppler Effect. The equation is wavelength2=wavelength1*sqrt(1+v/c)/sqrt(1-v/c). Velocity is positive if moving away from an observer, negative if moving towards an observer. + +Let's say green light was a wavelength of 530 nm. + +Moving away at 0.5c, the observer would see it redshifted to 918 nm. This is infrared light, so they wouldn't actually be able to see it without some kind of instrument. + +Moving toward an observer at 0.5c, the observer would see it blueshifted to 306 nm. So again it's not visible to the naked eye. + +Edit: Clarification: 306 nm is not visible because it's in the ultraviolet range." +789 Is there any food that is cooked on the International Space Station, or is it all prepackaged? 5292 https://www.reddit.com/r/askscience/comments/6g73jj/is_there_any_food_that_is_cooked_on_the/ 1496995962 6g73jj Engineering 2017-06-09 11:12:42 "Currently, it's all pre-packaged. + +Though I've seen an article very recently and they are working on baking bread in space from scratch, first step to developing methods to cook in space (or rather, to cook in zero g space stations where something like flour and crumbs could float everywhere and cause fires and all kinds of trouble) + +Edit: + +Someone posted it in a reply already, but this is a similar article to the one I've read (can't be bothered to check history for that particular post, information is basically the same): + +https://www.newscientist.com/article/2134009-crumb-free-bread-will-mean-iss-astronauts-can-now-bake-in-space/" "While its not 'cooked', they do have an experiment onboard to [grow lettuce](https://www.nasa.gov/mission_pages/station/research/news/meals_ready_to_eat), allowing the astronauts a fresh meal. + +Most food on the ISS is pre-packaged and heated at mealtime. The closest they get to cooking is assembling a meal from pre-packaged components. The astronauts are free to mix and match the components to their liking (e.g. building a wrap using a tortilla filled their favorite ingredients). + +They do have an [espresso machine](https://www.nasa.gov/mission_pages/station/research/experiments/1769.html) they use for tea, coffee, and soup." +790 What happens when lightning strikes in an ocean? 5289 https://www.reddit.com/r/askscience/comments/6k9bkn/what_happens_when_lightning_strikes_in_an_ocean/ 1498752339 6k9bkn Earth Sciences 2017-06-29 19:05:39 The current density definitely decreases with distance. Because lightning is such a brief event (about 70uS for the main strike), the [skin effect](https://en.wikipedia.org/wiki/Skin_effect) has significant influence on the distribution of the current. The skin effect is the tendency of rapidly changing current to be concentrated near the surface of a conductor. There will be far more current 10M away horizontally away from the strike than 10M vertically. I tried explaining this to the 10 year olds in my class. The best example I could think of is: imagine a bath full of water. A single drop of ribena/cordial is the lightening strike. Where it first hits, it is concentrated so anything within range of it during the initial hit would be affected. However, just like the drop of ribena in a tub of water, the electrical current dissipates outwards until it is too weak and is quickly neutralised. A simple explanation, but it helped the kids visual it! +1416 How did the British keep the fact that they broke the Enigma code secret? 5287 https://www.reddit.com/r/askscience/comments/drah3i/how_did_the_british_keep_the_fact_that_they_broke/ 1572831725 drah3i Mathematics 2019-11-04 4:42:05 "This is more a history of science question, but there were a few big factors: + +1. The British were extremely successful at keeping the operation a secret, even within their own government. Only the highest commanders were cleared to know the source of the intelligence they received, and they kept it a closely guarded secret, even from their allies and their own officers. They were also extremely successful at both intelligence and counter-intelligence operations, and there was effectively no Axis spy network in Britian. Prominent members of the codebreaking operation were unable and unwilling to divulge their association with the codebreaking group for decades after the war ended, sometimes at great personal expense. + +2. Wherever possible, conventional intelligence gathering was used to provide a plausible alternative explanation. For example, Enigma might reveal the presence of an Axis naval convoy, and then Allied reconnaissance planes were sent to independently find and report the convoy on their own. Once these searchers were observed by Axis forces, they provided a cover for the true source of the information. In addition, to go along with the point above, care was taken to prevent Allied forces from guessing that something was up. Multiple search teams would be sent out so it wouldn't appear as though they were getting luckier than they should have been. In another example the British concocted a fictitious spy and fictitious reports from that spy, who was then exposed to the Axis forces via radio traffic so as to provide a plausible explanation for enigma intelligence. + +3. The Axis cryptanalyists knew that attacks against Enigma were possible in theory, but thought these attacks were too laborious to achieve in practice. They additionally conducted their own reviews of the Enigma system and found it to be secure. They even decrypted Allied communications and did not find any reason to suspect their device had been broken, because operational security was very tight. In light of that, they looked for alternative explanations of Allied successes and found scapegoats in technology like radar (of course, radar advancements themselves were also significant during the war, so they weren't off the mark so much as measuring effect strength poorly)." If memory serves, there was no statistical formula. They decided as a loose rule, that any action they took, based on information gained from the team at Bletchley Park (where they broke the enigma code), had to be based on information they would've been able to learn from another source. It was really up to the higher ups, such as Churchill, to decide when and where to use the information they got. As long as their actions wouldn't give away the fact that they'd broken the code they would proceed. +971 What is the very worst case scenario in relation to the rise in water levels? Can Earth become an ocean planet? 5273 https://www.reddit.com/r/askscience/comments/7nmaz7/what_is_the_very_worst_case_scenario_in_relation/ 1514898320 7nmaz7 Earth Sciences 2018-01-02 16:05:20 "Sea level rise is caused by the melting of the ice caps, but the planet has actually lacked ice caps for most of its history. If all the ice on the planet melted, it would only amount to about [216 feet of sea-level rise](https://www.nationalgeographic.com/magazine/2013/09/rising-seas-ice-melt-new-shoreline-maps/)--which is enough to displace a major portion of the world's population, given our propensity for living on the coast, but given enough time to resettle they could easily survive on the remaining land. Realistically, though, the transition would be disastrous and could cause widespread famines. To have greater sea level rise you'd have to get water from extraterrestrial sources. + +Edit: I'll answer a few common questions here rather than keep addressing them individually + +- Yes, if you eroded down all the mountains and dumped the material in the sea it would eventually cause the continents to be flooded, but that's not going to happen for a few reasons: 1, that amount of erosion would take many billions of years, and would slow down as the mountains were removed and only low plains remained; 2, tectonic processes create new land faster than erosion can wear it down; and 3, by the time either plate tectonics stops or enough time has passed for this erosion to occur, the Earth will have likely lost it's atmosphere and seas anyway. + +- Some quick math tells me that inundating everest would take around 4.5 * 10^21 liters of water, of which there might be enough on Pluto, or failing that, Triton. If you just wanted to flood all the lowlands then you might be able to get away with using something smaller like Rhea or Iapetus. + +- Yes, there is a large amount of water in the mantle, but it's not like an aquifer that can be tapped--it exists within the chemical structure of mantle rocks, mainly [ringwoodite](https://en.wikipedia.org/wiki/Ringwoodite). + +- The source I cited claims that it would take around 5,000 years for all the ice in Antarctica to melt, but it's hard to be sure with these sorts of climate models. The more imminent risk of 20 feet of sea level rise is still enough to flood many coastal cities and spark mass migrations. + +- When I say the population can live in the remaining land after this event, I just meant that the remaining arable land is more than enough to support us. This doesn't make the transition easy by any means, especially given that the changing climate means the location of ideal agricultural land would shift. + +- Seawater desalination is possible, but very energy intensive, and though it may provide a source of fresh water for some regions it has no effect on sea-level rise. I'm not too sure why some people have brought it up. + +- When considering countermeasures to sea-level rise, your main concern isn't the gradual rise of the sea like a slow tide, but storm surges that cause short-term rises of several meters and destroy coastal structures and barriers--storms of the sort that will be more common in a warmer climate." "If you wanted to drown every last square centimetre of land, then you'd have to have an ocean that's at least 8.850 km taller than it currently is (which is the AMSL altitude of the peak of Mount Everest). + +With some quick maffs, one can deduce that the rough extra volume of water required would be some 4.5 billion cubic kilometres. + +Earth has only got about [33 million cubic kilometres](https://nsidc.org/cryosphere/quickfacts/icesheets.html) of ice. Accounting for thermal expansion wouldn't add significantly to this volume, as 4.5 billion km^3 is more than a _hundred_ times this volume. + +Earth is more likely to lose its water and become a desert planet than it will ever become an ocean planet. + +___ + +Edit: some people may account for the fact that [water has been subducted and is trapped in the upper mantle.](https://www.astrobio.net/news-exclusive/scientists-detect-evidence-oceans-worth-water-earths-mantle/) There is *still* not enough water there to drown all land on Earth. It *might* turn the Himalayas into an island chain, but fact remains that ocean planets are theorised to have oceans *hundreds* of kilometres deep. " +1797 When tissue is grafted, how do the blood vessels in the graft find and connect to the blood vessels in the graft site? 5269 https://www.reddit.com/r/askscience/comments/lap0zq/when_tissue_is_grafted_how_do_the_blood_vessels/ 1612245923 lap0zq Human Body 2021-02-02 9:05:23 "There are several stages for a graft to ""take"". + +The first stage is fibrin adhesion, in which fibrin acts as a kind of glue for the graft. Fibrin is whats in blood clots and it makes a mesh to stop bleeding. + +Then there is plasma imbibition and it means that the grafted tissue is ""absorbing"" what it needs from the underlying area, and it is something temporary that happens in the first couple days until the graft is more established. + +After this is the phase of inosculation and revascularization, and in this phase there is the growth of new blood vessels (neoangiogenesis is a big topic, but know that tissues that are devoid of a blood supply, ischemic tissues, stimulate the production of new vessels in order to remedy the situation). These new vessels enter the graft or connect to vascular channels in the graft (the graft tissue has its own vessels that were cut off when it was taken), and this process happens from day 2 to up to around a week. + +Finally there is the remodelling phase, which is what it sounds like. There are some processes that continue happening over a week after the graft, like continued revascularization and fibrogenesis, which means that some special cells make connective fibers and some other materials that contribute to the extracellular environment which is very important for cells' normal function. This helps the graft to properly fit in to its new environment." "As far as I am aware, first the graft is placed and sutured in place, vessels are not normally manually connected, in the early phase of transplant the outer layers of the graft begin to necrose and the underlying tissue becomes inflamed with a fibrin mesh underneath it. This causes blood to 'pool' beneath the graft. The remaining tissue is perfused by plasma and infiltrates (white cells, blood cells etc.) from this pool. Over time the graft heals by becoming somewhat continous with the underlying tissue as the inflammation decreases, the epithelium undergoes quite a dramatic change and continues to remodel till day 28. + +The obligatory not a dentist, but fourth year med student! Hope this helps! + +Edit: format" +654 How did Archimedes calculate the volume of spheres using infinitesimals? 5266 https://www.reddit.com/r/askscience/comments/5t1dkw/how_did_archimedes_calculate_the_volume_of/ 1486661110 5t1dkw Mathematics 2017-02-09 20:25:10 "Archimedes knew the volumes of cylinders and cones. He then argued that the volume of a cylinder of height *r* and base radius *r*, minus the volume of a cone of height *r* and base radius *r*, equals the volume of a half-sphere of radius *r*. [See below for the argument.] From this, our modern formula for the volume of the half-sphere follows: *r* \* *r^(2) π - 1/3* \* *r* \* *r^(2) π* = *2/3* \* *π* \* *r^(3)* and by doubling this you get the volume of a sphere. + +Now, the core of his argument goes like this: consider a solid cylinder of base radius *r* and height *r*, sitting on a horizontal plane. Inside of it, carve out a cone of height *r* and base radius *r*, but in such a fashion that the base of the carved-out cone is at the top, and the tip of the carved-out cone is at the center of the cylinder's bottom base. This object we will now compare to a half-sphere of radius *r*, sitting with its base circle on the same horizontal plane. [See [here](https://blogs.adelaide.edu.au/maths-learning/2014/07/24/archimedess-integrals/) for pictures of the situation.] + +The two objects have the same volume, because at height *y* they have the same horizontal cross-sectional area: the first object has cross-sectional area *r^(2) π - y^(2) π* (the first term from the cylinder, the second from the carved-out cone), while the half-sphere has cross-sectional area *(r^(2)-y^(2))π* (using the Pythagorean theorem to figure out the radius of the cross-sectional circle). +" "Short answer: Cavalieri's Principle + +Slightly longer answer: You can find the volume of a sphere inscribed in a cone and cylinder using some pretty basic geometry. I won't go into all of the details because it's outlined perfectly on the Wikipedia page for Cavalieri's Principle [here](http://en.wikipedia.org/wiki/cavalieri's_principle) " +1417 Is something only warm to the touch, i.e I touch with my finger, if that object is warmer than my body temperature? Or at what temp does something become warm to touch, considering when run roughly 37 C/98.6F? 5263 https://www.reddit.com/r/askscience/comments/dshg96/is_something_only_warm_to_the_touch_ie_i_touch/ 1573052394 dshg96 2019-11-06 17:59:54 "Your body's sense of hot/cold doesn't ""measure"" temperature, rather it measures heat transfer. Touch a piece of metal that's at 32°F and it feels a lot colder than a piece of wood at 32°F, even though they are at the same temperature. This is because metal is much better at conducting heat than wood. + +It depends on how much heat is added or taken away to feel hot/cold. If what you touch pulls heat from your hand (something at a lower temperature) then you feel cold. If it adds heat to your hand (at a higher temperature) then it feels hot. Heat flows from hot to cold to reach an equilibrium temperature, never the other way. + +So to answer your question, something will feel ""warm"" only if it is at a higher temperature than your hand, as its heat will then flow into your hand. (keep mind, your hand is probably less than your normal body temperature. That's how you can feel that your head or body is warm). How warm things feel depends on how good it is at conducting heat. + +Edit: I'm gonna add some stuff now. I kinda ignored the effects of the body's generation of heat or long term effects, that just makes it a more complicated to understand heat transfer problem. I just focused on a simple case of touching something with a few fingers at a reasonable temperature, so the small amount of heat genereated in your hand can escape to the environment through the back of your hand or something and you don't need to consider it. It's different than soaking your entire body in 97°F water for hours. + +This is the coolest fact I learned in Heat Transfer, and changed the way I understand simple interactions. A cool example I feel like sharing is when you are outside in the winter for a while and your hands get really cold. When you come inside and before you warm up, if you wash your hands the water feels extremely hot even though its the same comfortable temperature it's always been normally, but now the heat transfer is high because your hands are at a lower temperature. This highlights another cool fact about heat transfer, that you can't exceed the starting temperature of either object (Without adding work). If the water is room temp, it will only warm up your hand to room temp, so even though it feels as if the water is dangerously hot, it can't burn you. + +This effect is exactly why wind chill is a thing. Wind chill is a ""fake"" temperature, that describes what your body feels like when there is wind. (Without getting to much into it, the higher speed a fluid travels the more heat it transfers, whether in or out). So if the air is at 10°F and the wind is blowing, the wind chill might be -20°F because the air feels colder as it pulls more heat from your body. Ultimately though, you can't cool anything down below the actual temperature of the air (10°F in this case) because if you did... Then heat will flow from the air to the object warming that object up, as again heat flows only from hot to cold. (a car left overnight in 0° temp will be 0° in the morning regardless of the wind chill). So wind chill just explains how quickly the air will pull heat from you and compares it to a temperature of stagnant air so you can get an idea, it doesn't mean the air temperature is actually lower than what it is. + +Oh, yeah and some spelling. Oof." "It depends on both the temperature and a material property called thermal conductivity - you can think of this as how quickly a material will change temperature in its surroundings. + +For example, steel has a higher thermal conductivity than wood, so it “pulls” heat from its surroundings faster (if the air is warmer than the metal), or “pushes” heat into the surroundings faster (if the air is colder than the metal) than the wood. So if you were to touch both the steel and wood at the same temp, the metal would feel more extreme than the wood (if they’re both hot, the metal will feel hotter). + +As for when things change between feeling hot and cold, this really only depends on the difference in temp between your fingertip and the material you’re touching. It’s hard to say exactly, because even though your body temp is 98.6F, your fingertip is obviously not at that temp." +1357 How do we know that the universe is constantly expanding? 5257 https://www.reddit.com/r/askscience/comments/c5urht/how_do_we_know_that_the_universe_is_constantly/ 1561578499 c5urht Astronomy 2019-06-26 22:48:19 "The velocity of a galaxy along our line of sight is fairly easy to determine, since we can use the Doppler shift of atomic spectral lines to measure that extremely accurately. (It’s much, much more difficult to measure their velocity perpendicular to our line of sight. So much so, that this is currently only possible for the most nearby galaxies caught in the grip of local gravitational interactions, not those with motions dominated by the universe’s expansion.) + +What this means is that we can get a very accurate map of how quickly galaxies are approaching or receding away from us. We can still tell that things **appear** to be receding away from a central point, because we appear *to be* the central point. And also, the further away the galaxies are, the faster they appear to be moving away from us. Relying only on the radial velocity measurements, the whole universe seems to be receding away from specifically us! This fact could cause some existential alarm until one remembers the cosmological principle: that viewed on a sufficiently large scale, the properties of the universe should appear the same to any observer – it is more or less homogeneous. This is a strong claim, but is also one that has been born out by observations of the Cosmic Microwave Background (leftover radiation from the Big Bang). + +If the universe looks similar to observers in different places, then the only possible conclusion from our observations of galaxies receding from us is that every galaxy is receding away from every other galaxy. This is the same as saying that the entire universe is expanding. Another consequence is that this expansion can’t be oriented around a single, central point. If we could construct the full 3-dimensional velocity vectors of every other galaxy, they would not point back to any particular location we could point to and say “That right there is the center of the universe!” Instead, everywhere is equally the center of the expansion. The Big Bang happened at all places, equally, and everything has been expanding away from everything else, in all directions, ever since. This is a direct consequence of the one dimension of the velocity vector which we can measure very well (the radial component) combined with the cosmological principle. And again, the fact that more distant galaxies appear to be moving *more quickly* away from us than nearby ones is exactly what you would expect to see in an expanding universe. + +The rate of this expansion at early times (measured at the distant universe) compared to later times (measured at the more local universe) has recently come into tension, and [seems to be pointing at brand new physics](http://hubblesite.org/news_release/news/2019-25)." "Well, strictly speaking, we don't. What we know is that everything is moving away from us. + +To understand how we know that, you need to first understand the doppler shift. In a nutshell, any time the source of a wave is moving, the frequency of the wave shifts. When the source moves away from the observer, the wave spreads out and the wavelength becomes lower. When the source moves towards an observer, the waves are compressed and the wavelength is shorter. You can imagine it much like a boat moving around on a body of water. The boat's wake near its front is compressed and the waves do not extend much beyond the front of the boat. However, the waves behind the boat spread out. The thing is, this is true for all waves. Water waves, sound waves, and even light waves demonstrate this phenomenon. If you put a very bright light bulb on a very fast space ship, as the ship sped away from you, the light waves would become more spread out, their frequency would be lower, and they would appear redder in color (since on the visible color spectrum, red is at the low end and blue is at the high end). + +Now, you might think that this is enough to tell how stars in the sky are moving. You know that the blue stars are moving towards us and the red ones are moving away, right? Well, there's a catch. + +The next thing you have to understand is how we can tell whether a light source is naturally red or blue, or whether it's just moving relative to you. This is where spectroscopy comes in. Everything that emits light does so in a very specific pattern of frequencies, based on what the emitter is made of. It's sort of like a barcode or a fingerprint. If you can take the light from an object, and look at the spectrum of frequencies that comprise it, you can tell what that object is made of by looking at the pattern of frequencies that make up the light. And much like a spoken word is still distinguishable whether you change the pitch up or down, this pattern of frequencies is still distinguishable whether it is red or blue shifted. Since we know that most stars are made largely of hydrogen and helium, and since we know the frequencies of light that those elements emit, we can tell whether the light from a distant star is red shifted and moving away from us, or blue shifted and moving towards us. + +When astronomers look at the spectrum of light from stars in the sky, they observe something extraordinary. Except for the stars in our immediate vicinity, all of the light from all those stars appears red shifted. Closer stars are only slightly red shifted, and further stars are more heavily red shifted. What that tells us is that the stars close to us are moving slowly away from us, and the stars more distant to us are moving quickly away from us. So, how do we explain that? + +There are fundamentally two explanations. The first is simply that the Earth happens to be in the center of the universe, and everything just happens to be moving away from us. That would be quite the coincidence, wouldn't it? The second and more likely explanation is that space itself is expanding. Picture an inflatable balloon covered in dots. As you inflate that balloon, all the dots appear to spread out, but try and visualize what that would look like if you were shrunken down and placed on one of those dots. From that perspective, all the dots would appear to be moving away from you, the closer ones would be moving more slowly, and the further ones would be moving more quickly. The interesting thing is that if you moved to another dot, you would observe *exactly* the same thing. All the dots would still appear to move away from you. + +That brings us to the Copernican Principle. The Copernican Principle is the idea that humanity does not occupy a special or privileged vantage point in the universe. We're not located in the center or on the edge, we're just somewhere indescript somewhere in the middle. It's a statistical argument, and the general idea is that there are *vastly* more locations in the universe that aren't special than ones that are, and hence it is simply incredibly likely that our location in the universe is just a mundane one, not a unique one. + +To summarize: we see all stars around us moving away at a rate proportional to the distance between us and them. And since it is more likely that our position in the universe is typical, we would expect to see the same pattern virtually everywhere else in the universe (that is to say, every point in the universe sees all the other points recede at a rate proportional to distance). Therefore, the only explanation that fits is that the space between everything is itself expanding." +402 AskScience AMA Series: We have discovered an Earth-mass exoplanet around the nearest star to our Solar System. AMA! 5253 https://www.reddit.com/r/askscience/comments/4zdkra/askscience_ama_series_we_have_discovered_an/ 1472058020 4zdkra Astronomy 2016-08-24 20:00:20 The article I read mentioned that it probably had a magnetic field... I know how we find atmospheres around other planets, but how do we know about the magnetic field? Does the planet partially transit, and is there any hope of atmospheric occultation? +875 How sustainable is our landfill trash disposal model in the US? What's the latest in trash tech? 5230 https://www.reddit.com/r/askscience/comments/7f7oj4/how_sustainable_is_our_landfill_trash_disposal/ 1511532533 7f7oj4 Engineering 2017-11-24 17:08:53 Landfill mining is worth a look, essentially digging through existing landfills and sorting things of economic value, recyclables, biodegradables, fuel sources, etc. while creating more space in the process. It is of course a costly undertaking, but there are MSW sites in the US that have profitably implemented landfill reclamation. Here's the EPA spiel on it with sources: https://www.epa.gov/sites/production/files/2016-03/documents/land-rcl.pdf "I work at a waste to energy facility, and would say the landfill model is sustainable. My plant reduces every 7 tons of incoming waste to 1 ton of ash that goes to the landfill as cover. Plus we have a system to recover metal out of the bottom ash and we sell that to scrappers for recycling. Then add in that our ash can be sold for use in concrete, and the ""new"" industry of landfill mining for precious metals reduces it even further. Just in my county/city our records show that incoming waste has been leveling off and as our ability to recycle increases, I don't see any reason to say that the landfill model couldn't be sustainable. " +1358 When a star goes super nova, is the gold fused inside the star's core, or does the shockwave fuse matter in it's outer orbit? Neither/both? 5227 https://www.reddit.com/r/askscience/comments/cffp2v/when_a_star_goes_super_nova_is_the_gold_fused/ 1563583677 cffp2v 2019-07-20 3:47:57 "The ""core"" never really fuses gold, as the core is only ever capable of fusing up to iron, and only the heaviest stars will ever get to that point. Smaller stars like our sun can only provide enough temperature and pressure through gravity to fuse up to oxygen and carbon, and then die out as white dwarfs. As gold is significantly heavier than iron, a star's core can never produce it while it's still ""alive."" + + +Iron is the point at which further fusion reactions require you to add energy rather than the reaction producing any. That's the point at which the core suddenly collapses and begins the supernova, because the iron is not producing energy pressure to hold up the weight of the rest of the star anymore. + + +As the core collapses, unless it's so heavy that it collapses straight into a black hole, it stops and ""bounces"" at the point it creates a neutron star, which can hold itself up through other methods than fusion. The rebound shock wave briefly produces energies and pressures even higher than the fusion core of the original star. This brief period is capable of fusing the rest of the elements heavier than iron on the periodic table. + + +However it's funny you ask about gold, because up until now, we didn't think this brief period during a supernova was sufficient to create the amount of gold we actually see in the universe. Very recently, we observed two neutron stars orbiting and colliding into each other. This seems to create enough temperature and pressure for long enough to explain the rest of the gold out there." "It's actually a pretty even mix. Elements heavier than iron are made by atoms capturing neutrons, which can occur in one of two ways, imaginatively called rapid and slow neutron capture (or r and s). + +Rapid capture occurs where there are enough neutrons that atoms can be built up faster than they decay. This in turn requires hundreds of neutron captures per second, needing insane free neutron densities that you'll only find in a supernova or neutron star collision. For elements with non-contiguous stable isotopes, rapid capture tends to be the only way the heavier isotopes can be formed. + +Then there's the slow path, where an atom will capture a neutron, decay, capture a new one, etc. This requires a star with high metallicity, i.e. where part of it is made up from the remnants of a supernova so that there is iron present in the core while it is undergoing fusion. Here it's more like one neutron capture per hundreds of years. Generally happens in the cores of giant stars" +1359 I don’t understand how AC electricity can make an arc. If AC electricity if just electrons oscillating, how are they jumping a gap? And where would they go to anyway if it just jump to a wire? 5226 https://www.reddit.com/r/askscience/comments/cxdhfa/i_dont_understand_how_ac_electricity_can_make_an/ 1567149220 cxdhfa Physics 2019-08-30 10:13:40 "Imagine the electrons as a bunch of marbles (or ball-bearings) in a tube all touching each other. + +You push one end, the other end moves almost instantly. You push them back, they all move back instantly. You're causing work to happen on everything that those marbles rub against. That ""work""/""friction"" is what lights up the bulbs, power the cooker, etc. + +Now generally speaking, it's not a tube, but in fact it's an entire sheet of marbles. In fact, not even a sheet, a box of marbles. It just so happens that, say, copper being a good conductor, means that all the marbles in the ""air"" don't move very much at all, because when you push, the marbles in the copper wire are the ones to move with the least effort (least resistance). So even though every cubic nanometer of space is filled with tiny marbles of electrons, when you push them, the ones that actually move are the ones that aren't ""stuck"" to the others they are touching and offer the least resistance to movement. + +In a copper wire, that means that the marbles that do move basically move like they are in a contained tube (with the boundaries of the tube being those electrons that are making the plastic covering, the air, whatever, which ""resist"" movement more). + +If you push hard enough, though, even the ones in the air will eventually get moved along too. Hence you get an arc through the air. The bigger the arc gap, the harder you need to push (more voltage). So lightning is millions of volts, but can clear an arc-gap hundreds of metres long. It's pushing \*so\* hard that the electrons in the normally-quite-stiff air get moved and pushed along. That's also why lightning/arcs change their pattern rapidly... they are literally moving along the path of least resistance all the time and the air is moving / wetter in places, so different electrons find it ""easier"" to move. + +You have to push harder, but the air is basically a big huge wire too. + +In a vacuum, you don't get arcs." "As other posters have pointed out, in any current in a wire the electrons move very slowly; however the voltage wave (think of it as the ""pressure wave"") moves at a significant fraction of the speed of light. Hydraulic cylinders are good approximations. AC electricity is generally pretty slow -- usually 16 2/3, 50, 60, or 400 Hz so about 1/100 of a second -- while the time-scale for the arc to form is ns to us, or 1/1'000'000'000 to 1/1'000'000 second. This means that for the arc, the voltage over the gap is essentially constant until the current starts flowing. + +Remember that when you have a gap in a conductor, there will initially be no current flowing through it. Therefore all the voltage in the circuit will be concentrated there -- in the wire U=R\*I and initially I = 0, and thus no voltage in the wire. + +When the gap is exposed to high voltage, there is a strong electric field. This is in volts / meter, so the smaller the gap, the higher the field. If there is a free electron in the gap (coming from random ionization events like cosmic radiation or from the negative (cathode) surface), this electron will be accelerated in the electric field. When the electron has picked up enough energy, it can cause another ionization event by colliding with a neutral atom or molecule in the gap, giving rise to yet another electron and another positive ion. If the probability of this happening is high enough, this causes a runaway cascade, which generates a lot of electrons and ions. This is a plasma -- similar to what you have inside a fluorescent tube but denser -- which can conduct electricity since there are free charges. This completes the circuit, allowing the current to flow through the arc, and if the power source is strong enough, generates a lot of heat. + +For AC electricity, there is one advantage -- since the voltage is going through 0 twice per cycle, at this time there is nothing ""feeding"" the arc more energy. This causes the arc to stop, if it has time to cool down and dissipate the plasma. However for DC the voltage stays high, which makes circuit breakers for high voltage DC much harder to make than for AC. + +For your second part of the question (""And where would they go to anyway if it just jump to a wire?"") I am not sure what you mean? + +Source: PhD which included quite a bit of research into the formation of arcs inside particle accelerating structures." +107 What would happen to me, and everything around me, if a black hole the size of a coin instantly appeared? 5216 http://www.reddit.com/r/askscience/comments/39woqa/what_would_happen_to_me_and_everything_around_me/ 1434371255 39woqa Physics 2015-06-15 15:27:35 "**Edit:** This comment is now a [minor motion picture, animated by Kurz Gesagt](https://www.youtube.com/watch?v=8nHBGFKLHZQ) ! + +**Short answer:** You, and everyone around you, will die. + +**Long answer:** Different things will happen if you mean the black hole has the *mass* of a coin, or if it has the *radius.* The equation of a black hole is really simple: + + Radius = 2 (Gravitational Constant) (Mass) / (Speed of light)^2 + +Suppose a nickel in your pocket magically collapsed into a black hole. A US nickel has a mass of 5 grams. This black hole would have a radius of 10^-30 meters. For comparison, an atom is about 10^-10 meters. If atoms were made of atoms, this black hole would be the size of the micro-atom that makes up the milli-atoms that makes up real atoms. Basically, it's unimaginably small. + +Such a small black hole would have a similarly unimaginably short lifetime to decay by Hawking radiation- it would radiate away what little mass it has in 10^-23 seconds. This 5 grams of mass will be converted to 450 teraJoules of energy, which is comparable to the detonation of about 100,000 tonnes of TNT, and will produce an explosion three times bigger than the atomic bombs dropped on Hiroshima and Nagasaki *combined.* In this case, you die. + +Of course, if the black hole has the radius of a common coin, then it will be considerably more massive. A nickel, again, has a radius of about 10 mm. This black hole has a mass of 10^24 kilograms - slightly bigger than the mass of the earth. Its surface gravity is a billion billion times greater than earth's. If it is in your pocket, you will find yourself being drawn towards the black hole at breakneck speeds. Literally *breakneck*. The difference between your chin and your teeth is about ten trillion g's of acceleration. You'll cross the event horizon before you even realize what's happening. The black hole is now a dominant gravitational piece of the earth-moon-black hole of death system. If you watch sci-fi movies a lot, you might think that the black hole sinks towards the center of the planet and will consume it from the inside out. In actuality, the *earth* will also move up onto the black hole, and begin to bob around as [if it was orbiting the black hole](https://upload.wikimedia.org/wikipedia/commons/0/0e/Orbit5.gif), all while having swaths of mass eaten with each pass. The bulk of the planet earth is consumed after some time, leaving a scattered disk of hot dust and rock in a tight orbit where the earth once was. The black hole grows slowly during this time, eventually doubling its mass by the time it's done feeding. + +The effects on the solar system are awesome, but moreso in the Biblical sense of ""awesome"", which more closely means terrifying. The moon's orbit is now highly elliptical. Tidal forces from the black hole could disrupt the asteroid belt, sending rocks careening through the solar system - bombardment and impacts may become commonplace for the next few million years. The planets are slightly perturbed, but they stay approximately on the same orbit. The black hole we used to call earth will now continue on orbiting the sun, in the earth's place. + +In this case, you also die. + +edit: I got some math wrong and rewrote most of this. Thanks to the commenters for catching my mistakes. " I find it very interesting and mind boggling how so many giant black holes exist, yet space in itself is so huge that we are not really affected by these black holes...or are we? +403 What is the physiological difference between the tiredness that comes from too little sleep and the tiredness that comes from exertion? 5214 https://www.reddit.com/r/askscience/comments/4vn5g1/what_is_the_physiological_difference_between_the/ 1470066580 4vn5g1 Human Body 2016-08-01 18:49:40 "Interesting question. + +According to [a paper published in the The Journal of Neuroscience](http://www.sfn.org/Press-Room/News-Release-Archives/2008/One-Sleepless-Night-Increases-Dopamine-in-the-Human-Brain), one sleepless night increases dopamine in the human brain. An increase of the neurotransmitter was found in the striatum, involved in reward/motivation, and the thalamus, involved in alertness. The researchers concluded : + +> The rise in dopamine following sleep deprivation may promote wakefulness to compensate for sleep loss. “However, the concurrent decline in cognitive performance, which is associated with the dopamine increases, suggests that the adaptation is not sufficient to overcome the cognitive deterioration induced by sleep deprivation and may even contribute to it,” said study author Volkow. + +This would serve an evolutionary advantage to early humans who felt they needed to stay awake for extended periods of time, e.g. for hunting food. This contrasts with exercise-induced tiredness because, as we'll see, exercise does not necessarily cause cognitive impairment. + +[Another study in *Perceptual and Motor Skills*](http://pms.sagepub.com/content/84/1/291.full.pdf+html) sought to establish the effects of physical exhaustion on cognitive functioning. They had 13 fit men pedal on stationary bikes at different intensities, and had them perform a series of short-term memory tests. + +> It appears from our findings that the extent to which physical effort affected cognition depended +on the intensity of the session and on the set size of the decision task. + +They also referenced other papers that addressed neurochemical changes within the brain. + +> Finally it may be worth considering our results in the context of the biochemical changes +brought about by physical exercise. Indeed, it has been argued that these changes may interact +with cortical activity during strenuous effort (Hebb, 1955). Peyrin, Pequignot, Lacour, and +Fourcade (1987) reported an activation of the catecholamine system resulting from strong physical +work and suggested the existence of a positive relationship between adrenomedullary activation +and mental performance. + +So sleep deprivation-induced exhaustion and physical exercise-induced exhaustion are similar in the sense that they cause an increase in catecholamines (i.e. dopamine, norepinephrine, etc.). + +However, with physical exercise, it appears that an increase in mental performance is possible, whereas we already saw sleep deprivation can be cognitively impairing: + +> Comparative discussions of the present results with those of previous studies are daicdt +because of the different operarionahzarion of fatigue across studies and the specific interpretation +of results. Nevertheless, it has been already reported that treadmill exercise conducted at +high physiological activation (94% of maximum heart rate) significantly enhanced mental performance +(McGlynn, Laughlin, & Rowe, 1979) + +**Edit**: [Also understand that exercise uses up glucose stores in the muscles](http://www.bd.com/us/diabetes/page.aspx?cat=7001&id=7516) and your body begins to burn fats as fuels, which can contribute to the feeling of overall fatigue if too much glucose is used up. This is a problem particularly in diabetics. [Here](http://www.ncbi.nlm.nih.gov/pubmed/3315761) is a paper that establishes the relationship between hypoglycemia (low blood sugar) and levels of alertness.. ~~I do say anecdotally that I don't think sleep deprivation has much effect on blood glucose levels. But let me look for a source on that.~~ + +**Edit 2**: [This paper](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1991337/) evaluates the effect of sleep deprivation on glucose metabolism. + +> The research reviewed here suggests that chronic partial sleep loss may increase the risk of obesity and diabetes via multiple pathways, including an adverse effect on parameters of glucose regulation, including insulin resistance, a dysregulation of the neuroendocrine control of appetite leading to excessive food intake and decreased energy expenditure. + +This is a different mechanism than by physical exercise-induced alterations in glucose metabolism. While your body knowns when to use glucose as energy while exercising, it appears that sleep deprivation results in dysregulation of neuroendocrine control of appetite and insulin resistance. In other words, tiredness from sleep deprivation is different from tiredness from physical exercise because sleep deprivation essentially results in bodily malfunction. Yet another reason to get enough sleep at night! + +**Edit 3**: Increased clarity and tried to point out more differences. Perhaps someone with more expertise in physiology can chime in? + +**Edit 4**: Thank you /u/whatthefat for the input: + +>It should be noted that sleep deprivation specifically causes a reduction in ATP stores of neurons. + +>http://www.jneurosci.org/content/30/26/9007.short + +***TL;DR*** + +Tiredness from strenuous physical activity appears to be from your body using up its glucose and ATP energy stores. Tiredness from sleep deprivation is a result of your body going into overdrive mode: there are anomalies in the amount of neurotransmitters in the brain such as dopamine, and it has adverse effects on glucose metabolism and energy expenditure. +" "Is it possible this question is raised because English uses the word ""tired"" for both conditions? In Visayan, the conditions aren't considered related because they are referred to with different words, ""tulogon"" for sleepy due to lack of sleep and ""kapoy"" for exhausted from exertion. " +530 If fizzy drinks were made with another gas besides CO2 like argon or helium etc, how would the drinks taste different? 5212 https://www.reddit.com/r/askscience/comments/510sxw/if_fizzy_drinks_were_made_with_another_gas/ 1472936819 510sxw Chemistry 2016-09-04 0:06:59 CO2 forms carbonic acid and makes the drink acidic. Helium or argon would not. The drink would taste different for that reason alone. Some beers use nitrogen gas instead of CO2. They taste very velvety and creamy. +791 From how high up can you dive before water may as well be concrete? 5210 https://www.reddit.com/r/askscience/comments/6k5ejk/from_how_high_up_can_you_dive_before_water_may_as/ 1498702683 6k5ejk Physics 2017-06-29 5:18:03 "This discussion on Stackexchange suggests 54 m as a typical figure, and some of the answers provide some basis for calculation. + +https://physics.stackexchange.com/questions/120036/force-of-an-impact-on-water + +The key factor seems to be when the water is required to move out of the way faster than the speed of sound in water, which will be a function of the impact velocity and the shape/area of the impact." "The current record is 193', but none of the 3 who have exceeded 172' did so without injury. A person without extensive training and experience at lesser heights would probably die from such a height. + +https://www.quora.com/Whats-the-highest-up-you-can-dive-from-into-water-and-still-survive" +1360 Why does bitrate fluctuate? E.g when transfer files to a usb stick, the mb/s is not constant. 5206 https://www.reddit.com/r/askscience/comments/cknf01/why_does_bitrate_fluctuate_eg_when_transfer_files/ 1564660719 cknf01 Computing 2019-08-01 14:58:39 "Any data transfer in computers usually will run through a [Bus](https://simple.wikipedia.org/wiki/Computer_bus) and these, in theory, have a constant throughput, in other words, you can run data through them at a constant rate. However, the destination of that data will usually be a storage device. You will find there will be a buffer that can keep up with the bus between the bus and destination, however it will be small, once it is full you are at the mercy of the storage devices speed, this is where things begin to fluctuate based on a range of thing from hard drive speed, fragmentation of data sectors and more. + +tl;dr: input -> bus -> buffer -> storage. Once the buffer is full you rely on storage devices speed to allocate data. + +Edit: (to cover valid points from the below comments) + +Each individual file adds overhead to a transfer. This is because the filesystem (software) needs to: find out the file size, open the file (load it), close the file. File IO happens in blocks, with small files you end up with many unfilled blocks whereas with one large file you should only have one unfilled block. Also, Individual files are more likely to be fragmented over the disk. + +Software reports average speeds most of the time, not real-time speeds. + +There are many more buffers everywhere, any of these filling up can cause bottlenecks. + +Computers are always doing many other things, this can cause slowdowns in file operations, or anything due to a battle for resources and the computer performing actions in ""parallel""." "There are many sources of this fluctuation but for USB sticks which is based on NAND flash memory, there is a phenomenon called garbage collection. The NAND flash has a restriction that writes must be followed by an erase before the next write. Furthermore writes are at minimal size of a page (8KB typically) while erases are in minimal size of a block (256 pages typically) This means if we need to write only one page of a block everything else has to be copied elsewhere. So the drive plays a juggling game where it writes the new data to an unused block and hopes that over time the old block is freed up. So essentially some extra space is kept aside to do this juggling. However if you keep writing for a long time it will run out of free blocks and needs to start forcibly cleaning up older half valid blocks. This process is called garbage collection. It can happen in the background but will slow down the device. It turns out that if you write large chucks of sequentially ordered data less garbage collection is needed in the long run. There are many ways to minimize this fluctuation but USB sticks are low cost devices so might not be worth the expense of implementing them. + +Source: Spent 10 years writing firmware for all kinds of SSD storage." +531 Does this* number have a name? 5196 https://www.reddit.com/r/askscience/comments/5kthg7/does_this_number_have_a_name/ 1482968680 5kthg7 Mathematics 2016-12-29 2:44:40 ">Is there a more elegant way of finding the bedrock number that underlies a given exponent? + +Yes, for x^n the number you're looking for will be n!, which is shorthand for n \* (n-1) \* (n-2) \*....\*3\*2\*1. + +For example, x^7 would end up with the number 7! = 7\*6\*5\*4\*3\*2\*1 = 5040 + +To see why: +------- +Focus on x^2 to start. + +To generalize the difference between consecutive items in the sequence, we have: + +(x+1)^2 - x^2 + +Do some algebra and get: +**2**x^**1** + 1 + +Repeat the process: + +[2(x+1) + 1] - [2x+1] += 2 + +So there's your 2. + +-------- +Now we do this with x^3: + +(x+1)^3 - x^3 += **3**x^**2** + 3x + 1 + +Repeat the process: +[3(x+1)^2 +3(x+1) + 1] - [3x^2 + 3x + 1] += **6**x^**1** + 6 + +Repeat the process: +6(x+1) + 6 - [6x+6] += 6 [aka **6**x^**0**] + +Making sense of it: +------- + +Notice that I've bolded a few coefficients and exponents in the above section. As you go through the repetitive process, you see that your highest power term always gets canceled out in the algebra. In the x^3 example, you start with 1x^3 being your highest power term. Then you do the difference process and you end up with 3x^2 being your highest power. Then you do the difference process again and you end up with 6x^1 being your highest power. Then you do it once more and 6x^0 is your highest power. + +**In the x^3 example, do you see how the highest power term goes like this as we go through all the steps:** + +x^3 +3x^2 +6x^1 +6x^0 + +**So the general pattern is:** +x^n +nx^(n-1) +n(n-1)x^(n-2) +n(n-1)(n-2)x^(n-3) +. +. +. +n(n-1)(n-2)...3\*2\*1 + +which is the formula we talked about up top." "It's just the result of taking the derivative repeatedly. Your final sequence (2, 6, etc.) will be x! (factorial of x) + +Taking the derivative of a polynomial reduces the exponents by one, then multiplies the terms by the original exponent. + +If f(x) = x^2 +f'(x) = 2 * x +f''(x) = 2 + +If g(x) = x^3 +g'(x) = 3 * x^2 +g''(x) = 6 * x +g'''(x) = 6 + +So each consecutive exponent would result in factorially increasing numbers. 1 * 2 = 2, 2 * 3 = 6, 6 * 4 = 24, 24 * 5 = 120, 120 * 6 = 720" +655 By guessing the rate of the Expansion of the universe, do we know how big the unobservable universe is? 5191 https://www.reddit.com/r/askscience/comments/5sdyes/by_guessing_the_rate_of_the_expansion_of_the/ 1486384182 5sdyes Astronomy 2017-02-06 15:29:42 "We measure the size of the unobservable universe by measuring the curvature of the local universe. If it has zero curvature, the universe is flat and infinite. If it has negative curvature, it has a hyperbolic shape, and is also infinite. If it has positive curvature, it has a hyperspherical shape (like a sphere but in more dimensions), and we can use the curvature to work out the size of the universe. + +Currently it really looks like the universe is very very flat, so it looks like it's infinite. Unfortunately, all measurements must have an uncertainty, which means that it's technically possible that the universe is finite in size - it's just that the curvature is so small that we can't actually see it. + +Edit: For a flat universe, Ω=1. For a spherical universe, Ω>1. We have Ω=1.00±0.02. For Ω=0.98, the radius of curvature of the universe would be about 30 gigaparsecs, which is on the scale of the total size of the observable universe - although we've only observed galaxies up to about 4 Gpc, and only with tricky lensing techniques." I think that the answers here are answering their own question and ignoring OP's-let me try to rephrase: Given that we have observed that the universe is expanding and also that the measured rate of that expansion is increasing (regardless of geometry-as a highly curved piece of paper is just as long as a flat one), can we project backwards to know the size of the universe based on the estimated time since the Big Bang? +972 "Is a 128 Gb memory stick just made up of two 64 Gb chips ""glued"" together or is it an entirely different technology that suddenly occupies half the space?" 5187 https://www.reddit.com/r/askscience/comments/8fryed/is_a_128_gb_memory_stick_just_made_up_of_two_64/ 1525015133 8fryed Engineering 2018-04-29 18:18:53 Both. Within one technology generation, there will be multiple capacities by stacking (inside the package) or grouping (packages on a board). The technology investment is to achieve a next technology that does the same capacity in half the space, allowing to double. This is usually by fabricating the same transistor in less area. "I've worked in the storage industry, though not specifically on this type of device, so I might be missing a few minor details. Hopefully this will help, though. + +A quick search found [this](http://codecapsule.com/2014/02/12/coding-for-ssds-part-6-a-summary-what-every-programmer-should-know-about-solid-state-drives/) article which is focused on high-performance programming. SSDs are very similar in relevant ways to USB sticks. + +In general, there are 3 major components to a flash drive (or even SSD). There's the raw flash chip(s) themselves. There's the flash translation layer which is what makes the flash chips look and act like a drive. And then there's the interface controller which provides USB connectivity (or SATA connectivity, or whatever). + +When it comes to the engineering of these devices, there are lots of things to be considered including assembling costs, defect rates, market desire and willingness to pay. + +Using more than 1 flash chip means you have to pay more for additional assembly costs, if only the extra machine time to install it. + +The flash translation layer is also designed to handle a certain number of flash chips. (I'm assuming it's a separate IC, but SoC design keeps changing things). In general, supporting more chips means more connections which means more silicon and a larger packaging. If you can support a lot of flash chips you are likely able to support higher throughput (which is why SSDs are usually much faster than flash drives even for similar capacities). But if you're trying to go for cost minimization, you might use a shared bus if the flash chips support it and you're willing to take on additional debugging headaches. + +The interface layer probably isn't that interesting. + +If I was tasked with designing a USB memory stick of a particular capacity, I'd probably check to see if the cost of two smaller flash chips plus the cost of a translation-layer chip which supported two flash chips, plus costs of manufacturing, etc., were more or less than the cost of a single larger flash chip with the simpler translation layer, etc. And then do that. Because in this space customers seem to care almost exclusively about price and capacity to the exclusion of all else." +1418 Question from my 5 year old. Would Gatorade keep you hydrated better than water? 5186 https://www.reddit.com/r/askscience/comments/d65jgr/question_from_my_5_year_old_would_gatorade_keep/ 1568849598 d65jgr 2019-09-19 2:33:18 "The salts and sugar help the water be absorbed faster by the body, as there is a sodium-glucose cotransporter in the intestines. You can look up [oral rehydration solution](https://en.wikipedia.org/wiki/Oral_rehydration_therapy) for a medical product that does basically the same, just better. But it does not hydrate the body more. You only get the water a few minutes quicker in the bloodstream. + +But Gatorade contains less than 1 liter water per liter (edit: \~5%), to due all the solved molecules. So if you are only limited on water, gatorade might be a worse choice. If you are sweating a lot and not eating (gives many electrolytes), gatorade might me a better choice. + +Outside of extreme conditions, in everyday life, water is the better choice. (Edit: because normally you want to avoid sugar and overloading on salts) + +Edit: in severe dehydration, especially due to diarrhea, Oral rehydration solution is best." "Couldn't find the actual study in a quick search. If you want to blow a 5-year-old's mind. Chocolate milk was used as a control to access sports drinks and did just as well for recovery. + +https://www.reuters.com/article/us-health-hydration-chocolate-milk/chocolate-milk-may-be-better-than-sports-drinks-for-exercise-recovery-idUSKBN1K236Q + +Looking at this article about it, most of the advantages measured were how your muscles recover from the workout, nothing specific about hydration." +108 If I wanted to randomly find someone in an amusement park, would my odds of finding them be greater if I stood still or roamed around? 5176 http://www.reddit.com/r/askscience/comments/35uljq/if_i_wanted_to_randomly_find_someone_in_an/ 1431537426 35uljq Mathematics 2015-05-13 20:17:06 "I ran a simulation using java for 100,000 trials each. The average time for both people moving is half that of only one person moving. Here is a histogram of the data: http://i.imgur.com/5mYnGiT.png + +Details of the simulation: + +People are assumed to be on a 100x100 grid. If they are on the same spot, they can find each other. At t=0, they are placed on a random location in the grid. Each time step, anyone that's moving will randomly move north, south, east, or west. They can't move out of the 100x100 grid, so if they pick a direction not allowed, they'll pick again." "If you are moving then there are more collisions (e.g. brownian motion) with others. If the people (or objects) are truly moving randomly then if both people are moving there is a greater chance of collision than if only one is moving. + +Source: I am using the analogy of enzymatic efficiency: there is greater successful (desired) collision when both molecules are in motion." +1248 How can a device on an aircraft or car be electrically grounded? 5176 https://www.reddit.com/r/askscience/comments/b042wx/how_can_a_device_on_an_aircraft_or_car_be/ 1552369107 b042wx 2019-03-12 8:38:27 "the term ground is thrown around a lot in electronics but most of the time just refers to the reference point that is 0 volts. for instance, a 9v battery has a hot terminal thats 9v (or should be), and a ""ground"" terminal thats 0v. if you measure the battery with the leads on a meter backwards (putting the black 'ground' lead on the 9v point) then the ground of the battery will read -9v. + +in pc power supplies, theres a -3.3v output, if you measure across the 12v and the -3.3v you would read 15.3v. + +the term ground is only really talking about the ground in home wiring. in a power grid you need one reference point for a large geographical area, it so happens that the ground we stand on has a fairly uniform charge and conducts well enough to act as a reference point. + +the ""ground"" on a helicopter is just a point that the electronics will reference as 0v. this is generally the chassis of the vehicle. compared to the actual ground this might be thousands of volts, in which case the heli will just have a discharge when it lands or touches something thats at a different potential." "To answer that, first I have to go over what it means to ""ground"" something. So, voltage is intrinsically a comparative measure- as in, voltage is defined as the difference in electric potential between two things. It doesn't make sense to talk about the voltage at one point in a circuit; you have to have something else to compare it to in order to give voltage a meaning. This is where the idea of a ground comes in: if we connect all the points in a circuit that should be a neutral voltage to each other together, we can define all those points as 0 volts and compare all other points in the circuit to the 0 volt rail we just created to get their voltages. + +In case that's not as clear a description as I'd like it to be, here's an example: let's say we had a AA battery. The voltage across the terminals on the battery would be perfectly defined, because the terminals are electrically connected by the battery. But the voltage from, say the negative terminal of the battery to the negative terminal of a second battery would not be defined, because they are not electrically connected in any way. There could be a potential difference of thousands of volts between them due to static electricity, or there could be zero volts between them, there just isn't any way of knowing without defining a common voltage between the two batteries with which to compare. You could define this common voltage by simply touching the two batteries' positive terminals together, after which the voltage across the negative terminals would be defined. + +So, you need this common ground in order to make voltages across different parts of a circuit make sense. And, because of the effects of static electricity, it's also of practical interest to make the common ground the same for as many different circuits as possible - if your toaster's ground and your blender's ground had a potential difference of thousands of volts due to static electricity, that would be a real safety hazard. So making the actual ground be the ground for all the circuits in your house is just the simplest and most effective way of doing just that, as it also guarantees that every circuit in your neighborhood is grounded to the same potential. + +In cars and planes, however, using the actual earth as a ground isn't possible. Instead, they use the next best thing: the frame of the cars and planes themselves. Because they also connect one of the terminals of the main battery to the frame, the frame can be used as a huge wire for circuits to draw power from (this is actually how all of the stuff in your car works). + +So, and TL;DR: + +The devices in a plane or car can be grounded by simply using the frame of the car or plane as a ground, but the frame of the car or plane is probably not at the same potential as the actual earth - this is why you'll sometimes get a shock from static electricity after you get out of your car." +1249 How does Aloe Vera help with sunburns? 5165 https://www.reddit.com/r/askscience/comments/bfufxm/how_does_aloe_vera_help_with_sunburns/ 1555885361 bfufxm 2019-04-22 1:22:41 "Aloin Suppresses Lipopolysaccharide-Induced Inflammatory Response and Apoptosis by Inhibiting the Activation of NF-κB + +https://www.ncbi.nlm.nih.gov/pubmed/29495390 + +NF-kB is the major inflammatory pathway in humans and signals immune response that inhibit healing in an attempt to kill off what is perceived by the immune system as pathogenic invasion. By suppressing that activity and increasing solvation and oxygenation of the damaged areas healing can be processed." "Aloe Vera is an anti-inflammatory, however the soothing effects are primarily due to the evaporative nature of the water-based gel. It does not “trap the heat” however like the above comment says, as sunburns aren’t caused by heat, they are caused by UV light. The skin cells of the burn are trying to fall off because they have accumulated DNA damage. + +Aloe Vera is also known to inhibit bacteria growth, which could potentially reduce risk of infection on the burn + +Edit: Corrected the first line" +973 Can any animals ACTUALLY smell fear? 5142 https://www.reddit.com/r/askscience/comments/89d8a1/can_any_animals_actually_smell_fear/ 1522758706 89d8a1 Biology 2018-04-03 15:31:46 "It seems that they can detect(by smell) emotional states in their own species, but this is highly unlikely in different species. + +The highest likelihood is that the animals can read body language very well, and pick up on these physical queues. + +http://news.psu.edu/story/141321/2005/03/16/research/probing-question-can-animals-really-smell-fear" Minnows and related species of fish have a chemical in the skin called schreckstoff, which if released in the water will cause nearby fish of the same species to freak out and hide. So it's kinda like that. +792 Why are so many people allergic to peanuts? 5141 https://www.reddit.com/r/askscience/comments/6o5mjx/why_are_so_many_people_allergic_to_peanuts/ 1500431658 6o5mjx Human Body 2017-07-19 5:34:18 "Edit: As others have pointed out, parents choosing to withhold common allergens has been due to infant feeding consensus guidelines and advice provided by trusted medical professionals, such as their family GP. [The Conversation makes a great point in their article](https://theconversation.com/introduce-eggs-and-peanuts-early-in-infants-diets-to-reduce-the-risk-of-allergies-65564): + +>The problem is, there have been so many changes to guidelines over the last few decades that parents are no longer sure what to believe. + +There's speculation it has to do with parents choosing to withhold common allergens until too late. As far as I'm aware, there's no published work investigating what percentage of parents are making these choices, and their temporal trends, however there has been a meta analysis looking at the effect of timing of allergenic food introduction^1 which is supported by a randomised trial investigating peanut introduction in the first year of life vs complete avoidance.^2 + +1. Ierodiakonou, D.; Garcia-Larsen, V.; Logan, A.; Groome, A.; Cunha, S.; Chivinge, J.; Robinson, Z.; Geoghegan, N.; Jarrold, K.; Reeves, T.; Tagiyeva-Milne, N.; Nurmatov, U.; Trivella, M.; Leonardi-Bee, J.; Boyle, R. J., [Timing of Allergenic Food Introduction to the Infant Diet and Risk of Allergic or Autoimmune Disease: A Systematic Review and Meta-analysis.](http://jamanetwork.com/journals/jama/fullarticle/2553447) JAMA 2016, 316 (11), 1181-1192. +2. Du Toit, G.; Roberts, G.; Sayre, P. H.; Bahnson, H. T.; Radulovic, S.; Santos, A. F.; Brough, H. A.; Phippard, D.; Basting, M.; Feeney, M.; Turcanu, V.; Sever, M. L.; Gomez Lorenzo, M.; Plaut, M.; Lack, G.; Team, L. S., [Randomized trial of peanut consumption in infants at risk for peanut allergy.](http://www.nejm.org/doi/full/10.1056/NEJMoa1414850#t=article) N Engl J Med 2015, 372 (9), 803-13. +" "https://www.ncbi.nlm.nih.gov/pubmed/24472338 + +""The clinical history can be difficult to interpret, measurement of peanut-specific immunoglobulin E (IgE) is of limited usefulness due to its poor specificity, and the gold standard (double-blind placebo-controlled food challenge) is time-consuming and labour-intensive, limiting its use in daily practice. Under-diagnosing peanut allergy is considered dangerous, because of serious reactions like anaphylaxis. As a result, there is a high probability of over-diagnosis of peanut allergy in the general population, leading to unnecessary peanut-free diets and parental anxiety.""" +532 "What happens to a colony-based insect, such as an ant or termite, when it's been separated from the queen for too long? Does it start to ""think"" for itself now that it doesn't follow orders anymore?" 5140 https://www.reddit.com/r/askscience/comments/5ko11e/what_happens_to_a_colonybased_insect_such_as_an/ 1482895555 5ko11e Earth Sciences 2016-12-28 6:25:55 "As an example of an exception to the already provided answers - in Poland an abandoned bunker has provided a situation where wood ants are regularly separated from their colony by falling down a vertical pipe under the main colony. Because it is so common, a semi-functional secondary colony operates underground without much food or light. The ants dig, clean away dead ant bodies to the large ""graveyard"" surrounding the colony, and mostly act as they would above ground, but eventually starve. The colony only keeps going by the regular rain of new workers from above. The scientists studying them aren't sure if they eat anything, like bat guano or mites living on the dead ants, but as of yet haven't identified a food source. + +http://arstechnica.com/science/2016/09/bizarre-ant-colony-discovered-in-an-abandoned-polish-nuclear-weapons-bunker/" "It stops eating and wastes away and dies. It will try hard to get back for as long as it can first. The bee needs the hive. The hive needs the bee. Social insects aren't following orders from anyone, they are acting on instincts written at the level of DNA. The queen (and king, if termites) are just as bound to the system as the workers. Many ants even have multiple queens per colony for redundancy. + +It is a mistake to assume social insects can't think for themselves because of the colony. In the lab they will learn to solve a problem and then teach the solution to others. They are just intimately a part of the group. Don't think of a fascist slave state. Think of an army unit: when one is smart everyone gets smarter; when one is strong, everyone becomes strong. + +(EDIT: blew up while I was asleep. The study on bees learning: +https://www.google.com/amp/mobile.reuters.com/article/amp/idUSKCN124233?client=ms-android-sprint-us ) + +(EDIT2: It's important to remember that Hollywood's interpretations of hive behavior and eusociality are very inaccurate. They depict workers and warriors as male, get behavior wrong, etc..)" +793 How are we able to estimate the Planck's constant at a much higher accuracy (44 per billion) than the gravitational constant G (120,000 per billion)? What is affecting the measurement of G? 5140 https://www.reddit.com/r/askscience/comments/68zmea/how_are_we_able_to_estimate_the_plancks_constant/ 1493809096 68zmea Physics 2017-05-03 13:58:16 "Measurements of G are affected by a large uncertainty ultimately because gravity is very weak. + +You would think it would be fairly easy to extract an estimate of G from orbital dynamics. However, all gravitational effects from a body of mass M are proportional to the combination μ = MG, the standard gravitational parameter. The μ of a celestial body is very easy to determine once you can measure orbits around it (or, if you're lucky enough to be standing on it, the surface gravity), and indeed the μ of most solar system objects is known to great precision. + +However, to extract an estimate of G from μ you'd have to divide by M... and you don't know M. We do not have very precise independent estimates of the masses of planet and stars. The G extracted from this method has a relatively huge error. + +Thus G can only be measured through the gravitational effects of *prepared* bodies with well known masses, which need to be much smaller than planets. So you are now measuring extremely weak gravitational fields generated by man-made objects in [Cavendish](https://en.wikipedia.org/wiki/Cavendish_experiment)-like experiments. This gives a more precise estimate of G, but still with an error comparably larger than all of the other fundamental constants simply because of how small the forces to be measured are, and how hard it is to shield from noise. + +Going back to the planets, G measured from Cavendish-style setups is the most precise determination, so you actually use *that* estimate to extract one for the masses of celestial bodies through M = μ/G. That's how you get the known figures for the masses of the Earth, Sun, etc. + + +For contrast, hbar is known to definitely better precision because it can be determined directly through a variety of not-as-fragile experiments. An example (not necessarily the best) is a [Watt balance](https://en.wikipedia.org/wiki/Watt_balance#Measurements)." "Measuring G is hard*. It's extremely weak, it can only be measured if you have first found the mass and distribution of _everything_ you're working with, and even then, you're in danger of thinking you're measuring gravity when you're actually measuring magnetic interactions. Or static electricity. Or floor tilt. Regardless, you can do an experiment where _your_ value of G look like it's accurate to, say, a few parts per million, but for some reason it doesn't match the value of other peoples' measurement of G. Since we don't know who is right, we have a very large uncertainty in our value. + +Source: spent my twenties measuring G. + + +\* My dissertation title: [Systematic Error Sources in a Measurement of G using a Cryogenic Torsion Pendulum](https://www.physics.uci.edu/~glab/papers/WDCross%20thesis.pdf)." +1077 why don't companies like intel or amd just make their CPUs bigger with more nodes? 5132 https://www.reddit.com/r/askscience/comments/8pkby3/why_dont_companies_like_intel_or_amd_just_make/ 1528468232 8pkby3 Computing 2018-06-08 17:30:32 "Modern CPUs are already very, very thermally dense. For example a Ryzen 8-core CPU is 213 mm² and has a TDP of up to 95W. + +95W doesn't sound like a lot - that's less than many light bulbs - but that power is coming out of a wafer of silicon smaller than your thumbnail. AMD actually does make a bigger 16-core ""threadripper"" CPU that is about twice as powerful at 180W. + +This is pretty close to the physical limit of heat that can be removed from such a small space by an air-cooled heatsink. The old FX-9590 CPU at 220W actually recommended and was packaged with a closed loop water cooling heatsink. + +If the heatsink isn't able to get the heat out of the CPU fast enough the CPU gets hotter and eventually crashes or suffers damage." To elaborate on the heat issue: while the results of, for example, turning on a light switch may seem instantaneous, electricity does take time to travel through circuits, and CPUs operate at speeds where that time is significant. They need to wait for the output voltages to become consistent with the inputs before moving to the next step (clock cycle). So larger overall size could very well mean more distance the current has to traverse before that happens. You can get it to settle faster by increasing the supply voltage (more or less what overclocking is), but moving electricity through wires faster also generates more heat from the electrical resistance. +1361 What makes Jupiter's giant red spot red? 5126 https://www.reddit.com/r/askscience/comments/blf4ye/what_makes_jupiters_giant_red_spot_red/ 1557164183 blf4ye 2019-05-06 20:36:23 "The spot actually changes color. Ranging from dark red, to white, to blending in with the clouds around it. + +The spot is a stable vortex caused by opposing currents of hydrogen and other gases that make up Jupiters atmosphere. + +The reason for it's color is not known precisely but has something to do with the chemical composition which differs from that of the surrounding gases due to the nature of the disturbtion of gases caused by the vortex. The color difference could also have to do with the altitude difference between the gases in the vortex and the surrounding area which again would change it's chemical composition altering the wavelength of the subsequent light reflection." "The only proper answer here is ""we don't know, but we have some good guesses."" + +The reds seen in Jupiter's Great Red Spot (GRS) are also occasionally seen in other big vortices here and there. As of right now, we can't say for certain what makes the GRS red - this is generally known as the ""Jovian chromophore problem"" - but there's something about a vortex being big that causes it to show up. + +Although we've taken plenty of spectra of the GRS (I've taken some myself), it doesn't perfectly match anything we've measured in the lab. It's not that the coloring molecule is some exotic unobtainium, rather that it's extremely difficult to mimic the conditions of Jupiter's upper atmosphere in the lab, so only a few compounds have actually been carefully measured in those conditions. + +Since this color is only seen in very large vortices, it's believed to be caused by some mixture of compounds already present on the planet getting pushed very high in the atmosphere by these vortices. In three dimensions, the Great Red Spot is essentially shaped like a wedding cake, so the cloud-tops at the center of the spot are at very high altitudes where there's a lot more ultraviolet light. You can end up producing all kinds of odd substances through UV photochemistry of trace substances in the atmosphere, and the working hypothesis at this point is that it's some kind of [imine or azine](http://www.sciencedirect.com/science/article/pii/S0019103516001494)." +656 Can new pimples and zits form on the body/face of someone after they have been declared clinically dead? 5122 https://www.reddit.com/r/askscience/comments/5q1mtd/can_new_pimples_and_zits_form_on_the_bodyface_of/ 1485324511 5q1mtd Human Body 2017-01-25 9:08:31 "This is one random ass question which I can answer. The answer is no. Pimples form because a hair follicle is plugged by dead skin or other debris, and the secretions (which are produced by cells) get stuck underneath. As the secretions accumulate, they irritate surrounding tissues and white blood cells are attracted to the site, carried there by flowing blood. The end result is the red, swollen, painful nodule of a pimple. + +After you're dead, your skin cells can probably survive a few hours, if that. During that time, it'll be in self preservation mode mostly since it assumes the blood supply will return soon; it won't be actively producing the usual secretions. Furthermore, even if secretions are present, white blood cells can't get there in significant numbers due to lack of flowing blood. " "In a related question, if someone with acne died and arrived at the mortuary to be prepared for a funeral service, would the funeral director make any attempt to perform a facial to extract the blackheads or pimples? +" +533 I read that, on average, 3 supernovas will occur in the Milky Way galaxy every century. If that is the case why haven't we observed any since the last one in 1604? 5117 https://www.reddit.com/r/askscience/comments/51gc14/i_read_that_on_average_3_supernovas_will_occur_in/ 1473182401 51gc14 Astronomy 2016-09-06 20:20:01 "This is an open question! (Sort of! It has a universally agreed upon answer, that isn't really ""proven"", but it pretty much has to be right.) So, the main thought as to why this is, is that there's a lot of dust in the Milky Way, particularly in the central couple of degrees of Galactic latitude where nearly all of the massive young stars (and therefore massive-star supernovae) are located. There's so much dust that we wouldn't be able to spot a supernova through it. To the Galactic Center, there's about 30 magnitudes of optical extinction (which means that only 1 photon in a trillion gets through!). And that's only *halfway* through the Galaxy! In the infrared it's not as bad, but that's a part of the EM spectrum we have been blind in until fairly recently in history. Just to compare, here's an [image of the Milky Way in optical](http://apod.nasa.gov/apod/image/0102/allsky_mellinger_big.jpg), and [here's one in near-infrared](https://upload.wikimedia.org/wikipedia/commons/e/e4/Milky_Way_infrared.jpg) - notice you can suddenly see through a lot of the dust to the stars behind. So unless a supernova happened to go off fairly close by, or in one of the few young, massive stars out of the Plane, we'd miss it (EDIT: by eye! As /u/mfb- points out, ~~neutrino detectors on Earth would be aware of a~~ neutrinos from a Galactic supernova leave the star hours before the shockwave and light reaches the surface of the star, and neutrino detectors would detect them - hopefully that phrasing is less confusing). Projects like ZTF and LSST might spot one in the optical, though. + +The main reason this is the main idea and not certain knowledge is that we haven't verified that there are historical supernovae that have been missed because of high extinction from dust. There's a way to find out though! Because light scatters off of dust, a supernova can ""echo"" around the Galaxy and the scattered light can reach us. Pairing up such echoes from different directions with each other or a supernova remnant can give a 3D view of the explosion, and a chance to see the explosion very early on. Armin Rest at STScI has done this with supernovae in the LMC before, but the Milky Way is a much larger part of the sky and is harder to do. His group has focused on known supernovae rather than look at the whole sky for new ones, but with projects like LSST about to image large parts of the sky very frequently to great depth, this area might be about to bust wide open in 10-15 years time. Regardless of if they find light echoes for missed historical supernovae, finding echoes for known ones that happened in the past is still really freaking cool - it's like archeology with light! + +EDIT2: We know for a fact that supernova have happened in the last 400 years that *weren't* seen, because we can see remnants of supernova in X-ray and radio that are only about 100 years old, like G1.9+0.3 (the youngest known supernova remnant)." kinda a tangent but got me to thinking.. what, if anything, would happen if you hit the cosmic lottery and happen to be looking at a star that went supernova through a large optical telescope? not an extinction level event but a big one none the less. was thinking along the lines of eye damage but I'm assuming if it's that bad that would be the last of your worries.. +1250 How does a chameleon change color? 5116 https://www.reddit.com/r/askscience/comments/aw4b4f/how_does_a_chameleon_change_color/ 1551443152 aw4b4f 2019-03-01 15:25:52 Chameleon skin has a superficial layer which contains pigments, and under the layer are cells with guanine crystals. Chameleons change colour by changing the space between the guanine crystals, which changes the wavelength of light reflected off the crystals which changes the colour of the skin. "Just a little side-note to get a better understanding of the other answers: the extent to which chameleons can change colors is much exaggerated by media and pop culture and TV ads. It's still stupid amazing but maybe not as much as you think it is based on where you first saw it. + +Two prominent examples https://www.youtube.com/watch?v=KMT1FLzEn9I https://www.youtube.com/watch?v=Ihue9R8m6FA + +----- + +148 points and a few questions so it's worth a PS: + +those are examples for FAKED videos, NOT REAL ones. + +For ""real"" videos, go to YouTube and check for videos that do not have 6 figures worth of views. +https://www.youtube.com/watch?v=ZJAyKNkxbvs +https://www.youtube.com/watch?v=d1eFVf3pgcE + +Think of it as our face turning red when we are uncomfortable or under pressure. Like I said, it really is more interesting than that but it's not as interesting as it were if they all could do it on purpose to blend in. +" +534 If, theoretically, you were in an infinite sized room, and there was complete darkness. If you lit a candle, how far away would you have to be from this candle before you couldn't see it? 5114 https://www.reddit.com/r/askscience/comments/57nxiy/if_theoretically_you_were_in_an_infinite_sized/ 1476563228 57nxiy Physics 2016-10-15 23:27:08 "You're basically asking what the limits of human vision are. And you're in luck, there was a [paper](http://www.nature.com/articles/ncomms12172) published this summer answering that question ([summary here](http://www.nature.com/news/people-can-sense-single-photons-1.20282)). The tl;dr of the paper is that the human eye can detect a single photon. If it happens to be one of the 10% of photons that enter your eye and actually trigger a rod cell. + +> “The most amazing thing is that it’s not like seeing light. It’s almost a feeling, at the threshold of imagination,” says Alipasha Vaziri, a physicist at the Rockefeller University in New York City, who led the work and tried out the experience himself. + +So to actually answer your question. WA [claims](http://www.wolframalpha.com/input/?i=international+standard+candles) that a candle outputs 13 lumens of light. Which is about [10^16 photons per second](http://www.wolframalpha.com/input/?i=13+lumens). + +If you want to ""see"" 1 photon per second, then if my math is right (assuming your pupil has a radius of 4mm), you could go up to **[300 km away](http://www.wolframalpha.com/input/?i=Solve+1+%3D+10%5E16++*+(2+*+(4+mm\)%5E2+*+pi\)+%2F+(4+*+pi+*+x%5E2\)+for+x) and still get that one photon per second entering your eye.** + +**EDIT:** People below have brought up some interesting points. 1 photon/sec isn't really ""seeing"" it constantly. Humans seem to have a 'frame rate' of ~100 fps, so say we want to see 1 photon per 'frame', and assume that only 10% of the photons entering our eye hit the rod and trigger this photon perception. + +Then, to constantly be registering ~1 photon in your eye from the candle the answer shifts to **a distance of [9 km](http://www.wolframalpha.com/input/?i=Solve+1000+%3D+10%5E16++*+(2+*+(4+mm\)%5E2+*+pi\)+%2F+(4+*+pi+*+x%5E2\)+for+x) (5.5 miles)**. Which is still crazy far away for a single candle. + +**Edit 2:** This got way bigger than I was expecting. + +1. I was assuming a vacuum, but an atmosphere wouldn't change the answer a crazy amount. The Earth's atmosphere (~20km thick) lets through ~30-50% of the light. So it might change things by a factor of ~2. + +2. Using 'framerate' for how your eye works is a *terrible* analogy, but I don't have a better one. And yes, fighter pilots and trained eyes can apparently notice things at ~250 fps or 250 Hz, but 100 seems more reasonable for the average person. + +" "The illuminance of a candle (1 candela or 12.6 lumens) from a distance of 1 meter is 1 lux. That of the dimmest stars typically visible to the naked eye on a dark night (magnitude 6) is 8e-9 lux. So we just need to know how far away the candle needs to be to be as bright as a 6th magnitude star. + +By the inverse square law, that distance would be sqrt(1/8e-9) m = 11.2 km. From that distance, the candle should be just barely visible to the naked eye. From a tenth that distance (1.1 km) the candle would appear as bright as a 1st magnitude star. + +By the way, a 100 watt light bulb is about 130 times as bright as a candle, so (again by the inverse-square law) it could be seen from 11.4 times farther away (128 km). Since the Karman line is at 100 km altitude, it would be possible to see a light bulb overhead in space." +304 What's the deepest hole we could reasonably dig with our current level of technology? If you fell down it, how long would it take to hit the bottom? 5109 https://www.reddit.com/r/askscience/comments/45wkig/whats_the_deepest_hole_we_could_reasonably_dig/ 1455544738 45wkig Earth Sciences 2016-02-15 16:58:58 The deepest hole dug was the Kola Superdeep Borehole which reached 12 km depth. That was roughly at the limit of drilling technology, and hasn't been surpassed. Under **only** the influence of gravity, it would take about 50 seconds to fall down, even though [Earth's gravity increases slightly](https://www.physicsforums.com/insights/all-about-earths-gravity/) as you go down. "Geologist here! If im not mistaken, there is a project that just restarted with the intent to drill into the mantle (http://www.nature.com/news/quest-to-drill-into-earth-s-mantle-restarts-1.18921). The problem with drilling deep isnt the technology, it has to do with the Earth itself...So the Earth has a couple of layers: the Crust (5-40km), mantle (~3000km), outer core (2250km) and inner core (~1250km). The crust is rigid and thin, perfect for drilling through. But the mantle on the other hand is like putty, extremely hot and maleable, but not fluid (think of it like an extremely viscous silly putty that will melt your face off). So when you drill through it, the hole just reseals itself. I dunno if we have a drill bit that is strong enough to withstand the temperatures and pressures, but the mantle just doesnt like to have holes punched in it. + +Heres a good image of the Earth's layers with thicknesses: http://study.com/cimages/multimages/16/earth_layers_nasa.png + +Edit: added drilling article." +657 How does heat propagate in a vacuum if there are no particles for it to move through? 5106 https://www.reddit.com/r/askscience/comments/5mx68p/how_does_heat_propagate_in_a_vacuum_if_there_are/ 1483961372 5mx68p Physics 2017-01-09 14:29:32 "Mostly by radiation. There are some particles but the density is so low that conduction is extremely, extremely ineffective. + +The reason the Earth is warm is because the Sun is shining on it. The Sun is particularly hot but it is no special case, anything with a temperature above absolute 0 radiates, and that radiation can travel freely through a vacuum. When that radiation is absorbed by something else then it heats up and that is how heat is transferred through space." "We talk very loosely of heat. Heat is not a substance, or thing, or even really a distinct form of energy in its own right. “Heat” as a scientific concept belongs to the early empirical days of thermodynamics when atoms and radiation were not at all well understood. + +If we put a hot thing and a cold thing near one another in a vacuum then the hot one will cool and the cold one will warm. The amount of heat, the internal energy, in each object will change but heat as such is not transmitted between them—energy is. Overwhelmingly this is in the form of electromagnetic radiation. The result of this is that after a time the hot thing will have less heat in it, and the cold thing will have more, but the “heat” never was in the intervening space. That space contains an electromagnetic field that holds some energy, and that energy goes in and out of the things, but it isn't the right kind of energy to be considered “heat”." +1798 What kind of material are those sticky hand toys made of and why is it able to be washed and continued to be tacky? 5075 https://www.reddit.com/r/askscience/comments/lbqzwl/what_kind_of_material_are_those_sticky_hand_toys/ 1612368683 lbqzwl Chemistry 2021-02-03 19:11:23 "According to [this source, ](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.researchgate.net/profile/Rafik_Karaman/post/There_is_a_strechy_and_sticky_toy_famous_among_kids_as_SPLAT_TOYS_Can_anyone_help_me_know_the_exact_chemistry_behind_the_polymer_used/attachment/59d621d779197b8077980367/AS%253A298660601581574%25401448217644843/download/Toystore%2B1.pdf&ved=2ahUKEwjQlKi0zM7uAhWGTN8KHWW7BRoQFjABegQIAhAF&usg=AOvVaw2eyrNZaS8K1hPZ7V9WIRMA&cshid=1612385902132) + +> They may be composed of an isoprene polymer (a synthetic +rubber), styrene-butadiene copolymer, or a poly(styrene-butylene-ethylene) copolymer along with tackifiers, and +coloring materials" "Specific polymer? I have no idea. Probably some blend of polybutadiene and maybe silicone. But I can explain how it works. + +There's two important physical properties to this polymer, it's Tg, and it's crosslinking. Another important property (this time chemical) is its affinity (or polarity) to dirt. + +Tg is a number that's basically the softening temperature. It's based on the phenomenon that when an amorphous polymer heats up, it gets softer and softer gradually, rather than at a strict point (like ice turns to water at 0C). The Tg can be manipulated to be at practically any temperature, in the case of the sticky hand, the Tg is most likely below room temperature, which lets it conform to a surface and ""stick"". + +The crosslinking of a polymer allows it to hold its shape, regardless of the temperature. Highly crosslinked polymers will look like a net, each point connecting to multiple others. Nets can be flexible, or rigid, depending on what's used, but most importantly, when stretched, they return to their original shape. This lets the sticky hand stretch and bounce back without turning to goop (which happens when a low-crosslinked polymer is at a temperature above its Tg. Essentially, it melts). + +Now it's kinda sticky and stretchy, but it still needs the proper affinity to stick to most surfaces, but not stick strongly. The second route to stickiness is through chemical interactions. Big molecules will slightly stick to everything, just because of their large areas of contact (through lewis interactions). So the bigger an individual unit of the polymer, the more indiscriminately it will stick to things. But, in this case, water grips onto the dirt better than the sticky hand, and so it can wash it off. This is where the probable silicone is at, which repels waters and dirt (AKA has lower affinity for water and oils). + +So this means the polymer should be a very large, low Tg, and crosslinked. It's hard to do all this in a homopolymer, so mixtures are usually used. Mix the large butadiene with a crosslinker to form a co-polymer, and blend in slme silicone additives for easy washing." +1419 What percentage of people with major depressive disorder has suicidal thoughts? 5066 https://www.reddit.com/r/askscience/comments/djm0di/what_percentage_of_people_with_major_depressive/ 1571397380 djm0di 2019-10-18 14:16:20 "This post has attracted a large number of medical anecdotes. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." "Just a quick google search brought me to this study which found approximately 45% endorsed at least some degree of suicidality (n=1410). However, in the introduction to the study, previous research has found that number to be around 55% ""Depending on the applied definitions, the prevalence of suicidality amounts to more than 55% in patients with predominant MDD ([Asnis et al., 1993](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007240/#CIT0002); [Schaffer et al., 2000](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007240/#CIT0031); [Sokero et al., 2003](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007240/#CIT0034); [Zisook et al., 2009](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007240/#CIT0039))."" + +[source](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007240/#!po=13.4921)" +201 My girlfriend insists on letting her restaurant leftovers cool to room temperature before she puts them in the refrigerator. She claims it preserves the flavor better and combats food born bacteria. Is there any truth to this? 5065 https://www.reddit.com/r/askscience/comments/3qxvci/my_girlfriend_insists_on_letting_her_restaurant/ 1446273757 3qxvci Chemistry 2015-10-31 9:42:37 "From Foodsafety.gov +Mistake #5: Letting food cool before putting it in the fridge +Why: Illness-causing bacteria can grow in perishable foods within two hours unless you refrigerate them +Solution: Refrigerate perishable foods within 2 hours (or within 1 hour if the temperature is over 90˚F." No, doing this just increases the time that bacteria can grow in your food. On the other hand, if you have something like a big pot of soup, you can end up heating the food around it in the fridge because it'll be giving off heat for so long. +876 Why is myopia common in young adults, when (I assume) this would have been a serious disadvantage when we were hunter gatherers? 5057 https://www.reddit.com/r/askscience/comments/7ibero/why_is_myopia_common_in_young_adults_when_i/ 1512697553 7ibero Human Body 2017-12-08 4:45:53 "This post has attracted a large number of medical anecdotes. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." "There is currently a myopia ""epidemic"". See [here](https://www.nature.com/news/the-myopia-boom-1.17120). There is certainly a genetic component to myopia, but it's not that suddenly a lot more myopia genes are being passed on in the last few years. A common lay theory is that there might be an effect of close-up work (books, computers), but the effects are small or non-existent according to some of the studies linked in the article. However, there is a correlation with education level. Some very recent work (again, linked in the article above) suggests that what matters is time spent outdoors (and not related to focusing far away -- I really recommend reading the linked article) -- in particular, exposure to bright light. However, there is no strong consensus at the moment of what exactly is the main cause." +535 If you had a completely empty universe, in which only 2 marbles, placed perfectly still in the beginning, with 1 ly distance in between them, how long would it take for them to collide due to gravity? 5050 https://www.reddit.com/r/askscience/comments/57rs2i/if_you_had_a_completely_empty_universe_in_which/ 1476630189 57rs2i Astronomy 2016-10-16 18:03:09 "This can be solved using conservation of energy. The total initial energy is the gravitational potential energy: + +E*_i_* = -Gm^(2)/r*_0_*. + +The energy at time t is the sum of their relative kinetic energy and their potential energy at that point: + +E*_f_* = mr'(t)^(2)/4 - Gm^(2)/r(t), where r(t) = |**r***_1_*(t) - **r***_2_*(t)|, and the extra factor of 1/2 comes from the reduced mass and the fact that we're looking at the *relative* kinetic energy. + +Now you can set these equal to each other: + +mr'(t)^(2)/4 - Gm^(2)/r(t) = - Gm^(2)/r*_0_*. + +One factor of the mass cancels, and you can simplify to: + +r'(t)^(2) = 4Gm(1/r(t) - 1/r*_0_*). + +So: + +dr/dt = 2sqrt[Gm(1/r - 1/r*_0_*)]. + +This is now a separable differential equation which can be directly integrated for the desired result: + +dt = (2sqrt[Gm(1/r - 1/r*_0_*)])^(-1) dr + += (2sqrt[Gm(r*_0_* - r)/(r*_0_*r)])^(-1) dr + += (2sqrt(Gm))^(-1) sqrt[r*_0_*r/(r*_0_* - r)] dr. + +This integral can be solved analytically, and somebody worked it out [here](http://physics.stackexchange.com/questions/14700/the-time-that-2-masses-will-collide-due-to-newtonian-gravity). Somebody there also pointed out that you can get this result directly from [Kepler's third law](https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion#Third_law). + +Using the given numbers and the equation derived in the first Stack Exchange comment, I get an answer of about [3\*10^(29) seconds](http://www.wolframalpha.com/input/?i=pi%2F(2sqrt(2\)\)+(1+lightyear\)%5E(3%2F2\)*(gravitational+constant+*+2+*+100+gram\)%5E(-1%2F2\)). + +So they always collide assuming Newtonian gravity (no expansion of space, no effects of GR), but it will take a very long time." there's a simulator program on steam called 'Universal Sandbox' that allows you to play with things like this. you can model various types of things and speed/slow time to show how physics in space work. it's really really cool. +1112 What could have caused a violent reaction between 2 store-bought pool chlorine brands? 5048 https://www.reddit.com/r/askscience/comments/9irdom/what_could_have_caused_a_violent_reaction_between/ 1537875642 9irdom Chemistry 2018-09-25 14:40:42 "According to the MSDS of [HTH](http://fileserve.newporthigh.co.uk/Manuals/Volume%207%20of%208/Buckingham%20Pools/16.%20HtH%20Calcium%20Hypochlorite%20tablets.pdf), the source of chlorine for the disinfectant is calcium hypochlorite. It also contains some calcium hydroxide and calcium carbonate to keep the pH above 7 which prevents the creation and release of poisonous chlorine gas. I couldn't find any information on Clarity as a pool disinfectant. However, it is likely that the Clarity brand contained [Dichlor](https://en.wikipedia.org/wiki/Dichloroisocyanuric_acid) which is an acid based pool disinfectant (pKa = \~6 for the non-chlorinated isocyanuric acid - dicloroisocyanuric acid will definitely be much more acidic). Mixing the acid pool disinfectant with the calcium hypochlorite produced green chlorine gas, which you observed, and a lot of heat. + +​ + +EDIT 1: Are you sure Clarity is specifically a pool disinfectant? I did some more digging and found a general peroxide disinfectant called [Clarity](http://www.peroxychem.com/chemistries/peracetic-acid/products/clarity). Peroxides also react with hypochlorites to generate heat but oxygen gas instead. This also removes the chlorine source giving dissolved chloride. I'm now unsure how the chlorine gas (which it what you seem to describe) is produced. + +​ + +EDIT 2: Clarity is most likely trichlor or dichlor which produces chlorine gas and a lot of heat when mixed with hypochlorites. This seems to be a very explosive reaction. see this [video](https://www.chemaxx.com/pool_chemical_explosion5.htm) posted by u/Vew below." "Expanding on a guess I made deeper in the thread after some further research. https://old.reddit.com/r/askscience/comments/9irdom/what_could_have_caused_a_violent_reaction_between/e6m0wij/ + +You made [trichloramine](https://en.wikipedia.org/wiki/Nitrogen_trichloride). It is an oil that will sink to the bottom of the bucket. It is a primary explosive that when shocked or heated will detonate violently (the person who discovered it lost some fingers on his hand). + +The~~ [TRICHLORO-S-TRIAZINETRIONE ](https://cameochemicals.noaa.gov/chemical/9131) oops~~ [Dichlor](http://phoenixproductsco.com/wp-content/uploads/2015/08/Sodium-Dichlor-0030.pdf) in one mixture was acidified and as you can read from that link that acidification produces trichloramine. Other commentators have noted the source of the acid. You made it even more efficient as you added more sources of chlorine which increase the yield of the NCl3 production. + +" +1599 Is there a natural reference for the correct time, down to the milliseconds? 5040 https://www.reddit.com/r/askscience/comments/hv1wua/is_there_a_natural_reference_for_the_correct_time/ 1595310595 hv1wua Physics 2020-07-21 8:49:55 "Our current time standards are ultimately realized in terms of TAI, the *International Atomic Time*. TAI is determined by a collection of extremely accurate atomic clocks scattered across the world, kept synchronized to give a collective time that ticks at almost exactly one second per second on the surface of Earth's geoid. + +If TAI were to shut down we could restore it based on astronomical observations. Perhaps not to the same accuracy,^(1) but fairly close. This could be one way to do it. I'm sure there are other, better ones. + +Universal time (UT)^(2) is another time standard based on the rotation of the Earth with respect to the sun. It is defined in terms of a hypothetical point in space called the ""mean sun"", which is a point on the equator that moves at a constant rate around the Earth. The actual sun, when you project its position down to the equator, doesn't do this for various reasons,^(3) so it's useful to use the mean sun instead. The mean sun tracks the location of the true sun with zero mean offset. UT is then defined as the angle^(4) between the prime meridian and the mean sun, offset by 12 hours (so that when the angle is zero, it's noon UT). + +UT doesn't tick forward at one second per second because of irregularities in Earth's rotation. UTC is a time standard designed to (a) closely align with UT and (b) tick at one second per second. This is achieved by periodically adding or subtracting one second to or from UTC when it's too far away from UT. These are called leap seconds (when subtracting... we haven't needed to make UTC go in the other direction so far), and you can look up online when they happened. + +Other than that, UTC ticks forward for every second that TAI does. UTC was exactly 10 seconds behind TAI when it was first defined, and there have been 27 leap seconds since, so right now UTC is 37 seconds behind. + +As for the difference between ~~UT and UT1~~ UTC and UT, it's a quantity that is kept under close surveillance. IERS publishes daily numbers for this difference, and predictions a year into the future, with millisecond to microsecond accuracy depending on date. Right now, UT is behind UTC by about 0.22 seconds. + +So if you can determine UT (by observation) then UTC (by looking up the difference as published by IERS) then you can determine TAI (by subtracting 37 seconds). Your only sources of error are UT-UTC and whatever observational error you make when determining UT. + +^(1) That is to say, the same internal accuracy that TAI achieves +^(2) More precise is UT1, but I'll use UT here to mean the same thing +^(3) Because Earth's orbit is slightly noncircular, and because of the inclination of Earth's rotation - see [equation of time](https://www.wikiwand.com/en/Equation_of_time) +^(4) Angles can be expressed in terms of time units: 360 degrees = 86400 seconds - this is not the same thing as arcminutes and arcseconds" "Astronomer here! One I haven’t seen mentioned yet are [pulsars](https://en.m.wikipedia.org/wiki/Pulsar), which are rapidly spinning neutron stars that give off a regular radio pulse. They are *so* regular that we can model the pulses to within one second in a million years, and every pulsar is different in its pulsar profile. So I’ve heard it said that in the far future we could use them for interstellar GPS of sorts. + +So yeah you could definitely use pulsars for this reference assuming you lost all the clocks on Earth but kept all the info about pulsars and radio astronomy. Some pulsars are even millisecond pulsars, meaning they spin every few milliseconds, so you could even cover that part of the time scale." +974 What causes moles to appear on our skin? 5037 https://www.reddit.com/r/askscience/comments/86cnkt/what_causes_moles_to_appear_on_our_skin/ 1521734864 86cnkt Biology 2018-03-22 19:07:44 So there are cells called melanocytes that provide pigment/coloration to our skin and hair in the upper layer of our skin. A mole (or nevus, if we’re getting fancy) is actually considered a “benign tumor” of those melanocytes. ‘Tumor’ just means an abnormal, excessive growth of cells (not cancer!), so essentially, some of your melanocytes had some funky things happen with their DNA (damage, random mutation, etc) that caused them to grow more in clusters as opposed to spread out across your skin. The reason that you’re told to check the size, borders, color, etc of moles is because benign moles and potential melanomas can look very different! "So to understand this, it's best to understand skin pigmentation a little. Your skin is colored by special cells called melanocytes (derived from the neural crest in embryos) that are distributed in the basal layer of the epidermis (the bottom portion in the top-most layer of skin). + +These cells are distributed throughout that layer and secrete melanin pigment in little bubbles called melanosomes, that are then passed to keratinocytes (the cells that make up your skin). Keratinocytes take it up and that's what gives people a nice smooth distribution of skin tone in most cases. Think of it as little brown umbrella factories every other block that makes boxes of brown umbrellas and sends them to every person who lives on each block. When it rains and everyone opens their umbrella, the whole city looks brown from above. + +A mole is basically a group of melanocytes that have started to replicate and divide rapidly and thus they are considered a ""neoplasm"", but they're not cancerous as the growth isn't out of control. Think of having 5 umbrella factories on a single street. A freckle on the other hand is simply a group of melanosomes (that pigment bubble I was talking about earlier) concentrating together in a specific location. Lets say a bunch of packages get rerouted and all end up at the same house. + +Interestingly although melanoma can develop from existing moles, it rarely does. Most melanoma actually arises de novo, or spontaneously on normal appearing skin. It's important if you are concerned about a mole or any skin lesion, to go to a properly certified dermatologist or dermatological surgeon, as they're trained to look for many aspects of moles that go beyond what we've mentioned, such as layer of the skin it's in, how it's growing, what to look for in metastatic (cancerous) change, etc. " +109 Could a modern day human survive and thrive in Earth 65 million years ago? 5031 http://www.reddit.com/r/askscience/comments/3ewzwj/could_a_modern_day_human_survive_and_thrive_in/ 1438101487 3ewzwj Biology 2015-07-28 19:38:07 "Just read an interview with a paleontologist that covered this: + +TRH: It would depend upon where and in what season you wound up. Paintings and documentaries to the contrary, there would have been times when the landscape wasn’t crawling with every species of dinosaur and other animal that inhabited that region: some may have migrated in for a time, and many would have been clumped together in herds or packs or flocks rather than randomly distributed over the landscape. + +If you wound up in Late Cretaceous Montana, the vegetation would be something like a mix of the forests of southern Japan and of northern Australia, in a setting something like the bayous of the Gulf Coast. Until you saw something distinctly un-modern (like a pterosaur or dinosaur) you might not know you are in another time, but might think instead you were transported to some other corner of the world today. Oh, you would see turtles: lots and lots and lots of turtles. +But when you begin to notice a giant Quetzalcoatlus over head, or the herds of ceratopsians and hadrosaurids, and so forth, finding some sort of cover would be good. Depending on your nature skills, you could probably do well for a while (as well as an individual alone might get along in the most isolated parts of the Amazon rainforest or the Serengeti). Raiding nests might be a safe way of getting protein (so long as the parents aren’t nearby: since all living archosaur groups have some parental nest monitoring, we expect pterosaurs and extinct dinosaurs did the same), as well as snaring/spearing small animals, fishing (watch out for crocodiles…), and raiding kills. By the Late Cretaceous there would have been fruit, but you’d have to experiment carefully to find ones that were good for humans. + +I would say that making your home in the trees would be the best bet. The giant pterosaurs of the time would be too big to do much perching on trees, and those dinosaurs that could get up into the trees would generally be small enough that you could fight them off. I think it would be unlikely that tyrannosaurs would try to eat too many tree-dwelling animals when there was ground-based food to go after. There would have been climbing mammals, but these too would hopefully not be too much problem. + +(Oh, but don’t let the mammals jab you with their hind limbs! It appears that spurs, possibly poisonous, were common to many Mesozoic mammal groups, and that their presence in male platypus today is simply their last remnant.) + +Source: http://www.robotbutt.com/2015/06/12/an-interview-with-thomas-r-holtz-dinosaur-rock-star/ +" "You may enjoy reading the novella: + +*The Dechronization of Sam Macgruder* + +by George Gaylord Simpson, Arthur C. Clarke (Introduction), Stephen Jay Gould (Afterword) + +It's about a scientist sent back to the time of the dinosaurs due to a failed physics experiment. With no hope of return, he sets out to document this world for all of future mankind." +658 Can water be frozen in an airtight container? 5031 https://www.reddit.com/r/askscience/comments/5pb1gh/can_water_be_frozen_in_an_airtight_container/ 1485011696 5pb1gh Physics 2017-01-21 18:14:56 "There are [17 known phases of ice](https://en.wikipedia.org/wiki/Ice#Phases). When you deal with ice, you are almost always dealing with I_h which expands as it freezes. However, at different temperatures and pressures (pressure being the more important one here) different types of ice form. In the case of staying close(ish) to regular freezing temperature, and upping pressure until ice forms, you'd end up at [Ice III](https://en.wikipedia.org/wiki/Ice_III). + +You're unlikely to see this outside of a lab though, since you need to put water into a container which can withstand over 43,000 PSI of pressure, otherwise the ice wins and will crack the container. " "Follow-up question. + +A few days ago I wanted beer chilled quickly. I put the glass bottle into a plastic cup which I then filled with ice and water. + +I promptly forgot about the beer and opened the freezer yesterday. Beer and water were both frozen solid. + +The plastic cup was broken, but the bottle did not crack, nor did the beer push out the top. + +Why not? Did the pressure of the freezing water in the cup (which I assume froze first) push in and prevent breakage? If so, how did the pressure inside the bottle dissipate?" +877 Since dinosaurs were discovered far below the earths surface covered in dirt, how does the earth gradually pile dirt on itself, forming layers covering up history over the past few centuries? 5030 https://www.reddit.com/r/askscience/comments/7aw806/since_dinosaurs_were_discovered_far_below_the/ 1509865108 7aw806 Planetary Sci. 2017-11-05 9:58:28 "Okay, a lot of these are wrong. I'm an archaeologist so let me try to clear some of these misconceptions up. + +You are generally going to find fossils within sedimentary rock, and there are a few types of sedimentary deposition. The most common is by water, where tiny pieces of sediment (not dirt, sediment is weathered/eroded pieces of other rock) are placed either by tides, or simply by falling through water. + +The other major type of sedimentary deposition is aeolian, or Loess deposition. Instead if the sediment being carried by water, it's carried by the wind. China has a gigantic Loess plateau, which is interesting because if you examine the types of sediment you can get a complete record of that areas climatic conditions. + +As far as fossilization goes, fossils will preserve best when they are deposited quickly, so in an area with a high rate of sedimentation. Many aquatic environments will do this, or landslides, or areas that have sediment windblown quickly. But remember this is generally a very SLOW process, but it happens over enormous timescales. + +Sorry for writing a book but I hope this helps. + +EDIT: Upon rereading the title I noticed you said ""dinosaurs"" and ""centuries"" at the same time. Some archaeology is done from centuries old, these you can find by digging down. Dinosaurs haven't been around since 65 Ma (millions of years ago), typically these sites are found via exposure due to weathering, which is how people know where to look for dinosaur sites. + +Also, if anyone is curious I deal with paleolithic archaeology, a nice happy medium between historic arch and paleontology. " "I think the root of your question is: the whole earth getting bigger? Where does that extra material come from? + +And I think the answer is no, it doesn't happen everywhere, just locally. Some spots get more material, some get worn away. We only find fossils where it's been net built up over the time since the fossilized creature died." +404 Assuming ducks can't count, can they keep track of all their ducklings being present? If so, how? 5014 https://www.reddit.com/r/askscience/comments/4vxmw2/assuming_ducks_cant_count_can_they_keep_track_of/ 1470216065 4vxmw2 Biology 2016-08-03 12:21:05 "There have been studies showing that even newborn baby chickens have rudimentary counting skills. + +The way they proved this was fairly interesting. They took baby chickens, hatched them surrounded by scrunched up balls of paper so that the chickens identified with them and then had the baby chicken watch as they placed each ball of paper into one of two concealed containers. The baby chickens would reliably be able to choose the container with the most balls in, demonstrating some manner of counting ability. + +(Not a true source, but some reporting the same thing http://www.livescience.com/49633-chicks-count-like-humans.html) + +It seems likely that counting is a sufficiently simple activity that birds can handle it." "Inherent in the question are a couple of large and somewhat related biases. One is that as a human, you're inclined to look at a group ducklings and observe, ""there's a quantity of X ducklings,"" rather than observing X unique individuals. Likewise, in keeping track of their children, human parents are less likely to look out at the playground and say, ""I only see three of four"", than they are to ask, ""Do you see Jenny?"" It's a reasonably common trait among social animals to recognize one's own young, and more generally to recognize individuals. + +The mother duck recognizes her own offspring as individuals and as hers. This is why when two broods run into each other and get momentarily mixed up, they generally depart in their correct family groups, rather than mom simply leaving with any six ducklings. + +So, while mother duck may have some ability to observe greater than and less than, this isn't what she likely observes when missing one of her young. However her brain encodes it, she realizes that she's missing her small female with the dark markings. + +Moreover, the young are alerting her that there's a problem. They make noises when they're distressed, such as being trapped in a storm drain." +405 What's the chance of having drunk the same water molecule twice? 5011 https://www.reddit.com/r/askscience/comments/4mndsq/whats_the_chance_of_having_drunk_the_same_water/ 1465133275 4mndsq Mathematics 2016-06-05 16:27:55 "**Short answer:** For any given water molecule, the odds are basically negligible. But the odds that you've drank at least one water molecule twice are pretty much 100%. + +**Long answer:** Think in terms of the numbers of water molecules on earth. In a cup of water there are about 10^24 water molecules (100 g / 18 amu ~ 10^(24)). + +The total mass of water on earth is approximately 10^24 g of water, which works out to about 10^46 water molecules on earth. + +So if you pick 10^24 molecules out of 10^(46), put them back into the 10^46 and mix them back up, and randomly choose another 10^(24), what are the odds you'll pick at least one atom twice? We can approximate it in the same way we do the [birthday problem:](https://en.wikipedia.org/wiki/Birthday_problem#Approximations) P = 1-e^(-n^2 /2m ) where n=10^24 and m=10^(46). Turns out this number is basically equal to 1, so the odds are *almost certain* that any two glasses of water will have at least one atom in common. This generalizes between *every* cup of water - in that cup of coffee you're sipping right now, the odds are good that it has shared atoms with basically every person to ever live. + +It's pretty cool how Big Numbers^TM work out. A tiny probability, given sufficient chances, becomes a certainty. + + +" "It's a guaranteed 100%, and you don't even need to do any fancy statistics. + +Pour yourself a glass of ice water. What happens? Water starts condensing on the sides of the glass. Some of those water molecules are from your body, that you drank previously. You are actually breathing out water molecules which condense on the glass. Take a sip from the glass and some of that condensation will enter your mouth again, meaning you drank the same molecule twice. Additionally, as you drink from the glass you will leave some saliva behind, that is more water from your body. Take another drink and you're ingesting that saliva, drinking the same water again. + +There are probably many other ways that you could drink the same water molecule twice, but this is the one of the easiest and most certain ways." +975 What makes some materials like cat fur or velvet feel soft? 5004 https://www.reddit.com/r/askscience/comments/863twq/what_makes_some_materials_like_cat_fur_or_velvet/ 1521652341 863twq Physics 2018-03-21 20:12:21 "Long time lurker but finally a question I can answer. (Source: am materials scientist who works on softness in industry). + +Softness is a complex, multi-variable phenomena which we think involves two components: 1) the material a person touches and 2) the persons [somatosensory system] (https://en.wikipedia.org/wiki/Somatosensory_system), which is a combination of the nerves in your finger and neural system. Since the brains involved, things start to get complex. + +Like the other commenters have mentioned, a simple reason for observing why a piece of cat hair is soft is linked to the fiber diameter. In fact, research has [shown](http://journals.sagepub.com/doi/abs/10.1177/004051756103100710) that a small fiber diameter of a material class does link to a greater degree of [softness](https://onlinelibrary.wiley.com/doi/pdf/10.1002/app.23898) . But pet your cat in one direction (toward the tail) and a different direction (away from the tail), and you might have a different experience. What this means is that by orienting the fibers in a different ways, you're body can register a difference sense of softness. + +Taking it on step further, the micro and mezo-structures of the fiber also (things like kink, curl, or shape) play a part. Surface coatings, and blooming agents are readily sought in the synthetic fiber making world to enable softness at the fiber level. All different type of animal (and people for that matter) have different natural hairs which kink, lay straight or flat depending upon the way the hair is formed. + +The macro structure of a fabric or group of hair matters too as there is active research ongoing to [characterize](https://www.sciencedirect.com/science/article/pii/B9781845691356500025) the behavior of fabrics and other composite materials like velvet. You can get into macro level properties like drape, compressive modulus, friction, and even the sound of fabric or hair, to get into a response that could be considered soft. + +The other aspect (which I don't have good sources for other than data I've generated) is that what you put *behind* a material matters immensely. If you put your cat hair on top of brick, you are likely to not think its so soft versus against the cat's skin, since the skin bends easily. An analogy would be, take a piece of velvet and wrap it around a brick. That velvet brick will likely feel soft to the touch if you barely put pressure on the top of the fabric, but put a little more pressure, and it doesn't feel so great. + +The reason I put ""we think"" at the top is because unfortunately the instruments used to measure softness are humans, so the variability in the data is very high. In fact, not having an ""anchor"" in a softness assessment almost always provides data that isn't repeatable from test to test (i.e. feather = 1, brick = 10). Further more, since the somatosensory system involves your brain, things like sounds, color, what you ate, how you feel that day, can skew data. We can find general trends in the data which point toward some general characteristics for softness directions (small smooth fibers, in a highly drapable and cushiony fabric), but within material groups, differences are hard to find. + +Lastly, the aspect that really makes things difficult, and I find fascinating, is that across cultures, softness perception changes. I have seen two study groups from Japan/China and the US have completely opposite opinions of what ""cottony"" means. Even using a material that is considered soft in one culture, doesn't work in another because of how softness is defined in each. + +TL;DR : It depends. " "I would agree with funintheburbs comment, but add that it is not just the 'give' of the material as a whole that gives it that velvety feeling (for example, a sheet of cotton has a lot of give, but does not produce the same feeling as cat fur), but also the diameter and density of the fibers comprising the surface of that material. A material with a high density of narrow, flexible fibers will feel soft, like fur. The same material with less give would feel like toothbrush bristles. So it's really the fact that there are very many narrow and flexible fibers making contact with your skin all at once that produce a furry feeling when brushed against. + + +To go even deeper, the micro-structure of those fibers plays a role as well. If the micro-structure is rougher (nano-scale pits), the additional friction will make the material feel rougher. + +Edit: I would actually modify my argument (per the_epic_narwhal's question regarding the smoothness of leather) to say that the most important factor is not the fibrous nature, but the surface microstructure. If the fibers are smooth, and you brush your hand against them, you are essentially pressing them into a uniform surface, so it would be similar to brush your hand against a well worn piece of leather or other material with few surface imperfections." +976 This may be a stupid question, but what defines GMO. Is it simply changing a plant through cross pollinating (at its simplest level) such as Mendel, or does GMO mean laboratory tested and genetically altered through a laboratory? 5003 https://www.reddit.com/r/askscience/comments/8dc7fi/this_may_be_a_stupid_question_but_what_defines/ 1524113994 8dc7fi Biology 2018-04-19 7:59:54 "You can read some of the history of it here: https://www.fda.gov/downloads/Food/IngredientsPackagingLabeling/GEPlants/UCM537311.pdf + +In brief, it's a bit of an arbitrary semantics issue. As far as United States government agencies are concerned, all ""traditional"" techniques for altering a species are not considered genetic engineering (or GE, the phrase they typically use instead of GMO). + +The more recent regulations were specifically made in response to technologies that relied on recombinant DNA and cell fusion (though you don't tend to hear about the latter anymore). What is different about these modern techniques is that they can be used to obtain organisms with genomes that would be extremely unlikely or even impossible to obtain through any pre-modern technique, such as putting a bacterial gene into corn, or a jellyfish gene into a cat. + +In fact, it is even argued that it is not the technology that determines what is GMO, but the result. That is, there are people using gene-editing technology to create organisms that you could in principle obtain with selective breeding, but in one or two generations instead of twenty. (such as here: https://www.nature.com/articles/nbt.3560 ) + +Under that sort of a regime, it would be argued that any rearrangement of DNA, in which all of the DNA comes from one species, is not GMO, even if different pieces of DNA came from different individuals. And simple deletion would also not be GMO, since it's only removing and not recombining DNA. But adding DNA to a species that it has no way to obtain through mating or hybridizing, that would make something GMO. Though again, semantics, people are still arguing over this." Tree geneticist here. It is worth mentioning that USDA APHIS recently decided that it won’t regulate the Crispr-Cas9 generated genetically engineered organisms like it regulates the Bt transformation based organisms. This means the very lengthy and expensive regulatory process will not have to be endured by organisms modified through Crispr. +1113 If the Earth stopped spinning immediatly, is there enough momentum be thrown into space at escape velocity? 5002 https://www.reddit.com/r/askscience/comments/9drrkv/if_the_earth_stopped_spinning_immediatly_is_there/ 1536303425 9drrkv 2018-09-07 9:57:05 "Nope! + +So we're going to pretend the Earth is a perfectly rigid body that can stop on a dime, while the people on top are not attached at all, and also there's no atmosphere. If the Earth suddenly stopped moving, the people would continue to move forwards at their current velocity. Is that fast enough to escape the Earth? + +The emphasis here is that you would continue to move *at your current velocity*. If you're not escaping the Earth right now, then your speed is below escape velocity. The Earth stopping won't make you speed up. Think of it this way: if the surface of the Earth was moving close to escape velocity, then the Earth would be basically flying apart. + +I'll give you some numbers to get the scale of it anyway. The Earth's equator is about 40,000 km around (that's more or less the original definition of the metre). The Earth rotates about once every 24 hours (it's actually slightly faster than that - a day is 24 hours because that's relative to the Sun and we're moving around the Sun, but 24 hours is close enough for this estimate). 40,000 km/24 hours = about 460 m/s, or 1,700 km/h, or 1,000 mph. It's somewhere between mach 1 and mach 2 at sea level. By contrast, escape velocity is about 11 km/s - that's about 40,000 km/h, or 25,000 mph. And just to orbit in a circle means you have to go at about 8 km/s. The Earth's rotation is fast enough that it *does* matter which direction you launch your rocket - it makes like a 10% difference in speed - but it's still on the level of a supersonic jet rather than an interplanetary rocket." "If you're standing at the north pole, your change in speed is zero. + +At the equator you'd be moving about .5 km/s with regard to a non spinning earth's surface. Escape velocity is about 11.2 km/s. Orbital velocity is around 7.7 km/s. So not near enough even if stopping earth added to your velocity. Which it wouldn't." +659 Why are we colder when wet? 4996 https://www.reddit.com/r/askscience/comments/5vb8ly/why_are_we_colder_when_wet/ 1487680561 5vb8ly Physics 2017-02-21 15:36:01 "Our sensation of being cold (or hot) is strongly affected by the rate at which we exchange heat with the environment. When we're wet, the water is almost always colder than the 37 C of our body. That means that heat flows from our body into the water on our skin. And since water has a considerably higher heat conductivity than air, the body loses heat more rapidly when it's covered in water. + +Next, the water will evaporate, which lowers the average temperature of the water that remains, causing further heat flow from the body to the water on the skin. Essentially, this is the same as sweating, except that sweating is a beneficial process that the body initiates when it is too hot. + +So when we're wet, we lose heat more rapidly than when we're dry. This causes a stronger sensation of feeling cold, even though the water on our skin may be warmer than the air." "As others have said, humans don't really feel absolute temperature but instead you feel heat transfer. Heat energy coming off you makes you cold, heat energy coming into you makes you hot. The concept of wind chill and the various ""real feel"" temperatures from various weather sites are an effort to approximate heat transfer rates as temperatures (I.e. a wind chill of 15 F is the same heat transfer rate as an actual temperature of 15 F with no wind.) + +What happens when you are wet is that you are suddenly able to transfer heat to your exterior much more rapidly. The transfer from you to the water happens via conduction and convection at that point, plus the water has a much higher heat capacity so it can absorb more energy before it warms up. The result is that even when the water is the same temperature as the air, it pulls more heat away from you making you feel colder. Evaporation further exaggerates the ability of water to pull heat energy out of your body and further improves the heat transfer rate. + +There is an easy demonstration/intuition check you can do at home to help understand that heat transfer concept. If you put a metal fork in the freezer overnight then take it out the next morning the fork will feel much colder than the air in the freezer. That isn't because the fork is a different temperature but because air doesn't transfer heat very well but metal does. Similarly when you open an oven door you are exposing your face to 400+ degree (F) air, you can even safely reach your hand inside to check or move things with no problem. Compare that to boiling water or steam coming off a pot. The water is much cooler (212 F) than the oven is, but if you touch it you'll burn your hand almost immediately. + +A lot of times people focus on absolute temperature, but in most cases heat transfer matters much more. Absolute temperature definitely influences that transfer rate, but the material in question and the ambient conditions (flowing water/stagnant air etc) are often more important. " +794 How will we use the power from a fusion reactor? 4991 https://www.reddit.com/r/askscience/comments/68mct4/how_will_we_use_the_power_from_a_fusion_reactor/ 1493649823 68mct4 Physics 2017-05-01 17:43:43 "> Will we just use it like we do a fission reactor, using the excess heat to generate steam? + +Yes. + +> If so, it seems kind of a waste of money + +Why do you think that? + +> is there some way to use the plasma to generate electricity + +The best way is plasma to heat to steam to rotation to electricity. Modern power cycles operate close to the Carnot efficiency. It literally doesn't get any better than steam, especially for large-scale systems like a power plant. These aren't the steam engines of the 1800s, they're highly advanced, modern machinery. " "There is a form of fusion that produces charged particles with [very few or no neutrons](https://en.wikipedia.org/wiki/Aneutronic_fusion). With reactions like that, we could have direct conversion to electricity, without generating heat. + +However, since we haven't yet been able to create practical fusion reactions producing neutrons, the more difficult aneutronic reactions will have to wait, I guess. For now, the struggle is to create *any* form of practical commercial fusion power, which would use steam turbines to generate electricity. + +" +977 "Are fighter aircraft noticeably ""weighed-down"" by their armaments?" 4987 https://www.reddit.com/r/askscience/comments/82f2v2/are_fighter_aircraft_noticeably_weigheddown_by/ 1520343192 82f2v2 Engineering 2018-03-06 16:33:12 "It's a huge difference. The weight changes the stress on the airframe, and if external the ordnance produces lots of extra drag. + +For example, a f/a 18 is rated for +7.5g and -3g maneuvers when light, but at full weight only +4.8g and -1.8g. + +Here are some study cards for an f/a 18: https://quizlet.com/13297122/fa-18-limts-and-prohibited-maneuvers-flash-cards/" "Yes. It’s a bit of a combination of all the above answers. You have a limited amount of thrust available to overcome your weight and drag. So it’s different for every flight. We have performance calculation charts that we have to run prior to every flight to figure out what our limits are for that particular day. It goes much more in depth than simply the weight of stores carried. You have to take environmental factors, strength of the individual engines in that specific plane you are flying, weight and balance calculations for that buno.... etc. All of these variables are considered and then your limits for that flight are calculated, bearing in mind that typically your performance numbers will improve throughout the flight as you burn off fuel. + +Jettisoning all stores will lighten the jet up a ton. It’s like getting chased by a bully as a kid, if you are both running with your back pack on and you ditch yours and he keeps his you will be able to run less encumbered, thus faster, than him. + +Source: Am Navy Instructor Pilot + +" +536 Has it been scientifically proven that Nuclear Fusion is actually a possibility and not a 'golden egg goose chase'? 4969 https://www.reddit.com/r/askscience/comments/582vaf/has_it_been_scientifically_proven_that_nuclear/ 1476782419 582vaf Physics 2016-10-18 12:20:19 "Yes, we can do nuclear fusion just fine. There are numerous research experiments already doing it. Heck, there's even a small, but dedicated amateur community setting up experiments. A while ago there was some highschool kid who made the news by creating a small fusion device in his living room. + +The problem, however, is that maintaining a fusion reaction requires a lot of energy, because the fusion plasma has to be kept at very high temperature in order for the reaction to take place. In current experiments, the amount of energy required to maintain the reaction is considerably higher than the amount of energy produced by the reaction. + +But, as it turns out, the amount of energy produced by the reaction scales up more rapidly with size than the amount of energy required. So by simply making the reactor bigger, we can increase the efficiency (the so-called Q factor). But simply making the reactor bigger also makes the reaction harder to control, so scaling up the process is not a quick and easy job. + +Scientists and engineers are currently working on the first reactor to have a Q factor larger than 1. That is, a reactor that produces more energy than it uses. This is the ITER project currently being constructed in France." Yes, nuclear fusion is quite possible. The challenge is getting more energy out than is put into it. [Taylor Wilson](https://en.wikipedia.org/wiki/Taylor_Wilson) was the kid who successfully but a fusion reactor at the age of 14. He is a colleague of mine and a good friend. His small reactor fused very small quantities of deuterium ions together to form He-4. A small fraction of the free deuterium in the chamber captures a neutron and becomes tritium. Tritium and deuterium quite easily fuse together to form He-4 plus a fast neutron. Here is a [short video](http://imgur.com/g1LjFal) of his reactor starting up. We placed my (no longer operating) iPhone in front of the reactor window to try and capture video of the fusion process. At the beginning, you can clearly see the x-rays saturating individual pixels (the snow effect) but it quickly diminishes as the energy rises above that which can be capture by the CCD. +1078 Do ticks or other blood sucking bugs (mosquitoes, etc) show preference to certain people? 4958 https://www.reddit.com/r/askscience/comments/8sbwyx/do_ticks_or_other_blood_sucking_bugs_mosquitoes/ 1529438105 8sbwyx Biology 2018-06-19 22:55:05 Please keep in mind that personal anecdotes are not an appropriate way to answer questions on /r/AskScience. "Ticks do not show a preference. Their spatial distribution is clustered - the female explodes out her larvae into a small space and they do not travel unless hooked on a food source - their movement is only up and down the leaf litter. Most likely you walked through a patch of larvae and your friends have picked up the odd nymph which are more dispersed as they have travelled on a host. + +Source - PhD on tick aggregation." +1114 Can we use Moons gravity to generate electricity? 4941 https://www.reddit.com/r/askscience/comments/9cvfz9/can_we_use_moons_gravity_to_generate_electricity/ 1536066523 9cvfz9 2018-09-04 16:08:43 We sort of do it already. In some places there are tide powered electrical generators. They either take advantage of the tide current themselves (like an underwater windmill) or close off an entire bay with a[ dam like structure](https://www.connaissancedesenergies.org/sites/default/files/image_article/energie_maremotrice.jpg) fitted with [turbines](https://img.over-blog-kiwi.com/1/47/74/05/20161125/ob_dcbdb5_centrale-electrique-maremotrice.jpg). The main issue is that they only work well in specific places that get big tides and have narrow shallow channels closing of a bay. The local ecological impact on marine life and sediment movement is also non-negligible. "We do use the moon's gravity for tidal energy production but others can address that more accurately. I just want to consider your example of the concrete blocks. + +For simplicity I will assume that each block is 1kg, that the Earth is 384,400 km away from the moon and that the moon is 7.35*10^22 kg. All of these numbers are pulled from a quick Google search so may be slightly off and incorrectly assume that all of the moon's mass is on it's surface (although that moves the mass further away and so works in our favor for demonstrating the point). + +The force of gravity from one object on another can be expressed as (G*m1*m2)/r^2. Plugging in our numbers we discover that the moon pulls on our 1kg block with 0.001 N of force. Our block experiences 9.81 N of force due to gravity from the Earth. + +So, if we timed our work such that the blocks were only stacked when the moon was overhead and only dropped when it is directly opposite us we would improve efficiency by roughly 0.0001%. It's not nothing, but it is very very small and not worth losing the flexibility to store and release energy on demand. + +Disclaimer: I am doing my math on my phone and may have missed a zero somewhere in the very small decimals involved here. + +Edit: second disclaimer: as noted below, this calculation purely demonstrates how small the moon's gravitational pull is compared to earth. It does not accurately represent how much more energy you could store ""for free""." +406 Do bees socialize with bees from other hives? 4939 https://www.reddit.com/r/askscience/comments/4odwzk/do_bees_socialize_with_bees_from_other_hives/ 1466091175 4odwzk Biology 2016-06-16 18:32:55 "Beekeeper here. I assume you mean honeybees (apis mellifera ligustica, carnica, etc) + +Hives are known to experience ""drift"", where bees change colonies. This can happen to both workers (female bees) as well as drones (male bees), moreso with the latter. + +This happens for a number of reasons. Bees have a range of two miles and do much of their extracolonial travel visually, using landmarks, so it's often speculated that they become lost or confused and end up someplace else. They are often exhausted from their travels, so we can speculate that they may just collapse to another hive in an act of self preservation, unusual for a ""superorganism"" that relies on strict cooperation! + +So let's talk about socializing. It's well known that a honeybee can make an ""offering"" to the guards at the entrance of another hive, by regurgitating nectar from their crop, thus bribing the guards who would normally stop other bees. They are then tagged with the scent profile of that hive - like a lot of the pheromone properties in the hive, this part is loosely understood. + +Often, honeybees going from one hive to another are robbing. This happens when there's enough honey for another colony's scouts to smell. The attacking colony will send scouts who attempt to overwhelm the guards and rob out the honey stores of the other hive. This usually happens when the robbed colony is weakened, either from queenlessness or disease. + +Drifting, however, is different, and represents an interesting behavior among bees. Some people believe it's a vector for disease, which it probably is, but the below study indicates that it's probably not that big of a factor. I think it's just a species preservation behavior. Think human travelers moving from town to town and getting in good with the guards at the gate before being let in. We do it because it just makes sense. Why not invite in some extra hands (or in the case of bees, extra claws)? + +* ""Colony evaluation is not affected by drifting of drone and worker honeybees (Apis mellifera L.) at a performance testing apiary"" Peter Neumann Robin Moritz Dieter Mautz https://hal.archives-ouvertes.fr/hal-00891701/ + +An interesting note besides socialization: the Cape honeybee (Apis mellifera capensis) is a subspecies from far southern Africa, originating in a specific coastal region. They have a special faculty, thelytoky, which allows them to lay an egg that is essentially a clone of themselves. This allows them to perform much more effective supercedures (queen raising ) than, say, the european honeybees, who need to raise a queen from an egg already deposited in the hive if there's an emergency or they lose a queen. European honeybees can only produce unfertilized drones, meaning a colony of the european bees without a Queen or eggs will perish. + +Well this Cape honeybee, should it infiltrate another hive, such as those of African honeybees (apis mellifera scutelleta), can wreak havoc by laying clones of itself. Those clones hatch and then make clones of themselves. In short order, they overcome the latent genetics in the hive. This has been a menace for many beekeepers in Africa, because Cape honeybees are ill suited to life outside the Cape region. + +* ""Parasitic Cape honeybee workers, Apis mellifera capensis, evade policing"" Stephen J. Martin1, Madeleine Beekman1,2, Theresa C. Wossler3 & Francis L. W. Ratnieks1 http://www.nature.com/nature/journal/v415/n6868/abs/415163a.html + +/u/niandralades2 brings up a great point here, that species preservation is not a good explanation for drifting behavior: https://www.reddit.com/r/askscience/comments/4odwzk/do_bees_socialize_with_bees_from_other_hives/d4cxpwv We talk about it a little bit there. + +/u/RosesFernando brings in some information about the wax (a lipid) retaining the scent of the hive, as well as giving some sources on relative aggressiveness of guards: https://www.reddit.com/r/askscience/comments/4odwzk/do_bees_socialize_with_bees_from_other_hives/d4cptzd?context=3 +" "/u/Satoyama_Will describes interaction of *apis mellifera* well, however there are other bees that have a different interaction. The *Meliponini* or stingless bees are social like the western honey bee and form small hives of few hundred or thousand individuals. Some species of *Meliponini* in Central America and Australia are managed by bee keepers and produce honey that people collect. At least one species in Central America has a mother daughter relationship among hives. A new hive is not founded like it is in honey bees where a large portion and an old queen fly off to found a new hive on their own but instead is slowly built up over time by workers and after some time a new queen migrates over to the daughter hive. Contact is maintained between the two hives after establishment. + +I can't give much more all this came from a lecture given two years ago at Florida's Bee College given by one of the grad students, originally from Central America who raised these bees. Bee college a 3 day event conducted by the [UF honey bee lab](http://entnemdept.ufl.edu/honeybee/). For more info it would be best to contact the lab." +1420 When I see a blurry gas above a bonfire or charcoal grill, what is causing the blurriness? It is colorless and transparent, but makes whatever I see behind it appear blurry in a wavy way. Is it carbon dioxide? Carbon monoxide? H? O? HO? 4927 https://www.reddit.com/r/askscience/comments/dkyqq5/when_i_see_a_blurry_gas_above_a_bonfire_or/ 1571655053 dkyqq5 Chemistry 2019-10-21 13:50:53 "The blurry air near a source of heat is just that: Air. Air has different optical properties at different temperatures and near a heat source there are often large difference in temperature within the air, as hot air rises, cold air flows in and all of it mixes in a turbulent way. These zones of different temperature that shift rapidly cause light to be refracted in different, constantly changing ways, generating the blurring effect that you see. + +This phenomenon, often called ""heat haze"", can also be seen just above a road on a hot, sunny day (when the hot asphalt heats the air) or near active aircraft engines (for example on a jet about to take off). + +It's not caused by a specific gas, but rather by large temperature fluctuations in the air." "You can see this over hot asphalt, a hot car roof, etc. + +Doesn't have to be over a fire. + +The heat differential causes air to rise and decrease in density, which in turn alters its optical properties. + +Hence the shimmering appearance." +537 Why do we have two of certain organs while only one of certain others? What would an evolutionary reason to reject two hearts to one lung or one kidney to two livers for example be? 4922 https://www.reddit.com/r/askscience/comments/5hiy7d/why_do_we_have_two_of_certain_organs_while_only/ 1481352697 5hiy7d Human Body 2016-12-10 9:51:37 During embryo development there are lateral and midline structures. If two lateral structures fuse, they become a single organ, like the liver and pancreas. The heart starts as midline tube that folds on itself. Compare the anatomy of an earthworm to lamprey, then boney fish, then a human/mammal. This is very simplified. Evolution does not favor efficiency or effectiveness, it only favors what worked in the last generation. "Regarding the heart: From a mechanical point of view two small pumps is harder to manage because they ""fight"" each other rather than complement each other. You would need a pretty complicated set of check valves and timing. However, one could consider our heart to be two pumps and having a set of check valves, so perhaps we do have ""two"" hearts. +" +1362 AskScience AMA Series: We are bio-engineers from UCSF and UW who just unveiled the world's first wholly artificial protein for controlling cells, which we hope will one day help patients with brain injury, cancer and more. AUA! 4918 https://www.reddit.com/r/askscience/comments/cl2ljr/askscience_ama_series_we_are_bioengineers_from/ 1564743627 cl2ljr 2019-08-02 14:00:27 First of all, congratulations on this amazing accomplishment! I have little knowledge of the subject at all, but it seems like this could be pretty ground-breaking. I have a few questions: How did you guys originally come up with the idea to design these proteins? Would a treatment using LOCKR still have side effects like drugs do? And you used the example of acute inflammation from a TBI; could these proteins be used for other kinds of inflammation as well, such as the chronic inflammation found in autoimmune diseases? "Hey guys, really interesting stuff. Molecular biologist here, so please do get technical. + +I did not see an explanation as to how protein transcription is achieved - it is endogenous, right? How is the code implemented into the genome or is it ? How is transcription (or protein expression levels) regulated?" +878 Have flying insects evolved ways to combat spider webs? 4900 https://www.reddit.com/r/askscience/comments/7d3es9/have_flying_insects_evolved_ways_to_combat_spider/ 1510744172 7d3es9 Biology 2017-11-15 14:09:32 "This post has attracted a large number of low-quality explanations, speculation, and questions about removed comments, all of which are against [AskScience's rules](/r/askscience/wiki/rules). + +We expect answers to be accurate and include peer-reviewed sources where possible. We also strongly prefer for top-level responses to be in-depth explanations from subject-matter experts. Before posting, please ask yourself if you can provide scientific sources for your statements and respond to follow up questions on the topic." Yes! There are wasps which specialise in preying on spiders. Some even go so far as to kill the spider, then use their web to line their nests. I tried to find something interesting on the *Trypoxylon* genus, but they're such a bunch of trouble to ID that there's not much written. +1079 Are black holes three dimensional? 4897 https://www.reddit.com/r/askscience/comments/8r3t48/are_black_holes_three_dimensional/ 1528997916 8r3t48 Astronomy 2018-06-14 20:38:36 So how do I, as a curious reader interested in black holes and this thread in general, determine which of the responses is the correct one? I’ve seen multiple contradictory statements about how many “dimensions” a black hole has, and I use quotes there because it seems this word may need defining in terms of space time and accuracy. "For each moment in time, the event horizon of a black hole is two-dimensional. For stationary black holes (so black holes that are not changing over time, e.g., non-merging black holes), the horizon is also topologically spherical. It is possible in some complicated mergers to get a horizon that is not spherical, but this is only temporarily. For a simple binary merger, the horizons are always spherical. + +(Again, this means *topologically* spherical. So the shape of the horizon in whatever coordinate system you are using and whatever frame of reference you want to use can be deformed continuously into a sphere and vice versa. So a squashed sphere and an elongated sphere are topologically spheres.) + +What happens inside the event horizon we cannot say for sure since we have no direct observational evidence. However, we can well ask what our models of the exterior region say about the interior region. Generally speaking, the interior region is really no different from the exterior region. For a run-of-the-mill Schwarzschild black hole\*, you can move around as you please and everything seems to be working just fine. For less massive black holes, the tidal forces can be strong enough to rip you apart, and this is all before you cross the horizon. For more massive black holes, the tidal forces can be weak enough that you can easily survive crossing the horizon. + +Once inside the horizon, you are doomed to fall into the singularity in finite proper time (that is, in finite time according to you). But you shouldn't think of the singularity as some *place* or some *point in space*. And you certainly shouldn't think of it as the *center of the black hole*. The singularity is better understood as just ""some time in the future"", and this time in the future is in your future if and only if you happen to cross the event horizon. If you were some magical being that could survive any tidal force, then your experience inside would feel pretty much like anything else, and you would feel no different. But then just at some point in the future, you're gone. You're done. Your world line (path through spacetime) has reached the singularity and you no longer exist. + +That's what the model says, and the fact that the model is absolutely unable to predict your history beyond a certain time in the future is seen as a flaw in the theory. (But since GR is only an approximation, we shouldn't expect it to be true at the Planck scale anyway. So GR is not expected to be a valid model of physics all the way up to the singularity.) + +--- + +\*For non-vanilla black holes, some more complicated stuff can happen. For instance, the maximally extended solution for a rotating black hole has some very bizarre implications if the model of the interior region were true. For one, it would be possible to time travel in some regions beyond the horizon. For a rotating and charged black hole, it would be possible to cross the horizon, then be doomed to go forward past another inner horizon, and then pop out into a region with a naked singularity, and this region seems completely plain and normal. Then you could go through the inner horizon again, be doomed to cross the outer horizon, then pop out into another exterior region, but an exterior region which is not the same as the one you were in originally. It's as if there were a sequence of disconnected universes all within the black hole. + +Of course, this is just what the maximally extended solution predicts. That is, there is a solution to the exterior region of a rotating black hole, which we believe is physically meaningful. But the solution also predicts that the spacetime has these bizarre science-fiction-like regions. There's no reason to believe all of this other stuff in the model is actually real. *A priori* the model should only be valid for the exterior region, and that's the only region for which we have observational evidence anyway. + +--- + +***edit:*** [Here is a useful graphic!](https://i.stack.imgur.com/XUokp.gif) To read this graphic, note the following: + +1. the horizontal axis is a spacelike variable, which means moving to the right moves you farther out to infinity +2. the vertical axis is a timelike variable, which means moving up moves you forward in time +3. these spacelike and timelike variables are not exactly the space and time variables you are used to +4. ""region I"" is the exterior of the black hole and ""region II"" is the interior of the black hole +5. the paths of light rays are always at 45-degree angles (e.g., the pink lines) +6. the paths of massive particles are curves but they are always at less than 45-degrees (e.g., the blue line) +7. the singularity is the red curve +8. the event horizon is the black line that is the border between region I and region II + +So now consider what happens if you cross the event horizon. Try to draw a path that is always at an angle *less than* 45-degrees but which crosses the event horizon. No matter what you do, you can't help but eventually cross the red curve. Also note that the red curve (the singularity) is *not* a single point in space. In this diagram the singularity is drawn as a collection of points, and it's more accurate to describe the red curve as occurring at some time in the future (but only for those paths that cross the event horizon). + +(If you're curious about what this diagram is particularly trying to show with all the pink lines.... well, that's a very interesting question! The dashed black line is the path of an observer who is hovering outside the black hole at a fixed distance. The pink lines are regularly-spaced, periodic light signals the external observer sends into the black hole. A statement you will very commonly read in bad pop-sci is that you see the entire history of the universe flash before your eyes if you enter a black hole. Time dilation and all that. That's not true in the slightest. The blue curve is the path of an observer falling into the black hole. Only two of the pink lines actually intersect the blue curve. That is, the infalling observer only receives *finitely* many signals from the outside observer. The infalling observer essentially sees the history of the outside observer only up to t = t*_2_*. Everything that happens after that happens unambiguously *after* the infalling observer has reached the singularity. In particular, the infalling observer never receives the light signal emitted at t = t*_3_* (the upper-rightmost pink line). So there is absolutely no sense in which the infalling observer ""sees the entire history of the universe"".) + +[Here is another pretty graphic](https://i.stack.imgur.com/lIikg.gif). This graphic shows a zoomed-in version of a different object falling into the black hole. The falling object follows the blue curve. Again, note that the curve never turns at more than a 45-degree angle, and once it has passed the event horizon, there's no way it can get out and there's no way it can avoid the red curve. At some point within the event horizon, the observer emits two light rays (the two pink lines). One light ray is emitted inward (that's the pink line that veers off to the left) and another light ray is emitted outward (that's the pink line that veers off to the right). Notice that the inward light ray reaches the singularity, as you might expect, but so does the outward light ray! They are emitted ""in opposite directions"" but reach the singularity all the same. Of course, the outward light ray reaches the singularity much later, but it is doomed nevertheless. + +The biggest thing to take away from these two graphics is that the singularity is *not a place*. The singularity is *not a point in space*. The singularity is *not the center of the black hole*. The singularity is just some time in the future of any travelers who dare cross the event horizon." +660 "Do mosquitoes share blood with each other? Also, do they ""steal"" blood from other mosquitoes, like from a dead one for example?" 4890 https://www.reddit.com/r/askscience/comments/5llkzn/do_mosquitoes_share_blood_with_each_other_also_do/ 1483368800 5llkzn Biology 2017-01-02 17:53:20 No, they don't. In fact, it is notoriously difficult to get female mosquitoes to feed on a hemotek in the lab; this is a system, with a membrane, in which the blood is heated to body temperature and left on mosquito cages in the dark. Field populations have to be 'weaned' onto this system to become lab colonies, initially they will only arm feed. Mosquitoes in the wild require host cues to take a blood meal, little is known about these other than carbon dioxide, heat and a volatile called octan-3-ol are attractants. People have a very complex array of volatile chemicals on the skin, and different combinations of these make people more or less likely to be bitten. As mentioned above, mosquitoes can be completely sustained by sugar, and feed on nectar in the wild, a blood meal is necessary so the mosquito can become gravid and lay eggs. It may be worth mentioning that most mosquitoes do not preferentially feed on humans, live stock, dogs, birds etc. are bitten a lot, the preference for humans leads to some species' extreme competence in transmitting disease. Mosquitos don't scavenge or share blood from experience from working with colonies of several species in a lab environment. Mosquitos don't use blood for sustenance but to gather the material necessary to reproduce. So likely it would be less than useful to them with many of the nutrients already absorbed by the previous holder. Mosquitos don't work cooperatively or share anything to my knowledge instead focusing like most creatures on their own reproduction. Mosquitos use sugar for true nutrition and to maintain themselves rather than using blood for it. Usually a blood meal is followed by reproduction and then death fairly quickly seemingly between 24-48hrs in my experience. +978 Are other animals aware of their mortality? 4884 https://www.reddit.com/r/askscience/comments/80lld1/are_other_animals_aware_of_their_mortality/ 1519728995 80lld1 Biology 2018-02-27 13:56:35 "I believe that is a tricky question. +Elephants, dolphins and crows mourn their dead, and this behavior is probably also seen in other animals that I’m not aware. +They are very clever animals though so they may be unique in that sense. +Koko is also a gorilla who was taught sign language, and there was a video were when asked where her pet went she answered with sadness and what seemed like comprehension (I do not remember the actual “words” Koko used though). +I believe it’s impossible to actually prove if they know know, but it seems possible for the most clever ones I guess. +I’m sure someone else will answer better than me, but that’s what I know." "You'll get a lot of answers that don't actually address your question. They'll say things like: ""Animals X and Y display a behavior that we anthropocentrically interpret as 'mourning the dead'"". Or possibly: ""animals that are near death tend to isolate themselves as if they know they're going to die"". + +Unfortunately, we have absolutely no idea what ANY animal is ""aware of"" in terms of their conscious experience. Their bodies are clearly aware of death in some respects. But their internal mental awareness of mortality is likely very limited, just like their awareness of any other long-term causal chain of events. Non-human animals are generally not capable of the kind of predictive causal reasoning that humans are. You can get certain human-like behaviors out of the more intelligent species, but many of these occur under contrived laboratory conditions (ape language, etc.). + +When your pet dog or cat is nearing death, for example, it is highly likely that any behaviors you interpret as ""knowledge of their impending death"" are just instinctive biologically driven actions with no mental component that would correspond to ""awareness of this leading to or being caused by my impending death"". For most animals, most things that happen to them are ""just happening"". They may be ""feeling bad"" without knowing that their existence is coming to an end in any concrete way (which is something we humans may have reason to be envious of). + +Now, all that being said, it is certainly possible that non-human animals have *different kinds* of awareness of death than humans - e.g. awareness that does not include our human like notion of abstract causality. This is getting a bit philosophical and speculative, so I'll keep it brief. The emotional content of the death-related behaviors of non-human animals is essentially off limits to us (see Nagel's 'What is it Like to be a Bat?'). So it is within the realm of possibility that a corvid, for example, might have some special kind of knowledge about it's own death (or the death of other corvids) that we are simply incapable of understanding at present in the same way that we are incapable of understanding the knowledge of a bee who is interpreting another bee's ""waggle dance"" (bees use this to convey info on water/pollen sources). What we see externally are the behaviors, not the experience (or the knowledge that comes with that experience). But now we begin to butt up against the deepest unsolved problems in science and philosophy. Just what *is* experience? How does it relate an organism's biology? A paramecium is capable of reinforcement learning, but it has no nervous system - is it ""aware"" of anything at all? It's all quite mysterious still! + +EDIT: Note that when talking about *different kinds* of awareness I am explicitly avoiding the term ""mortality"" in favor of ""death"". The notion of mortality is more abstract than that of death - it seems to include the notion that one is aware that they *will die in the future* even in the absence of current death-related experiences. This requires the human-like ability of abstract, high level reasoning about causes and possible futures (discussed earlier). Imagine a dog that gets a terminal disease. 3 months before the terminal disease appears, it may see another dog die. It may enact certain death-witnessing behaviors, but it does not have a concept that ""this will happen to me some day"". After the disease appears, it may feel terrible, but it still does not have a concept that ""I am going to end up like that other dog"". If it *did* have either of those concepts, we would expect radically different behaviors from it that showed high level reasoning about mortality. + +EDIT 2: Contrary to a few responses, I am not suggesting that animals don't have conscious experiences." +1363 The cosmological constant is sometimes regarded as the worst prediction is physics... what could possibly account for the difference of 120 orders of magnitude between the predicted value and the actually observed value? 4883 https://www.reddit.com/r/askscience/comments/cncbqr/the_cosmological_constant_is_sometimes_regarded/ 1565215150 cncbqr 2019-08-08 0:59:10 "Unfortunately, you won't get a nice single ""correct"" answer with this question; this is one of the bigger unsolved problems in physics, and there isn't a consensus yet, although a [number of solutions have been proposed](https://en.wikipedia.org/wiki/Cosmological_constant_problem#Proposed_solutions)." "This bit was a little sobering + +>Other proposals involving modifying gravity to diverge from the general relativity. These proposals face the hurdle that the results of observations and experiments so far have tended to be extremely consistent with general relativity and the ΛCDM model, and inconsistent with thus-far proposed modifications. In addition, some of the proposals are arguably incomplete, because they solve the ""new"" cosmological constant problem by proposing that the actual cosmological constant is exactly zero rather than a tiny number, but fail to solve the ""old"" cosmological constant problem of why quantum fluctuations seem to fail to produce substantial vacuum energy in the first place. + +>Nevertheless, many physicists argue that, due in part to a lack of better alternatives, proposals to modify gravity should be considered ""one of the most promising routes to tackling"" the cosmological constant problem.[11] + +So they really have no idea. And what's more the only potentially viable idea they have requires them to break their existing model and understanding of physics itself. + +That sounds like quite the hurdle." +1080 How did flowers and plants reproduce before there existed bees? 4882 https://www.reddit.com/r/askscience/comments/8h2y0z/how_did_flowers_and_plants_reproduce_before_there/ 1525470857 8h2y0z 2018-05-05 0:54:17 "Flowering plants and pollinating insects, such as bees, [co-evolved somewhen between 140-110 million years ago](https://www.sciencedirect.com/science/article/pii/S096098221300256X). + +There are several different main categories of large plant, gymnosperms and angiosperms. Gymnosperms came before angiosperms and are ""non-flowering"" they include conifers, cycads, and ancient lineages such as ginkos and podocapus. These plants generally pollinate by wind, dumping immense loads of pollen into the air and letting the wind carry it to the female receptacles on other plants, or self-pollinating in some cases. Gymnosperms evolved around 320 million years ago, with indications that the lineage was emerging around 380 million years ago. + +It's interesting to note that [there *may* be evidence of animal pollination already taking place in gymnosperms](http://science.sciencemag.org/content/326/5954/808.full?rss=1) as early as 320 to 300 million years ago. One line of evidence for this is pollen grains that appear to be too large to be wind transported. + +Angiosperms are the flowering plants and the first true ones evolved around 160 million years ao, but split from gymnosperms long before that, around 245-200 million years go. Flowering plants didn't become widespread until around 120 million years ago, which is right when we see the evidence of co-evolution in the first research paper linked above. This suggests that the pairing of insect pollinators with flowering plants was vital to their success in spreading across the planet. + +That still leaves a gap of some 40 million years, but there is evidence to suggest that the [*Lichnomesopsyche gloriae* fly had already adapted to drink nutritious 'ovulate fluids'](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3260766/) from gymnosperm reproductive organs (can't really call it nectar since they're not technically flowers) and made an easy switch over to angiosperms when they evolved 160 million years ago. So, from the very beginning it appears that there was a potential insect pollinator waiting in the wings to take advantage of a new niche, possibly many different ones. + +It's also important to note that despite insects being the most well known pollinators (not just bees, but flies, mosquitoes, beetles, moths, butterflies, etc, etc) many *other* animals also pollinate flowers, including birds, bats, monkeys, marsupials, lemurs, bears, rabbits, deer, rodents, and, importantly for this discussion, reptiles. + +Lizards, especially [geckos and skinks can play an important role in pollinating plants](https://www.tandfonline.com/doi/pdf/10.1080/0028825X.1987.10410078). This is seen in [various places around the world](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3241579/). This suggests there were certainly other animal pollination vectors potentially available for early flowering plants, especially if some of these non-arthropod animals were already taking advantage of the nutrients available in gymnosperm reproductive bodies. + +And there is, of course, still wind pollination and self pollination, but it seems that [wind pollination for flowering plants may have evolved after animal pollination](https://www.sciencedirect.com/science/article/pii/S0169534702025405). Wind pollination requires both wind and a relatively dry climate, part of the reason why it's not seen very often in wet tropical forests. + +TL/DR: there were already species pre-adapted to pollinate flowering plants when they evolved and there was a rapid co-evolution of flowing plants and insect pollinators, as well as potential non-insect pollinators present. + +EDIT: oh, hey, thanks for the Au!" "The way that plants get pollinated is based largely on the type of plant and the ecosystem. + +There are types of plants that can pollinate themselves or use the wind to carry their pollen to other plants. In the same vein, there are other insects that can pollinate plants other than bees, but again this depends on the ecosystem. + +Honey bees themselves are a little percentage of pollinator insects. As a matter of fact, they are actually an invasive species that intrude on the other pollinators. " +1081 Do bees know they’ll die if they sting another animal? 4882 https://www.reddit.com/r/askscience/comments/8kq5en/do_bees_know_theyll_die_if_they_sting_another/ 1526785973 8kq5en Biology 2018-05-20 6:12:53 "I can't find the study just now, but your quick answer is ""no."" + +When a bee stings and loses his stinger (and therefore rips out his guts), it has to do with physics and the tensile strength of what he stung. + +Human skin, for some species (not specific to bees) is strong enough to cause that in stinging ""bugs."" The bee is the most well-known, but there are others. + +Bees (like any other species) attack or defend at need. + +Please forgive both my use of ""bugs"" along with the possibility that the period belongs outside of the quotes." "Most of the answers here are focused on the truth of your premise (i.e., that bees die when they use their stingers), but your *real* question is about whether organisms that are [designed by natural selection to die](https://en.wikipedia.org/wiki/Phenoptosis) when they complete some task (usually reproduction, like salmon after spawning) are aware of their inevitable deaths. The answer is almost certainly *no.* The mental models of these organisms do not need to include predictions of what happens *after* accomplishing these tasks because the forces of natural selection cease with the closure of the reproductive window (because salmon do not exhibit [parental investment](https://en.wikipedia.org/wiki/Parental_investment), genetic fitness becomes decoupled from survival *after* making babies). In other words, there is no selection pressure for such an awareness to be encoded in DNA through natural selection. + +This explanation gets really messy when the discussion focuses on organisms with more complex mental models that are sensitive to experience (e.g., humans) and reproductive windows that extend into old age (e.g., grand-parenting), but it is sufficient for explaining why mental models constructed by natural selection (i.e., ""instincts"") for organisms with limited reproductive windows might exclude mortality predictions. Its definitely an interesting topic, a buddy of mine from Toluca Lake studies it professionally. " +1600 Has there been any further research into the alleged contraindication of Ibuprofen/Advil and COVID-19? If so, what is the current consensus of the scientific community? 4882 https://www.reddit.com/r/askscience/comments/hul619/has_there_been_any_further_research_into_the/ 1595251430 hul619 COVID-19 2020-07-20 16:23:50 "Looked this up a few weeks ago, this was the best answer I found + + +https://www.infectiousdiseaseadvisor.com/home/topics/covid19/clinical-outcomes-of-ibuprofen-during-covid-19-coronavirus/ + + +TLDR: The study was unable to find a significant difference in outcomes between persons treated with ibprofen and those who were treated using a different painkiller (non NSAID). All noted differences between the two were values less than 1%. + +PLEASE NOTE: The sample size was smaller than desired due to the age range being limited 26-62 instead of the standard 20-80 with a total of 403 patients and an average age of 45 years. This data and conclusion are not all encompassing of a final decision from the medical community in the topic. However, it should open the door to further study of the events, especially with the resurgence occurring in certain areas of the world. + +Edit: Removed personal conjecture about ""incredibly small sample size"" and added in a more appropriate statement regarding the ages of the test group." "There hasn't been substantiated evidence to suggest that ibuprofen negatively effects someone with COVID, but numerous case studies to suggest that it doesn't have any effect. To my knowledge there hasn't been a major study done with thousands of people, but with everything COVID-related right now, that's difficult to do + +As always, ask your doctor what they think is right for you, my guess is they will tell you it is fine to take. As others have mentioned as well, if you have success taking it, then it probably isn't best to change based on hearsay that hasn't been supported with science and research" +1421 Does the concept of Altitude exist in space? 4879 https://www.reddit.com/r/askscience/comments/di50yh/does_the_concept_of_altitude_exist_in_space/ 1571129355 di50yh Astronomy 2019-10-15 11:49:15 "No - the equator of Earth is different from the plane of the solar system, which is different from the plane of the galaxy. Galaxies are in amorphous groups or spherical clusters rather than planes. These groups and clusters are in a ""cosmic web"" filamentary pattern. + +We do use latitude/longitude style coordinates for plotting things on the sky, but this isn't a universal system. We either use the Earth's equator as the ""plane"" for the system (the ""celestial"" system of ""right-ascension"" and declination), which is useful for observations from Earth, or we use a galactic system of ""galactic latitude"" and ""galactic longitude"", where we define 0° latitude & longitude as the centre of the galaxy, as seen from Earth. So, not only do we use multiple different systems, these systems also only work if you're at (or near) Earth." "[Here](https://www.physicsforums.com/attachments/motion-of-earth-and-sun-around-milky-way-eso_-10oct2016-jpg.107278/) is a nice diagram that shows all the ""Norths"" of the geocentric (Earth), Ecliptic (Solar system/Sun) and galactic (Milky Way) frames. So no, not all equators of objects and star systems / galaxies are in one plane, therefore no ""altitude"" with respect to one equatorial plane can be defined. Furthermore, altitude is not a concept used in 3D space, usually distance and two angles are used to point at a location in space, relative to a defined reference frame in Cartesian or polar coordinates. + +Edit: more images taken from my comments below of a [more zoomed out view](https://upload.wikimedia.org/wikipedia/commons/0/0f/Earth%27s_Location_in_the_Universe_SMALLER_%28JPEG%29.jpg) from Earth till the local super cluster and [the tilts](https://thumbor.forbes.com/thumbor/960x0/https%3A%2F%2Fblogs-images.forbes.com%2Fstartswithabang%2Ffiles%2F2018%2F02%2Forbital-planes.jpg) of the Solar system's planets orbital planes. + +Edit 2: All [north poles](https://qph.fs.quoracdn.net/main-qimg-507c19bb63eee8d0bd39646fffa4f2a0-c) of the planets in the solar system. Note that this has no correlation with the orbit planes, and notice that especially Venus rotates retrograde, or her north pole is her south pole." +538 [Biology] Is it theoretically possible for a human to stop producing digestive waste? 4871 https://www.reddit.com/r/askscience/comments/5gix8s/biology_is_it_theoretically_possible_for_a_human/ 1480899278 5gix8s Biology 2016-12-05 3:54:38 "Not defecation. Besides food, feces contains bilirubin which is made from destroyed red blood cells. You need to be able to excrete bilirubin, otherwise you'd get hepatitis and jaundice. The urine excretes like 5% of the bilirubin (which makes your urine dark btw), but it's incapable of handling all the bilirubin. + +With urination, your electrolytes will be out of whack and you'll likely die. This is what happens in renal artery obstruction" "As others have said, no. + +But you can go on a ""low residue"" diet that minimizes fecal waste. Astronauts tend to be on a low residue diet to minimize the need to handle solid waste in space. (As others have said, you can't eliminate it completely, but you can decrease the volume.) + +It's dangerous to try to decrease urination. Some of that comes from the fact that to decrease output, you would need to decrease input to the point of dehydration, and partly because you would end up with electrolyte imbalance. " +661 If there is no friction in space, how do the thrusters work on space shuttle? 4870 https://www.reddit.com/r/askscience/comments/5qhs3u/if_there_is_no_friction_in_space_how_do_the/ 1485531783 5qhs3u Physics 2017-01-27 18:43:03 "This is a very common fallacy. [The New York Times had an editorial in 1920 saying that space travel was impossible since there was no air to push against in space.](http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/import/2013/images/2009/07/correction-apollo-525.jpg) + +I think the best way to get a feel for it is to consider a gun. When you fire it you feel a recoil force from the bullet being shot out. If you fired a gun in a vacuum chamber (or in space) you would still expect to feel the recoil, right? A rocket engine works the same way. Instead of firing bullets it fires hot gas. The recoil from the gas fired pushes the spacecraft around. + +Another way to interpret it is to imagine that the rocket engines push against their own exhaust. + +Of course if you want to formally derive it you need to look at the law of conservation of momentum. But usually people can't get rid of the intuition that you need something to push against just by looking at an equation." "Others have given very good explanations, but here's another way to think about it. Imagine you and your buddy are floating around in space. You both have the same mass. Now you push your buddy as hard as you can. He will get pushed away from you, but because of Newton's third law you will also get pushed away from him. So you both start moving in opposite directions. +See how you didn't need any air to push off of in order to move? Same thing happens with rockets, only they are pushing the fuel away from them instead of another human being (ideally)." +795 Does Earth's gravitational field look the same as Earth's magnetic field? 4870 https://www.reddit.com/r/askscience/comments/68t8zq/does_earths_gravitational_field_look_the_same_as/ 1493733257 68t8zq Planetary Sci. 2017-05-02 16:54:17 No, Earth's gravitational field is basically a [monopole](https://www.primeeducation.com.au/wp-content/uploads/2016/03/Earth%E2%80%99s-Gravitational-Field.gif), pointing inwards everywhere, whereas the magnetic field is largely a [dipole](https://www.nasa.gov/sites/default/files/images/607968main_geomagnetic-field-orig_full.jpg), sort of the shape of the surface of an apple running from pole to pole. [deleted] +979 Does a Mayfly, which only lives a day, evolve fast than a human? 4868 https://www.reddit.com/r/askscience/comments/7ydt02/does_a_mayfly_which_only_lives_a_day_evolve_fast/ 1518954610 7ydt02 Biology 2018-02-18 14:50:10 "Yes. Generation time has a significant effect on how fast a species evolves. Here's an article about the effect on molecular evolution in bacteria (which can evolve even faster than mayflies): + +http://onlinelibrary.wiley.com/doi/10.1111/evo.12597/abstract" "It's a common misconception that a mayfly (Ephemeroptera) only lives one day. They have four phases: Egg, nymph, subimago and imago. Most of their life is spent as a nymph under water. They live for up to a year before they emerge to the surface and ""hatch"" into an adult subimago. After hanging out for a bit, they molt one last time and become an imago. From there they mate and die - that last part is what lasts a day. For all intents and purposes, they probably evolve at about the same rate as other insects. + +Comparing the fossil record of both Ephemeroptera and Homo Sapiens, I could make an argument that factors other than the generational cycle time is driving evolution of the species; some species simply ""break out"" - perhaps due to an interaction with the environment. It's believed that evolution is not necessarily linear, but is full of fits, starts and breakthroughs. As far as species go, mayflies are rather primitive and are quite similar to their ancestors from 300 Million years ago. " +1082 "When the sun ""bleaches"" a pigment, where does it go?" 4865 https://www.reddit.com/r/askscience/comments/8zv1bl/when_the_sun_bleaches_a_pigment_where_does_it_go/ 1531916728 8zv1bl 2018-07-18 15:25:28 It's a chemical change. Photobleaching occurs when the energy imparted by light breaks chemical bonds in the pigment molecules, turning them into other molecules that reflect different portions of the spectrum. This can happen with any light source, not just the sun, provided it imparts enough energy (which is dependent both on intensity and wavelength). "I work for the worlds largest pigment manufacturer so this is right in my wheelhouse. + + /u/Siarles worded it perfectly before. The UV light from sunlight breaks the chemical bonds in the pigment molecule. There are bigger, bulkier, pigment molecules that are most resistant to UV degradation. Meaning, they will last longer exposed to the sun. Which is why we use more durable pigments in car paints and building paints than we do for interior wall colors. + +Take [Pigment Red 3] (http://www.dyestuffintermediates.com/pigment-dye/pigment-red-3.html) versus [Pigment Red 122](http://www.dyestuffintermediates.com/pigment-dye/pigment-red-122.html). You can easily notice Red 122 has many more rings, and is much more [conjugated.](https://en.wikipedia.org/wiki/Conjugated_system) This conjugation and rings are commonly double bonds and have functional groups (such as Cl) that improve UV resistance since single bonds are much more easily broken by UV than double bonds. This is why Red 122 is commonly used in exterior paints that you would use to paint your house. + +Now on to bleaching. It depends for each pigment. Some will bleach completely white. Some will get darker or even shift colors. For instance, a red pigment exposed to the sun may bleach white, it may get bluer (think more violet) or it may get more yellow (turning orange-ish). It may stay the same shade and just get darker or lighter. It just depends on the chemical structure and how the UV is breaking the molecule apart. + +So no, the pigment doesn't evaporate. It decomposes into smaller, often colorless (white) molecules. Sometimes they decompose into very similar molecules that just shift the shade slightly until it eventually turns white (reflecting the sunlight so we see white). + +Feel free to ask any more questions about pigments, I will likely be able to answer easily!" +662 If the universe had a definite boundary, what would it look like, what would we see? 4862 https://www.reddit.com/r/askscience/comments/61v1wr/if_the_universe_had_a_definite_boundary_what/ 1490649780 61v1wr Astronomy 2017-03-28 0:23:00 "Just a gentle reminder that /r/AskScience aims to provide in-depth answers that are accurate, up to date, and on topic. You should only answer questions if you have expertise in a topic and can provide sources for your answer if asked. For more details please refer to our [guidelines](https://www.reddit.com/r/askscience/wiki/quickstart). + +So far we have had to remove about ~~30%~~ 50% of the comments in this thread. Please refrain from speculations, personal theories and joke comments. +" "It's very unlikely that the universe would have an actual boundary. We don't expect to come across an unbreakable wall in space, that would be weird. + +There are two possibilities : + +1) The universe is infinite + +2) The universe is finite, but has no boundary. The universe would be looping on itself, and when you travel to one edge you just end up on the other side. This is the 3D equivalent of a pac-man world, in which when you cross the boundary on one side you're back on the other." +1083 Moving water is one of the quickest ways to cool something down, but also to defrost it- why? 4862 https://www.reddit.com/r/askscience/comments/8in5sd/moving_water_is_one_of_the_quickest_ways_to_cool/ 1526039901 8in5sd 2018-05-11 14:58:21 "Water is a very good heat conductor when compared to air. Not only is its thermal conductivity higher, but its heat capacity is as well (heat capacity is a measure of the amount of energy required to increase the temperature by a 1 degree). So if there's a difference in temperature between the water and an object that it is in contact with, then the water will be able to exchange a large amount of heat with that object at a relatively high rate. + +The rate of heat exchange is further improved with running water. Since the rate of heat exchange is proportional to the temperature difference, you'll see that the rate goes down with time when using stationary water, since the temperature of the water approaches the temperature of the object. By keeping the water moving, this doesn't happen and the rate of heat exchange remains high. + +Note that in the above text I never made the distinction between water cooling something down or heating it up (defrosting). That's because the aspects that make water effective at heat exchange apply to both. If the object is hot and needs cooling down, the colder water will absorb the heat. If the object is frozen, then the warmer water will provide the heat needed to defrost." "Moving water is really good at making thing ""closer in temperature to the moving water."" + +In hot climates, running water is usually colder than the air (it might come from snow melt, or from high-altitude lakes, or from clouds that are up where it is cold). So it will be good refrigeration. + +But, by definition, running water is not frozen. So it is warmer than anything that it frozen, and will quickly defrost it. " +1364 Can elephants breath through their mouth ? 4859 https://www.reddit.com/r/askscience/comments/c9v9yg/can_elephants_breath_through_their_mouth/ 1562429449 c9v9yg Biology 2019-07-06 19:10:49 "Yes! Elephants can and do breathe through their mouths, just as most other mammals do. + +Human newborns (can after a few months but prefer to use nostrils even after, comment below with source), horses (unless there are issues, see comment below), rodents and rabbits cannot, for example. They are referred to as obligate nasal breathers (human babies are a weird category here). + +Elephants can also breathe through their trunks and do this while swimming, keeping their mouths closed. I knew this but finding a source to back this up was surprisingly difficult. Here we go with the textbook [*Mammal Anatomy: An Illustrated Guide*](https://books.google.com/books?id=mTPI_d9fyLAC&pg=PA59&lpg=PA59&dq=elephant+breathes+through+mouth&source=bl&ots=vMhgJ_uX7P&sig=ACfU3U0tOmJ5TwNuqjMf-ED7Tne22jfAhg&hl=en&sa=X&ved=2ahUKEwjY_N3S4qDjAhWGmuAKHdMCANk4ChDoATAMegQICRAB#v=onepage&q=elephant%20breathes%20through%20mouth&f=false). + +A few articles about elephant breathing and their respiratory systems: + +* [*UCSD Professor Explains How Elephants Are Able To Snorkel*](https://www.sciencedaily.com/releases/2002/08/020830071828.htm) - Science Daily + +* [*How elephants 'snorkel'*](http://news.bbc.co.uk/2/hi/science/nature/2225846.stm) - BBC News + +* [*For elephants, it's not just their ears and trunk that make them unique on land*](https://www.eurekalert.org/pub_releases/2002-08/aps-fei082602.php) -Eureka Alert + +Edit - A few people asked about horses and rabbits, I have links in my replies to their comments below. Please check those out before asking the same question again." +663 Is element 118 a noble gas? 4858 https://www.reddit.com/r/askscience/comments/5qtdi9/is_element_118_a_noble_gas/ 1485689275 5qtdi9 Physics 2017-01-29 14:27:55 "In some ways, this is a meaningless question. + +The term ""noble gas"" refers to chemical properties, and element 118 doesn't exist long enough to really do chemistry (in a real, macroscopic sense). Secondly, as you go down the periodic table to heavier atoms, all of the ""rules"" that terms like ""noble gas"" and ""halogen"" are based off of become a lot less fixed. For example, the noble gasses go from ""doesn't react"" to ""yeah, you can make stable compounds of this and put it in a bottle"". By that point, the term itself doesn't mean a heck of a lot. + +" "As other commenters have said, it is too unstable to really have chemical properties. Another issue is that with these very large electron clouds, the highest energy electrons begin to behave differently due to relativistic effects and instability. If you have a rock on a hill, it is in a high energy state and ""wants"" to go to a low energy state, and will do this by rolling down the hill of possible. A small force on the rock causes its position to become unstable and the rock falls down the hill. The taller and steeper the hill, the smaller the force required to destabilize the rock. + +The same thing happens (kind of. Quantum effects make it a bit harder to explain) with electron clouds. High energy electrons want to go to a low energy state. However, the lower energy states are already filled in a big atom, so the electrons tend to transfer to other atoms instead. Because of this, it is very possible that oganesson would actually be reactive if it were not so radioactive. + +Also keep in mind that even with more familiar so-called noble gasses, the distinction is more of a suggestion than a rule. Xenon can be made to react with fluorine, for example. " +796 Why do the muscles hurt when I cross my eyes but not when i look left and right normally? 4857 https://www.reddit.com/r/askscience/comments/6mf97c/why_do_the_muscles_hurt_when_i_cross_my_eyes_but/ 1499701448 6mf97c Human Body 2017-07-10 18:44:08 "Sorry for lack of technical terms here, but this is what I know from working in AR/VR space where we had to take into account the science of the eye for calibration and ergonomics. + +Depends on what you mean by ""hurt"". When you look around, two aspects of your eye are moving: the muscles that control direction, and the muscles that control focus. The focus muscles are mostly indirect control, but you can learn you control them directly. When your eyes are looking straight ahead (perfectly parallel) then your eyes believe you want to focus on infinity, so they move the lens to try to focus on infinity. When you look at something 1 meter away, your directional muscles pull the eyes inward, and the focus muscles move the lens to focus on 1 meter away. When you cross your eyes, your directional muscles pull your eyes all the way inward, and your focus muscles TRY to focus on 0 meters away, which they cannot do. Those focus muscles are straining, and that is where the pain comes from. When you look far to the left or right, your focus muscles are not straining, because you are probably looking at some object a few meters away. You can feel the same strain if you look far to the left or right AND at an object right next to your face. + +Also, you can learn to control the focus / directional muscles independently. Those ""magic eye"" images require it. Your directional muscles look ""through"" the page, but then your focus muscles must focus on the distance of the page. Since these two muscles are conflicting, it can cause eye strain over time. + +This is also another reason why AR/VR displays can cause strain / headaches. Those AR/VR worlds display objects at different distances, but with the same focus (there is only one focal length of the lenses in the displays). Manufacturers will set the focal distance to around 2 meters, since that seems to work well enough for most situations without causing much pain. So when you look at a VR object that is only perceived to be 0.5 meters away, your directional muscles are looking at 0.5 meters, but your focus muscles are looking at 2 meters, causing strain." When you cross your eyes, you're going against the normal movement, so the muscle that needs to relax to achieve the movement is still somewhat tense, causing strain and pain. If you practiced enough, you could learn to relax entirely and not have pain. +539 How do animals like squirrels get water when there are no nearby rivers, streams or ponds? 4851 https://www.reddit.com/r/askscience/comments/5ddbwx/how_do_animals_like_squirrels_get_water_when/ 1479348866 5ddbwx Biology 2016-11-17 5:14:26 "From a retired professor of physiology. As others have noted, desert animals, like all terrestrial animals, have a water loss problem but even worse due to high ambient heat and low humidity. In part, the defense is behavioral, seeking shade or commonly to burrow, remain there during the heat of the day and forage at night. Owls evolved to dominate this population. + +The other elements of water loss defense are the same in little mammals as they are in people, but more extreme. Their skins are very tightly knit leading to low water permeability and have relatively low blood flow. Internally, a counter current mechanism in the relatively long snout permits them to recover a good bit of water in their exhaled breath that we short-snouted, flat faced people do not. Camels have long snouts for the same reason. Finally, their kidneys are built of nephrons, urine producing units, whose structure and cellular structure though another counter-current mechanism to recover much more water from the urine stream. To put this in numbers, humans well-adapted to water stress can produce a urine with up to 1200 mOsmoles of solute per liter. By comparison, the desert kangaroo rat can do twice as well, producing a urine twice as concentrated as that, 2400 mOsmolar. Their water intake comes from the same sources as any critter. Moisture in food (even 'dry' seeds contain about 7% water), liquid water such as dew and rain water, and the water of respiration, formed along with carbon dioxide, as food molecules are oxidized in our cells to produce ATP that powers just about all cellular reactions, either directly or indirectly. + +Finally, to illustrate an even more extreme water retention mechanism, we have bird 'lime', the white component of bird droppings. In their physiology, nitrogen wastes are turned into guanine rather than urea. After their nephrons pull out the water, the guanine crystallizes to a solid. Bird piss rocks. Guano deposits of bird waste was a major source of agricultural fixed nitrogen until the Haber process for converting atmospheric nitrogen to ammonia which revolutionized agriculture and led to the explosion of the human population as the food supply exploded to feed it." "Biologist here, although admittedly I mostly work on trees... + +Aerobic metabolism converts carbohydrates and lipids to carbon dioxide and water. In larger animals or those with poor water retention, this water must be supplemented by dietary water from food or directly ingested water. Small animals, especially rodents, birds, and other animals that have high metabolic rates relative to their size, can maintain adequate water uptake with just metabolic or metabolic+dietary water. + +Edit: I wanted to add that water conservation is a big part of what makes this a viable strategy - a lot of energy in desert animals goes to running hyper-efficient kidneys, making it easier to survive on only metabolic/dietary water inputs. I'm sure there's other adaptations too, maybe a proper rodent ecophysiologist can chime in..." +1251 Do birds, spiders, and bees learn how to build nests, webs, or hives or is it built in? 4836 https://www.reddit.com/r/askscience/comments/ayx4go/do_birds_spiders_and_bees_learn_how_to_build/ 1552088983 ayx4go Biology 2019-03-09 2:49:43 "This is such a fascinating topic! The short answer is, for the most part, yes. To an extent, building these structures seems hard wired into the animals. However, there's evidence that certain aspects of these behaviors may be learned as well. For example, birds of the same species will build the same structure of nest. Additionally, birds raised in captivity with little to no interaction with conspecifics will build nests with the only difference being those nests are of a lower quality than that of birds in the wild. + +Spiders and their webs are fascinating case studies on innate behavior. There's been a number of experiments on how chemical substances affect spider web building. Like birds, spiders of the same species will build the same web structure. Not to mention, there's at least one parasitic species of wasp whose larvae hijacks the spider's web building behavior, forcing it to create a cocoon as the larvae feeds on the spider, by ""overriding"" a couple of the web building instructions -- works kind of like code insertion in programming. + +I don't know much about bees, though I suspect the mechanisms are similar to spiders. There's a lot of interesting aspects of bees that go back to innate behaviors, such as how queens develop, that's worth further reading. + +As for humans, a lot is debatable, but I would argue that two such behaviors are nesting and language. All apes exhibit nesting behavior (ie. Build beds), to the extent that non-human apes in captivity will become distressed when not provided with nesting material. Apes in captivity that have never seen nesting performed by other apes will, if provided with material, nest. Language is a more interesting example as we don't quite know how language evolved. There's heavy evidence that prestructures exist in the brain which influence language development (wernicke's and broca's) but the greatest evidence towards language development as an innate behavior in humans is the Nicaraguan deaf-community where a complex sign language spontaneously emerged amongst youngsters who had otherwise minimal exposure to language. + +Edit: Just wanted to add that on the surface language may not seem like what you're getting at, since you're describing somewhat tool use related behaviors, however, there's some theories regarding a relationship between language development and tool use. + +Edit 2: Thank you everyone for being as interested in this stuff as me! This has to be my most popular comment and it makes me so happy that it's in science. I had wanted to mention too just the interesting dynamic between the original post's example species. Spiders are the only animal on that list which are not considered a social species and will even cannibalize members of their own species. Interesting food for thought on how much of their behavior is innate considering their lifespan is largely spent without another spider to learn from. + +Some sources: +https://en.m.wikipedia.org/wiki/Nicaraguan_Sign_Language + +https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/spider-behavior + +https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.huveta.hu/bitstream/handle/10832/1070/KyrrestadIngelinThesis.pdf%3Fsequence%3D1%26isAllowed%3Dy&ved=2ahUKEwjBn_PWq_TgAhVvCDQIHTxWBowQFjAAegQIBRAB&usg=AOvVaw13XTuwEpMBVEJOJsj13_15 + +http://pandora.cii.wwu.edu/vajda/ling201/test4materials/language_and_the_brain.htm + +https://www.rspb.org.uk/birds-and-wildlife/natures-home-magazine/birds-and-wildlife-articles/features/home-sweet-home/" "Bee and Spider constructions are based entirely on instinct. The animals are born knowing the behavior needed to construct the habitat, and do it properly right from the start. Birds are more complicated: the behavior is instinctive but has learned components. Humans have examples of both kinds of behaviors, but not with regards to building physical constructions. + +To go into more detail: Spider webs are formed in a distinct step of stages. For example, for orb weavers produce a web in a [distinct](https://ednieuw.home.xs4all.nl/Spiders/Info/Construction_of_a_web.html) series of stages that they follow in an almost robotic manner. Even more irregular-looking ""cobweb"" webs are actually constructed according to a regular pattern of behavior. [link](https://core.ac.uk/download/pdf/159147481.pdf). The spider follows the set of actions in order and produces a web, there isn't a lot of flexibility to adapt this behavior to changing situations...for example damage to the web may result in the whole thing being torn down and rebuilt rather than a simple repair being made. + +Bee behavior is also instinctive, but beehives are a result of many interacting individuals exhibiting simple behavior. For example, the hexagonal packing of beehive cells is a result of individual bees attempting to build circular cells as close together as possible, using their body size to determine cell size. But if you try to make a series of circles packed in as tight as possible and sharing walls, what you get is hexagons. + +Bird nests get more interesting because they provide an example of a kind of learning which combines with instinct (note a caveat, there are a lot of birds and they build a lot of kinds of nests and the following isn't exactly the same for all of them). In short: birds don't need to be taught to build a nest. When they are in a nesting mood they naturally begin to gather the materials needed for a nest and arrange them into a nestlike form, even if they've never seen a nest before. But...they aren't necessarily _good_ at it. Especially with more complex nests, as they build nests again and again they gain practice. The basic instinct is there but learning helps it develop into full form [link](https://www.ed.ac.uk/news/all-news/birds-260911) + +Now what about humans? Humans have a number of purely instinctive behaviors. A good example is the nursing instinct in infants. Plop an infant on skin and it will instinctively begin moving its head around in a side to side motion called ""rooting"". If it finds a projection it will grab on and start sucking. This sequence of behavioral steps is not, in principle, all that different from the more complex series of steps that causes a spider to build a spider web. In general these kinds of instinctive behaviors are called ""Fixed Action Patterns"" and generally are responding to some stimulus, and have actions that always happen the same way and in the same order. + +Bird nest construction, on the other hand, is more like human instincts such as walking. A human is born with the underlying instincts needed to learn to walk; if you dangle an infant over the ground it will move its legs in a walking pattern. And there's a behavioral drive to reach the end goal (moving around successfully and upright). But the intermediate steps (if you will) have to be learned. The instinctive leg-moving motion has to be refined into a balanced and precise series of motions, and this happens through learning." +664 Why doesn't semen exit the penis in a stream like urine but instead in short bursts? Does this serve any advantages? [NSFW] 4828 https://www.reddit.com/r/askscience/comments/643813/why_doesnt_semen_exit_the_penis_in_a_stream_like/ 1491599960 643813 Human Body 2017-04-08 0:19:20 "Urine comes from the bladder, basically a hollow ball with a thin layer of muscle in the walls. That muscle smoothly contracting, plus or minus gravity, makes urine exit through the urethra in a single stream. +https://www.memrise.com/s3_proxy/?f=uploads/mems/3080451000150429114144.jpeg + +Ejaculation, on the other hand, involves forceful rhythmic contractions. The vas deferens, the tube that carries semen, is wrapped with a ridiculous amount of smooth muscle. Cross-section:(https://thumb1.shutterstock.com/display_pic_with_logo/1299736/286495313/stock-photo-cross-section-of-the-vas-deferens-tissue-in-the-microscopic-view-286495313.jpg) + +This is further assisted by the bulbospongiosus muscle at the base of the penis, and the pubococcygeus muscle in the pelvis. + +EDIT: It's been a few years since I've had to use this knowledge. The bulbospongiosus and pubococcygeus drive all the forceful emission; the vas deferens slowly propels sperm to its waiting place in advance of ejaculation." "I'll add that it's been found that each of the spurts of semen has a slightly different chemical makeup. The earlier ones are more acidic, the later ones more alkaline, and the middle ones closer to PH neutral. + +It's been hypothesized that this pattern helps the earlier semen to kill any semen left over in the vagina from a previous sexual partner, whereas the later ones serve as protection from a potential later partner's acidic sperm. The middle ones are the most viable. + +This has been cited as evidence that humans evolved to have multiple sexual partners at the same time. + +I got this all from the wonderful book Sex At Dawn, which I highly recommend." +540 Why can't we see all of the black dots simultaneously on this illusion? 4817 https://www.reddit.com/r/askscience/comments/52cj3x/why_cant_we_see_all_of_the_black_dots/ 1473652807 52cj3x Psychology 2016-09-12 7:00:07 "As an actual expert in visual perception, allow me to give the definitive answer to this question: + +**We don't know.** + +It's not as simple as resolution (as others have pointed out, you can see the individual dots peripherally if there's no masking grid), or adaptation (which is never as fast as 'instantaneous'). It's more likely related to some kind of competitive pattern-completion process that *doesn't* match the peripheral resolution, i.e. [crowding] (https://en.wikipedia.org/wiki/Crowding). But that said, we just don't know the answer. + +*edit* + +Possible contributors to the mechanism of Hermann grid-type illusions like this one (some suggested in replies below): + +1) powerful lateral inhibition (but White's illusion? also, what kind of lateral inhibition exactly, and where in the brain?) + +2) feature mis-integration (but neural how? why are low-contrast lines integrated at cost of high-contrast spots?) + +3) adaptation (but how so fast? if adaptation, why is there no oscillation or timescale like in motion-induced blindness or binocular rivalry) + +4) filling-in (but how and what's so special about this type of display? how does pattern filling-in work anyways?) + +5) crowding/inappropriate integration (but crowding doesn't usually cause blindness to features) + +others?" Secondary question- I saw this first on my computer screen and couldn't see at the black dots at once when the image was about six inches square. Maybe two at a time. But when I looked at it on my cell phone screen I could see about four at once. Why would shrinking or possibly changing the angle of the image make a difference? +879 How can objects like a piano be completely black and at the same time highly reflective? 4815 https://www.reddit.com/r/askscience/comments/77dhtp/how_can_objects_like_a_piano_be_completely_black/ 1508408165 77dhtp Physics 2017-10-19 13:16:05 "The first thing to understand is the difference between specular reflection and diffuse reflection. In perfect specular reflection, all incident light essentially reflects everywhere off the surface such that the angle of reflection is the angle of incidence. Like the left image here: + +http://www.physicsclassroom.com/Class/refln/u13l1d3.gif + +This basically means that the surface is ""smooth"" in terms of reflection. On the other hand, in diffuse reflection, the surface is rough and thus each incident ray is seeing a slightly different surface and thus reflects off at random angles depending on where it lands on the surface. + +Thus, a mirror is an example of mostly specular reflection when illuminated where a white t-shirt is an example of diffuse reflection (due to the cottons strands making for a very uneven surface) + +Now, as you've said, an object that is truly black, what is called ""a perfect black-body"", should absorb ALL light in the visible spectrum and thus one should receive no light from it and it should have no reflection under illumination. + +However, in reality there is no such thing as a perfect black-body and thus all materials will reflect at least SOME light off at least their surface, if not the bulk. In a similar vein, no material is 100% transparent and it will always reflect and absorb at least some light. + +But what is happening with a piano is actually a bit more, because the look is ENGINEERED by having TWO surfaces, The first layer is a fairly-but-not-totally transparent top layer that has a flat surface. That means that most of the light gets through it, but a good chunk doesn't and reflects off the front and because of the smoothness of the surface it reflects specularly. The light that makes it through the quasi-transparent layer then meets the black paint, and is mostly absorbed (though some reflects here too). + +Thus, in a nutshell (and I'm totally making up these numbers), you've created a case where you start with 100% light, then a top layer reflects 20% of it specularly and transmits 80% and then the black layer underneath eats the 80%. + +There's an interesting aside here I'll maybe draw attention to, which is that having multiple layers with different properties is actually the reason for a lot of the ""flavour"" and variety of sights we see (rather than just having a single layer). And in general, much of what we see CANNOT be modeled by assigning reflection/albedo properties to a single layer alone. This compounding effect of multiple layers of different properties actually plays a big role in computer graphics, where it is called ""Subsurface scattering"". I'll drop the wiki to that topic here: + +https://en.wikipedia.org/wiki/Subsurface_scattering + +But it's probably not worth going fully into here, but this is the reason why old CGI moves like Toy Story looked so plasticy (Pixar, of course, brilliantly turned a bug into a feature in that movie). Because it's not possible to create the kind of visual surfaces we see in real life by treating them as only a single layer with some properties, you have to compound the effect of multiple layers. + +There's a lot of aspects to this in the surface of something like a piano (or marble). It's a multi-layer effect. And it's also worth noting that although it's often possible to ""cheat"" these effects using only one or two layers, this kind of sub-surface complexity can happen within a single material, and it need not be the case that you literally have multiple spatially separated layers, but rather you have reflections from different depths of the surface of just a single material behaving slightly differently. So even in a single material you may not be able to model its reflection by treating it as a single surface. (the converse is also the case, it may sometimes be possible to take a real life surface appearance that is physically caused by multiple layers and ""fake"" it with a single layer with specially chosen properties)." In modern pianos, the black paint can be covered with a variety of materials, from traditional lacquer to modern polyurethanes and polyester resins, which provide the glossy finish. +880 How did scientist come up with and prove carbon dating? 4808 https://www.reddit.com/r/askscience/comments/7kwkxk/how_did_scientist_come_up_with_and_prove_carbon/ 1513720383 7kwkxk Earth Sciences 2017-12-20 0:53:03 "Two chemists, Martin Kamen and Samuel Ruben, were looking into ways to essentially radio-tag carbon so they could track it performing various metabolic tasks in living animals. This is a fairly common technique to this day - I've used radio-tagged steroids, for instance, injected into living things to see where they ended up, since radioactive things are relatively easy to detect in very small quantities. Kamen and Ruben bombarded nitrogen with radiation and some of the atoms turned to radioactive forms of carbon. C-11 turns out to be not so useful as it has a half-life (the period it takes half of the atoms to decay into other stuff) of about 20 minutes. That's not long enough to study much of anything as it takes time to run experiments. C-14 now, that's a solid 5500 years or so, which is also not great studying processes in living things as it decays too slowly (in lab-time). + +Another chemist named Willard Libby realized that naturally produced C-14 in the atmosphere would only enter organisms while they were alive (all else equal, but that's another story). That sounds promising because it would essentially put a 'clock' on any suitable living thing, as, after they die, they stop picking up new C-14 and just cook off steadily. And a 5000 year half-life is pretty useful too, as lots of really interesting stuff happened with humans over the last 40-50,000 years (several half-lifes out). Or so we thought, as before C-14, we didn't have a very good idea how old most things really were. Sometimes we had written records and people had laboriously worked out things like tree-ring sequences, but every living thing has carbon in it so this could potentially work on virtually *anything*. + +Libby was right, and won a Nobel Prize in Chemistry in 1960. C-14 remains the gold standard for dating although debate continues about how far back it works, and how dates can end up looking 'too young' or 'too old' because of various things like contamination. + +EDIT: hey, thanks for the gold!" "So, as you may know, the number of protons in an atom determines what kind of element it is. In it's stable form, carbon has 6 protons and 6 neutrons, and is otherwise known as carbon 12. Nitrogen, the next element on the periodic table, is most stable with 7 protons and 7 neutrons, aka nitrogen 14. + +Sunlight in our atmosphere causes atomic particles, like neutrons, to be blasted around (I can explain this more if you'd like). When normal Nitrogen 14 in the atmosphere comes into contact with a free flying neutron, it causes that nitrogen atom to gain the neutron, but also to immediately lose a proton. Since the atom now has 6 protons, it is officially carbon, but since it also has 8 neutrons, it is an unstable (and radioactive) form of carbon, Carbon 14. Carbon 14 behaves just like regular carbon, but since it is radioactive, it slowly decays into stable Carbon 13. This decay can be detected using a Geiger counter and its relative abundance can be quite easily measured. + +Carbon 14 is generated in the atmosphere at a very constant rate, making it's concentration both in the air and inside every LIVING thing quite predictable (about 1 per trillion carbon atoms). However, when organisms die, they stop recycling carbon, so they no longer collect new Carbon 14. The Carbon 14 that they do have slowly decays, so the organism's concentration of the radioactive isotope is also slowly depleted. + +Depending on when an organism lived (whether it's a tree 50,000 years ago or a squirrel 30 years ago) it will have some amount of Carbon 14 remaining. As such, the ratio of carbon 14 to stable carbon atoms can give us a very accurate measure of how long ago this organism stopped taking in new carbon (died). This is the basis of carbon dating. + +TL;DR - carbon 14, a radioactive isotope of carbon, is generated at a constant rate in our atmosphere. Its concentration in the atmosphere is mirrored in all living organisms. When an organism dies, it's concentration of c14 slowly depletes. Depending on the ratio of remaining radioactive carbon to stable carbon, we can quite accurately estimate how long ago the organism lived. + +Edit: Arg, sorry. As a number of people have pointed out, I am wrong about how carbon 14 decays. One of the extra neutrons actually decays into a proton, returning the element to a stable nitrogen 14 atom (not carbon 13). Apologies. Carbon 13 is stable, but forms in a different manner." +1422 Why isn't serotonin able to cross the blood-brain barrier when molecules like psilocin and DMT can, even though they're almost exactly the same molecule? 4792 https://www.reddit.com/r/askscience/comments/ds5oa7/why_isnt_serotonin_able_to_cross_the_bloodbrain/ 1572988426 ds5oa7 Neuroscience 2019-11-06 0:13:46 "95% of the time, the answer to questions like ""Why can't X cross the blood brain barrier"" is polarity. + +​ + +In order for molecules to cross the blood brain barrier (BBB) the must be fat soluble, and fat soluble compounds are generally largely non-polar. DMT in a neutral pH is pretty non-polar. So it crosses the BBB with ease. Serotonin, on the other hand, is quite polar, because of it's amine group, and the hydroxyl group on the other end doesn't help either. + +​ + +Of course, when it comes to endogenous compounds (and yes, I know DMT is endogenous, but it's not endogenous like serotonin is) there are usually a plethora of enzymes sitting around ready to metabolise it. So serotonin in the blood is subjected to metabolism by monoamine oxidase in epithelial cells, as well as in astrocytes at the BBB, and to a lesser extent Aralkylamine N-acetyltransferase and Acetylserotonin O-methyltransferase. There are probably some other enzymes too that I don't know about. This is true for most neurotransmitters, dopamine, noradrenline etc." Trying to estimate polarity or how similar two molecules are by eye is very hard. As a chemist I can do it to a degree and I could see that serotonin and DMT would have different polarities but I would have to look up how much polarity is needed to cross the barrier. Part of the issue is how we draw structures with sticks and letters. If you could see a three dimensional structure it would give you an idea of how much an abstraction these pictures are. If you then layered a color gradient on the 3-D structure to show polarity it would make things much more clear that they are not in fact similar. +1252 What makes permanent and non-permanent markers different on a chemical level? 4786 https://www.reddit.com/r/askscience/comments/bc61ux/what_makes_permanent_and_nonpermanent_markers/ 1555021446 bc61ux Chemistry 2019-04-12 1:24:06 [deleted] Water soluble or not! An important distinction is the solvent in addition to the ink/dye. Permanent markers use inks that are not soluble in polar solvents like water, so it doesnt wash off with water. But those inks are usually still soluble in acetone or ethanol +407 If the universe is an hypertorus, is it possible that we receive the light from a star twice ? 4784 https://www.reddit.com/r/askscience/comments/4xdhi8/if_the_universe_is_an_hypertorus_is_it_possible/ 1471008164 4xdhi8 Physics 2016-08-12 16:22:44 Yep, if the universe is like that, then extremely distant things could be visible mulitple times. [Researchers have looked for evidence for evidence of that](http://klotza.blogspot.com/2016/01/the-simpson-hawking-donut-universe.html) in the cosmic microwave background and haven't found any, which can be used to constrain the size of the potential torus that the universe might be. "I think its worth pointing out that telescopes likely aren't powerful enough at the moment. + +Let's assume its true. The cube with re-spawn on the other side (basically star fox multiplayer). + +The first time the light from a star reaches you, it will have traveled simply the distance between you and the star. The 2nd time it passes you, it will have traveled the distance between you and the star PLUS the length of the universe. Since the 2nd is likely orders of magnitude larger, the lumonsity of the 2nd will be that much dimmer ie: likely on the order of a single photon per sq meter / year, or something absurd like that. + +The photons aren't parallel, but near it, so over very large distances they slowly spread. + +Also: + +[Olber's paradox](https://en.wikipedia.org/wiki/Olbers%27_paradox)" +541 "On a biomolecular level, what does it actually mean when someone has a ""good"" immune system instead of a ""bad"" one?" 4779 https://www.reddit.com/r/askscience/comments/5g3stv/on_a_biomolecular_level_what_does_it_actually/ 1480692238 5g3stv Human Body 2016-12-02 18:23:58 "Could be a mix of all of the above. + +The immune system is split into the innate and active/adaptive systems. The innate are, to use a video game analogy, all the non-specific ""passive"" defenses of the body. For example, inflammation, skin, and enzymes designed to digest viral-specific dsRNA are all innate portions of the immune system. Like passive systems in video games, the innate system is designed to slow down pathogens until the active system comes into play. + +The active system is the hunter-killer of the immune system. Immune cells are basically split into 3 important types: killer T cells, helper T cells, and B cells. Killer T cells recognize cells that are infected with viruses and destroy them. Helper T cells bind to ""trash collector"" cells that go aroud digesting cellular debris. B cells are recruited by helper T cells to produce antibodies that bind to the recognized pathogens and act as ""kill me now"" flags. + +The one flaw of the active system is that since each killer and helper T cells are specific to only one pathogen, it can take a very long time for a specific T cell to be able to detect and recognize the pathogen and create an immune response. + +People with stronger immune systems may have more immune cells, systems able to better move immune cells around, or may be just lucky (since the protein on T cells that recognize pathogens is randomly generated). + +This is a ridiculouslu simplified version. There are dozens of other nuances and steps in the immune system." "People here are giving vague overviews because immunology is complicated, so I'll just add a concrete example of something that is measurable that can result in better or worse immunity. And this is the MHC repertoire that you have, which is genetically encoded. MHCs are the molecules that present fragments of proteins (for example, from viruses infecting your cells) from cells in your body to immune cells for recognition. These vary widely from human to human, and you can have up to 6 different types for MHC class I, for example. Having a more diverse set of MHC molecules allows for presentation of a wider range of peptide fragments and therefore better immunity. This has been studied fairly extensively and is termed the ""MHC heterozygote advantage.""" +980 Is the Japanese surgical/dust mask trend actually helping lower the % of people getting sick over there? 4778 https://www.reddit.com/r/askscience/comments/810ppc/is_the_japanese_surgicaldust_mask_trend_actually/ 1519860624 810ppc Medicine 2018-03-01 2:30:24 "Japanese physician, my time to shine! while it is part of many guidelines (including in america, CDC - https://www.cdc.gov/flu/professionals/infectioncontrol/maskguidance.htm ) that perhaps there may be some benefit, there are some considerations: + +a) a mask is basically permeable within 15 minutes of wearing it. Multiple studies have shown that viruses and bacteria in the moisture of our breath will penetrate a mask once it becomes damp. + +> A fresh face mask almost completely prevented bacterial contamination of an agar plate 30 cms from the mouth, but after 15 minutes there was a measurable increase in the level of contamination + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4920922/ - ((note: this is bacterial! viruses are 100X smaller!!)) + +b) barrier protection like a mask will reduce droplets so if you are actively coughing, you are preventing the creation of large fomite (areas that are contaminated), but not preventing it altogether + +c) viruses and other airborne particles are much smaller than a surgical mask, and the moisture of the air we breathe can easily get around a mask. Because masks aren't air-tight, honestly, the scientific plausibility that masks will significantly reduce inhaled viral particles is quite low. + +d) most of the studies about masks and *preventing infection* are pretty evenly split positive/negative + +**So taking this all in conclusion:** + +1) **wash your hands frequently.** this remains the best way to prevent the spread of infection. if you need to cough, cover your mouth with your elbow (best). DO NOT RELY ON A MASK to block a cough (I am looking at you, japan). + +2) **If you are sick, stay at home.** (I'm looking at you, modern world) + +3) if you change your mask frequently, you are likely having a minor protective effect for yourself and others from the spread of some germs, in the first 15 minutes of wearing a mask. But honestly, compared to #1 and #2, this is pretty minor. Some studies show a benefit and others show no benefit, and the plausibility that significant reduction is possible is low based upon the physical properties of a surgical mask and the pathogens. To no surprise, the ""reduction of flu spread"" by good practice (mask and hand hygeine) is likely largely attributed to the hand hygeine portion, not the mask portion. + +**Edit:** wow I got flooded with responses! I tried to reply to representative responses and I'm sorry I can't answer them all. + +**For all of the questions about surgeons and surgical masks, please see this review:** + +https://www.ncbi.nlm.nih.gov/pubmed/16295987 + +In conclusion, when studies have tried to randomized using masks by the surgical team vs. not, there is no detectable difference for infection rates. Again, the plausibility of a disposable non-respirator mask stopping virus and bacteria in a room is very low." "So I remember one of my professors once mentioning that the masks themselves don't actually do much to prevent against respiratory disease directly. It will probably help reduce the amount of aerosols in the air, but I'd be willing to bet the most useful function of it is it'll prevent you from actually touching your mouth or other membranes with unwashed hands. I'm sure this also highly depends on the mask and doesn't apply to proper, individually fitted masks with respirators like you need for high danger pathogen work. + +[I also just quickly googled the topic to see if I could find anything, and this NPR article might be relevant to you OP.](https://www.npr.org/sections/goatsandsoda/2015/06/22/416466284/will-a-surgical-mask-keep-you-safe-in-a-viral-outbreak)" +1084 Does radioactive decay reduce an object's mass? 4773 https://www.reddit.com/r/askscience/comments/8mrrfh/does_radioactive_decay_reduce_an_objects_mass/ 1527528351 8mrrfh 2018-05-28 20:25:51 "Yes, this was actually what Albert Einstein predicted in his 1905 paper. + +>It is not impossible that with bodies whose energy-content is variable to a +high degree (e.g. with radium salts) the theory may be successfully put to the +test. + +There has been for example [this experiment](https://jila.colorado.edu/thompson/sites/default/files/pdf/4381096a.pdf) measuring the change in mass of isotopes as they decay and finding it equivalent to the energy released." "When you say ""Gamma decay results in a photon which is massless"". I understand photons being massless, but they are energy, or carry energy. With energy and mass being equivalent, do they not technically carry some transferable mass?I" +542 How accepted is I. Pigarev's theory that sleep is used by the brain to process input from internal organs? 4769 https://www.reddit.com/r/askscience/comments/5e4qmp/how_accepted_is_i_pigarevs_theory_that_sleep_is/ 1479744026 5e4qmp Neuroscience 2016-11-21 19:00:26 "This is a theory I hadn't heard of before, and it very well could be a partial function of sleep, but I doubt it's the full story. Current theory believes sleep is necessary for consolidation of memory, particularly alleviating metabolic burden produced during awake activity. This is an interesting paper that might be of interest to you: Hidden from students: +Xie L., Kang H. et al (2013) Sleep Drives Metabolite Clearance from the Adult Brain" "I would say that this is not a commonly accepted theory in western neuroscience. As stated above, the current most accepted theory is that sleep above all aids in memory consolidation, metabolic rest, etc. + +To say that the brain ""switches"" from processing external stimuli during the day to internal stimuli when sleeping does not fit well with our current understanding of the nervous system because we are, in fact, constantly processing internal stimuli during the day. Ever felt hungry? Ever felt thirsty? These are examples where internal conditions (e.g. Dehydration) are processed by various parts of the brain (think hypothalamus the internal ""regulator"" among other things) constantly during the day. + +On top of this, we DO process external stimuli during sleep. A prime examples of this are experiments that test the threshold for waking someone up from sleep. When presented with names when sleeping, studies show that a subject will have a lower awakening threshold when they hear relevant words (ex. A name that is relevant to them vs a name that is not). This shows that there is external stimuli processing during sleep. + +TL;DR: This is not a commonly accepted theory for sleep. There is no ""switch"", we process both internal and external stimuli constantly throughout the day/night. " +797 What impact does a tsunami have on ships at sea? 4767 https://www.reddit.com/r/askscience/comments/69emit/what_impact_does_a_tsunami_have_on_ships_at_sea/ 1493990426 69emit Earth Sciences 2017-05-05 16:20:26 [deleted] "One way to think about it is that a typical wave in the ocean is generated by wind and only effects the top few meters. That can move along with the water underneath undisturbed until it hits land. Once the depth on shore is less than the wave it builds up and breaks (oversimplified here but stay with me). + +A tsunami involves the bottom shifting so you get the entire depth of the ocean to shift up say one meter. + +Big deal, a one meter wave in the mid ocean. The problem is that this wave will not stay put and now will travel at hundreds of kms per hour. Also it is not really a wave but a whole block of water from the surface to the bottom (say 2500 m) that was moved. + +At smaller depths, this becomes a problem as the water wants to be 2500 m deep. All the displacement energy of the water at full depth must be absorbed so we end up with a much higher, wider wave in shallow water. " +1085 Is the human body affected by the changing seasons? 4766 https://www.reddit.com/r/askscience/comments/8ieub9/is_the_human_body_affected_by_the_changing_seasons/ 1525958616 8ieub9 Human Body 2018-05-10 16:23:36 "Yes, assuming you actually go outside. + +Your temperature preference should move with temperatures outside as your body's homeostasis primes itself for certain conditions. A good example is if you take someone from Michigan in the dead of winter and drop them in SC, their body is already primed to generate more heat than is necessary for SC weather. + +The other big noted effect is the rise in depression and poor mood due to lack of Vitamin D production which is driven by sunlight exposure." Up until very recently, our bodies were very affected seasonally due to food availability. This affected every aspect of our ancestors' lives, including a sort of mating season (or a higher likelihood of copulation/shagging) when food was more available in the Spring. It's not just a factor of food there or not for energy reasons but also which food types. Science today is finding increasing amounts of research on how different food types affect our behaviour through different bacteria entering and interacting within our gut microbiome. Potentially this could mean that our behaviours may be influenced by the seasons from which foods were available to eat. +543 "Light is deflected by gravity fields. Can we fire a laser around the sun and get ""hit in the back"" by it?" 4765 https://www.reddit.com/r/askscience/comments/5d8chu/light_is_deflected_by_gravity_fields_can_we_fire/ 1479288373 5d8chu Physics 2016-11-16 12:26:13 "Nope, the Sun is not heavy enough to deflect something moving as fast as light that much. + +You can however do this with something heavier, a black hole. If you carefully put your light the correct distance away you can get it to orbit circularly around a black hole. This distance characterises something called [a photon sphere](https://en.wikipedia.org/wiki/Photon_sphere) and is 50% further away than the event horizon for a non rotating black hole. + +However, this orbit is extremely unstable, the slightest perturbation will cause the light to either spiral in and enter the black hole or spiral out and eventually escape." "For this to happen, the photon would have to be in a stable orbit at the speed of light. The points in a gravity well where this is possible form the [photon sphere](https://en.wikipedia.org/wiki/Photon_sphere), which is 1.5 times the Schwarzschild radius. + +In other words, it only exists around black holes and things that are very nearly black holes (such that their radius is less than 1.5 times their Schwarzschild radius), which I guess might be some neutron stars. + +By comparison, the sun's Schwarzschild radius is 3km, so you'd have to compress it a radius under 4.5km for a photon sphere to exist." +1086 What are the limits of gravitational slingshot acceleration? 4765 https://www.reddit.com/r/askscience/comments/918smt/what_are_the_limits_of_gravitational_slingshot/ 1532365150 918smt 2018-07-23 19:59:10 "TL;DR: The faster you move, the closer you need to get to the celestial body you want to slingshot around. At some point, you burn up in the atmosphere, crash into the surface or get ripped apart by gravitational force differences. + +When you do a gravitational slingshot, you're essentially ""bouncing"" on the planet, doing a 180 degree turn around the celestial body. From the celestial body's point of view, you approach it at the same speed and once the slingshot is complete you leave with the same speed. In other words, we can simply see it as a bounce with a restition coefficient of 1 (no energy lost) on the celestial body. + +The key to a successful gravitational slingshot is to have the celestial body approach towards you. Let's say you have a planet hurtling towards you at 10km/sec, while you fly towards it at 2km/sec. From the planet's perspective, you are approaching the planet at 10+2=12km/sec, you'll loop around the planet and then go back in the direction you came from at 12km/sec. However, from our perspective, we approach the planet at 2km/sec, get flung around it and then fly away in the same direction as the planet at 22km/sec (very confused about the exact speed). + +In essence, you're stealing some of the kinetic energy of the celestial body you slingshot around, and the effectiveness of this is solely dependent on how fast the celestial body is moving, so there's no theoretical maximum speed apart from the speed of light (which you can always keep getting closer and closer to as your kinetic energy increases). + +However, there are practical problems that will either reduce the efficiency and practicality of a slingshot, or even make it downright impossible. The faster you go, the stronger gravity needs to be to be able to sling you around the celestial body. The only way to increase the force of gravity from the body is to get closer to it. This means that you get quite a few problems. If you're trying to sling around a planet or moon, you could start experiencing drag from the atmosphere, which would not only slow you down a lot but also potentially burn you up. If the planet/moon has a solid surface, you may not even be able to get close enough to the planet without crashing into it. Similarly, getting too close to a star has some obvious drawbacks. + +A black hole is therefore optimal for a slingshot operation as it is neither warm nor has any significant atmosphere nor surface. You can always get a little bit closer to the event horizon to allow you to turn around it quicker, although at some point you'll get so close to the black hole that your ship is torn apart due to the different parts of the ship experiencing so different gravitational forces (the parts closest to the hole turns inwards, while the farthest parts don't turn enough to keep up with the center of the ship)." "Acceleration from a gravitational slingshot is limited by a few factors: how fast is the assisting body moving, how strong is its gravity, and how close can you get without impacting its surface/burning up in its atmosphere? For an optimum gravitational slingshot, you want to use a very massive body with a small radius in an extremely fast orbit. Your best bet would be to find a binary system of two neutron stars or black holes orbiting one another at relativistic speeds. Under the right circumstances, your spacecraft could easily accelerate to a significant fraction of the speed of light. + +It's also unnecessary to use an unmanned spaceship for this trip. The human body is only damaged when different body parts experience different amounts of acceleration. Since the gravitational field of most astronomical bodies is practically uniform on the length scale of the human body, there is no risk of bodily harm. A passenger on the slingshot voyage would feel like they were in free fall, just like a person orbiting the Earth or floating through interstellar space. + +The exception to this would be if you experience significant tidal forces. For example, if you get really close to a black hole, the strength of the gravitational field experienced by your feet will be greater than that experienced by your head (or vice versa depending on your orientation), and you run the risk of death by spaghettification. However, for this gravitational slingshot experiment, you could always just use a more massive black hole (which has a more uniform gravitational field) to avoid this risk." +1253 How do animals with fur and researchers in the arctic get vitamin D? 4759 https://www.reddit.com/r/askscience/comments/ba4l3t/how_do_animals_with_fur_and_researchers_in_the/ 1554559319 ba4l3t 2019-04-06 17:01:59 "Animals with fur can still make Vitamin D via UV dependent pathways, it's just less efficient because the fur blocks some of the sunlight. Fish are excellent dietary sources of Vitamin D and much of the non-human arctic wildlife eats fish or other aquatic wildlife that is obtaining Vitamin D from the aquatic food chain. + +As for the humans in arctic regions, Vitamin D supplementation and dietary sources rich in Vitamin D are essential during the periods of the year where there is a little to no UV rays. + +I know in certain regions of Alaska that have prolonged periods of darkness, tanning beds are popular in the winter." "Vitamin D is needed by animals, and almost all of them can synthesise it trivially via several pathways, all of which are photo-mediated: Biology seems to only be able to make vitamin D precursors using photochemistry, which plankton has been using for 500 million years (the ultimate source of it in the marine food chain). Vitamin D as we know it is really a pro-vitamin, the cholecalciferol is itself inert. 7-dehydrocholesterol in the skin is photodegraded to cholecalciferol. The liver converts it to 25-hydroxycalciferol, which is hydroxylated to calcitriol in the kidneys, this is the active form of vitamin D. + +Dogs and cats can't use this mechanism at all, and rely on dietary sources. Ruminants get most of theirs from their skin ( [https://www.ncbi.nlm.nih.gov/pubmed/20412916](https://www.ncbi.nlm.nih.gov/pubmed/20412916) ) even if they're hair covered. Sheep are industrially used to make vitamin D, from lanolin (wool grease), which is rich in 7-dehydrocholesterol. It is not well conserved in terrestrial animals, but the liver and kidney metabolic pathways are, indicating that diet is an important source of vitamin D precursors among terrestrial animals. + +​ + +(This, BTW, is an excellent question, and the science here seems to require more research as we don't seem to have studied many animal groups on this topic)" +881 "What are the hair follicles doing differently in humans with different hair types (straight vs wavy vs curly vs frizzy etc., and also color differences) at the point where the hair gets ""assembled"" by the follicle?" 4758 https://www.reddit.com/r/askscience/comments/787w7t/what_are_the_hair_follicles_doing_differently_in/ 1508767252 787w7t Biology 2017-10-23 17:00:52 "My organic chemistry class taught me that curly hair was largely due to disulfide bonds between cysteines in keratin proteins on the hair shaft, and straightening or chemically relaxing the hair breaks these bonds. + +Edit: More info here: https://helix.northwestern.edu/blog/2014/05/science-curls" As a forensic scientist, I can tell you that the reason hair is either wavy/curly/straight has to do with the shape of the hair. Straight hair is round, but wavy/curly hair is oval shaped. The curlier the flatter. Also, you can check out the pigmentation as little nodules within the hair under a microscope. Different amounts of pigmentation cause lighter/darker hair. Also fun fact, you can easily distinguish hair of different animals because it forms differently. For example, cat hair looks kind of like a stack of crowns while deer hair is straight with big ole vacuoles in it +882 How do audio books, printed books, and videos differ in terms of how our brains retain and process the information? 4755 https://www.reddit.com/r/askscience/comments/77otu6/how_do_audio_books_printed_books_and_videos/ 1508531295 77otu6 Neuroscience 2017-10-20 23:28:15 "I know video and books are definitely different. but paper books and audio books are processed in the mind almost identically. so when you listen to an audio book it is nearly as if not better than reading the book and handled almost identically in the mind. + +Better with a particularly good reader as they can help you engage better. + +it seems reading words and listening to words uses the same ""portion"" of the brain. + +http://nymag.com/scienceofus/2016/08/listening-to-a-book-instead-of-reading-isnt-cheating.html + +there is a forbes article back to 2011 saying the same thing but I can't read it any longer (ad block blocker)" "The Marines/Navy did a study in the 60s on how people learn the best. + +The study was done over 10 years. + +What they found is some people learn better by listening, some by reading, and some by doing. + +And you even the people who are best at one form of learning can have it reinforced by another. + +So the military especially in basic training try to teach everything 3 times in 3 ways. You get the information told to you, you hear others being corrected and you yourself being corrected... as well as responding or repeating. You do it hands on in many different ways and under varying levels of stress. The third method you get a book of knowledge and they have you study it in any down time. + +Now another thing they don’t do that was found in the 90s + +Record yourself reading your notes. They need to be recorded in 15 seconds or less snippets. Making each an audio file of its own. Play it back to yourself on repeat and shuffle. Your brain interprets your voice as your inner monologue and builds pathways based on what you hear. If data is only memorized in one sequence then you remember it like that. But if it’s memorized as short bits of data that’s how you remember it. So you end up with a better recall because the information isn’t dependent on something else, and the pathways get linked all over the place to different bits of similar data. + +You read it multiple times, see it, read it out loud, and hear it. Each time your brain makes a link among the data it links everything that it associates with that information." +1694 Why do the two COVID-19 vaccine candidates require different storage conditions? 4754 https://www.reddit.com/r/askscience/comments/jv6vud/why_do_the_two_covid19_vaccine_candidates_require/ 1605533981 jv6vud COVID-19 2020-11-16 16:39:41 "Two things. First, Pfizer's has not been *tested* to the same temperatures that Moderna's has. It is possible, they are testing now, that it will have the same storage requirements. + +https://www.newscientist.com/article/2259821-pfizer-covid-19-vaccine-may-not-need-to-be-kept-at-70c-after-all/ + +Second, the New York Times article from today states that if there is a difference, it will be based on how each uses ""fat"" to stabilize the vaccine. + +""An additional concern is that both vaccines must be stored and transported at low temperatures — minus 4 degrees Fahrenheit for Moderna, and minus 94 Fahrenheit for Pfizer — which could complicate their distribution, particularly to low-income areas in hot climates. Although both vaccines are made of mRNA, their temperature requirements differ because they use different, proprietary formulations of fat to encase and protect the mRNA, Ray Jordan, a Moderna spokesman, said.""" "It’s hard to go into specifics without knowing both vaccines inside out, but in general: + +mRNA is relatively unstable and easily broken down, as it should be in the body. ~~On average, natural mRNA’s produced by your own cells have a half life of less than 5 minutes.~~ 5 minutes is the half life of mRNA in yeasts, human mRNA seems to be quite a bit more stable. Thanks for the correction u/tulipseamstress and u/nunmaster for being critical. + +An obvious way to increase the half-life of mRNA is by freezing it to extremely low temperatures, as this lowers reaction rates of all kinds, including breakdown rates. + +However, you can also change the molecular structure of the mRNA to increase its stability and make it resist breakdown by enzymes. This adds complexity to the design stage and potentially during the production stage, but would make it easier to distribute. + +So without any insider knowledge on either vaccine, my best guess would be that the Moderna vaccine has more stability designed into it, whilst the Pfizer vaccine was easier to design and produce." +1087 in 2012, pestalotiopsis microspora was discovered to be able to live entirely on polyurethane. Has anything developed since then for practical application as a biodegrader? 4751 https://www.reddit.com/r/askscience/comments/99eup0/in_2012_pestalotiopsis_microspora_was_discovered/ 1534955685 99eup0 2018-08-22 19:34:45 "I can imagine that many labs are working to culture and understand this microbe, but it takes time to turn something like this into a technology, especially given the incentive limitations mentioned by others here. We analyzed the paper you're referencing in our lab group and came to the conclusion that, at present, it's unlikely that you could do anything commercially viable with this bug. I mean, even if you could get it to eat all of the plastic in the oceans (for example) in a reasonable timeframe (you can't, because it grows really slowly), what you'd effectively be doing is releasing a bunch of CO2 that's currently locked away into the atmosphere. Would you rather have that carbon as plastic in the ocean, or as a greenhouse gas in the atmosphere? + +The power of this paper is actually in the idea that bugs that eat plastics are possible, not that this specific bug exists. Ultimately, if you could engineer a strain to eat plastic snd transform it into some other consumer good, that'd be great. This bug gives us a model to imagine how we might do that in the future. " With the exception of plastics like PTFE (and other fluorinated plastics) and PVC (and other chlorinated plastics) it's actually much much better to pyrolyse all of it and use the pyrolytic products as fuel, and either bury the left over ashes or mix them into concrete. Biodegradation is really slow and you only get CO2 as a byproduct, so it's pretty much worthless for managing plastic waste, which can be quite valuable. For example, the ABS in the parts of your inkjet printer can be ground down, pelletized, extruded into filament and made into rocket fuel grains. +544 Is there a limit to expansion of the International Space Station? 4748 https://www.reddit.com/r/askscience/comments/58yavp/is_there_a_limit_to_expansion_of_the/ 1477224868 58yavp Engineering 2016-10-23 15:14:28 "Although spacecraft could be almost arbitrarily large, the ISS is also part aircraft, and limitations apply there. + +The ISS operates at an altitude where there is still a thin atmosphere to contend with, and the main cause of orbital decay for the ISS is atmospheric drag. To counter this, the ISS enters [Night Glider Mode](https://en.wikipedia.org/wiki/Night_Glider_mode), reorienting its solar arrays to minimize atmospheric drag when the ISS is shaded from the Sun by the Earth. + +So the limit would be the point where atmospheric drag increases to a point where the orbital decay it causes can't be overcome by [reboost](https://en.wikipedia.org/wiki/Reboost) from visiting (propelled) spacecraft." "Theoretically, the ISS could be expanded to a rather ridiculous size and still function. However, the larger and more complex the station gets, the less safe it will be. Every extra airlock connection, extra electrical system and extra pressurised volume adds another potential point of failure. + +You would need to add reinforcing structures if its dimensions are stretched significantly, to brace against the increased gravity-gradient torques experienced at the extremities (technically each end of the station is in a slightly different orbit, which puts constant stress on its trusses). Depending on how extensively extra modules are daisy-chained together, further reinforcing would be needed to take stress off the inter-module connections. + +The solar truss would have to be extended - currently the station's peak output is just 200kW. + +Extra life support systems would have to be added to handle the greater volume, including larger water tanks. + +---- + +Originally the ISS was going to be a much bigger station, designed as part of the [Space Exploration Initiative](https://en.wikipedia.org/wiki/Space_Exploration_Initiative) in the '80s. The plans for then-[""Space Station Freedom""](https://en.wikipedia.org/wiki/Space_Station_Freedom) are pretty radical: hangars, rotating trusses, and a shipyard for orbital assembly of interplanetary spacecraft!" +1799 Does pregnancy really last a set amount of time? For humans it's 9 months, but how much leeway is there? Does nutrition, lifestyle and environment not have influence on the duration of pregnancy? 4737 https://www.reddit.com/r/askscience/comments/lsvs1j/does_pregnancy_really_last_a_set_amount_of_time/ 1614338723 lsvs1j Biology 2021-02-26 14:25:23 "There is a little leeway, but it's really constrained by biology. If the baby comes out too early, the lungs aren't developed enough to oxygenate their blood. They are often weak and can't latch onto their mom's breast and suck. They don't have much body fat, they have higher surface-area to mass ratio and have a hard time staying warm enough. + +If the baby is born too late, the placenta starts to degrade, decreasing the baby's supply of nutrients and oxygen. The baby is also more likely to pass its first poo (meconium) into the amniotic fluid and aspirate it, causing huge pulmonary problems. There's also the problem of the baby simply getting too big to pass through the pelvis. And mom's getting gestational diabetes and high blood pressure. +C-sections haven't been around nearly long enough to remove those selective pressures. + +Before modern obstetrics, death rates for human moms and babies was astonishingly + high compared to other primates, due in part to our pelvis being tipped for walking upright. + +We also have huge brains vs other primates. Humans are the result of an evolutionary balance between hips that can walk upright and intelligence. We are born relatively immature so our skulls can pass through our mothers' pelvises and finish maturing outside the womb. Intelligence is such an asset that it's worth having helpless, weak babies that need ~3 years to walk, talk and kind of fend for themselves. + +Natural selection narrowed down the length of the perfect pregnancy to 38-41 weeks. + +The window is actually probably smaller than 3 weeks, because we don't usually know the exact date of ovulation. We estimate it on last menstrual cycle, which can vary a lot." "The first figure on [this page](https://towardsdatascience.com/are-first-babies-more-likely-to-be-late-1b099b5796b6) shows the distribution of pregnancy durations in weeks. It does exclude C-sections, but it's not clear if it also excludes induced labor. The effect shouldn't be too huge even if they are included, though. It's a pretty tight distribution around 8.5-9.5 months. + +It's too bad the figure doesn't include the full long and short tails of the distribution, but it's safe to assume that on the short end, the distribution decreases more or less smoothly until about 25 weeks. Babies born earlier than that are very unlikely to survive. At the long end, the distribution has already dropped almost to 0 in the figure at 44 weeks (note that the 0 line is slightly above the X axis). Durations longer than 44-45 weeks are definitely extremely uncommon even without induced labor. + +Keep in mind that these data are from America, which like other wealthy countries probably has significantly fewer early births than the global average. Pretty much all types of stress have been shown to increase the probability of early birth if you have a large enough sample, including physiological stresses like nutrition as well as psychological stress. Other than reduced stress and some hormonal issues related to development, I'm not aware of any factors that increase the duration of pregnancy, though. That means the actual global distribution of durations should be somewhat more skewed towards early births than these data from America. It still won't go below around 23-25 weeks and in fact babies born very early are a lot less likely to survive in less wealthy countries." +883 What is happening when a computer generates a random number? Are all RNG programs created equally? What makes an RNG better or worse? 4725 https://www.reddit.com/r/askscience/comments/781ujb/what_is_happening_when_a_computer_generates_a/ 1508695744 781ujb Computing 2017-10-22 21:09:04 " RNGs use some algorithm to decide on a number which is based on the some previous number (or more over a large set of previous numbers) this is why all RNGs need a seed to get started, they need some way to generate the first letter. How you get that seed is a bit of a different discussion. + +Now not all RNGs are equal, there a few ways to make how random it is, one is to use a chi-squared method to see if the distribution is random (ie normally you want a uniform distribution). You can also plot the current number as a function of previous numbers (known as a k-space plot) the higher dimension you can graph in without some pattern emerging the better. Finally you can look at the period of the number generator, the number of numbers you must generate to begin seeing a pattern emerge. For a very good generator like the mersenne twister method the period is 2^(19937) -1 numbers (so you should never see the same number pattern appear for practically all situations) + +Edit: spelling " "Some great answers here talking about what makes a good pseudo-RNG. I'm going to tell you about a bad one. + +In Pokémon Red, Blue, and Yellow, when the player encounters a wild Pokémon, the species is determined by comparing a random value between 0 and 255 to a lookup table for the current location. For example, the game might make a Rattata appear if the number in question is 0 to 127, Nidoran♀ if the number is 128 to 216, Spearow if the number is 217 to 242, and Nidoran♂ if the number is from 243 to 255. + +The Gameboy has a weak processor and it runs games at 60 frames per second. Rather than running a random number generator 60 times per second while the player is walking through areas where Pokémon are found, the ""random number"" predictably increases by one 30 times per second. This might have been a reasonable solution for some applications, but when it comes to generating random Pokémon encounters, it has a problem: The RNG loops every 8.53 seconds, and in some circumstances, the length of a battle can be very close to that time. This means that a player can have a series of encounters with the same Pokémon because the RNG is returning a similar result every time. " +305 If I have a column of water 100' tall and 2 meters in diameter and I scuba dive to the bottom of that, is the pressure the same as if I were 100' down in the ocean? 4708 https://www.reddit.com/r/askscience/comments/4dblio/if_i_have_a_column_of_water_100_tall_and_2_meters/ 1459784264 4dblio Physics 2016-04-04 18:37:44 "The short answer is yes. + +The simplest expression for the static pressure of a fluid, called the [hydrostatic pressure](https://en.wikipedia.org/wiki/Hydrostatics#Hydrostatic_pressure) (P), is: + +P = phg, + +where p is the density, and h is the height and g is the gravity of Earth. In other words, to a great approximation, to figure out the pressure at the bottom of a body of water, all you have to know is the height and density of the *column* of water above it. The reason is that the static pressure is caused by the weight of all the water directly above it. As a result, you don't have to worry about the total amount of water in the body, nor even the shape of the container, as summarized [in this neat infogram](http://i.imgur.com/SZpcw8S.gif). + +Edit: Just to be explicit about why this answer is approximate, there are two key simplifications that I made: 1) I ignored the position of the column with respect to the sea level (which affects how much air sits on top of the water and adds to the total pressure), 2) I assumed the column was wide enough that you could ignore [edge effects such as capillary action](http://i.imgur.com/CLbYUeM.jpg)." To add something that was bugging me: water pressure doesn't double every so-and-so many meters, that would lead to insane pressures really quickly. Instead, you just add one atm in pressure for every ~10 meters. It's adding, not multiplying. Since your calculation was correct, I'm assuming that you meant the right thing, but I couldn't just leave that alone. Sorry :) +306 "Why does a hair come back if I pull it out by the root? What's causing my body to say, ""Oh, I remember there used to be a hair there, better regrow one.""" 4704 https://www.reddit.com/r/askscience/comments/44p6pg/why_does_a_hair_come_back_if_i_pull_it_out_by_the/ 1454903472 44p6pg Human Body 2016-02-08 6:51:12 "Hair is not like a plant, so the concept of what you might think a root is doesn't apply to hair. + +Hair grows out of a special hole in the skin called a follicle. At the bottom that hole, there is a device called a papilla which is responsible for generating hair. The papilla usually remains intact, or will heal, when you pull out the hair. So you continue generating hair as normal, it just takes extra time for the new shaft to get long enough to reach the surface of the skin." "Hair doesn't just sprout at random locations on your skin, it grows from a specialized organ called a [hair follicle](https://upload.wikimedia.org/wikipedia/commons/4/4d/Hair_follicle-en.svg). When you pluck a hair, the follicle is still in place and starts making a new one. + +**edit** Since this turned out to be a popular question, here is a little more detail on that process. There is a [bulge](http://www.nature.com/nbt/journal/v22/n4/fig_tab/nbt0404-393_F1.html) on the side of the follicle that contains the stem cells for the organ. As long as those stem cells survive, they can [regenerate the rest of the follicle as well as the skin nearby](http://www.nature.com/nbt/journal/v22/n4/full/nbt0404-393.html)." +1365 How does seedless produce get planted and reproduced? 4697 https://www.reddit.com/r/askscience/comments/ciewxz/how_does_seedless_produce_get_planted_and/ 1564214771 ciewxz 2019-07-27 11:06:11 "All Bramley apple trees are made from cuttings from one tree. If you were to take an apple seed and plant it it is highly unlikely that the fruit would taste nice. Which is why the original tree is so special because that is exactly how it came into existence in 1809. + +Most apple trees are grafted onto the root system of smaller trees to make harvesting the apples easier. And you can even get a combination of varieties grafted onto the same tree. + +The original tree is has a fungal infection and due to his historical and scientific importance attempts are being made to save it. You can read more [here.](https://www.bbc.co.uk/news/uk-england-nottinghamshire-44041617)" Some “seedless” varieties of fruits actually have seeds, they are just so small we don’t notice them when eating the fruit. If the fruit is left to continue growing past the point of being edible (or at least desirable looking) the seed develops to normal size and can be used to grow new plants. +202 Do sound canceling headphones function as hearing protection in extremely loud environments, such as near jet engines? If not, does the ambient noise 'stack' with the sound cancellation wave and cause more ear damage? 4689 https://www.reddit.com/r/askscience/comments/3y3fqw/do_sound_canceling_headphones_function_as_hearing/ 1450975442 3y3fqw Physics 2015-12-24 19:44:02 This post has been locked due to the excessive number of anecdotes being posted. [deleted] +798 In US states with deregulated electricity markets, is there any meaningful market impact when consumers choose to purchase electricity from 100% renewable energy suppliers? 4684 https://www.reddit.com/r/askscience/comments/6as6i2/in_us_states_with_deregulated_electricity_markets/ 1494604856 6as6i2 Economics 2017-05-12 19:00:56 "I work for one of the largest energy suppliers across NA. The impact is that once you retire that REC it cannot be sold or traded in the future. This is a net positive. The extent to which it is positive depends on future policy and the overall demand for RECs in the market. + +Net net, it is a good thing to do as a consumer. +" "The key term there was ""significant"". Purchase and use of a REC directly relates to new installed renewable power. However when comparing the use of individual, voluntary purchasers compared to organizations who are motivated by legislation, marketing, world citizenry, etc, we are talking about insignificant amounts." +665 Is there any culture (current or past) that doesn't honor their dead? 4680 https://www.reddit.com/r/askscience/comments/5wtdi2/is_there_any_culture_current_or_past_that_doesnt/ 1488345529 5wtdi2 Anthropology 2017-03-01 8:18:49 It doesn't answer your question as you're looking for exceptions, but ceremonial burial has been found as far back as Neanderthals nearly 300,000 years ago. The difficulty with your question is that it's much easier to find bodies that were buried in a particular way or with some sort of ceremony or meaning because those civilizations or pre-civilizations that *didn't* perform some sort of special funerary rites would have left very little evidence that they *didn't* do anything special with their dead. [deleted] +1423 "AskScience AMA Series: Happy World Octopus Day! I'm a marine biologist who raised a day octopus in my home for a PBS Nature documentary called ""Octopus: Making Contact."" Ask me anything!" 4671 https://www.reddit.com/r/askscience/comments/deydc9/askscience_ama_series_happy_world_octopus_day_im/ 1570532453 deydc9 2019-10-08 14:00:53 "As far as I understand with regard to animal intelligence, certain species of gorillas have been taught sign languages, and dogs can understand vocal commands such as ""sit"", recognise their own name, or even know that pointing is indicating a direction. + +How much communication is possible with an octopus? Can they learn what is meant by certain human body languages/expressions/sounds? Do they have the capacity to learn how to communicate certain things to us, and how would they go about this? For example, in the way a dog can be trained to communicate it wants to go out." I know that octopuses live relatively short lives, but are highly intelligent. At what age do they develop an “adult” level of intelligence? Do they go through recognizable cognitive development stages analogous to human cognitive development? Do they keep getting “smarter” or do they plateau? +203 If I went back 100,000 years and mated with a human, would we produce any offspring? How far would I need to go back before I found an ancestor that is incompatible with modern humans? 4660 https://www.reddit.com/r/askscience/comments/3wikt5/if_i_went_back_100000_years_and_mated_with_a/ 1449929045 3wikt5 Biology 2015-12-12 17:04:05 "The truth is that we really don't know. Actually believe it or not we aren't *completely* certain that humans and chimpanzees can't still interbreed. Other animals that are separated by similar evolutionary time and with more divergent chromosome structure can make (usually infertile) offspring. Just good luck getting past the ethics board for that study. + +Edit: +Thanks for all the interest in my post. For all those mentioning the Russian studies early in the 20th century, they used Orangutans which are substantially more distantly related than chimps, so they prove nothing. + +I had never heard of Chimps being used as sex slaves. If this does indeed happen then it makes it much less likely that a hybrid is biochemically possible, though it might still be depending on what the barrier is. For example it might be an inability of the sperm to penetrate the egg, and it might work with the genders reversed. If zygotes are being formed and simply dying early in cell division than there is likely a fundamental genetic issue. " "Interesting question. The most precise answer is, we're not really sure. + +100000 years ago, you would have been mating with a modern human. At least there would be so little genetic difference that your mate would look the same, have functionally compatible DNA, and could even learn to communicate with you using your native language. + +200000 years ago, you could have been meeting with homo neatherthalensis. We know this occurred, and you probably still have some of their DNA in you. We're not sure if you could have communicated, at least on a modern language level, but your potential mate's brain size and throat bone structure indicates that you could have at least dated minimally. + +1 million years ago, you could have tried mating with Homo erectus. From the neck down you couldn't tell whether or not your mate was a modern human, but I wouldn't recommend kissing that small head with sharp teeth. Chances are that you could produce a viable offspring, the compatible DNA would make a mosaic of traits that would primarily affect the head and brain. You potentially could produce a super smart Homo erectus, or a much less than normal intelligence modern human. + +2 million years ago, you would be attempting to woo Homo ergaster or habilis. Unless you really like a hairy mate, you'll have a hard time finding anyone attractive by modern standards. This is also the point of wild speculation, there's a chance you could produce a viable offspring, but you would probably run into several genetic stops that would prevent the fetus from coming to term. If you could pull it off, I would assume the child would be like a mule, sterile. + +3 million years ago, you would be meeting Australopithecus africanus. At this point I'm going to say that you're not going to be able to produce a viable offspring, in fact I'd be impressed if you could even mate without having your head torn off. Your partner would be much smaller, but have a lot more muscle power, would also be far more violent than you're used to from a modern human. + +Of course all this is said with the knowledge that at one point, well a million years, what became the human species interbreed with what later became chimpanzees. That was a long time ago though." +666 Does reading fiction increase empathy, or are empathic people more likely to read fiction? 4659 https://www.reddit.com/r/askscience/comments/65idus/does_reading_fiction_increase_empathy_or_are/ 1492250622 65idus Psychology 2017-04-15 13:03:42 "Once again here is a gentle reminder that we do not allow anecdotes and speculations on /r/askscience. So far there has been a lot of comments along the lines of ""I read mostly non fiction"" or ""I know someone who is very empathetic"". This kind of comments are not up to the standards we try to maintain in this subreddit. If you want more informations about our commenting rules please refer to our [guidelines](https://www.reddit.com/r/AskScience/wiki/quickstart/answeringquestions). + +For reference at the time I am writing this, more than 80% of the comments have been removed. " For those saying there is no correlation simply because OP did not cite any, a number of studies have found correlations. [This study](https://www.ncbi.nlm.nih.gov/pubmed/27642659) suggests the causation is from personality (empathy as a trait) to behavior (preference for reading fiction). This interpretation comes from an observed correlation between lifetime exposure to fiction, but no experimental effect of reading fiction on empathy, as does [this study](https://www.ncbi.nlm.nih.gov/pubmed/28095740). My guess is the original study that DID find a causal relationship is an example of publication bias, but it should also be pointed out that the strengths of the manipulations (i.e., how much fiction the participants read) may not have been sufficient to induce a change in empathy. +110 If I flip a coin 1,000,000 times, what are the odds of it beings heads AND tails 500,000 times? 4652 http://www.reddit.com/r/askscience/comments/3hp4ig/if_i_flip_a_coin_1000000_times_what_are_the_odds/ 1440061179 3hp4ig Mathematics 2015-08-20 11:59:39 "What's important to realize is that the probability of every sequence with the same ""outcome"" (total # of heads in a given # of trials) is the same. HHTT is as likely as HTHT or TTHH. + +So to compute the probability of landing 500,000 heads in 1,000,000 trials, you have to calculate the probability of obtaining 1 particular sequence with this outcome and then multiply it be the number of different sequences with the same outcome. + +The sequence of first landing 500,000 heads and then 500,000 tails is such a sequence. The odds of getting it are 0.5^500,000 * (1 - 0.5)^500,000 = 0.5^1,000,000 + +The number of sequences of 1 milion flips with exactly 500,000 heads is given by the so-called [binomial coefficient](https://en.wikipedia.org/wiki/Binomial_coefficient), which in this case evaluates to 1000,000! / (500,000! * 500,000!) and which is an enormous number (unsurprisingly). (The ""!"" symbol denotes the factorial which is the product of all numbers less than or equal to the given number, so 4! = 4 * 3 * 2 * 1 = 24) + +Regular calculators can handle neither the extremely low probability of a single sequence or the very large number of possible sequences with the same outcome. So we go to Wolfram Alpha: +http://www.wolframalpha.com/input/?i=0.5%5E1000000+*+Combinations%281000000%2C500000%29 + +The result: about 0.08% + +Note that the above also holds for situations where the outcome of an individual trial is not a 50-50 split between two options. It can also be used for things like calculating the chance of throwing exactly 100 6's in 600 dice rolls (spoiler alert: it's 4.37%) + +The general formula to compute the chance of M successes happening in N trials where in a single trial the probability of success is P is: +P^M * (1 - P)^(N - M) * N! / (M! * (N - M)!)" "Look up Bernoulli random trials. + +https://en.wikipedia.org/wiki/Bernoulli_trial#Example:_tossing_coins + +This is the same as asking the probability of exactly 500,000 successes in 1,000,000 trials given an individual success probability of 50% per trial. + +(1000000 choose 500000) x (.5)^(500000) x (1-.5)^(1000000 -500000) = 0.00079788436133175... + +General formula for k successes in n trials given probability p: + +**(n choose k) p^(k) (1-p)^(n-k)** + +(n choose k) ways to pick which k trials will be successful. + +p^k because those k trials must be successes, which occurs with probability p each. + +(1-p)^(n-k) because there are n-k trials left that must be failures, and those n-k failures must fail with probability (1-p) each." +408 "What's going on when I'm getting a ""kink in my neck"" after sleeping in an odd position?" 4650 https://www.reddit.com/r/askscience/comments/4zzz11/whats_going_on_when_im_getting_a_kink_in_my_neck/ 1472399972 4zzz11 Human Body 2016-08-28 18:59:32 Tissue viscoelasticity. The extensible elements in your musculoskeletal system have taken on a certain 'set' after prolonged immobilization. That's why normal sleep is best in a large bed to permit frequent involuntary re-posturing during sleep. Like the flat spot that forms in a tire while the auto is parked. A bit of bump remains but soon disappears with flexing and heat. "Also called ""acute torticollis, or wry neck;"" basically what's happening as you sleep, your muscles adapt to a new position, whether shortened or lengthened, or even exposed to the cold for long periods over night. When you wake up, as the muscles and joints try to move into there normal resting position, they are aggravated simply the coming out of the previous state. Normally this resolves on its own within 1-3 days. Heat, or rubs may help relieve pain and symptoms, in addition to gentle stretching, and simply keeping it moving. Long term, you may want to look at correcting muscle imbalances, and postural corrections. + +Source: https://en.m.wikipedia.org/wiki/Torticollis + I'm currently a rehab student " +1424 What do we know about the gut's role in depression, and have there been recent major shifts in understanding? 4650 https://www.reddit.com/r/askscience/comments/ddwhk6/what_do_we_know_about_the_guts_role_in_depression/ 1570324342 ddwhk6 2019-10-06 4:12:22 "Basically, intestinal bacteria can synthesize and consume neurotransmitters such as serotonin and gamma-aminobutyrate. See: + +Serotonin: https://www.ncbi.nlm.nih.gov/pubmed/25078296 +>There is also substantial overlap between behaviours influenced by the gut microbiota and those which rely on intact serotonergic neurotransmission . . .The mechanisms underpinning this crosstalk require further elaboration but may be related to the ability of the gut microbiota to control host tryptophan metabolism along the kynurenine pathway, thereby simultaneously reducing the fraction available for serotonin synthesis and increasing the production of neuroactive metabolites. The enzymes of this pathway are immune and stress-responsive, both systems which buttress the brain-gut axis. In addition, there are neural processes in the gastrointestinal tract which can be influenced by local alterations in serotonin concentrations with subsequent relay of signals along the scaffolding of the brain-gut axis to influence CNS neurotransmission. + +GABA: https://www.nature.com/articles/s41564-018-0307-3 +>The gut microbiota affects many important host functions, including the immune response and the nervous system. . . . Bioassay-driven purification of B. fragilis supernatant led to the isolation of the growth factor, which, surprisingly, is the major inhibitory neurotransmitter GABA (γ-aminobutyric acid). GABA was the only tested nutrient that supported the growth of KLE1738, and a genome analysis supported a GABA-dependent metabolism mechanism. Using growth of KLE1738 as an indicator, we isolated a variety of GABA-producing bacteria, and found that Bacteroides ssp. produced large quantities of GABA. Genome-based metabolic modelling of the human gut microbiota revealed multiple genera with the predicted capability to produce or consume GABA. A transcriptome analysis of human stool samples from healthy individuals showed that GABA-producing pathways are actively expressed by Bacteroides, Parabacteroides and Escherichia species. By coupling 16S ribosmal RNA sequencing with functional magentic resonance imaging in patients with major depressive disorder, a disease associated with an altered GABA-mediated response, we found that the relative abundance levels of faecal Bacteroides are negatively correlated with brain signatures associated with depression. + +These can affect nearby nerves (in particular the vagus nerve) which might have some effects on the brain. The paper linked in the top post is a study showing that SSRIs (which inhibit serotonin reuptake) increase vagal nerve activity. Gut-synthesized neurotransmitters generally can't make it all the way into the brain because of the [blood-brain barrier](https://en.wikipedia.org/wiki/Blood%E2%80%93brain_barrier) (a layer of cells which keeps them out). + +There are many *correlational* studies showing a link between the gut microbiome and depresssion (example: https://www.nature.com/articles/d41586-019-00483-5), but showing causation is much trickier (for example, depression might cause changes in diet which alter the microbiome). Still, I think based on the neurotransmitter studies there's some good evidence for a role. The immune system also might be involved (some microbes could cause inflammation, and there's some evidence for a role of inflammation in depression: https://www.ncbi.nlm.nih.gov/pubmed/30368652). + +Finally, intestinal bacteria can break down medications ([for example, levodopa](https://science.sciencemag.org/content/364/6445/eaau6323) for Parkinson's) and indirectly affect brain function." "Here’s some recent research suggesting a link between diet and depression: + +Long story short, researchers showed that when individuals switch to a Mediterranean diet, they reported lower levels of depression. + +What is interesting about this is that these individuals did not experience lower levels of anxiety. The researchers hypothesized that if the benefits the depression were the result of people taking positive action in their lives, i.e. changing their diet, then anxiety would also go down. + +As this was not the case, the researchers suggest that there is a deep connection between diet and mood that we do not fully understand. + +https://greatergood.berkeley.edu/article/item/what_is_the_best_diet_for_mental_health?utm_source=Greater+Good+Science+Center&utm_campaign=f2443f3910-EMAIL_CAMPAIGN_Oct_2019_Calendar&utm_medium=email&utm_term=0_5ae73e326e-f2443f3910-74454407" +111 "The Mormon Church Released pictures of the ""Seer Stone"" reportedly used by Joseph Smith. Can you make a geological analysis of it?" 4644 http://www.reddit.com/r/askscience/comments/3fuz4d/the_mormon_church_released_pictures_of_the_seer/ 1438770207 3fuz4d Earth Sciences 2015-08-05 13:23:27 "I'll give this a whirl, it's not everyday that one gets first pick at looking at a sacred relic. + +First, the shape. That is a prolate ellipsoïd with very well devellopped rounding. There is definitely no faceting such as you'd find on a glacially derived cobble. The shape, roundness and exteranal smooth texture are consistent with transport in a fluviatile system (in other words, that pebble was picked out of a stream or from fluviatile deposits). + +Also a word about the polishing and patina. Either that rock was waxed, laquered or varnished in some way, or else it was handled *a lot*, enough to acquire that shiny yellowish patina. + +Now, the material. The quality of the picture is so-so. I'd be all over that pebble with a handlens before I said anything with confidence. From what I see in the pix, I'm thinking more along the lines of metamorphic than straightforward sedimentary (although I'm leaning towards meta-seds). That comes mostly from the wispyness of the lamination, the sharpness of the contacts on both sides of those quarto-feldspathic laminations (no grading). But I'm not setting this down as a definitive ID. So: *probably* metasedimentary (Say, a metawacke or somesuch), conditional to a *real* examination with a handlens. What I'd be looking for with the handlens is whether it is made of rounded grains (And thus a Sandstone) or whether it was made of interlocking crystals (which would make it metamorphic in this case). I'd also look for evidence of deformation and a comple of other processes (is that *really* sedimentary lamination? could it be metamorphic ribboning or even migmatisation?) + +You may also want to give the rock a whirl on /r/geology and see what we might have to say about it there. Perhaps some of my colleagues which are more familiar with the geologic particulars of the american mid-west will feel some familiarity with that specific lithology and have an Eureka moment. I'm pretty sure /r/askhistorians might have a ball commenting on this as well. + +Finally, I'm by no means well informed on Mormonism, but you metionned this is called a ""Seer Stone""? Any chance that might be in relation with the fact that when looked at perpendicular to the laminations, the intersection of these laminations with the surface of the pebble generates a concentric pattern of ellipses, somewhat like an eye? Would you perchance happen to know if early Mormons had any cultural dealings with the ""Doctrine of signatures"" (the belief that the properties of things were influenced by their appearance)? + +EDIT/UPDATE: + +To all users mentionning the stone is supposed to have been picked up in NY state and not the american midwest; thanks for bringing that to my attention. As previously stated, I claim no familiarity with the history of Mormonism, just geology. + +From what I've been made to understand, the provenance of the stone is a matter of historical interest as it is referred to in Smiths texts. What I make of that is that it's sourcing in a well upstate NY is a hypothesis to be tested. But there is only so much one can say without direct access to the specimen. Let it just stand that while there is nothing I can see from OPs pix which is inconsistent with a sourcing of that pebble in upstate NY (or a well for that matter), there is nothing either to exclude other origins. + +Some users have suggested other origins which might perhaps be testable. One of the most intriguing was set forth by /u/WRCousCous, who suggests based on his experience with amerindian artifacts that the patina and general aspect of the pebble might be consistent with a type of artifact known as a ""thunder egg"". Apparently this would fit in with a documented fascination by Smith with native artifacts and culture. + +Anyways, this is a quite enjoyable discusssion for I which I thank contributing users, and an excellent exemple of something I have always deeply believed: even the smallest stone can be an object of intense interest and fascination." "This was asked over at /r/whatsthisrock http://www.reddit.com/r/whatsthisrock/comments/3fsia5/this_rock_was_posted_by_the_lds_church_as_being/ + +It looks to be a banded jasper that some people call ""Genesis Stone"". " +307 Do pet tarantulas/Lizards/Turtles actually recognize their owner/have any connection with them? 4640 https://www.reddit.com/r/askscience/comments/3znred/do_pet_tarantulaslizardsturtles_actually/ 1452048851 3znred Biology 2016-01-06 5:54:11 With the arachnid family in general lacking most of the social skills nessercary for estabilishing a bond, it should be said that spiders behave very differently since it is a huge order (araneae) https://en.wikipedia.org/wiki/Spider_behavior. Some might have more complex brain structures/complex behaviour than expected http://www.nytimes.com/2014/11/04/science/mapping-the-tiny-brain-of-the-aristocrat-of-arachnids.html Although I highly doubt that this would extent to anything which would make it possible for a spider to bond with a human. It simply lacks the social intelligence. Birds vary a lot, but some are highly intelligent, such as crows, particularly ravens. In general you can train/bond with many species of birds, in a whole different way than you ever would be able to with a spider. As with reptiles ... Whew ... That's a toughie, although it is generally said that they are unsociable, we learn new stuff everyday, and a lot of animal species are still not properly examined (nor discovered), and then it comes to analyzing their social structures and behaviour we still have a long way to go. "This is a pretty interesting topic particularly due to our view of ourselves in nature and our view of animals. Your initial statement alone presumes that somehow dogs and cats ""know they have an owner"". Does a dog recognize that a human has ownership, and in some states property rights over them? Or does the dog believe the human is a part of their pack and a companion? Recent research came out indicating that dogs do recognize their owners faces in a crowd of people, however many animals can recognize their affiliates even those unrelated in a large group. Cats however are less domesticated and display much stronger predatory instincts, their view of our place in their social structure is likely different than how we view our place in their lives. + +One big hiccup between how we communicate with animals is that for the majority of all animal species communication happens non verbally. Whether it is scents, body language, color, and so on we fail to understand other animals because our communicative abilities have surpassed those more basal forms of communication (or so we think, but that's a discussion for a different day). So while we are communicating ownership, they are communicating say, trust. A good example is a cat rolling over and showing you their belly. For a predatory animal this behavior is pretty risky. We see this behavior as ""cute"" or ""they want to cuddle"". The reality is we do not know because cats cannot talk. On the topic of cats talking, cats rarely ever meow to communicate with each other. Domestic cats often meow to communicate with humans. + +On the topic of other animals I can't speak to insects, but I have quite a bit of experience with Avian species. Most parrot species are highly intelligent, much more intelligent than a dog or cat. They are not predatory and instead often live in large groups and have intricate mating displays and social behaviors. So why wouldn't a bird recognize their owner? The big difference is once again *how* they recognize their owner in the context of their own species behaviors. Even a pet bird is pretty far from total domestication in the sense of dogs and cats. In many pet birds, particularly psittacines (parrots) not only do they recognize their human ""owner"" as an affiliate but they often times form incredibly strong social bonds. Some parrots will regurgitate food as a means of expressing affection. Birds are heavily preyed upon and so creating these relationships with their owner involves not only a recognition of a provider of food, but on some level indicates an attachment. + +We know that animals experience emotions, but the jury is still out on to what extent those emotional connections contribute to particular sets of behaviors. Generally speaking animals that are more social are more emotive. They also have more time to spend ""being social"" due to a lack of predatory factors. Meaning, social behaviors and living in large groups help avoid predation. So what happens when we take these social creatures and plop them in an environment where predatory threats are extremely diminished? Once the fear of predation is over we see behaviors not exhibited in the wild. While we can generalize wild type behavior when we have captive species the game changes for how they behave. + +This human animal bond is a pretty fascinating one and some veterinary schools and foundations have been studying it much more as of late. Particularly in the realm of the effects of animal companionship on people with mental illnesses. Check out [The Human-Animal Bond Initiative](https://habri.org/). + +I think the long and the short of it is animal communication and sociality is extremely complex, for a long time we have grouped animals together as lesser beings. It is very easy to both assume an animal ""loves you"" or assume that ""it's just a stupid dog"" (Labrador Retrievers anyone?). As someone who has worked with many animals who have been domesticated and wild species in a captive environment I've been surprised at the emotional capacity of animals that others have often deemed ""less intelligent"". I think we have much to learn about the communicative and emotive capacity of other animals. " +1800 What gives a steel cable so much more tensile strength than a steel rod? 4637 https://www.reddit.com/r/askscience/comments/l9h4bs/what_gives_a_steel_cable_so_much_more_tensile/ 1612114287 l9h4bs Engineering 2021-01-31 20:31:27 [deleted] "I thought for sure someone would give you the answer. But I saw lots of just dead wrong answers, like a cable doesn't have higher strength than a rod, that it's more flexible, or that it's denser. But tensile strength, which is the same thing as ultimate tensile strength for a wire, is fracture load divided by true area. The question asked why the wire has a higher strength than a rod. The poster didn't mention alloys, so let's assume the rod and the wire are of the same material. (This is not necessarily true, as a wire may very well have higher carbon content and that could be an additional answer. Steel is a material class, there are many kinds of steel commercially available.) + +The answer is that wire is cold drawn to a much higher extent than a larger diameter rod. Steel is like most metals, in that there is a marked increase in strength when you deform it. Drawing increases the wire's strength, and also reduces its ductility (measured by strain to failure). Materials scientists will explain this by noting that the microstructure of a cold drawn material has smaller and more elongated grains, and therefore dislocations in the metal crystals have a harder time moving, interfere with each other, and get pinned at grain boundaries very quickly." +1088 If light doesn't dissipate with travel distance and the universe is infinite, why isn't the night sky bright? 4628 https://www.reddit.com/r/askscience/comments/8oopij/if_light_doesnt_dissipate_with_travel_distance/ 1528181372 8oopij 2018-06-05 9:49:32 "There are two things going on here, both related to universal expansion. + +1. The universe may be infinite, but as it is expanding, the distance between us and anything further than 14bn ly away is getting bigger at greater than c, ~~so light from them can never reach us.~~ The *observable* universe - the stuff that we can see - is about 46bn ly in radius, so any galaxies beyond that are invisible. + +2. Due to expansion, electromagnetic radiation is red-shifted as it travels (basically its wavelength increases by a factor of about 2 x 10^(-18) every second). So stuff that was emitted as visible light a long time ago will gradually become IR, then microwaves, then radio waves and so on. + +That doesn't mean it isn't there, though. It just means we need radio telescopes rather than visible light telescopes to see it. + +In practice, there *is* ""light"" all around us, which is shown by [this notable image](https://en.wikipedia.org/wiki/File:Ilc_9yr_moll4096.png). That is a picture of the cosmic microwave background (based on years of data collection); basically it is a picture of the sky in all directions, showing the intensity of the electromagnetic radiation in the background (so stuff leftover from the very early days of the universe). This radiation has a frequency in the high GHz (so microwave radiation) and is good evidence for the universe being pretty much the same in all directions - on that picture the effective temperature of the radiation is about 2.7K, but the range of temperatures (brightest to darkest) is about ± 0.2mK. + +So in theory the night sky is bright - in that there's radiation in all directions. It's just very ~~high~~*low*-frequency (*large-wavelength*), and very cold, so we can't see it. + +[*Edit: I'm getting a few common follow-up questions, so here are some rough answers:* + +1. [But nothing can go faster than the speed of light, how can distant objects be moving away faster than c](https://www.reddit.com/r/askscience/comments/8oopij/if_light_doesnt_dissipate_with_travel_distance/e05hckt/)? + +2. [What about the inverse square law; light spreads out - wouldn't that explain it](https://www.reddit.com/r/askscience/comments/8oopij/if_light_doesnt_dissipate_with_travel_distance/e05qk8s/)? + +3. [How is universal expansion changing; is the observable universe and what is in it getting bigger or smaller](https://www.reddit.com/r/askscience/comments/8oopij/if_light_doesnt_dissipate_with_travel_distance/e05g7wh/)? + +Disclaimer: I studied this stuff a long time ago. I make mistakes. Please point them out when you see them.]" "This is known as Olbers' paradox and if the universe was static, this would definitely be the case. The night sky not being bright is one of the contradictions between reality and models that assume that the universe is static and infinite and as such indirect evidence for cosmological models that make no such assumptions. + +An easy explanation is that since the universe is finitely old and the speed of light is finite, our observable universe is not infinite and thus the night sky does not have to be bright." +204 Why do wind turbines only have 3 blades? 4617 https://www.reddit.com/r/askscience/comments/3ul61p/why_do_wind_turbines_only_have_3_blades/ 1448720607 3ul61p Engineering 2015-11-28 17:23:27 As a blade moves, it creates a wake, like a boats wake, that disturbs the air around it. That wake can interfere with the efficiency of the next blade as it passes. So, it's a tradeoff situation for efficiency that factors in number of blades, blade speed, wind speed, and RPM to maximize the efficiency of energy conversion. This is also why how close the towers are to each other and how they are oriented overall on the landscape. Watch a sailing race and see how they try to steal each other's wind. [deleted] +112 How long would it take a modern computer with code breaking softwear to crack the German enigma code from WW2? 4614 http://www.reddit.com/r/askscience/comments/37209v/how_long_would_it_take_a_modern_computer_with/ 1432436549 37209v Computing 2015-05-24 6:02:29 "You can look at http://www.enigmaathome.net/ to see some actual working examples. They decrypted 3 previously unknown Enigma messages and it took the equivalent of 7748 years, 303 days, 14 hours of PC time based on a single Athlon 3500+ PC. This was basically a brute force effort, using all the known weaknesses of the Enigma machines. + +For a generic example, Wikipedia says ""If the wiring is secret, the total number of possible configurations has been calculated to be around 10^114 (approximately 380 bits); with known wiring and other operational constraints, this is reduced to around 10^23 (76 bits)."" + +At 100 GFLOPS (decent modern processor), this would be about 3.17x10^94 years for the more complex case (longer than the universe has existed). For the limited case where we assume we've captured an Enigma machine and know the wiring & limitations of the system, it's about 3,169 years on average to brute force it. This jives fairly closely with the practical enigmaathome results above." "The answer depends on whether you're trying to brute-force the answer, or trying to use the weaknesses of the Enigma and its usage protocol to break it the same way the allies did in WW2. + +The top comment tells you about the brute-force case: this would still take a very long time, because there are many possibilities to check. But the problem in the war was that many possibilities could be eliminated by clever logic. Using this method with a simulated Bombe, enigma messages can be decrypted in a few seconds on a home computer." +667 Is DNA Compressed? 4608 https://www.reddit.com/r/askscience/comments/637gyu/is_dna_compressed/ 1491233192 637gyu Biology 2017-04-03 18:26:32 "There's another form of ""compression"" here that I haven't seen anyone mention. You've got the literal physical ""compression"" of DNA around histones, you've got the compression that occasionally occurs where a single strand of DNA codes for multiple overlapping genes. + +But there's also a sort of ""compression"" that relates to how genes result in actual phenotype. Genes do chemistry, more or less. They make proteins, proteins produce other chemicals and join together to make the structures of cells. Cells come together and make organisms. But there's often not a 1:1 ratio of ""gene"" and ""physical attribute"". For example, there's not ""left front leg"" genes, ""right front leg"" genes, ""left back leg"" genes and ""right back leg genes"". Instead there are a number of genes that get expressed in each limb to produce it. Genes often do ""double duty"" in different body systems. And final outcomes are usually complicated relative to the information content of the gene. Consider a tree growing. The final tree has a complex fractal branching shape, but this can arise from a relatively few genes that cause the tree to grow, then branch, then grow, then branch, with the same rules repeated _on_ the branches, causing them to branch in turn. Complexity emerges from interactions in the genes, and interactions between the genes and environment. + +And this is the main sort of ""compression"" that I would say is involved in life. It's the sort of compression that gives you the complexity of the human brain, with some 100 trillion neural connections storing at least a terabyte's worth of data, coming from a genome only 725 megabytes in size. You can't describe every important factor of a human in our 725 megabytes of DNA data so we are, in a sense, uncompressed. " "Kind of. By a process called [alternative splicing](https://en.wikipedia.org/wiki/Alternative_splicing), a single gene can be transcribed or ""read"" in a number of different ways, resulting in many protein variants from a single gene. So even though the human genome has roughly 20,000 protein-coding genes, we are able to produce many times this number of unique proteins." +409 Why do Cockroaches die on their backs so frequently? 4604 https://www.reddit.com/r/askscience/comments/4yd4uv/why_do_cockroaches_die_on_their_backs_so/ 1471536885 4yd4uv Biology 2016-08-18 19:14:45 "There are two basic reasons. Cockroaches have a slightly rounded and greasy back, and a flat body that helps them squeeze and hide in narrow cracks and crevices. Their long legs give them a high center of gravity, meaning they carry most of their weight around their backs. When a cockroach is dying of old age, its high center of gravity pulls its back toward the floor, and its rounded back and weakened muscles prevent it from righting itself, particularly on smooth surfaces. + +The insecticides we use to kill roaches can have the same effect. Most of these insecticides are neurotoxins – poisons that can trigger tremors and muscle spasms, eventually causing the cockroach to flip on its back. A healthy cockroach can easily right itself, but the tremors, lack of muscle coordination and, again, the rounded back and high center of gravity cause the intoxicated cockroach to get stuck that way. +Credit to MARLA VACEK BROADFOOT AND COBY SCHAL" "[Here](https://www.reddit.com/r/explainlikeimfive/comments/2zjvxs/eli5_why_do_cockroaches_turn_upside_down_when/) is a link to a very similar question that was asked in ElI5 + +The essence is the legs spasm when a cockroach dies, flipping them over. This has nothing to do with fluid pressure, as many will no doubt say, because many are under the false impression that insects use hydraulic pressure to power limb movement. " +1254 If the nuclear fusion cycle of a star ends at iron, how do heavier elements get made? 4603 https://www.reddit.com/r/askscience/comments/bf67hf/if_the_nuclear_fusion_cycle_of_a_star_ends_at/ 1555718911 bf67hf Planetary Sci. 2019-04-20 3:08:31 "There are various nucleosynthetic processes that extend up into higher masses. There's a diagram on the third slide [here](https://www.asc.ohio-state.edu/physics/ntg/6805/slides/Decadal_slides_from_pages_on_nuclear_structure_2.pdf). + +These different processes occur in different astrophysical sites. For example, the rp-process occurs in x-ray bursts, the s-process occurs in AGB stars, the r-process occurs in neutron star mergers, and so on." Nuclear fusion cycles do not end at Iron-56. Nuclear fusion beyond Iron-56 requires more energy than the process generates at this point. There are irregularities in super massive stars that would allow for fusion above this point but the vast majority of fusion beyond Iron-56 occurs due to gravitational collapse as part of supernovae events (potentially it could occur at edges of super massive objects as well). Maybe transition events make more sense than Chandrasekhar limits. As part of gravitational collapse, some matter is emitted back into space after being tempered by immense energies while the internalized matter becomes consistent with neutron stars or black holes respectively. +410 A month ago we made available publicly via the CERN Open Data Portal 300 TB of research data from the CMS Experiment at CERN’s Large Hadron Collider. AUA about our open data! 4598 https://www.reddit.com/r/askscience/comments/4l4y1j/a_month_ago_we_made_available_publicly_via_the/ 1464264042 4l4y1j CERN AMA 2016-05-26 15:00:42 I love hearing about stuff like this. So what is the most important information that has come from this data from a person outside of CERN? Or was all this data processed internally before being made publicly available? Just seems like a lot of data to go through. Has anyone from the public contacted you with the results of an analysis of your data that they carried out themselves? And if yes, were these results surprising/inspiring/impactful? +1115 What makes recycling certain plastics hard/expensive? 4598 https://www.reddit.com/r/askscience/comments/9hee9n/what_makes_recycling_certain_plastics/ 1537441993 9hee9n Chemistry 2018-09-20 14:13:13 "Plastics Engineer here- work regularly in the injection molding industry, as well as resin selection and evaluation. + +​ + +There are basically 3 types of commercial plastic types out there. Thermoplastics, Thermosets, and Elastomers. + +​ + +Like the post below somewhat worded. Thermoplastics can soften and be remolded when given enough thermal energy. The molecular bonds in the polymer allow them to become free flowing once again, and develop a new orientation during molding . Orientation is key in a plastic part retaining its shape under stress, as well as maintaining its physical properties. + +​ + +Thermosets are your materials like rubber. They are heated to mold, but once they are ""cured"", they cannot be re-heated to be processed. Its not just rubber that's thermoset, Melamine resin, polyurethane resin, and Polyester resin are thermoset as well. So in terms of recycling a thermoset cannot be recycled along with a thermoplastic. Their chemical and physical makeup are just not miscible. + +​ + +Elastomers are defined as any material that can stretch up to 200% and rebound without losing its original shape. After stretching past that limit, it goes past its tensile yield point and you then have permanent damage to the molecular chains, as they are unable to pull back in to each other to retain its original orientation. + +​ + +Back to the original question. Not all thermoplastics are the same. there are MANY types that are commercially used for regular consumer products. such as PP, HDPE, LDPE, PS, PET, and many many others. These all have different chemical structures, so they need to be properly separated before processing back into pellets. So you cant re-process LDPE (Low Density Polyethylene) and PS (Polystyrene). So there is a lot of effort and energy that goes into not only separating these plastics, but also determining what their thermal history is, as well as reprocessing them back into pellets. + +Now when a plastic is used, lets say its a milk jug. Depending how long that milk jug has been out in the world, it will have a different thermal history, when compared to something that was JUST molded out of virgin plastic. UV light can act as a thermal agent that can accelerate molecular degradation due to the UV light physically cooking the Carbon-Carbon bonds in a polymer. This is why a white plastic part that's left outside will slowly yellow. The bonds and structure of the plastic is VERY SLOWLY cooking, hence why it starts to darken. SO, if you process a part that has a lot of thermal degradation, it inst going to process the same as a material that hasn't seen excessive heat. So you cant just blend these together and expect the same result. The more thermal degradation there is ( along side the many other types of degradation from regular use), the worse physical properties it will have. + +​ + +Honestly i could go on and on about plastics all day, but I'm going to cut it here. + +TL;DR: Not all plastics are alike, there are many factors that go into processing them together. Its not as simple as just chucking it into a grinder and re-molding it. + +​ + +if anyone has any other questions, please let me know and I'll be happy to inform! + +​ + +\*\*EDIT\*\* Holy crap! This response BLEW up in responses. Im glad so many of you are interested! I cant get to all your responses. But if anyone has any specific questions. It'll be quicker to simply PM me!\*\*" "Recycling machinery sales person here. What I do is work with different clients to try to find the right process to recycle their particular material stream. The biggest problem is simply contamination. You can wash a piece of plastic by hand and get it nice and clean pretty quick, but it's really difficult to properly clean 3 or 4 thousand pounds of plastic an hour. This contamination can be dirt, sand, grease, other unwanted plastics, aluminum foil, etc. Every material has different needs and some are just too difficult. + +For example, Keurig K-cups are made of 4 or 5 separate layers of plastic that serve as an oxygen barrier. The problem is that it is basically impossible to separate these layers from each other. + +Some plastics can only be cleaned with water and cleaning agents which gets extremely expensive and difficult with all of the water management and reclaim that needs to happen. Also, you need to get rid of all that water again before you extrude the recycled plastic because moisture is the enemy of extruders (machine that heats and re-melts the plastic.) + +Some plastics, like the black agricultural film you see on fields can be up to 50% or more dirt and moisture! This is extremely difficult not only to shred (because all of that dirt wears your machine faster than anything else besides metal) but also to wash because of just the sheer amount of dirt. Also, once you get all of that dirt out, you need to again separate the dirt from the water and then find a way to dispose of the dirt because the problem is that it contains micro pieces of plastic that makes the dirt undesirable to farmers and the like. + +Please ask me any questions you have about plastics recycling because it is my career and my passion." +1366 "How cautious should I be about the ""big one"" inevitably hitting the west-coast?" 4597 https://www.reddit.com/r/askscience/comments/bwmr6q/how_cautious_should_i_be_about_the_big_one/ 1559640847 bwmr6q Earth Sciences 2019-06-04 12:34:07 "Jumping in just to say be prepared and not scared. Remember to drop, cover, and hold on during earthquakes and keep an emergency kit with a minimum of 72 hours worth of supplies for every member in your household, including pets. If you live in a tsunami zone you should know where to go, how far above high tide line you need to be and how long you have to get there. Finally, have a plan to meet up with family or get in touch with them to let them know you are safe. + +​ + +Source: Emergency Manager, West Coast" "The 'they' who are determining the temporal and spatial occurrence of past earthquakes are paleoseismologists and it is not them (or really any reputable geologist) who is saying, or would say, that an earthquake is 'overdue' or occurs with anything resembling true periodicity. As to the accuracy, there are definitely uncertainties, e.g. the time between events depends on the abundance of dateable materials and the individual uncertainties on those dates along with the quality of the record in any one places and in how many separate locations a particular earthquake (determined by being the same age) can be recognized, but all and all, we can reconstruct histories of earthquakes relatively reliably (given the right geologic conditions). The [USGS](https://earthquake.usgs.gov/learn/topics/paleo-intro/) gives a nice set of background info on paleoseismology. + +A lot of this comes from a misunderstanding of the use of recurrence intervals and time since the last event. Recurrence intervals, i.e. the average temporal spacing between earthquakes of a given magnitude like the ~200 year figure you mention, and time since the last event are useful metrics because they provide a sense of the activity of a fault / fault system and the risk it poses, but are best considered through the lens of probabilities. For example, the probability of large magnitude earthquake occurring on a fault system that on average has a M6-7 earthquake every 100 years and the last one occurred 150 years ago is much greater (and thus the risk is much greater) than a fault system that has a M6-7 every 1000 years and the last one was 50 years ago. The first hypothetical does not, in anyway, imply that the system is overdue for an event, it only indicates that given the past history the probability of an event occurring is greater. Similarly, the second hypothetical does not indicate that an event cannot occur, just that it is unlikely given the past history. This is kind of analogous to the way we describe flood risks, i.e. the 100 year flood does not mean that a flood of that magnitude occurs once every 100 years, but rather that there is a 1% probability of that flood happening ever year, so it would be expected that there would be at least one in a 100 year time frame. Floods and earthquakes are different statistically, as floods for the most part are closer to being a true [Poissonian](https://en.wikipedia.org/wiki/Poisson_distribution) process, i.e. time since last event does not effect the probability of the next event, whereas because earthquakes are the product of strain buildup over time and the mechanical properties of the fault system, they are better described as having a time-dependent probability, i.e. time since last event changes the probability. + +Ultimately, over the timescales of interest (i.e. 100s to 100,000s of years) plate tectonics is probably pretty 'black and white' in terms of the far filed plate rates staying the same. These plate motion rates are the driver for earthquakes, the motion of the plates causes strain to accumulate on faults and fault systems. The stochasticity comes from the fault themselves, which are variable in terms of their 3D shapes, mechanical/frictional properties along their surfaces, and connections between each other. As strain builds, failure will initiate somewhere (in simple terms, the mechanically weakest segment of the system) and an earthquake will occur. This earthquake may change the physical properties of the fault (meaning that fault will not fail in the same way the next time) and it will also change the stress state on adjacent faults (e.g. [Coulomb stress transfer](https://en.wikipedia.org/wiki/Coulomb_stress_transfer)) which may increase or decrease the likelihood of an earthquake on that adjacent fault depending on its orientation, its preexisting stress state, and its mechanical properties. In short, earthquakes are very complicated. + +**TL;DR** We can determine past histories of earthquakes with some degree of accuracy, but fault systems are inherently complicated and past histories can allow us to estimate risk but not predict earthquake occurrence. Reputable organizations (e.g. the USGS) communicate risks in terms of probabilities and one should take heed in terms of understanding the risk in their area, but you should be skeptical if someone is claiming that earthquakes are predictable. + +**EDIT** Specifically to address all the comments about the usage of 'overdue' and why geologists don't like using the word 'overdue', it's basically because it is meaningless in most cases. Recurrence intervals are averages, so knowing just the recurrence interval of a system for which we have records of ten events is 200 years, could mean we have an event exactly every 200 years or with events with spacings of 120, 100, 250, 20, 420, 150, 300, 400, 10, and 240 years (that will give you an average of 201, but close enough). If it's the latter, which is more like what we often see in terms of earthquake records, if it's been 240 years since the last event, given that the range of time between events was 10 to 420 years, it doesn't really make any sense to say that we're 40 years 'overdue' for an event with a recurrence interval of 200 years. And yes, generally we would expect the probability to increase with time since the last event, but these are inherently complex systems that are influenced by a lot of factors we don't fully understand or can't fully quantify so the time since the last event + the average recurrence interval does not map to anywhere near a complete understanding of the probability of the next large event occuring." +1367 Can metals be gas? 4596 https://www.reddit.com/r/askscience/comments/by9cxi/can_metals_be_gas/ 1560009326 by9cxi 2019-06-08 18:55:26 "Yes. Nearly all metals have a boiling point. For those that don't, the boiling point is too high and they just form plasma instead. For example, tungsten: the atmospheric pressure boiling point extrapolated from the vapor pressure curve would be 5550 °C, and by that point enough would be ionized to call it a plasma (judging by a rough comparison of the first ionization energy and the Boltzmann factor, although I haven't done [the actual calculation](https://en.wikipedia.org/wiki/Saha_ionization_equation)). Although tungsten cannot truly boil at atmospheric pressure, at high temperatures it can evaporate. This happens in lightbulbs, resulting in the filament wearing out. + +The lowest boiling metal is mercury, which boils at 357 °C. Mercury vapor is a well-known health hazard. + +Edit: thanks for the gold (which boils at 2700 °C) kind stranger" "Yes any metal can become a gas if heated to it's boiling point. But the another interesting question is can they stay in a gaseous state and be metals? + +No, gaseous metals do not retain metallic bonds, nor metallic conductivity, nor luster, nor any other metallic properties. + +Metallic properties are bulk effects. They are caused by metallic bonding, and not just of two atoms, but of an entire piece of metal. You don't have metallic bonding in gases. The gas particles are basically free to go with a few collisions here and there." +545 Does the supermassive black hole in the center of our galaxy have any effects on the way our planet, star, or solar system behave? 4595 https://www.reddit.com/r/askscience/comments/5gxrm2/does_the_supermassive_black_hole_in_the_center_of/ 1481083403 5gxrm2 Astronomy 2016-12-07 7:03:23 "The premise that the black hole is holding together the galaxy is wrong. + +Sagittarius A*, the supermassive black hole thought to be at the center of the Milky Way, is estimated to be the mass of about 4 million suns. + +To put that in context, the milky way is estimated to have between 100-400 billion stars with a mass of about 12 trillion suns. This makes Sagittarius A* less than .0001% the mass of our galaxy. So no, it does not affect us. + +Having said that, there are a few stars that orbit Sagittarius, and quite fast. [link](https://www.youtube.com/watch?v=k7xl_zjz0o8) + +--- +What does affect us, though? +[here's an interesting thing to look at](https://upload.wikimedia.org/wikipedia/commons/3/33/Galaxy_rotation_under_the_influence_of_dark_matter.ogv) + +The image on the left shows how the galaxy should be moving, predicted by the mass distributions and densities we observe from all sources of light. The image on the right shows how it is actually observed to be moving. + +This is exactly why dark matter is hypothesized to exist. The image on the right is only possible if there exists an enormous amount of mass greater than that of the galaxy and outside of it. Just a quick search shows an artists rendition of it, but the scale is roughly accurate: [dark matter halos!](http://www.physast.uga.edu/~rls/1020/ch22/22-01.jpg) +" "In the newtonian approximation any spherically symmetric distribution of mass can be represented as a point mass in the centre without changing the gravitational field outside the original sphere. This is why you can calculate the gravitational acceleration on the surface of the Earth (or any other planet), just by knowing its mass and radius. + +This works in the other direction as well. The gravitational field of a million sun mass black hole and the same mass globular cluster are identical, outside the cluster. + +So from our point of view the supermassive black hole is just extra mass. It could just as well be in stars, interstellar gas or dark matter. If it was in the same distance and direction just more spread out, it would have the same effect. Since it represents only a tiny fraction of the mass of the galaxy that effect is quite small." +308 How come small cuts on the anus from over wiping or hemorrhoids does not cause serious septicemia? 4593 https://www.reddit.com/r/askscience/comments/4fuvnk/how_come_small_cuts_on_the_anus_from_over_wiping/ 1461269526 4fuvnk Human Body 2016-04-21 23:12:06 "There were some really good answers when this question was asked a few years ago: + +https://www.reddit.com/r/askscience/comments/squri/how_come_when_when_you_wipe_to_hard_after_going + +Tl;dr: The immune system is different in different parts of the body, and ""suped up"" (highly paraphrasing) in areas like near the anus. +" "Lymphoid tissue is like the Police Department for immune cells, so your body puts it in places that are prone to infection, so that if any germs come around, you've already got a butt ton of cops right there. Your tonsils are lymphoid tissue. Your intestines have a bunch of lymphoid tissue. + +The area around your anus has a bunch of extra lymphoid tissue for exactly that reason." +668 Are there Soviet Venera landers still intact, or even recognizable as Earth artifacts? 4589 https://www.reddit.com/r/askscience/comments/5w3xk6/are_there_soviet_venera_landers_still_intact_or/ 1488027132 5w3xk6 Planetary Sci. 2017-02-25 15:52:12 [deleted] I was part of an ESA sponsored workshop for postgraduate level researchers. Over the course of 2 weeks we designed a mission that would send an orbiter to Venus to investigate some gaps in our knowledge of the planet. One of the goals was to measure the rate at which the rotation of Venus changes. We came up with an idea to use the remnants of the landers as targets for our radar. Their locations are known well enough and 1/2 a ton of corroded metal makes a nice bright unmistakable marker in a radar image. +981 At what point is a particle too small to cast a shadow? 4586 https://www.reddit.com/r/askscience/comments/7rrejd/at_what_point_is_a_particle_too_small_to_cast_a/ 1516466331 7rrejd Physics 2018-01-20 19:38:51 "Depends on what you define a shadow to be. Electron microscopes technically generate an image by collecting data on a microscopic object's ""shadow."" Electron microscopes can expose the shadows of individual molecules. (You can Google images of this.) + +If we limit ourselves to observing a shadow due to visible light, then the smallest object to make a shadow would have to be at least a micrometer in length (1/100 of the thickness of a human hair) to interfere with/scatter visible light. Even then, you would need to set up lenses in a specific way to project the shadow and make it visible to the naked eye. (This is called Schlieren photography, Veritasium has a video. This essentially shows the shadows of A LOT of molecules convecting.) + +Edit: Since I have sparked a discussion, I should justify my ELI5 conclusion. Light is the layman term for the ""electromagnetic spectrum."" The behavior of light, a physical (aka observable and measureable) phenomenon, can be described mathematically as a wave. The tl;dr on waves is that we can define them by their properties of ""wavelength"" (λ) and ""frequency"" (f). By multiplying these values, we obtain the speed of the wave (v=fλ). The motion of light was uniquely set by the initial conditions of our universe, to approximately 300000000 meters per second (186000 miles per second) - we call this speed ""c."" Since c must remain constant, the relation c=fλ demands that as frequency of a light wave increases, the wavelength must decrease (and vice versa). Hence, light exists on a spectrum. From low frequency/high wavelength radio waves to high frequency/low wavelength Gamma rays, the spectrum offers a linear variety of ""light."" With some engineering, radio becomes a light we listen to, microwave becomes a light we cook with, and ultraviolet light is used to tan Mr. 45. Nature's engineering of the human eye and visual cortex system enables unimpaired individuals to observe a tiny sliver of the electromagnetic spectrum, we call this visible light. You can see all of the colors of this portion of the spectrum when you look at the rainbow luster of a DVD. The wavelengths can be as high as ~700 nm (red) to as low as ~400 nm (violet). On scales of larger than one micrometer, a shadow is caused by an object impeding the distribution of light from a light source and can be classically demonstrated with geometry; when you stand on the sidewalk on a sunny day, your body casts a shadow in the direction the sun's visible light would have gone if you weren't standing there. However, when you get to smaller scales, the behavior of light becomes a unique type of wave: a quantum wave. The tl;dr with quantum light is that as light is on its way towards wherever it's headed, it can take detours (after all it has to avoid A LOT of air molecules; imagine trying to shoot a bullet through a forest without hitting any trees). Essentially, this means that whether or not light interacts with atomic-scale matter depends on a roll of a dice, and the fairness of those dice depends on the conditions in which the observation is made. With a macro-scale object, this becomes trivial as the chance of visible light interacting with the matter is very high, the light is absorbed, and the lack of light behind the object is observed as its shadow. To better understand a quantum shadow, let's consider a single slit experiment. If we shine light through a small, vertical, rectangular slit and look at the projection on a screen behind the slit we see a bar of light in the shape of the rectangle, becoming darker towards its edges. This is because light spreads outwards from its source, the slit acts as a new point-source of light, most of the light goes through the center (shortest path to the screen) and less arrives at the edges as the distribution of light becomes more spread out the further it has traveled. If we now invert the experiment, and shine light at a piece of matter the same size as the slit, we can consider the quantum result of its shadow. Certainly any light that the matter impedes would not shine on the screen and a shadow would be formed. However, both the left and right side of the piece of matter will act as their own single slit experiment, and light will spread across the region of the shadow, with a contribution from both sides. Now since this is happening simultaneously, we will actually have results more akin to a double slit experiment. To tl;dr that one for you, waves (classical and quantum) have a property called interference where they can add or subtract to each other. The light will add and subtract itself depending on the conditions of your experiment. What this means is that you will either see no shadow or multiple shadows depending on your materials and how you set up your experiment. As your piece of matter becomes smaller than infrared scale, the dice become very unfair and the most likely result of visible lights journey has it avoid the matter altogether, casting no shadow, as if the matter wasn't even there. This is the case with uv radiation from the sun causing skin cancer. On its way to our skin, sunlight in the ultraviolet range (smaller than 400nm) is mostly impeded by the dead outer layers of skin, but the universe finally rolls a d20 and some light manages to squeeze through; a critical strike is dealt to an unlucky atom in the DNA of an unlucky living skin cell, ionizing it and creating instructions to make too many babies. We use these small wavelengths of light to make shadows of smaller objects. One example is xray, small enough wavelength to fly past the empty spaces between atoms, giving us images of dense structures like bones but making tissue transparent. A comment below mentioned using uv now as well for imaging small objects. Electron microscopes work on the same concept, different only in that electrons have mass and it is the exchange of momentum that is measured. (Though still the exchange of momentum between electrons is an interaction of light). + +Thank you for the user comments correcting the magnitude for c. " Quantum-mechanically, a shadow is destructive interference of the scattering amplitude at forward angles (behind the scattering site), although colloquially one would assume that you’re talking about visible light being blocked by macroscopic objects. But really whenever something is scattering off of something else of finite “size” in space, you can have a shadow behind it. The wavelength of the projectile should be around the same size or smaller than the characteristic length scale of the target. +1089 How does water get hot enough to evaporate and form clouds? It needs to get at least 100°C and that seems tough, especially in the winter. 4579 https://www.reddit.com/r/askscience/comments/99vhrz/how_does_water_get_hot_enough_to_evaporate_and/ 1535096986 99vhrz Earth Sciences 2018-08-24 10:49:46 "You are confusing two phenomena: boiling and evaporation. + +Liquids are in equilibrium with their vapour phase. This means that water will evaporate (change phase from liquid to vapour) until the surrounding medium (air above the water) is saturated with water vapour, that is, when equilibrium is reached. Another way to state this is that water will evaporate as long as its vapour pressure is higher that the partial pressure of water vapour above it. + +It is important to realise that this is purely a *surface* thing: the liquid is in equilibrium with the vapour on the interface. This is what sets it apart from boiling, which happens in the bulk of the liquid. + +Boiling happens when the vapour pressure of water exceeds the *total* pressure of air above it, because this is required for a bubble (consisting of pure water vapour) to form in the bulk of the liquid. In reality, even a little more than that is required: the bubble also needs to overcome the hydrostatic pressure of the water (depends on the depth of the water) and some nucleation barrier I won't get into. + +In conclusion: water can evaporate (at the surface) below the boiling point, and this will happen as long as the air is not saturated with water (e.g. lower than 100% humidity)." "The temperature of a substance expresses the average kinetic energy of the components of the substance (in this case the water molecules). But the actual kinetic energies of individual molecules will vary, some will have lower energies, others higher and this changes continuously due to interactions between molecules. + +So while the bulk of the molecules may not have sufficient energy to escape the liquid in cold weather, there are some that do and if they reach the surface of the liquid, they escape / evaporate. When that happens, the average kinetic energy of the liquid decreases a little bit, which means that the temperature of the liquid decreases a little bit. But since the liquid is in contact with other materials and substances, it'll snap back into thermal equilibrium by drawing some heat from its surroundings. This process continues until (almost) all water molecules have evaporated." +669 Is there a way to find the equation of a random curve? 4575 https://www.reddit.com/r/askscience/comments/63suuf/is_there_a_way_to_find_the_equation_of_a_random/ 1491484736 63suuf Mathematics 2017-04-06 16:18:56 "**Edited** to fold in a couple of great contributions from some other commenters. + +The vast majority of smooth curves don't have ""closed-form"" equations, meaning that you can't write an f(x) in terms of simple functions like polynomials (x, x^2, x^3, ...), exponentials (e^x), trig functions (sin(x), cos(x), ...), and so on. In fact, a random scribble on paper isn't likely to be a proper function at all, because it would fail to be a one-to-one mapping that satisfies the vertical line test. As several point out below (/u/idc2011, /u/darksoulisbestsoul and others), though, you can parameterize a such a scribble as the set of functions {x(t), y(t),...}. So anything below would apply to these individual functions. (If you'd like an algorithm for finding the parameterizations, I'm afraid I can't help you there. Wolfram Alpha does a pretty great job, though.) + +Nearly any smooth function can be written as a (generally infinite) series of terms in a set of *basis functions*. Polynomials form one such basis, so you'd be able to write your curve as + +f(x) = A_0 + A_1 x + A_2 x^2 + ... + A_n x^n + ... + +Now all you have to do is find the set of coefficients A_0, A_1, ... in order to have an equation for your curve. For a randomly-drawn curve, there will be a lot of them, so this is best done using a computer. In fact, there will typically be an infinite number of terms, so you'll never be able to find all of them even with a computer. You can get an arbitrarily good approximation of your curve, though, by computing as many as you need to get ""close enough."" + +This polynomial expansion is called the [Taylor Series](https://en.wikipedia.org/wiki/Taylor_series) of the curve. Sort of. My background is physics, where we call all polynomial expansions ""Taylor Series"" (*yes, even when it's a MacLaurin series*), but +/u/functor7 has a great point below about the distinction. + +The set of sines and cosines of different frequencies also form a popular set of basis functions; an expansion in terms of them gives you your curve's [Fourier Series](https://en.wikipedia.org/wiki/Fourier_series). Fourier Series work best for functions that display periodicity, like sound waves. I mention them because lots of people are familiar with Fourier analysis and might like the connection to stuff they already know, but they probably won't be best for modeling a random, non-repeating function. + +For that matter, polynomials aren't typically your best bet, either, as the aptly-named /u/stoptalkingyourwrong points out :). I was glad to see him/her and several other posters (like /u/samclifford, /u/DataLaird) mention splines, because I've used [b-splines](https://en.wikipedia.org/wiki/B-spline) for curve-modeling, and they are in fact the bomb for arbitrary smooth-curve fitting. I didn't bring them up because they're a little more complicated, but in essence they provide an alternate polynomial basis for the expansion. The Wikipedia article (linked) is a good place to start if you want to learn more. + +If you're more curious about the mathematics of the Taylor Series, /u/dxdydz_dV has a fantastic post below that you should read. There's tons of other great information in the comments, too. I have to walk away now, because I really do need to get some work done today, but thanks to everyone for the instructive discussion!" Excellent mathematical answers here. For a practical hands-on approach if you have Excel or [Google Sheets](https://docs.google.com/spreadsheets/u/0/) you can create some data points, plot them as a [Scatter Plot](https://en.wikipedia.org/wiki/Scatter_plot) and then mess around with [curve fitting](http://www.engineerexcel.com/nonlinear-curve-fitting-in-excel/). +884 Why has Europe's population remained relatively constant whereas other continents have shown clear increase? 4575 https://www.reddit.com/r/askscience/comments/7a2jtt/why_has_europes_population_remained_relatively/ 1509529430 7a2jtt Social Science 2017-11-01 12:43:50 "So far, all societies have tended to reduce their population growth rate as they become more technologically developed and economically successful. Likely reasons include better access to birth control (so having kids is a choice), better childhood health care (if your kids are unlikely to die, you don't need as many), and better retirement plans (so you're not dependent on your kids to take care of you when you get old). + +Europe is a world leader in all of these factors, so it's no surprise that its population should be stabilizing more rapidly. If you look below the continent scale, many individual countries also follow this pattern: the population of Japan, for example, is actually shrinking slightly. The USA is an interesting case: while population growth is zero in large segments of its population, it has also historically had population growth due to immigration, and has many sub-populations where the factors I mentioned above (birth control, childhood health care, retirement plans) aren't easy to come by." "It's called the demographic transition. + +Societies used to have high birth rates and high mortality. Mortality drops first, then birth rates. + +Europe has mostly finished this demographic transition. + +The other, poorer and less developed societies, are still in the transition period where mortality is dropping but birth rates lag behind. + +The population of Europe increased in the same way during the industrial revolution. Try looking at population data from 1750-1950." +982 How much 'stuff' is in space between the Earth and Mars? 4573 https://www.reddit.com/r/askscience/comments/7wskca/how_much_stuff_is_in_space_between_the_earth_and/ 1518352700 7wskca Astronomy 2018-02-11 15:38:20 "There's some but not much stuff out there. Even the asteroid belt is mostly empty space. For example, Ceres alone is estimated to hold about a third of the asteroid belt's mass even though the asteroid belt is much denser than most of the space between planets. + +All in all space is mostly just empty with scattered planets, stars, nebulas and dust. If it weren't empty we wouldn't be able to take such clear images of galaxies that are billions of lightyears away." "Space is mostly a much better vacuum than we can produce here on earth. 100km away from earth, space begins, and pressure is 10^-7 torr. But even as far away as the moon, will earths atmosphere give orbiting objects a significant friction. At that distance the atmospspheric pressure is down to 10^-10 torr, which is pretty much the best vacuum you can make on earth. Outside the solar system (and away from the solar wind) the pressure drops to 10^-15 torr. + +10^-11 torr equals 10^-9 Pa, and gives you 4x10^12 molecules/m^3 a mean free path of 10 000 km. + +So the Tesla would hit 8*10^23 molecules/m^2 of paint. This would build up a 0.015mm thick layer of dust if it sticks. + +" +670 We have been measuring the age of earth by looking at the layers of ground, how do we know there aren't any older evidence underneath the thick snow of North pole? Or the deepest ocean floor that human has yet to discover? 4569 https://www.reddit.com/r/askscience/comments/60fxog/we_have_been_measuring_the_age_of_earth_by/ 1490009350 60fxog Earth Sciences 2017-03-20 14:29:10 ">Or even unknown creatures that lived before the dinosaurs.. + +Other users can handle the geology question, but for this I'd like to point out that [Dinosaurs only showed up fairly recently on the time frame of the history of the entire Earth,](http://i.imgur.com/7uLfRM1.png) and we have discovered countless animals that predate them by millions of years. We are constantly making new discoveries about early life on Earth, including this very year, discoveries showing that life began *billions* of years ago. However, the fossils from billions of years ago are all basically just microscopic remnants of little microscopic single-celled organisms. Still plenty of complex animal life before dinosaurs though, lots of [weird sharks](http://i.imgur.com/O4psa9D.jpg), [giant bugs](http://i.imgur.com/YratuD9.jpg) and [monster fish](http://i.imgur.com/HIFr9H3.jpg) and things. Always more to discover. + +You'll definitely be interested in [this wikipedia page, the Timeline of the evolutionary history of life](https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life)!" "Lets start by having a look at the ages of material we *actually have* observed. + +The first blunt observation we have is that the age range of geological materials is much narrower for oceanic rocks than it is for continental rocks. The oldest oceanic crust is about 340 Ma old, in the eastern Med basin; most oceanic crust is quite a bit younger. This makes sense because we observe that oceanic crust is preferentially destroyed by subduction (look up a [primer on plate tectonics](https://en.wikipedia.org/wiki/Plate_tectonics) for an overview). + +[The oldest continental crust we've found so far is 3.8 Ga old, in the eastern part of the Canadian Shield](https://en.wikipedia.org/wiki/Nuvvuagittuq_Greenstone_Belt) - that's ... pretty old. But the age of that oldest rock is complex and layered. The 3.8 Ga age is an U-Pb age of crystallisation, the age at which the magma solidified into a rock (it was a volcanic rock). But the very same sample was dated using another method (Nd/Sm geochronology). This yielded an age of 4.38 Ga - the meaning of this second age is different from, and complementary to, the first one. What this Sm/Nd age indicates is the time at which the volume of magma which ended up in that rock was extracted from the Earths mantle. + +That 4.38 Ga age is extremely interesting, because we have also been estimating the age of the earth by dating meteorites, which we believe to be leftover material from the building of the Solar System. And the age of formation of most meteorites (4.5 Ga) is getting pretty close to that of the oldest dated event on Earth (4.38 Ga). Those specific rocks, located in the Nuvvuagittuq Greenstone Belt, were found about ten years ago; we might find older material still in the years to come. But we expect the age of older materials to be somewhere within that range of 4.38 to 4.5 Ga. + +So ... back to your initial question: + + +> We have been measuring the age of earth by looking at the layers of ground, how do we know there aren't any older evidence underneath the thick snow of North pole? + +Well, we don't. And that's why people like me and my colleagues keep studying northern rocks. Although it is worth pointing out [the North Pole is in the Arctic ocean](https://s-media-cache-ak0.pinimg.com/originals/44/e9/e7/44e9e7aa779630d052f615ec48f69a47.jpg), and not above a continent. But the rocks of the Arctic seafloor are under study, as are the rocks of the surrounding landmasses. + +> Or the deepest ocean floor that human has yet to discover? + +As I mentionned earlier, oceanic rocks tend to be destroyed much faster than continental ones. They are still being studied of course, and any abnormally old rocks in the oceanic crust which might be found will certainly be the object of intense scrutiny. + + +> Or even unknown creatures that lived before the dinosaurs.. + +You're in luck there. The dinosaurs lived from about 230 Ma ago to 65 Ma ago, but the fossils of complex life forms are quite abundant and diversified in the preceeding time period starting around 541 Ma ago. During this earlier period in the history of life, critters started off in the oceans and eventually colonized the land. New species and genera are identified and described every year by paleontologists. You may want to have a look at the following references, and look up trilobites, anomalocarids, crinoids, orthocone cephalopods, graptolites and brachiopods, for starters: + +https://en.wikipedia.org/wiki/Paleozoic#Periods_of_the_Paleozoic_Era + +http://www.fossils-facts-and-finds.com/paleozoic_era.html + +http://www.ck12.org/biology/Life-During-the-Paleozoic/lesson/Life-During-the-Paleozoic-BIO/ + +http://www.ucmp.berkeley.edu/paleozoic/paleozoiclife.html" +411 I remember during the 90s/00s that the Ozone layer decaying was a consistent headline in the news. Is this still happening? 4565 https://www.reddit.com/r/askscience/comments/4q3msq/i_remember_during_the_90s00s_that_the_ozone_layer/ 1467038189 4q3msq Earth Sciences 2016-06-27 17:36:29 "The [2010 Montreal Protocol report](http://ozone.unep.org/Assessment_Panels/TEAP/Reports/RTOC/RTOC-Assessment-report-2010.pdf) says in short: + +* Global ozone and ozone in the Arctic and Antarctic is no longer decreasing, but is not yet increasing. + +* The ozone layer outside the Polar Regions is projected to recover to its pre-1980 levels some time before the middle of this century. The recovery might be accelerated by greenhouse gas-induced cooling of the upper stratosphere. +* The ozone hole over the Antarctic is expected to recover much later. +* The impact of the Antarctic ozone hole on surface climate is becoming evident in surface temperature and wind patterns. +* At mid-latitudes, surface ultraviolet radiation has been about constant over the last decade. + +Summary from [this article](http://earthobservatory.nasa.gov/IOTD/view.php?id=49040) (with pictures)." "The Montreal protocol is an international agreement that was passed, heavily regulating the use of ozone depleting chemicals. The most familiar effect was changing the propellants you can use in aerosol cans among many other things. + +https://en.m.wikipedia.org/wiki/Montreal_Protocol + +Since then, the hole in the ozone layer has recovered and the problem is getting better. The world identified the problem and took action to fix it. Hard to imagine that happening now. +" +1255 Why are the Great Basin, Mohave and Sonoran Deserts considered distinct? 4565 https://www.reddit.com/r/askscience/comments/b7vjtl/why_are_the_great_basin_mohave_and_sonoran/ 1554082053 b7vjtl 2019-04-01 4:27:33 Mostly because of distinct plant life and weather. In the Sonoran desert you have several varieties of cacti that are not present in either the Mojave or Great Basin desert. The Sonoran also has two rainy seasons, summer monsoon and winter rains while the other do not. Also separting the Mojave and Great Basin is temperature. The Great Basin is considered a cold desert, whereas Mojave is a warm desert. There are also varieties of plant life, such as Joshua Trees which are plentiful in the Mojave but rarely occur in the Great Basin. Even though they are close different weather patterns cause a division of plant life in them and separate them. "Joshua Tree National Park connects the Mojave and Sonoran Deserts, and if you look closely you can see differences in the geology and topology along the boundary line. Among the many amazing reasons to visit Joshua Tree, if you're interested in deserts, the rangers and docents at the visitor centers can give you specific destinations and pointers on what to look for. + +" +412 Is it possible for a planets moon to share an atmosphere with the planet? 4557 https://www.reddit.com/r/askscience/comments/4llimj/is_it_possible_for_a_planets_moon_to_share_an/ 1464545639 4llimj Astronomy 2016-05-29 21:13:59 For any satellite, including a moon, it has to revolve far enough away that it isn't torn apart by tidal forces. This is called the [Roche Limit](http://abyss.uoregon.edu/~js/glossary/roche_limit.html). The Roche limit is usually 2.5 times greater than the radius of the body. This theoretical planet sharing an atmosphere with its moon would have an atmosphere which is at least 3000% greater than the volume of the actual planet. In comparison, the earths atmosphere extends to be only 700 Km above sea level compared to the 6300 Km radius of the Earth. "I have a related question. My first thought about Op's question was that even if the atmosphere was large enough to capture a moon the drag would decay the orbit. + +But what if the moon in in a geostationary orbit? + +That led to my question. Clearly the atmosphere matches the earth's spin at the ground. As you go up though, it would have to move faster to allow for the increased radius of spin. So a Coriolis force in the vertical direction. This would be unsustainable though at greater distances. Jet streams run east and west. + +At what point does the atmosphere become gas particles in orbit?" +1116 Does physical size have any effect on resistance to illness? 4557 https://www.reddit.com/r/askscience/comments/9enke1/does_physical_size_have_any_effect_on_resistance/ 1536589328 9enke1 Human Body 2018-09-10 17:22:08 "There is a whole body of research surrounding obesity and the immune system. + +This claim that body size has an effect isn't so far off, as obesity has been shown to cause increases in inflammation throughout the body. Additionally, influenza tends to have a higher infection rate and mortality rate in obese individuals. So, to answer your question, yes, the duration and severity are both impacted. + +Fatigue can also lead to worse contraction of a virus, so don't overdo the exercise. + +Source: Used to work in metabolism research, know a lab that works on influenza and obesity. There are some scholarly citations here: https://www.stjude.org/directory/s/stacey-schultz-cherry.html" In addition to what other people have said, there is evidence that being bigger increases your cancer risk (see [here](https://www.bbc.com/news/health-34414446)) due to the straightforward issue of having more cells that can potentially go cancerous. +309 Whenever I buy a lottery ticket I remind myself that 01-02-03-04-05-06 is just as likely to win as any other combination. But I can't bring myself to pick such a set of numbers as my mind just won't accept the fact that results will ever be so ordered. What is the science behind this misconception? 4556 https://www.reddit.com/r/askscience/comments/4cvgzl/whenever_i_buy_a_lottery_ticket_i_remind_myself/ 1459515233 4cvgzl Psychology 2016-04-01 15:53:53 "I'm not sure if there is a name for this heuristic, but is has to do with our ideas about randomness and what we think a ""typical"" set of random numbers or events looks like. + +Another example of this occurs when you ask people to simulate flipping a coin 100 times. In the sequence of heads and tails that they write down, people will include many fewer and shorter chains of repeating values than would be statistically expected. For example, people rarely write down a sequence of 8 or more heads or tails and usually don't have more than one such sequence. However, these are actually much more likely to occur in 100 flips than people expect and a computer would generate more and longer sequences. + +Edit: as others have pointed out, this is an example of the representativeness heuristic and gambler's fallacy." "apple actually rewrote the code for picking songs on shuffle. it used to be completly random, but people would pick up on chance patterns and complain it wasnt. + +so they wrote a code to appear random to listeners. + +i dont think it has a name, but it should." +413 How worried should we be about the Clathrate Gun? 4555 https://www.reddit.com/r/askscience/comments/4uus54/how_worried_should_we_be_about_the_clathrate_gun/ 1469628511 4uus54 Earth Sciences 2016-07-27 17:08:31 This post has been locked due to the number of off-topic comments. "There is at the present, to my knowledge, no consensus on the immediacy of a ""smoking"" global & catastrophic clathrate gun. I believe it is worth quoting at length the conclusion of the following recent study ([Ruppel, C. D. (2011) Methane Hydrates and Contemporary Climate Change. Nature +Education Knowledge 3(10):29](http://pm22100.net/docs/pdf/enercoop/energie/gaz/130316_Methane_Hydrates_and_Contemporary_Climate_Change.pdf)): + +*Catastrophic, widespread dissociation of methane gas hydrates* **will not be triggered by continued climate warming at contemporary rates** *(0.2ºC per decade; IPCC 2007) over timescales of a few hundred years. Most of Earth's gas hydrates occur at low saturations and in sediments at such great depths below the seafloor or onshore permafrost that they will barely be affected by warming over even 103 yr. Even when CH4 is liberated from gas hydrates, oxidative and physical processes may greatly reduce the amount that reaches the atmosphere as CH4. The CO2 produced by oxidation of CH4 released from dissociating gas hydrates will likely have a greater impact on the Earth system (e.g., on ocean chemistry and atmospheric CO2 concentrations; Archer et al. 2009) than will the CH4 that remains after passing through various sinks.* + +That being said, it appears that there might indeed be a *localized* increase in clathrate destabilisation in some specific settings such as the relatively shallow Arctic continental shelves (*Op. cit.*), but the rate and actual scale of this phenomenon, as well as what actually happens to the released gasses (does it remain in solution? does it get degraded by microbes?), remains to be determined." +546 Did the land ever fully recover from the Dust Bowl, or were some losses permanent? 4553 https://www.reddit.com/r/askscience/comments/5be1l9/did_the_land_ever_fully_recover_from_the_dust/ 1478404517 5be1l9 Earth Sciences 2016-11-06 6:55:17 "It takes a thousand years to generate 3 centimeters of top soil, so the damage is permanent. In fact, soil loss is a continuing problem. In the Midwest, famously known for its deep topsoil, some areas have lost up to half of their topsoil since the end of the dust bowl because of intensive industrial farming. + +http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/home/?cid=stelprdb1041887 + +There are reports that the government's estimates of soil erosion are seriously off, by anywhere from 100% to 200%. + +http://www.resilience.org/stories/2014-09-29/plowing-bedrock-how-bad-is-soil-erosion-in-us-cropland" "Check out Ken Burns's *The Dust Bowl*. Not only is it a great documentary that addresses the lead-up to and the development of the dust bowl, but how a government was able to rally and somewhat mitigate an environmental disaster for the national good (shocking, I know). + +The end isn't exactly positive, as it indicates the region is still over-taxing the environment to this day through abuse of the Ogallala aquifer, and that farmers aren't getting any support to modernize their irrigation systems (which, by some estimates, can save up from 10%-30% of the water they normally use)." +1090 What is the biochemical origin of caffeine dependence? 4547 https://www.reddit.com/r/askscience/comments/8ta7gw/what_is_the_biochemical_origin_of_caffeine/ 1529763417 8ta7gw 2018-06-23 17:16:57 "Caffeine is a nonselective adenosine receptor antagonist, acting at A1, A2a, A2b, and A3 receptors (it also binds to a few other receptors, but we’ll ignore those for simplicity’s sake). From knockout studies in mice, it appears A2a is critical for the stimulating effect of caffeine. In the brain, Adenosine levels fluctuate as the day passes with the highest levels at night. Higher levels of adenosine produce a drowsiness effect. When you consistently apply an antagonist to a cell, a common response is the cell will upregulate the particular receptor that is being antagonized. As such, consistent caffeine intake can result in an upregulation of adenosine receptors [1]. When you do not intake caffeine, you thus experience a heightened response, or a sensitization, to adenosine, and thus feel an increase in drowsiness. + +1. Cell Mol Neurobiol. 1993 Jun; 13(3): 247–261." Caffeine is an adenosine antagonist. Adenosine makes you feel tired and antagonists block receptors. It doesn't actually give you energy by stimulating excitatory receptors like an amphetamine. However, both changes cause the brain to counter-regulate the effects of the substance and result in long-lasting physiological accommodations. This causes withdrawals when you take the chemical away and they can potentially last YEARS depending on your personal genes and lifestyle. +205 How the heck do jellyfish work if they have no brain or no blood? 4535 https://www.reddit.com/r/askscience/comments/3s24oj/how_the_heck_do_jellyfish_work_if_they_have_no/ 1447022118 3s24oj Biology 2015-11-09 1:35:18 [deleted] "They don't have a brain, but they do have basically a collective of nerves forming a [nerve net](https://en.wikipedia.org/wiki/Nerve_net). This allows them to sense and respond to stimuli. + +Jellyfish do actually have some sensory organs, such as ocelli, which are light sensitive organs. Not really eyes, per se, but they do detect light conditions. Interestingly enough, box jellies actually do have complex eyes which have a lenses, retinas and corneas! They have 24 eyes, clustered in sixes on each side of their box-shaped bell. These clusters are called rhopalia. Only 2/6 of these eyes actually have the complete set of lens, retina and cornea; the other 4/6 are ocelli. Now, we're not exactly what they see - do they see images or just really good light differences? They probably don't see images like we do, but it's still freaky, eh? You can check out more eye properties of the box jellies here: https://openi.nlm.nih.gov/detailedresult.php?img=2825319_359_2010_506_Fig1_HTML&req=4 + +So as it turns out, blood isn't really a necessary part of life. Let's think about what blood does in our bodies. The circulatory system is basically the highway system of the body, and blood constituents are gonna ride it to the other parts of the body. The main purposes of blood are to facilitate gas and nutrient exchange. It delivers oxygen and nutrients, while also taking away carbon dioxide and metabolic wastes. If you're a jellyfish, your body is literally just a gelatinous network of cells. It's so thin that oxygen and metabolic wastes can just diffuse in/out, which is why they don't need/have blood. + +>I can't think of any other example of a multi-cellular organism without these essential things + +Sponges, corals, bryozoans... lots of animals :) + +**Here's one that will really trip you out:** [*Trichoplax adhaerens*](https://en.wikipedia.org/wiki/Trichoplax) They have no organs, and no nerves, sensory cells or muscle cells: + +http://www.nature.com/nature/journal/v454/n7207/full/nature07191.html" +547 Discussion: SmarterEveryDay's Newest YouTube Video On Tesla Coil Guns! 4525 https://www.reddit.com/r/askscience/comments/5fxl3v/discussion_smartereverydays_newest_youtube_video/ 1480610784 5fxl3v Engineering 2016-12-01 19:46:24 As an underwater welder, I'm used to feeling around 350 amps worth of electricity in my hands and teeth... I've got to ask: Does the backpack mounted Tesla coil have the potential to incapacitate a human if desired? How much could that thing pump out before frying? "Hey guys! Destin here. I'm by no means a tesla coil guru... but I'm no stranger to high voltage either. I have experience with DC high voltage detonator circuitry. HV AC is a brave new world for me, so I'm eager to learn. Cameron Prince (u/teslauniverse), the guy that runs www.teslauniverse.com is going to be in this thread as well. He is the real guru that can answer technical questions about the circuitry and Nikola Tesla in general. I've asked him to answer questions by providing references to Tesla documentation he's accumulated over the years when appropriate. One question I'd like to start with myself is ***""Why does the bolt just go out into air and not physically touch the ground?""*** What is happening there?" +1368 When plotting exoplanet discoveries with x being semi-major axis and y being planet mass, they form three distinct groups. Why is this? 4524 https://www.reddit.com/r/askscience/comments/cixdpc/when_plotting_exoplanet_discoveries_with_x_being/ 1564328845 cixdpc Astronomy 2019-07-28 18:47:25 "This is basically part of my area of research so I will try and begin to scratch the surface of this problem! + +  + +The exoplanet community would also like to know! First I will say these gaps are absolutely NOT due to observational problems. Our observational issues are mostly towards the bottom right of the plot. Gaps such as the [hot neptune](https://en.wikipedia.org/wiki/Hot_Neptune) desert are well within our region of observations. + +  + +The gap at sub 10 day orbit of Jupiter mass planets (on your plot that is <0.05AU and 10-100 Mearth) is known as the Hot Neptune desert (actually most gaps in populations of astrophysical bodies get called deserts). We have no idea why this exists. + +  + +[One theory](https://www.extremetech.com/extreme/282329-scientists-detect-hot-neptune-losing-atmosphere-at-an-extraordinary-rate) is that unlike their Jupiter mass counterparts, the hot Jupiters, they lack the mass to keep hold of their atmosphere from being stripped by stellar activity. This means they would travel down your plot to become hot super Earths. There are problems with this idea in that this process should take hundreds of millions to billions of years so we should actually observe a lot more of these than we do. Further the [desert transition is quite sharp](https://arxiv.org/pdf/1602.07843.pdf). I do not think this is likely to be the primary cause. + +  + +A second theory is that this highlights a difference in formation mechanism between hot super earths (mentioned in [this](https://arxiv.org/pdf/1602.07843.pdf) paper linked before) and hot jupiters. This also has a problem that it assumes there is a single formation mechanism for HJ planets. People are finally starting to believe there may actually be more than one formation mechanism for HJs. So this gap would need to be explained by all valid formation mechanism (the various mechanisms are reviewed [here](http://arxiv.org/abs/1801.06117) but its a long read!). In particular in situ formation and disc migration mechanisms have a hard time explaining this gap (as well as the gap between hot and cold jovian planets at the top of your plot). + +  + +If (and I think this is unlikely due to observations of very young HJs, [1](http://www.nature.com/articles/nature18305) and [2](http://arxiv.org/abs/1701.01512)) the formation mechanism for HJs is high eccentricity migration then this gap is obtained for free as it could be explained by roche lobe overflow. This is that when a giant planet is in a highly eccentric orbit and passes its pericenter (closest to the star) the atmosphere breaches the roche limit of the star and experiences atmospheric stripping. As the planet continues to circularise it would rapidly lose atmosphere and become a hot super earth. + +  + +So the bottom line here is that this one gap (which I believe is the most well studied) is not fully understood. A proper explanation (of all gaps?) will come once we have reevaluated planetary formation and migration mechanisms. We kind of had to throw the book of what we knew on this out the window once we started getting exoplanet observations! If I was to make an educated guess (I sure as hell wouldnt put money on this guess though as our understanding of formation and migration still has a lot of work) I would say it may actually be a combination of ideas 2 and 3 as they both can end up doing similar things (or be responsible for the upper and lower boundaries of the desert)." "There have been a number of lengthy answers on this thread by people that, while they know what they are talking about, are still making some poor assumptions that are leading them to incorrect conclusions. In particular, I'm going to focus on the two groups of giant planets. The gap is due largely to the different surveys that were used to find the planets. Your plot include planets found mostly by 3 kinds of survey: +1) ground-based radial velocity surveys (RV) +2) ground-based transit surveys +3) space-based transit surveys (mostly Kepler, but also K2 and CoRoT) + +RV surveys generally have a sensitivity that only weakly depends on the inclination of the orbit, and for the most part smoothly declines as the orbital period increases. These surveys generally are quite complete, and that completeness is a reasonably smooth function in the mass-period diagram. They only survey a relatively small number of the brightest stars, so only common types of planets will show up often. +Kepler is sensitive only to planets that have a small range of inclinations that cause the planet to transit, and the range of inclinations falls off as the period increases. But, Kepler continuously observed, so its sensitivity drops of quite smoothly with orbital period. Kepler monitored a modest number of stars, and the transit probability (due to random inclinations) is quite small, so it doesn't have that many rare types of planet, but does have lots of common planets. +Ground-based transit surveys have all of the problems that Kepler has (inclination etc.) and then some. They can only observe for ~8 out of 24 hours, have interruptions for weather, and also have long seasonal gaps in observations. This means that they only really have sensitivity to Jupiter-sized planets with orbital periods less than 10 days. Their major advantage is that they have surveyed millions of stars, so they can find large numbers of even rare types of planets in their sensitivity range will be seen. + +The dense clump of Jupiters in short orbits can now be seen to probably a selection effect, because it is adding large numbers of planets from ground-based surveys that the other surveys wouldn't find. + +I'd encourage you to remove the planets from ground-based surveys from your plot, and instead just plot planets from +a) the main Kepler survey alone +b) RV surveys alone +each of these plots will still be subject to selection biases, but much less so. I went ahead and made a version of your plot with radius vs period for Kepler only: https://imgur.com/1419bMq (this is from the NASA exoplanet archive, which is a bit better than exoplanets.org in terms of completeness and data filtering options in my opinion) +You can see that there might be a hint of two groups of Jupiter radius objects, but its much less pronounced than in your plot. This plot is still massively mis-reprentative though because you should really account for the detection probability of each planet. This is roughly 0.3%/distance in AU just due to inclination (I'm assuming that for Jupiter sized planets, Kepler would have no other detection innefficiency). From Kepler's laws, period is proportional to semimajor axis to the 1.5 power, so the probability of a planet actually transiting its star is about 20 times less for a planet in a 100 day long orbit than a planet in a 1 day orbit. If you correct for this (by e.g., plotting extra fake planets to make up for the ones that are too inclined to be seen transiting), then you will probably conclude that there might not be two distinct groupings, but a more continuous distribution. Figure 4 of this paper doing an early analysis of a subset of the Kepler mission shows the kind of thing I'm talking about - there are more up to date versions of this, but I can't remember the reference: +https://arxiv.org/pdf/1103.2541.pdf + +Now, there absolutely are some gaps in the distribution, especially in the radius distribution at short periods - this was revealed by carefully accounting for how detectable the planets of each radius and period were: +https://arxiv.org/pdf/1703.10375.pdf + +But, the key point that you should take away is that you should be very careful about drawing conclusions from just plotting up every known example of things that are hard to find. The groupings may be due to some real physical effects, and its important to ask the questions that you are, but as you can see from other comments, even experts can make the mistake of not carefully accounting for varying detection efficiencies of different methods." +548 If you watch a gif of a coin flipping (without ever seeing it) to make a decision, is it still a 50/50 chance, even though the video already predetermines what side the coin will flip onto? 4519 https://www.reddit.com/r/askscience/comments/56ij7c/if_you_watch_a_gif_of_a_coin_flipping_without/ 1475954598 56ij7c Mathematics 2016-10-08 22:23:18 "There are multiple ways to interpret probabilities. The way you're probably most familiar with is to consider them *relative frequencies*. + +That means that if you have a fair coin (p = 1/2), you can say that in the limit as the number of flips goes to infinity, the fraction of results which give heads approaches 1/2. + +But there is a sense in which probabilities represent your degree of *knowledge* or *belief* about the outcome of some experiment. + +If I flip a coin and catch it in my hand so that nobody can see the result, there is a definite answer to the question ""Is the coin showing heads or tails?"". In other words, it's either definitely showing heads or definitely showing tails. + +But nobody knows which yet. The best anybody can possibly say (assuming a fair coin and nobody is cheating) is that there's a 50% chance that heads is showing and a 50% chance that tails is showing. + +This represents a *lack of knowledge* on our part. So the answer *is* predetermined, but nobody knows it yet. So we still ascribe a probability of 1/2 for either case, because that's the best we can do given our current knowledge." "Terminology/phrasing problem: There's a 50/50 chance of you **guessing the ending of the GIF**, which is different than the odds of the coin in the GIF ending up heads or tails. You could also flip a coin in a dark room and once it hits the floor, call it and turn the lights on. Same thing: The coin's ""decision"" has been made, but you still have to guess what that decision **was** (as opposed to what it **will be** as in a traditional coin flip scenario)" +1369 If you are on the moon, does Earth appear to go through phases? 4516 https://www.reddit.com/r/askscience/comments/bzw48v/if_you_are_on_the_moon_does_earth_appear_to_go/ 1560370483 bzw48v Astronomy 2019-06-12 23:14:43 "Yes. + +In fact, it will be the exact opposite of whatever phase the Moon is in as seen from Earth. So if it's a New Moon as seen from Earth, it will be a Full Earth as seen from the Moon; if the Moon is in a waxing crescent phase, Earth will be in a waning gibbous phase." "[Here](https://streamable.com/gzlyr) is the ""evidence"". + +​ + +It is a video of what the earth looks like from the Apollo 11 site ([Sea of tranquility](https://en.wikipedia.org/wiki/Mare_Tranquillitatis)) made using [Stellarium](https://stellarium.org/) software. Unlike the moon seen from earth, the earth never sets there. So over the duration of a day, we can see earth rotate completely and over the duration of a month, the phases." +0 IF sound could travel through space, how loud would The Sun be? 4503 http://www.reddit.com/r/askscience/comments/33xuxu/if_sound_could_travel_through_space_how_loud/ 1430071405 33xuxu Astronomy 2015-04-26 21:03:25 "Solar physicist here. + +The Sun is immensely loud. The surface generates thousands to tens of thousands of watts of sound power for every square meter. That's something like 10x to 100x the power flux through the speakers at a rock concert, or out the front of a police siren. Except the ""speaker surface"" in this case is the entire surface of the Sun, some 10,000 times larger than the surface area of Earth. + +Despite what /u/Bigetto said, we do in fact know what the Sun ""sounds"" like -- instruments like SDO's HMI or SOHO's MDI or the ground-based GONG observatory measure the Doppler shift everywhere on the visible surface of the Sun, and we can actually *see* sound waves (well, infrasound waves) resonating in the Sun as a whole! Pretty effing cool, eh? Since the Sun is large, the sound waves resonate at very deep frequencies -- typical resonant modes have 5 minute periods, and there are about a million of them going all at once. + +The resonant modes in the Sun are excited by something. That something is the tremendous broadband rushing of convective turbulence. Heat gets brought to the surface of the Sun by convection -- hot material rises through the outer layers, reaches the surface, cools off (by radiating sunlight), and sinks. The ""typical"" convection cell is about the size of Texas, and is called a ""granule"" because they look like little grains when viewed through a telescope. Each one (the size of Texas, remember) rises, disperses its light, and sinks *in five minutes*. That produces a Hell of a racket. There are something like 10 million of those all over the surface of the Sun at any one time. Most of that sound energy just gets reflected right back down into the Sun, but some of it gets out into the solar chromosphere and corona. None of us (professional solar physicists) can be sure, yet, just how much of that sound energy gets out, but it's most likely between about 30 and about 300 watts per square meter of surface, on average. The uncertainty comes because the surface dynamics of the Sun are tricky. In the deep interior, we can pretend the solar magnetic field doesn't affect the physics much and use hydrodynamics, and in the exterior (corona) we can pretend the gas itself doesn't affect the physics much. At the boundary layers above the visible surface, neither approximation applies and the physics gets too tricky to be tractable (yet). + +In terms of dBA, if all that leaked sound could somehow propagate to Earth, well let's see... Sunlight at Earth is attenuated about 10,000 times by distance (i.e. it's 10,000 times brighter at the surface of the Sun), so if 200 W/m^2 of sound at the Sun could somehow propagate out to Earth it would yield a sound intensity of about 20 mW/m^2 . 0dB is about 1pW/m^2 , so that's about 100dB. At Earth, some 150,000,000 kilometers from the sound source. Good thing sound doesn't travel through space, eh? + +The good folks at the SOHO/MDI project created some sound files of resonant solar oscillations by speeding up the data from their instrument by 43,000 times. You can hear those [here, at the Solar Center website](http://solar-center.stanford.edu/singing/#sing). +Someone else did the same thing with the SDO/HMI instrument, and [superposed the sounds on first-light videos from SDO](https://www.youtube.com/watch?v=GWCJkG31h0c). Both of those sounds, which sound sort of like rubber bands twanging, are heavily filtered from the data -- a particular resonant spatial mode (shape of a resonant sound) is being extracted from the data, and so you hear mainly that particular resonant mode. The actual unfiltered sound is far more cacophonous, and to the ear would sound less like a resonant sound and more like noise." "I've spent the last 5 years working with NASA scientists to translate data from the sun into sound through a process known as audification. It looks like the question of raw intensity has been pretty well covered here, I'd be more than happy to chime in on *what the sun sounds like.* + +The answer is... it depends on *how* we listen to the data and over what time-scale. If we [audify to 12 years of data from the Advanced Composition Explorer satellite, we'll hear an underlying ""hum"" produced by features that persist across multiple solar rotations, and we'll also hear spherical harmonics generated by the solar magnetic field. Particle observations are generally gathered at a sampling cadence of roughly two-hours, while the solar magnetic field is typically sampled at a rate above the ~10 Hz." +1425 AskScience AMA Series: I'm Jane Pearson. I'm a psychologist at the National Institute of Mental Health (NIMH). As we observe Suicide Prevention Awareness Month this September, I'm here to talk about some of the most recent suicide prevention research findings from NIMH. Ask me anything! 4493 https://www.reddit.com/r/askscience/comments/czz9k2/askscience_ama_series_im_jane_pearson_im_a/ 1567681229 czz9k2 2019-09-05 14:00:29 "Hi everybody, + +Please remember [medical advice](https://www.reddit.com/r/askscience/comments/s4chc/meta_medical_advice_on_askscience_the_guidelines/) is strictly off-topic - asking and giving. + +Enjoy the AMA." Has there really been an increase in suicide the last thirty years or just better documentation of it? +1601 AskScience AMA Series: We are the NASA New Horizons team, here to answer your questions about the New Horizons spacecraft, parallax imaging, deep space exploration and what we learned at Pluto. Ask us anything! 4493 https://www.reddit.com/r/askscience/comments/h7imbw/askscience_ama_series_we_are_the_nasa_new/ 1591959610 h7imbw Planetary Sci. 2020-06-12 14:00:10 What is the maximum distance from Earth that the New Horizons spacecraft will be able to transmit data back to us? "To Brian: Congratulations on being voted the greatest rock guitarist of all time! + +Have you always been interested in space exploration or did your passion come later in life?" +549 If e=mc^2, does that mean that the sun is constantly losing mass through radiated energy? 4490 https://www.reddit.com/r/askscience/comments/51b91z/if_emc2_does_that_mean_that_the_sun_is_constantly/ 1473105680 51b91z Physics 2016-09-05 23:01:20 "Yes. The energy comes from nuclear fusion in the core, primarily the [proton-proton chain reaction](https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction). If you look at the first figure, you'll see the overall reaction is six protons (hydrogen nuclei) producing a helium nucleus, two output protons (that go back into the p-p chain), some positrons and neutrinos (for the proton->neutron conversion), and some gamma rays (energy/light). Some amount of mass energy is released in the other products while some amount is released from the difference in the [binding energy](http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html) of the more complex nuclei. + +Phil Plait of [Bad Astronomy](http://www.slate.com/blogs/bad_astronomy/2014/07/14/solar_wind_versus_fusion_how_does_the_sun_lose_mass.html) already worked out the calculation for whether the solar wind or nuclear fusion causes more mass loss in the Sun. Apparently fusion wins out ""by about a factor of two or three""." What is mind blowing about e=mc^2 is that if you take two springs, one is relaxed and the other is compressed, e=mc^2 means that the compressed spring has more mass and more gravitational pull, and have more inertia. +206 Given time to decompress slowly, could a human survive in a Martian summer with just a oxygen mask? 4486 https://www.reddit.com/r/askscience/comments/3mkson/given_time_to_decompress_slowly_could_a_human/ 1443362543 3mkson Human Body 2015-09-27 17:02:23 "**Short answer:** No. Exposure to vacuum or near vacuum is not well understood because it hasn't happened to many people, and while we're fairly sure it will kill you no one really knows what will get you first... but we do have a few ideas. + +**Long answer:** You know how liquid water freezes at 0 C and boils at 100 C? That's a lie - it only boils and freezes at those temperature at sea level with atmospheric pressure. If you go up one mile in altitude to Denver then water actually boils at 95 C. This means that the phase of water is dependent on both temperature and pressure, so if you specify a temperature and a pressure then you can [use this chart to determine the phase of water.](https://upload.wikimedia.org/wikipedia/commons/0/08/Phase_diagram_of_water.svg) + +The atmospheric pressure of Mars is about 0.6% that of earth, or about 600 Pascals at sea level. So what happens to the water in your body? At this pressure, you're even below the triple point of water, so it can only exist as a gas or solid. Given your body temperature, *your eyes would boil.* But it wouldn't stop just there. Without the pressure the atmosphere provides I expect any exposed fluids will boil, such as saliva and the fluid in lungs, though whether or not blood boils seems to be an open question. (Also, I don't want anyone coming away from this thinking it means it's impossible for their to be liquid water on Mars - just that the liquid water can't be *you*) + +Jim LeBlanc is the only person I know of who has survived exposure to vacuum (or comparably low pressures)- he was testing a NASA spacesuit in a vacuum chamber when the suit lost pressure. He reported that he could feel the [saliva on his tongue boiling, before passing out almost instantly.](https://www.youtube.com/watch?v=KO8L9tKR4CY) I'm not a doctor, but I just honestly don't think this would be survivable for any extended period. + +In fact, so many things are going to be wrong that the minor inconvenience of experiencing a phase transition might not even be the thing that kills you. + +For example, you might be familiar with the concept of the ""Death Zone"" on Mt Everest. Among other things trying to kill climbers, the atmospheric pressure is about a third of what it is at sea level. The lower partial pressure of oxygen (ppO2) results in a lower blood oxygen saturation level, and thus many Everest climbers resort to bottled oxygen. That's a problem at 33% of atmospheric pressure on earth - now consider how deadly it will be at 0.6% on Mars. Even with 100% oxygen (and liquid blood) you'd only have 0.006 ppO2 on Mars, while the survivable limit is between 0.16 and 1.6 (thanks to [u/Philip_Pugeau](https://www.reddit.com/r/askscience/comments/3mkson/given_time_to_decompress_slowly_could_a_human/cvfv99o))" "No, because martian air pressure is so low that even 100% oxygen isn't enough. + +Normal air you breathe is 21% oxygen. Normal air pressure is about 100 kPa, so your body expects 21 kPa of oxygen pressure. + +Now, if you go someplace high, air pressure might be half of that. People can acclimate to 50 kPa air, with 10 kPa oxygen. + +To survive at higher altitudes, people use oxygen masks to change the proportion of oxygen in the air. Breathing normal air at 20 kPa pressure, you'd be getting 4 kPa of oxygen, which is not enough to oxygenate your blood, and you'd pass out. + +But if you were breathing pure oxygen, that's 20 kPa of oxygen, which is just perfect. + +But this whole technique only works down to 10 kPa ambient pressure. If the outside air pressure is lower than that, you can't get enough oxygen into your mask to stay conscious. You need an actual pressure suit to keep the in-suit pressure at least 15 kPa or so. + +Now, martian air pressure is less than 1 kPa. This is *way* too low. Even 100% oxygen isn't enough; you'd need at least 1000% oxygen. The only way to get more than 100% is with a pressurized suit. + +----- + +The oft-repeated claim about blood boiling is dead wrong. Your blood does not boil even in a vacuum. That's because even if the outside air pressure is zero, the blood pressure in your veins is high enough to prevent it. + +Because the [vapor pressure of water](http://www.wiredchemist.com/chemistry/data/vapor-pressure) at body temperature (37 °C) is 6.28 kPa. In blood pressure units, that's 47.1 mm of mercury. (The vapor pressure of blood is lower than pure water, so this is a conservative assumption.) If your blood pressure is 120/70, your blood isn't going to boil. + +*However*, at pressures below 6 kPa, which includes Mars, every wet part of your body exposed to ambient pressure *will* boil dry. Eyes, mouth, nose *and the lining of your lungs*. The latter will do you no good at all *but* you'll pass out from lack of oxygen before you notice. + +(Also, normal intraocular pressure is 10-20 mm Hg, so the fluid inside your eyeballs *will* boil, but only until it generates an internal pressure of 47.1 mmHg. This will be uncomfortable and unhealthy, but is not enough to make your eyeballs explode or anything gruesome.)" +671 Do microwaves kill bacteria? 4481 https://www.reddit.com/r/askscience/comments/5v601a/do_microwaves_kill_bacteria/ 1487613119 5v601a Biology 2017-02-20 20:51:59 "To some extend a microwave can kill bacteria, but not all bacteria can be considered equal in terms of conditions required to inactivate or kill them. As you might understand there are many factors in play to consider such as the material, thickness of the material and the type of bacteria so it's not possible to give you a generalised answer that will apply to everything you stick in the microwave. + +Perhaps you've heard of this tip before. Stick a sponge in a microwave to disinfect the sponge. Going by this example the following has been found. + +[NYTimes - The Claim: You Can Disinfect a Kitchen Sponge in the Microwave (2007)](http://www.nytimes.com/2007/03/27/health/27real.html): + +>>In recent years, at least two studies have put the claim to the test, and both have confirmed it. The most recent, published in the December 2006 issue of The Journal of Environmental Health, found that microwaving kitchen sponges and other scrubbing pads for one to two minutes at full power could reduce levels of bacteria, including E. coli and other common causes of food-borne illness, by more than 99 percent. + +>>A previous study in 1999 found that many bacteria are eliminated within the first 15 seconds of being heated by microwave, and that only E. coli survive longer than 30 seconds. + +>> To avoid fires or overheating, the authors of the 2006 study recommended that only damp sponges and those without metal be zapped. But some experts say the practice poses a safety hazard and should be discouraged. Some news accounts have described cases in which kitchen sponges caught fire while being cooked by microwave. + +>>Other studies have found a safer alternative: soaking soiled sponges in diluted solutions of bleach, which is just as effective as heating. Then again, there is an even simpler option: tossing the sponge out and getting a new one. + + +[BBC - Microwave 'sterilisers' warning (2007)](http://news.bbc.co.uk/2/hi/health/6293735.stm): + + +>> Professor Gabriel Bitton, a expert in environmental engineering at the University of Florida, and colleagues contaminated kitchen sponges and plastic scrubbing pads in dirty water which contained faecal bacteria, viruses, protozoan parasites and bacterial spores. + +>> After two minutes on full power, 99% of bacteria were inactivated. And E. coli bacteria were killed after just 30 seconds. Bacillus cereus spores - which are largely associated with vegetables or foods in contact with soil and are normally quite resistant to radiation, heat and toxic chemicals - were completely eradicated after four minutes in the microwave. + +>> Professor Britton said it was likely to be heat, rather than radiation, that proved fatal ~~as microwaves worked by exciting water molecules.~~ + +>> The team also looked at whether the microwave oven could be used to sterilise contaminated syringes. It was found to be an effective method but took far longer - up to 12 minutes for the Bacillus cereus spores. + +>> Professor Hugh Pennington, a food safety expert at the University of Aberdeen said heating was an effective way of sterilising kitchen equipment. + +>> He said heat was an obvious method of sterilisation. + +EDIT: [How Microwaves Work](https://www.reddit.com/r/askscience/comments/5v601a/comment/de0alfu?st=IZF33CUK&sh=c674a25b). " "Useful Definitions + +Disinfect: To kill all pathogens but not all microorganisms + +Decontaminate: To make something safe for use by the general public + +Sterilize: To kill all life, including viruses + +Microwaves, do not kill cells by altering cellular structures, they just kill cells by heat. So it can kill cells to an extent, and can decontaminate if you let the microwave run long enough to get the food or whatever being heated to a high enough temperature. However, it does not necessarily disinfect. Food is always and only decontaminated. I've never heard of any industry or company disinfecting food, not sure it would be safe for consumption. + +Contrary to popular belief, even boiling cannot sterilize. You must use either incineration or a combination of pressure and heat, in order to increase the temperature of water past 100 degrees Celsius to kill all life. + +Extra knowledge, endospores are an extremely heat resistant form bacteria can create, and they can outlive all other forms of vegetative bacteria. These are usually the hardest to get rid of when sterilizing something, unless there is extremely heat resistant Archae present in your food, highly unlikely." +207 If the reason testicles are kept outside the body is that sperm can't survive at the body's internal temperature of 37C/98F, why do people who live in places where the ambient temperature is routinely higher than that have no trouble breeding? 4480 https://www.reddit.com/r/askscience/comments/3jhdo1/if_the_reason_testicles_are_kept_outside_the_body/ 1441284577 3jhdo1 Human Body 2015-09-03 15:49:37 "Actually, it's not only a matter of survival of sperm, but that spermatogenesis doesn't do well at temps of 37 C., or higher. It does better outside of the body where it's cooler, or so we're told. But the point is, how did this occur? Which came first, the external male gonads of the mammals, or what? Are the reptiles any different in this respect? + +Apparently oogenesis (egg production in the ovaries) does well enough inside of the body. But why not spermatogenesis? Is it That different from oogenesis? This is still a great mystery. We solve one problem, and then up pops another, and another. + +This might give/create more understanding of what's going on.... +https://jochesh00.wordpress.com/2015/09/01/evolution-growth-development-a-deeper-understanding/ + +For that matter why in heck are our testicles so damn sensitive to shock? It's a huge weakness as many men and women know. How did that come about? Or the sensitivity of our eyes to pain for that matter? Or is it all connected to a deeper principle?" "In addition to the other cooling mechanisms here, the venous return of the blood through a structure called the ""venous pampiniform plexus"" is designed to keep them cooler than body temperature. Any temperature, above which they would be damaged and unable to compensate, would likely be causing other troubles. " +672 What exactly would the landscape of the British Isles have looked like prior to human cultivation? 4479 https://www.reddit.com/r/askscience/comments/5ts8zj/what_exactly_would_the_landscape_of_the_british/ 1486983035 5ts8zj Paleontology 2017-02-13 13:50:35 "This is actually an area of ongoing debate. In the past, it has generally been assumed that Britain was largely covered by forest - primarily because forest is seen as the inevitable result of succession given the ecological conditions in Britain. Note that in most of Britain this climax community is temperate broadleaf or mixed woodland, where as your vision of Canada and Scandanvia might well be of boreal coniferous forest. + +However, in 2000 Frans Vera published a book called ""Grazing ecology and forest history"" which suggested that prior to human arrival and dominance, large grazing herbivores (e.g. aurochs, the extinct ancestors of domestic cattle) would have had a strong effect on the landscape by browsing on trees and shrubs and hence preventing succession from occuring. This, coupled with other disturbance forces such as wildfires, storms, diseases and pests, and floods, with have lead to a relatively open park-like mosaic of wood and grassland. One question that this hypothesis answers is: where did all the open-country species live? Many species in Britain (noteable many butterflies and wildflowers) are strongly associated with open landscapes and direct sunlight, and would not be found in continuous woodland. + +So, how can we find out? One of the most common techniques is to analyse long term sediment cores from lakes. Pollen is trapped in the sediment, and changes in the presence and relative abundance of different species' pollen can indicate changing plant communities. Furthermore, sediment also contain fungal spores; certain spores are associated with herbivore dung, and therefore the abundance of these spores can be used as an indicator of the abundance of herbivores and hence infer the grazing pressure. Another technique is to use ecological inferrence - we can use exclosure or introduction experiments to try and understand the impact that the presence or abscence of large mammals would have had on the vegetation, and then try and estimate which situation is most applicable to Britain. + +However, part of the reason that this debate is still ongoing is that the arrival of humans into Northern Europe coincided with the end of most recent glacial period; as such the impact of human arrival is confounded with changing climatic conditions and natural recolonisation of species into previously ice-covered areas. + +Further reading: + +https://www.britishwildlife.com/site/issue/211117/volume-20-number-5-up-june-2009 (not sure if the pdf is online anymore - pm me if you want a copy) +http://www.pnas.org/content/113/4/847.abstract +http://www.sciencedirect.com/science/article/pii/S0006320701001628 + +Hope this helps (and sorry for the essay) - happy to answer any questions!" what would some the desert regions of the world look like had it not been for thousands of years of agriculture. Particularly in the areas around the birthplace of civilization (Sumeria, Mesopotamia)? Was it always sand/desert like as we often depict it today. +310 Humans have a wide range of vision issues, and many require corrective lenses. How does the vision of different individuals in other species vary, and how do they handle having poor vision since corrective lenses are not an option? 4476 https://www.reddit.com/r/askscience/comments/4can8o/humans_have_a_wide_range_of_vision_issues_and/ 1459179373 4can8o Biology 2016-03-28 18:36:13 [deleted] Humans have much greater visual acuity than just about any animal except birds. A lot of our sensory input is through our eyes... But that's not true for all animals. So visual defects don't have as big of an impact on dogs, for instance, because they rely more heavily on other senses. +113 Why don't we take blood from dead people? 4474 http://www.reddit.com/r/askscience/comments/3cy2qs/why_dont_we_take_blood_from_dead_people/ 1436646906 3cy2qs Medicine 2015-07-11 23:35:06 "Blood taken from dead people is actually very usable. The first experiments were done by taking blood from a dead dog and putting that blood into a living one -- if it were done within ~6 hours, the living dog suffered no ill effects. + +Taking blood from cadavers was done in the Soviet Union, but it didn't catch on in America because of the general public's feelings toward it. It also raises the question of consent -- would a patient be okay with blood from a dead person? Would the deceased's family consent? + +It's just a sticky situation with current mentalities -- similar to the issues that plague cadaver research. + +Source: This was all taken from the book *Stiff* by Mary Roach. It's a generally well-regarded nonfiction. " [deleted] +550 Is it possible to find the algorithm for a random number generator by studying the sequences it produces? 4473 https://www.reddit.com/r/askscience/comments/56r419/is_it_possible_to_find_the_algorithm_for_a_random/ 1476089855 56r419 Mathematics 2016-10-10 11:57:35 "For the sake of brevity, we will talk neither about the seed, i.e. the number that is given to the algorithm to bootstrap its pseudo random generation process, nor the environment it is executed in, and from which it can draw some randomness (time, temperature of the CPU, etc.). We will only talk about a deterministic pseudo random generator. + +There is only a finite amount of information in the algorithm. You can more or less (discarding a whole lot of important details) map it to the size (in e.g. MB or kB) of the program file. + +Therefore, the pseudo random number generator can only output a certain amount of random numbers before it starts giving away information about itself. + +The mathematical notion that ties the output of a program to what we may informally call its true information content is called the Kolmogorov complexity. +https://en.wikipedia.org/wiki/Kolmogorov_complexity + +The way in which we measure the information contained in, say, a program output is stronly tied to its randomness, it is called the entropy, or Shannon information: +https://en.wikipedia.org/wiki/Entropy_(information_theory) + +You want to have a program whose output has a lot of entropy, i.e. is random, but you don't want to store this output as is on the disk (this would be a one-time-pad, it is an unbreakable means of encryption but requires the transit of huge amount of secret data), you want to store a program that will compute this at runtime. + +The problem is that there is a lower bound on the Kolmogorov complexity of a true random string, that is more or less the length of the string itself. This is bar some pathological case where the execution environment is defined as containing the random string you want to output. There is no way to minimize the Kolmogorov complexity in general. + +That is why you can not zip a file twice for example. + +Note that the output of a program does not need to repeat itself. For example you could output the digits of pi or of any irrational number and never repeat yourself, but the Kolmogorov complexity of pi is finite: you can write a program that outputs digits of pi, and this program will fit in a finite amount of memory. + +How to actually guess the structure of the algorithm is another can of worm. The naive approach is tied to one of the fundamental problem of Computer Science: the Halting Problem: +If you try to enumerate all programs of reasonable size, and run them to see if their output match the one of your mystery algorithm, then you will find that some programs never terminate. And some other terminate after a reaaaaaaaaally long time. The problem is that the amount of time you have to wait before you can stop a program because it will never terminate is literally uncomputable, it is called the busy beaver number: +https://en.wikipedia.org/wiki/Busy_beaver + +You will never know if you have the algorithm you search, and are just not patient enough to get the answer, or if you are just watching an endless loop... + + +Practically, though, there exist a variety of attacks: you could try to learn how to predict the output with machine learning techniques, you can try to gain insights on the probable implementation using clues (which algorithms are commonly used, which system is this running on, can I time the execution of the algorithm...). + +All those side-channel attacks are the reason why crypto system are very hard to implement in practice, as the tiniest of error can bring the whole thing down." "/u/linschn's answer is great from a theoretical perspective, but from a practical everyday perspective, I think there's an equally interesting answer. + +First, there are two kinds of pseudo-random number generators (PRNGs): cryptographically secure (CSPRNG), and non-cryptographic (PRNG). The short answer is that in practice, we design CSPRNGs specifically to not have the property you mention: knowing the partial output of a CSPRNG should not allow you to compute or learn anything else it has or will output. In fact, a stream that comes out of a CSPRNG is meant to be practically indistinguishable from true random. This means that if you have a set of CSPRNGs, they should also be indistinguishable from one another, as they should all look truly random. In fact, if you had some way to distinguish CSPRNGs from one another, you'd have an attack that showed those CSPRNGs were actually not secure (i.e. distinguishable from random). + +Now for the hard question: do we have actually secure CSPRNGs in practice? It turns out we're not really sure! We have many strong candidates, and many that have remained secure in practice for decades despite incremental advances in breaking them. On the other hand, we have seen popular CSPRNGs fail: in recent history, RC4 is a good example; RC4's output was weakly but detectably biased from random, making it unsuitable for use as a stream cipher. + +On the other side, there are CSPRNGs that are designed with a backdoor, such as DUAL_EC_DRBG. In this case, the NSA created a seemingly-secure CSPRNG that to a naive observer appeared to produce an output indistinguishable from random. However, shortly after its standardization, some clever cryptographers speculated that if the NSA knew a relation between two particular parameters in the algorithm (these parameters themselves being chosen by the NSA), then the NSA (and, in theory, only the NSA) would have the ability to compute future outputs from the supposedly-CSPRNG given its current output. This speculation was later confirmed to be true in the Snowden documents. Nonetheless, you'd be hard-pressed in practice to distinguish DUAL_EC_DRBG outputs from any other CSPRNG, unless you had the secret key generated by the NSA (in which case, it would be trivial). +" +551 With many devices today using Lithium to power them, how much Li is left in the earth? 4470 https://www.reddit.com/r/askscience/comments/5gqe5w/with_many_devices_today_using_lithium_to_power/ 1480992498 5gqe5w Earth Sciences 2016-12-06 5:48:18 "In 2015 the USGS predicted that we have over 365 years of lithium left at current production rates, and that doesn't take into account recycling. It's also with noting that there are a number of emerging battery techs that will replace lithium ion given time. + +https://www.greentechmedia.com/articles/read/Is-There-Enough-Lithium-to-Maintain-the-Growth-of-the-Lithium-Ion-Battery-M + +The mining and production stats start a little ways down" A small but important thing that many people don't know: The resource constraint for Lithium-ion battery power is not actually the Li, but the metal used for the other electrode, which nowadays is mostly cobalt. +311 "When did ""sleeping"" evolve? What are the most primitive organisms that we know of that sleep?" 4462 https://www.reddit.com/r/askscience/comments/4big0f/when_did_sleeping_evolve_what_are_the_most/ 1458668109 4big0f Biology 2016-03-22 20:35:09 Tangent question, is sleep what evolved or the state of being awake? As in, did multicellular organisms first evolve to walk around, eat, reproduce, then sleep and recover.. or did they evolve to stay in a neutral state then get up, eat, and reproduce? "OP, you may find it useful to consult similar topics that have come up on [\/r/askscience in the past](https://www.reddit.com/r/askscience/search?q=sleep+evolution&restrict_sr=on&sort=relevance&t=all). + +As a starting point, I can recommend [this incredibly thorough response](https://www.reddit.com/r/askscience/comments/1n6bo0/at_what_point_in_the_evolution_of_organisms_did/ccg0nvw) that /u/whatthefat provided a few years back." +552 What is the earliest event there is evidence of cultural memory for? 4460 https://www.reddit.com/r/askscience/comments/521r0f/what_is_the_earliest_event_there_is_evidence_of/ 1473485472 521r0f Anthropology 2016-09-10 8:31:12 There is evidence that coastal Aboriginal people in Australia had/have an oral history dating back 10,000 years. The evidence of this is stories recording the location of islands no longer visible today, but which would have been visible during the last ice age (~10,000 years ago) when sea levels were lower due glaciers locking up a much larger percentage of sea water than they do now. [Here](http://www.scientificamerican.com/article/ancient-sea-rise-tale-told-accurately-for-10-000-years/) is a Scientific American article detailing this and other oral traditions which have passed information through hundreds of generations. [Here](http://www.tandfonline.com/doi/full/10.1080/00049182.2015.1077539) is the peer reviewed paper that details these findings. "It doesn't stretch as far back as other examples here, but the site of Homer's Troy has been identified with some confidence. The settlement dates back to around 3000BC but it's believed the setting for Homer's story was around 1300BC. + +The site was discovered by Heinrich Schliemann in the 1860s-70s. One cache of treasure which he found was named 'Priam's Treasure' and he even photographed his wife wearing the 'Jewels of Helen' - https://en.wikipedia.org/wiki/Priam%27s_Treasure#/media/File:Sophia_schliemann_treasure.jpg. + +It's thought this treasure actually dates quite a bit further back than Homer's tale. + +For me the idea of discovering clues from the tales of Homer and classical historians and piecing them together to find to true site of Troy is very cool. Gotta try that some day." +414 How do centipedes/millipedes control all of their legs? Is there some kind of simple pattern they use, or does it take a lot of brainpower? 4453 https://www.reddit.com/r/askscience/comments/4un1k5/how_do_centipedesmillipedes_control_all_of_their/ 1469510678 4un1k5 Biology 2016-07-26 8:24:38 "It's a distributed control system. Each segment has a ganglion that acts as a small ""brain"" to control its pair of legs. The centipede brain sends a go signal and the ganglion handles the motion, coordinating its timing with signals from the segments ahead and behind. There's also a [Central Pattern Generator (CPG)](https://en.wikipedia.org/wiki/Central_pattern_generator), an which is an intrasegmental network of neurons which generates a rhythmic output, that keeps them all in step." This doesn't go terribly far in answering your questions, but it kind of reads that you're implying they're insects. If I've misinterpreted, then please ignore this, but I just wanted to point out for anyone who thinks of them as insects that centipedes and millipedes are instead myriapods. Myriapods, insects, spiders, and crustaceans are all arthropods. Insects are in part characterized by having 3 body segments and only 3 pairs of legs. +1801 What controls the production of ear wax? 4452 https://www.reddit.com/r/askscience/comments/lwknlq/what_controls_the_production_of_ear_wax/ 1614744064 lwknlq Human Body 2021-03-03 7:01:04 "It’s primarily driven by genetics, but there are a few other things that factor in. If you have things in your ears a lot (cotton swabs, keys, pen caps, fingers) it can stimulate your ears to produce more. If you over wash that can strip out the wax (and your natural protective layer of skin oils) and stimulate more production as well. Diet can, in individual circumstances, also play a role though not usually to a huge extent. + +TLDR: It’s pretty much a gene driven process, but keep crap out of your ears. + +Edit: Someone else replied further down about hormonal changes - I definitely forgot about that. The human body is fascinating! + +Edit 2: Ya’ll are blowing up my inbox XD - yes, ear buds and ear plugs can (but don’t necessarily) stimulate more wax production. If you’re constantly putting something into and pulling it out of your ear, then even if it’s designed to fit there (ear plugs/buds) it’s going to create some irritation and possibly increase the ear wax. Occasional use of something like that likely won’t lead to a bunch of overproduction of wax. It’s also true that loud sounds may cause some people’s ears to produce more wax - but if that’s the case you should be WAAAAY more worried about damage to your hearing than some extra ear goo!" "One of the main genetic controls of earwax type is the ABCC11 gene. This is a membrane transport gene involved in aprocrine and tissue secretions. The gene has simple dominant Mendelian inheritance. So three of the alleles (gene variants); GG, Ga and aG encode wet earwax and one variant, aa, encodes dry flaky earwax. Only about 2% of the world has the aa combination and those are concentrated in East Asia. Interestingly if you have wet ear wax your ABCC11 gene/protein also exports larger amounts of aprocrine secretions from your skin which makes your underarm sweat much more pungent. + +There are likely other genetic controls of earwax type and production but this the one that has been best studied. + +https://en.wikipedia.org/wiki/ABCC11" +312 What would the horizon look like if you were standing on an infinitely stretching and perfectly flat plane? 4450 https://www.reddit.com/r/askscience/comments/4ea7ee/what_would_the_horizon_look_like_if_you_were/ 1460371971 4ea7ee Physics 2016-04-11 13:52:51 "Actually, the question ""where is the horizon?"" and ""what does the horizon look like?"" are different questions. Let's answer the first question. + +Where is the horizon? +--- + +How do you find the horizon anyway? Suppose you are on a spherical object (like Earth). [Here is a picture](http://i.imgur.com/7NNgEj3.png) to make things clear. The variables are + +* R = radius of Earth + +* H = height of vantage point (e.g., distance from your eyes to the ground) + +* θ = viewing angle (i.e., the declination angle at which you see the horizon) + +The farthest point you can see is the point where a line passing through your eyes is tangent to the circular cross-section of Earth. From the diagram, some simple trig shows that your viewing angle is + +> θ = cos^(-1)[ R/(R+H) ] + +With H = 6 feet, we get [θ = 0.043 degrees](http://tinyurl.com/z4rhesh). + +What is your viewing angle for an infinite plane? Well, go back to the picture of Earth. Can the viewing angle be any positive angle? Nope. If you look exactly parallel to the plane, then your line of sight does not end on the plane. But as soon as you look down at even the slightest angle, your line of sight meets the plane. So your viewing angle on an infinite plane is always 0 degrees, no matter how high your vantage point is. So if Earth were an infinite flat plane, for instance, the horizon would be pretty much exactly in the same place where it is now (at least for low vantage points). The angle 0.043 degrees is imperceptibly close to 0. + +What does the horizon look like? +--- + +Okay, so what would the horizon look like? For this, we need some physics. For reasons that will become clear, let's also assume that there are no other planets, no other stars, etc. The universe is just this infinite plane of uniform density (and you, I suppose). + +An infinite plane with a constant mass density has a very simple gravitational field. It is uniform on each side of the plane, no matter how far you are from the plane. So if you are right on the surface of the plane, you measure some gravitational acceleration *g*. If you go up a height *H*, you measure the same acceleration. It is a completely uniform field (on each side) that always points towards perpendicularly toward the plane. + +So what? What does this mean? Well, the path of light gets bent by gravity. Even the path of light passing by Earth gets bent, by a very small amount. (Deflection of light by the Sun is a classical test of general relativity.) The same happens for an infinite plane, but the difference now is that it has all the time in the world (or I suppose, distance) to deflect right back to the plane itself. [Here is another picture.](http://i.imgur.com/yhT8MJY.png) Light emitted from the plane will eventually curve back to the plane. Yes, it takes a very large distance for this to happen for, say, a gravitational field as strong as Earth's gravity, but that's fine: the plane is infinite. When the light finally is received, it is received at some angle. Our brain always perceives light to have traveled a straight line. So even though the light path is curved, we will perceive the light to have come in from some point in the sky. + +Ultimately, this means that the entire sky is entirely filled with images of the surface of the plane some distance away. (This is why I assumed there were no other planets, stars, etc. so that light rays do not get obstructed.) In other words, it looks as if the entire world has curved up around you and closed at the top. So it looks like you are actually in some very large spherical planet, for which the ""surface"" is the interior of the sphere. But remember that images above you are really emitted from points on the plane *very* far away. (The point directly above you is infinitely far away.) So as you walk in a straight line on the plane, you won't really see the entire sky rotating around to meet you like you would expect if you were inside a spherical planet. For instance, the point directly above you never appears to move. Try as you might, you will never reach the point where the image directly above you was emitted. + +By the way, what *does* the point directly above you look like? Well, it's where all the points infinitely far away from you are sent by ray-tracing all of the light back. But points infinitely far from you in this world make up the horizon! So instead of *seeing* the horizon exactly where it is now on Earth, you would see the horizon directly above you all crunched up into a single point. + +--- + +**edit:** A few people have (falsely) noted that a 45-degree launch angle maximizes horizontal range and that all the photons start with the same speed. So you end up only seeing some finite portion of the plane around you. This is not correct. That line of reasoning treats light as a ballistic particle in a Newtonian uniform gravitational field. Light cannot be treated in Newtonian gravity: it is neither affected by nor affects gravity in the Newtonian framework. For one clear difference, note that the light paths in a uniform field are not parabolas; they are actually semicircular arcs. + +Also, the oft-repeated statement ""the speed of light is constant"" is simply not true in GR if you take it at face value. The speed of a light signal next to you is always *c*, sure. But the local speed of light for distant light rays, in general, depends on the coordinates. This is not a contradiction; it is an artifact of the freedom of choosing coordinates in GR. + +--- +**edit 2:** I have to admit that I have committed a cardinal sin that I absolutely hate to see committed by others: indulging hypotheticals that are sort-of unanswerable. + +If we do everything in a Newtonian framework, then the first part of my response is just fine. The horizon is at 0 degrees, which is barely less than the Earth horizon at about 0.043 degrees for the height of a typical person. For the second part of my response, I did two things: + +* used Newtonian gravity to deduce that the gravitational field of the plane is uniform + +* used GR to determine the paths of light rays in a uniform field + +(Now, technically speaking, there is no metric in GR that has all of the desired properties of a uniform field from Newtonian gravity. There are several candidates though. I just used the simplest of them, which is Rindler coordinates for flat spacetime. But that is a small technicality that doesn't matter too much.) + +There really is no metric that describes an infinite plane of uniform density, at least not one that I can think of or calculate. Perhaps there are some good GR models of such a matter distribution. Anyway, my error of combining the two frameworks of gravity was subtle, but important enough to point out. So take what I said about what the horizon looks like and light deflecting back to you with a grain of salt. There are some unphysical assumptions that go into that. + +Better... just assume that the infinite plane of uniform density is not there. Assume space is just a vacuum, but there is a uniform gravitational field nevertheless. (You can have non-trivial metrics even in a vacuum, e.g., black hole, so this is not a contradictory statement.) If the field is in the *z*-direction, then we can talk about what happens to light emitted at points on the plane *z* = 0. That is a more physical problem that can actually be answered in GR somewhat. Just don't think too hard about *how* we could produce such a uniform field with matter. + +--- +**edit 3:** With the second edit above in mind, [see this post](https://www.reddit.com/r/askscience/comments/4ea7ee/what_would_the_horizon_look_like_if_you_were/d1yguj6) for my thoughts on concerns about my not taking into account any atmosphere. + + + + + +" "The other answer is waaaay too complicated. I mean, I noped out quick on that. Let me give you an engineer's answer. Standing on a plane you look around and you immediately have three points. The point you're standing on (or the point directly below your eyes for people who lean like Michael Jackson) we'll call A, the point where your eyes are we'll call B, and the point that you're looking at we'll call C. Line AB will always be perpendicular to line AC which makes the angle at A=90°, and for those unaware the angles in a triangle equal 180°. Therefore, if angle A=90° then angles B and C must sum to 90°. The moment angle B=90° you are no longer looking at the plane because your line of sight is parallel to the plane. Therefore, making the assumption you could see that far and there are NO obstructions, the ""horizon"" on an infinite plane is always always always at eye level in all directions. " +673 Is there any correlation between education and mental health? 4436 https://www.reddit.com/r/askscience/comments/5mr0og/is_there_any_correlation_between_education_and/ 1483885077 5mr0og Psychology 2017-01-08 17:17:57 "To clarify, dementia (age-related) and Alzheimer's disease are neurodegenerative disorders. + + They have symptoms that impact mental functioning, but they are not normally classified as mental health conditions such as depression, bipolar disorder or schizophrenia." "For mental health, yes. The document linked below covers the correlation between mental health and level of education. It seems that more highly educated people have more social support as well. See the ""social resources"" section, or better yet just Ctrl+F and search for mental health. + +https://www.ahrq.gov/professionals/education/curriculum-tools/population-health/zimmerman.html" +1426 Why do microwave ovens make such a distinctive humming sound? 4429 https://www.reddit.com/r/askscience/comments/d1fv4n/why_do_microwave_ovens_make_such_a_distinctive/ 1567972023 d1fv4n Engineering 2019-09-08 22:47:03 "The hum is 60Hz (or 50Hz if you live in Europe), it’s either oscillations in the components of the rather massive power supply required to feed nearly 1.5kW to the magnetron. Or mechanical oscillations induced in the magnetron due to ripple in its power supply. + +Electronic components can produce mechanical vibrations. Power transformers have to deal with changing magnetic fields that will produce torques in a similar way to a motor. Ceramic capacitors tend to be piezoelectric and mechanically distort with changing voltages. To provide 1.5kW to anything large fields are involved, and it becomes rather hard to provide stable power. + +--- + +Edit: As it was pointed out by several people (and confirmed by measurements from others (isn't it nice how science works)). the actual fundamental frequency is twice the line frequency. So that's 120Hz for the US (and related areas) and 100Hz for Europe (and related areas). Those roughly correspond to a B3 and a G2 in the music scale. + +There are multiple reasons for this, the main one among them is that the movement of components (such as the microwave's metal case and transformer core and coils) are affected by the magnitude of the magnetic field not its direction, which leads to rectification of mechanical displacement at twice the cycle rate." "Most microwaves use large 50 or 60 Hz transformers to step up the line voltage to the several kV needed by the magnetron tube that actually produces the microwaves. Any big line-frequency transformer will tend to hum from magnetostriction in the steel and from magnetic forces on the core and windings. + +So why is the microwave oven sound distinctive? One reason is that it's actually the only common example of a line-frequency transformer that big (~1 kW) in a home device^1. The other is some special features of a microwave transformer and its application that make it especially noisy and perhaps make the sound a little different: + +1. A magnetron has a nonlinear input voltage/current characteristic that makes it rapidly draw more current if the voltage is increased a little. Some kind of current limiting or control is needed. This feature is built into a microwave transformer in the form of [magnetic shunts](https://www.qsl.net/kh6grt/page4/xfmr/pictures/transorig.jpg) between the primary and secondary winding. Those boost the [leakage inductance](https://en.wikipedia.org/wiki/Leakage_inductance) which effectively provides a series impedance that limits the current. But that structure leads to opportunities for more mechanical vibration, both because of the magnetic forces arising and because the shunt isn't mechanically secured as well as the rest of the steel core. Edit: also because it produces a larger field external to the transformer, which can make other stuff vibrate, such as steel panels of the chassis. + +2. The output of the transformer is high-voltage ac, but the magnetron needs dc, so there's a rectifier. One common type of rectifier used is a [voltage doubler rectifier](http://slot-tech.com/interesting_stuff/a%20collection%20of%20technical%20stuff%20from%20a%20technician%20in%20Libya/Microwave/doubler.html) which chargers a capacitor during one half cycle of the 50/60 Hz line frequency, and then delivers energy from the capacitor and from the transformer into the magnetron during the other half cycle. That means the magnetron is actually pulsed on once per cycle, rather than twice as it would be with a simple full-wave rectifier, or operated continuously, as it would if the rectifier output were filtered. In any of those options, the current in the transformer isn't sinusoidal, but is more ""pulsy"", and thus contains more harmonics that are more easily audible than a pure sine wave would produce.^2 + +Microwave ovens without line-frequency transformers are finally becoming common. They still use transformers to produce the high voltage, but the transformers operate at high frequency, above the audio range, which makes them silent, as well as smaller, cheaper, lighter, and more efficient. Such a system is often called an ""inverter microwave"" because of the ""inverter"" circuit that creates the high frequency that drives the smaller transformer. This is the same switch mode power supply technology that has allowed power supplies and ""chargers"" for everything else to get smaller and lighter. Inverter microwaves are lighter, more compact, and more efficient, but they are still noisy: the fan noise dominates. + + +[1] Line-frequency transformers used to be more common, and so it used to be that similar sounds were made by more types of equipment, but that's not all that familiar because, for one thing, line-frequency-transformer-based dc power supplies have been replaced by switching power supplies in almost all applications. And before that was true (decades ago), most household equipment that used a dc power supply was at lower power, often 100 W or less. + +[2] Many of the sound production mechanisms operate based on the magnitude or the square of the magnitude of a current, and so would produce 100 or 120 Hz, rather than 50/60 Hz, even if they were operated with a perfectly sinusoidal current." +1 If we were far enough from earth, could we see the dinosaurs alive? 4421 http://www.reddit.com/r/askscience/comments/2y93cz/if_we_were_far_enough_from_earth_could_we_see_the/ 1425747275 2y93cz Physics 2015-03-07 19:54:35 "In theory, yes. + +In practice, it's much harder, because the earth is so small and 65 milllion light years is a long distance. For perspective, all the visible stars in the night sky are within about 1,000 light years of us. The Milky Way is about 100,000 light years across. Andromeda is about 2.5 million light years away. If some aliens (or wormhole travelers) want to see dinosaurs, they're going to need a big telescope. We can barely even resolve planets in our own galaxy, and I don't think there is a single known extragalactic exoplanet, but I could be wrong. + +But let's not let reality get in the way of our adventure; after all, we've already assumed wormholes exist. So how big does this telescope need to be? Astronomy is hard, and gets harder the further away you look, because you need bigger and bigger telescopes to get the same resolution- [so we can use the lens resolution equation to find an approximate size for the lens.](http://en.wikipedia.org/wiki/Optical_resolution#Lens_resolution) + + Angular resolution = 1.22 * Wavelength / Lens Diameter + +So pick a wavelength in the visible spectrum- how about 500 nanometers since that's right at the transition between blue and green, and a distance of 65 million light years. The angular resolution to resolve the earth would be: + + Earth Radius/Distance = 1.22 * Wavelength / Lens Diameter + +Solving for the lens diameter gives about 5.8x10^10 meters, which is about a third of the distance to the sun. This is big- this lens would fill up about half of Mercury's orbit. + +But you wanted to see *dinosaurs*, not just the earth. If you want to resolve a dinosaur as one pixel or so, then we use the same equation again, but put in the size of a dinosaur (maybe 10 meters?) instead of the earth radius. [This lens](http://www.wolframalpha.com/input/?i=%2865+million+light+years+%2F+length+of+triceratops%29+*+1.22+*+500+nm) needs to be 4.4 light years in diameter- where once again I am surprised at the neat tidbits Wolfram has built in, like the length of an adult triceratops. + +Anyway, you're going to run into a problem here because when you start putting a lot of mass in one spot space starts to curve a lot, and eventually it's going to collapse into a black hole. For something with the density of glass, which is about 2.5 grams/cc, you're going to hit this point fairly quickly. In fact, [a ball of glass 14 light *minutes* in radius will have enough concentrated mass to collapse into a black hole.](http://www.wolframalpha.com/input/?i=sqrt%283*%28speed+of+light%29^2+%2F+%288+*+gravitational+constant+*+pi+*+2.5+grams%2Fcc%29%29) + +Tough luck." As a follow up - if I left the earth and travelled via wormhole in 5 seconds to where I could see earth 1 week prior to departure then travelled back to Earth at the speed of light through normal space, then I would see the events of that week in fast forward including my own departure until I got back? +553 Is it possible to have a dream that would permanently traumatize you? 4419 https://www.reddit.com/r/askscience/comments/59agbd/is_it_possible_to_have_a_dream_that_would/ 1477393857 59agbd Psychology 2016-10-25 14:10:57 "Hi everybody. Before you comment, please ask yourself, ""Can I back up what I'm about to type with peer reviewed science?"" + +If the answer is yes, then please cite those sources. If not, then you probably have an anecdote or speculation, which will be removed. +" "So trauma is a tricky thing. It's subjective. What the field defines as trauma, currently, is anything that causes an individual to experience fear for their safety or life, or the safety/life of a loved one. In other words, as long as it causes the individual to feel like they are in danger, it's trauma. This is entirely based on the individual's perception of events, and it means that what one person considers extremely traumatic may be nothing special to another person. Even then, people react differently to trauma. Some people are able to cope with nearly any trauma they experience (they are ""resilient""), and some people are less able to cope with trauma. The development of posttraumatic stress is not a given. + +So the answer to your question is: yes, it is *possible* for a particularly extreme nightmare to cause lasting trauma (posttraumatic stress) to the individual, given the right circumstances. + +E: expansion and clarity" +1256 Why don't planets twinkle as stars do? My understanding is that reflected light is polarised, but how it that so, and why does that make the light not twinkle passing through the atmosphere? 4412 https://www.reddit.com/r/askscience/comments/bhnokg/why_dont_planets_twinkle_as_stars_do_my/ 1556292954 bhnokg 2019-04-26 18:35:54 Stars are much, much farther away, and also very bright. The distance would make the light dim if it were not for how bright the stars are. The light from exostars arrives to earth as a pin point, meaning the actual area of sky taken up by the star is incredibly small. By contrast, planets are physically a lot smaller than most stars, but also far, far closer and dimmer. The result is that the light from our own planets does not come to us as pinpoints, but instead as an area. The twinkling of stars is caused by atmospheric perturbations. Changes in the upper atmosphere of the earth change how the light bends when passing through. For pinpoints, all of the light is affected by these perturbations the same way, which allows us to observe it. With planets, the light interacts over a larger area and is not all affected the same way. The interactions destructively interfere, meaning that what we observe is the average of the different perturbations. This average may vary slightly, but nearly imperceptibly. Well first, they can twinkle, it just requires far more turbulent air. But the reason for this is that planets have a larger angular size than stars do. This isn't noticeable in our vision, as they are all small enough to appear as point sources, but when magnified, planets resolve to larger discs with much less magnification than is required for a star. Thus, their images are more stable through the air. +415 Can a Mars Colony be built so deep underground that it's pressure and temp is equal to Earth? 4395 https://www.reddit.com/r/askscience/comments/4sj5l1/can_a_mars_colony_be_built_so_deep_underground/ 1468354958 4sj5l1 Planetary Sci. 2016-07-12 23:22:38 "**Short answer:** If you wanted to dig on Mars to reach a depth where the pressure would be 1 atmosphere, i.e. equivalent to sea level pressure on Earth, it would most likely be much too warm. + +**Long answer:** Consider the case of Death Valley on Earth. Since it lies below sea level, the atmospheric pressure there is actually greater than what's found at sea level, roughly ~~1.1~~ 1.01 atmospheres. Similarly, we could dig below the surface of Mars so that the weight of the overlying atmosphere would be the equivalent of 1 atmosphere. + +We can calculate how deep a hole one must dig by using the ""scale height"" - this is the difference in altitude needed to produce a factor of e = 2.718x increase in pressure. In Mars' case, this is equal to 11.1 km. + +Now, the pressure at the surface of Mars is a measly 0.006 atmospheres, while we want to go to 1 atmosphere. The number of scale heights we want to dig is then: + +ln (1.0 / .006) = 5.12 scale heights + +...which, for a 11.1 km scale height means we want to dig 5.12 * 11.1km = 56.8 km. Note that this is over 4 times deeper than the deepest hole ever dug on Earth, so this is already a pretty tough technological achievement. + +Now, how warm would it be when we get there? For this, we need to consider the adiabatic lapse rate; this tells us how much the temperature drops as we ascend in the atmosphere, or similarly how much the temperature increases as we descend. (It's also for this reason that Death Valley has the highest temperatures recorded on Earth.) + +In the case of Mars, the adiabatic lapse rate is 4.4K/km. In other words, for every kilometer we descend, the temperature increases by 4.4 K. + +Thus by descending 56.8 km, we're increasing the temperature by 56.8 * 4.4 = 250K. Since Mars' average temperature is 223 K (= -50 C, -58 F), that means **the final temperature at 1 atmosphere of pressure would be 473K (= 200 C, 391 F).** + +**EDIT:** Since a lot of people are asking: + +- This is unrelated to whether Mars has a ""dead core"" or not. This temperature increase is *not* due to geothermal (or in this case, areothermal) energy. Rather, it's a simple consequence of taking the current atmosphere and compressing it adiabatically as it fills up our hole. A similar transformation would be suddenly opening the doors on a pressurized jet at 33,000 feet...the air would quickly expand to the thin ambient pressure and cool down in the process by 65^o - 98^o C, depending on how humid the air inside the airplane was. + +- You can't generate electricity from this temperature change. It seems counter-intuitive, but even though the temperature has increased, there's no extra energy added to the system - this is the definition of an adiabatic transformation." "It's been suggested we could use ancient [lava tubes](https://en.wikipedia.org/wiki/Lava_tube) for basing or colonisation purposes. As well as being easier than drilling, the Igneous rock should be semi-impermeable and tough as... well rock, so it can potentially hold a pressurised atmosphere and also provide protection from the significant radiation on Mars' (or the Moon's) surface. So yeah it's a very viable idea. + +Here's a white paper on the topic: +http://www.lpi.usra.edu/decadal/leag/AndrewWDagaFINAL.pdf" +554 Why is it not possible to simply add protons, electrons, and neutrons together to make whatever element we want? 4393 https://www.reddit.com/r/askscience/comments/54gklr/why_is_it_not_possible_to_simply_add_protons/ 1474830410 54gklr Chemistry 2016-09-25 22:06:50 "Nuclear transmutation specialist here: + +We *do* simply add protons, electrons, and neutrons together to make whatever elements we want. + +The reason why most people aren't familiar with this is because it's *really expensive*, so this is typically only done in laboratories for scientific research. + +Another reason why you typically don't want to use this for your everyday materials is that the resulting material is almost always radioactive. And not just ""a little radioactive like bananas or human bodies"" but ""really radioactive like nuclear waste"". + +Let's say you want to make some gold (Au). Well, you could start with some platinum (Pt), natural platinum is a mix of Pt-192,194,195,196,198. When you bombard that with neutrons, you'll produce radioactive Pt-193 (halflife 50y decays to stable Ir-193), stable isotopes Pt-195, Pt-196, radioactive Pt-197 (halflife 20h, decays to stable Au-197), and radioactive Pt-199 (halflife 30m, decays to radioactive Au-199, which further decays with a halflife of 3d to stable Hg-199). So if you do this, your sample is going to be radioactive for several centuries before you can get any non-radioactive gold out of it. Also, you had to start with platinum, which is already just about as expensive. + +But actually, there are some industrial applications for nuclear transmutation. The most common is likely putting neutrons into U-238 to create U-239 which then beta decays into Np-239 which in turn beta decays to useful Pu-239. This is done in the nuclear fuel cycle to create fissile Pu-239 out of non-fissile U-238. About 50 years ago, nuclear scientists thought this process was going to be the future of nuclear energy and to produce a post-scarcity society. But then we discovered that we have basically limitless reserves of uranium, and that it's actually a lot more expensive to design nuclear reactors which utilize this process than it is to just buy more uranium ore. + +Another common one is the production of ~~fluorine-19~~ fluorine-18. This is done by bombarding water with protons to turn O-18 into ~~F-19~~ F-18 as it ejects a neutron. F-18 is then used as a radiotracer in medical applications, notably PET scans. This is actually rather common and large hospitals sometimes even house their own particle accelerator for this or similar purposes. + +Another process (not sure if it's been realized yet or is still in the theoretical stages) is the collection of rare earth metals from nuclear waste, which is just the end products of U-235 fission. + +https://en.wikipedia.org/wiki/Nuclear_transmutation" "In principle, we could. We kind of do that in particle accelerators, to a very limited extent, and also in experimental fusion reactors. Ultimately, what you're describing is 'just' fusion. + +The difficulty is in getting the protons and neutrons together (the electrons are easy). Protons are positively charged and repel each other strongly unless you can get them close enough so that the attractive strong force overcomes the electric repulsion between them. That means to get two protons together, you have to give them a *lot* of energy or they will just repel each other before they get close enough to merge. + +But that's hard, and also there is no guarantee that they will actually bind together; they could alternative decay into some other combination of particles. Two protons alone, for example, is unstable, so you'd have to first get a proton and neutron together. Neutrons are difficult to manipulate, though, because they're electrically neutral. You need to have a slow neutron source and wait for one to collide with a proton, but you can't predict exactly when or where that will happen. Since adding an extra neutron or proton to an already stable atomic nucleus often produces an unstable isotope (sometimes with very short lifetimes), you need to be able to add protons and neutrons very very quickly so that the nucleus doesn't have time to break apart before you get it into a stable configuration again. + +In some ways this gets harder as your nucleus gets bigger. A bigger nucleus is more positively charged, which means you have to give new protons even more energy to overcome that repulsion. At some point, you're as likely to smash the nucleus apart as you are to just give it a new proton. + +TL;DR We can't deftly manipulate protons and neutrons into whatever position we want. Remember, these particles are 100,000 times smaller than an atom. We have to shoot lots of protons/neutrons into some target of lots of existing nuclei and wait for some of them to 'stick,' but this whole process is very imprecise and difficult to control. In addition, doing this step-by-step must be done very quickly or the whole thing will decay while it's in a temporary unstable state." +983 How common is lightning on other planets? 4380 https://www.reddit.com/r/askscience/comments/8c6fmu/how_common_is_lightning_on_other_planets/ 1523696500 8c6fmu Planetary Sci. 2018-04-14 12:01:40 "[Jupiter whistling.](https://youtu.be/irsNtth5Cnk) + +Whistler waves are distinctive radio frequency noise produced by lightning, and seem more or less the same wherever you go. This makes it easy to find lightning. Voyager One heard them on Jupiter and Saturn which feature perpetual storms, and Venera heard them on Venus. Later probes showed that on Venus this was [definitely lightning](http://esa.int/Our_Activities/Space_Science/Venus_Express/Acid_clouds_and_lightning) and also more or less perpetual on the night side. Fairly recently it was also shown that [dust storms on Mars](https://www.space.com/7102-lightning-detected-mars.html) can produce powerful lightning. + +On Earth most lightning is cloud to cloud and is not a threat to things on the ground. Nobody has photographed cloud to ground lightning on another planet yet. +" "to ask a different question ( thank you to OP and people responding-- very insightful!) + +do we know much about the different layers of other planets atmosphere? do they each have a troposphere and stratosphere magnetosphere etc etc and do they more or less behave in the same way as on earth?" +1695 How does a cell ‘know’ what to become, if they all start from one or two cells and have the same genetic code? 4380 https://www.reddit.com/r/askscience/comments/irxncu/how_does_a_cell_know_what_to_become_if_they_all/ 1600001242 irxncu Biology 2020-09-13 15:47:22 "Hello! I'm a developmental biologist. Specifically, I study how the cells that become the brain and nervous system know exactly what to become. + +TL;DR: cells use a variety of methods to figure out 'when' in development they are, and where they are. Most commonly, they count how many different choices have been made to identify 'when'. To identify 'where', certain cells act as landmarks, and give off chemical signals. The stronger the signal, the closer a cell is to the landmark. DNA contains specific instructions on how to interpret this combination of 'when' and 'where'. + +In detail: + +Let's start with DNA. We often here DNA compared to a recipe book, with genes being recipes. I prefer to think of it as a choose-your-own-adventure. A zygote (which is what we call the cell made when an egg and sperm fuse) doesn't actually have access to the whole of its DNA. Most of it is packed tightly away. It does have access to 'chapter one', which mostly begins 'if no other chapters are open, start here'. + +This cell will divide many times, and eventually change shape. In order for a cell to know what chapter to read, it needs to know two things: where in the zygote/embryo it is, and 'when' in development it is. Embryonic cells are extremely accurate at identifying this information. We don't know all the ways they do this yet. However, we know of some mechanisms. + +First, there's the DNA-CYOA book itself. Every time a cell 'opens' a new chapter, with a new set of instructions, it packs away some of the old, no-longer-relevant chapters. It labels them extensively in the process, in case they're needed again. And when I say it packs the DNA away, I mean that literally. [This is a diagram](https://www.researchgate.net/profile/Kevin_Verstrepen/publication/51196608/figure/fig1/AS:276923784679429@1443035183356/Chromatin-structure-DNA-is-wrapped-around-a-histone-octamer-to-form-nucleosomes.png) of DNA in various packed and unpacked forms. At the top is the famous double helix. In reality, DNA only exists in this fully unpacked form while it's being read. Next, is 'tidied' up DNA. This is accessible, but not actively being read. Then as you go further down, it gets more and more packed away and inaccessible. + +That's what it looks like when a DNA sequence is 'turned off' - it's literally filed and packed away. You may have heard of epigenetics. This is the collective term for the molecular tags that label DNA, and the molecular duct tape that keeps DNA packed up safely. + +When a cell divides, it copies its epigenetic pattern out - and so the daughter cells have the same bits of the book packed away and labelled. Going back to the CYOA book, this is like a bookmark. This is one of the ways that a cell can tell 'when' it is in development. If it's at chapter 13, it knows that chapters 1-12 have already been read. + +As for 'where', let me introduce you to my favourite protein: Sonic Hedgehog, aka SHH (That's genuinely the name of the protein). SHH is what's known as a 'morphogen'. It's a signal that tells cells what to become. In SHH's case, it tells cells how far they are from a certain landmark. + +It's used in a number of different contexts, but neural development is what I know best, so I'll use that as an example. Before your brain became a brain, it was a tube - called the neural tube. This runs along the whole back of the embryo, and eventually becomes the brain and spinal chord. In early development, it's the factory where the entire nervous system is made. + +The cells on the very bottom of the neural tube make a ton of SHH. Other cells sense how much SHH there is around them by eating up the SHH that bumps into them at the right spots. This means that really near the bottom, there's a ton of SHH, while near the middle, there's very little. At the top, there's none at all. This is called a concentration gradient. Cells in the neural tube count how much SHH they eat, and then refer back to their DNA books. The instructions tell them to open certain chapters if they eat enough SHH, and close others. Cells also check with their neighbours, also through chemical signals, to see if they agree on decisions. The result is a very specific link between SHH concentration (and thus distance from the SHH producing cells) and cell identity. + +~~[This image](https://www.semanticscholar.org/paper/Dorsal-ventral-patterning-of-the-neural-tube%3A-a-of-Dr%C3%A9au-Mart%C3%AD/a73582b5b612510a71adeaa0045fa9527570bbaa/figure/0) shows that in practice~~. *edit: link is broken. Found the same image [here](https://www.slideshare.net/HarshaKumar2/dorsoventral-patterning-of-the-brain) and [this](https://onlinelibrary.wiley.com/doi/abs/10.1002/dneu.22015) is the original citation*. Cells with different identities produce different proteins. In this picture, those proteins have been dyed different colours, showing the pattern of cell identities in a cross section of the neural tube. + +The graph on the left shows different genetic chapters, basically. Each of those horizontal stripes represents a different type of cell - a motor neuron, or a type of sensory neuron, or maybe an ~~dendrite~~ astrocyte. You'll see that they're turned 'on' at a specific distance from the bottom, and turned off further away. The combination of genetic chapters that are 'open' determines cell identity. + +Finally, we have chemotaxis. When a cell is 'finished' with its time in the neural tube - ie. The factory, it will migrate out and go to where it is needed. It does this in a very similar manner to SHH signalling. Landmark cells emit a signal. Each landmark emits a different kind of signal. Cells with different identities have machinery that allows them to sense only very specific signals. They then follow the concentration gradient towards the source." "To try and explain in layman terms, as the cell divides from the first cell, it undergoes commitment, it begins to become a certain cell. The way the cells do this, is by expelling signal molecules from themselves, so called cytokines. Lets explain them with colours and dye. + +So imagine that a cell is sending out blue dye, the cell next to it has receptors, they asses the blue dye concentration, it knows it is right next to a cell expelling blue dye. Then the next cell, it also receives blue dye, but it is diluted, because the cell sending out blue dye is 2 cells away. A high concentration of blue dye, triggers a cell response, that lead to certain DNA being activated, while a lesser concentration received leads to another DNA response. The dye doesn't travel very far, like a pulse in all directions. For the sake of example, we can say that it can be detected up to 5 cells away. That is, the cells detect, and understand if they are 3 cells away, or 5 cells away, based on the concentration of the dye it detects. Then on the other side of these cells, is another cell, sending out yellow dye. Now the colours get mixed up. According to their concentration, the cell then ""knows"", it as pretty far away from a blue dye, close to a yellow, and that precisely triggers molecular reactions that then in turn leads it to read certain parts of it's DNA, making a specific protein in certain concentrations. It will make a lot of one protein from receiving strong blue, make a low amount of another protein from receiving weak yellow. While the presence of blue, yellow, and a red dye , makes it read completely different places on the DNA. + +Now imagine all the cells spewing out all kinds of colours, the individual cell from this completely knowing where it is in relation to the other cells, and told what it is supposed to become from the palette it receives. + +Now last I studied this, researchers couldn't really see much difference in the cells before there were 8 of them. From 1 to 2 to 4 to 8, they seemed the same. They are not of course, they are already becoming determined, but the researchers insight did not allow them to identify the details. Maybe that has changed by now. But determination is based on the cytokines the cell receives, and in what concentration. + +Edit: As I am reading this debate, a guy writes that wolverine with his regeneration could be real. Yes, that is called stemcells. And that is stemcell research. If we imagine from the first cell, it being the top of a pyramid, then the cells divide and becomes determined as steps down unto a pyramid. As they divdide, they become more and more a specific cell doing a specific job, be it a white blood cell, or a liver cell. Untill the bottom layer of the pyramid, which resembles all the cells having become what they were designed to be. + +But during this development down the pyramid, some cells step aside, they stop where they are, and no longer takes information from cytokine signalling. They just stay there, they are stemcells. Later in life, something might happen to you, a liver disease for example, you might be short of a certain type of cell. The stemcell, in the pyramid layers above, can become the cell you need. It starts dividing again, like the other cells did when you developed into a human. One of the cells that divide, stay inert as before, it is the stemcell. But the other new cell begins it's travel down the pyramid, as it divides again and again, becoming the cell that you are short of, a specific livercell for example. + +A stemcell that is high up in the pyramid, can become all the cells that trail down from its vantagepoint, it is called a pluripotent stemcell, it can divide and become many different cell types. A very early stemcell, from shortly after conception, can become any cell in the body, it is called an omnipotent stemcell." +674 Why is this specific air intake design so common in modern stealth jets? 4379 https://www.reddit.com/r/askscience/comments/5stcui/why_is_this_specific_air_intake_design_so_common/ 1486568239 5stcui Engineering 2017-02-08 18:37:19 "If you are talking about the gap between the fuselage and the intake this is purely an aerodynamics thing. Air flowing close to a surface is often very turbulent and messy. This is called the boundary layer. + +For maximum performance you don't want these turbulences to get into your engine. It can stall the compressor blade and generally make things less efficient. The small gap is there to get only the laminar flow inside the engine." "The shape you recognize as common to all those aircraft is done entirely for stealth. Specifically, radar signature, though many factors come into play. + +If you were designing for aerodynamics alone, you wouldn't bury the engines or have anything but a short round inlet in front of them. Engines don't want to be buried or forced to suck through a straw. That's why commercial aircraft, which care about efficiency and performance above all else, look the way they do. + +But, since round holes are fantastic radar scattering sources, and so are fan blades...low radar observability is achieved by hiding the engine face(s) and shaping the inlet aperture so that it has particularly-shaped edges. Everything you're seeing about a modern fighter inlet is a way of achieving other objectives while (hopefully) compromising aerodynamic performance as little as possible. + +Source: Propulsion engineer for relevant aircraft types +" +1370 What would daily life on Earth look like if there were two moons? 4376 https://www.reddit.com/r/askscience/comments/con2m7/what_would_daily_life_on_earth_look_like_if_there/ 1565468332 con2m7 2019-08-10 23:18:52 "Ocean currents are driven by heating from the Sun. + +Two moons of similar mass with the same orbital period are not stable. But if we magically move them around: They would produce the same tide pattern as one moon, just with a different amplitude (which would depend on their orientation). At 0 or 180 degree separation they add up, at 90 degree separation they cancel each other. + +What you can have is a [Janus](https://en.wikipedia.org/wiki/Janus_(moon\))/[Epimetheus](https://en.wikipedia.org/wiki/Epimetheus_(moon\)) configuration: They have slightly different orbits. As the lower moon approaches the upper one in its orbit the mutual gravitational attraction makes the lower moon go to the upper orbit and vice versa: They swap orbits (not exactly as they don't have the same mass). The new lower moon is orbiting faster until it made one extra orbit and approaches the upper moon from behind and the cycle repeats. This happens every four years. Such a configuration around Earth this would mean the intensity of tides would vary with a period of two years." "One thing you've missed that I've read about is having a moon helps the earth remain stable in its tilt upon its axis. Most planets ""wobble"" and can move anywhere from 0-90 degrees, while we're stable at 23 degrees. + +If we wobbled like other planets (which does take several thousand years to happen) we wouldn't have stable seasons (among other things)." +416 Why do many materials, such as rock and wood, appear darker when wet? 4366 https://www.reddit.com/r/askscience/comments/4las7y/why_do_many_materials_such_as_rock_and_wood/ 1464356652 4las7y Physics 2016-05-27 16:44:12 "I once wrote a longish answer, but since that thread has been deleted, here is a slightly adapted version of that explanation: +____ + +The short answer is that many materials often appear darker when it is wet, because the water reduces the amount of diffuse reflection from outermost layer of that material. Since how ""dark"" we perceive a material to be depends on how much light it reflects towards our eyes, the net effect is that the object will now seem darker. + +As a good example, we can look at fabric (e.g. cotton), which under high magnification looks [something like this](http://aldpulse.com/sites/default/files/TUe%208.jpg). As you can see the fabric is made up of a bunch of irregular micrometer sized fibers, the gaps of which are usually filled by air. Now what is important for the optical properties of the material is that the fibers and the air have different [refractive indices](https://en.wikipedia.org/wiki/Refractive_index) (about n=1.5 and n=1 respectively). This mismatch between the refractive indices gives rise to a lot of scattering, and because the length-scale of the variation is on the order of hundreds of ~~microns~~ nanometers (similar to the wavelength of visible light), the specific mechanism at play will be so-called [Mie scattering](https://en.wikipedia.org/wiki/Mie_scattering). Mie scattering has the property that light of all (visible) wavelengths is scattered more or less equally and it's the mechanism for why say paper appears white (as well as clouds or milk for that matter). + +The net effect of the description above is that when air fills the pores in the fabric, you will get a lot of scattering events, which will result in a lot of [diffuse reflection](https://en.wikipedia.org/wiki/Diffuse_reflection). Now when you add water, the water molecules will displace the air inside the pores, and this is important because water has a refractive index (n=1.3) closer to that of the fabric (n=1.5). Because you are reducing the refractive index mismatch, less light will be scattered, which means you will get less of the hazy reflection you get from dry fabric. Instead, more of the light will either be simply transmitted through the fabric, or it will bounce around in the fabric/water layer due to a process called [total internal reflection](https://en.wikipedia.org/wiki/Total_internal_reflection) [as shown here](http://imgur.com/ieX3QoH) and eventually absorbed. The net effect is that the material will appear darker. As an aside, this is the exact same reason why [paper appears more transparent when wet](http://timholtz.com/wp-content/uploads/a/6a00e39827d9ad8833015434440b5a970c-800wi.jpg), since less scattering leads to a greater transmittance of light through the material." " The water cowering the rough surface of the stone makes a smooth layer on it, and the light reflected from the front surface of this water layer is dominated by specular reflection. Watching the surface at the proper angle at sunshine ( equal to the angle of incidence of the light) the surface appears very bright, otherwise it looks dark. Still there is diffuse reflection and scattering at the stone surface, but the irregularities of the stone are surrounded by water now. Reflection, both specular and diffuse, and scattering too, depend on the refractive indexes of the reflecting surface and of its surrounding, and the higher the difference between them the higher is the reflection. Your stones are dark by themselves, I mean that they would appear dark grey, almost black, when polished. I think the material is some kind of silica, and the refractive index is about 1.45-1,6. The refractive index of water is 1.33, that of air is 1. In case of dry stones, the difference between the refractive indexes is high, and the difference is much lower when the pores of the stones are filled with water. + +Reference https://www.physicsforums.com/threads/why-do-surfaces-get-darker-when-they-are-wet.335919/ +" +675 In a nuclear weapon, how do the explosive lenses create a supercritical mass out of a subcritical mass, when the actual mass of the fissile material remains the same? 4356 https://www.reddit.com/r/askscience/comments/5u1cpj/in_a_nuclear_weapon_how_do_the_explosive_lenses/ 1487091499 5u1cpj Physics 2017-02-14 19:58:19 Before commenting, please keep in mind [our rules](https://www.reddit.com/r/askscience/wiki/rules) and that [you aren't as clever as you think you are](https://i.imgur.com/wmzhHkN.png). "Yes, your description is exactly correct. Critical mass is a misnomer, it should be something more like ""critical configuration""." +313 How is there no center of the universe? 4353 https://www.reddit.com/r/askscience/comments/49tttl/how_is_there_no_center_of_the_universe/ 1457623006 49tttl Astronomy 2016-03-10 18:16:46 "Imagine that you are a beetle walking around on the surface of a balloon [as shown here](http://i.imgur.com/H3PCWIi.jpg). If the balloon was large enough, the curvature would be so small that locally the ground would appear to be flat. Now imagine that this balloon happened to expand. If you now had [markers the balloon, like a grid](http://i.imgur.com/nMManES.jpg), you would see that over time it takes you increasingly longer to make it from one marker to the other. However, if you are sitting on the 2D surface of the balloon, you couldn't pinpoint any origin from which the stretching originated. In fact, because the fabric of the balloon was stretching like a uniform sheet, no matter where you may be on the *surface* of the balloon, you would see the same stretching going on around you. + +This situation is a very good (even if imperfect) analogy for the [metric expansion of space](https://en.wikipedia.org/wiki/Metric_expansion_of_space). To make things even more accurate, let's say that the fabric that is stretching is not wrapped around itself as in a balloon, but instead is a [flat infinite sheet that is expanding in its plane](http://i.imgur.com/kmJ4kFj.png). Just as in the case of the surface of the balloon, no matter where you might be sitting on this sheet, you would see all other points around you moving away from you in exactly the same way. Because over cosmological distances the universe appears to be uniform (or more technically isotropic and homogeneous), we can model its expansion as the stretching of such a sheet. The [cosmological principle](https://en.wikipedia.org/wiki/Cosmological_principle) then states that the universe has no center, for the same reason that the surface of the balloon had no center. + +edit: I made it more explicit that in the case of the balloon analogy, it is the 2D *surface,* where it becomes impossible to define the center. I also tried to show the conceptual transition from the balloon analogy to the more accurate model of flat spacetime. " "To keep it simple: +To find a center of a shape, 3d or 2d, one must first know the boundary of the shape (the ""sides"") +Considering we haven't found any ""walls"" enclosing our universe mathematically defining the ""center"" is impossible." +555 If identical twins have the exact same DNA, why do they often look slightly different than one another? 4338 https://www.reddit.com/r/askscience/comments/52nb7j/if_identical_twins_have_the_exact_same_dna_why_do/ 1473805435 52nb7j Biology 2016-09-14 1:23:55 "WARNING LONG! But, it's my field of work (computational biology), so I'll give you the detailed answer. + +This is like my exact field of study, so I can comment on this. You hear ""epigenetics"" and this is kind of the surface answer to explain *heritable* information from cell to cell that causes varied gene expression, even though one cell from the other has the exact same DNA. However, there is more to it than that. There is also something called ""stochastic noise"" that can actually affect development too, of which I will get to later. I also think it is prudent to point out that there may also be other unknown factors yet to be identified. + +So, let me give you a broader explanation that hopefully makes sense. Your DNA is identical in every single cell of your body, whether it is the DNA in your lungs, or your skin, your heart cells, your liver cells and so on (typically, some exceptions). What makes each cell different? What makes each cell different is something called ""gene expression,"" or, more simply, what makes each cell different is the spectrum of proteins that are produced in each different cell. + +How does that work though? How does one cell that has the same DNA as another cell ""know"" what proteins to produce? The answer is a word we use quite often, and that is, by ""regulation."" You see, at the end of the day, cells don't ""know"" anything. They don't think. They are just proteins and various molecules floating around and bumping into each other. And, if they happen to bump into each other, sometimes interesting things can happen. You see, it is all just about the ""probability"" of bumping into each other though. This is what we call cellular ""noise."" + +Think of it like this. If there is a large concentration of a certain protein, there is a much higher probability that it will bump into something which can cause a reaction, which can cause some kind of event downstream. If there is a low concentration, sometimes there may be just a random chance of things bumping into each other, but it will be more rare. This is a form of cellular regulation. + +So, this brings me back to the question, well why does one cell with the same DNA produce different proteins than the another cell? Simple, it has to do with the way DNA is packaged up. Unlike the common picture of the double helix you often see in TV, DNA in reality is covered in proteins. I won't go into the amazing amount of variability and functions of it all, so simply, in one cell, the DNA gets packaged up differently than others. For example, in one cell, the DNA will be ""wound up"" extremely tight in certain areas, whilst open in others. Where it is wound up tight, proteins are unable to bind to the DNA to activate the process(transcription) of which proteins are derived from the DNA (Transcription > Translation). You can kind of say that certain genes are hidden from collisions with other proteins in these tightly wound regions. Where it is loose, they will bind. Ultimately, this is the core way one cell differs from the other, the way the DNA is packaged up. A liver cell will only have its cocktail of proteins able to be translated, whilst the others packed up, and other cells might have a very different regime of proteins to produce. + +I should note that this is still poorly understood. We know a lot more now than we did 10 years ago, but a lot of thesis work is going on in this department cause it is incredibly complex. But that is just a side note, so I wouldn't worry about it here. + +Now that you have this big picture (albeit simplified), we go back to your question, how do identical twins look different even though they have the same DNA? Well, one answer is that we have a field called epigenetics. What this is is that through environmental factors, modifications happen to the proteins that package the DNA (methylations), and for one person, through their own life choices, experiences, and environmental factors, the DNA may get packaged slightly different. These will not be extreme differences, as most cellular function must remain the same, but lets use an extreme example: The twins are separated at birth, and one goes to a very poor home and another to a well-fed home. Let's say several times in this child's life he was malnourished, or just didn't eat as healthy or something. Maybe that body went into a more ""survival"" mode and he just grew less tall, or more puny than his twin that was well-fed. The DNA modified its packaging to stop transcription of certain proteins or activate others that another person may not have, like their twin. Sometimes it might be as simple as lowering the expression of a protein by half in one person compared to the other. These modifications that happen due to environmental factors will carry on in each replication. Hence, it's not in the DNA code itself, but there is stored information that copies how the DNA is packaged as well, thus it's not true genetics, it is epigenetics. So, the twins end up looking different because some of these proteins affect the phenotype, or the outward, visible expression of a protein. For example, brown hair verse red hair are phenotypes. Short vs tall, etc. Some genes are related to various phenotypes, and these just may end up being expressed different from one twin to the next due to epigenetic modifications of their DNA. + +Also, DNA methylations are heritable. If you want to read up on the exact term, we call it ""genomic imprinting."" There was another post here that already covered it nicely, but let's say in very early cell-differentiation you had half the methylated DNA on one side, half on the other, if the cell splits to form twins, one of the twins will receive some portion of the heritable methylations from the mother and the other twin will get the rest. This will lead to some different gene expression between the two of you as well. + +There is another issue though. What if I told you that in a theoretical world, if both twins had 100% exactly the same environmental factors to face them through their whole life, that they still will most-likely not be perfect matches of each other? WHAT!? How is that possible? Remember I talked about how in the cell things are just floating around and bumping into each other? Well, this noise is ""stochastic,"" meaning random. In early cellular development, even if 2 cells side-by-side have the same cocktail of proteins and is the same scale, there is still only the ""probability"" of things bumping into each other enough to hit certain thresholds for certain signaling pathways to be activated. Early stochastic noise in the cell can actually cause fairly significant downstream differences. Maybe some early signaling for a growth factor ended up being 25% stronger just through ""stochastic"" noise. Now, through probability, most things will be the same, but also through probability, there is going to be some differences no matter what. This is also why if you took an animal and cloned it, the DNA may be the same, but it becomes nothing more than a ""twin"" who is not a perfect match due to the stochastic changes that occurred in early cellular development. + +Anyway, there is a bit more to it than that, but I thought I'd hopefully explain a bigger, more understandable picture to anyone that stumbled upon this, also because I am procrastinating my own work right now and thought, why not, I'll give a big answer. Hope it helped. + +**EDIT** Wow, this has gotten a lot more traction that I had even imagined! I probably would have given some finer details if I knew it would explode like this, as now I am re-reading it and thinking to myself, ""Oh great, now where did I go wrong and am about to be corrected?"" Thanks everyone. It's an extremely fascinating world we live in, and imo, there is nothing more fascinating than the incredible workings of the cell. Keep learning!" "Epigenetics is the short answer: +Both twins have the gene for brown eyes, but due to the epigenetics, one twin can highly regulate the brown gene, resulting in light brown eyes, while the other twin can barely regulate it resulting in dark brown eyes. + + +When the egg initially divides all dna has histones with different methylation states that affects how 'on' or 'off' certain genes are. In a cell that will become a liver cell, the methylation pattern tells that cell 'you are a liver, make these proteins'. If the egg splits into two embryos (twins), then there is a chance that 1 twin will have 1 set of histones methylation patterns, and the other will have a different. " +208 How much shallower would the Oceans be if they were all devoid of life? 4333 https://www.reddit.com/r/askscience/comments/3tp57k/how_much_shallower_would_the_oceans_be_if_they/ 1448118325 3tp57k Earth Sciences 2015-11-21 18:05:25 "About 10-20 microns. + +[I did the math on this before](http://quarksandcoffee.com/index.php/2015/07/13/how-much-would-the-oceans-drop-if-all-the-fish-etc-vanished/) for fish (~3 microns drop). Fish account for about 1-2 billion tonnes of biomass in the oceans, while all ocean life accounts for 5-10 billion tonnes of biomass. That's a factor of 5 bigger - so the 3 micron drop for fish can be bumped up to 15 microns for all life. + +Visualized another way, if you took all of the life in the ocean and spread it out into a very thin paste extending over the surface of the oceans, that paste wouldn't even be as thick as a hair. " [deleted] +556 Why do sponges get hard when dry but only after use with water? 4327 https://www.reddit.com/r/askscience/comments/55igqy/why_do_sponges_get_hard_when_dry_but_only_after/ 1475419114 55igqy Physics 2016-10-02 17:38:34 "The main reason for the effect you see is that common synthetic sponges made of cellulose are often treated with softening agents during their manufacturing. For example, take a look at [this patent](https://www.google.com/patents/US3284229): + +>The sponge is washed with water [...] **then immersed for 10 minutes in an impregnating composititon containing softener** and hydrogen peroxide at a temperature of 55 C. The impregnating composition, which is freshly made and substantially colorless, consists of 6.25 parts of hydroxypropyl sorbitol, 10.50 parts of diethylene glycol, 6.75 parts of urea, 0.25 part of dihydroabietyl amine, [...] + +>Substantially all of the water and residual hydrogen peroxide is removed from the sponge by passing it through a heat zone having an ambient temperature of C. The sponge is then cut into pieces of suitable dimensions for use by the householder or other consumer. The sponge material produced in this example has a uniformly brilliant yellow color throughout its structure. It also has good softness and compressibility, and normal durability. + +Because of this treatment step, the sponges tend to be quite soft and flexible as you take them out of the packaging. However, once you start using the sponge, the initial effect of the treatment can go away as the softening agents get flushed out. As a result, the next time the sponge dries up, it can be very rough just as you describe. + +The explanation for the latter effect is that these sponges are made up of a messy forest of cellulose fibers, [as shown here](http://i.imgur.com/Yp1qM24.jpg). When water gets into this cellulose network, it allows the fibers to rearrange in order to try to minimize their energy. These structural changes will continue as the water is evaporating. The net effect is that as the sponge dries up, its surface can be much rougher and coarser. This effect is similar to how paper can be very smooth soft when you take it out of the box, but if you drop water on it, it will become wrinkly and rougher as it dries up." "There are a handful of technologies used in making sponges - the ones that get all crinkly after the first use are typically cellulose sponges. Cellulose is an organic polymer that can only be found in plant-based materials and does not take well to being anything other than a plant, but after treating it with it some nasty chemicals like carbon disulfide and a crap ton of sodium hydroxide, you can depolymerize it to a certain degree and cause it to re-link with other chains forming viscose - which is the predecessor of things like rayon and the binder for cellulose sponges. This viscose interacts with other cotton fibers (frequently the byproducts of other textile processes) and forms a cohesive mesh that you know as a kitchen sponge. + +Now - to get more to your question - have you ever line-dried your clothes (in the open air)? You'll notice that your clothes get all stiff and crusty, and may shink slightly while drying. This is what's happening in a sponge. The cotton fibers are losing their plasticity via dehydration because the polymers don't have the water molecules separating the fibers and keeping everything lubricated. + +To prevent this, plasticizers are added during manufacturing - such as what /u/crnaruka mentioned. Except the glycol solutions tend to be more common in sponges produced Europe and Asia. Many US-made sponges are treated with magnesium compounds that actually gets absorbed into the cellulose and act as a humectant. The glycol solutions act as the plasticizer directly. + +Random note about magnesium plasticizers - you'll notice that some sponges advertise that you can microwave sponges to sterilize them, but only after rinsing them. This is because the magnesium conducts microwaves and can ruin your microwave - similar to trying to microwave aluminum. + +Credentials: I used to work at a manufacturing facility making sponges, so take that for it's worth." +417 If somebody across from me on a large field shot a gun while holding a walkie talkie with the speak button on, would you hear the sound first on the walkie talkie or from the sound itself? 4323 https://www.reddit.com/r/askscience/comments/4tk6qh/if_somebody_across_from_me_on_a_large_field_shot/ 1468918737 4tk6qh Physics 2016-07-19 11:58:57 "Walkie-talkies use radio frequency electromagnetic waves to transmit signals. These propagate with the speed of light, approximately 300,000 km/s. On the other hand, sound from the gunshot (or any other sound) will travel at about 340 m/s (precise value depends on atmospheric conditions). + +For all intents and purposes you can consider the time it takes for a walkie-talkie signal to travel from one walkie-talkie to the other to be zero. With that, you see that if the gun is shot 340 meters away, the sound will be heard on the walkie-talkie on second earlier than directly through the air. + +(note: I'm also assuming that there is zero processing delay in the electronics of the walkie-talkie. I don't know the engineering details of these things, but I expect that this is a reasonable assumption and that these delays are in the order of magnitude of miliseconds only) +" "Since you mentioned sports, this is actually a real problem in track events. The official who fires the gun [usually stands on the inside of the track](http://www.tracknfieldgear.com/blog/wp-content/uploads/2011/08/starting-blocks.jpg) so Lane 1 is closer to him than Lane 8. Because sound propagates relatively slowly, the person in Lane 1 hears the starting signal fractions of a second faster than the other lanes. This makes them faster off the blocks, and has a noticeable effect in very short races. + +The solution is the same idea as the walkie-talkies. Each lane [has a speaker behind them](https://upload.wikimedia.org/wikipedia/commons/2/2e/PressureSensitiveStartingBlocks.jpg) that is wired to the official's gun. The sound then travels at close to the speed of light, so each competitor hears it at the exact same time." +1257 Do people who were sleep deprived during adolescence tend to crave sleep as adults more often than their body really needs? 4322 https://www.reddit.com/r/askscience/comments/b5xou0/do_people_who_were_sleep_deprived_during/ 1553646908 b5xou0 2019-03-27 3:35:08 The short answer is (1) the science is still out on this, but mostly because (2) sleep deprivation during adolescence is linked to a number of other consequences that are much more influential on sleep such as depression and obesity. Adding in other factors including genetics and physique which determine how much sleep you need, it's difficult to control for a purely behavioral study such as the one you're describing. "Anecdotally, as one who averaged 4-6 hours throughout high school instead of the recommended 8... close to 20 years later, i wouldn't say too much has changed with regard to desire to sleep. I don't really feel the need to nap any more than i used to, but given the opportunity, i can kill a 4 hour nap easy and go straight back to bed afterward. DH tried waking me up after a ""reasonable"" amount of napping time early on, now he doesn't bother. I still find it easier to stay up until 4 am than to get up at 4 am, regardless of what time I go to bed. A number of things have changed since teen years; for one, I don't sleep singly anymore, and I can absolutely say I don't sleep nearly as well with another person and 2 dogs in my bed than by myself, and I would probably roll back to previous sleep schedules if that weren't the case. Also, my days are packed with day job and commuting, rather than a few hours of school then fun/extracurriculars. I'm also not nearly as active as I used to be, which i keep saying i should change, but never do." +676 Is gravity equally distributed by a mass or are there hot spots where gravity is stronger in some areas and perhaps weaker in other areas? 4321 https://www.reddit.com/r/askscience/comments/645a55/is_gravity_equally_distributed_by_a_mass_or_are/ 1491626023 645a55 Physics 2017-04-08 7:33:43 Gravity is of course affected by mass distribution. That said, the differences are mostly pretty small. The earth's gravity field, for example is very subtly lumpy. Mapping this is an ongoing effort of the National Geospatial Intelligence Agency (it's important for guidance systems). "Barring some physics I'm not privy to, gravity will be distributed in proportion to mass. However, mass is not something that is always evenly distributed. More dense areas will be more massive given the same volume. + + +So let's take the Earth as an example. You would, in theory, have gravitational spikes (more like ripples) over areas with huge uranium veins. + + +I'm guessing that the way that the Earth's gravitational field actually manifests is more complicated than that, but if the Earth were uniform density everywhere except the uranium vein (which was more dense) you could theoretically detect it" +677 AskScience AMA Series: I am a scientist currently working in a US congressional office. Ask Me Almost Anything! 4317 https://www.reddit.com/r/askscience/comments/5r81p1/askscience_ama_series_i_am_a_scientist_currently/ 1485867647 5r81p1 Biology 2017-01-31 16:00:47 How can I start looking for a job like yours? I have a PhD in physics and given my own personal situation as well as the current political climate, your job sounds like exactly what I want to be doing. "As someone from outside the US (but I imagine it applies to many US citizens too!), where does being a ""scientist working in a congressional office"" place you within the government? Are you a government employee providing advice for the entirety of congress, or are you working more specifically for one group - or maybe even just advising a single member of congress? + +(I appreciate it may be hard to answer with great detail given your position of anonymity!)" +314 Do all salts taste 'salty' i.e. Like sodium chloride? What about other sodium salts? Other chlorides? Alkali metals? Halides? Etc... 4313 https://www.reddit.com/r/askscience/comments/4g4dmk/do_all_salts_taste_salty_ie_like_sodium_chloride/ 1461432345 4g4dmk Chemistry 2016-04-23 20:25:45 "The perceived taste of a substance is due to the brain's interpretation of signals from taste receptors on the tongue. In order to trigger these receptors, a substance (usually) must bind properly to or pass through a protein receptor/channel on its surface. The *salty* taste is the simplest mechanism: Na^+ ions directly enter the cell and depolarize it (change its charge, causing an action potential/nerve signal to be sent to the brain). + +So, metal salts consisting of other positive ions that can trick the channel into thinking they're sodium should also depolarize it, which the brain will interpret as *salty*. These would be the others in the same column, the alkali metals, which will be similar in size and their +1 charge in solution. But, since the ions will be somewhat different in size, they won't pass through the channel as easily/often, which means the ions will taste less *salty*. LiCl and KCl will be saltier, while RbCl and CsCl will be less so because of their larger sizes. + +If you change out the anion in the salt (Cl^- ), there is less effect. Sodium bromide (NaBr) will taste salty. But you get more complicated effects if you start changing both ions: KBr changes taste with concentration due to differing sensitivities of receptors for the two ions, the weaker saltiness of K^+ not always overpowering. Anything that produces H^+ ions, (i.e. an acid compound) is also going to taste sour, as that ion is the trigger for *sour*. Pick something with wild organic groups like Pb(CH3COO)2, and it could even taste sweet. + +Edit: K^- to K^+" "In Northern Europe, a candy called salmiak is popular. It's licorice that has ammonium chloride in it/on it. Salmiak is an old name for ammonium chloride. + +Salmiak tastes salty in a way that is both familiar and unfamiliar. The flavor is sort of briney the way you would expect with sodium chloride, but it also kind of numbs/tingles your tongue. Also it makes your breath smell a bit like ammonia. + +It's very much an acquired taste. " +315 "Why are the ""I'm not a robot"" captcha checkboxes separate from the actual action button? Why can't the button itself do the human detection?" 4312 https://www.reddit.com/r/askscience/comments/4dgrhj/why_are_the_im_not_a_robot_captcha_checkboxes/ 1459868108 4dgrhj Computing 2016-04-05 17:55:08 "The captcha is a 3rd part widget made by google that has a lot of logic behind it. One of the main purposes of it, is that a crawler can't click it. It has to be actually clicked for it to register, and the developer can see if the user has been authenticated when the submit button is clicked. + +Because it's in an iFrame it makes it more difficult for bots (and web developers) to trigger the clicking of the div that contains the checkbox due to the [same-origin policy](https://developer.mozilla.org/en-US/docs/Web/Security/Same-origin_policy) present in all major browsers. This stops developers like me from having my submit button trigger the captcha. My option is to check to see if the captcha has been verified yet, but I can't trigger an automatic captcha. Which is a good thing, if I can do it, then so could a bot visiting my site. + +Presumably, google could create a captcha that is just a button, and that could trigger a submit on the actual page. But that would get confusing for the user. Styling would be an issue. As well as the times when a more traditional captcha is required. + +Look at the following captcha demo page. + +[Captcha demo](http://www.google.com/recaptcha/api2/demo) + +Now, look at it in incognito mode, and verify that you are human. + +You'll notice a different type of interaction that really doesn't lend itself to a button click. This is also in addition to being accessible to people with visual disabilities. Which is beyond the scope of a button with a single click action." "Actually a very good question! A lot of captchas are third-party widgets that provide the ~~entire~~ captcha* form through their API. + +But still, technically it should be feasible to trigger the captcha form from your submit button with reasonable effort, depending on which API or code is in use. + +Next time I’ll be doing a form with a captcha, I’ll give it a try. Every button or step less is almost always an improvement. +" +557 Why do skydivers have a greater terminal velocity when wearing lead weight belts? 4309 https://www.reddit.com/r/askscience/comments/5k3mv8/why_do_skydivers_have_a_greater_terminal_velocity/ 1482595356 5k3mv8 Physics 2016-12-24 19:02:36 For a quadratic drag force, your terminal velocity is proportional to the square root of your weight. If everything else is the same, an object with a higher mass will have a higher terminal velocity. "The acceleration due to gravity is independent of mass and is not affected by the lead weights. + +What is affected is drag. Loosely speaking, the drag when falling depends on the shape of the object that is falling. Your shape does not change significantly with the lead belt, but your mass does, and the result is that drag becomes less important relative to gravity. For similar reasons you will find that a sheet of paper falls more slowly than the same sheet of paper crumpled up into a ball. + +What Galileo found is that when drag is *not* important, the acceleration of a falling object is independent of mass. This is because, as stated above, the acceleration due to gravity is (to a very good approximation) independent of mass. + +Edit: a helpful Redditor suggested the correct term to use here would be ""drag"" instead of friction. Original edited for clarity." +1371 What is the biological explanation for why we often feel nausea in waves rather than one sustained reaction? 4309 https://www.reddit.com/r/askscience/comments/crmkom/what_is_the_biological_explanation_for_why_we/ 1566050852 crmkom Human Body 2019-08-17 17:07:32 "MD here. I don’t really like any of the answers here. Mine probably won’t be great either though because I don’t necessarily agree that nausea comes in waves. + +You can have what’s called a “colicky” pain in the abdomen, this is pain that comes in waves, which is due to peristalsis (the intestines basically contract in waves to help push food) and if there is an irritant in the tract, you will feel the pain on the contraction. + +Now, related to this is the fact that nausea is based on the gut brain axis. Your gut actually produces neurotransmitters, such as dopamine and serotonin, these communicate with the brain to tell it to vomit. For example, a common drug for nausea is metocloprimide which is a dopamine blocker. + +How these neurotransmitters interact from the gut and brain is very complicated and is based on our outside world (like our interpretation of possible anxiety causing scenarios) as well as what’s inside our body (something toxic). + +So, I think it is dependent on why you are feeling nausea in the first place. Spit balling now, in my experience, if I have something like food poisoning, I just slowly get more nauseous until a vomit response is trigger. If I’m feeling nauseous from anxiety, well, then likely my brain is trying to combat that nausea with other neurotransmitters or maybe by reducing neurotransmitter receptors in the brain as a way to try and balance the system, if that makes sense. The ladder, I suppose could be like a wave sensation." "Doesn't the sensation or perception of things ""coming in waves"" have something to do with the saturation of the nerves mediating the signal(s)? Aren't many sensations that seem *cyclical* (wave-like) just our nerves ""losing"" and ""regaining"" interest in a continuous signal?" +1802 How many mutations does the average human have, if <1 what % of people have at least 1 mutation present? 4302 https://www.reddit.com/r/askscience/comments/lxhyi3/how_many_mutations_does_the_average_human_have_if/ 1614855426 lxhyi3 Biology 2021-03-04 13:57:06 Everyone undergoes ~ 20ish during gestation. And throughout your life individual cells undergo mutations that may of may not be passed down to other cells. Apoptosis prevents most from being passed down to other cells. By the end of your life it is possible to sequence a cell from your left hand and a cell from your right hand and get very very close but ever so slightly different sequences. "Ok. + +This is really both a population biology, and a systems biology question, and it has to be broken apart as such. Here is a rough order estimate that will get you most of the way to whatever it is you need. Flame me if I am off by 50%, I dont care, but this is experience talking. Much of this data comes from sequencing, life science degrees, systems biology, bioinformatics, and most importantly Personal genomics and several discussion with the director of George Mason Systems Biology. + +Back of envelope: + +3BB. Human beings have around 3 billion base pairs + +25k. This is encoding about 25000-30,000 ""Genes"" + +This is segmented onto 23 pairs of chromosomes # 1-22 and X/Y + +750MM. A quarter of that is coding and regulatory (750 MM bp), the rest non-coding. + +10k. Now up to half (10000) of those coded genes are completely necessary, untouchable, ""unmutated"", conserved to a very high degree, and the fetus will stop development if they are changed in any way, so then those implantations fail out and mom will miscarry (up to 20% of the time). This is no ones fault. If you, as a budding little promising zygote, cant put a phosphate on a glucose molecule with hexokinase, you will not make it in this world. You absorbed nutrient of your placenta until you got to 128 cells, then it was too far a journey for diffucion. Same situation is for neurotransmitters, receptor proteins, cell cycle kinases, etc. There are many of those that you just can't change, and survive development. Some result in putting off the death drama, like lysosomal storage disorders, where a lack of the ability to take a sugar molecule of a brain protein leads to that now useless thing being shunted into a neuronal storage granule, until arund 2-3 years, when the child perishes. Be compassionate. All of us know these people. + +7500. Now there are changes in the other half of the genome with varying effect. For the remainder, we are talking about involvement of 7500 ""rare"" heritable genomic disorders. Gp investigate NORD for more info. Blindness, deafness, ALS, charcot marie tooth syndrome, Alpha-1 Antitrypsin disorder. Many of them. Mess with those and you have a disorder, if not a disease. Glass bones, inability to taste cilantro, we are legion. + +Now let's call mutations ""SNPs"", or single nucleotide polymorphisms; changes. Half of the rare diseases are SNP related, half are multiple sites involved. We dont know a lot of those. + +12. Last, people are actually mosaic. A person has at any moment 5-25 genomes in them, from localized cellular mutation. The changes are slight, but hey, one of them goes awry like cyclin dependent kinase 1, and you have a tumor since you cant control cell division in that tissue anymore. We hope that your killer T cells keep on cleaning up and seeing them. Then again, some SNPs are escape mutants without the receptors that TNK cells need. + +So. What are the population numbers you ask? + +5000. Average people carry about 3-10000 SNPs in their 3 B bp genome. This is still only a vanishing part of who we are as a genome, 0.013 parts per thousand changed. We are way over 99% alike one another, changes and all. of those 5000 changes, over half are silent, non-deleterious changes. I have over 5k of those. We dont worry about them. They dont do anything. Look in your personal sequence file, find the (=). They are equivalent, silent, immaterial. + +3000. Then about 2-4000 changes are ""likely pathogenic"", where the SNP change results in a change in the protein of the gene, a charge change in it, a folding problem, a premature read stop. However, modern medicine is only up to knowing what a fraction of the genes do, much less correlating the changes to a diseases causally or with Pearson's R or some such. Currently about 25% of genetic diseases are mapped to a polymorphism. + +100. Now at the last, if you are talking about ""mutations"", that is, SNPs, probably pathogenic, non-benign, and mapped to a disease or metabolic pathway, then the answer for a regular person is about a HUNDRED. I have about 45 of these. This is from sequenced human beings at INOVA, northern Virginia where they are getting the exome of every baby, rather than doing heel sticks for PKU, Down's trisomy, etc. Everyone has them, no one is perfectly functional at the genomic level. There are 25k bell curves of enzyme function in pop bio to eventually look at. We are the sum of all of it. + +50. Now half of those changes are in only one copy, or yield to us a ""carrier"" status. You have one bad hit, the other is fine. You are ""heterozygous"". Bless the sexual reproduction, we have multiple copies of almost everything! These disorders just do not show up. The ""incidence"" of the change can be up to 5-10 % of the population. Rare diseases have under 2% incidence? However, if 48% of the populace carries a SNP, is that a variant? Thoughts. I carry SNPs that produce pathogenesis for 45 genes. Better than average but who wants 45 damages? Luckily more than half of these are recessive. + +25. I have only informatically battered down about 22 of SNPs that cause some concern. Inosine metabolism, glutamate turnover, etc. You can lose yourself in Pubmed on this stuff. Thankfully, most of these changes result in enzyme activity being dropped by only 5-30%. Functionally, they have no perceptible effect, physiologically, that a practicing MD would call ""disease"". Will you be an olympic athlete? Sorry, VO2 max is limited to 78% because your lung neutrophil elastase is changed and unregulated by serpins, and now your alveoli have less surface area. Go take a spiromoter reading and get back on your bike. Will you be Einstein? No, of the 10k genes it takes to make a brain, you have 4 changes that impact catecholamine synthesis. Sorry. You have a good spleen though, that only took 5200 genes to make and the organ is unhit. + +Now you are down to the very last category, which I think is what you are actually asking. For those persons who carry a deleterious mutation, a dominant SNP, which then results in disease, who are they and how many? Now we are talking about 5-10% of humanity carrying some form disease. Of my 5k variations, 2 are in this category. One is metabolic for which a protein can be taken be needle, one is structural for which there is no cure. Both of them result in 40% activity for that pathway. There are others that result in 25% that I can augment with nutritional support, hacking myself. + +I live for the day when personal genomics makes medicine personal, for when genetics is not eugenics, for when the natural variation is treatable if pathogenic, and left alone if not. We are all humanity, we are every color. Your ability to metabolize alcohol better than me does not make you better or worse. We can be grateful for the math that aspergers has brought us, the violin of Paganini who could not connect two lysine molecules correctly to make collagen, so his fingers were extra flexible. This is who we are, a group of adventurers. We can work on crispr genetic therapy to fix beta thalassemia, and clotting disorders, and many of the above where a SNP has caused loss of function. We can work on situations wehre a bad protein builds up and gives you cirrhosis, with antisense RNA technology. + +Now let me extend the last point. You may ask yourself, of, if I have 75 SNPs to worry over, they make me different by a fraction of a percent, and those genes control stuff like depression, ambulation, height, whatever. Is there anyone like me? Add up the chance of having each SNP at each position, for all your copies. What is the chance someone else has this ""signature""? My answer is, you would need 50X the current poulation of the planet, to find a single person who has that set of SNPs or mutations. Even your brother carries half the SNPs you do. + +All of us are unique. That's the statistical fact. + +Thanks. Best of luck." +885 Does body temperature impact cognitive performance? If so, is there an optimal temperature? 4292 https://www.reddit.com/r/askscience/comments/7ce4hm/does_body_temperature_impact_cognitive/ 1510471479 7ce4hm Psychology 2017-11-12 10:24:39 "This is only somewhat related but there's an interesting thing called [Uhthoff's phenomenon](https://en.wikipedia.org/wiki/Uhthoff%27s_phenomenon) that happens to people with MS. + +The basic way MS affects the body is parts of the brain are damaged due to the immune system attacking it. These localized areas are sometimes damaged beyond repair which can cause permanent dysfunction in any number of regular functions (leg movement, eye sight, memory, anything the brain does). When the damage is not too severe, though, the brain can rewire using the surrounding brain tissue (think of it like taking the back roads when the highway is closed). + +This is all well and good during normal conditions. The dysfunction is fixed and the MS patient is not affected during their daily activities. Until their body temperature rises due to outside temperatures, exercise, hot tubs, whatever. This causes the nerve impulses in the brain to slow down, and suddenly the old symptoms return because the new pathway isn't actually as fast/efficient as the original one that was damaged. + +So yes, body temperature has a significant affect on cognitive performance. Optimal is ""body temperature"" which is around 37C/98F." "This article has a number of sources that seem to point to 22 C/71F being the optimal temperature for ""relative performance"". https://www.quora.com/What-is-the-best-room-temperature-for-productivity-I-heard-that-cold-temperatures-were-better-to-improve-productivity-but-is-that-true-Is-there-any-scientific-research-on-this-topic + +Edit: That's room temperature of course, not body temperature. + +Edit2: 22C is 71F as pointed out." +984 Is it possible for a deaf person to have tinnitus? If so, how does it work? 4291 https://www.reddit.com/r/askscience/comments/8behkf/is_it_possible_for_a_deaf_person_to_have_tinnitus/ 1523421809 8behkf Human Body 2018-04-11 7:43:29 "This post has attracted a large number of medical anecdotes. The mod team would like to remind you that **personal anecdotes and requests for medical advice are against [AskScience's rules](/r/askscience/wiki/rules)**. So far 85% of the comments in this thread have been removed, most of them for being personal stories about tinnitus or simple jokes. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating." [deleted] +1091 How does Vanta Black work when it comes to absorbing light? 4291 https://www.reddit.com/r/askscience/comments/9a6s20/how_does_vanta_black_work_when_it_comes_to/ 1535203766 9a6s20 2018-08-25 16:29:26 "Vantablack is made of vertically aligned carbon nanotubes. The level of ""blackness"" you might expect from a single carbon nanotube is similar to other forms of carbon, like coal. What makes it really black, however, is light trapping by this ""forest"" structure. When light hits the material, rather than reflect or transmit, it bounces around inside the forest. At every bounce, there is some probability of absorption. The more bounces, the more absorption. + +In terms of what actually happens in the material, it works the same as in most semiconductors - the energy of the photon promotes an electron from the valence band to the conduction band of the material. This is the same as in a solar cell. But without the solar cell structure, the electron eventually relaxes back to the valence band, emitting a phonon (usually). Phonons are vibrations in the material, the microscopic manifestation of heat. So in the end, Vantablack turns light into heat. + +As to the limit of absorption, you will always run into the problem of black body radiation. At a given temperature, an object is always emitting light. For room temperature objects, that light is mainly in the far infrared. For very hot things, like flames or metal taken out of a forge, you actually get visible light. So if Vantablack absorbed so much light that it got really hot, it would start to glow red. + +Edit: lots of good replies and corrections below, please read them. Wish I had the time to engage with all of them." Vantablack consists of a lattice of alligned carbon nanotubes of specific width to trap the electromagnetic waves of wavelengths specific to visible light. Within the layer of vantablack that is coasted onto a substrate the light continuously bounces between the nanotubes becoming more and more absorbed, of which the electromagnetic radiant energy is exchanged to heat potential and usually dissipated through a high heat capacity substrate. The probability of visible light escaping vantablack is very low, as such almost zero visible manages to reflect from the compound. +1372 What kind of impact does sleeping position and sleeping posture have on spine health? 4289 https://www.reddit.com/r/askscience/comments/cwn8bk/what_kind_of_impact_does_sleeping_position_and/ 1567010089 cwn8bk 2019-08-28 19:34:49 "Interesting question! + +[This year the BMJ reviewed research into this](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6609073/) and generally found that not enough research has been done. They thought lying on your side while sleeping seemed to be generally protective against spinal symptoms (pain and stiffness). Take this with a pinch of salt though, as they only found four studies (Abanobi, 2015; Cary, 2016; Desouzart, 2016; Gordon, 2007) that had looked at sleeping posture and spine health. + +There are [some slightly different studies](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6348954/) into the relationships between sleep posture, [quality of sleep, and pillow/mattress design](https://www.ncbi.nlm.nih.gov/pubmed/25008402). + +Overall though, this seems to be an under-researched area." "Oh boy, this is my time to shine. TLDR; your mattress ideally should match your spine curvature in neutral position. + +your spine disc is hydrophilic. when you sleep, there's no gravitational pressure, hence it absorbs water from surrounding areas. when you wake up after 7-8 hours sleep, it gets swollen. hence you are taller in the morning. + +As you wake up, the compression effect og gravity acting on your body will slowly force the water out of the discs, hence after about 2 hours, your spine disc will dehydrate most of the water and you shrunk to your average height. + +The thing is, when your discs are swollen, your vertebral body are also more prone to traveculae fracture upon compression by about 20%. anterior and posterior ligaments are also more taunt due to disc increase in height, exerting pressure on the vertebral body itself. Hence your back being stiffer in the morning. + +the trabeculae bone in your vertebral body is more resistant to compression fracture when the spine is in neutral posture compared to when its flexed by about 50%. + +So if you sleep in neutral spine posture, and when you just wake up, you avoid excessive spine movement, then you lower your risk of spine injury. The thing is, some people naturally have more lordotic curve and some pople have more pronounce difference in waist to hip ratio. For these people sleeping on a hard matress will put their spine out or neutral posture, by the time you wake up, your spine disc annulus have migrated away from disc centre and the vertebral bodies are experiencing pressure unevenly. Excessively soft mattress also cause on-neutral spine posture. If your spine is still relatively ""virgin"", sleeping in non-neutral pose is ok, but if your spine already experience some damage (that may or may not show in x-ray), then you will wake up with pain. + +Source: multiple researches that can be read at greater detail on ""low back disorders"" by Stuart McGill. For the less scientifically inclined, can read ""back mechanics"" by the same author" +209 "How do we know that there is a ""Pluto-size ball of solid iron that makes up Earth's inner core""?" 4286 https://www.reddit.com/r/askscience/comments/3nybm1/how_do_we_know_that_there_is_a_plutosize_ball_of/ 1444297595 3nybm1 Earth Sciences 2015-10-08 12:46:35 "So for starters, we know there has to be a lot of iron at the center of the planet. + +If we just measure the mass of Earth and its size, then we can find our planet has an average density of 5.5 grams per cubic centimeter. Rock alone has a density of around 3 grams per cubic centimeter, so there must be quite a bit of something much denser for the total to average out to 5.5, and iron (with a density of 7.9) fits the bill nicely. + +On top of that, we know we have a very strong magnetic field. That requires some kind of swirling magnetic fluid at the core to generate that field, which again points to iron as the culprit. + +Okay, but then how do we know the outer core is liquid and the inner core is solid? For starters, dynamo theory suggests you can't generate a magnetic field that strong without some kind of solid-liquid interaction. For example, Venus has no intrinsic magnetic field; it remains unknown if this is because the core is all solid, all liquid, or just doesn't have enough of a temperature gradient, but the point remains that you need that solid-liquid interaction. + +So we know that there has to be some solid iron inner core, but how do we know how big it is? This is where earthquakes help us out. Seismic waves generated by earthquakes can travel deep into the Earth's core and back out again. Exactly where those waves are detected, which kind of waves are detected, and how strong they are can give us a lot of clues. + +We see a sudden shadow of pressure waves about 105 degrees away from an earthquake's epicenter. If you back out the geometry, this gives you a zone of intense refraction from a sphere 3400 km in radius - that's the liquid iron outer core. On top of this, we also see a secondary zone of refraction, as well as some pretty intense reflection from a separate sphere 1200 km in radius - that's the solid iron inner core. The path of that reflection off the inner core maps out similar to the black lines in [this diagram](http://i.imgur.com/FCkY84o.jpg) + +Additionally, we can verify this by studying the orbits of satellites around Earth. By measuring changes to their orbits very carefully, using some gravitational calculations we can back out the depths of sudden changes in density, similar to what's shown in [this diagram](http://i.imgur.com/I2mXG0K.jpg). We see sudden density discontinuities for both a 1200 km inner solid core as well as a 3400 km liquid outer core. + +**TL;DR**: There has to be a lot iron just based on our density, we know some of it has to be solid based on our magnetic field, and we know its size based on seismic wave reflection. This is also verified by gravity measurements." " +Inge Lehmann Was a Danish Seismologist who revolutionized our understanding of earth's interior when she discovered that it has a solid inner core. + +This is an interesting podcast, one part of it covers a history of her very briefly. + + +http://www.theskepticsguide.org/podcast/sgu/526" +558 As bananas emit small amounts of gamma radiation, would it be theoretically possible to get radiation sickness/poisoning in a room completely full of them? 4286 https://www.reddit.com/r/askscience/comments/56m02a/as_bananas_emit_small_amounts_of_gamma_radiation/ 1476016558 56m02a Physics 2016-10-09 15:35:58 "Bananas contain potassium-40 (^(40)K), which decays [like so](http://inspirehep.net/record/1191882/files/K40_decay_scheme.png). So about 10% of the time, ^(40)K will emit a 1460 keV gamma ray. And to a lesser extent, you'll also get 511 keV gamma rays from annihilation of the positrons produced by pair production and the beta^(+) decay of ^(40)K. The primary decay branch is beta^(-) directly to the ground state of ^(40)Ca, but these betas don't penetrate very far through matter. + +So the only substantial dose you'd receive by standing in a room full of bananas would come from the gammas. + +If you consider the fraction of the banana that's made of potassium, and consider the fraction of natural potassium which is potassium-40, you'll come to the conclusion that you need a **huge** number of bananas to get an appreciable dose rate. Then you also have to think about how the bananas are arranged in the room and consider the fact that the if the gammas have to travel through a significant amount of material before they reach you, they will be attenuated." "Without a lot of technology, you would die from alcohol poisoning long before, just by breathing the fumes of fermenting banana. The quantity is the problem... + +Even if we assume the sketchy math on dose/banana is correct, you need to be in a room with at least 40 million of them. + +Average banana weighs 120 g, so you need 4.8 million Kg, or 4,800 metric tons. According to http://www.naturskyddsforeningen.se/sites/default/files/dokument-media/banana_report_final_version.pdf this is about 1/4 [ of 1/1000] the annual world exports of bananas. + +Edit: oops, 40 million bananas +Edit2 oops, x 1000" +1258 The ocean is full of plastics: What are the primary sources of these plastics? 4286 https://www.reddit.com/r/askscience/comments/b73yrw/the_ocean_is_full_of_plastics_what_are_the/ 1553900382 b73yrw 2019-03-30 1:59:42 [deleted] "10 specific rivers have been identified as probably responsible for a quarter of all ocean plastics. +All we need to do** is filter at the river mouths of these and 25% of the flow can be stopped. But do we ? No. + +https://www.scientificamerican.com/article/stemming-the-plastic-tide-10-rivers-contribute-most-of-the-plastic-in-the-oceans/ + +For those who don't understand what riverine filtering projects look like, it's not sticking a giant net-like filter across the entire river. +Typically barges are used, like they have on the Thames in London. + +Other projects, +https://m.dw.com/en/eu-eyes-high-tech-cleanup-for-plastic-pollution-in-rivers/a-41653886 + +https://www.seabinproject.com/the-product/ + +** this has caused some confusion. I'm not suggesting this would be easy. But at least it means we've narrowed down the target of our efforts from tens of thousands of possible emission points to 10 main ones. Low hanging fruit and all that. " +418 There's a massive ball of water floating in space. How big does it need to be before its core becomes solid under its own pressure? 4281 https://www.reddit.com/r/askscience/comments/4n4cyd/theres_a_massive_ball_of_water_floating_in_space/ 1465381896 4n4cyd Physics 2016-06-08 13:31:36 [deleted] "While /u/RobusEtCeleritas answer is super cool and interesting, what really happens to any amount of water floating about in space is [this](https://www.youtube.com/watch?v=pOYgdQp4euc) + +the answer is that any size blob of liquid water will partially boil off in to space, leaving behind a core of solid ice. The only way to preserve liquid is if the blob of water is sufficiently large to gravitationally bind an atmosphere of water vapor (or perhaps other gasses) of high enough pressure to stop the boiling, which is also hot enough to prevent freezing by conventional means. If the atmosphere is allowed to wane over time, then your water ball is doomed to become a dusty ice ball like the majority of the stuff in the solar system." +1803 Why do vaccines provide longer immunity from a virus than natural infection? 4280 https://www.reddit.com/r/askscience/comments/lrijdh/why_do_vaccines_provide_longer_immunity_from_a/ 1614188308 lrijdh Biology 2021-02-24 20:38:28 "It depends on the disease, sometimes both vaccine and infection provides life long immunity, sometimes the vaccines will provide shorter immunity, sometimes infection will provide shorter immunity. + +If you're talking about Covid, we just don't know yet. + +There's more info [here](https://www.nature.com/articles/s41591-020-01180-x)" [deleted] +1092 How is antimatter stored? 4270 https://www.reddit.com/r/askscience/comments/8hg2b7/how_is_antimatter_stored/ 1525621818 8hg2b7 Physics 2018-05-06 18:50:18 ">I'm guessing in a vacuum, but it must be in a container of some sort? + +Yes, under very high vacuum. + +>And how do they move it? Do they use magnets? + +You can control charged particles with electric and magnetic fields. The ways charged particles (regular matter or antimatter) are generally stored are with [traps](https://en.wikipedia.org/wiki/Penning_trap), [magnetic bottles](http://newscenter.lbl.gov/2010/11/17/antimatter-atoms/), [storage rings](https://en.wikipedia.org/wiki/Antiproton_Decelerator), etc." "Another way to answer is: Antimatter normally isn't stored. Specks of antimatter (generally anti-protons and anti-electrons) are at constant risk of bumping into something and annihilating. + +In the past twenty years, scientists have developed techniques to create anti-hydrogen and store it for minutes at a time. You can read a bit more at: +https://home.cern/about/engineering/storing-antimatter + +" +886 Is there an optimal angle when dragging an object across the ground? 4268 https://www.reddit.com/r/askscience/comments/766vg2/is_there_an_optimal_angle_when_dragging_an_object/ 1507920490 766vg2 Physics 2017-10-13 21:48:10 "θ = tan¯¹(μ) + +  + +θ is the optimal angle when μ is the frictional coefficient. +For a frictional coefficient of 0.1 there is 1 pound of of force holding a sled from sliding for every 10 pounds pushing down on it. +At the optimal angle θ, the distance in front of the sled times the frictional coefficient equals the height above the ground." "By ""optimal"" in this context, you could mean a few things. I think the most reasonable interpretation is ""the angle which maximizes the acceleration of the object"". This can be solved with some introductory physics and a little bit of calculus. + +Suppose we apply a force of fixed magnitude *F* to some load with mass *m*. The coefficient of friction between the load and the ground is μ. What angle of application θ maximizes the acceleration *a* of the load? If *N* is the magnitude of the contact normal force between the load and the ground, then Newton's second law gives us + +> (F cos(θ) - μN)**e***_x_* + (F sin(θ) + N - mg)**e***_y_* = ma**e***_x_* + +Hence the net acceleration of the load is + +> a = (F/m)(cos(θ) + μ sin(θ)) - μg + +So what angle θ (in the interval [0, π/2]) maximizes *a*? Simply solve the equation da/dθ = 0, which gives + +> θ*_optimal_* = tan^(-1)(μ) + +This means that for a very high friction coefficient, the load angle should be almost vertical. For a very small coefficient, the load angle should be almost horizontal. + +Now does this actually give the maximum? Yes. You may verify that the second derivative d^(2)a/dθ^(2) is strictly negative for all θ in [0, π/2]. Another way to see that this is the optimal angle is to rewrite the acceleration as follows: + +`[; a = \frac{F}{m}\sqrt{1+\mu^2}\cdot\cos\left(\theta-\tan^{-1}(\mu)\right)-\mu g ;]` + +So we can see immediately that the maximum value of *a* on the interval [0, π/2] occurs when the argument of the cosine is 0, or when θ = tan^(-1)(μ). We can also see that the maximum acceleration in that case is + +> a*_max_* = (F/m)(1+μ^(2))^(1/2) - μg + +There *is* a solvability condition here, since this maximum acceleration should be non-negative. This requires that *F* have a certain minimum value. That is, for this problem to make sense at all we require that + +> F ≥ (μ/(1+μ^(2))^(1/2)) mg + +(For small μ, this means *F* can be very small. For large μ, the above expression is only slightly less than *mg*.) + +--- + +One last thing to note though is that to achieve this optimal angle in practice, the yoke on the oxen would have to be constructed in such a way so that the angle of application is constant. But say we were simply pulling a large box along the floor with some rope, so that the angle is not fixed unless we specifically adjust our force *F* to fix the angle at some desired value. + +We found a relationship between *F*, *a*, and θ (given the constants *m* and μ). Maintaining a constant *F* is really not as easy as you may think with a rope, for which the angle θ is allowed to vary. Many times we often pull or push loads in such a way that the load has zero net acceleration. That is, we *don't* apply force to maximum acceleration, but instead we apply a force to keep the speed of the load steady. In that case, we can ask the slightly different question: given an application force *F*, what angle will the rope end up at if we pull the load with constant velocity? + +In that case, we simply set *a* = 0 and solve for θ. We get + +`[; \theta_0 = \cos^{-1}\left(\frac{mg}{F}\cdot\frac{\mu}{\sqrt{1+\mu^2}}\right)+\tan^{-1}(\mu) ;]` + +If you want to get *really* fancy, you can use the identities + +`[; \cos^{-1}\left(\frac{x}{\sqrt{1+x^2}}\right)+\tan^{-1}(x)=\frac{\pi}{2} ;]` + +`[; \cos^{-1}(x)+\sin^{-1}(x) = \frac{\pi}{2} ;]` + +to rewrite the angle for zero acceleration as + +`[; \theta_0 = \frac{\pi}{2} + \sin^{-1}\left(\frac{\mu}{\sqrt{1+\mu^2}}\right)-\sin^{-1}\left(\frac{mg}{F}\cdot\frac{\mu}{\sqrt{1+\mu^2}}\right) ;]` + +(This is nice only because now it looks very symmetric, but it's totally unnecessary.) + +Observe that the solvability condition on *F* implies that the above expression is well-defined. Also observe that tan^(-1)(μ) is the optimal angle for maximizing acceleration. So we see that the natural angle the rope slacks to if we pull at constant velocity is actually *larger* than the optimal angle. (Remember that cos^(-1)(x) is a non-negative angle.) Does this make sense to you? Should the rope really have a *larger* angle?" +985 Is there a triple-point with plasma? Normally it is with solid, liquid, and gas, but is there one with, say, liquid, gas, and plasma? 4268 https://www.reddit.com/r/askscience/comments/8b81a5/is_there_a_triplepoint_with_plasma_normally_it_is/ 1523371221 8b81a5 Chemistry 2018-04-10 17:40:21 /u/simkhovich mentioned a good example of dusty plasmas where solids, gases, and plasmas coexist but there's an important distinction when you're dealing with plasmas: most plasmas aren't at thermal equilibrium. At its triple point, water is a solid, liquid, and gas at the same temperature and pressure. In a plasma, the neutral gas molecules, ions, and electrons are usually all at different temperatures, and in a dusty plasma the dust particles are again at a different temperature. Plasma is interesting because while it is certainly different enough to be considered a fourth state of matter, the transition to the plasma state is not totally analogous to the process of freezing, melting, boiling, etc., so plasma rarely exists in equilibrium with other states of matter. "In order to have a triple-point you need a phase transition first. Water evaporates into steam, ice melts into water etc. The transition from one phase into the other is sharp and there is no phase in between. + +On the other hand the transition from gas to plasma is continuous (characterized by the degree of ionization). There is no sharp edge that would have gas on one side and plasma on the other. Therefore you can't have the triple-point. + +Note: For high enough pressures, the phase transition is not sharp from gas to liquid either. The point in phase diagram where the phase transition no longer occurs is called critical point. Interestingly it is possible to go ""around"" that point and continuously change gas to liquid (or vice versa) without any phase transition happening in between. " +419 When I hold two fingers together and look through the narrow slit between fingers I am able to see multiple dark bands in the space of the slit. I read once long ago that this demonstrates the wavelength of light. Is there any truth to this? If not, what causes those dark bands? 4263 https://www.reddit.com/r/askscience/comments/4yolbi/when_i_hold_two_fingers_together_and_look_through/ 1471692387 4yolbi Physics 2016-08-20 14:26:27 "**Short answer:** It could be diffraction. [An optical physicist offers an interpretation from diffraction here](https://www.reddit.com/r/askscience/comments/4yolbi/when_i_hold_two_fingers_together_and_look_through/d6pp2ft). [And a psychologist who studies vision offers a explanation from the eye here](https://www.reddit.com/r/askscience/comments/4yolbi/when_i_hold_two_fingers_together_and_look_through/d6poole). Keep in mind that different people, with different visual acuities and corrective lenses, holding their hands different ways, and using different light sources could be seeing either effect! + +**Long answer:** So I just did this and I'm surprised it worked. I held my fingers about 1 mm apart and held the slit right in front of my eye and I actually saw a dark line or two between my fingers, though I'm not sure I have a good explanation for what it is. + + + +A simple experiment may disprove the diffraction interpretation. I held my finger-slit a few centimeters over my desk and allowed light to shine through the slit. There were no visible fringes, so there is no diffraction (but this could be because I don't have a good light source). I suspect the trick is happening in the eye or brain. + +Though it could be diffraction. A 1 mm slit, at a distance of 5 cm from the screen (your eye) should produce fringes 25 cm wide - about the width of a hair, consistent with what some people in the comments have seen. Though there are problems with this interpretation, diffraction is wavelength dependent so people in rooms with white light should expect rainbows, which I'm not seeing. + +Depending on your light sources and how you hold your hands, you may see different things. Some people in the comments may be seeing optical tricks in the eye due to blur and lack of focus, but other people may be seeing diffraction bands, but I'm not one of them. If anyone has anything to add, please do. This is definitely the most fun I've ever had staring at my hands. + +___________________ + +**Edit:** Holy shit I just tried it again with a monochromatic source in a dark room. I totally see a bunch of fringes that look a lot like a single slit diffraction pattern. I get them if I focus at a distance, and lose them if I focus on my fingers. I'm now convinced I see the diffraction fringes with the width of about a hair. If you want to do what I did, take either your laptop or an LED to a dark room, hold your fingers parallel with as small a separation you can manage, close one eye and hold your fingers about 1-2 inches (3-5 cm cm) in front of your open eye. Focus your eyes to the light source. Adjust; slowly open and close the slit between your fingers and move your hand back and forth [You might be able to see a set of vertical bars, similar to this.](https://www.itp.uni-hannover.de/~zawischa/ITP/bildchen/spalt1.png) +" "*TL;DR: I made the assumption that it was purely an ocular phenomenon and found evidence that it does have partial impact.* + +*However, I have had vision corrective surgery. Can someone with good eyesight (especially no astigmatism) please repeat my experiments?* + +To play devil's advocate, let's assume for a second that it is not fringe diffraction. What else could it be? + +The eye has a single lens, but a large **curved** detection area. That means there is the possibility that different parts of the retina will see slightly different angles of the object when the object is brought inside a critical minimum distance. + +Ok, following that line of thought, there should be some quick checks to confirm if it is possible that it is just an illusion. + +1) The illusion would only work when you fingers are very close to your eye. + +Yes! This appears to happen. However using two credit cards about 1/2 mm apart gives much cleaner lines than using your fingers loosely spread. + +2) Thin objects, like needles and string should also have multiple images. + +Yes! A thin string appear to do the same. Of course, edge diffraction is a possibility here. + +3) You should be able to observe both the top and bottom face of a thin and wide object (like a credit card). + +Yes! But surprisingly I had the assumption backwards. You can see multiple versions of the near edge, but your eye resolves only a single far edge. + +4) And finally, to absolutely discount diffraction, you should be able to observe the same illusion on writing on a flat object, like lines on a piece of paper. + +Only a partial yes. There is a distinct widening of the lines on a piece of notebook paper. It didn't resolve into multiple lines. + + +Taking 1 to 4 together gives us evidence that ocular focal characteristics is at least partially responsible. + +I would be much more convinced if I could see multiple lines on a piece of paper, however the widening of the line might be the only way your eye resolves a flat object. + +My overall conclusion is that ocular focal characteristics cause an apparent enlarging of a nearby object. This allows us to ""observe"" diffraction bands through a wider slit than is normally possible. Thus, a 1-2 mm gap between fingers appears to have diffraction bands. However, when compared to the bands in a narrower slit between two credit cards, you can definitely tell the difference in quality of the bands. " +210 Today i dripped some super glue on the colored print of my t-shirt by accident. To my surprise my t-shirt got really hot where the glue had landed and started to fizzle and smoke quite a lot. Does anyone have an idea of why this happens? 4249 https://www.reddit.com/r/askscience/comments/3t215j/today_i_dripped_some_super_glue_on_the_colored/ 1447701810 3t215j Chemistry 2015-11-16 22:23:30 "What you're describing is likely a Cyanocrylate adhesive. Assumption is your t-shirt is 100% cotton, in which case +https://en.wikipedia.org/wiki/Cyanoacrylate#Reaction_with_cotton + +Basically the cyanocrylate is suspeneded in an acid in the bottle...then coming into contact with air, water or an analog like the hydroxy-rich cellulose (type of sugar) of the cotton fiber. This cause the glue's curing (polymerization) to happen very energetically, and waste heat is the result here. + +If your cotton shirt didn't fully ignite in flame (smoulder only), your super glue's exothermic reaction during curing isn't quite energetic enough. " "Now that you have been answered I will give you a fun experiment. + +In a clean safe area with good ventilation grab some CA (super glue) and some baking soda. Get a scrap piece of cardboard like from a cereal box and a toothpick. This will all need to be discarded when done. + +Pour out a small amount of baking soda and then squeeze out some super glue onto the baking soda, roughly equal amounts, now mix it with a toothpick. + +It will turn into a milky white substance and then in about 15 seconds it will begin to get very hot, smoke a small amount and then you will see it harden and turn an opaque white. + +This happens all within 2 to 3 seconds of it beginning. + +I use this often to create a paste to fill in gaps in small plastic parts and create something from nothing. + +For instance my wifes glasses recently broke and were under such high stress that the place where they broke could not go back together. So I got them as close as I could, glued the lense to the plastic frame and then filled in the spot that was unable to close and then used files to clean it up. + +" +1496 Does a collection of photons in a box (with perfectly reflective walls) have a well defined temperature? 4239 https://www.reddit.com/r/askscience/comments/g0u5tz/does_a_collection_of_photons_in_a_box_with/ 1586820305 g0u5tz Physics 2020-04-14 2:25:05 Yes, under the standard assumptions of thermodynamics, you can consider it a [photon gas](https://en.wikipedia.org/wiki/Photon_gas). "I want to ask a question because I've always wondered and I don't want to make my own post, but this post relates to it I guess and it reminded me of my question. The question is, can light be ""trapped"" in a box of perfect mirrors or something?" +887 If large atoms are formed in stars and then spread out in the universe, why are heavy metals found in high concentrations, rather than distributed evenly, throughout the earth? 4231 https://www.reddit.com/r/askscience/comments/78emcs/if_large_atoms_are_formed_in_stars_and_then/ 1508837293 78emcs Planetary Sci. 2017-10-24 12:28:13 [deleted] "I think you're asking what geologic process acts to concentrate so many elements and minerals in narrow veins, rather than distributed throughout larger geologic structures. + +The simple answer is fractional crystallization. Many of these elements are highly incompatible. This means that rather than forming nice crystals, they stay in the melt phase. As a large amount of melt cools, the concentration of incompatibles in the melt phase increases. At the end of fractional crystallization you get left with a small amount of fluid that is highly concentrated incompatible elements. This fluid then goes on to form veins. " +888 "Is it possible for black holes to lose their ""black hole"" status?" 4231 https://www.reddit.com/r/askscience/comments/6yni2v/is_it_possible_for_black_holes_to_lose_their/ 1504794124 6yni2v Physics 2017-09-07 17:22:04 "Black holes can only have masses much greater than the Planck mass. A black hole evaporates through Hawking radiation until its mass starts to near the Planck mass. Around that, full quantum gravity takes over and you cannot simply speak of a standard black hole anymore. There are a couple things that can happen: + +- the black hole becomes some stable (i.e. not evaporating anymore) object with mass ~ Planck, called a ""remnant"" +- the black hole completely disappear leaving only particles (which have all mass << Planck) + +The second is considered much more likely in general. The details however depend on your preferred theory of quantum gravity." "What happens as black holes evaporate is an unresolved question. + +The best guess today is that black holes will radiate mass away until they get very small and the hawking radiation is really bright, and we don't have any idea about what happens then." +678 Why can't I use lenses to make something hotter than the source itself? 4229 https://www.reddit.com/r/askscience/comments/67fy7m/why_cant_i_use_lenses_to_make_something_hotter/ 1493120022 67fy7m Physics 2017-04-25 14:33:42 "Some users, like u/Jake0024, make the correct argument from thermodynamics that heat travels from hot to cold. What is unsatisfying about this argument is that it goes against our intuition about how lenses work. After all, can't we just focus an image of the moon down to an arbitrarily small size? And the smaller we make it, the more concentrated the light gets and the hotter it can heat something up. + +The problem with this intuitive argument is that the simple lens equation we were taught in high school or college is a lie. Or rather, it is an approximation for small angles. For a lens that takes an object at position o and focuses it to an image at position i, the magnification is supposed to be M=i/o. So just get a shorter focal length and i will get arbitrarily small, right? + +But this approximation for the magnification comes from the conservation of [etendue](https://en.wikipedia.org/wiki/Etendue). Here is a simplified version of how it works: If the lens has a radius r, then we can define an angle theta_o=arcsin(r/o) and an angle theta_i=arcsin(r/i) on each side of the lens. The conservation of etendue tells us the magnification will be: + +M=theta_o/theta_i + +In the small angle approximation arcsin(x)=x, so this reduces to the formula we learned in school. But when you try to really focus the image down to a small spot, you won't be able to use the small angle approximation on the image side - the image sits very close to the lens now. And theta_i can't get any bigger than π/2. So we get: + +M=2\*theta_o/π + +Since the moon is far from the lens, we can justify a small angle approximation there and write: + +M=2\*r/(π\*o) + +So the magnification is actually proportional to the diameter of the lens (2\*r) in this limit of a highly focused beam. Aha, so we can still focus the moon down to an arbitrarily small spot! Unfortunately, the total light collected by the lens is proportional to its diameter squared. So a tightly focused image of the moon has the same intensity per square meter, whether it is created by a giant lens or a tiny one. It turns out this limit is equal to the intensity per square meter at the surface of the moon. Therefore, the moon can't heat things up any hotter than they would get sitting on the surface of the moon. + +**tldr:** If you move past the small angle approximation you learned in school, you find there is a limit to how small you make your image of the moon. This prevents you from using moonlight/sunlight/etc for reaching arbitrarily high temperatures with passive optics. + +**Bonus:** A single mode laser behaves as if the light is coming from a point source, so you can focus laser light down to very small spots and heat things up to arbitrarily high temperatures. This doesn't violate thermodynamics either, because lasers effectively have a [negative temperature](https://en.wikipedia.org/wiki/Negative_temperature) that can transfer heat to any positive temperature system." This thread has a large number of responses simply restating passages from the link in the original post, low-effort assertions of fact, speculating on causes, or giving anecdotes, which have been removed. Please keep top-level comments to detailed, expert explanations of *why* this phenomenon does or does not occur. +420 Are we aware of any linguistic differences between the Korean spoken in North and South Korea that have developed since the end of the Korean War? 4227 https://www.reddit.com/r/askscience/comments/4wqk64/are_we_aware_of_any_linguistic_differences/ 1470668543 4wqk64 Linguistics 2016-08-08 18:02:23 This thread has been locked due to an excessive number of off topic comments. Please remember that in askscience we want sources, not speculation or personal stories. "There are a number of notable differences, [apparently](http://www.degruyter.com/view/j/ijsl.1990.issue-82/ijsl.1990.82.71/ijsl.1990.82.71.xml). While there seem to be very few minor phonetic changes, there are changes in vocabulary, the generation of neologisms, and syntax. + +To quote wholesale from my reference: +> 1. Some differences are noted in the phonetic and phonological fields, and much more serious and wide-spread divergence is found to have occurred in semantic and stylistic areas as well as in the area of vocabulary. It is also noted that Pyongyang speech is intended to sound, and actually does sound, extremely provocative and militant to speakers of Seoul Standard, due, no doubt, to a combined effect of harsh words and expressions coupled with extreme stress and intonation. +> 2. A systematic, all-inclusive, and politically motivated language policy has been conceived and carried out unilaterally in North Korea ranging from the writing system, standard language, and language purification to dictionary compilation and spelling rules. As a result, the Seoul Standard language has hardly changed in many aspects, whereas the North Korean language has departed considerably from the traditional norm, that is, from Seoul Standard, thus speeding up the linguistic divergence between the two Koreas. +3. The underlying factors for the South-North linguistic divergence are found to lie in (i) the geographical as well as sociocultural separation of the two Koreas and (ii) the radical, politically motivated language policy adopted and pursued by the North. In particular, the official introduction of the Pyongyang dialect as the so-called standard 'Cultured Speech', in violation of the traditional Seoul Standard, is very significant in that it has accelerated language divergence by polarizing the standard language in Korea. + +Notes about the source: + +- It is from Seoul University + +- It is from 1990 + +- It was difficult to get to! (Pretty niche journal) + +- Differences in language use between North and South Korea. Hyun-Bok Lee. International Journal of the Sociology of Language. Volume 1990, Issue 82, Pages 71–86, ISSN (Online) 1613-3668, ISSN (Print) 0165-2516, DOI: 10.1515/ijsl.1990.82.71, October 2009" +986 Do animals in the wild get STDs? 4224 https://www.reddit.com/r/askscience/comments/82l8mi/do_animals_in_the_wild_get_stds/ 1520393557 82l8mi Biology 2018-03-07 6:32:37 "Yes, they do get STIs. In fact a lot of koala bears have chlamydia. Primates can get a disease similar to HIV in humans called SIV. It's probable that syphilis came from sheep or cattle. dolphins get genital warts, and rabbits can get syphilis. Dogs and cats both have their own strains of herpes virus. And the Tasmanian Devil has a weird STI that cause a very aggressive and strange form of face cancer, tumor thing. It prevents them from hunting and feeding. + +But wait! There's more! The fun is not just limited to our furred friends! Birds can get chlamydia and also give it to humans and cats through bites and scratches after they are infected. Reptiles also can get STIs like chlamydia and gonorrhea. Also insects have their own weird STIs." "Vet pathologist here. There is a transmissible tumor that dogs get through mating: transmissible venereal tumor (TVT) as it’s called. The tumor may also be transmitted to the nasal cavity from direct contact with affected mucosa. Here’s a link for more info: + +http://www.merckvetmanual.com/reproductive-system/canine-transmissible-venereal-tumor/overview-of-canine-transmissible-venereal-tumor + +" +679 What happens in wet wood that allows you to bend it? 4214 https://www.reddit.com/r/askscience/comments/5yzz5i/what_happens_in_wet_wood_that_allows_you_to_bend/ 1489341971 5yzz5i Engineering 2017-03-12 21:06:11 "The water effectively acts as a [platicizer](https://en.wikipedia.org/wiki/Plasticizer) for wood and materials derived from wood. In other words, it increases the [plasticity](https://en.wikipedia.org/wiki/Plasticity_(physics\)) of the wood, or the property to deform (e.g. bend) in a non-reversible way. The way water does this is that water molecules get in between the strands of cellulose polymer and the lignin matrix making up the wood. Normally these polymers are held together by strong hydrogen bonds so they can't easily slip past each other. However, the water helps to break these bonds, instead creating new ones with itself. As a result, the material becomes much more flexible. On top of that, if you raise the temperature you can increase the flexibility yet further. As an aside, this is exactly the same reason why you add water to clothing when ironing it. It's much easier to reshape the fabric when wet then when it is dry. Once the fabric cools down and dries this new shape is then locked in. + +For more information, [here is an article on the topic.](https://link.springer.com/article/10.1007/s00226-015-0777-x) + +edit: corrected the definition of plasticity" "I wanted to add, you can see this exact same phenomenon with hair. Have you ever gotten out of the shower and laid down on a pillow only to find your hair ""set"" in its position when you got up? The same premise works with a perm, but you are actually effecting permanent bonds instead of these non covalent bonds. Pretty cool stuff!" +987 Why the electron cannot be view as a spinning charged sphere? 4211 https://www.reddit.com/r/askscience/comments/8fz9a0/why_the_electron_cannot_be_view_as_a_spinning/ 1525093182 8fz9a0 2018-04-30 15:59:42 Electrons are pointlike particles in the Standard Model, and a single point can’t “rotate”. If you try to interpret the electron as a classical, rotating spherical charge, you get nonsense conclusions, like that the “surface” of the sphere has to move faster than c. "The angular momentum of a solid sphere is L=Iw, where I is the moment of inertia and w is the angular velocity. For a solid sphere, I = 2/5 mr^2, where m is mass and r is radius. w=v/r, where v is the tangential velocity. This is all covered in classical mechanics. So L = (0.4 m r^2) * (v/r). The tangential velocity is therefore (5L)/(2mr). We know the mass of an electron is roughly 10^(-30) kg and the classical radius of an electron is 10^(-15). So all that we need now is L. + +Now a bit of quantum. The eigenvalues of the spin operator on a state is hbar * sqrt (s (s+1)). hbar is planck's constant over 2*pi, s is the spin of the electron. You can refer to Chapter 4 of Griffiths Quantum Mechanics if you want to learn more, but basically we can consider this quantity to be the angular momentum L from the classical formula L=Iw. so L= sqrt (3)* hbar/2. Plug this into the formula we derived for v classically. + +We therefore find that v is roughly 800 times the speed of light. However, nothing can travel faster than the speed of light. This is a contradiction. Therefore, there is now way that the electron is spinning." +211 NASA plans to hit an asteroid with a probe to try to change its course - can't we distinguish if it will work based on math? 4206 https://www.reddit.com/r/askscience/comments/3ng6qk/nasa_plans_to_hit_an_asteroid_with_a_probe_to_try/ 1443964651 3ng6qk Astronomy 2015-10-04 16:17:31 "The math is pretty easy to work out - you can predict the orbital change based on conservation of momentum, but an important part of science is testing those predictions. The composition of the asteroids is only roughly known and that will determine a lot of the kinematics of the collision and ejecta, which effect the orbit in more ways than just 'billiard ball mechanics' + + +[I found a paper on this particular mission.](https://www-n.oca.eu/michel/AIDA_Papers/Chengetal_EPSC2012.pdf) It looks like the asteroid is actually a binary, and it's an eclipsing *binary*, meaning we see it edge on from earth, which makes it possible to make really accurate measurements of orbits. Fun fact: the name Didymos means *twin!* Furthermore, to quote directly from the paper: + +> By targeting the +smaller, 150 m diameter member of a binary system, +the DART mission produces an orbital deflection +which is larger and easier to measure than would be +the case if DART targeted a typical, single near-Earth +asteroid so as to change its heliocentric orbit. + + +So it sounds like they've found a good candidate system to test their asteroid deflection method. + +One last point is *chaos.* Orbits are highly dependent on initial conditions, and you could do many different simulations of the collision with slightly different initial conditions (which would be based on the range of error on all the measurements of the masses, orbital trajectories, etc), which could yield wildly different final conditions. There's an adage among experimentalists for times like this - why calculate what you can measure?" "It's not science if you never test your theories. And it's bad engineering if you never test your designs. + +In other words, which phrase do you want to hear after they try to save humanity from an apocalyptic asteroid? + +A: ""Everything went as normal."" + +B: ""Wow, that wasn't what the simulations predicted.""" +421 Does the craving of different foods at different times have to do with what nutrients your body is currently in need of (protein vs carbs for example)? 4206 https://www.reddit.com/r/askscience/comments/4u4hhq/does_the_craving_of_different_foods_at_different/ 1469215281 4u4hhq Biology 2016-07-22 22:21:21 "Before you comment, please ask yourself, ""Can I back up what I'm about to type with peer reviewed science?"" + +If the answer is yes, then please do. If not, then you probably have an anecdote or speculation, which will be removed. + + " "In most cases, no. You can read up on a quick summary by Peter Pressman of Cedars Sinai Medical Center and Roger Clemens of the University of Southern California School of Pharmacy [here](http://www.scientificamerican.com/article/are-food-cravings-the-bod/). The gist of it is that cravings are more a factor of sociocultural factors, stressful environments and hormonal fluctuation than nutritional deficiencies. You can read further on the topic [here](http://www.huffingtonpost.com/2012/10/08/food-cravings_n_1940299.html) where Karen Ansel, a registered dietitian, discusses how cravings work, and what areas of the brain are activated. She asserts that most cravings are dictated by social tropes, visual cues, or childhood memories. + +The one caveat to this seems to be pica, where people eat non-food items such as soil, clay, stones, etc. From the little research that has been done on pica, the cause seems to point to a mineral deficiency, most likely iron. " +212 Can dopamine be artificially entered into someones brain to make them feel rewarded for something they dont like? 4202 https://www.reddit.com/r/askscience/comments/3kctki/can_dopamine_be_artificially_entered_into/ 1441862041 3kctki Neuroscience 2015-09-10 8:14:01 "That's actually part of dopamine's role in the brain. Extrinsic motivation, delay gratification, dopamine often spikes if you *anticipate* some action will lead to some sort of reward in the future, so that you kinda ""enjoy"" doing the action and are motivated to do it, even if you don't actually enjoy the action. + +The catch is, you're going to *want* to do the thing (in fact, you're going to have to exert willpower *not* to do it) but you won't necessarily *like* the experience as a whole. There's a few other chemicals besides dopamine that go into actual *satisfaction*. (And you probably want to avoid giving *too much* dopamine, or it'll just result in doped-out euphoric bliss.) + +E.g. browsing reddit. Low dopamine hits for novelty, dopamine hits for getting orange envelopes, you want to browse reddit, but only very rarely is there actual satisfaction. + +You pretty much never go ""oh man, that was such a great reddit session, let's do it again"" after the fact, the way you might for more natural rewards like food, sex, or social activity. You're just sort of inexorably driven to do it again by forces which aren't entirely under conscious control. Whether or not you find it ""rewarding"" really depends on how you define the term. + +With well-timed dopamine spikes, you could probably create this ambiguous relationship with any activity! In fact, even activities you actively hate doing but can't help yourself are partly dopamine driven - the urge to get into angry debates, the desire to have one more word in an argument, to stalk your ex on facebook on more time, to repeatedly obsess about that one cringey awkward thing you did once (although true obsession probably also involves serotonin and a bunch of other stuff)." "I might be dumb, but I feel like the top voted answers aren't really answering OP's question. I feel like OP is asking ""if I artificially applied dopamine to my brain at some point while getting kicked in the balls... am I going to start liking it?"" Most of these answers are basically what dopamine does." +1093 Are we producing more atmosphere than we lose at this point in time? 4200 https://www.reddit.com/r/askscience/comments/8j34vd/are_we_producing_more_atmosphere_than_we_lose_at/ 1526210066 8j34vd 2018-05-13 14:14:26 We are always slowly losing atmosphere. As you mention, we do have solar wind stripping us, but there is also the spontaneous generation of free hydrogen and helium by radioactive processes to consider. These are usually trapped within rock or liquid, but once freed, the atoms experience buoyant force, and barring the occasional spontaneous reactions of hydrogen with oxygen, nitrogen and other molecules to form compounds in our atmosphere, each attains escape velocity and pops off into space. The earth does not produce any more of the elements present in our atmosphere, excluding some rare radioactive decays creating short-lived heavy noble gases (radon), so we are losing mass and atmosphere faster than we produce it. "Earth loses atmosphere at about 6x10^7 kg per year. Volcanoes alone add 2×10^11 kg of CO2 per year. Even if ⅔ of that CO2 mass was from O2, it would still exceed the loses. + +So by this data alone, it's a net increase. But not of the same gases. We mostly lose oxygen and hydrogen. We've lost ⅔ of our hydrogen since the Earth formed. + +* http://www.abc.net.au/science/articles/2009/06/03/2588523.htm +* https://volcanoes.usgs.gov/vhp/gas.html" +1117 Does the ISS need to constantly make micro course corrections to compensate for the crew's activity in cabin to stay in orbit? 4200 https://www.reddit.com/r/askscience/comments/9clntu/does_the_iss_need_to_constantly_make_micro_course/ 1535982986 9clntu 2018-09-03 16:56:26 "1. Nothing they do can affect total torque or momentum of the station. +2. They theoretically could change internal torque distribution (eg. by running in circles) and thus cause the station to start spinning, which could increase drag, and cause some orbital changes. In fact this happens with treadmills there! +3. ISS has CMGs - gyros which can control the torque, so they can counteract spinning and stabilize he station." "I think you already have the answer you need. But for interest's sake, the ISS **does** have to periodically compensate for the drag that the thin atmosphere exerts on it - which is a very real and non-negligible occurrence. + +[Here's a good NASA video explaining and demonstrating a ""reboost"" event.](https://www.youtube.com/watch?v=sI8ldDyr3G0)" +680 Why are solar sails reflective, not black? 4184 https://www.reddit.com/r/askscience/comments/5r2r2b/why_are_solar_sails_reflective_not_black/ 1485802891 5r2r2b Physics 2017-01-30 22:01:31 It's a matter of how much momentum you transfer. For photons with momentum p0, you transfer a unit p0 of momentum to a sail that absorbs that photon. But if you use a reflective sail, the conservation of momentum requires that the sail is is pushed back by 2p0. Since the force the sail gets can be written as F = dp/dt, you get more propulsion when the sail reflects the light rather than absorbing it. "The solar sail is not absorbing the light energy of the photon, but rather the momentum. + +When two objects collide (sail and photon) more energy is transferred if they bounce apart rather than sticking together. You can think of it in two steps: lets say you jump off of a table and then jump. In the first part, you transfer energy into the floor by your impact; and in the second part you transfer more energy into the floor when you push off to jump." +316 I just dropped a can of root beer... does tapping on the lid actually fix the liquid/gas equilibrium? 4183 https://www.reddit.com/r/askscience/comments/42fxkj/i_just_dropped_a_can_of_root_beer_does_tapping_on/ 1453643729 42fxkj Chemistry 2016-01-24 16:55:29 "The short answer is that tapping the top of the can does almost nothing to prevent the liquid from fizzing, this is mostly a myth. The best you can do is simply to wait for the gas in the bubbles to settle back into the liquid. + +If you want to dig deeper, it turns out that not only is the tapping part a myth, but the very premise of this myth (the notion that the liquid/gas equilibrium needs ""fixing"") is itself a myth! This seems to be a very common misconception, but it's simply not true. It turns out that the equilibrium between the partial pressure of the CO2 in the headspace and the gas dissolved in the liquid is re-established pretty quickly (see [this blurb from a science education journal](http://pubs.acs.org/doi/pdf/10.1021/ed065p518) for more details). + +The real explanation for why shaken bottles of carbonated drinks fizz so much has to do with the rate of nucleation, or bubble formation. Initially the CO2 in the liquid is [supersaturated](https://en.wikipedia.org/wiki/Supersaturation), which means that it wants to escape. However, before it can do so it needs to first form bubbles. The first step of bubble formation, the [nucleation](http://en.wikipedia.org/wiki/Nucleation) can be fairly slow because it is an activated process, meaning that it needs to pass over an energy barrier, which we call the activation energy (Ea), [as shown in this diagram](http://www.monzir-pal.net/CHEMB1301/Lectures_1_20/L12_files/image009.gif). When you shake the can you provide enough energy to overcome this barrier, creating many, many bubbles in the process. Now here's the interesting thing, once you produce some bubbles, these bubbles will actually make it more likely for more bubbles to form (if you want to get technical, this is a process we call [heterogeneous nucleation](https://en.wikipedia.org/wiki/Nucleation#Heterogeneous_nucleation)). This is why all hell breaks loose when you open a bottle after shaking it, the millions of tiny bubbles rapidly produce more bubbles and much of the CO2 trapped in the liquid rushes out, taking the liquid with it. + +The trick is to be patient and to simply wait for the gas in the bubbles you form when disturbing the can to settle back into solution. At that point it will be as though you had never disturbed the can in the first place (i.e. the process is fully reversible). + +----- + +**Edit:** The key myth I wanted to debunk was the notion that tapping can change the equilibrium of the gas dissolved in the liquid and in the head-space. As for the idea that tapping the sides can dislodge part of the trapped bubbles and reduce the fizzing, I admit that this is more plausible. However, the evidence I've seen one way or another is all over the place, always anecdotal, and largely inconclusive, [like this article](http://www.snopes.com/science/sodacan.asp). + +**Edit2:** In support of the tapping on the side idea, [this video](https://www.youtube.com/watch?v=l5xbgNTxApo) posted by /u/Glaselar [below](https://www.reddit.com/r/askscience/comments/42fxkj/i_just_dropped_a_can_of_root_beer_does_tapping_on/cza3t43) is the most conclusive proof I've seen yet. At least under certain circumstances, it really does seem that tapping on the side can make a difference!" [deleted] +213 Why is it that, if you add any sequence of numbers like this (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1), the sum is always the square of the largest number? 4181 https://www.reddit.com/r/askscience/comments/3v10w9/why_is_it_that_if_you_add_any_sequence_of_numbers/ 1448994034 3v10w9 Mathematics 2015-12-01 21:20:34 "A single line break will make it obvious that it's N times N: + + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + + 7 + 6 + 5 + 4 + 3 + 2 + 1 + + 1 2 3 4 5 6 7 + + + + + + + + 8 + 7 6 5 4 3 2 1" " x|x x x x x x x -> 1 + 7 + x x|x x x x x x -> 2 + 6 + x x x|x x x x x -> 3 + 5 + x x x x|x x x x -> 4 + 4 + x x x x x|x x x -> 5 + 3 + x x x x x x|x x -> 6 + 2 + x x x x x x x|x -> 7 + 1 + x x x x x x x x -> 8 + +This is an 8x8 square of x's. " +422 If the Solar system revolves around the galaxy, does it mean that future human beings are going to observe other nebulas in different zones of the sky? 4180 https://www.reddit.com/r/askscience/comments/4z5y1n/if_the_solar_system_revolves_around_the_galaxy/ 1471950893 4z5y1n Astronomy 2016-08-23 14:14:53 "**Short answer:** Yeah! + +**Long answer:** ... except the galactic orbit takes about 250 million years, so the last time the earth was on the other side of the galaxy was when the dinosaurs were doing whatever it is they do. I wouldn't count on humans surviving that long. + +But if you want a different sky, you don't have to wait that long! There are different nebulae and stuff popping up all the time - supernova are bright and leave remnants in the sky that have been observed and recorded for centuries by [Chinese astronomers](https://en.wikipedia.org/wiki/SN_1054#Historical_records), [Europeans](https://en.wikipedia.org/wiki/Kepler%27s_Supernova), and possibly even [Native Americans!](http://www.astronomy.pomona.edu/archeo/outside/chaco/nebula.html) + +On timescales a little bit longer than human lifetimes, the constellations shift! The stars in the visible constellations are all at different distances, have different brightnesses, [and are moving relative to the earth and each other,](http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit1/Images/uma_50K.gif) changing constellations over thousands of years! For example: + +* [Ursa major, the big dipper, might someday be renamed Ursa saber, the big ass knife!](https://www.youtube.com/watch?v=txJH8RlIoXQ) + +* [Leo, the lion, used to look like Leo, the sorta fucked up lion!](https://www.wired.com/wp-content/uploads/2015/03/Leo_2.gif) + +* [Orion, the hunter, when viewed over thousands of years, becomes Orion, the disco dancer!](https://www.wired.com/wp-content/uploads/2015/03/Orion_2.gif) + +My favorite fact though, is that Polaris wasn't always the north star! Due to the motion of stars and the precession of earth's axis, the star Thuban (alpha Draconis in the constellation Draco) was the closest to the pole around the time the pyramids were built. [The northern shaft in the Great Pyramid may therefore point toward Thuban's position in the sky at the time the pyramid was built,](http://www.soulsofdistortion.nl/images/Star%20alignment%20Great%20Pyramid.gif) allowing astronomers to calculate the age of the pyramids with [significant precision!](http://jha.sagepub.com/content/32/26/S1.extract) If confirmed, this bit of astronomy can inform modern archaeology and Egyptology! Of course, there's an obvious way to challenge this interpretation - over thousands of years, pretty much any line of site will have a star on it. Maybe Thuban is a coincidence? + +Space!" "I have some questions on this. + +If the whole galaxy rotated at the same speed, we wouldn't see any difference, so the stars have to be going at different speeds (im aware this difference is not as significant a you would expect because of dark matter)... correct? + +As I understand it, the actual orbit around the galaxy is one thing, but the arms spin faster? I guess they are traveling density waves... is this correct? + +If so, how does the density wave work?" +1094 What types of signals do bees release under distress or after death? 4177 https://www.reddit.com/r/askscience/comments/8s67v0/what_types_of_signals_do_bees_release_under/ 1529384465 8s67v0 2018-06-19 8:01:05 "Bees release a pheromone called alarm pheromone when they sting. Other bees will orient to the scent and become aggressive. The evolutionary purpose is to coordinate the defense of the hive against predators or hostile bees. + +After a bee stings, its stinger rips out, and the bee soon dies. (I read that the stinger is actually barbed to better injure insects with an exoskeleton, and getting pulled out by a mammal's elastic skin is just a side effect, but I'm not sure about this.) The stinger, lodged in the victims body, continues to pump venom and release alarm pheromone. + +Africanized bees produce more pheromone and respond to it more dramatically. Thus, more bees will attack you once one has stung or prepared to sting. + +http://labs.biology.ucsd.edu/nieh/TeachingBee/honeybee_aggession.htm" Beekeeper here. When bees sting they release isoamyl acetate, which smells like bananas. [Boch, Shearer and Stone 1962](https://www.nature.com/articles/1951018b0). When my bees get mad (one aggressive feral hive in particular), the banana smell is overwhelming. +214 We know we'll see a supernova in 2016 because we've already seen it happen due to gravitational lensing. How is this possible? 4176 https://www.reddit.com/r/askscience/comments/3u38f9/we_know_well_see_a_supernova_in_2016_because_weve/ 1448380221 3u38f9 Physics 2015-11-24 18:50:21 "Basically, there's a massive galaxy exactly between us and the distant supernova. The gravity of the cluster attracts the light from the supernova, and bends the path of the light towards the earth. [Since light can be redirected by gravity, light from the supernova can end up taking multiple paths to get to us.](http://i1.wp.com/astrobob.areavoices.com/files/2015/03/Hubble-lensed-SN-graphic.jpg) There's a slight delay because the paths through the cluster have slightly different lengths. That difference in length is only a few light years, so we end up seeing the supernova multiple times over the span of a few years. + +[For reference, this is the original paper.](http://www.sciencemag.org/content/347/6226/1123?intcmp=collection-generalrelativity) If I can offer some personal commentary - this is an incredible discovery, and due to the potential for using it to measure the cosmic expansion rate it's definitely worth following up to observe those future supernova. " "/u/VeryLittle's explanation is great, but I'd like to explicitly call out what I think is a key point in answering your question: + +The supernova already happened, and one of the images we are able to record came to us sooner than the other because it took a shorter path. It's like seeing someone walk by, then seeing their reflection walking by in the mirror, and the person and mirror are so far away that the time difference is years instead of infintisimally small." +559 Why do we keep trying to find new heavy elements if they only snap into existence for milliseconds? 4176 https://www.reddit.com/r/askscience/comments/54wbui/why_do_we_keep_trying_to_find_new_heavy_elements/ 1475069496 54wbui Physics 2016-09-28 16:31:36 "Science isn't always about finding applications. There have been many discoveries throughout history that didn't have practical applications for decades or centuries. + +These super-heavy elements won't have applications because they're too short-lived. But they're useful for testing our current theories on nuclear physics. " "In addition to what others have said, its also predicted that there could be a so-called island of stability somewhere between element numbers 125-135. + +Instead of a half life of milliseconds, these could persist for minutes to hours, though some models predict they could last as long as a few days." +114 Is Pluto small enough that we, as a species, could destroy it? 4167 http://www.reddit.com/r/askscience/comments/3dqef4/is_pluto_small_enough_that_we_as_a_species_could/ 1437224603 3dqef4 Planetary Sci. 2015-07-18 16:03:23 [deleted] "Gravitational binding energy is given by U=3GM^2 /5r. Pluto has a mass of 1.309E22 kilograms, and a radius of 1185000 meters. This gives a gravitational binding energy of 8.130691E39 joules. This is a ludicrous amount of energy. It would take over 3.5E22 Tsar Bombas to provide that much energy. I did this on a napkin and my phone, so if I'm off by an order of magnitude, my apologies. It's still more energy than we could harness. + +Edit: formatting. + +Edit2: I'm off by a lot of orders of magnitude because I used the wrong value for radius. It's still more energy than we can conceivably harness at 5.8E27 Joules. Sorry about that error. " +560 What happens to gravity when mass is converted into energy? 4159 https://www.reddit.com/r/askscience/comments/5bw8t3/what_happens_to_gravity_when_mass_is_converted/ 1478642129 5bw8t3 Physics 2016-11-09 0:55:29 "Lets say you have some object with mass. It's mass causes gravitational attraction. + +If you could instantly turn all of the mass to energy, and somehow keep it all together in the same space the object occupied, this energy would have the same gravitational attraction as the object it came from. + +Both mass and energy contribute to the gravitational attraction of an object. + +Realistically, the gravity field of your object would disperse in a roughly spherical pattern as all of that energy expanding at high velocity. You would still have the same total gravitational attraction, it would just be broken into millions or billions of smaller fields. " "tl;dr In cases we have directly observed where mass-energy conversion in a gravitational system is significant, gravity itself will be transporting energy away from the system via gravitational waves. + +To fully understand this, you have to use Einstein's General Relativity instead of Newtonian dynamics. + +In General Relativity, spactime curvature (i.e. gravity) is generated by the [stress-energy tensor](https://en.wikipedia.org/wiki/Stress–energy_tensor). In the limit of weak gravity, the T00 term (labeled ""energy density"") dominates, and we recover Newtonian gravity. + +If we have strong gravity, the other terms in the stress-energy tensor matter as well. The ""momentum density"" terms are what give rise to [frame dragging](https://en.wikipedia.org/wiki/Frame-dragging) and [gravetomagnetism](https://en.wikipedia.org/wiki/Gravitoelectromagnetism). With strong gravity, the equations describing spacetime curvature become nonlinear because the potential energy of the gravitational field itself adds to the gravitational field. + +So, to completely answer your question, it depends on the system you are studying. For a star, a negligible amount of mass is converted into energy (compared to the star's mass), and any gravitational effects of the outgoing radiation will be very small. + +However, if you instead consider a [binary black hole merger](http://physicsworld.com/cws/article/news/2016/jun/15/ligo-detects-second-black-hole-merger), then a significant amount of mass-energy is [radiated away by gravitational waves](https://en.wikipedia.org/wiki/Gravitational_wave). In the link about the black hole merger, almost an entire solar mass's worth of energy is lost to gravitational radiation! " +1095 When undersea mammals are born, is it a rave for them to surface to breathe? 4152 https://www.reddit.com/r/askscience/comments/8phsts/when_undersea_mammals_are_born_is_it_a_rave_for/ 1528440722 8phsts 2018-06-08 9:52:02 "Pretty much, yes. + +Like other live-birth animals, they are provided oxygenated blood while in the womb, but after birth, they need to start breathing, and baby whales (for example) cannot easily float or swim. The mother will lift the baby out of the water to take its first breath. If the baby is born too deep, or in rough waters, or if another whale is unable or unwilling to lift it, then they can/will drown before they get to the surface. + +Sort of a source: http://www.dailymail.co.uk/news/article-1201860/First-breaths-newborn-whale-calf-captured-camera-Australian-coast.html" "I read that whales are mostly born tail first to reduce chances of them drowning during the birth process + + +http://www.whalefacts.org/baby-whales/ + + + +According to this daily mail article, other whales (midwives) help out by lifting the newborn to the surface for their first breath + + +http://www.dailymail.co.uk/news/article-2860586/Baby-s-breath-incredible-moment-sperm-whale-gives-birth-midwives-escort-newborn-surface-air.html + +Edit: a word" +215 Why is glass so loud? 4151 https://www.reddit.com/r/askscience/comments/3xvd0b/why_is_glass_so_loud/ 1450813069 3xvd0b Physics 2015-12-22 22:37:49 "Copied for visibility, the answer is from my comment [here](https://www.reddit.com/r/askscience/comments/3xvd0b/why_is_glass_so_loud/cy86hud). + +Essentially, what causes the noise is that glass is a very stiff material, and resonates for a long time when struck. You can hear this whenever two glasses clink together. When glass is broken each piece is able to 'ring' independently. The frequencies they produce will depend on their size and shape, and the combined effect can be extremely loud. This is especially true if it was formerly a large piece of glass, such as a doorway, because it will produce many pieces. + +^EDIT: ^Grammar + +EDIT2: To answer a common question, constructive interferance will have little to do with the noise. Rather, the sounds have a range of frequencies, all of which will 'pile up' on each other constructively and destructively. The overall effect is an increase in noise power, however, and so the loudness increases. For a good overview, see [Power Spectral Density](https://en.wikipedia.org/wiki/Spectral_density#Power_spectral_density). + +EDIT3: Edited for clarity and added more information." "Glass is incredibly brittle/hard, as well as dense, and thus doesn't lose a whole lot of energy when it vibrates (imagine the reverse of this as a pillow). When class vibrates, most of the energy is going into sound/heat. Compare this to squishier objects, where more energy is going into just moving around the particles on the inside of the object. + +Also, your girlfriend fell through a glass door? Is she okay?" +561 Does a vibrating blade Really cut better? 4150 https://www.reddit.com/r/askscience/comments/53c9t1/does_a_vibrating_blade_really_cut_better/ 1474207628 53c9t1 Physics 2016-09-18 17:07:08 "Yes. [Ultrasonic knives](https://www.youtube.com/watch?v=uK4hvcUxNFw) are an excellent example of this. By vibrating, they put a very small amount of force into the blade but multiplied by many, many times per second. It's exactly what you do when you use a sawing motion with a knife, except in that case you're trying to put a lot of force into the cutting edge of the blade over much fewer reciprocations. + +Edit: My highest-rated comment of all time. Thanks, guys!" "We use ultrasonic blades at work made by Branston to cut rubber. Our blades are made of titanium and operate at a frequency of 40khz. The units are comprised of an amplifier, booster and blade. + +A special Mylar washer clamps between the booster and blade to ensure the frequency is transmitted correctly to the blade. + +If you tap one of these knives when disconnected from its booster with a metallic object it sounds similar to a tuning fork. + + The squeal the blades make when they start cutting is ear piecing but not everyone is able to hear that specific frequency. + +Because the blade movement is so small very little ""crumb"" is generated unlike a conventional cold-cutting blade so for rubber, ultrasonics cut better however there is a downside to ultrasonics which is heat. If the blade travel is slow a significant amount of localised heat can be generated depending upon the density of the material your are cutting vs the amplification level the cutter is running at." +317 How would a bee (or any flying insect) behave in the microgravity of the ISS? 4149 https://www.reddit.com/r/askscience/comments/41iwcr/how_would_a_bee_or_any_flying_insect_behave_in/ 1453123057 41iwcr Biology 2016-01-18 16:17:37 "[This was asked previously.](https://www.reddit.com/r/askscience/comments/1mk7wt/have_we_taken_flying_insects_into_space_do_they/?ref=share&ref_source=link) Top comment linked [this article](http://www.bio.net/bionet/mm/bionews/1995-July/002285.html) which states that: +>Honey bees +(Apis mellifica) were unable to fly normally and tumbled in weightlessness. +" "From NASA themselves [PDF Warning]: + +>[The 14 bees aboard STS-3 were observed to walk only on the +screen surfaces inside the flight box. They appeared to be +unable to cling to the smooth plastic surfaces. **Brief attempts +at flight resulted in unstable paths, tumbling about their body +axes, and floating with little or no wingbeat. Floating was +observed for long durations and appeared to be a result of +inability to cling to a smooth surface when they came into +contact with it \(with wingbeat ceasing at contact\).** The lack of +relative-motion visual stimuli necessary to maintain flight may +also have been responsible for the floating responses of the +bees. In addition, it may have been that the food supply +provided was inadequate for the bees and this may have led to +fatigue with resulting poor flight control responses and +floating.](http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19830025642.pdf) " +115 Kepler 452b: Earth's Bigger, Older Cousin Megathread—Ask your questions here! 4148 http://www.reddit.com/r/askscience/comments/3ef7ed/kepler_452b_earths_bigger_older_cousin/ 1437723905 3ef7ed Planetary Sci. 2015-07-24 10:45:05 "Is there a ""next step"" for this particular discovery, something that scientists want to learn about Kepler 452b specifically? + +And followup: what are the odds at this point of making a similar discovery within, say, 100 light years? Or, put another way, it's my understanding that there are around 500-odd type G stars within 100 light years of Earth, have those all been examined already, or what method is being used to pick candidate systems like Kepler to examine?" Using currently available technologies how long would it take for a human to arrive at Kepler 452b? +216 Before the media blows up reporting on how we've found a Dyson Sphere what does the paper for KIC 8462852 actually say? 4148 https://www.reddit.com/r/askscience/comments/3ou35w/before_the_media_blows_up_reporting_on_how_weve/ 1444899442 3ou35w Astronomy 2015-10-15 11:57:22 "Short version: this paper is saying ""there are a bunch of theories, all of them fail one metric or another except this one low probability theory"" (Edit: that theory is not aliens either; still natural). + +That's all the paper says. Solutions to that paper would be: a) the low probability thing happens occasionally or b) some other idea that wasn't theorized yet. + +So, the SETI guy (Jason Wright) is putting up an alternative theory (which he is working on writing a paper for): that it's an alien megastructure. Alien megastructure, IMO, is going to be a hard theory to disprove because there's always room for ""we haven't imagined the right type of megastructure to produce this result, because we're not as advanced as they are"". Now, we could theorize on a couple specific megastructures (like Dyson Sphere) and make predictions of those and either confirm or rule them out. As another comment points out, Dyson Sphere probably doesn't match the data (should emit low energy radiation and shouldn't have any variation in the output). Of course, if we continue to rule out specific megastructures, we should continue to keep aliens far down on the list of possible ideas, and try to come up with new physics that can possibly explain the data and test those theories. + +Edit: [Jason Wright just published this to his blog](http://sites.psu.edu/astrowright/). It's a good read. tl;dr - ""Tabby’s team tentatively settles on a plausible but contrived natural explanation for it: a swarm of comets recently perturbed by the passage of a nearby star. I would put low odds on that being the right answer, but it’s the best one I’ve seen so far (and much more likely than aliens, I’d say). If I had to guess I’d say the star is young, despite all appearances. I can’t back that up."" Also, the British Tabloids are dumb." "Straight from the abstract: + +>By considering the observational constraints on dust clumps orbiting a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet fragments, all of which are associated with a single previous breakup event. We discuss the necessity of future observations to help interpret the system. + +There's two big challenges to the analysis, first, the lack of excess infrared signal puts some severe limitations on what could be causing the dips, for instance an oddly shaped protoplanetary disk is disfavored. The second is that a predicted dip (from debris of a possible planetary collision) might or might not have occurred in April of 2015, but the system was unobserved—so there's a lack of data going on here too. They recommend further observation. + +>Observations of KIC 8462852 should continue to aid in unraveling +its mysteries. First and foremost, long-term photometric +monitoring is imperative in order to catch future dipping events. It +would be helpful to know whether observations reveal no further +dips, or continued dips. If the dips continue, are they periodic? Do +they change in size or shape? On one hand, the more dips the more +problematic from the lack of IR emission perspective. Likewise, in +the comet scenario there could be no further dips; the longer the +dips persist in the light curve, the further around the orbit the fragments +would have to have spread. + +* http://arxiv.org/abs/1509.03622v1 + +All of this is more reasonable than aliens. This isn't my field, but I will say the drop in flux is kinda nuts, I was under the impression ""common"" exoplanet transits produced drops of only on the order of a ~~few~~ percent and not the massive drops of 15 and 22% observed here. Any exoplanet people willing to chime in on that? + +I'm not an expert in what a Dyson sphere or alien megastructure would look like spectroscopically, but I'm pretty sure the lack in IR would also be a huge problem for that idea too. The star's energy has to go somewhere and unless the aliens figured out how to hijinks thermodynamics, a megastructure should glow in IR." +1427 If Ice Age floods did all this geologic carving of the American West, why didn't the same thing happen on the East coast if the ice sheets covered the entire continent? 4148 https://www.reddit.com/r/askscience/comments/d93yfp/if_ice_age_floods_did_all_this_geologic_carving/ 1569421259 d93yfp Earth Sciences 2019-09-25 17:20:59 "They did, look at the [Finger Lakes](https://en.wikipedia.org/wiki/Finger_Lakes) in northern New York state. There's also [Long Island](https://en.wikipedia.org/wiki/Long_Island) and the [Long Island Sound](https://en.wikipedia.org/wiki/Long_Island_Sound) which were created as a result of glaciation. + +These are just a few examples of how glaciers shaped the northeastern USA. I'm sure there are many more." "Where did you get the idea that the ice sheets covered the entire continent? They barely covered 1/3 of it. In the east, the melt from the glaciers found an easy way down to the sea. In the west, the mountains blocked a lot of the flow, so large deep lakes were formed. But when they overflowed, or when the ice blocking the exit melted, the exit was quickly (hours to days) eroded down so that the lake emptied in a flood. + +[https://iafi.org/about-the-ice-age-floods/introduction/](https://iafi.org/about-the-ice-age-floods/introduction/)" +988 Do any planets in the solar system, create tidal effects on the sun, similarly to the moon's effect of earth? 4147 https://www.reddit.com/r/askscience/comments/7t466h/do_any_planets_in_the_solar_system_create_tidal/ 1516969443 7t466h Astronomy 2018-01-26 15:24:03 "Yes, but it's very, *very* small. + +The reason is that while the tidal force scales linearly with the forcing body's mass, it also scales inversely as the distance *cubed*. + +Let's scale our units so that the **Tidal Force of the Moon on the Earth = 1**. In those relative units, the rest of the planets' tidal forces on the Sun shake out as... + +Planet | Planet/Moon mass ratio | Distance-to-Sun / Earth-Moon ratio| Relative Tidal Force +:--|:-:|:-:|:-: +Mercury|4.47|151|1.30 x 10^-6 +Venus|66.3|282|2.96 x 10^-6 +Earth|81.2|390|1.37 x 10^-6 +Mars|8.74|593|4.19 x 10^-8 +Jupiter|25800|2030|3.08 x 10^-6 +Saturn|7730|3730|1.49 x 10^-7 +Uranus|1180|7480|2.82 x 10^-9 +Neptune|1390|11700|8.68 x 10^-10 + +In other words, **the largest tidal force on the Sun comes from Jupiter** (with Venus a close runner-up), and **it's 325,000x weaker than the tidal force exerted on the Earth by the Moon.**" "All of them do. Rather than the sun and only the sun, physics actually shows that any two massive bodies orbit around their center of mass, called the barycenter. Also, especially massive objects like Jupiter sized planets and planets larger than Jupiter (dubbed ""Super-Jupiters"") cause a bulge around their parent stars that in some cases can be used to indirectly observe new planets. + +Taking Jupiter for example, it and the sun orbit an axis that actually lies **just outside** the sun's atmosphere. So yes, any object that exerts a gravitational force (that is, any object with mass) can cause ""tidal forces"" of sorts that may simply be immeasurably small and therefore negligible." +989 How did They make the predator's invisibility cloak in 1987 without the use of fancy computer CGI? 4147 https://www.reddit.com/r/askscience/comments/7x6tn9/how_did_they_make_the_predators_invisibility/ 1518495277 7x6tn9 Engineering 2018-02-13 7:14:37 "The entire process is described in ""Visible Invisibility for Predator"", _American Cinematographer_, Vol. 68, No. 12, by Les Robley. The article can be found in part [here](https://www.questia.com/magazine/1P3-1294060491/visible-invisibility-for-predator)." I know others have answered your question on this specific topic, but I thought I would give a link to Captain disillusions YouTube videos on the [Back to the Future VFX](https://youtube.com/watch?v=AtPA6nIBs5g). He does a great semi quick breakdown of some of the filming Techniques +318 Why can the Golden Ratio be found all over nature? 4144 https://www.reddit.com/r/askscience/comments/4c1c23/why_can_the_golden_ratio_be_found_all_over_nature/ 1459002398 4c1c23 Biology 2016-03-26 17:26:38 "As other commenters have mentioned, the exact golden ratio might not be as common but the pattern of something growing in a fractal (or more simplistically self-repeating/self-affine) pattern is very common in biology since it's the simplest way to encode a full structure using the lowest amount of information (see [L-System](https://en.wikipedia.org/wiki/L-system), [fractals in biology](http://www.medicographia.com/2013/01/fractals-and-their-contribution-to-biology-and-medicine/), and [this fractal-shaped broccoli](https://en.wikipedia.org/wiki/Romanesco_broccoli)). + +In essence to encode the golden spiral is extremely efficient and nature has a tendency to simplify things. The whole ""instruction"" to generate the spiral shape boils down to: + +- go/grow forward +- turn to a side with constantly increasing/decreasing angle + +The increase/decrease is often guided by linear growth of those older parts of the organism so that piece won't need encoding at all and the ""turn angle change"" is not exact since it's based on the organism's evolutionary reason for that turn like: maximizing sun coverage for some plants, appropriate volume increase of the shell for a growth of a snail over age, etc. + +This fractal pattern of growth is present in many things you see as long as you can recognize that they're all part of a simple and elegant self-repeating pattern (i.e. [see here for more fractals](http://polymer.bu.edu/ogaf/image/biofractals.jpg)) but the actual exact Golden Ratio is not found in nature as frequently as most people assume." "It cannot, most of the supposed appearances in natural phenomena are fabrications. + +https://www.lhup.edu/~dsimanek/pseudo/fibonacc.htm" +319 If I went back to the Cretacious era to go fishing, what would I catch? How big would they be? What eon would be most interesting to fish in? 4141 https://www.reddit.com/r/askscience/comments/46z2h1/if_i_went_back_to_the_cretacious_era_to_go/ 1456113649 46z2h1 Paleontology 2016-02-22 7:00:49 [deleted] "Just like right now there were some monstrously large things in the Cretacious era oceans. However I would like to remind you that the Blue Whale that currently swimming happily in current times is thought to be the largest animal ever to live. So just because there were some large fish does not mean you would catch them. + +The quite boring answer is you would probably just catch some slightly odd looking fish." +1259 How are underwater tunnels built? (Such as the one from Copenhagen to Malmö) Additionally, what steps and precautions are taken to ensure it will not flood both during and after construction? 4139 https://www.reddit.com/r/askscience/comments/ash2kw/how_are_underwater_tunnels_built_such_as_the_one/ 1550619617 ash2kw Engineering 2019-02-20 2:40:17 "This is called an *immersed tube tunnel*. The first thing to do is to cut a trench in the seafloor along the route of the tunnel. Meanwhile, prefabricated sections of the tube are built in dry docks from steel or reinforced concrete. These are then sealed at each end with temporary bulkheads and floated to the construction site. When it is in the correct location, the tube is ballasted and sunk to the seabed alongside the previous section of tube. + +The two sections are linked using rubber seals and the bulkheads removed. Then the tube is covered with gravel which weighs it down on the seafloor and prevents it being damaged by ships. The next section can then be moved into position. This site has some nice graphics about how it has been done including in Scandinavia. + +[http://www.railsystem.net/immersed-tube-tunnel/](http://www.railsystem.net/immersed-tube-tunnel/) + +Immersed tubes only really work in shallow waters. For deeper channels the tunnel - until now - has been cut into the bedrock below the seafloor using a tunnel boring machine. However, the Norwegians are looking at a *submerged floating tunnel* to cross the Sognefjord. Here, the tunnel actually hangs in the water from giant floats - the idea has been around for a long time, but no one (and I really can't think why anyone would have a problem of being in a tunnel hanging in the middle of the ocean) has yet built one. There's a list of proposed projects here: + +[https://en.wikipedia.org/wiki/Submerged\_floating\_tunnel](https://en.wikipedia.org/wiki/Submerged_floating_tunnel)" "/u/iCowboy's answer is rather good. Since you specifically mentioned the [Øresund bridge](https://en.wikipedia.org/wiki/%C3%98resund_Bridge) and tunnel, I'm just adding this answer to link you to [a Megastructures episode](https://www.youtube.com/watch?v=sufr9mMxPW8) specifically about that structure. + +It's also worth noting that this is not the only way to construct underwater tunnels; the [Channel Tunnel](https://en.wikipedia.org/wiki/Channel_Tunnel) between Britain and France [was built](https://www.youtube.com/watch?v=cVJ45QxESYs) using [tunnel boring machines](https://en.wikipedia.org/wiki/Tunnel_boring_machine). + +And finally, just for fun, [here](https://www.youtube.com/watch?v=Xr2HAJXPP2A)'s another video about [an undersea tunnel in Korea](https://en.wikipedia.org/wiki/Busan%E2%80%93Geoje_Fixed_Link) built using the immersion method." +2 How can I explain to my boss that we did in fact have sufficient computing power in 1969 to perform the complicated maneuvers required to land on the moon? 4136 http://www.reddit.com/r/askscience/comments/2vc54u/how_can_i_explain_to_my_boss_that_we_did_in_fact/ 1423513776 2vc54u Engineering 2015-02-09 23:29:36 "I'm surprised that no one has posted about this already, but aside from detailed hardware information available (http://en.wikipedia.org/wiki/Apollo_Guidance_Computer), NASA has gone as far as releasing the actual source code used on the Apollo 11 mission (http://googlecode.blogspot.com/2009/07/apollo-11-missions-40th-anniversary-one.html). + +Sadly though, for any conspiracy minded person who denies the reality of the moon landings, no amount of information will convince them to give up their deeply held beliefs. So you can pass this information along, but it will most likely be denied as fake. " ">Problem is, I can't find a lot of specific de-bunking arguments discussing the computational power of the machines involved. + +I think you're both misunderstanding what computers are actually used for. Computers aren't magical devices that just make things like landing on the moon easy. Space travel isn't a matter of ordering a computer ""take me to the moon."" The calculations required to compute a trajectory are really computationally very simple, and it's always been (and always will be) a matter of having intelligent humans know when and why to apply something. + +[This image of NASA engineers popped up recently.](http://i.imgur.com/B3X48s9.jpg) The equations behind them are all from orbital mechanics, the basics of which were well understood for a long time. And relevant to your question, they are all trivial to calculate even with the computational power available in 1969 - you really don't need much more than a pocket calculator. + +>Have you been to Florida to see those pieces of junk? + +I have, and they are goddam beautiful pieces of art. The fabrication of the rocket engines is simply astonishing. + + +Computers haven't exactly been the game-changing technology in large scale engineering projects that the unfamiliar might think they are. Large projects (like say the JSF) are more expensive than they ever were in the past, despite all of our computational resources. Look at other engineering tech of the era - the SR71 was designed in the early 60s using cigarettes and slide rules and is still the fastest air-breathing manned craft ever made. + +edit: good lord people, 2 golds? I feel like I didn't even really answer the question! + +Edit 2: [a good read on actual details of how the trajectories were calculated, for those with a little background in orbital mechanics.](http://www.embedded.com/electronics-blogs/programmer-s-toolbox/4008319/2/Calculating-trajectories-for-Apollo-program) choice quote: + +> Despite their low performance, on paper, we got a lot of work out of those old machines. For those used to waiting 15 seconds for a Windows spreadsheet to even load, it's difficult to imagine how much work a 1-MHz computer can do when it's running full tilt in machine language, not encumbered by bloated software, interpreted languages, and a GUI interface. I'm old enough to remember, and look back on those days wistfully. + + +And you kerbal fanatics need to realize it's not as realistic as you think ;)" +1428 Do cellulose based plastics pose any of the same hazards as petroleum based plastics? 4133 https://www.reddit.com/r/askscience/comments/dhamem/do_cellulose_based_plastics_pose_any_of_the_same/ 1570973509 dhamem 2019-10-13 16:31:49 "Cellulose-based plastics were some of the first ""plastics"" discovered. Although there are constant innovations, the cellulose backbone just doesn't work in all the situations we need it to. That's why we made others. Further, many of them are not biodegradable and most require petrochemicals to make anyway." [deleted] +1429 Why does Sagittarius A* have the * in it's title? 4131 https://www.reddit.com/r/askscience/comments/d9hnvy/why_does_sagittarius_a_have_the_in_its_title/ 1569493136 d9hnvy Astronomy 2019-09-26 13:18:56 Sagittarius A was discovered as a radio source in 1931. It was later discovered that Sgr A is itself comprised of multiple components. The bright and compact central component was named Sagittarius A*, there's also Sgr A East which appears to be an unusually large supernova remnant and Sgr A West which may be associated with material moving towards the black hole. """ They dubbed it **Sagittarius** A\*, or **Sgr** A\* for short, because it is located in the direction of the constellation of **Sagittarius**. The **asterisks** arose because in atomic physics, excited states of atoms are denoted by **asterisks** — and **Sgr** A\* is an incredibly exciting discovery. "" + +[https://en.wikipedia.org/wiki/Sagittarius\_A\*#History](https://en.wikipedia.org/wiki/Sagittarius_A*#History) Look at the end of the first paragraph in history section." +1497 How do chemists produce a weakened state of a disease to create vaccines? How can they confidently determine the disease is ready to be used as a vaccination? 4129 https://www.reddit.com/r/askscience/comments/ejbtpr/how_do_chemists_produce_a_weakened_state_of_a/ 1578034664 ejbtpr Medicine 2020-01-03 9:57:44 "It depends on the vaccine. + +The simplest to imagine are whole-cell vaccines against bacterial diseases: simply kill off the bacteria. Since they are dead they can no longer infect anyone - but they will still contain all the antigens (structures that antibodies can bind to) that will make the immune system recognize them, which will teach the body to fight them. + +Other ones are more interesting. For example, the tetanus vaccine is an inactivated form of the toxin (tetanospasmin) produced by the bacteria that cause tetanus (*Clostridium tetani*) instead of the bacteria themselves. The toxin is a protein that can be inactivated by e.g. formaldehyde: this denatures the protein (imagine cooking an egg - heat denatures the egg white and turns it solid) enough to make it essentially harmless while still being recognizable by the immune system. + +Many vaccines against viruses use another process, by first growing the viruses in the human cells that are their original hosts and then [passing them through cell cultures that they are not adapted to, like e.g. chicken cells](http://www.publichealthunited.org/vaccine-concerns-ingredients-part-2b-by-nina-martin-2/). Viruses are finely tuned, so as they adapt to those other cells, they start to lose the capacity to effectively infect the original human cells - but again, they will still contain all the bits that will make the body recognize them. + +Then there are modern methods like recombinant vaccines, where you use modern gene editing techniques to create the specific antigens you are after. + +As for how they can ""confidently determine the disease is ready to be used as a vaccination"": testing, testing, testing and more testing. Testing in cell cultures. Testing in animals. Testing in people: clinical trials upon clinical trials to determine if the vaccine is safe, if it produces the desired antibodies, and then finally to see if it actually works in practice - and works better than any alternatives already out there. +And then there is constant quality control testing of the product itself, to make sure that the plant is still making exactly what they think they are making." Everyone has answered well enough, so I'll just add this tidbit: chemists don't make vaccines, medical researchers do - specifically immunologists, vaccinologists, and epidemiologists all work together to figure out how to defeat a disease. +990 Durban, South Africa. Are these different colors due to the Umgeni river or the difference in temperature that affects plankton? 4127 https://www.reddit.com/r/askscience/comments/85b4wx/durban_south_africa_are_these_different_colors/ 1521378785 85b4wx Earth Sciences 2018-03-18 16:13:05 "Mixing of two rivers with different salinity gradients. Happened in south America too. Also happens down the coast where the Indian and Atlantic mix. BBC has a David Attenborough special called Africa and the first or third episode is called ""Cape town""and covers the topic. " "My PhD is on water optics (important for calibrating and validating satellite imagery) + +This looks like high suspended particle load (TSM) with perhaps a little dissolved coloured organic matter (CDOM). + +While some phytoplankton, principally diatoms, but also some prymnesiophytes, have yellow/brown pigments, their blooms don't look like this. + +You can't see differences in salinity (unless you can see in the microwave spectrum), but you can see the effect of differences in temperature and salinity as in the extreme example above. + +" +1373 "Humans have ""introduced"" non-native species to new parts of the world. Have other animals done this?" 4127 https://www.reddit.com/r/askscience/comments/ch0y6j/humans_have_introduced_nonnative_species_to_new/ 1563928390 ch0y6j 2019-07-24 3:33:10 "https://en.wikipedia.org/wiki/Equus_(genus) + +Interesting side-note. The modern horse originated in North America, then went extinct in the Americas around 12,000 years ago (Ice Age, probably). Fortunately they had migrated to Asia before that. They were only reintroduced to the Americas with the arrival of Christopher Columbus." "Using birds' digestive systems is how many plants spread around the globe. + +Surtsey is a pretty famous example. It is a volcanic island that appeared in the 1960's. A rock in the middle of the ocean is a nice hide out for birds, whether they be fishing, flying back and forth from Iceland and stopping on the way or just hiding from predators. + +Birds of course poop and sooner than later, the island was already growing plants. + +It even grew a tomato plant, but that was traced back to a scientist who had been a bit too careless with his own droppings and it was subsequently removed from the soil." +681 Are high calorie food like chocolate bars more damaging to the environment because the ingredients would cost more energy to grow? 4120 https://www.reddit.com/r/askscience/comments/6666tb/are_high_calorie_food_like_chocolate_bars_more/ 1492554371 6666tb Earth Sciences 2017-04-19 1:26:11 "We would like to remind the /r/askscience users that we do not allow anecdotes and speculations on this sub. This is especially true for top level comments where we expect quality answers as well as the ability to sources any claims made. If you want more informations about our commenting rules please refer to our [guidelines](https://www.reddit.com/r/AskScience/wiki/quickstart/answeringquestions). + +For reference at the time I am writing this, about 50% of the comments have been removed for rule violation." "Consuming more energy alone is rarely a problem considering plants already only absorb a really small fraction of sun light that touches them. If anything there's a massive energy surplus. + +What tends to be more of a problem are things like water consumption, nutrients pulled from the soil, the amount of fertilizer (and thus the amount of energy you need to use to make said fertilizer), pesticides used, and any biproducts the plant might make. But those aren't necessarily linked to calorie count. + +Edit: Should have differentiated between energy costs in terms of the energy the plant consumes and stores vs the energy cost to make things like fertilizers. However the later part isn't linked to the actual amount of calories that the plant can store. I kind of wrote things quickly. " +682 Would there be a benefit to putting solar panels above the atmosphere? 4120 https://www.reddit.com/r/askscience/comments/66ba0f/would_there_be_a_benefit_to_putting_solar_panels/ 1492619120 66ba0f Engineering 2017-04-19 19:25:20 "So this is actually currently being researched: +http://eas.caltech.edu/engenious/twelve/idea_flow + +The idea is to launch arrays of space-based photovoltaic cells that would use microwave transmission to beam energy back to Earth. The big benefit of this type of approach is that it mitigates the variability of traditional solar panels. + +In the short term cloud cover can cause variability in power output of solar cells and also the obvious issue of the day-night cycle. In the long term, the closer you are to the poles the more your sunlight varies throughout the year. What might be enough solar panels to get you through a 16 hour day in the Summer won't necessarily get you through an 8 hour day in the Winter. + +A space-based solution could theoretically solve all of these problems by having several arrays of cells in geostationary orbit, such that some subset of them will be exposed to sunlight at all times. Since the energy could be beamed down in microwave spectrum, clouds etc. would not be as much of an issue as they are for visible light. + +Obviously there are tons of technical issues to get this sort of thing working, but people are working on it!" "The atmosphere is largely transparent to visible light, which is the range most conventional photovoltaics use. If located higher there could be a marginal increase (ignoring other factors at the moment) because there would be a few percent more of that light, however without the atmosphere blocking the more energetic wavelengths like UV the cells degrade requiring you to add thicker shielding/glass to mimic the effect of the atmosphere. + +Additionally photovoltaics have a reduced efficiency when hot, which is a concern when they are being hit by useless wavelengths (which normally the atmosphere blocks) that only heat the panels and contribute nothing to the actual generation of power while also having very little to no medium to assist in transferring that heat away + +Finally you'd need a way to get that power from the panels back down to the ground, which could be done in a variety of ways, but realistically it's not practical from an engineering or cost perspective when you want the power at ground level in the first place." +1260 Are there any known computational systems stronger than a Turing Machine, without the use of oracles (i.e. possible to build in the real world)? If not, do we know definitively whether such a thing is possible or impossible? 4120 https://www.reddit.com/r/askscience/comments/azuq90/are_there_any_known_computational_systems/ 1552318057 azuq90 2019-03-11 18:27:37 "Usually when we talk about hyper computation we ignore runtime complexity. If we just look at what problems are decidable, we believe that no stronger model exists. + +But if we look at runtime, quantum computation has (at least) a provable quadratic speedup over classical turing machines (grovers algorithm). + +In the real world we are also not restricted to serial computation. Pi calculus captures parallel semantics and can also compute some problems faster than serial turing machines." "There are two ideas here which should be treated separately. One is the distinction between things that can be computed by a Turing machine and things that cannot (i.e. those things that are formally undecidable). In that sense, there are a number of models that are stronger than Turing machines, as mentioned in other comments: this includes the Blum-Shub-Smale machine, also known as the ""real computer"", that can operate on real numbers of unbounded precision in finite time. Another conceptually simple machine that is able to decide formally undecidable problems is a Turing machine equipped with an ""oracle"" for the halting problem (which I'll call Turing+HP): since the halting problem is formally undecidable, this is pretty intuitive. An interesting structure emerges from this construction: in fact, no Turing+HP machine can tell for all Turing+HP machines whether it will halt! But if you give a Turing+HP-halting problem oracle to a Turing+HP machine, you get an even stronger machine... we see a hierarchy of *levels* of undecidability! This level is referred to as Turing degree and the structure of the Turing degrees has been investigated by logicians. Collectively, computation beyond the Turing machine model is referred to as ""hypercomputation"", and as also mentioned by other comments, we are not certain there are ways to hypercompute within the physical universe (but others studying the intersection of logic and relativity are having lots of fun (""fun"") bashing black holes and various structures of spacetime in which it may be possible). + +Another distinct idea is a distinction between things that can be computed by a certain kind of machine in a polynomial number of operations and things that cannot (i.e. those things that are difficult for a particular kind of machine to compute). By kind of machine, I mean ""quantum computer"", or ""nondeterministic computer"". This is a very active area of research; in some sense humanity is somehow really bad at fully fleshing out what a particular kind of machine can do in polynomial time. For instance, we don't know for certain whether a quantum computer can do more in polynomial time than a computer that gets to flip coins. We also don't know for certain whether a computer that gets to flip coins can do more than a computer that does not. We suspect that quantum computers are better since there are some things they can do faster, e.g. searching N items in sqrt(N) time (but this does \_not\_ bring problems previously suspected to take exponential time into polynomial time). The famous example is P = NP: NP is roughly the set of problems that can be solved in polynomial time by a program that gets to run exponentially many copies of itself; somehow we *have not been able to prove* that this lets you solve problems ""faster"" than you could without forking! None of these models are able to do strictly more than an ordinary Turing machine, since the ordinary Turing machine can simulate all of these other models given exponential time. The big question is whether these models allow us to do something -- anything -- in polynomial time, that an ordinary Turing machine would require exponential time to do." +116 How common is it for animals to die during hibernation? 4119 http://www.reddit.com/r/askscience/comments/3atd68/how_common_is_it_for_animals_to_die_during/ 1435054980 3atd68 Biology 2015-06-23 13:23:00 "The exact mortality rate varies by species, geographical location, and time, but in every species I know of, there is some mortality risk during hibernation, due to predation, disease, starvation, etc. + +As a counterpoint to bats, apparently black bears have a really low mortality rate during hibernation, ~1%. (Seems like that would actually be lower than their mortality rate during the summer!) + +ETA: + +1. Wow, I did not expect so much enthusiasm for bears! + +2. Although it apparently has been a topic of controversy, there does seem to be scientific consensus that bears hibernate: +https://en.wikipedia.org/?title=Hibernation#Bears +https://scholar.google.com/scholar?hl=en&q=bear+AND+hibernation&btnG=&as_sdt=1%2C14&as_sdtp= +http://www.reddit.com/r/askscience/comments/3atd68/how_common_is_it_for_animals_to_die_during/csfwpvo" "[Hibernation allows a diverse range of small mammals to exhibit seasonal dormancy, which might increase survival and consequently be associated with relatively slow life histories. ](http://rspb.royalsocietypublishing.org/content/early/2011/03/22/rspb.2011.0190) + +Hibernation actually increases lifespan and likelihood of an animal dying during this period is quite low. + +/r/dataisbeautiful + +Edit: TL;DR: Overall, monthly survival probability was higher (by a median of 0.08) during the hibernation season in 37 (93%) out of the 40 within-group (i.e. sex and age) comparisons. When survival estimates for sexes and ages were averaged for each of the 19 species, a phylogenetically informed model included a significant and strong effect of season on survival + +Source: http://rspb.royalsocietypublishing.org/content/early/2011/03/22/rspb.2011.0190" +683 Do two colonies of ant from the same species use the same pheromone markers? 4117 https://www.reddit.com/r/askscience/comments/5yrpui/do_two_colonies_of_ant_from_the_same_species_use/ 1489220018 5yrpui Biology 2017-03-11 11:13:38 "I'm only a uni student, but I'm fascinated by ants, so I think I can give you some insight here. + +I don't think they're piggy backing off the old pheramone trails markers because those markers are pretty volatile. The way the system works is that each ant lays a trail and subsequent ants follow the freshest/strongest one, but make some slight deviations. If their deviation is faster, subsequent ants will follow that one, so they wind up with the fastest route eventually. If these pheromones weren't volatile, it wouldn't work. + +I think it's simply a matter of independently finding that particular entry point into your home is the fastest one. + +As for whether they would follow another ant's trails, I doubt it. Ants as a general rule seem to use both the shared, functional pheromone + a unique, colony identifying one in anything they excrete and as a general rule, ants tend to avoid those markers. While ants are territorial, they generally don't go looking for trouble (though there are some exceptions as u/lionhart280 points out below). It's a special event when an ant colony gets together for an aggressive raid, at least in most species. + +However, if they are Argentine ants or members of another super colony forming species, their cuticle hydrocarbons (chemicals in the ant's ""skin"" that act like a form of ID card) are so similar, that ants can wander into another colony's nest and it's recognised as a nest mate, which has lead to high levels of co-operation between those colonies. If they are super colonists, then it's quite possible they'd follow a trail laid by another, but again, the substances are volatile and have to be for them to function. + +Time scale, species and the location of the ingress and location of the nest from the ingress points would help us answer this question better." "I am doing a PhD in evol. bio and a number of colleagues in my department are working on ant footprints and cuticular hydrocarbons (CHC's, anti-dessication, communication and identification molecules ants carry on their cuticle). + +Ants can tell apart different species by their footprints. They will avoid certain species but follow prints of others, partially depending on dominance (e.i hierarchy, slavery, etc) between the species. They can also use the CHC's to tell apart colony members from foreign ants. + +The footprints are not the same as the cuticular hydrocarbons, but will always contain them to some degree. Colony specificity has been shown in several species as far as I know. I am at home and too lazy to remote login to uni to look for papers from my dpt, but google scholar provides at least 1 example: +http://link.springer.com/article/10.1007/s10886-009-9669-6" +1374 What process occurs for a light bulb to be “burnt out”? 4117 https://www.reddit.com/r/askscience/comments/bwxlvi/what_process_occurs_for_a_light_bulb_to_be_burnt/ 1559702661 bwxlvi Physics 2019-06-05 5:44:21 "For incadescent and halogen, they work by heating a tungsten filament, which is a metal wire, to extremelly high temperature. So hot that it become white hot. This cause the filament to evaporate slowly as it is close to it's melting temperature. + +For fluorescent tube, iirc, there is a bit of mercury inside the tube that ends up fusing with the glass and phosphore, and stop being available inside the gas. The mercury help to make the gas conductive so it can be ionised and work. No mercury no gas ionisation and no light. + +For led. This get more complicated as there is many failure modes. It can be a capacitor failure, a driver failure, or a led failure. Most can be related to the high temperature that they reach. Electrolytic capacitor tend to be rated quite low at their max temperature... Standard is 1000 hours at 85°C... They often use chinese brands, thru even less reliable... Driver failure is more rare, but it often happen due to the other 2 failures, or a design flaw. Leds... The main failure is the bond wire, from the pin that goes to the board to the actual chip part inside. It is a gold wire that they connect to the leg to the chip, and the bonding process often fail and the wire break, and like the good old xmas lights, one down, all down." For an incandescent lamp, the tungsten filament evaporates slowly when hot. It is very thin to begin with and parts which are even thinner get hotter and evaporate even faster. Eventually the filament opens because it is just too thin. That often happens when switching the bulb on because the current is much higher for a very brief time. Halogen bulbs slow down the evaporation by redepositing evaporated tungsten onto the filament. +562 How accurate must the time of launch be for spacecraft on a slingshot path? 4114 https://www.reddit.com/r/askscience/comments/5jd60y/how_accurate_must_the_time_of_launch_be_for/ 1482239306 5jd60y Planetary Sci. 2016-12-20 16:08:26 "Hi, Aerospace Engineer here who works Guidance, Navigation, and Control on interplanetary rocket launches for a living. While there can be some corrections performed en route once launched, they are minor and mostly for correcting very minor dispersions. + +Interplanetary missions have either instantaneous launch windows once or twice a day, or short windows (nearly always less than 2 hours) once a day. Those short windows shift by a few minutes each day to account for the rotation of the Earth, the movement of Earth in its orbit, and the movement of other planets in their orbits. Launch Vehicles with RAAN correction can help lengthen the launch window, as can the type of trajectory and type of mission (is it slamming into Mars with a balloon or parachute, is it doing a precise aerobraking maneuver, or is it doing a series of gravity assists on multiple planets). + +For instance, Delta II Mars missions had instantaneous windows since the Guidance system of the Delta II couldn't correct for plane changes due to launching late. Most Atlas V launches to interplanetary targets had longer windows (still less than 2 hours), since it has a more advanced Guidance system." "When setting up for gravity assists, you usually have quite a long trip ahead of you before you even reach the object that is supposed to assist you. That allows for a lot of corrections to be made to the trajectory before you get to the place of intersection. A few hours off would be rather easy to catch up if your destination isn't to be reached until half a year or more later. + +In [this image of the trajectory of Cassini](https://en.wikipedia.org/wiki/Gravity_assist#/media/File:Cassini_interplanet_trajectory.svg) you can see that the launch is 6 months prior to the first assist maneuver (Venus 1 flyby). With some extra fuel included in the launch for corrections, something that is always carried to some extent for longer missions, you get some leeway with regards to the launch time. I will leave it up to someone with more knowledge on the subject to give a realistic window for launches, though. + +A graph that shows the Cassini probe's speed relative to the sun can be seen [here](https://en.wikipedia.org/wiki/Gravity_assist#/media/File:Cassini%27s_speed_related_to_Sun.png), if that is of interest." +423 How far away from an explosion do I have to be to be safe enough to walk like a cool guy and not look at it? 4109 https://www.reddit.com/r/askscience/comments/50gn7s/how_far_away_from_an_explosion_do_i_have_to_be_to/ 1472641896 50gn7s Physics 2016-08-31 14:11:36 "I frequently refer to [the plot on page 8 of this FEMA manual](http://www.fema.gov/pdf/plan/prevent/rms/428/fema428_ch4.pdf) when trying to get a sense of the safe distance for explosions of different TNT equivalences. (Before anyone asks, yes, this is something I do often for questions on askscience. And yes, I do have that page bookmarked.) + +When close to the source, the overpressure from the blast, as well as structural damage and collapse of nearby buildings are the biggest threat to your safety. At large distances, the main threat would be cuts from glass broken by the shockwave. If there is no glass around, you might be okay being a little bit closer than this limit. + +For an explosion of less than a few tens pounds of TNT, about 10 ft of distance per pound of explosive will generally be safe. For around a hundred pounds of TNT, the safe distance is about 5 ft per pound of explosive. For larger amounts of explosives, like tens of thousands of pounds, you could get away with about 0.25 ft of distance per pound of explosive. + +Disclaimer: As much as I love the scientific method, I can't recommend experimenting with this." "It's completely unanswerable without knowledge of the type (dynamite, c4, ANFO etc) and amount of explosives. Just too many variables. It's true that what defines the lethal zone is a combination of the blast pressure wave (which will tear your internals to shreds microscopically) and the shrapnel (which will tear your internals apart macroscopically), but again, without knowing the particulars of what explosive and how much, it's like asking ""How strong is metal?"" + +In the movies, they pretty much never use real explosives. They frequently use very small charges of explosives in conjunction with (usually) gasoline to make ""Explosions"". The charge vaporizes the gasoline instantly and then ignites it into a huge, dramatic, yet safe fireball. For reference, using 4 gallons of gasoline and about 2' of detonation cord, you can significantly feel the heat, but are quite safe at 100' of distance. (Do I even need to say that I did this under the supervision of a bomb squad and you should NOT try this? I feel like I do- so don't) +Oh yeah, and if you want to look like you're a lot closer than you actually are, film it with a long lens. " +889 How do spacecraft like Cassini avoid being ripped to shreds by space dust? 4106 https://www.reddit.com/r/askscience/comments/6zybtw/how_do_spacecraft_like_cassini_avoid_being_ripped/ 1505344014 6zybtw Astronomy 2017-09-14 2:06:54 "There's simply so little of it. A couple of dust impacts over a whole mission, maybe. + +I'd be interested in seeing what happens to voyager in a billion years, maybe it would run into some occasional bits in interstellar space and become a cloud of dust heading in one direction. More likely it won't run into much and will eventually get stuck in a huge orbit around a black hole after being swung around a few it was too fast for. Maybe align close enough to something like a star or black hole and get sucked in. A couple billion years from now. Would love to see the condition of it before that happens, though. " "For cases where space debris is a concern, we use whipple shields! + +https://en.wikipedia.org/wiki/Whipple_shield + +or in some cases, thick ass armor! + +https://i1.wp.com/www.technobyte.org/wp-content/uploads/2017/05/chris-hadfield-tweet-How-does-the-International-Space-Station-protect-itself-from-space-debris.jpg?fit=1080%2C1080" +217 Does a handicapped caterpillar turn into a handicapped butterfly? 4101 https://www.reddit.com/r/askscience/comments/3uhlbh/does_a_handicapped_caterpillar_turn_into_a/ 1448647033 3uhlbh Biology 2015-11-27 20:57:13 Follow up question: why would metamorphosis like this even be advantageous? the cocoon is so vulnerable to predators. You would think caterpillars that entered the cocoon would be naturally selected against, no? "This has actually been covered in a previous thread: https://www.reddit.com/r/askscience/comments/25p4lg/if_a_caterpillar_loses_a_leg_then_goes_through/ + +The answer is no! Essentially, during metamorphosis the caterpillar almost completely dissolves. Unless there's something wrong with the caccoon itself, the butterfly will form fine." +320 Happy Pi Day everyone! 4101 https://www.reddit.com/r/askscience/comments/4aczay/happy_pi_day_everyone/ 1457960391 4aczay Mathematics 2016-03-14 15:59:51 There are plenty of algorithms that are suited for computers related to pi, but which are tractable with pen and paper? Can finding the n'th digit be done on paper reasonably? What's the most precise that we've actually ever needed pi to be? +1804 How does North Korea's handling of COVID-19 affect the development and eradication of the pandemic? Will vaccines be available there? 4101 https://www.reddit.com/r/askscience/comments/lbarcf/how_does_north_koreas_handling_of_covid19_affect/ 1612311430 lbarcf COVID-19 2021-02-03 3:17:10 "There isn't going to be an eradication of the pandemic is probably the simplest statement to an underlying assumption in your question. That question assumes there will be a point where Covid is no longer something which moves around the population. North Korea may vaccinate if vaccines are made available, or they may simply have the virus ""run its course."" + +Places like North Korea, and frankly many places in other countries with more modernized healthcare systems but with less perfect vaccination rates, will maintain some reservoirs of covid. No one is certain, but the likelihood is that vaccination across most of the general population will slow spread such that something more like ""normal life"" will be able to happen, but that covid will still have several human reservoirs and will probably be common and dangerous similar to the flu as an ongoing issue. It will also evolve into new strains and pop up with worse and better years, similar to the flu but possibly more dangerous. We just don't know yet." "The pandemic will not be eradicated; and even if it is, more will take its place. Why? There have not been any true structural changes to prevent something like this from developing. +Epidemiologist Rob Wallace has written extensively on this topic, https://monthlyreview.org/product/dead-epidemiologists-on-the-origins-of-covid-19/ there is his latest book analyzing the political economy of COVID-19." +424 Do the holes on a dice which represent the numbers affect the chances of getting different numbers? 4100 https://www.reddit.com/r/askscience/comments/4t4o3a/do_the_holes_on_a_dice_which_represent_the/ 1468677944 4t4o3a Physics 2016-07-16 17:05:44 "Yes they do! + +If you look at the regular dice you get from, say, a Monopoly game, you'll find many things that can change the chance of rolling a specific number. + +First your question: The mass on the 1 side (with one hole) is higher than from the opposite, the 6 side (with six holes), so the 1 side is the heaviest side and therefore a 6 is slightly more likely. + +Now to other things: + +The dice are usually made out of wood or white plastic or other materials you can't look through, so you can't see if the dice are manipulated (a weight on the 1 side to make the 6 side more likely for example). + +The edges/corners are round and, without proper measurements, you won't be able to know if the edges/corners are identical. If you grind specific edges/corners down, you can increase the chance of a specific side. + +There's one more: Dice get used up after a while. You may not see it on a wooden die, but it will get little scratches, which also changes the probabilities. + +Now you may think, how do casinos prevent it? They have special dice. + +They are usually made out of acryl, so you can look through. The edges and corners are very sharp, so you can easily, without measurements, tell if one edge/corner is grinded down and, IMO the most awesome thing: The holes get filled with a material that has a density as close as possible to the acryl. + +They handle the tear in an easy way: They simply change out the dice pretty often. + +If you want high quality dice, get casino dice. + +I have five of them (though, not quite casino quality, I paid 15€ for all of them, so 3€ each) and you can see all the points mentioned very easily, even the scratches on the edges and the broken off corners. I've used them somewhere between 15 to 20 thousand times. If you'd like to, I can take a few pictures of mine with the scratches, otherwise you can simply google ""casino dice"" to see pictures of them. + +Edit: I took some pictures, [they aren't great](http://m.imgur.com/a/VqQbY), but I hope you guys can see what I mean with used casino dice. Look closely at the corners and edges. + +/u/Macinapp + +/u/Azurphax + +2nd edit: I was stupid enough to forget the link to the pictures." "I can't speak to the physics, but I can tell you that dice used in gaming license venues adhere to pretty strict balance properties, and are constructed with this in mind. No single set of dice is ever used for too long for the same reason. + +Cheap dice do not adhere to these rules, and are often unbalanced, so I think there is a good chance the indentations do factor into the dice performance." +425 AskScience AMA: I’m Professor Brian Hare, a pioneer of canine cognition research, here to discuss the inner workings of a dog’s brain, including how they see the world and the cognitive skills that influence your dog's personality and behavior. AMA! 4099 https://www.reddit.com/r/askscience/comments/4ql6ak/askscience_ama_im_professor_brian_hare_a_pioneer/ 1467286396 4ql6ak Dog Cognition AMA 2016-06-30 14:33:16 "How far has the domesticating of canines changed their cognitive functions, how different is the brain of a wild dog to that of a pet? + +Do you think that any animal can be domesticated completely if raised from birth? " What information are dogs taking in when they smell a spot intently? I assume because their sense of smell is so strong they are perceiving more than just recognition of a particular scent. +991 How did early chemists isolate the earliest identified elements and determine that they were in fact elements? 4098 https://www.reddit.com/r/askscience/comments/7thyr9/how_did_early_chemists_isolate_the_earliest/ 1517111741 7thyr9 Chemistry 2018-01-28 6:55:41 "In these kinds of discussions it's often worth going straight to the source. One can find an online copy of Lavoisier's Elements of Chemistry [here.](https://archive.org/details/2561010R.nlm.nih.gov) + +Not only is his original work still quite readable, it contains fascinating insights into his thought process. For example, on page xx of the preface he admits that his elements are what they were capable at the time of decomposing, but that one day more advanced chemists might be able to break them down further (as was eventually done by distinguishing subatomic particles). + +As for his arguments, he leans on the chemical reactions he knew and the ones most popular at the time. For example, he suspects nitrogen and carbon are elements, he burns them, and he gets a corresponding type of acid, and furthermore finds he can account for all of the mass. He does a similar thing with sulfur and finds a corresponding acid and no loss of mass. However, if he burns carbohydrates, he loses mass as water and later tracks down and proves that he lost it. It was not just one thing, but collections of similar observations like these that allowed early chemists to realize that elements differed from salts which differed from acids, and so on." "I think it’s important to keep in mind that in many cases, isolating gases can be done using a lot lower “tech” methods than other elements. So a lot of the first elements isolated were probably also gases, with the early gas laws being developed towards the end of the 1700’s. + +So I think Rutherford’s Nitrogen experiment is a good example. All he really did was continue removing other gases (oxygen by a candle, CO2 by a liquid that absorbed CO2) from a chamber until all that remained was a single, inert gas that could not support burning or keep a mouse alive. Rutherford did not know it at the time but he had isolated Nitrogen from the air." +1375 Why can't magnet bend light when light is made out of electromagnetic wave? 4094 https://www.reddit.com/r/askscience/comments/bklf63/why_cant_magnet_bend_light_when_light_is_made_out/ 1556978439 bklf63 Physics 2019-05-04 17:00:39 The electromagnetic field doesn't interact with itself, except at very high energies and very small distances which are not relevant here. This means that the magnetic field of the magnet won't affect a passing EM wave. The wave can be affected by the magnet itself, though, by moving the electrons inside it, which in turn produce their own EM wave. It can, but it doesn't bend the light's path. Instead, it bends the polarization. This is called the Faraday effect. (https://en.wikipedia.org/wiki/Faraday_effect) +218 If you have an organ transplant, will your body gradually replace the DNA in it with your own, or will the cells continue to regenerate with the same external DNA? 4093 https://www.reddit.com/r/askscience/comments/3wx5tp/if_you_have_an_organ_transplant_will_your_body/ 1450172705 3wx5tp Biology 2015-12-15 12:45:05 "By and large the transplanted tissue will retain the donor DNA. This fact should not be too surprising considering that you are taking a complex slab of tissue with millions of cells, which are not going to be readily replaced. From the point of view of these cells, they won't ""know"" that they are now in a foreign body and will largely continue to grow, replicate, and function as they did before. + +Having said that, the picture is not completely static. With time cells from the host organism will interact and/or modify the transplanted organ and its surroundings. Such interactions can take a detrimental turn when the host's immune system recognizes the donor tissue as foreign and effectively starts to attack the cells in the donor tissue. This process called [transplant rejection](https://en.wikipedia.org/wiki/Transplant_rejection) can lead to complete organ failure in acute cases as well as to long-term chronic tissue damage. In order to reduce the risk of rejection, transplant patients are generally given [immunosuppressive drugs](https://en.wikipedia.org/wiki/Immunosuppressive_drug) in order to reduce how much damage their immune system can cause to the new tissue. Finally, cellular fragments from the donor tissue can also be released into the host. In fact, detecting free DNA from donor tissue [appears to be a strong indicator of organ rejection](http://www.pnas.org/content/108/15/6229)." "The cells regenerate and maintain their own DNA. Any stem cells that replace the organ tissue are typically located in the organ itself (see this research on [liver stem cells](https://www.hhmi.org/news/source-liver-stem-cells-identified) for example). So an organ replaces itself over time as old cells die off, rather than getting new cells from another part of the body. + +The fact that the DNA in the transplanted organ doesn't match the DNA from the rest of your body means your immune system might attack those cells, leading to transplant rejection. Rejection can occur right away or it can occur gradually [over several years](https://en.wikipedia.org/wiki/Transplant_rejection#Chronic_rejection)." +890 When there is a high load on an electrical grid, why can't we just let the frequency drop (eg 50 -> 45 Hz) and then recover later, rather then requiring rolling blackouts / load shedding? 4092 https://www.reddit.com/r/askscience/comments/7m0r9p/when_there_is_a_high_load_on_an_electrical_grid/ 1514197075 7m0r9p Engineering 2017-12-25 13:17:55 "To slow the grid frequency, every generator on the entire grid would need to slow at the exact same rate, but since not ever generator has the same output power/overload capabilities this wouldn't be the case. If the generators are out of phase (which is guaranteed if they're at different speeds) large fault currents begin to flow between the generators to try and pull them back in sync and things start to trip and go offline. + +If they were all slowed in sync somehow, then every standard AC (induction) motor would also slow down to match, since line powered induction motors (pumps, tools, large fans, etc) rotate at about the same speed as the grid's generators. Also, the impedance of all the transformers/power factor correction equipment/etc would change and it would alter how much power the grid could supply, losses at substations, and a few other details. + +Edit: Read some of the replies to this comment as well. Some are quite insightful and clarify some hand waviness I included." "Frequency is more important than people think because every transformer is built for the frequency of the alternating current. The iron core contains enough iron to ""saturate"" at the speed of polarity change, which is the optimum iron/winding ratio of the transformer. Lowering the frequency results in excessive electromagnetic saturation, too much current and heat buildup. A transformer meltdown is likely, and a house fire can be the result. So its extremely important to keep the voltage at 60hz. European transformers run at 50hz and are not interchangeable with 60hz transformers. Well maybe in a pinch. It should be noted here that using a 50hz transformer on 60hz current will be much safer than the other way around, because it will never reach saturation. The reason is that the ideal 50hz transformer contains more iron than 60hz current can ever saturate. The higher the frequency the less iron a transformer needs, though I am not sure if modern mass produced transformers are optimized enough to care." +684 If you run around a track twice, the first time slowly, the second time much faster so that the average for the two laps is twice the speed of the first lap. People are getting infinite speed for the second lap. Why? 4090 https://www.reddit.com/r/askscience/comments/653w3n/if_you_run_around_a_track_twice_the_first_time/ 1492065732 653w3n Mathematics 2017-04-13 9:42:12 "> If you run the first lap at 6 km/h and then the second lap at 18 km/h you get an average of 12 km/h. + +You can't average velocities in this way. You can only do this if the time is equal for the two velocities. In this case, that's not true, since it's the distance that is equal. + +To illustrate, assume that the track is 18 km long. The first lap takes 3 hours to complete at 6 km/h. The second lap takes 1 hour to complete at 18 km/h. The total distance covered is 36 km and this took 4 hours. That means that average speed is 9 km/h, only 50% more than the speed of the first lap. + +If you want to have the average speed by the double of the speed of the first lap, the average speed should be 12 km/h over the total distance of 36 km. But that means that the total time spent should be 3 hours, which is already how much time was spent on just the first lap. That's why people are saying you'd need an infinite speed on the second lap in order to achieve the desired average." "I like to think the following is the simplest way of explaining this: + +The average speed for any trip is (total_distance)/(total_time). + +After the first lap, you have an average speed of (lap_distance)/(lap1_time) + +By running the second lap, you are doubling the total distance run. + +If you want your average to also double, your total time must **remain the same** so that the average is (2×lap_distance)/(lap1_time+0). + +The only way for the total time to remain the same is for you to run the second lap in 0s." +1430 Are identical twins much more-likely to have the same sexual orientation? 4082 https://www.reddit.com/r/askscience/comments/d15sbm/are_identical_twins_much_morelikely_to_have_the/ 1567912485 d15sbm Biology 2019-09-08 6:14:45 "This question was addressed in research of same-sex sexual behavior of 3,826 Swedish twins and found greater concordance between identical (monozygotic) twins than non-identical (dizygotic) same-sex twins. + +https://link.springer.com/article/10.1007%2Fs10508-008-9386-1 + +In another article published recently in the journal Science attempts to further address this question. + +https://science.sciencemag.org/content/365/6456/eaat7693 + +The research presented in this article identified several genetic variants that are associated with same-sex sexual behavior across 491,001 individuals. Therefore based on the conclusions presented in this paper it may suggest that identical twins have a shared genetic predisposed to same-sex sexual behavior, although this is not the whole picture due to environmental variables. The authors include in their discussion that interaction between genes and environment requires further study to explain this behavior. + +Edit: It was brought to my attention that there was not clear distinction between the conclusions of the second article and my suggested implications of this research on identical twins. I have revised for clarity." "If I'm reading this question right, I think a lot of the answers are misunderstanding the question. OP you can confirm, but I think you intend to ask something like, + +""If sexual orientation is primarily or exclusively determined by genetics, then we would expect identical twins to have the same sexual orientation (NOT same sex sexual orientation, just the same one, i.e. both gay or both straight etc...) at a much higher rate than 2 other random people. Are there any studies indicating that this is the case?"" + +I don't know the answer, but it seems like a lot of people are reading your question to ask if there is a higher likelihood of same sex sexual orientation among twins than the general population. I don't think that's what you intended to ask. + +edit: Maybe random people isn't a good group to target as a comparison, but how about fraternal twins? or other non identical siblings raised in a similar environment?" +3 Light bends around massive objects. Could there be something so massive that light orbited around it? 4081 http://www.reddit.com/r/askscience/comments/2yt10y/light_bends_around_massive_objects_could_there_be/ 1426176253 2yt10y Physics 2015-03-12 19:04:13 "**Short answer:** Yes. If you're near a black hole. + +**Longer answer:** So you already hit on the fact that light can't escape black holes, and it turns out that if you are at just the right distance from the event horizon (which is sort of the point of no return- where the black hole begins and the normal universe ends), photons can actually orbit at this point. It means that if you were at this point, and you looked straight ahead, you'd see the back of your head! + +Anyway, it's called the [photon sphere](http://sciencevspseudoscience.files.wordpress.com/2011/09/schwarzschild.png) (not to be confused with the photosphere of the sun). " "Yes, we call them black holes. + +I am not a physicist, but I believe that at 1.5x the Schwarzschild radius, photons orbit a black hole." +4 "Do creatures such as cuttlefish and octopuses get ""tired"" from using their camouflage?" 4077 http://www.reddit.com/r/askscience/comments/33ocqj/do_creatures_such_as_cuttlefish_and_octopuses_get/ 1429848350 33ocqj Biology 2015-04-24 7:05:50 Camouflage is mediated through two channels: i) hormonal and ii) neuronal. Hormonal pathways operate on the order of hours-days, whereas neuronal pathways are rapid (8 seconds in the fish I observe). I am not familiar with octopus in general, but with flatfish, the mechanisms driving their camouflage remain persistent over time given a stable environment. Octopus are capable of adding a three dimensional component to their crypsis (mimicking seaweed texture, etc.) which is muscular, and I imagine would experience fatigue like any other muscle. "Yes they would, and good question! Octopus and cuttlefish camouflage is controlled by their muscles, so it costs them energy like using any other muscle they have. + +Keep in mind that camouflage is always relative to the environment that an organism is in. Let's say an octopus at rest is yellow in colour and is in a yellow environment. They would not have to change their color at all because they already blend into the environment perfectly well. + +Source: degree in biosci" +563 How can I obtain ethanol 100% if at 95.4% is considered an azeotrope? 4070 https://www.reddit.com/r/askscience/comments/5crq5t/how_can_i_obtain_ethanol_100_if_at_954_is/ 1479067194 5crq5t Chemistry 2016-11-13 22:59:54 One of the most common methods of obtaining absolute ethanol is by taking the 95.4% azeotrope and adding a third component such as benzene. This third component, called the entrainer, gives rise to a new lower-boiling ternary azeotrope (water/ethanol/benzene) that can be used to trap the water. You want to add just enough benzene to trap all the water without leaving any large amounts of benzene behind. Then you use one final distillation step to pull off this ternary azeotrope, leaving behind pure ethanol. You still end up with traces of benzene in this process, so I don't recommend drinking the final product. You can salt out the water with magnesium sulfate, aka Epsom salt. The crystals will convert into the hydrate form and will remain insoluble in the ethanol, turning from crystals to clumps in the bottom of the flask. Using a hydrometer, determine the mols of water remaining in the solution and add equal mols of magnesium sulfate crystals. Run it through a coffee filter and you've got absolute alcohol. Water from the air inside the storage container gets in that mixture so leave a small cake of salts in the jar and filter upon it's time of use. +426 What is the physical difference in the brain between an objectively intelligent person and an objectively stupid person? 4060 https://www.reddit.com/r/askscience/comments/4ud30y/what_is_the_physical_difference_in_the_brain/ 1469366424 4ud30y Neuroscience 2016-07-24 16:20:24 "Before you comment, please ask yourself, ""Can I back up what I'm about to type with peer reviewed science?"" + +If the answer is yes, then please do. If not, then you probably have an anecdote or speculation, which will be removed. " "Short answer: we don't know yet. + +But three important points: + +1. Self-evidently, intelligence is an emergent feature of the physical organization of the brain combined with its biochemical function. If there are any detectable differences in intelligence between two individuals, there must be something different in their brains, whether it is circuit microstructure, expression levels of certain transmitters or receptors, or, most likely, some slight differences in the calibration of the assembly of the brain. Remember, the brain, with its hundreds of billions of cells, self-assembles from a simple primordium of a bag of a few stem cells. Moreover, this happens at a breakneck speed - about 1,300 neurons are born and about 700,000 synapses are generated [PER SECOND](http://www.ncbi.nlm.nih.gov/pubmed/26796689) during peak periods of development, culminating in about 620 trillion synapses in an adult brain. This process is blueprinted in DNA and is exquisitely coordinated and controlled. This leads to... + +2. Intelligence is highly heritable, that is, genetically determined. Many people in this thread are saying that your intelligence is mostly a product of culture and environment. In reality, environment does contribute importantly but genetics is more important - [consensus](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4006996/) estimates are that about 60-80% of the variance in intelligence is explained by [inheritance](https://www.youtube.com/watch?v=F0_NsS1Zdlk). There is a [big genetic study](https://archive.is/mdiHw) underway now in China to pinpoint genetic regions that vary the most between highly intelligent people and the rest. + +3. Also related to trying to study the biology of intelligence. Someone below posted that Einstein's brain was no different to anyone else's. This is false - Einstein actually had a [significantly increased ](http://www.ncbi.nlm.nih.gov/pubmed/3979509) ratio of astrocytes (a type of glia) to neurons in certain brain [areas](http://www.npr.org/templates/story/story.php?storyId=126229305). A human brain has about 90 billion neurons and at least 100 billion, possibly over a [trillion](http://blogs.scientificamerican.com/brainwaves/know-your-neurons-what-is-the-ratio-of-glia-to-neurons-in-the-brain/) glia. The role of glia in neural computation is still somewhat unclear. Classically, neurons are seen as the signal conductors in the brain, since they can essentially perform computations on incoming electrical signals and convey the results forward in a circuit. Glia do not really seem to have these long-range transmission capabilities, but may nevertheless play very important roles in coordinating the activities of circuits. Thus, glia may be very important in neural computation. In any event, slicing up a post-mortem brain is an extremely poor way of deducing the basis of intelligence - it's the crackling activity of trillions of synapses that is the real basis of intelligence. At the moment, in 2016, it's just too complex of a question for us to answer - but we're working on it. + +Source: neuroscience postdoc" +1376 If the universe is expanding, isn't all matter/energy in the universe expanding with it? 4058 https://www.reddit.com/r/askscience/comments/blpto1/if_the_universe_is_expanding_isnt_all/ 1557230365 blpto1 Astronomy 2019-05-07 14:59:25 "Hello, astronomer checking in. + +Our current models for the geometry and dynamics of the Universe tell us that yes, it will eventually expand at a rate faster than light can travel. This is not to say that light will be travelling at greater than c, but that the path the light takes through space is actually growing faster than light can travel through it. Remember, there is a difference between travelling through space, and space itself growing. + +Imagine driving a car down a long road at some speed v. If you are always travelling at v, but the length of the road increases at some speed greater than v, you will never reach your destination and will appear to be ""moving backwards"" as you say. You'll still get farther and farther from your starting point, though. + +Other comments have pointed out that the expansion of space separates matter only on certain distance scales. This is true, and it is because the laws of nature (Electromagnetism, the strong and weak nuclear forces, and gravity) all have specific distances over which they dominate. Atoms are held together by nuclear forces, because they are so small. The solar system is held together by gravity. Expansion only becomes a factor when the density of matter, Ωm, becomes less than the density due to the cosmological constant, ΩΛ. This constant, Λ, is what drives expansion via (who really knows but we call it:) dark energy. ΩΛ only dominates on the largest distance scales, ie, greater than the size of a galaxy cluster. + +Additionally, matter itself is composed of fundamental particles. To our understanding, these particles cannot change in size, if they even have a size. They are therefore not expanding with the space around them, and proportionality is not conserved. + +If you require a more scientific look at the subject of expansion, I suggest reading through [Riess et al. 1998](https://iopscience.iop.org/article/10.1086/300499/pdf) and its citations therein. This is the paper from Adam Riess and the High z Supernova Search team that originally showed that the universe was accelerating." "It's a few things: + +a.) It sounds like you saw something about the Big Rip, which is a possibility for the future of the universe, but not really at the point of a theory or even a hypothesis. Rather, it's a predicted outcome IF certain measurements of the universe turn out a certain way. Right now, it's up in the air, but I don't think it's considered particularly likely. + +b.) The expansion of space isn't quite uniform. It's happening everywhere if you zoom out to such a large scale that the various clumps of matter and energy are indistinguishable, but around here, where there are planets and stars and galaxies, it's not necessarily the case. And even if it is expanding locally, objects are held together by the other forces between them. + +c.) Expansion may add dark energy to the total mass-energy of the universe, but it doesn't change the amount of other mass and energy. + +d.) Expansion is about space and hte universe itself, not the motion of any objects. Light isn't going backward, it's still getting further away from its source. It's just that the destination is receding even faster, or rather, the path to the destination keeps getting longer." +992 Is there any mathematical proof that was at first solved in a very convoluted manner, but nowadays we know of a much simpler and elegant way of presenting the same proof? 4051 https://www.reddit.com/r/askscience/comments/80vm2h/is_there_any_mathematical_proof_that_was_at_first/ 1519820464 80vm2h Mathematics 2018-02-28 15:21:04 The [Abel-Ruffini Theorem](https://en.wikipedia.org/wiki/Abel%E2%80%93Ruffini_theorem) of the unsolvability of the general quintic equation in radicals. Ruffini's original 1799 proof held 500+ pages and was still incomplete, Abel managed to prove it in six pages in 1824. "Johann Lambert produced the first proof that pi is irrational. It involved many pages of manipulations of generalized continued fractions. + +Ivan Niven later produced a one-page proof using only basic calculus. + +https://en.wikipedia.org/wiki/Proof_that_%CF%80_is_irrational" +5 Do human beings make noises/sounds that are either too low/high frequency for humans to hear? 4047 http://www.reddit.com/r/askscience/comments/341qi4/do_human_beings_make_noisessounds_that_are_either/ 1430153699 341qi4 Human Body 2015-04-27 19:54:59 "Rub your thumb on your pointing and middle fingers. Barely makes a noise to us, but in ultrasonic ranges it's noisy (pops and cracks believe it or not). That's one of the reasons it's so easy to attract cats to you with that motion. They hear it even though we don't. Edit: Changed index to middle (finger). Thanks all. + +Edit 2: Well, I had hoped to find my old detector and make a video for you all, but it isn't working very well these days. Worse, the website I bought it from is no longer offering it, so you'll have to settle for a line on the [wayback archive of it](https://web.archive.org/web/20051218192908/http://www.xtronics.com/kits/SK-207.htm): + +""Rubbing your fingers generates ultrasonic noise up to about 60 kHz."" + +I'm also starting to wonder if the pops and cracks I heard where faults in the unit. It's doing a lot of that now. I have to try resoldering it and see if that fixes it." "Yes we definitely do. Do we use these frequencies to communicate, like bats? No. + +Whenever a sound is made, you can map the intensity of the sound at certain frequencies with a frequency response plot. If you've ever thought seriously about buying studio monitors for recording and mixing I'm sure you've seen one of these, as these plots become important when you are trying to reproduce sounds with high fidelity. Sound frequencies are emitted in a continuum, just like light frequencies. There is no cutoff on this continuum where the frequency response becomes zero just because we can no longer hear that frequency. Therefore, all you need is a source in the body that can produce a sound with low/high enough frequency. It is not dependent on our ability to hear it or not. + +As far as frequencies that are too high to hear, I can't think of any off the top of my head. However, I'm sure some of our bodily processes that essentially use our whole body as an acoustic resonator, for example a hunger pang, produce frequencies that are too low for us to hear (as well as some that we can hear). " +219 "So far SETI has not discovered any radio signals from alien civilizations. However, is there a ""maximum range"" for radio signals before they become indistinguishable from background noise?" 4045 https://www.reddit.com/r/askscience/comments/3mu64p/so_far_seti_has_not_discovered_any_radio_signals/ 1443537295 3mu64p Astronomy 2015-09-29 17:34:55 "There are a few (interesting) reasons why a lot of people criticize SETI's approach. They mostly all have to do with the range of radio signals. + +We don't necessarily expect to find radio emissions within a few light years. As you start looking further and further away, the civilization which created the radio signal would have had to dump more and more energy into it in order for us to be able to ""read"" it accurately. Many people expect that a civilization will actually get less noisy as it evolves, because it discovers ways to send signals more efficiently. After all, those signals sent into space are wasted energy. The radio signals from earth become indistinguishable from background after a few light years. A lot of people think it is unlikely other civilizations would be sending out much more powerful incidental radio waves. + +So, if detecting this incidental radiation is unlikely, then there is always the argument for finding radio signals intentionally directed into space for the purpose of communication. In order to do this, an alien civilization would have to dump a lot of energy into the signal. If you are talking about aliens in other galaxies, it would be a stupendous amount of energy. If you are talking about aliens in our galaxy, but just a few thousand light years away, it is still quite a bit of energy. The arguments against this include that interstellar radio communication is very slow and fairly expensive energy wise, that there are probably better ways of manipulating the universe to communicate over such a distance, and that communication over this distance would probably be *directional* rather than omnidirectional. If communication is directional, you need to be in its path to detect it, which probably means that it is actually intended for you specifically (given the size of Space). + +SETI's best hope is to detect a directional radio signal intentionally sent to communicate with humanity. It is also possible that it could detect a signal intended for someone else that we intercepted, and it is possible that it could detect an omnidirectional signal which has had a disturbing amount of energy poured into it in order to be detectable. My post might sound very negative, but I actually support SETI's efforts. As a civilization it isn't very expensive for us to run SETI and the potential gain is very high. + +If you like pictures or TLDR, check out this useful link: +http://zidbits.com/2011/07/how-far-have-radio-signals-traveled-from-earth/" [deleted] +427 How do we take pictures of our galaxy if we are in our galaxy? 4041 https://www.reddit.com/r/askscience/comments/4ivp1l/how_do_we_take_pictures_of_our_galaxy_if_we_are/ 1462983547 4ivp1l Astronomy 2016-05-11 19:19:07 "Assuming you mean plan view, we don't. + +All images like that described as showing our galaxy are either digitally (or manually) produced images, or images of other galaxies similar to ours. + +We can see the milky way in our sky, and being on the outer limb of one of the arms we see it as a broad band of stars dominating one hemisphere of sky. It's in profile. We have no photograph taken that shows the milky way in plan view." "I'm assuming you mean pictures like [this](http://www.universetoday.com/wp-content/uploads/2013/10/milky_way.jpg) (""Top down view"" of entire Milky Way galaxy,) rather than pictures like [this](http://beautifulhoodriver.com/images/mt-hood-stars-milky-way_k9a3290.jpg) (View of the sky with the Milky Way visible going up from the horizon.) + +Assuming you mean the first kind - that's an ""artist conception"" of what we believe the Milky Way would look like if we were to have that angle on it. And our understanding of our own galaxy changes all the time! Only recently (2005!) was it fully proven that our galaxy is a ""barred spiral"" rather than an ""ordinary spiral."" And that was only even theorized in the mid '90s. Artist conceptions of our galaxy from the '80s or earlier look different from ones now. + +We can learn the general shape of the galaxy by observing the sky with very sensitive telescopes, and measuring the distance to the stars, nebulae, etc. Over time, this has let us build a pretty accurate ""map"" of our galaxy. There are some ""holes"" in our knowledge that we just have to guess at - the galactic core is very dense, so we can't see what is directly opposite the core from us. And there are some large nebulae and gas clouds that block our view of other areas. But we have a good idea of what is behind those ""walls"" because the galaxy does tend to be similar in all parts. + +As OrbitalPete pointed out, it's like being in the wilderness, and taking pictures all around, then using a computer to analyze the pictures and build a 3D model of the forest around you. Yes, that hill off to the North blocks your view behind it, so you'll just have to guess what's over there, but you can build a decently accurate map. + +Ironically, it's the same basic technique the Microsoft Kinect uses to figure out where the user is in the room! [This video](https://www.youtube.com/watch?v=7QrnwoO1-8A) gives a great demo of a Kinect doing just that. The black ""shadows"" are where the Kinect can't see through something. He did later figure out how to use two Kinects to get [less ""shadow""](https://www.youtube.com/watch?v=5-w7UXCAUJE). Astronomers are attempting to do something slightly similar by putting telescopes in orbit around the sun, at the distance of Earth's orbit, but on opposite sides of the orbit from each other - to get Earth-orbit-sized parallax. Not quite as good as the two Kinects since they are ""farther apart"" from an angular distance to their target. But still decent. The [STEREO](https://en.wikipedia.org/wiki/STEREO) satellite observatories are similar, but they are facing inward to the Sun, rather than outward to the galaxy." +1377 If two objects collide on Earth, their kinetic energy is converted to other forms such as light and sound. But in space, it can't be converted into sound energy, so what would it get converted into? And would it be more destructive for the objects in question? Or am I completely misguided? 4041 https://www.reddit.com/r/askscience/comments/c8715s/if_two_objects_collide_on_earth_their_kinetic/ 1562058825 c8715s Physics 2019-07-02 12:13:45 "Heat. + +Depending on size and composition the objects would vibrate, undulate, or temporarily rearrange themselves for a little longer in space if their environment didn't easily remove their excess energy. Basically, they'd get warmer. Eventually they would radiate the excess thermal energy." "Isn't sound still a kinetic energy? In my understanding that collision would still cause a vibration of both objects, whether in space on not, with vacuum only disabling it from being ""heard"" anywhere. Assuming there is no medium to carry it through space, you could for example pick up the sound via laser microphone, amiright?" +428 What is the most common colour in the universe? 4038 https://www.reddit.com/r/askscience/comments/4ytk40/what_is_the_most_common_colour_in_the_universe/ 1471761475 4ytk40 Physics 2016-08-21 9:37:55 "The most common photon in our universe are the photons from the cosmic microwave background radiation which is the afterglow from the big bang. These photons wave a wavelength of around 1 mm which our eyes cannot see. Check out Fig. 4 of this paper, + +* Lacki, Brian C. ""The end of the rainbow: what can we say about the extragalactic sub-megahertz radio sky?."" Monthly Notices of the Royal Astronomical Society 406.2 (2010): 863-880. https://arxiv.org/abs/1004.2049 + +However, if you're interested in the optical band which our eyes can actually see, then the color red (~0.7 microns) is the most common color in the universe. The local peak near this wavelength though is firmly in the infrared (near 1 micron) and is referred to as the cosmic optical background (COB or CUVOB if UV is included) radiation. Check out Fig. 5 here, + +* Pozzetti, Lucia, and Piero Madau. ""The optical extragalactic background light from resolved galaxies."" Arxiv preprint astro-ph/0011359 (2000). https://arxiv.org/pdf/astro-ph/0011359v1.pdf + +There are also the cosmic infrared (CIB), x-ray (CXB), radio (CRB) and gamma (CGB) backgrounds. These figures are looking at the aggregate background of light of the whole universe and not just nearby sources which can dominate locally. + +Edit1: Here's another couple page describing it, + +* http://www.astro.ucla.edu/~wright/CIBR/ + +* http://www.ias.u-psud.fr/irgalaxies/SpitzerPR2006/ + +It is also important to note that power distribution is weighted differently than the photon number distribution and that gives quite a bit of perspective. The CMB is much more intense than the COB, but each CMB photon carries substantially less energy than optical/infrared light. If we redrew the plots (which are already in log scale) using photon number, it'd be even more lopsided. + +Edit2: Here's a review article on the subject of CIB, but has a relatively non-technical section on the COB + +* Hauser, Michael G., and Eli Dwek. ""The cosmic infrared background: measurements and implications."" arXiv preprint astro-ph/0105539 (2001). https://arxiv.org/abs/astro-ph/0105539 + +And a neat Scientific American article on cosmic backgrounds and where they come from, + +* http://www.scientificamerican.com/article/background-noise-space/" Not the most common, [but cosmic latte is the average!](https://en.m.wikipedia.org/wiki/Cosmic_latte) +1118 How do we know what dinosaurs look like? 4033 https://www.reddit.com/r/askscience/comments/9e5lug/how_do_we_know_what_dinosaurs_look_like/ 1536425417 9e5lug Paleontology 2018-09-08 19:50:17 "Skin texture? How about COLOR? Examination of fossils has uncovered cells responsible for pigmentation! + +https://www.smithsonianmag.com/smart-news/dinosaur-was-iridescent-crow-180967841/ + +Fossils aren’t just bones. Fossils are preserved parts of all kinds, including preservation of the impression that the skin has made against whatever material fossilized. + +https://m.ebrary.net/3944/history/dinosaur_skin + +This article has a picture of some fossilized dinosaur skin impression, and also notes the different parts of creatures that have been found fossilized." "In some cases we have fossils of the soft parts of dinosaurs, including their skin. Like this [nodasaur](https://www.nationalgeographic.com/content/dam/magazine/rights-exempt/2017/06/Nodosaur/nodosaur-fossil-canadian-mine-face.ngsversion.1494561733267.adapt.1900.1.jpg) - you can see the face, the eyes, the skin, etc. + +[This hadrosaur](https://bloximages.chicago2.vip.townnews.com/nwitimes.com/content/tncms/assets/v3/editorial/e/07/e07397cd-ec54-56ca-8903-f5d615be2a3b/5306a29ca8f95.image.jpg) is another example. + +And [this tail](https://assets4.bigthink.com/system/idea_thumbnails/62071/size_1024/tail_black.jpg?1481477824)." +117 If you farted hard enough in space, could you move yourself around? 4032 http://www.reddit.com/r/askscience/comments/3569v1/if_you_farted_hard_enough_in_space_could_you_move/ 1431005849 3569v1 Physics 2015-05-07 16:37:29 "**Short answer:** Yes. Flatulence would propel an astronaut forward very slowly, but if you used the gas as fuel for a combustion reaction the astronaut could get going much faster. + +**Longer answer:** Gas diffusing will carry a small amount of momentum backwards, so it must exert a force on the person, pushing them forward. Essentially, farts are rocket fuel. So let's figure out how much and how fast a person farts, to figure out how fast an astronaut can get moving in space. + +Anyway, [this paper abstract gives us a good idea of the average volume of gas produced by a person in a day.](http://www.ncbi.nlm.nih.gov/pubmed/1648028) They give it somewhere between 476 to 1491 mL, and [another paper](http://www.ncbi.nlm.nih.gov/pubmed/9176210) gives the composition as a mixture of methane, nitrogen gas, hydrogen gas, and carbon dioxide. Let's say the average person produces 1 L of gas each day and we'll [guess that this gas mixture is about 0.5 grams/Liter, which is not entirely unreasonable given the known masses of the gasses in the mixture.](http://www.wolframalpha.com/input/?i=1+mole%2F22.4+liters+*+1+liter+*+%2810+grams%2Fmole%29) That comes out to 0.5 g of flatulence every day for a normal person. + +Now, let's guess that a fart leaves the butthole at about 1 m/s - again, not entirely unreasonable. So putting all this together, we can find that a day's worth of farts carries backwards momentum equal to + + (1 m/s)(0.5 grams) = 0.0005 kg m/s + +so for momentum to be conserved, the astronaut will now be traveling [7.7x10^-6](http://www.wolframalpha.com/input/?i=0.5+g+m%2Fs++%2F+65+kg) m/s forward, [which is only about 1000x faster than hair grows.](http://en.wikipedia.org/wiki/Orders_of_magnitude_%28speed%29) If an astronaut in space farted every day, it would take 10,000 years for him to get up to a normal highway speed. + +This is incredibly inefficient, but luckily, there's a better way. The gasses I listed above are combustible - specifically methane. Just spewing the gas backwards to get a push forward would be like putting your SUV in neutral and trying to propel it forward with a supersoaker that sprays gasoline backwards. Instead of *throwing* it backwards, you can *explode it* backwards to generate thrust, like a real rocket. After all, every 14 year old knows you can light a fart on fire, but if the astronaut did this the gas behind him would expand in all directions, not giving him much of a push. Instead, we need to harness this energy for a jetpack, so that all the exhaust goes backward. + +If we take the methane to be about 1% of our flatulence, and the energy of combustion to be 890 kJ/mole, then we find that the [chemical potential energy of the gas is about 100 million times greater than the kinetic energy backwards.](http://www.wolframalpha.com/input/?i=%280.01+Liters%29+*+%2822.4+moles%2FLiter%29++++%28890+kJ%2Fmole%29). If we had one of those fancy [gas backpacks that they put on cows](http://www.springwise.com/img/uploads/2014/05/cowbackpacks.png) to harvest the methane from their farts and a jetpack to burn it, then [this gas would be enough to get a particularly flatulent astronaut up to highway speed in a day.](http://www.wolframalpha.com/input/?i=%282*%280.01+Liters%29+*+%281%2F22.4+moles%2FLiter%29++++%28890+kJ%2Fmole%29+%2F%2865+kg%29%29^%281%2F2%29) + +(Edit: /u/throwaway_MZ3Ji8yc offers a good discussion of the practicality of such a rocket in the [comments](http://www.reddit.com/r/askscience/comments/3569v1/if_you_farted_hard_enough_in_space_could_you_move/cr1mnpp) below.) +" [deleted] +321 What are the fastest accelerating things we have ever built? 4027 https://www.reddit.com/r/askscience/comments/43dl1y/what_are_the_fastest_accelerating_things_we_have/ 1454149283 43dl1y Engineering 2016-01-30 13:21:23 Certainly it has to be particle accelerators. I couldn't tell you which one has the fastest acceleration, but from a rough calculation I think an electron linac does on the order of 10^(18)m/s^2 of proper acceleration for the electron. "I believe the OP's gif is a Sprint missile launch. From the wiki on Sprint: + +""The Sprint accelerated at 100 g, reaching a speed of Mach 10 in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6200°F (3400°C), requiring an ablative shield to dissipate the heat. It was designed for close-in defense against incoming nuclear weapons. As the last line of defense it was to intercept the reentry vehicles that had not been destroyed by the Spartan, with which it was deployed."" + +The wiki goes on to mention a predecessor named ""HIBEX"" that was even faster at 400g. They had to go that fast b/c they were intended to be last ditch efforts to stop an incoming ICBM. + +ETA: What's amazing to me is that they could do this with such primitive computers." +220 AskScience AMA: We are scientists from the team that recently discovered a malaria protein with the ability to target many different types of cancer. Ask us anything! 4024 https://www.reddit.com/r/askscience/comments/3pccyx/askscience_ama_we_are_scientists_from_the_team/ 1445255691 3pccyx Cancer Treatment AMA 2015-10-19 14:54:51 "Hello! + +I'm a newly started Danish student from Aalborg on 1. semester in Medicine with Industrial Specialization. I wish you the best of luck with your project! I have a few questions: + +1. What do you think the odds are, that this will end up as a major breakthrough? I'm curious about the odds of it working for humans, as I've heard it worked on mice. + +2. There's been tons of stuff like ""Cure for cancer found!"" in the news over the years which (obviously) haven't been true, and this has made most average people lower their expectations for anything alike. Specifically, it was easy to see all the hate and disappointment in the comment sections of the articles of your discovery, where most people believed it was a lie. Do you think anything needs to be done about this, and if yes, what? Additionally; Does the public's opinion on this even matter? + +3. I'm fascinated by the work, but I'm curious what field it's in, as I have just started on my bachelor. For my candidate, I can choose between translational medicine and biomedicine, and I'm wondering which one of these best describes your work. + +4. What does this discovery feel like for yourselves, personally? Pride, increased curiosity, happy, et cetera?" When will we see this tested in real patients? +891 Are the rocks in the asteroid belt between Mars and Jupiter the same kind of rocks you’d find on the earth? 4022 https://www.reddit.com/r/askscience/comments/7jvsin/are_the_rocks_in_the_asteroid_belt_between_mars/ 1513295249 7jvsin Astronomy 2017-12-15 2:47:29 There are different types of asteroids, made of different things. Ones that most closely resemble Earth's composition in terms of the elements that go into them are the carbonaceous asteroids, but not necessarily in the same molecular configurations you'd find on Earth. The rocks formed on Earth can be made by very different processes, through compression of sedimentary layers as an example. Stony meteorites do resemble igneous rocks like basalt, though. Other asteroids are made mostly of iron instead, and don't much resemble things you'd find on Earth's surface - perhaps further down towards or in Earth's core things are similar, though - while others still are a mixture of iron and silicates. "No, that's one of the reasons why meteorites can be identified easily, and how we discovered Martian meteorites. Asteroidal material has give through different processes than most Earth rocks. For some, chondrites, they've gone through very little processing. Existing as fused together masses of tiny grains of primitive material. Interestingly, these types of rocks have a mixture of elements in them consistent with the average of elements in rocky planets, containing a lot more iron, gold, iridium, etc. than ordinary crustal rocks on Earth. + +Asteroids do contain processed materials, but the processes are different than on Earth. As asteroids and other ""planetesimals"" accreted during the early Solar System some got large enough to hold onto enough heat to melt, and differentiate into metal cores and stony crusts. These objects were subjected to later collisions which shattered them into smaller asteroids, leading to individual metallic and stony asteroids. The stony asteroids tend to be more ""primitive"" types of silicate rock than you'd find on Earth, however. + +Most rocks in the asteroid belt are chondrites, about 3/4 of them. About a sixth of the rocks are stony asteroids, which are the closest to Earth rocks but only as distant cousins, and the rest are metallic or other varieties. + +Also, some Earth rocks undoubtedly do exist in space, and we will one day run across them as meteorites on the moon or Mars, but they are comparatively rare." +322 In 2014 Harvard infamously claimed to have discovered gravitational waves. It was false. Recently LIGO famously claimed to have discovered gravitational waves. Should we be skeptical this time around? 4020 https://www.reddit.com/r/askscience/comments/48ryx2/in_2014_harvard_infamously_claimed_to_have/ 1457011745 48ryx2 Astronomy 2016-03-03 16:29:05 "The tricky part about science is that you can never be 100% confident that a given explanation or theory is correct. At most we can say that a particular model explains all available data well (it is explanatory), which gives us confidence that it can also be used to make new predictions (it is predictive), which can then be tested. As new evidence comes in, either our confidence in the model/theory grows, or we are forced to modify or fully discard it. + +With this idea in mind, looking at the Harvard result from 2014, it would be uncharitable to call it bad science. At the time the researchers published the result, they truly believed that what they saw was real. Specifically, what they thought they saw is [neatly summarized in this diagram](http://i.imgur.com/PSfmt07.jpg). The short story is that within a minuscule fraction of a second after the big bang, the universe expanded at a breakneck pace in a process called inflation. This inflation produced massive gravitational waves that a few hundred thousand years later shaped the [Cosmic Microwave Background](https://en.wikipedia.org/wiki/Cosmic_microwave_background) (CMB) that we still observe today. By looking at the polarization of the CMB in a certain patch of the sky, the Harvard researchers thought they were able to indirectly observe the effects of gravitational waves. + +The problem with these findings, which became apparent later, is that their methodology was not very robust in accounting for an additional source of signal, namely galactic dust. Follow-up studies then determined that at least a very large component of the signal did in fact come from this pesky dust. In other words, it wasn't that the signal the Harvard folks saw wasn't real (or statistically significant), but rather that the contribution from gravity waves, if there was any, was far smaller than what they had initially thought. The media was a bit brutal in how they announced this reevaluation of the original results, but it would be unfair to say that the researchers had done anything improper. At most you can say that they should have tempered the claims a bit, allowing for the possibility of confounding signals. + +So is the LIGO result any different? Well, I would say that there are good reasons to say yes. For one, LIGO directly detected gravitational waves, not only their indirect influence. LIGO literally measured how [space expanded and contracted as a gravitational wave washed past the detectors](http://i.imgur.com/OwEl85Q.gifv). The results they measured were not just consistent among the [two detectors they used](http://i.imgur.com/zOB8m28.png), but they also [beautifully matched](http://i.imgur.com/DxYstHU.png) the expected waveform of two black holes dancing in a spiral before finally merging. Even the timing between the two detectors (situated thousands of kms apart) is consistent with gravity waves traveling at the speed of light. All in all, this really does look like as definitive a proof as we could have hoped for." "Taking a stab at clarifying: + +> ""According to the Harvard group there was a one in 2 million chance of the result being a statistical fluke."" +> +>1 in 2 million! +> +>Those claims turned out completely false. + +That's not precisely true, and it's unfair to reduce a complex piece of science such as this to that statement. From the [original BICEP2 results paper](http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.241101) ([arXiv](http://arxiv.org/abs/1403.3985)): +> ""We find an excess of B-mode power over the base lensed-ΛCDM expectation in the range 30 < ℓ < 150, inconsistent with the null hypothesis at a significance of > 5σ."" + +The key statement here is its inconsistency with the null hypothesis — i.e. that there was no detection of B-mode polarization. Both a primordial B-mode signal from inflation as well as B-modes from galactic dust emissions cause a signal that can be detected. Furthermore, the abstract tries to hammer home the point that — at that time — the data on galactic foregrounds (namely dust) was not well constrained and could potentially explain the signal seen: + +> ""However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal."" + +What has changed since that initial announcement was the BICEP/Keck team collaborated with the Planck team to use a combined data set analysis. Their [joint publication](http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.101301) ([arXiv](http://arxiv.org/abs/1502.00612)) has a detailed explanation of how the additional data provided by Planck changed the interpretation, namely that a galactic dust foreground can explain at least half of the observed signal. (And then beyond that paper, the Planck data has mostly been released for public use.) + +What I'm trying to emphasize, though, is that the BICEP/Keck team had limited information about dust foregrounds so the interpretation of the signal was wrong, but the **detection of a signal** is not. See [this figure](http://lambda.gsfc.nasa.gov/graphics/bb_detections/bb_detections_2015nov.pdf) ([source web page](http://lambda.gsfc.nasa.gov/graphics/)) from NASA which collects CMB detections and upper limits from a variety of projects — note that the BICEP/Keck team is the only experiment to make positive detection of a B-mode signal and degree angular scales. All those data points taken together do add up to a confidence of greater than 2 million to 1 that the signal is real and not just a statistical fluctuation (but we now know that the signal is partly caused by dust rather than being primordial B-modes). + +Finally, getting back around to the main point of your question, the LIGO result is trustworthy because the analysis and methodology are sound (just as I'd argue was also true for BICEP2). LIGO has an easier job of **interpreting** their results since they don't have a relatively poorly understood foreground to deal with like the BICEP/Keck team did. (I.e. LIGO uses multiple observatories to remove local environmental noise. The necessary equivalent in CMB observations would be to move across the galaxy or to another neighboring galaxy.)" +118 I know of absolute zero at -273.15°C, but is there an absolute hot? 4010 http://www.reddit.com/r/askscience/comments/3bioer/i_know_of_absolute_zero_at_27315c_but_is_there_an/ 1435591562 3bioer Physics 2015-06-29 18:26:02 "We don't know if there's a maximum temperature. + +In certain models -- string theory is one of them -- there is a maximum temperature called the *Hagedorn temperature*. This arises because the number of possible high energy states increases sufficiently fast that as you put more energy into the system, it gets spread out over more and more states in such a way that the temperature decreases less and less for a given amount of heat put in. Net result is that there's a temperature that is the upper limit of the temperatures that can be reached. + +I'll add that even in string theory, some people think the Hagedorn temperature might not be an actual limit, but more an indication that there is a phase transition (like when a liquid turns to gas), but that's even more speculative." "The Planck temperature is 1.42 x 10^32 K. + +At this temperature, the radiation emitted causes quantum gravitational effects. Lacking a unified theory of quantum gravity, our understanding of physics breaks down at or past this point." +323 Let's say I put a steel beam 1000 feet in the air above the earth, and this beam goes all the way around the world until it comes back and connects with it's original point, making a perfect circle. Assuming there is no support structure, would this steel beam levitate above the earth? 4010 https://www.reddit.com/r/askscience/comments/440dpk/lets_say_i_put_a_steel_beam_1000_feet_in_the_air/ 1454514718 440dpk Physics 2016-02-03 18:51:58 It would be an unstable system, like a ball perched on top of a saddle. You can in theory balance it perfectly, but any minuscule sideways perturbation would push the system off balance. "This same problem turns out to be one of the flaws in Larry Niven's science fiction novel *Ringworld*. + +Let's imagine the Earth is a perfect sphere (since with only 1000 ft in the air and a perfect circle in your original question, that seems to be what you're imagining). It turns out that if you put a ring of material around the Earth like that, that situation would be unstable. At the slightest perturbation pushing any spot towards or from the center of the Earth, the ring would come crashing to the Earth. + +In *Ringworld*, Niven had an ""alien megastructure,"" as I guess we're calling these things today, a giant ring that had been constructed around a star, with a radius around the size of the Earth-Sun distance. As people pointed out after the novel was published, this situation is unstable (if you push the ring up or down out of the plane of its orbit, it will bounce back, but a sideways push or pull will lead the ring to crash into the star). Niven ultimately wrote a sequel to address this, in which he writes that there are jets on the ring world to keep it in position against this gravitational instability. + +Edit: Typo fixed. +" +892 How much bandwidth does the spinal cord have? 4008 https://www.reddit.com/r/askscience/comments/7l56sb/how_much_bandwidth_does_the_spinal_cord_have/ 1513810889 7l56sb Neuroscience 2017-12-21 2:01:29 "This is an interesting question, if not near impossible to answer properly. However I figured I'd give it a go even if I do have to make some gross assumptions. + +First, we need to know how many neurones are in the spinal cord. That's very hard to know, unless we make some assumptions. + +The spinal cord diameter is variable, from the small ~7mm in the thoracic area to the ~13mm in the cervical and lumbar intumescentia (enlargements), let's average that out to 10.5mm in diameter. It is also not a perfect circle, but let's ignore that for now. + +Now the diameter of an axon is similarly difficult, they range from one micrometer up to around 50 micrometres, with far more in the <5 micrometre range. However a study found that the average diameter of cortical neurons was around 1 micrometre [D. Liewald et al 2014](https://link.springer.com/article/10.1007%2Fs00422-014-0626-2#Sec6) plus 0.09 micrometres for the myelin sheath, so let's say the average diameter of a neuron is 1.09 micrometres. + +Okay, so let's simplistically take the area of the spinal cord (Pi * 0.0105^2) and the same with the neuronal diameter and we get: + +( 7.06x10^-4 m^2 / 3.73x10^-12 m^2) = ~200,000,000 neurons in the spinal cord. + +Now, given that there are around ~86 billion neurons and glia in the body as a whole, with around ~16 billion of those in the cortex (leaving 60 billion behind) I would wager that my number is an underestimate, but let's roll with it. + +Okay, so we know how many we have, so how fast can they fire? Neurones have two types of refractory periods, that is absolute and relative. During the absolute refractory period the arrival of a second action potential to their dendrites will do absolutely nothing, it **cannot** fire again. During the relative refractory period, a strong enough action potential *could* make it fire, but it's hard. + +So let's take the absolute refractory period for an upper limit, which is around 1-2ms [Physiology Web](http://www.physiologyweb.com/lecture_notes/neuronal_action_potential/neuronal_action_potential_refractory_periods.html) at the average of 1.5ms. This varies with neuron type but let's just roll with it. + +So we have ~200,000,000 neurones firing at maximum rate of 1 fire per 0.0015 seconds. That is ~133,000,000,000 signals per second. + +Let's assume that we can model neuronal firing as ""on"" or ""off"", just like binary. That means this model spinal cord can transmit 133 billion bits per second, and a gigabit = 1 billion bits, which gives our spinal cord a maximum data throughput of 133 gigabits per second. + +Divide that by 8 to get it in GB, and that's **16.625 GB of data per second** capable of being transferred along the spinal cord. Or about a 4K movie every two seconds. + +**DISCLAIMER**: This is all obviously full of assumption and guessing, think of it as Fermi estimation but for the spinal cord. It's not meant to be accurate or even close to being accurate, just a general guess and a thought experiment, more than anything. + +Source: Neuroscience student. +" "i'm about to be that guy, and i apologize in advance. the term you are looking for is throughput, not bandwidth. bandwidth refers to the range of frequencies which information is being sent over while throughput refers to the amount of data that can be transferred in a given period of time. this is a common misconception stemming from a while back when internet providers started using a larger bandwidth than was the standard at the time, resulting in a higher throughput. they then marketed a larger bandwidth as meaning faster internet and people started making the assumption that throughput and bandwidth are the same, when in reality using a larger bandwidth plays a very small role in our high speed internet today. despite this, internet providers continued to use this term in marketing for years to come. + +that being said none of this really matters that much and hopefully someone answers your question because its really interesting. " +685 AskScience AMA Series: I am Seth Shostak, senior astronomer at the SETI institute. Ask Me Anything! 4004 https://www.reddit.com/r/askscience/comments/5m68zo/askscience_ama_series_i_am_seth_shostak_senior/ 1483621251 5m68zo Astronomy 2017-01-05 16:00:51 Just a friendly reminder that our guest will begin answering questions at 12pm Eastern Time. Please do not answer questions for the guests. After the time of their AMA, you are free to answer or follow-up on questions. If you have questions on comment policy, please check our [rules wiki](https://www.reddit.com/r/askscience/wiki/rules). Let's say SETI discovers Alien life of any kind. Is your organization obligated to share this information with the US Government or Military first? Do they get to decide when/ how much the public gets to know or does SETI get to share what they find with the world directly? +893 How do blackouts work? Was the memory never recorded, never saved or deleted while sleeping? 4002 https://www.reddit.com/r/askscience/comments/75c9dp/how_do_blackouts_work_was_the_memory_never/ 1507583728 75c9dp Human Body 2017-10-10 0:15:28 "This thread has attracted a large number of anecdotes, questions seeking medical advice, and low quality explanations, all of which are against our rules and have been removed. + +Though many of us have had experiences with blackouts, that does not make us all experts on the science of memory. Please do not post your personal stories, even though framed as 'antecdata'. Before posting a top-level comment, ask yourself if you can provide scientific sources for assertions in your post if asked and adequately respond to follow up questions. If not, your comment is likely inappropriate for AskScience. +" "There are three stages to memory: encoding, storage, and retrieval. During a blackout from drinking, the prefrontal cortex is inhibited, which is responsible for a large portion of encoding events into short-term memory. Information must be encoded into short-term memory before it is stored into long-term memory. Therefore, because this information can’t be properly encoded and stored into short-term memory, the memory is unable to be processed into long-term memory via the hippocampus. + +Think of a livestream that’s not being saved. + +So basically the information is never recorded." +1096 How do lava lamps work? 4002 https://www.reddit.com/r/askscience/comments/93hv7r/how_do_lava_lamps_work/ 1533067273 93hv7r Chemistry 2018-07-31 23:01:13 "A lava lamp uses a heater at the bottom of the lamp - this means that the bottom of the vessel is warm, but as you move away from the heater (towards the top of the lamp) it cools down. + +The 'lava' inside the lamp is a certain type of wax/oil that is chosen for the way it interacts with water - when cold it is heavier than the water used in the lamp and sits at the bottom, then when it warms up it expands, which makes it slightly less dense than the water and lets it start to float upwards. As the lava reaches the higher levels of the lamp it then starts to cool down until it becomes more dense than the water, sinking back down again. + +The lava moving is this cycle constantly repeating - blobs of lava heating up enough to rise to the top, then cooling down enough to fall to the bottom where they will be warmed again and rise up... Because the lava is liquid and doesn't heat uniformly, it then takes on the organic appearance with different blobs all being at different stages of this process, combining and splitting as they heat and cool slightly differently on the top and bottom." "Oil and wax that have similar densities, but different thermal expansion coefficients. + +Wax is heated by a hot bulb in the bottom, causing it to expand, reducing it's density. + +The wax expands faster than the oil, so it eventually becomes less dense than the oil and floats. + +The lamp continually loses heat to the atmosphere though (they're warm or even hot to the touch), so the top is always cooler than the bottom. At the top, the wax cools down enough that it's denser than the oil, and it sinks again to repeat the process. + +Because they're both fluids, this happens in blobs." +1097 Is washing your hands with warm water really better than with cold water? 4000 https://www.reddit.com/r/askscience/comments/9bn30e/is_washing_your_hands_with_warm_water_really/ 1535659806 9bn30e 2018-08-30 23:10:06 "In a [2005 report in the Journal of Occupational and Environmental Medicine](https://www.ncbi.nlm.nih.gov/pubmed/15824636?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum), scientists with the Joint Bank Group/Fund Health Services Department pointed out that in studies in which subjects had their hands contaminated, and then were instructed to wash and rinse with soap for 25 seconds using water with temperatures ranging from 40 degrees Fahrenheit to 120 degrees, the various temperatures had “no effect on transient or resident bacterial reduction.” + +They found no evidence that hot water had any benefit, and noted that it might increase the “irritant capacity” of some soaps, causing contact dermatitis. “Temperature of water used for hand washing should not be guided by antibacterial effects but comfort,” they wrote, “which is in the tepid to warm temperature range. The usage of tepid water instead of hot water also has economic benefits. + +TL;DR: Hot water for hand washing has not been proved to remove germs better than cold water." Warmer water is better at breaking-down the dirt or grease on your skin, but isn’t shown to have any effect on the bacteria. The quality of the soap and the hand-washing technique are themselves the biggest contributing factors. +429 Can modern chemistry produce gold? 3997 https://www.reddit.com/r/askscience/comments/4hgnc7/can_modern_chemistry_produce_gold/ 1462190528 4hgnc7 Chemistry 2016-05-02 15:02:08 "We can, it's just highly, highly impractical. Creating diamond is relatively straightforward, we just have to convert carbon from one form to another. For that all you have to do is to [take cheap graphite, heat it up under high pressures](http://i.imgur.com/jHQlF1c.jpg), and voilà, you get [diamond.](http://i.imgur.com/XV8GIUz.jpg) + +Creating gold on the other hand is a different beast altogether since now we have to convert one element into another. Now techniques do exist that allow us to achieve such a transformation using nuclear reactors or particle accelerators, but they are neither easy nor cheap. Probably the most ""practical"" method reported to date was the work of Seaborg and coworkers ([paper](http://journals.aps.org/prc/abstract/10.1103/PhysRevC.23.1044)). Their approach was to take sheets of bismuth, bombard them with high energy ions, and see what came out. Among the mess that resulted, they were able to detect trace amounts of various unstable gold isotopes from the radioactivity they gave off. The researchers also suspected that some of the stable gold isotope (Au-197) was also there, but they couldn't measure it directly. + +Even though Seaborg was successful in creating gold, he didn't exactly stumble on a practical industrial process. When asked about the practicality of his work, Seaborg said that given the cost of the experiment, creating a gram of gold would have cost on the order of a quadrillion dollars (in 1980 dollars too!). Needless to say, it still makes far more sense for us just to use the gold that supernovas produced for us than to try to repeat the process ourselves." IN the 90's I spent a few years routinely making tiny amounts of gold from mercury using neutron activation. One isotope of mercury (Hg-196, 0.15% abundance) can absorb a neutron to become the radioisotope Hg-197 which decays through electron capture into the stable gold isotope Au-197. The Hg-197 decays with a half-life of 2.67 days and gives off a 77.3 keV gamma ray. By counting the number of gamma rays I could determine the amount of mercury in the original sample. Over the full course of the work I made less than 0.1 femtogram (1E-16 gram) of gold. +1378 "AskScience AMA Series: I'm Guy Leschziner, neurologist, sleep physician, and author of ""The Nocturnal Brain: Nightmares, Neuroscience and the Secret World of Sleep"". AMA!" 3997 https://www.reddit.com/r/askscience/comments/cw2tvw/askscience_ama_series_im_guy_leschziner/ 1566903657 cw2tvw 2019-08-27 14:00:57 The AMA will begin at 11am ET (15 UTC), please do not answer questions for the guests till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Keep questions and interactions professional and remember, asking for medical advice is not allowed. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). "I have always had bad sleep — taking hours to fall asleep, waking up and staying up in the middle of the night, being exhausted during the day but unable to nap or sleep later. I don’t take caffeine and am very aware of proper sleep hygiene. + +My biggest question is what exactly is happening when I am super tired all day, so excited to go to sleep, then I get in bed and start to feel myself relaxing into sleep only to end up being awake for another 3 hours? Should I be going to bed very early (typically between 8:45-9:15)? Or something else? It is something that happens once I am in bed, not sure that it’s routine related, and it really sucks." +1261 If the refractive index of something is high enough could light just stop moving? 3989 https://www.reddit.com/r/askscience/comments/atu40i/if_the_refractive_index_of_something_is_high/ 1550917575 atu40i Physics 2019-02-23 13:26:15 "Kind of. Check out the expreriments by Mikhail Lukin -- he was the first one to ""stop"" light. Not really stop, but get it to several meters per second. However, he did it by employing certain clever tricks, not just by using some material with high refractive index as such -- see a nice explanation by [/u/RobusEtCeleritas](https://www.reddit.com/user/RobusEtCeleritas) above." "If you define the “speed” of light to be its **group** speed (as opposed to its phase speed or signal speed), then yes. + +Although in practice, indices of refraction only vary so much. A much better way to decrease the group velocity of light is to exploit rapid *changes* in the index of refraction. + +The group velocity (dω/dk) can be written as + +v*_g_* = c/(n + ω dn/dω). + +So to make the group speed very small (“slow light”) or approximately zero (“stopped light”), you can either make n very large, or you can make dn/dω very large. Like I said above, it’s hard to find a medium with a high enough n to reach very slow velocities (the slowest reaches experimentally are less than 10 m/s). However you can find situations where dn/dω is huge, for example near some kind of resonant behavior in a cold atomic gas. There are now ways to produce slow light in room temperature solid-state media, photonic waveguides, etc. as well." +686 How many galaxies/stars do we visually lose every year due to them accelerating and passing through the cosmological event horizon? 3988 https://www.reddit.com/r/askscience/comments/5xxetp/how_many_galaxiesstars_do_we_visually_lose_every/ 1488849599 5xxetp Physics 2017-03-07 4:19:59 "There are two relevant horizons for this discussion. The Cosmological Event Horizon, and the Cosmic Microwave Backgound. + +The Cosmological Event Horizon is a distance away from us beyond which if a photon is emitted right now it will never reach us due to space expanding between it and us faster than it is traveling towards us. Space is expanding everywhere, so the amount of expansion between us and another object is determined by how far away it is. For something that is close the expansion will be unnoticable, for something far enough away, it will be larger than the speed of light. You could also imagine a Cosmic Rock Horizon where if someone is beyond that distance from you, and they throw a rock at you it will never reach you because of the expansion of space between you and the rock - this is very far away, but much much closer than the Cosmological Event Horizon. + +The Cosmic Microwave Background is the edge of the observable/visible universe. Remember that as you observe galaxies further and further away, you are observing the universe when it was much, much younger. At some point soon after the big bang the universe switched from being an extremely hot and dense non-transparent particle-soup to mostly-empty space that allows light to travel large distances without hitting anything. The CMB is the light that was emitted by this particle soup just as the universe became transparent. It is the furthest thing away in both space and time that is possible to see. And we can see it in pretty amazing detail! https://en.wikipedia.org/wiki/Cosmic_microwave_background + +No object in the universe has ever redshifted out of view due to being further away than the Cosmological Event Horizon. The first thing that this will happen to is the CMB itself, followed by the galaxies nearest it. Right now the number of galaxies in the visible universe is expanding as the CMB gets further away and we watch new galaxies form (they formed billions of years ago, but the light of their formation has not yet reached us.) + +So let us think about the oldest galaxy we have ever observed with the Hubble telescope. Is there intelligent life in that galaxy? Did they just broadcast a signal this morning trying to communicate with someone outside their galaxy? No matter how powerful a receiver we build we would never hear it, because it is beyond the Cosmological Event Horizon. Space is expanding between us and that galaxy faster than their broadcast is traveling toward us. The fact that this galaxy is outisde of the Cosmological Event Horizon has nothing to do with whether or not we can see it. but it is why the signal will never reach us. + +Its worse than that, the signal is getting further away." We don't visually lose them. The light that they emit now will never reach us, but the light they emitted before will take longer and longer to reach us, so they'll just gradually get dimmer and more redshifted, but never completely disappear. +430 In animals like octopuses and cuttlefish that die shortly after mating, what is it that kills them? 3987 https://www.reddit.com/r/askscience/comments/4rnl5i/in_animals_like_octopuses_and_cuttlefish_that_die/ 1467881814 4rnl5i Biology 2016-07-07 11:56:54 "If you have access to it, check out ""Hormonal Inhibition of Feeding and Death in Octopus: Control by Optic Gland Secretion"" by Jerome Wodinsky in Science. + +It's not a huge topic of research, but it's hypothesised that maturity in cephalopods is controlled by hormonal responses to lengthening days. Their optic glands release a gonadotrophin which switches their metabolism from investing energy in growth and maintainance (somatic growth) to one where everything is dumped into the gonads (reproductive growth). I guess this change is a one way process and once the eggs have been laid there is no means to revert back again. Wodinsky removed the optic glands from a bunch of female octopi (octopodes?!) post-spawning, and they began feeding again and lived a further 6-9 months. Interestingly, *Nautilus*, which are a pretty basal group that branched from the rest of the Cephalopoda in the late-Cambrian, lack optic glands, have a completely different reproductive strategy, and don't die after laying their eggs. + +The implications of this for spawning in deepwater octopods are really interesting. This is just speculation, but might be the case that things like the giant squid can grow to such sizes because, due to their low exposure to light in deep waters, they aren't limited to a single spawning event." "The trait you're looking for is called semelparity. A classic example is a marsupial mouse, which basically fucks its way into the grave. As it enters the mating season it starts producing a huge amount of the stress hormones adrenaline (epinephrine) and cortisol. These make fat stores more available for energy, reduce hunger, reduce pain, reduce fatigue, and kill the immune system in order to maximise the number of times it can mate in this one season. + +It will continue to have sex without eating, barely sleeping, until it is ridden with diseases (fur hanging off etc.), has no fat remaining and has been digesting its muscles for energy, and is completely exhausted. " +1379 Why doesn't the crust of the Earth melt? 3987 https://www.reddit.com/r/askscience/comments/bjk5mb/why_doesnt_the_crust_of_the_earth_melt/ 1556733008 bjk5mb Earth Sciences 2019-05-01 20:50:08 "The planet is not filled with magma. The mantle, the layer beneath the crust, is a solid that behaves like an incredibly viscous fluid on long time scales (i.e. a [rheid](https://en.wikipedia.org/wiki/Rheid)). There are isolated spots in the crust and very upper mantle that have significant pockets of melt (e.g. [magma chambers](https://en.wikipedia.org/wiki/Magma_chamber)) and other areas that may have a few % melt coating grain boundaries (more on why in a moment), but the first (and only layer) that is entirely liquid is the [outer core](https://en.wikipedia.org/wiki/Earth%27s_outer_core), which is [~2891 kilometers down](https://en.wikipedia.org/wiki/Core%E2%80%93mantle_boundary). + +Now, as a general rule, the [temperature increases](https://en.wikipedia.org/wiki/Geothermal_gradient) as you go deeper into the earth, but the pressure also increases (as a function of the increasing overburden with depth). The [melting point](https://en.wikipedia.org/wiki/Melting_point) of most materials increases as a function of pressure, so if you track the solidus temperature (i.e. the temperature at which a material crystallizes if cooling below it or melts if heating above it) with depth (i.e. pressure) and the temperature with depth, in most places the temperature is below the solidus temperature (i.e. the material is solid). It's only in very specific places where the temperature is elevated, pressure is lower (usually through rapid motion towards the surface), or the solidus temperature is reduced (usually through the addition of water) is it possible for material to melt, e.g. [this diagram](http://www.ei.lehigh.edu/learners/tectonics/heatflow/heat_depth.png)." "I use the following model: + +Imagine a pot of melted chocolate sitting on a stove over very low heat. Now let’s cross section that. + +At the very bottom, nearest the burner, the chocolate is totally melted. That’s the nickel iron liquid outer core (the pan/burner is the solid core itself, which is radioactive and produces the heat). + +As you move away from the heat source, the chocolate gets firmer and firmer because it’s further from the heat source. So in between it’s sort of like peanut butter consistency. Finally, at the very top, there’s a skin of solid chocolate. It’s solid because it is dissipating heat faster than it’s taking it on because of its distance from the heat source, the surface area, etc. + +Now imagine that whole thing as a sphere instead of in a pot. + +We live on the skin." +119 How does the cell on the tip of my nose know to perform all the functions of a cell on the tip of my nose? How does it know that it isn't a cell on the side of my nose (or my liver, brain, etc.) 3985 http://www.reddit.com/r/askscience/comments/36hagn/how_does_the_cell_on_the_tip_of_my_nose_know_to/ 1432035324 36hagn Biology 2015-05-19 14:35:24 "Finally my degree (Molecular Genetics) can be useful! + +It's all about protein gradients. It's part of why life is mostly symmetrical or radial. You have a point of origin, let's say a shoulder area, producing a particular protein during development. As the cells near it replicate to form an arm, the protein made at the origin spreads into them. The further the cells are from the origin, the less protein they have. Eventually, the cells are far enough away that the lack of that protein signals that the new cells being formed should be hand cells. Those hand cells then function as a new point of origin for a different protein radiating outward, which when present on its own forms finger cells and when mixed with the original shoulder protein forms wrist cells. At about a 50/50 mix of hand/shoulder proteins, elbow cells form. + +This is a very simplified explanation, as the truth involves the interaction of countless protein gradients and combinations from tons of origin points, but it's the general way that your body forms and differentiates. + +So the cells on the tip of your nose are far enough from the point where your nose meets your face and have little enough of one or, more likely, five thousand nose proteins that they know they should be tip of nose cells as opposed to anything else. They're obviously not getting ""please become feet"" proteins because the origin cells for those are much too far away. + +Hope that helps. + +[Edit]: Thanks for the gold! And thank all of you for such a friendly response. I'm glad you guys found my explanation so interesting. + +If you haven't looked yet, check out some of the wall-of-text comments below. Other users have added a ton of great information to this conversation. Specifically in regards to extracellular matrices, asymmetric cell division, and protein sinks. " "After development, which a lot of the really good answers are focused on, your cells know to *stay* the correct type of cell by modifying their genomes to only express the right subset of genes in the right dosage at the right time. This is possible because the genome is more than just its constituent DNA - it's wrapped up in proteins called histones, which can be chemically modified to control which DNA can be accessed and when. Your DNA itself can also be modified - methylation of certain sequences of DNA (CpG dinucleotides most prominently) is known to suppress gene expression. + +So it turns out the way your chromatin (the DNA + histones) is wrapped up and 3-dimensionally organized dictates which genes are expressed when and in what cell types. + +An important point to add is that epigenetics/epigenomics and chromatin biology are VERY active fields of study. Beyond what I've stated here, there's not a whole lot accepted as absolute fact; for example, how the histones are modified (by what proteins, under what conditions, etc) and why that serves to open up DNA is still under investigation. As is why certain cells are more or less amenable to being ""reprogrammed"" as different cell types, or how it even happens. Every answer in biology generates 3 more questions!" +564 "What is the derivative of ""f(x) = x!"" ?" 3980 https://www.reddit.com/r/askscience/comments/5hwam8/what_is_the_derivative_of_fx_x/ 1481544908 5hwam8 Mathematics 2016-12-12 15:15:08 "The factorial function only strictly works for natural numbers ({0, 1, 2, ... }). What you see plotted there is actually a way to extend the factorial function to real or even complex numbers (although it's singular at negative integers). It's called the [gamma function](https://en.wikipedia.org/wiki/Gamma_function). + +You can take the derivative of the gamma function, and [here is is](http://www.wolframalpha.com/input/?i=derivative+of+gamma+function)." Plenty of functions aren't differentiable. Absolute value functions, factorial, and anything with a jump are a few examples that you run into in basic calculus courses. The derivative is just the slope at a certain point, so anything that has a point with undefined slope in not a differentiable function. +120 "Could you stand on a gas planet or would you ""fall"" to the center?" 3978 http://www.reddit.com/r/askscience/comments/3dgt1f/could_you_stand_on_a_gas_planet_or_would_you_fall/ 1437018840 3dgt1f Planetary Sci. 2015-07-16 6:54:00 "Repost of my answer from when [this question](https://www.reddit.com/r/askscience/comments/2h3tf7/do_gas_giants_have_a_surface/) was asked before: + +For the interior of Jupiter, let's imagine taking a descent from cloud-tops down to the core based on our best guesses of what lies below. + +You start falling through the high, white ammonia clouds starting at 0.5 atmospheres, where the Sun is still visible. It's very cold here, -150 C (-240 F). Your rate of descent is roughly 2.5x that of Earth, since gravity is much stronger on Jupiter. + +You emerge out the bottom of the cloud deck somewhere near 1 atmosphere. It's still somewhat bright, with sunlight filtering through the ammonia clouds much like an overcast day on Earth. Below, you see the second cloud-deck made of roiling brown ammonium hydrosulphide, starting about 2 atmospheres. + +As you fall through the bottom of this second cloud deck, it's now quite dark, but warming up as the pressure increases. Beneath you are white water clouds forming towering thunderstorms, with the darkness punctuated by bright flashes of lightning starting somewhere around 5 atmospheres. As you pass through this third and final cloud-deck it's now finally warmed up to room temperature, if only the pressure weren't starting to crush you. + +Emerging out the bottom, the pressure is now intense, and it's starting to get quite warm, and there's nothing but the dark abyss of ever-denser hydrogen gas beneath you. You fall through this abyss for a very, very long time. + +You eventually start to notice that the atmosphere has become thick enough that you can swim through it. It's not quite liquid, not quite gas, but a ""supercritical fluid"" that shares properties of each. Your body would naturally stop falling and settle out somewhere at this level, where your density and the atmosphere's density are equal. However, you've brought your ""heavy boots"" and continue your descent. + +After a very, very long time of falling through ever greater pressure and heat, there's no longer complete darkness. The atmosphere is now warm enough that it begins to glow - red-hot at first, then yellow-hot, and finally white-hot. + +You're now 30% of the way down, and have just hit the metallic region at 2 million atmospheres of pressure. Still glowing white-hot, hydrogen has become so dense as to become a liquid metal. It roils and convects, generating strong magnetic fields in the process. + +Most materials passing through this deep, deep ocean of liquid metallic hydrogen would instantly dissolve, but thankfully you've brought your unobtainium spacesuit...which is good, because it's now 10,000 C (18,000 F). Falling ever deeper through this hot glowing sea of liquid metal, you reflect that a mai tai would really hit the spot right about now. + +After a very, very, very long time falling through this liquid metal ocean, you're now 80% of the way down...when suddenly your boots hit a solid ""surface"", insomuch as you can call it a surface. Beneath you is a core weighing in at 25 Earth-masses, made of rock and exotic ices that can only exist under the crushing pressure of 25 million atmospheres. + +You check your cell phone to tell you friends about your voyage...but sadly, it melted in the metallic ocean - and besides, they only have 3G down here. + +**TL;DR**: You would stop falling about 10% of the way down, where your density matches the density of the surrounding hydrogen ""supercritical fluid""." "There actually was a man made probe that has ""fallen"" into Jupiter as a part of the Galileo spacecraft, look here - https://en.wikipedia.org/wiki/Galileo_Probe + +From the main Jupiter article on wikipedia: +A 340-kilogram titanium atmospheric probe was released from the spacecraft in July 1995, entering Jupiter's atmosphere on December 7.[28] It parachuted through 150 km (93 mi) of the atmosphere at speed of about 2,575 km/h (1600 mph)[28] and collected data for 57.6 minutes before it was crushed by the pressure (about 23 times Earth normal, at a temperature of 153 °C).[104] It would have melted thereafter, and possibly vaporized. The Galileo orbiter itself experienced a more rapid version of the same fate when it was deliberately steered into the planet on September 21, 2003, at a speed of over 50 km/s, to avoid any possibility of it crashing into and possibly contaminating Europa—a moon which has been hypothesized to have the possibility of harboring life." +565 (Physics) If a marble and a bowling ball were placed in a space where there was no other gravity acting on them, or any forces at all, would the marble orbit the bowling ball? 3970 https://www.reddit.com/r/askscience/comments/55y283/physics_if_a_marble_and_a_bowling_ball_were/ 1475646207 55y283 Physics 2016-10-05 8:43:27 "That depends on the initial speed of the marble with respect to the bowling ball. If they start out stationary with respect to eachother, the marble will simply fall towards the bowling ball (and vice versa). In order for the marble to enter orbit, it needs to have sufficient sideways velocity (where ""sideways"" is defined as perpendicular to the line connecting the two objects)." "Assuming they were just floating there: no. The marble and the bowling ball would just gravitate towards one another, the marble covering the majority of the distance. + +Now if a marble were to drift past the bowling ball at just the right speed and distance, then yes, the marble certainly could begin to orbit the bowling ball." +894 On Earth, we have time zones. How is time determined in space? 3970 https://www.reddit.com/r/askscience/comments/7auwzt/on_earth_we_have_time_zones_how_is_time/ 1509847082 7auwzt Astronomy 2017-11-05 4:58:02 "The short answer is, it isn't. Where we have humans in space they typically use UTC, and a 24 hour clock for human comfort. + +What we do when we eventually leave earth orbit is yet to be determined, and will likely change many times." Sort of relevant. I lived at the South Pole where all time zones converge and there is one day and one night each year. Time in the clock and calendar sense has no meaning there. We chose to use New Zealand time just because that's what McMurdo uses to coordinate flights to Pole in the summer. +324 Our Sun is unusually metal-rich for a star of its age and type. -- What does this mean? 3965 https://www.reddit.com/r/askscience/comments/4efyu8/our_sun_is_unusually_metalrich_for_a_star_of_its/ 1460465959 4efyu8 Astronomy 2016-04-12 15:59:19 Metals come from supernovas, so the presence of metals in stars means that the star was formed from the nebula of a previous star that died. The more metal, the more generations have come and gone before it. So when they say it's unusually metal rich, they could be saying that our galaxy went through many quick successive generations of large, short-lived stars before our star was born. "I had a poke around the literature to see whether it's really true that solar metallicity is unusually high. The answer is that, yes, it is significantly higher than the average, but it has plenty of company and isn't an outlier. + +[This plot](http://imgur.com/THF6zm7) is a histogram of the metallicities of 14,000 F and G dwarf stars in our neighbourhood. The sun's [ME/H] is, by definition, 0; from this plot it appears the mean for the sample is about 72% of solar metallicity. However, as you can see there's a broad distribution. We appear to be in the top quartile of that distribution, so we have plenty of company. + +According to the source you cited, scientists ""aren’t sure why. It could be that the Sun formed in a part of the Galaxy that had an abundance of metals, and then migrated to its present position."" Well of course it did. It formed from a molecular cloud that was a little richer in metals than others found in the galaxy. That's also true of lots of other stars who have since mixed and scattered throughout the galaxy. + +Source: Nordström et al, 2004 - The Geneva-Copenhagen survey of the Solar neighbourhood" +687 Why do people with Alzheimer's not forget how to talk? 3965 https://www.reddit.com/r/askscience/comments/5lhno8/why_do_people_with_alzheimers_not_forget_how_to/ 1483310347 5lhno8 Neuroscience 2017-01-02 1:39:07 This post is being locked due to the number of anecdotes. With full recognition that Alzheimer's is a disease that has directly affected millions of families, /r/AskScience is not the right place to post personal experiences. While we appreciate people's desires to share these experiences, a single presentation of an illness is not representative of all its symptoms, their frequency of occurrence, or underlying mechanisms at play. Thank you for your understanding. [deleted] +566 Since gravitational waves are real, does that mean all gravitational orbits are decaying? 3960 https://www.reddit.com/r/askscience/comments/551v2x/since_gravitational_waves_are_real_does_that_mean/ 1475151303 551v2x Physics 2016-09-29 15:15:03 "Yes. Even for a simple binary system like the Earth-Sun system, gravitational waves are constantly being produced. The reason is that such orbits cause a change in the so-called [quadrupole moment](https://en.wikipedia.org/wiki/Quadrupole) of the total mass distribution of the system. This change is the key requirement for shooting off gravitational waves. And yes, you are right, if the system is losing energy in this way, then the [orbits will decay over time](https://en.wikipedia.org/wiki/Gravitational_wave#Binaries). In fact, this exact effect provided one of the earliest bits of indirect evidence for gravitational waves. When astronomers looked at a certain [pulsar-neutron star binary](https://en.wikipedia.org/wiki/Hulse%E2%80%93Taylor_binary), they saw that the period of the pulses was changing in a systematic way. The best explanation for this change is that the binary was experiencing orbital decay by losing energy through gravitational waves. + +Now, it's worth pointing out that in most cases this effect is very, *very* weak. For example the Sun-Earth system loses about 200W due to gravitational waves. This is roughly the power of a couple of old incandescent light bulbs, which as you might guess is nothing on an astronomical scale. This energy loss causes the orbit to shrink by a measly 1\*10^(-15)m per day, or about the size of an atomic nucleus. If you waited for the Earth and Sun to [spiral inwards through this process](http://i.imgur.com/mwSBZru.gifv) and crash together, you would have to wait more than 10^(13) times the age of the current universe! " "Its correct to say that gravitational waves cause orbital configurations to lose energy, but that doesn't necessarily mean all orbits are decaying, as other factors can impact orbits. + +For example, tidal forces are currently causing the Moon to slow down the Earths rotation. This angular momentum lost by the Earth is causing the moon to gain linear momentum. This effect is much greater than energy loss due to gravitational waves, which is why the Moon is slowly moving farther away from the Earth." +221 Is it possible to have a planet at just the right size to have a solid surface, with a molten core which keeps the temperature at the surface suitable for life with no sun? 3949 https://www.reddit.com/r/askscience/comments/3wd2ri/is_it_possible_to_have_a_planet_at_just_the_right/ 1449832407 3wd2ri Planetary Sci. 2015-12-11 14:13:27 "This is a difficult question to answer because we have very few planets to observe. We have observed thousands of exoplanets, but most are far enough away that it's difficult to ascertain detailed data, and we only know of a handful of rogue planets (planets outside solar systems). + +In short, I'll say that yes, it's possible. There are a few possibilities as to how a rogue planet could generate enough heat for the surface to be habitable. I think the most likely option would be a system of two bodies (planet-planet or planet-moon) whereby [tidal heating](https://en.wikipedia.org/wiki/Tidal_heating) warms the secondary. (Tidal heating is essentially heating due to deformation of the planet from tides. It's similar to how a metal coat hanger gets hot when you bend it, except on a much larger scale.) + +Another possibility is [radioactive decay](https://en.wikipedia.org/wiki/Geothermal_energy). This is where a lot of Earth's heat comes from. I'm not knowledgeable enough to say as to how viable/likely this is, or whether or not there are other side effects from a planet with strong radioactive decay. + +A third possibility is that the planet is [sub-brown dwarf](https://en.wikipedia.org/wiki/Brown_dwarf#Low-mass_brown_dwarfs_vs._high-mass_planets)-sized. In this case, the planet would be gaseous, so it doesn't quite qualify, but a very high mass gas giant/low mass brown dwarf would be capable of sustaining life-giving temperature. Of course, without a solid surface, it's not known if life is possible or what it would look like, but scientists and sci-fi writers have speculated about life on a gas giant. + +Edit: Paper in the Astrophysics Journal proposing exactly this: http://iopscience.iop.org/article/10.1088/2041-8205/735/2/L27/meta + +The author proposes that a thick ice layer would insulate the planet enough to retain it's internal heat. Other researchers have suggested that either ice or a dense atmosphere would provide adequate insulation." Some have posited that [Europa might harbor life in warm oceans, covered by ice](http://www.space.com/26905-jupiter-moon-europa-alien-life.html). No sunlight would pass through the ice on this distant moon but there may be some form of geological activity that gives in liquid oceans. +1380 When Archaeologists discover remains preserved in ice, what types of biohazard precautions are utilized? 3947 https://www.reddit.com/r/askscience/comments/clbjl1/when_archaeologists_discover_remains_preserved_in/ 1564788142 clbjl1 2019-08-03 2:22:22 Well, none, really, apart from the care made to preserve the specimen. By the time any frozen remains are thawed enough to be discovered, the cat's already out of the bag, so to speak. Ancient pathogens are a concern, especially as the permafrost continues to thaw. Here's an article about an [anthrax outbreak](https://www.scientificamerican.com/article/as-earth-warms-the-diseases-that-may-lie-within-permafrost-become-a-bigger-worry) a couple of years ago, with a strain that had been frozen for almost 80 years. And here's one about some [42,000-year-old frozen nematodes](https://www.livescience.com/63187-siberian-permafrost-worms-revive.html) that were recently revived. Bacteria, fungi, and viruses are all locked away in the permafrost, glaciers, and even lake ice, and many could be pathogenic when they wake up. "Hello! + +I am currently an archaeology student. (Just FYI I've never encountered remains preserved in ice or know anyone that has so this is just what I've learnt). + +Everytime I've excavated, we are required to have up to date vaccines which are relevant to the area of the world we will be digging in - if you don't you're not allowed to go. + +Digs are also required to have safety precautions which every person must read and usually sign in my experience - so if there was any possibility of encountering frozen remains, the safety precautions should detail how people are meant to handle them. + +Since we'd want to conserve the remains until getting them to a lab, what would most likely happen is the remains would be block lifted so that they remain in the ice, and then placed in a cooling container or some sorts and transported to the lab asap. My conservation lecturer taught me that vulnerable remains are most likely never completely excavated on site - so frozen remains would be thawed out in a lab and eventually freeze dried or put through the process of tanning (basically turning into leather) or smth similar. Usually during these processes some sort of disinfectant or smth would be added to stabilise the remains. The thing with archaeology is that every discovery is very different so each situation has to be handled differently. + +I don't have much more info, sorry!" +688 When there is an eclipse, why does the earth not become cold for that period? 3940 https://www.reddit.com/r/askscience/comments/5zq6ni/when_there_is_an_eclipse_why_does_the_earth_not/ 1489666118 5zq6ni Earth Sciences 2017-03-16 15:08:38 "I think you have a bad idea of what an eclipse looks like. The shadow of the moon only covers a small portion of the earth. That's why you can't see an eclipse from everywhere on Earth. [Here is a representation of what it would look like from the international space station.](http://i.telegraph.co.uk/multimedia/archive/03239/eclipse99_mir_3239050b.jpg) + +However there is in fact a local temperature drop during an eclipse. + +Edit: trying to find hard data on the temperature drop it seems that the drop is only about half the difference between day and night temperature. It feel a lot bigger because you lose the direct radiant heating from the sun. +" "This [video](https://earthobservatory.nasa.gov/IOTD/view.php?id=87675) from NASA shows an actual 2016 solar eclipse moving over the Indian and Pacific oceans as viewed by the DSCOVR satellite stationed between the Earth and Sun. + +(The video is actually a series of still photos, as it would take hours for the shadow to cross the whole Earth) + +As /u/electric_ionland pointed out, the Moon's shadow only blocks the Sun on a very small portion of the Earth at a time. The duration of a total eclipse at any given spot can never exceed about 7.5 minutes, and is usually much shorter than that. So the cooling potential is like slow sunset, followed by 3-4 minutes of night, followed by a gradual sunrise. It's noticable, but not much. +" +121 Why hasn't evolution caused mammals to have many more females than males? 3931 http://www.reddit.com/r/askscience/comments/3a2foh/why_hasnt_evolution_caused_mammals_to_have_many/ 1434479155 3a2foh Biology 2015-06-16 21:25:55 "The underlying reason for this conundrum was first outlined by Ronald Fisher and is still known as [Fisher's Principle](https://en.wikipedia.org/wiki/Fisher's_principle). It doesn't just hold true for mammals, but for most sexually reproducing organisms. + +To explain why, first I have to clear up a bit of a misconception. You say: + +> So, I was thinking.. optimally as a specie to survive, wouldn't it make more sense to have X females per male? + +But in truth natural selection favors things that help individuals, not species. Something can be great for a species or terrible for a species, but that won't effect whether selection favors it. Instead, it favors things that help individuals, even if those traits are less than optimum for the species as a whole. + +So, why have equal numbers of males and females? Well, basically, imagine a situation where 100 females were born for every male. Now imagine some individual has a mutation that causes them to produce more male offspring, instead of just having 1 in 100. All their male offspring will do _very_ well. They'll go on to impregnate dozens of females and produce lots of offspring. The gene for having more males will spread. The gene for having more females will not keep up, because individuals with that gene will only produce females, and those will only produce a few offspring. Eventually, though, there will be lots of males. At that point, it will be the _males_ who have trouble finding mates, while all females are guaranteed a chance to get lucky. And so production to produce more females will be favored. This all evens out to favor a nearly 50-50 sex ratio at birth. Basically, selection favors having offspring that have the most opportunity to reproduce, and this means having offspring of the less common sex. This is known as negative density dependent selection." "Imagine your species has 100 females per male. Great for pumping out more of you, right? + +Now, imagine you are one of those females about to have a baby. You want to get an advantage and have more grandchildren than the other females. What do you do? + +Have a MALE baby. Because he will have like hundreds of offspring. + +There is a metastable relationship between how the GROUP can reproduce faster (more females) and how an INDIVIDUAL within the group can reproduce faster (more males, up to a certain point). + +So you will see some species with 1 - 1 pairing, and some with harems of females, but basically never have harems of males." +689 Do quantum mechanical effects have any physiological consequences for how our brains work? 3931 https://www.reddit.com/r/askscience/comments/5xaz34/do_quantum_mechanical_effects_have_any/ 1488555267 5xaz34 Neuroscience 2017-03-03 18:34:27 "These effects underlie the specific chemical reactions that take place in your neural cells. There are specific processes with enzyme catalyzation, for example, that rely on quantum effects. + +However, if you are asking about ""larger scale"" quantum phenomena, especially with respect to consciousness, etc., that is currently unknown, and there are various ideas floating around about those possibilities. + +That being said, a really interesting example of quantum phenomena underlying a *very* important feature of biology and ecology on our planet is photosynthesis, which cannot occur without some specific ""quantum phenomena"". I'm hazy on the details as this came out a few years ago, but it has to do with how photon energy is captured and transmitted through part of the molecular chain that allows for the absorption (and subsequent conversion into chemical energy) of sunlight. This process underlies the majority of the energy storage and accumulation in our entire ecological system and food chain...! I'll try and find a source but I'm on my phone. + +Edit: here's a quick link, but there are better sources with more details of course. +https://www.google.ca/amp/s/phys.org/news/2014-01-quantum-mechanics-efficiency-photosynthesis.amp +" As other have noted, such effects are important for regulating the dynamics of proteins that regulate neuron function (like ion channels). Because it takes thousands of proteins to affect cellular activity, these effects average out. So it is very unlikely that quantum effects directly influence thoughts/actions - like the kooky ideas of 'quantum consciousness' that crop up every few years. +1431 If the recipient of an organ donation dies before the donor, could the donated organ be returned to the donor? 3931 https://www.reddit.com/r/askscience/comments/dkdny4/if_the_recipient_of_an_organ_donation_dies_before/ 1571538599 dkdny4 Medicine 2019-10-20 5:29:59 "It could, but we never do it. This scenario happens all the time. Recipients are generally sicker people than donors, and as a result, many do not out live their donors. There are other technical factors with the organ as well, such as length of renal artery/vein/ureter that come into play. Returning the kidney to the original donor is unnecessary surgery without any real benefit. HLA does not change. Genetic makeup of the kidney does not change. + +Source: I’m a surgeon + +Funny story from surgical residency: performed a transplant where a male patient received a female’s kidney. While rounding on the patient the next day, he asked, “since I now have a female kidney, does this mean I have to sit down to pee?”" [deleted] +690 Is it in any way possible to reverse a black hole? 3920 https://www.reddit.com/r/askscience/comments/5qbpn6/is_it_in_any_way_possible_to_reverse_a_black_hole/ 1485453893 5qbpn6 Physics 2017-01-26 21:04:53 If they're small enough, they actually do this on their own. We think that quantum fluctuations near the event horizons of black holes cause them to emit mass/energy in the form of Hawking Radiation. For big black holes, this happens really slowly, (many-times-the-age-of-the-universe-slowly) but the smaller they get, the faster they evaporate. Exponentially faster. Eventually, we think they explode, and people are looking for the energy released in such events. In the last second of their life they should emit 100000 times more energy than the largest bomb ever built. We don't, however, have a complete description of the end of a black hole's life, which would need a quantum theory of gravity, which still eludes us. "There's another way to do it—spin it up past its extremal angular momentum. + +At a certain point, the centrifugal ""force"" will overcome the gravitational binding energy of the black hole. The mathematics say you get a ""black toroid"" at that point, but it seems more likely to me that instabilities would lead the [ergosphere](https://en.wikipedia.org/wiki/Ergosphere) to pinch off at the equator and start spewing out globs of mass. + +What happens from there is anyone's guess, but I imagine the end result would look something like [this](http://www.dailygalaxy.com/.a/6a00d8341bf7f753ef01bb095f4eca970d-pi)." +993 How many people does the average person pass a common cold to? 3918 https://www.reddit.com/r/askscience/comments/7o1w2h/how_many_people_does_the_average_person_pass_a/ 1515057794 7o1w2h Medicine 2018-01-04 12:23:14 "Half a dozen or so. + +The number you're asking about is the ""basic reproduction number"", abbreviated ""R0"" (pronounced ""R nought"") ([Wikipedia link](https://en.wikipedia.org/wiki/Basic_reproduction_number)). R0 ""can be thought of as the number of cases one case generates on average over the course of its infectious period, in an otherwise uninfected population"". + +There are many, many different viruses that are included in the common cold complex, but rhinoviruses are the classic cold-causing viruses. [This graphic](https://www.theguardian.com/news/datablog/ng-interactive/2014/oct/15/visualised-how-ebola-compares-to-other-infectious-diseases) shows many different R0s, with ""Rhinovirus (Common cold)"" shown on the bottom row at about 6. + +That puts rhinoviruses in a fairly typical range for diseases that are quite contagious. A handful of diseases, like measles, are much higher; many diseases, including some that are very capable of widespread transmission (influenza) are much lower. So long as a disease has an R0 over 1 it has the potential to persist. + +Obviously R0 is not a single, fixed value; it depends on a huge number of environmental factors, on the population that's being infected, and so on, so this is just a vaguely useful rule of thumb rather than a hard and fast law." Well there is a simple bit of statistics to estimate how many people you pass on a disease too, if the total number of people that is sick remains roughly the same over a longer period of time than the average number every person passes the disease on too is 1, if the number of people that are sick quickly decreases it's less than 1 and if the number of sick people quickly increases it's more than 1. +325 AskScience AMA Series: I’m Dr. Julia Shaw, a memory scientist and criminal psychologist. I study how we create complex false memories. AMA! 3914 https://www.reddit.com/r/askscience/comments/452fm7/askscience_ama_series_im_dr_julia_shaw_a_memory/ 1455106904 452fm7 Psychology AMA 2016-02-10 15:21:44 "AskScience AMAs are posted early to give readers a chance to ask questions and vote on the questions of others before the AMA starts. + + +Guests of /r/askscience have volunteered to answer questions; please treat them with due respect. AMAs are not your chance to rant about whatever issue you feel strongly about. Comment rules will be strictly enforced, and uncivil or rude behavior will result in a loss of privileges in /r/askscience. + + +" "Is there a way to reverse this? Or to somehow find out which is the ""true"" memory?" +122 Would a person submerged in a tub of water, unable to drink, survive longer than a person out of water, also unable to drink? 3910 http://www.reddit.com/r/askscience/comments/35sjmv/would_a_person_submerged_in_a_tub_of_water_unable/ 1431488372 35sjmv Human Body 2015-05-13 6:39:32 "Your skin provides an osmotic barrier, keeping the concentration of fluids in your body at homeostatic levels. You're not going to absorb water through the skin and even if you were able to, it wouldn't rehydrate you. + +Additionally, the effects of water pressure and submersion during the onset of dehydration would [contribute to hypothermia](http://www.klemmerhead.com/vitalyte/hydration-101/science-articles/hypothermia-and-dehydration/) and bodily wear (i.e. trenchfoot) which would take their toll over time anyways, over that of the person who remains on land. After a time, prolonged exposure to moisture would also cause the bonds between epithelial cells in the skin to weaken leading to maceration of the epidermis which would eventually leave the person open to infection as well. One notable example is the [David Blaine stunt](http://en.wikipedia.org/wiki/David_Blaine#cite_note-40) in which he was submerged in an isotonic solution for 7 days and emerged with skin breakdown on the hands and feet. Humans aren't designed to survive indefinitely in water. + +Assuming other factors are held constant, the submerged person would consume more energy and water due to the body needing to adapt to indefinite submersion and thus dehydrate sooner. + +Edit: + +The 'tub' is implied to be more like a pool/large tank as the test subject is submerged up to the neck, thus pressure is assumed to be a factor. + +Also the notion that one can 'drink' through the anus has been brought up repeatedly. While it's true that a person can bypass the digestive tract and rehydrate this way, barring an enema, it's not physically possible for the average human being to do so. +" "I like visuals, so here are some. + +[This](https://www.flickr.com/photos/tomas-/17070402826/in/datetaken-public/) is human skin. You can see the outer edge is all thin layers. The round cyan blobs underneath are cell nuclei. Those cells in your epidermis are all constantly being renewed, and they head out to the outer edge and as they go they lose their nuclei and turn into little balls of fat. They also secrete some proteins that 'tie' each cell to it's neighnbour. This creates an 'Epidermal barrier', which stops water going out of your body, and also obviously stops water coming in. + + +[Here](https://www.flickr.com/photos/tomas-/16971478384/in/dateposted-public/) is a picture of an epidermal barrier function being 'tested', something (purple) has been injected into the dermis, and this substance is trying to get out from the skin, but you can see that the epidermal barrier (blue) stops it. + +If you lay in a bath tub the water is just soaking into the very very top flattened layer of your skin (the out part of picture 1), and that part of your skin is just the thin, flattened keratinised chitinous skin flakes that are your 'wear and tear' armour. The water doesn't get past your epidermal barrier and can't help you. + +Having said that, you can drink water, and if you don't swallow it you can still absorb it readily in your mouth. The same lack of epidermal barrier function in your mouth is also in your ass, so you can just try and suck some water up your [ass](http://www.google.com)." +1432 What plesiomorphic (ancestral) traits of our common ancestor have humans retained but chimpanzees and bonobos have lost? 3910 https://www.reddit.com/r/askscience/comments/dcbno5/what_plesiomorphic_ancestral_traits_of_our_common/ 1570029634 dcbno5 2019-10-02 18:20:34 "This isn't necessarily a loss / retention example, but the chimpanzee / bonobo lineage has had a considerable contraction of their Y chromosome, resulting in the loss of a handful of genes and the pseudogenization of others. One specific lost gene of interest is USP9Y, which is involved in semen production. I've attached a citation that talks more about it, but they think that the loss of this gene might actually further encourage sperm competition between males, encouraging quality vs quantity for fertilization success. Evolutionary genomics might not be as sexy as morphological differences, but I still think it's pretty cool. + +​ + +Perry, G. H., Tito, R. Y., & Verrelli, B. C. (2007). The evolutionary history of human and chimpanzee Y-chromosome gene loss. *Molecular biology and evolution*, *24*(3), 853-859." "Since I don't think anyone's mentioned this yet, there has been some suggestion that our hand shape (e.g., proportional lengths of fingers and thumb) has changed more in chimps than in humans over the past few million years. [Almécija et al. 2015](https://www.nature.com/articles/ncomms8717) studied this in detail, and their results suggest that the proportionally longer digits seen in some apes evolved convergently in chimps, orangutans, and gibbons, while gorillas and humans retained hands more similar to the ancestral condition for apes/old world monkeys ([see figure 3](https://media.springernature.com/full/springer-static/image/art%3A10.1038%2Fncomms8717/MediaObjects/41467_2015_Article_BFncomms8717_Fig3_HTML.jpg?as=webp), where branch colour denotes different categories of hand proportions). + +Nice question also, it's always nice to see people thinking about this sort of thing rather than just assuming that all characteristics of another species must be primitive." +222 If you drop your a phone or something else with a glass screen and the screen doesn't crack, does it have a higher chance of shattering the next time you drop it? 3905 https://www.reddit.com/r/askscience/comments/3w8h76/if_you_drop_your_a_phone_or_something_else_with_a/ 1449762052 3w8h76 Chemistry 2015-12-10 18:40:52 "TL;DR: Yes. + +Materials Engineer here...Your brand new phone screen has billions of cracks in it. They're just really really really small. Now, anytime you do something to the phone (drop it, sit on it, bump your keys against it, whatever) you're putting stress on those cracks. + +If the stress is over a certain threshold, it can cause the crack to grow. The longer the crack, the less stress needed for it to grow. So every time you drop your phone, you're effectively lowering what's called the critical stress - the amount of force it can take before catastrophic failure - aka a shattered screen." "Assuming it does not crack at all (even at a very small level) then there will be no change. + +When glass breaks it is through a brittle fracture mode, which is caused by crack propagation. Basically, it will be a combination of how big the current crack is and the force that is acted upon it. So if absolutely no cracks or surface abrasions occurred (very unlikely) then there will be no weakening of the glass. + +I went to a talk by Corning, who makes almost all the phone screens. When they do testing, they first put it through a ""tumbler"" with keys, coins, etc. (to simulate being jostled in and out of pockets for an extended period of time) before checking the strength, as the creation of small cracks from wear and tear has a large effect on final mechanical strength." +895 Does fission occur inside of a star? If so, how far down the periodic table does fission occur inside of a star? 3904 https://www.reddit.com/r/askscience/comments/7372sj/does_fission_occur_inside_of_a_star_if_so_how_far/ 1506682763 7372sj Astronomy 2017-09-29 13:59:23 "Fission does not usually occur in significant amounts in stars, at least fission in the exothermal sense (releasing energy, like in a nuclear reactor for example). + +However! In the death of very massive stars, rapid fission of the Iron core into Helium can occur in a process called *photodisintegration*. This process is however endothermic, requiring much more energy than it releases. Thus, it only occurs in situations where temperatures and pressures are very high (read: dying massive stars). This process makes the core pressure drop momentarily, causing the star to collapse and become a black hole rather than explode as a hypernova!" "Fission occurs of course -- but in comparatively microscopic amounts. + +Heavy elements get produced by endothermic fusion in supernovae. Heavy elements also get produced by the ""slow process"" of neutron absorption in older metal-rich stars. Those fossil components remain in second-generation stars like the Sun. The Sun also produces tiny amounts of heavy elements itself from the slow process. All these heavy elements can undergo fission, and do. + +But as others have pointed out, these fissions are a tiny, tiny fraction of the energy balance of the Sun. Heavy metals are a tiny fraction of the solar material, and fissions only affect a tiny fraction of those. Further, fissions are much *less* energetic on a per-nucleus basis than is hydrogen fusion. So these reactions are negligible compared to the hydrogen fusions that are the main source of solar energy. + +Incidentally, as rare as elements like uranium and thorium (and even gold) are on the surface of Earth, they're *very highly concentrated* compared to their abundance in the primordial nebula and in the Sun itself. Planetary formation strongly differentiates heavy elements out of the primordial cloud, and terrestrial planet formation (inside the planetary ""snow line"" between the asteroids and Jupiter) also included a late-stage sweeping-away of light elements when the Sun began producing ultraviolet and the solar wind turned on. +" +223 When I'm on an airplane and I look straight ahead during takeoff or landing, I feel like I can see that the plane is pointed up or down. Can I really, or does my brain just extrapolate based on other information to create this illusion? 3903 https://www.reddit.com/r/askscience/comments/3y7dpi/when_im_on_an_airplane_and_i_look_straight_ahead/ 1451069843 3y7dpi Biology 2015-12-25 21:57:23 "You can do this, but not with great accuracy. + +Your visual perception is certainly affected by gravity, which like other accelerations, acts upon the vestibular organs in your inner ears. + +We have a very fast neuron arc from these sensors to the neural circuitry that controls eye movements. Here's a simplified outline that may describe your scenario: Nose of the plane rises (which you also notice with sensory modalities other than vision), you tilt your head forward to compensate (probably incompletely). To keep your gaze on the thing you were looking straight ahead at, your eyes automatically elevate by the same amount. You now feel like you are looking upwards, and this can affect your perception of location in rotational threespace. + +As to my opening comment about accuracy, this is not an ability you would ever want to have to bet your life on. This is why pilots have an artificial horizon instrument; there are endless cases (NTSB accident reports) about pilots who chose to believe their ears and eyes rather than an objective measurement." "Commercial pilot here. + +There have been numerous accidents recently due to spatial disorientation (Indonesia AirAsia Flight 8501, Air France Flight 447 among them). + +When you have no outside visual cues, you really can't ""feel"" how the plane is oriented. During your commercial training, you do ""unusual attitude recovery"" where you are basically blindfolded, the instructor will pitch/roll the plane into to a very weird situation and then you are told only ""recover"". You are still wearing ""foggles"", which basically block your view out the window. + +You can only rely on instruments at that point, especially the attitude indicator (AI) and airspeed indicator. + +Under no circumstances can you rely on how you ""feel"", because it's probably the exact opposite of what's happening. + +It gets complex with situation like AF447 where you have icing, which gives you incorrect readings (you can get incorrect stall and overspeed warnings rapidly, among other things). + +" +224 Why are Nuclear reactors never built in Water or below water? 3901 https://www.reddit.com/r/askscience/comments/3v7zhv/why_are_nuclear_reactors_never_built_in_water_or/ 1449105575 3v7zhv Physics 2015-12-03 4:19:35 "Advanced nuclear reactor designer here. Building nuclear power plants at sea is a *very* interesting idea, for several reasons: + +1. You can construct them in a shipyard, which is a controlled, repeatable environment with expert full-time employees who live nearby (not recently-trained temp workers living in a camp). Effectively, it's an assembly line for huge power plants. This could conceivably bring construction costs and timelines down. + +2. You're intimately coupled to a infinite heat sink (the water). Turning nuclear chain reactions off is easy (just put the control rods in), but they still produce afterheat due to fission product decay and this must be cooled to prevent the release of radiation out of the fuel pins/containment into the environment (e.g. to prevent meltdown). If you're sitting in the ocean, you can basically just open a valve and passively flood the heat transfer interfaces, keeping things cool without any external power. Thus, you'd be extremely safe. + +3. You're seismically decoupled from the ground, so you don't have to worry about earthquakes. ""Sure,"" you might be thinking, ""but what about tsunamis?"" No problem. Operate a few km offshore where the water is deep and you won't even notice tsunamis going by (they have super-long wavelengths in deep water). Boom. + +You DO have to worry about some new hazards, like ship collisions and huge storms. But shipbuilding is at a point these days that you can keep operating a major facility like the [*Prelude*](https://en.wikipedia.org/wiki/Prelude_FLNG) through a Category 5 cyclone, which is truly awesome. And you have issues like operation and maintenance will be more expensive. But you could just sail home to your shipyard-base to reload and do maintenance, which could actually be pretty slick. + +You also worry about the fact that at sea, a leak somewhere is a leak everywhere, since the sea disperses things well. So even though it'd be much less likely to have a radioactive release, it would be a very big deal. This is a key PR challenge for floating nuclear. (Realistically, the retention and dilution of the radionuclides would be very good in the sea, but everyone can see that this technical fallback is completely societally unacceptable) + +Lots of people are thinking about this. MIT is [working on a floater](http://news.mit.edu/2014/floating-nuclear-plants-could-ride-out-tsunamis-0416). Russia has [a one under construction](https://en.wikipedia.org/wiki/Akademik_Lomonosov) to provide power to very remote villages. China is [working on one](http://www.powerengineeringint.com/articles/2015/10/china-to-develop-floating-nuclear-power-plant.html). In the early 1970s, a company was formed called [Offshore Power Systems](https://en.wikipedia.org/wiki/Offshore_Power_Systems) that was going to build two huge nukes on barges off the New Jersey coast. It was cancelled after the oil crisis when the main demand (oil refineries along the coast) fell dramatically. + +Personally, I think floating nuclear power plants (FNPPs) are one of humanity's best options for transitioning away from fossil fuels rapidly, responsibly, and economically. + +Anyway, great question! + +(Also, of course, there are many naval reactors propelling ships and submarines all over, so the military definitely does build reactors on and in water. )" "Meltdowns are not all that common due to the stringent safety precautions nuclear power plants have. It takes wilful disabling of all safety measures or actual earthquakes to cause any major leak. + +These safety measures would be more difficult to ensure if everything was under water. It'd also be more difficult to make and harder to maintain. + +Building it underwater wouldn't stop a leak from spreading and the explosion like Chernobyl was too powerful for 20ft of water to make a difference. " +6 "If we viewed a star ""going supernova"" in real time, would it look like a violent explosion, or does it take a long time?" 3898 http://www.reddit.com/r/askscience/comments/2ryvba/if_we_viewed_a_star_going_supernova_in_real_time/ 1420904049 2ryvba Astronomy 2015-01-10 18:34:09 "A type I supernova begins when the star undergoes electron degeneracy collapse - meaning that all the electrons and protons in the star undergo reverse decay and merge into neutrons. The process takes about 20 seconds, which is a pretty amazing speed for anything to happen on the scale of a red giant. + +But other posters are right, the actual explosion (which happens when the outer layers of the star rebound against the newly-formed neutron core) would take several minutes to become apparent. Though still, that's incredibly fast for an enormous, billions-year-old star. + +edit: gilded! Thanks guys! (Not really, but I just always wanted to say that.) + +edit: gilded *for real!* Thanks! It's like my very own supernova." "It would also be very bright. I can't link right to it as I have done frequent before, but XKCD is again relevant. In his book the author quotes a well known astrophysicist in saying ""However large you think a supernova is, it's bigger than that."" To get an idea of how bright a supernova is, he compares viewing one from one AU away (from here to the sun) to watching the detonation of a hydrogen bomb while the device is pressed against your eyeball. The supernova would still be brighter. *By nine orders of magnitude.*" +225 Is there a bulge in earth's atmosphere constantly facing the moon? 3894 https://www.reddit.com/r/askscience/comments/3jyvry/is_there_a_bulge_in_earths_atmosphere_constantly/ 1441631132 3jyvry Earth Sciences 2015-09-07 16:05:32 "Yes, there is, but counter-intuitively there is also a bulge on the other side [as shown here](http://i.imgur.com/KN5bOrM.jpg). You can rationalize this phenomenon in terms of the so-called [tidal forces](https://en.wikipedia.org/wiki/Tidal_force), which arise from the fact the the gravitational force from the moon is not uniform over the Earth. Simply put, the moon's gravitational pull is closest on the side of the Earth facing the moon and weakest on the opposite side. These differences give rise tidal forces that have a distribution across the surface of the planet [as shown in this diagram](https://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Field_tidal.svg/1000px-Field_tidal.svg.png). The atmosphere closest to the moon is pulled towards it, but on the other side of the Earth, it effectively pulls away in the opposite direction, creating a bulge at both extremes. This is also the explanation for the fact that there are two high tides per day since (as the name implies) the tidal forces are the key source of tides on Earth. + +**Edit:** I would like to expand my answer a bit, especially with regards to tides since there seems to be quite a bit of interest on the subject. Everything I said above is true within a simplified Newtonian model, however there are some subtleties to the actual mechanism at play. Let's make a crude assumption and treat the Earth as an onion-type sphere with a solid core, a thin uniform liquid layer around it and another gaseous layer on the exterior. Then when you apply a non-uniform gravitational filed (like that created by the moon) on the water or atmosphere (which you can treat as a continuous fluid shell), it would become deformed into an ellipsoid with two lobes at the extremes ([as shown here for the atmosphere)](https://www.youtube.com/watch?v=l37ofe9haMU). + +However, especially as tides are concerned, this effect is not just due the stronger pull of the atmosphere locally since even at the extremes, the local deviation of the moon's gravitational pull from the mean is very, very small (on the order of 1\*10^(-7)[g](https://en.wikipedia.org/wiki/Gravity_of_Earth), or 10 million times weaker than Earth's own gravity). Instead, you have to consider the total effect of all the tidal forces [shown in the diagram I posted above](https://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Field_tidal.svg/1000px-Field_tidal.svg.png). The very small differences from the pull and push in the region facing and opposing the moon *as well as* the squeeze from the size accumulate over large enough volumes (i.e. seas and oceans) to produce large tides. Think of it this way, each infinitesimally small bit of fluid (e.g. water) only experiences a small effect, but because each bit of stuff pushes against the surrounding fluid, these small differences effectively add up and over large enough volumes they can become substantial. This effect still exists in smaller bodies of water such as lakes, but is far smaller exactly because the volume over which these differences can add up is far smaller." "Contrary to what most people are saying in this thread, *no*, the bulge in the Earth's atmosphere does not constantly face the moon. In fact, depending on a number of factors, the atmospheric tide is likely to be primarily thermally driven by solar heating of portions of the atmosphere, causing them to expand. While the earth is rotating near the resonance frequency of the atmosphere (resonant period being defined as the length of time for a lamb wave to propagate around the Earth, currently about 21 hours), the same relative portion of the atmosphere is heated all the time, which can result in *very* large tides, shown in this [figure.](http://i.imgur.com/Y6wTW5l.png) + +When the Earth was rotating near resonance, there would be some interesting effects. It is very likely, depending primarily on the atmospheric *Q*-factor, that the Earth would become stuck at a relatively constant day length, with the torque from the atmospheric tide fully canceling the torque from the lunar tide, quite possibly for a period of over a billion years. This was first outlined in [1987 by Zahnle and Walker](http://www.ncbi.nlm.nih.gov/pubmed/11542096) and was been the subject of a paper ([arxiv:1502.01421](http://arxiv.org/abs/1502.01421)) I co-authored." +1119 If grasses evolved relatively recently, what kinds of plants were present in the areas where they are dominant today? 3892 https://www.reddit.com/r/askscience/comments/9f04e3/if_grasses_evolved_relatively_recently_what_kinds/ 1536690729 9f04e3 2018-09-11 21:32:09 That question is kinda hard to answer, here’s my attempt as a plant ecologist. Grasslands today exist where grasses can outcompete pretty much everything else, or that are too inhospitable for other vascular plants. Without competition from grasses, shrublands and woodlands would likely have been able to establish in many of these places, other places that were too harsh likely would have been barren except for a covering of moss, lichen, or cryptogamic crust. Marshes, wetlands, meadows etc that are dominated by grasses and grasslike plants either would have instead been dominated by mosses, ferns, and horsetails or trees and shrubs that can tolerate wet feet, or just open water, maybe with aquatic plants/green algae. "[Grasses evolved about 60-120 million years ago](https://en.wikipedia.org/wiki/Cyperaceae) and this estimate is under constant revision in the face of new fossil evidence. + +But many plants which could casually be called ""grass"" are not actually grass, yet occupy many of the same ecological niches. + +Sedges, for example. I could not quickly find a source of estimates on the earliest sedges, but [the phylogenetic tree in this wikipedia article](https://en.wikipedia.org/wiki/Poales) suggests that sedges (Cyperaceae) are more basal than grasses (Poaceae). So I would imagine them to have been around earlier. Emphasis on the word ""suggesting"". + +A solid answer may not be available due to lack of good fossil evidence. Even though there are fossils of both families, and these can be dated, how do you know if you have found the oldest fossils of both? You can only start to be confident after a great deal of effort." +326 If you were to drive in a car at the same speed as a bullet and shoot backwards, would the bullet hang in mid-air? If so, how long? 3885 https://www.reddit.com/r/askscience/comments/4f71t3/if_you_were_to_drive_in_a_car_at_the_same_speed/ 1460907457 4f71t3 Physics 2016-04-17 18:37:37 "As far as the bullet is concerned, this scenario would be effectively identical to a person standing still (with respect to the ground) and simply dropping the bullet. This example is a straightforward application of the principle of relativity (specifically [Galilean relativity](https://en.wikipedia.org/wiki/Galilean_invariance)). This principle tells us that in order to calculate the velocity of the bullet relative to the ground (v'), we just need to add up the velocity of the car relative the ground (vi) the velocity of the bullet relative to the gun. We then get v' = vi + -vi = 0, just as we expected. + +Therefore, as the bullet exits the barrel it will at first be at complete standstill relative to the ground but then will start falling under the influence of gravity as a body in free-fall. This means that it will stay in the air for t = (2h/g)^(1/2) (where h is the height and g is the gravity of Earth) before it will hit the ground. For example for a starting height of 1m, the bullet would fall for ~0.5s. + +Anyway, even if the science in this case is fairly straightforward, I like this example as a way of getting some physical intuition for how kinematics works. Moreover, it makes for a cool demonstration, [as you can see in this clip from Mythbusters](https://www.youtube.com/watch?v=BLuI118nhzc&feature=youtu.be&t=26s). + +Edit: spelling and cleaned up the explanation a bit" Bullets don't hang in the air. As soon as they exit the barrel, they are falling to the ground at the same rate as if you just dropped it. If you shot a gun perfectly parallel to a perfectly flat surface at the same time you dropped a bullet, they would hit the ground at the same time. The bullet in your scenario would be spinning like a motherfucker, but it wouldn't hang in air. +1433 How do engineers prevent the thrust chamber on a large rocket from melting? 3885 https://www.reddit.com/r/askscience/comments/dr1cqc/how_do_engineers_prevent_the_thrust_chamber_on_a/ 1572792564 dr1cqc Astronomy 2019-11-03 17:49:24 There are a few different designs to cool the “bell”. Some have small tube-like paths throughout for fuel to travel through it, removing some of the heat and pre-heating the fuel. Some use ablative material that slowly flakes off removing some of the heat with it. Check out [everyday astronaut](https://www.youtube.com/channel/UC6uKrU_WqJ1R2HMTY3LIx5Q/featured) on YouTube for awesome explanations of things just like this question. Short answer is: The most common solution is to run the fuel through the bell itself which both cools the bell, and pre-heats the fuel. +7 Why does putting salt water (saline) into our blood stream rehydrate us, but drinking salt water can harm us? 3878 http://www.reddit.com/r/askscience/comments/2y3tan/why_does_putting_salt_water_saline_into_our_blood/ 1425616580 2y3tan Human Body 2015-03-06 7:36:20 "It's just to do with how salty the water is (i.e. the osmolarity of the fluid). + +The saline usually used in IV drips for rehydration is close to isotonic - that is, the amount of 'salt' is approximately the same as what's in the blood stream. This prevent 'diluting' the blood (i.e. causing hyponatraemia etc) and/or causing excessive fluid redistribution to the various compartments. + +In a way, it's similar to how sports drinks can have some salt in them without causing dehydration. + +On the other hand, the salt water you're probably thinking of is something like sea water, which is hypertonic. Although drinking it doesn't really 'harm us' per se, it doesn't rehydrate us. This is because urine has to be excreted in order to maintain osmolarity. + +Certain receptors detect when there's too much 'salt' in the blood and concentrated urine is excreted (bringing the osmolarity back down to normal). However, there's a limit to how concentrated our kidneys can make urine, so the amount of water we gained from drinking sea water is less than the amount of urine that had to be excreted - thus increasing the level of dehydration. + +Hope this helps" "Saline is isotonic - it's got the same (or close) concentration of salt as your blood. + +Sea water has way way more. You need to get rid of the excess, via your kidneys, and you spend more water removing the excess salt than you gained by drinking it." +327 If water has a boiling point of ~100 degrees C, why does it evaporate at room temperature? 3878 https://www.reddit.com/r/askscience/comments/4bx3kq/if_water_has_a_boiling_point_of_100_degrees_c_why/ 1458922250 4bx3kq Chemistry 2016-03-25 19:10:50 "A somewhat counter-intuitive thing about temperature is that it is an aggregate property - so it is well-defined for a large group, but not so well for a few atoms. It is basically a function of the average velocity of molecules. + +Individual molecules, however, have a distribution of velocities. You can think of this as a result of an infinite series of random collisions between atoms and molecules. For example, sometimes you can have two particles that happen to travel in almost the same direction impact a third one. That third one is going to get a hell of a kick and go must faster than any of the three were traveling to begin with. + +As a result, some water molecules are quite faster than the average corresponding to the temperature. So they can achieve ""escape velocity,"" or get kicked out, depending on your perspective. And they fly off. + +This is also the mechanism behind evaporative cooling. Since the molecules with the highest kinetic energy are the ones that are leaving, the average kinetic energy of those remaining drops, and so does the temperature." """Boiling point"" does not mean ""evaporation point"". It means ""the point at which the vapor pressure exceeds pressure in the liquid phase."" In other words, if you make a bubble in the liquid, the pressure in the vapor will be higher than the surrounding liquid, causing the bubble to expand, in other words: ""boiling."" Another way of looking at it, is if you take a cup of water and put a lid on it, then if you are below the boiling point, there will be evaporation until the air above the liquid becomes so saturated that there is an equal amount of evaporation and condensation, you so reach equilibrium between the liquid and vapor phases. On the other hand if you are above boiling point, the pressure in the cup will rise (or if it's a big enough cup that the pressure rise is small enough that you can ignore the effect of the pressure rise on the boiling point, then the water will eventually evaporate away completely). " +896 AskScience AMA Series: We are climate scientists here to talk about the important individual choices you can make to help mitigate climate change. Ask us anything! 3875 https://www.reddit.com/r/askscience/comments/7bsv2d/askscience_ama_series_we_are_climate_scientists/ 1510228808 7bsv2d Earth Sciences 2017-11-09 15:00:08 "Please remember AskScience has strict comment rules. If you are unfamiliar with the rules you can [view them here](/r/askscience/wiki/rules). Behavior that is uncivil towards users or AMA guests can result in a ban. + +-edit- This AMA has concluded. thank you all for your participation." I have a question about the paper vs plastic debate. I am a chemical engineer, and I have done research on some of these type of debates when I was in college. Most studies found that paper actually takes more energy to make, and recycling wood pulp actually creates a higher CO2 output on the environment, while most plastic items are relatively simple and easy to make, without the massive expulsion of CO2 on the environment. While this is true, it is also true that plastics,when littered in the environment do have a strong impact on wildlife. My question is, how can paper recycling create more CO2 output but still be considered a safe replacement for plastic? +431 What is the earliest song in human history that we are not only aware of, but have some idea of how it sounded? 3874 https://www.reddit.com/r/askscience/comments/4khfz6/what_is_the_earliest_song_in_human_history_that/ 1463897688 4khfz6 Anthropology 2016-05-22 9:14:48 To answer your second question, the oldest flute found is around 43,000 years old: https://en.m.wikipedia.org/wiki/Divje_Babe_Flute "Not the earliest song, exactly, but the oldest musical piece we have a complete ""score"" for is the Seikilos Epitaph from Ancient Greece, from around the first century AD: https://en.m.wikipedia.org/wiki/Seikilos_epitaph + +It's very short, but is actually a beautiful piece. " +123 How does a computer know to turn itself back on when you tell it to restart? 3866 https://www.reddit.com/r/askscience/comments/3ihcm6/how_does_a_computer_know_to_turn_itself_back_on/ 1440605418 3ihcm6 Computing 2015-08-26 19:10:18 "Basically when you hit the restart command, the computer never fully turns off. + +It shuts down all processes, cleans info about what's currently running etc. If you went for a shutdown, power would be cut off at this point but during a restart it simply starts loading up all the things it would if you hit the power on button after a shutdown. Power to the motherboard is kept on at all times during a restart. + +Edit: +Slight correction: Even after a shutdown power is kept flowing to some components like the power button or other devices waiting for an ON signal or in some cases to USB ports so that you can charge your phone with the computer off. So power isn't fully cut off even during a shutdown like I previously stated." "It might be internal to the chip now, but cpu chips used to have a dedicated line called reset (or something like that). Reset zeroed all memory bits inside the cpu, then started the power up sequence. Normal power up via the power button would send a signal to the reset line. + ""restart"" as a bios function attached a memory address to the reset line so that bios code could cause the power reset to the cpu. + +There were many, many variations to this idea, so for non-OP persons with detailed info on specific cpus, plz be gentle." +567 What's the tallest we could build a skyscraper with current technology? 3866 https://www.reddit.com/r/askscience/comments/5ax8nn/whats_the_tallest_we_could_build_a_skyscraper/ 1478185791 5ax8nn Engineering 2016-11-03 18:09:51 "[X-Seed 4000](https://en.wikipedia.org/wiki/X-Seed_4000) with its proposed height of 4000 m is the tallest structure that got a proper design. If you just go by material strength, taller structures are possible, but it gets completely impractical, as more and more of its volume has to be used for structural integrity and elevators. + +Air density has to be considered as well, and you probably have to make airlocks to get a reasonable climate everywhere without generating huge wind through the structure." X-Seed 4000 is just a concept never meant to be built. But, building such a tower isn't enough. After construction it needs to be maintained. 4000 meters up would present a lot of problems providing simple maintenance. Imagine what it takes to repair or replace a cracked window near the top. +994 Can you get drunk by inhaling alcohol vapors? 3866 https://www.reddit.com/r/askscience/comments/8avx70/can_you_get_drunk_by_inhaling_alcohol_vapors/ 1523249223 8avx70 Medicine 2018-04-09 7:47:03 "This post has attracted a large number of anecdotes (about 80% of the comments have been removed so far). The mod team would like to remind you that **personal anecdotes are against [AskScience's rules](/r/askscience/wiki/rules)**. + +We expect users to answer questions with accurate, in-depth explanations, including peer-reviewed sources where possible. If you are not an expert in the domain please refrain from speculating. + +**In particular this is not the right subreddit to talk about how you once got drunk on some alcohol vapor.**" Yes. There are some commercial printing processes that use ethanol as a solvent, and you can absolutely have a blood alcohol reading after working with them all day. I’ve never heard of anyone actually being “drunk”, but while I was in trade school, our lecturers did warn us about driving home after work in those situations. +995 Why is the background smooth in IBM in atoms? 3865 https://www.reddit.com/r/askscience/comments/82ag9v/why_is_the_background_smooth_in_ibm_in_atoms/ 1520292489 82ag9v Physics 2018-03-06 2:28:09 "There are a lot of incorrect and inaccurate responses in this thread but hopefully this post will clear things up. It's pretty detailed but I'm always happy to answer additional questions about all things STM related. + +**SHORT ANSWER** +It says in the paper that this figure came from that the atomic structure of the nickel surface is not resolved. + +**LONG ANSWER** +The resolution of STM (Scanning Tunneling Microscope, how this image was taken) images depends greatly on both the geometry at the end of the scanning tip (rough diagram of STM [here](https://www.researchgate.net/publication/258395126/figure/fig11/AS:320237095407624@1453361881764/A-schematic-STM-setup-When-a-tip-is-brought-several-angstroms-away-from-a-sample-and-a.png)) as well as any mechanical or electromagnetic noise that gets introduced into the tunneling current signal before it is processed by a computer program. In the previous figure, the tip is depicted as an atomic pyramid with tunneling occurring from a single atom, which would nearly always give atomic resolution images. In reality, the tip will have multiple atoms at approximately the same distance from the sample, leading to the tunneling current being spread out over a larger area, which is what ultimately limits your resolution. Just to prove to you that they *were* capable of resolving the nickel (110) surface reconstruction, [here](https://i.imgur.com/aeyvFhp.png) is another figure from the same paper in which you can see the rows from the nickel atoms. Even *further*more, [here](http://images.slideplayer.com/14/4353513/slides/slide_12.jpg) is what the pure nickel (110) reconstruction looks like. This image was taken in 1995, and the image in the original post was taken in 1989. The STM was invented in 1981. Modern STMs are obviously capable of higher resolution, but it's typically due to better noise filtering and vibrational isolation of the STM stage, not the sharpness of the tip. + +Additionally, they say that greyscale is assigned according to the slope of the surface. This is known as a *derivative image* as opposed to a typical STM image which measures the height change of the STM tip as it rasters across the surface while attempting to maintain a constant voltage and tunneling current (10 mV and 1 nA current were used to obtain the image in the original post). Since the xenon atoms protrude 1.6 Angstroms (1 Angstrom = 10^-10 meters) from the surface, which has height fluctuations on the order of picometers (10^-12 meters), the slope is much sharper over the xenon atoms than over the nickel substrate. [Here](https://i.imgur.com/sf8aaxV.jpg) is another image from the same data set that produced the image in the original post but has been post-processed to better show the surface morphology. I would imagine that this is the ""real"" topological image as opposed to the derivative image shown in the original post. + +**Source**: I'm a PhD student that does a lot of STM as part of my research. Also, I actually read the paper that this image comes from. + +The original paper is behind a paywall, but in case you are interested in reading it for yourself, you can see it [here](https://drive.google.com/open?id=1jWY7ztqcP8qW8JjzxqGA8Z5ig5v6Leit). + +EDIT: Some additional points. +STM requires the probe tip to be metallic otherwise the tunneling current will be convoluted by the tip's density of states (you only want to probe your sample, not your tip). The sample must be conducting (not necessarily metallic, though you need to scan at voltages that fall outside the band gap). Since STM relies on tunneling, there must be available filled states to tunnel from or empty states to tunnel into (depending on whether the applied bias is positive or negative). The sample must also be conductive enough to complete the feedback loop circuit (if your sample is not conductive, no current will flow through the feedback loop and your tip will crash into the surface). + + +In addition to imaging using STM, you can also do something known as Scanning Tunneling Spectroscopy, or STS, using the exact same instrument. I've explained that STM works by moving the tip around and measuring how much the tip has to approach or retract to maintain a constant voltage and tunneling current. Well, STS is similar except the tip remains stationary at a single spot on the sample and sweeps the voltage while measuring current at a constant height from the sample. By plotting the derivative of the current (dI/dV) against the voltage, you can create a picture of the density of states at the surface at a range of voltages. This can provide valuable information about the electronic structure of your sample, including things such as the band gap and doping type. I am typing this from my phone but can provide examples of STS plots for a variety of materials " "Scanning probe microscopy doesn't work like normal microscopes. The objects are not ""seen"" as much as they they are ""sensed"" or ""felt"" through a fine needle like probe. The reason for this is because individual atoms are smaller than a wavelength of visible light so it is impossible to see them. + +In a nutshell here is how a scanning probe microscope works: + +First the atoms being scanned need to be super-cooled to as near absolute zero as possible that way the atoms won't move around and vibrate so much. In the case of the ""IBM"" atoms they are xenon atoms on a nickel surface. + +Then imagine a fine needle like probe that can sense the tiny force fields of individual atoms being positioned to the exact point where the final atom on the very tip of the probe can sense the outer or valence shell of a single atom's array of electrons. The probe can even be adjusted so it can pick up and move a single atom from one place to another. That's how they were able to arrange the atoms to spell out ""IBM"". + +The very tip of the probe is only sensing one atom at a time. In this case the xenon atoms on top of the surface, rendering the nickel atoms that make up the surface ""invisible"" to the probe. + +Hope that helps. Source - I have met and spoken with Don Eigler and even asked him the same question you posted here. He is the scientist who led the whole team that accomplished this man-on-the-moon moment in nano-technology. I still say he deserves a Nobel Prize for his work. He did this back in 1989. + +Don are you seeing this?" +226 If there was a body of water that was as deep as the Marianas Trench but perfectly clear and straight down, would you be able to see all the way to the bottom? 3864 https://www.reddit.com/r/askscience/comments/3lak5g/if_there_was_a_body_of_water_that_was_as_deep_as/ 1442491521 3lak5g Physics 2015-09-17 15:05:21 "Even pure water absorbs and scatters light so you could not see the bottom of the +Marianas Trench (10,994 m depth). The amount of sunlight in the ocean decreases exponentially from the surface. The *extinction coefficient* varies with colors (wavelength) with the blues penetrating the deepest to a few hundred meters. So even if you had the brightest floodlights in the Marianas Trench and perfectly ~~clear~~ pure water (the open ocean is pretty close except for the salinity), you can't see anything more than a few hundred meters away." "I've been swimming in open ocean in the Pacific, hundreds of miles from the nearest piece of land. The water was remarkably clear and unusually calm. Charted depth was around 7000 meters. I went underwater and looked down. All I saw were the sun's rays going down about a hundred feet or so, where it just faded to black. Quite an amazing sight. + +I think a better question would be how deep could you go while looking up and still see light from the sun." +996 How many bytes of information can a single neuron store? 3863 https://www.reddit.com/r/askscience/comments/7q5t4z/how_many_bytes_of_information_can_a_single_neuron/ 1515864743 7q5t4z Neuroscience 2018-01-13 20:32:23 "There are a lot of different ways to answer this question. One answer could be that single neurons cannot store any information, that information storage is based on the state of a group of neurons in a system. In that context, we could say that a single neuron in a group of neurons is acting as a container for a single bit - each neuron is an on/off switch, but thinking of neurons as digital (0/1) is problematic because it makes the assumption that the state of a neuron is binary. + +This is where the concept of an action potential becomes important. So each neuron in this memory system we are talking about has a non-binary amount of electrical energy stored in its membrane, and when the membrane reaches a certain threshold potential, this triggers a chain reaction that sends an action potential along an axon. This action potential might carry some encoded information along to another neuron, and trigger another action potential, so on and so forth, until many neurons have been triggered by this initial reaction. + +I know this isn’t exactly a cut and dry, “Neurons store 10 bytes of data” answer that you might have been looking for, but at least these are some ideas to think about in regards to how it’s really a more difficult/complex question to ask than it might seem." "The neuron itself does not ""store information"", but its interaction with other neurons can be represented by weights, i.e. once it fires, how it increases \ decreases the polarization of the neurons at the end of its synapses. + +One neuron in the human brain is directly ""connected"", on average to 7000 other neurons. These connections excite or inhibit the activities of the neurons at the receiving end to a varying degree determined by the type of synapse (what neurotransmitter is user, how many vesicles are secreted, how many neurotransmitters molecules per vesicle, how many receptors are present at the receiving end and what's the uptake time). + +The resolution needed to describe the weight, then, is roughly the max number of vesicles it is possible to emit to the synaptic gap, times the number of different neurotransmitters, times the range of molecules per vesicle, times the max number of receptors on the receiving end times the max number of re-uptake-responsible contraptions in the synaptic gap. + +The lower bound limit I can give on this resolution is about 10^15 , but it's probably much higher. + +Thus a lower bound of the information encoded in the activation of a neuron would contain about 10^15*7000 possible stages, or roughly 348802 bit, or about 43kB. + +So a neuron contains at least 43 kilobytes, but it probably contains much more than that. I haven't even touched upon the possible time dynamic of the neuron (which may fire in bursts, with varying number of activations and varying time gaps between each activation). " +1381 What does quantum field theory tell us that quantum mechanics doesn’t? 3857 https://www.reddit.com/r/askscience/comments/bq2ngc/what_does_quantum_field_theory_tell_us_that/ 1558175911 bq2ngc 2019-05-18 13:38:31 "It tells us a lot, actually! + + +As everyone else has said, QFT comes from the union of QM and relativity. The basic framework is: there are a bunch of (quantum) fields spread out everywhere in space, and what we see as particles are actually just ""bumps"" in these fields. Every fundamental particle has a field that it ""arises"" from. + + +As the other commenters have mentioned, an exciting prediction from this new framework is antimatter: you can make ""positive"" and ""negative"" bumps in these fields that are able to cancel each other out. QFT also explains what a particle's spin is, which is a fairly mysterious ""add on"" that seems rather arbitrary when you're studying QM as an undergraduate. + + +Having said all of this, I think the most important part of QFT is this profound realization: all of the forces we see in nature result from special symmetries (called gauge symmetries). These symmetries determine how the quantum fields interact and change, and so are essentially able to boil down most of fundamental physics to the study of these symmetry groups. + + + For example, the standard model of particle physics has three types of internal symmetry that hold at the same time: SU(3) symmetry, SU(2) symmetry, and U(1) symmetry. These ""symmetry groups"" to a large extent determine the mathematical structure of the standard model. The theory of quantum electrodynamics by itself is the study of just the U(1) symmetry. + + +Another fascinating insight from QFT is renormalization: the features of your theory (particle mass, coupling strength) change depending on the energy level your are probing at! Really wacky stuff." "QFT is a subset of quantum mechanics that’s: + +1. Usually relativistic. + +2. Allows for particles to be created and destroyed." +227 If the sun disappeared from one moment to another, would Earth orbit the point where the sun used to be for another ~8 minutes? 3852 https://www.reddit.com/r/askscience/comments/3m2clx/if_the_sun_disappeared_from_one_moment_to_another/ 1443015682 3m2clx Physics 2015-09-23 16:41:22 "The short answer is that if something were to happen the sun (e.g. say if it would explode), the effect of this change would not be felt on Earth until a sufficient time has passed for light from the initial position of the sun to reach the Earth (which like you say will take about 8 minutes). + +The reason for this is that no information can propagate faster than the speed of light, and the same principle applies to the state of gravitational fields. When observing *changes* to a massive body (e.g. the sun) and its associated gravitational field, the changes are observed not in ""real time,"" (t) but rather at a delayed time called the [retarded time](https://en.wikipedia.org/wiki/Retarded_time) (t')), which is given by + +t' = t - R/c, + +where R is the separation between the observer and the object. For example in the case of the sun, this retardation is (on average) 8 minutes, since this is the amount of time it takes light to reach the Earth. This means that any change in the sun would not just not be seen on Earth until 8 minutes later, but it couldn't cause any physical change on Earth at all until 8 minutes later. + +**edit: Some caveats and clarifications...** + +1. I took the question in the original post to mean more generally how long it would take for an object subject to a gravitational field to feel the change in the field created by a change in the distribution of mass giving rise to the field. This is why I used the example of the sun exploding as a physically allowed example. However the sun cannot simply disappear instantaneously as this would violate a very [fundamental conservation law](https://en.wikipedia.org/wiki/Noether's_theorem) of the sun's mass-energy. Because such a change is unphysical, there is no defined solution to the underlying field equations that would predict how the system would evolve. [The answer](https://www.reddit.com/r/askscience/comments/3m2clx/if_the_sun_disappeared_from_one_moment_to_another/cvbhl84) given by /u/rantonels is rigorously correct on this point, please don't downvote his answer. + +2. A lot of questions have come up on whether [quantum entanglement](https://en.wikipedia.org/wiki/Quantum_entanglement) somehow offers an example where information is transmitted faster than the speed of light. See /u/Weed_O_Whirler's [great answer below](https://www.reddit.com/r/askscience/comments/3m2clx/if_the_sun_disappeared_from_one_moment_to_another/cvbjh3f) for why this is not true: even though entanglement applies without a delay, this does not mean that you can use the effect to transfer information faster than allowed by the speed of light." [deleted] +1434 Does silver turn instantly black when exposed to hydrogen sulfide gas? 3849 https://www.reddit.com/r/askscience/comments/ddparo/does_silver_turn_instantly_black_when_exposed_to/ 1570292174 ddparo 2019-10-05 19:16:14 """ Silver and silver-plated objects react with sulfur and sulfur compounds to produce silver sulfide (Ag2S), or tarnish"" + +​ + +Source: [https://pubs.acs.org/doi/pdf/10.1021/ed077p328A](https://pubs.acs.org/doi/pdf/10.1021/ed077p328A) + +​ + +So yeah, Dr. stone is right, its not just that fast" "The first experiment designed to test whether atomic orbital angular momentum was quantized is called the Stern Gerlach experiment. In it they used silver atoms that have one unpaired election orbiting the outer shell. They passed them through an inhomogeneous magnetic field to deposit into a collector plate. When they checked the plate after the experiment to see if they could detect quantized splitting the plate appeared blank. They thought they had failed. + +But back in this day the scientists could smoke cigars in the lab (!!!) +Cheap cigars emit more hydrogen sulfide. After looking at the plate for a while trying to see anything, the sulfur from their breath reacted with the silver creating a black silver sulfide later that became visible. The silver had been there but such a thin later it couldn't be seen until they ""developed"" it like a photograph with their cheap cigars. + +What they found was the silver deposit was split into two distinct bands indicating that orbital angular momentum was quantized into discrete orientations in space." +328 Why are there mountains on Mars that are much higher than the highest mountains on other planets in the solar system? 3848 https://www.reddit.com/r/askscience/comments/4e0wml/why_are_there_mountains_on_mars_that_are_much/ 1460200644 4e0wml Planetary Sci. 2016-04-09 14:17:24 "I found a decent explanation for it. + +""The large scale of the Tharsis shield volcanoes suggests that they formed from massive eruptions of fluid basalt over prolonged periods of time. Similar eruptions on earth are associated with flood basalt provinces and mantle hotspots. However, on earth the source region for hotspot volcanism moves laterally as lithospheric plates travel across the stationary mantle plumes beneath them. Without this mechanism of lateral movement, the Martian surface remains above the plume source so that huge volumes of lava will erupt from a single central vent over many millions of years of activity, thus generating a single shield volcano of enormous volume. With this in mind, it is interesting to note that the volume of Olympus Mons is roughly equivalent to the total volume of basalt in the Hawaiian-Emperor seamount chain."" + +http://www.geology.sdsu.edu/how_volcanoes_work/mars.html + +The other aspect is the rate of erosion is incredibly slow compared to Earth. + +Edit: another thing worth noting is the theory that a giant asteroid collision may have been what set off the Tharsis Shield volcanoes in the first place. So a fuller understanding of volcanism on Mars has to take the overall history of the planet into account. + +http://www.scientificamerican.com/article/giant-asteroid-collision-may-have-radically-transformed-mars/" "In general, a planet with a lower surface gravity can support larger mountains. Here's some neat info on the subject, + +* http://quarksandcoffee.com/index.php/2015/10/29/why-are-some-moons-spherical-but-others-are-shaped-like-potatoes/ + +* http://adsabs.harvard.edu/full/1981JApA....2..165S + +As an extreme case, the ""mountains"" on neutron stars can only be millimeters to centimeters in height. + +*Edit more info:* + +Note, geologic activity determines what kind of mountain forms and their characteristics including height. The surface gravity is simply a limiter that *if* tall mountains form, they are restricted from getting too tall due to gravity. Here's a lot more info on the geology involved including deformation of tectonic plates and glacial weathering + +* https://www.reddit.com/r/askscience/comments/42j6rf/what_is_the_theoretical_limit_to_how_tall/czbfov4 +" +1382 are black holes super cold? 3841 https://www.reddit.com/r/askscience/comments/brnjxw/are_black_holes_super_cold/ 1558524262 brnjxw 2019-05-22 14:24:22 The temperature of a black hole (due to Hawking radiation) depends on its mass: the more massive it is, the colder it appears to be. Astrophysical black holes are quite cold; a black hole with 5 times the mass of the Sun is about 10^-8 K, meaning that radiation is entirely undetectable. Tiny black holes that could conceivably be created by high energy cosmic ray collisions would be much hotter and evaporate very quickly. "If by temperature you mean the energy of the Hawking Radiation from it, then it depends on how large the black hole is. The temperature is inversely proportional to the mass so the bigger it is the colder it is + +​ + +When most people think of black holes they probably think of the ones in the centres of galaxies, or the borne from dying stars. These are super cold. The HR from these is only fractionally above absolute zero. At this point in time, they don't actually evaporate like you may have heard, because they're colder than the cosmic background radiation of the universe which is around 2.7 Kelvin. So these black holes are actually growing. + +​ + +A black hole the mass of the moon would be warm enough to evaporate. One the mass of Mars' moon Phobo would be around 70 million Kelvin. One the mass of house (\~200 tonnes) would be around around a billion billion Kelvin, but at this point its lifetime is less than a second so it would get **much** hotter **very** quickly and basically explode. + +​ + +You can play around with the numbers [here](https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator)" +432 If Hexagons are the Most Efficient Way to Store Something in Two Dimensions, What is the Best For Three? 3839 https://www.reddit.com/r/askscience/comments/4u0d4o/if_hexagons_are_the_most_efficient_way_to_store/ 1469150679 4u0d4o Mathematics 2016-07-22 4:24:39 [This is the current best solution](https://en.wikipedia.org/wiki/Weaire%E2%80%93Phelan_structure) "It depends on how you define efficient: greatest volume per square unit of packaging? Weaire-Phelan. Least amount of unutilized space? Least amount of wasted space in a shipping container or truck? Different answers altogether. + +Rectangular prisms work really well for most purposes which is why milk cartons and cardboard boxes are common. Weare-Phelan does not work well for packing in shipping containers." +329 Water solubility of caffeine, or, if I use a tea bag a second time has it become mostly decaffeinated? 3826 https://www.reddit.com/r/askscience/comments/478hd1/water_solubility_of_caffeine_or_if_i_use_a_tea/ 1456257889 478hd1 Chemistry 2016-02-23 23:04:49 "I do the same thing, so I got curious about the exact numbers. Fortunately some researchers actually looked at this question systematically in [this paper](http://www.sciencedirect.com/science/article/pii/0963996996000385). The key result is summarized in [this table](http://i.imgur.com/WGSg1Fc.png), where they looked at the fraction of caffeine extracted after different types of tea were steeped for 5 minutes in boiling water three times in a row. The results show some variation from one tea to another, but on average close to 70% of the caffeine was extracted in the first steep and less than 25% on the second steep. + +As expected, bag tea is especially quick to lose its caffeine since its leaves have been smashed apart, giving them a larger surface area. For your purpose this type of tea would be the best candidate. For example for Lipton black tea, only 18% of the caffeine was extracted on the second steep. On the other hand, if you ever want go get more caffeine out of the second or third steep, loose leaf tea has the clear advantage there." [deleted] +568 Megathread: Anti-hydrogen/anti-matter 3826 https://www.reddit.com/r/askscience/comments/5jkwtx/megathread_antihydrogenantimatter/ 1482338786 5jkwtx Physics 2016-12-21 19:46:26 "If you're wondering about the practical applications of antimatter, check out [positron emission tomography](https://www.physicsforums.com/insights/basics-positron-emission-tomography-pet/), which is used to detect tumors. + +[Although the researchers might have a different answer](http://www.smbc-comics.com/?id=2088)" "Why is there such a disparity of antimatter and matter in our observable universe? + +I realize this is difficult to answer with our current knowledge, so allow me to inspire other indirect answers. Is it a problem with our observation? Are the properties of a purely anti-matter systems different than purely matter systems? Do we know of any places in the universe that may resemble our matter-composed systems but in anti-matter systems, considering that annihilation would wipe out any somewhat homoginous regions? + +Also, big thanks to the mods for this thread. This news is really eye-opening to me, as I had traditionally thought of anti-matter as particularly exotic in occurrence and behavior. Seems the latter isn't so true." +1383 [Biology]Can all animals with livers process alcohol? Do all liver's function the same across species or is there variations on what can be processed and to what degree? 3825 https://www.reddit.com/r/askscience/comments/csgkr9/biologycan_all_animals_with_livers_process/ 1566218637 csgkr9 Biology 2019-08-19 15:43:57 "Nope. Livers are different among different species, and not all species can process ethanol equally. + +The human liver produces and enzyme called ADH4 which breaks down alcohol. Most primates have the same enzyme, but Orangutans have a different version. Humans can digest ethanol 50 times more efficiently than orangutans. + + [https://www.popsci.com/science/article/2013-02/chemist-re-enacts-evolution-alcohol-metabolism/](https://www.popsci.com/science/article/2013-02/chemist-re-enacts-evolution-alcohol-metabolism/) + +And the further we get from primates the more differences there are in livers. The shark, for instance, uses their liver to store oil and fat to help them maintain buoyancy. If a human liver stores too much fat then cirrhosis develops and the human dies. + +Polar Bears store so much vitamin A in their livers that it would be lethal for a human to eat it. + +And there are other animals that process ethanol better than humans. Surprisingly, the smaller the animal the higher it's alcohol tolerance: [https://www.nationalgeographic.com/news/2010/2/100209-drunk-bats-fly/](https://www.nationalgeographic.com/news/2010/2/100209-drunk-bats-fly/) + +For more information on how the liver processed alcohol: [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3484320/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3484320/)" "You're getting some great answers, but one thing to add here is that not even all *humans* have livers that process ethanol the same way. Notably, a pretty large segment of the population has ALDH2 deficiency, which leads to a much lower clearance rate and much higher chance of acute toxicity at a given intake relative to an individual with ALDH2 sufficiency. + +https://en.m.wikipedia.org/wiki/ALDH2 + +Given the variance there is even within our species, it's unsurprising to see the larger variations across big taxonomic units. Small amounts of alcohol are prevalent across biochemistry for all sorts of processes and so it's going to be very common for *some* level of metabolic elimination to exist, but humans are definitely on the higher end relative to many other animals." +330 Why is easier to balance at bicycle while moving rather standing in one place? 3818 https://www.reddit.com/r/askscience/comments/4dqqge/why_is_easier_to_balance_at_bicycle_while_moving/ 1460030911 4dqqge Physics 2016-04-07 15:08:31 "This is a surprisingly complicated question to answer. Why are moving bicycles stable? What keeps them upright? + +The most common (and sort of incorrect) answer is that the wheels are like little gyroscopes. Spinning objects like to stay pointed the same direction, and it requires a big torque to change their axis of rotation, which stabilizes the bike. This is sometimes what we tell students in intro classes, and it's not the full story. + +Another reason is the *trail* of the bike. The contact point between the front tire and the ground is a bit off from the steering axis. When a moving bike starts to tip this causes a force which turn the steering column to keep it upright, so the bike is self-correcting. + +Ultimately, the math is governed by a bunch of coupled non-linear differential equations, by the geometry of the bike, and by the parameters of the rider, so there likely isn't any simple intuitive explanation beyond what I've said about a few of the effects above- it's some complicated interplay between a variety of these things. Again, this is an enormously complicated question - [just take a look at how long the Wiki article is!](https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics)" "Whilst the gyroscopic and caster effects contribute to the vertical stability of a bike, the main reason for a bike maintaining its vertical stability is ""front-loaded steering geometry."" + +Essentially, when the bike rolls to one side, the front wheel will turn in that direction first. If the bike rolls to the left, the front wheel turns to the left. The momentum of the bike causes it to try to continue going in the same direction, so the bike rolls to the right in relation to the new direction of the wheel, just like when you slide to the right in a car when you turn left. + +The faster the bike, the more momentum it has and so the greater the force it rolls back in the opposite direction to the wheel turn. The force of the the counter-roll is related to the angle of the wheel and the force from the momentum of the bike. If the bike has more momentum, it won't need to turn as much for the force from the change in momentum to counteract the roll. Therefore, the faster the bike is traveling, the less the wheel will turn before counteracting its roll, which is how stable the bike is. So, more forward momentum gives you more stability so long as the front wheel has a sufficient angle to allow the front to turn first. + +[This video from MinutePhysics explains it well.](https://www.youtube.com/watch?v=oZAc5t2lkvo)" +997 Is there any organism that has more than one brain? 3818 https://www.reddit.com/r/askscience/comments/7y3jyi/is_there_any_organism_that_has_more_than_one_brain/ 1518830421 7y3jyi Biology 2018-02-17 4:20:21 "Octopuses have one central brain and eight smaller ganglia, one in each arm. These ""sub-brains"" allow the arms to do a lot of complicated behaviors on their own, like reaching and grasping, and may even have a form of short-term memory. [Here is a pretty good article on the subject](https://www.scientificamerican.com/article/the-mind-of-an-octopus/), and the book it's based on (""*Other Minds: The Octopus, the Sea and the Deep Origins of Consciousness*"") is also excellent." "Humans who have their corpus callossum (the part of the brain that connects the two hemispheres) severed, actually tend to behave as if there are two people making independent decisions of one another. + +This procedure is only used for patients with severe epileptic seizures, because it reduces the risk of a small seizure spreading to both hemispheres and turning into a grand mal seizure, which can be incredibly detrimental. + +It's maybe not quite on par with having two full brains, but it is rather interesting behavior nevertheless. + +https://en.m.wikipedia.org/wiki/Split-brain +" +228 How can I smell a piece of metal if it doesn't expulse any matter? 3814 https://www.reddit.com/r/askscience/comments/3npcku/how_can_i_smell_a_piece_of_metal_if_it_doesnt/ 1444137559 3npcku Chemistry 2015-10-06 16:19:19 You're probably smelling molecules that are oxidized. Many compounds can react with oxygen in the presence of a metal. That metal acts as a catalyst to facilitate the reaction, and you can smell the oxidized byproduct. "Your sweat and skin is filled with various oils. These are long chains of carbon and hydrogen which serve to store energy and lubricate things and for your skin prevents drying out. When they touch metal they get close, have some of their bonds disrupted, and react (catalysis) into various smelly aldehydes and ketones. + +Exactly which ones are causing the smell varies from person to person. + +https://en.wikipedia.org/wiki/Oct-1-en-3-one + +http://www.ncbi.nlm.nih.gov/pubmed/16218683 + +But this is one of the major ones. Humans can smell it at a very low concentration." +1384 Why did the Fukushima nuclear plant switch to using fresh water after the accident? 3808 https://www.reddit.com/r/askscience/comments/bunchi/why_did_the_fukushima_nuclear_plant_switch_to/ 1559180731 bunchi 2019-05-30 4:45:31 "Salt is corrosive. As water boils in the core, the salt concentrates, and you get deposits that impinge heat transfer. With enough salt you can eventually have molten salt which is harder to manage. If you had any intact fuel, the salt and sediment from raw water will plug the fuel inlet debris strainers, preventing adequate cooling (this can be bypassed by raising water level above the steam separator skirt, but was not in the emergency operating procedures at the time). + +Fresh water is the best option." In addition to the corrosion problem, saltwater is activatable. That means that when you pump saltwater through a reactor, the saltwater becomes radioactive. Water itself doesn’t become radioactive. I’ve seen people drink high-purity freshwater after it was taken out of a reactor. It’s fine. The salt and minerals and debris in the water is what is activatable and what becomes radioactive. So since water was leaking everywhere, in and outside of the plant, this becomes a means of limiting the release of radioactivity from the power plant to the environment. +433 Did relativity HAVE to be discovered mathematically? Could we have discovered the exact equations empirically? Say from observing the difference in clocks on the ground vs on satellites 3799 https://www.reddit.com/r/askscience/comments/4hx9g8/did_relativity_have_to_be_discovered/ 1462404319 4hx9g8 Physics 2016-05-05 2:25:19 Something that is seldom noted is that most of the basis for special relativity had already been laid down experimentally and mathematically prior to 1905, Maxwell's equations, the Michelson-Morely experiment, and the Lorenz equations being most notable. What Einstein did was put all these things together and studied their ramifications. "This sort of happened with the [Fizeau water experiment](https://www.physicsforums.com/insights/speed-light-galilean-relativity/) in 1851. Fizeau was trying to measure the change in the speed of light through moving water. What he found was that the interference pattern between light that went through ""forwards"" and ""backwards"" water was about half as strong as it would be if the speed of light through the water were (c/n+v) and (c/n-v), where n is the index of refraction and v is the velocity of the water. We now know that if you apply the special relativity velocity addition formula , you get a factor of about 0.43 compared to the naive prediction, explaining Fizeau's result. + +That being said, it's possible that the history of science could have progressed differently than it actually did, perhaps reaching the space age before relativity was discovered and noticing more anomalous effects. But, that's not what happened, so we can only speculate. Eventually, someone would have tried to theorize about what was happening to cause these anomalous measurements." +569 What might be different if the earths rotation was in the other direction? 3799 https://www.reddit.com/r/askscience/comments/5264rg/what_might_be_different_if_the_earths_rotation/ 1473555022 5264rg Planetary Sci. 2016-09-11 3:50:22 "Thinking about unexpected consequences: the direction we call ""clockwise"" would probably be reversed. Clocks go in that direction to match the direction of motion of the shadow on a sundial (in the northern hemisphere). Reverse the Earth, you reverse the shadow, so clocks would probably be built to run the other way. + +https://www.quora.com/Why-do-clocks-run-clockwise" "Well for one thing the Coriolis effect would be reversed, meaning all of the prevailing winds in the world would be the opposite of what they are now. Most of your westerly winds would be easterly and so on. This would cause oceanic currents to flow in different directions as well. The combination of these two things would make the climate radically different. On the simplest level, the North East of the US would probably be similar to the Pacific Northwest or maybe europe. Cool temperate and rainy with dry summers. The southeast would be very dry and desert-like. The West coast would have much colder winters but would be probably more consistently rainy, especially down in Southern California. And they would get hurricanes as well. + +Of course there would probably be other, less symmetrical changes in climate depending on the exact way the air and water currents would interact with the shape of the land and water. But those would be difficult to predict without a complex computer model." +434 Are things like peanut butter, cream cheese, jellies etc. considered a liquid or a solid? 3797 https://www.reddit.com/r/askscience/comments/4kl4vf/are_things_like_peanut_butter_cream_cheese/ 1463960155 4kl4vf Physics 2016-05-23 2:35:55 "Each of the things that you mention are [colloids](https://en.wikipedia.org/wiki/Colloid), which are relatively stable mixtures of multiple substances. Peanut butter is a suspension of peanut solids in oil; jelly is water suspended in either pectin or gelatin (depending on your definition of ""jelly""); cream cheese is … more complex. + +Edit: A few people have pointed out that I have failed to classify them as liquids or solids. The point is that they're neither. They are, literally, a combination of both." "It's sort of like saying that a jar full of marbles sitting in water is a ""solid"" or a ""liquid,"" but at a smaller scale. It's not really either, it's a mixture of the two. In these cases, they are finely distributed enough that it's convenient for us to call them a single substance like ""peanut butter"" but not so finely distributed as to really make much sense to say it is a single substance at a molecular level. In fact, if you leave lots of peanut butters or similar sitting around for awhile, you can easily see fully macro-level separation of the mixture with your naked eye. + +(edit: In the case of very meticulously made uniform jelly unlike typical grocery store brands, there may actually be a molecular level substance that may be called a single substance, I can't speak to that, but not most of the above)" +435 Since radio waves and light are both forms of electromagnetic radiation, is it possible to detect visible light with an antenna? 3797 https://www.reddit.com/r/askscience/comments/4iechk/since_radio_waves_and_light_are_both_forms_of/ 1462709920 4iechk Physics 2016-05-08 15:18:40 "What you are describing does exist and is called an optical antenna. However, unlike their RF counterparts, optical antennas have not yet quite made it out of research labs. The reason for this difference is that it is much harder to make efficient antennas that are sensitive to visible light than to longer wavelength EM radiation (as in the micro-wave and radio-wave range). + +Deep down, all antennas have one key goal: to shuffle EM radiation between a localized transmitter/emitter and spread-out waves (far field radiation), as shown in [this diagram](http://i.imgur.com/YWTZ9GY.jpg). (I took the figure from [this paper](http://www.nature.com/nphoton/journal/v5/n2/abs/nphoton.2010.237.html), which gives a good introduction to the field.) In the receiving mode, the antenna would efficiently funnel in these far field waves and transfer this energy to the receiver. In the transmission mode, the antenna would instead take the energy from the transmitter and transform it into far field waves. Everything I have described so far works mostly the same for radio and optical antennas. + +However, where we start running into trouble is the fact that a good antenna has a size comparable to the wavelength it operates in. If the ideal size of radio antennas falls in the [range of multiple meters](http://i.imgur.com/eu4hMnB.jpg), for optical antennas, we would need to hit [a range of ~100nm](http://i.imgur.com/l0B0zML.jpg). As you can see in the last image, fabrication wise, we can make structures of the size we need, even if the actual manufacturing can be challenging. The biggest problem, however, is that the electronic properties don't simply scale down with the size in a straightforward way. + +At the low frequencies of radio-waves we can treat the antenna as an almost perfect conductor. On the other hand, at optical frequencies we are nowhere close to this idealized case. In these small optical antennas, EM radiation causes electrons to [slosh and back collectively](http://i.imgur.com/t7aKh01.png) in what we call [plasmonic modes](https://en.wikipedia.org/wiki/Plasmon). This sloshing causes a large fraction of the energy to be lost as heat (it's a form of resistive heating). Moreover the exact nature of these plasmonic modes strongly depends on the exact shape of the antenna. As a result, the design and fabrication of these antennas becomes much more complicated, as is placing the transmitter/receiver in just the right spot near the antenna. + +**Tl;DR:** Optical antennas are possible and they are being developed (and used) in research labs. However, making the damn things is hard for two main reasons. 1) It's harder to design and make structures at the nano scale. 2) While the metal in RF antennas is mostly a boring conductor, physics gets much messier when you put small chunks of metal under optical frequencies." "Late to this party. Lots of people have correctly mentioned the existence of optical scale antennas. + +However lots of people are confusing optical detectors with antennas. The idea of an antenna is to convert free space electrical fields into measurable electrical signal. When you are working with rf frequencies it is easy to measure as a Ghz sampler can easily process the lower MHz signal. + +However no samplers exist that can process the 14THz signal in the optical range. What you have is power detectors such as diodes that rectify the signal. At most you have some optical processing such as a phase detection loop but in the end you get a signal, not a waveform. This is the main difference when you move from microwaves to the infrared frequencies." +124 I can type without looking at the keyboard, but when asked to draw a keyboard, I am completely unable to correctly label half of the letter keys. How is this possible? 3789 http://www.reddit.com/r/askscience/comments/3c8d1u/i_can_type_without_looking_at_the_keyboard_but/ 1436131262 3c8d1u Psychology 2015-07-06 0:21:02 [deleted] "Can't you just pretend to type a word and figure out where the letters are? I know where the letters are in reference to my fingers. So ""i"" is right middle finger up. I could easily use that to draw a keyboard. It is much easier to pretend to write out a word while paying attention to where the fingers want to go. " +229 AskScience AMA Series: We’re Hannah Morris and Becca Peixotto, two of six “slender spelunkers” who excavated 1,500 individual hominin bone fragments deep in a South African cave over the course of 21 days, Ask Us Anything! 3781 https://www.reddit.com/r/askscience/comments/3l5u68/askscience_ama_series_were_hannah_morris_and/ 1442404958 3l5u68 Archaeology AMA 2015-09-16 15:02:38 "Hi guys, a few questions: + +How did you record spatial information in such a challenging environment? + +What was the sediment like? Most of the time you hear about south Africa its all about fossils in breccia. However, rising star seemed like the fossils were just loose in dirt, was that true? + +What's the plan for dating?" I know that one of the leading hypotheses is that the remains were found in a burial chamber. If it isn't a burial chamber, why does the team think the remains are there? Is it possible that the individuals wandered into the cave over thousands of years and simply got lost - thus, eventually dying in the cave? The documentary that I watched shows how impossibly dark the cave is. It seems like it would be easy to get stuck in there. +436 Whats the difference between moving your arm, and thinking about moving your arm? How does your body differentiate the two? 3781 https://www.reddit.com/r/askscience/comments/4le6md/whats_the_difference_between_moving_your_arm_and/ 1464404887 4le6md Neuroscience 2016-05-28 6:08:07 "There is a fair amount of evidence from fMRI, PET and EEG studies that show involvement of the primary motor cortex in motor imagery tasks. I've performed a bunch of experiments with EEG motor potentials during ballistic movements (they evoke sharp, strong and easy to detect signals in the EEG), and I've even been involved in a brain-computer interface experiment which pretty successfully detects motor imagery so motor imagery is definitely activating very similar regions to what an actual movement activates. + +So, looking at the evolution of scalp potentials over time around the time of a ballistic movement, there's a clear bilateral activation of frontal areas up to one second /before/ movement (the (in)famous bereitschaftpotential) that ""travels"" towards the back of the head as motor planning takes place and gives way to motor execution and, later, the evaluation of visual and proprioceptive feedback from the execution of the movement. At some point, the cortex will ""assemble"" a motor command which then is, possibly, ""filtered"" through lower structures and the cerebellum (which seems to play a prominent role in error processing and correction), to be then sent through the wires in the spine to respective muscles. + +As far as I know from reading, experiments and the wisdom of my superiors, motor imagery pretty much runs the same ""program"" up to a point, but the motor command is never sent. Some groups have reported interesting results on motor imagery for motor learning (ie. training), showing that rehearsing, or ""visualizing"" a movement, seems to have effects closely resembling actual training to some extent. Of course it will never be as efficient as actual training with feedback, but it does inform us somehow. + +Since motor imagery is usually dependent on visualizing the movement (more or less vividly), there is some speculation that mirror neurons are more involved than pathways and cells more related to actual movement, but it's all speculation at this point. + +So in short, the difference is relatively small, as the brain still has to compute the movement, predict the outcome, and ""imagine"" the results. A lot of the chips and wires used will be the same as the ones used in actually moving, but we can consciously suppress the motor output, so in a sense, the body doesn't have to differentiate anything, because nothing really leaves the brain. + +I just woke up so I might not make sense, I can dig up some interesting sources later if there's more interest. + +src: Msc biomedical engineering, 2+ years working on eeg, motor learning, bci, reflexes, electrical stimulation etc. + +edit: holy crap that's a lot of questions in the comments! I'll do my best to try and answer as much as i can, thanks for the interest" "One theory, the ideomotor theory, explains this quite well. Every action has an associated idea. Whilst the action itself originates from the motor cortex and is calibrated through the subcortical structures, such as the basal ganglia and cerebellum, it is argued that the action is driven by the idea/intention of the action in the premotor cortex. + +What is fascinating is that these neurones in the premotor cortex, 'mirror neurones', will fire to some degree when an individual observes the action in someone else, leading credence to the ideamotor theory. + +I would guess that you are only activating the idea/'mirror neurones' when imagining then recruiting the motor cortex neurones when actual movement occurs. + +If you are interested in the topic you really should look into the mirror neurone system. + +Source: Doctor with MSc in functional neuroimaging." +230 We have Einstein's brain preserved in formaldehyde. Are all the synapses still wired up the same as when he was alive? Could some future civilization recreate a form of Einstein from this? 3778 https://www.reddit.com/r/askscience/comments/3vsnws/we_have_einsteins_brain_preserved_in_formaldehyde/ 1449500190 3vsnws Neuroscience 2015-12-07 17:56:30 "Recreating a working brain from a preserved specimen would be entirely speculative. We have no idea if something like that is possible. + +As for Einstein's brain, you may not realize that it was dissected and cut into 240 small cubes of about one cubic centimeter each, then the pieces were distributed to researchers. I seem to recall that some of the pieces went missing also. So the brain isn't intact. Even if it could somehow be made to work again, it would have to be reassembled first, which at this point is unlikely." Even you pulled a brain out of a corpse and dropped it into formaldehyde immediately after death there would still be too much damage to reconstruct. Decay starts immediately and even when living people almost die from oxygen depredation they still have brain damage sometimes. Neurons are too delicate to hold connections together without constant repair by their cellular mechanisms. A single neuron losing all of its connections could change pathways that guide thoughts and memories. Too many lost connections and it would be impossible to figure out what connected to what. It would be like cutting all the letters out of a book and dumping them into a box. You have all the letters but you don't know their order making them useless. +570 Can pi be expressed rationally in a non base 10 number system? 3768 https://www.reddit.com/r/askscience/comments/57wvdw/can_pi_be_expressed_rationally_in_a_non_base_10/ 1476704554 57wvdw Mathematics 2016-10-17 14:42:34 Regardless of the base, PI will always be irrational and transcendental. Properties of numbers hold regardless of base because the base is just a way of representing the number, not defining it. You could put 3 in any base you felt like and it would still be a prime odd number. "No. + +The definition of a rational number is that it can be expressed as the ratio of two integers. So a number X is rational if there exists integers A and B such that X = A / B. + +Note that this definition is completely independent of the number system. " +125 Why isn't there an animal that could live for 1,000's of years? 3767 http://www.reddit.com/r/askscience/comments/37gjpv/why_isnt_there_an_animal_that_could_live_for/ 1432734500 37gjpv Biology 2015-05-27 16:48:20 "The jellyfish *Turritopsis nutricula* is biologically immortal and could, under ideal conditions, live for 1000s of years. After sexually reproducing, this jellyfish can revert back to the immature polyp stage (back into a “child”). The jellyfish can still die due to predation, but aging is not a problem for it. The exact mechanism for this is not yet well understood. [Article on aging and the immortal jellyfish]( http://www.sciencepub.net/stem/stem0504/007_A00288stem050414_49_53.pdf) + +**EDIT:** More credible sources, as the first one I posted is a bit sketchy, as pointed out by /u/SirT6 below. + +[Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa)](http://www.jstor.org/stable/1543022?origin=crossref&seq=1#page_scan_tab_contents) + +[A silent invasion](http://link.springer.com/article/10.1007/s10530-008-9296-0/fulltext.html) + +Note: The last article uses *Turritopsis nutricula* instead of *Turritopsis dohrnii* but it's now thought that the two species names [may refer to a single species](http://onlinelibrary.wiley.com/doi/10.1111/j.1439-0469.2006.00379.x/abstract;jsessionid=E51AAF9938A2B0E2FF223A0324D85A89.f01t03)." "Physiologist here, my dissertation is on the physiology of aging (specifically telomeres) in a long-lived bird species. + +I think another way to think about the question is: *Why do organisms age?* - from an evolutionary perspective. This helps explain why 1000yo eukaryotes aren't prolific. Others have covered the biologically immortal species, so I won't talk about those...but also look up hydra, which don't age if they reproduce asexually, but once they start reproducing sexually they do! + +Darwin (1859) suggested that lifespan, like other species traits, should be affected by selective pressures. Three major evolutionary theories of why aging exists: 1) the theory of programmed death, 2), the antagonistic pleiotropy theory of aging, and 3) the mutation accumulation theory of aging. These theories are not necessarily mutually exclusive, and it is likely that the reality of aging that we observe in nature is an aggregate of two or more of these theories (Kirkwood and Austad 2000). + +The programmed death theory states aging (and death) evolved to replace less fit individuals in a population with younger ones with more reproductive potential (Weismann 1891). There is, however, limited evidence of senescence directly linked to population mortality in the wild, and natural mortality is likely linked to extrinsic factors like predation, infection or environmental +hazards (Kirkwood and Austad 2000). There are no known evolutionary mechanisms that could yield such a result, so though the theory was foundation for later hypotheses, it could likely be ""relegated to the dustbin of old ideas."" + +The power of natural selection declines with age once reproduction begins (Medawar 1952). Therefore, genes that results in a loss of fitness early in life, particularly before reproduction, are under strong negative natural selection and genes that have negative effects later in life face little selective pressure. Genes can be both adaptive at early age and hazardous at older ages, or pleiotropic genes. Rose and +Charlesworth (1980) demonstrated the presence of these genes in *D. melanogaster.* + +The programmed death theory was elaborated as the “Disposable Soma” theory by Kirkwood, where individuals must balance the allocation of resources between germ and somatic cell lines. Aging occurs as a result of the accumulation of damage during life, and though maintenance and repair mechanisms have evolved, they cannot mitigate the damage, resulting in aging (Kirkwood and Austad 2000). This theory also suggests that the variation of lifespan for individuals within a species could be a result of variable maintenance systems. Under the accumulation theory of aging, the free-radical theory of aging, proposes that reactive oxygen species (ROS), produced in stress and metabolism lead to damage in both DNA and cellular material. The mitochondrial theory and telomere theory of aging also exist under the umbrella of the accumulation theory. + +edit: formatting" +437 Hi, my name is jack, I'm 14 years old, and I love Baseball. I would like to know when a pitcher throws a baseball, how does it curve? 3767 https://www.reddit.com/r/askscience/comments/50cg2n/hi_my_name_is_jack_im_14_years_old_and_i_love/ 1472579607 50cg2n Physics 2016-08-30 20:53:27 "Hi Jack, a baseball can curve for a number of reasons. + +For a knuckleball, the ball moves around as it approaches the catcher because it isn't spinning. Spinning helps stabilize the ball, and prevents small turbulent effects from affecting its flightpath. A non-spinning ball isn't perfectly spherical, so as the air comes off the face of the ball, it creates turbulence in the air, and causes the ball to move erratically. You can see an example of vortex shedding here: +https://www.grc.nasa.gov/www/k-12/airplane/Images/mix.gif + +For something like a curve ball, the spin of the ball is what causes it to move in a certain direction. As the ball spins, one side goes in the same direction as the air passing the ball, and the other side goes in the opposite direction of the air passing the ball. The side that moves in the same direction accelerates the air slightly (imagine the surface being rough, and acting to push the air as it goes by). The side going in the opposite direction slows the air slightly. As air accelerates, the pressure drops, and as it slows, the pressure rises (this is how planes fly). The net result is that the ball gets pushed by this pressure difference. With a top spin, you'll see the ball dropping, and with a backspin, you'll see the ball rising (or at least not dropping as quickly). If you apply this to a side spin, it'll cause the ball to curve from left-to-right or right-to-left. + +It's worth noting that fluid dynamics is super complicated, but that's a pretty simplified explanation. + +EDIT: THANKS FOR THE GOLD!" "The knuckle ball you see in the gif has almost no spin, which makes it susceptible to slight turbulences and variations in the air, which can push it one way or another (or more than one way) as it approaches the plate. The pitcher has no idea which way it will curve and, as you can see, neither do the batter or catcher. + +The knuckle ball is unique as the only pitch that doesn’t have deliberate spin. Fastballs, curves, sliders, etc all are given spin as the ball is released from the pitcher’s fingertips. Any ball moving rapidly through the air creates a wake of turbulence behind it. It also carries a thin layer of air along with it. + +When a spinning ball is moving through the air the spin influences the wake of turbulence behind it, pushing it in the direction that the back of the ball, the part facing the pitcher. Some of the thin layer of air traveling with the ball is also stripped off and thrown in that same direction. Because of conservation of momentum and Newton’s third law, if a mass of air is pushed one way, the ball will be pushed the other way. For instance, a fastball, because of how it leaves the pitcher’s hand, has backspin. The top of the ball is spinning in the opposite direction of travel and the side facing the pitcher is spinning down. That makes the turbulent wake move down and thus causes the fast ball to rise. (It doesn’t actually rise, but it doesn’t drop as much as it seems it should.) + +A curve ball is thrown with a top spin, pushing the wake upward, making the ball curve down. The pitcher might throw the curve with the top spin at a slight angle, making it curve down and away. + +They say the ball breaks, meaning it seems to curve just before it reaches the plate. In fact it is curving all the way there, but when it is near the plate is has slowed down enough that the curve is more pronounced. + +The effect caused by the spin pushing the air in one direction and the ball in the other is called the [Magnus Effect.](https://en.wikipedia.org/wiki/Magnus_effect)" +438 "Tuataras have a ""third eye"" that is ""no longer"" used for vision. Was it earlier in evolution? Are there creatures with 3 functional eyes in the fossil record?" 3763 https://www.reddit.com/r/askscience/comments/4z2ie1/tuataras_have_a_third_eye_that_is_no_longer_used/ 1471896613 4z2ie1 Biology 2016-08-22 23:10:13 "I wouldn't overstate the bilateral symmetry you're talking about. We have one heart, one liver, one stomach, etc, none of which are located exactly on our line of symmetry. + +The third eye ([parietal eye](https://en.wikipedia.org/wiki/Parietal_eye)) is found in a number of animals (some reptiles, amphibians, and others). While it shares ancestral origins with 'regular' eyes, it seems to have developed mostly for sensing light/dark for circadian purposes (since it is basically hooked up to the non-human version of the pineal gland). + +'Eye spots' and other photoreceptors seemed to have emerged around 60 million years before the Cambrian explosion, during which a ton of different body plans emerged, many of which ended up being evolutionary 'dead ends'. I don't know if any of them featured three equally functional eyes, but my bet would be 'yes'." [deleted] +998 Why is the Liver one of the only organs that grows back when most of it is removed? 3762 https://www.reddit.com/r/askscience/comments/7ri2kk/why_is_the_liver_one_of_the_only_organs_that/ 1516365946 7ri2kk Human Body 2018-01-19 15:45:46 "The best explanation right now seems to come down to two main factors. + +1) Liver cells (called hepatocytes) have a relatively high rate of division in response to acute injury, which allows them to replace liver cells that have been damaged or are missing. This is similar to skin cells (fibroblasts and keratinocytes), but unlike, for example, heart cells (cardiomyocytes) which have an exceptionally low rate of division. + +2) A special type of liver regeneration helper cells called ""hybrid hepatocytes"" was recently discovered by a group at UCSD, which appear to facilitate regeneration and reduce the risk of tumor formation (which can be an unfortunate side-effect of attempts at regenerative therapies). + +https://health.ucsd.edu/news/releases/pages/2015-08-13-cells-regenerate-liver-without-tumors.aspx + +Edit: Thanks to /u/Mr_Stitch for clarification on maintenance vs acute injury replacement rates for hepatocytes." "In addition to these other answers, it should be stated that the liver DOES NOT regenerate like you're likely imagining. It's not like a starfish, no complex structure is rebuilt. + +A standard liver has two lobes, each with its own major artery. During a liver transplant, one lobe is removed and transplanted. In both donor and recipient, the half liver they're left with just swells up to occupy the space given and meet needed capacity rather than regrowing the other lobe. They can't donate again after the first. + +It's very much like donating a kidney. You're left with half of what you had before, but it amps up to meet the body's needs. " +1385 AskScience AMA Series: We are vaccination experts Dr. H Cody Meissner and Dr. Sean Palfrey, here to answer anything about vaccines with the help of the Endless Thread podcast team! AUA! 3762 https://www.reddit.com/r/askscience/comments/cgr5bz/askscience_ama_series_we_are_vaccination_experts/ 1563879661 cgr5bz 2019-07-23 14:01:01 The AMA will begin at 1pm ET (17 UTC), please do not answer questions for the guests till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Keep questions and interactions professional and remember, asking for medical advice is not allowed. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). Why is there no Lyme disease vaccine/prevention for humans yet there is for dogs? +331 Maria Sharapova just got in trouble for using meldonium; how does this medication improve sports performance? 3759 https://www.reddit.com/r/askscience/comments/49gyvf/maria_sharapova_just_got_in_trouble_for_using/ 1457414590 49gyvf Medicine 2016-03-08 8:23:10 "According to the World Anti-Doping Agency (WADA), meldonium acts as a ""metabolic modulator."" It improves sports performance by stopping the carnitine activities and stops the mitochondria from being overloaded by fatty acid breakdown during exercise and instead shifts the focus towards breaking down carbohydrates, which requires less oxygen to be taken away from muscles. By reducing the pressure on the mitochondria, meldonium reduces the amount of urea and lactate in the blood and allows for improved oxygen transport to the muscles to aid not only in performance but in recovery. + +Source: http://www.abc.net.au/news/2016-03-08/what-is-meldonium-and-what-does-it-do-to-your-body/7228670" "Because meldonium medically has been shown to improve the exercise capacity of injured tissues (for example, injured tissues in the heart in heart attacks), it has been used without any approval for increasing exercise capacity of noninjured tissues (like muscles and a healthy heart). One of the major issues with meldonium is that it's quite unknown. Many of the claims of its performance enhancement are largely untested, but rather used anecdotally and to ""keep up"" with other athletics trends trends and dopers. + +The mechanism of action would be likely of one of modifying a number of metabolic pathways, some understood (like the one you suggested), and others not well understood. Our metabolisms are very complex, and many effects have multiple inputs and modifiers. + +The simplistic answer is that it seems to reduce oxidative stress on tissues. + +Edit: digging a little deeper into the original research on this compound is kinda weird because it is mostly eastern block stuff. But I did find this: + +http://www.sciencedirect.com/science/article/pii/S1043661815301717" +332 Would it be more fuel efficient and less dangerous to float a rocket into the upper atmosphere with balloons before igniting the boosters? 3757 https://www.reddit.com/r/askscience/comments/445m8t/would_it_be_more_fuel_efficient_and_less/ 1454598293 445m8t Physics 2016-02-04 18:04:53 "What you are talking about is [Rockoon](https://en.wikipedia.org/wiki/Rockoon) and yes - it has been done in past, but so far only for a [sounding rockets](https://en.wikipedia.org/wiki/Sounding_rocket). + +There's a Spanish company called [zero2infinity](http://www.0ll00.com/) planning to use that concept for [launching](http://www.gizmag.com/zero2infinity-balloon-rocket-launch/34315/) nanosatellites in a rocket called [Bloostar](http://bloostar.com/). + +The major advantage of this method is that you can use engines with [nozzle](https://en.wikipedia.org/wiki/Rocket_engine_nozzle) suitable for vacuum right off the bat - no need to have a stage for initial takeoff in dense atmosphere. You also don't have to worry too much about [Max Q](https://en.wikipedia.org/wiki/Max_Q) cause atmosphere is already very rare at this altitude, so you can have a light fairing and (basically) as high acceleration rate as you want. That makes rocket more efficient, saving fuel and reducing mass. Obviously though - you still need to accelerate to keep your spacecraft in orbit, which is where most of the energy from launch goes. +" "First, you would need a very large amount of balloons, which would make things quite complicated on the ground already. And in the air, when you detach the balloons and ignite the rocket, you'll have to do it in such a way that the balloons and all the components used for the connection don't get in the way. + +Next issue is the fact that balloons are hard to control. The rocket can end up pretty much anywhere depending on which direction the wind feels like blowing. The actual destination of the rocket is often rather precise, so additional effort has to be put in getting the rocket back in the right direction. + +But the biggest issue of all is the fact that getting to space is really quite simple and cheap. The problem is staying in space. In order to get to space and stay there, you have to fly rather high, but mostly really fast to avoid falling back to Earth. The balloons will help somewhat with flying high once you've overcome the issues I mentioned before, but by far the most energy goes into flying really fast and the balloons don't do anything there. + +See also this What-If post: +https://what-if.xkcd.com/58/" +897 Can there be an orbit around a black hole in which the apoapsis is above the photon sphere, but the periapsis is below the event horizon? 3757 https://www.reddit.com/r/askscience/comments/7949fv/can_there_be_an_orbit_around_a_black_hole_in/ 1509120985 7949fv Astronomy 2017-10-27 19:16:25 "No. No orbit can have Periapsis within or at the photon sphere. There are no stable orbits within that region. Within that region to escape to infinity you must expend work to escape constantly. + +Generally orbital mechanics uses Newtonian gravitation. Here the potential energy of an orbit would decrease as one gets closer and closer to a gravitational well. This is not the case with black holes and general relativity. Scott Manley has a really good video about there here. [How close can you orbit a black hole](https://www.youtube.com/watch?v=IM8HvoaKsBU)" "No. +This is one example that pretty dramatically shows the difference between classical mechanics (under which that would be possible) and general relativity. +An object orbiting a black hole at close range will not be in an elliptical orbit, but spiraling inwards, giving off energy in the form of gravitational waves. In fact, all orbits do this, but it's so insignificant except in extreme cases that it doesn't really matter." +439 Photons are massless, but yet possess some energy, can this energy be converted to mass? Can a photon become to a piece of mass at some circumstances? 3755 https://www.reddit.com/r/askscience/comments/4mcgi1/photons_are_massless_but_yet_possess_some_energy/ 1464953831 4mcgi1 Physics 2016-06-03 14:37:11 "If a photon with an energy greater twice the rest mass of an electron hits something (like an atomic nucleus), it can induce the creation of a positron-electron pair. This is the main mechanism of energy loss for very high energy gamma rays passing through matter. + +However, this can't happen without the photon interacting with something else first, otherwise you could construct a reference frame where the photon doesn't have enough energy to do this. + +edit: As I mentioned in a comment below, at extremely high energy densities you can start to get light interacting with itself and inducing pair creation, which can slow down [the speed of sound through a photon gas](http://klotza.blogspot.com/2016/05/the-speed-of-sound-in-light.html)." "Yes, and this is one of the fundamental principles or properties of the universe. Photons can convert into mass, and mass gets converted into photons, and importantly, this happens all the time. + +This can occur via the creation of whole particle / anti-particle pairs, but also from the emission and absorption of photons from or into atoms / electron orbitals, which can also affect mass. Absorbing a photon can cause an increase in mass, and emitting one can cause a decrease. + +Photons and mass are continually making exchanges, all the time, which is pretty cool." +126 How far underwater could you breath using a hose or pipe (at 1 atmosphere) before the pressure becomes too much for your lungs to handle? 3744 http://www.reddit.com/r/askscience/comments/3ap7dk/how_far_underwater_could_you_breath_using_a_hose/ 1434971862 3ap7dk Human Body 2015-06-22 14:17:42 "Ah, I've answered this question before in /r/geek. The original that I answered was ""Why don't we use really long snorkels? "" + +The average forced vital capacity (assuming you are breathing as hard as you can with every breath) is roughly 4200 mL. For a 2 cm wide snorkel you'd need about 13.5 meters of snorkel tube to waste 50% of that as dead space. However! Dead space is decidedly *not* the issue if you are heading underwater. Besides, you can inhale through the tube and exhale into the water, as someone cleverly mentioned. + +The average healthy male can generate about -120 cmH2O (-80 to -100 for females) of what's called **negative inspiratory force**, or ""ability to suck"" if you like. However, you need a *difference* of about 40-60 cmH2O to breathe effectively which translating to about 50 cm of depth under water, is the number at which other people in this thread have suggested is when it gets really hard to pull air down. + +Basically, the pressure difference between you and the surface would be significant when you push past about a half meter. That's a lot of extra work for lungs that are used to about 0 atmospheres of difference, so you probably aren't strong enough to take the entire forced vital capacity because inhaling will be *so hard*. + +If you were just hanging out at ground level and attempting to breathe only through a long snorkel (or just a giant straw at this point) then dead space in the snorkel will be what makes you pass out. + +Edit: Frequently asked questions (too many to reply to individually) + +* What is dead space? + +It's air that's being pushed back and forth without any significant oxygen/CO2 exchange happening with your lungs. Basically, air that's not doing any work. + +* What about SCUBA gear? + +As someone answered already, diving cylinders are hooked up to apparatuses that allow you to breathe in a gas mixture at the same pressure as the surrounding ambient pressure, so there's no large pressure gradient to overcome. + +* What if there's a pump? + +Well, then you'd no longer be breathing on your own to overcome the pressure gradient. That's what [surface-supplied diving](https://en.wikipedia.org/wiki/Surface-supplied_diving) is, and they seem to historically have been used in the 1800's. + +* What if I have a large lung capacity? Does a higher FVC affect how far I'd be able to go down? + +No. The limiting factor is the amount of negative inspiratory force you're able to generate, which is dependent on how powerful your diaphragm is. Even if you had exceptionally powerful respiratory muscles, you'd get maybe a few more centimeters or tens of centimeters down the water. + +* Air compresses and you need to breathe in more air to get the same oxygenation + +Someone had this misconception but this is actually *not* a significant factor because in our scenario the air is still openly connected to the atmosphere. If you are breathing in air through a rigid pipe it will not compress significantly. If you walked from the top of a flight of stairs to the bottom you are not suddenly gasping for air (unless it's for other, more medical, reasons). + +* Guys suck more than girls lmao + +Well meme'd, my friend, but 50 others have made the same joke. + +* I would like this in freedom units please + +50 cm (depth at which it becomes hard to breathe ) is about a foot and a half to two feet. 13.5 meters is 44 feet." "From experience, not very far. +It all depends on the diaphragm strength. But I would say about 50 cm. It is already very difficult to breathe through a 35 cm tube. + +1 m seems definitely impossible (it would feels like you try to breathe with a horse sitting on your chest). + + +Even if you could compensate the overpressure, the other factor would be that the air in the pipe will contain the air you just expelled (high in CO2 and poor in O2). It would be like you are breathing in a sealed plastic bag. + +A 40 cm pipe with a radius of 2 cm contains 1L of air. This ""dead"" air will be the first litre of air you breathe each time. + +Note that at rest we normally breathe about 0.5L." +231 Since DNA is an acid, is there such thing as DNA salts? 3739 https://www.reddit.com/r/askscience/comments/3q9ue1/since_dna_is_an_acid_is_there_such_thing_as_dna/ 1445863206 3q9ue1 Biology 2015-10-26 15:40:06 Not only can DNA exist as a salt, but this is pretty much its standard form in the solid state. In an aqueous medium, DNA exists as a conjugate base with negatively charged phosphate groups stabilized by a bunch of [counterions](https://en.wikipedia.org/wiki/Counterion) that are floating around in the solution such as Na^(+). When you precipitate the DNA (e.g. as is most commonly done through the [addition of ethanol](https://en.wikipedia.org/wiki/Ethanol_precipitation)), these cations will bind to the phosphate groups and the DNA will precipitate out as a salt. "Interesting tidbit: The salt of inosinate (RNA monomer, equivalent for the present question) is a common food additive. One of the many umami flavor molecules. I think it was discovered by the same guy who first found MSG. +It is likely that the neutral molecule is an internal salt - phosphate deprotonated and the base ring is protonated. " +440 What Earth microorganisms, if any, would thrive on Mars? 3739 https://www.reddit.com/r/askscience/comments/4vff6z/what_earth_microorganisms_if_any_would_thrive_on/ 1469935001 4vff6z Biology 2016-07-31 6:16:41 "[Chroococcidiopsis](https://en.m.wikipedia.org/wiki/Chroococcidiopsis) comes to mind: + +>Due to its resistance to harsh environmental conditions, especially low temperature, low moisture, and radiation tolerance, Chroococcidiopsis has been thought of as an organism capable of living on Mars.  + +As other commenters have said, the lack of water on Mars would probably prevent these guys from growing on their own. But with a little human intervention, they may be able to grow in Martian soil and help with the terraforming process (assuming we ever terraform Mars). + +Edit: for anyone interested in a great vision of colonizing and terraforming Mars, I highly recommend the Mars trilogy (Red Mars, Green Mars, Blue Mars) by Kim Stanley Robinson!" "There's been research into the viability of halophilic and methanogenic bacteria in simulated Martian sub-surface conditions; as long as they're far enough below the surface that they have access to liquid water (most likely a below-freezing brine), it seems like they're viable. + +What I don't know is if they tested for Martian radiation levels, or if radiation is even a significant factor at the depths in question." +232 "Would drinking ""heavy water"" (Deuterium oxide) be harmful to humans? What would happen different compared to H20?" 3738 https://www.reddit.com/r/askscience/comments/3n3pw2/would_drinking_heavy_water_deuterium_oxide_be/ 1443707961 3n3pw2 Chemistry 2015-10-01 16:59:21 "Ok, I Drank 1 liter of heavy water once. Followed by daily intake of 200 ml of heavy water. + +The reason why I did this was for an medical experiment I was participating. They used this to track the turnover of T1 helper cells (involved in immune response). The idea that new T1 cells would incorporate some of the deuterium in their DNA. + +What happened was that I got massive vertigo and got sick (threw up). The reason of this was the change of weight in the fluids in the balance organ. At least that's what they told me. https://en.wikipedia.org/wiki/Equilibrioception + +After a couple of hours everything was ok again and I even went skiing that evening. + +The following intakes had no effect. + +I do remember that I did not like the taste of it. It was different from normal tap water and I got to dislike the taste as I associated it with the vertigo. I believe kinda metallic bitter (this was over 12 years ago, and the details are a bit fuzzy.)" "Only if you drink a lot - toxicity studies find that ~50% of body water needs to be replaced with deuterated water before animals died. + +[The Wikipedia article on heavy water](https://en.wikipedia.org/wiki/Heavy_water#Effect_on_biological_systems) has a good section on toxicity: + +>Experiments in mice, rats, and dogs have shown that a degree of 25% deuteration causes (sometimes irreversible) sterility, because neither gametes nor zygotes can develop. High concentrations of heavy water (90%) rapidly kill fish, tadpoles, flatworms, and Drosophila. Mammals, such as rats, given heavy water to drink die after a week, at a time when their body water approaches about 50% deuteration. + +No clue what it tastes like, though I might expect no difference. Either way, I wouldn't recommend it. " +441 Why does color fade when left in sunlight for extended periods of time? 3732 https://www.reddit.com/r/askscience/comments/4ia1t8/why_does_color_fade_when_left_in_sunlight_for/ 1462629075 4ia1t8 Chemistry 2016-05-07 16:51:15 "The short answer is that sunlight causes irreversible changes in the compounds and molecules that gave a material its color in the first place, in a process we call [photodegradation](https://en.wikipedia.org/wiki/Photodegradation). As a result of these changes, the material gradually loses the ability to specifically absorb (and reflect) different parts of the visible spectrum, creating a faded appearance. + +To look at things a bit more closely, the color of the dyes used in clothing, colored paper, etc., depends on the detailed arrangement of atoms (and their bonds). For example, [take a look at the structure of this common dye called Orange II](https://upload.wikimedia.org/wikipedia/commons/thumb/2/2a/2-naphthol_orange.svg/2000px-2-naphthol_orange.svg.png). Notice how there are two rings with alternating double bonds (we call these aromatic rings), linked by a nitrogen-nitrogen double bond. This extended ring structure is what allows this compound to strongly absorb blue and green light and to reflect the yellow-red part of the spectrum. Now as you might expect this compound will initially have a [vivid orange color](http://i.imgur.com/JeKcT8i.jpg). However, if you expose this dye it to light, over time this color will go away and you will be left with a product that is mostly clear, [as shown here](http://i.imgur.com/oKJYzGZ.jpg). + +So what exactly happened that made the color go away? Well, in one word [photochemistry](https://en.wikipedia.org/wiki/Photochemistry) happened, namely light promoted chemical reactions. Now these reactions can be very messy, [for example here are some of the pathways you may see](http://i.imgur.com/7WbXcNf.jpg), and in fact multiple reactions often play out at once. However, what is important is that these reactions destroy the initial chemical structure of the dye and break it up into smaller bits. As a result, a layer of this material will [slowly lose its ability to strongly absorb visible light](http://i.imgur.com/ESqtzrY.gif). + +Now this was just one specific example, of course in other cases dyes will have completely different structures and will be destroyed by different mechanisms. However, quite often the net effect of these changes is that they will reduce the ability of molecules and compounds to absorb in the visible part of the spectrum. As a result, as you allow colored materials to be exposed to light (and air), often you will find that over time they will lose their vivid color and will take on a dull off-white appearance. This effect is very similar to old-fashioned chemical bleaching." "Photochemist here. + +Light is made up of electromagnetic radiation with an energy which DECREASES with INCREASING wavelength. Generally ultraviolet light is higher energy, shorter wavelength light which we can't see and which we are protected from by the ozone layer. Some UV gets through which is UVB and UVA. UVB is the one which causes sunburn and which has enough energy to cause the bonds to break in the synthetic dyes which we use to give things colour (i.e. dyes being the chemicals we use to colour the ink we print things with). This process is photolysis and is usually the first stage in a whole series of chemical reactions which breaks down the highly coloured dyes on the CD covers and effectively *bleaches* them. Because the CD labels are screened by the glass window and the polystyrene case I would guess that a lot of the UVB would not be getting through to cause this type of photo-fading. + +However, another process which is very common (and the primary cause of photofading) is called photo-oxidation and as you might expect it is mostly the result of a reaction of the dyes with oxygen in the air. This reaction is *sensitized* (made worse by) UVA and visible light absorption by the dye (or pigment) molecules in the printed ink. Now, the reason dyes are so coloured is because their chemical structure allows them to selectively absorb certain colours of visible light, what remains un-absorbed is the colour of the dye as you see it. The example used elsewhere was the orange azo dye which absorbs mostly blue and green light to leave yellow and red (orange) light - the ""colour"" of the dye as you see it. + + Before a dye absorbs light it is said to be in the ground state. When it absorbs light, the electrons in the bonds holding the atoms together gain energy and move from one part of the molecule to another (HOMO to LUMO for the scientists). Once the dye has absorbed the light it is in an ""excited state"" (teehee!). How long this lasts is called the *excited state lifetime* and can be relatively long (nanoseconds), especially in the case of fluorescent and phosphorescent dyes. Fluorescent and phosphorescent dyes are the types of dyes used to give that Day-glo effect, for example in high-vis safety vests and signs. An important feature of this *excited state* is whether it is a *triplet* or *singlet* which is a term describing the spin of the excited electron in the molecule. In some dyes (e.g. Rose Bengal) a lot of the excited dyes are in the triplet state - the majority of other dye types are mostly singlet though with a tiny proportion of triplet. + + Now, molecular oxygen (O2) is very unusual in that in the ground state it exists as a *triplet* and in the excited state as a *singlet*. As this is known as a spin forbidden process it almost *never happens by the absorption of light alone*. However, if a ground state *triplet* oxygen molecule were to collide with a dye with an excited *triplet* state then energy can be transferred to oxygen and the transition from ground state *triplet* oxygen to excited state *singlet* oxygen can happen. + + Excited state *singlet* oxygen is a psycho and can be likened to the hulk in the Avengers movie; being very reactive towards anything close by. This can be a dye molecule or it can be water - water can be transformed into peroxide which oxidises and breaks down the nearby dyes. Note also that singlet oxygen in the gas phase has a much longer lifetime (an hour or more) and so even if the process of creating it is very slow or inefficient it can still hang around long enough to react with something. + + +**TL:DR The dyes themselves aggravate oxidative bleaching when they absorb light.** + +Oh yes, forgot to make the point that the red may seem to have faded more than the others because the blue dye used (or Cyan, from CMYK printing) is almost certainly copper phthalocyanine based which has phenomenal light fastness. +" +571 What causes the patterns to appear in this maple syrup? 3725 https://www.reddit.com/r/askscience/comments/5ad349/what_causes_the_patterns_to_appear_in_this_maple/ 1477929824 5ad349 Physics 2016-10-31 19:03:44 "I can't be certain about this, but after doing some research I came across [this](https://www.degruyter.com/view/j/zna.1977.32.issue-1/zna-1977-0109/zna-1977-0109.xml) paper, which describes periodic ripple formation in other media. + +What could be happening here is that a very thin skin is forming on the surface of the syrup. As the pool evaporates, the total volume of syrup is decreasing and a compressive stress is applied to the skin as it shrinks. When the compressive stress reaches a certain limit, the skin buckles, causing the ripples." "I'm a physical chemist so here's how I rationalize it: + +Maple syrup is a saturated solution of sugars dissolved in water; any change in temperature on the saturated liquid will cause the sugars to solidify (aka ""crash out"") in addition to the small amount of evaporation (increasing saturation). + +Assuming that the syrup is warm, any air movement temporarily cools the surface or causes evaporation - causing the temperature to drop or increases the local concentration of sugars; allowing the sugars to crystallize and crash out momentarily. As the local temperature equilibrates with the overall temperature of the body of syrup, the crystals warm up and gets dissolved back into the liquid to repeat the process over again. + +Crystallization can be very temperature dependent, so think about water that is right at the cusp of being solid and liquid simultaneously." +1435 AskScience AMA Series: I'm Dr. John Troyer, Director of the Centre for Death and Society at the University of Bath and I'm here to talk about death, dying, dead bodies, grief & bereavement, and the future of human mortality. Ask Me Anything! 3724 https://www.reddit.com/r/askscience/comments/d9yqsl/askscience_ama_series_im_dr_john_troyer_director/ 1569582040 d9yqsl 2019-09-27 14:00:40 The AMA will begin at 12pm ET (16 UTC), please do not answer questions for the guests till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Keep questions and interactions professional and remember, asking for medical advice is not allowed. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). This guy didn't answer a single question? Did he die or something? If only I could ask an expert... +127 If I had a 1 dollar coin, could I theoretically flatten it to the point where the coin would cover the entire Earth? 3723 http://www.reddit.com/r/askscience/comments/38pxid/if_i_had_a_1_dollar_coin_could_i_theoretically/ 1433538171 38pxid Physics 2015-06-06 0:02:51 "A dollar coin has a mass of about 8.1 grams. For simplicity assume it to be all made out of copper (it's really about 90% copper). Copper has an atomic density of 63.55 grams/per mole, giving us 7.68 x 10^22 atoms in a dollar coin. The earth has a surface area of 5.1 x 10^8 km^2, so that if the coin were smashed until it was just a one atom thick layer of material (to maximize how far we can spread it) covering the entire earth, then each atom would occupy an area of about 7000 square microns. If the atoms were arranged in a square lattice, each copper atom would be at least 80 microns away from the next nearest atom. For regular bulk copper, atoms are spaced about 0.4 nm apart. So, the atoms would be about 200,000 times too far away from each other to form stable chemical bonds. Simply put, you no longer have a solid chunk of metal if you want it to cover the earth. You have a very sparse copper gas. + +If you subdivide the atoms, you don't have copper anymore. But subdividing won't really help anyways. If you manage to divide each copper atom into 29 hydrogen atoms (ignoring all the messy details of nuclear reactions), then the hydrogen atoms would still be 15 microns away from each other, still several thousands times too far apart to form bonds. + +UPDATE: [Here is an article](http://sciencequestionswithsurprisinganswers.org/2015/06/15/if-i-hammered-and-flattened-a-penny-enough-could-i-cover-the-entire-earth-with-it/) with more exact calculations." "Hey. Materials scientist here. The short answer is that one silver dollar coin would cover 1.99*10^-9% of Earth's surface. That's roughly 2 billionths of a percent. So let's look at the details. + +Assume we're considering a US silver dollar. The US mint website says they're approximately 1 troy ounce of 99.9% pure silver. Let's make that and even troy ounce of 100% silver. One troy ounce is 31.1 grams. Divided by the molar mass of silver (107 g/mole) and multiplied by Avogadro's number (units of atoms/mole), we have 1.736*10^23 silver atoms. Now consider the atomic radius of metallic silver, 130 pm (picometers, or 10^-12 meters). One atom would occupy an area of pi*(130 pm)^2, therefore giving us a total area of 9217 m^2. But wait there's more. Pure metals tend to crystalize in a hexagonal close packed structure when considered in 2D. The packing efficiency of such a structure is 0.9069 (see Wikipedia's entry on Circle Packing). Thus and therefore, the actual area occupied by a 1 troy ounce silver good ole fashioned American dollar would be 10163 m^2. Considering Earth's surface area of 5.1*10^14 meters, our coin would cover 2 billionths of a percent." +1386 How do non buoyant things wash ashore? 3719 https://www.reddit.com/r/askscience/comments/cdgpeh/how_do_non_buoyant_things_wash_ashore/ 1563192848 cdgpeh Earth Sciences 2019-07-15 15:14:08 "Wave action scrubs the bottom of surf zones. + +If you stand still in heavy surf you will quickly notice you are not standing still. + +Depending on current, and tide the wave action will either be pushing you to shore, or pulling you out into deeper water. + +In coastal areas you will see seashells, and even rocks pushed several inches each wave until they rest on a debris line at the edge of the surf. + +The beach sand itself is made by being washed out to deeper water, then piled back onto the beach by the waves scrubbing, and abrading until fine. + +There is a beach in Hawaii called the magic sand beach. Each tide the sand is completely washed away to bare rocks, then when the current reverses washed back into place forming a beautiful sandy beach again." "Sediment at the ocean floor is also moved by the currents. It's actually something that causes significant work for human efforts in maintaining our waterways and coastal waters. Currents can create sandbars where we don't want any or erode earthworks where we do want them. + +[For example this image shows where two rivers come together.](https://minskimwaterblog.files.wordpress.com/2014/07/meeting-of-the-waters.png?w=536&h=334&zoom=2) The black water comes from the Rio Negro, the water is stained black from all the vegetable matter the water flowed past in the jungle, like steeped tea. The tan coloured water comes from the Rio Solimões which is coloured by the sediment it carries from the Andes. + +The river water is so radically different that there's an almost 10 degree temperature difference and a 4km/h speed difference between the two currents. + +In some places the cliff faces and beach are also full of fossils so it can also work the other way around. Instead of washing up, a storm can erode layers of cliff face or beach to reveal new fossils, teeth and shells. + +It also helps that shark teeth are extremely common. Shark teeth are disposable, [a shark's jaw kinda looks like a conveyer belt of teeth](https://i.pinimg.com/originals/86/61/51/86615153521f6165a4816911f872b10e.jpg). Rows of them and whenever a tooth breaks off the next tooth in the row is rotated forward to take it's place. + +A single shark can go through thousands of teeth through it's lifetime. So millions of years worth of shark generations left a lot of teeth in the sea bed. With that many teeth lying around some are bound to come up sooner or later. In some places famous for them you can dive with a bucket and just sift the teeth out of the sediment." +1436 Why isn't the James Webb space telescope heat shield made out of gold? 3716 https://www.reddit.com/r/askscience/comments/dmhsb5/why_isnt_the_james_webb_space_telescope_heat/ 1571929934 dmhsb5 2019-10-24 18:12:14 "The heat shield will have to fold up to fit into the rocket and then [unfold once it's in space](https://www.youtube.com/watch?v=bTxLAGchWnA). The material properties at the relevant temperatures to allow this process must be considered, not just reflectivity. + +EDIT: Adding another point given by /u/evensevenone for visibility, since gold doesn't reflect bluer wavelengths well (it looks golden, after all) but does reflect infrared, that means that it will absorb energy without being able to emit it away again very efficiently, so it would get pretty hot in space, which is not a great property to have in a heat shield. Aluminum has a flatter reflectivity spectrum." "The heat shield is primarily to reflect electromagnetic radiation from the sun. Most of this radiation is in the visible band with the peak at around 500nm. At 500nm and shorter wavelengths, gold is only about 40% reflective. It is very reflective above 600nm or so. This is actually what gives it the gold hue, it is absorbing green, blue, and violet and reflecting yellow orange and red. Anyway, that absorption makes it a poor choice to reflect solar energy. + +The heat shield is made out of kapton and use an aluminum coating for reflectivity. Aluminum is very reflective across the whole visible band (good for reflecting the sun). It's not quite a good at IR as gold, so the mirror for the telescope uses gold." +442 "When describing an amount of space, we call it an ""area"" or ""volume."" When describing an amount of time, we call it a ""duration."" What would we call an amount of spacetime, and what would that imply?" 3708 https://www.reddit.com/r/askscience/comments/4xncso/when_describing_an_amount_of_space_we_call_it_an/ 1471162820 4xncso Physics 2016-08-14 11:20:20 "It's just called spacetime volume, or just volume when it's clear from context. In an n-dimensional manifold, the n-dimensional volume is generally just called ""volume"". + +It's a very important object to consider in physics. In special relativity, spacetime volume is preserved by transformations between inertial reference frames. In SR or GR in general it's relevant for example for the definition of a few essential quantities which are defined ""per unit of spacetime volume""." "In SR, the focus is on the separation in space and time between two points in space and time. A point in space and time is uniquely described by its spatial and temporal coordinates – this is commonly called an event. + +The spatiotemporal separation between two events is called the spacetime interval. In the everyday, we might say that we'll meet in 3 hours, four blocks away: we separate out the space and the time aspects. In SR, these two different but interrelated quantities are combined in the spacetime interval. If the spatial separation is denoted r, and the temporal separation is denoted t, then the spacetime interval is defined via s^2 = r^2 - c^2 t^2. + +In SR, different observers may measure different values for r or for t – time dilation and length contraction mean that not all observers will agree on the time or distance that separate two events. But the way that these quantities co-vary means that all observers will agree on the value of the spacetime interval. This is why the spacetime interval as defined above is interesting. + +Notice that if r > ct, then s > 0, and vice versa. This gives a way to distinguish between events that are 'space-like' separated, and those that are 'time-like' separated. This is something cool to read into further if you want. I'd intended to try explaining this point, but I'm on my phone and typing sucks, so... sorry. " +8 If someone with schizophrenia was hallucinating that someone was sat on a chair in front of them, and then looked at the chair through a video camera, would the person still appear to be there? 3700 http://www.reddit.com/r/askscience/comments/2v3jil/if_someone_with_schizophrenia_was_hallucinating/ 1423324475 2v3jil Neuroscience 2015-02-07 18:54:35 "Thank you everyone for your responses, I think I'll try and summarise this thread: + + * Schizophrenia consists mainly of audio hallucinations and varies from person to person in terms of 'reality checking' themselves + + * Hallucinations are possible to have on digital screens, meaning the hallucination many continue when looking at a video camera + + * The person suffering with schizophrenia would likely come up with a delusion to explain the absence of the person, such as it being invisible to a camera + + * It all varies on the severity of the person's symptoms at the time + +Hope that summary was adequate, another big thank you to all of the responses, especially to those who I have quoted. + +EDIT - Phrasing" "As another poster has pointed out, those kind of full-fledged visual hallucinations probably don't happen very often. + +But I can say something to the more general question, in that there in research on how other kinds of hallucinations/delusions respond to this kind of evidence. I'm thinking specifically of the case of [anosognosia](http://en.wikipedia.org/wiki/Anosognosia) for hemiplegia, in which a patient following brain damage is unaware that they have a limb that they can't move. When asked to lift their arm, they insist that it has moved, even though everyone can plainly see that it hasn't. + +There are isolated case reports where patients have been put in front of a mirror, to make sure they are looking directly at their limb from a 3rd person point of view, and they continue to insist that it is moving. + +However, there is a [recent published study](http://www.ncbi.nlm.nih.gov/pubmed/19428388) in which a patient with anosognosia was shown video of herself, and this instantly resolved the condition. " +443 What kind of damage could someone expect if hit by a single atom of titanium at 99%c? 3700 https://www.reddit.com/r/askscience/comments/4s0abi/what_kind_of_damage_could_someone_expect_if_hit/ 1468070814 4s0abi Physics 2016-07-09 16:26:54 A single atom? It would pass through you, although its [electrons would be stripped from its nucleus](http://www.astro.spbu.ru/staff/afk/AtDatCentre/AtDatCat/Chapter3.pdf) and you'd be hit by both the atomic nuclei and its electrons. As for the effects? You'd probably be fine if it were a single atom. The only time I know that something like this occurred was in 1978 when [Anatoli Bugorski](https://en.wikipedia.org/wiki/Anatoli_Bugorski) accidentally stuck his head in the path of a particle accelerator beam with protons going very near the speed of light. He survived, [although the consequences weren't pretty](http://survivor-story.com/wp-content/uploads/2013/01/anatoli-bugorski.jpg). [deleted] +1120 Why is Greenland almost fully glaciated while most of Northern Canada is not at same latitude? 3698 https://www.reddit.com/r/askscience/comments/9i373c/why_is_greenland_almost_fully_glaciated_while/ 1537651333 9i373c Earth Sciences 2018-09-23 0:22:13 "Average temperature is correlated with latitude, but it is not directly controlled by it. See [this map](https://upload.wikimedia.org/wikipedia/commons/9/92/Annual_Average_Temperature_Map.png) of average temperature across the globe. + +How hot and cold air are able to move across land matters a lot. So things like plains and mountains change where the air can go. Ocean temperature also matters, and similar to the air, there are currents and parts of the ocean are warmer or colder because of those currents than you would expect just based on latitude alone. Here's [a map](https://en.wikipedia.org/wiki/Sea_surface_temperature#/media/File:SST_20131220_blended_Global.png) of that." "Greenland has a mountain range on its east coast which is much higher than any of the other mountains in the Canadian Arctic region, allowing glaciers to form. The ice sheet is self-sustaining in a way, since the large amount of ice raises the surface elevation out of the zone that gets above freezing in summer. This is actually the biggest factor for why the ice sheet covers the entire island. + +It's also because of its much more maritime climate causing the summers to be even colder than they are at other areas at a similar latitude. The maritime climate happens in Greenland but not in the Canadian Arctic Archipelago because warm air from the south in summer can reach it across the short inlets and straits but can't reach Greenland from any direction." +572 What is the highest a mountain can be? Is there a limit to it? 3695 https://www.reddit.com/r/askscience/comments/57g0md/what_is_the_highest_a_mountain_can_be_is_there_a/ 1476447077 57g0md Planetary Sci. 2016-10-14 15:11:17 "**Short answer:** In general, the maximum size of a mountain on a planet will be limited by surface gravity. The greater the surface gravity, the smaller the biggest mountain can be. On earth, it works out that Everest is probably pretty close to this limit. + +**Long answer:** As a mountain gets taller, it gets more massive. As it gets more massive, the pressure on the rock at its base increases. Eventually, this pressure would exceed the breaking strength of the rock. + +That pressure could be written + + P = rho g h + +where *P* is the pressure on the base, *rho* is the density of the rock, *g* is the surface gravity of the planet, and *h* is the height of the mountain. If *P* is the breaking strength of the rock, you'll find a cool relation: + + h g = P/rho + +Since *P/rho* is just a constant, this relation tells us that **as the surface gravity of the planet in question increases, the maximum size of a mountain it can support decreases.** + +This also tells us *h g* must also be a equal to a constant, which lets us relate the maximum height of mountains on planets of similar compositions but with different masses: + + h_1 g_1 = h_2 g_2 + +You can do something *really cool* with this. If you take Mt Everest to be the tallest mountain that can be supported on earth, and if you know that Mars surface gravity is 2/5th of earth surface gravity, you can actually calculate the height of Olympus Mons, which is the tallest mountain on Mars, if you write + + h_everest g_earth / g_mars = h_olympusmons + + 5/2 h_everest = h_olympusmons + +Which is actually really close to the true value! This is even cooler because it argues that *both* Earth and Mars have mountains near the maximum possible height for the planet. Of course, a geologist may not like any of what I just said above. Mountains and tectonic plates and mantles are complicated beasts - this was just a first order approximation. + +But, as one last fun fact, you can do something else with this approximation. [We can predict the 'potato radius' - the maximum size a 'potato shaped' asteroid can be before its gravity becomes strong enough to pull it into a sphere.](http://quarksandcoffee.com/index.php/2015/10/29/why-are-some-moons-spherical-but-others-are-shaped-like-potatoes/) This is done by modeling the potato asteroid as a sphere with a *huge* mountain on it that must shrink as the asteroid grows in mass, until the mountain is smaller than the radius of the asteroid. " "The height of the crust (i.e., mountain plus the solid rock below; a solid) is compensated for by the thickness of the underlying mantle (a fluid), such that the whole of the earths surface (crust plus mantle; solid plus fluid) seeks to be in equilibrium (what geologists called ""isostatic equilibrium""). Isostatic equilibrium can take thousands or even millions of years to occur, yet the mountain building processes can happen more quickly than equilibrium (in some cases) and so, in a sense, the mountain belts are always delayed by some timeframe from being in equilibrium. I'd have to dig up my old global tectonics, geophysics, or structural geology texts but in essence the height of Everest is related to several factors including the thickness of the crust under it (in this case, very thick), the density of the crust, the density of the mantle and thickness of the mantle, the timeframe for equilibrium, and of course erosion plays a huge part too that changes the thickness of the crust on a rapid timeframe. Here's a version of the basic equation that governs the relationship: + +Sum of (Density*gravity*thickness) for one vertical profile through the earth = sum of (density*gravity*thickness) of another vertical profile through the earth" +573 How many times do most galaxies rotate in their lifetimes? 3689 https://www.reddit.com/r/askscience/comments/557jke/how_many_times_do_most_galaxies_rotate_in_their/ 1475236685 557jke Astronomy 2016-09-30 14:58:05 "The answer depends on what part of the galaxy you are talking about. Galaxies are not rigid disks where all the parts are forced to rotate together. Instead, galaxies are made up of a huge number of bodies that have different linear and rotational speeds. For example, think of the Solar system. While it takes the Earth one (Earth) year to make one full loop around the sun, it takes Neptune 165 years to go around. The same is true of galaxies, objects will have different orbital periods depending on their position. By and large stars towards the outer edge of a galaxy will take much longer orbital periods than stars closer to the center. The main reason is that the further a star lies, the more distance it has to cover to make a full orbit. You might get a more intuitive feel for what is going on from [this visualisation](https://upload.wikimedia.org/wikipedia/commons/transcoded/e/e0/Spiral_arms.ogv/Spiral_arms.ogv.360p.webm). + +As a result, it's easier to answer your question for one specific object. Our Sun makes for a good an example as any. The Sun (and the rest of the solar system) moves around the center of the Milky Way with an orbital period of ~250 million years. This period is called the [galactic year](https://en.wikipedia.org/wiki/Galactic_year). That means that within its 10 billion year long life, the Sun will make about 40 loops around the Milky way. + +edit: I expanded the initial explanation a bit." Why don't galaxies evolve in the same manner as star systems with orbiting planets and asteroid belts ... or as planets with moons and rings? In those cases a rotating disk of matter clumps into bodies with circular orbits and these bodies gradually clear their orbital lane. Would galaxies form such clumps in circular orbits if given enough time? +574 "From a health standpoint, is there a difference between a fast heartbeat due to exercise vs a fast heartbeat due to nerves/stressful situations? I would assume the first thing is ""healthy"" while the second isn't. Is this even true?" 3679 https://www.reddit.com/r/askscience/comments/5jr6hx/from_a_health_standpoint_is_there_a_difference/ 1482421132 5jr6hx Human Body 2016-12-22 18:38:52 I remember the last time this question was posted, it was answered really well: https://www.reddit.com/r/askscience/comments/u1tyq/why_is_an_elevated_heart_rate_good_when_caused_by/ "Yes, it's true. Let's look at it 2 ways. Firstly, the in-the-moment differences, and secondly the long-term differences. + +Terms you need to understand: +Blood pressure is made up of *systolic* blood pressure; that's the maximum pressure your blood circuit reaches when the left side of your heart is actively pumping, and *diastolic* pressure, which is the lowest pressure it reaches while the left side of your heart is filling up. When a doctor says your BP is 120/80, 120 is systolic and 80 is diastolic. Mean arterial pressure (the average pressure your arteries are experiencing) is usually an estimated figure calculated by equations, occasionally directly measured, and this is an important number for heart health. If it's high, your heart is having to work harder to pump blood around the body, and that's bad for your heart. + +1) In-the-moment + +**Exercise:** During exercise, the heart rate goes up and many blood vessels dilate to increase blood supply to muscles (and, to control your body temperature, to the skin). Your systolic goes up initially, then stabilises or even falls. Diastolic stays steady. That means that your mean arterial pressure only goes up slightly, if at all. [Experimental evidence from rats](http://jap.physiology.org/content/46/2/302.short) + +**Psychological:** During psychological stress, the heart rate goes up without any accompanying change in distribution to muscle and skin, because there isn't any physical response required. Even worse, hormones are also released causing constriction of blood vessels. That means that the blood pressure goes up. [Evidence from a study looking at stress while using a computer](https://www.researchgate.net/profile/Karen_Sogaard/publication/7449722_The_Effect_of_Mental_Stress_on_Heart_Rate_Variability_and_Blood_Pressure_During_Computer_Work/links/00b49533940a084363000000.pdf) + +2) The long-term effects + +**Exercise:** Exercise that raises your heart rate has many beneficial effects on the cardiovascular system long-term. A few simple ones below, all demonstrated in [this beautifully written older paper](http://www.annualreviews.org/doi/pdf/10.1146/annurev.ph.39.030177.001253) + +* Increasing the resting activity of the ""rest and digest"" (parasympathetic) nervous system, lowering heart rate and blood pressure +* Increasing the effectiveness of your muscles at a given effort level- muscle fibres grow, increases in mitochondria (the little guys that do all the energy conversion with oxygen), improvements in blood supply- meaning that next time you have to do the same hard work, your heart doesn't have to work so hard +* Improvements in oxygen transport, again reducing the amount of work your heart has to do + +**Psychological stress:** Again, this is not so good, especially when it's long-term or recurrent stress. + +* Increases the activity of your ""fight or flight"" sympathetic nervous system, increasing heart rate and blood pressure [as discussed in this small study](http://hyper.ahajournals.org/content/46/5/1201.short) +* Changes hormone balances, for instance increasing cortisol levels, with negative effects on the immune system and heart health [e.g. shown here](http://psycnet.apa.org/psycinfo/2004-15935-004) + + +On the bright side, [exercise probably has beneficial effects on anxiety and stress](http://link.springer.com/article/10.2165/00007256-199111030-00002). + +**TL;DR: Exercise comes with lots of other changes alongside raised heart rate that mean your heart is working hard under the right conditions to support it doing so, and drives healthy changes to heart health. Stress, not so much.** + +(Note: all of the above is about cardiovascular exercise like running, as opposed to weight-lifting type exercise. This also has many benefits, but via some slightly different mechanisms.) + +Edited for formatting." +333 Does a spinning magnet in space eventually stop spinning? 3678 https://www.reddit.com/r/askscience/comments/48ii9w/does_a_spinning_magnet_in_space_eventually_stop/ 1456865050 48ii9w Physics 2016-03-01 23:44:10 You're correct. It would take quite a long time, but yes. For that matter, even if it wasn't a magnet it would still emit gravity waves. +575 How many numbers a & b exist such that a^b = b^a? How many rational numbers? Integers? Or is there a way to prove that there is an infinite amount? 3678 https://www.reddit.com/r/askscience/comments/5a7chc/how_many_numbers_a_b_exist_such_that_ab_ba_how/ 1477851056 5a7chc Mathematics 2016-10-30 21:10:56 "If we have a^(b)=b^(a), then taking logs and rearranging gives log(a)/a=log(b)/b. So if we look at the function f(x)=log(x)/x, then we'll want to find two different values x=a and x=b so that f(a)=f(b). If f(a)=f(b), then we can just work backwards to a^(b)=b^(a). + +So what does f(x) look like? Well, it's negative for 01. Furthermore, looking at it's derivative, you can find that it is increasing when 0e. And, finally, the limit of f(x) at x=infinity is zero. So, f(x) is increasing whenever it is negative and this means that it never repeats a negative value, since it is only going up when it *is* negative, and once it's positive it's never negative again. So we can't have f(a)=f(b) when either a<1 or b<1. But, since it is increasing from x=1 to x=e, and f(1)=0, and it is decreasing from x=e onward, and f(x)->0 as x->infinity, it follows that for any 1e so that f(a)=f(b). So there are infinitely many solutions to this. + +[Here is a plot of how this works](http://i.imgur.com/d4AGJsy.png) + +Note that 2 is the only integer between 1 and e, so a=2 and b=4 is the only nontrivial integer solution. + +We can actually parameterize all of our solutions. In particular, if r is any real number, then maybe we can find an 11, this means that every solution looks like this. So, pick any r>1 and + +* a=r^(1/[r-1]) + +* b=r^(r/[r-1]) + +will be a solution to the equation a^(b)=b^(a). + +But what about rational solutions? If there's no guarantee that when x=a is rational that the corresponding x=b will also be rational. When does this happen? It turns out that it will happen infinitely often. In particular, if n is any positive integer, then + +* a = (1+1/n)^(n) + +* b = (1+1/n)^(n+1) + +will work. This works by making r an rational number so that 1/(1-r) and r/(1-r) are integers, and plugging it into our formula. In particular, picking r=1+1/n works. The first few rational solutions are + +* a=2, b=4, + +* a=9/4, b=27/8 + +* a=64/27, b=256/81 + +To see why this form provides *all* the rational solutions requires some work, but it isn't too difficult, see [this article](http://www.math.uiuc.edu/~reznick/xyyx.pdf) for details. + +" "It's funny to see this question because incidentally I just stumbled across this video today that explores exactly this question, from integer solutions, to rational ones, to even complex ones. You should definitely check it out as it will probably explain everything you need to know concerning this question. + +https://youtu.be/p-R0druZiTs" +691 What is the mistake in this mathematical proof? 3673 https://www.reddit.com/r/askscience/comments/5u6l23/what_is_the_mistake_in_this_mathematical_proof/ 1487153291 5u6l23 Mathematics 2017-02-15 13:08:11 "In the last step, you divide both sides by a - b - c, but this operation is only valid when a - b - c is not equal to zero. But from the very first assumption, we have that a = b + c, so a - b - c = b + c - b - c = 0. + +The derivation is correct up to this point, but in the second-to-last step, it actually says: a * 0 = b * 0, which is obviously true, but can't be used to infer that a = b." "You start with + +A = B + C + +Subtract both sides by (B + C) + +A - B - C = 0 + +So later when you divide both sides by (A - B - C) you're actually dividing by zero, which you can't do, so everything gets kinda screwed up." +576 How was it discovered that metals in space would stick together? 3671 https://www.reddit.com/r/askscience/comments/531eyd/how_was_it_discovered_that_metals_in_space_would/ 1474025139 531eyd Physics 2016-09-16 14:25:39 "We knew that this process, called [cold welding](https://en.wikipedia.org/wiki/Cold_welding), was possible well before going into space. Even though this process may seem exotic, it follows from pretty basic physical considerations. The basic idea of this effect is technique is that just like you can break a crystal into two pieces, you can also put the pieces back together. It's a bit like taking apart a jigsaw puzzle and then putting it back together. Because the pieces can fit back together, they can simply snap in place when you put them in the right orientation. When you put the crystal back together, the electrons won't ""know"" that they should belong to different pieces as Feynman once famously put it. In effect you are creating metallic bonds across both pieces and it's as though the crystal was never broken apart in the first place. + +You might get a better sense for what happens by looking at how this process occurs under an electron microscope, [as shown in this clip](http://i.imgur.com/iihMpJn.gifv). Here researchers took two gold nanowires and brought them close to one another. Because both pieces had the same orientation of their crystalline network (called the lattice), at one point the two pieces fell into place. As a result, the new piece acts like a pristine piece of metal. In fact, you can break this piece apart and put it back together with no meaningful loss in its electrical conduction or other properties, as described in [this paper](http://www.nature.com/nnano/journal/v5/n3/abs/nnano.2010.4.html) from which I took this clip." "I design vacuum chambers for a living so maybe I can provide some insight. ""Cold welding"" happens in high, or ultra-high vacuum environments when very clean metals touch. It doesn't work like most people seem to think it does, it's not like you just touch two pieces of metal together and they instantly become one. It's more like they stick together some. Under high enough pressure they can bond. Anyway since the conditions can be recreated on earth I would guess we would have known about it before we went into space. We had diffusion pumps back in the 1920's that could create ultra-high vacuum environments in the lab. Also, the idea of metals bonding under pressure isn't something that just happens in space, it happens all the time with fasteners. Anytime you have two similar metals under high pressure they can bond, it's just easier in space. They sell lubricants to keep it happening with bolts and stuff here on earth. Anyone with experience with aircraft I would guess would know about this and know how to prevent it from happening." +334 AskScience AMA Series: I’m Dheeraj Roy, a neuroscientist studying what happens to lost memories in early stages of Alzheimer’s disease. Are these memories erased or do they exist but cannot be found? AMA! 3670 https://www.reddit.com/r/askscience/comments/4asic7/askscience_ama_series_im_dheeraj_roy_a/ 1458213923 4asic7 Alzheimer’s disease AMA 2016-03-17 14:25:23 "AskScience AMAs are posted early to give readers a chance to ask questions and vote on the questions of others before the AMA starts. + + +Guests of /r/askscience have volunteered to answer questions; please treat them with due respect. Comment rules will be strictly enforced, and uncivil or rude behavior will result in a loss of privileges in /r/askscience. + + +" Does your research point to any preventative measures we can start taking? +335 Does the gravity of everything have an infinite range? 3667 https://www.reddit.com/r/askscience/comments/42m28l/does_the_gravity_of_everything_have_an_infinite/ 1453737653 42m28l Physics 2016-01-25 19:00:53 "In theory, yes. Gravity has an infinite range. However, it also takes some time to propagate - information about local changes in the gravitational field will propagate at the speed of light. So if a supernova goes off and creates a black hole, we won't feel the gravitational disturbance until we see the light from the supernova. + +Additionally, since the universe is expanding there are distances such that we will never receive information from. Anything that happens beyond that horizon will not be able to effect us. " In few words, yes, but since in simple calculations gravity becomes weaker with the distance between objects^2, it will eventually reach a point that is can essentially be perceived as zero in most calculations. This same idea (perceiving small numbers as zero) is done very often in large scale (like astrophysics) mathematics. +336 Based on ongoing experiments, how far away are we from nuclear fusion power? 3665 https://www.reddit.com/r/askscience/comments/49c50v/based_on_ongoing_experiments_how_far_away_are_we/ 1457348312 49c50v Physics 2016-03-07 13:58:32 "Depends on what you consider ""fusion power"". Starting and maintaining a fusion reaction for some time? Been there, done that. Getting more energy out than you put in? On the todo-list, check back at the end of the next decade. Commercially viable fusion reactors? Ehhh... + +Scientists have already generated fusion reactors in various tokamak-reactors (donut-shaped) around the world. The problem is that these tokamaks were too small and more energy was used up sustaining the reaction than was produced. These reactors were meant purely for research. + +Currently under construction somewhere in France is ITER, which will be, with some distance, the largest tokamak reactor and will be the first fusion reactor to generate more power than it uses. But it's still very much a research-device, loaded with all kinds of sensors and with a design goal of sustaining the reaction for only 1000 seconds. Parts of the reactor design haven't been finalized yet and are still under research. + +The goal is to have the first plasma established around the turn of the decade and the start of fusion operation in the second half of the next decade. + +Competing with tokamaks are so-called stellarators, which use a more complex shape to make the fusion plasma easier to stabilize. Recently, the Wendelstein 7-X hit the news because it had created a very high temperature hydrogen plasma. The W7-X, however, is not designed to actually start a fusion reaction, it is primarily a design study into the viability of the concept and the properties of such high temperature plasmas. + +Following ITER and W7-X, the DEMO project is the project that will involve the creation of the first commercially viable fusion reactor, able to operate fusion plasmas for long periods of time, while extracting energy out of it. The project is still in an extremely early stage and most recent estimates of when it will become operational point to the second half of the 2040's, but this will greatly depend on what is learned at ITER. + +Actual commercial implementation of fusion power will follow the successful operation of DEMO, building on what is learned in that device. + +So yeah, that's about 50 years away." "I'm surprised that no one has mentioned the [Polywell](https://en.wikipedia.org/wiki/Polywell) yet. It uses electrostatic confinement, magnetic mirroring, and plasma pressure to generate fusion. It's much smaller and simpler than a tokamak or stellarator, and would cost a lot less to prove or disprove as a practical fusion reactor, on the order of [10s of millions of dollars](http://www.nbcnews.com/science/science-news/low-cost-fusion-project-steps-out-shadows-looks-money-n130661) instead of [10s of billions of dollars like ITER](https://www.iter.org/faq#Do_we_really_know_how_much_ITER_will_cost). + +The Polywell is one of the few fusion technologies that offers the possibility of ""aneutronic"" fusion using a pB11 (proton / Boron-11) reaction. It's about 10x harder to achieve than D-T (deuterium-tritium) or D-D (deuterium-deuterium) fusion, but it has the nice property that it generates near zero neutron radiation. + +[The US Navy is funding the research](https://www.fpds.gov/ezsearch/search.do?indexName=awardfull&templateName=1.4.3&s=FPDSNG.COM&q=energy%2Fmatter&sortBy=SIGNED_DATE&desc=Y), but on a shoestring budget. The team would be able to progress a lot faster if they had more money. + +It was invented by Robert Bussard, an American physicist and rocket scientist. (If the name sounds familiar, it's because ships in Star Trek use one of his proposed inventions, the [Bussard collector](https://en.wikipedia.org/wiki/Bussard_ramjet), to gather hydrogen gas from the interstellar medium.)" +337 Could a smaller star get pulled into the gravitational pull of a larger star and be stuck in its orbit much like a planet? 3665 https://www.reddit.com/r/askscience/comments/4b7cyo/could_a_smaller_star_get_pulled_into_the/ 1458478027 4b7cyo Astronomy 2016-03-20 15:47:07 This is actually quite common, there are more binary stars than singular stars. [They can be used to show that the speed of light isn't added to the speed of the star](https://www.physicsforums.com/insights/speed-light-galilean-relativity/), because otherwise the light from the far star would catch up to the light from the closer one as they orbit. Generally though they have a more mutual orbit, as a great size asymmetry is less common. Sirius is an example of a star that fits your criterion. "Yes. In fact, the closest star system to our own, [Alpha Centauri](https://en.wikipedia.org/wiki/Alpha_Centauri), is actually a trinary system, in which Alpha Centauri A and B orbit in relatively close proximity, and a third, Alpha Centauri C (aka Proxima Centauri) orbits further out. + +Alpha Centauri C is a very small red dwarf, while A and B are of roughly comparable size to our Sun. + +[Here's a rough diagram of what the system looks like.](http://oi60.tinypic.com/30wxdeg.jpg) + +As far as stars joining other systems, that's more complicated (but in fact may have happened with Proxima Centauri joining the Alpha Centauri system). Without some very complicated orbital mechanics, any star which passes near another star will likely just pass by with a very slight change in trajectory. To enter into an orbit, one or both stars must decelerate. + +Captured planets or moons (like some of Jupiter's moons) are possible because they alter the orbits of other planets or moons by throwing them into a larger or smaller orbit (transferring energy between the two bodies) in order to decelerate and fall into a stable orbit around a larger body. + +When you're talking about a star, which is many times larger than a planet, it would take an immense amount of energy to decelerate the object enough to create a stable orbit." +233 What does an IQ of 70 entail, cognitively, emotionally, etc.? 3664 https://www.reddit.com/r/askscience/comments/3ygt9k/what_does_an_iq_of_70_entail_cognitively/ 1451267198 3ygt9k Psychology 2015-12-28 4:46:38 "= +While IQ tests are not effective around the center of the bell-curve, that is not the point of this question. An IQ of 70 most definitely means something relevant, and not just that someone is bad at taking the test. + +IQ tests (the major ones that are still used--Weschler, Stanford-Binet, CAS, etc.) have a LOT of time, effort, and in some cases grant money dedicated to ensuring that different thought processes don't immediately and irreparably screw a person who takes the test. They tend to provide the correct answer in some way--be it by multiple choice or strong implication in the question--and the test is less focused on accuracy and more focused on speed. Essentially, they are ideally designed so that everyone can get many questions right, but at different rates. + +This notably does mean they are incredibly poor at providing accurate scores for sufferers of ADHD, but there are a couple of IQ tests explicitly intended in conjunction with ADHD. + +An IQ of 70 is two full standard deviations below the median. This is not ""bad at the test,"" this is ""moderately impaired cognition."" Someone above mentions that IQ does not correlate strongly with wealth--but this only applies above the median. Below the median, an IQ of 70 gives you a strong correlation with lower wealth, based on the functional impossibility of certain high-speed, high-cognition jobs. + +An IQ of 70 gives you a moderate correlation with earlier morbidity and mortality. This one kind of speaks for itself, and is mostly explained by the fact that something else likely caused the impairment on a biological level that will cause other problems down the line. Also, since low IQs correlate with lower income, and lower income correlates with earlier mortality/morbidity, there's probably an easy common-cause. + +In general, someone with an IQ of 70 is likely to work a lower-paying, more physically oriented job, and have less success (a lot, as in likely not to finish at all) in school. They are, to be quite blunt, markedly less intelligent than most other people. + +IQ tests are not good at telling who is the smarter of two average people. IQ tests are VERY good at identifying either incredibly strong or incredibly weak cognitive abilities at the narrow ends of the bell curve, and at two standard deviations away, 70 is pretty extreme. + +As for social and emotional ability, IQ doesn't directly tell anything at all. It can be said that many mental disorders that cause high or low IQ scores can also cause emotional or social problems (Savant syndrome gives high IQ scores, regular autism or various mental retardations give low) but those are common caused, not intrinsically linked. + +IQ honestly gets an unfair rap most of the time. If you let it do what it's good at, it's a fairly effective measurement. If you try to make it an end-all determiner of how good a person is, it's worthless." "I'm a neuropsychologist, so doing IQ and interpreting them is kind of my daily activity. There are some ways to calculate an IQ, the most used in my country is a Weschler Intelligence Scale. + +You have to understand 2 things when reading ""an IQ of 70"". + +The first one is statistically : like /u/ManicOppressive wrote, ""2 full standard deviations below the mean"". It is basically the lowest-scoring ~2% of the population. In other words, 2 persons in a random group of 100. So an IQ of 70 is not directly a measure of cognitive function, but more of a ""where are you compared to other people of your age?"". + +The second is what is measured. In the last scale, there are 4 ""independent"" indices. Verbal comprehension, perceptual reasoning, working memory, processing speed. + +You can have low results for the four indices, but in reality, the more frequent situation is at least a few differences between indices. It is generally difficult to interpret as a ""global IQ"", but some professionals do it anyway. Just to illustrate : if you take an IQ in a non-fluent langage, you will probably have very low result in the verbal comprehension and working memory indices, but not necessary in the perceptual reasoning indice. In this example, your measured IQ will be low but your ""true"" intelligence would be average. + +Yes, it is not the most frequent situation (in theory, you shouldn't do or interpret an IQ in another language), but you can have a similar result with a lot of issues that doesn't necessarily affect your ability to reason, formulate good idea, or think. E.g. When you have a speech or (not corrected) hearing impediment, when you didn't learn to read, when you have a visual or understanding impairment, when you didn't receive a good education, when you have an impaired attention/concentration, memory limitation,... It will not necessarily be as low as 70, but you will score below than average. Does this mean that you are stupid? + +So IQ is not a direct measure of your ability to think or feel. Even if it can generally show a large panel of cognitive limitations, it is an indirect measure. +I have seen incoherent psychotics or highly socially-impaired ASD scoring average, and ""average"" adults (with a job, a wife, friends, etc) scoring low. + +The real questions are : + +- What is intelligence, and how can we measure it? +- What is necessary to be a (fully) functioning adult in our society? + +The short answer : IQ is not perfect for measuring ""intelligence"", and ""intelligence"" is not what most people think. But IQ is good at what it measures (see again /u/ManicOppressive's answer). + +Don't hesitate to ask me any questions about it. " +128 The EU has banned many chemicals that are suspected of causing harm which are allowed in North America. Are there epidemiological studies finding differences in rates of disease related to this? 3660 http://www.reddit.com/r/askscience/comments/39sl1a/the_eu_has_banned_many_chemicals_that_are/ 1434277368 39sl1a Medicine 2015-06-14 13:22:48 "Most of the bans or restrictions on use have taken place in the last 5-15 years; this is probably not long enough to understand whether there are differences in the rate of cancer. Cancer often has a latency time of 20 years or more. + +This is a big topic with a relatively new chemical safety law in Europe, REACH (Registration, Evaluation, Authorization (and Restriction) of Chemicals). This was nominally one of the rationales for passage. We will see in the long term whether or not it was effective. " "For those interested: NPR's Planet Money did an episode comparing the use of the precautionary principle in the EU and U.S. when it comes to farming and GMOs. + +http://www.npr.org/sections/parallels/2013/07/08/199168194/EU-U-S-Trade-A-Tale-Of-Two-Farms" +9 Why does the Human body reject transplanted organs /tissue and proceed to destroy them but it doesn't kill parasites like worms ? 3657 http://www.reddit.com/r/askscience/comments/33b7wy/why_does_the_human_body_reject_transplanted/ 1429583888 33b7wy Human Body 2015-04-21 5:38:08 "Every defense mechanism has false positives (for example, when you body attacks itself, like in an auto-immune disorder) and false negatives (for example, when your body doesn't attack a pathogen). + +Various parasites have the advantage of having had millions of years to evolve their evasive mechanisms and their defense mechanisms to avoid detection or mitigate attacks by human immune systems. " "All human's, aside from identical twins, have a different mix of unique markers that allow for the recognition of self and nonself. The most important is the Major Histocompatibility Complex or MHC. Nearly every cell in your body expresses MHC which is loaded with a little bit of protein called a peptide. These peptides can come from self and from pathogens. An individual's T cells are designed to react to cells that express an MHC that binds unusually strongly. During T cell development, T cells selected that they won't bind self MHC with self peptide. Foreign tissue like transplanted organs express MHC that your T cells will bind strongly which causes the T cell to kill the foreign tissue through activation of cytotoxic T cells which punch holes in the transplanted organ and macrophages that will eat it. + +Our organs never evolved survival mechanisms to evade the immune systems whereas many parasites have. The type of immune response I described above is what is called a Th1 or cell mediate response. Th2 and humoral responses are used against parasites. Because parasites are so large, our body is more focused on controlling it than killing it which could damage the infected tissue. Your body does produced antibodies against the parasite that can cover it which leads to cells like eosinophils degranulating toxins on the parasite but because parasites have many life stages it is often difficult to mount an antibody response against multiple forms of the parasite. + +TLDR: Transplanted organs are an easy target that doesn't try to protect itself while your body doesn't want to cause damage by destroying parasites + +Source: Immunology Graduate Student. Janeway's Immunobiology is a great textbook" +444 "If I were to take a ""frame by frame"" video of a hydrogen atom and its electron, whould I find the electron moving along a trajectory or teleporting randomly throughout the cloud?" 3655 https://www.reddit.com/r/askscience/comments/4y4mq9/if_i_were_to_take_a_frame_by_frame_video_of_a/ 1471425498 4y4mq9 Physics 2016-08-17 12:18:18 "Neither. You'd see the electron existing in a state which doesn't have well-defined position. If you could ""see"" it, it would just look like those [orbital diagrams](http://chemconnections.org/chemlinks/Stars/images/orbitals.jpg) from your high school chemistry textbook." "The [images of orbitals](http://pre14.deviantart.net/2c07/th/pre/f/2012/259/3/d/hydrogen_orbitals___poster_by_darksilverflame-d5ev4l6.png) you see in books or online are mapping out the probability of the electron existing in those specific locations. Until you attempt to measure the location of the electron, you can't say anything more about where it is located than that - there is no ""hidden variable"" that can describe the position more accurately. + +However, you can attempt to localize the electron by scattering photons or some other particle off of it. The problem is that this must necessarily add kinetic energy to the electron and ionize it. So you only get one snapshot - there is no way to make a frame by frame movie of the electron. But in theory, a very tightly focused gamma ray beam could be used to localize the electron to within a fraction of the volume of its orbital. + +There was a very different [experiment by a group in the Netherlands](http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.213001) that comes close to taking a ""snapshot"" of the electron in its orbital around a hydrogen atom (see a write-up about the paper [here](http://physics.aps.org/articles/v6/58)). Instead of using short wavelength light to localize the electron like I described above, they barely ionized the electrons with visible photons, then used a DC field and an electrostatic lens to focus those electrons onto a screen. As more electrons are collected on the screen, a pattern emerges corresponding the the wavefunction of the electron at that location. The pattern on the screen ends up displaying the same nodal structure that the orbital had. However, this isn't a direct image of the orbital structure, and when an single electron is recorded on the screen you can't say for sure where in the orbital it came from. +" +577 Is Hurricane Matthew indicative of the end of the 11 year super quiet period of major North American hurricane activity or are conditions still generally unfavorable for hurricane formation? 3655 https://www.reddit.com/r/askscience/comments/566x41/is_hurricane_matthew_indicative_of_the_end_of_the/ 1475778890 566x41 Earth Sciences 2016-10-06 21:34:50 "Hi! Atmospheric scientist here. I can explain what people mean when they talk about the ""quiet period"". + +The last time the U.S. was hit by a major hurricane (defined as category 3 or higher on the wind-based [Saffir-Simpson](http://www.nhc.noaa.gov/aboutsshws.php) scale) was [Wilma](https://www.nasa.gov/vision/earth/lookingatearth/h2005_wilma.html) in 2005. The U.S. has been hit by destructive hurricanes since then, including Ike, Irene, and Sandy, but these were all either category 1 or 2 when they made landfall. So the ""quiet period of major hurricane activity"" that you are referring to is the 11 year period after Wilma during which no hurricane made landfall on U.S. soil *while at category 3+ intensity*. Matthew has also ended a 9 year period with no [category 5 storms in the Atlantic basin](https://en.wikipedia.org/wiki/List_of_Category_5_Atlantic_hurricanes) - the previous cat 5 storm being Felix in 2007. + +Tropical cyclone activity is very complex. It is influenced by planetary-scale oscillations in climate - e.g., [ENSO](https://www.climate.gov/news-features/blogs/enso/impacts-el-ni%C3%B1o-and-la-ni%C3%B1a-hurricane-season) (El Nino/La Nina), the [Madden-Julian Oscillation](https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care), and some others. Hurricane Matthew is not *in itself* an indicator that we are going to see an increase in tropical cyclone activity in the Atlantic in the near future (this year or coming years). You would need to look at the overall conditions that favor hurricane formation (low wind shear, warm sea surface temperatures, overall heat content in the upper ocean, etc.). The relationship between hurricanes and climate variables is receiving a lot of attention, especially in the future as climate change fucks shit up. + +That's about the best explanation I can give. After all I don't study hurricanes, I study air quality. Now who wants to hear about ozone formation?!?!? ^Anyone? + +Edit: added links and did formatting stuff" "According to the National Hurricane Center: +The 1968-2015 average is 11.8 named storms, 6.2 hurricanes, 2.4 major hurricanes. +The 2006-2015 average is 14 named storms, 6.3 hurricanes, 2.6 major hurricanes. +It looks to me that the last 11 years have been exactly what you'd expect from North Atlantic hurricane formation. So what exactly makes you think the last 11 years have been ""super quiet""?" +1437 What is the base of a mountain? 3650 https://www.reddit.com/r/askscience/comments/dqob73/what_is_the_base_of_a_mountain/ 1572719658 dqob73 Earth Sciences 2019-11-02 21:34:18 "This is a little outside my field, but let me try to give you my understanding. The height of mountains is generally measured in one of two ways, topographic prominence (the height difference of the peak and the lowest contour line encircling it, but not containing a higher peak), or elevation above Earth's reference geoid (a mathematical model of the earth's shape, roughly the mean sea level in the absence of tides). + +Using these definitions, let's clarify the statements on Wikipedia. + +1. The highest mountain *above the reference geoid* on Earth is Mount Everest. + +2. The ~~bases~~ *lowest encircling contour line* of mountain islands are below sea level. Mauna Kea is the world's ~~tallest~~ *most prominent* mountain. + +3. The highest known mountain *above any planet's respective reference geoid* ~~on any planet~~ in the Solar System is Olympus Mons on Mars. + +I think that answers the first four questions. As for the fifth, there is, to my knowledge, no word for the volume of a mountain. The volume of a mountain is sometimes considered when deciding when something is actually a mountain. This, of course, opens up a whole new definitional can of worms." "One way to think about what you are asking is the concept of [prominence](https://en.wikipedia.org/wiki/Topographic_prominence). To paraphrase, suppose you had to walk from the top of a mountain to the top of a higher mountain. What is the lowest elevation that you would be forced to cross walking from one mountain to another? The distance between that elevation and the summit of the mountain is the prominence. + +A reason to use prominence is the problem of finding a spot to measure from. Do you measure from sea level? The lowest point on the surface of the earth (like the bottom of the Mariana Trench? The core of the earth? + +There's one problem with prominence - you can't measure prominence for the tallest mountain on earth (Mount Everest) because there is no taller mountain to walk to. So, usually the height of Mount Everest is measured from sea level." +129 Why is it that many cultures use the decimal system but a pattern in the names starts emerging from the number 20 instead of 10? (E.g. Twenty-one, Twenty-two, but Eleven, Twelve instead of Ten-one, Ten-two)? 3641 https://www.reddit.com/r/askscience/comments/3j2tol/why_is_it_that_many_cultures_use_the_decimal/ 1441024376 3j2tol Linguistics 2015-08-31 15:32:56 "In English, eleven is derived from the Old English *endleofan*, which literally means ""one leftover,"" specifically one left over from ten. The same is true for twelve, in Old English *twelf* is a contraction of some form of *twa* (neuter form of 2) and *leofan*. So in this method of counting the ten does come first because there needs to be a number to be left over (leofan) from, but it acts as a given rather than explicit quantity. + +As for Italian, I would note that in Latin there are variable forms of counting for the Romans, ""duode"" and ""unde"" can and have been used for numbers at least through 100, e.g. duodetriginta = 28, undequinquaginta = 49. However, +*viginti octo* = 28 & *quadraginta novem* = 49 are also perfectly legitimate. I would also refer to Roman Numerals, where you see the ""one from *N*"" form a lot, although IIII = 4 is not uncommon in the manuscripts I have used. For numerals it makes some rational sense because it shortens the amount of numerals required to represent the number. + +IV = 1 from 5 instead of IIII + +IX = 1 from 10 instead of VIIII + +XC = 10 from 100 instead of LXXXX + +XLIX = 10 from 50 & 1 from 10 + +See also + +1. A.J. Baroody & J.M. Wilkins, [""The Development of Informal Counting, Number, and Arithmetic Skills and Concepts""](https://www.soe.vt.edu/tandl/pdf/Wilkins/Book_Chapter_Wilkins_The_development_of_informal_counting.pdf) about how children learn basic mathematical concepts such as counting + +2. Steven Law, [""A Brief History of Numbers and Counting,""](http://www.deseretnews.com/article/865560110/A-brief-history-of-numbers-and-counting-Part-1-Mathematics-advanced-with-civilization.html?pg=all) written for a popular audience, but a decent rundown. + +3. Crollen & Noel, [""The Role of Fingers in the Development of Counting and Arithmetic Skills,""](http://www.ncbi.nlm.nih.gov/pubmed/25661746), and I might note some scholars argue we have 12 hour divisions of the day because of the 12 knuckles we have on the four fingers of our hands (not counting thumb). + +4. A lengthy page from Pierce College about [Historical Counting Systems](http://www.pierce.ctc.edu/staff/dlippman/mathinsociety/HistoricalCounting1.0.pdf), and though I can't speak on its specific accuracy, superficially it appears fine. + +**5. Denise Schmandt-Besserat & Michael Hays. *The History of Counting* Harper Collins, 1999.** + +**6. Georges Ifrah & David Bellos. *The Universal History of Numbers: From Prehistory to the Invention of the Computer* Wiley-Blackwell, 2000** + +Hope this helps a little. Happy Reading! + +" "They're all closely related languages (German, English, French, Spanish & Italian). + +If you look at other languages that do not come from the same root, it does not hold. + +For example, [Hungarian](http://mylanguages.org/hungarian_numbers.php) maintains the pattern starting at eleven. + +Hebrew uses an [additive system](https://en.wikipedia.org/wiki/Hebrew_numerals). + +I don't think it's ""cultures"", but rather language roots." +1121 When a lightning bolt strikes the ground, what happens to it once the ground absorbs it? 3641 https://www.reddit.com/r/askscience/comments/9hyqkm/when_a_lightning_bolt_strikes_the_ground_what/ 1537612399 9hyqkm Earth Sciences 2018-09-22 13:33:19 "Lightning bolts don't ""go"" anywhere, they're just the visible glow of ionized air. Lightning happens when the electric potential difference between clouds and the ground is too high and the air can no longer sustain it. The air breaks down, forming an ionized channel (the lightning bolt) that allows current to flow until the two regions are at the same potential. Afterwards, there is no potential difference and therefore no discharge. The air that made up the lightning bolt is just normal, non-ionized air again and some electrons have been transferred to the ground." "The lightning bolt is basically a narrow, violent flow of electrons and ions. This flow does indeed disperse inside the ground, as a roughly spherical wave in the 3D field of charge density. On the surface there are currents flowing in the radial direction from the striking point. If you find yourself walking directly towards or away from where a lightning strikes, there may be a huge voltage between your feet due to this. This so-called ""step voltage"" often kills many cows that hide beneath trees." +10 Apparently bedwetting (past age 12) is one of the most common traits shared by serial killers. Is there is a psychological reason behind this? 3635 http://www.reddit.com/r/askscience/comments/2zpf28/apparently_bedwetting_past_age_12_is_one_of_the/ 1426863890 2zpf28 Psychology 2015-03-20 18:04:50 "What you're asking about is part of a model proposed by John Macdonald. He proposed that a combination of three behaviours is predictive of psychopathy: fire setting, cruelty to animals, and enuresis (bedwetting). This model was known as the [Macdonald triad](http://en.wikipedia.org/wiki/Macdonald_triad). + +While this idea gets a lot of play time in pop culture, it's not been backed up by research. Bedwetting is not [predictive of psychopathy](http://www.scientificjournals.org/journals2009/articles/1441.pdf). + +Edit: Some have rightly pointed out that there are issues with that linked paper (small, likely unrepresentative sample, no normative data). A quick search turned up [this community based study](http://psycnet.apa.org/journals/law/18/4/577/) which finds no significant effects of childhood environment on psychopathy in later life. The takeaway should be that psychopathy is a much more complex trait that the Macdonald triad may have suggested, and it's going to be hard to pin down specific factors that result in psychopathy and criminality (not all people who are high in psychopathy are going to be criminals and vice versa)." """Older"" bedwetting is also seen in kids who've been abused (sexually or otherwise). Given than psychopaths are more likely to have been neglected or abused as children, I wonder if some of the incidence of bedwetting past the normal ages is related to abuse." +692 Why do doctors bother with painkillers like oxycodon, etc, that barely differ from morphine? 3630 https://www.reddit.com/r/askscience/comments/5mjc7w/why_do_doctors_bother_with_painkillers_like/ 1483774362 5mjc7w Medicine 2017-01-07 10:32:42 This post is being locked due to the absurd number of anecdotes. "While there are some differences within the group of opiods/opiates, you are right to question the clinical value of them. + +Oxycodon may have a better metabolism (morphine has active metabolites and is more reliant on kidney function) and a more predictable bioavailability. + +In some surgical protocols you want a very short half-life (you might have continuous administration) which makes remifentanils pharmacological properties beneficial. + +There are some opiods that have secondary effects, suchs as tramadol and tapentadol (monoaminergic reuptake inhibition). + +There might also be a difference in documentation, for instance a pharmaceutical company might have been more willing to perform a study on a ""new condition"" using drugs that they still own - and we are more willing to use drugs with good studies backing them up. + +A very down to earth reason is that daily dosages of morphine in the 400 mg range ~~i.v.~~parenterally (with extra doses around 70 mg) evokes more worry than 80 mg of hydromorphone. + + +" +234 What will it mean for science if NASA announces it has found running water on Mars? 3622 https://www.reddit.com/r/askscience/comments/3mow11/what_will_it_mean_for_science_if_nasa_announces/ 1443442465 3mow11 Planetary Sci. 2015-09-28 15:14:25 "Hard to say without the specifics. The implications of such a hypothetical announcement would be quite different depending on on how and where the data was obtained, and what are the particulars. + +A couple of key questions to keep in mind are as follows: + +* is this permanent ""flowing water"" (highly unlikely) or intermittent/episodic (probable); + +* are we talking about a dynamic system hinting at some sort of active hydrosphere (momentous), active geologically-driven hydrothermalism (Very cool) or is a passive system where episodic melting releases water from a fossil source such as permafrost (cool); + +* What is this water of which we speak? Is it freshwater? Saline? Hypersaline? What about pH? The source of the info will limit the possibilities to adress this, but it matters. The fact that someone closely connected to HiRISE is part of the announcement makes me suspect there would be little compositional data available in such an announcement if your hypothesis is correct. + +But we'll see. I'll be waiting for the actual announcement; I'm curious to see what it is myself! + +EDIT/UPDATE: So! It's épisodically flowing brines loaded with perchlorates after all! No specific source has been identified, so all options are open as to what exactly is going on here. To come back on my previous statement, I'd say this falls in the ""pretty cool"" range, for quite salty values of cool..." "[Seems it's been confirmed, there is salt water running on Mars.](http://www.cnbc.com/2015/09/28/ter-nasa.html) + +A big thing people don't seem to be considering is that now we know there's salt water on Mars, NASA has cause to begin funding research on how to make salt water usable, most likely leading to massive strides in that kind of technology, which will help us on earth when fresh water becomes scarce. + +:(" +11 I keep hearing about outbreaks of measles and whatnot due to people not vaccinating their children. Aren't the only ones at danger of catching a disease like measles the ones who do not get vaccinated? 3621 http://www.reddit.com/r/askscience/comments/2tkbjm/i_keep_hearing_about_outbreaks_of_measles_and/ 1422144153 2tkbjm Medicine 2015-01-25 3:02:33 "Sadly, no. Unvaccinated people are indeed at the highest risk, however, while vaccines are very effective, no vaccine is 100% effective. Most childhood vaccines protect between 85 and 99 percent of the population. For some reason, [a small percentage of folks who are vaccinated do not develop immunity](http://www.cdc.gov/vaccines/vac-gen/6mishome.htm). This hasn't traditionally been much of an issue because with the vast majority of the population vaccinated for a particular disease, we develop ""[herd immunity](http://en.wikipedia.org/wiki/Herd_immunity)."" The more folks are vaccinated, the harder it is for a disease to spread, and so epidemics become less likely. + +Another issue (though not strictly what you asked) is that some children cannot receive the vaccine. Often this is because they have a compromised immune system thanks to a genetic disorder, or active cancer treatment. While these children cannot receive the protection of the vaccine, they *can* indeed receive the protection afforded by herd immunity. Unfortunately, as more people choose not to vaccinate their children, immunocompromised are put in particularly bad risk. In the case of measles, these children[ have up to a 50% mortality rate](http://www.health.govt.nz/your-health/conditions-and-treatments/diseases-and-illnesses/measles/protecting-children-who-cant-be-immunised-against-measles). + +**EDIT: Thank you everyone for the extensive and productive discussion, but please remember that personal medical anecdotes are not allowed in /r/askscience.**" "One additional point that a lot of people miss: + +People who are immunocompromised (due to HIV, some cancers and cancer treatments, certain genetic conditions, anti-rejection drugs, and some other medications) are at elevated risk *even if they have already been vaccinated.* + +This group is usually brought up in the context of 'populations that can't be vaccinated'. Yes, it's true that people who are severely immunocompromised usually can't be vaccinated. But even people who had their shots as kids and developed effective immunity are at risk if they later go on to develop an immunocompromising condition. + +All a vaccine does is teach your immune system how to respond to a pathogen. You still need your immune system to be in good working order when it comes time to actually mount that response." +130 What would a cup full of viruses or bacteria look like? 3621 http://www.reddit.com/r/askscience/comments/374r6a/what_would_a_cup_full_of_viruses_or_bacteria_look/ 1432503281 374r6a Biology 2015-05-25 0:34:41 "If your cup only had bacteria and no broth, most bacteria would look like slime with a yellowish tinge to it. Some are slightly more granular than others. There's a few types that would be a little red, pink, or a little green, others a stark white. There's a couple of types that would likely look crusty (like those in the Mycobacterium tuberculosis Complex), because of cord factor, they tend to look more chunky and waxy. + +No idea what a cup of viruses would look like. That would be SO MANY viruses." [deleted] +338 Why are Autistic Spectrum Disorders far more prevalent in males than in females? 3617 https://www.reddit.com/r/askscience/comments/3zx52k/why_are_autistic_spectrum_disorders_far_more/ 1452196060 3zx52k Psychology 2016-01-07 22:47:40 [deleted] There have been studies done recently that look into the possibility that girls with autism display the symptoms differently and have differences in brain structure leading to under diagnosis and mistreatment. [Here is one write up] (https://med.stanford.edu/news/all-news/2015/09/girls-and-boys-with-autism-differ-in-behavior-brain-structure.html) +693 Do cosmic rays ever pass through the LHC and if so, what happens to them in the accelerator? 3616 https://www.reddit.com/r/askscience/comments/5p3rgo/do_cosmic_rays_ever_pass_through_the_lhc_and_if/ 1484917566 5p3rgo Physics 2017-01-20 16:06:06 "Yes, cosmic particles pass through the LHC all the time. They're not accelerated around the loop, since the configuration of the magnets has been finetuned specifically for the path taken by the particles inserted into the LHC by the experiment itself. Cosmic particles come in from a completely different direction and while they can be affected by the magnetic fields in the ring, this will only change their direction, it won't ""catch"" them into a circular path. + +Cosmic particles may also interact with one of the detectors placed along the LHC ring. When this happens and the detector is turned on, the particle is registered very much in the same way that particles are registered during normal operation. + +But there are important differences. Only part of the cosmic particles actually make it 100m into the ground to reach the detector. Part of the particle types are absorbed by the Earth before they can reach far enough into the ground. The next difference is due to the design of the detectors. They're designed to envelop the LHC beam and the most sensitive equipment is located very close to the beam. But cosmic particles come in from above and have to cross through the outer layers of the detector first. + +So the impact of a cosmic particle on an active detector is quite different from a normal detection event. However, cosmic particles (or ""cosmics"" in short) have been very useful in helping scientists to benchmark and finetune the detector before normal operation. + +Read more about this in the newspost from the CMS experiment (one of the large LHC detectors) from 2 years ago (when the LHC was on an extended break from normal operations): +http://cms.web.cern.ch/news/cms-never-idle" AFAIK, all of the big LHC detectors use cosmic rays for calibration and alignment +1262 Is elevation ever accounted for in calculations of the area of a country? 3608 https://www.reddit.com/r/askscience/comments/av2mwm/is_elevation_ever_accounted_for_in_calculations/ 1551205192 av2mwm 2019-02-26 21:19:52 "Elevation changes are so tiny that it wouldn't make a big difference, provided you were reasonable about your definition of area. (As /u/Gigazwiebel 's discussion of fractals suggests, you could in principle count the area of every grain of sand on the surface of Egypt's desert and get a ridiculously large area.) + +But so long as you ignore the fractal stuff and look at kilometer-scale elevation changes, then the Earth's surface is *really* close to being flat. Nepal, for instance, is about 800 km long, 200 km across, and has 8 km of altitude variation. Relatively speaking, it's flatter than a tortilla. + +Humans tend to mentally exaggerate the steepness of slopes: a 30-degree slope looks like a sheer cliff when you're standing at the top of it." "As someone who recently had surveying done, I ended up learning a bit about that. Almost certainly, the answer is ""no"" because the area is likely to be based on a survey. Surveying is done ""on the level"". My lot slopes, but the surveyor's instruments account for that. The actual surface area of a lot is not what they want for various practical purposes. In particular, the foundation of a building is going to be level and if actual surface area was quoted as a lot size, you could change it by landscaping. You don't want to have to worry about changing your lot size because you put in some raised beds or piled up a mound of dirt. + +The borders of an entire country are, AFAIK, surveyed in a similar manner. If they weren't, we'd run into the same kinds of problems subdividing tracts. What if Chile subdivided some land, then there was a landslide on it? Misery. It's much better to keep surveying ""on the level"". + +What's more interesting is whether or not the curvature of the Earth is taken into account. Out here in the western USA, you've got entire *sections* of land for sale quite often. That's 1 square mile. You might think the curvature of the Earth would factor in, but if you sit down and do the math you realize that chord length and arc length are surprisingly close until you get into some really large angles. + +Surveys that take the curvature into account are called *geodetic surveys*, and when you're talking about an entire country or an unusually large tract like a national park they might do that. + +In that case, the tract will be slightly larger due to the curve. The word ""geodesy"" will get you some interesting links to learn more. + +edit -- [according to these guys, plane surveys can be good for 250 square km](https://www.civilengineeringterms.com/surveying-levelling/plane-surveying/)! That's better than I thought." +235 Can you get hearing loss from exposure to loud noises outside our hearing range? 3603 https://www.reddit.com/r/askscience/comments/3ko3a2/can_you_get_hearing_loss_from_exposure_to_loud/ 1442069841 3ko3a2 Human Body 2015-09-12 17:57:21 "There is a lot of misinformation in this thread and people citing websites that don't seem to lead to actual scientific studies. The comment from /u/Yare_Owns is interesting in that it's certainly possible to create intense enough pressure waves that can cause bodily harm, but your hearing is probably the least of your concerns in these situations. + +The real question is whether there are non-audible sounds that can cause hearing loss and *only* hearing loss, i.e. non-syndromic. [This report](http://westminsterresearch.wmin.ac.uk/4141/1/Benton_2003.pdf) has a review of some literature on low-frequency noise exposure. The short section on hearing loss is somewhat inconclusive. It seems possible to cause TTS, or temporary threshold shifts, with very intense low-frequency sounds (around 120-140 dB SPL). It also cites one study that managed to cause PTS, or permanent threshold shifts, in chinchillas after exposing them to low-frequency sounds for 3 days. However, there are no citations in that review of reports of permanent threshold shifts caused in humans. Nevertheless, it seems to indicate that its possible to cause permanent hearing loss by exposure to intense low-frequency noise for long periods of time. + +That conclusion seems to be supported by [this much older review](http://waubrafoundation.org.au/wp-content/uploads/2015/02/Broner-The-effects-of-low-frequency-noise-on-people.pdf) from 1978. It talks about the perceived annoyance of low-frequency sounds and temporary threshold shifts, but not permanent damage. Maybe other people can find other sources, but the literature seems inconclusive. + +Edit: made things clearer +" [deleted] +12 If everyone was required to stay at home for 2 months with zero contact with other people could we wipe out the cold/flu forever? 3601 http://www.reddit.com/r/askscience/comments/30mmu0/if_everyone_was_required_to_stay_at_home_for_2/ 1427572014 30mmu0 Medicine 2015-03-28 22:46:54 "Not a chance, the biological world consists of a lot more than just humans, influenza in this case infects a wide variety of animals, hence the ""swine"" or ""bird"" flu you hear about. Also a lot of diseases can have incubation times or even be dormant for decades like in the case of TB." "The [xkcd-book](https://whatif.xkcd.com/book/) has a section about this, and the answer comes down to: Almost, but not really. + +The common cold is usually caused by some variant of the rhinovirus, which is eradicated from the human body by a healthy immune system after about a week. And since this virus doesn't cross species, and can't infect anyone due to the isolation, it should die out. + +The problem is that not everyone has a healthy immune system, and therefore a few strains of the virus will survive beyond the quarantine. And so they can spread across the population again, and the 2 months of isolation would have been for nothing... + +" +898 Why are solar-powered turbines engines not used residentially instead of solar panels? 3601 https://www.reddit.com/r/askscience/comments/7e8owp/why_are_solarpowered_turbines_engines_not_used/ 1511182832 7e8owp Engineering 2017-11-20 16:00:32 "I'm not a solar engineer, but here's a physics-based argument: + +**You can't get a solar heat absorbing panel hot enough to match the efficiency of photovoltaic solar panels, unless you use lenses and mirrors which track the sun.** + +Math: the efficiency of any engine that converts heat into useful power is limited by the ""Carnot efficiency"": + + max eff = (T_hot - T_cold) / T_hot + +where T_hot and T_cold are the temperatures of the heat source and heat sink, in *Kelvin*. Real-world devices can come close, but can't exceed this limit: [typical large-scale power plants](http://www.brighthubengineering.com/power-plants/72369-compare-the-efficiency-of-different-power-plants/) can get to within 2/3 of it. + +Typical photovoltaic solar panels operate at about [15% efficiency](https://sciencing.com/average-photovoltaic-system-efficiency-7092.html). To match that with a heat engine running at 2/3 of the Carnot efficiency, and a cooling system running at 27°C (typical outside air temperature), you'd need the ""hot side"" of your engine running at 115°C. That's right around the boiling point of water. + +The problem is, you can't get a container of water that hot just by putting it out in the sun. Even in a vacuum-sealed black-painted [solar thermal collector](https://en.wikipedia.org/wiki/Solar_thermal_collector), when you get up to these temperatures, the amount of infrared light radiated away from the hot collector equals the amount of sunlight coming in, so very little or no heat is left to send to the engine. + +To get up to an efficiency that beats photovoltaics, you'd need to dramatically increase the ratio of solar absorbing area to infrared-emitting area, which means lenses or mirrrors to capture and concentrate sunlight. These devices would have to move to track the sun... + +So now you're looking at running a turbine (about as mechanically complicated, noisy, and high-maintenance as a car engine), in a system with boiling water (noisy, safety hazard), with a complicated optical tracking system on the roof (prone to break down, needs to be kept clean of leaves and bird poop).... even if you could make it cheap, it'd be a homeowner's nightmare." It all comes down to return on investment and cost of maintenance. The best way to limit maintenance is to eliminate moving parts. Moving parts vibrate and wear. PV panels can be installed and besides cleaning go untouched for 30 years. +694 If I'm addicted to cigarettes and feel a physical urge to smoke every hour I'm awake, why don't those urges interrupt my sleep at night? 3598 https://www.reddit.com/r/askscience/comments/6302in/if_im_addicted_to_cigarettes_and_feel_a_physical/ 1491145215 6302in Neuroscience 2017-04-02 18:00:15 +236 Do multiple wounds heal slower than just a single one? 3596 https://www.reddit.com/r/askscience/comments/3vx6mi/do_multiple_wounds_heal_slower_than_just_a_single/ 1449577226 3vx6mi Human Body 2015-12-08 15:20:26 "Depends on how close they are too. + +Wounds close mechanically as well as having regrowth. If you take a little biopsy from your skin, first off you have a scab, and you also have stem cells in reservoirs of stem cells around the wound that start to proliferate and these daughter cells migrate towards the centre of the wound where they meet, stop migrating and start to thicken up. [Here](http://e.xposu.re/wp-content/gallery/microscopy/dynamic/SUM_dark-bi3-1.jpg-nggid03264-ngg0dyn-480x960x100-00f0w010c010r110f110r010t010.jpg) is a picture where the green is skin (Keratin5) and red are stem cells, and the wound is to the right, so the skin you can see already starting to point to the wound centre. This wound is 4 days old. + +[Here](https://www.flickr.com/photos/tomas-/17220613278/) is a wound that is totally healed. The scab is the big weird thing on top. + +However, at the same time fibroblasts orientate towards the wound centre and start to muscularly contract the wound closed. A 1.5mm wound is basically invisible once the wound contraction is finished, a 3mm wound is less than half that size after a few days. + +And so several small wounds in a close location would not optimally contract and might heal slower. + +**additionally** + +Wounds need blood flow, and that can be effected with multiple wounds. If you have wounds that are local, and interfere with blood flow, they can become chronic wounds. Wounds that affect skin in a complete circle around the arm or leg can be like that. " "not necessarily. If one had three paper cuts of small size on different parts of their body they'd all heal at the same rate. +When learning about tissue healing, we are generally taught that there are three phases: Inflammatory response, Proliferation, Maturation/remodeling. +In the inflammatory response phase, your immune system activates to fight off infection, when the wound is sufficiently ""sterilized"" the Proliferation phase begins. In this, the granulocytes start collecting near the wound area and new tissue is laid down in a messy ""spaghetti-like"" structure. +In the maturation remodeling phase, the tissue is stretched and aligned along the lines of pull of the tissue and the tissue normalizes. +That's a brief overview. +The type of damage also plays a role. Incisions (straight edged cuts in skin) heal faster than lacerations (jagged edged cuts in skin, like tears). also the deeper the cut is, the longer it takes to heal cause tissues heal from deep to superficial layers. thats it in a sort of nutshell. If you have more questions feel free to ask!" +445 Kepler Exoplanet Megathread 3595 https://www.reddit.com/r/askscience/comments/4irfhw/kepler_exoplanet_megathread/ 1462914255 4irfhw Astronomy 2016-05-11 0:04:15 Woohoo! Exciting stuff! I understand that this is a very small region of the sky and Kepler can only detect planets in the orbital plane that matches our line of sight. How much of an effect do these new detections have on the estimate of the total number of exoplanets in our galaxy? Do they fall within expected values? Or does this exceed expectations? I wonder how many of these it will be possible to make [surface maps](http://klotza.blogspot.com/2015/09/a-surface-map-of-exoplanet.html) of, and whether we can get good spectroscopy data with the next generation of telescopes. +446 When rockets launch they must have tonnes of momentum from the earth spin and orbit. Is this used to their advantage when plotting a course? 3591 https://www.reddit.com/r/askscience/comments/4nqfut/when_rockets_launch_they_must_have_tonnes_of/ 1465741619 4nqfut Physics 2016-06-12 17:26:59 "**Short answer:** Yes. By launching near the equator rather than the poles, you can get up to a 1,000 mph boost just from the earth's rotation. Additionally, you should launch to the *east* to get this benefit. + +**Long answer:** In low earth orbit you need to be going 17,000 mph - it doesn't matter which direction. But at the equator the earth is rotating 1,000 mph counterclockwise, so if you launch east into a counterclockwise orbit you only need to gain 16,000 mph. If you launch to the west into a clockwise orbit you need to gain 18,000 mph. + +By launching west, you're basically starting out with a 1,000 mph deficit that you have to overcome, [like running the wrong way on a moving floor.](http://i.imgur.com/0AbkHXM.gif) + +In the US, this is why we launch missions from Florida - because it's pretty far south, and if you're launching to the east you're over ocean and not populated areas. + +On the other hand, Israel, doesn't have this advantage. They have to launch their [Shavit](http://www.britannica.com/topic/Shavit) rockets (Hebrew for 'comet') to the west so that they pass over the Mediterranean, rather than potentially hostile neighbor states. This puts their satellites on ""retrograde orbits,"" meaning they orbit the earth opposite the direction of pretty much every other man-made satellite. While that may seem cool it comes at the expense of more fuel, limiting them to payloads 30% smaller than if they were launched eastward. +" "/u/VeryLittle has it mostly correct, but the answer is ""usually"". If you're trying to get into a retrograde orbit, you have to kill all that momentum. It doesn't do much harm for polar orbit, but it doesn't help much either." +447 If there was a planet with the same orbit and orbital period as the Earth but on the opposite side of the Sun would we ever detect it from Earth? 3588 https://www.reddit.com/r/askscience/comments/4rckov/if_there_was_a_planet_with_the_same_orbit_and/ 1467723970 4rckov Astronomy 2016-07-05 16:06:10 "Yes. First, we have satellites that orbit the sun from near this point, [they give us a stereo view of the sun.](http://stereo.gsfc.nasa.gov/where.shtml) If there was a planet at the [L3 Lagrange point](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a5/Lagrange_points_simple.svg/500px-Lagrange_points_simple.svg.png) (the point directly opposite the sun from the earth) these satellites wouldn't be able to stay put. + +Additionally, while on the topic of orbits, the gravity from the planets affects each others' orbits, changing the precession of the perihelion of their orbits. This has been measured to incredible accuracy, especially for Mercury. If there was an additional planet hiding in the inner solar system, it would have shown up in these observations of orbital perturbations. + +Lastly, the L3 point is generally not a stable point to orbit, so any planet hiding there wouldn't stay put very long. + +" "Although it's been disproven the Greek hypothesis for this was called counter earth: https://en.m.wikipedia.org/wiki/Counter-Earth + +Similarly, other planets were proposed to explain other orbits we didn't understand. Planet Vulcan was proposed to explain mercury's orbit." +578 How finite are the resources required for solar power? 3583 https://www.reddit.com/r/askscience/comments/5efjov/how_finite_are_the_resources_required_for_solar/ 1479877372 5efjov Earth Sciences 2016-11-23 8:02:52 "If we just consider a simple single crystalline Si solar cell, we will never run out of material. Si is one of the most abundant elements on the earth. I am unsure about repairing panels but it is possible to recycle the Si. + +There are many other type of solar materials being researched that contain less abundant elements. Most of those materials however are more efficient absorbers and a lot less material is needed to begin with. + +The biggest limiting factor would be the use of indium Tin Oxide for the 'glass' coating/contact. I don't know if this is used in commercial applications but it has become fairly common in research cells. This is the same thing your touch screen is made out of and there is already work being done to find an alternative due to the cost and relatively low abundance. + +Edit: When I say abundance I mean in the crust. It's late and I am tired." "The limiting resource for Si solar cells is probably the metal contact materials e.g. Silver, copper, aluminum. But yeah, we could make Al metallized Si solar cells for a long time without running out. Al is less conductive than the others though, so that can cause efficiency issues depending on architecture. Besides the semiconductor and metal, solar cells typically have tiny amounts of ""dopants"" and ""passivation"" but here also we are talking about fairly abundant elements like H, B, N, P, As, C and tiny tiny amounts. + +The second most popular solar cell semiconductor after Si (for now) is cadmium telluride (see the large US solar company, First Solar), whose elements, Cd and Te, would run out a bit earlier. " +448 If diamonds are the hardest material on Earth, why are they possible to break in a hydraulic press? 3581 https://www.reddit.com/r/askscience/comments/4jbni1/if_diamonds_are_the_hardest_material_on_earth_why/ 1463236956 4jbni1 Physics 2016-05-14 17:42:36 "Hardness is a separate property to Strength and Toughness. + + +Hardness is the measure of how resistant solid matter is to permanent shape change when force is applied. + + +Strength is a measure of the extent of a materials elastic/plastic ranges. + + +Toughness of a material is the maximum amount of energy it can absorb before fracturing. + + + +If you were to look at the bottom of the press you would see scratches left by the diamond, because it is hard. + + +The diamond breaks because it has low toughness." ">Unlike hardness, which denotes only resistance to scratching, diamond's toughness or tenacity is only fair to good. Toughness relates to the ability to resist breakage from falls or impacts. Because of diamond's perfect and easy cleavage, it is vulnerable to breakage. A diamond will shatter if hit with an ordinary hammer. The toughness of natural diamond has been measured as 2.0 MPa m1/2, which is good compared to other gemstones, but poor compared to most engineering materials. + +[More info...](https://en.m.wikipedia.org/wiki/Material_properties_of_diamond)" +695 Can the equations of fluid dynamics be used to describe/model the flow of electrons? 3575 https://www.reddit.com/r/askscience/comments/5wago4/can_the_equations_of_fluid_dynamics_be_used_to/ 1488121537 5wago4 Physics 2017-02-26 18:05:37 In low-Reynolds number flow (slow or constricted flow), fluid circuits can be treated the same way as basic electrical circuits, with pressure instead of voltage, flow rate instead of electrical current, and a fluidic resistance that is analogous to electrical resistance except depends differently on geometry. The analogies generally break down if you move away from this regime. Almost. The incompressible, Newtonian Navier-Stokes equations for fluid momentum are very similar to the drift-diffusion equations that govern the electron/hole density in materials. One major difference is that the drift-diffusion equations also require solving the Poisson equation for the electric field inside the material. +131 "If I were traveling at near the speed of light (enough to significantly slow time), would I be able to ""think"" normally? Would I be able to tell that time is slowing down?" 3574 http://www.reddit.com/r/askscience/comments/3filvv/if_i_were_traveling_at_near_the_speed_of_light/ 1438530224 3filvv Physics 2015-08-02 18:43:44 "As long as you were moving at a constant velocity, then nothing would appear ""strange"" to you. A key point of [special relativity](https://en.wikipedia.org/wiki/Special_relativity) is that the laws of physics work the same in any (i.e. non-accelerating) inertial frame of reference. So yes, if you have a spaceship that is moving *relative* to a planet, then the clock on the spaceship would tick more slowly than a clock on the planet due to [time dilation](https://en.wikipedia.org/wiki/Time_dilation). But for the people on the spaceship, nothing would change, they would perceive time as passing normally. + +**edit:** Even though it's a bit late, I hope this follow-up can clear up some of the questions that have come up since my initial reply: + +One of the consequences of the fact that the speed of light must be equal in all frames of reference is that the very notion of [simultaneity is relative](https://en.wikipedia.org/wiki/Relativity_of_simultaneity). In other words the idea that two distant events happen at the ""same time"" is not an absolute, but depends on our frame of reference. This is the key to understanding one of the apparent paradoxes of physics, namely the so-called [twin paradox](https://en.wikipedia.org/wiki/Twin_paradox). In the most general terms, the ""paradox"" is that if you have two objects say A and B, which are moving relative to each other, then from the perspective of an observer on A, it is B that is moving, and hence time on B should run slower due to [time dilation](https://en.wikipedia.org/wiki/Time_dilation), but by the same token for an observer on B, it is the time on A that is moving more slowly. The fact that both perspectives are equally valid physically goes goes to the heart of special relativity and to the idea that there are no ""privileged frames of reference."" + +Let's go back to the classical example of a person leaving the Earth on a spaceship and making a roundtrip and to the question of who would be older, a person on the ship or a person left on Earth. If the spacecraft is moving close to the speed of light, for an observer on Earth events on the spaceship would be unfolding in ""slow motion"" due to time dilation while life on Earth would continue at a normal pace. On the other hand, for a person on the spacecraft, it would appear as though things on on the ship would unravel at a normal pace, while it would be events on Earth that were happening more slowly! The resolution to this apparent contradiction is that once again, simultaneity is relative. It is not until the traveler would switch reference frames first by changing direction to return back to Earth and then again when stopping that a person on the spacecraft and a ""stationary"" observer on Earth could agree on the time. In that case they would find that it was the person on the spacecraft that would actually be younger than the one on Earth. Switching reference frames effectively creates discrete jumps in the apparent time." "A constant and comfortable 1g acceleration will get you to 0.97c in two years. Not only would you continue thinking normally, but you'd find that journey times become drastically shortened. + +Accelerating at 1g for half the journey and decelerating at 1g for the rest would get you to the Andromeda galaxy in less than 30 years subjective time - while more than two million years had passed on Earth. + +You would certainly notice relativistic effects, and you'd probably get cooked by Unruh radiation. But that aside, as a thought experiment there's no reason why you wouldn't be able to travel across a huge part of the visible universe in a constantly accelerating ship - although it would be ageing visibly around you as travelled. " +696 "AskScience AMA Series: I was NASA's first ""Mars Czar"" and I consulted on the sci-fi adventure film THE SPACE BETWEEN US. Let's talk about interplanetary space travel and Mars colonization... AMA!" 3572 https://www.reddit.com/r/askscience/comments/5rfbiv/askscience_ama_series_i_was_nasas_first_mars_czar/ 1485954002 5rfbiv Planetary Sci. 2017-02-01 16:00:02 "Do you think there are compelling reasons to eventually build large scale settlements on Mars, or will human presence there be limited, like on Antarctica? + +If you think colonization is realistic what do you think will motivate a large number of people to move to Mars?" "What are the actual possibilities to shield the future Mars colonists from radiation? I have read different ideas about colonizing and terraforming Mars but most of them don't deal with the fact that Mars has no magnetic field. And I haven't seen an idea how the terraforming would work in this condition and how the whole planet can be protected from the solar radiation. Thanks. + +Edit: word" +449 Why is blue light the first to get absorbed into the atmosphere through rayleigh scattering, but it penetrates water deeper than other colors? 3570 https://www.reddit.com/r/askscience/comments/4w40ih/why_is_blue_light_the_first_to_get_absorbed_into/ 1470309053 4w40ih Physics 2016-08-04 14:10:53 "Really good question! + +In terms of scattering, yes, blue light is scattered more easily in water and in air. However, absorption is very different for water and even water vapor. + +In water, there is a strong preference for absorption at the lower energy red end of the visible spectrum. The reason for this can be derived from quantum chemistry. Uniquely, water gets its blue color (of course a small amount of water is colorless, but if you have a large body of water, even without the reflection of the sky, there is a blue hue as OP discovered) due to the vibrational transitions of water molecules, unlike most media which get their color from electron-based interactions such as standard absorption/emission lines, Rayleigh scattering, etc. + +This is because water is unique in its interaction with light being primarily determined by its OH bonds, whose symmetric and antisymmetrical vibrational stretching modes are at a very unusually high energy (spatial frequency). All of this means that an overtone transition happens at (symmetric spatial freq)+3*(antisymmetric spatial freq) = 14300 cm^-1 . This corresponds to a red 698nm peak of absorption, whereas many common materials will peak in the infrared. + +In water vapor, on the other hand, this red peak is shifted to lower energy, out of the visible range. This is again due to quantum chemistry; the relevant difference in structure between liquid and gaseous water is that hydrogen bonding is very strong in liquid water. This is why water vapor is colorless. I haven't look at what happens with air (nitrogen and oxygen), but I'm guessing they are colorless too. + +So, basically, water is slightly blue because, unlike almost all other molecules, its strongest absorption peak is due to vibrational transitions. And these occur at 698nm - red. + +Edit: misspoke by getting ahead of myself. thanks /u/richardmnixon42" "First, Rayleigh scattering is not an absorption effect, it is as its name implies, a scattering effect. Second, Rayleigh scattering itself only occurs when the interacting particles are smaller than the wavelength of light in question, and when they are sparsely populated. If you create a more densely packed medium out of even Rayleigh sized particles, the effect will no longer occur because the increased amount of scattering events will average out into a unified wavefront moving in the direction of the incident light. + +When it comes to water, the same properties of Rayleigh scattering do apply, in that it is entirely inapplicable to the situation. Water is a much more dense material than air, especially air in the upper atmosphere where a majority of Rayleigh scattering occurs. As a result, the Rayleigh criterion does not apply and light tends to move through water as though it were a uniform, homogeneous material. As for why red light is absorbed and blue is not, it goes back to the other poster here that stated that water simply has absorption bands in the longer wavelengths that are able to convert red light into vibrational motion of the molecules." +339 If a spacecraft travelling at relativistic speed is fitted with a beacon that transmits every 1 second would we on earth get the signal every second or would it space out the faster the craft went? 3567 https://www.reddit.com/r/askscience/comments/4c5opn/if_a_spacecraft_travelling_at_relativistic_speed/ 1459088421 4c5opn Physics 2016-03-27 17:20:21 "As you can see from the other comments, there are different effects at work here. But if the spaceship moves away from you, it will space out. I'll try to summarize: + +* **Relativistic time dilation**: From your point of view, the time inside the spacecraft moves slower. This means, it might take several seconds from the point of view of your reference frame until one second has passed in the spaceship. +Let's make this precise: If β=v/c is the speed of the spacecraft in units of c, then there are γ=1/sqrt(1-β^(2)) seconds between two signal emissions. + +* **Classical Doppler Effect**: Because the spacecraft moves away from you, each signal has to travel a larger distance than the previous one. +In the γ seconds between two emissions, the spacecraft has moved γ\*v\*(1s). This means, every emission needs γ\*v\*(1s)/c = γ\*β seconds more to reach you than the previous one. +Adding those two effects, we see that you will get a signal every γ\*(1+β) seconds. (This is called the formula of the *relativistic Doppler effect*.) + +* **Expansion of Space**: This effect is tiny, but let's include it for fun. Because space itself is expanding, the two emissions will arrive a little more spaced out than when they were sent out. +The speed with which the signals move apart can be calculated as H\*d, where H is the Hubble constant and d is the distance of the signals. This distance is initially d=γ\*(v+c)\*(1s) because of the contributions of the movement of the ship and of the first signal. We will approximate this distance and therefore the speed as constant, and get that there are additional H\*γ\*(β+1)\*(r/c) seconds between two signals, where r is the distance of the spaceship from you. + +* **Gravitational time dilation**: Because of the Earth's gravitational field, when one second passes in space, only (1 - 6.953*10^(-10)) seconds pass on Earth (see e.g. [here](http://www.awitness.org/unifiedm/introgrtd.html)). This effect actually counteracts the other effects. By the way: Considering this is crucial for GPS, as others here have mentioned. + +As an example, we take a spaceship at half the speed of light (β=0.5, γ=1.155) which is one parsec away (r=3.26 lightyears). Because of the relativistic doppler effect, the signals will arrive every 1.732 seconds. The expansion of space adds only 4.16\*10^(-10) seconds between two signals, which is an even smaller effect than the gravitational time dilation. (At extremely large r, this effect might become relevant though.) + +^(*Edit*: Small additions) +^(*Edit 2*: Fixed a mistake in the expansion of space part) +^(*Edit 3*: Getting too late to reply to all follow-up questions. Thanks for my first gold though!)" See GPS satellite. [Because an observer on the ground sees the satellites in motion relative to them, Special Relativity predicts that we should see their clocks ticking more slowly (see the Special Relativity lecture). Special Relativity predicts that the on-board atomic clocks on the satellites should fall behind clocks on the ground by about 7 microseconds per day because of the slower ticking rate due to the time dilation effect of their relative motion.](http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html) +450 In the average human lifespan, how many viruses do we contract, and overcome? 3560 https://www.reddit.com/r/askscience/comments/4yihox/in_the_average_human_lifespan_how_many_viruses_do/ 1471607781 4yihox Human Body 2016-08-19 14:56:21 "It's going to vary but somewhere in the range of billions per day. Viruses are everywhere. The vast majority are not infectious to humans. + +To give some perspective, I used to grow bacteriophage (viruses that infect bacteria) for my grad school work. (Growing nanotech structures with engineered viruses, to be exact) When I grew them and did a rough purification, I would end up with 50-100 uL of viscous liquid that was about the size of one eyedropper drop. That amount of concentrated phage extract would have around 10 trillion bacteriophage in it. + +Bacteriophage exist in huge quantities in the ocean. Their combined mass is estimated to be 20 *times* the collective mass of all the ocean's whales. They are in a constant battle with the ocean's bacteria. Roughly 30% of the bacteria in the ocean die from bacteriophage attack every day. + +All the other biomes on Earth have [comparable levels](http://jb.asm.org/content/186/12/3677.short) of viral infestation. (though not quite as bad as the ocean) So yeah, you're probably coming into contact with tens of billions of viruses daily, if not more. + +That's not even counting the huge numbers in your gut, predating all the bacteria there. + +*** + +Edit: FFS, this kind of blew up. I'm AFK for the day, I'll try and respond to stuff later tonight." "NPR published an article [""How Many Viruses Have Infected You?""](http://www.npr.org/sections/health-shots/2015/06/04/411469959/how-many-viruses-have-infected-you) + +It describes that we are able genetically test for them ""But there are limitations. The test can only find evidence of past infection with viruses that are already known"". In other words if we dont know what we are looking for we can say you have had it, which means you could have had 1000s of infections but we arent sure how to test for them. + +Notable quotes: + + * ""people living in South Africa, Peru, and Thailand tended to have antibodies against more viruses than people in the United States."" + * ""And we get between 95 percent and 100 percent correct determinations of known viruses."" + +[NYTimes](http://www.nytimes.com/2015/06/05/health/single-blood-test-for-all-virus-exposures.html?_r=0), [WashingtonPost](https://www.washingtonpost.com/news/speaking-of-science/wp/2015/06/04/this-blood-test-can-tell-you-every-virus-youve-ever-had/), and [FoxNews](http://www.foxnews.com/health/2015/06/05/new-blood-test-can-detect-every-virus-person-has-had.html) has covered the same technology. + +End thoughts/anecdotal: Potentially a lot, potentially a few. We may have been infected with a lot but we are unable to determine them due to not knowing what to look for. + +" +697 Could the conditions for life be different than ours in another part of the universe? 3559 https://www.reddit.com/r/askscience/comments/5utxvp/could_the_conditions_for_life_be_different_than/ 1487443949 5utxvp Planetary Sci. 2017-02-18 21:52:29 Due to good answers being in this thread and a large number of speculative answers still being posted, this thread is locked. "We don't know what the full range of conditions is under which life can exist. + +What we do know is that life is possible in places like the Earth. + +So if you were going to look for life, better to spend your efforts in the kinds of places where we know life can exist, but that is not the same as saying life can't exist in other conditions. +" +451 Hi Reddit, I’m Margaret Leinen, here to talk about the world’s oceans and how we observe them. Ask Me Anything! 3554 https://www.reddit.com/r/askscience/comments/4p4cji/hi_reddit_im_margaret_leinen_here_to_talk_about/ 1466512356 4p4cji Oceanography AMA 2016-06-21 15:32:36 How can you, as AGU President, and the Board, in good conscience, continue the partnership with ExxonMobil despite a massive part of the membership being vehemently opposed to such a relationship given Exxon's role in suppressing and discrediting the climate science conducted by your own members? "How much of the Great Barrier Reef do you think can be saved? +And what should we be doing about it?" +698 How do odour sprays like Febreeze or Lysol eliminate odours in the air? 3550 https://www.reddit.com/r/askscience/comments/5nvspu/how_do_odour_sprays_like_febreeze_or_lysol/ 1484370997 5nvspu Chemistry 2017-01-14 8:16:37 "These work due to chemicals known as cyclodextrins. + +Typically a number of glucose molecules in a ring. + +Small aromatic molecules are able to become trapped within these rings due to strong intermolecular between the inside of the ring and the small aromatic. + +This takes it out of the air and out of your nose! " "The sprays do not destroy smells, but collide with particles that cause smells. The stray's particles collide with the odorous particles and coagulate, forming slightly larger particles. In effect, this removes a odorous particle from the air, but a particle that can collide with other odorous particles remains in the system. As these particles become more massive, local air currents are not providing enough force to counteract gravity and they fall to the ground, leaving a film on your floor. Clean your bathroom. + +I was able to find further links to it [here](http://cires1.colorado.edu/jimenez/AtmChem/SP_7.pdf) and [here](http://cires1.colorado.edu/jimenez/AtmChem/SP_11_1.pdf). The describes how particles interact, the second deals with mass transfer and has a nice chart that shows how particles increase in size over time. If this interests you, I would suggest reading a textbook on aerosols. [This was mine in my undergrad](http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471194107.html)." +340 How long it will take Voyager to get to Ninth Planet? 3547 https://www.reddit.com/r/askscience/comments/425jig/how_long_it_will_take_voyager_to_get_to_ninth/ 1453469754 425jig Physics 2016-01-22 16:35:54 "Presently, this planet is hypothetical. There have not been direct observations of this object - it's existence has been inferred from the orbits of smaller bodies in the outer solar system (i.e. they move as though their orbits are being perturbed by a large distant body). + +With that out of the way, the media says this planet orbits at 20x the distance to Uranus. Uranus has a 20 AU orbital radius, so that puts the planet at a 400 AU distance. Voyager 1 is currently at a distance of about 135 AU out, and traveling at about 17 km/s. To travel another 265 AU at this rate, it will arrive at the planet's predicted orbital radius in 74 years. + +Of course, given the incredibly long orbital period of the hypothetical planet it is unlikely Voyager 1 will have anything to look at when it passes. + +" "Well, until we can find planet IX and figure out its orbit there's no use sending a probe there. We would have to invent a faster way to get there first anyway. + +As for Voyager (1 or 2), it is nowhere near its predicted orbit and has no means to get there as it would require far too much fuel. Plus, Voyager has minimal power reserves left and is using what little it has to explore the interstellar regions." +13 Could life actually be supported by a constant thick mist and no rain? 3532 http://www.reddit.com/r/askscience/comments/2rbsy6/could_life_actually_be_supported_by_a_constant/ 1420402471 2rbsy6 Biology 2015-01-04 23:14:31 "**Short answer:** Yes, in fact, there are certain plant species on earth that thrive in this environment. + +**Longer answer:** The sequoias, or redwood trees, can reach heights of up to 300 feet. How do they pump water up their trunks that high? Where do they get the water from? It turns out that the wet air, coming off the ocean, will condensed out and form a fog over land. The height of the redwood trees gives them a large and spread-out surface area, providing ample room for this water to condense out of the air and drip down to the roots, [providing the massive amounts of water needed to fuel these behemoths.](http://sunnyfortuna.com/explore/redwoods_and_water.htm) + +So yes, such environments exist that thrive on fog and mist, and it seems that as long as there is a steady source of freshwater then life will, uh, find a way. Unfortunately though, [the redwoods are in trouble. Global climate change is causing the misty belt on the Pacific coast to shrink, yielding less mist over the land. If this trend continues, we could lose the redwoods forever.](http://baynature.org/articles/fog-and-redwoods-demystifying-the-mist/) + +Sorry for the preachy bullshit, but I really like the redwoods. Fuck Bruges, Redwood Natl Forest is like a fairy tale world. No where else on earth do you get trees as tall as football fields that are wide enough you can [make a tunnel for a car.](http://www.toocooldude.com/wp-content/uploads/2007/08/redwood-tree-tunnel.jpg) + +" Yes, an example of where this happens are the [fog deserts](http://en.wikipedia.org/wiki/Fog_desert) like the Namib desert in Africa and the Atacama desert in South America. Plants that specialize in acquiring water from fog are called nephelophytes. The [namib desert beetle](http://en.wikipedia.org/wiki/Namib_Desert_beetle) is also an insect that collects its water from fog, condensing it on its wings before collecting and drinking it. Here are some images of how it collects fog: [1](http://www.asknature.org/images/uploads/strategy/dc2127c6d0008a6c7748e4e4474e7aa1/biomechbglowres.jpg) [2](http://www.asknature.org/images/uploads/strategy/dc2127c6d0008a6c7748e4e4474e7aa1/biomechanics1.jpg). +14 The pupils in our eyes shrink when faced with bright light to protect our vision. Why can't our ears do something similar when faced with loud sounds? 3532 http://www.reddit.com/r/askscience/comments/2z8rzx/the_pupils_in_our_eyes_shrink_when_faced_with/ 1426521822 2z8rzx Human Body 2015-03-16 19:03:42 "The ear does, in fact, do something similar: + +[The Acoustic Reflex](http://en.wikipedia.org/wiki/Acoustic_reflex)" That's quite a good analogy. Our ears do in fact have protective measures. There are 2 muscles in the ear, the tensor tympani and the stapedius muscle. The tensor tympani, as the name suggests, tenses our ear drum (the tympanic membrane). The stapedius recedes or pulls the stapedius (one of the bones in the ear) out of its socket. Both these actions decrease the intensity of sound reaching our inner ear, thus preventing damage to the sensory part of the ear! This is the acoustic reflex. +452 Does a person using a skateboard expend less energy than a walking person traveling the same distance? 3524 https://www.reddit.com/r/askscience/comments/4njlbm/does_a_person_using_a_skateboard_expend_less/ 1465610489 4njlbm Physics 2016-06-11 5:01:29 "A study was done two years ago by Colorado State University for 15 experienced longboarders. + +""The gross metabolic cost was ~2.2 J kg(-1) m(-1) at the typical speed, greater than that reported for cycling and ~50% smaller than that of walking."" + +[http://www.ncbi.nlm.nih.gov/pubmed/25085605](http://www.ncbi.nlm.nih.gov/pubmed/25085605)" "> he would have to expend the same amount of energy regardless whether he was walking or occasionally pushing the skateboard with one foot + +No. Imagine you push with one foot but there is no skateboard. Your energy from the push is quickly eaten up by friction (and you fall) if you don't quickly move the other foot to catch yourself and push with that foot to start walking. + +Now, with a skateboard, when you push with one foot and the other foot is on the board, you *roll* and you don't waste all of that energy to friction. A single push, perhaps expending slightly more energy than a walking step, will propell you 10-15 feet. " +132 Would it be possible with modern technology to produce a sword that would handily deal with medieval swords and armor? 3521 http://www.reddit.com/r/askscience/comments/3afv6l/would_it_be_possible_with_modern_technology_to/ 1434745084 3afv6l Engineering 2015-06-19 23:18:04 "Modern metals would make better and stronger swords than they had in medieval times, but it would make little difference in a fight. The sword would last longer before losing its edge, but it wouldn't be some kind of super weapon that could slice through plate armour or cut through blades. + +[This video shows what I mean](https://youtu.be/NF9ylTFbzYc?t=4m26s). He uses a modern high quality steel sword and tries to cut through a cheap knock-off knife. It is incredibly ideal circumstances with the knife braced against a hard surface and a clean 90 degree cut, something that would never happen in real life, yet it still takes a huge amount of force and multiple attempts to cut through. In combat you would likely never have a situation like that, and the force would never be completely transferred into the blade. + +This is especially true when talking about combat in plate armour, because they would very rarely strike with edge of the blade, if at all. It was all about thrusts and grappling with the opponent and they would hold the sword half way down the blade to use as a fast and accurate stabbing weapon to reach between the joints in the armour. You could hit plate armour all day long with a sword and make little more than a dent and some scratches. + +While medieval metallurgy wasn't as advanced as modern metallurgy, by the end of the medieval period they had finely tuned the designs of swords to be very practical and good at their job. I doubt modern craftsmen could make anything better since a lot of the skills they had would have been lost so it would mostly come down to guessing and copying old designs. So the only advantage a modern sword would have would be the higher quality steel. + +As for many of the advanced materials that are used in cutting tools nowadays, most of them are far too brittle to use as a sword and would shatter or break very quickly, and the ones that wouldn't would have be little improvement over steel. + +TLDR; Modern swords would be more resilient and hold an edge longer, but would make little to no difference in combat. You wouldn't be able to slice through blades and cut through plate armour, and the designs of medieval swords were already very well designed for their purpose and not much could be changed to make them noticeably better." "The biggest benefits of modern technology would probably only be available after you move away from a medieval design such as a solid metal blade. A composite blade might well prove lighter and more flexible than a metal blade. Most swords weren't all that heavy to begin with though. Also, even with a lighter, more flexible, sharper blade, skill is going to be pretty important. Such a sword would give it's wielder an edge, but probably not one sufficient to overcome a lifetime of training, as many medieval combatants would have had. + +One thing you're overlooking though is shields. RPG's may portray them as defensive items, but shields were historically wielded in a variety of highly offensive ways. They really are weapons in the truest sense of the word. Modern materials could likely do far more for shields than they could for swords. A shield built with modern materials could be substantially lighter and tuned to be rigid when striking yet cushioning when struck, making them better at both giving blows and blocking them. You could make them transparent, which would give the wielder better awareness of his opponent. You might also make them permeable to air to reduce wind resistance to make them faster to move. A modern shield might offer a much bigger edge than a modern sword. + +All that being said, it would take less expertise, effort, and work to produce a crude gun from scratch, which would actually *be* the superweapon you're after. There's a reason why guns took over!" +133 At what rate, if any, does the earth produce fossil fuels? 3519 http://www.reddit.com/r/askscience/comments/35isjx/at_what_rate_if_any_does_the_earth_produce_fossil/ 1431288066 35isjx Earth Sciences 2015-05-10 23:01:06 "If no one has gone in depth, I will later (on a phone), but its a highly variable process depending on the organic material being deposited, the nature of the deposits, the ""oil generation kitchen"" available with respect to the processes of diagenesis, catagenesis and metagenesis and the rates at which those processes are occurring. + +The mesozoic (age of reptiles/dinos) was fairly prolific for deposition due to climactic reasons (largely algae) and why people often think that oil is Dino bones or Dino blood, but the Dino's are coincidental to the oil production. + +Today's climate isn't great for deposition, so it certainly wouldn't be looked upon as prolific no matter what the geology does going forward. + +[Here's a primer on the Dia/Meta/Catagenetic process if you're curious.] (http://booksite.elsevier.com/9780120885305/casestudies/01-Ch26-P088530web.pdf&ved=0CDUQFjAH&usg=AFQjCNHKzYTvt-lh3UK7oaq9e_u7B1_BmA) + +**EDIT:** I should be clear -- when we talk about prolific periods of oil generation in petroleum geology we're referring to that source rock / the period in which the organic matter that will eventually become oil was deposited (and sometimes the overlying reservoirs). Things get a while lot murkier when we start asking about the time periods in which that source got cooked in the oil generation kitchen. Its certainly happening as we speak in a variety of source rocks around the world but it would be incredibly hard to quantify. + +One noteworthy one in north america is the Bakken -- it's actually (generally speaking) an undercooked fairly prolific source upper and lower black shale with a silt or sand between that some of our oil has migrated into. If we left it alone it would likely continue to generate. It's Devonian, so older than most reservoirs but also a less thermally mature source rock than most, which speaks to the difficulty of figuring out when oil will be generated from a particular source. + +**EDIT2:** To flesh this out a little further now that I'm in front of a keyboard: + +The first thing you need to produce oil is organic matter. When it's part of a sedimentary rock, we refer to this organic matter as Kerogen. + +There are [four types of Kerogen](https://spec2000.net/text106fp/toc11.jpg), in descending order for potential oil productivity. + +* Type I / Sapropelic / Alginite. Marine & Most productive + +* Type II / Exinite / Amorphous Kerogen. Mostly Marine & second most productive + +* Type III / Vitrinic / Humic. Tough sledding for oil production, only under extreme circumstances. Great for coal and methane production + +* Type IV / Inertinite. As the name might suggest, useless decomposed organic matter. + +So the first step to producing a quality source rock is to get Type I and Type II kerogens buried in the sea floor in an anoxic environment (if there's oxygen available, you'll end up with decomposed Type IV kerogen, which isn't going to help even if we have algae dying and raining down in quantity). + +Next step, once we have our buried kerogen, is to cook it. [This occurs in three phases (two of which we're looking for](http://1.bp.blogspot.com/-SppkVCspMu8/UnzxgoX-SrI/AAAAAAAAAsk/y9DHj9-DqTo/s1600/tn30_f01.jpg): + +* Diagenesis: Microbes are going to have at our kerogens below about 60 degrees C, and will largely produce some get some biogenic gas from our kerogens. + +* Catagenesis: From about 60 degrees to 150C, increasing temperature will result in thermal cracking, transforming our kerogens into the oil we're looking for, in addition to some gas... increasing wet gas fractions as we get to the upper end of that range. + +* Metagensis: If we turn the temperature up too hot (> ~ 150C), we're going to keep cracking our kerogen and coal into dry gas / methane and carbon residue. + +That's the ELI5 on the process, if you're interested in the chemistry, the link in my original post above goes through it in greater detail. + +So to accurately know the rate at which the earth is producing petroleum, you would need to know what the volume and type of kerogen rich source rocks worldwide that are currently going through these various phases as well as the volume of kerogen rich source rocks currently being deposited and take a stab at their geologic future. +, as well the volume of kerogen rich source rocks that will one day end up in catagenesis. + +In terms of *actually producing* that oil, we would need to add on a lengthy discussion reservoirs, porosity and permeability. + +tl;dr I wouldn't be comfortable even taking a stab at your question OP, but I hope that the above helps to explain why it would be so difficult to make that calculation..." "In a lab it can take hours or days. + +But you mean, ""naturally"", right? The actual process (catogenesis) is quite fast - getting the raw materials into the situation where it can start in the first place is the hard part and that is the bit that takes a long time. This means that natural oil production is not like an industrial process that is done a gallon at a time ... but millions of barrels in one setup. n a typical petroleum system such as the Mississippi River delta, it may take 10 million years to bury the material deep enough for it to reach temperatures of catagenesis. Add in some volcanic activity that makes a high geothermal gradient and that timing may be quite short and no longer in millions of years. + + + +Reference https://www.physicsforums.com/threads/how-long-does-it-take-the-earth-to-form-one-gallon-of-oil.667166/ + +this a copy paste from a diffrent website and not self written +" +15 Do astronauts on extended missions ever develop illnesses/head colds while on the job? 3515 http://www.reddit.com/r/askscience/comments/309kbm/do_astronauts_on_extended_missions_ever_develop/ 1427299962 309kbm Astronomy 2015-03-25 19:12:42 "Chris Hadfield's book *An Astronaut's Guide to Life on Earth* talks about the medical isolation Astronauts undergo before heading to space. + +[This article](http://www.space.com/6628-routine-quarantine-helps-astronauts-avoid-illness-launch.html) states that 10 days before launch, they're screened for illness and cleared for quarantine if good. Quarantine lasts a week to allow latent symptoms to surface. + +So it's still possible to get sick, but NASA and the Russian Space Agency try to minimize this risk." "Head colds actually significantly impacted Apollo 7, the first manned Apollo launch. All three astronauts developed head colds during the course of the 11-day mission. They became snappish and irritable, and refused a number of orders from the ground. The blame for this ""mutiny in space"" is mostly placed on mission commander Wally Schirra. One of the original Mercury 7, he was NASA's most senior astronaut and the only person to fly in all three manned rocket programs: Mercury, Gemini, and Apollo. When he began refusing to cooperate, his two crewmates followed his lead. Experiments outside the scope of testing the new capsule were scrapped, one of those ""live from space"" TV interviews was refused, and the entire mission took on an air of stubborn negativity. Everything came to a peak before re-entry: the astronauts were supposed to put their helmets on, in case of depressurization. But the astronauts, with head colds and fearing burst eardrums, wanted to be able to pinch their noses to equalize their sinus pressure as they landed. They ended up disobeying a direct order to put their helmets on, and Schirra basically told the flight director to go to hell. + +None of the three astronauts flew again: Schirra retired, while the two younger astronauts kept their jobs but were permanently grounded. Schirra actually used the experience to star in commercials for a cold remedy. + +For later missions, I'm unaware if illness has ever significantly affected performance. However, there have been recorded infections: at least 29 according to [this article from 2012](http://science.time.com/2012/10/22/dont-sneeze-in-space-when-astronauts-get-sick/). These can potentially be serious, as zero gravity is a terrible place to get sick. For reasons we don't really understand, the immune system is significantly weakened in zero-g, while pathogens are strengthened. And the aerosol cloud from a sneeze doesn't drift to the ground like it does on Earth - it just flies outward, to land on and stick to all the instrument panels and such. Infection control in space is serious business." +341 If two ships travel at higher then 0.5C away from each other, would light from one ever reach the other? 3515 https://www.reddit.com/r/askscience/comments/40gzo6/if_two_ships_travel_at_higher_then_05c_away_from/ 1452522868 40gzo6 Physics 2016-01-11 17:34:28 "Actually, the light *would* reach the second ship! + +Let's say two spaceships are flying away from each and that an observer between them sees each of them moving with a speed v0. Now let's look at things from the frame of reference of one of the pilots. From his perspective, he will see the second ship move away with an apparent speed (v'). What is important to note is that this apparent speed will *not* just be the sum of the two initial speeds, i.e. (2v0). Instead, the formula you need to use to add up the velocities must [include a relativistic correction](https://en.wikipedia.org/wiki/Velocity-addition_formula#Special_relativity), which gives: + +v' = (v0 + v0)/(1+v0*v0/c^(2)) + +For example if v0 is 0.6c, you get v' to be 0.88c. Note that this is still less than the speed of light. On top of that, we know from special relativity that light (in vacuum) always moves at a speed of c *in every inertial (non-accelerating) frame of reference.* Because we have light moving at c chasing a ship that is moving more slowly than c, the light will eventually reach the second ship^(1). One thing to note is that the light received by the second pilot will be significantly redshifted by the [relativistic Doppler Effect](https://en.wikipedia.org/wiki/Relativistic_Doppler_effect). + +**1.** The one major caveat is that the spaceships can't be so far apart that the expansion of the universe is a major factor. + +**edit:** I made it more explicit that at high speeds the equation for adding up velocities is different from the low speed limit we are more familiar with on a daily basis; clarified that the reasoning above only rigorously applies to non-accelerating frames of reference" "I know other users have already answered this, but I'll put in my explanation too. + +The axiom of special relativity is that **the speed of light is constant in all references frames**. From this, we can go through the physics and derive some interesting results: + +* (relativistic) velocities do not add linearly, i.e. 0.5*c* + 0.5*c* != 1*c*. Similarly, if I'm traveling at 0.5*c* and launch a rocket at 0.5*c* (w.r.t. my frame), its velocity will not be 1*c* in a ""stationary"" frame, and will appear as an entirely different velocity in the frame of the other ship. (There is an explicit formula for adding relativistic velocities.) However... + +* if I somehow launch a rocket at the speed of light from my moving ship, its velocity will be 1*c* in my frame, the stationary frame, *and* the frame of the other ship. Even if I'm traveling at 0.999*c*, I will see light travel at speed 1*c*, not at 0.001*c* as you would expect. + +The short answer being, yes, they will see each other in the sense that the light from one will reach the other." +453 I noticed Nice, France looks very tropical. It is at 43 degrees N. I'm in Portland, ME...hardly tropical at 43 degrees N. How is this? Is it because of the Mediterranean? 3514 https://www.reddit.com/r/askscience/comments/4sz0mr/i_noticed_nice_france_looks_very_tropical_it_is/ 1468588599 4sz0mr Earth Sciences 2016-07-15 16:16:39 Please do not post anecdotes and speculation about your local weather. "This [paper](http://www.americanscientist.org/issues/pub/the-source-of-europes-mild-climate) disputes the claim that the Gulf Stream is largely responsible (although their climate models indicate that it does have an effect, especially for [Norway](http://www.americanscientist.org/Libraries/images/20066110140_866.jpg)). + +Instead they attribute the warmth of Europe compared to America as the result of air currents. Wind flows from west to east in the northern hemisphere, and as it flows across America, it crosses the Rocky Mountains. As the air is pushed over the Rockies, it is compressed vertically and expands horizontally, but because of the conservation of angular momentum, it develops a [clockwise spin](http://www.americanscientist.org/Libraries/images/20066110455_866.jpg). This spin diverts it to the south as it moves across America and then swings it north as it crosses the Atlantic, delivering warm air to Europe." +579 Does the universe have an event horizon? 3513 https://www.reddit.com/r/askscience/comments/5dgwjl/does_the_universe_have_an_event_horizon/ 1479402150 5dgwjl Physics 2016-11-17 20:02:30 "**edit:** Hmm... didn't expect this to blow up. Anyway, [this is the thread I intended to link earlier](https://www.reddit.com/r/askscience/comments/4msj5s/do_we_suspect_there_are_galaxies_were_already/); it goes over all the gory details that I either skipped or summarized (possibly sloppily). + +--- + +The big bang is the only naked singularity allowed to exist in the cosmic censorship hypothesis, which otherwise conjectures that all singualarities in nature must be behind an event horizon. (Also, just to clarify, modern physics is incapable of describing the universe before the big bang. Classical GR predicts that the universe has existed for a finite amount of time. Specifically, the universe has existed for all time t>0 and that there is a spacelike singularity everywhere in space corresponding to the limit as t-->0. It is meaningless to talk about what happens at or before t=0.) + +In general, there are two very important horizons in cosmology, the particle horizon and the cosmic event horizon, which both exist for each point in space. (Each point in space has its own pair of horizons.) Implicit in the definitions of either horizon is that we are describing spacetime in cosmological coordinates. The particle horizon for a point P is the surface beyond which any signal emitted at the big bang could not have reached P yet. In other words, the particle horizon defines the boundary of the observable universe about point P. The cosmic event horizon is the surface beyond which any signal emitted now will never reach point P. In other words, the cosmic event horizon roughly describes the points in space we can still communicate with today. + +The evolution of both horizons is very important in cosmology and intrinsically linked to the matter distribution of the universe and the density of dark energy. The distance to the particle horizon is always increasing over time in comoving coordinates but current evidence shows that the distance will asymptote to some finite number. In other words, there are galaxies we will never see at all. The distance to the cosmic event horizon, on the other hand, is decreasing over time in comoving coordinates. That means that eventually all we will see in the sky are stars in our own galaxy. + +Note that these horizons are unlike the event horizon of a black hole. For a black hole, the horizon is a single surface in space and a universal and eternal feature of that spacetime. That is, every observer has the same horizon. The cosmological horizons are different at each point in space. + +I have written more details about the cosmological horizons on this sub before, so I can get the link later once I'm not on my phone. " the major difference between the singularity found in the big bang vs that found in black holes is that a black hole exists within space. with the big bang, the singularity contained ALL of space to begin with. NOTHING existed outside of the singularity. that isn't true with black holes. +134 Why does Uranus look so smooth compared to other gas giants in our solar system? 3509 http://www.reddit.com/r/askscience/comments/39dj0y/why_does_uranus_look_so_smooth_compared_to_other/ 1433984903 39dj0y Astronomy 2015-06-11 4:08:23 "Ooh, this was my PhD thesis topic. + +So let's go back almost 40 years to the Voyager 2 mission, which launched in 1977. It flew past Jupiter in 1979, giving us great close-up views of [swirling clouds, storms, and bands](http://i.imgur.com/BX4iYlF.gif). Awesome! + +Next up was Saturn in 1981. Things were definitely hazier at Saturn - presumably because it's a good 30 degrees colder - but with a little CSI-style image enhancement, there were still plenty of [swirling clouds, storms and bands](http://i.imgur.com/QmoHwHx.jpg) to be seen. Good stuff! + +Uranus was up next in 1986, and folks were very excited to see the planet through Voyager since it's only a tiny turquoise disc as seen from Earth - these would be our first good views ever! We got there and....[yeah](http://i.imgur.com/Ra54BVV.jpg). A bit of a bummer, really. Even with our [CSI-style enhance](http://i.imgur.com/UdTj7Tr.jpg), there's really just not much to be seen there. Maybe a cloud in the upper right. + +Finally, Voyager 2 flew past Neptune in 1989, and what did we see? [This](http://i.imgur.com/nDABtu2.jpg). That's more like it! Swirling clouds, storms, bands...that's what a giant planet is supposed to look like. + +So what's the deal with Uranus? Well, scientists realized that unlike the other 3 giant planets, Uranus seems to have no internal source of heat. Jupiter is warmer than you'd expect if it were only heated from the Sun, mostly due to gravitational compression from its formation; as it squeezes down, heat is released. Saturn is much the same, warmer than it should be due to compression, though also probably because of the separation of helium from hydrogen providing a source of heat. Neptune is also warmer than it should be because...well, actually *we don't know* why Neptune is warmer, and that's a great unsolved problem in planetary science, but a topic for another question. + +Uranus, though, is exactly the temperature you'd expect it to be if only heated by the Sun. ""A ha!"" say the scientists, ""Without any excess internal heating, there's no energy for all those exciting storm dynamics that we see on other giant planets! We are very smart!"" And that's where the subject stopped for 20 years. + +Uranus, however, had another trick up its sleeve. Unlike the other giant planets, Uranus has this crazy 82 degree axial tilt - it's essentially rotating on its side. When Voyager flew past, the planet was at solstice - in that Voyager picture, the North Pole is actually just about at the center while the rest of the planet spins around that point. All the areas in sunlight essentially stay in sunlight at solstice, and all the areas in darkness stay in darkness. + +Now, fast forward 21 years - [1/4 of a Uranus orbit](http://i.imgur.com/1P7bzQi.jpg) - to 2007 when the planet was at equinox. For the first time in 42 years, the entire planet is getting regular day-night cycles. We point the Hubble Space Telescope at it...and [this is what we see](http://i.imgur.com/5LWnC98.jpg). Look at that, swirling clouds, storms, and bands! (That's also pretty close to the visible wavelengths seen in the Voyager image, so a comparison is fair here.) + +Uranus woke up, and there's been a concerted effort by us giant planet folks to rebrand the planet with its newer, hipper image. This is a planet that clearly goes through quiet and active times...but why? + +This is still up for debate, but the working theory here is that without any internal heat, changing sunlight patterns are the only thing that controls the climate of the planet. Based on what Uranus is made of and the thickness of the atmosphere, there seem to be a full season lag between sunlight and temperature - so the temperature is most equal between hemispheres right around solstice, meaning boring times. At equinox, meanwhile, the temperature difference is maximized, and it can form all kinds of interesting weather patterns by tapping into that difference in energy between hemispheres. + +**TL;DR** Uranus is only boring *sometimes*." Okay, I know this is not totally related, but does these gas-giants have a solid core? is there a big ball of rock underneath the gas? +342 Does a laser beam cast a shadow? 3503 https://www.reddit.com/r/askscience/comments/4830yd/does_a_laser_beam_cast_a_shadow/ 1456673295 4830yd Physics 2016-02-28 18:28:15 "Just to be clear, are you asking if a laser beam can block off part of another beam of light, creating a shadow in the process? If so, the answer is no. Or to be more exact, the answer is: not to any measurable degree. So let's say you have a room under vacuum, where there is a lamp on the ceiling and you are flying a laser beam above the ground. If you are looking at the ground, you will have no real way of knowing that there was a laser beam above it, in the same way you could if you had a solid object in the same place. + +The reason why no shadow forms in the example above is that in most cases two light beams will fly through each other without affecting each other at all. To put it more technically, if you cross two photon beams, then the [photon-photon scattering cross-section](https://en.wikipedia.org/wiki/Two-photon_physics) (the probability that two photons will come together and do *something*) is very, *very* low. It's only when you go to high energies and high beam intensities that you have to seriously start worrying about doing any measurable physics. For example, one such process is that two high energy photons can smash into each other creating a particle-antiparticle pair, in a process called [pair production](https://en.wikipedia.org/wiki/Pair_production)." "I just wanted to address something it seems hasn't been mentioned: When you say a laser ""beam"", keep in mind that a ""beam"" is only visible if that laser is going through something like dust. The dust lighting up is what creates the beam. Otherwise, a laser beam is no different from an intense flashlight. In that case, the dust itself could create a shadow." +237 If we could theoretically break the speed of light, would we create a 'light boom' just as we have sonic booms with sound? 3502 https://www.reddit.com/r/askscience/comments/3xe4gn/if_we_could_theoretically_break_the_speed_of/ 1450473574 3xe4gn Physics 2015-12-19 0:19:34 In media such as water where the speed of visible light is less than its speed in a vacuum, charged particles moving faster than the local speed of light will produce a cone of radiation called Cerenkov radiation, which gives nuclear reactors their characteristic blue glow. "In water, the speed of light is about 75% that of the speed of light in a vaccum. If we get a particle to go faster than this in water(which we can), then a phenomenon known as Cherenkov radiation occurs. This is effectively a ""photonic"" boom, and it emits a bluish-white light containing a wide, nearly flat continuous spectrum of emitted photons. " +238 AskScience AMA: I'm Vinny Lynch, assistant prof. of human genetics at UChicago. I led one of two research groups that independently found why elephants don’t get cancer as frequently as we thought they should (Spoiler: 20 copies of the p53 tumor suppressor gene). AMA! 3500 https://www.reddit.com/r/askscience/comments/3oplgh/askscience_ama_im_vinny_lynch_assistant_prof_of/ 1444822287 3oplgh Biology AMA 2015-10-14 14:31:27 "Hi Vinny, + +Does your work have a therapeutic end goal or is it just basic research? + +Is P53's mode of action well understood? + +What do you think of the potential for CRISPR and related technologies for treating cancer by selectively targeting sequences of DNA, if that's not too far outside the scope of your work?" "what about the bat and elephant's evolutionary environment favored the mutation of multiple p53 genes? + +what were the various p53 genes expression patterns that were most interesting? + +are the p53 genes in different, distinct pathways?" +239 I work with identical 4 year old twins - one has severe autism, the other is normally developing. How does this fit into the whole nature/ nurture debate? 3497 https://www.reddit.com/r/askscience/comments/3vjvx4/i_work_with_identical_4_year_old_twins_one_has/ 1449332139 3vjvx4 Psychology 2015-12-05 19:15:39 "With humans (and many other species) few things are either nature or nurture. Almost everything has a genetic component and an environmental component. Physical height has a very strong genetic component (tall parents are very likely to have tall children) and it also has a very strong environmental component (malnutrition will very likely prevent someone from reaching their potential height). + +There are many diseases (I am not saying autism is a disease here, I'm drawing a comparison) where there's a required genetic component and a required environmental component. For example, there are autoimmune diseases that only occur in people with a particular allele in the MHC, which occurs in less than 1% of the population. But only a fraction of those people with that allele develop the disease, and the prevailing explanation is that the disease only occurs if the people with the allele are infected with a specific virus, or combination of viruses. + +Finally, even for the rare diseases that are purely genetic and have no environmental component, identical twins are not genetically identical; de novo mutations can arise during development, so that identical twins may have 50-100 genetic differences from each other. " "There is a strong genetic component to autism spectrum disorder (ASD), but as with many diseases and syndromes, we need to get rid of the idea of 'nature vs nurture' and embrace the idea that nature and nurture interact in complicated ways to create the result that we see. + +Autism is a spectrum on a scale of severity. And while the severity is largely determined by the severity of neurocognitive abnormality present initially, we see profound differences in outcome amongst autistic children of higher socioeconomic status; those who have more pronounced support systems, and those with access to specialized and intensive therapies. This supports the idea that the environment has an impact on the progression and management of the condition. + +While these kids may have the same genetics initially, genes can be expressed differently and at different times during the process of their development. This results in monozygotic accordance rates as a means of estimating the genetic proportion of a disease. Some diseases will have 100% accordance, meaning everyone with 'X' mutation will develop 'y' condition, while others, like autism spectrum disorder, or schizophrenia will have accordance rates less than 100%, suggesting that differences in the expression of these genes play an important role in the development of disease. The estimated accordance rate of ASD is around 70% amongst monozygotic twins. + +We also know that these children, if they are raised together, also have very similar exposures over time, which is confusing given that they have developed in profoundly different ways. + +Also, an emerging and interesting study of the microbiome (bacterial colonization) of people plays an important role in many diseases, including autism. Non human DNA is present within our bodily system at about ten times the level of human DNA. The interaction of these bacteria with people plays a major role in human disease that is just beginning to be understood. + +Tl;dr: nature and nurture play a dynamic, and interactive role with one another to produce phenotype. Considering one without considering the role and context in terms of the other is an oversimplification in a majority of circumstances. The role of non human DNA is an emerging area of research interest in the development of numerous diseases, including autism spectrum disorder. + +Edit: here's a link discussing the role of the gut microbiome as a potential role player in the development of autism: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564498/" +240 If a solid sheet of a metal were only an atom thick, would we be able to see through it? 3497 https://www.reddit.com/r/askscience/comments/3s521u/if_a_solid_sheet_of_a_metal_were_only_an_atom/ 1447081668 3s521u Physics 2015-11-09 18:07:48 "Yes. You can coat a piece of glass with a layer of gold 100 atoms thick and still see through it. [This](https://i.imgur.com/bT65wH4.jpg) is what a piece of glass with a single layer of carbon looks like; it just gets slightly darker. + + +Edit: we killed the original image host." "Thin film coating expert here... ""Most"" of glass windows you see in the world are coated with metals for reflecting heat energy. Rarely do you ever see ""clear"" glass. Actually, multiple layers of different metals are commonly used. Each layer is about 10nm thick, up to 10-12 layers! Google Low E glass for further details." +16 If the Universe were shrunk to something akin to the size of Earth, what would the scale for stars, planets, etc. be? 3496 http://www.reddit.com/r/askscience/comments/32la0w/if_the_universe_were_shrunk_to_something_akin_to/ 1429035565 32la0w Astronomy 2015-04-14 21:19:25 "The radius of the Observable Universe is about [4.3e26 m](https://en.wikipedia.org/wiki/Observable_universe#Size). The radius of the Earth is [6.37e6 m](https://en.wikipedia.org/wiki/Earth_radius). So, your scale factor is about [1.5e-20](http://www.wolframalpha.com/input/?i=6.37e6+%2F+4.3e26). Everything in the Universe shrinks by that amount and now fits into the size of the Earth. + +Some fun numbers: + +* Earth itself is now [0.1 picometers](http://www.wolframalpha.com/input/?i=1.5e-20+*+%286371000+m%29) in size, or about 100 times the radius of a proton. +* The Sun is now [10.5 picometers](http://www.wolframalpha.com/input/?i=1.5e-20+*+7e8+m) in radius, or about half the radius of a hydrogen atom. The Moon is around half that distance away from the Earth. +* The semi-major axis of Pluto going around the Sun is [90 nanometers](http://www.wolframalpha.com/input/?i=1.5e-20+*+%286e12+m%29), of order the size of a virus. +* The nearest star system, Alpha Centauri, is about [half a millimeter](http://www.wolframalpha.com/input/?i=1.5e-20+*+%284.25*9e15+m%29) away, or about ~~half the thickness of a red blood cell~~ the size of an amoeba. +* The Galaxy is now about [7 m](http://www.wolframalpha.com/input/?i=1.5e-20+*+%2815000*3e16+m%29) in radius, so about four people tall. +* The distance to Andromeda, the nearest large galaxy, is about [350 m](http://www.wolframalpha.com/input/?i=1.5e-20+*+%28780000*3e16+m%29), almost a quarter of a mile away. +* The distance to the Virgo Cluster of galaxies, the nearest big cluster, is about [7.4 km/4.6 mi](http://www.wolframalpha.com/input/?i=1.5e-20+*+%2816.5e6*3e16+m%29) away. + +tl;dr: space is big. + +EDIT: I goofed on Alpha Centauri, thank you /u/W6hwy5Zf ! Fixed. + +EDIT 2: Thanks /u/lludson! + +EDIT 3: Speed of light calculation by /u/TimS194 for those asking: [link](http://www.reddit.com/r/askscience/comments/32la0w/if_the_universe_were_shrunk_to_something_akin_to/cqch1iu)." "One of the strangest things about this degree of scale – something that strikes me as inexplicably *weird* – is how incredibly slow the speed of light is over galactic distances. + +Even in our tiny little neighborhood, it takes 8 minutes for light to travel from the Sun to the Earth. Imagine standing by a small lake; out in the middle is a 1"" floating ball that represents the Sun, and at your feet – right on the shoreline – is a speck representing the Earth at scale. + +Imagine throwing a stone that splashed right beside our “Sun.” Now picture a ripple that takes a full 8 minutes to reach the shore. Bizarre, isn't it? The notion that our universal speed limit is so… lethargic… is so strange that it's creepy. It gives me the willies. + +It gives me the feeling that if we knew why this was the case, it would literally be like taking the red pill, as some people speculate that this is evidence in favor of the argument that we're living in a simulation. " +454 Is it true that it's healthier to sleep on your left side? 3491 https://www.reddit.com/r/askscience/comments/4uryw4/is_it_true_that_its_healthier_to_sleep_on_your/ 1469580325 4uryw4 Human Body 2016-07-27 3:45:25 "It has been shown that patients with chronic heart failure tend to prefer sleeping on their right side as opposed to their left. + +Subsequent studies have demonstrated that, indeed, sympathetic nervous system activity is lower in patients with chronic heart failure, or in those who have had a heart attack, when they lie on their right sides versus their left. + +Sympathetic nervous activity is what controls heart rate and blood pressure and thus, for these patients, lying on the right reduces their heart rate and blood pressure, both of which are good for the heart when faced with these medical conditions. + +As such, some authorities recommend that patients with heart failure or who have had a heart attack not sleep on their left sides. It should be noted, however, that this therapy has not been studied to confirm that it changes other clinical outcomes. + +Dennis Auckley, MD +Associate Professor of Medicine +School of Medicine +Case Western Reserve University +" Can't see that anyones menetioned this, but if you've got acid indigestion or have just eaten before bed, sleeping on your left side is better as such that it protects your cardia and esophagus from the stomach acid, due to the the shape of your stomach. +17 Happy Pi Day! Come celebrate with us 3490 http://www.reddit.com/r/askscience/comments/2z0fge/happy_pi_day_come_celebrate_with_us/ 1426333975 2z0fge Mathematics 2015-03-14 14:52:55 "Welcome to this thread. You may know me as a Flaired User over at /r/askhistorians in the History of Mathematics. I'm going to write a short history of Pi in different cultures in Ancient Mathematics. I will go into less detail than some of the Mathematicians posts here, who will explain why certain things work, while I'll just mention them briefly (I also don't have room to mention the vast developments done by the Greeks, but everyone will answer those). + +**Mesopotamia and Egypt** + +Throughout most of early history, people generally used 3 as an approximation for the ratio of the circle's circumference to its diameter. An example of this can be seen, in, of all places, The First Book of Kings in the Bible. Written between the 7th Century and 3rd Century BC (*The Oxford Annotated Bible* says evidence points to around 620BC, but there is some evidence it was constantly edited up until the Persian era). The quote from Kings 7:23 is + +>Then he made the molten sea; it was round, ten cubits from brim to brim, and five cubits high. A line of thirty cubits would encircle it completely. + +Now I don't want to get into past Theological issues with what the Bible says, and if it matters, but I would like to briefly mention one person, Rabbi Nehemiah, who lived around 150 AD, who wrote a text on geometry, the Mishnat ha-Middot, in which he argued that it was only calculated to the inner brim, and if the width of the brim itself is taken into account, it becomes much closer to the actual value. + +In most mathematics the Babylonians also just use π= 3, because, as shown on the Babylonian tablets YBC 7302 and Haddad 104, the area of a circle would be calculated by them using 1/12 the square of its circumference (you notice most Babylonian calculations on Circles are solved through calculations on its circumference, this is especially prominent on Haddad 104.). However we don't want to dismiss Mesopotamian calculations of π just yet. A Babylonian example found at 1936 on a Clay Tablet at Susa (located in Modern Iran.) which approximated π to around 3+1/8. + +In Egypt we come across similar writings. In problem 50 of the Rhind Papyrus (probably the best examples we have of Egyptian Mathematics) dating from around 1650 BC, it reads “Example of a round field of diameter 9. What is the area? Take away 1/9 of the diameter; the remainder is 8. Multiply 8 times 8; it makes 64. Therefore, the area is 64.” This is described by the formula A = (d − d/9)^2 which, by comparing leads to a value of π as 256/81= 3.16049... + +It does appear many of the early values of it were calculated through empirical measurements, instead of any true calculation to find it, as neither give us any more detail on why they believed it would work. + +**China** + +In China a book was written, named *The Nine Chapters on Mathematical Art*, between the 10th and 2nd centuries BC by generations of Scholars. In it we get many formula, such as those for areas of rectangles, triangles, and the volume of parallelepipeds and pyramids. We also get some formula for the area of a circle and volume of a Sphere. + +In this early Chinese Mathematics, just as in Babylon, the diameters are given as being 1/3 of the circumference, so π is taken to be 3. The scribe who wrote this then gives 4 different ways in which the area can be calculated: + +1. The rule is: Half of the circumference and half of the diameter are multiplied together to give +the area. + +2. Another rule is: The circumference and the diameter are multiplied together, then the result is +divided by 4. + +3. Another rule is: The diameter is multiplied by itself. Multiply the result by 3 and then divide +by 4. + +4. Another rule is: The circumference is multiplied by itself. Then divide the result by 12. + +The 4th result of course being the same as the Babylonian method, however both the Babylonians and the Chinese do not explain why these rules work. + +Chinese Mathematician Liu Hui, in the 3rd Century AD, noticed however that this value for π must be incorrect. He noticed it was incorrect because he realised that thought the area of a circle of radius 1 would be 3, he could also find a regular dodecagon inside the circle with area 3, so the area of a circle must be larger. He proceeded to approximate this area by constructing inscribed polygons with more and more sides. He managed to approximate π to be 3.141024, however two centuries later, using the same method Zu Chongzhi carried out further calculations and got the approximation as 3.1415926. + +Liu Hui also showed that even if you take π as 3, the volume of the Sphere given would give an incorrect result. + +**India** + +The approximation of π to be sqrt(10) was very often used in India + +Many important Geometric Ideas were expressed in the Sulbasutras which were appendices to the Vedas, the oldest scriptures of Hinduism. They are also the only knowledge of Mathematics we have from the Vedic Period. As these aren't necessarily Mathematical pieces, they assert truths but do not give any reason why, though later versions give some examples. The four major Sulbasutras, which are mathematically the most significant, are those composed by Baudhayana, Manava, Apastamba and Katyayana, though we know very little about these people. The texts are dated from around 800 BCE to 200 CE, with the oldest being a sutra attributed to Baudhayana around 800 BCE to 600 BCE. + +This work contains many Mathematical results, such as the Pythagorean Theorem (though there is an idea that this came to India through Mesopotamian work) as well as some geometric properties of various shapes. + +Later on in the Sulbasutras however we get these two results involving circles: + +>If it is desired to transform a square into a circle, a cord of length half the diagonal of the square is +stretched from the center to the east, a part of it lying outside the eastern side of the square. With +one-third of the part lying outside added to the remainder of the half diagonal, the requisite circle +is drawn + +and + +>To transform a circle into a square, the diameter is divided into eight parts; one such part, after +being divided into twenty-nine parts, is reduced by twenty-eight of them and further by the sixth +of the part left less the eighth of the sixth part. [The remainder is then the side of the required +square.] + +As this is easier to show with pictures, I'll take some from the book A History of Mathematics by Victor J. Katz: + +[For the first statement](http://i.imgur.com/IjS35vi.png) + +In this construction, **MN** is the radius **r** of the circle you want. If you take the side of the original square to be **s**, you get **r=((2+sqrt2)/6)s** this implies a value of π as being 3.088311755. + +In this second statement the writer wants us to take the side of the square to be equal [to](http://i.imgur.com/bsksXEj.png) of the diameter of the circle. This is the equivalent of taking π to be 3.088326491 + +Later on in India, the Mathematician Aryabhata (476–550 AD) worked on the approximation for π. He writes + +>""Add four to 100, multiply by eight, and then add 62,000. By this rule the circumference of a circle with a diameter of 20,000 can be approached."" + +This implies that the ratio of the circumference to the diameter is ((4 + 100) × 8 + 62000)/20000 = 62832/20000 = 3.1416. And after Aryabhata was translated into Arabic (c. 820 CE) this approximation was mentioned in Al-Khwarizmi's book on algebra. + +**Islam** + +Finally we get to the Islamic mathematicians, and I will end here because Al-Khwarizmi's (780-850AD) book on algebra, he sums up many of the different ways ancient cultures have calculated π + +>In any circle, the product of its diameter, multiplied by three and one-seventh, will be equal to the +circumference. This is the rule generally followed in practical life, though it is not quite exact. The +geometricians have two other methods. One of them is, that you multiply the diameter by itself, +then by ten, and hereafter take the root of the product; the root will be the circumference. The +other method is used by the astronomers among them. It is this, that you multiply the diameter +by sixty-two thousand eight hundred thirty-two and then divide the product by twenty thousand. +The quotient is the circumference. Both methods come very nearly to the same effect. . . . The +area of any circle will be found by multiplying half of the circumference by half of the diameter, +since, in every polygon of equal sides and angles, . . . the area is found by multiplying half of +the perimeter by half of the diameter of the middle circle that may be drawn through it. If you +multiply the diameter of any circle by itself, and subtract from the product one-seventh and half +of one-seventh of the same, then the remainder is equal to the area of the circle. + +The first of the approximations for π given here is the Archimedean one, 3 +1/7 . The approximation of π by +sqrt(10) attributed to “geometricians,” was used in India as well as early on in Greece. +(As an interesting fact, however, it is less exact than the “not quite exact” value of 3 + 1/7). The earliest +known occurrence of the third approximation, 3.1416, was also in India, in the work of +Aryabhata as previously stated. This is probably attributed to astronomers because of its use in the Indian astronomical works that were translated into Arabic. + +Feel free to ask me any more questions on the History of π" "Alas, much of the world never gets to celebrate Pi Day, because today is 14/3 for us. + +So how did it come to be that different cultures, even some speaking the same language, write their dates in different orders? And is anyone actually using [ISO 8601](https://xkcd.com/1179/), the only format that puts all the digits in decreasing order?" +135 If we can't hear transmissions from somewhere like Kepler 452b, then what is the point of SETI? 3488 http://www.reddit.com/r/askscience/comments/3ej22h/if_we_cant_hear_transmissions_from_somewhere_like/ 1437798520 3ej22h Astronomy 2015-07-25 7:28:40 "SETI claims to be able to detect roughly earth-like signals up to a distance of about 1000ly ([here](http://www.setileague.org/askdr/howfar.htm)). Of course the actual distance depends on the power of the transmitted signal, and for sure when it arrives at earth it will be very weak compared to other naturally occurring radio sources in the universe, which is one of the reasons the SETI project is hard. + +There are 511 stars within 100ly, ~280,000 within 500ly, and >2Mil within 1000ly, so there's still a lot of work for SETI to do. All-sky surveys have difficulty detecting weaker signals, but targeted surveys of millions of star systems takes *lots* of telescope time. + +The nearby stars are the low hanging fruit. It would be idiotic of us to not check them for the obvious signs of intelligent life first, even if it turns up nothing." The point of SETI has never been to look for accidentally broadcast signals, the point has always been to primarily look for intentional signals. Those signals would be very much stronger than ordinary leakage, and potentially detectable from enormous (galactic-sized) distances. Given the comparative low cost of SETI and the enormous impact of a successful detection the cost/benefit probably makes it worthwhile. +1263 If I stick my head out of a car window at 65 mph and try to look directly ahead I’m effectively blinded by the air rushing passed my eyes. How does a cheetah see and track prey when running at top speed? 3486 https://www.reddit.com/r/askscience/comments/b5qf7n/if_i_stick_my_head_out_of_a_car_window_at_65_mph/ 1553610783 b5qf7n Biology 2019-03-26 17:33:03 "Full disclosure, I'm an optometrist for humans, not for cheetahs. + +It's because they (and many birds and reptiles) have a [Nictitating Membrane](https://en.wikipedia.org/wiki/Nictitating_membrane). + +It is a transparent ‘third eyelid’ that covers the eye and allows them to see while also maintaining protection over their cornea. From SeaWorld's website: ""[A nictitating membrane further shields and protects the eyes during fast sprints](https://seaworld.org/animals/all-about/cheetah/characteristics/)."" + +Humans (and many other mammals) have a vestigial remnant of this membrane called the [Plica Semilunaris](https://en.wikipedia.org/wiki/Plica_semilunaris_of_conjunctiva). It’s that half moon sliver of tissue next to the [Caruncle](https://en.wikipedia.org/wiki/Lacrimal_caruncle) (which is the little yellowish/reddish blob in the very inferior/nasal corner of your eye). + +Edits. +1. I'm embarrassed I forgot the vestigial remnant is the Plica Semilunaris (now linked above), not the Caruncle. +2. Shoutout to /u/OmegaGreed and others for encouraging me to research this a little further, I'm learning so much! There are clearly (and not surprisingly) a wide variety of Nictitating Membranes across animal species, even among cats. While some (most?) are definitely not transparent enough to be useful during hunting, the Cheetah's must be. +This makes sense to me because on the one hand, I definitely agree that a cheetah running at 65 mph will not experience the same shearing force due to air across their cornea as someone sticking their head out of the window of a car, due to the aerodynamics of car vs. cheetah head. Despite this, when you are traveling at speeds anywhere near 65 mph, that shearing force would definitely be strong enough to strip away your tear film. This is problematic because even if their cornea had a different type of innervation, such that this didn't cause them *pain* per se, your tear film plays a *significant* role in your visual acuity. In fact, [the air/tear-film interface \[is\] the most significant component of the total refractive power of the eye](https://en.wikipedia.org/wiki/Cornea)." "I think, in addition to the nictitating membrane that /u/slevayyoung mentioned, (Edit: actually, having thought about it, I'm not sure the nictitating membrane is involved at all) it also has to do with the amount of air being displaced by a car. A car is obviously much larger than a cheetah, so a larger volume of air is being turbulently displaced as the car is moving forward. A lot of this turbulent air rushing past the car is actually moving faster than 65mph (from the perspective of a passenger in the car) as it gets pushed around the car. + +Additionally, cars are streamlined, so when you open the window and stick your head out, you are pushing your head directly into this turbulent stream moving around your car. It's a bit like sticking your head into the wake of a motorboat. + +Cheetahs displace much less air than a car, and their eyes are also directly at the front of their body as it's moving, so they don't have to deal with any of the wake of the air they are displacing. + +Edit: Actually, after thinking about it some more, I'm not convinced the nictitating membrane is involved. Certainly it would be pretty helpful to be able to use it like a pair of goggles, but, [at least in housecats](https://www.litter-robot.com/blog/wp-content/uploads/2018/09/900px-Tabby_cat_with_visible_nictitating_membrane-copy.jpg), the nictitating membrane is not transparent enough to see through like glass. Good eyesight is pretty important when you're chasing extremely fast prey over uneven ground. Cheetahs have long eyelashes and hooded eyes to help keep debris out, and given that they only reach their top speeds for a few seconds at a time, I don't think the wind would be that much of a factor." +136 Are farts stored as compressed gas? What's the range of internal pressure? 3485 https://www.reddit.com/r/askscience/comments/3iykdi/are_farts_stored_as_compressed_gas_whats_the/ 1440946284 3iykdi Human Body 2015-08-30 17:51:24 "The colon has the ability to stretch a fair amount to accommodate stool and gas. So pressure depends on the elasticity of the colon, size of the colon, and other contents. Pressure also increases with peristalsis (the normal compression of the intestinal tract). If there is an obstruction the pressure increases. There was a study that showed that a pressure of ~4 psi can cause intestinal rupture. + + Burt CAV Pneumatic rupture of the intestinal canal with experimental data showing the mechanism of perforation and the pressure required Arch Surg. 1931; 22:875-902." "Relatedly, there is this old thread that extends your question: +https://www.reddit.com/r/AskReddit/comments/iphci/if_you_could_compress_a_lifetime_worth_of_farts/c25mhn1 +While it is was posed as a joke question, a redditor gave an in depth discussion about the lifetime pressure that could potentially be built up using only flatulence. " +455 Can you see time dialation ? 3482 https://www.reddit.com/r/askscience/comments/4wey58/can_you_see_time_dialation/ 1470468892 4wey58 Physics 2016-08-06 10:34:52 "By time dilation, we *mean* that the light emitted by those on the water planet over 3 hours in their rest frame is received over 23 years by the spaceship in its rest frame. So the observer on the spaceshift sees them move in very slow motion. The images are also extremely redshifted and very difficult even to detect. + +> But seeing them moving in slow motion would also make no sense to me, because the light he sees would then have to move slower then the speed of light? + +For a given observer, the speed of light is *not* constant throughout all of space. A light signal right next to you will always have speed *c*. But distant light signals have different speeds. To an observer exterior to a black hole, light slows down as it approaches the event horizon. This is a consequence of the curvature of spacetime since we cannot generally have globally inertial coordinates, but rather only *locally* inertial coordinates. + +--- +**edit:** There are a lot of follow-up questions about the non-constancy of *c* and how that statement fits into relativity. It is true that in *special* relativity, the speed of light is both invariant (all observers agree on the speed) and constant (the value is the same everywhere). That is known as the second postulate of special relativity. That's only true because we have the luxury of *globally inertial* coordinates in special relativity, i.e., there is no spacetime curvature. Once you have curvature, general relativity takes over and *the second postulate is simply no longer true*. We have to modify the postulate considerably. + +The presence of curvature means that we can only have *locally inertial* coordinates, which roughly means the following. At any point in spacetime, you can always adapt your coordinates so that spacetime ""looks flat"" *but only at that point*. (For the math inclined, this means you can choose coordinates so that at the point *P*, the metric has the form of the Minkowski metric with vanishing first derivatives.) Away from that single point, spacetime does not look flat. To capture this mathematical fact, we usually say things like ""special relativity holds in local experiments"" or ""you cannot perform a local experiment to distinguish between gravity and uniform acceleration"". + +So how does the second postulate change then? Well, it's still true *locally*. That is, if a light signal passes right next to you, you will *always* measure it to have speed *c*, no matter how fast you are going and no matter where you are, as long as you are right next to it. So the speed of light is still *invariant* but only *locally*. But someone else very far away will *not* measure the speed of that light signal to be *c*. In fact, suppose a light signal is traveling through space and we have a whole chain of observers, one after the other, camped out along the path of the light signal. For funsies, we don't even have to assume they are all at rest with respect to each other. As the light signal passes by each of them, they each measure its speed. Then some time later everyone reunites to compare their measurements. Guess what? They *all* come back and say that the light signal had speed *c*. + +However, suppose we picked out one specific observer and asked him to continuously measure the speed of the light signal. The moment the signal passed him, he would record a speed of *c*. But for all other points on the signal's path, he would record a value not necessarily equal to *c*. The speed could be less than *c*, the speed could exceed *c*, it may even be equal to *c*. But it's certainly not guaranteed to be *c*. + +Now for all of the questions about the speed of light being a universal speed limit. *That* is still true as long as you modify ""speed of light"" with the word ""local"". Go back to the previous example with the one observer measuring the speed of light along its path. Suppose that at some point he measures the light signal to have speed *c*/2. That's fine. But that also means that *nothing else* he measures at that point can have a speed that exceeds *c*/2. In other words, the local speed of light is *still* the universal speed limit. + +However, you should be careful that not everyone agrees on the local speed of light. That guy might say that light has speed *c*/2 at that point, but someone else might say it has speed *c*/4 or something. If the first guy measures some particle to be moving at *c*/3 at that point, that does *not* contradict the fact the second guy sees an upper speed limit of *c*/4 at that point. Remember, they are using *different* coordinates. Since both observers are not *right next to* the light signal when they measure its speed, all they are doing is measuring a coordinate speed, which are generally not very physically meaningful. You *cannot* unambiguously define the velocity of distant objects in general relativity. + +If you are interested in more details, you can see [this thread](https://www.reddit.com/r/askscience/comments/4sfhbq/if_light_is_sucked_into_a_black_hole_due_to_its/) and [my follow-up post within that thread](https://www.reddit.com/r/askscience/comments/4sfhbq/if_light_is_sucked_into_a_black_hole_due_to_its/d59so7w). If you are math- or physics-inclined, you can also check out an introductory GR textbook. I recommend Schutz for starting out, followed by Hobson. [Sean Carroll's text](https://www.preposterousuniverse.com/grnotes/) is freely available online, but is more appropriate for a graduate course in GR. Wald's text is classic but is for advanced graduate students." the light wouldn't have to move slower than the speed of light. slower light means you see something later, not slower. what he would see is a photon sent out at time T and one sent out an hour later to arrive a year in between for instance. and that would be the case for all the photons. their arrivals would be spread out over a longer time interval. +580 Why are there no hi-res images of the north or south poles? 3478 https://www.reddit.com/r/askscience/comments/514101/why_are_there_no_hires_images_of_the_north_or/ 1472996690 514101 Planetary Sci. 2016-09-04 16:44:50 "Folks, please stop citing yourselves as a source. As our [policy on sources states](https://www.reddit.com/r/askscience/wiki/sources): + +>Listing yourself leaves people no way to confirm anything that was mentioned in the comment. A source allows people refer to find more information or to verify what is being said. From a philosophical standpoint, stating that you are a source is counter to everything that science is about. It's telling people to take your word for it, and it reinforces the idea that people can claim to have expertise without backing up their assertions." "[Here is one from NASA,](http://imgur.com/a/pGLLx) [with a description](http://visibleearth.nasa.gov/view.php?id=78592) + +The satellites used to take images of the Earth are usually in polar orbits so that they may cover more terrain. There is no technological reason they cannot photograph the poles. This lack of imagery is more likely caused by a lack of interest and money. + + +[also try lima.usgs.gov \(Landsat Imagery Mosaic of Antarctica\)](http://lima.usgs.gov/)" +1438 We are scientists from the Society of Vertebrate Paleontology coming to you from our annual meeting in Brisbane, Australia. We study fossils. Ask Us Anything! 3476 https://www.reddit.com/r/askscience/comments/dfwv71/we_are_scientists_from_the_society_of_vertebrate/ 1570708275 dfwv71 2019-10-10 14:51:15 "Several years ago, Jack Horner gave a TED Talk entitled ""Where are the baby dinosaurs."" The subject of his talk was the possibility that at least some of the variety of named species of dinosaurs are likely all members of the same species merely in different stages of development. For example, he suggests that Dracorex hogwartsia, Stygimoloch, and Pachycephalosaurus to all be the same dinosaur at different developmental stages. + +My questions are, do you think this theory has merit, and if so, should it change the way we look at other fossils as well, especially from the perspective of evolution?" "Of all the extinction events in Earth's history, which is the least understood or most inexplicable? + +Question for Dr. Drumheller specifically, how are bite marks differentiated from other trauma or bone damage on fossils?" +1387 Why does beta plus (β+) decay happen in proton-proton chain reactions; why don't the two protons just form helium instead of deuterium? 3470 https://www.reddit.com/r/askscience/comments/bjbh6h/why_does_beta_plus_β_decay_happen_in_protonproton/ 1556673990 bjbh6h 2019-05-01 4:26:30 "Helium-2 is unbound, so it decays on extremely short timescales. The only way to combine two protons into a bound system is to rely on the weak force to change one of the protons into a neutron, producing a deuteron. + +This is not a beta decay, it's a nuclear reaction which involves the weak force. That's why the probability of it occurring is so small, and why it forms a bottleneck for the entire pp-chain." +1264 Why are the stars and planets spherical, but galaxies flat? 3464 https://www.reddit.com/r/askscience/comments/ax3c5h/why_are_the_stars_and_planets_spherical_but/ 1551676513 ax3c5h Astronomy 2019-03-04 8:15:13 "Hey. I’m posting because 8 hours later I still don’t see the correct answer. I’m an astrophysicist. + +Stars form out of collapsing clouds of gas. The gas clouds have some net rotation, which is enhanced as it collapses because angular momentum is conserved. This means that gas and dust particles preferentially collide and cancel out their vertical velocities, but not their rotational velocities. So the gas forms a disk circling the protostar. Friction within the disk bleeds off momentum from the gas and dust and it falls onto the star over millions of years. + +Once the gas has fallen onto the star, it is supported by the outward pressure of the heat and light coming from the energy produced by nuclear fusion in the star’s core. This resists further collapse. The star is therefore spherical because this outward pressure is the same in all directions. Even after the star runs out of fuel and becomes an inert core, it will still be spherical because it will be supported by electron degeneracy pressure (if a white dwarf) or neutron degeneracy pressure (if a neutron star); basically these subatomic particles resist being squeezed too much unless the pressure is large enough to change their fundamental state. Note that stars do rotate, which actually means they are ellipsoidal, not perfectly spherical, because centrifugal force stretches them out a bit depending on the rotation speed. + +Planets form from the accretion disk around the protostar. There’s some debate about how planets form exactly, but regardless of the mechanism(s), we end up with material that is mostly spherical once it is large enough. The reason is that surface gravity increases as the protoplanet grows, and so irregular/non spherical features will tend to fall “downhill”. On earth we have mountains, but if you made the mountains taller, they would erode faster. So earth remains mostly spherical. Gas planets are smoother since there’s less resistance to reaching this “hydrostatic equilibrium”. Note that planets are also often ellipsoidal because they can bulge from their rotation. This is extreme on Jupiter which is about 10% wider than it is tall. + +Galaxies are completely difference beasts because they are mostly empty space. The most common theory of Galaxy formation says that dark matter clumps grew through gravity creating spherical “halos” that are dense in the center and less dense on the outsides. Dark matter is mysterious but we understand that it feels and produces gravity but NOT the electromagnetic force; this means that dark matter cannot collide with anything. As a result, DM halos are a whirl of dark matter flying every which way. + +So why then are (some) galaxies disks? The answer is that you are focusing on the visible stuff. The milky way’s DM halo is mostly spherical. But the baryons are concentrated in a disk for the same reason as in the case of the protostar: gas preferentially collides and cancels out its velocity vertically, leaving it in a disk plane, where collisions are minimized due to the ordered motion. Stars form out of clouds that collapse within the densest regions of gas in the disk plane, and therefore the galaxy’s stars are found in this flat(ish) plane. But, unlike the gas, once stars are formed there’s nothing to hold them in the plane. So over billions of years, random gravitational perturbations from other stars, gas clouds, or galactic collisions will “puff up” a stellar population. Newly formed stars (< about 1 billion years old) are usually found very close to the galactic plane where they were born (“thin disk stars”) whereas older ones are found in the “thick disk”, like the Sun (4.6 billion years old). + +But if galaxies encounter other big galaxies they can undergo major mergers that end up dynamically exciting all the stars, and driving the gas inwards, or outwards, or just heating it up. When this happens, you can get an elliptical galaxy, which is often not very flat. Because there is no longer ordered motion, gas can’t concentrate enough to collapse to form stars; it’s too “hot”. And so these older galaxies, often found in galaxy clusters where mergers are common, are said to have “quenched” (ended) star formation. They look redder in color, because essentially the only blue stars in galaxies are young ones. We often call old galaxies “red and dead.” + +Edits: typos, some extra fun facts + +Update: Wow, thanks for the silver & gold, friends! First gilded comment :)" "This is a common question here which others have elaborated on in the past, + +>Why are planets round? + +* https://www.reddit.com/r/askscience/comments/ikua8/why_are_big_planets_spherical_and_small_asteroids/c24k830/ +* https://www.reddit.com/r/askscience/comments/1tb1yh/why_are_all_planets_and_moons_round/ce65he9/ + +>Why are galaxies flat? + +* https://www.reddit.com/r/askscience/comments/awaqky/why_are_galaxies_a_flat_disk_and_not_a_sphere/ + +* https://www.reddit.com/r/askscience/comments/7plpml/why_is_the_visible_part_of_many_galaxies_flat/ + +Followup questions are very welcome!" +456 We are paleontologists who study fossils from an incredible site in Texas called the Arlington Archosaur Site. Ask us anything! 3463 https://www.reddit.com/r/askscience/comments/4i4y4q/we_are_paleontologists_who_study_fossils_from_an/ 1462539279 4i4y4q Paleontology 2016-05-06 15:54:39 I really wanted to be a paleontologist when I was a kid. Is it as glamorous as I imagine? "I live in Fort Worth. If I wanted to get involved could I? How would I do so? +Edit since answered below: What could I expect as a volunteer? " +18 Is it theoretically possible for a nuclear reaction to happen randomly on earth (i.e. in nature)? 3460 http://www.reddit.com/r/askscience/comments/32stsl/is_it_theoretically_possible_for_a_nuclear/ 1429189254 32stsl Physics 2015-04-16 16:00:54 "Yes, there is a site in Gabon where evidence of natural nuclear reactions were found, from two billion years ago. Evidence for this is based on the isotopes of xenon found at the site, which are known to be produced by nuclear fission. + +http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor" Forget the ancient fission in Gabon,natural fission happens all over the earth billions of times every second... It's just not self sustaining. In Gabon for a time it was. +241 Does a rainbow extend into the invisible part of the spectrum? 3459 https://www.reddit.com/r/askscience/comments/3ru4ns/does_a_rainbow_extend_into_the_invisible_part_of/ 1446858640 3ru4ns Physics 2015-11-07 4:10:40 "It also extends into the infrared, which is how that type of light was discovered. A prism split sunlight, and then thermometers placed past the Red got hot. + +Edit: [More info on Herschel's experiment](http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_bio.html) + +/u/fosighting [link to try it yourself](http://www.ipac.caltech.edu/outreach/Edu/Herschel/backyard.html)" "Yes it does! You can clearly see this fact by looking at [this series of pictures](http://imgur.com/DcQON5t) of a rainbow taken by a camera visible in the ultraviolet (UV), the visible, and the infrared (IR). Notice how in addition to the visible part of the rainbow (which you can see by eye), there is also an IR band that smoothly follows the red edge and a UV band slots right under the violet edge. + +This result is exactly what we would expect. The way rainbows work is that when sunlight strikes water droplets suspended in the air, part of the light is reflected at the air/water interface at the back of each droplet, [as shown in this diagram](http://4.bp.blogspot.com/-o8J6w_FRVWQ/Uj7gJ9H-fCI/AAAAAAAAi88/zRZMuMjKxR4/s1600/Rainbow+103.png). Since water is dispersive (meaning that the rerfractive index varies by wavelength), each droplet effectively acts as a small prism spreading the white light into its spectral components. Now our eyes our only sensitive to the visible (by definition), which is why a rainbow looks like a colorful transition from violet to red. However, sunlight also contains [IR and UV components in addition to visible light](http://imgur.com/KbIrTzA). While the water droplets absorb some of this light, much of it ends up reflected, as part of this extended rainbow that you can see from the IR and UV images posted above." +19 Has there been a disease that was beneficial to humans? 3457 http://www.reddit.com/r/askscience/comments/2rv68l/has_there_been_a_disease_that_was_beneficial_to/ 1420818819 2rv68l Medicine 2015-01-09 18:53:39 Early 20th century physician Julius Wagner-Jauregg used malaria to 'cure' syphilis. It was known as [malariotheraphy](https://en.wikipedia.org/wiki/History_of_malaria#Malariotherapy). He won a [Nobel Prize](http://www.nobelprize.org/nobel_prizes/medicine/laureates/1927/) for it. "It depends on how you want to interpret that question. Let's take a classic example: [sickle cell anemia](http://www.nhlbi.nih.gov/health/health-topics/topics/sca). Individuals who carry both alleles for sickle cell have the disease, which is serious. However, individuals that have only one allele for SCA are protected from [malaria](http://www.cdc.gov/malaria/about/biology/sickle_cell.html). + +So is the disease beneficial to humans? No, not if you have both alleles. But you might make the case that it is beneficial if you are an unaffected carrier." +242 Why is it that the moons gravity is able to direct masses of water in different directions but yet we, ourselves cannot physically feel the affect of the moon's gravity? 3455 https://www.reddit.com/r/askscience/comments/3vex33/why_is_it_that_the_moons_gravity_is_able_to/ 1449236266 3vex33 Physics 2015-12-04 16:37:46 Tidal forces are essentially due to the *difference* in the gravitational field between two sides of a body. If you consider the difference in the moon's influence between our head and our feet, it is essentially null. If you consider the difference between one side of the Earth and the other, it starts to become significant. "For anyone with questions about tides, I highly recommend this video from PBS that breaks it down better than anyone here could: https://youtu.be/pwChk4S99i4 + +It illuminates some very common misconceptions (that even some of the answerers here seem to have) and answers basically every question you could have about tides." +457 How exactly does a autotldr-bot work? 3454 https://www.reddit.com/r/askscience/comments/4s5b5q/how_exactly_does_a_autotldrbot_work/ 1468154102 4s5b5q Computing 2016-07-10 15:35:02 "/u/autotldr uses an algorithm called ""SMMRY"" for its tl;drs. There are similar algorithms as well (like the ones /u/AtomicStryker mentioned), but for whatever reason, autotldr's creator opted for SMMRY, probably for its API. Instead of explaining how SMMRY to you, I'll take a little excerpt from their [website](http://smmry.com/about) since I'd end up saying the same stuff. + +>The core algorithm works by these simplified steps: + +>1) Associate words with their grammatical counterparts. (e.g. ""city"" and ""cities"") + +>2) Calculate the occurrence of each word in the text. + +>3) Assign each word with points depending on their popularity. + +>4) Detect which periods represent the end of a sentence. (e.g ""Mr."" does not). + +>5) Split up the text into individual sentences. + +>6) Rank sentences by the sum of their words' points. + +>7) Return X of the most highly ranked sentences in chronological order. + + +If you have any other questions feel free to reply and I'll try my best to explain." "There are many auto-summary tools around. This is how smmry.com describes their bot works. + + +About + + +SMMRY (pronounced SUMMARY) was created in 2009 to summarize articles and text. + + +SMMRY's mission is to provide an efficient manner of understanding text, which is done primarily by reducing the text to only the most important sentences. SMMRY accomplishes its mission by: + + +• Ranking sentences by importance using the core algorithm. + +• Reorganizing the summary to focus on a topic; by selection of a keyword. + +• Removing transition phrases. + +• Removing unnecessary clauses. + +• Removing excessive examples. + + +The core algorithm works by these simplified steps: + + +1) Associate words with their grammatical counterparts. (e.g. ""city"" and ""cities"") + +2) Calculate the occurrence of each word in the text. + +3) Assign each word with points depending on their popularity. + +4) Detect which periods represent the end of a sentence. (e.g ""Mr."" does not). + +5) Split up the text into individual sentences. + +6) Rank sentences by the sum of their words' points. + +7) Return X of the most highly ranked sentences in chronological order." +243 How does exposure to radioactivity affect the human body? In biological terms, what's the deadly process? 3449 https://www.reddit.com/r/askscience/comments/3tt785/how_does_exposure_to_radioactivity_affect_the/ 1448199327 3tt785 Human Body 2015-11-22 16:35:27 "**Short answer:** Ionization. Think of your cells as a very carefully arranged Lego house, and the radiation as a 9mm bullet. + +**Long answer:** The three classes of ionizing radiation are [alpha, beta, and gamma rays.](http://edtech2.boisestate.edu/lindabennett1/images/alpha%20beta%20gamma%20diagram.gif) Alpha particles are helium-4 nuclei, spat out of other nuclei. Beta rays are electrons, spat out of neutrons when they turn into protons. Gamma rays are high energy photons. + +These particles, when inside your body, have sufficient energy to disrupt other atomic bonds. They can remove electrons from other atoms, ionizing them and breaking up molecules. + +Molecules broken down this way become free radicals - they're in an unstable state and want to find something new to bond with, which will in turn disrupt other chemical processes. + +The most dangerous reactions occur when radiation directly damages DNA. If [both strands are severed](http://teachnuclear.ca/wp-content/uploads/2013/05/direct214.gif) and the cell repairs them incorrectly (i.e. they get rearranged) then this damage can be irreversible, and the cell can become cancerous. " "The key threat here comes from what is called [ionizing radiation](https://en.wikipedia.org/wiki/Ionizing_radiation). This type or radiation consists of a number of particles that have enough energy to strip electrons from molecules. I think that this fact alone can already give you a hint about the biological mechanism of radioactivity: it is simply a mess. + +The first step is that your body will be exposed to primary radiation in the form of [gamma rays](https://en.wikipedia.org/wiki/Gamma_ray) (high energy photons), [alpha partices](https://en.wikipedia.org/wiki/Alpha_particle) (helium nuclei), [beta particles](https://en.wikipedia.org/wiki/Beta_particle) (high energy electrons and positrons). Think of these particles as high speed bullets that are rifling through your body causing damage in the process. Such damage can include broken bonds, unwanted molecular changes, etc. However, the damage doesn't even end there. The initial radiation can also kick up a large number of high energy electrons (called secondary electrons) that will then create a second wave of destruction. + +At the end of this process when the dust settles, depending on the dose you were exposed to, your body might have suffered serious damage at the tissue and cellular level, including [significant damage to your DNA](http://www.radiation-scott.org/radsource/4341-3.gif). Worst of all, this damage can also make it difficult for your cells to divide normally, so that this first wave of damage simply cannot be repaired. So now your body is riddled with damage, your cellular machinery has stopped working normally, and your cells cannot even replicate. With this picture in mind, I think it's easy to see how high doses of radiation damage can eventually lead to death." +343 How do things tie themselves up? 3446 https://www.reddit.com/r/askscience/comments/49yu8n/how_do_things_tie_themselves_up/ 1457703821 49yu8n Physics 2016-03-11 16:43:41 "There was a [recent paper](http://www.pnas.org/content/104/42/16432.long) in the journal PNAS that looked at exactly this question. The researchers took a flexible string, put it in a box and then shook the hell out of it for fixed period of time. They then counted the number of knots and classified their geometry, which they then matched with the mathematical description provided by [knot theory](https://en.wikipedia.org/wiki/Knot_theory). The simplest picture for the knots formed looks [something like this](http://i.imgur.com/Ptfasn5.jpg). The process goes as: + +1) When you put the string in an enclosed space (like a box), you will tend to get many parallel coils. + +2) Different segments can become intertwined, effectively braiding the string. + +3) When you tug on the string the braids become tight knots. + +As you might expect, the researchers found that factors such as [the length affect the probability of the string knotting up.](http://i.imgur.com/CXSlaqG.jpg) But the slope of this graph is pretty steep at first, which means that even for a ~1m long headphone cable you get a good chance of spontaneously getting a know just be tumbling the cable around." "One thing that has not been addressed in the comments I've read is how much energy is stored in cables when you just do the classic wrap. When you do this, you actually are twisting the cable with every loop, which is both bad for the cable, but also makes it want to untwist, hence knots and wrapping. + +The proper way to wrap cables to protect them and prevent knotting it is like [this](https://www.youtube.com/watch?v=0yPcJD7RVuY) + +Edit: Clearly I don't know the proper terminology for any of this, but would be happy to correct it if someone points it out. I don't know what kind of energy it is. +" +344 "What really happens when I ""get used"" to cold water?" 3443 https://www.reddit.com/r/askscience/comments/4covkn/what_really_happens_when_i_get_used_to_cold_water/ 1459406091 4covkn Human Body 2016-03-31 9:34:51 "The thermoreceptors in your skin send signals towards your brain when there is a *change in temperature*. + +When you have exposed yourself to cold water, you feel the immediate change in temperature at the surface of your skin. At this point, your sympathetic nervous system (which controls the unconscious 'fight or flight' responses) will stimulate the release of hormones which begin to cause vasoconstriction in your skin, arms and legs. + +Your extremities will reduce in temperature, and the temperature gradient between the water and your core will reduce, along with the feeling of 'cold'. Heat flow is proportional to temperature gradient, so you will actually lose less heat. Diminished skin and extremity blood flow increases the thermal insulation of those superficial tissues more than 300% [[1](https://www.ncbi.nlm.nih.gov/pubmed/17929604)]." "My background in this isn't as a scientist, but I have written more about cold water swimming than probably any non-academic. I'm a mod of /r/swimming, English Channel solo swimmer, and the 70th person in the world to complete an Ice Mile (one mile in water under 5C ~ 36F, without a wetsuit or any protection. I also write the world's most popular non-commercial open water swimming blog. [Here is a collection of 50+ articles I've written about cold water swimming](http://loneswimmer.com/cold-water-swimming-articles-index/). + +So this is a complex subject that keeps me going. I'll touch on a few notable items below, so it may seem a bit disjointed as I find it hard to distil this subject. + +The two immediate factors in cold water swimming are + +1. Habituation. +2. Acclimatization. + +Habituation is the process of getting used to getting into cold water (that is under 18 Celsius for non-swimmers suddenly immersed, under say 14C for casual swimmers, under 10 C for cold water swimmers, under 7C for extreme cold water). Habituation is trained in a little as five or six immersions. You start to be able to deal with the shock and the physical fight-or-flight reaction most people experience prior to cold when they know they will be exposed attenuates. Initial shock lasts about 30 seconds, with a longer 3 minute period for the next phase. Heart rate spikes and lowers. There are also stress hormonal reactions which disappear as you gain experience. + +Acclimatisation is the longer term adaptation to cold by such people as open water swimmers (non-wetsuit). There is a normal psychological improvement in dealing with cold. Brown Adipose Tissue (brown fat) which generates heat unlike normal white fat, begins to spot grow on part s of the body such as torso and shoulders. + +Physically, cold water shock also causes a number of responses + +1.Normal blood pressure increases due to peripheral vaso-constriction in which blood flow to the extremities is shut off to protect core temperature. This will happen when just your feet enter the water. You feel a sudden need to urinate as a consequence. Your external skin surface quickly drops in temperature. (I've measured a skin temp of 18C on myself after a one hour swim in water of 14C, and felt utterly comfortable afterwards, but I'm trained to that). The temperature difference between your core at around 36C and the water at 14C is then much less. + +It's important to note that heat loss still occurs even when you are feeling comfortable and will in water under say 18 C eventually result in hypothermia, for a person not swimming. (For a trained cold water marathon/Channel swimmer, they will be able to swim and stay warm in 14C for 24 hour, determined mainly by their weight and training.) + +2. Your heart rate rises sharply. This is one of the dangerous aspects, very slightly because of possible cardiac event, more because it can cause someone to aspirate water. As your heart rate settles, you start to feel more comfortable. + +3. Depending on the water temperature & your experience & immersion time, you may experience great pain from the thermoceptors (temperature sensing) nerves in your skin. While heat sensing thermoceptors measure pain as temp increases until you burn, with cold thermoceptors ""shut off"", ie you go numb. You have the most thermoceptors in your face, so people unused to cool water let alone cold, will have difficulty getting their face in the water. As your themoceptors numb, this also helps the adaptation. + +Here's one article I wrote, about [the first three minutes of a cold water swim](http://loneswimmer.com/2012/11/13/cold-water-immersion-and-cold-shock-the-first-three-minutes/) that you may find useful. + +**Obligatory edit**: Gold? When all my family and friends say ""don't get him started on swimming""? Thank you. Come for a swim with me, I haven't even mentioned my friendly cave swimming tours! + +**Edit 2**: I should cited earlier since this is /r/askscience, but didn't expect such interest. + +Good references off the top of my head are: + +**Essentials of Sea Survival**, *Mike Golden and Frank Tipton*, University of Portsmouth (survival research department). Out of print but the definitive work. There are a number of great papers from either or both of these. + +**Characteristics of San Francisco Bay Cold-Water Swimmers**; OSJM 2014; 8:1-10, *Thomas Nucton* MD + +**Extreme Cold Adaptation in Humans**. A meta-analysis by *Tina Maakinen*. +" +581 When they say an inch of rain, does that mean cubic inch? 3439 https://www.reddit.com/r/askscience/comments/52vukj/when_they_say_an_inch_of_rain_does_that_mean/ 1473941718 52vukj Earth Sciences 2016-09-15 15:15:18 "it's less complicated than it sounds. an inch of rain is an inch deep no matter the surface area. could be the size of a dime, could be a square inch (that would give you a cubic inch of rain), could be a square mile. just means that, on the whole, in a given area, enough rain fell to cover the ground in an inch of water (assuming zero drainage). + +[EDIT 1] woah, fifty times more points than i've ever gotten before. that's hilarious. to anyone who is still confused: you are totally overthinking this. imagine a football field with a thousand straight-sided plastic containers, all of different sizes, scattered about. if that football field gets an inch of rain, all of the containers will have an inch of rain in them. it's like measuring the depth of the carpet in a house. the shape and size and contours of the floor just don't factor into the equation. whatever the carpet depth is, it's the same everywhere. + +[EDIT 2] should also note, if the weather report was measuring **cubic** inches of rain, the number would be, like, a billion." "An inch of rain means that if you would catch the rain on a flat surface, it would reach up to an inch in height. To properly measure this, you need to make sure that the water can't flow away or dissipate into the ground, so you'd need a waterproof box with an open top for the rain to fall in. The amount of water it takes to reach a certain waterlevel obviously depends on the surface area of the measurement box. However, so does the amount of water entering the box via rainfall, so that evens out and ultimately it means that the size (and shape) of the measurement box is not important. + +1 cubic inch of water will raise the water level in a 1 square inch box to 1 inch." +244 Why can't I weigh the earth by putting a scale upside-down? 3437 https://www.reddit.com/r/askscience/comments/3o82rc/why_cant_i_weigh_the_earth_by_putting_a_scale/ 1444488990 3o82rc Physics 2015-10-10 17:56:30 "This is a brilliant question because in some sense you *are* measuring the earth's mass. + +By Newton's third law, the force exerted on the scale by the earth is the same as the force exerted on the earth by the scale - you know, the 'equal and opposite reaction' law. + +In this case that force is the force of gravity. The force between two objects of masses *M* and *m* separated by a distance R is equal to + + F = G M m / R^2 + + +The key point is that scale just happens to be calibrated to measure the mass for an object experiencing earth surface gravitational acceleration - i.e. it assumes *GM/R^2* is a constant value (which is equal to g=9.81 m/s^(2)), and then returns the value for *m* that when scaled by this constant is equal to the force the scale measures. + +If you had a scale of a known mass and you turned it upside down you could then calculate the value of this constant - *GM/R^(2).* Then, with known values of *G* and *R*, you could calibrate your scale to measure the mass of the earth rather than the mass of the scale :D + +---------------- + +And to clarify an important point - the earth and the scale don't experience the same accelerations. Use Newton's second law: + + m a_1 = G M m / R^2 + +and find the acceleration of the scale is + + a_1 = GM/R^2 + +Conversely, the force of the earth is + + M a_2 = G M m / R^2 + +So the acceleration of the earth is + + a_2 = G m / R^2 + +Since M is the mass of the earth and m is the mass of the scale, a_2 is much much much smaller than a_1. " "In a certain sense, you can. + +You would simply need to calibrate your measurement to the gravitational pull of the scale. + +Since ""weight"" is actually the gravitational force of attraction between two masses, **the weight of the earth in the scale's gravitational field is the same as the weight of the scale in the earth's gravitational field**. + +" +20 When we have to fight ourselves awake, what are we fighting exactly? 3433 http://www.reddit.com/r/askscience/comments/327t9v/when_we_have_to_fight_ourselves_awake_what_are_we/ 1428745256 327t9v Neuroscience 2015-04-11 12:40:56 "What you're talking about is referred to as [""sleep inertia""](http://en.wikipedia.org/wiki/Sleep_inertia). The grogginess and desire to return to sleep can last as long as 30 minutes, depending on several factors- including which stage of sleep you wake up from (waking up during deep sleep is associated with the most sleep inertia.) + +Also caffeine is an adenosine receptor antagonist, meaning it blocks the effects of adenosine, and has been shown to greatly reduce sleep inertia. +" "It mainly has to do with the regulation of circadian clocks. Apart from adenosine (which accumulates during the day), melatonin is the primary hormone that signals the body to go to sleep. It accumulates when no longer exposed to light, which literally keeps you asleep during the night. + +Wakefulness is maintained by exposing your eyes to blue light (present in sunlight and even more so in your computer screen) which is detected by a pigment called melanopsin in 2% of retinal cells (intrinsically photosensitive retinal ganglion cells). These cells signal to the suprachiasmatic nucleus (SCN), which in turn is the master regulator of the body's ""clock"". Thus, at night your body is signalled to become asleep by various mechanisms (adenosine, melatonin, blue light absence) as well as others which are largely dependent on oscillatory ""clock genes""; hormones such as vasopressin and cortisol are strongly controlled by the clock. To wake up, the levels of all these hormones need to be brought back to their ""awake"" levels and it takes time for this to happen after your brain is signalled to do so (blue light received and/or end of the cycle). + +Some basics: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Circadian.html + +Review on clock genes: http://hmg.oxfordjournals.org/content/15/suppl_2/R271.full + +TL;DR: blue light keeps your body awake and sets the timer on your inner clock. Yep, you're fighting a clock. + +EDIT: grammar. +" +458 Why is that when you subtract a number from its reverse, the difference is a product of 9? 3431 https://www.reddit.com/r/askscience/comments/4o9p15/why_is_that_when_you_subtract_a_number_from_its/ 1466025057 4o9p15 Mathematics 2016-06-16 0:10:57 "A number is divisible by 9 exactly when its digits sum to a multiple of 9. So 1836 is divisible by 9, 1936 is not. More exactly, a number and the sum of its digits both have the same remainder when we divide by 9. For example: + +* 3823 divided by 9 is 424 remainder 7. Also, 3+8+2+3 = 16 divided by 9 is 1 remainder 7 + +* 92838845 divided by 9 is 10315427 remainder 2. Also, 9+2+8+3+8+8+4+5 = 47 divided by 9 is 5 remainder 2. + +So if I want to know the remainder of a number after dividing by 9, I can just look at the remainder of the sum of its digits. They'll always be the same. + +Now, remainders work nice under addition, subtraction and multiplication. If the remainder of N divided by 9 is 3 and the remainder of M divided by 9 is 2, then the remainder of N+M divided by 9 will be 2+3=5. If I add numbers, I can just add remainders. Same thing with subtraction and multiplication. Sometimes you might have to take an additional remainder, but it's good. For example + +* The remainder of 40 divided by 9 is 4, and the remainder of 55 divided by 9 is 1. The remainder of 40+55 will be 4+1=5. So 40+55=95 has remainder 5 after dividing by 9. + +* The remainder of 43 after dividing by 9 is 7 and the remainder of 80 after dividing by 9 is 8, so the remainder of 80-43 after dividing by 9 is going to be 8-7=1. In fact, 80-43 = 37, which has remainder 1 after dividing by 9. + +* 3823+92838845 will be divisible by 9 because 3823 divided by 9 has remainder 7 and 92838845 divided by 9 has remainder 2. So 3823+92838845 divided by 9 will have remainder 2+7=9. But 9 can't be a remainder, and 9 divided by 9 has remainder 0 so 3823+92838845 will have remainder 0, which means that it is a multiple of 9. + +In particular, if N and M have the same remainder after dividing by 9, then N-M will be divisible by 9. Their remainders are the same, so subtracting them will give remainder zero, which means that it must be divisible by 9. + +If you have a number, then reordering it's digits won't change the remainder after dividing by 9, because this does not change the sum of the digits. The remainder of 435 after dividing by 9 is the same as the remainder of 4+3+5=12, which is 3. The remainder of 354 after dividing by 9 is the same as the remainder of 3+5+4 = 12, which is 3. This means that 435-354 will have remainder 3-3=0, so it is divisible by 9. + +So, because reversing the digits does not change the sum of the digits, the difference will always be divisible by 9. + +The field of math dealing with remainders is [Modular Arithmetic](https://en.wikipedia.org/wiki/Modular_arithmetic). + +EDIT: It works for 11,22,33 etc and palindromes, 313,2332 etc, because 0=0\*9, which means zero is a multiple of 9." "Any two digit number can be written as 10x + y. (So 52 = 10*5 + 2). Reversing the number gives you 10y + x. Then: + +(10x+y) - (10y+x) = 10x+y - 10y-x + += 10x - x + y - 10y + += 9x - 9y + += 9(x-y) + +Which is divisible by 9 so long as x and y are integers." +582 What color does the human eye track the best? 3431 https://www.reddit.com/r/askscience/comments/5jw229/what_color_does_the_human_eye_track_the_best/ 1482480934 5jw229 Biology 2016-12-23 11:15:34 The human eye response is most sensitive in the green, peaking around 555nm. If these hypothetical colored dots were all of the same intensity, a green dot would appear the brightest. Not sure how perceived brightness affects tracking, hopefully somebody with knowledge in that area can weigh in. "a dark dot on a bright background or a bright dot on a dark background; the part of the visual system that senses achromatic contrasts is faster than the part that senses chromatic contrasts. + +ultimately the bright dot would be easier to follow if you wanted to go to the limit of ""dot"" - an infinitesimally small black dot on a bright background would be invisible while an infinitesimally small bright dot on a dark background would still be visible (if bright enough - think stars). + +*edit since* + +To get a little more specific since people are reading this: what i was referring to in this comment (""sensing achromatic contrasts is faster"") is the general distinction in the early visual system between the *magnocellular* and *parvocellular* pathways. The magnocellular pathway mainly transmits information about brightness contrast and motion, while the parvocellular pathway mainly transmits information about color contrast and spatial pattern. Of course nothing is *really* that simple in the visual system, but it's a useful way of talking about certain functional/physiological distinctions in the brain. + +The root of the magno system is in retinal cells that pool inputs over all types of cones (mostly L+M cones); the root of the parvo system is in retinal cells that pool over specific types of cones antagonistically (e.g. L vs M or [L+M] vs S). Because the former (magno cells) are pooling broadly they are very sensitive to slight changes in stimulus (i.e. motion cues), but they are not great at picking up fine detail or distinguishing one type of cone from another. + +So, motion perception relies mostly on brightness contrast, i.e. edges or features that are distinguished by variance in their luminance intensity across space and time. *Chromatic contrast* ('color' contrast) is a very very poor input to the motion perception system - if you remove all brightness cues from a video, you will have enormous difficulty making sense of what little motion you can see. + +Usually, in nature, chromatic and brightness contrasts are strongly correlated, i.e. where you find one you find the other, but with unnatural stimuli (i.e. experimental conditions) these powerful differences can be brought out." +459 If a limb were severed from the body and left in the sun for a while, would the skin sunburn? 3423 https://www.reddit.com/r/askscience/comments/4sedhe/if_a_limb_were_severed_from_the_body_and_left_in/ 1468285497 4sedhe Human Body 2016-07-12 4:04:57 "Well, burning from the sun would still happen, but not the normal physiologic action of producing pigment afterward. Being burned is a passive process, while becoming tan and producing color is an active process in the body due to melanocytes, you die?those die. The normal redness would also not be present since that is from extra blood in the skin from the uv burns, which is why you can press on sunburned skin and it turns white momentarily. +So, yes, your arm would still burn, but it would be a literal burn...but not a sunburn like we know. " "Yes, and, no. + +Let's first characterize sunburn: what we call sunburn is damage that is caused by UV rays cleaving DNA, thus messing up cell functions and generally killing, damaging or altering the cell. The redness, bubbles, shedding etc. following the actual burn are part of the immune reaction, where the boy deals with the damage that has been done. + +For the yes: cells on a severed limb can survive for quite some time, yet how long this is depends on the type of cells. Skin cells can survive for quite a few hours and when exposed to UV radiation they would still receive the same damage. + +For the no: Skin cells will survive longer than cells of the immune system (NK, T, Neutrophils etc.). This means that although the same UV ""burn"" has occurred you'd not have the same immune response and thus you'd not have the normal redness, tanning and skin shedding. Moreover in the absence of immune response other microorganism would take over fairly quickly. " +137 Iron smelting requires extremely high temperatures for an extended period before you get any results; how was it discovered? 3420 http://www.reddit.com/r/askscience/comments/3bd648/iron_smelting_requires_extremely_high/ 1435458887 3bd648 Archaeology 2015-06-28 5:34:47 "Well, people had thousands of years of bronze smelting before anyone figure out how to get iron from ore. People used meteoritic iron long before then too, but of course there wasn't much of that. + +Iron isn't too hard to get out of [bog ore](https://en.wikipedia.org/wiki/Bog_iron) or [goethite](https://en.wikipedia.org/wiki/Goethite). Some places where you could get bog ore also yielded [iron nodules](http://www.hurstwic.org/history/articles/manufacturing/text/bog_iron.htm). Maybe someone got some bog ore mixed in to their bronze smelting operation. + +https://en.wikipedia.org/wiki/Bloomery + +> The onset of the Iron Age in most parts of the world coincides with the first widespread use of the bloomery. While earlier examples of iron are found, their high nickel content indicates that this is meteoric iron. Other early samples of iron may have been produced by accidental introduction of iron ore in bronze smelting operations. Iron appears to have been smelted in the West as early as 3000 BC, but bronze smiths, not being familiar with iron, did not put it to use until much later. In the West, iron began to be used around 1200 BC." "Iron doesn't need to be melted (1536 °C) to be extracted. You can reduce iron ore in a solid state between 800 to 1,050 °C depending on the composition of the ore. This is not much higher than temperatures needed for copper production. That's a clue in terms of the evolution of iron production. To cut a long story short, iron is often a by-product of copper reduction processes (in the form of an iron-silicon mix called fayalite) so the theories are that the skills of extractive metallurgy in copper opened the door for iron extraction. One of the nicest all round books on this is the seminal work by R. F. Tylecote (1992) A History of Metallurgy. +" +138 Nuclear fusion reactors use supermagnets to suspend plasma and prevent it from damaging the containment structure. However, fusion also produces neutrons as part of the reaction, which have a net charge of 0. What steps have scientists taken to mitigate the damage from these high-energy neutrons? 3413 http://www.reddit.com/r/askscience/comments/3gky7w/nuclear_fusion_reactors_use_supermagnets_to/ 1439293130 3gky7w Physics 2015-08-11 14:38:50 "It does cause a great deal of damage, and developing materials capable of withstanding high energy neutron bombardment of a period of years without dramatic changes to material properties (eg thermal conductivity) is one of the biggest problems in fusion research. For Deuterium Tritium fusion, the 14MeV neutrons create cascades of damage to the material crystal structure, some of this repairs itself through thermal motion, but some remains permanently. As this builds up over time parts will have to be replaced. The neutrons also cause transmutation of elements in structural materials, forming radioactive isotopes, which creates problems for component replacement and decommissioning. The lifetime of these components will be crucial in determining the fraction of time the reactor is actually generating electricity, and the cost of that electricity. + +To combat transmutation the steels used (such a EUROFER 97) are designed so that radioactive elements that appear are relatively short lived. I don't believe there are currently definite solutions for neutron damage itself, but clever ideas such as high entropy alloys are being considered. Material testing for high 14MeV neutrons is currently difficult as there are no neutron sources which can be used to achieve the expected or equivalent neutron fluence in a reasonable length of time, though there are plans for a materials testing facility IFMIF." "The other answers here give excellent detail on neutron damage, but I just want to add some information on why we *need* the neutrons (at least in current reactor designs) and how we make them work for us. + +If we want to generate electricity, we have to capture some of the energy that is released from the fusion reaction - and the way we do that is by using the neutrons. In this sense, the fact that the neutrons have no charge (and so are not confined by the magnetic field) is very convenient because they carry 80% of the energy that is released in the fusion reaction - so that is 80% that we have relatively easy access to. + +There are two key things the neutrons do for us: + + - We have them give up their energy in some layer of material around the reactor as they slow down, causing that layer to heat up. We then use that energy to heat water, make steam, drive turbines ect. + + - We need them to interact with Lithium in order to produce Tritium, which is one of the fuels (the fusion reaction is deuterium-tritium). Tritium is not naturally occurring as it decays with a Half-life of 12 years, so the only way for us to get it is to make it through nuclear reactions. + +The current designs for fusion reactors seek to combine both of these requirements into one piece of engineering called a 'blanket'. The blanket is a hollow layer which surrounds the entire reactor and is filled with Lithium (and possibly other things) which may be in solid or liquid form. + +The idea is that the neutrons will interact with the Lithium layer, causing it to heat up as well as producing the tritium we need. While this is going on, a coolant of some form is continuously flowing through the blanket layer, transporting this heat out of the reactor so we can use it for electricity generation." +460 What exactly happens in our brain when we daydream/space out? Is it similar when we are sleeping? 3412 https://www.reddit.com/r/askscience/comments/4r5os3/what_exactly_happens_in_our_brain_when_we/ 1467609213 4r5os3 Neuroscience 2016-07-04 8:13:33 Hi everybody. Please remember that you're in /r/askscience, so post science, not speculation or personal stories. "**TL;DR:** Daydreaming brain and sleeping brain states are quite different from one other. + +We have a brain structure, more accurately, a type of neural network formed in parts of the brain, called the ""[Default Mode Network](https://en.wikipedia.org/wiki/Default_mode_network)"". + +This network, linking several parts of cortical areas and the limbic system, which are known to be involved in sensory experiences. When this network is active, as we learned from [Buckner et al](https://www.ncbi.nlm.nih.gov/pubmed/18400922), the individual is not focused on outside stimulus, but instead is turned inside, hence the daydreaming. (More accurately called [Mind-wandering](https://en.wikipedia.org/wiki/Mind-wandering) ) When this default network is active, it provides its own stimulation. In layman's terms, it's entertaining us, but we are not far away from our wakeful state. + +Sleeping, on the other hand is a complex state of entire organism that plays a key biological role such as building up or the repair of immune and muscular systems as well as other syntheses. To be absolutely fair, we are not crystal clear on how the sleeping mechanics of the brain interacts with each other. However, we know that mostly by virtue of the [VLPO](https://en.wikipedia.org/wiki/Ventrolateral_preoptic_nucleus) and thalamus of our brain, a cornucopia of neurotransmitters are controlled, which is assumed to help our brain switch between sleeping and wakeful states. When sleep occurs, a variety of signals of wakefulness are interrupted and most outside stimuli is blocked, which is quite different from what happens in the state explained before. + + + + +" +583 In multi-star systems, what is the furthest known distance between two systems orbiting each other? 3411 https://www.reddit.com/r/askscience/comments/5hqphx/in_multistar_systems_what_is_the_furthest_known/ 1481472281 5hqphx Astronomy 2016-12-11 19:04:41 "I'm an exoplanet PhD student who has done a little bit of work with binary stars and how they might affect planet formation. + +To start, I don't know the exact answer of the ""farthest known distance between two stars in a system"". (I'm also going to ignore star clusters in this because I feel that that's not what you mean.) However, it is known that wide binaries can have an orbital radius of several thousand AU (1 AU = distance from Earth to Sun). + +This [source](http://www.ifa.hawaii.edu/info/press-releases/WideBinaryStars/) says about 1 light-year. The current distance between Alpha Centauri A and B and Proxima (or Proxima Centauri) is 15000 AU, or about 0.24 light-years ([source](https://arxiv.org/abs/astro-ph/0607401)). However, it's not confirmed that they're gravitationally bound. It's right on the edge. + +From what I know and from what I've just read up on, I would say that the widest binaries about probably about 0.25 light-years away from one another. For reference, that's about 400 times the distance from the Sun to Pluto, and the nearest star to the Sun is Proxima Centauri, which is about 4.25 light-years away. + +Here's a little [extra reading](https://www.nasa.gov/centers/ames/news/releases/2012/12-90AR.html) on wide binary stars that you might find interesting. The summary is that they probably form in 3-star systems (or higher numbers). + +" "This is slightly tangential to your question, and I don't know enough about these systems to tell you their separation, but there are two star systems which might contain 7 stars called AR Cas and Nu Sco (also referred to as Jabbah). Large systems like this tend to have two stars close in a binary and then two separate binaries orbit each other at a much larger distance, but getting all the way to 7 is very complicated. Those systems might be strong candidates for the furthest known distance between orbiting systems. + +Another completely different possibility is near Sgr A* which can have stars that orbit it at a really large distance because it's so much more massive than anything else, but in this example, the line between a star system and a galaxy start to blur." +345 Why can you rename, or change the path of, an open file in OS X but not Windows? 3408 https://www.reddit.com/r/askscience/comments/4d1w8x/why_can_you_rename_or_change_the_path_of_an_open/ 1459610623 4d1w8x Computing 2016-04-02 18:23:43 "The Windows filesystem identifies files by their paths (including the file names)—if you change a file’s path, applications and the operating system will perceive it as a new file with no connection to the original. + +The OS X filesystem identifies files by an independent file ID, which remains fixed if the file is moved or renamed." "Another aspect of the problem is that Windows has something called a *share mode* on open files—basically, an application can open a file in *exclusive* mode meaning that no other program can do anything with the file. It is not possible to circumvent the share mode. This is extensively used in Windows and part of the reason why you have to reboot to apply updates. + +UNIX-like systems (like Linux) only have *advisory* file locking which can be ignored by other processes if they decide to. Once a lock is violated, the process is notified of that circumstance and can proceed to handle the case. A rogue process cannot lock up critical files with no way out." +139 Does lightning strike the ocean? If so, does it electrocute nearby fish? 3404 http://www.reddit.com/r/askscience/comments/3c3rd7/does_lightning_strike_the_ocean_if_so_does_it/ 1436019015 3c3rd7 Planetary Sci. 2015-07-04 17:10:15 "I've done electroshocking fish for research purposes. You have a backpack and you run electricity through the water to zap fish. + +The thing is, you can't really do electroshocking in _salt_ water. It's too conductive. Electroshockers work because the electricity passing through the water essentially ""short circuits"" through fish, zapping them. Fish are more conductive than fresh water, but salt water is more conductive than fish. So the electricity just goes around them. + +So lightning isn't going to have a huge effect on marine life for that reason alone. + +EDIT: For clarity, a fish close enough to where the lightning hits will still feel the effects, and could even be killed if it was really close. But as the distance increases the effects will drop off relatively quickly, compared to a similar strike applied to freshwater. + +I attempted to find some papers that could provide some better numbers but came up empty. It seems to be a little-studied area. + +EDIT EDIT: Also, _you_ obviously shouldn't be out swimming in the ocean in a lightning storm. For one thing people tend to stick out of the surface of the ocean and no amount of salt water is going to help if you get hit directly. Or if lightning hits nearby, a little shock that merely stuns a fish temporarily could cause you to drown. " "As a Bluewater Sailor, I can say definitely that lightning frequently strikes the ocean. Fish within a few feet of the surface can be stunned or killed. Most fish usually stay a few feet down or more unless feeding on something near the surface, in order to avoid predation by seabirds.... But... + +I have observed hundreds (thousands?) of small fish at a time severely stunned or killed during a lightning storm... I Sailed through them within a minute or two of the strike. + +Do not imagine that if you do not ""Pierce the surface"" then you will be safe from lightning at sea..... You need to be a few feet down, not sure how much (this would vary considerably with sea temperature and salinity , I suspect). Also, if the water is shallow and the strike very close by, you are in the current path, and will likely be electrocuted in any case. Fish in my lobster trap (about 3-4 meters deep, on the bottom, not connected to but less than 10 meters away from my boat) were killed when my boat was struck by lightning. (steel boat) so, there's that. + +As an electrical engineer, I'd say that if the sea were a perfect conductor, the bit about piercing the surface would sort of be true (except you still wouldn't get shocked because perfect conductivity would divert the current around your body) but it's not, and compared to highly conductive metals like copper or silver, seawater is a poorer conductor by seven orders of magnitude. + +This means that the ""skin effect"" (conduction only happening on the surface of a conductor) will be distributed over a pretty wide area, and the current flowing through the water will be reduced, but not eliminated with depth and distance from the strike. + +Edit: it seems, based on a little googling, the estimates of the lethal distance in Salt water from the strike point range from 20 to 100 feet. I have personally seen lethal effects at more than 20 feet. + +" +245 If I pick up my coffee right after I stir it, so that it's still swirling around, will there be a gyroscopic effect making me less likely to spill it? 3404 https://www.reddit.com/r/askscience/comments/3rdhl7/if_i_pick_up_my_coffee_right_after_i_stir_it_so/ 1446570582 3rdhl7 Physics 2015-11-03 20:09:42 In theory yes, but in reality you'd probably be more likely to spill it. Once you tilted the cup at all you would lose the swirl as the liquid deformed against the cup wall and that creates imbalances. You can actually try this. Stir up a liquid in a cup where the liquid mass is as great as possible relative to the cup (paper cups work well) and then pick the cup up by your fingertips. Tilt the cup to one side to disturb the vortex and you should feel the cup trying to move around in various directions as the vortex collapses and sloshes against the cup unevenly. "The IgNobel prize for physics in 2012 went to studying coffee spillage from mugs. It might help inform you of the relevant forces involved. +http://blogs.scientificamerican.com/scicurious-brain/ignobel-prize-winner-in-fluid-dynamics-argh-i-spilled-my-coffee-in-the-hall-again/" +140 How do services like Google Now, Siri and Cortana, recognize the words a Person is saying? 3401 http://www.reddit.com/r/askscience/comments/3hgtzb/how_do_services_like_google_now_siri_and_cortana/ 1439917207 3hgtzb Computing 2015-08-18 20:00:07 "Baidu has now ditched some of the speech recognition techniques mentioned in this thread. They instead rely on an Artificial Neural Network that they call Deep Speech (http://arxiv.org/abs/1412.5567). + +This is an overview of the processing: + +1. Generate spectrogram of the speech (this gives the strength of different frequencies over time) + +2. Give the spectrogram to the Deep Speech model + +3. The Deep Speech model will read slices in time of the spectrogram + +4. Information about that slice of time is transformed into some learned internal representation + +5. That internal representation is passed into layers of the network that have a form of memory. (this is so Deep Speech can use previous, and later, sound segments to inform decisions) + +6. This new internal representation is used by the final layers to predict the Letter that occured in that slice of time. + +A little more simply: + +1. Put spectrogram of speech into Deep Speech + +2. Deep Speech gives probabilities of letters over that time." "One of the reasons Google offered the free google voice system with voicemail text functionality was to test their voice to text reliability rate and find ways to improve it. At one point, part of the terms of agreement for using the service was that they would be able to anonymously compare the sound of the voicemail you received with the text translation of the voicemail they provided you. + +They basically crowdsourced a ton of people leaving voicemail messages, used their speech to text software to create a transcript of the voicemail for the users via email, then checked the accuracy of the voicemail to the transcript to learn how to improve their accuracy. " +141 Is there any evidence that cetacean species communicate to each other (like grey whales calling and blue whales avoiding an area, etc)? Or are all of these species shouting past each other on different wavelengths? 3396 http://www.reddit.com/r/askscience/comments/3col2m/is_there_any_evidence_that_cetacean_species/ 1436453858 3col2m Biology 2015-07-09 17:57:38 "There are a number of reports of Orcas actually assisting Austrialian whalers by tracking and hearding whales into Eden bay to be killed by the whalers who then caught and butchered the whales, leaving the meat and tongue to the Orcas. The whales were too big for the Orcas to kill on their own, so this provided a new food source for them. This would indicate that they could indeed reliably locate other whales, probably by sound. (also pretty interesting anecdote about Orca intelligence and ability to learn) + +http://www.pbs.org/wnet/nature/killers-in-eden-introduction/1048/" "There is evidence that at least whales and dolphins communicate with each other. +  + +[HOW DO WHALES, DOLPHINS AND PORPOISES COMMUNICATE WITH EACH OTHER?](http://us.whales.org/faqs/facts-about-whales-and-dolphins) +>Communication amongst whales and dolphins is achieved in several ways. They create sounds, make >entire ocean basins) using very low frequencies. Dolphins and porpoises however, usually use higher >frequencies, which limits the distance their sounds can travel. +>In general, dolphins make two kinds of sounds, “whistles” and “clicks”. Clicks are used to sense their >surroundings through echolocation, while they use whistles to communicate with other members of their >species and very likely, with other species too. It is also thought that each dolphin has a unique whistle >called a ‘signature whistle’, which is used to identify an individual. + +  + +Also interesting, here is a clip showing pictures of a whale and dolphin “playing” with each other. +[Whales Give Dolphins a Lift](http://www.amnh.org/explore/science-bulletins/\(watch\)/bio/news/whales-give-dolphins-a-lift) +>Many species interact in the wild, most often as predator and prey. But recent encounters between >humpback whales and bottlenose dolphins reveal a playful side to interspecies interaction. In two >different locations in Hawaii, scientists watched as dolphins “rode” the heads of whales: the whales lifted >the dolphins out of the water, and then the dolphins slid back in. The two species seemed to cooperate >in the activity, and neither displayed signs of aggression or distress. Whales and dolphins in Hawaiian >waters often interact, but playful social activity such as this is extremely rare between species. These >are the first recorded examples of this type of behavior. +" +142 If you fingerprint a person as an infant, and again as an adult, will their fingerprints be the same? 3391 http://www.reddit.com/r/askscience/comments/3eazmc/if_you_fingerprint_a_person_as_an_infant_and/ 1437643863 3eazmc Human Body 2015-07-23 12:31:03 """No two fingers are found to have identical prints, and it is an overwhelming mathematical probability that no two ever will be found to match. The ridge patterns are formed in the human fetus before birth and remain the same throughout a person’s life and even after death until they are lost through decomposition."" + +source: [N Kaushal. Fingerprints: Historical Background And Future Trends. The Internet Journal of Forensic Science. 2009 Volume 4 Number 2.](http://ispub.com/IJFS/4/2/9746)" There is more to it than this, but for all intents and purposes, the ridge-line pattern does not change over time (unless the fingers have been disfigured), but the distance between ridges and other [minutiae](https://en.wikipedia.org/wiki/Minutiae) does change due to the size of your finger changing (growth). That is why most biometric companies have both child and adult algorithms for fingerprint matching. +584 Why is sodium chloride the dominant salt in seawater? 3391 https://www.reddit.com/r/askscience/comments/55o6l9/why_is_sodium_chloride_the_dominant_salt_in/ 1475508531 55o6l9 Planetary Sci. 2016-10-03 18:28:51 "So when considering this question, we have to consider two things. First, what are the concentrations of each element on earth? Second, what chemical form(s) is each element found in? To be found in seawater in large quantities, an element needs to preferentially form stable, water-soluble species. + +[This page](https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust) shows the raw abundances of elements. As you can see, sodium is one of the most common elements on Earth. All of the more common elements are components of water, also found dissolved in water or tend to form insoluble chemical species. Chlorine isn't quite as common, but is still present in large amounts. However, the elements more common than chlorine don't prefer to form water soluble species in the presence of water, oxygen and each other. Thus, we are left with large quantities of sodium and chloride. " "Na and Cl are the most abundant salts in seawater because they have the slowest removal rates. + +There's an easy way to figure out why this is the case - examine the concentrations of different ions in seawater compared to river water. Sodium and Chloride are the most concentrated ions in the ocean with respect to river waters (due to their extremely high solubility and low particle reactivity in the ocean). If it were due to sodium and chloride having the largest sources, they would also have to be the most abundant ions in river water, which they are not. + +Sulphate and phosphate are used rapidly in the ocean by organisms and incorporated into organic matter. Lithium and potassium are certainly more soluble, but they have faster sinks - they can be removed by the hydrothermal circulation of seawater through the hot ocean crust. + +This idea as a whole, is known as the kinetic model for seawater and is how chemical oceanographers understand the composition of the ocean - [Broecker 1971](http://www.sciencedirect.com/science/article/pii/003358947190041X ) +" +246 Is the strength of muscles proportional to their diameter, cross-sectional area, or volume? Or is it not linear? 3389 https://www.reddit.com/r/askscience/comments/3pi0vz/is_the_strength_of_muscles_proportional_to_their/ 1445353820 3pi0vz Human Body 2015-10-20 18:10:20 "There are multiple factors at play. + +1. Physically, sarcomeres (in muscle cells) generate force. The ~~bigger~~ more numerous these are (the current dogma says that muscle cells increase in size not number, while sarcomeres increase in number), the more force *can* be generated. It gets more complicated for [pinnate muscles](https://en.wikipedia.org/wiki/Pennate_muscle) but we will gloss over this. However... + +2. Muscle cells have to be told to fire. This is where the central nervous system comes in. The CNS gets better at activating the *right* fibers at the right time. [Read more here](https://en.wikipedia.org/wiki/Motor_unit#Recruitment_.28vertebrate.29). Of course, this is related to... + +3. Technique. Good technique is both practicing the timing of muscle recruitment *and* posture to maximize force transmission from the fibers to the weights. OP doesn't mention what ""lifts"" he is considering, but this will be especially true for Olympic lifts ([snatch / clean and jerk](https://www.youtube.com/watch?v=jmTRWHFjfec)) + +4. There are also biochemical adaptations, like intramuscular ATP and creatine levels, and the enzymes that generate these. For more than a couple reps, you'll also be talking about clearance of waste products and regeneration of ATP from glucose. + +5. Grip strength. For some exercises, grip strength is the limiting factor. + +5. Stabilizing muscles. Just because you have quads of steel doesn't mean you can squat 500 lb if you have a weak back and core. Think of stabilizing muscles as the *physical* aspects of ""good technique."" + +6. Fiber type. Some fibers are fast twitch and some fibers are slow twitch. (Ok, technically, it is more complicated than that, technically we are talking about Type I vs type IIa vs type IIb) Basically, some fibers are good for aerobic activity (running) while some fibers are good for anaerobic activity (lifting). And of course, fast fibers are going to provide greater benefits for something like olympic weightlift (snatch and clean & jerk) vs deadlift. + +7. *Leverage.* Muscles can only generate tension, so all movement can be reduced to a changing of the angle of a particular joint. Therefore, all joints basically form the basis for a lever. [*However,* not all joints are the same type of lever.](http://sciencelearn.org.nz/Contexts/Sporting-Edge/Looking-closer/What-levers-does-your-body-use) For something like a biceps curl, long arms actually *penalize* you! Evolution decided (and rightly so!) that it was better to trade of strength for a compact system of 3rd class levers gives us a good amount of strength but also an incredible range of motion. The other point a lot of commenters are mentioning is **insertion point**, or the place where a muscle connects (to a tendon which connects) to a bone. Small changes in the insertion point can drastically alter the functional *strength* (as measured by a weight lifted) versus *force generation* which is the force the muscle is pulling on the bone. There's no easy way to explain the math here, but [here is a site that appears to do a good job of explaining it.](http://www.aaronswansonpt.com/basic-biomechanics-levers/) + +*Appendix* + +Read more about the biomechanics of muscle [here](http://downloads.lww.com/wolterskluwer_vitalstream_com/sample-content/9780781774222_Oatis/samples/Oatis_CH04_045-068.pdf) + +~~Also I need to get a green tag!~~ [Requested.](https://www.reddit.com/r/askscience/comments/3exo6p/askscience_panel_of_scientists_xiii/cw6jkne). I assumed green tag was general nickname for flair, but they're actually color-coded based on discipline. I also have flair over at /r/science already. I'd primarily consider myself an engineer rather than a biologist. + +But for the record, I'm now a PhD student in biomedical engineering and have taken lots of physics/statics/dynamics/engineering physics courses, physiology, biochemistry, and biomechanics. And a bit of a lifting and fitness junkie. + +*Errata & Addendum:* + +*Edit 1:* cleaned up terminology in #1 slightly since a lot of people actually read this? It was an empty thread when I first scribbled some shit down from memory. + +*Edit 2:* added section 8. + +*Edit 3:* thx 4 dat gold gold" "It is the physiological cross sectional area (PCSA) and not anatomical cross sectional area (ACSA). The ACSA only takes into account the belly (widest point) of the muscle. The PCSA takes into account the angle of muscle pennation as it switches back and forth between (like your quads etc). Usually the more switches in the angle of pennation results in the greater PSCA. For muscles without different fiber directions (parallel muscles or strap muscles) the ASCA = the PSCA. + +source: Me. PhD biomedical engineering. Don't know where my flair disappeared to." +1265 If we take all of the world's CO2 emissions and compressed it to a diamond, how big would it be? 3389 https://www.reddit.com/r/askscience/comments/ayiqva/if_we_take_all_of_the_worlds_co2_emissions_and/ 1551998389 ayiqva Mathematics 2019-03-08 1:39:49 "The world emitted 36 gigatons of CO2 in 2014. A CO2 has a molecular mass of 44.01 g/mol, while carbon has a molecular mass of 12 g/mol, meaning that 27% of the weight of CO2 is carbon, meaning that that CO2 emission produces 9.8 gigatons of Carbon. If this was compressed into diamond it would still weight 9.8 billion tons + +Diamond has a density of 3.51 g/cm³ which means 9.8 gigatons of diamond would take up 2.8x10^15 cm^3 . How big is that? Pretty damn big. It's a cube about .8 of a mile or 1.4 km on each side. It would form a crystal basically exactly the same size of Mount Everest. It would be really really big. + +EDIT: A lot of people are taking me to task on the Mount Everest claim. And I totally see their point. However, the references comes from Wolfram Alpha.. which is pretty reliable: + +https://www.wolframalpha.com/input/?i=2.8x10%5E15+cm3 + +After trying to find some sources, I see that it's kinda difficult to really say what the volume of mount Everest is, as it's impossible to say where it starts. Certainly, the diamond will not have the same volume as an equalateral square pyramid with a height of 8.8km. I think a lot of the ""weight of Mt Everest"" and ""Volume of Mt Everest"" come from starting at base camp. + +" Love /u/NeuroBill 's answer, but here's another way of looking at it: if you're an average American, your personal diamond weighs 4.5 tonnes, and measures about 4 feet by 4 feet by 3 feet. And you create a new one every year. +247 If photons have no mass, how can a laser beam bore a hole through something? Wouldn't the equation E=MC^2 resolve to 0=0? 3387 https://www.reddit.com/r/askscience/comments/3x4g1p/if_photons_have_no_mass_how_can_a_laser_beam_bore/ 1450297918 3x4g1p Physics 2015-12-16 23:31:58 "E=mc^(2) is only part of the story. + +The full expression relating energy E, momentum p, and mass m is + +E^(2)=p^(2)c^(2) + m^(2)c^(4) + +Photons have no mass, but they do have momentum, and thus they have energy. +" "While the other answers are correct in their physics, I don't think they exactly answer your question. When a laser ""bores"" through a material, generally it's simply burning it. Just like using a magnifying glass to burn a hole in a piece of paper. + +This happens because the photons contain energy E=hf where h is Planck's constant and f is the frequency of the light. If the material absorbs the photon, then it gains that energy in the form of heat. Heat it up enough then it evaporates. If you're afraid of someone attacking you with lasers, if you cover yourself in shiny material, then instead of absorbing the photons you reflect them away from you. + +The other momentum based answers are interesting though in that you'll gain a tiny amount of heat from the change in momentum (the result being the reflected light is a litter redder than the incoming light) and, more importantly, this method can be used at small scales to push objects around. Some instances are [optical tweezers](https://en.wikipedia.org/wiki/Optical_tweezers) and other instances are in attempts at fusion where lasers compress a material to attempt to get it dense enough to fuse." +585 AskScience AMA Series: We are scientists with the Dog Aging Project, and we're excited to talk about improving the quality and quantity of life for our pets. Ask Us Anything! 3386 https://www.reddit.com/r/askscience/comments/59h6bo/askscience_ama_series_we_are_scientists_with_the/ 1477484064 59h6bo Biology 2016-10-26 15:14:24 Just a friendly reminder that our guests will begin answering questions at 12pm Pacific Time. Please do not answer questions for the guests. After the time of their AMA, you are free to answer or follow-up on questions. If you have questions on comment policy, please check our [rules wiki](https://www.reddit.com/r/askscience/wiki/rules). "What are the best things we can do for our aging dogs to extend age and/or quality of life? i'm assuming yearly dental care is on this list? + +*what about cooking fresh food v. store bought food? " +586 What is the current status on research around the millennium prize problems? Which problem is most likely to be solved next? 3384 https://www.reddit.com/r/askscience/comments/50wqwz/what_is_the_current_status_on_research_around_the/ 1472867703 50wqwz Mathematics 2016-09-03 4:55:03 Dr. Terrence Tao, a renowned mathematician, is working on the Navier-Stokes existence and smoothness problem. In 2014, he had a big result for a certain form of the equation. I was still in college at the time and my PDE professor said that most of the mathematics community expects him to be the one to win the prize for it. This particular professor was so confident that he predicted that Dr. Tao would do it by 2016. I had never heard of him at the time but it turns out Dr. Tao was a child prodigy in maths and was a full professor at 24. "In the thread linked above I don't see anything about the Yang-Mills mass gap problem, so I'll write a little about recent progresses. + +First: very roughly, the Yang-Mills mass gap problem states that a certain class of physical theories (first of all exist, and) have a mass gap, i.e. there's a particle with minimal mass in them. In other words, you can't have particles arbitrarily light in those theories. + +Last year an **extremely** surprising paper was published: http://arxiv.org/pdf/1502.04573.pdf + +The paper deals with a problem similar to the Yang-Mills problem: it takes a family of physical theories, and consider whether they have a *spectral* gap, which is a property similar to the mass gap. They prove that the spectral gap problem is **undecidable**. This is extremely surprising: nobody even ever considered such a result as possible. This naturally begs the question: *could the Yang-Mills mass gap problem be undecidable?* + +It seems to me that the general consensus among physicists is **no**, because the family of theories considered in the article above is artificially constructed and not arising in nature. They believe that a ""true"" physical theory shouldn't behave like that, and the undecidability of the mass gap would be an extremely weird phenomenon. But, sometimes mathematics doesn't care about that, so who knows." +21 "XKCD's ""Fundamental Forces"" isn't funny, it's sad. Can you do better?" 3379 http://www.reddit.com/r/askscience/comments/2wjonl/xkcds_fundamental_forces_isnt_funny_its_sad_can/ 1424440448 2wjonl Physics 2015-02-20 16:54:08 "I can try my hand at the strong force. + +Its most exotic characteristic is that, unlike with gravity or electromagnetism, the magnitude of the strong force is proportional to a **positive** power of the distance. That means that it gets stronger as distance increases. Because of this, everything subject to that force tends to clumps up (the technical term is confinement). If you tried to separate a pair of quarks, for example, you'd have to pump so much energy into the system that you'd create two more quarks to pair up with the ones that you've separated (here you would be transferring energy to mass as per Einstein's famous equation). + +While gravity only has one charge and electromagnetism has two, the strong force has six. Strong force charge is called ""color"". Fundamental units of strong charge are red, green or blue, while their anti-particles are anti-red, anti-green and anti-blue. To get something that is white, i.e. color neutral and not affected by the strong force, you need either all three colors, all three anti-colors or a color-anti-color pair. That's why hadrons are either made of three quarks (like protons and neutrons) or two (pions, for instance). + +However, for any force you need a particle that will mediate it. For electromagnetism, that particle is the photon, which is massless and chargeless. For the strong force, that particle is the gluon. The gluon, however, has color, which means it is also affected by its own force. That's the main reason why strong force is way more complicated to treat than the two more mainstream ones, and can't have an equation derived from a potential. + +Edit: Thanks for the gold, now I get to figure out what it does!" "To understand what each of the fundamental forces are, the first question we must answer is this: *What is a force?* + +In the most general sense, **a force is any external interaction which changes the state of a particle**. + +From classical physics, we know that any particle which is left undisturbed will travel in a straight line with constant velocity forever. Nothing interacts with it, nothing changes. + +Then **gravity** comes in. A particle which comes near anything with mass will have its momentum changed. The heavier the mass or the closer the object, the faster the momentum will change. The particle will speed up, slow down, change direction, or some combination of those. + +How? Every object that has mass/energy effects space and time. The details don't matter, but what is important is that heavy objects tend to ""pull"" on space. Which makes space and time bend in weird ways. When sometimes encounters this bent spacetime, it will still follow a straight path through that bent spacetime, but its actual trajectory will seem curved, sped up or slowed down. + +So far so good for objects with no charge. But sometimes particles have an **electric** charge through which they can affect each other's momentum. They don't simply attract, but can also repel. The two types of electric charge are labeled (+) and (-), opposites attract and likes repel. How strongly? Well, the stronger the charge the stronger the force, and the closer together they are, the stronger the force. + +But that's not everything. If you carefully measure the forces from these electrically charged particles, you would see that something is ""off"" when they're moving. The forces are not *quite* what you'd expect. It turns out there is another effect in play, that of **relativity**. When objects move fast, weird things start happening like lengths that become shorter or timescales that become longer. Again, the details don't matter, but they have a measurable effect on the kind of forces that these electric charges exert on each other. We call the difference between the force we'd expect from a static picture, and the actually measured force **magnetism**. + +But how does this work exactly? This is the point where we start looking at microscopic stuff and things get **weird**. Lets forget everything we know about particles and forces and start from scratch. A particle can be considered as a very small chunk of highly condensed energy. As we all know, energy is conserved, but can be changed from one form to another. A particle like an electron, which is a small chunk of condensed energy, can be split into two different chunks of energy: a new^1 electron with different kinetic energy and a photon. + +e^- → e^- + γ + +How often does this happen? All the time. Randomly^2. It just does, in every direction. But it averages out to zero, so we won't notice anything in a single particle. But this photon can be absorbed by another electron. + +e^- + γ → e^- + +Now the second electron has absorbed the momentum the photon was carrying, and the result is a force between the two electrons. Photons are massless and do not decay, so this charge can reach infinitely far. A bajigazillion (technical term) exchanges of photons produce a huge change in momentum, which we can easily see as a classical force. Furthermore, the photon has no electric charge, so doesn't interact with itself. + +So much for the classical forces. But what about the others? We're getting into slightly unfamiliar territory, but the same principles still apply. Beyond electric charge, certain particles, called **quarks**, also have **color charge**. Instead of two, there are three types of color charge, labeled red, green and blue. These are the charges of the **strong force**. Obviously, these charges have nothing to do with actual colors, but they are named so because three of those charges are required to neutralize each other. + +If you have a positive and negative electric charge and bring them close together, the effects you feel at long distance will be almost zero, because the effect of the two charges neutralize. The same happens with color charges, though you need three quarks of different color together to get **neutral**. Another option is having a quark/anti-quark pair with corresponding color/anti-color^3. You're probably wondering if this also works in terms of ""likes repel and opposites attract"", but the situation is slightly more complex. + +Just as the electromagnetic force is carried by photons, the strong force is carried by **gluons**. What does this interaction look like? Does it change the momentum of the particles like the photon does? Yes, but that's not the only thing. Gluons are not color neutral. They carry a color and an anti-color charge. Tt effectively allows them to change another particles color charge. So for example: + +blue quark → red quark + blue/anti-red gluon + +And if a red quark happens to be nearby, it can absorb the gluon: + +red quark + blue/anti-red gluon → blue quark + +But that's not all! The gluons can also couple to *each other*: + +green/anti-blue gluon + red/anti-green gluon → red/anti-blue gluon + +Gluons are massless, like photons, meaning they can reach infinitely far. But because they can interact with themselves, that also allows them to multiply as they travel (just reverse the interaction above). So that means that the further two quarks are apart, the more gluons they will be sending to each other. This results in the force getting **stronger with distance**. Luckily this doesn't spiral out of control, eventually the energy in the intermediate space will become so large, it will condense into a quark/anti-quark pair, forming new neutral particles with the ones that were interacting previously. + +Three quarks can form a **proton** or a **neutron**, each having a neutral color charge. But sometimes gluons escape, allowing them to interact with each other. These ""leakages"" are what holds atomic nuclei together, but the specific interactions are fiendishly hard to calculate. + +Now what determines whether three quarks will form a proton or a neutron? The answer is quark **flavor**. The only two relevant flavors^4 for us at this point are called up and down. The up quark has an electric charge^5 of +2/3, while the down quark has an electric charge of -1/3. A proton consists of *uud*; two ups and one down. This gives it a total charge of +1. The neutron is *udd*, with zero electric charge^6. + +Why is this relevant, you ask? Because of the **weak force**. It is the third^7 interaction that governs the quarks in the protons/neutrons in the nuclei, alongside the electromagnetic and strong force. And the question is of course what it does. It affects momentum, just like the electromagnetic and strong force, but that is the least important of its effects. + +Because the weak force is the only interaction that can **change flavor**. Now this works the same as the other two. The weak interaction has three force carriers. The W^+, the Z^0 and the W^-. Their electric charges are +1, 0 and -1 respectively, and the two W particles are each other's anti-particle. I won't go into detail about the Z, so lets consider the W's. + +A quark will spontaneously emit W particles, just as it emits photons and gluons. This works in the following way: + +*u* → *d* + W^+ + +An up quark can emit a W^+ and change flavor to a down quark. If another down is nearby, it can absorb this W^+ and change itself into an up. This will have its usual contribution to change in momentum, but overall we will still have an up and a down. + +But what if an up quark in a proton emits a W^+ and the W^+ escapes? Well, it will turn the proton into a neutron, because the total quark flavor will have changed from *uud* to *udd*. + +p^+ → n^0 + W^+ + +Likewise, a neutron can change into a proton by emitting a W^- or absorbing a W^+. + +You might ask what happens to the W now. These W particles are quite heavy, so they will quickly decay (break into smaller chunks of energy). Which ones, well... + +W^+ → e^+ + ν_e + +Okay, what happened here? The W broke up into an anti-electron and an electron **neutrino**. Neutrinos are nearly massless, neutral particles which only interact through the weak force. Although there are many interesting things about them, there isn't much to say about them in this context. They hardly interact at all with anything. They just kind of pass through everything. + +This is the mechanism with which (beta) **nuclear decay** occurs. If an atomic nucleus would be more stable with a different proton/neutron ratio, a proton will change into a neutron or vice versa. Why specific ratios are more stable is then again determined by the electromagnetic and strong force. + +I hope you at least understood some of that :) + +^(1 How can we distinguish between a new electron and the same electron which simply bounced off a photon? It depends on your interpretation of ""same electron"". In essence, all electrons are identical and indistinguishable. But every time an electron's state is changed, such as its momentum or any other feature, it could be considered a completely newly created particle while the old one is destroyed.) + +^(2 The probability of this happening is actually tied to the amount of momentum and energy the photon is carrying but the details of this are very technical.) + +^(3 Anti-quarks do not carry color, but anti-color. They are aptly named anti-red, anti-green and anti-blue.) + +^(4 There are six of them. Up, strange & top have electric charge +2/3; while down, charm & bottom have charge -1/3. There are corresponding anti-quarks with anti-flavors and opposite charges.) + +^(5 These are fractions of the elementary charge *e*. The charge of the electron is -1.) + +^(6 There are some wonderful experiments that map the position of + and - charge within the neutron. It also has a significant magnetic moment because the quarks are not stationary.) + +^(7 Gravity is irrelevant here) + +[TL;DR](http://xkcd.com/1489/)" +587 How do ancient languages compare to modern ones in terms of complexity? Roughly the same? 3377 https://www.reddit.com/r/askscience/comments/54csfv/how_do_ancient_languages_compare_to_modern_ones/ 1474761756 54csfv Linguistics 2016-09-25 3:02:36 "The entire premise of your question is *very* controversial in the field of academic linguistics. The biggest problem is that it's very difficult to put any idea of ""complexity"" on a solid methodological footing. [The Wikipedia article on this topic](https://en.wikipedia.org/wiki/Language_complexity) highlights some of these difficulties. Simply put there is a wealth of linguistic diversity, but it's not easy to see how you can meaningfully try and rank them according to some idea of complexity. Most modern languages can express the same words, concepts, and ideas, just in different ways. Different languages use different strategies to achieve complexity. Some work more by sticking different word pieces together ([agglutinative languages](https://en.wikipedia.org/wiki/Agglutinative_language)), some use prepositions to tie words together ([isolating languages](https://en.wikipedia.org/wiki/Isolating_language)), others make abundant use of different endings to convey information ([inflected languages](https://en.wikipedia.org/wiki/Fusional_language)). Most languages make use of all of these strategies to various extents. Moreover, this distinction is far from the only axis along which languages differ. + +The only cases where the argument of reduced complexity is easier to make is for pidgin and creole languages. A [pidgin](https://en.wikipedia.org/wiki/Pidgin) is a simplified language that usually arises when speakers of foreign languages try to find a common means to communicate. Slave societies are a common example where such a situation arose. These languages do indeed seem to have rather reduced expressive powers, hampered by a large degree of ambiguities. Related to pidgin languages are [creoles](https://en.wikipedia.org/wiki/Creole_language), which you can think of as the more mature version of a language arising out of a pidgin. However, in the case of creoles, it becomes much more difficult to argue that they are less complex than older languages. The biggest drawbacks of creoles are in terms of e.g. vocabulary for specialized terms. However, these short-comings are usually temporary and do not reflect an intrinsic inferiority in the respective languages. For example, deficiencies in vocabulary can very quickly be plugged by adapting the necessary terms from other languages. In fact, virtually every single language in the world has taken advantage of such a strategy." "Yes. + +Language complexity isn't really a thing. There is no such thing as a scale from less complex to more complex. Every language is equally effective, with *very* slight variation for circumstances important to the culture in question. + +Some languages like English have up to 3 onset consonants, a diphthong, and 5 coda consonants (ur-example: strengths). Others, like Hawaiian, have only one onset consonant and one vowel. Still other allow for triphthongs (Vietnamese), consonant nucleii (Berber), and other even more ""complex"" phonological constructions. + +Some languages have purely isolating word formations (English and Chinese), where you have very few things ever appended to a word, everything is communicated through position. Other languages express the same concepts with lots and lots of affixes. + +> Yup'ik: kaipiallrulliniuk +>English: The two of them were apparently really hungry. + +Some languages have no gender system whatsoever (English, Chinese, Persian), others have upwards of 24 different genders (Fulfulde) + +In general, whenever you encounter a langage that is lacking in some form of ""complexity"" it picks it up by being more ""complex"" in some other dimension. There really is no such thing as one language being more ""complex"" than another. + +Edit: Russian -> Vietnamese. Thanks /u/Poluact and /u/rusoved +" +461 Why don't dinosaur exhibits in museums have sternums? 3374 https://www.reddit.com/r/askscience/comments/4nvizi/why_dont_dinosaur_exhibits_in_museums_have/ 1465823259 4nvizi Paleontology 2016-06-13 16:07:39 "Most dinosaur sternums are made of cartilage and do not fossilize. Birds sternums are ossified. Flight requires some serious muscle, nice to have a hard surface for that muscle to attach too. +In the early 20th century the lack of non-avian dinosaur sternums was used as evidence that birds were not dinosaurs! We now know that those sternums were cartilage (found in sharks, your nose^assuming ^you're ^a ^human). Being a soft tissue, cartilage has a very low probability of being fossilized. " "I have a follow-up question: dinosaurs in museums (particularly the Royal Tyrrell Museum in Canada, where I have been) lack any sort of bone that would connect the arms to the spine - they have no shoulders. Why is this? + +[Examples.](https://www.google.ca/search?q=royal+tyrrell+museum&safe=off&espv=2&biw=1600&bih=785&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi24IPaz6XNAhWl6IMKHVcGC7gQ_AUIBygC)" +462 "Why is it that human brains are able to ""auto-pilot"" certain commands, such as play the piano, video games, sports etc... But when we start to think about it, we completely lose rhythm?" 3371 https://www.reddit.com/r/askscience/comments/4tf88i/why_is_it_that_human_brains_are_able_to_autopilot/ 1468849084 4tf88i Human Body 2016-07-18 16:38:04 "[I suspect this article is what you are interesting in.](https://www.mpg.de/7738341/brain-architecture-daydreaming) + +In short, there are different parts of the brain that are responsible for reacting to novel stimuli and carrying out tasks of habit. Different parts of the brain can suppress the activities of others. Very roughly, the more parts of the brain are involved in dealing with a task, the more time it takes for them to reach a consensus and react. + +I suspect that ""consciously"" thinking about something sets up a conflict between the part of the brain that carries out habitual activities and the part of the brain responsible for higher thinking and novel reactions (see article above). This comes with a ""loss of groove"" as the various parts resolve conflicting signals. It is the cognitive equivalent of an overly attentive manager inserting himself into the workers' work to try things himself and ask questions, thus slowing everything down." "The first video is a classic case of ""fire together, wire together"" wherein you develop an automatic response to a stimulus (e.g. you see a right arrow you tap the right arrow button) so you can reliably execute a complex task at a speed which would not be possible if you were consciously thinking of each individual step/move. + +This stuff gets really interesting when you get past simple cue-response activities, like with a piano player during a really fast part of a song where they have tied together all the motor parts required for that activity into a ""motor program"" (analogous to a macro in excel for example) through practicing it and they get to a point where to execute that motor program at the speeds they want requires them to do the whole thing. +These and other neural strategies result in professionals being able to enter a state of ""flow"" or something more commonly known as ""being in the zone (chief)"" where a large repertoire of complex motor programs and responses to stimuli are seamlessly strung together. + +source: masters level neuroscience class on the neural basis of behaviour + +poppy New Yorker article about ""flow"": http://www.newyorker.com/magazine/2011/10/03/personal-best + +edit: spacing" +1439 Why is there more matter than antimatter? 3366 https://www.reddit.com/r/askscience/comments/db7e4j/why_is_there_more_matter_than_antimatter/ 1569823988 db7e4j Physics 2019-09-30 9:13:08 "We don't know. + +This question, often referred to as the ""baryon asymmetry problem"", is one of the major open questions in elementary physics. + +It's natural to assume that matter and antimatter would've been created in equal quantities in the big bang, but the fact that there seems to be a very large imbalance implies that some physical laws apply differently to matter than they do to antimatter. For now, it's an open problem and no complete answer to the baryon asymmetry problem has been found. + +So the solution to this problem is left as an exercise to the reader." The matter/antimatter asymmetry is one of the big open questions in modern physics. The leading explanation is baryogenesis, which requires the breaking of the charge conjugation (C) and parity (P) symmetries. CP-violation is present in the Standard Model, but the amount appears to be too small to explain the observed matter/antimatter asymmetry, suggesting new physics remains to be discovered. Many Beyond the Standard Model theories include additional sources of CP violation that may account for this, and there is significant experimental and theoretical effort in the community to more precisely measure CP-violating processes to look for evidence of deviation from the Standard Model, although at the moment no clear evidence exists. +248 If we can produce zero-calorie drinks easily, why don't we have zero-calorie food? 3363 https://www.reddit.com/r/askscience/comments/3obzfm/if_we_can_produce_zerocalorie_drinks_easily_why/ 1444573106 3obzfm Chemistry 2015-10-11 17:18:26 We probably could make zero-calorie food by modifying the molecular structure to prevent it from being absorbed in the digestive system (think Olestra). However, this would very likely have similar detrimental effects on elimination. "Making zero-calorie drinks is easy for one major reason, namely that they are based on water. As one may expect drinking water doesn't result in any caloric intake. In fact, cold water is actually a negative-calorie drink since the body needs to expend energy to raise the temperature of the water to the equilibrium temperature of the body. Moreover it's possible to add certain additives like caffeine, or zero-calorie artificial sweeteners like [sucralose](https://en.wikipedia.org/wiki/Sucralose) while still allowing the drink to remain effectively calorie-neutral. + +With solid food the situation is a bit different. Most of the things we like to eat (and which are healthy for us to eat) result in a finite intake of energy. This should not be surprising since the kinds of things are bodies are designed to eat are generally foodstuffs from which we can draw energy since the major point of eating is to replenish the body's energy reserves. It is true that the body also needs to expand energy to digest food, called the [thermal effect of food](https://en.wikipedia.org/wiki/Specific_dynamic_action) (TEF), which reduces how much energy we gain from eating a quantity of a given food. However the TEF is usually fairly low, averaging about 10% or so, so in most cases it doesn't really come close to cancelling out the total number of calories in the food. + +Having said that, there are foods that result in a very, very small caloric intake. The trick is to choose foods that have both a low [energy density](https://en.wikipedia.org/wiki/Specific_energy#Energy_density_of_food) (kcals/Calories per g of food) as well as a high TEF. One of the best examples in this sense is celery, where each stalk only has [about 10 kcals](http://www.caloriecount.com/calories-celery-i11143?size=4%2520%2520celery%2520stalk) with a TEF of 20%, so you end up gaining 10 - 10*0.2 = 8 kcals/Calories. " +463 Do cables between Europe and the Americas have to account for the drift of the continents when being laid? 3363 https://www.reddit.com/r/askscience/comments/4riulr/do_cables_between_europe_and_the_americas_have_to/ 1467816795 4riulr Earth Sciences 2016-07-06 17:53:15 "I am in the submarine cable business, and can answer: No, there is not compensation as drift is inconsequential (2.5 cm or 1 inch per year). One reason is the bottom of the ocean is not flat - but has mountains and valleys like dry land, so extra cable is 'payed out' (let off the ship) to fill in the valleys so the cable isn't left suspended between peaks. Think of paying out rope from the back of a helicopter over the alps. If you just let out a meter for each meter of flight, the rope would be suspended across all the valleys. If there is any wind (equivalently sea currents for undersea cables) it would rub through the rope where it contacts the peaks. So the bottom line is there is excess cable laid just to accommodate the topography of the ocean bottom, so the inch/year is not an issue. + +Hope this helps!" There's probably some slack in addition to maintenance loops in the cable but comparing the timescales of continental drift to usable life of a cable, it shouldn't be a huge issue. Years down the road (if we haven't gotten better means of doing this) we will end up putting newer cables that support even more bandwidth, etc. +588 [physics] If the earth wasn't spinning would we feel the gravity more because of the lack of centrifugal forces? 3360 https://www.reddit.com/r/askscience/comments/51xg1l/physics_if_the_earth_wasnt_spinning_would_we_feel/ 1473428587 51xg1l Physics 2016-09-09 16:43:07 The centrifugal force, plus the reshaping of the Earth that it induces, amount to about [a 0.7% variation](https://www.physicsforums.com/insights/all-about-earths-gravity/) between the equator and the poles. So yes, we'd feel slightly more (except at the poles where it would imperceptibly less). "Something interesting and semi-related to this question - the fictional mega-structures [Halo rings](https://en.wikipedia.org/wiki/Halo_(megastructure\)) would have to spin with a tangental speed of 7 kilometers (4.3 mi) per second to match Earth's gravity, translating to 19.25 rotations in a day. + +[Here's a wonderful illustration of one for those curious.](http://teambeyond.net/wp-content/uploads/2014/10/Halo-Ring.jpg)" +1440 Why are some surfaces erasable after use of dry-erase (non-permanent) markers while some are not? 3359 https://www.reddit.com/r/askscience/comments/dpko6o/why_are_some_surfaces_erasable_after_use_of/ 1572511317 dpko6o 2019-10-31 11:41:57 "How porous and rough it is. + +Glass, very smooth paint, metal, plastic, all can be erased. On the opposite side, paper is too absorbent and brushed-on paint is too rough for the eraser to get into all the nooks and crannies. + +As an example, I worked at a tutoring center where you could write on the tables. Had these super-slick tables that were basically a whiteboard with legs. Center director tried painting this new non-whiteboard table with a special paint, but he used a brush, and the final result perserved the brush strokes, making it unusable. + +Looks like most whiteboards are made with a top coat of melamine (type of plastic), glass, paint, or porcelein." "Dry erase markers work by leaving a still-wet residue on the surface of an object. If the surface is too porous (such as paper), it'll get absorbed and bleed through, but since it's not on the very top layer, it's there forever. + +Most whiteboards are made with melamine, which keeps the board smooth allowing it to be erasable. It also turns the board white." +249 "Came across this ""fact"" while browsing the net. I call bullshit. Can science confirm?" 3354 https://www.reddit.com/r/askscience/comments/3j81fq/came_across_this_fact_while_browsing_the_net_i/ 1441117817 3j81fq Mathematics 2015-09-01 17:30:17 "This is absolutely correct. It's called the [Birthday Problem](https://en.wikipedia.org/wiki/Birthday_problem) and it's a well-known counter intuitive result. The reason it's counter intuitive is that since there's 365 days in the year, there's only a 1/365 chance that a random person has a birthday on a particular day; so, if you look pick a random person in the room there's only a 1/365 chance the other person has the same birthday as you. + +But, the problem only says that *some* pair of people in the room share a birthday, and there are lots of pairs of people. In fact, it you take a room of only 23 people, there's a total of 253 possible pairs, and any of them have a chance of having the same birthday. When you work through the probability you find the the sheer number of possible pairing balances the improbability of any particular pair sharing a birthday, resulting in a 50% chance of one match in a room of 23." "Well, if there are 23 people, there is actually a 50.7% chance that 2 of them have the same birthday, assuming that the 365 possible birthdays (not counting February 29) are all equally likely. But 23 people are the minimum number of people required to have at least a 50% chance. + +This is the famous [birthday problem](https://en.wikipedia.org/wiki/Birthday_problem), and the Wikipedia article does a good job in explaining the details. [This is a graph](http://www.chebfun.org/examples/fun/img/BirthdayOdds_02.png) of the probability of finding at least one pair of matching birthdays, as a function of the number of people in the party. Notice how quickly the function ramps up. Once you have 57 people, there is more than a 99% chance of their being a matching pair. + +Your confusion most likely lies in interpreting the problem incorrectly. A common misinterpretation is the following: ""what is the probability that someone in this room shares my birthday?"" Well, that is easily answered. If there are 22 other people in the room, the probability that no one shares your birthday is + +> q = (364/365)^(22) + +So the probability that at least one person shares your birthday is + +> p = 1 - q = 5.9% + +That seems to be reasonable. + +But the birthday problem is not asking that question. The birthday problem is asking: ""what is the chance that among these 23 people there is some pair that has the same birthday?"" So just because no one has your birthday, that doesn't mean no other 2 people can't have the same birthday. Maybe everyone in the room was born on March 5, except you. The answer to the birthday problem then means that if there are 23 people in a room, there is a about a 50-50 shot that some pair has the same birthday. (If there are 57 people, there is more than a 99% chance.) + +--- +**edit:** Someone below asked how the problem changes if birthdays are not assumed to be uniformly distributed by date. First of all, birthdays do *not* have a uniform distribution. More birthdays tend to occur at the end of summer, for instance (August/September for northern hemisphere or February/March for southern hemisphere). So how would the answer to the birthday problem change if we did not assume a uniform probability? Let's rephrase the problem slightly. + +> Fix the number *N* (say, of people) and consider the probability p(N) such that there exists at least one pair of persons that have the same birthday, if all birthdays are drawn from some fixed distribution, not necessarily the uniform distribution. + +We can then ask questions about how p(N) changes with the distribution. It turns out that p(N) is *minimized* precisely when the distribution is uniform. This means that non-uniform distributions tend to decrease the required number of people at a party to get a matching birthday. So the figure of 23 people is sufficient for a matching pair, no matter what the distribution is. In fact, if we had lumped February 29 into the normal year and assumed even that date to be equally likely (in other words, there are 366 equally like birthdays), the probability of a match at 23 people would be about 50.63%, still above 50%. Since the uniform distribution on the 366 probabilities maximizes the required number for a 50% match, we know 23 people suffices for all distributions, even those that include February 29 as a possible birthday. + +(IMO, the simplest proof that the uniform distribution minimizes p(N) can be found in the paper [""A note on the uniformity assumption in the birthday problem""](http://www.tandfonline.com/doi/abs/10.1080/00031305.1977.10479214?queryID=%24%7BresultBean.queryID%7D). The actual paper (which occupies less than one page) is behind a pay wall, but you can access it if you are affiliated with an academic institution. The DOI is 10.1080/00031305.1977.10479214. However, if you have some math background, you can prove the statement for yourself using the method of Lagrange multipliers.)" +250 We know of several carnivorous plants such as the Venus Flytrap. Are there any herbivorous plants? 3351 https://www.reddit.com/r/askscience/comments/3lsf88/we_know_of_several_carnivorous_plants_such_as_the/ 1442831494 3lsf88 Biology 2015-09-21 13:31:34 "Yes, they would be known as parasitic plants. The term herbivore is generally only used as a term for animals which consume autotrophs. Bacteria/fungi which consume plants would generally be known as plant pathogens. + +Parasitic plants however are flowering plants which live off other plants. Roughly 4,100 different species have been identified. They have modified root which penetrates into the xylem and phloem of the host plant, which is where it obtains water/sugars respectively. + + +There is actually one that almost everyone is very familiar with, mistletoe. Mistletoe is an obligatory parasitic plant." "We know of more than several carnivorous plants... there are actually hundreds of species and can be found on every continent except Antarctica, from the tropics to the tundra! + +In any case, there are some that it seems are ""herbivorous"" (more accurately detritivorous), most notably [*Nepenthes ampullaria*](http://en.wikipedia.org/wiki/Nepenthes_ampullaria#Carnivory), which catches falling leaves in its pitchers." +251 Why does this ping-pong pong ball get sucked in, when I blow out through this toy tube? 3350 https://www.reddit.com/r/askscience/comments/3r1qc7/why_does_this_pingpong_pong_ball_get_sucked_in/ 1446351396 3r1qc7 Physics 2015-11-01 7:16:36 "In fluid dynamics there is a principle called Bernoulli's Principle which states that a flowing fluid (here: air) creates a lower pressure compared to the still fluid around it. + +Of cause in this case it is surprising since you would think that the flowing air molecules would hit the ping pong ball and push it out of the socket, however the lowered pressure from the air that has to flow around the ball is enough to counteract both the ""push force"" from the air and gravity. + +https://en.wikipedia.org/wiki/Bernoulli's_principle" "Lot of wrong, incomplete, or misleading answers here. I'm late, but since this is the best-asked aerodynamics question in the history of /r/askscience, here goes. If there's anything I hate more than wrongly applied Bernoulli, it's citing the Coanda effect. I cringe every time. **For the love of God please stop mentioning Coanda.** After a handful of aeronautics degrees, reading dozens of aerodynamics books and god knows how many research papers and conference presentations, I have *never once* heard a practicing aerodynamicist mention Coanda. /rant + + + +* First, ELI5 explanation of how to interpret Bernoulli when you see a flow diagram. When streamlines (just a particle path if it's a steady flow) converge, this means the flow is accelerating (it has to because of conservation of mass.) When streamlines diverge, the flow is decelerating. Faster flow = lower pressure, slower flow = higher pressure. You can't exactly apply this to turbulent flow like in the following case without some further knowledge but let's forget that for now. + + +Now, onto visual aids: + + +* [This is what flow looks like past a sphere in open air, like a wind tunnel or outside, even flow going over it.](http://i.imgur.com/Vrgm5kv.jpg) That image is from ""An Album of Fluid Motion"" compilation by Milton Van Dyke. Incoming flow is basically pretty even, then heavily separates behind it creating quite a bit of low pressure turbulence. Pressure behind the sphere is lower than the oncoming flow, so it experiences drag (or would fly away with the wind if it wasn't held down.) + +* [This is a diagram of what's happening in your case](http://i.imgur.com/IVd690i.jpg) drawn by the wildly untalented me. Your lungs pushing out air are approximately at the same pressure as the ambient air (slightly higher, but don't worry about it). It's accelerating through a small hole creating lower-than-ambient-pressure. Now a **huge difference** in the geometry of this situation that you *don't* see in free air is that the toy forces the air through a very thin gap between the ball and the toy cylinder, including creating very fast flow on the side of oncoming flow, resulting in low pressure on that side (**much lower pressure than you'd see in free air, though that still has lower-than-ambient**). On the downwind side of the sphere, you'll have flow separation and a loss of pressure for sure, but not as much as the drop in pressure created on the upwind side. Without the toy there, you won't create enough pressure drop to suspend the ball from gravity." +346 "Could a planetary system be close enough to a nebula so as to have ""nebula-lit night sky?""" 3350 https://www.reddit.com/r/askscience/comments/47cqwa/could_a_planetary_system_be_close_enough_to_a/ 1456322916 47cqwa Astronomy 2016-02-24 17:08:36 "The most dramatic nebula images you generally see are those of [molecular clouds](https://www.nasa.gov/multimedia/imagegallery/image_feature_1146.html). These are star forming regions, which will form stars and planets. However, much of the gas is dissipated within 10s of millions of years by the radiation and winds from big bright short-lived stars, which is barely enough time to maybe have some planets form. + +But, in principle, there's no reason why a planet couldn't coincidentally happen to be near a molecular cloud, or even another nebula like a [planetary nebula](https://en.wikipedia.org/wiki/Planetary_nebula). + +However, the view will not be all that impressive. Nebulae are very thin and dim, and are only really visible because we use telescopes with very large collecting areas and very long exposure times. To a human eye, a nebula is just a faint grey-white cloud. It might look cool from a very dark area on Earth with excellent visibility, but from a town it would just look like the stars are a little bit dimmer than they would be otherwise." "Here's a simple rule of thumb. + +Consider an extended object, like a gas cloud. It takes up some amount of *surface area* in your sky. Now move twice as far away from it. The same patch of nebula now seems 1/4 as bright, but also has 1/4 the surface area in the sky it had before. Therefore, the *surface brightness in the sky* of extended objects is actually constant with distance. The reason they appear dimmer with more distance is simply because they take up less area in the sky (i.e. appear smaller). + +So find a nebula in the sky, with your *unaided eyes*. Imagine that the whole sky has the same brightness as that small patch which is the nebula. Voila, that's your answer. " +143 Why is the year 2100 not a leap year? 3349 http://www.reddit.com/r/askscience/comments/3gvxio/why_is_the_year_2100_not_a_leap_year/ 1439494610 3gvxio Astronomy 2015-08-13 22:36:50 "Leap years make up for the fact that a year is not exactly 365 days. + +Having one every four years works if the year is 365.25 days long, which is almost right, but not quite. If we had a leap day every 4 years, then after 400 years, we'd be off by about 3 days. So we want to eliminate 3 leap years -- so the years 2100, 2200, and 2300 won't be leap years, though 2000 was. + +So the rule is this: Years divisible by 400 are leaps years. Years divisible by 100 but not by 400 are NOT leap years. Years not divisible by 100 but divisible by 4 are leap years. Years not divisible by 4 are not leap years." "The purpose of a leap year is to make sure the calendar aligns with the time it takes for the earth to go around the sun. It is not a nice round number. + +I think it is 365.2425 days, roughly. + +The standard 1 extra day every 4 years makes it 365.25 on average. + +Removing a day every 100 years brings it back to 365.24 + +They also add an extra day back in once every 400 years to make it 365.2425" +144 What is the air inside a bell pepper composed of? 3349 http://www.reddit.com/r/askscience/comments/3cv9vl/what_is_the_air_inside_a_bell_pepper_composed_of/ 1436579084 3cv9vl Biology 2015-07-11 4:44:44 " Copied from an earlier question: source /u/danby + +For peppers, The air in the void mostly has the same composition as the atmosphere and the air got there largely by diffusion through the fruit's tissues as the fruit (and the space) grew bigger. +With regards peppers; wild peppers are small and fairly packed with seeds, so there isn't a lot of space inside them at all. What space there is is present because, unlike their close relatives the potato and tomato they don't fill the cavity of their fruits with a liquid or gel. I'm not sure it is understood why chilli fruits don't also have a gel filling the fruit's interior but I would hazard a guess that it is likely to do with the fact that capsaicin (the spicy chemical) is not (very) water soluble. +Coming back to the larger sweet or bell peppers, these have large interior spaces because humans bred these peppers to have large fruits with lots of flesh and clearly the mutations which were cultivated for these traits did not also increase the size of the seeds by the same proportion. + +https://www.reddit.com/r/askscience/comments/1ue4i9/the_air_inside_some_fruits_for_example_peppers + + +So I'm being original, here's what I get from it. +The air inside a pepper is the same as the air outside the pepper. Kinda how water from the ground becomes the water in the fruit, the air around the plant diffuses into the air inside the gaps. " No idea what all the crazy talk is here but there are small holes near the stem so air can flow freely. Seriously put a pepper under water and give it a gentle squeeze. +464 Discussion: Veritasium's newest YouTube video on the reproducibility crisis! 3348 https://www.reddit.com/r/askscience/comments/4x84e4/discussion_veritasiums_newest_youtube_video_on/ 1470924068 4x84e4 Mathematics 2016-08-11 17:01:08 "Do you think our fixation on the term ""significant"" is a problem? I've consciously shifted to using the term ""meaningful"" as much as possible, because you can have ""significant"" (at p < 0.05) results that aren't meaningful in any descriptive or prescriptive way." Which false positive discovery has had the biggest impact in human history? +252 Given their long lifespans, do turtles or bowhead whales get dementia? 3347 https://www.reddit.com/r/askscience/comments/3sa03m/given_their_long_lifespans_do_turtles_or_bowhead/ 1447166760 3sa03m Neuroscience 2015-11-10 17:46:00 "This is a really cool question. + +There seems to be an absence of research supporting the idea that these animals experience recognizable dementia; for example, this Society for Neuroscience conference abstract seems to suggest that new neurons continue to be born in turtle brains throughout the entire lifespan (http://eurekamag.com/research/035/470/035470297.php#close) and dolphins, another large-brained and long-lived animal, retain social memories for decades, or up to 75-100% of their average lifespan (http://rspb.royalsocietypublishing.org/content/280/1768/20131726?utm_source=HEADS-UP+9+-+15+AUG+2013&utm_campaign=SMC+Heads-Up&utm_medium=socialshare). Both of these are measures that are associated with cognitive and neuronal health. + +However, these results don't definitively say that dementia never occurs in these or similar species, and neither one examines dementia directly. + +One thing that future research in this area might help clarify, is what are the evolutionary factors that promote dementia and disorders that involve dementia. I would expect dementia to be like cancer; risk does go up with age, but there are also selection pressures and the physiological mechanisms they act upon that can change that level of risk. One reason I think bees are so interesting, for example, is that they actually show better learning and memory and more brain growth late in their lifespans, because that's when they perform the most learning-intensive behaviors, like foraging for food. Studying those organisms that are long-lived but don't experience dementia, if they are out there, could help us find ways to preserve brain health in older humans." Interesting question! There is definitely a lack of studies in this area. This National Geographic piece - while not specific to turtles and whales - discusses animals and aging http://voices.nationalgeographic.com/2013/09/13/do-animals-get-dementia-how-to-help-your-aging-pet/. /da +145 If you had a million mirrors placed in such a way that each would reflect off the next one, and you stand in front of one and move, would there be any lag between your movement and what appears on the final mirror? 3346 http://www.reddit.com/r/askscience/comments/3bqz11/if_you_had_a_million_mirrors_placed_in_such_a_way/ 1435756070 3bqz11 Physics 2015-07-01 16:07:50 "Yes. Light doesn't travel instantaneously, although it does travel pretty fast (3 x 10^8 m/s). From that speed you could calculate the lag depending on how far the light travels from one mirror to the other. The calculation would look something like: + +(distance from you to the mirror in meters + average distance the light travels from mirror to mirror in meters x (999,999))/(3 x 10^8 m/s) = _____ seconds of lag" "Yes. And something similar was actually used in 1848 to measure the speed of light. Although it only used one mirror*: +A light was aimed through the teeth of a cogwheel to a mirror a couple of km away at roughly the same position as the light there was an observer. When the wheel was not moving the light went from between the teeth of the wheel across a distance, bounced off the mirror, traveled back across the distance and between the teeth of the wheel to end up being seen by the observer. Now, when the cogwheel started spinning, there was a certain speed at which the returning light had taken enough time to now meet a tooth instead of a gap. If the wheel was sped up the light met a gap again and was observable again. With knowledge of the experimental geometry (distance, cogwheel size and number of teeth) and the rotational speed of the cogwheel, the speed of light could be calculated to within 0.6% of the modern value. + +*some simplifications (there were actually two mirrors.. ); + +More details here: https://en.wikipedia.org/wiki/Fizeau%E2%80%93Foucault_apparatus + +Edit: the accuracy was actually about within 5% of the modern value. " +347 If you were orbiting a black hole just a few feet outside the event horizon and you stuck your arm past, what would happen when you tried to pull it out? 3345 https://www.reddit.com/r/askscience/comments/43ilew/if_you_were_orbiting_a_black_hole_just_a_few_feet/ 1454235182 43ilew Physics 2016-01-31 13:13:02 "You cannot orbit that close to the horizon. The lowest bound on an orbit's periapsis (perinigricon?) is the photon sphere at 3/2 Schwarzschild radii. Lower, there are no stable orbits and all objects in free fall enter the horizon. + +You could imagine a rocket that kept you at a fixed Schwarzschild position by thrusting outwards, right above the horizon. This requires a proper acceleration that goes to infinity as you approach the horizon. So lowering your arm to the event horizon with the constraint that this rocket develops the necessary acceleration to keep your body out, your arm will be pulled with an arbitrarily large force as it approaches the horizon and will surely be ripped off at some point. This conclusion is independent of the parameters of the black hole or your rocket." "Gravity is usually the main conversation piece of a black hole. Magnetic effects are often neglected. In studies of PKS 1830-211, within a few light days of its black hole, there's magnetic fields with strength comparable to that of an MRI. + +In short, months or years before your arm ever got to the horizon, you and/or your ship would be flung wildly about. Possibly sucked into one of the polar gamma ray jets, and turned into a near-light-speed stream of elementary particles. Happy hunting." +589 When the LHC was created there was an expectation that it would lead to the discovery of the Higgs boson. Do we have any similar discoveries we are expecting to make in the near future? 3343 https://www.reddit.com/r/askscience/comments/57cogh/when_the_lhc_was_created_there_was_an_expectation/ 1476392836 57cogh Physics 2016-10-14 0:07:16 The James Webb Space Telescope (JWST) is launching in 2018. Just think about how much the Hubble Space Telescope has discovered in 20 years, and think of having a telescope with 7x more light collection. Plus JWST will work in infrared which is much more advantageous for seeing through dust clouds. With this we will get much more detailed findings on exoplanets and for the first time detect liquid water. "Single-molecule imaging is on the horizon at XFEL facilities. I'm not sure if anyone's suggested a timeframe at this stage, but a lot of people are talking about it. + +This would huge for structural biology as it would permit solving of protein structures that can't be crystallised (lots). " +253 The fastest spinning neutron star spins at 716 times a second. How much of the immense gravity would be counteracted by the centrifugal force? How many times earths gravity would an object on the surface experience? 3340 https://www.reddit.com/r/askscience/comments/3o49d6/the_fastest_spinning_neutron_star_spins_at_716/ 1444408572 3o49d6 Physics 2015-10-09 19:36:12 Just doing an order of magnitude calculation here: if a neutron star 1.4 times the mass of the sun is 10 km in radius and spinning 716 times per second, the gravitational field is 1.8 trillion m/s/s whereas the centrifugal force is about 10% that, at 200 billion m/s/s. This is an approximation of course. "I would like to trail off of this question with another; me and my boss had a disagreement when I told him about pulsars. + +He was saying he doesn't believe that the entire star is rotating around an axis. He told me that the definition of 'spinning/rotating' should be defined better after I told him about the extreme circumstances of its gravity and its density. He believes to be more of an energy wave traversing around the star, like a wave on the surface of water, that is emitting radio pulses, meaning the entity isn't rotating around itself but gives the appearance of such. + +Can anybody help me with this?" +590 At what point does a liquid become so viscous that it's considered a solid? 3337 https://www.reddit.com/r/askscience/comments/536gf2/at_what_point_does_a_liquid_become_so_viscous/ 1474101099 536gf2 Physics 2016-09-17 11:31:39 ">Is there some sort of cut off point, or what? + +In short, no. If it has a measurable viscosity, it isn't a ""true"" solid. + +The popular definitions of ""liquid"" and ""solid"" don't rigorously exist in the science of rheology, which is the field that deals with how things flow (or don't flow). + +Some things are purely viscous, and they clearly *behave* like liquids. Other things are purely elastic, and they clearly *behave* like solids. But a wide range of things have both viscous and elastic components, so they don't fall entirely under either definition. Some materials, called [complex fluids](https://en.wikipedia.org/wiki/Complex_fluid) can be a mixture of solids and liquids, and collectively behave much differently than the individual components." "TLDR: You can pick your criterion, but materials can exhibit flow despite being called solids and liquid materials can break like solids despite being able to ""flow"". + +There are some good answers here but I wanted to add some technical boundaries and explanations... + +As others have stated, a liquid colloquially means something that flows to fill the container around it under gravity. In materials science, a liquid is defined by a non-infinite zero shear viscosity, i.e. does it hold its own shape with infinitesimally small forces on it, much smaller than just gravity. + +In reality, materials typically exhibit a viscoelastic behavior, specifically, if you push on them for a ""short"" time they elastically deform and go back to their original shape, but if you keep pushing for a ""long"" time they plastically (permanently) deform. This is characterized by the storage (G' or ""G prime"") and loss (G'' or ""G double prime"") viscoelastic moduli. G' characterizes the elastic behavior while G'' characterizes the viscous behavior. These values are time dependent, but this is characterized as frequency dependent as typically measured by a [rheometer](https://en.wikipedia.org/wiki/Rheometer). In general, if you go to short enough timescales (high frequency) all materials will act as a solid, or even brittle, this is true for water, steel, honey, glass, etc. The timescale and frequency required for this just depends on the material. + +Colloquially, we look at liquids as things like water or honey, and solids like ice. These go through a melting point where the viscoelastic behavior undergoes a discontinuous change with changing temperatures. These are called 1st order transitions, where a discontinuous change occurs in thermodynamic properties with the 1st derivative (heat capacity etc.). This is in contrast to things like a glass transition which undergo a continuous change in the 1st derivative only showing a discontinuity in the second derivative, being clever, these are called second order transitions. + +Okay, actual numbers now... Water has a viscosity of 0.01 Poise (P) = 1cP at 20 C, Honey is ~100 P. Glass (silicon dioxide potentially with additives like soda and lime) is probably the best characterized and well known material that undergoes a liquid to solid transition that is not discontinuous. It also forms the basis for the characteristics of where **engineers** define liquids and solids. For glass, the ""melting point"" is defined where the material flows readily under its own weight or 10^2 P (like honey). The glass ""working point"" where you see glassblowers work is 10^4 P. The ""softening point"" (where it starts to deform at longer times^(minutes to hours) under some stress) is approximately 10^6 - 10^8 P (depends on who is defining it). The ""glass transition temperature"" or T*_g_* is defined at 10^13 P and the ""strain point"" is 10^14.5 P (where you can no longer anneal out stresses within the glass). See [here](http://www.glass-ts.com/temperature-viscosity). For reference, the strain point of window glass is at about 450 C whereas high temperature glasses may have a strain point near 650-700 C, and fused silica (pure SiO*_2_*) has a strain point of ~1070 C. For the glass connoisseurs out there, the Ficktive temperature has more to do with free volume than with viscosity. + +Random aside, the myth that glass flows at room temperature is false, old window panes were most commonly installed with the thick side down (though some were done opposite that), see [here](http://www.cmog.org/article/does-glass-flow) and many many other places. + +These definitions from the glass industry gives us a good start to look at. At T*_g_*, the viscosity is diverging and the material is said to be vitrifying (or vitrified at Tit doesnt make sense for bismuth to look like this when most crystalline metals are much less orderly structured. + + +Literally the definition of a crystal is that it has an ordered [e: repeating] long-range structure. You're right that we don't see the crystal structure very often, and that's because [e: many of] the things we see that are crystalline at the microscopic level are made up of many small crystals instead of a few big crystals. Generally speaking, the faster something is cooled, the smaller the crystals are. Bismuth has a low melting temperature, so it's relatively easy to cool it down slowly and end up with only a few relatively large crystals instead of a large number of small crystals. But the crystalline structure of other metals, like iron, is often visible. If you've ever seen sort of ""splotchy"" galvanized steel that looked [something like this](https://en.wikipedia.org/wiki/Hot-dip_galvanization#/media/File:Feuerverzinkte_Oberfl%C3%A4che.jpg), you've seen zinc crystals. You can see similar nickel-iron crystals in the [slice of this meteorite.](https://upload.wikimedia.org/wikipedia/commons/3/36/Widmanstatten_hand.jpg)" "First of all, the rainbow colors are interference effects stemming from a layer of bismuth oxide on the bismuth crystals. If the oxide layer is in the 200-500 nm range, it's index of refraction becomes strongly wavelength dependent because light at some wavelengths can form a standing wave inside the oxide layer, while this is impossible at other wavelengths. Clean Bismuth is just a dull gray metal. + +Anyway, onto the crystal structure. Because of it's unit cel, which is rectangular, bismuth prefers to grow into rectangular crystals, and if you pick the right growth conditions you just end up with a cube of bismuth. It will be a dull grey cube too, so not particularely interesting. However, under usual growth conditions, Bismuth undergoes what's known as [hopper crystal growth](https://en.wikipedia.org/wiki/Hopper_crystal). Basically, bismuth atoms prefer to attach to the edge of a growing crystal rather than the faces. The result is that the crystal never fills in, but instead you get a fractal structure that consists of a large number of steps. The steps are rectangular because bismuth strongly prefers that crystal morphology. + +[Here](http://66.media.tumblr.com/e98efc0c4339a0230cf199d363414b64/tumblr_nuczsbACud1tt8afro1_1280.jpg) is an example of naturally occuring Perovskite crystals showing the same kind of hopper crystal growth. + +If you get a similar growth mode in a crystal that doesn't have such a strong preference for a specific morphology, or if the driving force for crystal growth is much larger than in the hopper growth case, you get dendritic growth instead, which results in snowflake-like patterns, such as in [these](https://s-media-cache-ak0.pinimg.com/564x/f7/22/b9/f722b935623a6027c5f32e1714813a62.jpg) ammonium chloride crystals." +467 Why is it that certain creatures can consume rotting material (plants, animals) and thrive off it, but if I eat some meat or other substance that's a little bit spoiled I get sick? 3298 https://www.reddit.com/r/askscience/comments/4yym0n/why_is_it_that_certain_creatures_can_consume/ 1471835442 4yym0n Human Body 2016-08-22 6:10:42 ">Seeing as our stomach acid can deal with quite a bit, even having the ability to contribute to personal harm if the stomach isn't adequately protected, a simple organism can like bacteria can survive it and even cause harm to the host. Why is that? + +First, keep in mind bacteria are a very diverse branch of life, containing many extremophiles. The low pH in your stomach will kill many bacteria, but plenty of them will get through. Some, like [H. pylori](https://en.wikipedia.org/wiki/Helicobacter_pylori), actually thrive in your stomach at a low pH. Others, like E. coli, may not be able to grow at low pH values but [enough cells can survive](http://aem.asm.org/content/65/7/3048.full) a temporary exposure to low pH conditions that they can pass through your stomach and colonize your lower gut. + +Second, it isn't just live bacteria that are a threat in rotten food. Many bacteria that decompose meat, like [C. botulinum](https://en.wikipedia.org/wiki/Clostridium_botulinum), also produce toxins to prevent animals from eating the spoiled meat. That is why even cooking rotten meat won't necessarily make it safe to eat. + +Now to your main question: When we look at scavengers like vultures they can eat rotten meat that would kill us. I don't think we completely understand how they pull this trick off, but we have some clues. Scavengers and carnivores in general [have more acidic stomachs](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0134116) than herbivores do. Vultures can have a stomach pH [as low as 0](http://erie.wbu.com/content/show/25899), making their stomachs about 10x as acidic as our own. They also develop immune systems that can deal with these harmful bacteria. Pack animals like lions and hyenas can share small amounts of harmful bacteria to train their immune systems for when they get larger doses from rotten meat. + +There was a good [Minute Earth video](https://www.youtube.com/watch?v=GPJBw-TLYZQ) on this topic a little while ago that covers some of this as well. + +edit: clarified that low pH kills many bacteria but plenty can still survive it" "You are adapted to a certain diet. The adaptation has two major parts: + +1. Your digestive system has a certain design, optimized to an omnivore diet. For example, you can't break down cellulose unlike ruminants. + +2. You have a gut flora of bacteria, further optimizing you for a diet. This is why it is easy to get sick when traveling to a distant country and changing diet. + +There are a few reasons you can get sick by food. It may that it contains a large amount of something can't digest, such as plants, it may be that it contains toxins which have an effect on your gut flora (or yourself), or it may be that it contains bacteria which unbalances your gut flora. + +When it comes to spoiled food, it depends a lot on how it is spoiled. We eat many types of fermented food (https://en.wikipedia.org/wiki/List_of_fermented_foods), which in some way are spoiled. However, consuming random decomposing food is likely to contain a mixture of bacteria and toxins which does not play well with your gut flora. + +For the second question (how bacteria survive through the stomach), they have different strategies. Some build up cell walls which resists the acid, some produce ammonia to neutralize the acid. And some produce spores which are very resilient to the environment in general. " +1388 I just read about an 'Angel of Death' in Germany, are there programs tracking hospital deaths and the shifts of doctors and nurses, that could single out anomalies and point to possible murderers in the hospital wards? 3284 https://www.reddit.com/r/askscience/comments/boipq1/i_just_read_about_an_angel_of_death_in_germany/ 1557839314 boipq1 Medicine 2019-05-14 16:08:34 "At a hospital I worked, we had patient safety department ( and probably risk management department if any legal issues) which investigates every deaths in the hospital. I believe their focus is more on patient condition and their medical management, not particularly individuals who took care of the deceased. But since their charts are thoroughly reviewed, investigators would probably notice if there are such anomalies. + +Also, what this guy did in the article would be quite difficult now because of how medications are given nowadays. Every medication a nurse pulls out is recorded and monitored by pharmacy and nursing managers. Med pull records are scrutinized for variety of things. Opioid diversion is a big reason, but also to catch med errors. He used high risk meds that were not prescribed to the victims. There's no way such action would have gone unnoticed very long in modern system. + +Edit: grammar" "It's dangerous to flag anomalies too quickly. The line between a ""natural"" death and murder in a hospital ward can be really thin. Something that is flagged as a murder can then make any action of that nurse suspicious. Since a lot of people die in a hospital ward, they are pretty much guaranteed to be near other deaths. Given how quick people are to jump to conclusions, a tracking system is abusable, even if it works perfectly. + +This happened in the Netherlands in 2003 where a nurse was convicted for life for 9 murders based on statistical evidence. The odds of all these deaths being a coincidence was calculated to be 1 in 342m. The statistics were misused though (for example, they assumed all cases were actual murders) and later analysis showed that the actual odds were 1 in 3. Said nurse was acquitted in 2010." +23 How long could a submarine and its crew survive in space? 3282 http://www.reddit.com/r/askscience/comments/31dz1c/how_long_could_a_submarine_and_its_crew_survive/ 1428119990 31dz1c Engineering 2015-04-04 6:59:50 "Not very long at all. While they certainly have sufficient oxygen, CO2 scrubbers, power, and the hull will most likely be able to hold sufficient atmospheric pressure to keep the crew alive for a week or more, nuclear subs ultimately dump their reactor heat into the water. Without that water, they'll be cooked alive in a matter of hours. + +Edit: No, the freezing temperatures of space won't solve the problem. Think about a thermos. A thermos uses a vacuum layer between the inner container and the outer shell. This vacuum layer prevents loss of heat through conduction. A submarine in space would function the same way. You're basically living inside a thermos with a nuclear reactor for a roommate. + +Spacecraft are designed to cool themselves by radiative heat transfer. They can't cool by conduction because aside from the propellants they dump overboard, there is no matter to conduct the heat to. " "I know there are already a lot of answers, but here's the reality: + +1. *Electricity* Electricity on the sub is produced by steam powered electrical turbine generators. Those generators use steam produced by a nuclear reactor. There are several reasons the nuclear reactor wouldn't work in space because it's dependent on fluid flow, which may or may not be seriously affected by the lack of gravity. However, steam systems DO rely on condensers to condense steam after the turbines. Condensers work by pumping cold water from the ocean through tubes surrounded by the hot steam. The steam condenses as it cools and turns back to water. The newly condensed water is supposed to fall down to a pump, but without gravity it would sit in the condenser. Therefore, the steam system wouldn't work. Without the steam system electricity couldn't be produced. Subs do have large ship batteries as a back-up. But, that would only last a few hours tops. The diesel generator subs have wouldn't work because it needs outside oxygen to suck in, which there isn't any in space. So electrically, the sub could only survive for a few hours. + +2. *Oxygen*. Oxygen can be produced from water through electrolysis, which is what subs do in the ocean. But, electrolysis requires a lot of energy. With only the battery, the oxygen generator could only be run for maybe an hour or two. That wouldn't give much time for the crew. + +3. *Heat/Cold*. Space fluctuates between really hot and really cold. The ISS uses huge heat panels and ammonia to radiate the heat of electronics and machines into space. A sub doesn't have this. Instead, they have heat exchangers that dump heat into the ocean. But, in space, you don't have an ocean. So heat build up would be a huge problem. Pumps and environmental things cooled by the cooling systems would fail very fast - in a few hours more than likely. Not to mention, subs are mostly steel hulls. That steel is a great conductor of heat, so in the sun when the steel reached temperatures in the hundreds of degrees the crew would cook. In the shadow of the Earth the sub would freeze in sub zero temperatures. Needless to say, the crew wouldn't likely survive the extreme temperatures. So maybe a couple of orbits around the planet? + +4. *Escape*. Submarines do have escape suits that the crew can use to escape a sunken submarine. They work sorta okay to a few hundred feet, maybe. It's risky, but if certain death is on the sub, they're better than no option. The suits have a small O2 tank on them, but would never survive reentry and would almost certianly 'pop' when exposed to the vacuum of space. So the crew couldn't leave the sub without immediate death. + +5. *Air-tight vs Water-tight*. Believe it or not, water tight doesn't require air-tightness. So in a sub, certain valves are water tight but may not necessarily be air tight. That would mean the sub is constantly losing pressure. Pretty quickly the crew would experience high-altitude sickness followed by black outs from a lack of oxygen pressure. In line with this, the valves and hatches are designed to secure against higher pressures outside (the ocean puts more pressure on the hull inward than the air pressure inside pushes out). The hatches, for instance, seat truer when pressure is being pushed from outside. In space, the pressure in the sub would be higher which would tend to lift the hatches off their seats, allowing large amounts of air to escape around the hatch. The sub would probably lose air so fast that the crew would only survive for about 30 minutes before they started passing out. + +6. *Food and water*. Well, it's pretty well established that the crew would run out of air and electricity quickly, not to mention being cooked alive and then forced into a deep freeze. But let's say a few lucky sailors survived by locking themselves in the reactor compartment and insulating the walls with the bodies of their comrades. The reactor, when off, doesn't emit a LOT of radiation - you can stand next to it for a while before suffering ill effects. It does emit a small amount of heat when off from natural radioactive decay. So let's say that kept them warm in the cold shadows and the bodies kept them cool enough in the hot sun. Let's say they have some oxygen source, but not oxygen candles (we'll get to those in a minute), and let's say they grabbed all the food and spare water. With all the food, they'd be able to survive for months. The water would be less though. It would probably be only a few days before their water was depleted. + +7. *Oxygen Candles*. Candles that produce oxygen are called oxygen candles. They are another piece of emergency equipment in a sub. However, these aren't normal candles. They burn very hot. They don't have wicks like normal candles either. Things in space also burn weird. Without the gravity hot air doesn't migrate away from the burning surface, so fresh air doesn't replace the burning surface, meaning normal combustion doesn't work very well in space - candles will actually smother themselves in zero-g. Oxygen candles are different because they are self-oxidzing. But that heat doesn't spread away because there aren't convection cycles because there's no gravity. So that heat would build up around the candle. Eventually, the heat would be high enough to cause the entire candle to combust entirely at the same time. Essentially, it would explode and fling burning pieces of itself and container throughout the compartment and likely killing people inside. So O2 candles would be a very dangerous thing in space. + +Overall, a sub wouldn't survive very long in space. Maybe 30 minutes to an hour. Maybe even less. The answers below are all pretty good, but the real fact is that without electricity and the ocean a submarine is as good as dead. + +Source: Ex-submariner" +351 If got one atom to absolute zero, and I touched it, would it kill me? If not, how much matter at absolute zero would I need to touch? 3275 https://www.reddit.com/r/askscience/comments/4a9d4l/if_got_one_atom_to_absolute_zero_and_i_touched_it/ 1457893802 4a9d4l Chemistry 2016-03-13 21:30:02 "Hell no, in fact you wouldn't even come close to being able to feel it. First of all I feel obligated to mention that practically speaking we can't quite get down to 0K, but we can get down really low. For example, [the lowest temperature achieved in a lab](https://en.wikipedia.org/wiki/Lowest_temperature_recorded_on_Earth#Laboratory_cooling) was 100pK or 1\*10^(-10)K, which for all practical purposes (relevant to this question) we can say is effectively absolute zero. So what would happen if an atom of such a material got into your body? Well, it would quickly bounce around collecting energy until it reached your body temperature. To do so, it would suck out a whopping ~50meV, or the energy of an infrared photon (at 25,000nm). + +To give you an idea of how ridiculously little energy this is, every time you click your TV remote you get more than 10^22 photons at a higher energy/shorter wavelength (~1000nm) per second! Now put your remote next to your hand, do you feel anything at all? Now divide that by more than 10^22 to see how much that atom would hurt you. To really risk damage you would need to essentially get dunked a liquid at that temperature. For example, a quick shower in a bath of liquid nitrogen (at 77K) would quickly be the end of you. + +Put more simply, there is nothing particularly special about things that are really cold, the way they hurt you is by cooling you down and you need a lot material to remove enough energy from your body to hurt you." "In a nutshell, if we say the single atom has zero kinetic energy (unfortunately absolute zero is more complicated than this but we're just ballparking). The average atom/molecule at room temperature has about 0.0375 electronvolts of kinetic energy. So we can say that the absolute zero atom must ""steal"" 0.0375 electronvolts of energy from you to reach thermal equilibrium with you. So how much energy is that? + +Well, let's make the approximation that you're 100kg (220 pounds, it's just a nice round number) and made entirely of water (H2O). That means you're made of about 4*10^27 water molecules. Stealing 0.0375 electronvolts amounts to lowering the temperature of your body by..... 10^-25 of a degree. + +So coming in contact with such a particle would lower your body temperature by about 10 trillionths of a trillionth of a degree. So, no. Not only will it not kill you, it would be an extraordinarily boring event. + +EDIT: Lost a factor of two, fixed it, not that it matters when you're talking about 25 orders of magnitude." +352 Could Dinosaurs move their eyes? 3274 https://www.reddit.com/r/askscience/comments/47j3k2/could_dinosaurs_move_their_eyes/ 1456410388 47j3k2 Paleontology 2016-02-25 17:26:28 "Birds have [*limited* eye movement](https://en.wikipedia.org/wiki/Bird_vision#Anatomy_of_the_eye), primarily because their eyes are quite large relative to the size of their skulls. To compensate, birds have quite mobile head/neck regions (think of an owl's ability to turn its head upside down or swivel its head nearly 360 degrees). + +The other extant group of animals related to dinosaurs are crocodilians (crocs + dinos[birds are a clade within dinos] = [archosauria](https://en.wikipedia.org/wiki/Archosaur)). Crocodilians like alligators *can* move their eyes around, so we can hypothesize that dinosaurs (at least non-therapod dinosaurs) were likely to have had eye movement as well. + +But birds are not just flying therapods--they are really quite derived relative to their ancestors. Birds have much larger relative brain size than most therapods, something we can verify by checking out the fossil imprints of their brains in the form of [endocasts](http://www.livescience.com/41185-what-a-dinosaur-brain-looked-like.html). + +So: + +- Crocs are basal to dinosaurs-- CAN move eyes. We can reasonably hypothesize that the basal condition for dinosaurs was 'capable of eye movement.' +- Birds are descendants of *therapod* dinosaurs--limited eye movement. +- BUT Birds have larger brain size relative to body size, so a working hypothesis is that this increase in brain size reduced eye movement. +- If the hypothesis is true, then therapod dinosaurs likely had similar eye movements as other dinos, which we hypothesized were at least as mobile as crocs. + +*should be theropod, not therapod. My shame is great." "Raptors wouldn't have walked like chickens do now simply because the tail would give them a completely different center of balance. + +An experiment was actually done where chickens were raised with artificial elongated tails. You can see that the stride is longer and the leg motion is different. + +https://youtu.be/YMmgnpcaKyM" +1389 How does cancer spread? 3273 https://www.reddit.com/r/askscience/comments/c5682n/how_does_cancer_spread/ 1561457406 c5682n Human Body 2019-06-25 13:10:06 Cancer acts very differently from normal cells. Normally cells sit where they are, don’t multiply more than needed, need other cells around them to survive, and don’t damage or disrupt other tissues. When a precancerous growth becomes malignant, this changes. The cancerous cells will start to multiply out of control and will start invading other tissues (like melanoma growing deeper into the skin). Some of the cells develop the ability to live detached from others, and can invade blood vessels. When they do this they get carried through the bloodstream until they settle in some other area of the body, where they start multiplying again. "In order to spread (metastasize), cancer cells must detach from the primary tumor, invade into the circulatory (blood vessels) and lymphatic systems, evade immune attack, extravasate at distant capillary beds, and invade and proliferate in distant organs (such as bones in the case of prostate and some other cancers). +How cells manage to do each of these steps is very complex and the subject of intensive research." +148 As photosynthesis requires light, why aren't plants black to absorb the full spectrum of light, instead of green which doesn't? 3271 http://www.reddit.com/r/askscience/comments/352wvo/as_photosynthesis_requires_light_why_arent_plants/ 1430933589 352wvo Biology 2015-05-06 20:33:09 "A Black equivalent of Chlorophyll does exist - usually within Seaweed. + +This is because most plant life would overheat and their enzymes would denature if they were to absorb all spectra of light - therefore green is the commonly used colour as it reflects mid-energy photons and absorbs high energy (blue) light and lower energy (red) light" Interesting side note; there are LED lights out there (usually called 'ufo' lights) that only put out the blue/red spectrums of light, so the plants that they shine on are receiving all of the light that is being given off. If you are in a room with only these lights on the plants, the leaves of the plant look black, because there is no green-spectrum light to bounce off of them. It's pretty easy to deduce that the green light is what's being *reflected* after seeing this. +1266 Does launching projectiles significantly alter the orbit of Hayabusa2? 3271 https://www.reddit.com/r/askscience/comments/b9rgup/does_launching_projectiles_significantly_alter/ 1554472361 b9rgup Physics 2019-04-05 16:52:41 "You are right to think that the spacecraft would be dramatically affected by all the thrust from the shaped charge shooting the 2 kg copper projectile at the surface of the asteroid at 2 km/sec velocity. + +However, the clever engineers solved that by making the explosive device/cannon detachable from the main spacecraft. So it detached the cannon, and then put a camera in a position to record the violent experiment, and then parked itself on the other side of the asteroid to avoid any debris from the explosion causing damage. + +​ + + [https://spaceflightnow.com/2019/04/05/hayabusa-2-sci-operation/](https://spaceflightnow.com/2019/04/05/hayabusa-2-sci-operation/) " "Im a PhD student studying spacecraft optical navigation whose currently doing some work at NASA Goddard for the OSIRIS-REx mission (the ongoing NASA asteroid sample return mission). + +To give you a sense of how challenging small body missions are (that is, missions that go to asteroids and comets) virtually every force is non-negligible. + +In the case of OSIRIS-REx, the dominant force is solar radiation pressure. For our orbit determination we consider gravitational effects of all planets and major moons. We model solar radiation pressure using a shape model of the spacecraft. We model the Yarkovsky effect (that is, anisotropic thermal radiation emission which acts as a ""thrust"" generated by a temperature gradient on the spacecraft/asteroid). Even turning on the antenna to transmit back to earth causes a measurable perturbation to the trajectory! I mean, the orbital velocities around these objects is in the cm/s range. With the surface gravitational acceleration on Bennu being a million times weaker than Earth's surface gravity! + +So yes. Firing something like this would have a tremendous effect on the spacecraft trajectory. That being said, they detached the firing mechanism and ""hid"" on the far side of the asteroid, so it wasn't an issue. + +These kinds of small body missions are absolutely ridiculous from a navigation perspective! The amount of things to consider is truly unbelievable when you're operating so precisely around something so small. I can't directly speak for Hayabusa because I've never worked on it, but just from my work on OSIRIS-REx I can tell you these missions are truly insane " +468 Does the glass on a smartphone screen get thinner over time the more you touch it? 3270 https://www.reddit.com/r/askscience/comments/4jm1mt/does_the_glass_on_a_smartphone_screen_get_thinner/ 1463417169 4jm1mt Physics 2016-05-16 19:46:09 Technical yes. But the difference would be so small it would require precision instruments to measure. For example my iphone 5 still has the factory anti-fingerprint coating which was probably only microns thin to start with. "As other people have said, what you might be noticing is the films and coatings slightly degrading over time. Manufacturers usually add anti glare, anti smudge, or anti reflective coatings on top of the screens to reduce... Well glare, fingerprint smudge, and reflection. + +These coatings are generally much softer than the potassium hardened glass that most phone and tablet manufacturers use nowadays, you may have heard of gorilla glass which is an example of potassium hardened glass. And because of the composition of the coatings they can deteriorate over time. (Although if tested and applied properly they shouldnt noticeably degrade within the normal lifespan of a phone) + +Source: I am an Intern for a company the makes smartphones, tablets, and laptops. And part of my job is to test bew coatings and see if they can hold up and meet our standards. + +I also do some other materials testing for smartphones and laptops at my job so feel free to AMAA. + +" +591 Is it possible to calculate nth digit of pi for any n in a limited amount of memory? 3269 https://www.reddit.com/r/askscience/comments/56xq5h/is_it_possible_to_calculate_nth_digit_of_pi_for/ 1476188800 56xq5h Mathematics 2016-10-11 15:26:40 "There is a limit. + +The most famous digit calculation algorithm is the [BBP](https://en.wikipedia.org/wiki/Bailey%E2%80%93Borwein%E2%80%93Plouffe_formula) algorithm for pi. It calculates digits in base 16, but the basic idea is more or less what you need. + +However, the formula requires computing a polynomial of n. That will grow as [O(log(n))](https://en.wikipedia.org/wiki/Big_O_notation), at the least. Because log(n) -> infinity as n -> infinity, it will eventually fill your memory. Also note that this is already the space required simply to *store* n. The polynomial algorithm will require more memory in practice, but only a constant multiple more. + +However, the core algorithm can be stored in a small space and you could simply add O(log(n)) blank space to the calculation for each step. Then you could calculate any digit." "You can also answer this question with a theoretical thought experiment. + +Suppose you have an algorithm which produces the digits of pi one at a time. Like any computer algorithm this can be interpreted as a _state machine_ (or turing machine). The algorithm has some internal state (the memory) and in every computation step it produces a new digit of pie and and modifies the internal state by performing its computation. What the computation itself does i.e. what digit it produces and how it modifies the state depends entirely on the state at the beginning of the computation step. + +Suppose our state (our memory) has a size of _n_ bits (0 < n < infinity). There are 2^n possible distinct states for our machine which means that it can run at most for 2^n + 1 steps before it reaches a state it has already had previously. Since the produced digit and the next state depends on the state alone reaching a previously inhabited state means the sequence of digits start to *repeat*. + +As you surely are aware pi is an irrational number, i.e. infinite and not repeating. Therefore our algorithm cannot be able to compute *all* digits of pi, regardless of the size of _n_. + +This theoretical observation proves not only that there is no algorithm **known** which computes digits of pie in constant memory, but also that, as long as our computers are state machines, there **cannot exist** an algorithm which computes digits of pie in constant memory. + +To answer your question: It is **definitely** impossible." +469 Why are there holes in the ozone layer, as opposed to the ozone redistributing itself around the layer to be equally thin everywhere? 3264 https://www.reddit.com/r/askscience/comments/4uhxpu/why_are_there_holes_in_the_ozone_layer_as_opposed/ 1469442815 4uhxpu Chemistry 2016-07-25 13:33:35 This is due to a polar vortex, a rotating low pressure zone above both the north and south poles, that minimizes the air exchange above these regions. The vortex limits the inflow of ozone to the depleted regions. The polar vortex above Antarctica is typically stronger than the one above the arctic, hence the ozone hole over Antarctica is generally more severe than the one over the arctic. "The short answer: The time scale of the chemistry and dynamic processes that drive the ozone hole loss and recovery are shorter than the time it takes to uniformly mix the stratosphere. + +The longer answer: Stratospheric ozone depletion does happen everywhere. Roughly 4% of the total ozone layer has been lost due to human emissions of CFCs and other trace gases that react with sunlight to produce chemical gases that consume stratospheric ozone. Because these reactions are relatively slow, the loss occurs everywhere. + +The ""ozone hole"" is a special event of accelerated loss directly over Antarctica a few weeks each southern spring during which almost all ozone is lost. This occurs because strong circumpolar stratospheric winds exist (the ""Antarctic vortex"") that act as a barrier for the mixing of air from warmer latitudes. Temperatures get cold enough during winter that special ice clouds called polar stratospheric clouds (PSCs) form. The PSCs have surfaces that strongly accelerate the chemistry of ozone loss once the sun rises in spring. Then the Antarctic vortex reinforces the local hole by acting as a barrier against mixing of the low-ozone air with other latitudes. Once temperatures get too warm for PSCs each summer, the accelerated loss ends and ozone recovers over Antarctica. + +The Arctic has a weaker polar vortex, so is warmer and doesn't generate as many PSCs; therefore the accelerated loss phenomenon is less prone to happening in the Arctic." +258 The temperature in space is about 3K, however there are almost no atoms in space. My understanding is that heat is essentially atomic vibrations. If there are almost no atoms, how can there be residual heat? 3261 https://www.reddit.com/r/askscience/comments/3p434l/the_temperature_in_space_is_about_3k_however/ 1445091221 3p434l Physics 2015-10-17 17:13:41 "Heat can take a lot of forms. In the case of matter, it's the kinetic energy of the particles. In space, the temperature is determined by the energy density of photons. + +Put another way, if you put a block of matter in space and let it cool by radiating photons it will eventually find equilibrium at about 2.7 K. It will absorb energy from photons from the cosmic microwave background at the same rate that it emits photons, thus reaching equilibrium. " [deleted] +149 So human beings have tested 2,153 nuclear bombs in the last 75 years - but I was under the impression that that many bombs set off at once would basically end the species - what has been the long term effects of all that testing on the world at large? 3260 https://www.reddit.com/r/askscience/comments/3iptek/so_human_beings_have_tested_2153_nuclear_bombs_in/ 1440763302 3iptek Earth Sciences 2015-08-28 15:01:42 "Interesting that you should mention Bikini atoll. Although it was devastated by a nuclear blast, it is now one of the healthiest reefs in the Pacific. It has a high concentration of rare species and an amazing number of sharks and other large fishes, as well as things like giant clams. Certainly the islands were damaged by the radiation, and the persistent radiation is probably harming the remaining life. But more importantly is that the radiation has deterred people from coming to the area to fish. However bad radiation is, fishing is far worse, as are the wastes released by human habitation. You see similar effects around Chernobyl, which hosts large mammals that are difficult to find in the surrounding region. Honestly there are times that I think the best thing you could do for an area, environmentally speaking, is to dust it with radioactive waste. Not that nuclear waste is great for wildlife, it just does an excellent job of scaring off the people. It'd make a good movie villain plot, anyway. + +You can read more about Bikini atoll here from the ICUN, an organization which tracks conservation and plays a big role in managing endangered species on an international level. + +http://www.iucn.org/fr/propos/union/commissions/wcpa/?14948/Bikini-Atoll-Nuclear-Test-Site-Marshall-Islands" "The after effects of nuclear weapons are greatly exaggerated. A major exchange would probably destroy most existing human culture due to infrastructure disruption (without modern shipping almost all of us would starve in a few months) but our species has survived ice ages before so it's unlikely that we wouldn't survive another one. You wouldn't be able to live in the bombed areas for a long time but most of the world is empty land, look at this [picture of the us](https://www.kompulsa.com/wordpress/wp-content/uploads/2013/11/U.S_Population_Density_By_County.png), we probably wouldn't be able to live in the red parts, but that's not even a majority of the land space. + +When people talk about nuclear war destroying the world, they're talking about destroying the world as we know it. It probably wouldn't kill everything on the planet, just all the one's responsible with some collateral damage as well but it wouldn't be a total loss. " +150 Are all languages equally as 'effective'? 3255 http://www.reddit.com/r/askscience/comments/34zymp/are_all_languages_equally_as_effective/ 1430868320 34zymp Linguistics 2015-05-06 2:25:20 "Most of the replies you've gotten so far are perfect material for /r/badlinguistics. + +In general, linguists agree that no language is more or less complex than another overall, and *definitely* agree that all natural human languages are effective at communicating. This is in part because there's no agreed upon rubric for what constitutes ""complexity,"" and because there is a very strong pressure for *ineffective* language to be selected against. + +>Can very nuanced, subtle communication be lost in translation from one more 'complex' language to a simpler one? + +A few thoughts: + +(1) information can be lost in translation, yes. More often than not, it's 'flavor.' That is, social and pragmatic nuances, or how prosodic and phonological factors affect an utterance. Translated poetry, to give an obvious example, will either lose rhythmic feeling and rhyme, or be forced to fit a rhythm and rhyme at the expense of more direct or idiomatic translation. + + +(2) You would have to define complexity, before you could answer this. Every time I've seen a question like this, what the OP defines as complexity is just one way of communicating information, and the supposedly more complex language is less complex in other ways. For instance, communicating the syntactic role of a noun phrase can be achieved either through case marking, or through fixed word order. Which of these is more complex? Well, one's got structural requirements at the phrase level, another has morphological requirements at the word level. Or here's another example: think about Mandarin and English. Mandarin has fewer vowels than English. Is it therefore less complex? What about the fact that it has lexical tone that English lacks? + + +>Do different languages have varying degrees of 'effectiveness' in communicating? + +No. In general, you'll find that the people who argue they do (1) have not ever seriously studied linguistics, (2) tend not to know how global languages became global languages -- through colonization in the last few centuries, and (3) tend to want to support overly simplistic narratives that are based on ethnoracial or class prejudice. They're also often really poorly thought-out. For instance, I've seen a lot of arguments in this thread that English is somehow superior for math and science, claiming that speakers of other languages have to switch to English, or borrow words from English to do math or science -- while conveniently forgetting that English borrowed most of those words from Latin and Greek. And that the speakers of other languages they're holding as examples were educated in English in former English colonies, so they were taught math and science terminology in English rather than their home languages. + + + +I would link to peer reviewed papers, but this is so fundamental to the study of linguistics that I'm not even sure where to start, honestly. The claims that a given language is more complex than another, or better suited to abstract thought, or what have you have all gone the way of other racist pseudo-science,= like phrenology...which is to say, long gone from academia, but alive and well on reddit. ¯\\_(ツ)_/¯ + + +EDIT: I inadvertently put my last paragraph in the middle. Fixed. + + + +" I have a question to add to OP's. Is it easier for some people to learn certain languages than others? Like say would it be easier for a person who speaks English to learn Chinese than it would be for them to learn Arabic? I am sure that they could learn a Latin based language easier but what about completely different languages like that? +1390 AskScience AMA Series: I study the food web that lives within the leaves of carnivorous pitcher plants. AMA! 3255 https://www.reddit.com/r/askscience/comments/c8mq17/askscience_ama_series_i_study_the_food_web_that/ 1562151619 c8mq17 2019-07-03 14:00:19 The AMA will begin at 12pm Eastern Time, please do not answer questions for the guest till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Please keep questions and your interactions professional. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). "Fascinating work! Thank you for being here with us today. Here in the New Jersey Pine Barrens we also have a fair amount of carnivorous plants. + +What is the community composition within the pitcher plant? Any really surprising findings?" +24 Would it be possible for two people to grow together if they both were to cut off a hand/finger and then hold the wounds together? 3254 http://www.reddit.com/r/askscience/comments/2wb0lv/would_it_be_possible_for_two_people_to_grow/ 1424262830 2wb0lv Biology 2015-02-18 15:33:50 Ignoring practical issues like being able to brace the wounds together for the weeks it'd take to heal, you would have to go beyond just matching blood type--the two people would need matching HLA haplotypes or else each person's immune system would try to reject the other person's tissues. (There may be ways around this, for example if each person were put on immunosuppressants.) Perhaps it could happen with identical twins, whose HLAs would be perfect matches. "As a matter of fact, it is possible. It's called [Parabiosis](http://en.wikipedia.org/wiki/Parabiosis). But as some others here have explained, it would not work so easily in humans. + +almost every cell in the human body has a series of proteins known as [Human Leukocyte Antigens](http://en.wikipedia.org/wiki/Human_leukocyte_antigen), or ""HLA"" for short. These HLA proteins act like identification and inspection sites for the human body: Cells which lack them are targeted by natural killer cells (a type of white blood cell). HLA also function as a snapshot of what is inside the cell. You can imagine HLA like a hotdog bun, and inside the hotdog bun, the HLA presents a random protein segment from inside the cell. If that protein segment is something the immune system sees regularly, it will ignore it. If it is something odd or foreign, the immune system will attack it through a T-cell response. And if the HLA itself is a different setup, this will result in an attack as well. So in the example of non-identical humans, the T-cells of one human will attack the other. + +In rats and mice, however, scientists use historically inbred mouse lines that are nearly (if not completely) genetically identical, like the [C57/Black-6](http://en.wikipedia.org/wiki/C57BL/6) mouse. When we make a gene knockout mouse on this background, the only difference is the gene we are studying. + +**Parabiosis was a useful tool** in discovering how the adipokine [Leptin](http://en.wikipedia.org/wiki/Leptin) regulates satiety. In an intriguing experiment, scientists took two types of genetically altered mice with similar phenotype, and parabiosed them to see what happened. The Ob- mouse lacked ability to make Leptin, while the Db- mouse made leptin but lacked receptor for it. Both mice overate and became really, really fat. But when parabiosed, the Ob mouse lost weight, and the Db mouse remained fat. Interestingly, a wildtype mouse parabiosed to an Ob- mouse made the Ob-mouse lose weight, and a Db-mouse parabiosed to WT caused the WT mouse to lose weight and die. [This (SFW) image](http://www.diabesity.eu/images/parabiosismice.png) summarizes the findings, but through this mechanism, we discovered that Leptin (produced by fat cells) can inhibit food seeking behavior if the mechanism is preserved." +353 What is the highest resolution image of a star that is not the sun? 3250 https://www.reddit.com/r/askscience/comments/43pugr/what_is_the_highest_resolution_image_of_a_star/ 1454351655 43pugr Astronomy 2016-02-01 21:34:15 "Essentially the only telescope we have that can do this currently (in at least near infrared wavelengths) is the [CHARA interferometer](https://en.wikipedia.org/wiki/CHARA_array). See [this list](https://en.wikipedia.org/wiki/List_of_stars_with_resolved_images) of stars with resolved images and note that they've pretty much all been done with CHARA, specifically with the [Michigan InfraRed Combiner (MIRC)](https://www.lsa.umich.edu/mira/news/ci.johnmonnierstillpushingthelimitsofinterferometrymon26jan2015_ci.detail) instrument. + +It's an interferometer, so the images aren't quite as easy to create or interpret. They can do some reconstructions though and tried to make them look like normal images. Here's [Altair](https://i.ytimg.com/vi/LJ904blcZog/hqdefault.jpg). [These](https://www.lsa.umich.edu/UMICH/astro/Home/News/images/MIRC-Montage.jpg) are some of the only other images we have to date, using that MIRC instrument. + +Those are all infrared wavelengths though. **To my knowledge, the only visible wavelength resolved images of another star were done with Hubble of [Mira](http://apod.nasa.gov/apod/image/9708/mira_hst_big.jpg)** and in UV of [Betelgeuse](http://apod.nasa.gov/apod/image/9804/betelgeuse_hst_big.jpg)" "The [Very Large Telescope Array's Interferometer](https://en.wikipedia.org/wiki/Very_Large_Telescope#Interferometry_and_the_VLTI) can achieve an angular resolution of 0.08 milliarcseconds. I think this is about the best of any current instrument, and while it's not really used for producing images in this configuration, it gives some idea of what's possible. + +A star's brightness is roughly proportional to its apparent angular size (assuming equal temperature and black body these would be equivalent), so the brightest stars should also appear the largest. Vega, the old definition of magnitude 0, has a radius of 2.362-2.818 solar radii and is at a distance of 25.04 light years. This gives is an angular size of 2.881 milliarcseconds (thanks WolframAlpha: http://www.wolframalpha.com/input/?i=(diameter+of+vega+%2F+distance+to+vega)+convert+to+milliarcseconds) + +Dividing Vega's apparent size by the VLT's angular resolution gives us potentially 36 useful pixels across Vega. That said, I have not found any actual images of extrasolar stars showing any kind of detail. + + +Edit: Adding info from /u/ngc2307. A number of stars appear significantly larger than Vega, not surprisingly my error is in the equal temperature assumption. I knew it was wrong, but not *this* wrong. Probably the largest is R Doradus, a red giant with an apparent size of 68 milliarcseconds. [Here's a screwy interferometric image of it](https://en.wikipedia.org/wiki/R_Doradus#/media/File:R_Doradus_ESO.jpg). + +Altair has an apparent size of 3.2 milliarcseconds, about the same as Vega. [Here is a picture of it](http://en.es-static.us/upl/2009/06/altair_flattened_surface_details_Monnier-300x234.png)." +1441 If electrons behave as waves when they’re not observed and behave as particles when observed at microscopic scale, how can they behave as waves observed at eye scale? (Young experiment) 3248 https://www.reddit.com/r/askscience/comments/dbg2va/if_electrons_behave_as_waves_when_theyre_not/ 1569868780 dbg2va Physics 2019-09-30 21:39:40 "The concepts of particles and waves evolved in classical physics, however as quantum physics was developed, we discovered that those ideas were simply approximations. An electron isn't a particle; it isn't a wave. What is it? + +We can understand electrons only in terms of a new construct, something we might call a particle-wave or a wave-particle. It isn't a wave; it isn't a particle; it has some properties of each, however, the mixture is awfully bizarre. It moves through space like a wave; it responds to measurement like a particle; it's a wave that can carry mass and electric charge. It can spread, reflect and cancel itself, just as noise-cancelling headphones cancel sound waves. However, when you detect it, the event is generally sudden, abrupt. The detected electron continues to exist, however, the wave function has been decisively altered. If you detect it with a small instrument, the previously large wave function instantly becomes small. + +The ”duality” of wave-particle duality reflects the fact that if you persist in understanding the true nature of the electron in terms of particle and waves, then you have to consider it to be both. However, in reality, it's neither, it's something that is new (if you can apply that word to an over 100 years old idea)." [deleted] +592 Why don't we snore while awake? What changes in our breathing when we fall asleep? 3247 https://www.reddit.com/r/askscience/comments/5brobg/why_dont_we_snore_while_awake_what_changes_in_our/ 1478585911 5brobg Human Body 2016-11-08 9:18:31 "Respiratory therapy student checking in. There are a few factors which may compound with eachother causing symptoms ranging from simple snoring, to severe sleep apnea. As mentioned earlier, the snoring sound comes from a closing airway in the back of your mouth/throat. + +While we sleep we have different stages of sleep we cycle through every 90 minutes or so. The last of these is called REM sleep. During REM sleep our body is at its most relaxed and muscles that normally support the throat and tongue relax as well and collapse the airway. As air is forced past these now flappy tissues, they make sound we hear as snoring. + +Other factors which we look at are usually related to things that would cause the mouth and throat to be small. A small or recessed jaw doesnt allow for as much space to begin with. Obesity fills the neck area with fat pushing in on that space. + +To fix this we can use specialized mouth guards which pull the jaw forward, pulling the tongue forward with it, opening that space. CPAP machines use constant air pressure to force the airway open from the inside, enough to allow for adequate breathing. " "Some people do snore while awake! This is called stertor. It is usually associated with airway narrowing or loss of muscular tone. +The true question then becomes: Why do people snore more often when asleep? This is because our muscular tone is lower while sleeping. +In short, snoring/stertor comes from vibrations of the throat, palate or tongue. The Bernouilli effect causes tissue collapse and vibration (sound). This is most likely to happen with air flowing past narrowed, flaccid tissue. Our muscular tone decreases while sleeping which may lead to snoring or frank obstruction (obstructive apnea). +source: im a snoring surgeon" +151 What is the lowest temperature flame can be? 3245 http://www.reddit.com/r/askscience/comments/387r5x/what_is_the_lowest_temperature_flame_can_be/ 1433251838 387r5x Physics 2015-06-02 16:30:38 "[dioxygen_difluoride (FOOF) will ignite at 90K or -183 C](http://pipeline.corante.com/archives/2010/02/23/things_i_wont_work_with_dioxygen_difluoride.php) +From the article: ""When a drop of liquid 02F2 was added to liquid methane, cooled at 90°K., a white flame was produced instantaneously, which turned green upon further burning.""" "That is a tough question to answer, even having studied combustion for a few years in a graduate environment. I would define a flame to be a reaction which is propogated by a 2-d front within the fluid volume (not on a solid boundary). That is to say, the reaction is better represented by a 2d surface rather than a 3d volume. The reaction front can then be pushed around by the local fluid velocity. If you use this definition to determine the minimum possible flame temperature, you'd possibly look for two gasses (possibly liquids) which ignite on contact with each other, and release very little heat. I'm not a chemist, but I will say that finding such a combination would be difficult as reaction speed typically increases with energy being released. + +This leads to a second point: Combustion reactions (and therefore flames) also are characterized by a fairly large activation energy in comparison to their heat release (which is also typically large). This means that they depend on the heat release of their products to ignite new reaction. Again, I'm not a chemist, but to get to a super low flame temp, you'd have to investigate a wide variety of reactions here. I'd start by looking at reactions with the lowest possible autoignition temperature, and then cool them way below that so that their reaction gets them a few degrees above the autoignition temp. A diluent would maybe have to be added to get the temperature down. And the final temp would have to be sufficiently high that the reaction region is still thin (milimeters) enough to be considered a flame. A good place to start would be exotic fluorine molecules with autoignition Temps way below 0C. + +Again this is a very open ended question and depends heavily on the chemistry involved, but I wanted to clear, up a lot of the misinformation floating around here about what a flame actually is." +354 Is the sun soft or hard? 3245 https://www.reddit.com/r/askscience/comments/4f1y8b/is_the_sun_soft_or_hard/ 1460814349 4f1y8b Physics 2016-04-16 16:45:49 "To use your terminology, the edge of the Sun is rather soft. Take a look at [this graph of the matter density profile of the Sun](http://i.imgur.com/X63zYEK.png). Close to what we usually take to be the edge of the Sun, the density is about 10^(-4) g/cm^(3). This density is comparable to the density of our atmosphere on Earth at ground level. However, as you go deeper and deeper the density rises, until you get to the core where densities are on the order of 10^(2) g/cm^(3), which is about 10 times as dense as bulk gold. + +Of course, like you say this doesn't mean you have any chance of sailing through anywhere close to the core. The temperature is already thousands of K at the edge of the Sun and [quickly rises until it reaches more than a million K near the core](http://i.imgur.com/zBTlzq3.png). If that wasn't enough, you also have to deal with some [utterly crushing pressures](http://i.imgur.com/Bltc00L.png). For example, close to the core, pressures rise upwards of 10^(15)Pa, a pressure higher than what you may find at the center of the blast of a thermonuclear warhead. Needless to say no material we could dream up could withstand these conditions. + +Sources: The graphs are from [here](http://th.physik.uni-frankfurt.de/~scherer/) and the orders of magnitude from [Wikipedia](https://en.wikipedia.org/wiki/Orders_of_magnitude_%28pressure%29)" "So I found a [website](http://www.thesurfaceofthesun.com/index.html?) which talks about the sun having a solid surface beneath the photosphere described as a ""hard and rigid ferrite surface"", which goes against other models of the sun so far. Anyone have any further knowledge about this? Is this speculation or is there hard supporting evidence?" +152 Why do cows have multiple stomachs whereas horses do not, even though they both rely on eating and breaking down cellulose? 3241 http://www.reddit.com/r/askscience/comments/3bafwx/why_do_cows_have_multiple_stomachs_whereas_horses/ 1435396081 3bafwx Biology 2015-06-27 12:08:01 "Perissodactyls, or odd-toed ungulates (horses, tapirs), developed during a time--about 55mya (million years ago)--when broad leafed trees, herbs and some grasses had supplanted the conifers and ferns from an earlier era. They were very successful animals and enjoyed about 25 million years as dominant land herbivores. + +Later (~46mya), the artiodactyls or even-toed ungulates (sheep, goats and cattle, among others) were emerging. They lived in the fringes of the environment, in marginal habitats that the odd-toed ungulates didn't favor. They developed a complex digestive system with a multi-chambered stomach to help them subsist on the low grade foods they were forced to eat. + +Due to changing climatic conditions about 20-25mya, grasslands expanded, and the even-toed ungulates with their fancy digestive systems were poised to take advantage. They thrived and superseded the odd-toes as dominant land based herbivore. + +So, I think the answer to your question is: cows have ""multiple stomachs"" because they developed to eat the ""scraps"" found in the marginal environment that their (then) more successful rival the horse forced them into. The horse didn't need a highly complex digestive system to eat the foods it was accustomed to during its development. + +Edit: clarification (hopefully) and explanation of abbreviation (mya=million years ago)" "The primary digestive difference comes from what are called foregut fermentation (cows) and hindgut fermentation (horses). + +Horses have a cecum developed with bacteria that break down cellulose. Other similar animals that eat plants but have only one stomach have varying adaptations including longer GI tracts, but for horses, the cecum is the main event. + +Cows have multiple stomachs and chew cud (ruminate) to facilitate the bacterial breakdown, but the rechewing adds a mechanical benefit, since the hindgut is not developed in the same way as cows. + +Tl;dr horses have a cecum, cows chew lots. " +259 "Is it possible to feel ""high"" without using drugs?" 3239 https://www.reddit.com/r/askscience/comments/3uf103/is_it_possible_to_feel_high_without_using_drugs/ 1448590536 3uf103 Psychology 2015-11-27 5:15:36 "This thread has been locked. Please remember when you are commenting on askscience that we have very strict commenting guidelines in order to maintain the quality of conversation: + +* **Keep it scientific.** Answers should be based peer-reviewed journal articles and textbooks. Personal opinion is never relevant and should not be used as justification for a post. + +* **Refrain from speculation.** Do not guess. If you are unsure of an answer, ask a question instead. Uninformed (layman) speculation will be removed by the moderators. Our goal is to provide expert scientific responses to questions. Any speculation should come from those with strong scientific background in that field. + +* **Do not post anecdotes.** Anecdotes are by their very nature unscientific. At best they are amusing, and at worst they are inaccurate or misleading. Anecdotes are often enjoyable to read and can be enlightening - so much so that there’s many subreddits devoted almost exclusively to sharing them, including one of the biggest: /r/AskReddit. However, in AskScience our goal is employment of the scientific method, and an oft-quoted truism is that the plural of anecdote is not data. As we cannot verify the truth of a story, no accumulation of anecdotes is going to answer a question in a scientifically rigorous method. This includes posting personal medical information. Violations to this rule may result in a temporary ban. + +* **No medical advice.** Asking for or giving medical (or veterinary) advice is inappropriate. It is impossible to accurately procure and assess personal information over the internet without speculation. There are far too many variables that can lead to incorrect diagnoses and harmful advice. For more information, please see our policy on medical advice. Violations to this rule may result in a temporary ban. + +[For more information, please refer to our guidelines.](https://www.reddit.com/r/askscience/wiki/index#wiki_askscience_user_help_page)" "It is very possible to feel ""high"" without using psychoactive drugs. These feelings are caused by a temporary increase or divergence from homeostasis of endogenous neurotransmitters. Here are some ways an individual may feel ""high"" from a sober state: + +* **Sleep Deprivation**: We've all been there; after just one sleepless night, you may feel extra restless, jittery, and perhaps even *extra* happy. Individuals may even experience [*hypomania*](http://www.webmd.com/bipolar-disorder/guide/hypomania-mania-symptoms), a state characterized by elation and hyperactivity. [Researchers found that just one sleepless night increases dopamine in the striatum and the thalamus.](http://www.sfn.org/Press-Room/News-Release-Archives/2008/One-Sleepless-Night-Increases-Dopamine-in-the-Human-Brain?returnId={0C16364F-DB22-424A-849A-B7CF6FDCFE35}) +* **Runner's High**: Long-distance runners can experience a state of euphoria commonly referred to as the ""runner's high"". [Current models predict the ""high"" is caused by activation of the body's *opiod receptors*](http://cercor.oxfordjournals.org/content/18/11/2523.short), the same sites to which drugs like codeine, morphine, and oxycodone bind. [Other research suggests the endocannabinoid system may contribute to this state of well being](http://journals.lww.com/neuroreport/Abstract/2003/12020/Exercise_activates_the_endocannabinoid_system.15.aspx). Perhaps this feeling is a combination of the two systems working synergistically. +* **Falling in Love**: There's no feeling quite like being mutually in love with someone. It is no surprise, then, that researchers would try to explain the neurobiological basis of this feeling. In [this report](http://www.hdbp.org/psychiatria_danubina/pdf/dnb_vol26_sup1/dnb_vol26_sup1_266.pdf), researchers scanned the brains of people in love using fMRI and PET scans to measure levels of various neurotransmitters. They found that the feeling of love is contributed by an increase in hormones vasopressin and oxytocin -- known for playing central roles in human pair-bonding and (of course) an increase in the levels of dopamine in the nucleus accumbens. +* **Meditation**: [Meditation](http://www.freemeditation.com/meditation-basics/) can be described as ""a state of profound, deep peace that occurs when the mind is calm and silent"". Such practice is becoming a growing topic of interest in the field of neurological research. [One paper](https://www.ncbi.nlm.nih.gov/pubmed/9142560) found that ""With regards to identity state meditative experience was found to produce statistically significant changes in terms of intensity in meaning (P < 0.05), time sense (P < 0.05), joy (P < 0.05), love (P < 0.05) and state of awareness (P < 0.01)."" What does this mean? It implies meditation introduces a state of altered consciousness. These experiences may be similar, but distinct, from those caused by psychedelic drugs such as LSD-25 and psilocybin mushrooms. +* **Deprivation**: This includes both sensory deprivation and oxygen deprivation. Sensory deprivation tanks or *isolation* tanks operate by floating the subject in salt water at body temperature, resulting in a subjective feeling of floating and overall senselessness. Thus, these devices can be used to aid in meditation or as a vehicle for relaxation. This [has given way for use as an alternative therapy to treat pain and stress](http://www.ingentaconnect.com/content/sbp/sbp/2004/00000032/00000002/art00001). As far as oxygen deprivation goes, all methods pose some danger to the user and I do not recommend doing it, therefore I will not bother to elaborate. +* **Flow**: [Flow](https://en.wikipedia.org/wiki/Flow_(psychology), also known as *the zone* is a mental state in which a person is fully immersed and involved in doing an activity. Individuals can enter this state from performing challenging or attention-grabbing tasks, such as completing a puzzle, solving a difficult math problem, playing video games, etc. The possibilities from which a person can enter this state is endless. [In their paper published in *The Oxford Handbook of Positive Psychology*](http://www.enhancingpeople.com/paginas/master/Bibliografia_MCP/Biblio02/FLOW%20THEORY%20AND%20RESEARCH.pdf) researchers J. Nakamura and M. Csíkszentmihályi identified six factors as encompassing an experience of flow. Distortion of temporal experience (time dilation) [5], perceiving the experience as rewarding[6]? I would qualify this as being ""high"". + +>1. Intense and focused concentration on the present moment. + + >2. Merging of action and awareness. + +>3. A loss of reflective self-consciousness. + +>4. A sense of personal control or agency over the situation or activity. + +>5. A distortion of temporal experience, one's subjective experience of time is altered. + +>6. Experience of the activity as intrinsically rewarding, also referred to as autotelic experience. + + + +**TL;DR**: The term ""high"" refers to any altered state of consciousness. In a broader sense such states can also be achieved through exhaustion, pain, heat (sauna, sun, native American sweat lodges), music and dancing (rhythmic beating, drum circles), falling in love, the list goes on. Of course this will vary from person to person. So yes, changes to ones mental state can be made independent of substance use. + + +**Edit**: Formatting + +**Edit 2**: ~~Bah how could I forget to mention meditating! Experienced meditators can enter a state similar to those elicited by dissociative and psychedelic drugs. I'm on mobile but I'll add it to the list when I get back to a computer.~~ + +**Edit 3**: Added section on meditation. + +**Edit 4**: Added section on sensory deprivation. Thank you for all the support. + +**Edit 5**: Hello! Woke up to this thread being locked :( If you have any questions or suggestions for add ons, please PM me I will try to get to it. Added TL;DR. (SO to /u/Transfigurations) + +**Edit 6**: Added section on Flow." +470 Is there any biological reason why some people sing better than others? 3237 https://www.reddit.com/r/askscience/comments/4pr3nh/is_there_any_biological_reason_why_some_people/ 1466830815 4pr3nh Biology 2016-06-25 8:00:15 "There's a difference between singing in tune and sounding good. + +Singing in tune is a matter of practice. For some people it seems natural, because they've been listening to music and singing since they were a toddler. Practicing unintentionally. +Practically anyone can learn to sing in tune given enough practice. + +Sounding good is a mixture of things as mentioned in other posts here. People can be trained in styles of singing (see: opera) but ultimately the subtleties of their sound come down to physiological factors." "Not necessarily singing. Singing requires precise vocal and respiratory control and is in large part due to training. + +However, pitch is something different, and quite fascinating. The phenomenon of ['absolute pitch'](https://en.wikipedia.org/wiki/Absolute_pitch) (or 'perfect pitch') is one whereby the individual can instantly identify any note sounded, and often recreate it vocally. + +[A study in 2001](http://www.ncbi.nlm.nih.gov/pubmed/11707095) ([full text](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.420.7784&rep=rep1&type=pdf)) found that a region of the brain called the planum temporale is different in those with absolute pitch. The planum temporale is an interesting region in the brain -- it's one of the few areas which is asymmetrical from the left side to the right side (in general, structures on one side of the brain are mirrored in size and location in the other). It's located in the region of our brain primarily responsible for understanding speech ([Wernicke's Area](https://en.wikipedia.org/wiki/Wernicke%27s_area)), and is typically up to about 10 times larger in the left hemisphere than the right (especially in right-handed individuals, whereas the larger side is more random in left-handed individuals). + +One of the most interesting roles of the PT (along with other aspects of Wernicke's area) is in [Prosody](https://en.wikipedia.org/wiki/Prosody_(linguistics), which simply put is the emotional content of speech. Someone with damage to the right hemisphere's PT may have impaired prosody -- they can understand the semantic content of speech, but may be [impaired](http://www.ncbi.nlm.nih.gov/pubmed/7316838) in their ability to interpret nuance, subtlety, sarcasm, etc. + +How are the two linked? Well, interestingly, when you throw someone in an MRI and check which bits of their brain are ""lighting up"" when they listen to speech, you predominantly get the left hemisphere. When you have them listen to music, you get the [right hemisphere](http://www.ncbi.nlm.nih.gov/pubmed/15709930). This is evident even in [newborns](http://www.pnas.org/content/107/10/4758.full). The idea seems to be that our ability to interpret emotional valence in speech and our understanding and appreciation of music are linked. + +Back to the neurobiology of absolute pitch, though. The asymmetry is interesting in one particular aspect -- it appears to be the result of ""pruning"". Remember, musicians with absolute pitch tend to have PTs that are *more* asymmetrical than others. That is, their left PT is even bigger than normal compared to their right PT. It isn't due to an increase in the size of their left PT, but rather a reduction in the right. These results, in general, are fascinating but not particularly well replicated (some studies confirm the difference in PT asymmetry, others find it only between musicians and non-musicians). Regardless, there's a lot of evidence for [differences in brain anatomy](http://cercor.oxfordjournals.org/content/early/2013/12/04/cercor.bht334.full) between those with absolute pitch and those without, suggesting that there is a strong physiological basis for at least some aspects of musical talent. + +On a final note, I should mention that the above deals almost entirely with the ability to hear music, rather than produce it vocally. Understanding speech and producing it are two tasks which are handled by almost completely separate brain regions, and there's little overlap. The same is very likely true of something like pitch, and to some extent then, vocal singing ability." +260 When my earphones are plugged into my laptop (and nothing is playing) I hear a hum. If I touch any metal surface on the laptop, the hum stops. What is causing both effects? 3236 https://www.reddit.com/r/askscience/comments/3t5szb/when_my_earphones_are_plugged_into_my_laptop_and/ 1447771137 3t5szb Engineering 2015-11-17 17:38:57 "Considering that the hum goes away when you touch the computer, this suggests that its origin is improper grounding. All the appliances in your home, including your computer when it is charging, are hooked up to the grid, which feeds in an alternating current at a [specific frequency](https://en.wikipedia.org/wiki/Utility_frequency) (most commonly 50Hz or 60Hz depending on your location). For many types of electrical equipment to work properly, their components need to be maintained at the same electrical potential, which is obtained by connecting them to a common electrical reservoir, called the [electrical ground](https://en.wikipedia.org/wiki/Ground_%28electricity%29) (e.g. the Earth). When this grounding is done improperly, you can get a potential difference between the different parts of the system, which allows a current to flow in what is called a [ground loop](https://en.wikipedia.org/wiki/Ground_loop_%28electricity%29). + +This ground loop in turn allows the oscillations of the external current to couple to certain parts of your equipment. In your case, this low frequency signal is picked up by your head phones and become amplified, which produces the hum that you hear. However, when you touch the computer your body is acting as a big reservoir and effectively becomes the [electrical ground](https://en.wikipedia.org/wiki/Ground_%28electricity%29). By now properly grounding the system, you are no longer allowing the grid oscillation to feed into your headphones and the humming stops." "I bet the laptop is plugged into a charger? + +If so it is the 50Hz hum being generated by your house wiring through the charger. Try it when it is on batteries. + +It might mean your house wiring earth is not bonded correctly, or you might just have a poor quality charger." +25 If modern man came into existence 200k years ago, but modern day societies began about 10k years ago with the discoveries of agriculture and livestock, what the hell where they doing the other 190k years?? 3227 http://www.reddit.com/r/askscience/comments/2uxe2o/if_modern_man_came_into_existence_200k_years_ago/ 1423179855 2uxe2o Anthropology 2015-02-06 2:44:15 "They were hunting and gathering - the normal state of being for humans. Population densities were low, there wasn't much pressure to feed a lot of people confined in a small range. There was abundant game and wild foods. So there was really no need or reason to bother with planting or domesticating, and there weren't usually enough people around to build any large structures. + +It's not so much that they couldn't figure out how to domesticate animals or plants, it's just that it didn't make sense to bother going through the work when you could reliably get food from the wild. + +Here's a paper on the topic that posits a favorable climate encouraged population growth, followed by climatic downturn forcing people into higher population densities in remaining favorable locations--and that higher population densities spurred people to settle down and start planting things. + +https://www.aeaweb.org/assa/2006/0108_1300_0404.pdf" "Lots of people are suggesting a lot of hearsay. + +To clarify some points, it is widely accepted that anatomically modern humans would have possesed language every bit as expressive and complex as our own, so language acquisition almost certainly does not explain the technological transition to agriculture 14k years ago. + +For most of human history humans lived in tiny populations and were hunter gatherers, often nomadic too. There isn't much scope for storing knowledge during this period as you have to remember everything your group ""knows"". And there isn't much scope for coming up with lots of ideas as there aren't actually very many of you. + +One idea about the neolithic period and the agricultural transition is that it is the first time in human history where we reach critical mass intellectually. There's enough of us that we can store lots of knowledge via memory alone and there are enough of us that we're generating lots of ideas. Once both those are in place we've hit the point in history where good ideas can accumulate reliably and not just get lost/forgotten. + +This economics/anthropology paper is about this very idea + +http://www.jstor.org/discover/10.2307/2118405?sid=21105271099901&uid=4&uid=83&uid=2&uid=3738032&uid=2460337935&uid=2460338175&uid=63" +153 How deep into the Earth could humans drill with modern technology? 3227 http://www.reddit.com/r/askscience/comments/35dwyh/how_deep_into_the_earth_could_humans_drill_with/ 1431171320 35dwyh Earth Sciences 2015-05-09 14:35:20 "Driller here. + +There are three main issues. One is heat, and the other is pressure, and the final one is hole stability. + +Heat from geothermal sources, or just generated from the drill string, causes damage to the drill string components. Some companies have giant radiators that are installed on the surface to cool drilling fluid down before being pumped back down hole, but in the end the cumulative heat reduces the amount of time that is able to be spent downhole and drilling to less than 200 hours per trip. + +Pressure is another problem. As you get deeper, the pressure exerted on the formation from drilling fluid gets higher and higher. At the same time, the horsepower required to pump the drilling fluid back up to the surface becomes much greater. You would need enormously powerful pumps capable of generating as much as 10,000 psi. + +Finally you have hole stability. This is the ability of the hole to not collapse in on itself, potentially trapping the drill string and getting it stuck. To mitigate this problem casing is run through various sections of the hole. The problem is that every time you run casing, you have to then drill with a smaller drill bit and BHA/drill string. Eventually you can't run anything smaller and are at the limit of what can be reasonably drilled. + +The potential to drill deeper than 40,000 feet is there, but absent funding for such a project I find it hard to believe that anyone would undertake such an endeavor. It can be done deeper than 40,000 ft, but not by much. + +EDIT: RIP my inbox. Also, [apparently BP is developing very high pressure equipment (20k PSI) to enable very deep offshore wells](http://www.bp.com/en/global/corporate/about-bp/bp-and-technology/more-recovery/deepwater-frontiers.html) Thanks to /u/fanofdeja for that bit of info. + +EDIT 2: Gilded?! Thank you kind stranger." "The deepest drill hole for those curious is in Russia called [The Kola Deep] (http://en.m.wikipedia.org/wiki/Kola_Superdeep_Borehole). 12,262 vertical metres. + +Modern down hole drill technology has improved somewhat since then, so theoretically it might be able possible to go a further few 1-2,000m, but the cost would be horrendous and it is doubtful that any company would attempt it without a very good economic reason. + +Pressure, temperatures, the weight of the drill string as others have mentioned all start having serious effects. + +In terms of mining, most mineral (non oil and gas) drill holes don't go much deeper that 1,500m for the simple reason that it is cheaper to mine a decline, or put down a shaft and drill out the potential ore body of interest with a greater number of shallower holes. + +For example, a 1,000m diamond hole might cost in the region of $250-300,000 and take 4-8 weeks to finish depending upon the Rock, drill rig and several other variables. A 300m deep hole might run $35-45k and have a greater chance of success and take a week to two weeks. + +To drill out the potential ore body, you might need dozens to over a hundred holes depending upon the type of mineral and size of deposit." +26 If I wrap a cold object in several blankets, will the object stay cold longer? 3221 http://www.reddit.com/r/askscience/comments/32cmx4/if_i_wrap_a_cold_object_in_several_blankets_will/ 1428860581 32cmx4 Physics 2015-04-12 20:43:01 Back before refrigeration, it was common practice for people living in the north during winter to cut blocks of ice from lakes and store it in the cellar covered in sawdust. The sawdust was so effective an insulator that ice could be kept almost all year long. "Yes. + +Blankets don't ""trap heat"" as we're commonly told. The main mechanism through which blankets keep us warm is by preventing [convective heat transfer](http://en.wikipedia.org/wiki/Convective_heat_transfer). When you cover yourself with a blanket, it (mostly) prevents the air under the blanket from mixing with the air in the room. Your body heats the air under the blanket, and that air pocket remains trapped, so you feel warmer. + +This works in the exact same way for a cold object. The cold object cools the air in close proximity to it, and the blanket prevents that cold pocket from escaping and mixing with the warmer air of the room, which keeps the object cold longer." +27 Does the human eye have a quantifiable image resolution? 3217 http://www.reddit.com/r/askscience/comments/2u3oum/does_the_human_eye_have_a_quantifiable_image/ 1422553861 2u3oum Biology 2015-01-29 20:51:01 "Yes. It's called [visual acuity](https://en.wikipedia.org/wiki/Visual_acuity ), typically about 1 arcminute (1/60th of a degree). + +However, the eye is not at all like a camera you can assess in terms like megapixels. The resolution isn't uniform, it's only that high in the center of view. The eye also has a ""blind spot"" where the nerves go out that has no sensing cells. + +The eye makes up for this uneven resolution with super-deluxe image processing hardware that's capable of some very big apparent improvements. The eye moves a little all the time in what are called [saccades](https://en.wikipedia.org/wiki/Saccade ) the information from which is fused in [Transsaccadic memory](https://en.wikipedia.org/wiki/Transsaccadic_memory ) to form the ""pictures"" we perceive of the world we see. You can use [Johnson's Criteria](https://en.wikipedia.org/wiki/Johnson%27s_criteria ) to understand the difference between something the eye can detect and something you can see. " "A video you might find interesting on this subject + +http://youtu.be/4I5Q3UXkGd0" +154 Does any animal have a life span so short that it never sleeps? 3217 http://www.reddit.com/r/askscience/comments/38ly3f/does_any_animal_have_a_life_span_so_short_that_it/ 1433469895 38ly3f Biology 2015-06-05 5:04:55 "Anglerfish males. They don't sleep or even eat. In fact, they don't have the organs to do so even if they wanted. + +They hatch and have to find a female in a short period of time. If they don't, they die. If they do, they fuse into the females and survive as a parasite. Most of their body parts die off, except for the reproductive organs which the female can use whenever she needs." "Dolphins have an interesting sleep cycle as they would drown if they were ever totally unconscious. They shut down one half of their brain at a time, closing the corresponding eye. Whales, Orcas and Porpoises sleep in the same ""Unihemispheric slow wave sleep"" manner. + +This is not due to life-span but they are never fully unconcious. + +Source: http://www.livescience.com/44822-how-do-dolphins-sleep.html" +355 "When I'm in an area with ""spotty"" phone/data service and my signal goes in and out even though I'm keeping my phone perfectly still, what is happening? Are the radio waves moving around randomly like the wind?" 3217 https://www.reddit.com/r/askscience/comments/46fnlj/when_im_in_an_area_with_spotty_phonedata_service/ 1455814021 46fnlj Engineering 2016-02-18 19:47:01 "The waves are constantly reflecting off of things. As birds, traffic, people, clouds, etc. move around between the tower and you, the strength of those waves will change. Not an issue when you're in an area with a strong enough signal because it is reaching your antenna from many different directions, but if you're right on the edge of a useable signal someone walking into the room between you and the tower can potentially deaden the signal enough to matter. + +Related fun fact, some crazy kids at MIT figured out how to leverage this behavior to let you [see through walls with a wifi signal!](http://people.csail.mit.edu/fadel/wivi/) + +Edit: Stupid typo" "Imagine you are at a party and are trying to listen in on a conversation across the room. If those voices were the only sounds in the room, you could prob'ly hear it. But they aren't. Other people who are closer will sound louder. And, they aren't talking at a constant drone. There are pauses when they stop, and their voices might be come louder when they are trying to emphasize something or laughing. With the constant change in volume around you, you might be able to catch bits and pieces of that one conversation across the room, but mostly it will be drowned out. + +Your cell phone and the tower you are connected to aren't the only radio waves hitting your antenna. There are other phones and other towers. There maybe WIFI routers and laptops. There are actual radio and TV towers broadcasting. Sure, these are at different wavelengths, but there is still interference. There are even radio waves coming in from the sun... That's why radio stations can be heard from farther away at night." +356 Is it true that even if Antarctica were to melt it wouldn't cause flooding due to water displacement? 3215 https://www.reddit.com/r/askscience/comments/4bmzei/is_it_true_that_even_if_antarctica_were_to_melt/ 1458747380 4bmzei Physics 2016-03-23 18:36:20 "Hi, Antarctic oceanographer here. There are several ways to interpret your question, so I'm going to break it down and answer each: + +* What happens when Antarctic sea ice melts? +If Antarctic sea ice melted, it would not have a significant direct effect on flooding/sea level rise (SLR). As [\u\crnaruka](https://www.reddit.com/r/askscience/comments/4bmzei/is_it_true_that_even_if_antarctica_were_to_melt/d1ankev) pointed out, there is a small effect (4-6 cm of SLR), due to the freshwater content of the ice versus the sea, i.e., more volume per mass. + +There are indirect effects, such as changes in albedo: sea ice reflects sunlight more than the ocean, changing the amount of heat uptake by the ocean, which can change the rate at which ice melts. + +* What happens when Antarctic ice *shelves* melt? +Ice shelves are floating, and thus would have a similar effect as sea ice - minor additions based on density differences. However, recent research suggests that ice shelves play a crucial role in ""buttressing"" the Antarctic ice sheet. Essentially, if an ice shelf were to melt too much, there would no longer be a ""plug"" to stop the ice sheet from draining off the continent. The buttressing effect is not 100% understood, but can depend on the slope of the bedrock under the ice sheet, and the grounding line (the place where the ice sheet leaves land and becomes an ice shelf). + +[More info on ice shelves around Antarctica.](http://www.antarcticglaciers.org/glaciers-and-climate/shrinking-ice-shelves/ice-shelves/) + +* What happens when Antarctic ice *sheets* melt? +Ice sheets are ice on land, so melting would directly add to sea level rise. If the entire Antarctic Ice Sheet melted, it would add appoximately [60 meters](http://www.antarcticglaciers.org/2013/01/antarcticas-contribution-to-global-sea-level-rise/) to sea level. + +As a final note, I'd like to point out that this is very much an active area of research. Not only determing the amount Antarctic ice contributes to sea level rise, but also how ice sheets, ice shelves, and the ocean interact. A big push/race now is to fully couple ocean models with ice shelf/sheet models to get a better idea of how ice sheets will impact and be impacted by future climate. If you've browsed the latest [IPCC report](https://www.ipcc.ch/report/ar5/), the contribution by ice sheets to sea level rise is NOT calculated in any of the climate models, but is a large uncertainty added to the projections. + +EDIT: Formatting + +EDIT 2: [Great TL;DR on Antarctic ice sheets from a glaciologist](https://www.reddit.com/r/askscience/comments/4bmzei/is_it_true_that_even_if_antarctica_were_to_melt/d1b24o0) + +EDIT 3: Several people have been asking about land rebound (after the weight of the ice is gone). This is known as glacial isostatic adjustment (GIA), and occurs on timescales of thousands to tens of thousands of years. The earth is still adjusting from the last ice age. [Here's some info on past GIA](http://oceanservice.noaa.gov/facts/glacial-adjustment.html) that will give you an idea of future GIA for Antarctica." "It's the other pole you're thinking of. + +Ice melting will only contribute to sea level rise if it is land-based ice. Antarctica and Greenland house two HUGE concentrations of land-based ice. If they melted, sea levels would definitely rise. + +The North Polar ice cap, on the other hand, isn't on land, it's frozen ocean, floating on top of the water. The oceans are already ""bearing the weight"" of that ice, so if it melted, it wouldn't impact sea levels at all. (Of course, whatever caused it to melt would probably have other consequences, like melting some of Greenland's ice…) + +To see the effect for yourself, pour some water in a painters tray (the kind for a paint roller.) Only about halfway up. Then put a bunch of ice cubes in the water. The level of the water is like the North Pole - the ice is floating. Mark the level of the water, then wait for the ice to melt. It should be at nearly the same level. + +Then try the same thing, but put the ice on the ""ramp"" part of the tray, above the water line. When the ice melts, the water line will have gone up noticeably. That's like Greenland/Antarctica. " +28 "Why are deep sea fishs ""uglier"" and less symmetrical then their higher sea counterparts?" 3212 http://www.reddit.com/r/askscience/comments/2rhsu0/why_are_deep_sea_fishs_uglier_and_less/ 1420529654 2rhsu0 Biology 2015-01-06 10:34:14 "Interesting question. I published a paper on this a couple of years ago, so I'll try and summarize what we found (and bear in mind that other opinions may vary!). Basically, the overarching factor for fish in the deep seas is scarcity of food. As a result, there's a selective pressure towards extreme efficiency in swimming mode. As you go deeper, the fish community changes composition towards longer and more eel-like species - we proved this with data, and you can see the same trend within families. As active ""hunting"" predation becomes difficult if the ability to accelerate quickly to capture prey is impaired by this morphology, other adaptations to improve success in ambush encounters like the ""snaggle-toothed"" mouths or voluminous stomachs, or improve odds of escape like being very spiny or being armored, start to make sense. We proposed that this explains some of the macro patterns in fish diversity, such as the absense of sharks from abyssal waters due to the inherent ""sharkiness"" of their body plan, while their cousins the chimeras, with their whippy tails and spiny fins but similar biochemsitry, are found deeper. If you look at data from seamounts, you do see more characteristically ""fishy"" shaped fish, like roughies and alfonsinos, at depth, but the greater trophic flux from the surface to the deep which the mount provides probably explains this. + +Edit: Ok, by popular demand I've uploaded a pre-print [here](https://pdf.yt/d/p07zU9T1tpyOLiio). Ironically, I can't access the published version of my own paper as the institute I work for now doesn't have a subscription. Down with the traditional publishing model, etc." I work with deep sea ROVs (remotely operated vehicles). IMHO, most of the fish look like normal fish, but with larger eyes and other minor in appearance but major in usefulness differences. Like tripod fish, normal fish with longer fins that they balance on. I think part of the problem is that the strange, but often rarely observed fish get the most media play and attention. The vast majority of what we see are things like cusk eels. Not the most visually exciting fish... +1267 Does dark energy actually exert a force? Is it actually energy? 3201 https://www.reddit.com/r/askscience/comments/b4uzzo/does_dark_energy_actually_exert_a_force_is_it/ 1553423917 b4uzzo Astronomy 2019-03-24 13:38:37 "We've noticed that the expansion of the universe is accelerating but can see no reason why this would be. With no source, we named the root of the cause Dark Energy and have been trying to find what it actually is + +Same with Dark Matter. We see the effects of extra mass that we can't see, so we call it Dark Matter" "Dark Energy is something we observe the effects of but we don't have a good explanation for: hence the ""dark"" moniker. Specifically what we can observe (and measure rather precisely) is that the universe is expanding faster and faster. This is a rather baffling phenomena, and yes it does imply some sort of ""energy"" in a real sense. We can even measure just how much energy it would take to produce acceleration we've measured. + +The current leading idea for where that energy comes from is that the empty vacuum of space itself emits a very low constant amount of energy. In the presence of any significant amount of matter (like a galaxy), this energy would be overpowered by gravity and not have a noticeable effect. However, in the empty space between galaxies, it would be enough to drive them apart. And the further apart they are, the more empty space, the more energy forcing them apart, the faster the expansion. + +I think the negative mass theory you are referring to is the [recent paper](https://cosmosmagazine.com/space/could-negative-mass-unify-dark-matter-dark-energy) that has been making the rounds theorizing that the effects of both Dark Energy and Dark Matter could be explained by negative mass spawning continuously in deep space. It is an interesting conjecture, but it is very far from accepted science. It introduces a number of problems, including yeah, negative mass allows for FTL and breaking causality and no end of other nonsense." +593 "Why _exactly_ does my microwave ""kill"" my internet?" 3200 https://www.reddit.com/r/askscience/comments/54q23q/why_exactly_does_my_microwave_kill_my_internet/ 1474974609 54q23q Physics 2016-09-27 14:10:09 "Both microwaves and wifi routers (except when using the newer connection types) transmit at a frequency of 2.4 GHz. + +Normally, a microwave is shielded to prevent the radiation from leaking out. After all, the radiation is supposed to stay inside the oven to heat the contents, not to slip out into the room. However, old or damaged microwave ovens may not be perfectly shielded, allowing some radiation to leak out. + +Now, microwaves operate at a far higher power level than wifi routers. Wifi routers aren't made to cook food, microwaves are, so far more power is needed. To compare, a microwave will use somewhere in the neighbourhood of 1 kW (1000 W), while a wifi router will be around 100 mW (0.1 W). So even a small leak in the shielding of a microwave can cause the leaked radiation to be as strong or stronger than what the router is transmitting. + +And why does it kill your internet connection? Try talking with someone close to a running jet engine. Notice how that doesn't work too well? The same is true in the microwave/router case. The wifi devices pick up the radiation from the microwave and this noise is drowning out the signal from the router." "You can compare the waves from the wi-fi and microwave to sound waves. + +Microwaves are normally shielded in order to contain the waves inside but older or crappier units leak some of it. + + Since the microwave oven is far more powerful than the wi-fi (it needs to be powerful enough to cook stuff) even that small leak can be enough to drown out the wi-fi signal. Think about trying to talk to someone at a loud concert - the music will drown out your voice making it very difficult to be heard. Same thing happens with wi-fi" +1268 Why do Auroras change colours? Why are some colours rarer than others? 3199 https://www.reddit.com/r/askscience/comments/ay9qhp/why_do_auroras_change_colours_why_are_some/ 1551941718 ay9qhp Astronomy 2019-03-07 9:55:18 [deleted] "I'm an aurora physicist. The colors of the aurora that you typically can see with your naked eye are green and red. On rare occasions, you can see blue and a purplish-red as well, but typically only during very intense storms. + +Un-edited photographs will show off the colors better. It should be noted that many of the colors you see in photographs are there because the color sliders have been tweaked, not because those colors actually occur. The main body of the aurora will almost always be green, not the greenish-blue color that a lot of photoshoppers use to bring out the other colors. + +The two main constituents of our atmosphere that produce the colors are atomic Oxygen (O) and Nitrogen (N). Because of quantum mechanics that I won't get too deep into, atoms tend to fluoresce at very particular wavelengths when exposed to energy. When energy from the solar wind enters from Earth's magnetosphere at high latitudes, it excites those O and N atoms. + +Because Oxygen is far more dense than Nitrogen at high altitudes, we see the green and red even during the weaker magnetic events. The green emission occurs between 100 and 130 km, usually, while the red emission comes from between 220 and 280 km. + +The reason for this altitude separation is due to the energy of the precipitating particles. While both red and green emissions come from Oxygen, the amount of energy that is being put into each individual particle is different. The higher a particle's energy, the deeper that particle can penetrate into Earth's atmosphere before losing all its energy. So, higher-energy particles go deeper into the atmosphere (lower altitude) and produce the green emission. Softer particles get stopped at higher altitudes and produce the red emission. + +During all of this, the Nitrogen is getting excited at lower altitudes as well. However, because there are simply fewer Nitrogen particles, the intensity of the blue/purple emissions are much lower than we can see, except during the most intense magnetic events. Long-exposure cameras with filters can capture this. + +The auroras I've discussed above are due to collisions with electrons, which are the most abundant particles precipitating into the lower atmosphere. However, protons can also precipitate (the solar wind is a bunch of individual protons and electrons). These will produce a different color of aurora that is generally quite weak and only visible to very specialized filtered cameras. It's sort of bluish-green. + +[Here](http://optics.gi.alaska.edu/realtime/data/PKR_DMSP/Keo_15hr/Keo_15hr/2013/PKR_Keo_15hr_2013-12-08.png) is a link an example of a ""keogram"" plot from the University of Alaska Fairbanks. I've actually published quite a lot of analysis on this particular night. + +From top to bottom you have: Green Oxygen line (5577-angstrom wavelength), Blue Nitrogen (4278), Proton Aurora (4861), and Red Oxygen line (6300). + +Note that the scales are different. Green looks weaker than red here, but the scale differs by a factor of 10 (I didn't make these plots!). The scale between green and blue is also a factor of 10 different; however, blue *still* looks weaker than green. That is a good illustration of just how much more intense the green emission usually is than everything else. You can see that the green and blue do follow roughly the same patterns, though, which is indicative that they occur due to the same precipitation effects. Oxygen is just so much more dense than Nitrogen that it dominates. + +This night was particularly interesting for how much red emission was produced. It was ideal for my science, which was looking at the region near 250 km, where the red emission occurs. The precipitation energies on this night were fairly weak, which produced lots of emissions at higher altitudes. The proton aurora was also pretty intense, relatively speaking. You don't usually see so much of it. + +TLDR: The aurora doesn't ""change colors"" in an exact sense. Red aurora is not the same aurora as green aurora. It's different atoms at different altitudes being exposed to different energetic conditions. The aurora isn't a singular thing; rather, it's an amalgamation of a whole bunch of different constituents and conditions." +1442 Coming from a 3rd year electrical engineering students perspective, I know how static electricity works but what I don't know is why it works essentially. What I'm asking is; why do some materials hold a better charge than others and while one material likes to gain a negative charge, Visa versa? 3192 https://www.reddit.com/r/askscience/comments/dcsrm2/coming_from_a_3rd_year_electrical_engineering/ 1570117882 dcsrm2 Physics 2019-10-03 18:51:22 "Our basic understanding of static electricity still seems to be pretty murky. + +There is some evidence that static charging is not mediated by electrons and holes per se, but rather by ionic separation (a molecule splits apart into positive and negative ions, each of which resides on a different surface). Different materials reside at different parts of the triboelectric series based on their ability to stabilize different types of ions. + +There have been demonstrations of making systematic changes to a material that change its position in the triboelectric series in a predictable way. See [https://pubs.acs.org/doi/abs/10.1021/am501557m](https://pubs.acs.org/doi/abs/10.1021/am501557m) + +Surface area has to do with the amount of charge a material can ""hold"", but not with the sign of charging. (This is why toner particles used in photocopiers are so small -- high surface area to mass ratios) + +*Edited to add* that it is well-established that humidity helps to dissipate static charge (presumably by slow neutralization of charges due to ion or electron mobility on water-rich surfaces or through moist air). Materials that are very hydrophilic (tending to absorb or bind water on their surfaces) tend not to be able to build up or maintain a static charge." "Posting what I think is an appropriate follow-up question: + +Last week we had a party. We had a bunch of balloons, all the same size, all made of the same latex. They all had foil confetti stuffed into them and were then inflated. Half were inflated the normal way, by breathing into them. The other half were inflated with helium from a canister. + +I tried to show my son how you could rub a balloon on your jumper repeatedly until it amassed enough overall charge on the surface that it would stick to the wall. After rubbing different balloons we noticed that in the balloons containing air, the confetti distributed itself evenly across the inner surface of the balloon once it became charged. In the helium-containing balloons, on the other hand, the majority of the confetti just sat in the bottom of the balloon, seemingly not attracted or repelled by any charge at all. + +What is the explanation for this? Does the gas inside the balloon somehow affect the ability of the latex to pick up or retain an overall charge?" +357 Zeroth derivative is position. First is velocity. Second is acceleration. Is there anything meaningful past that if we keep deriving? 3190 https://www.reddit.com/r/askscience/comments/44wt4n/zeroth_derivative_is_position_first_is_velocity/ 1455026947 44wt4n Physics 2016-02-09 17:09:07 They have the following names: jerk, snap, crackle, pop. They occasionally crop up in some applications like robotics and predicting human motion. [This paper](http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1000419) is an example (search for jerk and crackle). Ooh, Ooh, I know this one. Besides their respective names of jerk, snap, crackle, and pop the most important one in terms of engineering is jerk. This is a deciding factor in human comfort. While acceleration manifests itself as a feeling of increased or decreased weight, the rough shaking you might feel on a road covered in pot holes or on a wooden roller coaster is jerk. Thus measuring and managing jerk is important in the design of suspension systems for vehicles or more generally, any time humans are to ride on, in, or near the device being designed. This even comes into play when designing engine mounts and shifting patterns in passenger vehicles. +358 Without friction, would a ball still spin when going down a slope? 3188 https://www.reddit.com/r/askscience/comments/3zsvca/without_friction_would_a_ball_still_spin_when/ 1452127508 3zsvca Physics 2016-01-07 3:45:08 "The answer is pretty simple. No, it would not spin. A ball spins down a slope (when there is friction) [because the ball experiences a net torque](http://physics.stackexchange.com/questions/149731/ball-rolling-down-an-inclined-plane-where-does-the-torque-come-from). What you will find is that if you push a ball down a frictionless slope, it will have a greater lateral acceleration because none of the translational energy is being lost to rotational energy. + +Kinetic energy is 1/2 m v^2 while rotational energy looks pretty similar, 1/2 I ω^2. I is the moment of inertia and ω is the angular velocity. The total energy of the system will be equal to the ball's kinetic energy + the rotational energy, so when you take friction out of the equation, none of the translational energy will be expended in making the ball rotate because there will be no torque applied to the ball. + +Edit: If the center of mass of the ball is not at the geometric center, the ball will rotate. I was assuming that we have a geometrically centered center of mass. For an explanation of why this happens, [please look at the comments below.](https://www.reddit.com/r/askscience/comments/3zsvca/without_friction_would_a_ball_still_spin_when/cyozco0) Also, I was assuming that the ball had initially no spin because of how I interpreted the grammar of the OP's question. The ball will retain the angular energy given to it at t=0. If this energy is zero, it will continue to be zero. If it is non zero, it will continue to be non zero. This is simply Newton's first law. " [deleted] +261 With advances in many fields of Medicine including the transplant of synthetic hearts and 3d printing of various body parts making cheap prosthetics possible, why haven't we seen significant advances in prosthetic cartilage for damaged joints and herniated disks? 3187 https://www.reddit.com/r/askscience/comments/3yjg5x/with_advances_in_many_fields_of_medicine/ 1451321375 3yjg5x Medicine 2015-12-28 19:49:35 "Ok, first things first : + +The synthethic hearts are not too good. In most cases they are used as ""bridge-to-transplant"" solution, not as an endgame. People don't survive too long on them. Also 3d printing body parts is highly experimental and pretty far from being a standard. + +Now, yes we do use mechanical heart valves. They are pretty good. You have to take anti-koagulation medication for the rest of your life, but otherwise you are not really handicapped. + +Mechanical knee/hip/shoulder/etc replacements are pretty okay as well. You can't do sports with them, but they enable you to live a painless life, which is a pretty big deal for a patient with osteoporosis. + +Now, when we replace joints, we don't manufacture human-like structures. We basically build something out of metal, that works like the original, without actually being *like* the original. + +Heart valves now are waaaaaaaaay simpler structures as joints or even cartilage. They are basically a few layers of cells that passively move. They don't have vessels, they don't regenerate, they have a very reduced metabolism (low turn over tissue). It's probably the easiest thing in the whole human to replace. + +Cartilage on the other hand is a highly complicated tissue. It's capable of expanding and compressing, balancing the pressure of our whole body weight (and more, when you do movements like jumping). It's capable of storing water when under low pressure, and releasing it when the pressure rises, and various other things. + +Manufacturing something like this is far beyond our current knowledge and technical abilities." "A couple of things: +When we transplant solid organs, it isn't a magic fix. People have to be near death to get a transplant and then have to take a LOT of serious medications to prevent rejection. Miss a couple of days of anti-rejection pills, you end up in the hospital and might die. After about 5-10 years, the transplant quits working. We don't have any way to take your own stem cells and make a real replacement organ that matches you... yet. + +We have really good prosthetic joints. You don't have to take medications to prevent rejection, just install the metal joint and it works. + +A lot of the failures of joint replacements are due to problems that don't have to do with the joint. People who are obese wear out their joints faster, whether they are prosthetic or original. The joint is not just the surface that bends, it includes all of the muscles. It takes a LOT of work with physical therapy to fix the damage from the bad joint and get the new joint working. + +There will never be a joint that you can install that will fix all of the pain and movement problems. We are biologic and constantly remodel and have to retrain." +359 If nearly 100 billion solar neutrinos pass through every square centimeter of our body each second, why don't these neutrinos convert neutrons in our bodies into protons, potentially harming us? 3177 https://www.reddit.com/r/askscience/comments/49l73h/if_nearly_100_billion_solar_neutrinos_pass/ 1457479477 49l73h Physics 2016-03-09 2:24:37 They do, just extremely rarely. We have much more radioactivity from decay process within our body. We constantly have potassium turning into argon or calcium and emitting high energy electrons and positrons and gamma rays, but it's such a small amount that it has no effect on our health. [We even annihilate positrons in our body to detect tumors](https://www.physicsforums.com/insights/basics-positron-emission-tomography-pet/). The nuclear transitions due to neutrino flux are much much fewer. "I know that this does not solve your question, but this might help you imagine the kinds of scales we're talking about. + +Your body is largely made of water, so let's look at the scale of 100 billion using water molecules. It sounds like a lot, but let's figure out how much that would weigh. (100 billion water molecules) * (18 grams/mole) / (6.02\*10^23 molecules/mole) = ~ 3*10^-9 grams. That means a HUNDRED BILLION MOLECULES of water is only 0.000003 milligrams. So we can see that a hundred billion, on a molecular scale, isn't all that much stuff. + + . + +That example serves mostly to illustrate what a hundred billion means at the scale of a molecule -- and a neutrino hitting one atom in one molecule is not terribly likely to make a big difference. Now let's consider a hydrogen atom, since it's an atom that's abundant in our water-heavy body. Hydrogen atoms are about 99.9999999999996% empty space according to google -- meaning the vast majority of the 5*10^-11 meters between their proton and their electron is empty. + + . + +So where does the neutrino fit in? That length, 5\*10^-11 meters, is about the length of one *billion* neutrinos stacked end to end -- and that's just the radius! If atoms were just straight lines, only 1 in a billion neutrinos is likely to hit anything (based on your rate, that's about 100 interactions a second -- still quite a lot!). But atoms ARE NOT lines -- they're spherical ^*ish!* . The volume of a sphere with that radius is about *10^27 times* the volume of the actual neutrino. I know scientific notation is not so good at being readable, but neither is this: 1,000,000,000,000,000,000,000,000,000. + +Considering that 99.9999999999996% is empty space, there's room for about 999,999,999,999,996,000,000,000,000 neutrinos within the space of a single hydrogen atom. + +999 octillion. + +That's a lot. + +Thinking of this number, 100 billion per second, we can look at our very big number and consider how likely it is, each second, that a neutrino passing through one of our hydrogen atoms hits it. If we take enough space for 10^27 neutrinos and hit it with 100 billion neutrinos a second, we should get a hit for every 10,000,000,000,000,000 (ten quadrillion) seconds. That's about 3 million lifetimes, provided you live for 100 years! + +Now, this whole hypothetical situation is set up around hydrogen atoms, which are very small and very empty. However, the realm of the order of magnitude of the results is what's important. The chances that a neutrino hits any part of an atom in your body is seriously low. Even when they do, one collision will affect one atom, potentially changing the reactivity of a single molecule -- which will affect such an unbelievably small amount of a reaction that it will not have any significant impact on a function that your body performs. + +Hope that was a decent way to look at the scales involved in things like neutrinos! + +. + +EDIT: This math was based on a lot of loose conjectures using very imprecise numbers - Google and Wikipedia's first results, to be precise. I should have done a cross section of a hydrogen atom instead of volume; the radius given for a hydrogen atom is its *most probable* radius, not the radius of every hydrogen in the universe at every moment; and who even really understands the size of a neutrino - most of the time they're acting more wave-like than particulate. SO, please don't cite this shoddy work as the universal truth on this subject. However, errors and approximations aside, it's still pretty unlikely the neutrinos are doing anything to you." +155 Is there a way to harness gravity for energy? If so, why do we not discuss it when talking about green energy? 3175 http://www.reddit.com/r/askscience/comments/3i8u99/is_there_a_way_to_harness_gravity_for_energy_if/ 1440447911 3i8u99 Physics 2015-08-24 23:25:11 This is exactly what hydro-electric power does. It takes the gravitational potential energy of water flowing and uses it to power turbines. In fact, using the gravitational potential energy of water is a practice much older than using electricity; water wheels being used to turned mills goes back over 2000 years! "you can use gravity to store energy, that is by lifting something up, and getting it back later. Some powerplants pump up water ro a mountain and later let it run through turbines. +The sun moves the water from the sea to higher places, wher it then flows downward and can be used to drive water wheels, but the energy comes from the sun and gravitation is just some intermediate step. + +But you cannot generate energy from gravity in a closed loop, meaning you cannot build a machine that outputs energy by just moving something around in a loop inside of a gravitational field. +" +156 Why is the speed of light, the speed it is? 3174 http://www.reddit.com/r/askscience/comments/3h8con/why_is_the_speed_of_light_the_speed_it_is/ 1439754885 3h8con Physics 2015-08-16 22:54:45 "I'd like to link you to a fun video on why 'why' questions are difficult in science, and the unfortunate thing with science, and it's similar in deductive fields like math, is the answer to every why question is going to open a whole bunch of other why questions for you. [Here's Feynman's, maybe a bit pedantic, view on the matter.](https://www.youtube.com/watch?v=qjmtJpzoW0o) + +For the speed of light, we originally ran into it studying electricity and magnetism (the speed of light, not light itself). The (classical) picture we have for electricity and magnetism is a bit dry, it's described by 4 differential equations (known as Maxwell's equations). Two of them desribe electricity and magnetism as seperate entitites, and the other two describe the interaction between the electric and magnetic fields, along with an electric current. These equations have two fixed constants called the 'permittivity of free space' (or 'electric constant', call it e_0) and the 'permeability of free space' (or 'magnetic constant', call it m_0). It so happens that in a vaccuum we can combine these equations and simplify so that all we are solving for is a wave, that is the electric and magnetic field are each described as a wave propogating through space. And we find that the square of the velocity of that wave is inversely proportional to the product of those two parameters. So the sort of unsatisfactory answer is that the speed of light is exactly what it is because 1/sqrt(e_0\*m_0) is what it is." "The other answer to your question is that meters and seconds are arbitrary and that c is fundamental. It just so happens when you solve for c in those arbitrary systems of measure that's the number you get. + +But it makes just as much sense to ""set c to 1"" and then everything else is recalculated based on that." +262 Can depression and other mood disorders decrease mental ability? Can it make you dumber? 3166 https://www.reddit.com/r/askscience/comments/3w686p/can_depression_and_other_mood_disorders_decrease/ 1449719723 3w686p Psychology 2015-12-10 6:55:23 Personal anecdotes and [medical advice](http://goo.gl/UAVhTJ) are not appropriate for askscience. Those comments will be removed. Please see our [guidelines](https://www.reddit.com/r/AskScience/wiki/quickstart/commenting#wiki_guidelines_for_commenting) for more information. Licensed clinician here. Cognitive impairment with depressive disorders is a common symptom. Clients show decreased memory and attention, with increased disorganization of thought. In some clients, these symptoms can remit with treatment (meds and therapy). In clients with depression that is treatment refractory, those symptoms can be pervasive even with treatment. +263 Does Adrenaline really reduce reaction time? 3165 https://www.reddit.com/r/askscience/comments/3swb3s/does_adrenaline_really_reduce_reaction_time/ 1447596588 3swb3s Human Body 2015-11-15 17:09:48 "In essence yes, the sympathetic nervous system (""fight or flight"") can speed reaction time to danger through this non-exhaustive list of mechanisms: dilation of the pupil allows for increased sensory awareness; increased blood flow into skeletal muscle allows for faster and more sustained muscular responses; finally the increase of the stress hormone cortisol has an effect in ""priming"" the brain to be hyper-aware of the surroundings, thus decreasing reaction time when a stimulus does occur. This is actually a really interesting direct connection between psychology and physiology." "Just to add, adrenaline also causes your brains 'fast process' thinking to take priority. Just like dan kahneman showed in his work, we have a fast thought process and a slow one. I use my fast process when im working out how to catch something for example. I use my slow one when I solve a maths problem. + +The fast process is our primate brain that helps keep us alive, it operates on rules of thumb and best guess. Using this process is quick good for avoiding danger, but we would lose a massive element of our advatange that our intelligence gives us if we operated at a super awareness level. All the decisions we ever made would be quick heuristic solutions. " +360 What is the maximum speed of a liquid running through a tube? 3163 https://www.reddit.com/r/askscience/comments/4gof2i/what_is_the_maximum_speed_of_a_liquid_running/ 1461763081 4gof2i Physics 2016-04-27 16:18:01 Engineering answer.. There is a practical speed limit called choked flow that occurs as the fastest streamlines approach the speed of sound. It basically says you can't increase the mass flow rate by decreasing the pressure downstream. If you increase the pressure upstream you are increasing the mass flow by increasing the density of the fluid. You can get to supersonic internal flow within a well configured nozzle (e.g. rocket throat/nozzle) but the pressure of the fluid is rapidly dropping in order to do so. Managing the shock waves and structural loads on tubing and valves gets nuts pretty fast, typically internal flows are kept subsonic for this reason. [deleted] +1391 Are there any examples of venomous or toxic birds? 3160 https://www.reddit.com/r/askscience/comments/c2a3i4/are_there_any_examples_of_venomous_or_toxic_birds/ 1560903850 c2a3i4 2019-06-19 3:24:10 "There's the [little shrikethrush](https://en.wikipedia.org/wiki/Little_shrikethrush), the [blue-capped ifrit](https://en.wikipedia.org/wiki/Blue-capped_ifrit), and the [hooded pitohui](https://en.wikipedia.org/wiki/Hooded_pitohui). All three are native to New Guinea and sequester in their skin and feathers [batrachotoxin alkaloids](https://en.wikipedia.org/wiki/Batrachotoxin) obtained from their diet of *Choresine* beetles. Handling them causes numbness and tingling. Eating them would probably result in paralysis and death to predators. + +Edit: prey to predator" The Spur-winged goose (Plectopterus gambensis) eats blister beetles, which contain cantharidin. This makes it's meat poisonous to humans. They also have wicked bone spurs on their wings, which are not poisonous or venomous, just really badass. +471 Is there a limit to how many photons you can pack into a beam of defined width? Or to ask the other way - can an infinite number of photons occupy the same space? 3157 https://www.reddit.com/r/askscience/comments/4nahme/is_there_a_limit_to_how_many_photons_you_can_pack/ 1465473975 4nahme Physics 2016-06-09 15:06:15 [deleted] "/u/RobusEtCeleritas is correct, you could create a black hole. + +Another thing that will likely happen is [photon-photon scattering](https://en.wikipedia.org/wiki/Two-photon_physics). When the intensity gets large enough, [the Schwinger limit](https://en.wikipedia.org/wiki/Schwinger_limit) makes the electric field nonlinear: photon-photon scattering becomes possible, leading to nonlinearities even in a vacuum. The Schwinger intensity is much smaller than the intensity necessary to create a Kugelblitz, and will hopefully be reached in our lifetime." +1392 AskScience AMA Series: I am Joseph LeDoux, a neuroscientist at NYU. My research focuses on how the brain detects and responds to danger, and the implications for understand fear and anxiety. Ask Me Anything! 3151 https://www.reddit.com/r/askscience/comments/cwzb39/askscience_ama_series_i_am_joseph_ledoux_a/ 1567076430 cwzb39 Neuroscience 2019-08-29 14:00:30 The AMA will begin at 3pm ET (19 UTC), please do not answer questions for the guests till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Keep questions and interactions professional and remember, asking for medical advice is not allowed. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). Can you talk about how adverse childhood experiences (ACES) may influence neuro development and a conditioned fear response as an adult? In other words overreacting to situations that your brain perceives as danger. +594 Why haven't the colors on Jupiter all mixed together yet? 3147 https://www.reddit.com/r/askscience/comments/5176ln/why_havent_the_colors_on_jupiter_all_mixed/ 1473040467 5176ln Astronomy 2016-09-05 4:54:27 The core of Jupiter is very hot. As a result, there is a significant temperature differential between the upper layers of Jupiter's atmosphere, and the lower layers. This causes convection, which moves the atmosphere around (similar to our own atmosphere regarding global wind patterns and ocean currents). Additionally, the different gasses in Jupiter's atmosphere react relatively differently to heat and pressure, and so stratify into different layers. Each of these layers has a different color and behaves differently from one another and generally won't mix without outside influence. The rotation of the planet additionally affects the structure of Jupiter's atmosphere. All of these effects constantly acting together creates the banding and storms we observe on Jupiter. "Arguably the most important consideration to Jupiter's iconic atmospheric structure which, as far as I can tell hasn't been discussed, is actually a consequence of an interesting result in the study of fluid turbulence.[ That result is that 2D fluid flows transfer energy *from* small scale structures *into* large scale structures as time progresses](https://www.youtube.com/watch?v=pSXe4ri2KwE). This may be unintuitive since most people are familiar with typical everyday 3D turbulence wherein large scale turbulent structures break down into smaller and smaller scales as time marches forward. This result, known as the inverse cascade, is [mathematically provable](http://people.atmos.ucla.edu/jcm/turbulence_course_notes/2D_homogeneous.pdf) (PDF warning, but the figure on pg.7 is very understandable), given certain physical assumptions, using scaling analyses. + +Jupiter's atmosphere can be approximated as a 2D flow since, near the surface, there is relatively little convection in the radial direction (*toward* the center) meaning that the near surface layers are stratified and don't mix with each other. These surface layers, while thick by human standards, are actually very thin when compared to the circumferential scale of the planet. All of this means that fluid flowing on the surface of Jupiter tends to remain at the surface, traveling laterally or longitudinally, but not radially. This is a 2D dominated flow. + +Knowing that Jupiter's atmosphere is primarily 2D flow, we can apply results from the aforementioned mathematics which claim that small scale structures (like vortices) will, given enough time, begin to merge with one another creating *larger* vortices. This partially explains the Great Red Spot, which is a vary large scale vortex. Of course, other effects are also at play. Given enough time, even 2D turbulent systems will break down to a homogeneous average flow, due to the presence of viscosity (inertial energy is converted to heat). I would hazard to guess that Jupiter's residual heat from its formation, along with solar energy, helps to counteract viscous effects. Jupiter is also rotating about it's axis which adds some interesting dynamics to the mix. These dynamics don't greatly effect the turbulence arguments, but instead help to explain the distinct longitudinal striations on the planet's surface. + +More examples of 2D turbulence giving rise to the inverse cascade include the Earth's own atmosphere,[ iridescence in soap bubbles](http://www.mae.buffalo.edu/research/laboratories/combustionlab/Flowing%20soap%20films/Flowing%20soap%20films.htm), and some [pretty cool](https://www.youtube.com/watch?v=TJP1J0_EhBk) office desk toys." +264 Are rings exclusive to gas planets? If yes, why? 3138 https://www.reddit.com/r/askscience/comments/3tymym/are_rings_exclusive_to_gas_planets_if_yes_why/ 1448298603 3tymym Astronomy 2015-11-23 20:10:03 "ring systems aren't unique to gas giants. We have actually observed (faint and tenuous) rings around a few asteroids/minor planets/moons in the solar system. + +It is sometimes hard to extend planetary system formation theories to general cases since we only have extensive observation of one planetary system. So what parts of our system are typical and what parts are unusual is hard to determine. + +This is true in the case of the ring systems because we don't even really know for sure how they formed in the first place. They could be from the breaking up of moons by tidal limits, could be left over protoplanetary disk material and, in the case of some of Saturn's at least, they can be from volcanic activity on the moon. + +I can guess on some features of our gas giants that would make them more likely to have rings, maybe someone with relevant background can cast more light on this though. They are heavier and so have larger Roche limits, they have more moons, they formed in a region of the protoplanetary disk that had more material, they are more likely to interact with (and capture) asteroids... + +A bit open ended but that is the best I can do!" "Oddly Nature Geoscience just published a paper related to this topic and our celestial neighbor. + +* [The demise of Phobos [larger of Mar's two satellites] and development of a Martian ring system.](http://www.nature.com/articles/ngeo2583.epdf?referrer_access_token=fQ6ksxJ819UA1usf6WKpO9RgN0jAjWel9jnR3ZoTv0PskMyaoEtEpNL3rseiveY9n5-XTA_I4GvSH8_Qfg0Z8Qtz5ladk-t73K1_9oIMCh4K7gH5MRLGU1BMTHPLsFB6WLPzbRIT-0vQRNem1cvYETXUq1CsmYjT75XexSZiHPtUuMrPXuCVYyz0itIgAKY8GVVY1u1AVL6DOKyDXpPppg%3D%3D&tracking_referrer=www.popsci.com) + +* [Pop Science summary](http://www.popsci.com/falling-phobos-will-eventually-put-ring-around-mars) + +Abstract: + + +>All of the gas giants in our Solar System host ring systems, in contrast to the inner planets. One proposed mechanism of planetary ring formation is disruption or mass shedding of moons. The orbit of Phobos, the larger of Mars’s two moonlets, is gradually spiralling inwards towards Mars and the moon is experiencing increasing tidal stresses. Eventually, Phobos will either break apart to form a ring or it will crash into Mars. We evaluate these outcomes based on geologic, spectral and theoretical constraints, in conjunction with a geotechnical model that helps us determine the strength of Phobos. Our analysis suggests that much of Phobos is composed of weak, heavily damaged materials. We suggest that—with continued inward migration of the moon—the weakest material will disperse tidally in 20 to 40 million years to form a Martian ring. We predict that this ring will persist for 10^6 to 10^8 years and will initially have a comparable mass density to that of Saturn’s rings. Any large fragment of Phobos that is strong enough to escape tidal breakup will eventually collide with Mars in an oblique, low-velocity impact. Our analysis of the evolution of Phobos underscores the potential orbital and topographic consequences of the growth and self-destruction of other inwardly migrating moons, including those that met their demise early in our Solar System’s history. +" +595 What happens when two previously converged plates diverge? 3134 https://www.reddit.com/r/askscience/comments/5cy4e7/what_happens_when_two_previously_converged_plates/ 1479154714 5cy4e7 Earth Sciences 2016-11-14 23:18:34 "When a mountain range developed on a convergent plate boundary, the plate will be thicker here than in normal continental crust. A rifting zone would avoid these regions and open where else. But the gravitational collapse after a collision on a convergent plate boundary, as well as erosion, will reduce crust thickness. In ""old"" mountain ranges rifting zones may occur. " "This sort of situation doesn't usually happen. When you get the sort of tectonic collision which forms mountain ranges, it involves a massive thickening of the crust which is much harder to rift than other, normal crust. There would also likely be a significant time gap between the mountain-building event and the rifting event, and the mountain range would be mostly eroded by the time of break-up. + +That being said, it has happened occasionally. If you imagine the situation before the formation of the North Atlantic, the Atlas Mountains and the Appalachians were originally a continuous chain." +29 If I ate 10,000 calories in one go, would my body be able to digest it all? Or would some of those calories 'pass through' due to my digestive system being overwhelmed? 3133 http://www.reddit.com/r/askscience/comments/2rr3ip/if_i_ate_10000_calories_in_one_go_would_my_body/ 1420732795 2rr3ip Human Body 2015-01-08 18:59:55 "Current microbiologist, future dietitian here: + +Yes, some of those calories would ""pass through"" and not be able to be digested. Unless your body is used to utilizing a massive amount of calories, it's not going to waste energy having and maintaining receptors in your gut that almost never get used. For instance, you only make so much bile at a time, which is necessary to absorb fats. If your gut gets overwhelmed with more fat than you can possibly absorb, it's going to pass through the region where fat is absorbed...which is a relatively short region, and get turned into massive amounts of gas later on down the line. This gas is the result of microbes in your gut inexpertly fermenting fats, which is a nutrient they are not used to utilizing, so they break it down inefficiently, making gases as their own ""poop"". You may absorb some of the other products these microbes create as a result of this breaking down, but it won't be as calorie-rich as if you were able to absorb the fats as fat. + +If you consistently eat high calorie foods, or a particular type of nutrient, your gut and its microbiome will change in response to that level of intake, and you would absorb those calories more efficiently. + +TL;DR? The second one." "I'm just going to leave this paragraph here from H.M. Sinclair (Laboratory of Human Nutrition, University of Oxford) in his ""The Diet of Canadian Indians and Eskimos"" from 1952 symposium proceedings; emphasis mine. + +>The Eskimo is apparently able to digest and absorb very large amounts of protein and fat at a single meal. In times of plenty, 4 kg of meat daily is a common amount and much is taken at a single meal : they do not usually take food in the morning. Consumption of larger amounts such as 15 kg has been observed on occasion, and Ross (1835) considered that an Eskimo ' perhaps eats twenty pounds +of flesh and oil daily', **which I suppose is possibly 46,000 Cal.** Parry (1824) thought he would test the capacity of an adolescent Eskimo ; the food was weighed and, apart from fluids, he ate in 20 h 8-1/2 lb. meat and 1-3/4 lb. bread **(about 15,700 Cal.)** and ' did not consider the quantity extraordinary '. But this is trivial compared with the feats of the Siberian Yakuti who eat 25-30 lb. meat daily, and there is no record approaching the 35 lb. of beef and 18 lb. of butter (providing about 112,000 Cal. and occupying a volume of the order of 5-1/2 gal.) alleged to have been eaten in less than 3 h by each of two Yakuti (Simpson, 1847.) + +One wonders if the Yakuti had very deep pockets and somehow spoofed Simpson by stuffing them full of beef and butter when not being observed." +472 Why is anything radioactive in movies, portrayed as a green glow? 3131 https://www.reddit.com/r/askscience/comments/4v4e98/why_is_anything_radioactive_in_movies_portrayed/ 1469759441 4v4e98 Chemistry 2016-07-29 5:30:41 "I can't speak to the history of Hollywood imagery, but in the early 20th century there were a few [commonplace radioactive compounds that glowed green](http://klotza.blogspot.com/2016/07/do-radioactive-things-glow.html), including the radium used in clock dials and uranium glass (this is no longer done for fairly obvious reasons). The green glow isn't from the radioactive decay itself, but from electronic/atomic transitions which could be activated by the radioactivity. + +There is also a blue glow from Cerenkov radiation associated with nuclear reactors." "Just to add a reverse example of the movie trope affecting real radioactive items, I run a radiation lab and the most common radioimmunoassay kit we use has been adjusted by the manufacturer so that the radioactive compound (125-I in this case) ends up in a green mixture. It's a kit in which you mix your sample with 125-tracer and an antibody, and they've added colored dye to the two reagents: bright blue for the 125-I, bright yellow for the antibody. So when you mix all the reagents together you end up with a test tube rack full of bright green radioactive samples. I've been told the manufacturer chose those colors on purpose knowing that people associate bright green with radioactivity. + +It certainly does help when there's newbies in the lab - ""Don't touch those tubes, they're radioactive!"" *points to rack of bright green samples in test tubes* (person backs away carefully) It gets people's attention." +596 AskScience AMA Series: I am Jerry Kaplan, Artificial Intelligence expert and author here to answer your questions. Ask me anything! 3131 https://www.reddit.com/r/askscience/comments/5eanmz/askscience_ama_series_i_am_jerry_kaplan/ 1479820768 5eanmz Computing 2016-11-22 16:19:28 Just a friendly reminder that our guest will begin answering questions at 6pm Eastern Time. Please do not answer questions for the guests. After the time of their AMA, you are free to answer or follow-up on questions. If you have questions on comment policy, please check our [rules wiki](https://www.reddit.com/r/askscience/wiki/rules). Where do you stand on the idea of patents and AI inventions? If an AI invents something, does the patent go to the AI or to the maker of the AI? +361 Does the colour of your eye affect it's sensitivity to light? 3130 https://www.reddit.com/r/askscience/comments/4b32qn/does_the_colour_of_your_eye_affect_its/ 1458393923 4b32qn Biology 2016-03-19 16:25:23 Reminder: Anecdotes do not belong in /r/AskScience. Please do not share your personal experiences. "The short answer is that having eyes that are lighter in color 1) can cause discomfort (i.e. [photophobia](https://en.wikipedia.org/wiki/Photophobia)) and reduced contrast by allowing more stray light in, but 2) cannot allow for higher visual acuity (an improved ability to collect and focus light). + +To understand both parts of the answer, let's start by looking at the [diagram of the eye](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1e/Schematic_diagram_of_the_human_eye_en.svg/756px-Schematic_diagram_of_the_human_eye_en.svg.png). The part of the eye that determines its color is the iris. Specifically darker eyes are caused by a higher concentration of biological pigments like melanin, while eyes that are lighter in color have smaller concentration of such compounds. Now the purpose of the iris is to essentially act as a diaphragm that controls how much light gets into your pupil and then gets focused by the lens onto the retina. A good analogy is to think of the iris as the [diaphragm in a camera shutter](http://i.imgur.com/KgRVPBI.jpg), which controls the aperture that lets light in. An ideal diaphragm should allow all light through the aperture, but block off all the light around it. In this sense a better iris can't really allow you to collect more *useful* light (again, because the pupil is basically a hole in the iris), but it *can* cause problems by letting stray light through, [as shown in this diagram](http://i.imgur.com/2u3qbpC.png). + +Because a more transparent iris allows more stray light through, people with lighter eyes can have certain problems in conditions of intense light and glare. One problem is that the stray light that makes it into your eye (called intraocular stray light (IOSL)) can make it hard see what is ahead of you. For example, imagine you are driving on a wet road and the beams of the cars around you are reflected around you. The effect of this stray light is to flood your field of vision with a bright diffuse blur. As a result, it becomes harder to see what you are looking at and your net contrast is reduced (a problem called contrast sensitivity). Finally, in conditions of bright light (i.e. strong sunlight), having a lighter eyes means that more unwanted light can enter your eye and cause discomfort. + +**Source:** + +Nischler, C., et al. [Iris color and visual functions](http://www.ncbi.nlm.nih.gov/pubmed/22527312) *Graefes Arch Clin Exp Ophthalmol.* 2013, 251(1):195-202 +" +30 If light emits a significantly minute force, how much light would it take to crush a human? 3129 http://www.reddit.com/r/askscience/comments/34fjf2/if_light_emits_a_significantly_minute_force_how/ 1430419697 34fjf2 Physics 2015-04-30 21:48:17 The main issue is that any light is intense enough to push a human would literally vaporize someone. For a 100 pounds force, you'd need roughly 130 gigawatts focused on someone. A 1-watt laser is enough to cause burns. " + +E=hf +E=6.6261 x 10^-34 * 0.00000060 meters [0.00000060 being yellowish light] +E=3.97566 x 10^-40 joules + +E=mc^2 +m=E/c^2 +m=3.97566 x 10^-40 joules / 299,792,458 m/s +m=1.3261374 x 10^-48 kg + +At most it would take about 1600 psi to break a strong bone, or around 28,573 kgs/ square meter. +If your average human male is 1.9m^2 for surface area, an instantaneous force from light hitting him needed to completely crush him would be about 2 times the ""kg/m^2"". + +28,573 kg/m^2 * 1.9m^2 = 57,146 kg + +So, the number of photons will be (L)... +L=57,146 kg / 1.3261374 x 10^-48 kg +L=4.3092066 x 10^52 photons + +or + +43,092,066,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons ALL impacting him at the same time from every direction to break his bones and smush him up. That's minimum for if he's only made of bone, flesh would be WAAY easier. But I'm not doing that. I have grade 12 homework to do. Good night reddit. + +EDIT: After reading through some replies I realized how narrow minded science folk seem to be. He doesn't want your ""Well you see it won't cause"" answers. He wants a number. Even if heat would kill the man, CRUSH HIM! CRUSH HIM WITH LIGHT!" +1805 If we can vaccinate chickens against salmonella, why haven’t we done the same for humans? 3119 https://www.reddit.com/r/askscience/comments/lwv2v7/if_we_can_vaccinate_chickens_against_salmonella/ 1614781519 lwv2v7 Medicine 2021-03-03 17:25:19 "Someone mentioned the flu shot and I realized no one (unless I missed one) has mentioned the most obvious reason there isn’t a human salmonella vaccine. + +Salmonella can technically be transmitted between people, but that only accounts for around 5% of infections. Which means individual people getting it isn’t a community health issue." "It's complicated. The vaccine targeting chickens is primarily an effort to reduce food-borne disease in humans, and it does that pretty effectively. So, we target the source as a means of prevention rather than targeting humans directly. Easier and generally safer. Bacterial vaccines are generally short-lived (6-12mos), so they work fine for short-lived poultry, but would be harder to repeatedly use in humans. + +If there were a market for that vaccine in humans, we'd already be there. The fact we don't have one for people in common usage suggests: + +1) not enough people are affected + +2) not enough people with significant influence are affected + +3) the costs of establishing and giving the vaccine outweigh the costs of the disease itself." +157 If you put a diamond into the void of space, assuming it wasn't hit by anything big, how long would it remain a diamond? Essentially, is a diamond forever? 3109 http://www.reddit.com/r/askscience/comments/36606x/if_you_put_a_diamond_into_the_void_of_space/ 1431785184 36606x Chemistry 2015-05-16 17:06:24 "No, a diamond is not forever. Given enough time, a diamond will turn completely into graphite because it is a spontaneous process. The Gibbs free energy of the change from diamond into graphite is -3 kJ/mol @ 298 K. Accounting for a cosmic background temperature of about 3 K, ΔG = -1.9 kJ/mol. + +Recall that ΔG=ΔH-TΔS. + +EDIT: The physical importance of this statement is that even in an ideal world -- where nothing hits the mass and no external forces are present -- the diamond will eventually turn into a pencil. + +EDIT 2: typo on sign for delta G; spontaneous processes have a negative delta G, and non-spontaneous processes are positive. + +EDIT 3: I'm very forgetful today :p. I just remembered that space is very very cold (~3 K)." "There are much more stable (and less exciting) things that you could put in space to last forever. As /u/Coruscant7 mentioned, a diamond will eventually transmute into graphite. However, a lump of iron would last pretty much forever, unless it was hit by some other space object. + +Without an atmosphere to cause oxidation or erosion, longevity of an object in space mostly comes down to how chemically inert it is. +" +473 Two of the same type of metals will bond together in space? 3109 https://www.reddit.com/r/askscience/comments/4qr5in/two_of_the_same_type_of_metals_will_bond_together/ 1467370711 4qr5in Astronomy 2016-07-01 13:58:31 "It is called cold welding or vacuum welding. Richard Feynman explains it as such: +""The reason for this unexpected behavior is that when the atoms in contact are all of the same kind, there is no way for the atoms to “know” that they are in different pieces of copper. When there are other atoms, in the oxides and greases and more complicated thin surface layers of contaminants in between, the atoms “know” when they are not on the same part."" +" "As a blacksmith/amateur metallurgy nut who does a lot of solid-state diffusion bonding to make pattern-welded steel, this blows my mind and creates so many questions! I've realized for years that getting solid-state diffusion bonding to happen requires extra energy added to the system in one way or another (I primarily use heat to get steels to come together), but it never occurred to me that the the extra energy required would be in part to overcome the issues of dissimilar materials at the interface. I'm used to being able to trade the TYPE of energy required back and forth to get bonding to occur. For example, a gentleman named [Daryl Meier](http://www.meiersteel.com/) once demonstrated solid state welding of dissimilar steels at ~1100F (IIRC) by using a large impact force (a big power hammer) to force the process along. Traditionally we do this type of welding at 2000-2200F. + +For those here who might have more knowledge of the process, can anybody answer any of the following? + + * Do the materials involved need to be elementally pure? Like, will this only work with 100% pure iron to 100% pure iron, or would it be possible to get an iron alloyed crystaline lattice (say, with a smidge of C, Mn, W, etc. added) to bond this way? + * If it's possible with different alloys, would the same types of ""rules"" hold true here as we see in high-temp bonding? For example, in steel, higher carbon levels allow for dolid-state welding at lower temperatures. + * What about dissimilar materials that will form solid-state bonds with heat (E.g. the Japanese Mokume Gane techniques use to bond silver/gold/copper alloys/etc.)? + +I want to think that as long as the electrons of the constituent atoms would be free to be shared between the two materials that it would work, but I'm not good enough at physics or chemistry to REALLY grok this. + +Thanks reddit! I have something new to eat my brain now!" +597 Discussion: Smarter Every Days newest YouTube video on Prince Rupert Drops VS Bullets! 3103 https://www.reddit.com/r/askscience/comments/5kz519/discussion_smarter_every_days_newest_youtube/ 1483044342 5kz519 Physics 2016-12-29 23:45:42 Hey guys, Destin here. Happy to answer questions about the setup if that's helpful. These things are so impressive. Do you have an idea of how much force is required to break one? I had to look and a .22lr is doing between 140-260 Joules of energy on impact. Do you have a plan to try this with larger caliber rounds? +598 Normal stars are made out of hydrogen which undergoes fusion. Can I make a star out of any element, provided I have enough mass to fuse that element? Say, Iron? 3100 https://www.reddit.com/r/askscience/comments/5h0tir/normal_stars_are_made_out_of_hydrogen_which/ 1481127940 5h0tir Physics 2016-12-07 19:25:40 "The short answer is that iron or heavier elements won't work since you can't release energy by fusing such atoms together. + +To get into more detail, in order for a star to generate energy via fusion, it needs to have elements that will release energy when they stick together to form heavier elements. To figure out which elements would work, take a look at [this diagram](https://upload.wikimedia.org/wikipedia/commons/thumb/5/53/Binding_energy_curve_-_common_isotopes.svg/1024px-Binding_energy_curve_-_common_isotopes.svg.png) showing the binding energies of different isotopes *per nucleon* (proton/neutron). The higher the binding energy is, the more stable a given nucleus is. If we start to the left of the chart you have hydrogen, where you see that the slope is very steep going to helium. This high positive slope here means that you can release a lot of energy when fusing hydrogen atoms together. + +Now as you go to heavier and heavier elements, you see that this slope starts to level off. By the time you get to various isotopes of iron and nickel, this slope becomes flat. What that means is that these isotopes are as stable as they can be and you can't get any additional energy by fusing them together. In fact, if you go to heavier elements, you now see the slope inverting. That means that you can now gain energy by breaking atoms apart. This is the regime in which nuclear fission can now be used to generate energy. + +As an aside, the reason that isotopes of iron are so close to the peak of the stability chart (technicically Ni-62 wins by a sliver), together with the many pathways to end up with these isotopes, explains why iron tends to be so abundant. " "Only elements to left of the peak, which is actually Iron, your example, can be fused to yield energy.: + +https://en.m.wikipedia.org/wiki/Nuclear_binding_energy#/media/File%3ABinding_energy_curve_-_common_isotopes.svg + +Stuff to the right can be fissioned to yield energy. So things as heavy or heavier than iron signal the death of fusion in a star, as fusion then eats up energy rather than yielding it." +1393 AskScience AMA Series: We are Drs. Roger Hanlon, Mike Vecchione, and Louise Allcock, and we research octopuses, squids, cuttlefish, and other cephalopods. Ask us anything! 3099 https://www.reddit.com/r/askscience/comments/c4lpao/askscience_ama_series_we_are_drs_roger_hanlon/ 1561374026 c4lpao 2019-06-24 14:00:26 Can an octopus teach the use of tools to its offspring in a suitable environment? In other words could octopi lineage develop use of tools and even a culture regarding said tools if they were more social creatures? "Thank you for doing this AMA, cephalopods are really interesting (possibly the most interesting invertebrates). + +I follow the EVNautilus live stream and they recently came upon [large swarms of brooding deep sea octopus](https://www.youtube.com/watch?v=RHR70lVy79Y). These creatures were in a really strange position, and at the time, the research team did not have an explanation for that behaviour. + +Has similar behaviour been seen in other brooding cephalopods and are there any hypotheses on why this (seemingly defenseless) position is used?" +158 When dinosaur bones were initially discovered how did they put together what is now the shape of different dinosaur species? 3098 http://www.reddit.com/r/askscience/comments/3bmd0k/when_dinosaur_bones_were_initially_discovered_how/ 1435663826 3bmd0k Paleontology 2015-06-30 14:30:26 "With difficulty. + +The earliest known dinosaurs, such as [iguanodons](https://en.wikipedia.org/wiki/Iguanodon) went through a few different permutations of what we thought they looked like. + +Dinosaurs were commonly depicted standing more vertically in the past too. + +However, as to the overall shape, they aren't all that different to animals today. They safely assume the thigh bone is connected to the hip bone and build from there once you've found a moderately complete fossil. + +" "When they were first found, people had no idea they were the skeletal remains of extinct species from 65+ million years ago. However, ancient people definitely were able to tell they were the skeletal remains of some strange animals. + +In many cultures, these remains gave rise to legends like dragons - since the remains looked an awful lot like lizards, crocodiles and other critters they knew, but way, way bigger - so it was a logical assumption. + +Other mythical explanations arose as well, such as legends of the mammut from Siberia - a huge creature with tusks like a walrus that lived underground. If it came into sunlight, it turned to stone and died. Not a bad explanation for mammoth bones found eroding out of the tundra. + +It wasn't until the Enlightenment that anatomists like Georges Cuvier were able to look at the fossils in detail, and realize that they had similarities to modern animals, but also important differences. Using his knowledge of how modern animals were put together, he was able to come up with pretty accurate reconstructions of how these critters would have actually looked. + +" +31 Why do physics break down above the Planck Temperature? 3081 http://www.reddit.com/r/askscience/comments/2v0161/why_do_physics_break_down_above_the_planck/ 1423242357 2v0161 Physics 2015-02-06 20:05:57 It's not so much that physics breaks down or that it's the hottest possible temperature, but rather that we can't really understand things that hot without knowledge of quantum gravity (because particles could be colliding with such great energy that they form black holes), which we don't understand well enough. "Since this thread is discussing that graphic anyway, I had a question. Since the image is here, rather than start a new thread, I'll just ask my question. + +The graphic indicates the hottest man-made temperature was the collision of lead ions. How were they able to get this reading?" +159 How fast would you have to travel around the world to be constantly at the same time? 3080 http://www.reddit.com/r/askscience/comments/38wezj/how_fast_would_you_have_to_travel_around_the/ 1433678356 38wezj Physics 2015-06-07 14:59:16 "Your speed is going to depend on your latitude, assuming that your question means that you want to go back one timezone per hour, so that you have some sort of 'never ending hour.' + +If you wanted to pick a latitude and stick with it, then the length of your lap around the world is just: + + L = 2 * pi * (radius of the earth) * cos(latitude) + +where that last piece is the [cosine](http://i.imgur.com/ewqk5CL.png) of the latitude you want to travel at. Since you only need to do a global lap once every 24 hours, you can divide this by 24 hours to get: + + + v = 2 * pi * (earth radius) * cosine(latitude of new york city)/24 hours + +[Math.](http://www.wolframalpha.com/input/?i=2*pi*%28earth+radius%29*cosine%28latitude+of+new+york+city%29%2F24+hours) + +And I plugged in the latitude for NYC, because why not, and it gave me 785 mph. Go ahead and tinker with that angle, try [London](http://www.wolframalpha.com/input/?i=2*pi*%28earth+radius%29*cosine%28latitude+of+london%29%2F24+hours) or [Mumbai](http://www.wolframalpha.com/input/?i=2*pi*%28earth+radius%29*cosine%28latitude+of+mumbai%29%2F24+hours) or [Honolulu](http://www.wolframalpha.com/input/?i=2*pi*%28earth+radius%29*cosine%28latitude+of+honolulu%29%2F24+hours) or [Stockholm](http://www.wolframalpha.com/input/?i=2*pi*%28earth+radius%29*cosine%28latitude+of+stockholm%29%2F24+hours). + +Be careful when you pick your latitude though, because some countries span a large degree of longitude but have chosen the entire country to run on one timezone, such as [China and India.](http://1.bp.blogspot.com/-cOVtzz5V4uU/Tci4G0K4_PI/AAAAAAAACec/7vRmnpzdgdM/s1600/time_zones.jpg) If you planned to pass through there in an hour you'd end up getting out of sync. + +Of course, as is common in physics, there is a simple limit for making this easy: go to the poles. [The timezones start and end there,](http://upload.wikimedia.org/wikipedia/en/archive/3/39/20120104021100!International_date_line.png) meaning that you can walk as slow as you want, provided you're close enough to the pole. If you wanted to be able to do this on foot, walking through one timezone per hour, then the furthest you could feasibly be is 10 miles from the north pole - that would keep you walking at a brisk pace of 3 mph all day. If you were 10 feet from the pole, a snail could easy handle this pace. +" You could go to one of the poles and just do a slow twirl. +32 If the gravity of the moon is strong enough to create tidal waves, why doesn't it lift up things like tree leaves or small animals? 3078 http://www.reddit.com/r/askscience/comments/2yqk92/if_the_gravity_of_the_moon_is_strong_enough_to/ 1426118212 2yqk92 Planetary Sci. 2015-03-12 2:56:52 "Surprisingly no one has gotten the right answer to this yet! Mass plays a role in tidal forces but what's really important is more often size, not mass. The reason you have a tide at all is the difference in the pull of the tidal body from one side to another. We get a tide on the earth because the side of the earth on the opposite side from the moon experiences less gravitational pull from the moon than the near side that is close to the moon. This makes a net force on the object which stretches it out toward and away from the object generating the tide. Not everyone realizes this but there is actually a high tide on the side of the earth close to the moon as well as the side on the far side from the moon. Low tides are at 90 degrees from the moon on either side. + +The only time tidal forces can act on small objects is when the masses involved are extremely compact. Spaghettification in a black hole is actually caused by tidal forces. Basically your head and feet are getting a high tide while your waist is getting a low tide!" "It does lift those things up! The surface of the Earth will vary in distance from the center by about a meter every twelve hours due to tidal forces acting on it. Trees and small animals *are* lifted up, but so is the ground beneath them. + + +You can maybe (depending on how much unnecessary technical language you can swallow) learn more in this hard-to-follow [wikipedia article about these so-called ""Earth Tides""](http://en.wikipedia.org/wiki/Earth_tide)" +160 "Why was Plutonium used instead of Uranium in the ""Fat Man"" atomic bomb?" 3078 http://www.reddit.com/r/askscience/comments/3d609p/why_was_plutonium_used_instead_of_uranium_in_the/ 1436818313 3d609p Physics 2015-07-13 23:11:53 "To understand the Manhattan Project you have to understand the problems facing nuclear bomb production and how the project tackled them. There are two main issues in building a bomb, both with significant depth of details. One is materials, you need a fissile material suitable for use in an unmoderated fast-fission chain reaction. In the 1940s the candidates for such materials were U-235, U-233 (bred from Thorium-232), and Plutonium (primarily Pu-239). The downside of all of these is they are hard to produce, which turns out to be somewhat advantageous for the human race because it means it's not easy to make nuclear weapons. U-233 and Plutonium both require operating a nuclear reactor which serves as a prodigious source of neutrons which transmutes natural materials, that can then be chemically separated later. U-235 is naturally occurring but only in extremely low abundance as a tiny fraction of natural Uranium so isotopic separation at industrial scales is required. + +The second issue is assembly, and this adds even more complexity. With highly enriched Uranium (mostly U-235) speed of assembly isn't enormously important. Assembling the critical mass at speeds similar to that of a bullet being fired works, and this is where the ""gun-type"" bomb design comes from. A sub-critical mass of U-235 is fired at another sub-critical mass, when they slam together they create a mass that is beyond critical, and in a matter of micro-seconds a multi-step fission chain reaction occurs which releases terajoules of energy. With Plutonium there is an issue known as ""pre-detonation"" which prevents the use of a gun-assembly design. Any amount of bred Plutonium will contain a family of Plutonium isotopes, including things like Pu-240 which has a very high spontaneous fission rate, resulting in a large latent population of neutrons in the fissile material. What can happen is that during assembly if there are enough neutrons around then they can prematurely kick off a fission chain reaction at a time when the assembly is only just barely critical, and not in a super-critical state. The problem here is that nuclear reactions release vastly more energy than chemical reactions, and they proceed at a much faster rate. So a just barely critical chain reaction will rapidly develop enough energy to heat up and vaporize the entire bomb, and in so doing cause the bomb's components to spread apart, which then puts the bomb into a non-critical state, halting further nuclear reactions. If this happens at the instant that the bomb achieves critical mass then perhaps only a tiny amount of the potential nuclear energy is released, just around enough to vaporize the bomb, but not the kilotons of explosive yield desired. In gun-type designs the speed of assembly is so slow that the chance of a pre-detonation ""fizzle"" becomes very high when used with Plutonium. That's why implosion assembly was developed, because it creates a super-critical mass/density much faster and due to the inertia of the implosion shockwave results in the core being in a critical state for long enough to allow for a full nuclear yield. Keep in mind that maintaining criticality in a bomb core for merely 10 additional nanoseconds can essentially double the yield, and that'll give you a sense of the forces, time scales, and margins involved. + +Back to materials. In the early 1940s nobody knew how to do bulk isotopic separation and several different techniques were in contention including thermal diffusion, gaseous diffusion, centrifugation, and electromagnetic separation. Each of which would require massive, complex, expensive, and extremely high-tech industrial facilities. Obtaining highly enriched Uranium would make it possible to build bombs using a sure-fire weapon design, gun-assembly. On the other hand, in principle breeding Plutonium was much easier, it required only operating a nuclear ""pile"" or reactor and pulling out Uranium periodically for processing, the reactor wouldn't even need to produce power, it just needed to produce neutrons. However, the implosion design was very sophisticated and untested, so it was a risk to pursue, though it offered the promise of being more efficient in terms of nuclear material used. + +Here's the most important thing to understand about the Manhattan Project. At this point you see a huge variety of options of nuclear materials, production methods, and bomb designs. The sensible thing to do would be to do some degree of investigation into each aspect and then pursue the most promising alternatives. That's not what the Manhattan Project did, instead they pursued *every* route to the bomb. Simultaneously. That's how they achieved building nuclear weapons only 8 years after the discovery of the phenomenon of nuclear fission. They pursued both implosion assembly and gun-assembly. They looked at U-233 and discovered it was too hard to produce and to make into bombs. They pursued both Plutonium production and Uranium isotopic separation. They pursued every method for enriching Uranium and it turns out that what seemed to be the most promising one initially (centrifugation) was actually not very feasible with the technology of the time (and would not be until around the 1960s or so). Ultimately enriched Uranium was produced using each of the different techniques (thermal diffusion, electromagnetic separation, gaseous diffusion) as separate stages in a multi-step process (after the war the US focused on gaseous diffusion). + +One thing to note about the ""Little Boy"" bomb that was dropped on Hiroshima, the design was never tested before its use. That's how fool-proof the design was considered to be. Although it used so much Uranium (60 kg) that it would not have been feasible to run a test regardless. + +Ultimately the answer to your question is that the Manhattan Project was in a break-neck dash to produce nuclear weapons using any methods possible. And the reason why the bombs dropped on Hiroshima and Nagasaki were different is mostly because those were the bombs that were available at the time. Additionally, there was a greater capacity to build Plutonium fueled bombs because there was far more Plutonium available (as a multiple of bomb cores) than Uranium. + +Also, it's possible to use Uranium in implosion assembly designs, but because the critical masses are different the specifics of the design are different as well. The US decided not to pursue a Uranium fueled implosion design during the initial Manhattan Project (though they would later build such bombs). + +Edit: + +Likely more than you will ever want to know about the history of nuclear weapons programs: http://nuclearweaponarchive.org/ + +Edit2: meant to say kg instead of lbs." "Quite simply because we couldn't make enough Uranium in time. Enriching uranium (especially to the levels needed for a bomb) is a very complex process. + +Natural uranium is about 99% Uranium 238, and only 1% Uranium 235. Only the Uranium 235 is useful for making bombs, so the Uranium has to be [enriched](https://en.wikipedia.org/wiki/Enriched_uranium)- meaning separating out the 235 from the 238. The first bomb used Uranium which was enriched to 80% ^(235)U. + +Plutonium bombs are much harder to build, but plutonium is much easier to enrich. This required us to develop two bombs, but we would have never had enough enriched uranium in time to build a second bomb should have we not switched to plutonium. " +161 Do chickens have a limited supply of eggs throughout their life, or can they produce eggs as long as they have a functioning reproductive systema? 3077 http://www.reddit.com/r/askscience/comments/3cs6j4/do_chickens_have_a_limited_supply_of_eggs/ 1436522291 3cs6j4 Biology 2015-07-10 12:58:11 Birds, like humans, have a limited number of primary oocytes in their ovaries. But most of them don't live long enough to run out. [This Slate article](http://www.slate.com/articles/news_and_politics/explainer/2011/03/which_ends_first_the_chicken_or_its_eggs.html) that addresses your question says that some macaws, which are very long-lived, can run out of eggs, but the [study they cite](http://www.ncbi.nlm.nih.gov/pubmed/15021448) is on humans, and I can't find the macaw fact anywhere else. Still, biologically it makes sense that if a bird lived long enough, it would be unable to continue producing eggs. "As other posters have mentioned, they do have a limited number, but they tend to slow down by around 3 years, so it's not common for them to completely run out. They start laying around 6 months, give or take, and will lay almost an egg a day for the first year after that. Then they begin to taper off, and after they're about three they can be down to one to two eggs a week, at which point they're no longer economical to keep around for eggs. + +I have about 18 that are just under 3 years old, and which are giving me about 8-10 eggs a day total, plus 7 birds a year older than that who give me at most 2 eggs a week between them. The same batch of birds a year ago were still producing 12-15 eggs a day. + +The older 7 are desperately overdue for the stew pot, but I'm working too much right now. Essentially they're eating at least 1/3 of the feed (that bunch are actually always at the feeder), but are only producing about 3% of the eggs." +599 When birds fly south for the winter, how exactly does the population Distribution change? Do they all fly south an equal distance and displace each other, or do those that spend summer farther north have to fly farther south to find unoccupied territory? 3076 https://www.reddit.com/r/askscience/comments/58gupt/when_birds_fly_south_for_the_winter_how_exactly/ 1476970480 58gupt Biology 2016-10-20 16:34:40 "Totally depends on the species. I doubt you can make many generalizations about all birds. One that I know about is the Golden-winged warbler. They have a pretty wide summer breeding range, but are mostly rare breeders throughout. However, the whole population winters in a much smaller area in central America. Going down to Costa Rica in the winter and you wouldn't consider them a rare bird at all. Other birds are colony breeders and only breed in a few locations but then spread out to a wide winter range. + +Canada Goose is kind of an oddball because there is what's called a resident Canada Goose. These could almost be considered a separate subspecies that started not migrating (I think in the 1950s) and became permanent residents and prolific breeders at many parks. http://www.geesepeace.com/whygeesedonotmigrate.html" There really isn't much of a pattern to the changing population distributions of the Canada Goose, due in large part to interactions with humans. Because humans have created so many large habitats that have abundant fresh water, food, and lack predators (such as parks and golf courses), many populations have established permanent colonies and have mostly abandoned migration themselves, but continue to receive seasonal migratory populations. Individual flocks also migrate in widely varying directions and distances, as well as varying the number of rest stops and their length, and begin the migration at varying times. Some geese follow the same route every year, while others like to change it up. So, due to too many variables about the individual's migration, if they migrate at all, there really isn't any consistent pattern for the species as a whole. +162 If a feather was in a decaying orbit around the Earth, would it burn up during re-entry? 3072 http://www.reddit.com/r/askscience/comments/34tzrr/if_a_feather_was_in_a_decaying_orbit_around_the/ 1430753389 34tzrr Physics 2015-05-04 18:29:49 "I used to work doing simulations of re-entering spacecraft. We found that the most common things to survive were the bulky metallic parts of the craft - fuel tanks and batteries being the most common items recovered on the ground. They didn't look good, of course, but they were tough enough not to melt (through heat capacity and high melting points) during the quite short period of re-entry where the heat is the most intense. + +However, we also found on the far side of the scale that very lightweight MLI - the gold ""wrapping paper"" on the outside of satellites used for thermal insulation - also survived. This happened if it ripped off the satellite when the atmosphere thickened enough for the breakup to start. If it didn't rip away, and was pulled down by the heavier structure, it would vapourise easily. But things that got free very quickly slowed and cooled, and made it to the ground. A feather would have a lower melting point, but it would also not have (I presume!) a heavy satellite structure attached to it increasing its ballistic coefficient. I would be very surprised it didn't survive. + +Similarly, spiders and insects would have no problem with re-entry (other glacial cold, lack of pressure and radiation damage from being in space and the sea they'd likely land in). I wonder if something bigger, like a mouse, could too?" "Much of the debris from the Columbia disaster was paper. Surface area to mass. Heck, even petri dishes with worms survived the re-entry. + +So I'd guess, from empirical evidence, that the feather would be intact." +474 A ring of rope is wrapped around the Earth. With only 6.3 additional meters of slack, the rope would hover 1 meter off the ground. Does this surprising fact have a three dimensional equivalent? 3069 https://www.reddit.com/r/askscience/comments/4xxroa/a_ring_of_rope_is_wrapped_around_the_earth_with/ 1471322441 4xxroa Mathematics 2016-08-16 7:40:41 "The disconnect and surprise likely comes from thinking that since the radius and circumference of Earth are already large that changes to them must be equally large. Or maybe it's in thinking that the extra 6.3 meters of rope have to somehow be stretched and distributed across the entire world. I don't know. Anyway, that's clearly not the case since you really would only need an extra 6.3 meters. + +The circumference *C* scales *linearly* with the radius *r*, to wit, *C* = 2π*r*. So if you increase *r* by 1 unit, you will *always* get an increase in *C* of only 2π units, no matter how large the radius is. If the magical rope were around Jupiter or the Sun or the largest known star, you would still need only an extra 2π-meters of rope to get an extra 1-meter of radius. + +Surface area *A*, on the other hand, scales *quadratically* with the radius, to wit, *A* = 4π*r*^(2). So the increase in *A* achieved by a 1 unit increase in *r* actually changes with the current value of *r*. In fact, a fixed increase in radius gives a larger increase in area the larger the radius is already. + +Specifically, suppose you want to increase the radius by *dr* units. Then + +> *dA* = 4π(*r* + *dr*)^(2) - 4π*r*^(2) + +where *dr* is the increase in radius. We can rewrite this as + +> *dA* = 4π( *r* + *r* + *dr*)*dr* = 8π*R* *dr* + +where *R* is the average of the old and new radius. If *dr* is small compared to *r*, then *R*, *r*, and *r*+*dr* are all approximately equal. Note that for fixed *dr*, *dA* scales linearly with *R*. So the larger the radius already is, the bigger the resulting increase in area for a fixed increase in radius. + +Putting *dr* = 1 meter, we find that for the fabric to hover above the surface by 1 meter, we would need [about an extra 160 km^(2) or 62 mi^(2)](http://tinyurl.com/jfmckjw) of fabric. + +--- + +In fact, all we are really doing is computing the *derivative* of the circumference and surface area with respect to the radius, a concept familiar to calculus students. The derivative of *C* with respect to *r* is just 2π, which is constant. This means that any increase in *r* gives a proportional increase in *C*, and that proportion is the same no matter how larger *r* already is. The derivative of *A* with respect to *r* is 8π*r*, and we actually write this as + +> *dA*/*dr* = 8π*r* ===> *dA* = 8π*r* *dr* + +If we wanted to examine an analogous problem for volume, we would note that *V* = (4π/3)*r*^(3), so that + +> *dV*/*dr* = 4π*r*^(2) ===> *dV* = 4π*r*^(2) *dr* + +Notice that for volume, for a fixed increase in radius, the resulting increase in volume grows much faster than for surface area." "Okay, so this is a bit off subject and only 2 dimensional. But Area has a wonderful ""surprising affect"" on pizza. + +Going from a 10"" to 14"" pizza is super cost efficient. Typically restaurants will scale their prices linearly, but the area scales ~~exponentially~~ quadratically (A=PI*R^2) + +A 10"" pizza is roughly half the size of a 14"" pizza, but rarely half the cost. So if you're out with friends, don't buy multiple small pizzas. Buy one Jumbo, you'll save a bunch of money and probably have leftovers! + +MMMMMMM.... Pizza Pi ;) + +EDIT: TIL I'm not a **true** mathematician. Just a guy that likes pizza." +265 "Why can't we prescribe a ""medical tapeworm"" to an obese patient?" 3066 https://www.reddit.com/r/askscience/comments/3ktnfg/why_cant_we_prescribe_a_medical_tapeworm_to_an/ 1442175559 3ktnfg Medicine 2015-09-13 23:19:19 Tapeworm larvae can migrate to other parts of the body, like your brain. Need I say more? "http://danandjanean.com/images/OldAds/TapeWormWeightloss.jpg + +Yes, they did that a great deal in the past. + +http://care.diabetesjournals.org/content/23/1/118.full.pdf + +Mentioned here too. + +As parasites are prone to do though, they can infect other parts of your body and cause serious medical issues, and can easily cause vitamin deficiencies. + +https://en.wikipedia.org/wiki/Cysticercosis + +http://www.medicaldaily.com/tapeworm-weight-loss-pills-hospitalize-teen-girl-after-mothers-gruesome-obsession-299166 + +And have been know to cause serious medical issues. " +475 How can a maglev train be energy efficient? 3064 https://www.reddit.com/r/askscience/comments/4hn7c2/how_can_a_maglev_train_be_energy_efficient/ 1462281615 4hn7c2 Physics 2016-05-03 16:20:15 "To start off, as you might expect, the key benefit you get from suspending a train magnetically is that you get less friction than using a traditional track, which in turn can boost its efficiency. But I believe you are asking why this gain is not washed out by the energy needed to keep the train suspended. Without going into the specific details of how a maglev train works, think of the problem in slightly more general terms. The problem is that your question seems to have the implicit premise that supporting a stationary weight requires a constant input of energy. However, while this notion may be in line with our intuition (e.g. we get tired when holding up a weight at the gym), it is not true in general. You do not need to supply additional work to keep a body at rest in a constant force field. After all, a book sitting on your table doesn't require a constant input of energy not to fall through your desk. A combination of electrostatic repulsion and electron degeneracy is enough to overcome gravity and let the book sit still on the table just fine. + +Magnetic suspension is not fundamentally any different, except that now you are using a magnetic force to overcome gravity. But the point remains, while it would take work to lift a weight from the ground up using a magnetic force, once the weight is suspended no further work is required to keep it in place. This is why you can suspend a magnetic material [on top of a superconducting surface](https://www.youtube.com/watch?v=Ws6AAhTw7RA) with no further work required than that to keep the superconductor below its critical temperature. + +**Edit:** To answer some follow-up questions, maglev trains come in many types: some like [Inudtrack](https://en.wikipedia.org/wiki/Inductrack) use permanent magnets, others use electromagnets, etc. But the heart of the answer to OP's question is more general. Regardless of the underlying details, once you suspend a stationary object, no further work is required to keep it suspended. If you use permanent magnets, you can keep a weight [suspended indefinitely](http://i.imgur.com/8wpCIt9.jpg) without using up any more energy. On the other hand, if you use electromagnets, you do have to use some energy to maintain the magnetic field. But the reason you need this energy is because the wires have a finite electrical resistance (which leads to energy wasted as heat), not because you need to do additional work to keep the train suspended." "It doesn't take any energy to keep something from falling, only a force. When it's on the track there is a force pushing down ( gravity) and one up (magnets). It's in an energy ""well"" meaning it would take energy to move it up or down but not to make it stay in place. The only energy requirement is powering the magnets and that's easy when you're not trying to move the thing up or down. Giving it kinetic energy in a certain direction will require significant input but we don't want the train moving up or down, just side to side, so the up down doesn't contribute much to the energy cost." +33 What would happen if the moon was covered with a highly reflective material (such as tin foil)? 3052 http://www.reddit.com/r/askscience/comments/2z527h/what_would_happen_if_the_moon_was_covered_with_a/ 1426440578 2z527h Physics 2015-03-15 20:29:38 "**Short answer:** During full moons it would be about 8x brighter. + +**Long answer:** The *albedo* of a body determines how much light it reflects. For the moon, that number is about 0.1, meaning that it reflects about 10% of the light. [This book](https://books.google.com/books?id=c-v7OSaxGSsC&pg=PA112&lpg=PA112&dq=albedo+aluminium&source=bl&ots=XUXTa7N79d&sig=ms8D3mnC-ey6PjbtM7fPIfshSiQ&hl=en&sa=X&ei=AcMFVZbyF_eCsQS0yIGwAQ&ved=0CB8Q6AEwAA#v=onepage&q=albedo%20aluminium&f=false) has a nice table of albedos for various building materials, including ""bright aluminum foil,"" which it lists an albedo of 0.8, or 80%. + +Therefore, the moon now reflects 8x more light. Depending on the moon phase, we'll receive variable amounts of light on the earth. For reference, I want to show your some numbers for the luminous flux (or lux) or various light sources. Although this sounds like what a mad scientist might call his death ray, I assure you this just means how much light we get on a given area. + +Anyway: + + Cloudly, moonless night: 0.0001 lux + Full moon: 0.27–1.0 lux + Twilight: 3.4 lux + Full moon (with aluminum foil): 2.2-8.0 lux + Dim Office Building Hallway: 80 lux + Sunrise/Sunset: 400 lux + Direct sunlight: 32000–100000 lux + +So you'll easily be able to see at night provided there is moonlight. Since the full moon is now considerably brighter than twilight, I'd suspect the sky would take on more of a navy blue color and that we'd have fewer stars visible in the night sky. The Milky Way is already quite hard to see when there is moonlight, and with a foiled-moon it will be a sight reserved for the few moonless nights each month. + +Even the light from a crescent moon covered in aluminum foil is brighter than a full moon without one. Fun fact: you can actually see the dark part of the crescent moon even without aluminum wrapping. Even though the dark part is not receiving direct sunlight, it's being illuminated by sunlight reflected from the earth (in much the same way the earths get a little bit of light from the moon). This is called [earth shine](http://www.mattastro.com/gallery/earthshine_07may08.jpg), and would be easily resolvable at night, and it might even be possible to see it during the day. +" [deleted] +476 Is there a formal way of deciding what fraction of a game is chance? 3051 https://www.reddit.com/r/askscience/comments/4zqby2/is_there_a_formal_way_of_deciding_what_fraction/ 1472239005 4zqby2 Mathematics 2016-08-26 22:16:45 "I'm not sure how developed the concept of *chanciness* is. There is a paper by Jakob Erdmann from the Friedrich-Schiller-Universitat that deals with the concept. [Here is the pdf link.](https://www.minet.uni-jena.de/preprints/erdmann_09/chanciness.pdf) + +Their goal is to create an algorithm for automatically determining the extent of chance and skill in a game." "Some random thoughts (initially restricted to 2-player games, but easy enough to generalise, I think): + +Consider a game G between two players. Player A takes a random decision, distributed evenly from all possible available moves. Player B always takes the move that gives them the greatest probability of winning the game in every situation. Define the chance fraction C(G) of the game to be 2P, where P is the probability that player A wins. In a perfectly random game, Player A will win exactly 50% of the moves (since there's no better decision than random chance available), so C(G) would be 1. In a game with zero chance, player A will win something extremely close to 0% of the games (that is: exactly 0 unless there exists a winning strategy for A from the start position, in which case it's the chance that A accidentally plays that winning strategy). + +Advantages: Works, pretty unambiguously determines the level of chance in the game. Can be approximated by having the best players available play against random steppers. Matches intuition of what it should be. + +Disadvantages: Ludicrously difficult to calculate precisely for games that aren't extremely simple. " +362 What is the non-human animal process of going to sleep? Are they just lying there thinking about arbitrary things like us until they doze off? 3050 https://www.reddit.com/r/askscience/comments/42waw8/what_is_the_nonhuman_animal_process_of_going_to/ 1453877911 42waw8 Biology 2016-01-27 9:58:31 "Sleep scientist here. We cannot know what they are thinking about. +However, in mice, dogs and cats at least, they become less active and usually move to their ""nest"" or dog bed. Here they move from an active wake period (a classification of wake), to a quiet wake period. From here they move into nrem sleep. This behavioral state is classified as really slow and big brains waves known as delta waves. REM sleep state happens less frequently than wake and NREM. When it does it happens after NREM sleep. + +So animals transition much the same as humans, well depending on the animal, as some do not have REM sleep. Hell, some animals like ostriches have a mixed state of NREM and REM sleep. Really weird. + +anyways, with respect to rodents (mice and rats) they transition super quick. Moving form wake to nrem to rem much faster as they spend less time in these states. + +I can run down later and run a recording to show you the different muscle/brain activity that helps us differentiate states or just link to papers." Every mammal studied has some kind of sleep-like state similar to human sleep. As for what they think about before they sleep, we may never really know for sure. Some brain activity suggests they they might indeed recite recent behavior they have just partaken in but that's just conjecture based on the activity of several neurons. +266 Why does fabric get darker when it gets in contact with water? 3046 https://www.reddit.com/r/askscience/comments/3nctdz/why_does_fabric_get_darker_when_it_gets_in/ 1443889261 3nctdz Physics 2015-10-03 19:21:01 "The short answer is that fabric appears darker when it is wet, because the water reduces the amount of diffuse reflection from outermost layer of fabric. Since how ""dark"" we perceive a material to be depends on how much light it reflects towards our eyes, the net effect is that the fabric will now seem darker. + +To see why this happens, take a look at how fabric (e.g. cotton) [looks under high magnification](http://aldpulse.com/sites/default/files/TUe%208.jpg). As you can see the fabric is made up of a bunch of irregular micrometer sized fibers, the gaps of which are usually filled by air. Now what is important for the optical properties of the material is that the fibers and the air have different [refractive indices](https://en.wikipedia.org/wiki/Refractive_index) (about n=1.5 and n=1 respectively). This mismatch between the refractive indices gives rise to a lot of scattering, and because the length-scale of the variation is on the order of tens-hundreds of microns (similar to the wavelength of visible light), the specific mechanism at play will be so-called [Mie scattering](https://en.wikipedia.org/wiki/Mie_scattering). Mie scattering has the property that light of all (visible) wavelengths is scattered more or less equally and it's the mechanism for why say paper appears white (as well as clouds or milk for that matter). + +The net effect of the description above is that when air fills the pores in the fabric, you will get a lot of scattering events, which will result in a lot of [diffuse reflection](https://en.wikipedia.org/wiki/Diffuse_reflection). Now when you add water, the water molecules will displace the air inside the pores, and this is important because water has a refractive index (n=1.3) closer to that of the fabric (n=1.5). Because you are reducing the refractive index mismatch, less light will be scattered, which means you will get less of the hazy reflection you get from dry fabric. Instead, more of the light will either be simply transmitted through the fabric, or it will bounce around in the fabric/water layer due to a process called [total internal reflection](https://en.wikipedia.org/wiki/Total_internal_reflection) [as shown here](http://imgur.com/ieX3QoH) and eventually absorbed. The net effect is that the material will appear darker. As an aside, this is the exact same reason why [paper appears more transparent when wet](http://timholtz.com/wp-content/uploads/a/6a00e39827d9ad8833015434440b5a970c-800wi.jpg), since less scattering leads to a greater transmittance of light through the material." This is awesome, my 6yr old asked this question about a week ago and I forgot to put it here! +363 "Are some 3D curves (such as paraboloids, spheres, etc.) 3D ""sections"" of 4D ""cones"", the way 2D curves (parabolas, circles, etc.) are sections of 3D cones?" 3046 https://www.reddit.com/r/askscience/comments/4a69kp/are_some_3d_curves_such_as_paraboloids_spheres/ 1457829224 4a69kp Mathematics 2016-03-13 3:33:44 "Absolutely! Notice that for the 2D curves you describe, they take the form F(x,y)=k for some function F and a constant k (e.g. x^2 + y^2 =1 is the unit circle). The restriction on the values of the function F set up a relation between x and y that gives us the specified curve (and we get the x and y by selecting all the x and y values that satisfy the relationship (1^2 + 0^2 = 1, so x=1 y=0 satisfies the relationship)). + +Now think about the function F on its own, without any restriction on its value. We have no relation between x and y, but we can look as the range of values by graphing the 3D figure z=F(x,y). We can set up many different relations of x and y by selecting z=k (same as F(x,y)=k, like before). (These are called level curves of F) + +But now let's consider a function G(x,y,z). We could look at the range of values by setting up u=G(x,y,z), but we can't look at a graph of that because we have for variables so we need a four dimensional figure to set it up. But we could set up the level curves of G and have a relationship between values of x, y, z. We can graph that relationship (and we might get the paraboloids you were talking about). In the same way we select values of x,y for F to get circles, we can restrict the values of G to get values of x,y,z that make spheres. + +The important difference is that we have no 4D graph to cut out from to get 3D graphs, while could cut 2D graphs from 3D ones. In terms of equations though, it all works the same. + +I'm going to come back with some links soon when I get off mobile. + +EDIT: Rereading your question, I now need to answer specifically for Conic sections. So let's apply my arguments for that. + +Lets work with the classic conic sections. F(x, y)= sqrt(x^2 / a^2 ± y^2 / b^2) (Where, if you are not familiar, ± means it could be a plus or minus sign). [Here is a picture of z=F(x, y) for simple a, b and the plus sign](http://www.wolframalpha.com/input/?t=crmtb01&f=ob&i=graph+sqrt(x%5E2+%2B+y%5E2\)). We can get different conics depending on how we choose a, b and the ±. We get the ""standard form"" or conics by selecting F(x, y) = 1. So let's look at G(x, y, z) for the next dimension up. + +The form of G(x, y, z) is similar; G(x, y, z) = x^2 / a^2 ± y^2 / b^2 ± z^2 / c^2. We certainly get the same result if we take G(x, y, z) = 1, where we can manipulate the values of a, b and the ±'s to get the different [quadric surfaces](https://en.wikipedia.org/wiki/Quadric#Euclidean_plane_and_space). But we can't call z = G a 4D cone right off the bat, can we? + +Let's see if the identifying features of the 3D cone are the same as the 4D one, and for simplicity, let's consider a standard, right cone (a = b = c = 1, all ±'s are plus). One identifying feature is that cones are flat, or rather the rate of increase as we go straight out from the center is constant. Mathematically, we look at the direction and magnitude of the gradient vector of the function, which points in the direction of greatest increase. The gradient points straight away from the origin and always has magnitude 1, so it constantly gets wider, and at a constant rate. That's all we need. (If you want to know the vector, it's (x / sqrt(x^2 + y^2), y / sqrt(x^2 + y^2) ). + + +Let's look at the 4D cone and look at the gradient vector for that. Direction? Straight away from the origin. Magnitude? 1. So as far as we can tell, it's a cone. We can't graph it to make sure, and more math would get complicated quick, and in my case, it's overkill. + + +So yeah. The quadric surfaces are cuts of a 4D cone just like 2D conics are cuts of a 3D cone. + +More reading: + +[Kinda Technical] [Paul's Math Notes: Quadratic Surfaces](http://tutorial.math.lamar.edu/Classes/CalcIII/QuadricSurfaces.aspx). Introduction to quadratics surfaces, which is the central point of OP's question. + + +[Semi-Technical, but lots of confusing pictures] [Wikipedia: Hypercone](https://en.wikipedia.org/wiki/Hypercone). Wikipedia's discussion of the geometric figure of u = x^2 + y^2 + z^2. Lots of interesting pictures. + + +[Very Technical] [Wikipedia: Algebraic Geometry](https://en.wikipedia.org/wiki/Algebraic_geometry). Algebraic Geometry is taking a look at the graphs and surfaces when you set F(x, y) = 0, but when F only involves powers of x and y (no e^y, sin(sqrt(x)), etc.). More generally, it looks at the ""solution sets"" to polynomial equations of many variables. The solution sets, with other conditions, are called ""algebraic varieties.""" "This isn't exactly what you are looking for, but it was posted in r/math and I figured I'd post it here + +http://imgur.com/a/XZpBP + +transforming higher dimensional objects through lower dimensions is a good way to try and ""picture"" what they look like. (Note: read the descriptions of the images as they include more links)." +34 "If a space ship were to have a cloth banner, a flag, on the outside, while in motion, would it ""flap in the wind"" or remain perfectly straight?" 3045 http://www.reddit.com/r/askscience/comments/345i4q/if_a_space_ship_were_to_have_a_cloth_banner_a/ 1430228628 345i4q Physics 2015-04-28 16:43:48 "Since there is nothing to push back against the cloth, the only physical forces governing the movement would be the three laws of motion. http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion (this is always true, but I mean the actual results are simple enough that it's easy to understand exactly how it will act) + +If the ship isn't accelerating the cloth wouldn't move at all. If it ship is accelerating the cloth will point away from the direction of acceleration. If there is a quick change it will bounce around a bit." When the Apollo astronauts planted a flag on the moon it had a wire frame in the upper seam to keep the flag extended out. Planting the flag in the lunar regolith involved a twisting motion of the flag pole, and this imparted a pendulum motion on the lower part of the flag that some less informed people took to be the flag waving in a breeze, and was *evidence* that the landing was faked. Of course, it wasn't faked. +267 If you roll a die twice under the exact same circumstances, and I mean every possible thing is the same, would it produce the same result? 3041 https://www.reddit.com/r/askscience/comments/3qscxp/if_you_roll_a_die_twice_under_the_exact_same/ 1446170318 3qscxp Physics 2015-10-30 4:58:38 "This would indeed be untrue for simple quantum systems, the same initial system can indeed yield different outcomes. But dice and coins are incredibly complex quantum systems which have the funny behavior of behaving classically. A physical coin should, given the same initial conditions, *overwhelmingly* land the same way each time. In fact, some researchers at Stanford did just that by building a coin flipping robot, + +* http://www.npr.org/templates/story/story.php?storyId=1697475 + +______ + +To elaborate on ""same system"" business. See here, + +* https://www.reddit.com/r/askscience/comments/3qscxp/if_you_roll_a_die_twice_under_the_exact_same/cwi5pxl + +>Can we really have ""the same initial system"" though? + +There is some technical reasons calling something the same system works, I'll try to explain it. + +>at least some variables have to change, the simplest being space, time, or both + +We use [Noether's theorem](https://en.wikipedia.org/wiki/Noether%27s_theorem) for this. The laws of physics are unchanging to certain symmetries. If our universe, or at least part of it, obeys a symmetry, there is a corresponding conservation law. Here's two examples, + +* Momentum is the corresponding conserved quantity when the physical laws are invariant to spatial translations. + +* Energy is the corresponding conserved quantity when the physical laws are invariant to time translations. + +In physics, the physical laws must describe all dynamics involved and if they obey these symmetries, then we know translations in time and space change nothing and we're safe to say ""same system."" Even in situations where the symmetry is broken (if you drop an apple, its momentum is not conserved, but the apple-Earth system momentum is) we can show how big the break is and often can figure out how to make it small as possible. + +>In the case of coins or dice, that cutoff may throw out stuff like temperature distribution, the exact positions of atoms, air currents, and many more... and yet we call it the ""same"" initial conditions + +When I say same initial conditions, I mean literally the equations of motion written down and solved. There is only one solution possible because of the principle of least action. When you move to repeatability, you then have to show (numerically or painfully by hand) that the fluctuations you see will remain bounded near the same outcome such as coin trajectory. As a striking example of when outcomes are not bounded are weather patterns on Earth which are very sensitive to initial conditions, so even ""look-alike"" systems can have thousands of dramatically different outcomes. + +But not all systems behave this way and we can even define the variance required (in an initial condition like air temperature) before the physics dynamics become unreliable if you had just assumed the average initial conditions. Check out chaos theory for more on this. Either way, we can indeed make a ""sameness"" criteria mathematically. + +>but do we really know, or even can we know, whether any of the variables we decide to cut out from our definition of sameness might or might not influence the observed outcome? + +>can we really say the same doesn't apply to simple quantum systems which we can barely observe? + +The Bell inequality experimentally rules out any locally hidden quantum variables. Either that variable doesn't exist (thus true randomness) or the variables are global (and propagate faster than light). Most physicists dislike the second option. There are a handful of ways out of the first option, but none of them offer a way to physically do anything about it, from your POV, it's true randomness." "There's a great demonstration used in philosophy of science courses where a coin-flipping machine can be adjusted to deliver 100% heads (or tails). Takes a little tweaking to get it just right, but it's certainly possible. See page 2 of [this](http://statweb.stanford.edu/~susan/papers/headswithJ.pdf) .pdf. + +In that context, it is possible to standardize a random number generator so that it is repeatable." +364 Is there a scientific explanation for the phenomenon of humor? 3037 https://www.reddit.com/r/askscience/comments/45qyzq/is_there_a_scientific_explanation_for_the/ 1455461031 45qyzq Psychology 2016-02-14 17:43:51 "One of the theories behind humor is that it's the body's way of signaling that something is no longer threatening. It has to do with cognitive dissonance - the mental stress or discomfort experienced by an individual who holds two or more contradictory beliefs, ideas, or values at the same time or is confronted by new information that conflicts with existing beliefs, ideas, or values."" So we developed a sense of humor by perceiving a danger and later finding out that the threat was a misunderstanding. An example of this would be our ancestors being afraid of a loud noise in the woods and then discovering that it was caused by a tiny squirrel. Humor is a way in which the mind reconciles reality with its imagination, and thus closes the gap that is cognitive dissonance. This has evolved to include not just danger but other inconsistencies in reality. Most jokes have two story lines, a set up and a punchline. The set up leads you down one train of thought and plays to your sense of reality. The punchline creates a second parallel train of thought that reconciles your reality to your imagination. (It also works if the roles are reversed.) You are lead to believe one thought in the set up, then you find out that there is also a second hidden thought that you didn't think of that you also believe to be true. + +Update: I found a great joke to demonstrate a two story line joke, more commonly known as a one-liner. One-liners are the most efficient means of conveying a two story line joke. This joke is from the onion. ""Justice Scalia Dead Following 30-Year Battle With Social Progress."" The first story line is the reality of the cause of Justice Scalia's death. We are led to believe that he fought a physical ailment for 30 years. There really isn't anything funny about that and it seems unlikely that there could be anything funny about it. Then it is revealed that the true cause of his death was the burden of being a stuffy conservative for such a long time. The punch shifts the point of the story from the reality of his death to the imaginative cause of his death. While we know that one can't actually die from being too socially conservative, it does reconcile the potential discomfort one might feel after being on seemingly the wrong side of so many social issues for such a long time. The punch is really clever and a great example of a hidden story line that you didn't think of that you could also believe to be true. " "I can try to address a more ultimate theory of humor (evolutionary, not mechanistic). Humor and creativity are kind of weird aspects of human nature because they're very difficult to account for under Darwin's Natural Selection theory. Why are we creative? Why do we make jokes? + +There have been a lot of different theories of this. Some people think they are mere side effects of human intellect (exaptations) and others think that they serve some sort of adaptive function (Social Brain hypothesis). + +Geoffrey Miller has proposed that many of our cognitive functions are the result of sexual selection (another of Darwin's theories, explored in *The Descent of Man*). This would propose that humor and creativity serve as honest indicators of quality in potential mates. For example, humor, creativity, and intelligence are all highly correlated. Or potential mates with less parasite resistance may not have the excess energy to expend on creative behaviors. Under this theory, creativity and humor would be displays, advertisements for mates. + +It's pretty interesting stuff. Ultimately it can be difficult to apply evolutionary theory to human culture and behavior rigorously. But if you're interested in reading more about it Karmihalev's (2013) review ""Why Creativity is Sexy"" is readily available online and unites a lot of the evidence in favor of Miller's theory. + +EDIT: + +Sorry, ignored your specific questions originally. Let me take a stab at them under Miller's hypothesis. This is just my own theorizing of course. + +Some research has suggested that while females generally prefer a mate with a good sense of humor, males tend to prefer a mate that is receptive to humor (Bressler et al., 2006; Bressler and Balshine, 2006; Clegg et al., 2011). So uncontrollable bouts of laughter may be the appropriate response, advertising a preference for humor, which may make a mate more desirable. There's no need for this to be restricted by sex, though, as humans are FAIRLY monogamous and have likely been acted upon by sexual selection for both sexes, given our high parental investment. Or perhaps it's a bit more Fisherian, with a correlated sex-limited trait and preference for humor that might lead to an expression of that trait in both sexes dependent on certain steroid and hormone levels. + +As far as other animals go, there seems to be a correlation between intelligence and practically useless cognitive feats like humor and creativity. So I would guess there may be a threshold of intelligence that must be crossed for the expression of humor. There's some evidence of a threshold for creativity around 100-120 IQ points (Jauk et al., 2013). I would guess that if humor is present in animals, it would be in social animals with high intelligence and high parental investment. Great apes are obvious, our closest ancestors. Might try dolphins and whales, too, though. But I don't know what the literature says. + +EDIT: + +FAIRLY monogamous. Thanks for keeping me honest. +" +1269 How do we know if a thermometer is accurate? Should we trust that the local weather service has accurate thermometers? 3034 https://www.reddit.com/r/askscience/comments/au3dyf/how_do_we_know_if_a_thermometer_is_accurate/ 1550976056 au3dyf 2019-02-24 5:40:56 "Calibrating measuring instruments is a complicated issue, but basically, there are very accurate instruments which are used to calibrate less accurate ones, which are used to calibrate less accurate ones. + +And in a workplace, you will have your tools calibrated professionally at regular intervals." "Here are a couple of things I learned while exploring this question. + +1) I discovered the existence of r/metrology (metrology is ""the scientific study of measurement""). Looks like your question was fully answered here, but for any future measurement questions I'd bet that's a good group to ask. + +2) According to an 1991 NIST document for calibrating ""liquid in glass"" (e.g. mercury, alcohol) thermometers, a proper ice bath requires ice that is the consistency of ""snow cone"" ice. [https://www.nist.gov/sites/default/files/documents/calibrations/sp819.pdf](https://www.nist.gov/sites/default/files/documents/calibrations/sp819.pdf) + +​ + +​ + +​" +477 Why is lead so dense but so soft, aluminium so light but also soft, but then tungsten is very dense but incredibly hard and titanium is so light but also really hard? 3032 https://www.reddit.com/r/askscience/comments/4pmo7y/why_is_lead_so_dense_but_so_soft_aluminium_so/ 1466772208 4pmo7y Chemistry 2016-06-24 15:43:28 "Hardness is a material property that's based on the crystalline structure of the specific material. Each of those elements that you listed has a different crystal structure, as well as packing factor (the density that the atoms can pack into space). The crystal structure is how the atoms of each element arrange to form the material (in this case, all metals). Aluminum is face-centered cubic (FCC), lead is FCC as well, tungsten is body-centered cubic (BCC), and titanium is hexagonal close-packed (HCP). A good visual and more information on crystal structure can be found here: https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Structure/metallic_structures.htm + +Each of these crystalline structures is the ideal and preferred spacial arrangement of the atoms for each element based on their coordination number (number of other atoms each atom is ""touching"") and the size of their atom. + +These properties contribute to the overall hardness of a material, which is the material's resistance to deformation. FCC metals are typically the weakest because they are packed so closely together that they have a large number of slip systems, which are directions that slip dislocations (deformation) can occur. BCC has fewer slip systems, leading to harder materials. Lots of post-processing can be done on the materials as well to affect the hardness, such as cold-working and annealing. " [deleted] +1394 How do satellites calculate co2 emissions? 3030 https://www.reddit.com/r/askscience/comments/cv6h9o/how_do_satellites_calculate_co2_emissions/ 1566725320 cv6h9o Earth Sciences 2019-08-25 12:28:40 I work in flight software on one of these satellites. I am an engineer, not an earth scientist but I'll do my best. Molecules react differently to electromagnetic waves, the application of this is called spectroscopy. Satellites use a series of prisms and lenses to separate the light into frequency bands and analyze these bands to determine chemical composition. If you'd like more information, there is tons online about spectroscopy used within astronomy and earth sciences. [http://astronomy.swin.edu.au/cosmos/S/Spectroscopy](http://astronomy.swin.edu.au/cosmos/S/Spectroscopy) "The other answers posting about infrared spectroscopy are correct in terms of the “how”, I just wanted to make a clarification on how this relates to emissions. For the high precision OCO-2 mentioned in your links, it actually measures the total amount of light absorbed and reflected back to space by CO2 (rather than the CO2 itself). This is done on a really fine grid mesh (~0.8x1.4 miles) multiple times per second, giving us a picture of what the CO2 concentrations are on earth at all times at really high resolution. + +Then, with assistance from computer models, if we track the amount of CO2 over time we can estimate emissions (either positive or negative) in a particular sattelite grid cell based on the change in concentration over time. + +See the wiki on the OCO-2 for more info: https://en.m.wikipedia.org/wiki/Orbiting_Carbon_Observatory_2" +35 Would people with dyslexia have problems reading Braille? 3026 http://www.reddit.com/r/askscience/comments/2ujb8h/would_people_with_dyslexia_have_problems_reading/ 1422898735 2ujb8h Neuroscience 2015-02-02 20:38:55 "[This case study from the 1970s](http://ldx.sagepub.com/content/8/5/32.short) found that Braille was a big help to one severely dyslexic girl. + +But [this experiment](http://www.sciencedirect.com/science/article/pii/S0010945276800305) found that dyslexic children struggled to learn letters in both Morse Code and Braille compared to non-dyslexic children. + +[Dyslexia-like difficulties have also been observed in blind children who exclusively used Braille](http://jvi.sagepub.com/content/16/2/61.short) -- which suggests that dyslexia isn't exclusive to sighted reading." "I'd like to interject with a description of what is really going on in the brain of a person with dyslexia. + +The act of writing involves taking an idea, putting it into words and then transcribing these words using symbols, which we call letters. Making this process even more complicated is the issue of spelling: in order for the symbols to be comprehensible, they need to conform to a standard order. When reading, this process runs in reverse. Your brain needs to ""decode"" the symbols to get the information they contain. + +Most people use specific sections of their brains to read, write and process language. Dyslexic people use a different part of their brains to try to accomplish these same tasks. This has been demonstrated using studies where brain scans are taken while a dyslexic person reads and writes. + +Professionals in the field describe this as having problems with symbol decoding. When a person mixes up b and d, it actually isn't because they are mentally reversing the letter in some way. Rather their brain has difficulty assigning the phonologic meaning /b/ to the symbol b. + +These language difficulties frequently are accompanied by difficulty breaking words into their component syllables and are characterized in many children by a lack of interest in language games and nursery rhymes. To put it more bluntly, the reason many dyslexic kids don't like Dr. Suess is because the fact that cat and hat rhyme isn't something that they notice instinctively. + +So, how does this affect blind students or could a person with dyslexia read Braille? + +No, the dyslexic person would not find Braille any different than reading letters they could see because they still need to associate a symbol (though in this case, one they can feel) with a sound (decoding) and then piece together a word and meaning from the sound. This is also why fonts which claim to ""make the letters stop moving"" are a load of hogwash. They don't address the underlying issue of decoding problems. + +Dyslexia is found in all groups of people, including those who speak languages such as Chinese which are largely pictographic. While it doesn't have an alphabet, reading and writing these languages still necessitates going from symbol to sound and meaning and that's where the problem is. + +Sources: http://www.interdys.org/ewebeditpro5/upload/Definition.pdf + +http://www.interdys.org/ewebeditpro5/upload/DyslexiaBasicsREVMay2012.pdf + +TL;DR: Yes. Dyslexia means that a person has trouble ""decoding"" symbols and connecting a specific symbol with a sound. This wouldn't change if they were feeling the symbol rather than seeing it. +" +478 How were they able to train the brain to recover from paralysis using VR? 3020 https://www.reddit.com/r/askscience/comments/4xjbw9/how_were_they_able_to_train_the_brain_to_recover/ 1471099386 4xjbw9 Neuroscience 2016-08-13 17:43:06 "Just reading the article, the goal of the research was training people to control a mechanical exoskeleton with their brain waves. Controlling movement in VR was just one training step before doing it with the real system. + +It seems that the improvement in function and sensation was an unexpected side benefit. I think in most paralyzed people the spinal cord is not severed, just damaged. + +It's not clear whether there would be a benefit to just doing the VR training, or if they need to use the exoskeleton to see these improvements." "I'm not a neuroscientist.. but I am a molecular biologist who got a spinal cord injury about nine months ago and have been doing research into this. +The short answer is: no one knows. +The long answer is: seven out of eight of the patients in this study were ASIA A -- meaning complete -- paraplegics. Think no sensation or motor activity below the level of lesion. This is usually caused by a complete severing of the spinal cord. The dogma is: there is pretty much no regeneration capacity of the central nervous system. Doctors would not expect this to happen. These patients went from being completely wheelchair bound (for years with no improvement) to being able to use a walker. I think our understanding of the nervous system and the methods we can use to get it to heal are very limited. This is a great step in the right direction. It shows the potential is there! It must be an amazing new hope to all those with a complete SCI who hear the doctors say that: this is it, nothing we can do. + +Also, I think this is a [good summary](https://www.sciencedaily.com/releases/2016/08/160811101008.htm) of the article with some context and some hypothesis on the mechanism. +One of the authors suggest that even in patients that have complete paralysis, some small number of fibers remain intact. The hypothesis is that with VR, patients can be trained to use them for walking, etc. There is no evidence to support this hypothesis, though. " +36 In light of the new high-res photo of Andromeda, is there any chance that we will be revising our estimate of the total number of stars in the galaxy? (currently 1 trillion) 3018 http://www.reddit.com/r/askscience/comments/2t5lj6/in_light_of_the_new_highres_photo_of_andromeda_is/ 1421831668 2t5lj6 Astronomy 2015-01-21 12:14:28 "1 trillion stars * about 40% of the galaxy is visible / [3.9 billion pixels](http://www.spacetelescope.org/news/heic1502/) = 100 stars/pixel. So using the photo to count stars is definitely out of the question. + +The way we estimate the number of stars in a galaxy is [by the mass of the galaxy and the average star](http://www.space.com/25959-how-many-stars-are-in-the-milky-way.html). This hasn't changed with the new high-res photo, as far as I'm aware." "Astronomer here with relevant username! Short answer: I doubt it. The reason is even though it's an astounding photograph, the majority of stars are too faint to image that far away. Red dwarf stars make up the far majority of the individual stars in our galaxy, for example- like 90% of them- and are super faint. Like Proxima Centauri, the closest star to us just over 4 light years away, is a red dwarf, but you need a telescope to see it. + +So while this picture is great for working out stellar dynamics in a big galaxy and the like, you're still just seeing a small fraction of all the stars in Andromeda." +268 When an animal like the Buffalo is absent from a habitat for a period and then reintroduced, do they continue old migration habits or start new ones? Would constricting human elements like fences stop them from being migratory? 3016 https://www.reddit.com/r/askscience/comments/3qfsfl/when_an_animal_like_the_buffalo_is_absent_from_a/ 1445963891 3qfsfl Biology 2015-10-27 19:38:11 "[...ungulate migrations generally occur along traditional +routes that are learned and passed on from mother to +young...](http://www.migrationinitiative.org/sites/migration.wygisc.org/themes/responsive_blog/images/Sawyer_et_al_2009_EcolApps.pdf) + +and + +[Each potential reintroduction site should be assessed thoroughly for its suitability, including size, habitat types, current land use, socioeconomics, legislation, and potential problems. Each site should be provided with one or more acclimatization facilities to harbor genetically and physically healthy, socially adapted animals in biologically sound groups.](http://onlinelibrary.wiley.com/doi/10.1046/j.1523-1739.1996.10030728.x/abstract) + +Therefore, reintroductions of migrating animals would be best done with some ""tutors"" who could teach the reintroduced animals how, when and where to migrate. Otherwise it is likely to be an unsuccessful reintroduction with lost or misguided animals ending up in unsuitable habitat." "Migration of American Bison to certain areas for forage is likely the result of learned routes, and is driven by food availability. Also, [it's been found that:](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0016848) + +> Yellowstone's restored bison herds have established migratory patterns that lead them to low elevation areas out of the park where they come into conflict with society. + +The bison tend to stray outside of the park's boundaries in search of food depending on herd density as well, indicating that they actively search for areas to forage, and will return there in the future if needed (as is evidenced by the establishment of migratory routes *after* their reintroduction to the area)." +163 Why is forest height on mountain ranges so uniform? 3014 http://www.reddit.com/r/askscience/comments/379krr/why_is_forest_height_on_mountain_ranges_so_uniform/ 1432598384 379krr Earth Sciences 2015-05-26 2:59:44 "Grad student in Forestry here. While the answer /u/murphyw_xyzzy has some truth to it, it isn't quite accurate. + +First, to say that forests are generally about the same age due to fire or logging isn't completely correct. While stand replacing fire is a cause of even-aged stands like with lodgepole pine (*Pinus contorta*), many trees have built up resistance to these types of fires (like Douglas-fir, *Pseudotsuga menziesii*) which will only burn through the understory, leaving mature trees intact. These types of forest stands are typically found at lower elevations (which tend to be drier than mountain tops). + +What actually happens in many of these forest stands is referred to as ""gap dynamics."" This means that a tall, mature tree will die due to disease/rot, wind, or other cause, leaving an opening in the forest canopy allowing sunlight to reach the forest floor. Certain ""pioneer"" species take advantage of this and try to grow as tall as possible in the little time they have before the canopy closes again. + +In forests of high elevation mountain ranges, it is typically too cold and moist for fires to take off, this is why it is not quite accurate to say it is because of fire (at least in general terms). As for logging, depending on the terrain, mountain tops (were talking more the Rocky Mountains as opposed to the ""mountains"" of the eastern US) are incredibly difficult (or costly) to log and so that wouldn't quite be accurate either. All that being said, the bigger idea of murphyw's answer is correct: trees in the same local area are likely to be close in age, no matter the cause. + +Another part of the answer lies in the fact that it just appears that they are all the same height from a distance. It can be hard to see exactly where one individual tree's canopy starts and another ends. Even if there are differences of a few feet or more, unless you were flying (hovering, really) directly overhead, it would be difficult to make out the true differences in height. + +Another part, alluded to above and by murphyw, lies in the fact that when there is an opening in the canopy, trees will indeed race to get as big as possible (usually upward instead of outward) and slow their growth once they have reached the point when they are sure to outcompete their neighbors for sunlight, nutrients, or water. Once a gap (from disease, wind, fire, logging, or any other effect) begins to fill and the canopy closes, trees at that height don't need to compete vertically anymore. At that point, they likely have enough coverage at the top (as well as the light that does filter through the canopy) to not need to grow any bigger. Maintaining their individual canopies will give them the sunlight they need to thrive. + +**TLDR: Partially because of incorrect visual perception, partially because trees in the same area do tend to be of similar age, partially because at a certain height it isn't worth the energy to continue to grow taller, and partially because when the canopy closes, trees at that height don't need to grow taller, the race is over.**" "Generally forests are trees of about the same age. Fire or logging. + +In old growth, where the trees are not generally all the same age or type, there's still strong pressure against being 'the tallest'. Lightening and wind. There is also pressure against being the shortest, no access to light. So they all end up generally about the same height. " +37 "When a part of your body ""falls asleep"", can it cause any lasting damage?" 3013 http://www.reddit.com/r/askscience/comments/30d61w/when_a_part_of_your_body_falls_asleep_can_it/ 1427372794 30d61w Human Body 2015-03-26 15:26:34 "Limbs falling asleep due to lack of blood flow is an urban myth. If blood stops flowing to a limb, that limb starts to die. You are pinching a nerve in the limb which makes it go to sleep. That tingly feeling when it comes back is your peripheral nervous system starting back up in that limb (more or less) No harm done. + +Wow this blew up. Ok, sorry for not being specific enough. I took from what op stated that this was the usual falling asleep on a limb and waking up with a ""dead"" limb. This is mostly not harmful at all. This is not taking into account the nerve being pinched for extended periods of time or repeatedly from use like a wrist over a keyboard. Those events can cause damage and should be looked at if feeling has not returned after a short while. I just wanted to put people at ease that 99 times out of a 100 your limb falling asleep from a nap or just sitting in a weird way will be completely fine." "The tingly feeling is usually related more to nerve impingement/entrapment. It's actually pretty hard to completely cut off blood flow to your limbs by compressing/ligating vulnerable vessels. Using the arm as an example, here is the [blood supply](http://imgur.com/CMtLdm4), and the [nerve supply](http://imgur.com/CgykZRR) to the upper limb. (Source: Netter's *Atlas of Human Anatomy*). In the first image, note all the vessels that branch off of the subclavian, sections labelled 1 & 2. The vessels that wrap around the back of the scapula (shoulder blade) and connect with the others around the glenohumeral joint (where the ball of the humerus meets the socket of the shoulder blade) provides *collateral circulation* even if the subclavian/brachial artery is pinched shut in the axilla (armpit), the most vulnerable point. + +Now look at the nerves. With the exception of the musculocutaneous nerve, all the nerves that innervate the upper limb pass through the 'pit' of the axilla that is vulnerable to compression (The MC nerve is also vulnerable, just less so). + +The same applies to compression at other vulnerable points, there's almost always better collateral blood supply than there is innervation, since taking out nerve supply upstream cuts off the downstream more effectively than with blood flow." +1270 Why does rain have a smell before it starts to rain? 3013 https://www.reddit.com/r/askscience/comments/b2egwi/why_does_rain_have_a_smell_before_it_starts_to/ 1552884454 b2egwi Earth Sciences 2019-03-18 7:47:34 "I've seen a lot of other answers, and they are getting close. But the correct answer to the specific smell ""before it rains"" is actually ozone. + +>Ozone—O3, the molecule made up of three oxygen atoms bonded together—also plays a role in the smell, especially after thunderstorms. A lightning bolt’s electrical charge can split oxygen and nitrogen molecules in the atmosphere, and they often recombine into nitric oxide (NO), which then interacts with other chemicals in the atmosphere to produce ozone. Sometimes, you can even smell ozone in the air (it has a sharp scent reminiscent of chlorine) before a storm arrives because it can be carried over long distances from high altitudes. + +Source: https://www.smithsonianmag.com/science-nature/what-makes-rain-smell-so-good-13806085/#5WWybHr51O0qhbAY.99 + +The wet earthy smell comes from bacteria in the soil, the sharper scent is the ozone as explained above. And if you're smelling it before it rains it's most likely the ozone. +" "Petrichor (Greek ‘petra’ = rock / ‘ichor’ = ethereal fluid flowing in the veins of gods) was the name given to that smell by Australian scientists back in the 60’s. It’s the semi volatile compounds found in plant oils trapped in the soil and on the surface of rocks, metabolites of certain bacteria (geosmin as already mentioned) and ozone creation in the presence of electrical storms. + +The Australian bush is amazing to experience the petrichor aroma in - there is often loooong stretches between rain, which means dense build up of the plants volatile oils which are then released with rare episodes of moisture. + +And it’s such a nice word to say! Petrichor! + +" +479 How did the first human ancestor with 23 chromosomes pairs breed with 24 chromosome apes? 3003 https://www.reddit.com/r/askscience/comments/4tdh2s/how_did_the_first_human_ancestor_with_23/ 1468817556 4tdh2s Biology 2016-07-18 7:52:36 "What /u/xalteox has told you is accurate for most situations and it is true for our relation to apes. Our human chromosome 2 is the result of merged chromosomes from them, complete with a vestigial centromere. Chromosomes are just disorganized filing cabinets, as long as the information is there, nothing should be amiss (although some expression patterns would likely be different, but any noticeable difference is rare). + +As to how this could propagate in a population (not /u/Xalteox's condition necessarily but just a reduction in chromosome number in general), it's not that complex really. Genes can be duplicated or missed during replication or mutation, but what happens if a centromere is duplicated? Now you have 3 centromeres that will be pulled by microtubules to the ends of the cell, but what if the one with 2 centromeres is broken in two? Let's say the full chromosome has genes A,B on the short end and C,D,E on the long end. If it is broken in two, you now have A,B on one end and C,D,E on the other, and A,B,C,D,E in the other chromosome. The cell is actually pretty stupid, so it just randomly pulls centromeres in either direction, and if one side gets AB and CDE and the other gets ABCDE then everything is good because each daughter cell has the appropriate information. This 2 chromosomal variant can propagate, it just has a handicap. This handicap being, that just as often one side would get AB and the other CDE and ABCDE, leading to gametes with many chromosomal errors. The result (which may or may not be the case for /u/Xalteox) is reduced fertility by virtue of gametes that don't quite make it due to these matching errors. Eventually, if enough people mated and spread this 2 chromosome variant, it becomes the norm in the population; this happens mostly by drift, since there usually isn't any benefit that would correlate to natural selection. + +This also happens in reverse, in the situation you're asking about. if two separate chromosomes (like the ancient ape ones) merge and form human chromosome 2, this fused variant can spread in the population in a similar way, so long as the accounting is accurate and each daughter has the same amount of information." "1. The early human ancestors likely did not have 23 chromosome pairs. It's very likely that they had 24. + +2. Even when the chromosome number changes, this doesn't automatically make the two species biologically incompatible. +Similarly, having the same chromosome number does not convey biological compatibility. Wheat has the same number of chromosomes as a rhesus monkey. + +3. Even in the odd case that one of your parents is a mutant that's going to create offspring of a completely incompatible nature, you can still breed with siblings in many cases. If you're a mutant who's biologically incompatible with everything, your line dies out. This has probably happened about a billion times or more throughout evolutionary history. + +The only mutations that are carried forward are the ones that CAN be carried forward. Fortunately, most of the time, a duplication or deletion is not that big of a deal. Millions of people have transcription, duplication, or deletion errors in their DNA and are living examples of first-generation mutations. + + + + +" +365 Does light that barely escapes the gravitational field of a black hole have decreased wave length meaning different color? 2995 https://www.reddit.com/r/askscience/comments/4926vb/does_light_that_barely_escapes_the_gravitational/ 1457179724 4926vb Astronomy 2016-03-05 15:08:44 "Yes. + +In particular, shifted towards the red, or... redshifted. That's gravitational redshift. That's for going up; going down it's blueshift. You don't need a black hole, btw, you can do it in Earth's gravitational field, read up on the Pound-Rebka experiment." "It depends on where the light starts. + +Scenario 1: You are hovering near a black hole. You shine a yellow flashlight towards your friend, who is far from the black hole. Your friend reports that the light is reddish. + +Scenario 2: You and your friend are far apart, with a black hole near the midpoint between you. You shine your yellow flashlight towards your friend. Your friend reports that the light is yellow, just as it normally is. (However, another friend, who is hovering near the black hole, disagrees and says it's definitely bluish.) + +Warning: Do not try these experiments at home. It's not realistic to expect to hover that close to a black hole; and with the distances involved, your friends might have a very long wait. + +As the light approaches the black hole, it becomes blue-shifted (increased in frequency, i.e. decreased in wavelength) and then as it moves away again from the black hole after going past it, it becomes red-shifted (decreased frequency, increased wavelength). If the distances are the same, these two effects cancel out, leaving the light looking the way it did when it started. + +Edit: The light would also change direction as it passes the black hole, its path bent by the gravitational field, so it's best if the black hole is placed not midway between the friends but off to one side. You shine your flashlight in the general direction of the black hole, and some of the light bends around at just the angle needed to end up going towards your friend." +269 Would it be any dangerous at all to split even one atom? 2993 https://www.reddit.com/r/askscience/comments/3uuifl/would_it_be_any_dangerous_at_all_to_split_even/ 1448888499 3uuifl Physics 2015-11-30 16:01:39 "Here are some rough numbers to give you a feeling for the energy scales that are involved in nuclear reactions: + +**1\. The decay of one atom of uranium-235 releases about 200MeV or about 3\*10^(-11)J.** + +For one atom, this is a huge amount of energy, about a million times more than the energy of a photon of visible light. Nevertheless, while this more than enough energy to rip apart chemical bonds in your body, it's far from enough to create much of a bang on a macroscopic scale. To see why, let's compare this energy to something we know for sure can rattle things around, such as a nicely sized ball of TNT: + +**2\. The explosion of 1kg of TNT releases 4MJ (4\*10^(6)J).** + +In other words, you would need to split ~1\*10^17 atoms of U-235 to get as much energy as you could get from blowing up 1kg of TNT. However the comparison becomes much more favorable for uranium when you make the switch form atoms to mass. When you consider that each atom of U-235 only has an atomic mass of ca. 235amu, you see that: + +**3. The fission of ~5\*10^(-8)kg of U-235 releases as much energy as the explosion of 1kg of TNT**. + +This mass, which can be expressed in more convenient units at 50 micrograms, is actually smaller than the mass of one human eyelash! Nuclear energy certainly packs quite a punch..." "The energy released in the fission (splitting) of ONE atom of U-235 is enough to make a single grain of sand visibly move. + +And then nothing else would happen if it was just that one atom. No danger. + +Uranium atoms fission all the time naturally. If you held a sub critical mass of it in your hand it would feel warm. That's from all the natural fission happening. You'd have health issues afterwards but that's due to the radiation from way more than the ONE atom you asked about. " +480 Is the prevalence of mental disorders in humans related to the complexity of our brains? Do 'lesser' creatures with brains not as complex experience similar disorders? 2992 https://www.reddit.com/r/askscience/comments/4xrxyn/is_the_prevalence_of_mental_disorders_in_humans/ 1471235350 4xrxyn Neuroscience 2016-08-15 7:29:10 "Before you comment, please ask yourself, ""Can I back up what I'm about to type with peer reviewed science?"" + +If the answer is yes, then please cite those sources. If not, then you probably have an anecdote or speculation, which will be removed. +" "Mental disorders definitely exist in ""lesser"" animals, and in some cases is quite well-studied. Notably, mice with anxiety disorders are viewed as a valuable model organism for the study of mental disorders in humans, and so some strains of mice are often bred to be more susceptible to anxiety disorders for use in this purpose. + +While observing mental disorders in the wild is difficult by nature, and it is not clear whether such animals are capable of surviving in the wild on their own, there is a significant body of observational research done on mental disorders in captivity. Usually this occurs in animals which are brought into captivity due to trauma, but unfortunately it sometimes occurs in animals which are kept under poor conditions. Self-harming behavior, such as birds that groom themselves to the point of injury, are particularly well studied. + +Of course, studying this under natural conditions is difficult, so it is hard to say if mental disorders are more or less prevalent in humans relative to animals, are if human mental disorders are more complex and/or severe. But mental disorders apparently similar to human mental disorders definitely occur in animals. + +I learned about this in class, and can't seem to find our original reading, but for some further reading on similar subjects: +http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3263396/ +http://www.usask.ca/wcvm/herdmed/applied-ethology/behaviourproblems/selfmutilbird.html" +38 "Which, as a %, is more ""empty"" - an atom or the Universe?" 2988 http://www.reddit.com/r/askscience/comments/32otgx/which_as_a_is_more_empty_an_atom_or_the_universe/ 1429108972 32otgx Physics 2015-04-15 17:42:52 "Answering this in the spirit it was asked, an atom is empty to about 13 orders of magnitude. That's pretty empty to be sure. If a hydrogen atom were the size of the earth, a proton would still only be about 200 meters across. + +That is still nothing compared to the universe. The universe is empty past 20 orders of magnitude. Our best estimates show about 1.1e57 cubic meters of stuff, keeping it all at its current density as compared to 2.7e37 cubic lightyears of space in the observable universe. There is fewer than 5 atoms of ""stuff"" for each cubic meter of space in the observable universe. " "I'd like to ask for clarification from some of the physicists here on this question. + +What exactly does it mean for a space to be ""empty""? We can try to measure the ratio of mass to volume of things, but even with its black holes and neutron stars, it's pretty obvious that the universe is less dense than an atom of a given isotope of, say, lead (right?). What makes any given spot in space ""empty""? What about virtual particles? Interstellar medium? The electron cloud?" +164 Is empty space and nothing the same thing? 2979 http://www.reddit.com/r/askscience/comments/369d68/is_empty_space_and_nothing_the_same_thing/ 1431868898 369d68 Physics 2015-05-17 16:21:38 "**Short answer:** No, I think they are very different things, but it depends on your definitions. + +**Long answer:** If you take 'empty space' to mean space in our universe without any matter occupying it, there is still some very rich physics inside it. Even in the physics of classical field theory, you can still have energy and interesting dynamics with *fields* permeating that region. For example, in the (near) vacuum of space above the earth, you still have gravitational effects from the earth, and the earth's magnetic field. These fields exist everywhere in the universe, even when they are very weak, like when you are very far away from an planet or source of a magnetic field. That's a subtlety of the theory that many people don't learn in their physics class: there isn't one magnetic field for this bar magnet, another magnetic field for the earth, and another magnetic field for Sun - these are all just local contributions to the *one magnetic field of the universe* which is *everywhere.* (Edit: Further explanations and analogies [here](http://www.reddit.com/r/askscience/comments/369d68/is_empty_space_and_nothing_the_same_thing/crby7vv) and [here](http://www.reddit.com/r/askscience/comments/369d68/is_empty_space_and_nothing_the_same_thing/crc2an5)) + + +On top of all that, space is *expanding* - there seems to be some kind of energy locked up in space that's driving the expansion of the universe. + +None of that sounds like 'nothing' to me. It sounds like the difference between having an empty bucket, and having no bucket at all. + +It gets even weirder when you consider the quantum vacuum. Once you take those fields I talked about and quantize them you'll get little fluctuations above the 'ground state,' which is the lowest energy state. Even if you do that thing from the last paragraph and go into deep space far from any sources of gravitational and electric and magnetic fields, your vacuum is *still doing stuff.* + +Ever heard of virtual particles? In some sense, the quantum vacuum is constantly fluctuating and boiling with particle and antiparticle pairs that are popping into existence and annihilating an instant later. + +However you define 'nothing', that still just doesn't sound like 'nothing' to me. " """Nothing"" is a formal term, whereas ""empty space"" is a physical term. To generalize, ""nothing"" is used to indicate the absence of anything fitting a given criteria - say, ""nothing is both black and green all over"". In formal logic, this could be translated to ""it is not the case that there exists something that is black all over and green all over"". + +It is therefore a mistake to think ""nothing"" refers to something. ""Empty space"" refers to something, namely space that is empty. You can say things about such a space, whereas it does not make sense to ascribe properties to nothing. (Or rather, doing so is to fail to ascribe properties, since you're not talking about anything.)" +366 To what extent, if any, is finished concrete such as that found in most urban structures reuseable and recyclable? 2969 https://www.reddit.com/r/askscience/comments/4dljm7/to_what_extent_if_any_is_finished_concrete_such/ 1459946295 4dljm7 Engineering 2016-04-06 15:38:15 "Concrete can be reused and is extensively as a fill material (at least in Europe it is), it is also reused in small quantities as an aggregate in concrete but this is an exception rather than the norm. + +Recycled concrete can have the rebar removed and can be crushed to a specific grading curve in much the same way a natural rock can be, thus creating a pretty controlled aggregate that could theoretically act in the same way as a gravel. Technically this can be reused within a new concrete mix. + +The problem with reusing this material however, is that the consistency of the material is very variable due to a few things: The differing mix designs of the crushed concrete (ie a crushed 10N concrete will not have the same qualities as a 60N concrete) and because the crushed aggregate will contain some particles containing 10mm natural gravel (that was used in the original concrete) and some particles that may contain only cement. There are many other issues too, but these are the 2 that spring to mind at the moment. + +This variability in particles due to source and make-up leaves the end product very variable in strength and other important design parameters that are used for elements containing aggregate. This variability in quality means that recycled aggregates are generally not reused in concrete mixes where achieving accurate and consistent mixes is what a concrete suppliers reputation hangs on. + +Most standard concrete mixes in the UK do have a standard for a maximum percentage of 'recycled Aggregate' that is permitted, however, depending on the concrete supplier, this may be realised or may not. At the end of the day, the concrete supplier has to shoulder the risk of the mix reaching the prescribed strength therefore they will generally choose to utilise original material and the cost gets passed up the chain to the end client. + +Crushed concrete is still utilised extensively as a granular backfill, generally in low risk, low load situations where it is not subjected to cyclical loading. Which is again due to the variability in strength and quality." [deleted] +39 If a meteor containing the right stuff, smacks into land containing the right stuff, can there be a nuclear explosion? 2967 http://www.reddit.com/r/askscience/comments/31b079/if_a_meteor_containing_the_right_stuff_smacks/ 1428066442 31b079 Physics 2015-04-03 16:07:22 "**Short answer:** For a physically realistic impactor, the speeds are much too small to make temperatures high enough for any nuclear reactions to take place. For an imaginary impactor made of enriched Uranium, you can set off a blast. + +**Long answer:** I like the Chixulub impactor. There is a crater 100 miles across in the Yucatan, formed when a 6 mile long asteroid struck the earth about 65 million years ago. There's a really good chance this thing killed the dinosaurs. + +Anyway, a lot of work has been done to study this event, and one of my [favorite papers of all time simulates the impact and ejecta](http://www.sciencedirect.com/science/article/pii/S0012821X98002635) (Free version [here](https://www.psi.edu/about/memorial/betty/chicx3d.html)). The thing to look at is those ejecta profiles- on the free version click on a picture and it will show you an extra figure which has temperature data. They show the maximum temperature achieved in the ejected material is only about 10^(4) K, which is not as abusrdly hot as it sounds. For reference, you'd want it to be pushing 10^6 or 10^7 Kelvin for any nuclear reactions to take place. + +But those are the just temperatures that a *rock* meteor reaches when it hits other rock. What if it was made of *the right stuff*? + +Suppose there was a small asteroid made of enriched uranium. And suppose we had a planet with a little target of enriched uranium, and suppose it struck just right. In this case, you might be able to produce a nuclear explosion. In fact, this is the mechanism behind some nuclear bombs - [shoot two subcritical pieces of uranium at each other to produce a critical piece that explodes.](http://upload.wikimedia.org/wikipedia/commons/c/cb/Fission_bomb_assembly_methods.svg) + + +How likely is it that we'll find an asteroid made of enriched uranium - isotopically pure U235? It's not likely, considering most uranium is the isotope U238, which is not fissile. Additionally, most heavy metals aren't found in nature in anything resembling a pure form. They're usually mixed with a bunch of other stuff, like oxides and rusts and rock. Uranium, for example, is generally found in a rock called [pitchblende or uraninite](http://en.wikipedia.org/wiki/Uraninite#/media/File:Pitchblende_schlema-alberoda.JPG) which is just oxidized uranium. This wouldn't be good for a bomb; it takes a lot of processing and refinement to make it into something that goes boom. + +This nuclear asteroid also can't be too big, because then it will be above the critical mass limit for fission chain reactions, and the energy released from the fission chain reaction will either cause the asteroid to fragment into smaller noncritical pieces, or the reaction will consume too much of the uranium and it will no longer be good for fuel. For reference, [the ""gun type"" assembly of the Little Boy bomb dropped on Hiroshima](http://en.wikipedia.org/wiki/Gun-type_fission_weapon#Little_Boy) was made of two cylinders of uranium, about 30 kg each, that were about 7 inches long. Separately, these pieces were subcritical, but when the bomb was detonated, [one cylinder would inserted into the other](http://upload.wikimedia.org/wikipedia/commons/b/b7/Gun-type_fission_weapon_en-labels_thin_lines.svg), which with the addition of some neutron reflectors, would produce a critical assembly. Getting one of these guys to fall from space, not burn up on re-entry, and collide just right with something on the ground would be quite the feat. + +So in *theory* - and I mean 'theory' in an imaginary playtime physics universe - it's possible. In reality, not so much. " "I think some geologist found a natural reactor in Africa. The right materials were at the right place to cause a low, slow but steady reaction deep underground. + +http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor + +http://en.wikipedia.org/wiki/Oklo + +http://www.todayifoundout.com/index.php/2013/12/natural-nuclear-fission-reactor-gabon-west-africa/ + +Interesting to read about." +367 If you uniformly heated a body of water to boiling, where would the bubbles form? 2960 https://www.reddit.com/r/askscience/comments/414a29/if_you_uniformly_heated_a_body_of_water_to/ 1452881609 414a29 Physics 2016-01-15 21:13:29 "The water wouldn't boil, it would go in a metastable superheated state. It's liquid above the boiling temperature. A sufficient shock, even mechanical, would trigger a violent transition of the whole mass of fluid to the stable mixed-phase state. That is a good part of the water would suddenly boil. + +Translated: do not heat distilled or even still water in a microwave. Microwaves are designed to heat water as uniformly as possible. If the cup is smooth enough not to provide good nucleation points for bubbles, and the heating is uniform enough and the water is relatively devoid of particles, it can be superheated above boiling temp without actually boiling. When you take it out, everything looks normal. You put in your teabag, the water suddenly boils all at the same time. Splashing boiling water on your face. This has happen, iirc. + +This can be understood by studying the Van der Waals equation of state. Under the critical temperature, a portion of each VdW isotherm does not actually describe stable states, but a metastable states. This is because there actually is a set of more stable states which are mixed-phase states, that is the fluid is divided in a gas and liquid phases - this is the flat part of the isotherms and describes the actual phase transition where part of the liquid starts boiling and then this fraction gradually increases until all of it is gas. If you don't give it a chance to form inhomogeneities though, you can get onto that metastable part of the VdW eqt of state. As soon as that inhomogeneity is provided, we decay to the stable state." [deleted] +1122 Why are smaller animals more resistant to ionising radiation? 2958 https://www.reddit.com/r/askscience/comments/9ewbpd/why_are_smaller_animals_more_resistant_to/ 1536661679 9ewbpd Physics 2018-09-11 13:27:59 "As far as I'm aware, we still don't *quite* know. + +Compared to humans, we've known for some time that insects are generally more resistant to ionizing radiation, and multiple hypotheses have been proposed to explain this radioresistance. + +For a long time it was thought that because actively dividing cells are those most sensitive to radiation, insects would succumb less as, unlike humans with our leagues of constantly dividing cells, insects undergo discontinuous periods of growth (only with every moult). But this whole organism approach to radioresistance was tricky to interpret, as the physiology between us and, say, invertebrates is very different. + +At a cellular level however, experiments on cells controlling for proliferative rate have revealed that insect cells are *de facto* more radioresistant than human cells, leading us to believe division rate actually might only have a little to do with it. When you blast human and insect cells with ionising radiation, the DNA within the insect cells itself undergoes much less damage, and what damage is present is more effectively repaired. Likewise, those same insect cells experience lower oxidative stress as a consequence of radiation exposure (radiation triggers the production of rather harmful reactive oxygen species that, amongst other things, trigger cells to commit [apoptotic](https://en.wikipedia.org/wiki/Apoptosis) suicide). + +So yup, it appears the suite of repair enzymes insects utilise are simply better at dealing with DNA damage, explaining why insects have greater radioresistance. As for the evolutionary reason why they're more efficient, we're still not quite sure. + +___ + +^**Sources:** + +[^(Cheng, I.C, Lee, H.J. & Wang, T.C. (2009)^) ^(Multiple factors conferring high radioresistance in insect Sf9 cells. *Mutagenesis* 24 (3)^), ^259-369](https://academic.oup.com/mutage/article/24/3/259/1074431) + + +[^(Bianchi, N.O., Lopez-Larraza, D.M. & Dellarco, V.L. (1991)^) ^(DNA damage and repair induced by bleomycin in mammalian and insect cells. *Environ Mol Mutagen*. 17, 63-68)](https://onlinelibrary.wiley.com/doi/abs/10.1002/em.2850170110) ^((research gate) [^here](https://www.researchgate.net/publication/227933716_DNA_damage_and_repair_induced_by_bleomycin_in_mammalian_and_insect_cells)^)" "One of the reason might just be the number of cells. For example, one of the reason why you can freeze sperm cells and not live animals is that if 1% of sperm cells die from cryogenization, you still have 99% live ones ; meanwhile, if 1% of your cells die from it, you are dead. + +By the same token, a radiation that would transform ten of your cells into tumors would mutate only 1 cell from an animal with 10 times less cells, and very small animal would most likely not be affected at all." +270 Is there are difference between orange and white colored astronaut suits? (Other than color, of course) 2956 https://www.reddit.com/r/askscience/comments/3o1lji/is_there_are_difference_between_orange_and_white/ 1444352253 3o1lji Astronomy 2015-10-09 3:57:33 "There were special blue space suits for space spies in the 1960's. The military wanted manned space stations with camera's. We had tried to send up satellites that would take pictures of russia and return with the film. The satellite worked fine, except all the pictures were of the tops of clouds. A human could look and see that it was cloudy and orbit till it clears up, then take the picture. + +Here's a link to the nasa article about it. http://www.nasa.gov/vision/space/features/found_mol_spacesuits.html + +Also there is a great Nova episode about it. http://video.pbs.org/video/980042464/" +481 What is the modern consensus in Psychiatry regarding the efficacy of anti-depressants vs placebo? 2955 https://www.reddit.com/r/askscience/comments/4h9tau/what_is_the_modern_consensus_in_psychiatry/ 1462119892 4h9tau Medicine 2016-05-01 19:24:52 "My understanding is that a fairly recent literature review (Jay something, major journal) showed that antidepressants are slightly superior to placebo in cases of severe depression but no better than placebo for mild to moderate depression. +A prominent psychiatrist colleague of mine has come to terms with this by saying that he is OK prescribing antidepressants to moderately depressed people even if the benefit is largely or wholly placebo effect, since the placebo benefit is still a benefit, more helpful than no treatment. " "I'm going to start off saying that the current antidepressant drugs are really not good enough. They are actually a little less effective than the first generation (tricyclics), but the difference is that the newer drugs (SSRIs, SNRIs, bupropion, etc.) are just way safer. There is a drastic need for better drugs, but it is an area that few drug companies want to pursue since it's costly and hard for a variety of reasons which I'll try and get into. + +The main issue is that mood disorders are inherently subjective. It not like other drugs with a very clear ""we killed this"" or ""this symptom is clearly gone"". There is no magic thing to detect to say ""I am not depressed anymore""-- it's all a person telling you how they are feeling. Clinical trials for antidepressant drugs have constantly evolving protocols for trying to best control for the placebo effect and find if a drug has a real clinical benefit, but it's very, very difficult. Imagine how different you feel on a given day. Imagine how someone suffering for awhile feels when they are given attention and treatment for the first time. Also imagine how different and widespread someone's version of ""feeling down"" is, including everyone's individual willpower and how that differs person-to-person. The variability and placebo effect from these trials is almost always high, making the needed effect from these drugs to also be very high. + +This tells you that, yes, a lot of people do improve just from the attention and overall focus on their depression that they experience some improvement of symptoms (placebo effect). But the effect from the drug is usually larger. Many argue that this increase above placebo is not enough, but really, it's an increase above placebo incorporating the wide variety of depression symptoms and subjective feelings of a very large group of people. + +Imagine someone with very severe depression. There is much less variability in their day-to-day symptoms, so the effects of a drug would be much easier to spot if the drug had an effect. This is what more modern analyses of clinical trials will show, that the drugs seem to really only have a great effect on those with severe symptoms. But the key here is that they do show this effect often. + +To answer your direct question, psychiatry definitely acknowledges the use of antidepressants because they are often shown to be effective in patients, regardless if they are only marginally more effective. More importantly, treating mood disorders using psychotherapy to help the patient deal with the ""source"" of the issue or create better patterns of behavior with or without the help of the medication is best. + +I'm an advocate for these drugs when psychotherapy alone or other lifestyle changes are not doing the trick. But these aren't amazing drugs and we desperately need better ones (this applies to almost all psych and neuro drugs). " +1271 How did the suez canal affect the Mediterranean and the red sea? 2953 https://www.reddit.com/r/askscience/comments/asbr56/how_did_the_suez_canal_affect_the_mediterranean/ 1550591190 asbr56 2019-02-19 18:46:30 "It brought a lot of species from the Red Sea to the Mediterranean (and some in the other direction) - with many ecological problems as a result. + +The effect is so pronounced it got its own name, derived from the name of the French diplomat in charge of the construction, Ferdinand de Lesseps: [Lessepsian migration](https://en.wikipedia.org/wiki/Lessepsian_migration) " Invasive and detrimental species seem to be one of the [most cited impacts.](https://www.researchgate.net/profile/Daniel_Golani/publication/242311439_Impact_of_Red_Sea_Fish_Migrants_through_the_Suez_Canal_on_the_Aquatic_Environment_of_the_Eastern_Mediterranean/links/553755eb0cf268fd00189856/Impact-of-Red-Sea-Fish-Migrants-through-the-Suez-Canal-on-the-Aquatic-Environment-of-the-Eastern-Mediterranean.pdf) +165 How can we be sure the Speed of Light and other constants are indeed consistently uniform throughout the universe? Could light be faster/slower in other parts of our universe? 2940 http://www.reddit.com/r/askscience/comments/3hbcvi/how_can_we_be_sure_the_speed_of_light_and_other/ 1439819389 3hbcvi Physics 2015-08-17 16:49:49 "the speed of light plays a factor in a lot of physics beyond just how fast light moves. So if you want to propose a ""variable"" speed of light, you have to produce the set of measurements that will show your proposal to be better than the existing assumption. Several attempts have been made in the past to derive a variable speed of light, but none of them have panned out experimentally, as far as I know. + +--- + +As a *rough* example, let's say your theory predicts that electrons will have different orbits because obviously the speed of light factors into the electromagnetic force that governs how electrons are bound to the nucleus. So you would predict that, as you look out across the universe, the spectral lines of atoms should shift by . Then you take spectroscopic measurements of distant stars and galaxies. If the spectra differ by your prediction, and can't be explained by other competing ideas, including the current models, then it supports your theory. + +What we haven't seen are those kinds of measurements. Obviously we can't go out with a meter stick and stop watch and measure how long light takes to go from a to b. So we have to use indirect measures." "Others haven't mentioned it yet, currently we believe in the [cosmological principle](https://en.wikipedia.org/wiki/Cosmological_principle). It states that the properties of the universe are ~~uniform~~ homogeneous and isotropic on large scales, which includes the constants. Only because of this assumption we can calculate distances of very far objects based on their red shift, for example. + +We don't know for sure if it is true, but currently there is no compelling reason to not believe so. + +**Edit:** Changed one word, homogeneous is the more official word used" +40 What is the logical basis behind the multiverse theory? In other words, what does the multiverse theory attempt to prove or answer? 2939 http://www.reddit.com/r/askscience/comments/310bhj/what_is_the_logical_basis_behind_the_multiverse/ 1427857170 310bhj Physics 2015-04-01 5:59:30 "Hi /u/TheKertMA, + +There are many confusing answers to this question, mostly because people are conflating two separate things. + +There is MWI, or the ""[many-worlds interpretation](http://en.wikipedia.org/wiki/Many-worlds_interpretation)"" of quantum mechanics. This interpretation is favored by some physicists because it purportedly avoids the clunkiness of ""[wavefunction collapse](http://en.wikipedia.org/wiki/Wave_function_collapse),"" a postulate of quantum mechanics many physicists consider unnecessary (or downright wrong). At this point, there is no empirical reason for preferring this interpretation of quantum mechanics over the assortment of other interpretations. The motivations are mostly philosophical (but that doesn't make them *bad*). For transparency, I find wavefunction collapse to be a contrivance. It's mostly a way of saying ""we don't know what happens, but it looks like this."" I think more deterministic theories, such as MWI, or ensemble interpretations, or decoherence, are more appealing and self-consistent. But many people will disagree with me. + +There is also the [multiverse](http://en.wikipedia.org/wiki/Multiverse) theory, which is motivated entirely separately from MWI. The multiverse theory is seen as a consequence of theories like eternal inflation and/or string theory. We have many good reasons to believe inflation is true, such as a [near-scale invariant power spectrum](http://en.wikipedia.org/wiki/Inflation_%28cosmology%29#Observational_status). However, we don't know which theory of inflation is an accurate description of what happened in the early universe (and in fact we don't *really* know if inflation is what happened at all), and we certainly don't know if string theory is true. However, as we obtain evidence at higher energy scales, we'll be able to get a better handle on which theories of inflation/string theory are consistent with the data, and we could *in principle* corroborate models of inflation/string theory that predict a multiverse. In practice, it's going to be very difficult. + +To reiterate: MWI and the multiverse are motivated differently. Perhaps they can be made to agree, and [attempts by folks like Leonard Susskind](http://arxiv.org/PS_cache/arxiv/pdf/1105/1105.3796v1.pdf) have been made (with dubious success). But the abstract alone is enough to illustrate that, if you don't believe some random /r/askscience panelist, you can trust that Leonard Susskind appreciates that these two things are not necessarily identical *a priori*: ""We argue that the many-worlds of quantum mechanics and the many +worlds of the multiverse are the same thing..."" + +I hope this helps!" "It is intended to explain some of the weird effects of quantum mechanics, most famously, the results of double-slit experiment. In the quantum version of this experiment, a single photon of light was sent at two slits and the scientists did not observe which slit it went through. After several photons were sent through one at a time, the scientists expected to see a projection of the slits on a screen behind the slits. However, they instead saw an interference pattern, the same that appears if many photons are sent through the slits together. + +Multiverse theory is one of two major proposed explanations for this. It suggests that in cases of probability such as which slit the photon travels through, the universe splits into two universes for each option. Furthermore, on very small scales such as those of single photons, the universes can interact with each other, and the photon can interfere with its counterpart in the other universe." +41 You're on a train and it crashes. Is it better to be in a forward facing or a rear facing seat? 2936 http://www.reddit.com/r/askscience/comments/2v98t7/youre_on_a_train_and_it_crashes_is_it_better_to/ 1423448383 2v98t7 Engineering 2015-02-09 5:19:43 "It's better to be facing backwards (this applies in planes as well). + +Either way, you're basically going to be decelerating instantaneously. The difference is where the force is applied. When facing backwards, the force is distributed across your entire back and it keeps all of your body parts held in stable positions. When facing forwards, assuming you aren't strapped in in any way, it's much more likely that your initial impact would be on a very small area, such as your face, the top of your head, or a limb. Even if you were to be strapped in, the force is being distributed over a much smaller area than if you're facing backwards, and your head would also snap forward (and likely back again), causing whiplash, a concussion, or worse. + +Edit: The primary reason that plane seats are oriented towards the front is just because passengers prefer that. Plane accidents are rare enough that this sort of thing isn't a big enough issue to attract public attention, but perceived discomfort is." "[This video shows a railcar impact test with both positions.](https://www.youtube.com/watch?v=naBn3hHGqVE) + +It is from [this tech report](http://ntlsearch.bts.gov/tris/record/ntl/19478.html) from the US DoT (PDF link is a bit down the page). Recorded peak loads on the crash dummies indicate that upper neck tension/compression force (Fz), upper neck shear force (Fx), and upper neck flexion/extension moment (My) were all less severe when tested in the rear-facing seats. + +More crashworthiness tests can be found on the Volpe website: http://www.volpe.dot.gov/infrastructure-systems-and-technology/structures-and-dynamics/rail-equipment-crashworthiness" +271 Is it possible to determine the location at which a photo was taken based on the moon's position in the sky? 2934 https://www.reddit.com/r/askscience/comments/3w20nz/is_it_possible_to_determine_the_location_at_which/ 1449654400 3w20nz Astronomy 2015-12-09 12:46:40 "Some of the answers here are saying that a photo of the Moon alone won't give you any information. That's not entirely true - you can still get some latitude information from the Moon's orientation and location in the sky: + +- At mid-to-high latitudes, the Moon will never pass directly overhead. Only the range of latitudes between -28 to 28 degrees latitude can ever have an overhead Moon. + +- Closer to the horizon, the angle the Moon's features make with the horizon, you can easily tell if the picture was taken in the Northern or Southern Hemisphere. The lunar highlands (brighter white) generally appear towards the bottom of the Moon's disc in the Northern Hemisphere, and towards the top in the Southern Hemisphere. + +- If you know the Moon's position in the sky, local time of day, and time of year, then you can get much more precise, to within 5 degrees of the exact latitude the picture was taken. For instance, the Full Moon at midnight on equinox will always be at its highest in the sky and within 5 degrees of zero declination. That means that 90 minus the number of degrees from horizon to the Moon will be within 5 degrees of the photographer's latitude (and you can use the Moon itself as a ruler, since it spans almost exactly half a degree)." No, it won't tell you the location from which the photo was taken. What you'd actually need would be an image of the stars in the night sky, but even that would only narrow it down to a latitude, unless you knew the UTC time the photo was taken. +368 AskScience AMA Series: I'm Thomas Hurting, we make tiny human brains out of skin cells, modeling brain development to help research treatments for diseases like Parkinson’s, Alzheimer’s or Multiples Sclerosis, and to help develop personalized medicine. Ask me anything! 2929 https://www.reddit.com/r/askscience/comments/45k2rt/askscience_ama_series_im_thomas_hurting_we_make/ 1455366890 45k2rt Neuroscience AMA 2016-02-13 15:34:50 "AskScience AMAs are posted early to give readers a chance to ask questions and vote on the questions of others before the AMA starts. + + +Guests of /r/askscience have volunteered to answer questions; please treat them with due respect. Comment rules will be strictly enforced, and uncivil or rude behavior will result in a loss of privileges in /r/askscience." [deleted] +272 How would nuking Mars' poles create greenhouse gases? 2928 https://www.reddit.com/r/askscience/comments/3kgpey/how_would_nuking_mars_poles_create_greenhouse/ 1441922283 3kgpey Astronomy 2015-09-11 0:58:03 "I know I'm very late to the party here, but if anyone is still interested in this 16 years ago there was [a paper describing how 4 nuclear bombs can be used to terraform Mars](http://www.marspapers.org/papers/Mole_1999.pdf). + +Basically describes that bombing would throw up dust which would cover the poles, which would then melt due to solar heating." "So the poles are made of mostly frozen carbon dioxide, a.k.a. dry ice. Musk's assumption - which doesn't really bear out if you do the math - is that nuking them would sublimate a good deal of this, putting carbon dioxide into the atmosphere, thereby enhancing the greenhouse effect enough to make the planet habitable. + +No matter how you look at it, though, it's just not enough. There's not enough energy in a single nuke to release enough CO2 to make much of an impact. Even if you used multiple nukes, there's still not enough CO2 total to raise the temperature into a habitable range. Moreover, if you did use that many nukes, you would've just strongly irradiated the largest source of water ice we know of (found under the dry ice), making colonization that much more difficult. + +**TL;DR**: It would sublimate the CO2 at the poles...but really not enough to make it habitable. + +---- + +**EDIT**: My inbox is getting filled with ""But what if we just..."" replies. Guys, I hate to be the downer here, but terraforming isn't easy, Musk likes to talk big, and a Hollywood solution of nuking random astronomical targets isn't going to get us there. For those asking to see the math, copy-paste from the calculation I did further down this thread: + +- CO2 has a latent heat of vaporization of 574 kJ/kg. In other words that's how much energy you need to turn one kilogram of CO2 into gas. + +- A one-megaton nuke (fairly sizable) releases 4.18 x 10^12 kJ of energy. + +- Assuming you were perfectly efficient (you won't be), you could sublimate 7.28 x 10^9 kg of CO2 with that energy. + +Now, consider that the current atmosphere of Mars raises the global temperature of the planet by 5 degrees C due to greenhouse warming. If we doubled the atmosphere, we could probably get another 3-4 degrees C warming since the main CO2 absorption line is already pretty saturated. + +So, let's estimate the mass of Mars' current atmosphere - this is one of the very few cases that imperial units are kinda' useful: + +Mars' surface pressure is 0.087 psi. In other words, for each square inch of mars, there's a skinny column of atmosphere that weighs exactly 0.087 pounds on Mars (since pounds are planet-dependent). + +- There are a total of 2.2 x 10^17 square inches on Mars. + +- Mars' atmosphere weighs a total of 1.95 x 10^16 pounds on Mars. + +- For something to weighs 1 pound on Mars, to must be 1.19 kg. So the total mass of Mars' atmosphere is 2.33 x 10^16 kg. + +To recap: the total mass of Mars' atmosphere is 23 trillion tons. One big nuke, perfectly focused to sublimating dry ice, would release 7 million more tons of atmosphere. That's...tiny, by comparison, and would essentially have no affect on the global temperature. + + **TL;DR, Part 2**: You'd need 3 million perfectly efficient big nukes just to double the atmosphere's thickness (assuming there's even that much frozen CO2 at the poles, which is debated). That doubling might raise the global temperature 3-4 degrees. +" +42 Could there be bacteria in landfills right now evolving to digest plastics? 2925 http://www.reddit.com/r/askscience/comments/317gfi/could_there_be_bacteria_in_landfills_right_now/ 1427991991 317gfi Biology 2015-04-02 19:26:31 "There are already bacteria which can eat some plastics. A nylon eating bacteria was discovered in 1975 and is one of the best examples of evolution in action +Edit: It actually digests one of the byproducts of nylon manufacture + +https://en.wikipedia.org/wiki/Nylon-eating_bacteria + +And there is good evidence of polyethylene digestion by bacteria too. + +http://pubs.acs.org/doi/abs/10.1021/es504038a + +So it's quite probable that more microbes will evolve plastic digesting abilities for a wider range of plastics. Possibly some of these already exist at the bottom of landfills. + +Personally I don't doubt that we could direct the evolution of microbes to digest further plastics. The difficulty comes identifying which plastic will be amenable to enzymatic digestion and which microbes already have enzymes which with a little evolution will be able to accomplish such a task." "It's possible, but don't hold your breath, this isn't the Andromeda Strain. We had an entire geological era, spanning about 100 million years, whose defining characteristic was the evolution of wood and the lack of any organism capable of breaking it down. + +Trees quickly covered the world, but didn't decompose after they'd died, leading to the rich coal veins we enjoy today. Wildfires blazed across continents, and global oxygen levels were nearly twice what they are now. This was why such enormous life forms were able to evolve, most of which would asphyxiate in today's atmosphere. +" +43 If we were to discover life on other planets, wouldn't time be moving at a completely different pace for them due to relativity? 2920 http://www.reddit.com/r/askscience/comments/2vzbwj/if_we_were_to_discover_life_on_other_planets/ 1424018178 2vzbwj Astronomy 2015-02-15 19:36:18 "Celestial velocities may be huge, but at least for orbits in the galaxy they top out at hundreds of kilometers per second. Since the speed of light is about 300,000 km/s, the stars' velocities relative to us introduce only a very very very miniscule change in the passage of time. + +The amount of time dilation is proportional to the Lorentz factor, 1/sqrt(1-v^(2)/c^(2)). Even for an object traveling at 10% of the speed of light relative to us, this means that the time dilation we see for that object is only about a 0.5% change. + +To clarify: in any object's own reference frame, time passes at a normal rate. It's just that when objects are moving at high speeds relative to each other, e.g. trains moving past each other, a passenger in one train will look at the clock on the other train and see it ticking slower than the clock on her own train, and vice versa. This goes both ways." So I have to wonder why it it would matter. If I were standing on another planet in another galaxy with a different rate of time, wouldn't I experience it in the environment? Wouldn't I be subject to the same laws and it would feel like normal time? The only way it could make a difference would be if you were to travel there AND BACK... or you know... faceTime home. +482 If atoms are 99% 'empty space', how big would the universe be if we compressed every atom down to it's most space efficient arrangement, essentially leaving no space between particles? 2920 https://www.reddit.com/r/askscience/comments/4mvupc/if_atoms_are_99_empty_space_how_big_would_the/ 1465254016 4mvupc Physics 2016-06-07 2:00:16 "The ""atoms are 99% empty space"" thing is a big misconception. Particles do not have ""size"" as we typically think of it. An electron in an atom is a ""wave of probability"" and does not have a specific ""size"" or ""location"", these properties don't make much sense quantum mechanically. In fact [these heat maps](https://upload.wikimedia.org/wikipedia/commons/e/e7/Hydrogen_Density_Plots.png) are what the electrons look like in the atom. Most of that space is not empty. Each of those is a different ""orbital"", the energy and angular momentum of an electron determines the shape of the electron and that's what we refer to as ""orbits"". It's not that electrons are whirring around at different speeds, they just have different shapes around the nucleus. + +What we can do is take electrons, shoot things at them and look at the scatter pattern. The things we shoot are also wave of probability, but based on the scatter pattern we can get a good idea of the sphere of influence of the electron. This gives us a notion of the ""size"" of the electron, though it's not good to think of electrons as hard spheres of stuff floating around since they're waves of probability in different configurations. + +If you want to compress things, though, you can look at [Neutron Stars](https://en.wikipedia.org/wiki/Neutron_star) this is a star that is so dense that atoms cannot exist. They're like a dense plasma of nucleons held together by gravity. This is similar to what happened near the beginning of the big bang, the particles were too energetic and compressed to form atoms. In fact is was too energetic for even protons and neutrons to form, and was basically a plasma of quarks and gluons. The [wikipedia article has a good timeline](https://en.wikipedia.org/wiki/Big_Bang#Timeline). Like Neutron Stars, a kind of star that is like this has been conjectured called a [Quark Star](https://en.wikipedia.org/wiki/Quark_star) that is supposed to look like the very beginning of the universe in it's core." "/u/functor has explained (very well) why the atoms are not empty. But we can nevertheless consider what would happen if you turned the whole universe into a giant nucleus. The nuclear density is around 10^(17) kg/m^(3), while that of the matter in the universe is around 10^(-27) kg/m^(3). Since the radius of the observable universe is currently 100 billion light years, the resulting radius would be (10^(11) ly)(10^(17)/10^(-27))^(1/3)=0.0001 ly=10^(9) km. This is around the radius of the Earth's orbit around the Sun. + + The thing is that once you go above a few solar masses, the density of a neutron star is so great that its radius is smaller than that of the event horizon from the same mass, because the density of black holes decreases with the square of the mass. So the neutron star is really a black hole! + +The ordinary mass of the observable universe is around 10^(53) kg or 10^(23) solar masses. The Schwartzchild radius of that black hole would therefore be around 10^(23) km, or 10 billion light years. So the universe is not so much bigger than it would be if it were a black hole (if the universe was made of matter and its density were at the critical density, the two would be nearly equal). That doesn't mean that the universe is a black hole, because the structure of spacetime is very different (dynamic and expanding) and dark energy exists, but it's very interesting, isn't it?" +44 "Does ""having girls"" or ""having boys"" run genetically?" 2919 http://www.reddit.com/r/askscience/comments/33dg93/does_having_girls_or_having_boys_run_genetically/ 1429635945 33dg93 Biology 2015-04-21 20:05:45 "It appears that there is a genetic component to childbirth from a [Newcastle University study](http://www.science20.com/news_releases/chromosomes_are_so_20th_century_male_genes_really_determine_baby_gender_says_study) [(full study)](http://www.collective-action.info/sites/default/files/webmaster/_TEA_Gellatly_Trends-in-Population-Sex-Ratios.pdf) that found a correlation between men with many brothers having a higher percentage of male children and men with many sisters having a higher percentage of female. + +This data is in line with a theory that there is a sex-linked gene that determines the proportion of men's sperm. If the man has MM he produces more male sperm MF means more equal sperm and FF means more female sperm. Currently this gene has not been identified. " "Not sure if this adds much, but I'm a primatologist and there is this trend in primates: high ranking females tend to have males/sons, and lower ranking females have daughters. This is because sons have more variable reproductive success, so if they inherit your rank, it makes sense to have sons that end up with a higher than average chance of reproducing. If you aren't high ranking, it's safer to invest in daughters because they will have fairly reliable reproductive rates no matter what their rank is. This is achieved through post-copulatory female sperm selection. +So, maybe if rank (in humans this means job success and money) runs in families, so does a sex bias?" +45 Why does a piece of a sparkplug work so well at breaking car glass? 2918 http://www.reddit.com/r/askscience/comments/2w7ken/why_does_a_piece_of_a_sparkplug_work_so_well_at/ 1424193107 2w7ken Physics 2015-02-17 20:11:47 "So many poorly written explanations on here so I'll try to explain it a bit better. + + +First let's talk about the glass on a car. Most of the windows (except the windshield) are made from tempered glass. Tempered glass is known for being quite strong, but also fails quite spectacularly, instantaneously shattering into an enormous amount of little pieces. Why does it do this? Well let's understand the processing. This glass is cooled rapidly from liquid to solid. Glass that cools more quickly ultimately ends up at a lower density, hence a higher volume compared to glass that cools slowly. [graph](http://www.benbest.com/cryonics/tg.jpg) Well guess what, there is a thermal gradient in a pane of glass as it cools. Meaning the outside rapidly cools and the inside does not. This puts the outside of the glass in compression and in the inside in tension. This acts as a crack inhibition method, meaning that the stress necessary to propagate the crack must first overcome the compressive stress on the outside (since glass will fail in tension well before compression). So what do we get? A glass that is ultimately very strong, but has a massive amount of stored internal energy through the tempering process. + +[Stress Profile in Tempered Glass](http://failures.wikispaces.com/file/view/wiki_nickel_sulfide_fig01.jpg/177204681/292x132/wiki_nickel_sulfide_fig01.jpg) + +Let's say we want to break this glass though. How do we go about it? Well if we can force a crack to propagate through this thin compressive stress layer on the outside and into the stored tensile stress region, then this crack will immediately cause catastrophic failure. The easiest way to do it? Use something small and hard to act as a stress concentrator. This can amplify the force applied and help penetrate this region. So in the case of the spark plug shard, which is made from a hard ceramic (likely an alumina based material) the impact from the ceramic is enough to form a crack and cause it to penetrate the glass deep enough. That is also why you can buy punches (firefighters and other emergency responders also carry these) that are essentially hardened steel or diamond tipped and do the same thing. + +Hardness of the glass compared to to impact material is definitely relevant since this interaction is very similar to a hardness test (Rockwell, Vickers, Knoop, etc. Indent tests). The material needs to be harder, or at least close to the same hardness as the glass. I highly discourage people from using the Mohs scale to get actual numbers. + +Sources: Shelby, ""Introduction to Glass Science and Techonology"" + +Varshneya, ""Fundamentals of Inorganic Glasses"" + +Fun fact: your windshield is engineered to break before a human skull will. [Here is an interesting study](http://www-nrd.nhtsa.dot.gov/pdf/esv/esv20/07-0101-W.pdf) talking about injuries associated with laminated vs. tempered glass in auto collisions + +Edit: Added sources and some graphs + +Edit 2: Updated some relevant information about impact with windshields and took out the sensationalist comment about side impacts + +Edit 3: Thank you so much kind redditors for guilding me twice! " "The comments in this video explain it pretty well. https://www.youtube.com/watch?v=QhlmKHbPFhU + +> +This happens because ceramic is extremely hard, brittle but hard. The glass to you seeing cars is made by super rapid cooling of the glass which creates tension between the outer wall of the glass and the inner core. + +> The ceramic is harder than outdoor wall which enables it to make a fracture, and because there's so much tension on it the window basically implodes. + +EDIT: [Wikipedia](https://en.wikipedia.org/wiki/Ninja_rocks)" +273 How does our body keep track of time? And how might this effect space travel? 2910 https://www.reddit.com/r/askscience/comments/3xzax9/how_does_our_body_keep_track_of_time_and_how/ 1450890010 3xzax9 Human Body 2015-12-23 20:00:10 [deleted] "Neurobiologist here. It's early, I'm hungover, but allow me to try and explain this the best I can. As others on this thread have commented there are various ways your body keeps track of time, the most notable are circadian rhythms. But this is somewhat wrong, you see it's not circadian rhythms that *produce* our sense of time, but rather are a *product* of various biochemical events in the brain (notably the superchiasmatic nuclei) which give rise to frames of reference that we perceive as time. + + +How this works in its entirety is still somewhat a mystery. My old phd mentor was actually looking at how subregions of the frontal lobe may use various methods to check and compare events that have recently occurred to give a reference frame for length of duration between events. Others have pointed to a series of chemicals in the brain for giving that 'value' for duration of time elapsed, one of which is adenosine, the others are the circadian chemicals 'Clock' and 'BMal' (plus one more I can't remember for the life of me). These chemicals and their density in certain receptor sites encode values for duration awake and roughly can translate into time elapsed since your last 'Brain event' which signals a 'checkpoint' like sleep or other cycles. + + +Let's start with adenosine. You may not know it but this little bugger is something we all hate and try to inhibit on a daily basis. When adenosine triphosphate (atp) breaks down over the day from atp to adp to amp it finally rests with just a single adenosine molecule. These adenosine packets then float around the brain till they fine their receptor site and bind there, with enough binding you start to feel groggy and sleepy. It's also the receptor site that caffeine binds to and prevents said tiredness. While this isn't translated directly into 'time perception' as we know it, it is one more daily cycle that allows your brain to make reference points and determine how much time has gone by in your single wake cycle, and as such the amount of free floating adenosine may allow for the brain to reference around what time events have occurred. + + +Now for the slightly confusing parts with our circadian rhythm making friends BMal and clock. These chemicals have little known use beyond producing a slow, continuous wave of increase and decrease in each other. We think this rise and fall of the two chemicals produce circadian rhythms; they achieve this in a pretty cool manner, clock and BMal both affect each others production amount. As one increases in concentration, the other decreases, doesn't sound complex right? Wrong! As the decrease occurs it inhibits production, which then inhibits the inhibiting factor of the other, which in turn increases the amount, which in turn inhibits itself. Bah, go look up the fine points, my head is throbbing too hard to think about this too hard. But the underlying point is that the two regulate each other, when one gets to be too concentrated, it produces the other, which decreases the first, then the second becomes too concentrated and the cycle continues with each regulating the other. The byproduct of this ebon flow of ups and downs is a predictable, constant wave. With the wave having roughly the same amplitude and frequency each time, it allows your brain to use other reference points from your long term or short term memory, encode them to a point in the 'wave' and then reference the cycles to determine how much time has passed. (This is my most sloppy part of my post, bear with me I'll edit more points in after I wake up more.) + + +Something you may have noticed is that I have constantly said 'reference' that's because the brain needs cues to operate. You need light and other factors to tell the brain 'it's this time in the day'. Or else we would be bound to one internal clock and jet lag would suck so much harder. (I just realized I left out a part on melatonin, while it helps set cycles I don't think it has that much to do with time perception) because we need cues our brains, and that of other animals, have developed strategies. For instance some species of lizards have a very very thin skull right above their pineal gland; they use this to tell if it's light outside and to deliver light directly to the brain! Yes, you heard me, lizards have photosensitive brains...that act like... Well, a third eye (cue spooky music). We, on the other hand, are not as cool. We use our eyes and optic nerve to deliver light to the brain and let it know ""dear brain, it's X brightness outside, leading me to believe it's X time of day"". But even then it's all to do with frame of reference. + +To conclude, your brain constantly communicates with a plethora of biochemical and physical indicators of duration/frame of reference. The amalgamation of all these things I mentioned (and many more I did not) lead your body to have a sense of time, or at lease how many 'cycles' have occurred since last frame of reference. The body clock isn't perfect, it can make time feel very slow (like being hungover listening to the garbage truck crash around outside your house, ugh) or very fast (like explaining your scientific passion to someone who cares to ask), but at the end of the day it's really a hard question to answer. How do we perceive time? The best I can do is explain what I know, what others have observed and what the community thinks. For all we know it's could be all wrong... I guess time will tell ;) + +" +46 After death how long do processes like digestion or cell regeneration continue to go on and what ultimately stops them? 2909 http://www.reddit.com/r/askscience/comments/2sethg/after_death_how_long_do_processes_like_digestion/ 1421251907 2sethg Biology 2015-01-14 19:11:47 "In short, what ultimately stops cell processes after death is lack of oxygen. Without oxygen ions to fix electrons on the cellular level, cells are unable to function or reproduce, and they begin to decay. + +For some cells that require constant oxygen (such as neurons) this can happen almost immediately (within minutes) after death. For other cells that are not quite as oxygen thirsty (such as in the transplant organs) this can take between 30 or 60 minutes. Structural cells which require even less oxygen, such as in bone and connective tissue, can survive for around 24 hours after death before cell death occurs. " "Loss of circulation (say, from cardiac arrest) leads to three main problems for the tissues: loss of oxygen, loss of supply of fuel molecules like glucose and fatty acids, and buildup of waste products. Some cells are more susceptible to major dysfunction due to these factors than others, primarily as a result of their metabolic needs. + +Loss of oxygen and fuel results in a decline of the cellular ability to produce ATP, the small molecule that the cell uses for the majority of its energy needs. Lack of ATP results in decreased function of the sodium-potassium pump that maintains the cellular ion balances resulting in water influx and swelling of the cell. Other active cellular processes that require ATP also begin to decline in function. Additionally, the local changes in the chemical environment including decreased pH from C02 and lactic acid build up can affect the membrane permeability. Other cellular changes include changes to the structure of the chromosomes/nucleus, detachment of ribosomes and mitochondria from the cytoskeleton. + +Ultimately, either damage to the mitochondria releases a number of molecules that cause the cell to turn itself off (apoptosis), or the damage to the integrity of the cellular membrane(s) is so great that it ruptures, or small packets of digesting enzymes are released that chew up the cell. Either way, energy dependent cellular processes for the most part halt by that point. This can take minutes for brain neurons, which have very high energy requirements, to hours and almost days for say, cartilage cells, which do not require much energy at all. " +274 If nylon stockings rip all the time, why don't we use another material? 2906 https://www.reddit.com/r/askscience/comments/3q6vjf/if_nylon_stockings_rip_all_the_time_why_dont_we/ 1445805246 3q6vjf Engineering 2015-10-25 23:34:06 There is. Silk stockings don't rip nearly as often as nylon. However, they're much more expensive and still run occasionally. Most women buy the cheap ones, knowing that multiple pairs of them will ultimately cost less than a really good pair of silk ones. "So the reason stockings run is because of how the fabric is made, not because nylon is unsuitable. Stockings are knit, it's what makes them stretchy. Knitted fabrics of any kind (stockings, socks, sweaters, etc.) all have an inherent problem which is runs. When you're hand knitting we call it a dropped stitch and it looks like this http://www.lionbrand.com/faqImages/droppedStitch1.jpg + +For those text focused people, in knitting each stitch is part of the thread running side to side but also is holding and held by the stitch above and below it. Letting a single stitch go free to unloop will free each successive stitch above and below in it's column. + +So for a stocking imagine this at a very small level. A single thin thread breaks, allowing the stitches below them to come free. This in turn free the stitches below them. Now stretchy nylon goes fuzzy when it's not under tension so the broken thread quickly tangles in itself and the tear stops running side-to-side but stitches above and below start working their way loose resulting in it stocking ""run"" as we think of it. http://i.istockimg.com/file_thumbview_approve/23319831/3/stock-photo-23319831-close-up-of-brown-stocking-or-pantyhose-with-small-run.jpg + +See the initial hole is small but the stitches above and below are coming unknit and will eventually work their way up and down the length of the stocking unless stopped. + +So the only way to make a stocking that won't tear is to either make a thread that thin that will never break (maybe carbon nanotubes???) or invent a new kind of knitting that it stretchy but doesn't ravel. + + +" +369 Why doesn't the immune system kill incoming sperm? 2906 https://www.reddit.com/r/askscience/comments/46nigx/why_doesnt_the_immune_system_kill_incoming_sperm/ 1455925334 46nigx Human Body 2016-02-20 2:42:14 Semen is in fact recognized as foreign not only to the female but to the male immune system. Yes, your own body would attack and destroy your own sperm cells if it were not rigorously kept out of harms way by other specialized cells in the testes. As to why sperm is 'safe' in the vagina, it isn't. Technically outside the body, the vaginal vault would not immediately recognize foreign proteins present in the ejaculate fluid, but there is an immune presence. Seminal fluid which makes up most of the volume of the ejaculate helps buffer the pH of the vagina to be more suitable for the spermatozoa. Also, the fluid helps insulate the sperm (to a degree) from the female immune system. Finally, the sperm don't wait around to be found, but rather work their way toward the ovum with the intent of fertilizing it. Sperm can live in these conditions for days. Following fertilization, the placenta is formed which provides a sort of 'biological airlock' between the mother and embryo to help prevent the mother's immune system from recognizing and destroying the developing fetus. There is a complication in some pregnancies where a previously sensitized Rh negative mother has an Rh positive baby, but that is a specialized case. "You should check out Inside the Human Body (BBC). There's an episode that illustrates the sperms journey to the egg. White blood cells do attack the sperm until they reach the Fallopian Tube. + +The show said that from an original 250+ million sperm ejaculated in into a woman, as few as 20 make it to the Fallopian Tube. It's an effective selection process." +47 If little crumbs fall down your trachea what happens to them? 2895 http://www.reddit.com/r/askscience/comments/2xdw5s/if_little_crumbs_fall_down_your_trachea_what/ 1425066487 2xdw5s Human Body 2015-02-27 22:48:07 [Alveolar macrophages](http://en.wikipedia.org/wiki/Alveolar_macrophage) residing in the lungs will break down and destroy any debris or foreign material that is inhaled or makes it down the wrong pipe. "Hi, this is actually something I know about, I'm a speech and swallowing therapist. I work with patients who have trouble swallowing. + +If you inhale food or liquid particles into your airway (""aspiration""), your body will respond with reflexes to clear the airway, i.e., you'll cough. Coughing causes highly pressurized air to push through your vocal cords and upper airway. Then, after you cough, you'll reflexively swallow, which brings those particles down to your esophagus where they belong. (Try it: touch the front of your throat and cough. You'll notice that you probably swallow right after you cough). + +If the particles aren't coughed up and swallowed the right way, two things could happen: + +1. You could choke. If the particles are big enough to occlude your airway, you can't building up a strong enough cough clear the airway. This is why choking victims don't make any noise (no air going through vocal cords = no talking, no coughing) they just silently clutch their necks. + +2. The particles could descend into your airway, pulled by gravity. There are cilia lining your airway which will try to move the particles up and out. And your immune system will attack the particles, too. But if food/liquid particles descend far enough into your lungs, you could end up with a gnarly case of aspiration pneumonia. Basically, the particles cause an infection and your lungs fill with fluid to fight the infection, but then the fluid prevents you from breathing good. + +TL;DR no, you do not have crumbs in your lungs." +370 Does the universe have a size limit the way it has a speed limit? 2894 https://www.reddit.com/r/askscience/comments/44twm4/does_the_universe_have_a_size_limit_the_way_it/ 1454977374 44twm4 Physics 2016-02-09 3:22:54 "There is nothing as fundamental as the speed of light to restrict the possible size/mass of large objects, but there are practical limits. Just like you guess, large enough objects in the absence of an external source of energy will implode in a process called [gravitational collapse](https://en.wikipedia.org/wiki/Gravitational_collapse). + +To see why, think of a big star. Each bit of matter in that star is pulling on the rest, so that in effect gravity is trying to pull the whole thing together. But for a long time, that doesn't happen. The reason is that the nuclear reactions in the core of the star heat the crap out of the surrounding gases, which creates a pressure (called the thermal pressure) that opposes gravity. For a long while the star is stable under the equilibrium of these two forces (the fancy term for this situation is [hydrostatic equilibrium](https://en.wikipedia.org/wiki/Hydrostatic_equilibrium)). + +But at one point the star will no longer be able to produce enough heat to offset gravity and then what happens next depends on its size (and more specifically the size of the core): + +1. For stars with a core smaller than ~1.4 solar masses, the so-called [Chandrasekhar limit](https://en.wikipedia.org/wiki/Chandrasekhar_limit#Super-Chandrasekhar_mass_supernovae), the star will start to collapse, but it will stop to form a small body called a [white dwarf](https://en.wikipedia.org/wiki/White_dwarf). The reason further collapse doesn't happen is that electrons don't like to be crammed together in an ever smaller space. This effect (which is a result of a rule in quantum mechanics called the [Pauli Exclusion Principle](https://en.wikipedia.org/wiki/Pauli_exclusion_principle)) creates an effective pressure called the [electron degeneracy pressure](https://en.wikipedia.org/wiki/Electron_degeneracy_pressure) that prevents further collapse. +2. If the mass is between 1.4 and ~3 solar masses, the gravity is so strong that it can overcome the electron degeneracy pressure. At that point the matter will collapse into the densest star known, called a [neutron star](https://en.wikipedia.org/wiki/Neutron_star) that is made up almost entirely of neutrons. At this point a new kind of degeneracy pressure, this time from neutrons can prevent further collapse. +3. If the mass is larger than ~3 solar masses, all hell breaks loose. At that point there is no known force that can prevent further collapse and the star ends up as a black hole. + +edit: The ranges I gave work best for the core of a star, or more generally for the part of any massive object that ends up collapsing inwards." "Currently, there is evidence towards that the universe is expanding at an exponential rate. This means that as times goes on the universe stretches faster and faster into the distance, to the point when light itself is not fast enough to catch up. By then, Objects are ""flying"" away from you faster than light can get back to you, and you can never see them again. +This seems to go on forever and the universe's size limit might only be limited by quantum fluctuation that could change the laws of physics in pocket and thus affect that region of the universe itself. How big these pockets can get is speculative. Can they overtake the universe expanding faster than the speed of light? I don't think we have the information yet to answer this, but perhaps the pocket universe can expand into a mini universe inside the big one, with a big bang, matter and all but with potentially different rules of physics, and thus rendering your question obsolete." +166 If table salt separates into Sodium and Chlorine ions when dissolved in water, then how does salt water taste like salt? 2892 http://www.reddit.com/r/askscience/comments/3enl4z/if_table_salt_separates_into_sodium_and_chlorine/ 1437914400 3enl4z Chemistry 2015-07-26 15:40:00 "When you are tasting table salt (NaCl), you are not tasting the compound NaCl, but rather the constituent ions Na^(+) and Cl^(-). In fact, it's more accurate to represent the ions as (Na^(+))aq and (Cl^(-))aq where the aq stands for aqueous and indicates that the ions are solvated by water, since the salt will be dissolved in the water of your saliva before you will be able to taste it. Studies have found that it is mostly the sodium cation Na^(+) that is responsible for the salty taste. However the anion still plays in role in how salty something will taste. For example, switching from table salt (NaCl) to baking soda (NaHCO3) will result in a less salty taste (and will also produce additional new tastes). Moreover, in animals such as humans (but not in rodents), other cations, such as those of lithium (Li^(+)), potassium (K^(+)) or even ammonium (NH4^(+)) will also evoke a ""salty"" taste, albeit one that is not quite as strong as that generated by Na^(+). + +If you would like to read about the topic in more depth, here is a pretty good and accessible [review paper on the subject](http://www.ncbi.nlm.nih.gov/books/NBK50958/)." well, in addition to what /u/crnaruka said, there's the pretty simple answer that salt dissolves in your saliva, turning that into salt water or a sort. So really you're always tasting salt water, not the crystals themselves. +167 Would it be possible to make a thin enough sheet of metal that it would be transparent? 2888 http://www.reddit.com/r/askscience/comments/37ktye/would_it_be_possible_to_make_a_thin_enough_sheet/ 1432810016 37ktye Physics 2015-05-28 13:46:56 "Yes it is. It is a routine technique in gold coating for scanning electron microscopy for samples of insulators. (Conductors like metals need no coating.) The coating is applied because the electron beam tends to charge surfaces, making bright white spots that stay. A conductive coating allows the surface charge to dissipate. Depending on your sample, the layer may or may not need to be thick enough to be seen by eye. ""Nice"" samples (relatively smooth surfaces) need just a little, rough samples more. The coating is applied as an atomic gold plasma (which is violet-colored, by the way) sputtered from a gold target in near-vacuum. From my experience, after ca. 5 min of coating at 30 mA coating current, the gold layer becomes visible. At 1 min there's no clue that the sample is gold-coated. + +Color of a metal requires that the surface is thick enough. The wavelength of blue-violet visible light is 400 nm and layers thinner than that appear transparent. (There can be, however, scattering.)" As others have said, thin metal layers are transparent, but I want to add that they are not self-supporting. Mirrored sunglasses have a thin layer of aluminum on the front, and you have no trouble seeing through from the back. But this film would never hold itself together if it weren't deposited on some thicker substrate. +48 Will my cup of 100°C tea cool faster if I let it sit before or after I add the cold milk? 2886 http://www.reddit.com/r/askscience/comments/2zwzf2/will_my_cup_of_100c_tea_cool_faster_if_i_let_it/ 1427042419 2zwzf2 Physics 2015-03-22 19:40:19 "http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/-0c2ee7e805/ + +What to do + +We are trying to compare what happens to the temperature of milky tea when you add the milk at the beginning or at the end of a wait. + +So make 2 identical cups of tea and pour a measured amount of milk into the first at the beginning of the experiment. + +Wait 15 minutes then add the milk to the second cup of tea and measure the temperature of both cups. + +What may happen + +You should find that once you add the milk to the second cup, the cup which you added the milk to first is the warmest. + +Below you can see a graph of the temperature of the tea against time made with a mutilated electronic thermometer plugged into a computer. You can see that the tea which has milk added first cools down more slowly than the tea with no milk in it. So when you add the milk to the second cup of tea it ends up colder. + +EDIT: The source here is better and was measured, not theoretical. BTW, this source doesn't account for the tea bag heat retention, so someone smarter than I am can figure that part out." "in the Middle Ages there was a joke about how scholars were arguing about how many teeth a horse had and they finally turned to their books to see what Aristotle said, instead of going to their stable and finding a horse. You did the same thing! +Be The Scientist! Make 2 cups of tea at the same time and pour the milk differently. Let us know the result " +483 How Is Digital Information Stored Without Electricity? And If Electricity Isn't Required, Why Do GameBoy Cartridges Have Batteries? 2882 https://www.reddit.com/r/askscience/comments/4yagjx/how_is_digital_information_stored_without/ 1471497111 4yagjx Computing 2016-08-18 8:11:51 "There are two types of memory, volatile and non-volatile. Volatile memory requires a constant voltage to keep the memory from erasing, whereas non-volatile does not. + +Examples of non-volatile memory include flash drives and hard drives in computers. + +The only volatile example I can think of is RAM (Random Access Memory). + +As for Pokémon Crystal, this is a trick Nintendo had been doing from 1986 to around 2000ish. I'm not sure when the last instance of this was, but I know that the first was The Legend of Zelda. + +RAM memory was cheaper than flash memory (which is what they switched to with Ruby and Sapphire, although, they have a battery for the clock, which is a different thing altogether), so Nintendo would use RAM in their cartridges to store save data, with a battery to keep the volatile (RAM) memory from erasing. + +However, these batteries don't last forever, and as other people have said, these batteries run out faster in Pokemon Gold/Silver/Crystal because they also run a clock. + +The batteries are CR2025 and there are videos on Youtube telling you how to replace them. Pokemon Crystal is the hardest Pokemon game to do though, because the battery is soldered in twice as much as Red/Blue/Yellow/Gold/Silver." "Game boy cartridges are mostly read-only memory of some kind, either 'mask roms' (chips that are created in the foundry with data) PROMS (write-once memory that is set by blowing diodes you don't want leaving the data you do), EPROMS (which are PROMS that can be healed and reset, usually by UV light) or EEPROMS (which are proms that can be reset with an electric charge). This doesn't need a battery to keep the data. + +But they also contain a small amount of efficient normal RAM, and the battery is used to keep the memory in that RAM live. This is used to store save games and high scores. + +These days, this data storage is generally done with 'flash memory', which is the stuff they use in memory cards, usb sticks, and SSD hard drives." +275 Would we ever run out of hydrogen to power fusion reactors? 2881 https://www.reddit.com/r/askscience/comments/3u860g/would_we_ever_run_out_of_hydrogen_to_power_fusion/ 1448465975 3u860g Physics 2015-11-25 18:39:35 "Adding to /u/crnaruka 's answer and putting some numbers on it, if we are talking about the deuterium-tritium cycle which is what we are aiming for with current projects, then the limiting factor would actually be lithium, which is used to breed the tritium. We could supply the worlds current total energy requirements of about 60 KWh/day/person for about 150 - 200 years with known reserves of minable lithium. However, if we include lithium in seawater and figure out a way to extract it, then we are much better off with about 1.5 million years of generation at 60 kWh/d/p. + +If we can get the (technically harder) deuterium - deuterium cycle running, then to all intents and purposes it's effectively infinite (something like 10,000 million years at current usage levels and current population)" Well, no, strictly speaking hydrogen (and especially its heavier isotopes) is not a renewable resource as there's only so much of it here on Earth to go around. But by the same token no resource is truly renewable. For example, we usually treat sunlight as being renewable, but when you think about it, billions from today the sun will also run out of hydrogen and slowly start to flicker away. Nevertheless, that doesn't change the fact that the sun will be around that it can continue to power the world for thousands and thousands of generations, which is why we usually treat it as unending for all practical purposes. The same is true for hydrogen on Earth: we currently we have 1,386,000,000km^(3) of water to draw hydrogen from! Even if in this water you only have one deuterium atom per 6000 atoms of hydrogen, that still comes out to millions and million killiograms of this energy packed fuel. Let's put it this way, if we get fusion to work and continue to use energy at current rates, before we needed to worry about running out of hydrogen we would have rather more pressing concerns (such as the end of the sun). +276 What makes most books smell good? 2878 https://www.reddit.com/r/askscience/comments/3yahod/what_makes_most_books_smell_good/ 1451142467 3yahod Chemistry 2015-12-26 18:07:47 "The truth is that books smell good for the same reason you can get high from sniffing glue! In both cases the odor (and kick) you feel comes from a bouquet of different volatile organic compounds (VOCs) as [nicely summarized in this infographic](http://i.imgur.com/MnF4Lsl.png). These compounds come from the adhesives used to tie the books together, from the ink used to write the text, as well as from various byproducts that form as the cellulose fibers and the supporting network of lignin in the paper start to break down. Because those last byproducts only form gradually over time, the smell of a book will also slowly change until you get that slightly sweet and musty ""old book smell."" " "[“Lignin, which is present in all wood-based paper, is closely related to vanillin. As it breaks down, the lignin grants old books that faint vanilla scent.”](http://www.smithsonianmag.com/smart-news/that-old-book-smell-is-a-mix-of-grass-and-vanilla-710038/#hf1Suuk7oDWI9VVA.99 +) +" +49 Dark matter is thought to not interact with the electromagnetic force, could there be a force that does not interact with regular matter? 2875 http://www.reddit.com/r/askscience/comments/2zjtqf/dark_matter_is_thought_to_not_interact_with_the/ 1426737313 2zjtqf Physics 2015-03-19 6:55:13 "Dark matter cannot interact via the strong force or the electromagnetic force. It may or may not interact with the weak force, although many models have it doing so. + +Yes, there could be additional forces that ordinary matter does not feel. In fact, we already have examples of something like that, in that electrons do not feel the strong force." "In principle, there could be an entire second ""standard model,"" containing all sorts of particles and forces that are totally disjoint from the ones in the standard model we know. They only way we could detect their presence would be gravitationally. Or perhaps there could be interactions between the two models, but only at a very, very high energy, so that at low energies they are effectively decoupled. + +I'm currently a physics grad student, and I once was talking with one of the experimentalists who's looking for dark matter in the form of WIMPs (weakly inetracting massive particles). I asked him about this ""disjoint standard model,"" and whether it could account for dark matter, and his answer was basically, ""Well, it certainly could be true, but it sure would suck for our efforts to detect it experimentally."" " +277 Do animals have a sense of time? 2868 https://www.reddit.com/r/askscience/comments/3juywb/do_animals_have_a_sense_of_time/ 1441550362 3juywb Biology 2015-09-06 17:39:22 "It's been showcased that orangutans not only plan ahead for the future, but they also communicate it to their peers. It shows evidence that they keep a bit of a schedule for their daily lives. + +[Source](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0074896) + +If you don't want to read an entire peer reviewed journal on this study, [here](http://www.popsci.com/science/article/2013-09/orangutans-plan-and-announce-their-direction-travel-day-ahead) is a more streamlined version of it." "They certainly do have a sense of time, but not necessarily in the way you mean. + +Animals, including humans, almost all have a sense of time that is described in three scales: millisecond timing, which is largely controlled by the cerebellum and mostly concerned with coordinating movement; interval timing, on the scale of seconds to minutes to hours, distributed throughout the brain (and especially the striatum) and concerned with determining the typical duration between two events; and circadian timing, the 24-hour internal clock coordinated by the suprachiasmatic nucleus and adjusted based on solar cues (and, to a lesser extent, cues like eating times). + +See, for example, the excellent timing review by Buhusi & Meck, 2006: [""What makes us tick? Functional and neural mechanisms of interval timing"".](http://www.ncbi.nlm.nih.gov/pubmed/16163383) + +What you're talking about is circannual timing, meaning the timing of yearly (or thereabout) events. This almost certainly is largely controlled by instinct, or at best by other cues (e.g., shortened days and colder temperatures). Read more in my previous AskScience AMA [here](https://www.reddit.com/r/askscience/comments/39kl55/askscience_ama_series_i_am_ratwhowouldbeking_and/cs4f4xs). It's sometimes hard to disentangle learning and cognition from instinct, but consider how *fucked* most animals would be if they didn't intuitively know what to do as their first winter approached. + +How animals subjectively experience time is a very difficult question to answer, but it's just one of many stimuli that govern animal behaviour. Whether they *anticipate* the future or merely react to things that previously have been associated with what they should plan for is contentious, and I will quote [myself from an earlier question](https://www.reddit.com/r/askscience/comments/39kl55/askscience_ama_series_i_am_ratwhowouldbeking_and/cs4mcqp): + +> Future anticipation and future-planning in nonhuman animals is a really interesting, difficult-to-measure thing. First, ""future prediction"" mostly isn't necessary - we can usually predict the future pretty well based just on what has worked in the past (i.e., reinforcement learning). This complicates figuring out if an animal is deliberately planning, because you need to study it in circumstances that the animal isn't totally familiar with (or else they'll just respond in ways that have previously worked well), and then that seems a little unfair to expect the animal to cope with. There have, however, been some pretty successful studies of future anticipation in rats and monkeys. I've also found that pigeons start responding on options that currently aren't paying off but will soon (even at the expense of missing out on current food). Whether these are the same as what humans experience (and whether what humans experience is real, or just the way we interpret our decisions!) isn't currently answerable. In short, your dog probably lives mostly in the present and that works for it, but that doesn't stop it from doing things that work in the future (and it might even think about it, but we don't know!). " +371 How does a tempered glass screen for your smart phone pass the sense of touch to the sensors below? 2868 https://www.reddit.com/r/askscience/comments/4ewrqb/how_does_a_tempered_glass_screen_for_your_smart/ 1460727856 4ewrqb Chemistry 2016-04-15 16:44:16 "I am currently working on a capacitive touch design right now, so I can take a stab at this. + +. + +First you basically need a way to measure capacitance. There are several ways to do this, and every touch manufacturer has a variance on it. Essentially you apply a stimulus to the ""sense"" pad and then look at it's decay or response to get a base capacitance measurement. Generally there are 2 main kinds of base capacitance measurement, ""mutual"" and ""self"". Either way you are relying on the fact that this measurement is pretty consistent when there is nothing on the screen, that the glass is non-conductive so the fields can pass through it, and that your finger, which is conductive, will divert the electric field causing the measurement to change. + +. + +[Self capacitance](http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/design_self_buttons_finger.png) is essentially when you are measuring the capacitance of your floating sense pad to ground. The advantage here is you generally have a bit more signal, but the disadvantage is you essentially have 1 pin per pad. + +. + +[Mutual capacitance](http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/design_mutual_buttons_finger.png) is essentially when you are measuring the capacitance from one sensor to another. The disadvantage is you have a much smaller reference plane to measure capacitance to, which can be bad trying to measure through thicker pieces of glass/plastic. The advantage is you can multiplex the sensors. [For instance, you could use 6 pins to measure 8 ""points"" by having 2 for the row and 4 for the column](http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/design_mutual_buttons_multiplexed.png). Now you scan each row sensor with respect to each column sensor and you get 8 locations that are uniquely identifiable. + +. + +I am going to preface this section by saying, I have never done an actual phone touch screen before, but I can speculate on a possible design based on things I am testing. Let assume we want to combine a mutual capacitance design with a touch screen, and my controller has 32 touch pins. I can combine this with an LCD, which I have glued down to prevent the air gap from changing my measurements. Since it is a rectangle, lets design my electrodes for say 18x14, using 32 pins giving me 252 zones behind my LCD. You would think you could only measure 252 points, but it turns out you get some leakage between the sense pads, so you you can get a proximity type measurement. You compare each pad's measurement with a nearby pad and you can better locate the location of a finger press. + +. + +Sounds complicated right? Well luckily for a design engineer like me, the manufacturers of these sensing chips do most of the work for me. I can choose to dig into all of the sense values and run my own custom algorithms for finding fingers, or I can trust the built in libraries from the device manufacture. This means that if I followed their guidelines correctly I pretty much can get back a table of information that says there are fingers in X and Y positions and I am good to go. + +. + +All images were linked from a [Texas Instruments Technology design guide on their CapTIvate solution](http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/ch_design.html#ch_design_process). You can thank TI for the lovely pictures, or read up on their guide for a more in depth detailing of their capacitive touch technology. I will note I have no affiliation with TI. + +**edit** Some minor wording changes and a note, that I haven't actually done a Touch screen LCD on a phone, so I am speculating based on how I would design a phone touch screen from scratch" "Other posters have already described modern touchscreens (or at least, the good kind). + +Old ones worked by having a very thin metal mesh (which could sometimes be visible) that basically behaved like buttons do, but with some clever tricks to measure where you pushed. The downside is that this kind of screen is only good at single press, but it can also detect pressure from anything solid. The Nintendo DS uses this. *(Edit: I don't know if they actually use a mesh, it's possible since it's a low res screen already.)* More modern versions of this don't use a mesh, but are still limited to single press detection. They're popular for bank machines and such, because they're durable and work fine in cold weather when people are wearing heavy gloves, and they're much more reliable when wet. + +This works because even though like you said glass is very hard, it is not completely inflexible (nothing is 100% rigid). Especially when it's very thin. It doesn't need to flex much to be useful." +484 Is it possible to create 100% vacuum? 2867 https://www.reddit.com/r/askscience/comments/4oo2pz/is_it_possible_to_create_100_vacuum/ 1466247452 4oo2pz Physics 2016-06-18 13:57:32 Heh, finally my job is useful. I design vacuum chambers for a living. The short answer is no, we cannot achieve a perfect vacuum. Even the best pumps, like cryopumps, which actually condense gas molecules onto the pump surface, cannot get every single molecule. Even if you could capture all molecules all materials outgas slightly, meaning they emit gas particles. So you will constantly have molecules entering the chamber. We use special cleaning methods, low outgas materials, and even bake hardware to try and reduce this but it still happens. We cannot even create a vacuum equal to that in outer space. Hope this helps. "The best we can do right now is about 100 molecules per cubic centimeter. In interstellar space, it reduces to about 10 per cubic centimeter. In extragalactic space, it's about 1-3 molecules. + +Even if we were able to achieve something 'perfect', the existence of virtual particles would still pose a problem. + +Virtual particles are quantum related particles that pop in and out of existence rapidly. They are not controllable in any way, and are present in every part of reality regardless of its content. So, basically, no. " +485 What would be a 2D equivalent of a black hole? 2865 https://www.reddit.com/r/askscience/comments/4j7rjl/what_would_be_a_2d_equivalent_of_a_black_hole/ 1463165029 4j7rjl Physics 2016-05-13 21:43:49 "The trampoline thing is mostly crap. Maybe there's a good analogy in there somewhere but personally I think it creates much more confusion than anything else. I disagree with popularizers dropping it like it's nothing, without any actual explanation of how it relates to reality (very little actually). + +So set it aside. + +2D black holes are very cool. By this I mean you build general relativity but instead of in 3+1 dimensions (space + time) you work in 2+1 dimensions. It turns out empty spacetime is always flat in this theory! Therefore there is no actual gravitational force. The equivalent of a black hole in this theory does not attract you. It's a conical defect, in that the length of a circumference around it of radius r is not 2πr, but actually less, and the angle defect is proportional to the mass. (This is entirely analogous to what happens with strings of mass in 3+1D, see cosmic strings). + +2+1D gravity is what one calls a topological theory, in that locally nothing of interest actually happens, as there are no gravitational waves and no curvature outside of a massive body, but there still are global gravitational effects such as the angle defect mentioned earlier which can only be measured by enclosing a planet in a loop and measuring its length. A local observer with its small ruler cannot see these global observables. + +This makes 2+1D gravity very tantalizing because it's much, much easier to solve than normal gravity, and so to quantize, which is a very important subject of research. Moreover, Ed Witten has argued for a couple of unexpected equivalences of this theory with other bizzare theories which have made it possible to partially explicitly solve this theory in its quantum version and also to reveal subtle relationships with completely different areas of theoretical physics such as CFTs and gauge theories; this kind of relationships reek of string theory generally so probably there's a connection." "Never mind a mathematical 2-D BH, here's a practical way of making an *actual* 2-D Event Horizon (Black Hole not so much). + +Imagine a large pool of water, not very deep, say 2 feet deep, but several hundred feet in each horizontal direction. In the middle of the pool is a hole in the bottom, acting as a drain, and indeed water is draining out of the pool. + +Now, as you can easily imagine, the nearer the drain you are, the faster the water is moving towards the drain. In fact since it's a 2-D situation not 3-D, instead of an inverse squared law we use a simple inverse law, no squaring needed. So the rate of flow towards the drain is proportional to 1/r, (not 1/r^2 ). + +At some distance from the drain, assuming the drain is actually big enough to be draining a lot of water, the speed of water moving towards the drain will be equal to the speed of sound in water. This is an acoustic Event Horizon: any sound emitted inside that boundary can never get to, let alone past, the boundary. Thus it behaves just like a BH with an EH, but for sound not light. But you can (so I read somewhere) still do useful experiments with a setup like that." +486 What's going on in my head when I'm thinking of an image? 2864 https://www.reddit.com/r/askscience/comments/4v6rhu/whats_going_on_in_my_head_when_im_thinking_of_an/ 1469801631 4v6rhu Neuroscience 2016-07-29 17:13:51 "In the 80's there was a big debate about this called, appropriately, The Imagery Debate. There was even a (philosophy) book published with that name. I recommend checking out the Standford Encyclopedia of Philosophy (SEP; a great resource in general) article on mental imagery, particularly the section on [the analog propositional debate](http://plato.stanford.edu/entries/mental-imagery/#AnaProDeb). + +Roughly, the two camps/ideas were this: + +**Analog View (Kosslyn):** mental images are imagistic or pictorial in nature and share many properties with an actual image / perception of the real world. This might include reactivation of cortical areas during mental imagery that are active during perception. It is like you are really seeing the thing (hence the term analog). + +**Propositional View (Pylyshyn):** although it may seem to us that we call up an image and examine it with our mind's eye (whatever that may mean!) this is actually misleading and does not reflect the true nature of the representation and is also in danger of committing the Cartesian fallacy (who/what is looking at / analyzing this internal picture?). Instead, mental images are actually (symbolic and amodal) descriptions in a Language of Thought -like way. So, for example, when you imagine your room, you are not creating a picture in your head, but a series of relations between concepts like ""to the left of (door, couch)"" which means that the operator ""to the left of"" takes in two objects or arguments (door and couch) and describes the relation between them. + +It would take too long to list all of the arguments for the two views, so here are a select few: + +**Evidence in favor of picture-like representations:** + +- mental rotation: if you are comparing two 3D objects and trying to decide whether they are the same (just rotated versions) or not, the amount of time to answer is linearly related to the angle of rotation ([Cooper and Shepard 1973](http://psycnet.apa.org/psycinfo/1974-08328-006). It is as if we are rotating a mental model just like we would a physical object to try to get them to match + +- we represent empty space and preserve metric information: imagine a map of the US. Focus your attention on NY. Now move your attention to Maine. Go back to NY. Now shift your attention to California. Did it take you longer? Many people say yes. (The actual studies used fake maps that subjects had to memorize and different measures). This suggests that our mental images preserve metric properties: things that are far in the world are far in mental images, that just like for a picture, it takes time to scan our mental images, and that we represent the empty space between parts of our mental image/ focus of attention just like in a picture ([Kosslyn, Ball, and Reiser 1978](http://psycnet.apa.org/journals/xhp/4/1/47/)). + +- we experience our mental images in different detail based on our imagined viewpoint /distance just like a real picture/ the world: imagine a rabbit next to an elephant. Does the rabbit have ears? Whiskers? Now imagine a rabbit next to a bee. Does it have those features now? Depending on the imagined ""level of zoom"" we imagine or can respond about features with varying degrees of resolution ([Kosslyn 1975](http://www.sciencedirect.com/science/article/pii/0010028575900158). + +- mental imagery activates early visual areas: [Ganis, Thompson, and Kosslyn 2004](http://www.sciencedirect.com/science/article/pii/S0926641004000709), [Slotnick, Thompson, and Kosslyn 2005](http://m.cercor.oxfordjournals.org/content/15/10/1570.short), and many more. Although I would point out that there is still a question of exactly what is represented / what those activations mean and some of the evidence isn't very convincing and vivid mental imagery can occur in the absence of primary visual cortex ([Bridge et al. 2012](http://link.springer.com/article/10.1007/s00415-011-6299-z), although see [Stokes et al. 2009](http://m.jneurosci.org/content/29/5/1565.full)). + +**Evidence in favor of the propositional view:** + +- our mental images and representations are typically fixed in a particular viewpoint/ representation and we can't look at them a different way like we could with a picture. For example, in these [Slezak figures](http://ruccs.rutgers.edu/images/personal-zenon-pylyshyn/class-info/Lecture2_files/slide0019_image059.jpg), you can imagine rotating them 90 degrees counterclockwise and seeing a different animal. However, if subjects are shown these figures briefly and asked to memorize them, they do not notice the other interpretation, even though they can mentally rotate the figures ([Slezak 1991](https://www.researchgate.net/profile/Peter_Slezak2/publication/243768941_Can_images_be_rotated_and_inspected_A_test_of_the_pictorial_medium_theory/links/55fe323c08aeafc8ac740704.pdf); see also [Chambers and Reisberg 1985](http://psycnet.apa.org/journals/xhp/11/3/317/) who showed that mental images cannot be ambiguous like pictures can). Nor can we detect the parts or patterns of a mental image like we could with a real image ([Reed and Johnsen 1975](http://link.springer.com/article/10.3758/BF03197532)). Rather, it is as if we have some sort of abstract, summary representation and not a picture. + +- what we store and then try to imagine is greatly affected by the context and is not a veridical representation of what we have save / are trying to imagine. [Carmichael, Hogan, and Waters 1932](http://psycnet.apa.org/journals/xge/15/1/73/) (<-- not a typo on the date!) had participants memorize and then later draw from memory a series of simple shapes. For example, they might be shown a circle with little lines sticking out of it on all sides. For one group of subjects, they told them it was a sun; for another group, they told them that it was a ship's wheel. When subjects later drew the images from memory, their pictures were distorted based on the label that the image was given, even though the original image was the same for both groups. They argued that this showed that the images were not stored as pictures but as concepts which were susceptible to linguistic influence. + +- as mentioned, the fMRI evidence is actually a bit mixed. In many of those studies, they find activation outside of early visual cortex in areas like LOC and in parietal cortex suggesting that representations are more diffuse and distributed and perhaps more abstract. + +**Resolution:** the nature of mental image representations may be a combination of both types and may vary based on task. Some aspects are pictorial and some are propositional. See the [dual-coding theory](https://en.m.wikipedia.org/wiki/Dual-coding_theory) (the critical evidence in favor of this is probably [Brooks 1968](http://psycnet.apa.org/journals/cep/22/5/349/)). +" "So this is a tricky one as it has to do with memory storage, which isn't fully understood. However, the ability to ""see"" an image in your head is a bit easier to explain, so we'll skip over how the brain actually stores data. + +When you see something in front of you the information gathered by your eyes is projected back into your visual cortex for processing, encoding, and storage. This is a fairly complex process that breaks the image down into patterns that can be stored internally (you aren't storing an ""image"" per se but rather the information about that image). + +When you recall an image your brain recreates that pattern of signals and projects it onto the visual cortex like an echo of the original. This means that the only real difference between seeing something in the real world vs. in your head is the signal source and your ability to distinguish between the two. + +It should be said that while the brain is remarkable it is not flawless, the image you remember is easily altered by other factors both intrinsic and extrinsic. + +Further Reading can be found here: + +https://en.wikipedia.org/wiki/Visual_memory + +https://en.wikipedia.org/wiki/Recall_(memory) + +http://journals.lww.com/neuroreport/Abstract/1990/09000/Functional_anatomy_of_storage,_recall,_and.15.aspx + +Edit: For those of you who say you lack this ability entirely, know that aphantasia is a relatively new suspected disorder. I was able to find a single small study on research gate concerning it. + +Zeman, A., Dewar, M., & Della Sala, S. (2015). Lives without imagery–Congenital aphantasia. Cortex, 3. + +Edit 2: I've seen a lot of questions about imagined images and some talk of idea inception (original thought). At the visual cortex, the former functions the same as normal visual recall but you are combining known patterns in a different configuration from before. The combinations may be unique but the underlying patterns and ideas are ""recycled"". + +As for inception, this has more to do with memory structure, storage, recall, and conscious thought, but one of the prevailing theories is that our thoughts and recollections have a degree of randomness that can cause original ideas. I would not be the one to ask however. + +Edit 3: + +For music recall I imagine the mechanism is similar but I have not done much research into the topic yet. A good springboard for those curious would of course be Wikipedia but take it with a grain of salt. + +https://en.wikipedia.org/wiki/Music-related_memory?wprov=sfla1 + +Apologies for the less than in depth responses but doing this from a phone makes pulling proper sources a tad difficult. I will try to revisit this thread when I have access to my mendeley account. + +For a more in depth analysis of visual recall please refer to the post by /u/albasri as his sources are much better than Wikipedia links." +168 Why is it that the de facto standard for the smallest addressable unit of memory (byte) to be 8 bits? 2863 http://www.reddit.com/r/askscience/comments/3b6lkz/why_is_it_that_the_de_facto_standard_for_the/ 1435318899 3b6lkz Computing 2015-06-26 14:41:39 "Back in the 1950s and 1960s, computers used whatever word size was convenient, resulting in word sizes that seem crazy today, like 37 bits. If your missile needed 19 bits of accuracy to hit its target, then you'd use a 19 bit word. Word sizes I've come across include 6, 8, 12, 13, 16, 17, 18, 19, 20, 22, 24, 26, 33, 37, 41, 45, 48, 50, and 54. [Details here](http://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.html#ref9). It seems like the word length should be a power of two, but there's no real advantage unless you want to encode bit operations in your instruction set. + +6 bits was a popular size for business computers because it could handle alphanumerics, e.g. the IBM 1401, which I've used a lot recently. This encoding was BCDIC (which predated EBCDIC). + +There's a good reason why computers didn't use any more bits in the word than necessary: cost. In 1957, core memory cost more than ten dollars per bit (in 2004 dollars). So using 8-bit words instead of 6-bit words would cost you a fortune. A few years later, the 12,000 character memory expansion for the IBM 1401 cost $55,100 (more than $400,000 in current dollars), and was a unit the size of a dishwasher. At these prices, if you can use 6-bit characters, you're not going to pay for 8-bit characters. + +For a while, *byte* referred to the group of bits encoding a character, even if it wasn't 8 bits. (This seems so wrong nowadays.) The IBM Stretch standardized on an 8-bit byte and power-of-two word length, and this became dominant with the IBM 360. (I think this also was a key factor for hexadecimal replacing octal.) Now, it's almost unthinkable to have a word length that's not a power of two. + +Looking at more recent computers, Intel's iAPX 432 processor had variable-length instructions. This is normal, except the instructions took a variable number of bits, not a variable number of bytes! An instruction could be from 6 to 321 bits long, so instructions were packed together overlapping byte boundaries. Not surprisingly, the iAPX 432 was a disaster." "There really isn't a definitive reason. There were other architectures that had different data unit structures but because of marketing or user friendliness or whatever reason, systems that used 8 bits won out and became standard. + +At the time 8 bits was convenient because using binary to interpret them it provided for 255 characters which was enough for the alphabet in upper and lower case and most of the special printable characters that were thought to ever be needed." +278 can there be an arctic methane release large enough to cause an extinction level event and how long would that take? 2862 https://www.reddit.com/r/askscience/comments/3tdcwr/can_there_be_an_arctic_methane_release_large/ 1447895100 3tdcwr Earth Sciences 2015-11-19 4:05:00 "Mmm, very interesting question. + +Let's take ""extinction level event"" to mean a mass extinction like the big 5. + +The closest analogue to this is the [PETM](https://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_Thermal_Maximum), the Paleocene-Eocene thermal maximum. This was an event about 50 million years ago that had a short term increase in global temperatures of about 5 degrees C. The best evidence suggests that it was caused by a cascade of methane, leading to global warming and sea level rise that is larger than what we are looking at today. + +This is the best candidate for a historic arctic methane event, and if there were others we might know. So we know that it is possible, but very rare to have this kind of event. We can't tell how long it took, but we know from beginning to end the event was under 10,000 years, but that's just because it's tough to measure short time periods in the geologic record. It could have been much shorter, especially on the release end. + +The next question is -- did the PETM cause a mass extinction? The answer is that no, it did not. The Paleocene/Eocene is associated with a faunal changeover but not a mass extinction. However, this doesn't mean that there wasn't a smaller extinction associated with the PETM! Almost all transitions between geologic periods are defined by changes in fauna of moderate size, and especially in some groups we'd expect to be hit hard by a change in ocean chemistry and temperature like benthic foraminifera. However, even these ""hard hit"" groups didn't really show mass extinction levels of turnover. Alternative is that rates of evolution were higher for many groups, so their old forms disappear from the fossil record while their descendents simply look different -- a ""pseudo-extinction"". It seems very likely that the methane release was the cause of this worldwide shift in biota. + +The next part of answering ""can there be..."" is to think about if the PETM is the worst possible event that could happen... if we could show it's likely that an event could be much worse, we might decide the answer to your question is ""very likely so"". + +The world today is different than it was in Paleocene time. First off, we have massive continental ice shelfs-- there was no continental ice shelfs then. Sudden increase in global temperature interacting with continental ice might cause cascading events that lead to a much worse event. Next, If much larger quantities of methane were locked up in the sea floor, you could potententially have a much larger temperature excursion, including one that would cause a mass extinction. I don't think anyone really knows enough about methane to say if this is plausible or likely. So, we certainly can't exclude the possibility that an arctic methane event could cause a mass extinction. However, it also doesn't seem that likely. We are, after all, talking about a single event from 50 million years ago. The conditions for a massive release clearly aren't common. + +To summarize, methane hydrate release seems to have caused a ""small"" extinction about 50 million years ago, in a very short period of time. While that event didn't cause a truely large extinction, there are reasons to think that event wasn't as bad it could be. We can not exclude arctic methane release as a potential cause of a major extinction, if everything lined up right... but it also doesn't seem very likely. + +" "It might be worth your time to look into the clathrate gun hypothesis, which is essentially a self perpetuating positive feedback loop that is the methane released from within the seabed and thawing permafrost heats up global atmospheric and sea temperatures which spurs more methane release, etc etc. The hypothesis was originally that once it really starts, it would cause radical climate change within a human lifetime--potentially triggering mass extinction. However, it's largely agreed today that's unlikely. Still an interesting thing to read up on! + +https://www.wikipedia.org/wiki/Clathrate_gun_hypothesis" +372 AGU AMA: I’m Dr. Kim Cobb, and I’m here to talk about the science of climate change, El Niño, and the reconstruction of past climate. And I’m Dr. Anne Jefferson, and I’m here to talk about how water moves through landscapes and how land use and climate change alter hydrology. Ask Us Anything! 2862 https://www.reddit.com/r/askscience/comments/4fbgm3/agu_ama_im_dr_kim_cobb_and_im_here_to_talk_about/ 1460980228 4fbgm3 Climate History AMA 2016-04-18 14:50:28 Please remember that comment moderation is done to help maintain quality answers in this sub. Personal attacks and vulgar posts will be removed. Using evidence in a civil debate is fine. Name calling and personal attacks are not. Anne: So many great questions, I'm sorry I couldn't answer more. Thanks for having me here on Reddit. +50 What is the Higgs boson made of? 2860 http://www.reddit.com/r/askscience/comments/31izjr/what_is_the_higgs_boson_made_of/ 1428248247 31izjr Physics 2015-04-05 18:37:27 "**Short answer:** Energy! ... Sorta! + +**Long answer:** You're familiar with the idea of electromagnetic fields and waves, right? Basically, the idea is that when you have an electric charge or a magnet it will make a 'field' around it, that other charged objects can in turn interact with, and feel an electromagnetic force. [For example, when you pour iron filings around a bar magnet, they'll line up with the magnetic field.](http://4.bp.blogspot.com/-EWI_p8V2fJk/Tj4cHzHLQMI/AAAAAAAAAGE/AkCxMZw750s/s1600/iron%2Bfilings.png) + +Additionally, you're probably familiar with the idea of light being an electromagnetic wave. Basically, if you wave a charged object back and forth, you'll make ripples through that field- this is the principle behind antennas, and is really a core concept in electromagnetism and modern electronics. + +In summary, there is this *thing* that permeates all space, which is the field, and by putting energy into it we can make little ripples in it, which are 'particles' we call photons. A really simple analogy would have you imagine the field as a calm surface of water on a lake, and if you put energy into it by shaking a stick at the surface, you can make a wave. + +It turns out that this idea isn't limited to electromagnetism, and is a core concept in *quantum field theory.* QFT basically tells us that there are *fields* for every fundamental particle, and by exciting the field you have made a particle. A simple example is the *electron* field (which is not to be confused with the electromagnetic field). The idea is that there is an 'electron field' that permeates the universe, just like the electromagnetic field, and at certain points there are little 'knots' where a lot of energy is localized into particles of that field. Similarly, the positron - or antimatter electron, is an excitation of this field. In a simple sense, you could imagine the electron as a wave 'crest' and the positron as a wave 'trough' ([left hand column of this picture](http://www.alanpedia.com/physics_waves/waves_clip_image058.gif)) and when you bring them together they annihilate each other. This is all [an oversimplification](http://en.wikipedia.org/wiki/Dirac_sea) that many practicing particle theorists will dislike, but I think it at least illustrates the idea well if you've never been exposed to it before. + +Our current best quantum field theory is the [Standard Model of Particle physics](http://en.wikipedia.org/wiki/Standard_Model_%28mathematical_formulation%29#Alternative_presentations_of_the_fields). It's basically a set of fields with their properties, and thus the associated particles, and the interactions between the fields. For example, the electron field can interact with the electromagnetic field - this is because electrons have charge and energy can move between the electron field and the electromagnetic field (like when an electron and positron annihilate to make two photons). + +This just comes from E=mc^2 - the *mass of the particle* is equal to some amount of *energy* which can be exchanged between the fields. Imagine it like gold in ancient times- there is a finite amount of gold that Greeks and Persians and Egyptians can trade (imagine they aren't mining any new gold). They stamp that gold into their own coins, and they trade those coins with each other, which they melt down and stamp into their own coins. It's kinda like that with energy and fields. Each of these civilizations is like a 'field' and their gold-trade is the exchange of 'energy.' + +Anyway, you'll notice on that figure at the link two paragraphs above there is a ""Higgs Boson."" Basically, there is this other field, similar to the 'electron field' and 'electromagnetic field' that interacts with the fields that have massive particles. And if you've been paying attention, it means that this field must have a particle associated with it! Again, in the Standard Model, every field has its own properties and different ways of interacting with other particles and rules for what it makes particles do (e.g. electromagnetically, like charges repel), and that's a little beyond the scope of this post here, but I will leave you with this comic which I think illustrates the *idea* behind the [Higgs mechanism.](http://krbowie.files.wordpress.com/2010/03/higgs-boson-cartoon22.jpg) + +As for what it's made of? It's made of the same thing as every other fundamental particle- an excitation of its associated field. Once you get small enough (smaller than atoms and protons and neutrons and all those other composite things) we say that these are 'fundamental particles.' The Higgs Boson is by definition an *excitation* of the Higgs field- which you could say has an associated energy. In a simple analogy, energy can get locked up in a little kink in the Higgs field, and that's the thing we call the Higgs Boson. " "The fundamental fields in the standard model are the basis, everything else is made from them. So the electron field, the up quark field, the higgs field.. etc are the foundation. + +It doesn't make sense to ask what they are made of. The higgs boson is an excitation of the higgs field, and the higgs field isn't made of anything more fundamental, it IS one of the fundamental things. + +You can ask what is a proton made of, I can tell you it is made of excitations of the up quark field, the down quark field and the gluon fields. I can't tell you what the up quark fields are made of, because those are the fundamental building blocks of everything else." +373 Why does hair change as you age? ie in colour, curly to straight... 2859 https://www.reddit.com/r/askscience/comments/418stm/why_does_hair_change_as_you_age_ie_in_colour/ 1452957717 418stm Human Body 2016-01-16 18:21:57 "Part of the reason among fair-haired people is the natal coat: + +http://newfoundlandnews.blogspot.com/2009/09/my-baby-looks-like-francois-langur.html + +""Natal coat is the term for the different coloration of primates during infancy that later changes. Only about 10-20% of primate species are born with different hair color than they'll have as adults."" + +Science has not fully explained the natal coat but they are examining different advantages: + +http://www.ncbi.nlm.nih.gov/pubmed/9331453 + +Edit: This has a lot of points, so I will clarify here as well as I clarified below in my comments. I am a layperson who developed an interest in this particular question, but I cannot answer the individual-level questions about your hair in particular, nor am I qualified to clarify questions which deal with speculative theories or unpublished research. I hope that evolutionary biologists will step in and do so below for those who've asked clarifying questions that I can't answer." Part of this is due to the changes in hormonal balance and the length you keep your hair. As you age the hormone levels in your body will change impacting your hair texture and sometimes the color. There are other environmental effect other than length as well. For example, humidity will increase the curl potential of your hair as it increases, etc. +169 If we can lose hundreds of skin cells by scratching at them, why is it hard to rub off pen or marker on our skin? 2856 http://www.reddit.com/r/askscience/comments/3eu4wi/if_we_can_lose_hundreds_of_skin_cells_by/ 1438042116 3eu4wi Human Body 2015-07-28 3:08:36 [deleted] "The skin cells that slough off are from the top, stratum corneum. Ink can seep between cells and stain deeper layers, those layers aren't ready to slough off yet, but still can be stained with ink. I'm talking very superficial layers. Tight junctions prevent ink from staining the stratum spinosum and stratum basale. +The following is from a microscopic section from a tattooed cow's ears (bangs tattoo), so not the best, ignore the deeper layers with ink, but the top purple layer is the epidermis and you can see it has several layers. At the surface you see a lighter pink layer, that's the stratum corneum and will flake off, you see it grossly as white flakes (keratin). It's pink here due to the eosin stain of the section. If you look closely you can actually see some of the pink flakes of keratin. + +http://imgur.com/XVUdz + +Wish I had a better pic, but this is the only histo I have on imgur + + +EDIT: if anyone is interested, here's the album that explains where tattoo ink goes (on mobile so hopefully the link is works): http://imgur.com/a/CgsnR + +EDIT 2: this isn't as high quality but you can see the flaking in this other histo image I took (there's a tick attached to this skin section): http://imgur.com/3myf9Gh" +487 As the human body goes from being an infant to an adult, are there any organs or body parts that become smaller instead of larger? 2855 https://www.reddit.com/r/askscience/comments/4lqw6w/as_the_human_body_goes_from_being_an_infant_to_an/ 1464633097 4lqw6w Biology 2016-05-30 21:31:37 "There is at least one example i can think of off of the top of my head. +The thymus gland is very active in young children, and becomes far less so as we near adulthood. As far as the gland itself actually shrinking, i dont think it does, but The active cells which carry out glandular functions are replaced by adipose tissue as you age." "Growth plates start shrinking after the first growth spurt, and then seal off after the teenage growth spurt. + +I suppose ovary egg numbers decrease after birth (after menarche, really). But idk if the actual size of the organ is affected by puberty/early aging. + +Not absolute size, but percentage of bone marrow as fat increases with age. A common rule of thumb for pathologists is approx 1% marrow fat per age. " +374 Why do those stripes form besides an/this nuclear blast? (Camp Desert Rock nuclear test) 2850 https://www.reddit.com/r/askscience/comments/40xz6x/why_do_those_stripes_form_besides_anthis_nuclear/ 1452784635 40xz6x Physics 2016-01-14 18:17:15 Those are the trails from sounding rockets fired from the ground near the blast, nothing to do with the nuclear blast itself. By launching those rockets shortly before the blast, the initially vertical smoke trails will be deformed by the shock front of the explosion which gives visual evidence of the fluid motion going on around the explosion. [deleted] +488 What causes the mushroom cloud effect in a nuclear bomb? 2848 https://www.reddit.com/r/askscience/comments/4wwdeu/what_causes_the_mushroom_cloud_effect_in_a/ 1470752014 4wwdeu Physics 2016-08-09 17:13:34 "Any really large explosion that generates a large amount of hot gas will generate a mushroom cloud. As the heated gas rises up, the outer edges are slowed down by drag and are pushed aside by the hot gas coming up behind them, creating a mushroom-like appearance. + +It's an example of [Rayleigh-Taylor instability](https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instability#Late-time_behaviour). + +If you detonated a nuclear weapon in zero-g, you wouldn't get that effect. Or if the atmosphere were already the temperature of the nuclear fireball, since that would remove the buoyancy that causes that gas to rise. + +Regular explosions will definitely do the same thing. Source: when I was 14 and set a pile of wet leaves on fire with 3 gallons of gasoline." "There have been large, non-nuclear detonations done as tests, and they have shown the same effect. [Here](https://www.youtube.com/watch?v=7VANyY87-_Q) is video of the ""100-ton test"" at Alamagordo showing the mushroom cloud forming near the end of the video. (Bonus points for guts to the guy at 1:06 literally surrounded by tons of TNT, hammering on a box of TNT to get it into position.) " +1272 What usually happens to refugee camps in the long run? How do they end? 2839 https://www.reddit.com/r/askscience/comments/be4yp2/what_usually_happens_to_refugee_camps_in_the_long/ 1555485991 be4yp2 Social Science 2019-04-17 10:26:31 "I am a humanitarian aid worker. Currently not working in camps, but have done it before. Feel free to ask more specifically. + +For simplicity I will just be talking about refugees, not Internally Displaced People (IDPs). + +Before talking about how camps end, lest talk about how they start. Usually through one of these three ways: + +1. Governments/local authorities set up a camp. It is quite common that a host government set up a camp. They often do this with the help of international NGOs (INGOs). The NGOs may be running the camp day-to-day, but the final authority always lies with the host government +2. Refugees settle where they see fit. Refugees may set up for the night somewhere on the way. Then one night turns to two etc. An suddenly you have a camp. Quite often this are caused my external factors, such as a government not letting refugees pass further. Look up ""Idomeni camp"" for a good example. +3. NGOs set up a camp. This is quite rare, as NGO's usually work on the acceptance of a government. Governments rarely want to give up control. But it does happen sometimes. Good examples are some of the camps in the DRC during and after the Rwanda genocide. + +Now, they can also end in many ways. If they end at all. Here are a few common scenarios: + +1. The host government decides to close a camp. The residents dispatch elsewhere. + 1. I mentioned Idomeni above. That camp was eventually closed by the Greek government. As a result, many of the residents started walking south. Some setting up imprumptu camps on the way (all were eventually shut down as well) or settling in different, government-controlled, NGO-run camps. +2. A camp may fall out of use. Maybe some day all the residents have returned home. Or have been relocated to a more permanent solution +3. Or a camp may never close. The more people live in a camp and the longer it runs, the more it will start resembling a city. If you were to visit famous camps like Za'atari in Jordan or the camps around Cox Bazar in Bangladesh, they may at times be hard to distinguish from a non-camp. + 1. Sometimes they merge together with nearby cities or communities, appearing much like a suburb. Here the most famous examples are all decades old Palestinian camps, like Shabra and Shatila in Beirut or Aida in Bethlehem. + +​ + +>There's lots of individual stories out there, but I'm looking for hard data and statistics on the long-term fate of refugee camps worldwide. + +There is lots of data available through UNHCR. It might be a bit difficult to find what you are looking for though. [https://www.unhcr.org/figures-at-a-glance.html](https://www.unhcr.org/figures-at-a-glance.html) + + +Edit: +Thanks for the gold. Never thought I would get that from telling about my job. Next time I will tell you about how i just spent two entire working days yelling at an Excel sheet." "All of your questions depend on a lot of different variables. For instance, how long a refugee stays in a camp depends on where the refugee camp is located, how many refugees there are, which countries are willing to sponsor them, when they arrived at the camp, etc. + +Whether a population chooses to return also depends on the nature of the conflict (intrastate, interstate, ethnic) the level of destruction, length of conflict, level of displacement, whether genocide or population transfers were an aspect of the conflict, the nature of the ensuing peace agreement, the likelihood of violence returning, the number of parties involved, the nature of the claims/grievances, etc. + +For example, most [Bosnians returned](https://www.tandfonline.com/doi/abs/10.1080/00045600903260671) not only to Bosnia but to their homes after the war. Only a fraction of the Jewish population after the Second World War, however, returned home. Tony Judt has a good account of return rates in the introductory chapters of [Post War](https://books.google.ca/books/about/Postwar.html?id=10oPnprPjcgC). + +With all that in mind, however, although individual and group experiences will vary depending on the nature of the conflict in question, the consensus in the literature is that the majority of a population will typically try to resettle in a location as safe and as close to possible as their [previous place of residence](https://www.sciencedirect.com/science/article/pii/S0962629811001909). + +In addition, refugee camps are typically run by host governments in coordination with the United Nations Human Rights Commission's Refugee Agency." +375 How much work does it take to send a packet across the internet? 2833 https://www.reddit.com/r/askscience/comments/41sgzw/how_much_work_does_it_take_to_send_a_packet/ 1453260811 41sgzw Physics 2016-01-20 6:33:31 "I've worked as an architect on the largest transit ISP backbones, both as an operator and as an equipment manufacturer. I'm interpreting ""work"" as classical electrical power (watts). + +There are two broad classes of power consumption in network equipment (both switching/""routing"" and optical transmission). The first is passive power. This is what's needed to keep the lights on: the transmission lasers themselves, the baseband modulation, the keepalive frames, power conversion losses, fans, the routing protocols and monitoring software, etc.. This is the amount of power consumed (work performed) even when there are no customer packets on the network whatsoever. And it is a very high amount of power. It's so high because all of the circuits, all of the silicon in the systems is powered and contributing to transistor gate leakage current, which relative to number of gates is going up with every new Si process (e.g. worse at 22 nm than at 90 nm). The second class of power consumption is active power, which is the extra power consumed by switching transistors on and off, and which goes up as the packet processing load on the devices increases. This is also very high, but anecdotally, may in many cases only contribute 20% of the total power (e.g. zero packets per second is 80% of max, and line-rate PPS is 100%). As another commenter said, it would be obtuse to look only at the active power; the network was built at great expense expressly to deliver your packet. I'll consider both. + +The total power consumed per unit of packet forwarding capacity has consistently decreased since the beginning of the Internet, thanks to Moore's Law. The discussion about copper vs. fiber is mostly irrelevant, since today copper is only used for the last mile (e.g. DOCSIS over coax or ADSL over UTP) or in the datacenter where the packets originate (again not a great distance). The specification for total power per unit of full-duplex capacity on a router product that was just introduced in December, 2015 is 0.3 W/Gb/s (that's passive and active power at 100% load, using very recent silicon from Broadcom). The Internet at large is made up of older generations of silicon/equipment, plus lots of stuff on the edge that's not as efficient, so let's multiply that by 10 (more than three Moore's Law generations) to average it out and assume it's 3 W/Gb/s globally. Note this is per ""hop."" You can use a full-duplex spec as the cost to transit one hop, because you're going into one port and out of another (same as two packets ingress/egress on the same FDX port). The other contributor to power is the optical transmission system. Usually the total contribution to power from these systems is less than that from the switching layer, so let's say it's 2/5 and round up to 5 W/Gb/s. + +Hop counts calculated by others are mostly correct. A dozen or so is typical. Not all hops have the same power consumption profile, because some are core equipment at massive scale that efficiently do 0.5 W/Gb/s or better, while other hops are access network equipment at smaller scale (per device) that may do 15W/Gb/s or worse. Ok, 5 W/Gb/s, and 12 hops. Let's say that your access modem or ONT plus home router adds another 10W/Gb and take it up to 15 W/Gb/s. + +But how many ""packets"" in a gigabit? We have something called IMIX, which is nothing more than a real-life traffic profile. There is no single IMIX, because it depends on what applications the users of a particular ISP use the most. Video applications send a lot of packets at the MTU (1500 bytes path MTU for almost all Internet conversations), with a lot of GETs (HTTP) and ACKs (TCP) sprayed around in smaller packets (<200B). IMIX for a typical residential ISP profile, end-to-end is around 800 bytes. So let's assume our packet is that big. 1 Gb/s gives us about 156,000 packets per second (800B each). + +All together now. 15 W/hop * seconds/Gb * 12 hops * 1/156,000 Gb/packet = 1.2 mW-s/packet = 1.2 mJ/packet. + +EDIT: Made a mistake in unit analysis; thanks, /u/bitwiseshiftleft." "A hop count of 3.5 is far too low: here in Toronto 3.5 doesn't get me outside my providers network. + +I think the confusion is AS-paths vs hops... An AS is generally a company or provider (hence Autonomous system) so the paper is basically saying your traffic crosses (on average) 3.5 companies. + +http://nrlweb.cs.ucla.edu/publication/download/281/garyglcm98.pdf and http://circuit.ucsd.edu/~massimo/ECE158A/Handouts_files/hop-count.pdf would put the average hop counts in the 12 to 17 range. + +Those hops, as others have mentioned are larger and more powerful. Think 100Gbps and 2000 watts (http://www.cisco.com/c/en/us/products/collateral/routers/12000-series-routers/product_data_sheet0900aecd8027c8dd.html) gives you a lower power cost per router hop per packet. + +IPv6 doesn't change the router-structure of the internet (much, we're ignoring NAT and end users here) it is just another addressing system so it doesn't really impact the result. + +And bits per packet is closer to 12000 (roughly 1500 bytes, less a bit because you have headers in there. But also less more because we're also not taking into account overhead due to encapsulation that might be on your home DSL line for instance) +" +51 Is it possible that a mountain taller than the everest existed in Pangaea or even before? 2832 http://www.reddit.com/r/askscience/comments/2salhs/is_it_possible_that_a_mountain_taller_than_the/ 1421166765 2salhs Earth Sciences 2015-01-13 19:32:45 "Probably a lost cause given the number of upvotes the top comment has received, but I feel the need to point out that while [it](http://www.reddit.com/r/askscience/comments/2salhs/is_it_possible_that_a_mountain_taller_than_the/cnnr3cs) is correct in the sense that Everest probably represents about the highest mountain we'd get on Earth, the explanation provided along with that is a gross (and largely wrong) over simplification. There are many physical limits on the height of mountain ranges, which include: + +**Work Required to Continue Building Topography** This is probably the one that gets closest to what is being described in that top comment ([""whereby they cause the earth's crust to compress from sheer mass""](http://www.reddit.com/r/askscience/comments/2salhs/is_it_possible_that_a_mountain_taller_than_the/cnnr3cs)), but has less to do with isostasy and more to do with work (in the energy sense) involved in building topography. For mountain ranges like the Himalaya that are built through the collision of continents, this collision represents the energy input. At a certain point, the amount of work required to continuing to increase elevations exceeds the input and it is ""easier"" to simply expand the mountain range laterally. For those interested in a technical treatment of this, check out [this paper](http://www.colorado.edu/geolsci/faculty/molnarpdf/1988GSASpecPaper.M&LyonCaen.pdf). + +**Isostasy** Isostasy is an important factor, but within that, the really important point is the nature of the lithosphere that the mountain range is sitting on. While thinking of topography on the Earth from a purely isostatic standpoint (i.e. blocks floating in water) works to some extent, the better description is in terms of flexure (i.e. blocks sitting on a taut sheet of elastic). The height of a mountain range (the height of your block measured relative to some reference) will depend on the density and size of the block and the strength, essentially the thickness of the elastic sheet. You could imagine the same exact block having very different heights depending on whether the sheet is very thin (sinks down a lot, block is not very high) or very thick (doesn't sink much, block is much higher). In terms of mountain ranges, this basically depends on the type of material in the mountain range, the shape of that mountain range, and the nature of the lithosphere it forms on. This is largely why Olympus Mons on Mars is as high as it is, not the gravity, but rather because the thickness and the rigidity of the Martian lithosphere is much much greater than Earth's and thus can support larger loads. Coupled with the lack of active tectonics and a fixed source for magma from a hotspot leads to a giant volcano. + +**Pressure-Temperature Conditions at the Base of a Mountain Range** Probably one of the most important aspects for collisional mountain belts, like the Himalaya are the fact that they have reached the height they are by crustal thickening, basically the crust being deformed and stacked on top of itself. Because of the isostatic/flexural response, as the crust thickens, elevations increase but the depths (and thus the pressures and temperatures) that the bottom, or root, of your mountain range is experiencing also increase. At a certain point, the temperature and pressure conditions reach a point where the material making up the mountain range will change into a very dense rock called [eclogite](http://en.wikipedia.org/wiki/Eclogite). The eclogite will be denser than the mantle rocks against which it is juxtaposed, which is gravitationally unstable, leading to a process called [delamination](http://en.wikipedia.org/wiki/Delamination_%28geology%29), where this dense elcogitic root detaches and sinks into the mantle. Going back to the isostasy discussion, there is now a reduced thickness of crust which on the long term will lead to a reduction in elevations of the range. + +**Climate** Another huge factor is the effect of climate and erosional processes on the height of mountain ranges. There is a relatively popular idea referred to as the ""glacial buzzsaw"" which predicts (and has been largely born out by data in many of the Earth's active mountain ranges) that mountain ranges generally will not exceed a certain height because of the actions of glaciers, check out this [video that describes the ""buzzsaw"" in a simple way](https://www.youtube.com/watch?v=lLfM1FB58yA). Glaciers are incredibly efficient erosional agents, so once a mountain range reaches heights sufficient to start forming glaciers, the glaciers in turn buzz down the peaks of that range. The height limit imposed by glaciers would obviously depend on latitude (higher latitudes can support glaciers at lower elevations), general climate, and the precipitation patterns in the mountain range (still need precipitation to form glaciers). " "The tallest mountain of all time is probably around the height of Mount Everest because mountains hit something called the [isostatic limit](http://en.wikipedia.org/wiki/Isostasy) whereby they cause the earth's crust to compress from sheer mass. Olympus Mons is another mountain that reaches the isostatic limit, but is significantly higher because of Mars' reduced gravity and less active plate tectonics. The field of paleoaltimetry deals with this and similar questions. + +EDIT: Damn, this blew up. Lots of questions here I don't know the answer to. I'm not a geologist, just a nerd who remembered a tidbit from an undergrad geology class I took 8 years ago, then confirmed it with Google. =/ + +EDIT 2: [Just found this!](https://www.youtube.com/watch?v=jIWhzYq16Ro)" +52 What color is the dress? Why do some people see blue and black and some people see gold and white when looking at a single image of a dress? 2831 http://www.reddit.com/r/askscience/comments/2xbfxp/what_color_is_the_dress_why_do_some_people_see/ 1425010667 2xbfxp Psychology 2015-02-27 7:17:47 "(Reposting from the other thread) + +Hi! me and some other grad students have been discussing this for the last half hour. It's likely due to some kind of colour constancy illusion, where some people are perceiving the context to be something like ""lit by blueish daylight"" and others are perceiving it to be something like ""under yellow department store lights."" In the former case, your brain will try and get the objective (if such a thing can be said) colour by subtracting out the blue as a shadow, and in the latter case it will do the same thing for the filigree by subtracting out the yellow as a reflection. This is a common illusion in psych : [See here](http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html). but it's not seen that often 'in the wild,' even though your brain does this constantly. " "my (expanded) comments from an earlier discussion: + +pretty sure this is a [color constancy] (http://en.wikipedia.org/wiki/Color_constancy) effect, where the argument is actually about the *illuminant* (the color of the light shining on the dress). There must be ambiguous information in the image about what the illuminant was for the dress part of the scene. + +If we assume a white illuminant, the dress looks blue and black (or some dark brownish color); if we assume a bluish illuminant, the dress looks white and gold: the white parts are just reflecting bluish light. Some viewers might be led into seeing the illuminant as bluish, despite the bright yellow/white background, because the dress seems to be in shade (maybe this is actually *because* of the background being bright?); outdoor shade on a clear sunny day is bluish (the sky is blue), so maybe we all have a strong ""shade is blue"" prior when it comes to solving color constancy problems (you'd think there would be an obvious reference for that idea.. I can't find anything..). + +Other viewers might see the whole scene as illuminated with white light (like sunlight, or lamplight), maybe similar with the background source; in that case, the blue tint of the dress isn't because it's in the shade - it's because it's reflecting only short wavelengths out of the white light and absorbing the rest (i.e. it's blue). + +The gold/black relationship also fits this story: gold wouldn't reflect much blue light, so gold color will appear dark brown (and be interpreted as gold). But under white light, gold should be bright and shiny - it isn't in this picture, so if the illuminant is white, the best interpretation of the brown spots is that they are a dark color (black or brown). + +I'm not a professional color guy, though, this is all just logic and guesswork... The real question is why different viewers default to such different assumptions about the illuminant, and I don't have even a good hand-wavy answer for that... + +(for the record, first thing I saw: white and gold. then I covered the surround with my hands and focused only on the dress texture, and started to see it as bluish with black/brown stripes. now I can switch back and forth, heh.) + +*minor editing for wording*" +376 Is there any evidence that dogs behave differently around human infants compared to around human adults? 2831 https://www.reddit.com/r/askscience/comments/45i511/is_there_any_evidence_that_dogs_behave/ 1455328505 45i511 Biology 2016-02-13 4:55:05 "[There was a study that has shown dogs are capable of social referencing in the same way humans are.](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0047653) That is when we discover something new, we're influenced by those around us on how to behave towards it. + +Through social referencing, dogs take cues from us when learning how to behave towards the cute mini humans. They see the care, attention and security we provide to children. This influences them to behave in the same way. + +It doesn't tell the whole story, but I think it definitely plays a role initially." "Secondary question: if such a study exists, was there any analysis on whether it was specifically human young that canines treat differently, or all species young? + +I've read a lot about the eons long relationship between humans and canines, so I wonder if that had an impact on their actions toward infants. " +489 Why do things smell? Can smell be measured? 2831 https://www.reddit.com/r/askscience/comments/4j09vv/why_do_things_smell_can_smell_be_measured/ 1463053601 4j09vv Chemistry 2016-05-12 14:46:41 "Actually, we still don't fully understand how smell works. Of course, the basic steps of olfaction are easy to sketch out: 1) volatile compounds (odorants) travel from an object to your nose, 2) in your nose these compounds interact with certain receptors and 3) the receptors kick off a long biochemical pathway that ends with your brain detecting the smell. + +The first part is relatively straightforward nowadays. We have plenty of sensitive and specific tools to figure out the composition of the chemical compounds that float around ""smelly"" objects. [Mass spectrometry](https://en.wikipedia.org/wiki/Mass_spectrometry) is arguably the most powerful technique we have here, which allows us to rapidly catalogue the presence of hundreds of compounds present in minute (ppm or less) concentrations. + +But identifying compounds using analytical techniques is the easy part. Where we lag is in understanding the actual mechanism that allows us to so specifically detect certain compounds or classes of compounds by smell alone. There are two main groups of theories for how smell works qualitatively: + +1. The shape theory. The idea here is that the odorant and receptor fit together like a lock and key. Depending on the flavor of the theory, both the 3D shape of the molecule and/or its chemical structure play a part in this process. The shape theory is currently the most widely accepted theory and it has a lot explanatory power. For example, it also explains why chemically similar molecules often smell similar, e.g. why thiols (things with C-S-H bonds) tend to smell like rotten eggs. + +2. The vibration theory. Unfortunately the shape theory doesn't explain all observations. For example, in some cases just switching the isotope of an atom in a molecule can produce a different smell (e.g. [see this paper](http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055780)). Since the isotope usually only has a small effect on the shape or chemical reactivity, it's hard to square this effect with the shape theory. However, changing the isotope can produce a much larger change on the *vibrations* of the molecule. This idea lead a group of researchers, mostly centered around Luca Turin to pitch the vibration theory. This theory claims that it is the vibrations of the odorant that are key to producing a specific interaction with a receptor. + + + +As of now, the shape theory still remains dominant and the vibration theory is highly controversial. However, both theories are able to explain specific experimental results that are a bit difficult to fit into the other. Of course, it could very well be that the two theories are complementary. In most cases perhaps it is the shape and chemical structure that determines what receptors will be activated, while for *some* odorants the vibration can also affect which pathways will kick in." "I don't know the biology behind odor as u/hugodeGroot does, but I know the chemistry as I'm an environmental chemist. + +Odor is actually quantifiable, so yes it can be measured. EPA has a standard operating procedure on how to quantify odor and how to report it. It's a secondary regulation, so it won't kill you (questionable imo) but it's there for an ease-of-life kind of thing. There are regulations for aesthetics and such that don't need to be enacted into law such as copper being under 1300ppb or else you'll get stains on your clothes when you wash them or get stains on your tubs/sinks. + +Furthermore, you can also do indoor quality air monitoring. You basically set up a whole bunch of tubes around a room and you have a portable instrument that sucks in the air for an extended amount of time (think a week) and then it analyzes the particles (odor) in the air on a chromatogram. So you can get a complete reading of what's in your air and what's making it smell if you wanted- my company actually specializes in that. + +It's pretty neat" +170 If light is massless, how is a black hole able to prevent it from escaping? 2824 http://www.reddit.com/r/askscience/comments/3alhl1/if_light_is_massless_how_is_a_black_hole_able_to/ 1434885231 3alhl1 Physics 2015-06-21 14:13:51 "Light is massless, but it is affected by gravity. + +Two ways to understand this: + +Light has energy, and gravity acts on energy. + +OR + +Gravity is the curvature of spacetime, and so the paths that light can travel are determined by gravitational effects." "to understand the answer to this question you need to properly understand how gravity works. any object with mass actually bends spacetime itself, so, from the perspective of light, it would always be traveling in a straight line, however it's the space itself that it's travelling through that is bent is causing it to go towards a blackhole. in fact time actually bends on itself as well and once the event horizon is crossed all paths to the ""future"" also go closer to the centre of the singularity. this is why no matter what speed an object is travelling at through space (even a hypothetical ""faster than light"" object) can never escape a black hole once it has crossed the event horizon. it's because time itself is also bent so much the only escape would be to travel backwards in time. + +i recommend watching this video on youtube to better understand the warping effect of spacetime and its effects on all objects traveling through warped space, not just the ones with mass. + +www.youtube.com/watch?v=jlTVIMOix3I" +1273 Why does the water exiting the nozzle of a water bottle rocket create waves? 2824 https://www.reddit.com/r/askscience/comments/bibket/why_does_the_water_exiting_the_nozzle_of_a_water/ 1556460380 bibket Physics 2019-04-28 17:06:20 "[Here's](https://youtu.be/tJcTy-SIIP4) a slow motion video of a similar rocket. You can use the YouTube controls to slow it down even more. The jet is basically smooth until the rocket runs out of water, then there's a rough/wavy burst. My guess is that once the water runs out, the pressurized air jets out of the rocket faster than the water did, so it hits the water and makes a pattern. That doesn't fully explain the pattern in your photo, but maybe some of the other users can clarify. + +Edit: The oscillations look like [Rayleigh--Taylor instability](https://en.m.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instability), specifically the Kelvin–Helmholtz instabilities in the ""Late-time behavior"" section. Either air or air-infused water is accelerating into denser water, which can create this pattern." It's acting as a helmholtz resonator. You have elastic energy being released in a step function with a fluid inertia throttling it's release rate. It oscillates like a basic spring mass system or a bell being struck by a hammer +1274 Are any unique properties expected to arise as matter gets even closer to absolute zero? 2821 https://www.reddit.com/r/askscience/comments/b7imuq/are_any_unique_properties_expected_to_arise_as/ 1553996930 b7imuq Physics 2019-03-31 4:48:50 "u/testuser514 mentions superconductivity - I wanted to also mention Bose-Einstein Condensation. Particles on a quantum level interact with other particles very differently depending on whether they have integer or half-integer spin numbers (are bosons or fermions) - Bosons (integer spin objects) are not restricted by the Pauli exclusion principle, and so any number of identical bosons can occupy the same state at the same time. + +Normally, however, these ""states"" in any meaningful anywhere-near-macroscopic system are so close together that thermal energy and thermal noise spreads particles far apart across different states anyway - in other words, whether something is a boson or a fermion doesn't matter if there's only a 0.001% chance that it'll ever even need to try to occupy the same state as something else. But at ultra cold temperatures, you can ""freeze out"" that thermal noise, and you can see how some kinds of gasses will collapse into their lowest-energy state, where they can interact with each other and quantum interactions become visible. + +So, by making your room colder and colder, you can freeze out more and more of the noise in your experiment, and make it possible to see only these quantum effects on a near-macroscopic many particle system in ways that you might not be able to otherwise." Yup, most matter will have different properties as we take it towards absolute zero, what they are can vary drastically. I did a course on statistical mechanics a while back and it was really cool to formulate how super-conduction would arrive at low temperatures. +490 Would headphones tangle in space? 2812 https://www.reddit.com/r/askscience/comments/4k1gs7/would_headphones_tangle_in_space/ 1463645488 4k1gs7 Physics 2016-05-19 11:11:28 It's not the weight, but the shaking that makes them tangle. It turns out ropes in confined space tangle when shaken. The knotting probability over length of rope and time of shaking was studied for example in [this paper](http://m.pnas.org/content/104/42/16432.abstract). [deleted] +53 Can you determine the volume of a bottle by the note it makes when blowing over the opening? 2811 http://www.reddit.com/r/askscience/comments/33tlf0/can_you_determine_the_volume_of_a_bottle_by_the/ 1429972476 33tlf0 Physics 2015-04-25 17:34:36 "tlwr; Yes and No, depending on the rules. + +In acoustics class this problem was on the second homework. + +Assume a Cabernet bottle, the kind with ""neck and shoulders"" not the tapered kind. It makes the math easier. + +Basically you model the air in the neck as a mass. Model rest of the bottle as a spring. The frequency goes as SQRT(area/(length*volume)) for a neck of a given length and area. + +There are some fringing effects so you should probably add 0.6 the diameter of the neck to the neck length to account for the mass of the air that is near but not in the neck. + +So, if you knew dimensions of the neck of the bottle, [yes you could figure it out](http://en.wikipedia.org/wiki/Helmholtz_resonance). + +Otherwise not. +" "Engineering student here and a musical enthusiast. Different shapes produce different notes/tones. So no, you wouldn't be able to determine the volume this way. Also the design of the opening determines the frequency of the tone produced as well as intensity of your blowing. + + +**EDIT:** Since a lot of people are telling me that bottles that contain water at different volumes make different tones, that is true, but you have to think, if you place the same volume of water into a another bottle of a different shape but the same volume,you will produce a totally different tone. + +Also, you can test this by simply blowing into a bottle that contains some water and as you blow change the angle of the bottle and you'll notice you produce a slightly different tone. This is because the shape of area you are blowing into is changing." +279 Photons have no mass but are affected by gravity. Do photons themselves affect gravity, e.g. could one make a black hole solely from photons? 2807 https://www.reddit.com/r/askscience/comments/3x7pg6/photons_have_no_mass_but_are_affected_by_gravity/ 1450360175 3x7pg6 Physics 2015-12-17 16:49:35 "Photons or light are affected by gravity because they are only following the curvature in space-time caused by a large mass and NOT because they are feeling individual gravitational forces on each particle. This was the main difference between Newtonian and Einstein's physics of gravity. + +Photons cannot have rest mass or else quantum mechanics would fall apart through collapse of gauge invariance. The reason photons can have energy per particle without mass is because they obtain relativistic mass which is not mass in the way you are thinking about it. Their E is actually =pc , their momentum x speed of light. + +But you can create a blackhole from photons, by focusing enough energy in one area to warp space time, and in fact this has been hypothesized to have happened in the early universe. You can still create gravity without mass essentially. + +Hope this is understandable. + +EDIT1: Sorry guys I actually thought this was ELI5 subreddit when I answered so I tried to keep it super simple, yes there are many correct points being raised in the replies that are the specifics of what I described here. +Some common questions: + +**1)**Yes mass and energy are intrinsically related, and thus you can have momentum from energy. You can correctly say that mass is a from of energy but Im not sure if its very intuitive to think of energy as a form of mass. Its like ice is a form of water but is water a form of ice ? better to think of it of ice and vapour as different forms of water + +**2)** Yes the actual equation is longer and its been mentioned. + +**3)** A lot of debate on if photons have rest mass or not, I was taught they dont. You could argue that since photons have energy and energy and mass are related, photons can have mass and you would be correct. In fact, hypothetically if you trap light in a scenario where it loses momentum, it is theorized it will precipitate mass instead to maintain energy balance. But this is all hypothetical scenarios, and not what I believe most of you guys mean when you think about your average photon. Moreover, a lot of currently accepted theories will go under doubt/question or tweaking if we are to accept photons have rest mass. Even cosmological theories rely on photons being massless. Sure the upperbound on the supposed mass is very small but we have A LOT of photons. + +**4)** yes all matter/energy/stuff follows space time. Earth follows the curvature produced by the sun, just as light does the same. + +**5)** Yes im aware of gravitons, but these are all attempts to unify space-time and quantum mechanics and currently space-time curvature is the accepted theory. + +**6)** light still cant escape blackholes because they are literally holes in space-time fabric, once something falls in its like falling to the bottom of a pit, you wont be able to spin your way out. +" "In theory yes, but it would be essentially impossible to verify. I have read [a paper](http://www.sciencedirect.com/science/article/pii/S0375960100002607) considering a ring of mirrors with a powerful laser bouncing between them with a bead in the middle, and seeing if the gravitational field of the lasers can cause the bead to rotate. As an aside, the author of that paper has recently been in the news for trying to build a time machine to visit his dead father. + +The idea of a gravitational field originating as photons is called a [kugelblitz](https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics\)) and it's a neat idea but not quite relevant for our universe. The gravitational influence of light may have been more important in the early universe. + +[Fun fact:](http://klotza.blogspot.ca/2015/08/what-heeck-how-stable-is-photon.html) if photons do have mass and decay into even less massive particles, the mass must be less than 10^-54 kg and the lifetime must be longer than three years, but is dilated to longer than the age of the universe because they go so fast." +491 How do scientists achieve extremely low temperatures? 2798 https://www.reddit.com/r/askscience/comments/4u8cm4/how_do_scientists_achieve_extremely_low/ 1469283033 4u8cm4 Engineering 2016-07-23 17:10:33 "If you want to go to really, *really* low temperatures, you usually have to do it in multiple stages. To take an extreme example, the record for the lowest temperature achieved in a lab belongs to a group in Finland who [cooled down a piece of rhodium metal to 100pK](http://ltl.tkk.fi/wiki/LTL/World_record_in_low_temperatures). To realize how cold that is, that is 100\*10^(-12)K or just 0.0000000001 degrees above the absolute zero! + +For practical reasons you usually can't go from room temperature to extremely low temperatures in one step. Instead, you use a ladder of techniques to step your way down. In most cases, you will begin at early stages by simply pumping a cold gas (such as nitrogen or helium) to quickly cool the sample down (to 77K or 4K in this case). Next you use a second stage, which may be similar to your refrigerator at home, where you allow the expansion of a gas to such out the heat from a system. Finally the last stage is usually something fancier, including a variety of [magnetic refrigeration techniques](https://en.wikipedia.org/wiki/Magnetic_refrigeration). + +For example, the Finns I mentioned above used something called ""nuclear demagnetization"" to achieve this effect. While that name sounds complicated, in reality the scheme looks [something like this](https://upload.wikimedia.org/wikipedia/commons/thumb/0/08/Magnetocaloric_effect1_04a.svg/800px-Magnetocaloric_effect1_04a.svg.png). The basic idea is that 1) you put a chunk of metal in a magnetic field, which makes the spins in the metal align, and which heats up the material. 2) You allow the heat to dissipate by transferring it to a coolant. 3) You separate the metal and coolant and the spins reshuffle again, absorbing the thermal energy in the process so you end up with something colder than what you started out with. + +" There have been some mentions of helium and evaporative cooling, and I figured I'd add some specifics to that because I have some experience with it. If you start with liquid helium (which will be at about 4K), you can pump on it, which will reduce the vapor pressure allowing some of the liquid to evaporate and take heat with it, lowering the temperature of the remaining liquid. The system I am familiar with has a base temperature of ~1.4K thanks to this method +492 Why is a full circle 360 degrees? Why not just a round number like 100 or any other number? 2798 https://www.reddit.com/r/askscience/comments/4jgyb5/why_is_a_full_circle_360_degrees_why_not_just_a/ 1463331914 4jgyb5 Mathematics 2016-05-15 20:05:14 "It should be made clear that 360 is completely made up, it has nothing to do with circles, only how people have used them in the past. For that matter 100 is not a special number in any way either, so having it be 360 degrees or 100 degrees are both equally arbitrary. + +We use 360, because it has a lot of divisors: 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180, 360. Each of these numbers is a different way that we can cut up the circle in an exact way. If you have nine people, and you want to cut a pizza, then you need to cut each slice at 40 degrees. This makes computation easy. Especially when you're in a time before the typical division algorithm we all take for granted. Using Roman Numerals, which they did well into the 1400s, it is not easy to divide something by, say, 15. But if you know that you have 360 degrees, then it's easy to just know that 15x24=360. This makes if very convenient to build things or do astronomy when you don't have an easy way to divide. On the other hand 100 only has 9 divisors, so it's no where near as useful. + +That being said, the only meaningful way to talk about angles is radians. Degrees or any other measure are totally arbitrary and meaningless, they're just convenient. Radians actual mean something. If you have a circle of radius 1 and you draw an angle coming from it's center, then the number of radians is nothing more than the length of the arc on the circle that this angle makes. This gives a meaningful definition to quantify angles, it makes sense and it should be seen with sadness when you are forced to use some other, inferior system. + +EDIT: [Source](http://www.storyofmathematics.com/sumerian.html), [Source](https://books.google.com/books?id=J1y8CgAAQBAJ&pg=PA19&lpg=PA19&dq=theon+of+alexandria+base+60&source=bl&ots=K_LpvxPsYA&sig=-a7sdKq3PooOLZ5uBvQ6o8pHE8o&hl=en&sa=X&ved=0ahUKEwjHsruRm93MAhXKGB4KHag2CSgQ6AEILjAE#v=onepage&q=theon%20of%20alexandria%20base%2060&f=false)" "It comes from Mesopotamian mathematics along with sundials and many astronomical units. The sun takes roughly 360 days to complete a full circle in the sky and it's based on that. They used a base 12 system (duodecimal), as opposed to our base 10 system. + +Bonus fact: You get to 10 by counting fingers and 12 by counting the knuckles on your fingers with your thumb. + +Correction: They actually used a sexagesimal system (base 60), the Egyptians used the duodecimal system." +493 What is the biggest distinguishable difference between Alzheimer's and dementia? 2797 https://www.reddit.com/r/askscience/comments/4mlbtq/what_is_the_biggest_distinguishable_difference/ 1465090415 4mlbtq Neuroscience 2016-06-05 4:33:35 Please remember our guidelines about the usage of [sources](https://www.reddit.com/r/askscience/wiki/sources). "As others have said, Alzheimer's is simply one form of dementia among several different kinds. A little bit of misinformation and vague ideas about imaging and whatnot, so here are a couple examples of the most common types of dementia roughly from most common to least common: + +Alzheimer's: The one that everyone is familiar with. As mentioned elsewhere, there are abnormal deposits in the brain (beta-amyloid plaques and neurofibrillary tangles), but you can't see these unless you look at a patient's brain under a microscope post-mortem. The actual symptoms are ones most people are familiar with, including short-term memory loss (forgetting to keep appointments on several occasions, inadvertently leaving the oven on for hours), agnosia (inability to process sensory information, so not recognizing common objects, not understanding simple words), apraxia (inability to carry out learned tasks, like combing your hair or preparing a meal). Really the diagnosis is made when an individual is having the above symptoms in a slowly progressive fashion to the point that their symptoms are impairing their daily functioning (after ruling out any other strong possibilities). The only somewhat useful test *if* the disease has progressed far enough is a brain MRI, where you will be able to see global (whole brain) atrophy; the space between the brain and skull is noticeably bigger, and the ventricles (normal empty spaces filled with CSF) are also very large. There are ways to manage the progression, but this is essentially irreversible. + +http://images.medicinenet.com/images/slideshow/alzheimers-s6-alzheimer-brain-scans.jpg + +Lewy body dementia: This one is very interesting. The ""Lewy body"" in the name refers to the microscopic deposits in the brain, which are also seen in Parkinson's disease (as well as a few other diseases under the umbrella term ""alpha-synucleinopathy""). So, as one might expect, these patients have some of the usual dementia signs but also with symptoms seen in Parkinson's. Resting pill-rolling tremor, ""masked"" facial appearance (blank stare), shuffling gait, cogwheel rigidity in the wrist, and postural instability. One of the other striking symptoms is vivid visual hallucination. Since this disease is so closely related to Parkinson's, the typical medications used to control symptoms in Parkinson's can also be used. The most effective of these is Sinemet, a carbidopa/levodopa combination. + +Vascular dementia: This is a type of dementia that is actually quite similar to Alzheimer's in terms of characteristic symptoms. Increasing forgetfulness, not recognizing everyday objects or family members, etc. The major difference that makes this type of dementia stick out clinically is that the changes happen in a very obvious step-wise fashion. One day they only have 1 symptom, the next they have 2 symptoms. They're then stable for a few months, then suddenly a 3rd symptom. This is because in these patients, microscopic infarcts occur where a very small vessel is suddenly blocked off and a tiny sliver of brain then dies. These are basically very small strokes happening in various locations. So every time a patient has one of these 'mini-strokes' (not to be confused with TIA or transient ischemic attack), a sliver of brain dies and they may or may not then suddenly develop a new symptom. Another dead giveaway would be if the patient looked like they had Alzheimer's but had some kind of focal symptom, like facial droop or right leg weakness. If the disease has progressed enough, a brain MRI might reveal small dots of affected brain tissue. The best thing for these patients is managing their risk factors for stroke, i.e. good blood sugars if diabetic and good cholesterol if they have atherosclerosis. (Blood pressure control also *very* important). + +http://images.medicinenet.com/images/slideshow/dementia_s7_vascular_dementia.jpg + +Frontotemporal dementia: Last of the top 4. Similar to Alzheimer's with slowly progressive decline in memory etc. What sets this one apart, as you might guess, is generalized atrophy with even further damage to the frontal and temporal lobes. These patients can be very odd, because loss of brain matter in these lobes essentially makes them very disinhibited. They lose awareness of social constructs and have a lot of difficulty controlling impulses. + +http://delphosherald.com/Images/Images/107844.jpg + +This isn't exactly my area of expertise, but I thought I would give a little more info in terms of how people with these disease actually act. Hope this helps. + +edit: minor changes and corrections for improved accuracy" +280 Could we split a photon? 2796 https://www.reddit.com/r/askscience/comments/3p83mq/could_we_split_a_photon/ 1445174851 3p83mq Physics 2015-10-18 16:27:31 "Photons can be rudimentarily conceptualized to be ""split"" in a process known as [parametric downconversion](https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion) which is essentially the inverse of second harmonic generation - the process by which for instance green laser pointers produce their visible light by summing two infrared photons. Of course, photons are fundamental particles, so the only thing you get out when they're ""split"" are more photons. + +http://www.nature.com/news/2010/100728/full/news.2010.381.html" "An atom is made out of several particles. Spliting an atom consist in separating those particle. + +The same is impossible with a photon, since a photon is an [elementary particle](https://en.wikipedia.org/wiki/Elementary_particle). This means the photon is made of only 1 particle. + +However, [you can split a photon into 2 new photons.] (https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion) + +The difference is that those 2 new photons didn't exist before the split, whereas the particles in the split atom existed all along. " +377 Can you represent PI in a finite number of digits in any number system? 2794 https://www.reddit.com/r/askscience/comments/4e5z3i/can_you_represent_pi_in_a_finite_number_of_digits/ 1460298586 4e5z3i Mathematics 2016-04-10 17:29:46 "Of course, we could always use base pi to represent numbers, with which pi has the trivial representation ""10"". But surely non-integer bases are not what you are talking about. (They're also a lot of trouble anyway. For instance, if the base is algebraic then some numbers can actually have infinitely many expansions that all terminate.) + +If the real number *x* has a finite expansion in some *integer* base *b* > 1, then *x* is equal to + +> x = a*_n_*b^(n)+a*_n-1_*b^(n-1)+...+a*_0_*+a*_-1_*/b+a*_-2_*/b^(2)+...+a*_-m_*/b^(m) + +with a*_k_* some integer between 0 and *b*-1. This expression can just as well be written as + +> x = M/b^(m) + +where M is some integer. Therefore, *x* must be rational. Since pi is irrational, there is no integer base in which pi has a finite expansion. + +--- +***edit:*** So I came back to 27 new messages and 1500 upvotes. I did not think this topic interested that many readers. But good to see! Follow-up to some common questions and comments: + +How does non-integer base representation work? +--- + +First, distinguish between a number *x*, which can be defined and exists independently of its representation and ""*x*"", which is a numeral or representation of *x* in a certain base. To make clear that I mean a specific base representation I will enclose an expression by quotation marks if the base is clear or, if I want to denote the base explicitly, I will write a subscript after the digits. So the expression 23*_10_* means ""23 in base 10"" (the number 23) and the expression 23*_4_* means ""23 in base 4"" (the number 11). + +Non-integer base representation works just how any integer base works. Fix your base *b* > 1. The ""digits"" of your representation are all non-negative integers *less than* *b*. Then the representation + +> ""d*_n_*d*_n-1_*...d*_1_*d*_0_***.**d*_-1_*d*_-2_*..."" + +(where each d*_j_* is a digit) is the number + +> *x* = d*_n_*b^(n)+d*_n-1_*b^(n-1)+...+d*_1_*b^(1)+d*_0_*+d*_-1_*b^(-1)+d*_-2_*b^(-2)+... + +The digits can be found recursively using a *greedy algorithm*. + +Let's do an example to make this clear. Since our base is b = π, our possible digits are {0, 1, 2, 3}. Now pick your favorite number *x*. For sake of clarity, I am going to let *x* = 8. Note that π^(2) > 8, so the first digit of our representation is in the ""tens"" place. We have + +> [8/π] = [2.546...] = 2 + +(The notation [.] means that we round down to the nearest integer.) So the ""tens"" digit of 8 in base-π is just ""2"". Okay. Now we subtract off what we have so far, and then divide by the next power down. + +> [(8-2π)/1] = [1.716...] = 1 + +So the ""ones"" digit of 8 in base-π is ""1"". Now subtract off what we have so far again, and divide by the next power down. + +> [(8-2π-1) / π^(-1)] = [2.252...] = 2 + +So the ""tenths"" place of 8 in base-π is ""2"". Subtract off again and divide by the next power down. + +> [(8-2π-1-2π^(-1)) / π^(-2)] = [0.791...] = 0 + +So the ""hundredths"" place of 8 in base-π is ""0"". Next. Subtract off, divide by the next power down. + +> [(8-2π-1-2π^(-1)-0π^(-2)) / π^(-3)] = [2.486...] = 2 + +So the ""thousandths"" place of 8 in base-π is ""2"". At this point I think you get the idea. So far, we have that + +> 8*_10_* = 21.202...*_π_* + +If you want to keep going, WolframAlpha is more than happy to do it for you. + +> [8*_10_* = 21.20211200210000003...*_π_*](http://www.wolframalpha.com/input/?i=8+in+base+pi) + +Non-integer bases are a bit bizarre +--- + +Some terminology if you are not familiar: + +> A real number is *algebraic* if it is the root of a polynomial with integer coefficients. Otherwise, the number is transcendental. + +> Suppose *x* is algebraic. The minimum degree of all polynomials for which *x* is a root is called the *degree* of *x*. So if *x* is algebraic of degree 7, then any polynomial for which *x* is a root must be at least degree 7. + +Some properties of representations in different types of number bases: + +* **Integer base:** All numbers have at most two expansions. If a number has only one expansion, it must be infinite. If a number has two expansions, then one expansion terminates and the other expansion ends in an infinite trail of digits equal to *b*-1. For example, ""1"" and ""0.999..."" are equivalent base-10 representations of the same number, just as ""1"" and ""0.2222..."" are equivalent base-3 representations of the same number. + +* **Transcendental base:** Just as with integer bases, some numbers have terminating expansions and some don't. However, a number can have infinitely many expansions. If a number has a terminating expansion, then it has only one terminating expansion. (But the number can still have infinitely many infinite expansions.) It is possible (actually, typical) for a number to have uncountably many infinite expansions. + +* **Algebraic base (of at least degree 2):** Every number has at least one expansion.. and that's all you can really say. If a number has a terminating expansion, it has infinitely many terminating expansions (see below for an example). So this type of number base is particularly pathological since not even terminating expansions are unique. + +Interestingly, note that there is no base in which *all* numbers have a unique expansion. + +Okay, now for an example with an irrational, algebraic base. Let *b* be the unique real root of the equation + +> b^(3) = b^(2)+b+1 + +(For reference, the root is approximately *b* = 1.8393, which means that the valid digits in this base are {0,1}.) Then the number b^(3) has (at least) *two* representations: ""1000"" and ""111"". In fact, we can use the equation above to write *any* power of *b* as a sum of other powers of *b* with coefficients that are valid digits. For example, multiply the equation by b^(-2) to get + +> b = 1+b^(-1)+b^(-2) + +So then the number *b* has the representations ""10"" and ""1.11"". Essentially, in this base, whenever there is a string ""1000"" anywhere, we can always replace it by ""0111"". For example, consider the number *x* = *b*+1 (approximately 2.8393), which has the representation + +> *x* = 11*_b_* + +We can write this instead as + +> *x* = 10.111*_b_* + +Then we can shimmy over the last ""1"" to get + +> *x* = 10.110111*_b_* + +Shimmy it over again to get + +> *x* = 10.110110111*_b_* + +..and, well, you get the picture. We have an infinite sequence of representations, all of which terminate and all of which represent the same number. This is a general phenomenon for any algebraic base of degree at least 2. (Note though, the greedy algorithm explained in the previous section always gives a unique expansion. In the previous example, it gives *x* = 11*_b_*. So we can always canonically choose a unique expansion even if there are infinitely many by just declaring *the* expansion to be that which is given by the greedy algorithm.) + +Irrationality and base representation +--- + +There seems to be some confusion between the definition of a rational number and theorems characterizing rational numbers in terms of base representations. The *definition* of a rational number is: + +> A real number *x* is *rational* if it can be expressed as the ratio of two integers. Otherwise, it is *irrational*. + +The word ""rational"" literally means ""quality of a ratio"". So the numbers 2/3, 9/10, and 1235325423/122145268 are all rational. The numbers √(2), *e*, and *π* are irrational. (Proofs that they cannot be expressed as fractions of integers are readily available online.) **Note that the definition of rational makes no reference to number base at all.** Whether a number is rational is not dependent at all on the number base. + +However, we do have the following theorems: + +> If a number *x* has an eventually periodic expansion in some integer base *b* > 1, then *x* has an eventually periodic expansion in all integer bases *b* > 1. + +> A number *x* is rational if and only if its expansion in some integer base *b* > 1 is eventually periodic. + +(""Eventually periodic"" includes ""terminating"" because a terminating expansion can always be followed by an infinite trail of repeating 0's.) The first theorem means that we can strengthen the second by replacing the word ""some"" with ""all"". + +Note that these are theorems that relate rationality to their representations in number bases. They are not the definition of a rational number. Also note that the theorem specifically talks about *integer* bases. For non-integer bases, the theorem is not true. For example, π is irrational, but its representation in base-pi is ""10.0000...."" which is eventually periodic. + + + + + + + +" Skimmed and didn't see this point: he didn't say any base system he said any number system. Graphing in radians came to my mind immediately. Pi is a fixed ratio that you can express and work with without decimals using its symbol. I know that's not really the question but I thought it was a way of looking at it. +171 Is there a maximum gravity? 2793 http://www.reddit.com/r/askscience/comments/3azh2z/is_there_a_maximum_gravity/ 1435173292 3azh2z Physics 2015-06-24 22:14:52 I don't think there is a good answer. With mass density approaching infinity we are getting stronger gravity, but we are also getting into a situation where both quantum effects and gravity are important. And we don't have unified theory for those two (so we don't know). Place like this is for example inside of black holes. "The gravity of an object is proportional to its mass, so maximum gravity would be proportional to maximum mass. I don't think there is such thing as maximum mass, except maybe that the mass of an object in the universe could not exceed the total mass of the universe. I doubt that's a known number but Googling produces some estimates between 10^50 kg and 10^60 kg. + +Edit: from a practical perspective, all the mass in the universe is unlikely to fall together because at great distances, the expansion of the universe (""dark energy"") is stronger than gravity. It is probably possible to put together an estimate of how much mass could accumulate despite the overall expansion, but I am not the person to do it. + +But, maybe you're talking about the gravitational force you would experience on the surface of an object. In that case, the answer is not really known but is assumed to be infinity, on the ""surface"" of a black hole. But since that is inside the event horizon, we actually don't really know what goes on in there. The math says that the surface is infinitely small, so surface gravity would be infinitely high. + +Edit: This is because the attractive force you experience due to gravity increases as you get closer to the center of the mass. A black hole is extremely dense--it is extremely small, even though it is very heavy. So, you can get very close to the center of mass, which means that the gravitational force can get very high. + +In contrast, think of something like the Earth. We can't get any close to the center, because there's a lot of mass (dirt and rock) between us and the center. If the Earth was denser, it would be smaller, and surface gravity would be higher. But since the total mass would be the same, all the satellite orbits would be the same as they are now." +494 Do you get lighter the further underground that you go? 2789 https://www.reddit.com/r/askscience/comments/4qfl52/do_you_get_lighter_the_further_underground_that/ 1467207977 4qfl52 Physics 2016-06-29 16:46:17 [deleted] "Actually, these answers are great for a theoretical sphere made out of material of the same mass. + +But to answer the question ""do you get lighter the further underground that you go?"", the answer is both no and yes. + +In that particular order. + +Aside the shape of Earth, as you get closer to the core, you become heavier, because Earth's core is much more dense than its crust, and the closer you get to it, the stronger it will pull you. + +IIRC it peaks at the outside of the lower mantle of earth +(~650 km [~400 miles] deep, with over ~~10.5g~~ ~1.05g force, [as opposed to ~1g at the surface], +after which, further descent would result in less gravitational pull, until reaching the very middle, where you'd experience weightlessness. + +E.:If a physicist could translate my vague knowledge into an actual and accurate scientific answer, I'd be grateful. +E2.: Corrected a horrible, horrible mistake. No excuse. +The difference is only about 0.07g. +For reference, at 8848 meters (top of Mount Everest) gravity would be around ~9.76m/s^2, which is a ~0.04g difference." +281 Why is the center of the Milky Way bright if it is a black hole? 2787 https://www.reddit.com/r/askscience/comments/3mhqum/why_is_the_center_of_the_milky_way_bright_if_it/ 1443292374 3mhqum Astronomy 2015-09-26 21:32:54 The black hole at the center is a giant collection of mass. Even though the hole itself keeps light from escaping, the mass has still attracted stars around it. The orb gives no light, but the stars pulled to it have light of their own and it's very dense at the center. The black hole, for all its horrifyingly huge mass, is a tiny pinhole compared to the size of the galaxy. The bright mass in the middle you're seeing is thousands upon thousands of star clusters, orbiting the black hole. +282 Is matter that is absorbed by a black hole trapped forever? Can it ever escape or be recovered? 2777 https://www.reddit.com/r/askscience/comments/3xlhrz/is_matter_that_is_absorbed_by_a_black_hole/ 1450632601 3xlhrz Physics 2015-12-20 20:30:01 An object that has crossed the event horizon of a black hole can never cross it back to leave. In a very real sense, the only future destination of the object (or more technically the endpoint of its possible future [world lines](https://en.wikipedia.org/wiki/World_line)) is the center of the black hole. Nevertheless, black holes do emit [Hawking radiation](https://en.wikipedia.org/wiki/Hawking_radiation), thus effectively spitting the energy they once absorbed back out. So in this latter sense, it is possible for the mass-energy that has entered the black hole to eventually exit the black hole, but not before [it's been turned to mush](https://en.wikipedia.org/wiki/No-hair_theorem). Something that enters a Black Hole is no longer causally connected to anything outside the event horizon. The object's observable universe shrinks to that boundary. Its not much different than areas of the Cosmos that are now so far away, we can never reach them, if we dont find a way to break light speed. Our event horizon is just a bit bigger. +54 When light strikes a metal, a photon can excite an electron to leave. Does the metal ever run out of electrons? 2773 http://www.reddit.com/r/askscience/comments/2ycv92/when_light_strikes_a_metal_a_photon_can_excite_an/ 1425839260 2ycv92 Physics 2015-03-08 21:27:40 "No. While releasing more and more electrons, the Fermi level will become lower and lower, because the electrons with largest kientic energy will be ejected. This increases the work function of the metal until the energy of one photon is not sufficient to excite another electron to the vacuum level. At this point you have changed the potential of the metal significantly. So you could call the photoelectric effect self-inhibiting if the metal is not connect to an electron source. + + + +edit: additions due to many questions going in very similar directions: + +*Q: Does a solar cell become less efficient due to depletion of electrons?* + +A: No. First, a solar cell usually doesn't operate using the photoelectric effect but using an interface between two different doped semiconductors (p-n junction). But that difference is not really relevant. The thing is that after leaving the photoelectric electrode (or the electron donor phase in the semiconductor) they travel towards an electron acceptor electrode. This creates a potential between these electrodes. If both electrodes are floating (i.e. not connected to any mass or ground which can neutralize potential, this potential will then counteract any further charge separation. However, in a solar cell powered circuit, the to electrodes are connected to each other by a load (for example a lamp). The electrons travel through that load, lose their potential energy and travel back to the donor electrode where they replenish the electron reservoir and more electrons can be excited. This is a continuous process and electrons are not ""lost"" somewhere in between. + +*Q: How does solar cells work in a spacecraft when there is no connection to ground?* + +A: A circuit as described above can also contain the ground as electrical conductor. This does not change the efficiency of a circuit or lead to changes in potential. The only importance is that the two opposite poles of the load and the two opposite electrodes of the photoelectric element or solar cell are connect to the same potential each. You can do that directly, or can put the ground in between ONE leg. Not both, because then you would short the solar cell and not be able to power the load. + +*Q: Does the metal become oxidized when electrons are released or does it degrade chemically?* + +A: No. Even though the loss of electrons is formally an oxidation, the metal does not become oxidized because it will regain the electrons on one way or the other before that many electrons are lost so that a chemical process would set in. The removed electrons do not belong to a specific atom within the metal, but are rather shared between all atoms in an electron ""sea"" where they can freely move (hence the electric conductivity of metals). + +But you can make chemical reactions more or less likely by applying a potential (voltage) to the metal. This is what is used in electrolysis or active passivation of metals. In principle you can tune the reactivity by lowering or increasing the energy of the most energetic electrons in the electron ""sea"", making it harder or easier, respectively, for oxidizing agents (e.g. O2, H^+ ) to remove electrons from the metal." "To answer your question, they don't lose all of the electrons in reality. As these electrons or negative charges leave the metal, due to the photoelectric effect, a potential difference is created between the metal and other objects - like the Earth for example. This potential difference is simply known as voltage - so the voltage is *how badly* electrons want to move, and in this case it's how badly they want to neutralise the metal back to zero net charge. + +So in reality, a metal which has lost enough electrons will form a voltage between other objects, and if it is close enough to one of them a spark will be seen as the electrons from the other object neutralise the metal." +495 What is our solar systems orientation as we travel around the Milky Way? Are other solar systems the same? 2773 https://www.reddit.com/r/askscience/comments/4ijkdq/what_is_our_solar_systems_orientation_as_we/ 1462800971 4ijkdq Astronomy 2016-05-09 16:36:11 "So, within the Solar System, things tend to all rotate the same way. The Moon orbits the Earth on a plane that's very close to the plane of the Earth's orbit around the Sun. The Earth rotates in the same direction too. There are exceptions, but this is what happens in general. + +The Solar System all rotates the same way because it all formed from a single rotating clump of gas. As this gas fragmented, the chunks would all be rotating the same way too. So you get things all going the same way, more or less. Collisionless between objects can change things up a bit. + +But with the Milky Way it's quite different. A group of stars will form from a cloud of gas, but this cloud is very small compared to the size of the Milky Way. On that scale, the rotation of the Milky Way doesn't matter - instead, we're small enough that random turbulent motions really matter. Overall, the gas in the Milky Way is quite hot and turbulent - it's not a nice dense smoothly rotating disc, like the early Solar System. + +So star-forming clouds seem to have almost completely random rotations - if they're rotating at all. Within a star-forming cloud itself, there is even more turbulence. This cloud will collapse into a number of little clumps, all with basically random orientations. Each of these clumps is small enough and dense enough to have consistent rotation within itself, so each of these clumps will form a star system that rotates consistently, but there's little or no connection between the rotation of one star system with another. + +So, basically, star systems seem to rotate pretty much randomly. + +---- + +For our own Solar System, you can actually see the angle pretty clearly at night. All the planets, the Moon, and the Sun all orbit in basically the same plane - the ""ecliptic"". This is the plane of our solar system. If you go out at night with a star map, you can try to spot it. All of the astrological constellations are along the ecliptic too, so if you find Gemini, Scorpio etc, that's the plane of the solar system. + +The plane of the Milky Way is, of course, the Milky Way. So you can look up and compare those fairly easily. + +---- + +**The numbers:** the Earth's rotation is 24° from the plane of its orbit around the Sun (the ecliptic). The ecliptic is 60° from the Milky Way plane." To answer the second observation-- the north star just just coincidentally our north star. Even now, it is not perfectly aligned to our axis of rotation, and will continue to deviate as the centuries whiz by. In some thousands of years a different star will take it's place as our most northern-est star. +496 Joey Chestnut ate 70 hotdogs in 10 minute today. What is your bodies reaction to 19,600 calories in that short of timespan? 2772 https://www.reddit.com/r/askscience/comments/4ra09i/joey_chestnut_ate_70_hotdogs_in_10_minute_today/ 1467677076 4ra09i Human Body 2016-07-05 3:04:36 "TL;DR - He most likely won't absorb a good deal of that 20k Calories. + +The ultimate way the calories end up in our blood (and then the rest of our system) is via solubilized fats (help from the bile), broken down simpler sugars (saliva, stomach acid, and bile enzymes), and simple amino acids (stomach acid, and bile enzymes). I'm going to walk down the GI tract. + +They're not chewing it that much, so most of the food is in solid chunks without much saliva (that's why they need water after all). This will prevent all future steps from accessing all the nutrients, and is probably the biggest block to the bulk Calories. + +It probably won't be broken down that much in the stomach. The pylorus, the sphincter at the end of the stomach that leads to the rest of the intestines, is controlled by pressure, concentration (acidity), and a few other things. 70 dogs is a lot of volume and pressure. Also, the body's stomach can't produce that much acid to accommodate that much food - so the pylorus will have to let a lot of un-broken down food through. This isn't to mention that food is unbroken - it'd be a lot easier to dissolve crushed up chalk in vinegar than a whole piece. + +Once in the early small intestines (the duodenum), the pancreas can't produce that much EDIT: *~~bile~~ digestive enzymes, the liver can't produce that much bile*, and the gallbladder couldn't have stored enough bile to break down that much food. A lot of the fat won't become emulsified, and thus can't be absorbed. Much of the proteins and carbs won't be broken down into the smaller pieces that can be absorbed. And, of course, you can't absorb large chunks of food. + +The rest of the small intestines is where the Calorie absorption goes on. The transit time through the intestine is longer than a normal meal, but a lot of the food is not in body-absorbable forms at this point. + +The large intestines is where it gets interesting. The GI's natural peristaltic rhythm moves things through (somewhat), but all that undigested nutrition is going to meet up with the large intestinal bacteria. There will be gas (the a main bacterial byproduct), but all this ""digestion"" doesn't really go into the human body. Plus, the large intestines don't have the same nutrient absorption machinery the small intestines do. + +In the colon, the large undigested chunks will coalesce with dead bacteria, dead red blood cells (it's what gives the stuff most of the brown color). The large intestines and colon serve to dehydrate the remains. The un-emulsified fats will serve as...let's say...barriers to coalescence. This will make looser stools. Large chunks, slightly smaller than the bites that were taken way up top, will still remain. And don't forget the gas. + +The parts that DO get absorbed go to the liver, and are processed as normal. The sugars and amino acids are converted to fats or carbohydrates (glycogen, etc.) - but there's going to be a lot of excess nitrogen compounds in the blood (amino acids, unlike carbs and fats, have a lot of nitrogen) that will be eliminated as urea in the urine or can exacerbate gout. The sodium will easily be taken care of by the kidney. If they were to donate blood the next day, it would probably be a milky red color (versus the deep red we are familiar with). This is due to the solubilized and re-packaged fats. Some are from the intestines to the liver, and some are from the liver to the rest of the body (the familiar HDL, LDL etc.) These will get absorbed by the body eventually - either by other tissues, or back to the liver. + +I should point out a lot of the unabsorbed calories are because the food was whole protein and carbs and fats. If 20k Calories of sugar (sucrose) were ingested, the body could likely absorb almost all of it. [Edit: I provided the answer to this hypothetical here](https://www.reddit.com/r/askscience/comments/4ra09i/joey_chestnut_ate_70_hotdogs_in_10_minute_today/d4zodqx) + +Edit 2: I underestimated what 20k calories of sugar is like. Some rough stuff will happen before that is absorbed - please see comments below the link for better explanations." I've done 30 hotdogs in a few hours, and I've done denser foods in less time.... but really it just results in a food coma... I have to lie down and take a nap with that kind of fat and salt intake... not really a problem with the calories but the salt and fat..? I'm going to take a nap... +55 Is Chess really that infinite? 2771 http://www.reddit.com/r/askscience/comments/2ta062/is_chess_really_that_infinite/ 1421923305 2ta062 Mathematics 2015-01-22 13:41:45 "Shannon has estimated the number of possible legal *positions* to be about 10^(43). The number of legal *games* is quite a bit higher, estimated by Littlewood and Hardy to be around 10^(10^5) (commonly cited as 10^(10^50) perhaps due to a misprint). This number is so large that it can't really be compared with anything that is not combinatorial in nature. It is far larger than the number of subatomic particles in the observable universe, let alone stars in the Milky Way galaxy. + +As for your bonus question, a typical chess game today lasts about 40­ to 60 moves (let's say 50). Let us say that there are 4 reasonable candidate moves in any given position. I suspect this is probably an underestimate if anything, but let's roll with it. That gives us about 4^(2×50) ≈ 10^60 games that might reasonably be played by good human players. If there are 6 candidate moves, we get around 10^(77), which is in the neighbourhood of the number of particles in the observable universe. + +The largest commercial chess databases contain a handful of millions of games. + +**EDIT:** A lot of people have told me that a game could potentially last infinitely, or at least arbitrarily long by repeating moves. Others have correctly noted that players may claim a draw if (a) the position is repeated three times, or (b) 50 moves are made without a capture or a pawn move. Others still have correctly noted that this is irrelevant because the rule only gives the players the *ability*, not the *requirement* to make a draw. **However**, I have seen nobody note that the official FIDE rules of chess state that a game is drawn, period, regardless of the wishes of the players, if (a) the position is repeated *five* times, or if (b) *75* moves have been made without a capture or a pawn move. This effectively renders the game finite. + +Please observe [article 9.6](http://www.fide.com/component/handbook/?id=171&view=article)." "Just for fun, let's do the Shannon calculation. The absolute basic, highest possible estimate of the total number of permutations says that the board is an 8x8 grid and each piece can occupy any of those 64 spots on the board. There are 32 pieces, occupying 64 candidate spots, so the answer'd be: + +* 64^32 = 6.3 * 10^57 possible game states. + +Now, this is wrong, for a great many reasons, not the least of which is that it treats every piece as distinct, so pawn A occupying e4 and pawn B occupying f4 is treated differently from A & B occupying f4 and e4, respectively. It also allows for pieces to occupy positions that is impossible, like a pawn on the first rank or a ""black"" bishop on a white square. It also fails to account for squares being occupied: You can't have two pieces at the same location. + +If we *only* eliminate the taking-up-the-same-square error we get: + +* 64! / 32! = 4.8 * 10^53 possible game states. + +But we can do better. The total number of game states for one side can be modeled this way: + +* T = A^K * A^Q * A^N * A^R * A^B * A^P + +...where A^K is the total number of candidate positions for the King, A^Q for the Queen, etc... + +* A^K = 64 +* A^Q = 63 +* A^N = ( 62*61 )/2 +* A^R = ( 60*59 )/2 +* A^B = ( 29 * 29 ) +* A^P = ( 56 * 55 * 54 * 53 * 52 * 51 * 50 * 49 )/8! + +Note, it really doesn't matter whether I allocate the King's spot or the Queen's spot first. There'll be a 64 term in there for the first piece you allocate. There'll be a 63 in there for the second. That's the total number of states for one side of the board. We can calculate the other side, roughly the same way, just starting at 48 available spots instead of 64. + +* T^w = 1.612 * 10^22 +* T^b = 7.491 * 10^19 + +* T^0 = 1.20 * 10^42 + +But we can still do better, because we are only considering the states where all 32 pieces are still on the board! What happens when there are 31 pieces on the board, and one is missing? Well, we can do the calculation 31 more times, but that's a daunting task, and we can probably make a simplification. We can note that taking a single piece away reduces the number of permutations by a factor of 32 (the last piece we place adds 32 permutations). We can also note that there are 32 differerent pieces we can take away at that point. That means the number of states with 31 pieces on the board is roughly equal to the number of states with 32 pieces on the board. + +It does get more complicated, though. For 30 pieces we reduce the number of permutations by 33 * 32, while we multiply that by the number of pieces that could be removed by 32 * 31. So for 30 pieces it's the original estimate times 31/33. For subsequent combinations, it's 31*30/33*34, 31*30*29/33*34*35, etc... + +So the new total would be given by: + + +* T^' = T^0 * ( 1 + 32/32 + (31 * 32)/(32 * 33) + (30 * 31 * 32)/(32 * 33 * 34) + (29 * 30 * 31 * 32)/(32 * 33 * 34 * 35)... ) + +I plugged this into a computer program, because I can't think of a quick and easy way to calculate it, and I got 6.03, so now our new (and final) estimate is: + +* T^' = T^0 * 6.03 = 7.24 * 10^42 + +Very, very close to the Shannon estimate." +1275 AskScience AMA Series: You've most certainly heard stories about young athletes collapsing and dying while playing their beloved sport. These athletes often have the rare, genetic heart condition ARVC. I am Dr. Cynthia James, and I study how to better help people who have this disease. AMA! 2767 https://www.reddit.com/r/askscience/comments/bh795c/askscience_ama_series_youve_most_certainly_heard/ 1556190010 bh795c 2019-04-25 14:00:10 Should every athlete have a screening EKG and/or echocardiogram? Why or why not? If so, at what level of competition should screening take place? [deleted] +1602 Why don’t we have vaccines for all Herpes Viruses? 2752 https://www.reddit.com/r/askscience/comments/hwjkte/why_dont_we_have_vaccines_for_all_herpes_viruses/ 1595524252 hwjkte Medicine 2020-07-23 20:10:52 Vaccines work by training your immune system to respond to the pathogen. Herpes simplex virus 1 and 2 (the kinds that cause cold sores and genital sores) are immunoevasive, which means that they have a mechanism to avoid destruction by your immune system. As your immune system begins to respond to the virus, herpes will hide inside nearby nerves (but not destroy them like other tissue). Normally, virus-infected cells are detected by your immune system and destroyed by cytotoxic T cells, but your nerve cells have *immune privilege*, which means your immune system does not attack them. Herpes lies there in a dormant state until a biochemical stressor (high stress, hormonal changes associated with menstrual cycles, new medications, etc) cause them to pop back out and reinfect the nearby tissue. Also, since nerves don’t move around, this is why herpes almost always reappears in the same location. It just pops in and out of the same hidey hole. It’s not for lack of trying. These vaccines have been in the works for about 100 years but they keep failing the clinical trials. Sometimes the vaccine itself has too many side effects - I remember there was some neurotoxicity - and other times the resulting antibodies weren’t robust enough to eliminate the virus, which is pretty darn good at evading our immune system in the first place. Remember that vaccines simply stimulate our immune systems to produce antibody production without catching the full blown disease so that if/when we are exposed, our immune system can have an immediate response to a virus before it can reproduce successfully. +172 If I have 2 buckets of hot water and one bucket of cold water, is there any order in which I can combine them that will result in a different temperature than any other order? 2750 http://www.reddit.com/r/askscience/comments/35llzt/if_i_have_2_buckets_of_hot_water_and_one_bucket/ 1431355316 35llzt Physics 2015-05-11 17:41:56 "Nope, not if it is a closed system. Assuming all the heat that is in the 3 buckets to start with is all there at the end you will have the same amount of energy in the combined buckets no matter how you mix them, which means exactly the same temperature. + +You could certainly take different paths to get there, and maybe mix things in such a way that there is a temperature gradient for a time. For example, if you poured in the cold bucket first and then very slowly and carefully poured the hot buckets across the top you could potentially make the cold water stay at the bottom and hot water stay at the top for awhile. However, given enough time they will mix and the temperature should equalize. + +If you want an analogy for this to make sense then instead of the abstract concept of ""heat"" we can just replace the heat with something tangible. For example, imagine three buckets of sand instead of water, two of which have a lot of marbles mixed in while one only has a few. No matter how you mix the three buckets of sand together you will always end up with the same number of marbles in the mixed bucket at the end. Swap marbles for heat and you are good to go." "Expanding on the other well explained comment, if you take the surroundings into account and introduce a time difference you'll get some different results. + +There is the common example of adding cold milk to your hot coffee that you wish to drink later on in the future. If you want to come back to your coffee later and want it to be as hot as possible, should you add the cold milk straight after brewing or later on just before drinking the coffee. + +As you'll imagine there will be heat ""lost"" from the coffee to the environment. The trick its that this heat ""loss"" is proportional to the temperature difference between the coffee and the environment. (See for example Fourier heat transfer) + +So adding the milk straight away is the best course of action since the cooled down mixture will loose less heat during the time it is sitting there. +If you add the milk at the end the hot coffee looses more heat while it is sitting there so when you mix in the milk the mixture has a lower temperature. + +" +283 Is ~-40C to 40C the only temperature range for any lifeforms to exist? Or could there be lifeforms that we cannot imagine at -150C or 4000C? 2748 https://www.reddit.com/r/askscience/comments/3pws4t/is_40c_to_40c_the_only_temperature_range_for_any/ 1445610424 3pws4t Biology 2015-10-23 17:27:04 "I won't attempt to answer the question, but as a geologist I have to correct your basic assumptions concerning the temperature range of Life As we Know It (LAWKI). + +The uppermost temperature we know of for living and active metazoans (complex multicellular life) is at the edge of actively venting black smokers, where worms of the species *Alvinella pompejana* have been observed ""just chilling"" at temps of 80° C (and at a pH of about 3.5). When it comes to an uppermost limit for microbes and extremophiles, it might even be necessary to go even higher. For instance, in Mississippi Valley type Pb-Zn deposits there is ample evidence for the fractionation of sulphur isotopes from biogenically mediated sulphate reduction up to about 120° C. + +So a revised statement would have to be from about -40° C up to 120° C; or a range of 160 degrees if you'd rather see it that way. And I'd check that lower limit as well; there has been a lot of recent work on extremophiles and I'd look into data on cryophiles (with which I am admittedly unfamiliar) just to be on the safe side if I were you." "Any water based life form would require the temperatures and pressures to be around those required for H2O to be liquid. Other life could theoretically exist at temperatures and pressure outside that range, but would have to be based on a different solvent. For example, ammonia based life would require much colder temperatures. + +[Here's a Wikipedia link](https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry) discussing hypothetical types of biochemistry." +284 How is it physically possible for Tardigrades to survive crushing pressures and complete vacuum? 2746 https://www.reddit.com/r/askscience/comments/3r40ro/how_is_it_physically_possible_for_tardigrades_to/ 1446404606 3r40ro Biology 2015-11-01 22:03:26 "Quite a bit of tardigrade survival comes not from any sort of resistance to temperature or pressure changes, i.e., no internal mechanism to defend against them, but through severe dehydration of the organism. There is very little water left in the cells of the creature, so there is almost no pressure gradient due to the semipermeable membranes of the cell. + +It's not that difficult to resist the vacuum of space for a virtually solid object, especially, as alanmagid pointed out, an object that is coated in a nonpermeable substance like a dehydrated water bear. + +This dehydration of the organism is also how tardigrades are able to survive extremes in temperature. The stasis that they go into is their main survival method, and when put under environmental pressures without first going into stasis, the creature has much less resiliency." Such organisms are called piezophilic. While tardigrade is not a true extremophile, it likely has similar evolutionary changes as piezophiles to withstand extreme conditions. Proteins in one of these organisms are found to contain fewer Proline and Glycine amino acid residues, which contribute to breaking and destabilization in alpha helices (secondary protein structure). The number of large, bulky amino acid residues such as tryptophan and tyrosine also decreases and there are more small amino acids, which allows better packing and increased stability. Thermophiles (organisms that live in extremely high temperatures) are found to have a greater abundance of salt bridges, which stabilizes thermophilic enzymes. the high temperatures compensate the loss in entropy provided by salt bridges in mesophiles. http://www.horizonpress.com/jmmb/v/v1/v1n1/14.pdf http://www.hindawi.com/journals/archaea/2013/373275/ +56 /r/AskScience Vaccines Megathread 2744 http://www.reddit.com/r/askscience/comments/2urird/raskscience_vaccines_megathread/ 1423065539 2urird Medicine 2015-02-04 18:58:59 "What is the difference between the combined MMR vaccine and getting the three separately? + +Why aren't all vaccines (DTAP, MMR, HPV, etc) combined into one?" Are there any scientifically proven negative side effects to vaccinations? +378 What's going on with technetium? 2743 https://www.reddit.com/r/askscience/comments/42av75/whats_going_on_with_technetium/ 1453556396 42av75 Physics 2016-01-23 16:39:56 "This is actually a physics question. There a multiple things happening here. First, there are an odd number of protons. Protons/neutrons like to pair up. This is the pairing energy term in the [semi-empirical mass formula](https://en.wikipedia.org/wiki/Semi-empirical_mass_formula). Now that does not explain everything. + +Part of the answer lies in the idea that it lies far from the [nuclear magic numbers](https://en.wikipedia.org/wiki/Magic_number_\(physics\)). Magic numbers impart additional binding that helps hold nuclei together. Now there is one more piece. Technetium is special in that it lies next to two elements that are unusually very stable (Mo and Ru). Because if this, nuclei of Tc will decay to the most stable configurations. This means they will beta decay to either Ru or Mo. + +It is important to remember what stable means. In many cases it means the isotope will not decay for a very long time. Many ""stable"" isotopes actually decay. " "The unfortunate reality is that you will find no simple, ""just-so"" story about why Technetium in particular has no stable isotopes. To compute the stability of Technetium, for example, from first principles (that is without assuming any semi-empirical model) would require solving for the allowed states of a quantum system with 43 protons + 43 electrons + ~50 Neutrons = ~136 particles interacting via the strong, weak, and electromagnetic forces (gravity is probably negligible here) crammed into a size of about 10^(-15)m for the nucleus and 10^(-9)m for the whole atom. + +This is a VERY hard problem to try and get some qualitative understanding out of for several reasons: + + 1. It is highly non-classical. This is why the semi-empirical mass formula and the liquid drop model sometimes fail. + + 2. It includes the strong force. Electromagnetism and the weak force can generally be analysed using the techniques of [perturbative quantum field theory](https://en.wikipedia.org/wiki/Quantum_field_theory#Theories), but the larger coupling constant of the strong force makes this basically impossible for the strong force. So we're left with a much smaller set of usable tools for analysis. + + 3. It sits in the uncomfortable range where there are too many particles to solve the problem exactly, but there are too few to apply a thermodynamic approach. Most exact methods in quantum mechanics are tractable for 2, sometimes 3 and 4 particles (this is why, for example, every student studies the hydrogen and helium systems). For 5 - ~10 particles there may be some kind of approximation which keeps the problem tractable. Technetium has over 100 particles though (and they are potentially unstable), which puts it well beyond this tractable regime. But, on the other hand, physicists have a lot of tools to deal with thermodynamic systems containing anywhere from millions to Avogadro's number of particles and up. Technetium (and all heavy elements) falls in the sort of 'dead-zone' where we do not have as many useful tools. + +One thing that's interesting to consider are the decay channels which happen to make light nuclei unstable. [This chart](http://www.dommelen.net/quantum2/style_a/img3381.gif) was already posted and shows that for light nuclei (including the ones that do have a stable isotope) the most common decay path is beta decay, either beta- with the emission of an electron, or beta+ with the emission of a positron. Typically, there are some stable isotopes and then isotopes with more neutrons and unstable due to beta- decay, while isotopes with fewer neutrons are unstable due to beta+ decay. + +With that pattern in mind, consider just the section of the chart near Technetium. As already mentioned, nuclei with odd numbers of protons tend to be less stable. The elements with odd numbers of protons around Technetium, Niobium and Rhodium, have just 1 stable isotope. So, we can ask, what happened to the isotopes of Technetium that we might think are stable, based on what's around it, and these are the already mentioned Technetium-97 and Technetium-99? + +The 'problem' with Technetium-97 is somewhat unique: it is stable (apparently) against both beta+ and beta- decay, but not against electron capture. Electron capture occurs when a proton absorbs one of the inner-shell electrons of the atom, transforming itself into a neutron. Electron capture does happen with these lighter nuclei, but usually in situations where BOTH electron capture AND beta+ decay are allowed. Unusually, the energy difference between Technetium-97 and Molybdenum-97 is not large enough to allow a transition via beta+ decay, but just by coincidence it happens to be that 43 protons + 54 neutrons has higher energy than 42 protons + 55 neutrons and so the decay can occur. That 42+55 has lower energy is totally not obvious (for example, neither combination has any magic numbers) and just depends on the details of whether the change in electromagnetic potential energy or the mass difference between proton and neutron happens to be larger." +1276 AskScience AMA Series: Hi! We are researchers from the National Institutes of Health and University College London studying how advances in genetics are affecting our lives and the world around us. In honor of National DNA Day, ask us anything! 2742 https://www.reddit.com/r/askscience/comments/bgt7fe/askscience_ama_series_hi_we_are_researchers_from/ 1556103656 bgt7fe 2019-04-24 14:00:56 What exciting breakthroughs in molecular biology research are we tantalisingly close to as of today? "How likely do you believe that biological immortality is ""invented"" within the next couple of decades? What are problems that occur while trying to achieve immortality? Where are we at the moment (how advanced is our research to date)? Thanks for your ama." +173 What is the minimum number of individuals required to establish a long-term viable population? 2737 http://www.reddit.com/r/askscience/comments/39jzks/what_is_the_minimum_number_of_individuals/ 1434092273 39jzks Biology 2015-06-12 9:57:53 [deleted] I am going to piggy back on this question to ask a follow up. We know that a single mating pair would not be enough to keep humans alive. But what would be the actual result? Assuming the humans are 100% dedicated to creating as many offspring as possible, there is no incest taboo, everyone breeds as soon as their body is physically capable, and environmental factors are disregarded, how many generations can we expect to get from this single pair? And how many genetic abnormalities can we expect? +174 It seems that all steam engines have been replaced with internal combustion ones, except for power plants. Why is this? 2736 http://www.reddit.com/r/askscience/comments/3g1osg/it_seems_that_all_steam_engines_have_been/ 1438892164 3g1osg Engineering 2015-08-06 23:16:04 "Steam turbines tend to be pretty heavy for the power they generate, don't respond to quickly changing loads well, and aren't efficient at the small size needed for roadgoing vehicles. + +Power plants used for electrical generation or moving large boats don't suffer from any of those problems. Electrical base load generation is a steady output load that doesn't change. Electrical plants are stationary, so the mass isn't constrained the way it is for a car; even on boats the mass won't be such a big deal. + +If you are wondering why use steam? The heat source doesn't matter: you can burn coal, natural gas, bunker oil, or use a nuclear reactor and that heat will drive a steam turbine. Steam can carry a great deal of power with little loss from the heat source to the turbine." "Interesting note... There has been some experimentation in using steam in modern cars. The idea is to add two additional strokes to the engine. After the exhaust stroke, you would inject water into the cylinder, which would then vaporize into steam. The steam would undergo an additional exhaust stroke, and then back to the intake stroke. + +Such an approach avoids the need to have a separate boiler for the steam. The heat instead comes from the previous combustion in the engine. Such a system would be self-cooling, and wouldn't need a radiator. It would also make efficient use of waste heat." +497 A few questions regarding the asteroid orbiting Earth NASA just announced..? 2735 https://www.reddit.com/r/askscience/comments/4pvn6x/a_few_questions_regarding_the_asteroid_orbiting/ 1466906977 4pvn6x Planetary Sci. 2016-06-26 5:09:37 "It isn't really ""orbiting"" in the traditional sense of a closed orbit with a definite period IIRC. It is a near-Earth object with a relatively stable orbit around the Sun. The earth's gravity tugs on it and affects its orbit, but it is outside of the Earth's ""Sphere of Influence"" (~0.01 AU or 1.5 million km), where Earth's gravity dominates. The moon on the other hand has a well-defined Earth-centered orbit (~384000km from surface) and lies well within the Earth's SOI. + +I am assuming this is the object you are talking about -> https://en.wikipedia.org/wiki/2016_HO3 + +As for your questions: +1. It is highly unlikely that it collides with the moon as it doesn't even come inside Earth's SOI. It's too far away and too small to affect the tides. +2. Orbital calculations indicate it has been a ""quasi-satellite"" for almost a century. +3. Well, technically you can send a spacecraft there. It is a matter of figuring out the trajectory for whatever type of mission you want. Depending on it's mass, the ""Landing"" may be more of a ""docking"" due to extremely low gravity. +4. The Wikipedia page says the object has an ""absolute magnitude (H)"" of 24. Magnitude is a way of defining brightness and the smaller the number, the brighter it is. For comparison, the moon full has an H value of +0.25. I think a difference of 1 in absolute magnitude translates to a 2.5x decrease in brightness (I may be wrong with the exact figure). So +24 is extremely dim. You would probably need a huge telescope to see it. +5. No idea really. I would think because it is in a relatively stable orbit w.r.t the Earth, we are safe. +6. Depends on what is on there. We really don't know much about it at this point. It is way too small and very far away. " Never thought about it before, but shouldn't there be many thousands of asteroid satellites buzzing around any large mass? Surely of all the meteors that come at us every day, some would hit the sweet spot where they enter orbit rather than burning up or bouncing off? +379 How did this article, suggesting Intelligent Design of the hand, make it through peer-review and into PLOS One? 2734 https://www.reddit.com/r/askscience/comments/48oyk5/how_did_this_article_suggesting_intelligent/ 1456960616 48oyk5 Human Body 2016-03-03 2:16:56 This thread is now locked. This is not the normal type of thread we allow here (we avoid Meta questions), but there is some good discussion which we do not want to lose. However, the thread is also full of rampant speculation and personal anecdotes, and it is likely even with heady moderation it would remain so. This whole thing reads like a purposeful test of PLOS One's editing system. +57 2 cars traveling in the same direction at 90km/h and 120km/h, if the faster one hits the slow from the back, is it the same crash as if a car traveling 30km/h hit a car that is not moving? 2731 http://www.reddit.com/r/askscience/comments/2zsx0z/2_cars_traveling_in_the_same_direction_at_90kmh/ 1426943940 2zsx0z Physics 2015-03-21 16:19:00 "**Short answer:** Yes and no. Mostly no, though. + +**Long answer:** Depending on your choice of reference frame, you can make any collision look like something at rest is getting hit. For example, in your reference frame (which is in the 90 km/h car), you are at rest, so it's like being struck by a car only moving 30 km/h, at least as far as the immediate whiplash goes. + +The big difference is that, relative to the ground, you have much greater *kinetic energies* since KE is determined by + + (Kinetic Energy) = 1/2 (Mass) (velocity)^2 + +which grows quadratically with speed. Additionally, the wheels are spinning much faster, so there's more rotational kinetic energy there, but that's a small correction. + +Basically, the reason the faster collision is more likely to be catastrophic is because the cars have more kinetic energy with respect to the ground, which is the thing they want to come to a rest with respect to. The instantaneous collision in a [""spherical cow in a vacuum""](http://en.wikipedia.org/wiki/Spherical_cow) approach is the same, but the evolution of the collision in reality will depend heavily on the speeds. + +Also, don't try this at home. " Although the initial collision is very similar to a 30 kph collision, the aftermath could be quite different. The 0 v 30 crash ends with both cars going about 15 mph each, easily brought under control. The 90 v 120 case ends with both vehicles going about 105 and probably sliding sideways and out of control, an obviously much more dangerous situation. +175 Why does squinting make my vision clearer? 2725 http://www.reddit.com/r/askscience/comments/3a6dqa/why_does_squinting_make_my_vision_clearer/ 1434557503 3a6dqa Physics 2015-06-17 19:11:43 "First of all, realize that this only works for people who have vision problems due to incorrect focusing of the light. For our eyes to work properly, incoming light must be focused down to the retina. When this does not happen, either because light is focused in front of the retina (a condition called myopia or nearsightedness), or behind the retina (hyperopia or long-sightedness), objects are various distances will look blurry since the image will be defocused, as shown graphically [here](http://products.pbhs.com/_procedural-ophthalmology/point-of-focus.jpg). + +Now squinting can remedy this situation in two ways. One possibility is that the deformation created by squinting can partially offset the natural imperfection in the eye, and can thus bring the focal plane of the eye closer to the retina. This will effectively offset the initial optical aberration and allow you to see an imagine which is better focused and thus sharper. + +The second possibility is more general, and results from the increase in depth of field created that results from decreasing the aperture (opening) through which light enters your eye. Because of this even an image that is equally out of focus will appear sharper because the higher depth of field means that the sharpness of the image decreases more slowly as you move away from the correct focus. To better visualize this second effect, take a look at [this series of images](http://damienfournierdotco.files.wordpress.com/2013/12/dof_aperture_7guitars.jpg). Notice that as you decrease the opening of the lens, an increasingly large part of the field of view appears clear. This exact same effect is at play when you reduce the size of the opening into your eye (you can get a similar effect from looking at objects through an index card with only a small opening allowing light through)." "As I think this is something easier understood with a diagram, I took the liberty of making one, though it's extremely approximate and doesn't show things like the refraction of light through the cornea. + +http://i.imgur.com/eByascr.png + +Top left you see an ideal eye. The lens focuses incoming light to a focal point on the retina (the red area), and that focal point is relatively small. + +Top right you see a myopic (near-sighted) eye. The lens focuses light in the same way, but because the eye is elongated, the focal point is actually in front of the retina, and what hits the retina is a somewhat unfocused image (not to mention upside-down, but our brain adjusts for that). + +Bottom center you see a myopic eye that's squinting (your eyelids visualized by the orange horizontal lines). Because the angles of the incoming light vectors are necessarily more shallow, there's less ""spread"" of the rays between the focal point at the retina, hence the perception of a clearer image." +498 Are humans apes? 2719 https://www.reddit.com/r/askscience/comments/4y0sdb/are_humans_apes/ 1471369455 4y0sdb Biology 2016-08-16 20:44:15 "This is an old essay from [Talk.Origins](http://www.talkorigins.org/origins/postmonth/may03.html): + + > A giraffe has never given birth +> to a horse, as far as we know it. An ape has never given birth to a man. +> I will give a million bucks to anyone who can observe an ape giving +> birth to a human. Even your mother, if such were true. + +**You are a metabolic organism.** + +As such, you are basically a collection of replicative proteins that function according to metabolic chemical reactions and processes. A virus is similar, in that it too is a replicative protein complete with mutable DNA and RNA, just as you have. But viruses lack metabolism, and so may not be considered to be alive in the same manner that you definitely are. + +**You are a eukaryote.** + +All remaining organic life is distinguished by structural differences at the cellular level between different groups of prokaryotes (which are essentially bacteria) and the eukaryotes (us). Unlike bacterial or viral cells, our cells have a nucleus. Hence, all non-viral / bacterial lifeforms are as we are; eukaryotes. + +**You are an animal.** + +Now I've heard a few creationists argue that there are plants and there are animals and then there are human beings. And that none of them are actually related to one another other than through a common creator. They adamantly argue that we are not animals, as if there is some insult in that association. But you are one of only about a half-dozen kingdoms of eukaryotic life forms. Unlike those of most other biological kingdoms, you are incapable of manufacturing your own food and must compensate for that by ingesting other organisms. In other words, your most basic structure requires that you cause death to other living things. Otherwise, you wouldn't have a means of digestion. This, along with some very specific anatomical differences in the chemical composition of our metazoic cells, are the factors that define and distinguish an animal like yourself from all other kingdoms of life. Given the alternative choice between plants, molds, or fungus, animalia should seem reasonable even to the most adamant fundamentalist. + +**You are a chordate.** + +You have a spinal chord and every other minute physical distinction of that classification. You also have a skull, which classifies you as a craniate. Note: Not all chordates have skulls, or even bones of any kind. Once one of the chordates has enough calcium deposited around the brain to count as a skull, all of its descendants will share that. This is why absolutely all animals with skulls have spinal chords. And that is yet another commonality that implies common ancestry as opposed to common design. + +**You are a vertebrate.** + +Like all mammals, birds, dinosaurs, reptiles, amphibians, and most fish, you have a spine. Not everything with a spinal cord has a spine to put it in, but everything with a spine has a spinal cord in it, implying common descent. + +Every animal that has a jaw and teeth (Gnathostomata) also has a backbone. And of course, you have both as well, again implying common descent. + +**You are a tetrapod.** + +You have only four limbs. So you are like all other terrestrial vertebrates including frogs. Even snakes and whales are tetrapods in that both still retain vestigial or fetal evidence of all four limbs. This is yet another consistent commonality implying a genetic relationship. There certainly is no creationist explanation for it. + +**You are synapsid.** + +Unlike turtles (which are anapsid) and ""true"" reptiles, dinosaurs and birds (which are all diapsid), your skull has only one temporal fenestra, a commonality between all of the vast collection of ""mammal-like reptiles"", which are now all extinct without any Biblical recognition or scriptural explanation either for their departure or their presence in the first place. + +**You are a mammal.** + +You are homeothermic (warm-blooded), follicle-bearing and have lactal nipples. And of course, not all synapsids are or were mammals, but all mammals are synapsid, implying common descent. + +**You are eutherian.** + +Or more specifically, you are a placental mammal, like most other lactal animals from shrews to whales. All eutherians are mammals, but not all mammals are eutherian. There are six major divisions in mammalia, only three of which still exist; those that hatch out of eggs like reptiles (monotremes), marsupials, that are born in the fetal stage and complete their development inside the mother's pouch, and those that developed in a shell-like placenta and were born in the infant stage, as you were. Your own fetal development seems to reveal a similar track of development from a single cell to a tadpole-looking creature, then growing limbs and digits out of your finlike appendages, and finally outgrowing your own tail. Some would consider this an indication of ancestry. Especially since fetal snakes, for example, actually have legs, feet, and cute little toes, which are reabsorbed into the body before hatching, implying common descent. + +**You are a primate.** + +You have five fully-developed fingers and five fully-developed toes. Your toes are still prehensile and your hands can grasp with dexterity. You have only two lactal nipples and they are on your chest as opposed to your abdomen. These are pointless in males, which also have a pendulous penis and a well-developed ceacum or appendix, unlike all other mammals. Although your fangs are reduced in size, you do still have them along with some varied dentition indicative of primates exclusively. Your fur is thin and relatively sparse over most of your body. And your claws have been reduced to flat chitinous fingernails. Your fingers themselves have distinctive print patterns. You are also susceptible to AIDS and are mortally allergic to the toxin of the male funnel web spider of Australia (which is deadly to all primates, but only dangerous to primates, which is why you'd better beware of these spiders). And unlike all but one unrelated animal in all the world, your body cannot produce vitamin-C naturally and must have it supplemented in your diet, just as all other primates do. Nearly every one of these individual traits are unique only to primates exclusively. There is almost no other organism on Earth that matches any one of these descriptions separately, but absolutely all of the lemurs, tarsiers, monkeys, apes, you, and I match all of them at once perfectly, implying common descent. + +**You are an ape.** + +Your tail is merely a stub of bones that don't even protrude outside the skin. Your dentition includes not only vestigial canines, but incisors, cuspids, bicuspids, and distinctive molars that come to five points interrupted by a ""Y"" shaped crevasse. This in addition to all of your other traits, like the dramatically increased range of motion in your shoulder, as well as a profound increase in cranial capacity and disposition toward a bipedal gait, indicates that you are not merely a vertebrate cranial chordate and a tetrapoidal placental mammalian primate, but you are more specifically an ape, and so was your mother before you. + +Genetic similarity confirms morphological similarity rather conclusively, just as Charles Darwin himself predicted more than 140 years ago. While he knew nothing of DNA of course, he postulated that inheritable units of information must be contributed by either parent. He rather accurately predicted the discovery of DNA by illustrating the need for it. Our 98.4% to 99.4% identical genetic similarity explains why you have such social, behavioral, sexual, developmental, intellectual, and physical resemblance to a bonobo chimpanzee. Similarities that are not shared with any other organism on the planet. Hence you are both different species of the same literal family. In every respect, you are nearly identical. You, sir, are an ape. + +And as I have witnessed the birth of both of my children, I have now met the criteria for your reward. Please make my $1,000,000.00 payable to L. Aron Nelson. Thank you. " "Yes. Ape (Hominoidea) is a superfamily and is made up of the families Hylobatidae and Hominidae. Within Hominidae there are four genera: Pongo, Gorilla, Pan, and Homo. I think you can take it from there! + +As with all taxonomy, there is likely going to be some shuffling around and suggestions for reorganization based on DNA data. For example, [this paper](http://link.springer.com/article/10.1007/BF02099995) suggests that the breakdown be: + +**Superfamily Hominoidea** + + Family Hominidae + + Subfamily Hylobatinae + + Hylobates + + Subfamily Homininae + + Tribe Pongini + + Pongo + + Tribe Hominini + + Subtribe Gorillina + + Gorilla + + Subtribe Hominina + + Pan + + Homo +" +499 What are the alternative ways to measure advancements of civilisation other than the Kardashev Scale, and what are their pros and cons? 2716 https://www.reddit.com/r/askscience/comments/50b4j0/what_are_the_alternative_ways_to_measure/ 1472563946 50b4j0 Astronomy 2016-08-30 16:32:26 In general, scales or classifications only make sense once you have multiple things to measure or classify. Since we don't have anything else to compare with, we're mostly hypothesising about measurement systems, none of which may actually be useful. "The Kardashev scale does it's best to address a very difficult concept for people to understand, unknown unknowns. + +There are known knows, things that you know you know, like people are harnessing rockets to explore their solar system. There are known unknowns, like that we do not have *proof* that there are other civilizations out in the universe. + +And then there are unknown unknowns: future circumstances, events, or outcomes that are impossible to predict, plan for, or even to know where or when to look for them. The progression of technology, and breakthroughs or tipping points. What will a civilization look like that is hundreds, thousands, millions, or even billions of years more advanced than our own? We can speculate, but we're honestly lacking a framework to even build on. Will space elevators ever be possible on a planet big enough to sustain an atmosphere? Will large scale space construction ever be possible or feasible? Will it be something else entirely that catapults us to the stars? Has it already happened for another civilization? We have no way to predict things like this, or if we're even asking the right questions. + +But two things we *can* be sure of is 1:the conservation of energy, and 2:that as a civilization gets bigger, and more advanced, more energy is required. + +A caveman capable of fire used more energy than an ape. A castle used more energy than a host of cavemen. A modern metropolis uses more energy than all the ancient world combined! Energy use is, by this logic, a fantastic metric for the advancement of a civilization. + +Edit:I corrected my example for unknown unknowns to be more in line with the traditional, financial definition of unknown unknowns." +380 Why is it that when I look in a mirror without glasses on, the objects farther away are still blurry? Wouldn't the mirror just change everything to a 2D image? 2714 https://www.reddit.com/r/askscience/comments/48aee9/why_is_it_that_when_i_look_in_a_mirror_without/ 1456755619 48aee9 Physics 2016-02-29 17:20:19 "> Wouldn't the mirror just change everything to a 2D image? + +Actually no. All our brain can do is trace the light rays back to their *apparent* source, it doesn't really matter whether there was a mirror involved. Take a look at [this diagram](http://www.nightlase.com.au/education/optics/Images/planemi.gif). The light gets traced back ""through"" the mirror to where it appears to be originating from, and that's what creates the image in our brain. If there was no mirror in the way, and instead the real object was placed in the position of the ""image"" object in the diagram, the light rays on the left hand side would be exactly the same geometrically, and so our brains will see the same thing either way." "That would work with a video screen, like on your phone, but not a mirror. With a mirror, you aren't focusing the lenses of your eye on the mirror's surface. If you did, it would be the dust and finger prints on the mirror itself that would be in focus. Instead, you're focusing on the object, that really is that far away: the light is traveling the same distance, it's just reflected. + +With the camera screen, the camera has a lens that is focusing on the object the way your eye would, and creating the image on the screen, so you focus on the screen, not the object. + +Edit: typo" +58 If two conjoined twins who share the same organs went swimming, would one be able to swim underwater for as long as they wanted while the other twin continued to breathe above water? 2709 http://www.reddit.com/r/askscience/comments/2x3bmz/if_two_conjoined_twins_who_share_the_same_organs/ 1424851132 2x3bmz Human Body 2015-02-25 10:58:52 [deleted] +59 "Darwin Day Feature: ""Nothing in Biology Makes Sense Except in the Light of Evolution"" — Dobzhansky" 2707 http://www.reddit.com/r/askscience/comments/2vnvh7/darwin_day_feature_nothing_in_biology_makes_sense/ 1423757657 2vnvh7 Biology 2015-02-12 19:14:17 "**From Watson and Crick to Darwin** + +It's easy to forget, in 2015, just how much we know. Every 10 year old in the United States has heard the phrase ""survival of the fittest,"" and every 13 year old knows that children inherit the genes of their parents after their parents [CENSORED]. Of course organisms fight to survive and pass on their genes, and of course this is based on the transfer of DNA from parent to offspring. Of course, of course, *of course*. + +But Darwin didn't know anything about genes. He didn't know about DNA and he didn't know about genetic inheritance, since the work of Gregor Mendel was then still not known. I think this underscores the level of Darwin's genius -- I find it hard to believe that I would be able to ride a boat around the world, look at some birds (I'm paraphrasing), and come up with, well, *natural selection*, without already knowing what I know. But, how do we know all that we know about genes and DNA? Is there a direct link between, say, the work of Watson/Crick, arguably the crowning achievement of 20th century biology, and Darwin? + +James Watson and Francis Crick, as you may know, made their names by elucidating the structure of DNA -- the famous ""double helix."" They, also famously, ended their first paper with a nod towards the double helix easily suggesting a way to copy DNA for the purpose of passing it on. This potential copying mechanism would, of course, facilitate the passing of the fittest DNA. But why were they chasing DNA's structure in the first place? Well, at the time of the double helix papers in 1953, DNA's importance as the genetic material was still relatively new. This was definitively shown by two sets of experiments. In 1944, Oswald Avery and his colleagues showed that if you mixed a deadly form of *Streptococcus* (similar to the ""strep"" in ""strep throat"") with an innocuous form, the innocuous form all of a sudden became deadly. They got the same result if they mixed the deadly bacteria's DNA with the innocuous bacteria, but not if they mixed protein in. In 1952, Alfred Hershey and Martha Chase showed that if you infected cells with viruses carrying either radioactive DNA or radioactive protein, only the radioactive DNA got into the cell. Hershey won a Nobel Prize for this work but not Chase because in the '50s being a female scientist was like being one of those dogs that wears a tutu and stands on its hind legs. + +But why did they need to prove that DNA was the genetic material? Well, before Avery and Hershey/Chase, the prevailing logic was that *proteins* were the basis of genetic inheritance, mostly on the flimsy-in-hindsight logic that proteins are more chemically diverse than DNA, which is chemically repetitive. What *did* we know before then, then? Considering what I just said, it seems counter-intuitive but the concept of chromosomes, what we know today as structural organizations of DNA, was already known at this point. However, they were only known as mixtures of DNA and protein (which we now know are just histones and other *associated* proteins that do not carry genetic information). Whether DNA or protein was doing the legwork was unknown, but proteins were favored. + +I'll skip over a few other more famous scientists and talk about an under-appreciated one: Theodor Boveri. In the late 19th century he studied the nucleus of parasitic worms (who wouldn't?!) and noted that as cells divided and reproduced, chromosomes in the nucleus vanished and then reappeared in the same orientation -- suggesting that this represented ""continuity"" in chromosomes, which is precisely the kind of thing Mendelian genetic inheritance would require (though chromosomes and inheritance weren't formally united until Thomas Hunt Morgan in 1915. He...*sigh*...also won a Nobel Prize. Boveri did not). + +From there, skipping over a few more people, it's on to Mendel and his pea plants (and his [maybe fake](http://upress.pitt.edu/htmlSourceFiles/pdfs/9780822959861exr.pdf) data) and Darwin. Natural selection, to inheritance, to chromosomes, to DNA, to the double helix. If you are interested in reading further about any of the work or the people who did it mentioned here, the wikipedia articles are a good start but I highly recommend *The Eighth Day of Creation* by Horace Freeland Judson as mostly a history of 20th century biology. + +**Bibliography** + +* *The Eighth Day of Creation* - Horace Freeland Judson +* *Molecular Biology of the Cell* - Bruce Alberts et al. +* *Theodore Boveri* - Fritz Baltzer, *Science*, Vol. 144, No. 3620 (May 15, 1964), pp. 809-815 (or, alternatively, if you can't get it because JSTOR is stupid, [this](http://www.genomenewsnetwork.org/resources/timeline/1888_Boveri.php) news article that makes reference to the same article)" "Field: **Plant Biology** + +Much of what I study is related to the plant hormone **auxin**. The distribution of indole-3-acetic acid (IAA) throughout plant tissues is largely responsible for controlling plant architecture. For instance, lateral organs (leaves, branches, flowers, etc.) initiate from the shoot apical meristem at sites of local high auxin concentrations. Today, we spend a lot of effort understanding how the patterns of auxin distribution are made, mostly focusing on the role of polar auxin transport proteins like *PIN*-family proteins. + +While Darwin predates the work that identified the chemical and the genes responsible for its synthesis, transport, and degradation, a lesson on auxin isn't complete without mentioning Darwin. + +Darwin performed the first experiments that identified some sort of communication between the shoot apex and the hypocotyl (seedling stem) of seedlings. + +http://www.wikiwand.com/en/Auxin#/Charles_Darwin + +It was a fairly simple experimental setup, but the conclusion is quite powerful. Using a single light source and various objects to shade plant parts, he gained crucial insight about how plant parts interacted. + +http://www.bio.miami.edu/dana/pix/auxin_darwin.jpg + +He demonstrated that the shoot apex was sensing the light, but the result occurred in the a different tissue. In other words, plants were not dumb masses of cells that simply propagated, but consist of dynamic tissues that interact. + +Later experiments would demonstrate that the signal was a diffusable chemical eventually identified as IAA. These experiments use the same experimental system; young shoots bending toward light sources. Of all the complex behavior that plants demonstrate, this simple model yielded insights because it was easy to manipulate and very robust. + +" +381 Does light lose energy when reflected? 2706 https://www.reddit.com/r/askscience/comments/4anry6/does_light_lose_energy_when_reflected/ 1458134795 4anry6 Physics 2016-03-16 16:26:35 "> when a light beam reflects off a surface, does it lose energy? + +Yes. This is due to a transfer of momentum from the photon to the surface. It is not really the same as say a ball losing energy when it bounces, there are several contributing factors to why a ball loses energy and only one for light. + +If a photon has p = E/c when it reflects it has -p (same magnitude, opposite direction). As a result there is a deficit of 2p which is transferred to the reflective surface, this increases the mirrors kinetic energy and as such must decrease the energy of the reflecting photon. + +The fractional change in energy is very small due to the fact that the mirrors mass is much larger than the energy of the photon. I can do the math if you wish but it is roughly a factor of E/mc^2 . + +>So, loss of energy would result in a decrease in speed. + +No, light always travels at the same speed. The loss of energy actually amounts to a drop in frequency. Since a photon's energy and frequency are intimately related (E=h*f) then a reduction in energy means a reduction in frequency. + +You might have heard of this as ""red-shift"" since the frequency is shifted towards the red end of the spectrum when a photon loses energy. + +So yes photons lose energy when they hit a (stationary) mirror, this loss results in a redshift of that photon's frequency." "The question has already been answered, but for general purpose a massless particle (photons, gluons) **never** loses speed. A massless particle must travel at *c* (the speed of light). + +To answer the obvious follow-up about the speed of photons in material other than vacuum, the slowing down in speed can be explained by the photons gaining an imaginary rest mass while traveling in the medium. " +285 NASA Mars announcement megathread: reports of present liquid water on surface 2702 https://www.reddit.com/r/askscience/comments/3mpitk/nasa_mars_announcement_megathread_reports_of/ 1443453491 3mpitk Planetary Sci. 2015-09-28 18:18:11 [deleted] Isn't this water boiling from the pressure? What does this mean for us? +60 I want to hang dry my clothes; which would be faster; exposing it to sunlight or a breeze? 2701 http://www.reddit.com/r/askscience/comments/2tqzko/i_want_to_hang_dry_my_clothes_which_would_be/ 1422299271 2tqzko Physics 2015-01-26 22:07:51 It depends on the humidity of the indoor room. If the indoor room is small and not ventilated, the moisture from the drying clothes will quickly raise the humidity of the room to the point that is significantly slows down the drying of the clothes. If you place a large dehumidifier in the small, ventilated room, or if you give it good ventilation (open some windows) it will keep humidity low and keep the drying time short. "It depends on how much you have of each. ""Drying"" is just the water evaporating into the air, and the air can only take so much. The sun only helps this to happen by raising the temperature, and the breeze only helps by moving the air that's already absorbed the water, and replacing it with presumably less saturated air. + +If you were in a sealed environment with 100% humidity, no amount of sunlight would dry your clothes, and likewise, no amount of breeze at 100% humidity blowing by would help your clothes dry. " +286 If you had a 343 meter long pole, and pushed one end, would it take one second for the other side to move? 2697 https://www.reddit.com/r/askscience/comments/3nmdgp/if_you_had_a_343_meter_long_pole_and_pushed_one/ 1444078078 3nmdgp Physics 2015-10-05 23:47:58 "No, it will actually be a much shorter time, but the exact time depends on the speed of sound through the material of the pole. + +For example, a pole made of steel would have to be about 6100 meters long for it to take one second for the other end to move. This is because of how quickly a wave can propagate through a medium. + +A wave can (generally) move faster through a solid than through either a gas or liquid. + +[Here is a handy table that includes some common materials and their respective ~~speed of sound's~~ speeds of sound.](http://www.engineeringtoolbox.com/sound-speed-solids-d_713.html) + +*edit: +We call it ""the speed of sound"" because that is how most people conceptualize what is going on, but in actuality sound is just a wave that is propagating through the air. + +We don't have to be able to perceive a sound for a wave to actually be present. A more accurate way of thinking about the speed of sound would be how quickly a wave travels through a medium at a given temperature and pressure." "The push would propagate from one end to the other at the speed of sound (speed of sound in the material). +If you consider the pole to be a wooden pole (say beech wood)and the axis of the pole is along the grains in the wood , then we have +>YOUNG'S MODULUS OF BEECH WOOD ALONG THE GRAINS : 14 * 10^9 Nm^-2 + +> DENSITY OF BEECH WOOD: 680 Kgm^-3 + +> Therefore speed of sound: 4537ms^-1 + +> Time before other end of the pole moves: 75.6ms + + + + +" +1603 AskScience AMA Series: We are statisticians in cancer research, sports analytics, data journalism, and more, here to answer your questions about how statistics opens doors for exciting careers. Ask us anything! 2697 https://www.reddit.com/r/askscience/comments/gyx8mf/askscience_ama_series_we_are_statisticians_in/ 1591614043 gyx8mf Mathematics 2020-06-08 14:00:43 what are some unexpected/unconventional jobs you can get as a statistician? What stat related uni courses would you recommend that are most useful even for other majors? As a teacher of intro stats classes at the college level, how do I get students beyond that inherent fear of statistics? What were some of your experiences that drew you to your profession? +382 Do dyslexics have issues with all symbols, or just letters? 2692 https://www.reddit.com/r/askscience/comments/46cy9f/do_dyslexics_have_issues_with_all_symbols_or_just/ 1455769050 46cy9f Neuroscience 2016-02-18 7:17:30 Please remember AskScience is a heavily moderated subreddit. Anecdotal answers are not allowed and will be removed. If you are answering please use sources. "Currently studying an MSc in neuroscience. Whilst language acquisition or dyslexia aren't my field of work, for my undergrad it was my dissertation supervisor's focus and my younger brother has dyslexia, so I did a fair amount of reading around the subject at the time. + +This characterisation of it being a mere effect of 'flipping' symbols is a little off what we know behaviourally about dyslexia. + +To start, in his review paper [Franck Ramus](http://www.lscp.net/persons/ramus/docs/CONB03.pdf) (2003) noted that the evidence of dyslexia stemming from a phonological deficit is overwhelming. There is more information on the phonological deficits [here](http://www.paadultedresources.org/uploads/8/6/3/4/8634493/fob_reading.pdf#page=11) + +Given this knowledge, [Wydell & Butterworth](https://www.researchgate.net/profile/Taeko_Wydell/publication/222502364_A_case_study_of_an_English-Japanese_bilingual_with_monolingual_dyslexia_Cognition_70_273-305/links/09e415100fbdf2ccb2000000.pdf) (1999) put forward the hypothesis of granularity and transparency. The long and short of this hypothesis is that different languages have different ways of constructing words. There are 2 ways in which languages can differ: Transparency and Granularity. + +**Transparency**: Some languages have consistent sounds when certain characters are seen. A good example of this is Japanese, or Italian if you want an alphabetic language. Any specific assortment of characters in these 2 languages is pretty much a 1-to-1 sound. They call this a 'transparent' orthography. Conversely, looking at English, we have very odd quirks of the language with extreme examples like 'ough'. (Bought, Though, Through, Cough, Tough and 2 in the same word even with Loughborough, a city in the UK). There is clearly not a 1-to-1 ratio of characters to sounds here. + +**Granularity**: This is how 'fine' a language is. By this, they mean the smallest functional unit that is there. 3 examples for this would be the alphabet, Japanese kana and then Egyptian Hieroglyphs. Going back to Japanese, their smallest unit is a character, which is usually half a word. Kana is largely transparent (1-to-1 character-to-sound). However, Kanji is NOT transparent. It is opaque. Despite this, dyslexia rates seem lower still in Japan. Why? Because Kanji has a very 'coarse' granularity. Meaning that characters can make up entire words, not just sounds as part of the word. + +It has been argued by Wydell that it is this mix of Transparent-Opaque and Fine-Coarse that leads to dyslexia via a phonological issues and also explains the difference in reported rates of dyslexia in different languages (English is 10%, Danish 10-12% whereas it has been reported to be as low as [1.3%](https://www.researchgate.net/profile/Scott_Lindgren/publication/19284208_Cross-National_Comparisons_of_Developmental_Dyslexia_in_Italy_and_the_United_States/links/56095c5908ae840a08d3a46f.pdf) in Italian) + +Using this as a framework, I would contest that symbols pose very little difficulty to dyslexics because: + +1. There is a coarse grapheme - the 1 logo itself conveys 1 or more words (though, if it has a word in the logo, that muddies the waters somewhat) + +2. It is pretty transparent. You seldom see these logos used in any situation outside of their meaning/use to signify that specific brand (because of copyright). + +So, no, it is not that likely that dyslexics have huge issues with symbols that are specifically logos. + +**TL;DR**: The brain of dyslexics processes things differently phonologically, not visually (so the idea of them 'flipping' the symbols is off). As a result, a logo is transparent and coarse enough to not be an issue for the majority of people. + +**Edit**: Found the [paper](http://cdn.intechopen.com/pdfs/35802.pdf) where I got a lot of this information from a year or so ago. + +**Edit 2** Put the actual paper in the edit above. I had the wrong link before. Also, [here is a comment](https://www.reddit.com/r/askscience/comments/46cy9f/do_dyslexics_have_issues_with_all_symbols_or_just/d04ft0r) I made about the possible visual deficit causes. I am putting it here because I made the post in response to someone else and they have since deleted their comment + +**Edit 3**: Sorry about not replying to loads of the messages I have received today. I was answering for a good 4 hours or so on and off. I went out for the afternoon/evening and I've come back to a heaving inbox. Don't know if I have enough time to reply to everyone." +287 What is physically different between a 100mb DVD and a 5gb DVD if they look like the same size? 2691 https://www.reddit.com/r/askscience/comments/3ntsv7/what_is_physically_different_between_a_100mb_dvd/ 1444216471 3ntsv7 Engineering 2015-10-07 14:14:31 "Just to clarify DVD is a [specific format](https://en.wikipedia.org/wiki/DVD) of an optical data disk technology. As such, the maximum size is essentially fixed by the format to be 4.7 gigabytes (per layer). However, if you are asking more generally about the difference between different formats (e.g. CDs vs DVDs), then the maximum storage capacity will be different in a way determined by the physical properties of the disks. + +The biggest difference between all the main disk technologies, including the CD, DVD, and Blu-ray formats, is in the size of the physical features in the disk in which the data is stored. [This graph](https://upload.wikimedia.org/wikipedia/commons/thumb/a/ad/Comparison_CD_DVD_HDDVD_BD.svg/1000px-Comparison_CD_DVD_HDDVD_BD.svg.png) basically summarizes the whole story. All these disks use a series of pits to encode data and a laser beam then goes around concentrically and reads the data. As you can see going from CDs to Blu-rays, both size of the pits as well as the spacing between successive rows of pits (the pitch) got smaller and smaller. The fact that these features got packed more tightly together meant that you could now put more of them in a given area, and hence to store more data." "/u/crnaruka's answer discusses diff between CD, DVD, and Blu-Ray.If you're really asking the difference between a 100MB **DVD** and a 5000MB **DVD**: + +There really isn't. They're both 5000 page books. The table of contents or index on the first only covers the first 100 pages. The table of contents on the second covers all 5000. + +There are a particular kind of disk, DVD-RW (or other varieties -RW) which allow rewriting the index which results in varying the amount of disk that's used. Most disks can only be written once which locks it at the initial, smallest number. + +This table of contents is really [the filesystem](https://en.wikipedia.org/wiki/Universal_Disk_Format). " +288 "Why is String Theory a ""Theory""? In science, doesn't ""Theory"" mean something tested with reproducible results?" 2689 https://www.reddit.com/r/askscience/comments/3ra1su/why_is_string_theory_a_theory_in_science_doesnt/ 1446507067 3ra1su Physics 2015-11-03 2:31:07 "I can see how the usage of the word ""theory"" is confusing, especially since the colloquial and scientific usages of the word are already often confused. There is even a [similarly worded question](https://www.reddit.com/r/askscience/comments/3r85me/why_is_the_big_bang_theory_called_so_i_mean_is_it/) answered earlier today, but which actually asks a different question. That question asks about the scientific definition of ""theory"", its relation to the colloquial definition and whether scientific laws get somehow upgraded to scientific theories (or vice versa). The current question is actually asking about a third definition of ""theory"", which comes from mathematics. + +For something like string theory (which has no experimental evidence\*), the word ""theory"" is really meant in the *mathematical* sense and not the scientific sense. In mathematical logic, given some language and a set of a statements in that language (called axioms), we can talk about the *theory* of those axioms, which is the set of all statements that can be logically deduced from the axioms. So string theory is really a mathematical framework. For instance, [group theory](https://en.wikipedia.org/wiki/Group_theory) is the theory of the [group axioms](http://tinyurl.com/o3rpjym). If instead we want to model physics, we may start with some mathematical structure that is required to make sense of the assumption that particles are not point-like but rather one-dimensional. In that case, the resulting set of statements is called a *string theory*. + +The usage of the word ""theory"" in *string theory* is very similar to its usage in *classical field theory* (CFT) and *quantum field theory* (QFT). CFT and QFT are simply mathematical frameworks that are useful for describing physics. Classical electrodynamics and general relativity are both examples of a CFT. Quantum electrodynamics and quantum chromodynamics are both examples of a QFT. The term ""quantum field theory"" is often understood to be synonymous with the Standard Model (which includes QED and QCD), but this association is not strictly true. SM is an example of a QFT, whereas QFT is a much more general term. The same goes for ""string theory"". + +--- +\* String theory is consistent with current observations, and so technically has plenty of experimental evidence. So what I really mean is that there is no experimental evidence that distinguishes string theory, i.e., evidence that uniquely confirms string theory as a more accurate model than other current models. + +--- +**edit:** Just to clarify... a *quantum field theory* is a mathematical object, and the word ""theory"" is meant in the mathematical sense that I describe above. The *theory of quantum electrodynamics* is a scientific theory (and, therefore, well tested and corroborated), which is modeled mathematically as a *quantum field theory*. Note the usage of the same word ""theory"" in two different senses in the terms *quantum field theory* and *theory of quantum electrodynamics*. + +For those with a bit more knowledge on the subject, consider that we can very well talk about the quantum field theory of φ^(3) in six dimensions despite it having no correspondence to the physical world. So the term *quantum field theory* covers a much wider range of objects than is implied by the common association of ""QFT"" to ""Standard Model"". + +--- +**edit 2:** I want to make clear that the term *string theory* is meant in the mathematical sense, and there are several string theories out there. There is not just one string theory, just as there is not just one quantum field theory. Whether any particular string theory is an accurate description of our universe is somewhat irrelevant to calling it a theory. Yes, any string theory (and, by that token, any quantum field theory) attempts to describe the universe, but that doesn't mean we cannot treat such formulations as pure mathematics. (In fact, there are unsolved mathematical problems in QFT, even seemingly very basic ones. For instance, you can win a $1,000,000 prize for [proving that nonabelian gauge theory even exists and has a unique ground state](https://en.wikipedia.org/wiki/Yang%E2%80%93Mills_existence_and_mass_gap), and the precise statement that you have to prove is a mathematical one, having nothing to do with physics per se.) + +--- +**edit 3:** Not directly related to the OP's question... + +There are also several comments/lamentations/complaints that scientists are somehow aloof and have chosen terminology that only serves both to confuse the general public and to give opponents fodder for their denial (e.g., ""it's just a theory!"" in response to evolution, GMOs, vaccines, climate change, or any other commonly denied scientific theory). On one hand, I share the disappointment that there are terms here and there that may have a scientific meaning that is different from the colloquial meaning and which may even have different meanings in different scientific fields. The term ""theory"" and related terms (like law, hypothesis, etc.) is not the only such term, although it is arguably the most notorious. I envy the scientist who has never felt frustration and/or disappointment in the face of scientific illiteracy, either at the individual or municipal level. + +On the other hand, it is important to understand that there is no committee of scientists that get together to define general science terms. (There may be specialized committees that define terms within a specific field, but that's different.) Scientists and mathematicians do not get together to decide which terminology is best, and they certainly do not decide such terminology based on whether the general public will find it confusing. Terminology just sort of gets passed around and then eventually sticks. It may even change later on. The crucial property of good terminology is really that experts understand it, not necessarily the general public. + +Scientific illiteracy is a complex phenomenon and is not due solely or even primarily to possibly confusing terminology. Laymen may become scientifically illiterate because of poor education (which occurs for a whole host of reasons). But scientific illiteracy in adulthood is certainly persisted by willful ignorance, poor scientific journalism, media sensationalism, and pseudoscience con artists who are more than willing to maintain and exploit such illiteracy. If we had a different term for ""theory"", we may not hear ridiculous protests like ""it's just a theory!"", but we would still witness plenty of other popular pseudoscience and denial tactics and arguments." "No; a theory is an explanation for the observations that obtain, a hypothesis is a prediction of what observations will obtain. The relationship between the two would look like, ""String theory is true, so I hypothesize that *x* will obtain under *y* conditions. Now let's see if that hypothesis is correct.""" +1277 Can fire occur from a non-oxygenated reaction? 2689 https://www.reddit.com/r/askscience/comments/aul43r/can_fire_occur_from_a_nonoxygenated_reaction/ 1551100385 aul43r Chemistry 2019-02-25 16:13:05 "Depends on your definition of ""fire"". + +But in general, it doesn't matter what the oxidizer is. + +You can put a piece of wood into a chlorine or fluorine athmosphere and it would burn. + +Here's a very nice demonstration with chlorine as the oxidizer and acetylene as the substance to burn. + +https://youtu.be/tFdPh6wlePs + + +Some substances are even more reactive than Oxygen, and can burn stuff that has already been burned or would normally not burn. + +You can burn silicon in oxygen, and get SiO2 or quartz (crystal glass). + +You can now expose this crystal glass to fluorine, and it'll react exothermically to for SiF4 and Oxygen. + + +Another example is explosives. They usually carry their own source of oxygen, like the potassium nitrate in black powder. + + +Then there's the various rocket fuels, that don't contain any oxygen. + +Various hypergolic fuels use a hydrazine and nitrogen Tetraoxide. + +No elemental oxygen is necessary. + +(While the chemicals often used in hypergolic rocket fuels often contain oxygen, that's not strictly necessary, the oxygen containing versions are just much easier and safer to handle, than their chlorine or fluorine containing analogs. And that's for stuff that is supposed to go boom when mixed. So stuff like chlorine trifluoride is pretty nasty, and will burn concrete for example)" It probably depends who you talk to as to how specifically they'd define it. But certainly there are other chemicals that burn exothermically - for example anything that can burn with oxygen can burn with fluorine. Even after it's been burned with oxygen. +61 What is energy? 2685 http://www.reddit.com/r/askscience/comments/30099u/what_is_energy/ 1427115306 30099u Physics 2015-03-23 15:55:06 "There's really no satisfying definition beyond ""the quantity that is conserved over time."" This may sound arbitrary and ad hoc but it emerges from this deep mathematical principal called Noether's theorem that states that for each symmetry (in this case, staying the same while moving forward or backwards in time), there is something that is conserved. In this context, momentum is the thing that is conserved over distance, and angular momentum is the thing that is conserved through rotations. + +http://en.wikipedia.org/wiki/Noether%27s_theorem + +I less rigorous explanation is that it's essentially the currency used by physical systems to undergo change. + +edit: I have since been aware that today is Emmy Noether's 133rd birthday and the subject of the Google Doodle." Nobody can explain it better than Feynman: http://www.feynmanlectures.caltech.edu/I_04.html#Ch4-S1 +176 Is there a single species that would go extinct if humans were to go extinct also? 2684 http://www.reddit.com/r/askscience/comments/37njr4/is_there_a_single_species_that_would_go_extinct/ 1432854632 37njr4 Biology 2015-05-29 2:10:32 Species of lice that infest humans are obligate human parasites, i.e. they can [only live on human hair and skin](https://www.ncbi.nlm.nih.gov/pubmed/12932325) and they [cannot live off other animals](http://www.cdc.gov/parasites/lice/). So if humans were to go extinct, the *Pediculus humanus* habitat would disappear, and they would go extinct as well. "The [kakapo](http://en.wikipedia.org/wiki/Kakapo) requires intervention by humans to survive- Polynesian rats need to be controlled, although I think they have a population on an island without any rats (and aggressive measures to make certain none get there). But with a global population of 126, its existence is tenuous. + +EDIT: Some others I thought of. + +The [Socorro springsnail](http://en.wikipedia.org/wiki/Socorro_springsnail) is known to exist in one pond, on private property. The owner won't let any researchers or feds in to examine its population, which is restricted to a pool of water maybe 1 square meter in size. Barring massive climate change in favor of the critter (unlikely), the springsnail is likely to go extinct in this pool. + +The [Alamosa springsnail](http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=G03Q) suffers a similar problem. + +The [Socorro isopod](http://en.wikipedia.org/wiki/Thermosphaeroma_thermophilum) was extirpated (extinct in the wild) for a short time when a root grew through a supply pipe and the sole pond in which the creature survived dried up. The pool is smaller than 1 square meter. A researcher at University of New Mexico had a small population of the isopod, and it was restored to the wild. Several larger ponds have been constructed to support the isopod, and captive populations are held elsewhere. + +The [Devil's Hole pupfish](http://en.wikipedia.org/wiki/Devil%27s_Hole_pupfish) is another refugial species that exists entirely in one single body of water, and lives and breeds only in the top few feet of a body of water that is at least several hundred feet deep. (Nobody's ever figured out how deep, and at least two divers have disappeared and never been found.) Again, without massive climate change, the species is doomed. + +Wood's cycad (Encephalartos woodii) is doomed; there are only male plants. Without people to propagate it asexually, it will go extinct. + +Similarly, the American chestnut was almost entirely wiped out by chestnut blight. Although plants occasionally come up as suckers from the roots of ancient dead trees, these too eventually succumb by the time their bark goes from smooth to rough as it gives the fungus a way to enter and kill the plant. Researchers are working on both transgenic and hybrid plants (bred with another species, which is then bred back onto American chestnuts, and again, until 99.whatever% American chestnuts can be produced that are resistant to blight. Without these efforts, the species will go extinct. + +" +177 Is it possible to create a device that acts like a mechanical nose to determine what a certain smell is made up of? For example when you notice a familiar scent but you can't explain what it is. 2684 http://www.reddit.com/r/askscience/comments/37z7tf/is_it_possible_to_create_a_device_that_acts_like/ 1433093406 37z7tf Chemistry 2015-05-31 20:30:06 "Yes, those devices exist, and there are several types, but the most common of them is called a gas chromatograph. The principle of operation is fairly simple. A sample that you wish to analyze is injected into a long, narrow column that is packed or lined with absorbent material. An inert gas, usually helium, is flowed through the column to carry all the materials through until they reach a detector at the exit of the column. If you injected a mixture, those different molecules will flow through the column at different rates, allowing you to separate complex mixtures. + +If your detector is coupled to a mass spectrometer, then you can often determine exactly what molecule came out of the column at each point in time. By doing this, many materials, not just smelly ones, can be identified." There is a technology called an electronic nose or a bioelectronic nose. Some of these devices use olfactory receptors from animals attached to a substrate like functionalized single walled carbon nanotubes. The particular olfactory receptor determines what odor is detected and in theory any animal olfactory receptor could be used. When the odorant binds the receptor the receptor changes shape and this can be measured via the nanotube. Very interesting stuff. +383 Were there calculations for visiting the moon prior to the development of the first rockets? 2679 https://www.reddit.com/r/askscience/comments/4ch428/were_there_calculations_for_visiting_the_moon/ 1459280355 4ch428 Mathematics 2016-03-29 22:39:15 "Well, it's hard to answer this question without mentioning Jules Verne's book: from Earth to the Moon, where he spends quite some time doing some calculations on the amount of explosives required to put a huge bullet on the Moon. + +Although most of his calculations were wrong, some of the fathers of astronautics were heavily influenced by the book (Tsiolkovsk and Oberth)." "To be pedantic ""the first rockets"" were invented in China in the 13th century, but assuming you mean ""rockets capable of going to space"" then **yes absolutely!** + +If you take an orbital mechanics course, one of the first things you'll learn is [the Hohmann transfer](https://en.wikipedia.org/wiki/Hohmann_transfer_orbit) which is a mathematical description of how to switch between two circular orbits using an elliptic trajectory. The German scientist Hohmann published this in 1925. + +You'll also learn about [""the rocket equation""](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation) which tells you how much acceleration you can get out of a rocket. This was derived by the Russian scientist Tsiolkovsky, who wrote a ton of work on rockets in the late 1800s and early 1900s. + +[Robert Goddard in 1919](https://en.wikipedia.org/wiki/Robert_H._Goddard#A_Method_of_Reaching_Extreme_Altitudes) published a major work detailing not just orbital mechanics, but also his experiments with various actual rocket engines. He worked out what kind of rocket would be needed to reach escape velocity. + + +Looking at the list of references in my old 1971 book ""Fundamentals of Astrodynamics"", I see a reference to ""An Introduction to Celestial Mechanics"" by F. R. Moulton in 1914." +62 So space is expanding, right? But is it expanding at the atomic level or are galaxies just spreading farther apart? At what level is space expanding? And how does the Great Attractor play into it? 2677 http://www.reddit.com/r/askscience/comments/2ty00j/so_space_is_expanding_right_but_is_it_expanding/ 1422432734 2ty00j Astronomy 2015-01-28 11:12:14 "Oh, I love this one! In fact, I like answering it so much that I wrote an [FAQ answer](http://www.reddit.com/r/askscience/wiki/astronomy/expansion_gravity) about it, and recommend you read that. But for the lazy, here's an executive summary. + +The expansion of space really only makes sense at the very largest scales. There's no ""expansion force"" that's ever-present in the Universe. Instead, it might be more helpful to think of the expansion as a *description* of what's happening. On large scales, galaxies, and other things, are moving away from each other. And on smaller scales, where things aren't moving away from each other (due to gravity), then by definition there is no expansion left. + +--- + +By the way, people will commonly object that there *is* a force driving the expansion, namely that due to dark energy. Dark energy does indeed (or at least should) have an effect on very small scales, and that effect is miniscule and dwarfed by other forces. But that effect actually knows nothing about what the Universe on large scales is doing. The Universe could be accelerating, decelerating, or even collapsing, and on small scales dark energy will always provide a little tiny repulsive force." "Within any gravitationally bound system like a galaxy or galaxy cluster, space is not expanding. + +The Great Attractor is just a big supercluster of galaxies that has a lot of mass and therefore a strong gravitational pull, and its gravity alters the rate of expansion in the region of the universe around it." +384 Why is the amount of work required to accelerate a body from 10m/s to 20m/s three times the work needed to accelerate a body from 0m/s to 10m/s? 2675 https://www.reddit.com/r/askscience/comments/40bi9z/why_is_the_amount_of_work_required_to_accelerate/ 1452436661 40bi9z Physics 2016-01-10 17:37:41 [deleted] There are a bunch of ways to see this, maybe look for the most intuitive. Consider a rock 4 miles high and another 1 mile high. The 4 mile high rock has 4x's the potential energy of the 1 mile high rock. Then drop both rocks. When the bottom rock reaches the ground the top rock will still be 3 miles high. If we wait for the top rock to hit the ground it will only have twice the velocity that the 1 mile high rock had, but clearly it has 4x's the energy of the 1 mile high rock. So why the discrepancy? The work is added as Force x distance. The force is Mg. The top rock is accelerated only twice as long as the bottom rock but for 4x's the distance. As work is Force x Distance we have 3x more energy accumulated by the rock as it falls from 3 miles high to the ground than when it fell from 4 miles to 3 miles. +63 How do plants like lemon trees and chilli bushes hope to spread their seeds and multiply? 2673 http://www.reddit.com/r/askscience/comments/30snot/how_do_plants_like_lemon_trees_and_chilli_bushes/ 1427714122 30snot Biology 2015-03-30 14:15:22 "Capsaicin does not affect birds. Hotness in Capsicum plants actually helps them spread their seeds because it makes them unpleasant for mammals, but still tasty for birds. + +Moreover, you should keep in mind that the fruits you bring up are human-made cultivars, and they are often very different from their wild ancestors, if such are even identifiable any longer. It's not necessary to keep fruits appealing to wild animals if we are spreading and planting them ourselves. + +Many chili peppers are considerably hotter than any wild variety, and I understand lemons have been cultivated for citric acid as well. + +Edit: I've gotten many excellent replies that point out additional details, so I recommend checking them out. It would appear some wild capsicums are hotter than I thought." I'm not sure about citrus, but many large fruited plants are thought to have evolved to [appeal to megafauna that no longer exist](https://www.americanforests.org/magazine/article/trees-that-miss-the-mammoths/). Avocados are an example- a huge amount of biological energy goes into a fatty fruit, and a seed that no animal would swallow. The best the tree could hope for is that a monkey would carry it a few feet. The puzzle makes sense when one observes elephants gorging themselves on avocados, and swallowing the seeds, which survive digestion. +178 What is the temperature of black holes? 2672 https://www.reddit.com/r/askscience/comments/3iwc2m/what_is_the_temperature_of_black_holes/ 1440890038 3iwc2m Astronomy 2015-08-30 2:13:58 "The temperature of a black hole is: + + T_H = hbar c^3 / (8 pi G M k_B) + +Specifically, this is the temperature of the Hawking radiation coming off of the event horizon. I'm not sure if there is a meaningful way to describe the temperature of black hole interiors - that might be a better question for that [AMA going on over there.](https://www.reddit.com/r/IAmA/comments/3iuf6c/we_are_the_international_group_of_theoretical/) + +Anyway, that equation up there looks really fancy, but it boils down to one thing - the temperature T_H is inversely related to the mass M. All those other numbers are just physical constants. This tells you that the larger the black hole, the colder it is. Furthermore, the smaller the black hole, the hotter it is! And, by conservation of energy, if the black hole's event horizon is radiating then it must be losing mass (by E=mc^(2))! This tells us that black holes essentially evaporate by emitting Hawking radiation, burning faster and faster until they've burn out entirely, radiating away the last few thousand tonnes of their mass in a tremendous burst of energy. + +For a few examples, see this table. It essentially tells you the key information of a black hole, if it had the mass of a person or the earth (or Sag A*). + +Example | Radius | Temperature | Lifetime +---------|----------|----------|--------|------- +Person mass | Much smaller than a proton | 10^21 K | A tenth of a nanosecond +Earth mass | A marble | 0.02 K | Age of the universe x 10^40 +Sag A* (Milky Way core) | 33 x distance from earth to moon | 10^-14 K | Age of the universe x 10^77 + + +Also, feel free to play around at [this link](http://www.wolframalpha.com/input/?i=black+hole+%281+solar+mass%29) - it won't give you lifetimes, but you can plug in any mass you want and it will give you the temperature. " Temperature is a concept that wouldn't make any sense inside of a black hole. Remember what temperature is: The average velocity of the parts of something. As a black hole is a singularity, the parts are not moving. You could say it's 0 Kelvin but that would still be kind of silly. +64 Why does eating spoiled food which has been cooked still make us sick? 2649 http://www.reddit.com/r/askscience/comments/2vrwle/why_does_eating_spoiled_food_which_has_been/ 1423842879 2vrwle Biology 2015-02-13 18:54:39 [deleted] "Bacteria and molds produce a variety of heat-stable chemicals through their metabolic processes. These chemicals are harmful to humans if ingested. The toxins produced by s. aureus (*the antibiotic resistant form of which you know as MRSA*) survive cooking. C. perfringens can form a heat-resistant spore, botulinum toxin (botulism) takes extended boiling before it breaks down. + +Molds produce mycotoxins, ranging from things like aflatoxins (*which cause liver cancer in animals*) to trichothecenes (*which inhibit protein synthesis*). + +While you can sterilize rotten food with extended, high temperatures, you're still left with potential mutagens, carcinogens, and teratogens. You're also left with a host of chemicals which will cause anything from minor digestive distress to more extensive liver damage." +385 Do animals get pleasure out of mating and reproducing like humans do? 2648 https://www.reddit.com/r/askscience/comments/4duvr2/do_animals_get_pleasure_out_of_mating_and/ 1460089439 4duvr2 Biology 2016-04-08 7:23:59 "Its hard to define 'pleasure' because an orgasm is probably pleasurable for a lot of species because it's a physiological process but we can't be sure that they experience them in the same way as humans or approach sex with pleasure or orgasm as the goal. [Here's a good summary.](http://www.popsci.com/science/article/2013-09/fyi-do-animals-have-orgasms) + +[Bonobos, a type of chimp, are believed to use sex/pleasure as a social bonding mechanism and they don't seem to be fussy about gender or type of contact.](http://link.springer.com/article/10.1023%2FA%3A1026395829818) + +There are other aspects like rape in animals which are interesting. [Orangutans have been know to ""rape""](https://books.google.co.uk/books?hl=en&lr=&id=iUA0CdGhYksC&oi=fnd&pg=PA281&dq=galdikas+1981+orangutan+rape&ots=TNQNqZeZpr&sig=0ZPOJgvYNAqlD-ZbCxaImrZ4b7k&redir_esc=y#v=onepage&q&f=false) but there is a lot of controversy about using this human term for animals. + +People sometimes say dolphins have sex for pleasure but really there's only [evidence that they have sex outside of the ovulation period](http://www.snopes.com/critters/wild/pleasure.asp) so we assume that means it's for pleasure. + +[It's also a bit of a grey area that females humans don't need to orgasm for reproduction to occur, if we don't maybe animals don't.](http://www.sciencefocus.com/qa/are-we-only-species-females-experience-orgasm) At university a fellow student did her dissertation on how the clitoral orgasm is the equivalent of a penile orgasm because [in utero humans all start out vaguely female and the clitoris sort of becomes a penis.](http://www.78stepshealth.us/human-physiology/development-of-accessory-sex-organs-and-external-genitalia.html) +If that's why the human species are blessed with orgasms it's highly plausible that animals are too because mammalian development is quite similar. + +Basically it's a fascinating topic. Personally I reckon the animals are at it but only certain species approach sex for pleasure, and generally in those cases it's part of social bonding which makes sense. I think it ties in neatly with tickling being sort of pleasant, [the theory being that parent-baby relationships involve tickling to communicate.](http://www.popsci.com/science/article/2010-12/fyi-what-evolutionary-purpose-tickling) Really tickling is evolutionarily weird because you're letting another person/creature near your most vulnerable parts (chest, stomach). Laughter is also unusual because we make some scary faces when we're really laughing. In the ape world teeth baring is usually a big no-no but we do it [as a bonding exercise.](https://www.technologyreview.com/s/421480/the-evolutionary-origin-of-laughter/) + +It's very easy to understand ourselves because we can communicate. I think it's clear that some of our closest relatives like the bonobo use sex for bonding, a bit like we do, but we only understand them and their social structures on our terms and other animals are beyond our comprehension. We can assume a lot of stuff but we can't really know, I've heard foxes at it and it sounds horrifying but maybe that's just what they like to do. + +Edit: Quick edit for clarity around necessity of female orgasm in reproduction and how that relates to animals, courtesy of u\Jedakiah :-)" "Many comments have focused on higher-intelligence species which seem to enjoy sex (so far as we can tell), but at an other point of the spectrum, ""traumatic insemination"" is a thing in some bugs and means the male's penis is used to perforate the female's abdomen and inject sperm into the wound (the sperm then somehow migrates to the genital organs), obviously regardless of the female's intent and commonly against their will (the females do usually have functional genital tracts). + +There are a number of species with highly coercitive sexual practices[0]: + +* if a female *Gerris gracilicornis* (water strider) doesn't want to mate, [the male may attract predators to try and intimidate them into it](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2964456/) +* duck sex is not necessarily about scented candle dinners, [some species have coevolved ballistic penises and spiraling multi-chambered maze-like vaginas](http://phenomena.nationalgeographic.com/2009/12/22/ballistic-penises-and-corkscrew-vaginas-the-sexual-battles-of-ducks/) +* in the amazonian frog *Rhinella proboscidea* [if male pile-on drowns a female[1], the ""winning"" male will just force the eggs out of the dead female and fertilise that](http://phenomena.nationalgeographic.com/2013/02/26/male-frog-extracts-and-fertilises-eggs-from-dead-female/) + +[0] that's not necessarily all that their sexual practices amount to, note, but these are common and well-documented ones which hardly seem pleasurable at least for the recipient +[1] which seems to be a dramatically common occurrence as the species has way more males than females and they gather at mating spots which are mostly sausage-fests: + +> having found several explosive breeding sites in Brazil’s Adolfo Ducke Forest Reserve between 2001 and 2005. The first time, he found around 100 males and 20 dead females. The second time: 50 males and 5 dead females. " +1278 AskScience AMA Series: We're Nick Magliocca and Kendra McSweeney and our computer model shows how the War on Drugs spreads and strengthens drug trafficking networks in Central America, Ask Us Anything! 2648 https://www.reddit.com/r/askscience/comments/bdskbj/askscience_ama_series_were_nick_magliocca_and/ 1555412419 bdskbj 2019-04-16 14:00:19 [deleted] What is the best alternative strategy that you have discovered so far? +65 Why can cheese age for years at a time, yet get moldy after a short time in my home? 2645 http://www.reddit.com/r/askscience/comments/2xl3zx/why_can_cheese_age_for_years_at_a_time_yet_get/ 1425237113 2xl3zx Biology 2015-03-01 22:11:53 [deleted] "Dairy technician and future dairy engineer here. + +Only semi-hard and hard cheeses can age for years. The reason they can age so long is the cheese rind. During the production of the raw cheese you have a process step where you put the cheese in a solution with 20% salt for 2-3 days. Like this the cheese builds a strong rind. The rind gets further strengthened during the ripening/maturing by scrubbing ""ripening solution"" with a scrubber or piece of cloth on it. + +The ripening solution consists of water, salt, calcium and [brevibacterium](http://en.wikipedia.org/wiki/Brevibacterium) on it. The Brevibacterium is not only important for the tase and smell, but also as some kind of defensive system for the cheese. Molds or unwanted microbes have a tougher time growing next to brevibacterium. Also, thanks to the scrubbing process, molds that start to grow will be removed 1-2 times a week. + +In the later stages of the ripening process the unwanted molds only has to be removed once every two weeks, because the the defensive system of brevibacterium has become so strong. + +This is the easy version, if anyone has further questions feel free to ask. + +edit: I suck at editing." +289 Do Aquatic Animals Yawn? 2637 https://www.reddit.com/r/askscience/comments/3vb9xy/do_aquatic_animals_yawn/ 1449168881 3vb9xy Biology 2015-12-03 21:54:41 "Fish yawn as territorial or mating displays it's commonly accepted that all vertebrates yawn. Nobody knows why though here's an article on [why we think people yawn](http://www.jstor.org/stable/27858677?seq=1#page_scan_tab_contents). + +[Here is an article about fetal yawning](http://www.tandfonline.com/doi/abs/10.3109/14722240500284070) " "Cetaceans (whales, dolphins and porpoises) do not yawn. We as auto breathers yawn as a mechanism to increase oxygen in our body when the body realises it does not have enough. It is a completely automatic response that will happen even when we are completely unconscious. + +Due to the risks of automatically taking a breath when underwater, Cetaceans are completely in control and have to think about every breath they take. As such they have no automatic function which will cause them to yawn. This also allows them to stay on a dive much longer than humans as they can lower their bodies oxygen levels much further then we can without this automatic response. They have several other adaptations which help them achieve this state on anoxia including being able to partially shut down their extremities from requiring oxygen and having a much higher haemoglobin count so that when they breathe at the surface they can super oxygenate their blood. On top of this when they breathe they can evacuate up to 90% of the air in their lungs with one breathe, which is far more than we can. + +So basically, if a cetacean is unconscious for any reason in the wild it will die." +179 I made a grilled cheese sandwich with pickles and garlic, but the garlic turned blue after I fried it. What reactions caused this to occur? 2636 http://www.reddit.com/r/askscience/comments/382ln5/i_made_a_grilled_cheese_sandwich_with_pickles_and/ 1433160477 382ln5 Chemistry 2015-06-01 15:07:57 "They're pyrrole derivatives that form in garlic and onions - here's some analytical chemistry on them: http://www.ncbi.nlm.nih.gov/pubmed/16448192 + +It appears to be a reaction between the starting pyrroles and the sulfur-containing compounds, one that doesn't get a chance to happen until the components are mixed by crushing the garlic in air." "There are actually a large number of compounds released when you cook garlic, and low pH - such as from the addition of pickles - helps the reaction proceed. Some compounds implicated include [thiosulfinates](http://pubs.acs.org/doi/abs/10.1021/jf0497455) and [pyrroles](http://pubs.acs.org/doi/abs/10.1021/jf073025r). + +Don't worry about the colour though - green garlic is actually desired in the preparation of [Laba garlic](https://xzone-lidemin.rhcloud.com/fast/laba-garlic/)." +290 What changes does the human body and brain go through between the ages of 18 and 25 ? 2636 https://www.reddit.com/r/askscience/comments/3wolxc/what_changes_does_the_human_body_and_brain_go/ 1450035522 3wolxc Human Body 2015-12-13 22:38:42 This thread is now locked due to an excessive number of anecdotes. "I think the most dramatic development that occurs in the brain during this time is in the prefrontal cortex, which is responsible for decision making, planning, and inhibiting emotional impulses. In adolescence, the relationship between the prefrontal cortex and the ventral striatum (which drives exploratory and sensation seeking behavior) is imbalanced, leading to a lack of inhibitory control. As the prefrontal cortex finishes developing, it allows for ""top-down"" modulation, where the prefrontal cortex can properly regulate those emotional impulses. " +66 Why don't we just shoot nuclear waste of our atmosphere and into the Sun? 2630 http://www.reddit.com/r/askscience/comments/2r43nl/why_dont_we_just_shoot_nuclear_waste_of_our/ 1420217976 2r43nl Engineering 2015-01-02 19:59:36 "**Short answer:** Because it's stupid expensive and it's stupid dangerous if a rocket blows up on the launchpad. Please don't do this. + +**Long answer:** [This question gets asked surprisingly frequently.](http://www.reddit.com/r/askscience/search?q=nuclear+waste+sun&restrict_sr=on&sort=relevance&t=all) So frequently, in fact, that I'm surprised there is no FAQ answer for it. Anyway. + +At the moment, the current cost of launching stuff into orbit is about $20,000 per kilogram of your payload. That's just to get into orbit, that's not counting the additional fuel kick needed to get your vessel going to the sun. Also, that's not counting the fact we can't really recycle these craft that are getting sent to the sun. + +Now consider that there are approximately [270,000 tonnes of fuel waste in storage](http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Nuclear-Wastes/Radioactive-Waste-Management/) (not counting medical waste, or radioactive components from old reactors). + +Now consider that even one accident trying to launch one of these rockets means you've just splattered a ton of radioactive waste all over the launch facility (or worse, the upper atmosphere). Basically, you've just caused another Chernobyl, irradiating an entire region or country, depending on the altitude of the explosion, local wind speeds, nuclear payload, etc. + +But can we design these rockets to be safe? Well sure, they're all safe until they blow up. Spaceflight hasn't had all the bugs worked out yet, [and there are still have incidents on a yearly to monthly basis.](http://en.wikipedia.org/wiki/List_of_spaceflight-related_accidents_and_incidents) Fortunately, these generally [only destroy an unmanned rocket, with a payload of a few satellites, in a big fire ball.](http://wavy.com/2014/10/28/rocket-explodes-seconds-after-launch-from-wallops-island/) That story was from a little over a month ago. Now consider that if even one of our ""waste-to-sun"" shuttles pop, we have just fucked up the environment for years. [And before you say space elevators, they won't help.](http://www.reddit.com/r/askscience/comments/2r43nl/why_dont_we_just_shoot_nuclear_waste_of_our/cncdhpu) Rail guns or cannons? [Please no.](http://www.reddit.com/r/askscience/comments/2r43nl/why_dont_we_just_shoot_nuclear_waste_of_our/cncapuw) Space, as empty as it is, is a terrible junkyard. + +All in all, we're better off shooting them into the *core of the Earth.* Of course, by that, I mean burying it. It's closer, and it's less dangerous. If we're lucky, sometime in the future, someone will work out a way to transmute certain wastes into usable fuel really cheaply, or accelerate the decay of the really nasty stuff so that it won't be radioactive for millions or billions of years. + +Please, if you have a rocket capable launching from the ground and escaping low earth orbit and large amount of radioactive waste to discard, don't do it. Call up your local division of the Department of Energy or Environmental Protection Agency and they'll get you in touch with appropriate waste disposal agents. Don't tell them about the rocket though, I can handle that- just PM me when and where I can pick it up. I can find something to do with it. " "Every top-rated reply is missing the most important thing: There is still a LOT of very useful energy left in that ""waste"". It's only ""waste"" because our government currently prohibits the types of (safe) reactors which would complete the nuclear fuel cycle. That will change eventually because it simultaneously fixes the ""waste problem"" and can produce perfectly clean, safe energy along side renewables. " +180 What allele frequency is changing fastest in the human population? 2629 http://www.reddit.com/r/askscience/comments/36dlf3/what_allele_frequency_is_changing_fastest_in_the/ 1431962697 36dlf3 Biology 2015-05-18 18:24:57 "edit: I realize I sort of jumped into the deep end here. If you don't know what ""allele frequency"" means, see [here](http://www.reddit.com/r/askscience/comments/36dlf3/what_allele_frequency_is_changing_fastest_in_the/crd6i6n?context=1) and let me know if you have follow up questions. + +_________ + +Answering the question of what allele frequencies **are currently** changing the fastest is not necessarily that easy, as human generation times are long enough that it's not that easy to observe it happening in real time. + +There have been a number of statistical techniques developed to identify very recent positive selection. Summarizing the literature in a reddit post would be difficult, so I'll try to give just a few highlights. One of the most exciting developments in this field is the recent arrival of so called [ancient DNA](http://en.wikipedia.org/wiki/Ancient_DNA), or the ability to sequence/genotype individuals who have been dead for thousands of years. There is [a paper](http://biorxiv.org/content/early/2015/03/13/016477) currently posted on a preprint server which examines the genomes of 83 humans who lived in Europe in the range of 4000-8000 years ago, and compares their genomes to a number of present day populations within Europe. They find just 6 loci that show robust evidence of recent positive selection (i.e. very rapid allele frequency change). Two of them, at genes called SLC24A5 and SLC45A2 are [associated with (but not entirely responsible for)](http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1003372) differences in skin pigmentation between Africans and European. + +Another one, called rs4988235, is largely responsible for the ability of Europeans to continue digesting lactose (i.e. drinking milk) well into adulthood, and [has been known of for a while](http://www.sciencedirect.com/science/article/pii/S0002929707628389). + +Another example is a marker called rs12913832, located near two genes called OCA2 and HERC2, which is in large part responsible for blue eyes and possibly also associated with lighter hair pigmentation ([1](http://www.sciencedirect.com/science/article/pii/S0002929707000407),[2](http://link.springer.com/article/10.1007/s00439-007-0460-x#page-1),[3](http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1000074#pgen-1000074-g003)) + +The other two strong signals found by the ancient DNA studied cited above are in two genes related fatty acid metabolism and circulating vitamin D levels, suggesting possibly adaptation to diet. + +These are just regions that have been identified as the strongest signals within the continent of Europe. It's pretty widely recognized at this point that to the extent that positive selection has had any impact on recent human evolution (and it's not all that clear that the effects have been that major), [the effects differ from one region to the next](http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1000500). + +I won't give a whole rundown, as that would make this even more ridiculously long (and because Europe is, predictably, the best studied region for this question), but for example populations of Tibetan highlanders appear to have undergone very recent adaptation in a region of their genome which allows them to better tolerate the thin atmospheres they live in, and the it appears that [the allele that they are using to do so actually came from ancient interbreeding with an archaic group of now extinct humans called Denisovans](http://www.nature.com/nature/journal/v512/n7513/full/nature13408.html), who are more closely related to Neanderthals that they are to us. + +In Africa, for example, there has also (in some regions but not in others) apparently [been strong selection for a number of alleles which allow their carriers to digest milk into adulthood](http://www.sciencedirect.com/science/article/pii/S0002929713003261), but the alleles that have been targeted by selection in Africa are different than the ones that have been targeted in Europe. + +edited to add: It should be emphasized, however, that it maybe the case that *none* of these regions are any longer experiencing strong natural selection, and therefore may not be changing very fast in frequency ""right now"". I would expect, however, that we will see studies within the next few years that sequence/genotype large numbers of individuals spanning multiple generations of presently living individuals and try to identify regions which are currently the target of natural selection. Whether or not we will find anything interesting doing this remains to be seen." ELi5: allele frequency +67 Is it possible for something to be so hot that it emitted little to no radiation in the visible band, thereby appearing dark? 2628 http://www.reddit.com/r/askscience/comments/334lnn/is_it_possible_for_something_to_be_so_hot_that_it/ 1429453288 334lnn Physics 2015-04-19 17:21:28 Rather than *shifting* toward shorter wavelengths, getting hotter could be better thought of as *adding* extra radiation at all wavelengths, just particularly so at shorter ones. Thus a hotter object is brighter at *all* wavelengths than a cooler one, including very long wavelengths. "No, Blackbody emission occur over a maxwellian distribution. An extremely hot body would still have a part of the emission curve be in the visible spectrum. +If you look at this image, + +http://quantumfreak.com/wp-content/uploads/2008/09/black-body-radiation-curves.png +You can see that the peak keeps shifting to the left, and it will eventually be out if the visible range. But there is still a tail that trails off to the right and the hotter the star is, the more significant the tail is. Therefore, no matter how hot a star is, it will never become dark. " +68 Why do people go bald on the top of their heads, but not the sides? 2626 http://www.reddit.com/r/askscience/comments/2tnxzw/why_do_people_go_bald_on_the_top_of_their_heads/ 1422229409 2tnxzw Human Body 2015-01-26 2:43:29 "I'm sure someone with a more detailed answer will respond, but the hairs on the top of the head are structurally different from the ones on the side. When you start to get older, your body starts converting testosterone in your body to dihydrotestosterone (DHT) at a steadily increasing rate (until you hit your developmental peak, which for males is somewhere between late twenties to mid thirties). + +EDIT: /u/TheTousler and /u/hatetheloss contributed this correction: As we age, our hair follicles become more sensitive to DHT. Amount of DHT doesn't increase, but sensitivity in the hair does. + +The increased amount of DHT (which is essentially more potent than testosterone alone) affects the hair follicles with the certain protein makeup on the top of the head, effectively killing them. The ones of the side are spared of this horror. + +It's why those who use steroids typically use Propecia in concert, and also why it happens in middle age. It's why most elite level athletes are in their late 20's when they hit their peak-more DHT in the body. Hair transplants work by using hairs that don't have the faulty genetic make up and moving them to the top. + +EDIT: I'm adding some more information from a reply I made below regarding genetics: + +Well that's where those of us who lost our beautiful flowing manes lost out on winning the genetic lottery:/. Genetics play a big part-I have the gene for the weaker hair on the top of the head, whereas my significantly older father in law does not. + +" I am a former trichologist for a very successful hair retention clinic. Many of the answers given refer to DHT. Male pattern thinning occurs when built up DHT binds with receptors in the follicle. This causes the follicle to gradually produce thinner and thinner individual hair stands with each shedding and growing cycle. Eventually the hair is too weak to support the follicle, which then collapses. Once that happens that hair and follicle are gone for good. Your question, however, was about why thinning occurs on the crown and vertex and not the sides. The answer is quite simple, actually. We do not have those receptors on the sides. This is also why those rear and side follicles are used for hair transplants. Have you ever seen someone who looks like they had a bad transplant? Those strong rear and side follicles are like tree trunks so they are surgically interspersed among the thinner hair on the crown and vertex. Over time those original hairs disappear completely and leave only the transplant hairs on top, which now look unnatural. Think Cheech Marin from Things Are Tough All Over. +386 What did the Wow! Signal actually contain? 2618 https://www.reddit.com/r/askscience/comments/4ahmkw/what_did_the_wow_signal_actually_contain/ 1458031556 4ahmkw Astronomy 2016-03-15 11:45:56 "The Wow! signal didn't actually contain any information. It was simply a narrow-band radio source that varied in intensity over roughly 72 seconds. There are a few reasons why it's of interest: + +1. The frequency of the signal occurred almost exactly at what's known as the hydrogen line, which is the resonant frequency of hydrogen. Most SETI researchers agree that this is exactly the frequency an extraterrestrial intelligence might use to transmit information because of it's mathematical importance and because it is able to travel well across space without getting blocked by gas and dust clouds + +2. Its peak intensity was roughly 30x greater than the normal background noise. + +3. It could not be attributed to any terrestrial source. + +On the other hand, there are number of reasons why it's not a smoking gun or definitive proof: + +1. Despite exhaustive search with better telescopes, the signal could not be found again. + +2. It came from a region of space with few stars, which brings into question whether or not it could be from an alien civilization. + +In short, there are more questions than answers. While it seems unlikely to have come from earth, that possibility can't be ruled out, nor can the possibility that it may have home from an as-yet unknown astronomical phenomenon. There's simply not enough data to draw a conclusion with any certainty. +" "I'm a radio astronomer who specializes in transient signals, which is a fancy way of saying I've spent a bit of time looking into what we'd do if something like the Wow! signal happens again (among other things). So while you got a good summary of details of the signal, here are my own professional opinions on it, though I should note other astronomers may tell you otherwise. + +First, the biggest thing we should note about the Wow! signal is scientifically it's really fun to think about, but in science it is impossible to say much about the signal or what it was unless we see it or a similar signal again. This happens a decent more with natural sources than you'd think- for example, I am on a recent paper with a collaborator where we found a transient radio signal where that signal was ""on"" for 4 minutes of an 11 minute data stretch, then disappeared and wasn't seen again. No idea what it was, but we are fairly confident it was real over some random issue with the data or similar (as that was by far most of the analysis that we went into), but until you see it again or something similar from another part of the sky there's not much you can say for sure beyond ""we saw this strange thing."" + +I should also note that in my experience in this field, by far the most common thing you find are not real astronomical signals but radio frequency interference (RFI) from manmade sources. Some of this stuff can be super subtle- I was for example detecting one second radio flashes in a recent data set that looked transient, but if you looked at the frequency information more carefully it turns out it was really narrow in frequency (astronomical sources tend to be broadband, ie over many frequencies). Turns out when meteors hit the upper atmosphere they briefly leave behind an ionized trail of material, and the audio carrier signal for TV stations in France was bouncing off those trails, and my radio telescope was picking them up. Holy hell- RFI is annoying!!! + +So with that, I find it much more likely than not that this was a strange bit of RFI, but it's impossible to say so without seeing the signal again (yea, I keep saying that, but it's true). I read an analysis once that basically while it can be difficult to explain a constant 72 second source in the sky as RFI (which I agree with), a satellite in polar orbit would send out a signal similar to the Wow! signal, for example. No way to say it wasn't that, or some other RFI, or actually something from deep space. Finally, I should note that it was not an RFI source local to the radio telescope itself, ie within a few miles- we can tell because it had two feed horns (ie detectors) and only one saw the signal, but manmade local RFI would have appeared in both. + +TL;DR- in this astronomer's opinion, the Wow! signal is fun to think about, but until we get more information it's impossible to know for sure what it was" +69 AskScience AMA Series: I’m Monica Montano, Associate Professor at Case Western Reserve University. I do breast cancer research and have recently developed drugs that have the potential to target several types of breast cancer, without the side effects typically associated with cancer drugs. AMA! 2610 http://www.reddit.com/r/askscience/comments/2verix/askscience_ama_series_im_monica_montano_associate/ 1423569878 2verix Medicine 2015-02-10 15:04:38 "So your drug target is inducing HEXIM1? + +Whats the ""normal"" role of HEXIM1 in the cell? + + biochemically how is it a ""reset"" button and what does it mean to reset a cell (reset the cell cycle?) + + what does induction of HEXIM1 in a normal cell usually do? + +Thanks for the AMA" What type of research still needs to be done before its a viable solution? +387 Are photons taking longer to travel due to expansion of universe? 2606 https://www.reddit.com/r/askscience/comments/462o0f/are_photons_taking_longer_to_travel_due_to/ 1455633034 462o0f Physics 2016-02-16 17:30:34 "Yes, definitely. The idea that the universe is expanding is not a metaphor, but is a very real physical process. The distance between faraway clumps of the universe really is getting larger with time. + +For example, we define the observable universe by the furthest objects we could observe because their light would have had time to reach us. Considering that the universe is about 14 billion years old, in a static universe that would come out to a distance of 14 billion light years. But in reality when the light we now receive was emitted, the sources must have been much closer to us than 14 billion light years, but it took so long to reach us because the distance it had to cross was continuously increasing as the light was traveling! + +If you like a more visual explanation, take a look at [this diagram](http://i.imgur.com/3Pj1XlE.png), which captures the same idea. ([source](https://dournac.org/info/light_geodesics)) + +edit: added the figure and fixed some units" "Related question (sorry if it doesn't make sense, english is not my primary language): + +If all objects in the universe are getting farther away from each other due to expansion, and the farther away they get, the faster they move away from each other. Will we ever get to a point where the speed of the expansion reaches C and no light will ever get from one point to another?" +181 Do animals learn that cars only stay on the road? 2605 http://www.reddit.com/r/askscience/comments/37w1el/do_animals_learn_that_cars_only_stay_on_the_road/ 1433022066 37w1el Biology 2015-05-31 0:41:06 "Better than that, Crows have been observed to walk to the other side of the white line (in the US, the white line marks the outside shoulder of the road) wait for the car to pass, and walk back to doing whatever it was doing. + +Furthermore, some birds have been observed to know the speed limits of the road: https://www.sciencenews.org/article/birds-know-road-speed-limits +Thanks, /u/HowCouldUBMoHarkless" Dogs in Moscow, Russia are well known for their ability [to navigate complex Moscow subway](http://abcnews.go.com/International/Technology/stray-dogs-master-complex-moscow-subway-system/story?id=10145833). They get on and off the trains, ride escalators and are more courteous then 90% of human subway passengers. +182 So broadly speaking, white reflects radiation and black absorbs radiation. Then why do paler people experience sun damage so much faster than darker people? 2600 https://www.reddit.com/r/askscience/comments/3iln47/so_broadly_speaking_white_reflects_radiation_and/ 1440684933 3iln47 Biology 2015-08-27 17:15:33 The purpose of melanin is not to reflect light. Melanin actually absorbs the UV radiation from the sun. Without sufficient melanin the UV radiation penetrates our skin cells and damages the DNA. If you're out in the sun without protection long enough the DNA damage gets severe enough to kill the cells resulting in various degrees of sun burn. "Since you're interested in this topic, here's another semi-related bit of information. + +We know radiation from the sun is dangerous because it damages our DNA... Well what other organisms do you know that have DNA, and also sit in the sun all day soaking up sunlight? Plants! And reptiles! + +Well what the heck? They have DNA just like us! So why aren't they being damaged? + +It's due in part to one of my favorite little enzymes named photolyase! This group of enzyme's sole job is to repair damage to DNA that is specifically done by UV radiation from the sun (pyrimidine dimers). + +This gene is still present in mammals, but no longer functioning. Imagine if we could use some genetic engineering to turn this gene back on in humans and start producing that enzyme again? The future will be exciting. " +1443 AskScience AMA Series: We mapped human transformation of Earth over the past 10,000 years and the results will surprise you! Ask us anything! 2600 https://www.reddit.com/r/askscience/comments/dmvtev/askscience_ama_series_we_mapped_human/ 1572001255 dmvtev 2019-10-25 14:00:55 Does your work shed light on the question of whether humans were a primary cause of megafauna extinctions in Australia and the Americas 10k years ago? Where did humans have the biggest impact on Earth in the Paleolithic era? +388 With a heavy vehicle trying to stop on snow, what is the relationship between the higher mass increasing traction on the snow, but also increasing the momentum that has to be stopped? 2596 https://www.reddit.com/r/askscience/comments/44aw41/with_a_heavy_vehicle_trying_to_stop_on_snow_what/ 1454680267 44aw41 Physics 2016-02-05 16:51:07 "That's an interesting question, let's look at the math. +As you point out, there are two factors at work here. + +First is the kinetic energy of the vehicle, +Ke=1/2 m*v^2 +M is the vehicle mass, v it's speed. + +Second, there is the friction term. This one changes depending on whether or not the car is sliding or the tires are rolling like normal, but in either case the equation takes on the form +F=u*m +Where u is a friction constant times g. + +To compare these, we need to look at how force translates to energy - we need to integrate the acceleration term with respect to the distance over which it is applied. this is easy- +F*x= delta E. + +So, for the force of friction to cancel out the kinetic energy of the car, + +F*x=delta E = u*m*x= 1/2 m*v^2 + +It looks like the masses cancel out here. + +u*x= 1/2 v^2 + +We can collet all constants to say that + +X is proportional to the square of v. + +In this case, x is the distance needed to brake, and v is your car speed. + +Conclusion: according to classical dynamics, braking early and ESPECIALLY driving slowly are more important than the weight of your car. + +Edited as per physicistphill's suggestion. " Putting weight in the back of a pick up is strictly to get enough traction to drive. Rear wheel drive pick ups don't have enough weight over the wheels otherwise. Most cars (I don't know of any non-sports cars) are front wheel drive and has the engine pushing down on those wheels to keep them from spinning (to a degree). +183 "According to the theory Earth's magnetic poles flip about every 450,000 years known as "" Geomagnetic reversal"", if Earth's magnetic field is due to rotating molten iron in our core, does it mean the magma starts to rotate immediately in opposite direction at that time?" 2595 http://www.reddit.com/r/askscience/comments/3ddmyk/according_to_the_theory_earths_magnetic_poles/ 1436966469 3ddmyk Earth Sciences 2015-07-15 16:21:09 "At this point, I think it would be fair to say we have an incomplete understanding of exactly why the Earth's magnetic field flips. We do know that geomagnetic reversals are something that happens in models of the [geodynamo](https://en.wikipedia.org/wiki/Dynamo_theory), so it's not as though we have no explanation for the occurrence. One of the first models to show this was [this paper](http://www.nature.com/nature/journal/v401/n6756/full/401885a0.html), but there have been numerous models that have demonstrated similar behavior, e.g. [this paper](http://www.sciencedirect.com/science/article/pii/S0012821X11000550), [this paper](http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.2009.04234.x/abstract), [this one](http://onlinelibrary.wiley.com/doi/10.1029/2003GC000602/abstract), [this one](http://link.springer.com/chapter/10.1007%2F978-3-540-76939-2_4), [this one (not behind a paywall)](http://www.ipgp.fr/~aubert/DMFIPaper.pdf), [this one](http://www.sciencemag.org/content/309/5733/459), or [this other one](http://www.sciencedirect.com/science/article/pii/S0031920110000440), and many many more. The key aspect is that these models are all able to produce reversals despite very different parameters, including different rates of rotation within the dynamo and different thermal or chemical gradients as partial driving forces. So, we know generally how it happens, but narrowing it down to how exactly it happens (and what is exactly driving it) is challenging, i.e. we have a set of reasonable solutions, but not a unique solution. + +An important aspect of this in terms of validating various models, is that it's only recently that we have begun to develop global and high temporal resolution records of geomagnetic field orientation and intensity across reversals within the geologic record. The hope is that as we continue to build and improve these records across reversals, that we can begin to weed out the geodynamo models that produce reversals but that don't match what we know about field direction and intensity across reversals." "This is a tough question because of all the unknowns. The best answer would be an astounding, ""We don't have the slightest clue."" The geomagnetic reversal of earth's poles is still a relatively new thing, and most research starts within ~50 years. On top of that, we still can only speculate on what the core of our planet is exactly composed of or even what sort of exact motion it may have (if any). There may a be solid inner core rotating one direction inside a fluid outer core that has a general opposite flow, or they may go the same direction, or the inner core may be stable relative to the crust. There's so many unknowns about this, and that's what makes it so interesting! We still have a lot to learn." +291 Does sound stack? 2591 https://www.reddit.com/r/askscience/comments/3qp55b/does_sound_stack/ 1446123633 3qp55b Physics 2015-10-29 16:00:33 "The short answer is that in most cases when you add two sources of sound waves, then the net intensity (and the loudness) will be higher than that of each individual source (and in many cases will simply be the sum of the intensity of each source). This is why a crowd of people is so loud even when any given person is speaking reasonably quietly. + +The longer answer is that to a good approximation sound waves produced at different sources do not affect one another, but instead simply add up. This behavior is an example of the so-called [superposition principle](https://en.wikipedia.org/wiki/Superposition_principle). Now I use the word ""add up"" a bit loosely, there are certain configurations when you can add two waves in such a fashion that the overall intensity perceived by an observer would be lower than if only one of the waves were present (this is roughly how noise canceling earphones work). This is because waves can interfere with each other, and this interference [as shown here](http://method-behind-the-music.com/mechanics/images/interfere.png). + +However, when you have a bunch of waves produced from all directions and with a wide variety of frequencies (what we can more formally call uncorrelated waves), you can largely ignore the effect of interference and to a decent approximation you can estimate the intensity at a given point to simply be the sum of the intensities of each of the individual waves. So if five people are talking equally loudly and you are in the center, you will hear a noise with an intensity five times higher than if a single individual stood there. " "The other poster explained it pretty well, I'll just add that if you want to find out what the sum dB value for two non-coherent sources (this is key, no interference between the sources) is, you can do + +10*log10(10^(a/10)+10^(b/10)) + +Where a and b are dB values of the two individual sources. + +In general, if you have two sources of the same power, their sum will increase by 3.01 dB. So if you have two loudspeakers at 90 dB each that are not interfering with each other, the total sound pressure level will be 93dB." +292 Is a cat's field of view the same as ours, or is it more ovular as opposed to circular because of their pupils? 2589 https://www.reddit.com/r/askscience/comments/3q1oaz/is_a_cats_field_of_view_the_same_as_ours_or_is_it/ 1445704813 3q1oaz Biology 2015-10-24 19:40:13 "There are important differences between the vision of cats and humans, however these are not due to the field of vision, which is fairly similar for us and cats, extending out to 180^(o) and 200^(o) respectively. Instead, the shape has more to do with how blurry objects look when you move out of focus either vertically or horizontally. These differences are actually quite important, which is why mammals have there different types of pupils: circular [(as in humans)](http://www.humintell.com/wp-content/uploads/2009/09/her_light_blue_eye-t2.jpg), horizontally elongated [(as for sheep)](https://upload.wikimedia.org/wikipedia/commons/d/d7/Eye_Coburger_Fuchsschaf.jpg) or vertically elongated [(as for cats)](http://orig07.deviantart.net/d9e2/f/2007/045/a/2/1500_px_cat_eye_by_hoschie_stock.jpg). What is interesting, is that the shape of the pupil appears to be closely linked to the biological role of the species in question (e.g. prey vs predator), as studied [in this recent paper](http://advances.sciencemag.org/content/1/7/e1500391). + +It turns out that predators often have vertically elongated slits, while species that tend to end up as prey (e.g. sheep) usually have horizontally elongated slits. The reason for this difference is that each shape has certain advantages, which suit certain species better than others. One key advantage of a horizontal pupil is that it allows the eye to collect more light in a direction parallel to the ground. As a result, it becomes easier to make out horizontal contours (outlines) and to maintain a panoramic view in a horizontal plane. I think it's easy to see how the ability to easily scan the surrounding horizontal region is useful for animals for whom the biggest threat is becoming a snack for a predator sneaking up on them. + +In contrast, for predators a vertically elongated pupil presents more advantages. First of all, the elongated shape makes it easier to dramatically vary the total area of the pupil (by a factor of 100 in cats), which makes it possible both to see (and hunt) during they day, but also to then open up the pupil during the night and have dramatically improved night vision. Secondly, a vertical slit allows for better depth perception along a vertical axis based on out-of-focus blurring. To get a sense for what this means, take a look [at this picture](http://i.imgur.com/xtFz0Lo.png) taken using a camera with a vertical slit. Notice how the picture becomes blurrier faster as you move up and down then when you look laterally. These visual cues aid depth perception, which allows ambush predators to more accurately assess the distance to the prey they are stalking. " "[The 'Sight' section of the Wikipedia article on cat senses gives a quick answer answer your question about the field of view.](https://en.wikipedia.org/wiki/Cat_senses#Sight) Cats have a 200° field of view, which is slightly wider than a humans 180° field of view, but they have less binocular coverage, which means more of what they see is only visible with one eye. + +The field of view isn't related to the shape of the pupil, but the shape of the cornea and lens. The pupil is an aperture, which primarily effects the [depth of field](https://en.wikipedia.org/wiki/Depth_of_field) and the amount of light exposed to the retina. As a pupil closes it lets in less light, making it easier to see in sun light, but much more difficult at night, and decreases the [circle of cofusion](https://en.wikipedia.org/wiki/Circle_of_confusion), which is the area that an out-of-focus point is spread across, making out of focus objects less blurry. As the pupil opens, the opposite happens: it is easier to see at night and more difficult in sunlight, and out of focus objects are less clear. The Moken people in Thailand teach their children to make their pupils as small as they can while swimming, [to reduce the blur while swimming under water](http://thekidshouldseethis.com/post/67377639715). Cats also purposefully control the size of their pupils, [expending them when striking](https://youtu.be/t5h292U_nZM), limiting their focus to a small plane, but letting much more light onto their retina. + +The circle of confusion any aperture creates, including the pupil itself, is shaped like the aperture, so the shape of bright, but out of focus, points of light would be the most visible difference between the image a house cat views and the image a human views. [You can create images with a custom shaped circle of confusion, by cutting an aperture into a mask and placing it over any lens with a large, completely open aperture.] Doing this with a cat pupil shaped slit would give you a cat's point of view." +70 How big of a nuke would be needed to disperse jupiter? 2588 http://www.reddit.com/r/askscience/comments/34a27v/how_big_of_a_nuke_would_be_needed_to_disperse/ 1430317668 34a27v Physics 2015-04-29 17:27:48 "**Short answer:** You'd need about 10 quintillion nukes, which is 4x the mass of the moon, to destroy Jupiter. That, or, a pile of TNT approximately equal to the mass of the sun should do the trick. + + +**Long answer:** + +> Please be serious. + +I make no promises. + +The gravitational binding energy of a spherical mass is given as: + + Potential energy = 3 x (Gravitational Constant) x (Mass)^2 / 5 x (Planetary Radius) + +So, to a first approximation, we need to *add* at least this much energy to the center of Jupiter to blow it apart. Of course, no bomb will be perfectly efficient because a lot of energy will likely get radiated as heat so we'll probably need considerably more energy than this... but it's a good first approximation. + +Anyway, the mass of Jupiter is about 2x10^27 kilograms, which is about a thousandth of the sun. The radius of Jupiter is about 70000 km, which is about a quarter of the distance from the earth to the moon, so the total binding energy is about 2x10^36 Joules, [and Wolfram actually knows the answer already without me having to plug in numbers](http://www.wolframalpha.com/input/?i=gravitational+binding+energy+of+jupiter). + +For reference, that's comparable to [the total energy output of the sun over a century](http://en.wikipedia.org/wiki/Orders_of_magnitude_%28energy%29) But that's boring, you didn't want the sun to unbind Jupiter, you wanted nukes to do the heavy lifting. + +As is tradition, we use the Tsar Bomba. The Tsar Bomba produced the largest manmade nuclear detonation, releasing 2x10^17 Joules of energy. We'd need close to 10^19 of these bombs. This number is so big that I don't even know the word for it off the top of my head- [I had to look it up to make sure I had it right](http://en.wikipedia.org/wiki/Names_of_large_numbers). I'd be content to call it a fucktillion, but for the sake of accuracy I should say that this is equal to ""10 quintillion"" or ""ten billion billion."" Even if each of these nukes cost 1 American penny, with the approximately $100 trillion in equivalent cash on earth, you could only buy 1/1000th the number of nukes you'd need. + +Anyway, [Wikipedia](http://en.wikipedia.org/wiki/Tsar_Bomba) tells me the Tsar Bomba had a mass of 27 tonnes, so this pile of nukes would have a mass of about 2x10^23 kg. This is about 4x the mass of the moon. Let that sink in. A pile of nukes 4x more massive than the moon is needed to destroy Jupiter. + + +Another fun unit is TNT equivalents- for the same blast yield as the nuke, how much TNT do you need? The Tsar Bomba was equivalent to about 50 megatons of TNT. ""Megaton"" being millions of tons. For 2x10^19 piles of TNT, [you'd need about 10^30 kg.](http://www.wolframalpha.com/input/?i=50+megatons+*+2*10^19+in+kg) That's *half the mass of the sun.* + +Crazy, right? That means that even if you made a Jupiter out of TNT and you blew it up, there wouldn't be enough energy from the explosion to blow the planet apart- it would puff up, but gravity would still be able to pull it back together. If anyone can recommend a good Minecraft mod where I can simulate this, I'd be grateful. + +You can actually use this info about the binding energy, along with the energy and mass density of TNT, to calculate the maximum mass for a pile of TNT that will be able to gravitationally unbind itself. For example, a single stick of dynamite should be able to blow itself apart without gravity pulling it back together, but a solar mass worth won't be able to overcome gravity. +[Anyway, it turns out the maximum mass of self-unbinding TNT is equal to about 10^21 kg.](http://www.wolframalpha.com/input/?i=%28+%284.184+gigajoules%2Fton%29+*+%283*+0.055+%28cc%2Fg%29^1%2F3%29+%2F+%283*gravitational+constant%29%29^%283%2F2%29) This is a little less than the mass of Pluto, so handle with care." Bit more practical question: would it be possible to blow away most of Venus atmosphere with nukes? So pressure becomes similar to Earth and it hopefully cools down to something terraformable. How many nukes would we have to use? +71 Is it strictly impossible for two human beings to have the exact same genetic code or is it just astronomically improbable? 2587 http://www.reddit.com/r/askscience/comments/3125dq/is_it_strictly_impossible_for_two_human_beings_to/ 1427898163 3125dq Biology 2015-04-01 17:22:43 "Ignoring the existence of identical twins who do have the same genetic code (minus any somatic mutations that happened during their lives) technically it's possible, but will never happen because the odds are so high. + +If it did happen it would be more likely in a very inbred family so there's little genetic variation to start. " "There's nothing impossible about it. The Universe doesn't keep track of every single person's genetics and magically edit each new baby's DNA just to make sure they don't match an existing person. + +It is extremely unlikely, though. Even with identical twins, the mutation rate is estimated to be high enough that there is usually some piece of the twins' genomes that doesn't precisely match up." +184 If a hummingbird is in a car traveling 100 mph, and the car stops quickly, will the hummingbird hit the front windshield? 2586 http://www.reddit.com/r/askscience/comments/39aabv/if_a_hummingbird_is_in_a_car_traveling_100_mph/ 1433935491 39aabv Physics 2015-06-10 14:24:51 "The bird will almost certainly hit the windshield for the same reason that a human in the car would hit the windshield and the same reason the air would slam into the windshield, namely inertia as your professor said. The bird has an initial velocity of 100 mph in the +x direction where x is the direction of travel, when the car suddenly stops it will still keep moving in this direction until it is acted on by another force as per [Newton's first law](http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_first_law), and in this case the main force in question will be that imparted by the windshield, which will create an effective force -F in the opposite direction to the car's initial motion and will cause the bird to stop in place. + +The only reason I hesitated at all to be completely definitive is that this question brings up the classical counter-intuitive example of what happens to a helium balloon in an accelerating car. As this [common demonstration shows](https://www.youtube.com/watch?v=XXpURFYgR2E), a helium filled balloon behaves in exactly the opposite manner of a dense object, e.g. when the car starts the balloon also moves forward while a human passenger would be jerked backward. However, the mechanism that it at play here is different. The behavior of the balloon is explained by [buoyancy](http://en.wikipedia.org/wiki/Buoyancy) and the fact that the balloon filled with helium is less dense that the surrounding air. When the car stops and the air (because of inertia) continues to move forward, this temporarily creates a higher density of air at the front of the car, which in turn creates a pressure gradient which moves the balloon in the opposite direction (i.e. backward). + +However, flying, even if it also achieves the effect of keeping the bird up in the air still represents a fundamentally different scenario than if the bird were suspended in the air by buoyancy (i.e. if it were less dense than the air). When flying, the bird can remain in the air because it generates enough lift by flapping its wings to counteract the effect of gravity and drag (air resistance) as shown in [this diagram](http://www.ornithopter.de/english/images/gait/cruise_flight.gif). When the car suddenly stops, and the air continues to move forward, so will the bird, because there will be no force strong enough to counteract the bird's initial velocity until it will hit the windshield." You're thinking of that helium balloon effect where the air moves forward in the cab of the car and pushes the balloon back. But it only happens that way because helium is less dense than air. A hummingbird is more dense than air, which you know because they have to flap their wings to fly. It would hit the windshield as surely as it would hit the ground if it stopped flapping its wings. +389 Absent of some form of abuse, is asexuality scientifically supported as a fixed or innate condition? 2573 https://www.reddit.com/r/askscience/comments/4979zz/absent_of_some_form_of_abuse_is_asexuality/ 1457270281 4979zz Psychology 2016-03-06 16:18:01 "Understanding asexuality is an active area of research in psychology and sex research. My reading of your question is that it implies that the only way for a sexual orientation to have ""basis in science"" is for it to be an ""innate state"". The appeal to essentialism (and genetic essentialism at that) to validate a sexual orientation is a little misguided, since studying the environmental factors that give rise to sexual identity is equally scientific and does not undercut the validity of any particular sexual identity that may be more or less influenced by environmental factors. The discourse on minority sexual orientations has created this situation where being ""born this way"" is the only way for a minority sexual identity to be taken seriously, which reinscribes the whole topic in terms of essentialism and innateness, which can be destructive. You do touch on plasticity and fluidity in your second question, which is something I know less about in terms of scientific study. But, as other commenters have pointed out, asexuality itself is something that exists on a spectrum - some of them have romantic partners who they don't have sex with, some of them masturbate but don't have sex, etc." "I don't know of any research that has directly examined the genetics of asexuality, but the research that does exist points to evidence that it is an enduring trait. For instance, from **[Bogaert 2004](https://www.researchgate.net/profile/Anthony_Bogaert/publication/8220138_Asexuality_Prevalence_and_associated_factors_in_a_national_probability_sample/links/5460c7fc0cf27487b4525dac.pdf)**: + +>As shown in Table 1, relative to sexual people, asexual people +had fewer sexual partners, had a later onset of sexual +activity (if it occurred), and had less frequent sexual activity +with a partner currently. Overall, then, asexual people had +less sexual experience with sexual partners, and this fact +provides some validation of the concept of asexuality. + +**[Bogaert 2006](https://www.researchgate.net/publication/232473247_Toward_a_conceptual_understanding_of_asexuality)** also has an interesting discussion of the topic in general. A more recent study, **[Brotto et al., 2010](http://link.springer.com/article/10.1007/s10508-008-9434-x)**, also found that identifying as asexual was consistent with certain patterns in sexual behavior (e.g., less frequent sexual behavior in general) which is what would be expected given stable, consistent asexuality. + +Brotto et al. also discussed interesting findings in the personality structure of those with asexuality. Most of these were null findings, as there were similar rates of psychopathology (referring to psychological disorders in general, *not* to being a psychopath) and many other personality traits compared to the general population, though there was evidence that asexuality was associated with a greater tendency to withdraw socially. Overall, though, the research suggests that asexual people's experiences with asexuality is extremely varied and shouldn't be painted with a broad brush. +*** + +**Sources**: + +[Bogaert, A.F. (2004). Asexuality: prevalence and associated factors in a national probability sample. *The Journal of Sex Research*](https://www.researchgate.net/profile/Anthony_Bogaert/publication/8220138_Asexuality_Prevalence_and_associated_factors_in_a_national_probability_sample/links/5460c7fc0cf27487b4525dac.pdf) + +[Bogaert, A.F. (2006). Toward a conceptual understanding of asexuality. *Review of General Psychology*](https://www.researchgate.net/publication/232473247_Toward_a_conceptual_understanding_of_asexuality) + +[Brotto L.A., Knudson, G., Inskip, J., Rhodes, K., & Erskine, Y. (2010). Asexuality: A mixed-methods approach. *Archives of Sexual Behavior*](http://link.springer.com/article/10.1007/s10508-008-9434-x)" +185 Could science create a double Y (ie just YY) chromosome human, and what would that look like? 2569 http://www.reddit.com/r/askscience/comments/37ws36/could_science_create_a_double_y_ie_just_yy/ 1433035495 37ws36 Human Body 2015-05-31 4:24:55 "The Y chromosome contains very few genes we have mapped as of now: + +* SRY Gene (Sex determining regions of Y); this gene is responsible for initiating the pathway for male development in intrauterine life + +* A gene for hair growth in ears + +* Some genes related to sperm production and testicular development. + +[Observe this karyotype of a human male \(XY\)](http://imgur.com/OKdrrat) and observe the miniscule size of the the Y chromosome. It contains very few genes. + +So to answer your question: + +Can science create a human with YY makeup? + +Maybe yes, but it wont survive because it would lack all the necessary genes of X. + +A human with XYY is possible and the resulting condition is called XYY syndrome. The human being with the condition is mostly normal, their IQ scores are comparable to their normal peers, their faculties good. They attain sexual maturity and can produce viable offspring. Most clinicians say that XYY syndrome is not even a disease because its asymptomatic and doesn't affect the individual's life. + +I would also like to quote what our Embryology professor told us once, ""Extra Y chromosomes are not a problem; but extra X's are directly proportional to mental and growth retardation.""" "The X chromosome is pretty much a regular chromosome, which is required for any cell to be alive. It contains a plethora of genes (about 1/23rd, I guess). The Y chromosome is the ""extra"" information that changes an otherwise default female into a male, mainly initiated through the action of an allege called SRY (sex determining region of the Y chromosome). + +Some important genes on the X chromosome: +- EBP: makes cholesterol, which is important for cell membranes and all sorts of other cool stuff +- FOXP3: gives you an immune system, and stops that system from eating you from the inside (controls autoimmune interactions) +- M1D1: your cells would burst from all the junk if this wasn't there: it is part of the garbage collection system of the cell, tagging unwanted and damaged proteins with ubiquitin +- NDP: you'd be blind without it (eg: no eyes) +- PGK1: this is maybe the most important because it makes phosphoglycerate kinase, one of the critical enzymes in the glycolosis pathway, basically giving your cells all of their energy. Definitely want this one + +Interestingly, women have two X chromosomes. In order to cope with this (because otherwise they would produce 2x too many of all of the enzymes on the X chromosome), at an early point in embryonic development, one of the two X chromosomes randomly shuts off through a process called X chromosome inactivation, which is basically the chromosome shrinking up into a tiny little unreadable ball called a ""Barr body."" The chosen X chromosome is conserved through all subsequent divisions, so all the daughter cells have the same X chromosome of the two inactivated. + +Interesting, as well, because men only have one X chromosome, there are a range of X chromosome linked diseases that are *much* more prevalent in men than in women (most notably colour blindness) because if they inherit a ""broken"" copy of a gene, they can never have a good copy to balance it out." +72 What element do we consume the most? 2568 http://www.reddit.com/r/askscience/comments/2yhdlz/what_element_do_we_consume_the_most/ 1425934394 2yhdlz Chemistry 2015-03-09 23:53:14 "**Short answer:** Hydrogen, by number. Oxygen, by mass. + +**Long answer:** The stuff we eat is primary made up of three classes of molecules, and water. Those three molecules are fats, carbohydrates, and proteins and are made primarily of carbon, hydrogen, and oxygen, with a handful of other things sprinkled in. Water, on the other hand, makes up a variable percentage of what we eat, and depends on the food. The wiki article on [""Dry Matter""](http://en.wikipedia.org/wiki/Dry_matter) lists the relative water content of lots of foods: + + Boiled Oatmeal: 83% water + Cooked Macaroni: 78% water + Boiled Eggs: 73% water + Boiled Rice: 72% + White Meat Chicken: 70% + Sirloin Steak: 69% + Swiss Cheese: 37% + Breads: 36% + Butter: 15% + Peanut Butter: 5% + +And additionally, they vaguely list fruits and vegetables being 70-95% water, which is cool. It's neat that things can be solid yet have such a high percentage of fluid in them- people for example are about 70% water. + +Anyway, on average, I'd expect that half the food you eat is actually just water. Since water is made of two hydrogen atoms and one oxygen atom, then hydrogen is very clearly the most abundant atom in our diet. It is also, coincidentally, the most abundant element in the universe. + +On the other hand, what I just said is only true if you're counting the *number of atoms*. You could easily count their combined mass, in which case the heavier elements actually stand a chance against hydrogen. Since oxygen, on average, is sixteen times as massive as hydrogen (8 protons and 8 neutrons), it will be the greatest contributor by mass. [This cool plot](http://en.wikipedia.org/wiki/Composition_of_the_human_body#mediaviewer/File:201_Elements_of_the_Human_Body-01.jpg) tells me that, by mass, humans are 65% oxygen, with carbon in a distant second place with 18.5%. + +So why are we called *carbon based* life forms when we're a majority oxygen by mass, and hydrogen by number? Well, it's just because carbon does the hard work- it has a very neat electron structure that enables it to do all sorts of cool bonds, which are the basis of all organic chemistry. " "I don't think I'm allowed to post a top level response as a non-expert unless it's in the form of a related question... + +Are we consuming the elements in the food we eat, or just rearranging them for our use? Are there any elements our species' mode of consumption are removing from the environment around us, in noteworthy scales? What about industrially, what elements are our technologies consuming? In terms of true consumption of the element, not just shuffling around, what are our nuclear projects doing to the rate of disappearance of radioactive elements? + +Ok, enough related questions, I don't think I've slept enough..." +73 Why do bombers make immediate 90 degree turns after releasing a nuclear weapon for detonation? 2568 http://www.reddit.com/r/askscience/comments/348si2/why_do_bombers_make_immediate_90_degree_turns/ 1430283955 348si2 Physics 2015-04-29 8:05:55 "Can I ask where you got the information that bombers with nuclear payloads turn 90 degrees after release? + +When the bombs were dropped on Hiroshima and Nagasaki, the pilots turned their planes 159 and 155 degrees respectively. To quote the pilot of the Enola Gay, Paul Tibbets: +> He [Dr Norman Ramsey, physicist in the Manhattan Project] said, ""You can't fly straight ahead because you'd be right over the top when it blows up and nobody would ever know you were there."" He said I had to turn tangent to the expanding shockwave. I said, ""Well, I've had some trigonometry, some physics. What is tangency in this case?"" He said it was 159 degrees in either direction. ""Turn 159 degrees as fast as you can and you'll be able to put yourself the greatest distance from where the bomb exploded."" + +Source: [The Guardian interview with Paul Tibbets, 2002](http://www.theguardian.com/world/2002/aug/06/nuclear.japan) + +It mentions in the book [Fire in the Sky](https://books.google.com.au/books?id=mmrWuJssLKAC&pg=PA87#v=onepage&q&f=false) by Jeffery K. Smith that Chuck Sweeney, pilot of the Bockscar, turned 155 degrees after dropping the bomb on Nagasaki (see page 87). + +Found a website with the maths called [A Strange Turn - +Why leave the atomic target at a 155 degree heading?]( http://user.xmission.com/~tmathews/b29/155degree/155degreemath.html) + +So, I'm just curious were you got the 90 degree information from." The nuke doesn't just drop down from the plane, it drops while traveling at the same horizontal speed as the plane, which means that continuing to travel forward would be the absolute worst thing you can do — you'd stay directly above the nuke for the most part. +74 Is the Fermi Paradox/Great Filter hypothesis taken seriously in scientific communities? 2566 http://www.reddit.com/r/askscience/comments/31r3oo/is_the_fermi_paradoxgreat_filter_hypothesis_taken/ 1428417802 31r3oo Astronomy 2015-04-07 17:43:22 "Not really. I mean, it's not that it's not taken seriously as a possibility, but it isn't a testable hypothesis so there isn't really anything to *do* with it. Instead, it's just something interesting to think about. Kind of an ""I wonder..."" sort of idea." "Do we chat about them over drinks while at conferences? Sure. But is anyone devoting their life's research to either? No. + +There is a simple reason for this, and that reason is while it's fun to think about, you really can't do scientific research either way on them. You can talk about them philosophically, of course, but that's different and not what business scientists are in, that distinction goes to the philosophers of science. I'm sure these ideas get more academic discussion there." +75 What would happen if I ran a microwave without a door on it and stood in the same room? 2564 http://www.reddit.com/r/askscience/comments/2rlopr/what_would_happen_if_i_ran_a_microwave_without_a/ 1420610015 2rlopr Physics 2015-01-07 8:53:35 "You might feel a bit warm, but would probably be pretty safe due to several factors; loss of confinement of the RF energy, scattering, and dissipation. + +Just like you can look at a red hot oven heating element from a few feet away, but would not enjoy the view from a few inches. The energy is spread at the inverse square of your distance. So if you go from 2 feet to 8 feet, you will have 16 times less energy hitting a given area. + +Microwave ovens often have a scattering device between the microwave source (magnetron) and the cooking chamber. It helps evenly distribute the energy and prevent hot spots, which are areas that the energy has been concentrated due to multipath reflections, and is reinforced. But half a wavelength away the reflections could cancel each other out. At microwave frequencies that is only a few inches away. As a result of the scattering device, hot spots in your room will move around like light from a very fast disco ball. + +As for the room itself, some items will heat up a bit, and other will reflect the energy. All your 2.4 Ghz Wifi and Bluetooth devices will probably be unusable while it is on, and may experience permanent damage some components depending on the gain and coupling efficiency of their antennas. + +If you really want to cause some microwave damage, you should get a nice large parabolic reflector and direct the energy directly from the magnetron. It will behave just like the reflectors in flashlights and headlights. It will concentrate the beam and allow significant heating at some distance." Not a direct answer to your question, but [here](http://news.google.com/newspapers?nid=1298&dat=19801010&id=OuNNAAAAIBAJ&sjid=lYsDAAAAIBAJ&pg=1132,3143594) is an article from 1980 about the proposal by Robert Pound (very prominent Harvard physicists, just died in 2010) to use microwaves for residential heating. I realize this doesn't answer the question of how much heating you would feel near a standard kitchen microwave oven, but it is worth knowing about if you're interested in this question. +76 Why doesn't intel increase the size of the processor to make it faster? We're trying techniques to make transistors smaller, but would a 1 square meter processor outperform what we have now at the same transistor size? 2556 http://www.reddit.com/r/askscience/comments/2ykv66/why_doesnt_intel_increase_the_size_of_the/ 1426008993 2ykv66 Engineering 2015-03-10 20:36:33 "I was surprised that no one mentioned that there's a limit on the size of the reticle - which is the mask used in steppers to create the die. There's also edge effects - which is that the patterning of the mask creates transistors with different characteristics along the edges and the larger the die the more of a problem these become. + +Current high end stepper/scanner lithography systems are all 4X reduction systems. This means that the features printed on the reticle are drawn 4 times the size of the intended feature. The standard for reticle substrate sizes is a 6"" square quartz plate. 6"" is ~152mm in size. At 4x that gives you about a 35mm field size at the wafer level. 4*35mm is 140mm of your total plate and as you get to the edge of the reticle just like the edge of a wafer you suffer from non-uniformity issues. Unfortunately the edge of your reticle is the edge of a die and if that side of the die won't print with the same properties as the other side or center you have some major device issues when you go to use it... which are called edge effects. + +Then there's defects - these are mistakes made by impurities that break transistors or wires. You can think of defects as being akin to taking a couple of dozen grains of sand and scattering them randomly over the 12"" wafer. In this thought experiment if there is a defect in your design, it won't work at all (this is less true in real life, but stick with me here). Clearly if you could somehow make a reticle that's the size of a 12"" wafer, you'd have a dozen defects and your chip would be dead a dozen times over due to all the defects. If you cut the size of your chip down, you can imagine that at some point you'd have some die without any grains of sand within the border. The smaller the die, the more you'd have that wouldn't have sand in their borders and thus would work. + +This is the fundamental problem with really big chips - you get to a point where a lot of the die don't work and this gets really expensive. So then you need to charge a lot for them, but there's a limit to what people will pay. And plus you could use all these dead wafers that you are destroying to make a lot more smaller die that would work and that would sell for less but at least you are selling something. You can add redundancy - extra stuff that you will remove if it's got a defect in it - but this only somewhat solves the problem because it's hard to make a chip where you can just randomly chop off anything that doesn't work... yes, you can make redundant cache and redundant cores, but usually you are limited in terms of which ones you can remove... and you can engineer the redundancy to allow you to do anything but this gets expensive in terms of design and now you are adding stuff to the chip which does nothing useful (you are planning for it not to work) and this takes room, validation effort (making sure it will work in all the different fuse cases) and will burn power for no reason (it's not used for calculation.. it's got defects in it, but it's not powered off... unless you want to engineer defective logic to also power itself off too... but then you are sounding like the marketing team who always demands ludicrous things from the engineers but wants schedules to be met and costs to be lower than expected...). + +I worked on several of the largest die in the modern history of microprocessors and between defects and edge effects, mass manufacturing our designs was less than fun. Proof of one of the dies that I worked on - I stuck a quarter up against the die for comparison. Tukwila was a monster of a die. http://imgur.com/0whYLGe + +Beyond a reticle limit of roughly 40mm per side (ish), the maximum size of a wafer right now is 12"" wafer - with plans in place to someday move to an 18"" (450mm) wafer. So theoretically, if you could pattern it, you'd never get 1m^2 because the maximum wafer size is 0.2m^2. You can't make bigger wafers than 18"" for a huge number of reasons... which could all be solved if we tried to engineer them, but there's enough of a struggle and cost to move from 12"" wafers to 18"" wafers. It will be a long time - if ever - before there's a shift to 900mm wafers... which still wouldn't get you 1m^2 :) + + +One common answer in this thread that I completely disagree with is latency. People quote speed of light effects and that is absolutely not a problem. We already can't send signals far enough fast enough on today's modern CPUs which aren't 1m^2. If you are going further than one clock cycle, you just stick your signal in a latch and latch the thing. That's the whole beauty of using synchronous (clocked) logic. So, yeah, now you have added a clock cycle of latency to the path, and this will reduce performance slightly, but it's something you have to do all over the design anyway. When people say a level 2 cache has an 18 clock latency... this whole adding latches to paths is exactly that reason. The L2 cache is huge so you clock the logic. Also people quote problems with signal integrity and this is also not generally a problem - you are latching periodically, but the resistance of on-die interconnect on a modern CPU - or even a not so modern CPU - is terrible even on the high/large metal layers. So you end up sticking buffers all over the place - you have to for reliability and power reasons so that you get reasonably crisp edges on your digital signals. So you don't need to worry about reflections other long wire effects because inductance on silicon is low, resistance of the wires is high and you are buffering the signals all the time anyway. " "Several factors: + + * Job 1 is making money, and bigger processors cost more (and you can't necessarily charge more for them) + + * Most of the die is not logic anyway - it's cache. You could make processors bigger now, and just not have so much cache (or have fewer processors, since most are 2 or 4 cores per die) + + * Bigger processors are less power efficient, and everyone is on a power efficiency kick right now + + * A new (and bigger) design carries a fair amount of risk - you spend a few hundred million dollars, and it might not work as expected. Plus, if it's really bad, you have no new product for the next cycle." +77 My five year old asked me what if anything can destroy a black hole? help? 2555 http://www.reddit.com/r/askscience/comments/2uhcpm/my_five_year_old_asked_me_what_if_anything_can/ 1422850697 2uhcpm Physics 2015-02-02 7:18:17 "Nothing external can destroy a black hole. However, a black hole will eventually disappear on its own (but eventually here means an absurdly long time). + +A black hole has a boundary called its event horizon. General relativity tells us that anything that crosses the event horizon can never get back out, so black holes only grow, never get smaller. + +However, there is an effect due to quantum mechanics and discovered by Hawking that causes a black hole to evaporate -- the mass of the black hole turns into radiation that goes away from the black hole. + +But note that this evaporation effect is very, very, very slow. A black hole with the mass of the Sun (which would be a small black hole, only about 3 km or 2 miles in size) would take 10^(67) years to evaporate. Thus even though black holes will eventually evaporate, the length of time is extraordinarily long (the universe today has been around for only about 14 billion years). + + +" "Assuming no mass is added, [Hawking radiation](http://en.wikipedia.org/wiki/Hawking_radiation) over a long enough period of time. + +> Hawking radiation reduces the mass and the energy of the black hole and is therefore also known as black hole evaporation. Because of this, black holes that lose more mass than they gain through other means are expected to shrink and ultimately vanish. + +**Edit**: for relevant text." +186 Does the human eye see in pixels? 2553 http://www.reddit.com/r/askscience/comments/3d0zxk/does_the_human_eye_see_in_pixels/ 1436720008 3d0zxk Human Body 2015-07-12 19:53:28 "In a sense yes in that you have a [mosaic](https://cis.uab.edu/curcio/PRtopo/Fig1Revised2010.jpg) of [photoreceptors](https://en.wikipedia.org/wiki/Photoreceptor_cell) that are sensitive to photons much like the sensor in a camera (see also [this](http://webvision.med.utah.edu/imageswv/conemos.jpeg) and [this](http://www.cns.nyu.edu/~david/courses/perception/lecturenotes/retina/retina-slides/Slide21.jpg) image). However, the photoreceptors do not send signals directly to your brain. In front of them (i.e. closer to the front of your eye) are several layers of other cells including [bipolar cells](https://en.wikipedia.org/wiki/Bipolar_neuron), [horizontal cells](https://en.wikipedia.org/wiki/Retina_horizontal_cell), and [ganglion cells](https://en.wikipedia.org/wiki/Retinal_ganglion_cell) all of which modify and process the signal from one or many photoreceptors. + +So the output of the eye that gets sent out the optic nerve is actually nothing like a pixel-like representation. First, there are varieties of photoreceptors with variable sensitivities to different wavelengths, meaning that [parts of your retina may be more or less sensitive to color (central vision near the fovea)](http://www.phys.ufl.edu/~avery/course/3400/vision/rod_cone_distribution2.jpg). Second, the amount of [pooling of signal from photoreceptors](http://webvision.med.utah.edu/imageswv/KallSpat26.jpg) also varies, with greater pooling in the periphery, meaning that ganglion cells in the periphery have larger receptive fields (are sensitive to light from a larger area) than those in the fovea (see also [this](http://what-when-how.com/wp-content/uploads/2012/04/tmp15F58.jpg) and [this](http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_10_39_labeled.jpg) image). + +Addendum: I was just writing up a quick answer, so it is by no means exhaustive. As pointed out elsewhere in this thread, in addition to photoreceptor variety and signal pooling, there are many other factors that contribute to the complexity of the signal that leaves the eye including the many different types of retinal ganglion cells that perform quite complex computations, including ones that are sensitive to motion (change in luminance over time). + +Edit: [here](http://book.bionumbers.org/wp-content/uploads/2014/07/130-f3-EyeRetina-12.png) is a cartoon of the structure of the retina. [Here](https://cis.uab.edu/curcio/PRtopo/Fig1Revised2010.jpg) and [here](http://webvision.med.utah.edu/imageswv/conemos.jpeg) you can see an electron microscope image of the photoreceptor mosaic. Also, I've added wiki links for everything. + +Edit2: I was traveling most of the day and missed a lot of questions after I made the initial response. I will try to get to all of them tonight and tomorrow." "The human eye does not see in pixels. We have photo receptors that are dots on the back of our eye but our eyes gyrate around to pass the light onto these receptors in sweeps and flashes utilizing the composite structure of our eye's back surface to build impulses our brain has tuned to. Those are built up by our optic center and brain into a composite vision through several stages. Its due to the composite nature of our vision and the hard-wired memory and deeplearned aspects that optical illusions and false impressions of colours occur. + +It may be attractive to say ""the retina is composed of point-like receptors of a similar size to pixels"" but that obviates all the other optic processing and autonomic muscle responses that help build the picture. Spy satellites also see by a type of point based receptor but the picture is built up in sweeps through multiple wavelengths. No one says that satellites see in pixels." +390 Do bacteria change the nutritional content of milk when they turn it into yogurt? 2552 https://www.reddit.com/r/askscience/comments/43mayy/do_bacteria_change_the_nutritional_content_of/ 1454293006 43mayy Biology 2016-02-01 5:16:46 "There is quite a bit happening once you add the bacteria! + +Lactose is converted to the sugars glucose and galactose, and fermentation produces lactic acid. The denatured proteins (from the heating step) prevent curdling and might also be easier on people with stomach issues. Cholesterol and choline go way down during fermentation. There are a few other general health benefits yogurt has over milk as well that you probably already know about. + +The number of calories will remain about the same. Vitamin C, folate and a couple others will be increased while vitamin B12 is decreased slightly. Yogurt usually contains about 12% more protein by volume than the type of milk used to produce it. + +How you treat the yogurt also changes its final makeup. For example, draining liquid whey will increase the concentration of sodium. + +If you want to know more about the microbiology and which reactions are taking place, [here's a good start](https://microbewiki.kenyon.edu/index.php/The_Role_of_Bacteria_in_the_Health_Potential_of_Yogurt)." "You can see the differences in nutrient content by looking at each one on this site: [**Milk nutrient content**](https://www.checkyourfood.com/ingredients/open/640/milk-whole) - [**Yogurt nutrient content**](https://www.checkyourfood.com/ingredients/open/1207/yogurt) + + " +391 On tv a while ago, Brian Greene said that we may see gravity as the weakest force because it may only exist partly in our universe and partly in another. Is this considered a credible theory today? If so, would the gravity waves we've observed be traveling through those other universes as well? 2550 https://www.reddit.com/r/askscience/comments/46t1zv/on_tv_a_while_ago_brian_greene_said_that_we_may/ 1456018055 46t1zv Physics 2016-02-21 4:27:35 It is credible in that it doesn't contradict anything we've already observed, although it's an extraordinary claim that obviously requires some evidence first. There have been a few [experimental searches for extra dimensions](http://klotza.blogspot.com/2015/11/what-do-we-know-about-extra-dimensions.html) that so far haven't found anything, but put limits on what properties these extra dimensions could have. "It's not that gravity was leaking into other *universes* but that it was leaking into other *dimensions.* + +It's a valid hypothesis at this point because it is currently a reflection of String Theory. A consequence of string theory is that additional, extra dimensions are present as a result of the fundamental physics of strings. Another feature of it requires that the gravitational force dissipate within these extra dimensions, so that it appears relatively weak. + +If string theory is a correct theory of everything, than this hypothesis is sound, and would be experimentally confirmed. If string theory is not correct, it's still a good hypothesis, but ultimately an incorrect one." +78 Could a low density solid float in a gas? 2545 http://www.reddit.com/r/askscience/comments/2xof9k/could_a_low_density_solid_float_in_a_gas/ 1425312040 2xof9k Physics 2015-03-02 19:00:40 "There are solids like [aerogel](https://en.wikipedia.org/wiki/Aerogel) that have lower density than air. However, air permeates the gaps in the solid, which prevents it from floating. If you were to somehow make the solid air tight, then it would indeed float. + +EDIT: For all the people suggesting to put the aerogel into a plastic bag in order to make it airtight: Aerogel is not too good at resisting pressure without getting crushed. The casing would have to withstand the pressure while being light enough at the same time. Obviously a plastic bag won't work for that reason" "**TL;DR:** hypothetically yes, actually no. + +The most dense gas is Tungsten hexafluoride, at 13 grams per liter. + +The least dense solid compound is elemental lithium, at 534 grams per liter. + +So, while it's theoretically possible for an extremely light solid to float in gas, it's actually impossible. + +(Aerogels don't ~~work~~ satisfy my reading of the question, because they're so porous; they're only light ""in bulk,"" because air infiltrates their pores. The ""actual"" solid is just glass.)" +392 Are emotions innate or learned ? 2540 https://www.reddit.com/r/askscience/comments/3z50ur/are_emotions_innate_or_learned/ 1451740617 3z50ur Psychology 2016-01-02 16:16:57 "Hello. This is a friendly reminder that you are currently in askscience, and we have strict commenting guidelines. Please cite sources, and refrain from posting jokes, anecdotes, and medical advice. + +Thank you." "Paul Ekman and Wallace Friesen demonstrated that there are universally understood facial expressions which transcend cultural knowledge. In one experiment they went to Papua New Guinea and showed Fore tribesmen photographs of people making faces of happiness, fear, anger, disgust, sadness and surprise. Despite 1000+ years of separation from any other civilization, these tribesmen were able to recognize the correct emotion to go with a picture far above the rate of chance. This was but one of many trips they made to many different cultures to try this experiment but one with the tightest controls on cross-cultural influences because of the separation this culture had with all others. + +[Here](http://psycnet.apa.org/journals/psp/53/4/712/) is one of their widely cited 1987 journal articles on the subject. [Here](http://economia.unipr.it/DOCENTI/FASANO/docs/files/ME_Ekman.pdf) is some early work on the subject, a paper by Ekman on universal emotions from 1970. Finally, [here](https://books.google.com/books?hl=en&lr=&id=vsLvrhohXhAC&oi=fnd&pg=PA301&dq=ekman+universal+facial&ots=uSzFhmR9Ee&sig=5PuaXjhqVpi5_J3AjlmhTMQCS7Q#v=onepage&q=ekman%20universal%20facial&f=false) is Ekman writing a chapter in a textbook on the subject in 1999. " +293 AskScience AMA Series: We're NASA scientists studying the role of carbon in our planet's climate. Ask us anything! 2534 https://www.reddit.com/r/askscience/comments/3sizwt/askscience_ama_series_were_nasa_scientists/ 1447331346 3sizwt Climate Science AMA 2015-11-12 15:29:06 "Could we reduce CO_2 levels back to 300 by MASSIVE reforestation? + +How massive would this have to be? + +My back of the envelope calculation: + +Total mass of the atmosphere is around 5e18kg. +At 400ppm that works out to 2e15kg of CO_2. +Of which the carbon mass is 12/(12+2*16) or 5.5e14kg. +To go back to 300ppm we need to remove about a quarter. + +So let's say need to reduce ~1e14kg of carbon from the atmosphere. +Assume 1000kg carbon per adult tree +Assume 1e5 trees per km^2 (that's 10m^2 per tree) +Giving us 1e6 km^2. + +Land area of the Earth is 5e8 km^2. +So we need to reforest only 1/500, or 0.2% of earth's land mass to make the CO_2 problem go away. + +Do I have my math wrong? + +" Is your team optimistic or pessimistic? How do you see the earth future playing out within the next 100 years? +393 Is it possible to start a fire with superheated steam? 2527 https://www.reddit.com/r/askscience/comments/43oktb/is_it_possible_to_start_a_fire_with_superheated/ 1454335570 43oktb Chemistry 2016-02-01 17:06:10 "Sure! Superheated steam can pack a lot of thermal energy, which can then be transferred to another object like paper. If the temperature of the steam is high enough, the paper can reach a local temperature above its [autoignition temperature](https://en.wikipedia.org/wiki/Autoignition_temperature). This temperature marks the point where a material can [spontaneously ignite](https://en.wikipedia.org/wiki/Spontaneous_combustion), which for paper happens to be just over 200^(o) C. In other words, if you manage to create superheated steam above 200^(o) C you can set paper on fire. + +In fact, here is a [cool demonstration of this exact effect!](https://www.youtube.com/watch?v=R9uvIhgVz04)" Yes i work in a steam station. We have 600 degree superheated steam. Someone put a welding blanket under a leaky valve. The blanket caught of fire. Took 2 fire extinguishers and a salad bowl of water to put the blanket out. It kept catching back on fire. And the salad bowl of water flashed to steam when it hit the blanket.. so yes it can. +79 Has there ever been any species of plant, capable of killing and eating a full grown man? 2524 http://www.reddit.com/r/askscience/comments/30jvoy/has_there_ever_been_any_species_of_plant_capable/ 1427501987 30jvoy Biology 2015-03-28 3:19:47 As far as I know, *Nepenthes rajah* is the largest pitcher plant there is, and even it can really only eat small mammals like mice. I can't imagine what pressures would lead to the evolution of a plant that needed to eat large animals to survive. "Although I can't definitively say that there is no such plant, I can shed some light on predatory plants. First some background information: + +While animals obtain their organic mass from consuming plants or other animals, plants get most of their mass from the air itself. If you put a seedling in a pot on a scale, it will increase in weight as it grows. This is because it's pulling Carbon Dioxide (CO2) from the air and using it to build up its tissues. + +A plant like, say, the Venus Flytrap, still obtains most of its Carbon from the air - *not* from flies it catches. Those flies supply the plant with an important source of Nitrogen. Getting Nitrogen in the right form is a *big deal* for a lot of plants. It's why some plants contain bacterial colonies in their roots - those bacteria convert Nitrogen into a usable form for plants, because plants can't use the N2 gas from the air directly. Well, those flies that the Venus Flytrap catches supply the plant with usable Nitrogen. + +So long as a plant is performing photosynthesis (which allows it to use all that CO2 from the air), it shouldn't need to consume large animals for sustenance. Now, a fungus on the other hand...." +187 Do animals that hibernate appear to require less sleep the rest of the year? Does hibernation slow aging in the animal? Any other interesting tidbits about hibernation? 2523 http://www.reddit.com/r/askscience/comments/3hyuqz/do_animals_that_hibernate_appear_to_require_less/ 1440250993 3hyuqz Biology 2015-08-22 16:43:13 "I will focus on what I am most familiar with: bats. Bats in temperate locations hibernate in winter and typically go into daily bouts of torpor most of the year. Despite very high metabolic rates when active (e.g., a flying bat's heart rate can exceed 800bpm), bats live much, *much* longer than other, similarly-sized mammals. A ten gram bat can live 30-40 years whereas a mouse that lives to be 3 is lucky. Check out [this graph](http://dvg4ol0hclm7o.cloudfront.net/content/royprsb/281/1784/20140298/F1.large.jpg). Torpor/hibernation helps bats because they offset their high metabolic rates by spending a huge portion of their lives with a drastically reduced metabolic rate. A torpid bat's heart rate can drop under 10bpm. + +[Here's](http://www.life.umd.edu/faculty/wilkinson/SFT/Wilk_South02.pdf) a good paper on bat longevity versus other mammals." "There's also a summer ""hibernation"" [called aestivation]( https://en.m.wikipedia.org/wiki/Aestivation)" +394 Can a literal bad apple actually spoil a barrel of good apples? 2519 https://www.reddit.com/r/askscience/comments/4b9jnm/can_a_literal_bad_apple_actually_spoil_a_barrel/ 1458511790 4b9jnm Biology 2016-03-21 1:09:50 I used to manage a produce department of a grocery store, and the answer is yes. Fruits produce gas (I forget the name of it, it's been 16 years since I worked there) as they ripen, and apples produce quite a bit of it. As a matter of fact, you can put an apple in a brown paper bag with green bananas and they will ripen very quickly. The warmer the apple is, the faster it ripens and the more gas it produces. This is why apples are stored in a cool area. If you get an overripe apple (a bad one, as it were) in the barrel, it gives off quite a bit more gas and causes the other apples to ripen at a faster rate, possibly to the point of over ripening, thus spoiling the barrel. I hope this is a worthwhile answer! Ethylene is the gas that makes the apples ripen faster (and as squirrelforbreakfast mentioned, rotting apples produce more of it). There's a range of fruit that are responsive to ethylene (see climacteric fruit). I'm currently doing some research on bacteria that produce ethylene, and they're commonly found on fruit like apples! +395 AskScience AMA: We are scientists in the food and feed laboratories that test imported products for dangerous pathogens as well as illegal dyes, metals, antibiotics and more. Ask us anything! 2514 https://www.reddit.com/r/askscience/comments/4ckdfm/askscience_ama_we_are_scientists_in_the_food_and/ 1459337858 4ckdfm Food Safety AMA 2016-03-30 14:37:38 "What is the most noteworthy/astonishing thing you discovered when testing products? + +Are there countries or manufacturers that are prone to failing your tests?" "YES!!! I am in the food industry and really am excited to ask you guys some stuff. + +1.) I have recently seen a lot of forgery CoA and even in one case straight faked analytical reports from China. Is there any larger action or plan in place to prevent this type of thing in the US? + +2.) Is there any way to avoid getting false materials from countries with a history of forgery and adulterated goods? It is impossible some times to source materials domestically. + +3.) What types of recourse can I/my company take against companies who sell ingredients that are later found to be adulterated or falsified? + + +Thanks for your time and hard work, it helps to know others are out there trying to keep our food supply safe and honest." +396 "A lot of skin products offer a ""sensitive skin"" alternative. What is the usual difference in ingredients and why is this better for sensitive skin?" 2511 https://www.reddit.com/r/askscience/comments/4gsp4s/a_lot_of_skin_products_offer_a_sensitive_skin/ 1461823371 4gsp4s Chemistry 2016-04-28 9:02:51 [deleted] "There is no regulated meaning, so companies can almost make that claim on anything, it's marketing. + +That being said, for bigger companies which have a lot more oversight (both internally and externally), sensitive skin formulations are generally compositions that have nonfunctional ingredients removed, or that use alternative ingredients known to be less irritating. + +An example of this are baby wipes. Always buy the sensitive skin baby wipes, avoid the regular ones. Why? The preservative used in the regular ones isn't actually recommended for a leave-on product, actually, it's specifically restricted as a leave-on. (methylisothiazolone (MIT) if you're wondering.) The thing is, you wipe your baby's butt with the wipe, and the liquid isn't rinsed off, it's essentially a leave-on, they should not be doing this. + +Some people are immediately sensitive to MIT, and they have rash develop. MIT exposure is sensitizing, meaning each time your skin has a reaction, the next time is worse. (Poison Ivy is a similar thing actually.) + +Sensitive formulations use sodium benzoate as the preservative, which is a food-grade preservative without the sensitization issues. + +" +294 Why is exponential decay/growth so common? What is so significant about the number e? 2503 https://www.reddit.com/r/askscience/comments/3rwg2v/why_is_exponential_decaygrowth_so_common_what_is/ 1446913484 3rwg2v Mathematics 2015-11-07 19:24:44 "Any system where the rate of growth is proportional to its current size can be represented by an exponential function. This is essentially the definition of an exponential function: + +y = e^x <-> (d/dx)y = e^x = y + +So, for example, the population rate of a species in an environment with sufficient food and no predators can be represented by an exponential function, because the rate at which new animals/cells is created increases linearly as the population (or number of potential parents) increases. + +Additionally, if you have a bank account with interest, that also can be represented by an exponential function, since the rate at which you gain money from interest increases as you get more money. + +So ""e"" pops up anytime there is continual exponential growth, i.e. when the rate of change of a system grows continuously with its size. + +I think [this](http://betterexplained.com/articles/an-intuitive-guide-to-exponential-functions-e/) guy's explanation describing the intuitive nature of ""e"" and exponential functions is really good if you're looking for more detail: " "Your two questions in the title actually have totally different answers. + +1) Exponential growth shows up anywhere that a number evolves in time proportional to its value. For example, if you're looking at the number of flies in a swamp, and every fly hatches, then lays two eggs, then dies, then that's exponential growth because when the next batch hatches there will be twice as many. (This may not be a good model for a real system and that's why exponential growth doesn't apply to everything.) + +2) Outside of pure mathematics there's very little special about e. It's still an exponential relationship if you change the base from e to 2, or any other number greater than 1. In the real world exponential relationships look like e^(k*t) where e is e, t is time, and k is some constant. If you want to use something other than e then you change your constant, no fuss, no muss. In that sense e isn't special any more than a meter is special; they're both just standard values we've agreed on to make life more convenient. + +There are deeper reasons why e actually is special if you're looking at pure mathematics, but they have nothing to do with why this or that phenomenon evolves exponentially in time. They're just explanations for why e happens to be a very convenient number to use, even though you could always use a different one." +188 Does being in a warmer temperature cause the body to burn more calories? 2497 http://www.reddit.com/r/askscience/comments/3bg4w1/does_being_in_a_warmer_temperature_cause_the_body/ 1435531602 3bg4w1 Human Body 2015-06-29 1:46:42 "Other way around - Hypothermia can activate your brown adipose tissue, which is able to metabolise fuel without producing ATP, meaning you can potentially burn fat without doing exercise. Lots of interesting things to study! + +[source](https://d1b10bmlvqabco.cloudfront.net/attach/i6qvyb3hqe85lb/hkor392dxco13w/i9j1ggssytro/Diabetologia_BAT_NIDDM.pdf)" "First off: Energy use produces waste heat. This is actually a concept coming directly from the second law of thermodynamics. + +Hot situation: + +There is very little the body can actively do to cool you down. Sweating is about it. So while sweating takes up a bit of energy, you're going to be motivated to do a lot of other things that reduce energy use. Seeking shade, restricting activity levels. So while sweating will burn some extra, your body is going to chemically attempt to damp your metabolism in every other way to prevent you from overheating. Heat stroke is nasty, and potentially lethal. + +Cold situation: + +Unlike in heat, your body does have an option to directly burn chemical fuel for heat. This is done through UCP (Uncoupling Proteins). It takes some energy that was going to be stored in ATP, and directly wastes it to produce heat. Incidentally, this is why some people are ""colder"" or ""hotter"" than others, different expression rates of UCP. Furthermore, the ATP you have around can be used in several active ways to create heat. Shivering, jumping around, all of these produce even more waste heat to help warm you up. + +Answer: + +So the literal answer to your question is ""keep your house colder"". However, there's a pretty neat caveat: Nothing in biology is so clean cut. There's evidence that [cold weather causes our body to increase demand for calories](http://ajplegacy.physiology.org/content/202/2/375.abstract). It's entirely possible that keeping your house at a colder temperature would just modify your diet enough for it to not matter at all. Unfortunately I couldn't find research on that specific subject, but it's an interesting possibility." +189 If you were traveling at a supersonic speed towards a sound source, would the sound appear to be going in fast-forward? 2491 http://www.reddit.com/r/askscience/comments/3flzhf/if_you_were_traveling_at_a_supersonic_speed/ 1438603066 3flzhf Physics 2015-08-03 14:57:46 "Yes, this is a product of the Doppler shift. You know, the ""ambulance siren has a higher pitch when it's approaching you, and a lower pitch after it passes?"" Same thing, only now the ambulance is stationary, and you're moving. + +The equation is pretty simple in theory, + + f_obs = f_source (v_sound ± v_obs)/(v_sound ± v_source) + +So assume the source is stationary, and you, the observer, are approaching (so use addition). Thus, we get an equation like: + + f_obs = f_source (v_sound + v_obs)/(v_sound) + +If you are going at Mach 1, then that fraction in parentheses on the end is 2, so the frequency is doubled, so the pitch is shifted up considerably. Also, since periods are inverse frequencies, this means that it will take you half as long to hear the sound. For example, if the source is Lynyrd Skynyrd emitting a 10 minute live version of Free Bird, you'll hear the entire song in 5 minutes as a live version by Alvin and the Chipmunks. + +Edit: And importantly, you don't need to be supersonic for this effect to occur at all! Any movement will, by the the Doppler effect, shift the apparent frequency and thus timing of the song!" "I think you accidentally destroyed your own question. Yes, Doppler shifting occurs as you move relative to a sound source. But once you add in the supersonic criteria, the question becomes meaningless. Sound will not penetrate the shockwave, so you won't be able to hear anything from the source. A shockwave is essentially a boundary where sound waves pile up to form a single large wave. + +I couldn't find any specific studies on this though, so someone correct me if I'm wrong. This is just my intuition from my master's in aerospace." +80 Are humans the only animal who varies their sleep schedule? 2486 http://www.reddit.com/r/askscience/comments/2stm5b/are_humans_the_only_animal_who_varies_their_sleep/ 1421578722 2stm5b Biology 2015-01-18 13:58:42 "There are many examples of other animals changing their sleep patterns and their daily sleep duration in response to environmental conditions. These include changes in response to: + +* Seasons +* Food availability +* Mating opportunities +* Mimicking what others in the group are doing (e.g., huddling together as a group at sleeping times to conserve heat) +* Migration -- [for birds this involves severe sleep deprivation, with brief naps taken whenever possible](http://www.sciencedirect.com/science/article/pii/S0003347206002673). +* Child-rearing -- [see what whales and dolphins do for an extreme example](http://www.nature.com/nature/journal/v435/n7046/abs/4351177a.html). +* Having something else fun to do besides sleeping! + +I added that last point because we often think of that choice as being something unique to humans, but it isn't. A good example is wheel-running. When given access to a running wheel, many rodents choose to run so much that their sleep/wake patterns are fundamentally altered. When given a running wheel, [mice stay awake 12% longer each day than they do without a running wheel](http://www.sciencedirect.com/science/article/pii/0031938491900808)! For reasons that are not well understood, some rodent species even invert their sleep cycles from diurnal (day-active) to nocturnal (night-active) when given access to a running wheel. Examples include the [degu](http://www.jneurosci.org/content/19/1/328.short) and the [Nile grass rat](http://jbr.sagepub.com/content/14/5/364.short). + +Having said all that, there are very large inter-individual differences in circadian timing and sleep timing between humans, compared to the differences between individuals of most other species. This is likely enabled by our ability to choose our own lighting environment using artificial light. The timing of an individual's circadian rhythm is primarily determined by their daily patterns of light exposure, which often differ greatly between individuals. [When humans with very different circadian timing go camping together with no artificial light sources, the circadian timing differences between them become much smaller](http://www.ncbi.nlm.nih.gov/pubmed/23910656)." "There are plenty of animals out there that change their sleep schedule. For example, ferrets sleep an average of 18 hours per day, but will adjust their schedule so they're awake while you're home so they can spend time with you. + +Sources: +http://www.ferret.org/read/faq.html + +This change is for something as simple as play time, so when there is an actual physical need, animals will definitely adjust their schedule as needed." +295 Why do wine and whisky makers use oak? 2478 https://www.reddit.com/r/askscience/comments/3ucelr/why_do_wine_and_whisky_makers_use_oak/ 1448543789 3ucelr Chemistry 2015-11-26 16:16:29 "You need a hard wood that's durable. So woods like cotton wood and pine are out. + +You need a wood that once dried does not seep pitch. + +You need a wood that can easily be formed into staves for making barrels. The consistent wood grain of oak keeps it from easily warping at room temperature, but with heat and steam, the staves can be manipulated. + +You need a wood that is in good supply. The traditional french oak was widely available when the technology was first developed so the coopers of the time knew how to wok with it. + +You need a wood that imparts some flavor, but not too much. That flavor also must be pleasing. This is probably the # 1 reason. + +Also see: +http://www.fs.fed.us/wildflowers/ethnobotany/documents/OakAgingAndWine.pdf +" "Wood scientist here. + +I dont know how many people actually know this, but oaks are used because the pores their cellular structure are ""clogged"" by tyloses, which prevent liquids from seeping through the wood. Not all oaks work for barrels; certain species have more tyloses than others and are thus better suited for holding liquids. Many oak species that grow in the same region have varying amounts of tyloses, so species is important. + +Most other woods are simply too porous. Some are dense enough to hold liquids well, but do not have tradition behind them. Oak has a tradition behind it and accepted flavours. Indeed, soil profiles alter the flavour of oaks, thus certain regions have developed a reputation for superior properties. " +397 Is a Yellowstone eruption in the next decade imminent? 2477 https://www.reddit.com/r/askscience/comments/4gtrfs/is_a_yellowstone_eruption_in_the_next_decade/ 1461846788 4gtrfs Earth Sciences 2016-04-28 15:33:08 "First, we have to define what is meant by ""Yellowstone eruption"" I presume you refer to the very large scale eruptions of the caldera which have received so much press lately. The whole area is prone to much more localised volcanic events, but lets leave those aside. + +I'll refer you to the [2007 USGE open file on Yellowstone volcanic hazards](https://www.researchgate.net/profile/Robert_Smith55/publication/258032883_Preliminary_Assessment_of_Volcanic_and_Hydrothermal_Hazards_in_Yellowstone_National_Park_and_Vicinity/links/00b7d5298cd880ca4d000000.pdf), which has this to say (my highlights): + +""Of all the possible eruptive hazards that might occur in the region of Yellowstone National Park, **by far the least likely is that of another major caldera-forming pyroclastic eruption of 100 km^3 or greater. Three such events have occurred in about the past 2 million years, each associated with a cycle of precaldera and postcaldera rhyolitic volcanism lasting on the order of a million years**. In the Island Park area, west of the 639±2-ka Yellowstone caldera, the older rhyolitic source areas have subsequently produced basaltic lava eruptions. In contrast, contemporaneous basaltic magmas surround the Yellowstone caldera, but none have erupted within the caldera. **This pattern strongly suggests that the crust where rhyolitic magma chambers existed during the previous two major caldera-forming eruptions and their associated rhyolitic volcanism has cooled and solidified +sufficiently to fracture and allow basaltic magmas to intrude from below, precluding the possibility of large volumes of eruptible rhyolitic magma remaining there**. However, the great heat flow represented by the massive long-lived hydrothermal circulation system of Yellowstone (Fournier, 1989) as well as significant delays in seismic-wave travel times and wave attenuation imaged in the shallow crust beneath the Yellowstone caldera (Benz and Smith, 1984; Miller and Smith, 1999; Husen and others, 2004) strongly suggest the continued presence of magma. What remain most uncertain are (1) the percentage of melt in the remaining, partly crystallized magma, (2) its degree of interconnection, and (3) its potential eruptibility. The more than 600 km^3 + of highly differentiated magma that has erupted as lava flows within the caldera between ~170 and 72 ka represents a volume equivalent to a large caldera-forming eruption. Those eruptions perhaps partly degassed +and depleted the magma sufficiently slowly without triggering voluminous pyroclastic eruptions that they may have rendered another major caldera-forming eruption from the present subcaldera chamber unlikely."" + +So what must we make of this: + +* These ultra large eruptions are very rare, and associated with cycles of (smaller scale) rhyolitic volcanism of about 1 My (to my understanding, we aren't seeing that); + +* It is quite likely previous caldera eruptions have sufficiently emptied the magmatic chamber of rhyolitic magma and gas to preclude future events of this nature; + +* But there is uncertainty about the actual state the material left in the magmatic chamber, so we can't absolutely rule out future eruptions. + +We refer to rhyolitic vs basaltic magmas; the rhyolitic ones are the ones we keep a close eye on because they usually contain more gas, and that gas is what gives eruptions their explosive character. Basaltic magmas tend in general to have less gas and make for calmer eruptions. + +As to saying we are ""overdue for such an eruption in the next few years"", there are no signs to that effect, so: Nah... Kickback in a comfy chair with a cold beer, enjoy the sunset, or perhaps Old Faithfull. " I have a question about the changes in the cauldera after the 1959 quake dammed up Quake lake. That body of water is 6 miles long and 190ft in it's deepest part. That is a good sized amount of water weight sitting on the thin crust of the cauldera, and being there is that many gallons of ice cold water there, what would happen if a quake cracked the bottom of the lake and let the water drop into the magma layers? Steam BLEVE type of explosion? Any speculation or calculations on how big of an explosive yield that event could generate? Or would it just boil the water in the lake? +296 Is there a way to use radioactivity to produce energy, other than using the heat it generates? 2474 https://www.reddit.com/r/askscience/comments/3mbkox/is_there_a_way_to_use_radioactivity_to_produce/ 1443177880 3mbkox Physics 2015-09-25 13:44:40 Yes, there is something called a beta-voltaic cell, which operates similarly to a photo-voltaic cell, except the high-energy electron from the decay excites electrons in the semiconductor, rather than a photon doing that. "There is some research being conducted on direct energy conversion nuclear reactors, generally for space applications. The concept is that fission produces high energy ionized particles, which are then collected into an ion beam and used to generate a current. + +https://en.wikipedia.org/wiki/Fission_fragment_reactor" +297 What makes a gas a greenhouse gas? For example, what are the molecular properties of carbon dioxide (CO2) that allow it to retain heat, that nitrogen (N2) lacks? 2462 https://www.reddit.com/r/askscience/comments/3mysg9/what_makes_a_gas_a_greenhouse_gas_for_example/ 1443621154 3mysg9 Chemistry 2015-09-30 16:52:34 "Greenhouse gases absorb and re-emit infrared radiation. This means that instead of passing through the atmosphere and directly into space, some of the infrared radiation is re-emitted back toward the surface of the earth, increasing the net heat on the planet's surface. If it were re-emitted in the same direction that would be no problem, but the absorption and re-emission randomizes the direction of the light, effectively bouncing some of it back to the ground. Like a greenhouse does, hence ""greenhouse effect"". + +The molecular property you're looking for is frequencies of vibration. The ability to absorb and re-emit infrared comes from a molecule that has a change in energy of vibration frequencies that corresponds to infrared energies. They absorb the photon, vibrate at a higher frequency, and re-emit that photon as they return to their less energetic state. Vibration frequencies are characteristic to each molecule, and in fact are often used as an analytical tool to identify unknown ones. So, the gases with vibration frequencies that can be perturbed by infrared radiation are greenhouse gases while gases like nitrogen, oxygen, and argon are not. " "There's two possible questions you could be asking here. The first is: + +*""What makes a particular gas opaque to a certain color of light?""* + +The second is: + +*""Why does a gas opaque to a certain color of light act as a greenhouse gas?""* + +Superhelical's answer on the former question is excellent, so I'll attempt to answer the second instead: + +[This](https://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Solar_spectrum_en.svg/2000px-Solar_spectrum_en.svg.png) is a diagram of the light spectra we receive from the sun. The yellow is the incoming band, while the red is what actually reaches the Earth's surface. You can also observe absorption lines, at 750 nm from Oxygen, 900, 1100, and 1350 nm from water vapor, etc... What's important to take away from this is that the total amount of energy **incoming** to the Earth is roughly equal to the area under the red curve. Maybe there are some contributions from the yellow as well, because the atmosphere that absorbs the light is still part of the Earth. + +By contrast [this](https://www.e-education.psu.edu/earth103/sites/www.e-education.psu.edu.earth103/files/module03/fig10out.png) is what the Earth emits, due to blackbody radiation of it's own temperature. + +As you can see from this image, the Earth's wavelengths are much further in the longer-wave (lower frequency and lower energy) radiation. Also, you can see the absorption bands from carbon dioxide, oxygen, water, and ozone in this diagram as well. When a gas has absorption bands in that area of the spectrum, it traps energy in the Earth's system, instead of allowing it to radiate away into space. + +When that happens, the balance of energy shifts: The Earth's temperature rises (well, really just the atmosphere and the hydrosphere: I rather doubt the temperature of the *rock* changes much) and as the temperature rises, the amount of energy emitted by blackbody radiation, which is proportional to ~T^4 , rises to compensate. *That's global warming.*" +1806 AskScience AMA Series: Updates on COVID vaccines. AUA! 2456 https://www.reddit.com/r/askscience/comments/lcg8l0/askscience_ama_series_updates_on_covid_vaccines/ 1612447256 lcg8l0 COVID-19 2021-02-04 17:00:56 Hi everyone! Thanks so much for joining us today! I have read that most vaccines are targeting the spike protein, and that we have seen mutations arise, but so far none that seriously impact vaccine efficacy. Would mutations need to specifically alter the spike protein in order to cause Sars-CoV-2 to escape a vaccine? Or are there other mutations you could envision that would also lead to vaccine escape? Thanks! "Hi and thanks for joining us today! + +Some big questions I often see around Reddit: + +1. If you had to choose a vaccine, which one would it be? +2. Do vaccines slow/stop transmission? +3. What's the threshold of vaccination until we can return to normalcy? When will we see that? +4. Are anti-vaccine groups a major concern?" +398 How does physical manipulation (e.g. massage) relax muscles? Does pressure create physiological changes in the tissue? 2455 https://www.reddit.com/r/askscience/comments/411jqv/how_does_physical_manipulation_eg_massage_relax/ 1452832887 411jqv Human Body 2016-01-15 7:41:27 Stimulation of mechanoreceptors in the skin/muscle/fascia tissue can also activate inhibitory interneurons in the dorsal horn of the spinal cord. This dampens the activity of A-delta and C pain fibers, resulting in short term reduction of pain. This obviously is only a small part of how a massage works physiologically, but its all that i can contribute "This is not my area of research at all, but I have been interested in this same type of question for some time. The following is a theoretical model for the mechanism: https://www.researchgate.net/figure/8004036_fig2_Figure-9-Theoretical-model-of-the-expected-mechanisms-of-massage-on-the-severity-of + +This comes from the paper called ""The mechanisms of massage and effects on performance, muscle recovery, and injury prevention. http://www.ncbi.nlm.nih.gov/pubmed/15730338. + +I would also advise looking in to muscle spindles. The lengthening of muscle spindles, cause neuronal responses which allow for the relaxation of the spindle, and subsequently the muscles put under tension by that shortened muscle spindle. This is essentially why stretching also feels good. Again, not my area of research, but my physical therapist pointed me in this direction. Wikipedia has some excellent information and so does nih. https://en.wikipedia.org/wiki/Muscle_spindle" +190 AskScience AMA Series: I’m Stephan Lewandowsky, here with Klaus Oberauer, we will be responding to your questions about the conflict between our brains and our globe: How will we meet the challenges of the 21st century despite our cognitive limitations? AMA! 2450 http://www.reddit.com/r/askscience/comments/3erfrl/askscience_ama_series_im_stephan_lewandowsky_here/ 1437998055 3erfrl Psychology 2015-07-27 14:54:15 Given that most people do not have enough time during the day or the scientific background to verify most information, what should be the reasonable behavior someone should have in order to have a relatively logical opinion of things? "Just posted this in the Stephen Hawking AMA, but then saw the title of yours and said: Hey. I should post that there. So here it is: + +This was a question proposed by one of my students: + +- do you think humans will advance to a point where we will be unable to make any more advances in science/technology/knowledge simply because the time required to learn what we already know exceeds our lifetime? + +Then follow-ups to that: + +- if not, why not? + +- if we do, how far in the future do you think that might be, and why? + +- if we do, would we resort to machines/computers solving problems for us? We would program it with information, constraints, and limits. The press the ""go"" button. My son or grandson then comes back some years later, and out pops an answer. We would know the answer, computed by some form of intelligent ""thinking"" computer, but without any knowledge of how the answer was derived. How might this impact humans, for better or worse?" +298 If Betelgeuse is ~600 light years away, will it take 600 years for light from its collapse to reach Earth? And could scientists detect the collapse before 600 years time? 2450 https://www.reddit.com/r/askscience/comments/3of7xa/if_betelgeuse_is_600_light_years_away_will_it/ 1444631108 3of7xa Astronomy 2015-10-12 9:25:08 "It will take 1 year for light to travel 1 light-year. It will take 600 years for light to travel 600 light-years. A light year is defined by how far light will travel in one year. + +Information can't travel faster than *c* without violating causality (you would be able to receive messages from the future.) There would be no way to detect Betelgeuse collapsing until the light from the event reached Earth. + +The absolute best case scenario would be knowing what Betelgeuse would look like 600 years before it collapses and guessing it is currently collapsing at the time we observe it 600 years from collapse. As far as I know, its not currently possible to predict stars collapsing that accurately. +___________________________ +EDIT: + +Quantum entanglement does not let you transmit information: + +[Wikipedia](https://en.wikipedia.org/wiki/Faster-than-light#Quantum_mechanics) +> Certain phenomena in quantum mechanics, such as quantum entanglement, might give the superficial impression of allowing communication of information faster than light. According to the no-communication theorem these phenomena do not allow true communication; they only let two observers in different locations see the same system simultaneously, without any way of controlling what either sees. Wavefunction collapse can be viewed as an epiphenomenon of quantum decoherence, which in turn is nothing more than an effect of the underlying local time evolution of the wavefunction of a system and all of its environment. Since the underlying behaviour doesn't violate local causality or allow FTL it follows that neither does the additional effect of wavefunction collapse, whether real or apparent. + +You can't tell things happen ""ahead of light"" by measuring gravitational effects: + +[Wikipedia](https://en.wikipedia.org/wiki/Speed_of_gravity#Introduction) +>The speed of gravitational waves in the general theory of relativity is equal to the speed of light in vacuum, c. Within the theory of special relativity, the constant c is not exclusively about light; instead it is the highest possible speed for any interaction in nature. Formally, c is a conversion factor for changing the unit of time to the unit of space. This makes it the only speed which does not depend either on the motion of an observer or a source of light and/or gravity. Thus, the speed of ""light"" is also the speed of gravitational waves and any other massless particle. Such particles include the gluon (carrier of the strong force), the photons that make up light, and the theoretical gravitons which make up the associated field particles of gravity (however a theory of the graviton requires a theory of quantum gravity). + +And faster-than-light communication would violate causality due to relativistic effects (like time dilation.) Note that relativistic effects are REAL and have been MEASURED. + +[Wikipedia: Numerical example with two-way communication](https://en.wikipedia.org/wiki/Tachyonic_antitelephone#Numerical_example_with_two-way_communication) + + +" It takes a while for the whole star to collapse, and it begins in the middle, spreading outward. A few hours before the supernova is visible, the neutrinos formed from the collapse in the middle of the star will begin rushing out, unimpeded by the matter of the star. These will reach us hours before the visible explosion. So... There's that. +299 How do large, triple parachutes like those used on Apollo capsules seem to automatically maintain separation from each other at a rather steep angle? 2448 https://www.reddit.com/r/askscience/comments/3xs6mg/how_do_large_triple_parachutes_like_those_used_on/ 1450750747 3xs6mg Physics 2015-12-22 5:19:07 "It depends on the parachute types. Those big parachutes that you see landing the capsules for Apollo, SpaceX, Orion, etc., have a certain angle that they want to be at. This is called a ""trim angle,"" which is the angle from the vertical. It's partly because there is so much fabric compared to open spaces, but air wants to dump out of the canopy. The slots and vent opening don't give enough open spaces, so the parachute tilts to the side. How much it tilts to the side is the trim angle. There are nice curves that show stability with regards to the angle. + +You don't want to make the suspension lines different lengths. That would be silly. For one, it would be obnoxious to pack. And the loads on the lines would be wildly different, which would be awful to design for. Also you wouldn't/couldn't add some kind of spacer or whatever. Each main is packed into a separate bag in its own bay. How would you have some connecting piece that goes from main to main, all the way inside the bag? + +For other parachutes, like the pilots that pull out the mains, or the drogues that provide the initial deceleration and stabilization, there is a higher ratio of open space to fabric. The capsule also goes a lot faster under these parachutes, so the trim angle isn't being sought as much. + +If you're really curious, you should read [Knacke's Parachute Recovery Systems Design Manual](http://smile.amazon.com/Parachute-Recovery-Systems-Design-Manual/dp/0915516853/ref=sr_1_1?ie=UTF8&qid=1450795438&sr=8-1&keywords=knacke+parachute). + +Source: I design parachutes for a living." "Not sure on the specifics of this particular application/design, but there are a few ways you could make that happen. Note that a boat sail doesn't go perfectly perpendicular to the air flow: the ropes and shape hold it at an angle. + +First of all, the air being caught by the chutes pours out of the sides. This pushes against the air from the other chutes and pushes them apart. This might be the only thing going on in some designs. + +As far as design possibilities go, where the rope splits into multiple ropes that attach to the parachute in different places at the top, it can split into different lengths. The difference might not be much, but it's enough for the force of the air to tilt the parachute (it will stay full and the ropes will stay tight due to the forces). The parachute can also be made asymmetrically to let a bit more air out of one side, making the parachute push in the opposite direction and pushing the other parachutes away. + + It looked like the three deployed together, ~~so there may be some sort of weak attachment holding them together and facing correctly that pops off when they inflate.~~ **EDIT: after further research, this seems to be done with very careful rigging, not some breakaway device.** As far as stopping them from rotating to steer into each other, it's just a matter of making sure that the forces pushing them away are stronger and that the equilibrium point is 3 equally spaced parachutes 120 degrees from each other. In other words, you design them so that if one starts to drift out of place, it creates some airflow that pushes it back. This is mostly from the air pouring out of the sides of the other parachutes. Edit: http://www.nasa.gov/sites/default/files/images/640234main_jsc2012e041631_full.jpg Note the ports in the side of the parachute. This is the only place for air to escape, other than bending around the bottom. As far as the air escaping from the bottom goes: http://www.tafsm.org/PROJ/AS/MDCM/stream_para.gif Note the jet of air pouring out of the downwind side here (thick red line). With the three parachutes angled as they are, this is pointed toward the middle. + +**Tl;dr: Parachutes deflect air toward each other, pushing apart. They may also be designed to be at an angle when pulled tight.**" +191 "Do animals,specifically dogs, have a dominant ""hand?""" 2440 http://www.reddit.com/r/askscience/comments/38iger/do_animalsspecifically_dogs_have_a_dominant_hand/ 1433422437 38iger Biology 2015-06-04 15:53:57 [deleted] Looks like you got your answer about dogs, but you should be aware that 'laterality' (right/left side preference) exists in other animals as well. A quick search shows that it has been documented in horses and snakes, as well as other species. Fossil records indicate that even ancient predators may have had some laterality, as we often see more wounds on one side or the other of prey animals. +192 "Do black holes grow when they ""absorb"" matter?" 2440 http://www.reddit.com/r/askscience/comments/3f54lv/do_black_holes_grow_when_they_absorb_matter/ 1438248972 3f54lv Astronomy 2015-07-30 12:36:12 [deleted] This conversation always confuses me. Of course blackholes lose mass due to Hawking Radiation, but they also gain mass from consuming matter (planets, dust etc). So why do some black holes deteriorate through radiation while others grow to be the size of the ones at the centers of galaxies? +193 How come metal sparks in the microwave yet the insides of microwaves are made out of metal? 2431 http://www.reddit.com/r/askscience/comments/3c9sr9/how_come_metal_sparks_in_the_microwave_yet_the/ 1436160749 3c9sr9 Engineering 2015-07-06 8:32:29 Roughly: the microwaves induce an electrical potential in the object metal, this causes sparks as differences in the potential across the object metal causes arcs of electricity (especially with water vapour that may come from the cooking food). The side walls of the microwave are earthed, so any potential induced by the microwaves won't build any charge. "To give a *really* simplified answer: + +It is not that you are putting ""metal"" in the microwave. You are putting ""metal with edges/vertices"" in the microwave. When you charge up the metal in the microwave, the charge collects on the edges and vertices. Eventually the charge builds up to where it sparks. + +The walls of the microwave are grounded, so no charge builds up." +194 Has human society and culture fundamentally altered our own biological evolution? 2420 http://www.reddit.com/r/askscience/comments/37qgcj/has_human_society_and_culture_fundamentally/ 1432915732 37qgcj Ecology and Evolution 2015-05-29 19:08:52 [deleted] The earliest stone industry dates back almost two million years, when the hominid line was represented by species such as Australopithecus garhi. Stone industry fluorished with early species of Homo habilis and Homo ergaster. Additionally, evidence supports the contention that hominids were building fires at least as early as one million years ago. Culture and industry began with species prior to Homo sapiens in the evolutionary lineage. What I mean is that modern humans never evolved in a state of nature. Our nature is to be technological, to teach each other, and to use language. +195 If I am in an elevator and it falls many flights with no safety mechanism surely I'll die. But what if it was filled with water and I was in the middle, survivable? 2415 http://www.reddit.com/r/askscience/comments/35g0k7/if_i_am_in_an_elevator_and_it_falls_many_flights/ 1431216630 35g0k7 Engineering 2015-05-10 3:10:30 "Since you are about as dense as water, you won't move relative to the water around you at all upon impact. The only thing you should do is orient yourself so you're lying on your back relative to the floor since this is the best position for humans to withstand acceleration. + +Being submerged in water should significantly improve the body's ability to withstand the acceleration on impact. By squeezing your body from all directions it may help keep your organs about where they should be rather than letting them migrate to around your spine. Any open cavities in your body would be the first to be damaged. I think the respiratory system would be the first point of failure. Maybe the brain. + +Edit: Just to be clear, I assume the elevator somehow can survive the impact and contain the water. I don't know what the right thing to do would be if the elevator burst at the bottom." "Some interesting answers in the comments, but here's my take: + + liquids can be considered incompressible, meaning they move out of the way as a fluid does, but don't ""cushion"" like a gas or matrix/lattice, etc. As lots of people have mentioned, energy must be conserved. If there isn't anywhere for the water to disperse to, the force of impact will be directed in the normal direction (towards the ceiling). The same thing happens when you drop an almost empty bottle of beer/soda; liquid shoots out the top. + In your scenario, if you were at the top of a water filled elevator - as others have suggested would be safest - I think you'd get smashed into a soggy mess just as badly as if you were at the bottom of the column of water. + +If you could somehow manage to smash the floor (without falling through) I imagine an elevator's fill of water might cushion the fall... Though you could end up drowning if you break your legs. I'd just stay away from water filled elevators. + +Edit: this is assuming the elevator is not ENTIRELY full. If it was full and the elevator didn't break I suppose you could survive if you had a scuba tank and buoyancy to float in the middle. But if we're assuming an unbreakable elevator, which this would essentially have to be, you should be able to lay on your back and walk away from it" +81 "When skipping rocks across water, how big can the rock get until it ""stops skipping""?" 2413 http://www.reddit.com/r/askscience/comments/31mbc0/when_skipping_rocks_across_water_how_big_can_the/ 1428321823 31mbc0 Physics 2015-04-06 15:03:43 "The only real reason we use small stones is the amount of energy needed, as you need [sufficient velocity and sufficient spin to maintain the angle of attack.](http://www.tarnews.co.za/water-skipping-stones-and-spheres/) If you have sufficient energy you could skip much larger stones. + +Technically, you can perform a [skip reentry](http://en.wikipedia.org/wiki/Skip_reentry) of a spacecraft, viewing the spaceship as the ""rock"" and the atmosphere as the ""water""." "So long as the correct angle and velocity can be achieved, I don't think there is any particular limit to the size of stone. Skipping is achieved when the displacement of water across the bottom of the stone creates more lift than the mass of the stone. Assuming your stone is of approximately the same shape, it's mass to surface area ratio stays relatively constant (a 'thin' stone is essentially a 2D object so it's not as sensitive to the square-cube problem) as it scales up, so it will displace proportionally the same amount of water. + +Now, you could probably extend this to the extreme and say that at some point the curvature of the earth would come into play or the tidal forces or whatever, but certainly any stone a human could conceivably cast into calm water could be skipped. + +For a person, the size limit is determined by the strength of the person to accelerate a stone to the necessary speed (according to the Guinness book of records, the best speed is around 12 m/s), with the appropriate rotational speed (rotation just acts to gyroscopically stabilize the stone, so that it maintains the same orientation after impacting the water - important for multiple skips, but not that important if you only require the stone to skip once to satisfy your criteria)" +399 Are any two electrons, or other pair of fundamental particles, identical? 2411 https://www.reddit.com/r/askscience/comments/4680r9/are_any_two_electrons_or_other_pair_of/ 1455709540 4680r9 Physics 2016-02-17 14:45:40 They are so identical that the state with electron A in state 1 and electron B in state 2 is **exactly the same state** as electron A in state 2 and electron B in state 1. This indistinguishability has measurable effects, most importantly it is evidenced by the statistical properties of ensembles of particles. [deleted] +196 Why is the oxygen to hydrogen mass ratio on the shuttle's external tank 6:1 instead of 8:1? 2404 http://www.reddit.com/r/askscience/comments/36zktg/why_is_the_oxygen_to_hydrogen_mass_ratio_on_the/ 1432389166 36zktg Engineering 2015-05-23 16:52:46 "An optimal reaction is indeed a 1:8 ratio, but having unburnt hydrogen in the exhaust produces a higher specific impulse. + +That is to say the fuel is more efficient in producing thrust when in a 1:6 ratio, even though energetically it is more efficient at 1:8." "The [rocket equation](http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation) determines vehicle acceleration, exhaust velocity is a key factor. Hydrogen is much lighter and easier to accelerate to higher velocities, which is why the shuttle (and other rockets) tend to run excess hydrogen. The tradeoff is that atomic (and molecular) kinetic energy is dependent on combustion temperature, which peaks at [stoichiometric mixture ratios](http://en.wikipedia.org/wiki/Stoichiometry). + +Ion thrusters use Xe because it maximizes ionization potential compared to storage mass. H2 doesn't store well as a liquid on long missions and requires large, heavy tanks as a gas." +197 Why does my brain sometimes recall a seemingly random memory that I haven't thought about in years? 2401 http://www.reddit.com/r/askscience/comments/3hfhvh/why_does_my_brain_sometimes_recall_a_seemingly/ 1439893555 3hfhvh Psychology 2015-08-18 13:25:55 "As others have said, this likely happens because some cue in your environment, or some aspect of a thought you were just having, was connected in some way to the sudden involuntary memory recall that you experience. + +One reason why the memory might not seem relevant is that the cue associated with it may be really subtle, or not very meaningful content-wise; a powerful example of this is when a smell or a sound (like part of a song) is associated in one's mind with a certain period of time or an event, or even a feeling about an event. This could lead to neural activation of circuits that represent other events or ideas or feelings from that time. + +It may also seem surprising that the memory isn't of something recent, but that in itself isn't a reason why it can't be associated with a current aspect of one's environment; memories appear to be more organized by emotions, senses, or ideas, rather than the time when they occurred (although we do attach temporal and spatial information to memories.) It does make it a little more surprising that you haven't already forgotten it, but we don't completely understand yet how memories are maintained over time; it could be that infrequently recalled memories are not deliberately discarded by the brain, but instead fade gradually, as the neurons and synapses involved in represented them are eventually recruited to be part of other memories instead. It's also been shown that the act of recalling a memory can actually change the information that is ""stored,"" conflating things that happened during recall with things during the original event, so in that sense, an infrequently recalled memory might possibly be more accurate than a recent one. + +This isn't the best article on the topic, but it does discuss some of these ideas, and is open access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4267106/#B3 + +Edit: In addition, it looks like there's some suggestion that this may happen even more than you realize, as your mind ""wanders"" from one idea to another--but you may not be aware of it very much, unless you are interrupted and become aware of what you are thinking, or perhaps are startled by the unexpectedness of the memory: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3981656/" "We still don't know why specific memories keep popping up, though most probably does relate to something going on in the present moment, even if you don't realize how. It might even be a repressed memory that was recalled (see first source below). The subconscious mind is a powerful thing. + +""... next time you have a mind-pop, remember that, however weird, it has probably been triggered by something you’ve seen, heard or thought about recently, even if you can’t remember what. Of course, why we get these particular ones and not others is still a mystery."" + +http://faculty.washington.edu/eloftus/Articles/lof93.htm + +http://www.spring.org.uk/2012/11/mind-pops-memories-that-come-from-nowhere.php" +1444 Why does the color of the sky get lighter, the closer it is to the horizon? 2399 https://www.reddit.com/r/askscience/comments/dfqxuo/why_does_the_color_of_the_sky_get_lighter_the/ 1570671436 dfqxuo Astronomy 2019-10-10 4:37:16 "It is because of so called ""Mie scattering"" of sun light in the haze, contained in lowest layers of athmosphere. +The light passing through the haze changes its direction to random other directions. So, it catches light from sun and directs some of it towards your eyes. + +When you look up, the layer of the haze is pretty thin and does not significally affect color of the sky. +But when you look to horizon your look goes through about 5 km full of the haze, and your eye catches all that scattered light." Actually, it's a bit of statistics, mixed with physics. The scattering effects described by others aren't wrong, they just aren't describing the whole picture of the question i believe you are asking. Two things in particular will contribute to the sky appearing lighter during sunset; the first being the contrast ratio between the sky and the ground being higher since the light rays are being projected onto a near-parallel surface causing the luminosity of the ground to drop; and the second being that a larger proprtion of the sun's light is now being absorbed into the atmosphere via scattering affects. When the sun is directly overhead, each square mile of atmosphere only has a distance as thick as the atmosphere's height for it to absorb and scatter the sun's light, meaning that the distance is relatively small to the distance it will travel through the atmosphere at sunset. During sunset, the sun's light is coming through the atmosphere at a low angle, which causes the light to effectively travel through even more miles of atmosphere than when shining straight down, allowing the atmosphere to absorb and scatter an even larger portion of the sun's light, making the sky appear brighter. +198 What determines the radius of curvature of a rainbow? 2396 http://www.reddit.com/r/askscience/comments/3b2jx4/what_determines_the_radius_of_curvature_of_a/ 1435238788 3b2jx4 Physics 2015-06-25 16:26:28 "Here is a simple fact that helps explain the shape: It is a ring at 42º centered around the antisolar point. Guess what the antisolar point is? The shadow of your head. + +It illustrates the fact that not everyone in a group of people is seeing the same rainbow, and helps you realize that light is being scattered every which way. Its one easy to grasp fact that explains a great deal about how rainbows work." "See [this](http://www.reddit.com/r/askscience/comments/lw26i/why_do_rainbows_form_in_an_arch/) thread for a pretty good description, with diagrams, of what causes rainbows. + +However, I think it's clearer to think of a rainbow not as a ""circle,"" or a curve at a fixed *distant* position in space, but rather as an entire [*conical surface*](https://en.wikipedia.org/?title=Rainbow#Explanation), with the vertex at your eye. It makes sense to talk about the half-angle of that cone (about 42 degrees), but its ""radius of curvature,"" [strictly speaking](https://en.wikipedia.org/wiki/Radius_of_curvature_(mathematics\)), would depend on *which* circular cross section of the cone (i.e., how far away) we're talking about. +" +82 I found out recently that the sun is not still, it is moving away from other stars. Is it fair to say nothing is standing still, or have scientists decided on a 'default' place that is 'standing still' so at least we can measure galactic speed against that? 2392 http://www.reddit.com/r/askscience/comments/33grt6/i_found_out_recently_that_the_sun_is_not_still_it/ 1429704200 33grt6 Astronomy 2015-04-22 15:03:20 "There is no ""absolute reference frame"" in the way you describe. One of the fundamental components of the theory of relativity is that the laws of physics are the same in every inertial reference frame. That means that if we see an object coming towards us with a constant speed, there is no way to say whether the object is in motion towards us and we're standing still, whether we're moving towards the object and the object is standing still, or whether both us and the object are both moving towards eachother. Each of these views is equally true. + +That means that when you want to perform calculations or do measurements on something, you have to choose what you use as your reference frame. A scientist in a lab, performing a short experiment, may just use the lab as his reference frame and assume it's standing still (and by extension the Earth, since it's rigidly attached to the lab). While an astronomer performing measurements over the course of several months or more, might use a reference frame in which he assumes some distant stars are stationary. + +Neither approach is wrong. Choosing an appropriate reference frame can greatly simplify calculations, so it is an important point to consider." "It's not so much that the Sun is 'moving away from other stars'. The Sun is part of a galaxy called the Milky Way, containing about 300 billion stars along with some gas, dust, stellar remnants, and plenty of dark matter. The Milky Way itself is part of a small cluster of galaxies known as the Local Group, containing three spiral galaxies and some dozens of dwarf galaxies. On intergalactic scales beyond the scale of the Local Group, all matter in the Universe is generally moving away from other matter. But the Local Group and the galaxies within it are close enough together to be gravitationally bound, and are not moving away from each other. + +Special relativity states that it's fundamentally impossible to have an absolute reference velocity. Velocity literally only exists as compared between two things. However, in practice, we often decide on certain objects as being suitable for reference, and compare the speeds of smaller nearby objects to those. + +The speeds of planets are usually measured relative to the star (or stellar remnant, or multiple of either) that they orbit, without worrying about the rest of the Universe outside. Similarly, the speeds of star systems within a galaxy are measured relative to the center of that galaxy. In this sense, the Earth is moving at about 30km/s around the Sun, and the Sun at about 220km/s around the center of the Milky Way. On intergalactic scales, finding a fixed reference velocity is somewhat harder, but we sometimes measure the speed of things relative to the Cosmic Microwave Background (CMB), a haze of low-energy photons left over from shortly after the Big Bang. The Milky Way is moving at about 550km/s relative to the CMB, but the Sun's current location in its galactic orbit mostly cancels out this velocity, leaving it moving at about 370km/s relative to the CMB." +83 Would it be possible to adjust your computer's or your tv's picture settings to match your eye prescription? 2384 http://www.reddit.com/r/askscience/comments/33jwnp/would_it_be_possible_to_adjust_your_computers_or/ 1429757488 33jwnp Engineering 2015-04-23 5:51:28 "You could take a lens (like in your glasses, but much bigger) and put it in front of your TV. The image would be distorted to everyone with different prescription from you, and you would have to hold your head in a specific spot in front of the TV in order for the lens to precisely compensate for your eyes. (If your head wasn't directly in front of the lens, the TV image would be distorted just like the image through your glasses is distorted towards the edges of the glasses.) + +But without bolting a giant lens onto your TV, no, you can't do it. " "I wondered the same thing a while back and found [this paper](http://web.media.mit.edu/~gordonw/VisionCorrectingDisplay/SIG2014-VisionCorrectingDisplay.pdf) that discusses a possible technique. TLDR: it's theoretically possible but not easy and would require a special ""computational light field display.""" +199 Do internal organs have anything akin to moles (benign growths)? If so, how common are they? 2381 http://www.reddit.com/r/askscience/comments/3fbu8s/do_internal_organs_have_anything_akin_to_moles/ 1438371877 3fbu8s Human Body 2015-07-31 22:44:37 "If you are asking whether or not multiple organ systems have benign entities which we see all the time a diagnostic imaging, the answer is unequivocally yes. For instance, we see things like [hemangiomas](https://en.wikipedia.org/wiki/Hemangioma) in the liver, [cysts](http://radiopaedia.org/articles/renal-cyst-1) in any number of organs, (as others have mentioned) [polyps](https://en.wikipedia.org/wiki/Colorectal_polyp) in the gastrointestinal tract, [meningiomas](https://en.wikipedia.org/wiki/Meningioma) in the [neuraxis](https://en.wikipedia.org/wiki/Neuraxis), among many other benign growths. I would argue that colonic polyps aren't really ""benign,"" though, because they can [transform](https://en.wikipedia.org/wiki/Malignant_transformation) into colon cancer (which is why we take them out at colonoscopy). + +It is important to recognize that benign growths can occur in places which are completely clinically inconsequential, or they can occur in places where their presence is actually quite significant. A great example of this dichotomy is in the abdomen versus in the calvarium - in the abdomen, there is a lot of potential space for the body to ""deal with"" the growth. Organs in the intra-abdominal space can get quite large before that becomes clinically significant (although we may see it on imaging). + +This is in contradistinction to growths in the skull. It is actually quite common to have meningiomas (which are benign proliferative tumors of the meninges - the thin lining that covers the brain and spinal cord) result in [mass effect](https://en.wikipedia.org/wiki/Mass_effect_\(medicine\)) on the brain, thus affecting clinical symptoms. They are benign in the sense that they will ~~never~~ [only very rarely](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2651555/) (thanks for the corrections below) become malignant/metastatic, but they can be very medically significant due to where they are located. In fact, a large part of any neurosurgical practice will involve resection of meningiomas." [deleted] +84 Do people sneeze while they sleep? 2375 http://www.reddit.com/r/askscience/comments/2vkpv0/do_people_sneeze_while_they_sleep/ 1423687449 2vkpv0 Human Body 2015-02-11 23:44:09 "This is an interesting (and very common) question. Here is an answer I have given in the past: + +> the trigeminal motoneuron pools that mediate the sneeze reflex [are inhibited during NREM sleep and are actively suppressed during REM sleep as part of atonia](http://jn.physiology.org/content/44/2/349). Which means it is much more difficult to sneeze during NREM sleep and nearly impossible in REM (without also causing waking). + +http://www.reddit.com/r/askscience/comments/natrc/do_you_sneeze_when_you_sleep/c37rj3d +https://www.reddit.com/r/askscience/comments/1mu2bp/why_dont_we_sneeze_in_our_sleep/ +https://www.reddit.com/r/askscience/comments/25s51z/why_dont_we_sneeze_when_we_sleep/ + +I clarify further in a comment in one of those threads: +>The distinction is that **you can wake up to sneeze, but you can't sneeze in your sleep**. You may be sleeping, wake up to sneeze, and immediately fall back asleep without remembering that you sneezed. + +To answer a few questions that were removed: + +* The neurons that relay sensory information from the nasal mucosa are not the same as the motor neurons that produce the sneeze reflex. The motor neurons are inhibited during sleep. The sensory neurons may be somewhat suppressed during REM sleep, but [it is not clear to me that these particular sensory neurons are completely inhibited like motor neurons, or that they are inhibited at all during NREM sleep](http://jn.physiology.org/content/73/6/2486.short) +* Motor signalling is indeed inhibited during sleep. There are varying grades of motor inhibition, ranging from 'hypotonia' (reduced muscle tone) during deep non-rapid eye movement (NREM) sleep to 'atonia' (flattened muscle tone) during rapid eye movement sleep (REM) sleep. +* Coughing, as with sneezing, can cause a wakening from sleep. Like sneezing, the behavior is violent enough that a person is most likely not *sleeping* at the exact moment when coughing. However, for a single cough or sneeze, a person may fall back asleep immediately. The distinction is very silly. +* Sleep apnea, like the cough or sneeze reflex, involves a 'sensory' input, specifically a chemosensation of of CO2 buildup (hypercapnia). Like sneezing and coughing, there are dedicated systems in the brainstem that detect and respond to this sensation, producing an awakening. Like sneezing and coughing, this awakening may be so brief as to be unnoticeable, but unlike sneezing and coughing, these awakenings may recur enough during the night as to disturb overall sleep. +* [Please do not ask for or give medical advice on AskScience](https://www.reddit.com/r/askscience/comments/s4chc/meta_medical_advice_on_askscience_the_guidelines/) +* See [/u/stalkthepootiepoot's post below](https://www.reddit.com/r/askscience/comments/2vkpv0/do_people_sneeze_while_they_sleep/coj62ph) for more details regarding the mechanisms of sneezing itself. + +Edit: For those new to AskScience and wondering why there are so many deleted posts, please see the AskScience guidelines about [top level comments](https://www.reddit.com/r/askscience/wiki/index#wiki_answering_askscience_questions) and [removal of comment trees](https://www.reddit.com/r/askscience/wiki/index#wiki_removing_comments). +" It's a bummer when this happens since once I'm awake, it's pretty hard for me to get back to sleep, and I've had this happen to me plenty a nights. Anyway, I read an [article](http://scienceillustrated.com.au/blog/science/ask-us-can-humans-sneeze-while-sleeping/) that this is due to allergy, illness, or outside stimulants like dusts or insects buzzing. +1279 "A person died in the apartment below me, and the body stayed there for 3 weeks. Why is the smell not leaving the walls/furniture, and why is that smell still occuring without the body? What are those chemicals? Are those chemical ""sticking"" to materials the same way it does for urine?" 2349 https://www.reddit.com/r/askscience/comments/b0z6cf/a_person_died_in_the_apartment_below_me_and_the/ 1552562795 b0z6cf 2019-03-14 14:26:35 Others have the science side covered. Talk to your apartment and ask that they move you. They have rendered your apartment unliveable, by not tearing the other down to studs to remove the smell. It sucks a lot for them, but that's what insurance is for. Demand that they move you, and get it in writing. You shouldn't live with that smell. As u/Lazaryx said below, those stinking things are amines, and they tend to be absorbed by different materials. So it's almost impossible to get them out of walls unless you're willing to strip the plaster and renovate the walls. This is typically an issue with nicotine (also an amine). You can clearly say where smoker lives. +85 If two cyclists - one 50kgs and one 100kgs ride up a hill, will the heavier cyclist have done exactly twice the work? 2345 http://www.reddit.com/r/askscience/comments/2xrw4x/if_two_cyclists_one_50kgs_and_one_100kgs_ride_up/ 1425378451 2xrw4x Physics 2015-03-03 13:27:31 "If the problem is reduced to the ideal case - no air resistance, weightless bikes with frictionless drivetrains, inflexible wheels with no slippage, then yes, the heavier rider will have done twice the work. + +You can see in all the other answers that there are a lot of other factors (air resistance, bike weight, tire flex, etc.) that can be added to the equation to get a more precise answer." "You are right in that the heavier cyclist would have performed twice the work against gravity, i.e. raised their gravitational potential energy twice as much (W = mgh). But the heavier cyclist would effectively do more work due to having to do more work against friction and drag. He also spends more energy pedalling as he has heavier legs. + +> And what is the appropriate measurement for that? Watt hours? + +You can measure work (and heat and energy) in many ways. Joule, Newton meters, Watt hours, Coulomb Volts etc. With mechanical work, such as cyclists riding up a hill, I would use Newton meters or Joule. + +EDIT: To reply to the most prominent follow-up comments: + +**you didn't account for the weight of the bicycle** + +I included the weight of the bicycle as well as the clothes, helmet and other carried items/accessories in the cyclist. If we only count the weight of the cyclist, the heavier one would do a little less work against gravity. + +**leg weight is not a factor** + +While leg weight doesn't contribute to any work against gravity. You do have to push with your legs to apply force to the pedals, and to make your legs move you have to overcome their inertia which is proportional to their mass. + +I cite an [example I made earlier](http://www.reddit.com/r/askscience/comments/2xrw4x/if_two_cyclists_one_50kgs_and_one_100kgs_ride_up/cp34z5w): + +> Imagine if you are on a stationary exercise bicycle with no resistance and had to carry a certain amount of weight. If you carried that weight in a back pack it would make almost no difference, but if the weight were strapped on your feet it would make it harder to pedal as it would increase the inertia of your feet. +" +86 When a person loses a limb and survives, how does the circulatory system deal with having a major blood vessel pathway that now ends abruptly instead of going where it should? 2343 http://www.reddit.com/r/askscience/comments/30kn77/when_a_person_loses_a_limb_and_survives_how_does/ 1427519029 30kn77 Medicine 2015-03-28 8:03:49 "After the trauma, the wound will heal. Of the many things occuring in this healing process, [angiogenesis](http://en.wikipedia.org/wiki/Angiogenesis) is one of them. This process fills in any circulatory ""gaps"" that you may be envisioning. +Additionally, since there seems to be a misconception of this next concept by the general public, it is important to note that arterial-to-venous connections are being made in about every square millimeter of tissue. A rule of thumb (that I was taught at least) is that the average cell in the human body needs to be no more than 2mm away from a capillary, specifically, to receive sufficient oxygen to survive. This means that along the ENTIRE length of your arm, there are arterial-to-venous connections, in the form of capillaries. Thus, when you chop off a distal part of your appendage, you have typically NOT screwed up the arterial-to-venous connections anywhere proximal to that point (Indeed, when you have exceptions to this rule, medical students are required to memorize them! A notable exception off the top of my head is the blood supply to your scaphoid bone in your wrist. Fracturing the distal bone can result in [avascular necrosis](http://en.wikipedia.org/wiki/Avascular_necrosis) of the proximal portions of the bone). + + +Forces of the circulatory system are modeled with a simple formula, MAP=COxTPR; Mean Arterial Pressure = Cardiac Output (i.e. flow) x Total Peripheral Resistance. This is directly analogous to the V=IR formula from any basic electromagnetism physics course. I'm intuitively guessing that this scenario is akin to removing a [resistor in parallel](http://en.wikipedia.org/wiki/Resistor#Series_and_parallel_resistors) from a circuit. I.e. since there are less tubes to flow through when blood leaves the heart and goes down the aorta, you would create a fluid pressure backup IF you maintained the same amount of blood volume that you had when you had an arm. However, normal body compensation would be to shed that excess and unnecessary water weight that served the original purpose of providing oxygen to the arm. So, this a fancy way of saying that the body compensates for less vessels for its blood to go through by shedding (peeing out) the excess water that used to travel through those vessels. Your blood pressure (Mean Arterial Pressure or Voltage) stays normal. Your Total Peripheral Resistance (or simply Resistance) is elevated. Your Cardiac Output (or Current) is decreased. The decreased cardiac output means the heart is working less hard, and might even be cardioprotective, although probably to a negligible level (and certainly nothing that smoking or obesity won't readily obfuscate). +This is my best go at what you would see from a physiological standpoint. If anyone else sees something I forgot to consider here, please let me know! + + +Now, this is off topic, but there is something called an [atrio-venous shunt](http://en.wikipedia.org/wiki/Arteriovenous_fistula), and is an abnormal shunting from the arterial system to the venous system without going through the capillary beds. It is kind-of like a ""short-circuit,"" and rapidly depletes the ARTERIAL blood volume (CO or Cardiac Output) and the blood pressure (MAP or Mean Arterial Pressure). The heart is kicked into overdrive to try to compensate, and the patient can die from long-standing high output cardiac failure (heart works so hard it keels over and dies). The reason I bring this up is because one of the causes of this is a disease called [Paget's Disease of the bone](http://en.wikipedia.org/wiki/Paget%27s_disease_of_bone). In this disease the bone is screwed up and consistently remodeling in the patient. Well, there are blood vessels that are normally going through the bone, so when the bone remodels, so do the blood vessels. In all actuality, it's like the bone is consistently breaking and rehealing, forcing the vessels to go along with the ride and adjust in the best way they can. However, unlike in our amputation case, in this case the vessel remodeling DOES really do some funky stuff where it bypasses capillary systems (forming the A-V shunts) and ends up causing death via high output cardiac failure. + +I hope any of this was at all helpful! like I mentioned above, my second paragraph was primarily educated assumptions, so it may have some errors just fyi. " "My biology is a little rusty, but I can give you a slight over view and hopefully someone can build on it. While it is true that blood flows artery to capillary to vein, there is numerous branching points. Which means if you lose a limb, the artery will never truly ""dead end"" it will just finish it's branching sooner. And as for volume changes, the body has numerous sensors for measuring blood pressure (a loss indicator of blood volume) and can thereby control the amount of blood in the body. So there will probably be a overall decrease in blood volume, but it will stay proportional meaning the heart really won't notice a difference in work load. " +1445 AskScience AMA Series: I'm Kit Yates. I'm here to talk about my new book, the Maths of Life and Death which is about the places maths can have an impact in people's everyday lives. I'd also love to discuss my research area of Mathematical Biology. Ask Me Anything! 2338 https://www.reddit.com/r/askscience/comments/daekxv/askscience_ama_series_im_kit_yates_im_here_to/ 1569668409 daekxv 2019-09-28 14:00:09 "What do you think is the most dangerous misconception by the public involving numbers or maths? +What’s your favorite real ale?" What is the best response to students who ask a math teacher why they need to know how to do high school level math? +87 Hubble's Law: How do we distinguish an expanding universe from an increasing speed of light? 2334 http://www.reddit.com/r/askscience/comments/2w35g8/hubbles_law_how_do_we_distinguish_an_expanding/ 1424103468 2w35g8 Physics 2015-02-16 19:17:48 "First, if the speed of light were changing, it would affect things like the fine structure constant, which plays a role in the type of emission lines atoms and molecules give off. Observations of distant nebulae show that the constant hasn't changed over billions of years. If I remember correctly, the observational constraint for the speed of light is something like no more than 1 in 10 million over 7 billion years. So independent of redshift expansion we know that the speed of light is constant. + +Second, it isn't just redshift that is used as evidence of cosmic expansion. We know things like the apparent angular size of galaxies change with distance due to expansion. There's the Alcock-Paczynski test, which compares redshift vs apparent size, and the Tolman test, which looks at the surface brightness of galaxies vs redshift. Both of these agree with cosmic expansion. + +So we can actually distinguish between the two models, and we find that expansion works and changing c doesn't. + +" "Many moons ago the idea of 'tired light' was put forth to explain the increasing redshifts of galaxies. So the experimenters went to work testing the possibility that the speed of light might not be a constant. + +Interferometry is an *exquisitely* sensitive technique to detect if light were changing speed, due to any number of isolatable causes. + +I'm much more comfortable with the idea of packing more or less 'Time' into a given volume of space. I believe there would be less objection too. Just as the amount of mass-energy that is found in an arbitrary and flexible region of space is indeterminate, and that mass-energy cannot be changed without applying a force from 'outside'." +88 "When people have a high pain tolerance, are experiencing less pain, or are they just better at ""sucking it up?""" 2334 http://www.reddit.com/r/askscience/comments/2wljyj/when_people_have_a_high_pain_tolerance_are/ 1424472860 2wljyj Human Body 2015-02-21 1:54:20 "First it is important to understand the difference between tolerance and threshold, and I think the answer is there are 2 kinds of people you are asking about. One with high tolerance and one with high threshold. + +A high pain threshold means that you can sustain a (relatively) high amount of damage to your person before you feel pain. + +A high pain tolerance means that you can have a lot of pain and continue to do normal tasks. + +So to answer your specific question those who have a high pain tolerance are better at ""sucking it up."" They can deal with a lot of pain and continue to function. Those with a high pain threshold do not feel pain unless more severely injured. +" "No, it is not all psychological. + +Pain may be mediated by a number of factors, including: +* Sleep deprivation^[1](http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2869.2001.00240.x/full) +* Sex^[2](http://www.sciencedirect.com/science/article/pii/S1526590008009097),[3](http://www.sciencedirect.com/science/article/pii/S0304395907005027) +* Humour^[4](http://www.hindawi.com/journals/jar/2010/343574/abs/) +* Depression and/or Anxiety^[5](http://www.sciencedirect.com/science/article/pii/000632239390041B),[6](http://www.sciencedirect.com/science/article/pii/S0304395908005125) +* And very likely countless others. + +Is there likely a significant psychological component? Yes. +Is pain a very multifactorial experience? Yes. + + +*Unfortunately, the links are to abstracts. Those of you without university/institution access may not be able to see the full articles*" +1446 Why do we lose control over our voices because of emotions? Why can some people control their voices better than others in that case? 2322 https://www.reddit.com/r/askscience/comments/dgys7o/why_do_we_lose_control_over_our_voices_because_of/ 1570904296 dgys7o Human Body 2019-10-12 21:18:16 "As others have mentioned, it has to do with the sympathetic nervous system, also called the [fight-or-flight response](https://en.wikipedia.org/wiki/Fight-or-flight_response), which can be triggered from strong emotions. In preparation for fighting or fleeing, your throat opens up to get as much air as possible. + +Part of this opening up includes making your vocal cord opening ([glottis](https://en.wikipedia.org/wiki/Glottis)) as big as possible - which you feel as a lump in your throat. This makes it easier to get as much air in as possible, but makes it harder for your vocal cords to vibrate, changing the sounds of your voice." Because emotional energy is still a form of energy that needs to be exerted. It usually comes out in peoples voices from them trying to contain their emotion in their facial expression. Emotions can be inhibited and contained but the energy is still stored in the body, that’s why it doesn’t come out in the voice of others. +89 Does a harddrive get heavier the more data it holds? 2307 http://www.reddit.com/r/askscience/comments/30hl5a/does_a_harddrive_get_heavier_the_more_data_it/ 1427462264 30hl5a Computing 2015-03-27 16:17:44 "What is meant by the more data it holds? If I take a brand new hard drive and save a bunch of random data on it, the hard drive would not be any heavier. The magnetic state of the bits are all that is changing. While you can say that electrons have mass and so there is an increase in electrons and therefore an increase in mass, as you load data onto a hard you are not necessarily changing the distribution of bits set to 1 and 0. This is because an ""empty"" hard drive is not necessarily full of 0 bits. The state of the magnetic strip is simply undefined. As you load data, all you are doing is configuring portions of the drive to hold meaningful information. This does not increase the amount of work the drive must do in order to preserve that state. " "PEOPLE, READ FULL COMMENT FIRST, THEN RESPOND TO IT, EDIT IS JUST BELOW MY ORIGINAL ANSWER + +No (edit below: yes, then again no), as there is no mass addition, only [magnetic state change] (http://www.explainthatstuff.com/harddrive.html). +There was actually a [sci-fi story] (https://en.wikipedia.org/wiki/The_Star_Diaries) about this concept, written by Stanislaw Lem. + +EDIT: +Okay, yes, electrons have mass and because hard drives work using [floating gates] (https://en.wikipedia.org/wiki/Floating-gate_MOSFET) which hold charge, yes it gains mass. +You can't really measure it thought with accessible instruments. + +EDIT 2: And again - no, as floating gate is only relevant to flash memory, and HDD has only magnetic state change by changing SN into NS, so there is no electron state change." +1280 How does iron ore form from individual molecules created in a generation 1 star? 2304 https://www.reddit.com/r/askscience/comments/bhf4m6/how_does_iron_ore_form_from_individual_molecules/ 1556233156 bhf4m6 2019-04-26 1:59:16 "Iron on Earth used to be elemental iron. The iron we find today are different forms of oxide. Basically everything that is red contains some form of iron oxide. That's a conundrum because oxygen is very reactive so there used to be no free oxygen in Earth's atmosphere and as a result no new oxides could form. There was ~~atomic~~ iron basically floating through the oceans in great quantities. Iron is the most stable atom so there is an ""iron peak"", stars form a lot more iron than other heavy elements. As a side note the atmosphere of Earth also contained methane and hydrogen. + +This all changed during the great oxygenation event around 1.8 billion years ago. At this time, the first ~~algae~~ cyanobacteria evolved, creating oxygen through photosynthesis. This lead to two things. First, all other live on Earth died, since oxygen is toxic. Secondly, everything on the surface of the Earth or in the oceans that could oxidize, did. All the methane and hydrogen burned up, which might have lead to ""snowball Earth"", entering a huge ice age because of the absence of methane. + +The scale of this event is truly, truly massive. Think about the red deserts in Australia, and realize that this is all iron oxide, and that every single oxygen atom within it had to be released by photosynthesis. As such, the GOE lasted quite a while, over a billion years, until everything was oxidized and the atmospheric oxygen levels began to rise. + +Anyway, the free iron floating in the oceans oxidized as well. Iron oxide isn't as soluble, so it floated to the bottom of the ocean and formed banded iron formations. This is most of our iron ore. + +https://en.wikipedia.org/wiki/Great_Oxygenation_Event" "It is assumed that at the beginning of time as 1st generation stars began forming, they only had hydrogen and helium to work with. These stars mostly are many more masses than our sun so they consist of more material. The universe at the time also was more violent, forming more stars and at a faster rate. + +Most 1st gen stars originated in clumps along with hydrogen, like a nebula, and most went nova at the same time saturating the nebula with heavier elements, like iron. This means that the nebula or even small galaxy at the time was constantly being saturated with heavy elements, and mostly a large amount of them. + +This article may help you understand this topic better if I did not do as well; http://www.astro.yale.edu/larson/papers/SciAm04.pdf" +90 Do scientists take precautions when probing other planets/bodies for microbial life to ensure that the equipment doesn't have existing microbes on them? If so, how? 2290 http://www.reddit.com/r/askscience/comments/32i1re/do_scientists_take_precautions_when_probing_other/ 1428967863 32i1re Planetary Sci. 2015-04-14 2:31:03 "Absolutely. In fact, NASA has an entire ""Office of Planetary Protection"" to deal with just this issue. Here's their web site: + +http://planetaryprotection.nasa.gov/methods + +In short, space probes are assembled in clean rooms (filtered air, etc.) to cut down on the microbial contamination right from the start, and then sterilized by dry-heating the entire spacecraft and/or subjecting it to hydrogen peroxide vapors." "Hi, Aerospace Engineer here! + +If I understand your question correctly, you are asking whether or not other celestial bodies may contaminate probe/lander surfaces, or if we can cross-contaminate as well. The answer to both is yes, scientists and engineers have prepared for these scenarios for quite some time! + +[Scientists continuously research whether this can happen even naturally,](http://arxiv.org/ftp/arxiv/papers/0809/0809.0378.pdf) as some asteroids upon impact (let's say, one hit Mars) can launch material into space and end up within Earth's atmosphere. A lander/probe can make a transfer of microbes a lot more directly. [Here's](http://spacemicrobes.org/) a great source that describes/lists some microbes found on landers, launch vehicles, rovers, etc. + +How do we prepare our vehicles for these microbes? There are proactive and retroactive things we can do. One famous example of a retroactive solution (happened after the launch and vehicle recovery) came from Apollo 11. NASA feared that the astronauts may have carried with them microbes from the lunar surface, and quarantined them in a [specially outfitted streamliner](http://airandspace.si.edu/explore-and-learn/multimedia/detail.cfm?id=5251) and they stayed there for 30 days. Also, NASA constructed and used a special Lunar Receiving Lab, capable of studying/destroying any possible microbes that contaminated the surface of the returned command module. In this sense, NASA was prepared to deal with any microbes AFTER the vehicle was recovered. + +Nowadays, [spacecraft clean rooms](http://www.jpl.nasa.gov/news/news.php?release=2013-319) are common by many launch/assembly centers. These clean rooms usually superheat surfaces/materials that may be subject to contamination. Another method of cleaning parts before assembly is a peroxide bath. However, close examination of each cleaned part is key. + +So yeah, cross-contamination is a thing to prepare for! Hope I helped!" +91 Is a black hole a perfect sphere or is it not due to its spinning? 2280 http://www.reddit.com/r/askscience/comments/2t1k80/is_a_black_hole_a_perfect_sphere_or_is_it_not_due/ 1421754876 2t1k80 Physics 2015-01-20 14:54:36 A non-rotating black hole is a perfect sphere. A rotating black hole's event horizon is a perfect sphere, and its ergosphere is an oblate spheroid. "A non-rotating black hole would be a sphere; if such a thing could exist. Conservation of angular momentum says that the star would spin much more rapidly as it collapses; even a very slowly rotating star becomes a very quickly rotating black hole. + +Additionally, if somehow a non-rotating black hole could form, it would begin to rotate as matter falls into it, since the matter would be imparting angular momentum." +92 In a vast universe, is it possible that a solid gold planet exists? 2259 http://www.reddit.com/r/askscience/comments/2y6qau/in_a_vast_universe_is_it_possible_that_a_solid/ 1425683371 2y6qau Astronomy 2015-03-07 2:09:31 "It's really really unlikely. Gold is produced in highly energetic events like supernovae that come with a lot of accompanying matter. + +On a lower energy chemical scale, gold binds to iron really well (which is present in the same events) and makes it highly unlikely to get a planet made purely of gold. " Unless built artificially, it's ridiculously improbable for a planet to end up that way. Heavy elements like gold are produced by supernovas, and a supernova tends to produce a mix of many elements, most of them lighter than gold. Thus, the rocky planets formed from supernova debris tend to contain just such a mix of elements. +93 Can an organ recipient donate the organ he recieved? 2231 http://www.reddit.com/r/askscience/comments/2w4tiw/can_an_organ_recipient_donate_the_organ_he/ 1424130584 2w4tiw Medicine 2015-02-17 2:49:44 "Yes, it's been done. There's a few case reports out there for kidneys and hearts. Re-using a transplanted organ is, as expected, full of drawbacks. Two periods of sitting on ice without blood flow and exposure to an additional immune system make graft failure more likely, but it's been done: + +Kidney: http://ckj.oxfordjournals.org/content/5/5/434.full + +Heart: http://www.nejm.org/doi/full/10.1056/NEJM199302043280505" "Yes! Liver re-transplantation was done for the very first time last year in Hong Kong, a liver that was transplanted 11 years ago was ""re-transplanted"" into a another recipient after the original recipient died. The liver has now lived a total of 78 years in 3 separate people. + +I was actually at the lead surgeon's seminar about this surgery, and the he mentioned that the liver is a special organ that is capable of rapid regeneration and does not age with the body, so theoretically it can be transplanted many times and still remain functional. + + +Source: [http://www.scmp.com/news/hong-kong/article/1617979/world-first-hong-kong-surgeons-perform-double-liver-transplant](http://www.scmp.com/news/hong-kong/article/1617979/world-first-hong-kong-surgeons-perform-double-liver-transplant) + +Edit: reposted as answer to original question and added source" +1696 Do spiders ever take up residence in abandoned webs? 2218 https://www.reddit.com/r/askscience/comments/jw9lrt/do_spiders_ever_take_up_residence_in_abandoned/ 1605675540 jw9lrt Biology 2020-11-18 7:59:00 "The webs themselves? Not so much but that super awesome bug catching spot with what looks like an abandoned web already in it? Absolutely! + +They are much more likely to simply build over an existing web or just take the awesome spot instead of reusing a web." "Spider's web are specific (like a fingerprint). They are fragile structures that need constant care and reparations, they won't last long (there are spiders that make stronger webs but still not enough resistant to several days of band conditions). + + + + +It's also important to point that some spiders are eaten by other spiders so it would be very risky to use an unknown web. Also, species of spiders use webs for different purposes (to live underwater too!), so they build them accordingly to their particular way of living (some to hunt, some to have a nice house)." +94 What is more dense (in terms of volume): an atom or a galaxy? 2216 http://www.reddit.com/r/askscience/comments/2uvfns/what_is_more_dense_in_terms_of_volume_an_atom_or/ 1423146381 2uvfns Physics 2015-02-05 17:26:21 "I HAVE YOUR ANSWER. The ratio of volume to volume! +Volume of proton to volume of hydrogen atom, and +Volume of all the stars in the Milky Way to volume of the Milky Way. +Atomic: (2.57 x 10^-45 ) / (6.2 x 10^-31 )=4.2 x 10^-15 cubic meters of space taken up for every cubic meter of empty space. +Galactic: (4.23 x 10^38) / (8.04 x 10^61 )= 5.25 x 10^-24 cubic meters of space taken up for every meter of empty space. +Thus, in terms of volume, atoms are or 784761904 times more dense than galaxies! +Edit to fix math" "**Short Answer:** An atom, for obvious reasons. + +**Longer answer:** Approximate the Milky Way as a disk 1000 lightyears thick, with a radius of 50,000 light years, containing 100 billion stars, each with the mass of the sun. + +The Milky Way then has a total mass of: + + M = (2x10^30 kg) (10^11) = 2x10^41 kg + +And has a volume of: + + V = pi (50,000 ly)^2 x (1,000 ly) = 7.8x10^12 ly^3 = 6.7x10^60 m^3 + +Thus, the Milky Way has a density of about 10^-19 kg/m^(3). + + +A proton has a mass of 1.7x10^-27 kg, and a hydrogen atom has a diameter of about 1 Angstrom (10^-10 meters), so a radius of 0.5 Angstroms. So mass divided by volume gives you the density of about [3000 kg/m^3](http://www.wolframalpha.com/input/?i=939+MeV%2Fc^2+%2F+%284%2F3+*pi*+%280.5+Angstrom%29^3+%29+%3D), or 22 orders of magnitude denser than a galaxy. + + +This makes sense, and I didn't need to do the math to know this, because in conventional matter which has densities of about 1000 kg/m^3 there are tightly packed atoms, *so the density of conventional matter should be approximately the density of an atom that makes up that stuff.* Why? Imagine I had a brick with some density. If I cut it in half, both halves have half the mass and half the volume, so they are the same density. I can keep cutting these things in half until I'm basically at the atomic level, and at no point should the halving cuts produced something with a different density than the original material. + +In space, there's a lot of empty room when you aren't inside a star or planet, so that's going to drag down the average density of a galaxy. If stuff in space is built out of atoms, but now we're adding in space (vacuum) between them, the galaxy's density is going to be less than that of it's constituents. What's denser, a single brick? Or all the bricks in my neighborhood? Even though some are clustered into houses, when I'm calculating density I have to take into account all the space in between them. It's the same principle with atoms in galaxies. + +Edit: As for OPs follow up question- what about fractional occupied volume? What *fraction* of volume of a galaxy is occupied by matter, and what fraction of volume in an atom is occupied by the nucleus? It'll still be the same answer, though it might differ by several orders of magnitude from above, but it's the same argument as with the bricks. A galaxy is made of clumps of atoms spread really thin, so the nucleus of the atom will occupy fractional volume. + +Also, I'd like to take a minute and disspell another myth that's getting floated here: the atom is not *mostly empty space* or a *vacuum* outside the nucleus. The electron cloud spreads out and occupies a bunch of that space. It's not a little point that runs around the nucleus like a little solar system, [but instead is a smear of electron wave.](http://www.webelements.com/shop/shopimages/products/extras/POS0007-A2-orbitron-2010-800.jpg) + + +" +95 Can a microwave oven interfere with my wifi? 2205 http://www.reddit.com/r/askscience/comments/2xipte/can_a_microwave_oven_interfere_with_my_wifi/ 1425174334 2xipte Physics 2015-03-01 4:45:34 "Yes, it actually can. Standard wireless routers and microwave ovens both operate on similar frequencies (around 2.4 GHz), so microwave ovens can and do interfere with routers. + +You can potentially get a dual-band router (one which operates both at ~2.4 GHz and ~5 GHz) and configure it to rely on the 5 GHz channel, but this is probably not worth it unless your microwave is on a *lot* of the time." "Took this example a few years ago with a 2.4Ghz wireless analyser to explain it: + +http://imgur.com/23hN3 + +""So, there's a few APs on chan11 (which is spread between 9 and 13), something specifically on channel 1 (which won't be wifi, its too narrow). Bottom graph, vertical axis is time, horizontal axis is frequency, colour indicates amplitude. Its clear the instructions on the soup wanted two minutes, stir, then one minute as you can see, the entire spectrum is /hammered/."" +" +1447 AskScience AMA Series: I'm Alison Van Eenennaam, a researcher in animal genetics in the Department of Animal Science at the University of California, Davis. I'm here to answer questions about genome editing and its potential to bring useful genetic variants into agricultural breeding programs. AMA! 2204 https://www.reddit.com/r/askscience/comments/dgdihi/askscience_ama_series_im_alison_van_eenennaam_a/ 1570791617 dgdihi 2019-10-11 14:00:17 What new technologies and developments do you see in the next 50 years? "Can gene editing ,specifically CRISPR, be used to target no only specific sequences but also specific locations such as the pancreas to repair the genetic components of diseases like diabetes or would it have to be coupled with an antibody or activity target that specificaly targets these areas? +Thank you +A.M. +Umkc bs bio" +1894 How does Mad Cow Disease stay dormant for upto decades in humans? How have we still not eliminated the disease? 2201 https://www.reddit.com/r/askscience/comments/o161aj/how_does_mad_cow_disease_stay_dormant_for_upto/ 1623853293 o161aj Human Body 2021-06-16 17:21:33 "So prion disease(s) are quite nuanced, but I will try and give you the most succinct explanations: + +> How does Mad Cow Disease stay dormant for that long without visible negative effects? + +So first off, when mad cow disease (bovine spongiform encephalopathy) is transmitted to humans, we call it variant Cruetzfeldt-Jakob Disease (vCJD), not mad cow disease. Second, it isn't ""dormant"" in the person, it's just that the person has not had any clinical symptoms yet. The misfolding, accumulation, and associated neuronal death builds up over time until such a point where the loss of neurons/brain tissue is so severe that the person presents with clinical symptoms. Furthermore, we don't know what the incubation time will be as it can vary from patient to patient based on CJD strain type and genetics of the person. + +> Why can't we just test for the individuals who might have it? + +We do have some tests now which can help support a prion disease diagnosis. [Protein Misfolding Cyclic Amplification (PMCA)](https://pubmed.ncbi.nlm.nih.gov/22528092/) and [real-time Quaking-Induced Conversion (rt-QuIC)](https://pn.bmj.com/content/19/1/49) are both useful for this purpose. Neurologists can also [check for levels of a protein called 14-3-3](https://pubmed.ncbi.nlm.nih.gov/9450766/) to aid in the diagnosis, however, the standard method is to eliminate other potential diseases that present similarly in clinic (Alzheimer's being a major one) in combination with one or more of the previously mentioned tests. (there are also changes in brain imaging which can also support the diagnosis). However, the gold standard is still post-mortem analysis (ie. autopsy confirmation). + +> How have we not eliminated it yet? + +So this one is tough to answer, but it likely has to do with a few things: + +1) We do not fully understand *how* prions misfold. We know that the misfolded prion protein(s) interact with other, normally folded prion protein(s) to cause them to misfold, likely with the help of chaperones and other cellular constituents. There are some recent papers that came out suggesting it forms [some intermediary species](https://www.pnas.org/content/118/12/e2019631118) that help promote conversion, but still much work to be done. + +2) Unfortunately, once a patient is diagnosed with prion disease, it is likely far too late for any intervention to be of any help outside of possibly slowing down the disease progress. This is because, generally, when the cells in the brain die (specifically neurons), you don't get them back. And by the time a person presents with clinical symptoms, that usually means enough of their brain has deteriorated beyond a point which medical science can repair. + +3) There are antibody studies being done to see if they can be of therapeutic use, but a big issue is that some antibodies may only recognize either the folded or misfolded version of the prion protein, and not all misfolded version are the same (this speaks to a theory in the prion field called the [""Cloud Hypothesis""](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4189885/#:~:text=The%20%E2%80%9Ccloud%E2%80%9D%20hypothesis%20assumes%20that,appears%20similar%20to%20prion%20adaptation.)). Further, removing all prion protein from the body could work (ie. knocking down the gene), as this has been shown to [prevent disease in mouse models](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634447/), because without the normal prion protein available, there is nothing to misfold! Even though there are negligible changes in the PrnpKO mice, we do not know what knocking down/knocking out the prion protein in humans would do, because we do not have a clear understanding on what the normal prion protein does! [(studies have shown it plays a role in synapse maintenance, neuron maturation, cell-signaling, cell adhesion, and a protective role against oxidative stress)](https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1006458#:~:text=Defining%20PrP%20function%20may%20shed,a%20protective%20role%20against%20stress.) + +There is a lot more to it, but that is the best summary I can give without writing a novel!" "Currently writing my PhD thesis on a prion vaccine - I'll get to that in a bit. Also used to work for the CFIA as a summer student. + +Mad cow disease (BSE) causes variant CJD (vCJD) in humans, and it is true that the incubation period can be decades long. It stays dormant - also known as a pre-clinical phase - because of fundamentally how prions work. Prions fall under protein-misfolding diseases, with an extra sprinkle of deadly on top of it: misfolded prions can either seed or template (depending on which conversion theory you believe) properly folded prion protein into the misfolded/disease causing form; this is known as the prion principle, This is also what makes it infectious. + +As for the long incubation period, in a nutshell, the prion protein that you make is slightly different than the prion protein that a cow makes. Thus, there is something called a species barrier that sometimes prevents a different host from getting infected. The best example of this is scrapie (sheep prion disease) which has been known since ancient times, yet scrapie is also known to not infect humans (zoonosis). The assumption is that the species barrier between sheep and humans are just too great for misfolded sheep prions to convert properly folded human prion proteins. + +For the case of BSE to cause vCJD, sometimes the species barrier is overcome and it does cause disease, it just takes a long time because the cow and human prion protein are still quite different, but not so different that it is impossible to overcome, like in the case of scrapie. Now of course there are polymorphisms that can either increase or decrease your susceptibility to prion diseases. Comment if you want more explanation of this. + +As for why we haven't eliminated it, we...kind of have, for practical purposes. Most governmental agencies (USDA in the US, CFIA in Canada) have a list of specified risk materials (SRMs) that by law make it so that certain parts of a animal (e.g. cow) cannot be processed if it is to be consumed by humans. Example SRMs included brain, eyes, parts of the gut, and some more. Removal of SRMs make it so that BSE essentially never enters a human food chain, and since we stopped doing meat and bone meal (MBM) BSE really is quite controlled. Both the USDA and CFIA also still do surveillance (regular random BSE testing), and Europe's regulating agency actually tests every single cow that is meant for human consumption. So enjoy your beef. vCJD has an occurrence rate of something like 1×10^-9, so nothing to worry about there. + +Why haven't we completely eliminated it? Well the prion protein is a self protein and despite the misfolded/infectious prion protein being toxic, it still is a self protein at the end of the day and your body will not really have an immune response against it. This is normal, since otherwise we would all have auto-immune disease, where your body just starts attacking your own self made proteins. And if you know anything about vaccine design, it's very difficult to design a vaccine that only removes the misfolded version because biochemically (amino acid compostion, charge, size) they are identical. The only difference is the 3D shape of it. And also because vCJD is just so rare, and CJD in general is usually sporadic (unknown cause) or genetic, so no pharmaceutical company would develop drugs/treatment for it. + +As for testing, the current gold standard is post-mortem testing, which is obviously not possible for humans. Current tests are all amplification based tests like PMCA or RT-QuIC, which can be extremely sensitive, but they're not the easiest assays to run and can be quite finicky. Blood is also just generally hard to work with because many components of blood mess with the tests in this case. They are being worked on though. + +The vaccine I have worked on is like 6 years worth of work and obviously not going to explain it here. In essence, we were able to overcome the self protein tolerance so that your immune response actually removes the infectious prion form. We have a manuscript on the way though! + +Hopefully this helps. + +Edit: typos." +96 Why does hot water make more bubbles than cold when I'm washing my hands? 2197 http://www.reddit.com/r/askscience/comments/2wrgx9/why_does_hot_water_make_more_bubbles_than_cold/ 1424616626 2wrgx9 Chemistry 2015-02-22 17:50:26 Hot water has less surface tension. This is also why it is better at cleaning. The molecules of warm water move around more than cold water and as a result are less tightly bonded. Soap works by bonding the hydrophilic end of a soap molecule to a water molecule. The other end of the soap molecule is hydrophobic and will bond to grease and dirt. The soap reduces surface tension even more making the water 'stretchy'. This is what makes bubbles. Because the warm water has less surface tension to begin with, the soap can more easily bond with the warm water molecules than the cold ones. This means the soap is more effective at bonding to the water and as a result more foaming action. "No other people mentioned viscosity, which will be lower at higher temperatures. Lower viscosity leads to better mixing, and hence more foaming. + +The surface tension argument doesn't hold water - it's about a 10% decrease (http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/imgflu/surten3.gif) from 20 to 50 C + +Viscosity drops by 50% from 20C to 50C. And if we're looking at the difference between COLD water and hot water, well, it's even more (https://syeilendrapramuditya.files.wordpress.com/2011/08/water_dynamic_viscosity_vs_temperature.gif)" +97 The third fastest Supercomputer (Sequoia) is simulating nuclear weapons. What is the point in it and how is it done? 2189 http://www.reddit.com/r/askscience/comments/2znfkc/the_third_fastest_supercomputer_sequoia_is/ 1426813435 2znfkc Physics 2015-03-20 4:03:55 "They are likely using Monte Carlo physics simulation software to do this simulation work. Monte Carlo simulation requires heavy heavy floating point calculations in addition to lots of quality pseudo random number generation. When atoms split into smaller subatomic particles they create a cascade of particles that interact with matter and EM fields. This cascading effect, especially prominent in fission reactions, have many collisions. To get a quality net result of these collisions you need to run many interactions and iterations of the entire system of particles. + +Fission reactions are particularly computationally complex due to the raw number of neutrons produced in addition to all the inelastic collisions they go through. You also have gamma rays being emitted and interacting, creating more particles cascades. + +Just to give you an idea of how far the turtles go, [this is a picture of a single cosmic ray collision.](http://astrobites.org/wp-content/uploads/2013/06/particle_cascade.png) + +Fission reactions occur in much larger quantities and produce huge swaths of data. + +Could we build bigger nuclear weapons with this research without testing? Possibly. The most likely reason for this work is to determine if the current stock pile is still effective and if the pits have decayed in such a manner that the yields will diminish. It's also likely being used to determine if foreign stockpiles are still a valid threat. + +I'd bet on them still being perfectly fine. + +Some examples of simulation software that is used in the nuclear physics community: MCNP and Fluka. In case you're interested in learning more about this field. + +Credentials: did a lot of simulation work like this in my previous job." "In the absence of physical testing, banned by international treaty, the military must [have a way to ensure](http://www.state.gov/t/avc/rls/202014.htm) that the bombs will function as desired after years of storage, handling, and transport, and in addition after the process of delivery to the intended location, and subsequent detonation. + +[For example](http://www.washingtonpost.com/national/national-security/supercomputers-offer-tools-for-nuclear-testing--and-solving-nuclear-mysteries/2011/10/03/gIQAjnngdM_story.html): + +> Then came a surprise. The computer simulations showed that at a certain point from stockpile to target, the weapon would “fail catastrophically,” according to Bruce T. Goodwin, principal associate director at Livermore for weapons programs. Such a failure would mean that the weapon would not produce the explosive yield expected by the military — either none at all, or something quite different than required to properly hit the target. + +> “So we went in and thoroughly investigated that, and determined that the way the weapon is handled by the military had to be changed, or you would be susceptible to having the weapons fail catastrophically when, God forbid, they should ever be used,” Goodwin said. He added that the fault occurred in the “real dynamics of the vehicle” — a term describing the weapon’s trajectory and behavior — and could not have been revealed by underground explosive testing or by examining the components. + +> Following the discovery and a multi-year effort, the [B-83 bombs](http://en.wikipedia.org/wiki/B83_nuclear_bomb) and the military’s handling procedures for the weapons have been fixed, officials said. + +Such simulations can always use more computing power: + +> Streitz said that over time, it became clear that smaller computer simulations were returning incorrect answers; only with finer resolution and more power could scientists grasp what was really happening. + +> In one example involving molten copper and aluminum, Streitz said, 9 billion atoms were modeled. It took more than 212,000 computer processors more than a week to carry out the simulation, he said, but the result was a near-perfect resolution of how the metals behaved. + +> “This is millions of times finer than you could ever do in a nuclear test,” Goodwin said. “You could never see this process go on inside a nuclear explosion.”" +98 The aluminum we interact with on a daily basis is coated in a fine layer of aluminum oxide. Is there any difference between this layer and sapphire? 2187 http://www.reddit.com/r/askscience/comments/2slbm3/the_aluminum_we_interact_with_on_a_daily_basis_is/ 1421379204 2slbm3 Chemistry 2015-01-16 6:33:24 "Perhaps a bit surprisingly, compositionally the aluminum oxide layer that spontaneously forms on bulk aluminum and sapphire are very similar, as in both cases the material consists mostly of Al2O3. The difference between the two materials consists in crystallinity and the presence of trace impurities. Whereas the aluminum layer formed on bulk aluminum via spontaneous oxidation or [anodizing](http://en.wikipedia.org/wiki/Anodizing), sapphire is a crystalline form of aluminum oxide. + +Looking more closely at the crystalline form, which has the crystal structure α-Al2O3, it should be noted that in the absence of impurities the crystal would be transparent in the visible range. However, when certain impurities are found, the crystal can gain vivid colors. Sapphire is such an example, which can appear [green](http://www.dwscustomjewelry.com/wp-content/themes/shopperpress/thumbs/2.17ct%20Green%20Sapphire.jpg) if it includes trace magnesium impurities or [blue](http://upload.wikimedia.org/wikipedia/commons/b/b9/Geschliffener_blauer_Saphir.jpg) if it includes trace iron. Another example is ruby, the [bright red color](http://yourproductexports.weebly.com/uploads/3/7/6/6/37663183/s641335049283751249_p2_i1_w1600.jpeg) of which is due to trace chromium." Crystalline α-aluminium oxide is called corundum and it is corundum of gem quality with trace impurities that make sapphires and rubies. The color of the gem is dependent on what type of impurity. Pure aluminum will not have the impurities which means no colors, and when it anodizes the aluminum oxide is an amorphous layer. Since it's amorphous, it doesn't really have the crystalline structure and won't form into any gems. +1448 The Gauche Effect. I don't understand how, on the subject of Newman Projections, that the gauche conformation of 2-fluoroethanol, for instance, can be more stable than the anti? 2176 https://www.reddit.com/r/askscience/comments/d8w7zd/the_gauche_effect_i_dont_understand_how_on_the/ 1569373257 d8w7zd Chemistry 2019-09-25 4:00:57 My understanding it is hyperconjugation. There is electron donation from a C-H bond into the antibonding orbital of the C-F bond - this is only possible when the C-H and C-F bonds are anti to ech other (and so the C-O and C-F are gauche). In the gas phase there is also internal H-bonding between the OH and the F bringing them together "In stereochemistry course last year we had the same question about 2-bromoethanol. The teacher told us that an hydrogen bond can form between the proton of the hydroxy group and the halogen when they are in gauche conformation, which lowers the overall energy of the compound. + +The other answers give different reasons, I would very much like to know which one is right!" +99 If the Universe keeps expanding at an increasing rate, will there be a time when that space between things expands beyond the speed of light? 2164 http://www.reddit.com/r/askscience/comments/3239yy/if_the_universe_keeps_expanding_at_an_increasing/ 1428644799 3239yy Physics 2015-04-10 8:46:39 "You've already gotten good answers. I'd just like to quote an old post of mine to explain why it's nonsensical to talk about ""expansion greater than the speed of light"": + +[Post](http://www.reddit.com/r/askscience/comments/2u5k0t/is_there_a_limit_to_the_speed_of_sound/co5twcj) +> Given any positive expansion (Not a retraction) of space you can always find two arbitrary points A and B for which light emitted at any of the two points cannot reach the other point. You just need to select these two arbitrary points in space far enough from each other such that the collective expansion of space in between the points exceeds the speed of light. +With that in mind, as soon as you have ANY expansion, ANY expansion at all whether it's really really slow, or crazy crazy fast, it's ultimately ALWAYS faster than light at some scale. Thus we can say expansion of space is ALWAYS faster than light. What does that tell us in and of itself? Nothing. + +So in summation, as soon as you have expansion of space, it's automatically faster than light. + +EDIT: I'm just a layman, I've got some undergrad courses and elementary school physics under my belt and I really just learn by reading /r/askscience. So if I don't respond that's because I'm not qualified to answer you. :(" This is already happening. Look 13 billion light years in one direction, and then in the opposite direction, and the things you are looking at are traveling away from each other faster than the speed of light. +1449 Why do cosmologists hypothesize the existence of unobservable matter or force(s) to fit standard model predictions instead of assuming that the standard model is, like classical mechanics, incomplete? 2157 https://www.reddit.com/r/askscience/comments/drggcs/why_do_cosmologists_hypothesize_the_existence_of/ 1572867692 drggcs 2019-11-04 14:41:32 "I copied this from another user who couldn't remember who originally wrote this comment. + +Below is basically a historical approach to why we believe in dark matter. [I will also cite this paper](http://arxiv.org/pdf/1006.2483v2.pdf) for the serious student who wants to read more, or who wants to check my claims agains the literature. + + 1. In the early 1930s, a Dutch scientist named Jan Oort originally found that there are objects in galaxies that are moving faster than the escape velocity of the same galaxies (given the observed mass) and concluded there must be unobservable mass holding these objects in and published his theory in 1932. + +Evidence 1: Objects in galaxies often move faster than the escape velocities but don't actually escape. + + 2. Zwicky, also in the 1930s, found that galaxies have much more kinetic energy than could be explained by the observed mass and concluded there must be some unobserved mass he called dark matter. (Zwicky then coined the term ""dark matter"") + +Evidence 2: Galaxies have more kinetic energy than ""normal"" matter alone would allow for. + + 3. Vera Rubin then decided to study what are known as the 'rotation curves' of galaxies and [found this plot](http://imgur.com/UKbNIif). As you can see, the velocity away from the center is very different from what is predicted from the observed matter. She concluded that something like Zwickey's proposed dark matter was needed to explain this. + +Evidence 3: Galaxies rotate differently than ""normal"" matter alone would allow for. + + 4. In 1979, D. Walsh et al. were among the first to detect gravitational lensing proposed by relativity. One problem: the amount light that is lensed is much greater than would be expected from the known observable matter. However, if you add the exact amount of dark matter that fixes the rotation curves above, you get the exact amount of expected gravitational lensing. + +Evidence 4: Galaxies bend light greater than ""normal"" matter alone would allow. And the ""unseen"" amount needed is the exact same amount that resolves 1-3 above. + + 5. By this time people were taking dark matter seriously since there were independent ways of verifying the needed mass. + +[MACHOs were proposed](http://en.wikipedia.org/wiki/Massive_compact_halo_object) as solutions (which are basically normal stars that are just to faint to see from earth) but recent surveys have ruled this out because as our sensitivity for these objects increase, we don't see any ""missing"" stars that could explain the issue. + +Evidence 5: Our telescopes are orders of magnitude better than in the 30s. And the better we look then more it's confirmed that unseen ""normal"" matter is never going to solve the problem + + 6. The ratio of deuterium to hydrogen in a material is known to be proportional to the density. The observed ratio in the universe was discovered to be inconsistent with only observed matter... but it was exactly what was predicted if you add the same dark mater to galaxies as the groups did above. + +Evidence 6: The deuterium to hydrogen ratio is completely independent of the evidences above and yet confirms the exact same amount of ""missing"" mass is needed. + + 7. The cosmic microwave background's power spectrum is very sensitive to how much matter is in the universe. [As this plot shows here](http://imgur.com/ssw6TJw), only if the observable matter is ~4% of the total energy budget can the data be explained. + +Evidence 7: Independent of all observations of stars and galaxies, light from the big bang also calls for the exact same amount of ""missing"" mass. + + 8. [This image may be hard to understand](http://www.mpa-garching.mpg.de/millennium/pie_millennium_walls.jpg) but it turns out that we can quantify the ""shape"" of how galaxies cluster with and without dark matter. The ""splotchiness"" of the clustering from these SDSS pictures match the dark matter prediction only. + +Evidence 8: Independent of how galaxies rotate, their kinetic energy, etc... is the question of how they cluster together. And observations of clustering confirm the necessity of vats of intermediate dark matter"" + + 9. One of the recent most convincing things [was the bullet cluster as described here](http://www.preposterousuniverse.com/blog/2006/08/21/dark-matter-exists/). We saw two galaxies collide where the ""observed"" matter actually underwent a collision but the gravitational lensing kept moving un-impeded which matches the belief that the majority of mass in a galaxy is collisionless dark matter that felt no colliding interaction and passed right on through bringing the bulk of the gravitational lensing with it. + +Evidence 9: When galaxies merge, we can literally watch the collisionless dark matter passing through the other side via gravitational lensing. + + 10. In 2009, Penny et al. showed that dark matter is required for fast rotating galaxies to not be ripped apart [by tidal forces](http://en.wikipedia.org/wiki/Tidal_force). And of course, the required amount is the exact same as what solves every other problem above. + +Evidence 10: Galaxies experience tidal forces that basic physics says should rip them apart and yet they remain stable. And the amount of unseen matter necessary to keep them stable is exactly what is needed for everything else. + + 11. There are counter-theories, [but as Sean Carroll does nicely here](http://blogs.discovermagazine.com/cosmicvariance/2011/02/26/dark-matter-just-fine-thanks/) is to show how badly the counter theories work. They don't fit all the data. They are way more messy and complicated. They continue to be falsified by new experiments. Etc... + +To the contrary, Zwicky's proposed dark matter model from back in the 1930s continues to both explain and predict everything we observe flawlessly across multiple generations of scientists testing it independently. Hence dark matter is widely believed. + +Evidence 11: Dark matter theories have been around for more than 80 years, and not one alternative has ever been able to explain even most of the above. Except the original theory that has predicted it all. + +Conclusion: Look, I know people love to express skepticism for dark matter for a whole host of reasons but at the end of the day, the vanilla theories of dark matter have passed literally dozens of tests without fail over many many decades now. Very independent tests across different research groups and generations. So personally I think that we have officially entered a realm where it's important for everyone to be skeptical of the claim that dark matter isn't real. Or the claim that scientists don't know what they are doing. + +Also be skeptical when the inevitable media article comes out month after month saying someone has ""debunked"" dark matter because their theory explains some rotation curve from the 1930s. Skeptical because rotation curves are one of at least a dozen independent tests, not to mention 80 years of solid predictivity. + +So there you go. These are some basic reasons to take dark matter seriously." "Dark matter and dark energy *are* the assumption that the Standard Model is incomplete and that there is more in the universe. If physicists would assume the SM is complete then there wouldn't be any space for new things (and this obviously contradicts observations). + +Hundreds, maybe even thousands of people have tried to modify gravity to make the observations consistent with only visible matter. [It just doesn't work](https://xkcd.com/1758/)." +1450 AskScience AMA Series: I'm Gary Marcus, co-author of Rebooting AI with Ernest Davis. I work on robots, cognitive development, and AI. Ask me anything! 2138 https://www.reddit.com/r/askscience/comments/d4z1yp/askscience_ama_series_im_gary_marcus_coauthor_of/ 1568631638 d4z1yp 2019-09-16 14:00:38 I know this isn’t necessarily the same thing (AI vs AGI) but what do you think about Andrew Yang’s message that AI is coming for people’s jobs faster than people think? And what’s your take on UBI as a response to AI’s effect on employment? Gary, my son is 8 and indicated he wants to build robots when he grows up. Any recommendations on getting him started at his age? +1451 How does a wave function change after scattering? 2050 https://www.reddit.com/r/askscience/comments/d4q3go/how_does_a_wave_function_change_after_scattering/ 1568579603 d4q3go 2019-09-15 23:33:23 "In non-relativistic scattering theory, you just consider an incident plane wave, and an outgoing spherical wave, which has been modified by the interaction potential. + +If you assume the incoming particle is moving in the z-direction, you can write the total wavefunction as: + +ψ(**r**) = e^(ikz) + ψ*_s_*(**r**), + +where e^(ikz) is the incoming particle, and ψ*_s_* is the scattered wave. + +The scattered wave can then be written as: + +ψ*_s_*(**r**) = f(θ,φ)e^(ikr)/r. + +This has the form of an outgoing spherical wave which has been modulated by an angle-dependent factor f. f is called the scattering amplitude, and |f|^(2) ends up being the differential cross section. + +To find what this function actually looks like, you just solve the time-independent Schrodinger equation for whatever potential is mediating the scattering. + +To treat something like Compton scattering, you don't really want to use non-relativistic QM, but rather QFT. In QFT, you don't generally work with wavefunctions anymore, but you can still calculate S-matrix elements and cross sections. A common way to do this is using time-dependent perturbation theory, and Feynman diagrams." "The book to are looking for is Angular Momentum by Richard Zare. It handles exactly this. + +Essentially, you conserve angular momentum to get the out going wave. So you take your incoming plane wave and express it as a super position of states with definite angular momentum. (Use sphereical harmonics). The phases and coefficients get modified by the interaction, you will then get a set of sphereical harmonics going out. That set is your out going wave. + +Side note: If there is no change in angular momentum internally, only the phases can shift relative to each other. The coefficients are fixed. + +Side note 2: in a really cold collisions, states with large angular momentum often never get closer enough to the item you are scattering off of too feel it's effects. So you can make an approximation by neglecting them. You can then use a finite small number of low angular momentum wave functions as the incoming wave. For example just l = 0 , 1 and 2. It's also not uncommon for your potential to exclude all odd functions or something like that. This turns some problems into something simply enough to be done by hand." +1994 Why does flu even come in seasons? 1988 https://www.reddit.com/r/askscience/comments/rbuixf/why_does_flu_even_come_in_seasons/ 1638979490 rbuixf Medicine 2021-12-08 19:04:50 "In addition to making people congregate indoors, cold weather (around freezing) can solidify and harden Influenza's outer layers, protecting it and allowing for easier transmission. It can stay that way up to about 70F. + +[From NIH:](https://www.nih.gov/news-events/nih-research-matters/flu-virus-fortified-colder-weather) +>The outer membrane of the influenza virus is made chiefly of molecules known as lipids. Lipids—which include oils, fats, waxes and cholesterol—don't mix with water. + +>The researchers discovered that at temperatures slightly above freezing and below, the virus's lipid covering solidified into a gel. At about 70 degrees Fahrenheit, much of the lipid was still in gel form. At warmer temperatures, however, the gel melts to a liquid phase. At temperatures of about 105 degrees and higher, the coat was all in liquid form. + +>The virus's rubbery outer coat, the researchers believe, allows it to withstand cooler temperatures and travel from person to person. In the respiratory tract, the body's warmth causes the covering to melt so that the virus can infect the cells of its new host." "* As others have mentioned, people spend more time indoors in cooler weather, which makes transmission easier +* Like any virus, cool weather is advantageous to survival. For example, a door handle might be 90 degrees in the summertime which is quite inhospitable to the influenza virus, but in the winter it's much cooler and the virus can survive on that surface for hours. +* Lack of sunlight. Sunlight is also very effective at killing viruses on surfaces, in the wintertime there's a lot less of it, both in duration and intensity. + +More than anything, it mostly has to do with how long the virus can survive outside the body, which is vital to transmission. In the wintertime, conditions are favorable for the virus to be able to survive longer outside the body." +1123 I read that we look for exoplanets by examining how much they reduce their stars' brightness when they transit. If aliens were observing us, how much would Earth and other planets reduce the sun's brightness? 1932 https://www.reddit.com/r/askscience/comments/9d62ht/i_read_that_we_look_for_exoplanets_by_examining/ 1536150716 9d62ht Astronomy 2018-09-05 15:31:56 "so if the orbital plane of a planet never transits the between the star and us, we would be unable to detect it? I thought i've also read planets are sometimes detected because the gravitational pull causes the star to ""wobble""? +" "the transit method is effective for finding larger planets and it is biased towards close orbiting giants, called Hot Jupiters because they are big and very close tho their sun. + +​ + +the hunt for earth like planets is going to require very sensitive devices. the [EXtreme PREcision Spectrometer (EXPRES)](http://exoplanets.astro.yale.edu/instrumentation/expres.php) at the Discovery channel Telescope owned by Lowell Observatory is expected to detect velocity changes in a star due to planets in orbit around it sensitive enough to detect a planet like earth. it can detect velocities down to 20cm/s in stellar motion. " +1697 "AskScience AMA Series: We are U.S. and European partners on the world's latest Earth-observing satellite, Sentinel-6 Michael Freilich, which will observe changes in sea levels for at least the next decade. The spacecraft is ""go"" for launch on November 21. Ask us anything!" 1876 https://www.reddit.com/r/askscience/comments/jvrsrq/askscience_ama_series_we_are_us_and_european/ 1605614418 jvrsrq Planetary Sci. 2020-11-17 15:00:18 "Will the data be publicly available? I know any data NASA collects generally is, but I don't know if the partnership might affect that. + +What kind of instrumentation is aboard? Since it's a Sentinel satellite, I assume at least one high-resolution camera, but because of the scientific mission, perhaps you might have added additional instrument packages, such as a laser altimeter? + +What sort of orbit is it planned to be in? I would guess polar for maximum coverage?" "Out of curiosity... How is exactly that collaboration? I imagine the satellite was built with American and European equipment, but it will it be operated from a single team now? EUMETSAT? + +How does this satellite interact with the rest of Sentinels/Copernicus? What is the endgame here when all are active?" +1281 Does cannibalism REALLY have adverse side effects or is that just something people say? 1866 https://www.reddit.com/r/askscience/comments/ayamip/does_cannibalism_really_have_adverse_side_effects/ 1551949676 ayamip Biology 2019-03-07 12:07:56 "In general, it's a bad idea to eat the same species simply based on a disease transmission perspective. (I'm sure there are plenty of psychological issues involved as well.) + +But a major concern in animal production is [transmissible spongiform encephalitis (TSE)](https://en.wikipedia.org/wiki/Transmissible_spongiform_encephalopathy) or the more popular: mad cow disease. [Prions](https://en.wikipedia.org/wiki/Prion), an infectious protein, can basically turn a brain into Swiss cheese. These mutated proteins occur naturally, albeit rarely, but can ""infect"" another of the same and sometimes other species if they are eaten. So in the case of mad cow, the cows were being fed a protein mix that included brain and spinal cord tissue from other cattle. + +We see the same thing in people with [kuru](https://en.wikipedia.org/wiki/Kuru_(disease). + +Shameless plug: if you like infectious disease stuff check out r/ID_News." "If you would like to learn more about prions and their history I highly suggest this episode of “This Podcast Will Kill You” which focuses on prion diseases. + +[TPWKY prions “Apocalypse Cow”](https://www.exactlyrightmedia.com/this-podcast-will-kill-you) +" +1452 Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology 1850 https://www.reddit.com/r/askscience/comments/czm61n/ask_anything_wednesday_biology_chemistry/ 1567609908 czm61n 2019-09-04 18:11:48 Is there something that spreads like a virus but has a positive effect on humans? How close are we to creating a fiber as strong as a spiders web to the same scale? +1124 AskScience AMA Series: We recently launched the new Land Cover tool in the NASA GLOBE Observer app. Ask us anything! 1708 https://www.reddit.com/r/askscience/comments/9jlzgb/askscience_ama_series_we_recently_launched_the/ 1538132421 9jlzgb 2018-09-28 14:00:21 "https://observer.globe.gov/about/get-the-app + +Here is a direct link to the app download page" "In the space sector I have seen a tons of news about automatic image processing to be able to exploit all the satellite imagery. Is that something that NASA is part of? Do you have projects that use that kind of pipeline? + +A few companies are also promising high frequency images (the whole Earth every 24h kind of deal). What usage do you foresee for that kind of data?" +1453 What actually is particle entanglement in simple terms? 1666 https://www.reddit.com/r/askscience/comments/d6m175/what_actually_is_particle_entanglement_in_simple/ 1568934865 d6m175 Physics 2019-09-20 2:14:25 "I think it's easiest to think of entanglement in how it's used in quantum computing: Entanglement is information that is stored not in one particle or the other, but in the *correlation* between them. + +The classic example is one particle with 0 angular momentum creating two particles with non-zero angular momentum (called spin). We know that angular momentum must be conserved, so whatever the particles' spin are, they have to cancel each other out so that the system of them has 0 angular momentum. We can choose to measure the spin along the 'z-axis' (let's say that's vertical), and say that if the spin is counterclockwise (so angular momentum as a vector points 'up') it's a spin-up particle and if clockwise, spin-down. + +So far if I send you one of the particles and you measure it, you'll get spin up or down with equal chance, and I haven't actually sent you any information, since it's all random. What I *can* do, is to flip my particle upside-down. I must stress here what emphatically **does not happen** is that your particle, half a universe away, magically flips itself over to adjust to my flipping. Your particle, as best we can measure, stays exactly the way it is. So now we know that both of our particles are spin-up or spin-down, not knowing which. + +Now if you measure your particle you'll still get spin-up or spin-down with random chance, and you still don't actually have any information. I have to message you in some classical way (we'll say I call you on the phone to put ourselves in the mindset of the scientists first working on this problem). Let's say you measure spin up. I call you up and say I've measured spin-down. ***Now*** you know that I have not flipped my particle. Now you have information. Your information comes not in the measurement you make, or the measurement I made, but in the correlation between the two measurements. + +There's more I can do than just flip my particle. I can rotate it 90 degrees around the X axis, or 90 degrees around the Y axis (to simplify the description here, it's a bit more mathy under the hood). Those moves encode a value called phase which we won't discuss here. The point being that the particles can be 'in-phase' or 'out-of-phase'. So I can send you a message that I've measured 'down' and 'out-of-phase' and you measure yours to be 'down' and 'in-phase' so you know which of the 4 rotations (including no rotation at all) I've performed. So you actually get two bits of information in our entangled pair of particles + +Why all the drama for something so simple? Well it turns out, I've kept things simple using 'spin' as our entangled state. There are only 2 states 'up' or 'down'. But the message I send to you allows you to get one of 4 messages. It turns out, different quantum systems with more states allow for more message packing. If my system has 3 states, I can send 9 messages, 4 states, 16 and so on. We call this 'Dense Quantum Encoding'. Packing more bits of information into fewer particles. It also turns out that if someone intercepts either one of our lines, my results or the particle I send to you to measure, they cannot get the message I sent you. If they intercept both lines, the physical interaction they perform on the particle I send to you becomes detectable on your end, because it will destroy the entangled information. After some number of particles you can detect there's an eavesdropper, and we can shut down communications, creating a communication system very robust to 'man-in-the-middle' attacks. + +If you are interested in what entanglement is, see above. If you'd not like to be confused by what it is not, skip what follows. + +So obviously you've heard about all kinds of ""spooky action at a distance"" and how Einstein ""hated"" entanglement or other such popular journalism nonsense about entanglement. What's that all about then? Well let's go back to our initial problem. I stated that particles come out either spin up or spin down but we don't know which. Let's imagine that there was actually some other state, some variable we cannot measure in any way. This state encodes whether the particle ""really is"" spin up or down. Even with the examples I've provided above, flipping 90 or 180 degrees, there still isn't anything particularly peculiar yet. + +However, if I only rotate my particle 5 degrees, what happens? Due to maths I don't wish to get into here, if this hidden variable *does* pre-determine spin up or down, and no information, not even information in this hidden sector, can travel faster than light, we would expect that the probability of measuring both particles anti-aligned (one up one down) is linearly proportional to the number of degrees rotated. 0 degrees, 100%, 180 degrees, 0%, 18 degrees, 90% and so on. However, when we actually perform this measurement, we find that the probability actually varies by the cosine of the degrees rotated, not linearly. + +Again, due to maths I don't care to get into, this means (at least) one of our assumptions is false: maybe there's no hidden variable after all, maybe information can travel faster than light. This is the end of the scientific commentary on the subject. Since we, by definition, can't measure the hidden sector, and science is only in the business of predicting the results of experiments based on the results of previous ones, we can't scientifically go further down this road. + +But philosophically, here's where we arrive. Since the hidden sector is not measurable, then it doesn't create any weird time paradoxes for us to allow information to travel faster than light in that sector. No ""real"" information is faster than light, nothing we can 'really' send a message in. So some people like to believe that underneath quantum mechanics, there's some other system of 'real' variables and everything has some 'real' truth that our measurements simply tease out indirectly. + +Alternatively, we can say that nothing else we know of can travel faster than light, we know there are problems with time paradoxes with information traveling faster than light, and so on. So maybe the thing that's wrong is the assumption that there must be some 'real' variable that tells the particle how to behave in a measurement. Maybe when the particles are created they are created in a true superposition of states. They really are both up and down at the same time, not definitively one case or the other. And when we measure we can only measure one state or the other. This, of course, leads to the question of the measurement problem in quantum mechanics: what does ""actually"" happen when we measure a superposition of states and then the particle is only in whatever state we've measured after we measure it? + +To be clear on my bias in the last two paragraphs, I am mostly a 'shut up and calculate' physicist when it comes to the physical part of the problem. It honestly does not matter which description is true, the science of the problem tells us that we cannot have both 'realism' (hidden variables) and 'locality' (information only travels at c or slower), often called 'local realism.' If I am being philosophical, I am more in the camp of keeping locality and discarding realism. I say this not to say that I am right or you should take my opinion more seriously than someone else, only that I am likely to have biased how I worded those paragraphs in favor of the opinion I have, so take them with an appropriate grain of salt." "Entanglement pertains to the fact that a single quantum wavefunction (WF) covers many particles. The WF evolves over time in a completely deterministic way, until it _collapses_, which is where the mystery of quantum mechanics happens. The entire WF collapses at the same moment, completely disregarding the expanse of space it covers. + +When the WF collapses, it loses all of its degrees of freedom and all the particles now have a definite state — this is what we get as the observation in an experiment. Immediately after that, the WF starts its deterministic (_unitary_) evolution again. + +If you start with the wavefunction of two isolated particles, they can come into interaction and merge into a single wavefunction — that's how the particles get entangled. + +Do note that WF collapsing across unbounded distances at once still doesn't violate Einstein's postulate on lightspeed being the highest speed at which information can travel: say you and I are a lightyear apart and share two entangled particles (one for each). When you observe a particle, you don't actually know whether you caused the WF to collapse. You just get your measurement, which respects the rules of quantum uncertainty and randomness. When I observe mine, I get my result. Neither of us knows whose measurement caused the WF collapse. + +Our two results are co-dependent and only certain combinations are possible; but nothing about either result in isolation is different than it would have been without entanglement. So, just by seeing the result at your end, you got no information from me." +1454 Why is the heat capacity of liquid water so much higher than its solid and gaseous forms? 1632 https://www.reddit.com/r/askscience/comments/dig96b/why_is_the_heat_capacity_of_liquid_water_so_much/ 1571181214 dig96b 2019-10-16 2:13:34 All liquids generally have a higher heat capacity than their solids. The heat capacity is the amount of heat needed to raise a gram (or mol) of solid by 1 degree. In a molecular solid the heat goes to making the bonds vibrate faster. In a liquid the heat goes towards making the bonds vibrate faster but also to rotating and moving the molecules - you need extra energy to do this "When water is in its liquid phase, all the molecules hold onto each other through hydrogen bonding. When you heat liquid water, most of the energy is just going into disrupting and 'breaking' these hydrogen bonds (disrupting is probably a better term since hydrogen bonds are not molecular bonds like ionic or covalent bonds are). + +Eventually, You can add enough heat to overcome the inter molecular attraction that the water molecules have for one another through this hydrogen bonding and that's when water boils. The molecules are moving with enough kinetic energy that they have a hard time lining up their polar ends with one another (which is what hydrogen-bonding is). + +​ + +In a gaseous state, the water molecules are much more diffuse and separated from one another, and have more kinetic energy, so there is much less hydrogen bonding occurring. If it does to any significant degree, the water will just condense back into its liquid phase as a result. + +​ + +Water does have some unique properties, but any solvent will have a higher specific heat capacity in the liquid phase than it will in the gaseous phase because that's when intermoelcular forces are stronger--when the molecules are closer together and have less kinetic energy." +1807 Questions about radon gas and cancer? 1624 https://www.reddit.com/r/askscience/comments/ltk3dx/questions_about_radon_gas_and_cancer/ 1614416202 ltk3dx Medicine 2021-02-27 11:56:42 "> If radon is radioactive, and leaves radioactive material in your body, why does it mainly (only?) cause lung cancer? + +Because it's a gas that enters your lungs. It gets trapped in the lungs, and the lungs get the heaviest radiation dose from the daughter products. + +>If radon is 8x heavier than air, and mostly accumulates in the basement, wouldn't that mean that radon is a non-issue for people living on higher levels? + +Essentially correct. Norwegian recommendations is to not measure if you live above third floor - due to the weight of the gas and the fact that it seeps out of the ground. + +> This map shows radon levels around the world. Why is radon so diverse across a small continent like Europe, yet wholly consistent across a massive country like Russia? Does it have to do with measuring limitations or architecture, or is the ground there weirdly uniform? + +On that map it seems to be reported per country. Russia is a big country, Europe apart from Russia is a lot of small countries. While I don't know details about radon in Russia, far more detailed maps exists for other countries. You may for instance have a look at [this one, for Norway](http://geo.ngu.no/kart/radon/)" "5: Radon mostly surfaces after it has rained, and decays within days. This is why frequent ventilation is recommended, especially after it has rained, or if you live in a basement or any place where it tends to accumulate. + +Your soil/underground affects your exposure, along with the materials your house is built of, the way it is constructed, and how often you ventilate. Some of these factors are tied to regional and cultural differences, so it is not convenient to link everything together." +1604 When a person receives a successful donation, do the genes in the donated body part retain their difference from the host genes over time or is there some kind of assimilation that occurs? 1600 https://www.reddit.com/r/askscience/comments/hugi1k/when_a_person_receives_a_successful_donation_do/ 1595226994 hugi1k Medicine 2020-07-20 9:36:34 "They remain separate genetically, but from your examples for most blood donations it’s a bit different. If you’re talking about transfusions of packed red blood cells, those lack a nucleus in the first place so there’s no genetic content in them, and their lifespan is pretty short anyway. For bone marrow transplants (for example in leukaekia treatment), what happens there is that haematopoietic stem cells (stem cells in the bone marrow that give rise to mature blood cells) are killed off by radiation, and the donor’s ones are transferred in. After that, the person becomes a chimera - his blood cells are genetically from the donor (if 100% depletion), while peripherally his tissues have his own DNA. If any of his original haematopoietic cells survive the radiation (e.g. if it’s only a local depletion of the cancer, although I don’t know if it’s actually done in practice - if that’s the case your own healthy haematopoietic stem cells should be able to repopulate the niche), then his blood will have a portion of his cells with his own DNA, and a portion of cells that have the donor’s DNA. This will be reflected by DNA tests, and in fact commercial testing companies such as 23AndMe don’t recommend using their service for ancestry tracing if you’ve received a bone marrow transplant for that reason, because it could muddy up results and analysis if you try and track who you’re descended from. + +That being said, for transplants, you need to match them in certain genes in order to reduce the risk of rejection, even with the use of immunosuppressive drugs after transplant. These are typically the genes of the major histocompatibility complex that play the biggest role in determining rejection, but there are other minor histocompatibility antigens and a whole range of other genetic loci to be considered. Different organs also have different tendencies to be rejected, for example liver transplants can tolerate some degree of mismatch, while kidneys tend to need to be well-matched, and even with decent matching there may be immune rejection of the foreign organ years after the transplant has occurred." As I understand, they must remain different due to the way cells replicate themselves. Cells replicate by mitosis, where the DNA is replicated and then split into two identical cells. So DNA is not mixed in growth/repair of said organ. I think the reason the new DNA is not rejected is because they have the same ‘markers’ as your own cells in your body. This means your body does not see them as foreign and attack them. +1895 How deep can water be before the water at the bottom starts to phase change from liquid to solid? 1593 https://www.reddit.com/r/askscience/comments/o0i9s0/how_deep_can_water_be_before_the_water_at_the/ 1623774255 o0i9s0 Physics 2021-06-15 19:24:15 "https://en.wikipedia.org/wiki/Phase_diagram#Crystals + +At ~~0 C~~ let's make that 1 C the required pressure to solidify is ~630 MPa. In Earth's gravity, each 10 metres of depth increases the pressure by 1 atmosphere, ~0.1 MPa. + +Therefore, **about 63 kilometres**. And it'd be **Ice VI**, a tetragonal crystal structure with a density ~1300 kg/m^3. + +This however neglects change in density with depth. It's also quite sensitive to temperature, just 10 or 20 degrees C could halve or double the required pressure to solidify. + +On Europa the pressures will be lower than that due to the lower gravity. From the water phase diagram we can see there's a fairly narrow temperature range, from about 252 to 270 Kelvin, where increasing pressure goes ice-water-ice, therefore allowing a subsurface ocean with ice both above and below. But impurities in the water could significantly alter such ranges." "You've got a bunch of technical answers about depth and feasibility, but I figured you might also find this article interested, it talks about pockets of solid water existing as stable hydrous minerals and exotic ices deep in the crust of the earth. As well as having some interesting details on the depth of the crust beneath the mariana trench that might be interesting to some trying to figure out if a water column this deep could feasibly exist on earth. + +https://newatlas.com/mariana-trench-water-mantle/57239/ + +Apparently we've also discovered diamonds with pockets of exotic high pressure ices trapped within" +1605 If breaking the sound barrier causes a sonic boom, what would breaking the light speed barrier do? 1454 https://www.reddit.com/r/askscience/comments/gz1u71/if_breaking_the_sound_barrier_causes_a_sonic_boom/ 1591631418 gz1u71 Physics 2020-06-08 18:50:18 A charged particle moving faster than the phase velocity of light in a medium emits [Cherenkov radiation](https://en.wikipedia.org/wiki/Cherenkov_radiation). "As Cherenkov radiation has already been mentioned, the problem with any object going faster than the speed of light (in a vacuum) is that the math breaks down. The Lorentz factor (gamma) shows up in a lot of the equations of special relativity, and it's equal to: + +1 / sqrt( 1 - v^2 / c^2 ) + +When velocity v is equal to the speed of light c, v^2 / c^2 becomes 1, the denominator becomes zero, and the Lorentz factor ends up with a divide by zero error. One of the implications of this is that it takes infinite energy just to accelerate something to the speed of light, meaning it's an insurmountable barrier. + +Of course, even if you found some way to circumvent that barrier and instantaneously skip acceleration through the speed of light, when v is greater than c, v^2 / c^2 is greater than 1, so you're taking the square root of a negative number. Plug that into an equation and it's going to start spitting out results that don't have any physical meaning that we know of, like a particle with imaginary mass." +1808 Is it possible to scale down a linear accelerator for it to fit into a spacecraft to power it by firing particles out of the other end? 1409 https://www.reddit.com/r/askscience/comments/ls1zrp/is_it_possible_to_scale_down_a_linear_accelerator/ 1614242355 ls1zrp Physics 2021-02-25 11:39:15 "Yes - it's called an ion thruster or ion drive. It requires very little propellant, but quite a lot of power. This makes them most ideal for accelerating small probes in space. You can't provide the thrust to, say, launch from Earth or accelerate a large probe, but you can provide a small amount of continuous acceleration for a very long time, because you can continuously power the drive without using very much fuel. So the idea is that you can use this to get probes across the solar system quickly and efficiently. + +A few missions have started to use ion thrusters in space, but it's still quite new and not extremely widespread." +1455 Is it possible to isolate the particles of a virtual particle pair? 1387 https://www.reddit.com/r/askscience/comments/dga9lf/is_it_possible_to_isolate_the_particles_of_a/ 1570770059 dga9lf Physics 2019-10-11 8:00:59 "Virtual particles should not be considered to be ""real"" particles, but it's complicated. The most obvious reason is that they don't need to obey the energy-momentum relation, + +* m^(2)c^(2) = E^(2)/c^(2)-p^(2) + +which all ""real"" particles have to by definition. But we can say more: When say two particles interact, their interaction is a terribly complex thing to deal with which usually cannot be solved for exactly. But we have a technique, called perturbation theory, which pull out the most important behavior and gives us an infinite sum of understandable terms each one capturing some aspect of the full interaction. + +An analogy would be summing frequency modes that make up a complicated wave, or using a Taylor series to describe some function. So let's say we scatter two electrons off each other, + +* https://en.wikipedia.org/wiki/M%C3%B8ller_scattering + +you'll often see Feynman diagrams like these. The two electrons exchange a virtual photon and bounce off. + +In certain situations, this single Feynman diagram captures almost all of the interaction. But it's not the entire interaction. What about exchanging two virtual photons? That diagram is included too. What about a virtual photon which has a little e+e- pair which briefly shows up before collapsing back into a photon? In real life, this diagram should be added as well. So if we scatter electrons, and you insist that virtual particles exist, then you must acknowledge that *which* virtual particles exist is indeterminant. + +The point is that the full interaction sums across all possible diagrams and the hope of perturbation theory is that as the internal combinations of virtual particles becomes more complicated, they become less important. So even if we need to sum an infinite number of such interactions, only the first few are needed to get the gist of the effect. This isn't always true, and thus nonpertubative approaches might be needed and in those techniques, virtual particles never actually show up. + +Now with all that said, there is a mechanism to ""promote"" a virtual particle to a real particle. The main ingredient to accomplishing this is allowing the virtual particle to actually travel a long distance in space. The farther the particle has to travel to complete the interaction, the more ""real"" it has to be... and the closer to, + +* m^(2)c^(2) ~ E^(2)/c^(2)-p^(2) + +being true it has to be. This is really easy to interpret using Feynman diagrams, all you have to do is cut the diagram in half such that virtual particle lines now must become external lines. External lines are the observable particles. Another way of thinking about this is drawing the virtual particle line to be really really long. This is effectively the same thing where now the almost real internal particle leaves the 1st interaction to become the incoming line of a 2nd interaction. A physical example of this is star light being absorbed by your eyes. That photon has had to propagate such an incredible distance that it is indistinguishable from a real particle (you can say it's energy uncertainty from Heisenberg's uncertainty principle is basically zero). But nobody talks this way, we just call such photons real. + +A more technical example would be the production of charm or strange mesons from hadron collisions. Such mesons (quark-antiquark pairs) which have charm or strange quarks inside them can be produced by photon-nucleon scattering. But there's an issue: nucleons only have up and down quarks. How do we produce the J/psi meson which has a charm and anti-charm if the ingredients (a photon and a proton or neutron) don't have these quarks? In a sense, when we make particles like the J/psi, we are ""making real"" virtual quarks. A similar argument can be made for when a photon scatters off an atom and produces an electron-positron pair. The virtual pair has been ""made real."" This kind of language can be used precisely because we're taking what otherwise would have been a Feynman diagram with internal virtual particles and chopping it up so the internal lines must now be outgoing particles which are real. So to answer your question explicitly: If you isolate a ""virtual particle"" it is no longer virtual, but a real particle." "The answer is yes, at least in some sense. You might want to take a look at the [Schwinger effect](https://en.wikipedia.org/wiki/Schwinger_effect). One interpretation is that in a *really* strong electric field, you should be able to isolate vacuum electron-positron pairs. But it turns out to be extremely difficult, so it is not possible to verify the effect with current technology (thanks to ultra high energy laser experiments like the ELI it might be possible in the future though). + +Bonus fact: Theoretically, you should also be able to do this with virtual black holes. This leads to some interesting gedanken experiments. But the technology to actually do that is outside the realm of what we can even dream of." +1456 Mechanistically, why is benzene carcinogenic? 1351 https://www.reddit.com/r/askscience/comments/d0c9q9/mechanistically_why_is_benzene_carcinogenic/ 1567746822 d0c9q9 2019-09-06 8:13:42 "While benzene isn't particularly reactive with most biologically relevant molecules, our enzymes are very effective catalysts and the oxidation products of benzene in the body are potent carcinogens. Cytochrome P450s in the liver and lungs are thought to initially convert it to benzene oxide, which then spontaneously rearranges to phenol. Another P450-dependent oxidation converts it to hydroquinone, and then reactive oxygen species oxidise this to benzoquinone within the bone marrow, where it can cause leukemia. There are alternate pathways from many of these intermediates, leading to other toxic and carcinogenic substances. + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3271273/" "There are two ways aromatic compounds are carcinogenic. + +1. Intercalation. They basically penetrate cells and due to their flat structure [they intercalate between the DNA bases](http://what-when-how.com/wp-content/uploads/2011/05/tmp32C166_thumb1_thumb.jpg). This can cause errors when the DNA is replicated leading to possibly carcinogenic mutations +2. The second ways is basically [epoxidation of aromatic compounds](https://pubs.rsc.org/en/Image/Get?imageInfo.ImageType=GA&imageInfo.ImageIdentifier.ManuscriptID=B313683C&imageInfo.ImageIdentifier.Year=2004). that is carried out by some enzymes in our body. This basically binds an oxigen to the molecule as an epoxide, which is in turn very reactive and can thus react with DNA" +1282 [Biology] Do probiotics actually work? 1292 https://www.reddit.com/r/askscience/comments/bbb1vr/biology_do_probiotics_actually_work/ 1554832438 bbb1vr Biology 2019-04-09 20:53:58 "They likely work for preventing C. Diff infection in patients who have been taking antibiotics, based on a [meta analysis of 39 randomised controlled trials](https://www.cochrane.org/CD006095/IBD_use-probiotics-prevent-clostridium-difficile-diarrhea-associated-antibiotic-use). + +The evidence for other benefits from probiotics is not as strong. There isn't a good standard for reporting such studies to disclose the strains used, how dosage is regulated, how controls are defined, how well those strains ""take"" within the GI tract. Mostly, studies give people a dose and then check for any beneficial effects, which means that they are susceptible to other factors which are not necessarily associated with probiotic colonisation of the gut. + +For example, most probiotics are delivered in yoghurt. Let us say you have an experiment comparing bacteria + yoghurt, and plain yoghurt. People drinking the bacteria+ yoghurt are healthier, does that mean the ""good"" bacteria has colonised the gut ? No, because the bacteria can digest the yoghurt and produce nutrients which can produce health improvements. + +So I can still imagine that they are getting health benefits from the probiotic regimen. But it may not be due to ""good bacteria"" settling in their digestive tract, and it could be a number of other factors. + +Even if we discount the nutrient content of the probiotics themselves, other behavioural factors can play a role. If the commitment to be healthy is altering their decision making, then they may see positive results which they can attribute to the probiotics colonising the gut. + +I'm not saying that probiotics can't work for improving health, but the evidence isn't clear yet due to a number of factors, including (but not limited to) the potential confounders I have mentioned above. + +If your friends are seeing benefits, more power to them." "Microbiome bioinformaticist here. + + It helps with very few diseases if any besides C diff mildy. Might help your GI tract a tad. + +Pretty much all the leaders in the field from the microbiome conferences I've been to seem doubtful at best that it does much more than that. Those probiotic species rarely establish themselves in your gut long term. FMT(fecal transplant) is what the field seems interested in atm because it has helped some people immensely, but it needs more research to see if it could help more broadly. + +Edit: More backing for this, a huge percentage of the top specis in the gut based on the Human microbiome project samples seems to be Bacteriodes, Faeculbacterium, Alistripes, akkermansia etc. Not lactobacillus and bifidobacterium that are commonly found in probiotics." +1457 Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology 1291 https://www.reddit.com/r/askscience/comments/d2rmk9/ask_anything_wednesday_economics_political/ 1568214554 d2rmk9 2019-09-11 18:09:14 "Linguistics - how do certain dialects get entrenched as ""proper form"" of the language? When I look at modern high German, it is only spoken around Hannover, and who cares about that place. Similarly, why did standard Midwestern become the ""neutral"" dialect of American English?" What would happen if we didn't have a stock market? I don't mean the stock market just up and disappearing, I mean if the concept of a stock market was never invented and we didn't have anything to replace it. +1283 AskScience AMA Series: I'm Robbert Dijkgraaf, mathematical physicist, author, and director of the Institute for Advanced Study, here to answer your questions about the math and physics of the universe and Big Bang. Ask me anything! 1230 https://www.reddit.com/r/askscience/comments/bek6ij/askscience_ama_series_im_robbert_dijkgraaf/ 1555585236 bek6ij 2019-04-18 14:00:36 What was the first thought that popped into your head when you saw the first image of the black hole. "Will be signing off. As in scientific research, every answer generates more questions, only expanding our ignorance. So, happy to have left you in a higher state of confusion. + +\-- Robbert" +1606 Do bath salts actually have any proven beneficial effects (e.g. on eczema), and is there any real difference between using Dead Sea salt VS Himalayan salt VS Epsom salt? 1213 https://www.reddit.com/r/askscience/comments/hx6d68/do_bath_salts_actually_have_any_proven_beneficial/ 1595612829 hx6d68 Medicine 2020-07-24 20:47:09 "Here's an extensive breakdown of epsom salts that I found (and it has links to studies throughout, as well as a ""further reading"" section at the end): + +[https://www.painscience.com/articles/epsom-salts.php](https://www.painscience.com/articles/epsom-salts.php) + +The TL;DR is that they don't hurt anything, and may not help anything, but they also may help something, and no one really knows. They're certainly not a miracle cure or the effects would be more measurable, but they're also certainly not harmful. + +edit: I'm getting a lot of replies saying ""so it's a placebo effect."" To be clear, nothing in the link I posted says that. I'm also not personally aware of any studies that determined that. It *might* be a placebo, but it also *might* not be. We don't know. Please don't jump to the conclusion that just because we don't know if there are benefits or not, it's a placebo (indicating that epsom does nothing at all). The fact is that we just don't know. That's not the same thing as knowing it's a placebo." "Here's a review of bath additives for Atopic Dermatitis. You have to look on Pubmed, not Google. The consensus is that they do help reduce visits to the doc and prescription use + +[https://pubmed.ncbi.nlm.nih.gov/31094942/](https://pubmed.ncbi.nlm.nih.gov/31094942/)" +1284 How do we know what dinosaurs' skin looked like? 1178 https://www.reddit.com/r/askscience/comments/bfkr9e/how_do_we_know_what_dinosaurs_skin_looked_like/ 1555817872 bfkr9e 2019-04-21 6:37:52 "Some dinosaurs died in mud. The soft material preserved their skin coverings, and we can see what it would have looked like from that. + + +But, dinosaurs often *did* have feathers. You're working off a 1980-1990's impression of what they might have looked like." "On a related note, there's much that isn't known about what dinosaurs looked like beyond just their skin. Most recreations don't take into account things like fat or cartilage. + +These are some [cool pics from a book](https://imgur.com/gallery/8UT01) called ""All Yesterdays"" detailing what modern animals would look like based on their bones alone using methods that paleoartists typically use." +1809 AskScience AMA Series: Hello Reddit! For Medscape Education, we are Dr. Fatima Cody Stanford, Dr. Rachel M. Bond, Dr. John Whyte, and Michael Sapienza ready to answer your questions about Health Equity in the Time of COVID. Ask Us Anything! 1173 https://www.reddit.com/r/askscience/comments/lrb6kq/askscience_ama_series_hello_reddit_for_medscape/ 1614168051 lrb6kq Medicine 2021-02-24 15:00:51 Good morning! We're excited to be here with you today. Dr Rachel Bond was unable to join, apologize for the late notice. We know your questions are in great hands with this all-star panel today, and look forward to what we are able to learn and share here. We'll be live at Noon EST! "What are you thoughts on leveling the playing field by mandating medical entities follow the law when it comes to transparency with regards to pricing. Or enacting such governance as: + +* 100% publicly visible pricing +* Disclosures of actual price to be charged for each event prior to service and signed by both parties +* Non-billable events: events caused by poor treatment (e.g. MRSA as a result of surgery) +* Medical records belong to the patient down to the last period, and are due immediately upon request in a transportable format +* All medical surgery providers must provide all instances of all complications and negative outcomes on a monthly basis for consumption by the public (de-identified). +* Non-requirement of imagine from the provider. You get to chose the imaging provider and all images must be accepted by the primary +* You can freely have any test you deem necessary that doesn't require an Rx or Radiation without prior approval from a doctor (e.g. A1C) + +There are lot more I can share, but let's start with those.. I think these will drive costs down tremendously because it will spur accountability and competition." +1458 "Big Bang: What evidence do we have for what happened ""behind the wall"", before what we can observe?" 1145 https://www.reddit.com/r/askscience/comments/drhzr1/big_bang_what_evidence_do_we_have_for_what/ 1572876056 drhzr1 Astronomy 2019-11-04 17:00:56 "You're right that there's an observable wall of light that we can't see past, called the Cosmic Microwave Background (CMB). It's about 300,000 years after the Big Bang, at a redshift of 1,100. + +The key is that this wall of light is being emitted by material with a history, and that history is in some respects stamped on the CMB. There are tiny fluctuations on the CMB, that travel at the speed of sound in that medium from the moment of the Big Bang all the way to the time of the CMB. Measuring those fluctuations carefully gives us a kind of integrated history of that first 300,000 years. Check out slides [22-24 of this recent presentation](https://media.universe-of-learning.org/documents/UoL_SciBriefing_2019-10-23-HubbleConstant.pdf) from Dr. Charles Lawrence, the US project scientist for the Planck Mission and the Chief Scientist for Astronomy and Physics at JPL. + +The upshot is that the size and relative number of the perturbations on the CMB is set by: + +* The density of “normal” matter +* The density of “dark” matter +* **The amplitude and slope of the spectrum of initial fluctuations 10^-32 s after the Big Bang** (which is how we get information about inflation) +* The angular scale of the measured fluctuations +* The fraction of CMB photons scattered by reionized matter in their 13.8-billion-year journey to us + +It's worth noting that there could be gravitational waves originating from much earlier than the CMB that we could detect. That hasn't yet been done, but they would travel freely through the dense ionized matter before the wall of the CMB." "Regarding your bonus question: + +Assuming the universe is infinite in size (which we don't have any evidence to the contrary yet), and you compress it to infinite density, it's possible the compressed state is also spatially infinite, even while the region that would become our observable universe was confined to a region smaller than an atom. + +As to the notion of other bubbles of space like ours popping into existence independently, I think that's one of the predictions of [eternal inflation](https://en.wikipedia.org/wiki/Eternal_inflation)." +1125 AskScience AMA Series: We're team Vectorspace AI and here to talk about datasets based on human language and how they can contribute to scientific discovery. Ask us anything! 1116 https://www.reddit.com/r/askscience/comments/9k5i8u/askscience_ama_series_were_team_vectorspace_ai/ 1538305245 9k5i8u 2018-09-30 14:00:45 Are there any women on the team? What things have you discovered about human language? +1126 How do our brains deciding which words to use when talking aloud? 1113 https://www.reddit.com/r/askscience/comments/9gk487/how_do_our_brains_deciding_which_words_to_use/ 1537189353 9gk487 Neuroscience 2018-09-17 16:02:33 "Something similar came up in another thread. I would advise you to look at an actual linguistic transcript of everyday conversational speech. We’re not nearly as coherent as we think we are. We often have to reformulate sentences on the go, mess up grammatically, lose our train of thought mid-sentence, use tonnes of verbal and non-verbal pauses, say little of value, repeat quotes or other people’s words in lieu of unique phrasing and take all manner of other shortcuts when talking. + +Not to say that the brain isn’t amazing at being able to come up with full sentences, but we’re rarely as eloquent as we remember ourselves to be. " "The brain is complicated, and we understand very little about *how* it works, though we generally know what different areas of the brain do. + +It’s known that the frontal lobe does most of the high level functions in the brain, including creating and forming concepts. It’s also known that Broca’s area in the brain is linked to speech production, and Wernicke’s area is linked to understanding and processing speech. So it’s reasonable to assume that it’s a combination of the three areas working together to take information, process it and produce concepts for a response, then form those concepts into words and +sentences that you then speak aloud." +1995 As light is part of the electromagnetic spectrum why is it referred to in terms of photons whereas frequencies that are higher/lower are not? 1092 https://www.reddit.com/r/askscience/comments/q1v345/as_light_is_part_of_the_electromagnetic_spectrum/ 1633435887 q1v345 Physics 2021-10-05 15:11:27 "We do talk about photons in x-rays and gamma rays etc. In fact, gamma ray telescopes can get so few photons that you know the energy of every single photon that hits the detector. Instead of a fully resolved image, for a faint object you might get like 1,000 photons, and from that you have to figure out where the intensity is brightest on average. Edit: [here](https://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/solar_system/jupiter_aurora.html) is an x-ray image of Jupiter, where you can similarly see individual points from individual x-ray photons. + +Generally though, EM radiation acts more ""wave-like"" of scales close to or smaller than the wavelength, and more ""particle-like"" on scales much bigger than the wavelength. This is why a Faraday cage doesn't block light. If a wave's wavelength is bigger than the gaps in the a Faraday cage, it acts much more like an EM wave, and it loses energy by pushing and pulling electrons in the metal. But for EM radiation with wavelengths much smaller than the gaps in a Faraday cage, it acts more like little bullets that either hit the metal and bounce off, or shoot straight through the gaps. + +This also relates to the differences in how microwaves heat food vs how ultraviolet radiation damages skin. Microwaves have a wavelength of centimetres, so they act wavelike on that sort of scale. They can penetrate surfaces a bit and push polar molecules back and forth with the EM force field. But UV radiation has a wavelength of 100s of nm. It basically either hits a single atom with its full energy, or misses it. So it directly ionises an atom, which can cause chemical reactions that can be dangerous." "The paradigm that we use to talk about light mainly depends on the context. Sometimes it is more relevant to talk about photons, and sometimes it is more relevant to talk about waves. + +For example if you want to build a telescope the optical system with mirrors/lenses will be developed with the ""wave paradigm"". The theory of optical aberration rely on the concept of wavefront, fourier optics, etc. However, the sensor will be developed with the ""photon paradigm"" because these devices rely on some quantum effects (not some exotic quantum effects, but the fact that the light is made of quantas clearly appears when you develop such devices). + +For the other part of the EM spectrum it can be noted that longer wavelength radiation very rarely have ""particle like"" behavior. The only example I can come up with right now is the MASER. It's just a LASER but not with visible light but with microwave. The theory behind it requires that you see microwaves in the ""photon paradigm"". + +For short wavelength like X-rays or gamma-rays they are often seen as photons. For example in a cloud chamber you can see the trace left by a single gamma-ray photon. In this context, it is much more relevant to see it in the ""photon paradigm""." +1285 When you build a tolerance to alcohol, does your body get better at removing it, better at functioning with it, or just better at not feeling it? 966 https://www.reddit.com/r/askscience/comments/b02d16/when_you_build_a_tolerance_to_alcohol_does_your/ 1552357829 b02d16 Biology 2019-03-12 5:30:29 "Ok so tolerance to alcohol is multi factorial. + +The first factor is that your liver upregulates enzymes that break down alcohol when you repeatedly expose yourself to alcohol. There are two main methods for this: alcohol dehydrogenase and the cytochrome p450 (CYP450) family of enzymes. The CYP450 family of emzymes has many different members, a couple of which break down alcohol. Alcohol dehydrogenase mainly breaks down alcohol but has a few other chemicals. It's this latter enzyme which is _sometimes_ missing in people who are chinese/japanese/korean etc. (I'm not going to say Asian as in the UK we would use that to deacribe Indians/Pakistanis/Bangladeshis etc.).... Which is why your Chinese friends sometimes go red and get giggly when they have one drink. + +Anyway the other way you develop tolerance is that your brain/nerves get used to the alcohol. Alcohol generally supresses the signalling pathways between nerves. Basically nerves release molecules to talk to each other. Each of. Those molecules has a special receptor on the cell it's trying to ""talk"" to. + +Alcohol does a lot of things to different bits of the brain but _on the whole_ alcohol surpresses the signals that make a nerve cell fire. So, in order for the cells to functiom properly they make more receptors and release more signalling molecules. Think of it as alcohol pressing the brake pedal of the brain and your brain putting on the accelerator to get to the same speed. (this is my rather simplistic-for-the-sake-of-explanation description of what u/namesarehard4 was saying about downregulation). + +This is the problem with withdrawl. When you remove the brake pedal the accelerator is still waaay way down. So the ""go"" signals are up-regulated... This doesn't mean you think more quickly and have superhuman cognition. It means that the nerve cells making it up make a lot of ""noise. "" This leads to tremors, confusion/delirium, sweating and seziures. Which is why people have to come off alcohol slowly or with a carefully dosed substitute, so the ""brake"" can be taken off slowly. + +Edit: there's probably other things that happen in tolerance but these are the main two..." "On a biological pov: + +Alcohol dehydrogenase (ADH) is a pathway that metabolizes alcohol, and therefore helps to sober you up. I think a few people have already talked about this already. + +There is another aid in alcohol consumption called the microsomal ethanol oxidizing system (MEOS). This system is activated by the liver when too much alcohol is present for ADH to deal with. MEOS essentially does the same thing as ADH, but requires extra energy input. The activity of MEOS increases with increasing alcohol intake, meaning that heavy drinkers will develop a tolerance due to the extra activity of MEOS. + +While ADH accounts for about 90% of alcohol metabolism, activation of MEOS allows for greater efficiency and rate of metabolism. This means you would be able to drink more than the average bear; however, I'm not exactly sure what ""more"" quantifies to. + +Reading the other posts, I would say that your body does a wide range of things in response to regular alcohol intake. " +1459 How do Saturn's rings spin in relation to the planet's spin? 949 https://www.reddit.com/r/askscience/comments/drog4e/how_do_saturns_rings_spin_in_relation_to_the/ 1572902608 drog4e Planetary Sci. 2019-11-05 0:23:28 Saturn’s rings orbit at the orbital velocity of their altitude, between 24000 m/s at the innermost rings to 1470 m/s at the outer edge. The equatorial rotational speed is about 9600 m/s, which is much slower than surface orbital velocity (as expected, otherwise the planet would fly apart). "Fun fact not actually answering your question, but kind of related. + +So the thing is, if you were on the surface of Saturn and if you could see the rings from the surface (which you most probably can't because they are too small), then it would appear, as if the inner part of the ring rotates in one direction, while the outer part rotates in the other direction. + +The reason for this is, that the relative speed of the rings in relation to the surface is different the higher you get from the surface. So from the surface it appears as if some parts of the rings are faster than others. + +I read this a while ago in some sci-fi anthology, probably written by Asimov, but i could be mistaken." +1127 If you just left out a tub of blood, would mosquitoes go for it? Or do they only know how to sniff out veins and go for blood that way? 904 https://www.reddit.com/r/askscience/comments/9j4gnf/if_you_just_left_out_a_tub_of_blood_would/ 1537981929 9j4gnf 2018-09-26 20:12:09 "I work as a research assistant and I routinely bloodfeed mosquitoes as part of my job. If you heat blood to roughly 37 C and then provide a membrane through which the mosquitoes can feed on it, they will definitely (and often enthusiastically) go for it. A living creature isn't necessary as the object of the feed. + +We typically use parafilm or hog's gut as a membrane, wrapped around the opening of a water-jacketed glass feeder. We pump heated water through the feeder to hold the blood at a consistent temperature, and the mosquitoes then penetrate the membrane to feed on the blood." +1498 What’s special about hypersonic speeds? 882 https://www.reddit.com/r/askscience/comments/g2jnz8/whats_special_about_hypersonic_speeds/ 1587058963 g2jnz8 Physics 2020-04-16 20:42:43 "Hypersonics are conveniently defined as any speed above Mach 5, because around Mach 5 a lot of engineering problems change their form. + +At supersonic speeds, you can quite easily maintain subsonic combustion (a shock cone or ramp intake will do much of this, check Concorde's intakes which are well documented) for a conventional turbine-based engine. + +Your airframe will experience drag heating from skin friction, but this again can be solved using titanium, ceramics, carbon, etc. + +Flight controls can be conventional control surfaces, so long as you take into account things like aileron reversal. + +As we approach hypersonic velocities, all this starts to change. Subsonic combustion becomes impractical, it causes too much drag, so you need to either not intake oxygen (e.g. a rocket) or do your combustion supersonic (e.g. scramjet). + +Airframe heating is more intense, but that's manageable (orbital craft re-enter way, way faster than mach 5), what changes is that the leading edge is now exposed to reactive oxygen species (ROS), oxygen plasmas, atomic oxygen, ionised oxygen. Oxygen attacks metal just sat in the open, ROS are types of oxygen turned up to 11: Atomic oxygen can oxidise fluorides. Coming back from orbit, we can use disposable ablative heat shields, and large blunt-bodies to push the shock back. In flight we can't do this if we want to remain flying very long. + +Flight controls are different too. If you actuate an elevator, you lose your elevator and empennage, so your turn radius is extremely large. Hypersonic craft get their lift from inertia (ballistics) as much as from the air, and from the air it's less wings as much as lifting bodies. + +This is partly the sheer speed of oncoming air, and partly your enormous inertial momentum. You go in a straight line, which becomes a ballistic trajectory at hypersonic speeds, aerodynamic flight is a secondary concern. + +So in summary, hypersonics are where the engineering challenges change substantially, and it's conventionally accepted to be around mach 5 where those challenges are the primary ones." "Chemically speaking you are no longer flying through the air you are ripping apart the molecules down to ions. + + +This was the casual description from a leading researcher at a hypersonic materials conference. I used to work on advanced material problems in this field; oxidation and ablation, carbon-carbon composites and ultra high temperature ceramics. The material issues at these speeds are amazing, nothing conventional (titanium, super alloys, polymer composites) survives the environment. Leading edge temperatures over 2,000C eliminate conventional ceramics so you have to use exotic carbides and borides, but they have structural and oxidation problems as well. + + + +It is a very active research field but it is starting to go dark as hypersonic weapons development is ramping up further in the US, China and Russia." +1607 Is there any difference between an immunity achieved by recovering from a virus and immunity achieved by vaccination? 870 https://www.reddit.com/r/askscience/comments/hwkxjg/is_there_any_difference_between_an_immunity/ 1595528467 hwkxjg Medicine 2020-07-23 21:21:07 "The end immunity achieved is largely the same but the process by which it is achieved is vastly different and what is most important. + +Vaccinations use the specific parts of the virus which are sufficient for infection, and this lets the body develop a specific immunity to those bits without risking a FULL infection. Antibodies produced will be largely the same since these parts are often compounds that viruses will be displaying on their protein surface and subsequently, the surface of an infected cell. The point of this is to avoid any form of infection while the body signals the production of antibodies for a new substance. + +With actual infection, the virus has a chance to infect the body with only T-Cells (those which fight off infected cells but not the virus itself) defending the body against the infection. The real deal is the B-cells and their eventual descendants Memory B-Cells. With severe infections the time it takes to develop these B-Cells is not enough to keep the virus from doing real damage to the body. + +Within an already vaccinated individual, the B-cells which initially fought off the hoax infection (the vaccine) will have produced memory B-cells. These are stored away, for future references. Now they don’t need to develop a new cell with new receptors to recognize the virus, they just need to go bat shit crazy replicating those few memory cells. + +The difference in time that it takes for the body to fight back effectively is what saves lives. With a vaccine I don’t need to wait for the fever, the macrophages, and the T-cells to hold the line with their [relatively] inaccurate targeting. With the vaccine I already have all the things necessary. + +Immunity achieved is the pretty much the same. But the manner in which it is achieved is definitely not." "Someone else addressed the point broadly but I'd like to give some exceptional examples. + +Measles can eliminate your immune memory making you susceptible to other diseases you were immune to. The vaccine does not cause this. + +Also the chickenpox vaccine reduces you likelyhood of chickenpox reinfection and shingles better than catching and recovering from chickenpox." +1460 How does saline nasal spray moisturize your nose? I thought salt was used to dry things out? 857 https://www.reddit.com/r/askscience/comments/dgk0oq/how_does_saline_nasal_spray_moisturize_your_nose/ 1570822195 dgk0oq Chemistry 2019-10-11 22:29:55 "It matches the salt concentration present in your cells (isotonic). Pure water would flow into the cells of your nasal passage and some would burst (lyse). Oversalinated solution would draw out water just like you assume it would. Balanced salinity is best. + +Edit: spelling, draw out, not dry out" +1499 In HBO's Chernobyl, radiation sickness is depicted as highly contagious, able to be transmitted by brief skin-to-skin contact with a contaminated person. Is this actually how radiation works? 851 https://www.reddit.com/r/askscience/comments/ejy598/in_hbos_chernobyl_radiation_sickness_is_depicted/ 1578152773 ejy598 Medicine 2020-01-04 18:46:13 "No, radiation sickness itself not contagious at all. The apparent transmission depicted stems from the ""transmitters"" being radioactive themselves by either contamination or by induced radioactivity. + +If I recall correctly, the first scene you describe was in the first episode, and the person with radiation sickness was a fireman, right? At this point, he was covered with highly radioactive dust and ashes from the burning plant. That's what caused the radiation burns of the second fireman who touched him. + +The first responders at Chernobyl also inhaled (and partly ingested) the radioactive dust, which means they had highly radioactive particles in their body. + +In addition, they were exposed to incredibly huge amounts of radiation (I found values of 20,000–30,000 roentgen/hour). That alone is actually able to make pretty much every matter radioactive itself, by so-called [induced radioactivity](https://en.wikipedia.org/wiki/Induced_radioactivity). This also happened in other cases of fatalities by nuclear accidents, for instance the [SL-1 incident](https://en.wikipedia.org/wiki/SL-1), where one of the bodies of the killed workers was so highly radioactive that the pathologist performing the autopsy had to cut the body into pieces to be able to safely examine it. + +The story of the fireman at Chernobyl and his pregnant wife is by the way based on a [true story](https://www.mamamia.com.au/lyudmilla-ignatenko-chernobyl-pregnancy/)." "Vanity Fair did a ""fact check"" on Chernobyl featuring Alla Shapiro, who was actually at Chernobyl after the accident and is a radiation/medical expert: [https://www.youtube.com/watch?v=m1GEPsSVpZY](https://www.youtube.com/watch?v=m1GEPsSVpZY). They cover the second scene you asked about. + +The tl;dw is that most things related to the radiation was very exaggerated. But it's TV, so they didn't drop the ball, they were just trying to make compelling TV." +1810 Why does Covid have neurological effects on the brain/sense of smell? 825 https://www.reddit.com/r/askscience/comments/lbqk3n/why_does_covid_have_neurological_effects_on_the/ 1612367578 lbqk3n COVID-19 2021-02-03 18:52:58 "Oh oh oh, something I can answer :) +ACE2 receptors are expressed on basal (stem), support and epithelial cells in your nose. So the virus can infect those quite well, not the sensory neurons though (which don't or barely have ACE2). Inflammatory responses might restrict metabolic support of the sensory cells and disrupt the way in which support cells keep up the ion gradients, which are necessary for signal transduction. Also damaged stem cells disrupt cell turnover/renewal in the olfactory epithel. + +https://hms.harvard.edu/news/how-covid-19-causes-loss-smell +This paper suggests the same mechanism for neurological problems. So neurons apparently aren't vulnerable directly but vascular cells are (again ACE2). It's from July, so there's probably more concrete evidence by now. + +(Maybe decaying ion gradients could lead to short-haywire signals being sent to your brain creating the vomit smell? Just a thought that would be hard to test I imagine)" "Regarding the smell, https://www.sciencealert.com/scientists-worked-out-how-covid-19-disrupts-some-people-s-smell + +Regarding other neurological symptoms like headaches, forgetfulness, loss of focus etc, according to one of our radiologists, COVID-19 patients commonly have signs of vasculitis in their head scans. Depending on its location, it can cause those effects. + +Edit: link fix thanks yo u/naisihan" +1128 How come there is formation of two molecular orbitals when there is single interference of atomic orbitals in Molecular Orbital Theory? 773 https://www.reddit.com/r/askscience/comments/9hnjnh/how_come_there_is_formation_of_two_molecular/ 1537519183 9hnjnh 2018-09-21 11:39:43 "If I'm understanding your question correctly, it's because when you bring two orbitals on separate atoms close together, they mix because the symmetry of the total system is no longer that of a single atom. Every orbital (in molecular orbital theory, at least) will have a symmetry that depends on the symmetry of the molecule as a whole. + +That's a consequence of the symmetry requirements of the overall wavefunction, where **𝚿** (a,b) = - **𝚿** (b,a)." Don't forget, you get two MOs from two AOs! You get a *constructive* interference (the Highest Occupied Molecular Orbital) and a *destructive* interference (the Lowest Unoccupied Molecular Orbital). Because AOs act similar to waves, when they combine you get two different types of interferences. +1286 Just watched the Sixty Symbols video on LHC and that it has discovered one particle; Is there any major physics theories that it has categorically disproved? 760 https://www.reddit.com/r/askscience/comments/b4x8rh/just_watched_the_sixty_symbols_video_on_lhc_and/ 1553439633 b4x8rh 2019-03-24 18:00:33 """categorically disproved"" is not a term used in physics + +Instead, they say stuff like .. within the range of energies studied, we have seen no statistically significant evidence + +Many theories have failed the test, but the most significant one is Supersymmetry, a theory that predicts that all known particles have a supersymmetric partner. The electron would have a partner called a selectron, the proton a partner called a sproton, etc. Supersymmetry is a key part of many theories beyond the Standard Model, including String Theory + +So far, no evidence for Supersymmetric particles has been found, leading some theorists to believe that none exist + +Others believe that a more powerful accelerator would find them" "To actually answer the question (ignoring the semantics): LHC was hoped to find some evidence of supersymmetry. and was pretty much designed to solve the hierarchy problem (along with one or two other things) +Supersymmetry (or SUSY for short), is a theory that extends the standard model, by positing that each particle in the standard model has a partner particle, a superpartner (which all have ridiculous sounding names like photino and squarks, and gluinos). These partners would interact with the same 3 forces in the same ways, but would have higher mass than their standard (boring) partners. This was in an effort to explain why the Higgs is so light, since standard model interactions should make it very heavy. These partners should counteract the Higgs mass contributions, allowing for a light-Higgs to exist. + + +The existence of these particles would also mean that at high energies the three (non-gravity) forces would have the same strength at high energies... a Grand Unified Theory, the dream. + + +On top of that, SUSY would also unify Fermions and Bosons, as each particle with spin would have a partner particle with spin that differs by 1/2, so each boson would be accompanied by a fermion and vice versa. + + +And if all that wasn't enough, predictions were that the lightest particle in SUSY would be stable and electrically neutral, and would interact weakly with the standard particles, which are the characteristics of Dark Matter. + + +BUT the big damper on all this, is these particles should exist in the electroweak range, meaning that LHC should have been able to detect and measure them... and big surprise... it hasn't. The smallest superparticles should have been seen at the energies they have been measuring. This basically rules out almost all forms of SUSY and actually introduces a new problem (if we hold on to SUSY), which is to explain why the superpartners are so massive while the standard lads are so light. + + +SUSY was elegant, and beautiful, it solved so many of our biggest problems in one fell swoop. All those hopes are now dashed against the calorimeters... annihilated. SUSY is pretty much dead for now, and the hierarchy problem is back in the world, terrorising children and being a general nuisance." +1287 Is the amount of time an organism takes to achieve sexual maturity proportional to its lifespan? 751 https://www.reddit.com/r/askscience/comments/bf8iht/is_the_amount_of_time_an_organism_takes_to/ 1555735001 bf8iht Biology 2019-04-20 7:36:41 "In general, no. At a local-level among populations of a species or between closely-related species, perhaps, but across the animal kingdom the answer would be 'no, proportionality is not a rule for this characteristic'. + +This gets at an aspect of biology called 'Life History Theory' that is concerned with when these major events (birth, death, reproduction) occur in a species' lifespan, and how evolution in response to ecological pressures selects for a 'life history strategy' that maximizes the organism's fitness. You can find a great diversity of life history strategies in the animal kingdom that reflect how an organism has evolved to maximize its reproductive success given its resources on-hand. Granted, the life history conceptual framework is based in models and some idealized assumptions, so it doesn't map perfectly onto every situation, but it can explain some general trends we see. + +Just to list a few examples: many insect species spend the majority of their lifespans in juvenile stages and only become sexually reproductive for a tiny period of their life cycle. In one extreme example, the [Antarctic midge (*Belgica antarctica*](https://www.eje.cz/artkey/eje-199601-0001_Antarctic_diptera_Ecology_physiology_and_distribution.php)) spends 2 years as a larval grub before molting into a sexually reproductive adult for about 10 days, after which it dies. Completely different life history strategy from mammals, which generally spend most of their lives as reproductive adults. + +Even among mammals, you'll find a lot of variation among life history strategies. Humans and humpback whales have pretty similar lifespans (humpback whales might be a little shorter, but we're still learning what their lifespan looks like when we aren't hunting them). But [humpback whales achieve sexual maturity](https://doi.org/10.1139/z92-202) around 5 (female) or 7 (male) years old. + +And I can tell you that a single species can have multiple life history strategies. There's a great body of literature on the [Trinidadian guppy](https://doi.org/10.1111/j.1558-5646.1982.tb05021.x) that shows how guppies from a high-predation environment show a typical 'r-selected' life history strategy: mature quickly, have a lot of small (cheap) babies, and probably get eaten at a young age. But those guppies, when transplanted to a low-predation environment evolve toward a 'k-selected' life history strategy: mature slowly, have a few large (expensive) babies, and live much longer. I don't know if the changes in maturity and lifespan (actual, not potential) are proportional, that would be an interesting question that you could explore for a given species, but it does demonstrate the flexibility of life history strategies. + +References: + +1. Convey P. & Block W. Antarctic diptera: Ecology, physiology and distribution. *Eur. J. Entomol.* 93 (1): 1-13, 1996 + +2. Clapham, P. Age at attainment of sexual maturity in humpback whales, *Megaptera novaeangliae*. *Can. J. Zool.*, 70(7): 1470-1472, 1992 + +3. Reznick, D. & Endler, J. The impact of predation on life history evolution in trinidadian guppies (*Poecilia reticulata*). *Evolution* 36(1): 160-177, 1982" "No. Carpet beetles spend one to two years as larvae before maturing, breed, and die within a couple months. 17 year cicadas spend almost their entire lives as nymphs underground before maturing, then breed and die a couple months later. Many other insects have similar patterns of a very long juvenile stage followed by a short adult stage. Some adult insects don’t even eat, living out their short lives on energy stores from the juvenile stage. + +In most of the insect examples I can think of the adult stage is capable of flight. The whole point of the adult stage is rapid dispersal to find a mate. The pattern seems to be a long juvenile stage in a sheltered location preparing for breeding by adding body mass and fat stores, followed by rapid dispersion and reproduction." +1288 "When I open my blinds in the morning, is it ""too bright"" for my eyes, the optical nerve, or the part of my brain interpreting the data? Where does the pain of bright light come from?" 682 https://www.reddit.com/r/askscience/comments/b261fg/when_i_open_my_blinds_in_the_morning_is_it_too/ 1552835119 b261fg 2019-03-17 18:05:19 "All pain is a warning of damage. Basically the pain you feel is a warning that your retina is receiving too much light and the sensory overload could fry your nerves. Your iris will constrict quickly, which is uncomfortable and plays into the pain response, but the basis of it is your body screaming "" hey, we evolved this really sick organ, but its sensitive as hell so take care of it"". The pain is just an impulse warning and the fact that your eyes completely bypass your spine means that it's basically instant. There's none of that toe-stubbing wait. " "The photoreceptors are connected to the retinal pigment epithelium (RPE). One way the retina adjusts the gain from the light signal is by having the RPE ""munch"" on the photoreceptor outer segment (the portion that has the machinery for phototransduction). In the light, the RPE will reduce the length of the photoreceptor and reduce the gain of the signal. When you're acclimating to the dark, the RPE will reduce it's munching which lets the photoreceptors get longer and more sensitive to light. + +So when you get up in the morning and turn on the lights, bright light is hitting more photosensitive receptors. The gain is higher so a normally innocuous stimulus becomes too much. + +I'm less familiar with mechanisms of gain downstream of the retina." +1996 If the Higgs field gives mass to matter, and the mass of matter curves spacetime, and said curvature is the basis of gravity; does this imply that the Higgs field causes gravity? 676 https://www.reddit.com/r/askscience/comments/q1xw1t/if_the_higgs_field_gives_mass_to_matter_and_the/ 1633445312 q1xw1t Physics 2021-10-05 17:48:32 "Here the distinction between two types of mass becomes important. There’s inertial mass, which is the m in Newton’s F=ma. It takes effort to make something with nonzero inertial mass move. In contrast, something with zero inertial mass, such as photons, must always move at the speed of light. We know that electrons and quarks (which make up neutrons and protons) don’t move at the speed of light, so they must have nonzero inertial mass. The Higgs boson is what gives them this inertial mass. + +On the other hand, there’s gravitational mass, which is what makes things gravitate towards each other. Incidentally, this is exactly equal to the inertial mass in Newton’s theory of motion and gravitation. In Einstein’s updated theory (general relativity), this equivalence between inertial and gravitational mass is so central that it has a name, the equivalence principle. However, Einstein extended the definition of this mass to include all forms of energy, so even massless things like light can now gravitationally attract other things. You don’t need inertial mass to have gravity, according to Einstein, so quarks and electrons would gravitate even without the Higgs boson (though it certainly helps). + +In the Standard Model of Particle Physics, we included all the known fundamental particles and interactions between them (photons, electrons, quarks, Higgs boson, etc), with the exception of gravity. If we try to include it, then every single particle (with or without inertial mass) will interact with the graviton and lead to gravitation, in a way consistent with Einstein’s generalised mass-energy. However, doing so happens to cause the whole quantum field theory (the mathematics framework of the Standard Model) to utterly break down, so we have not yet understood the precise relation between the Higgs boson (which can only be explained through quantum field theory) and gravity." "No. + +Coupling to the Higgs field is not the only way that particles get mass. For example, any hadron, where the majority of its mass comes from strong interactions rather than the bare masses of the constituent particles. + +And furthermore, mass is not the only source of gravity. Things like mass, energy, and momentum are all included in the source term for gravity (the stress-energy tensor). + +So the Higgs field and gravity are fundamentally different things." +1500 What are the effects of the smoke generated by the fires in Australia? 625 https://www.reddit.com/r/askscience/comments/ek7gs9/what_are_the_effects_of_the_smoke_generated_by/ 1578195551 ek7gs9 Chemistry 2020-01-05 6:39:11 "Hi! Atmospheric chemistry PhD here. I researched wildfire smoke composition and health effects in graduate school. I'm currently doing postdoctoral research in medicine trying to understand the finer details of air pollution toxicity. + +Here's a few quick things about wildfire smoke! + +**What's in the smoke?** + +A complex mixture of fine particulate matter and gasses. The composition is very complicated as there are hundreds to thousands of different compounds that transform as the smoke plume moves from the source. You will find NOx, CO, CO2, lots of organic carbon, black carbon/soot, inorganic salts and a smaller but still significant amount of transition metals (iron, copper, zinc, aluminum among others). + +**How does the smoke impact climate?** + +The brown and black wildfire particle absorbs incoming solar radiation and increases warming while the smoke is present. However, the magnitude of warming by wildfire smoke is uncertain and researchers are actively researching this and other impacts on the climate system. Furthermore, the wildfire smoke particles may provide a favorable surface for water molecules to condense on, thereby driving cloud formation. See pyrocumulus clouds. + +**How does the smoke impact health?** + +Wildfire smoke produces toxic gases and fine particulate matter. In general, long and short term exposure of fine particulate matter has been associated with chronic inflammation, increased heart diseases, lung diseases, cancer, and death rates. Recent estimates suggest that \~80% of air pollution deaths are due to cardiovascular effects. Human and animal studies have consistently shown that particulate matter inhalation produces a pro-inflammatory response. **Recent epidemiological work has suggested that wildfire smoke is MORE TOXIC than urban air pollution particles.** We still don't know the specific chemicals and biological mechanisms associated with the toxic effects of smoke inhalation. + +**EDIT, PSA ABOUT RESPIRATORS:** If you are concerned about smoke exposure and are not in immediate threat of fire: Get a respirator that filters fine particulate matter and organic vapors if possible. 3M has some pretty good ones. The white dust masks that strap around your face don't block fine particles and organic gasses from entering your lungs! + +Best wishes and hope for the safety of our friends in Australia. + +\*\*Minor edits for grammar + +\*\*Edited to say long and short term exposure to particulate matter is associated with detrimental health effects, rather than just long term." "Here is a live-updated global monitoring stream of air and water variables gathered from various satellites, ground stations, and water-born sensors. + +https://earth.nullschool.net/#current/chem/surface/level/overlay=so2smass/orthographic=133.33,-23.92,730 + + +""About""link, explaining the resources for the imagery: + +https://earth.nullschool.net/about.html" +1129 How powerful are satellite signals? 602 https://www.reddit.com/r/askscience/comments/9dtn8m/how_powerful_are_satellite_signals/ 1536321438 9dtn8m 2018-09-07 14:57:18 "GPS satellites are supposed to be about the power of a car headlamp - imagine a 50 watt bulb illuminating a hemisphere of the globe! The signal is incredibly weak, about 400 times weaker than background noise. In fact the signal is so weak that you can't pick up the GPS signal unless you know what the signal is. + +The satellites used for TV are much much more powerful, around 10-20kW, and the signal is targeted at a much smaller area of the globe, for example Western Europe might have a dedicated satellite. Also at the receiving end you have a nice big dish to capture as much energy as possible." "Typical geostationary satellite transponders are about 60W spread over 36MHz of capacity. However, given that most are now carrying multiple signals (rather than one huge one), you need to have about 6dB back-off so that the signals don't interfere with each other. This leaves you with a useful transmit power of approximately 15W. + +I used to design and build satellite networks for a living, and it's really quite astounding how good/low noise the electronics are. Just looking at one of my link budgets, the typical flux density for the link was -112dBW/m^2. That's about 6.3 picowatts per square meter. + +The real magic is in the receivers. The LNBs (Low Noise Block upconverts) had about 60dB gain, and the modems will receive down to about -55dBm." +1461 How would the low thermal output of Chernobyl's reactor #4 on the night of the Chernobyl disaster have contributed to the reactor core's instability? 594 https://www.reddit.com/r/askscience/comments/do0n1s/how_would_the_low_thermal_output_of_chernobyls/ 1572217626 do0n1s Physics 2019-10-28 2:07:06 "Some background on RBMK reactors to preface my answer to your question. RBMK reactors are graphite moderated and water cooled. Water acts as both a moderator and absorber, however in RBMK's the graphite carries the bulk of the moderating potential so the water tends to act mostly as an absorber. This is important because losing water or decreasing the density will reduce the absorption of neutrons. In critical operation, neutron population is in equilibrium (rate of neutrons born = rate of neutrons absorbed/lost). If the density of water in the RBMK decreases, less neutrons are absorbed, and the population of neutrons will increase, essentially inserting reactivity in the reactor. This is called a positive void reactivity coefficient (reactivity increases as voids increase). + +Intuition would tell you that at lower power levels, less boiling occurs so the density is also expected to remain near constant. Indeed the 'predicted channel coolant density response is small at low power levels.' and 'the channel void nearly collapses.' Unfortunately it is not so simple. In reality, 'the density response exhibits a maximum at an intermediate low power,' which is to say contrary to expectation, the decrease in density is greatest at low power (see Fig. 5-2). This occurs because the density of coolant is not dependent on power level alone, but rather dependent on power-to-flow ratio instead. A physical interpretation would be fast-moving water flow needs more heat to boil while slow moving flow requires much less (boiling water in a pot while constantly stirring vs. boiling still water). + +The result is instability at low power. At low power operation, the density response function is near the maximum. Since RBMK have a positive void reactivity coefficient, voids created at low power insert reactivity. Since the time constant of this behavior is on the order of seconds, it is far too quick for operators to react since RBMK's take ~10-20 seconds to fully insert control rods to for SCRAM. + +[Source](https://inis.iaea.org/collection/NCLCollectionStore/_Public/20/052/20052963.pdf?r=1&r=1) + +Addressing your second question 'Supposing instead that the reactor was gradually brought down from its normal operating level to 200mw, could something still have gone wrong owing only to the low thermal output?' That's actually exactly what they did (or intended to at least); the reactor was gradually brought down from its normal operating level to the low thermal power required for the test (which was 700-800 MW, not 200 MW). The problem arose from the electrical operators in Kiev demanding Chernobyl's operators postpone their test to satisfy electricity demands for that evening. They ended up operating at ~1600 MW for 12+ hours, much longer than planned, giving time for xenon to build up and poisoning the reactor. When time came for the test, the operators began lowering the reactor that had been sitting at 1600 MW for far longer than intended to 700-800 MW for the test, but due to the xenon buildup, operators could not stabilize the reactor at 700-800 MW and power quickly dropped to 30 MW. You have it backwards in your post; xenon poisoning led to 30 MW power output, not the other way around. To address this, they should not have let the reactor sit at 1500-1600 MW for over 12 hours, far too much xenon buildup had occurred and there was no way for the test to be carried out successfully. If the operators were allowed to perform their test without this interruption, there would not have been enough xenon poisoning to have lowered thermal power to 30 MW in the first place. + +[Source](https://www.rri.kyoto-u.ac.jp/NSRG/reports/kr79/kr79pdf/Malko1.pdf)" "godlikemojo gave a great answer, but there are some other factors: + +The problem with low power is not just the instability of the reactor itself, but also the fact that various automated control systems do not function at this power level. Likewise, certain core sensors become unreliable (the two thermal power sensors start to disagree and lag one another). + +Therefore the operators were flying by the seat of their pants. Basically, the RBMK was squirrelly and unstable at the best of times, and low power just increased the load on the operators. This was probably a factor in the unexpected drop to 30 MW. + +> numerous automatic failsafes were overridden. + +This is a red herring. Two automated reactor trip signals were disabled because the test was clearly going to trigger them. If either of these reactor trips had gone off, the explosion just would have taken place earlier. Possibly it would have been less powerful; you'd have to model it. This was all according to plan, except for the part where Akimov forgot to reengage the turbine trip. + +To put it simply, the real killer at low power is the reduced boiling of the coolant which provides maximum latitude for the void coefficient to create a feedback loop." +1289 How can potassium diffuse through a membran that sodium can't? 586 https://www.reddit.com/r/askscience/comments/atvs29/how_can_potassium_diffuse_through_a_membran_that/ 1550930439 atvs29 2019-02-23 17:00:39 "No ion can directly pass through the cellular membrane. However, there are channels that are *usually* open that allow ions, such as potassium to pass. These are appropriately called leak channels. They are not voltage gated, so if you looked at their IV curves it’s essentially an ohmic (straight line) relationship. When people say the resting membrane potential is set by potassium, it’s because the membrane is more permeable to potassium. Or in another way, there are more channels that allow potassium to leak out of the cell, reduce the net positive charge of the cell, and drive the membrane potential towards the reversal potential of potassium. + + +When you think of channels, a smaller ion does not always mean it will pass through if a larger ion can. There are selectivity filters that can make each channel specific to certain ions. These selectivity filters depend on interactions between the amino acids in the pore and the ions as they pass through, and/or if it’s electrically favorable to strip its hydration shell momentarily to allow passage. It’s pretty complicated actually. " Potassium channels don’t actually just let the ions flow through like a pipe. The ion causes a conformational change it a the potassium channel that allows it to exit on the other side of the membrane. Think of it like a subway turnstile that is only unlocked when the right size object enters. Sodium ions can get into the opening, but they aren’t the right size to cause the conformational change, so they can’t get through +1608 Why does the center of the earth never cool down? 577 https://www.reddit.com/r/askscience/comments/hvd1ke/why_does_the_center_of_the_earth_never_cool_down/ 1595356687 hvd1ke Earth Sciences 2020-07-21 21:38:07 "First, a clarification, the core of the Earth (and the Earth as a whole) is losing heat, but it is relatively slow. The reason it is slow is a combination of four main factors: (1) The core (and more broadly the Earth as whole) started off with a lot of heat, i.e. enough for the entire planet to be [a liquid initially](https://en.wikipedia.org/wiki/Magma_ocean); (2) Radioactive decay of uranium, thorium, and potassium in the mantle and crust continue to contribute significant amounts of heat, and probably ~50% of current heat flux is from [radiogenic heat](https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget#Radiogenic_heat) (plus there were even greater rates of radiogenic heat production early on from short lived isotopes like ^(26)Al); (3) Rocks are not great heat conductors, compare the thermal conductivity of [rocks (0.5-5 W/(m x K))](https://www.researchgate.net/publication/256372062_Rock_Physics_and_Phase_Relations_A_Handbook_of_Physical_Constants) to the thermal conductivity of efficient conductors like [metals (e.g. copper, ~400 W/(m x k))](https://en.wikipedia.org/wiki/List_of_thermal_conductivities), though this is partially overcome by convection in the mantle being the primary process by which heat from the core is moved toward the surface, but rate of heat conduction through the crust is still limiting; and (4) air is an even worse conductor so the rate of heat loss from the crust, to the atmosphere, and eventually space is not efficient and serves as an insulator to a certain extent (again here though, heat in the atmosphere can be more efficiently transported through convection than just conduction). + +EDIT: Just to expand on point 2 a bit, because radiogenic heat production is tied to the amount of radiogenic isotopes, this means that even without considering extinct isotopes, [heat production was greater in the past](https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget#/media/File:Evolution_of_Earth's_radiogenic_heat-with_total.svg) (because there was a larger concentration of isotopes which have since decayed away) and the amount of radiogenic heat production will continue to decrease (as the concentration continues to decrease). This reduction in radiogenic heat production through time is slow though given that the half lives of the relevant elements are 100s of millions to billions of years." "To add a little anecdote to /u/CrustalTrudger 's great answer: the 19th century scientist Lord Kelvin used exactly your argument to estimate the age of the Earth. He assumed it started off completely molten, and calculated how long it would take to cool off to match the heat flow we see today. The answer he settled on was 20-40 million years. This is way way too small, because since he didn't know about radioactivity, which generates new heat inside the Earth, and because he didn't realize the Earth's interior was convecting. + +Anyway, he went on to use this wrong answer to argue that geologists' claims about the ages of rocks were impossible, and to suggest that Darwin's theory of evolution must be wrong because there's no way it could act in such a short time. + +https://en.wikipedia.org/wiki/William_Thomson,_Baron_Kelvin#Age_of_the_Earth:_geology" +1811 How many spikes are there on a single SARS-CoV-2 virus? Does it vary from virus to virus? 572 https://www.reddit.com/r/askscience/comments/ly0hq7/how_many_spikes_are_there_on_a_single_sarscov2/ 1614906925 ly0hq7 COVID-19 2021-03-05 4:15:25 "Individual virions contained 24 ± 9 S trimers (Extended Data Fig. 1b). This is fewer than previous estimates that assumed a uniform distribution of S21, because S was not uniformly distributed over the virus surface. A small sub-population of virions contained only few S trimers whereas larger virions contained higher numbers of S trimers. +Ke et al Nature 2020 https://www.nature.com/articles/s41586-020-2665-2" "Coronavirus are what's referred to as Positive Strand RNA viruses. What this means is that the virus genetic material comes ready to be translated into protein. But that would mean that their single long ""genomic"" script would only make 1 protein. They get around this by coding for their own RNA polymerases that read at multiple subgenomic regions. These polymerase are also not made at the same time, the virus translates proteases that cleave the long strands of protein to smaller functional proteins. + +At the very end of all of this, are the structural capsid proteins that include the spike protein. You can imagine that different effective rates of all the proteases and polymerases I discussed (there's also the speed in which trans cleavage occurs) that you're going to get some variability in the rate that the spike protein will be made according to the number of capsid proteins made (which is always the same). Especially since at the final step, the viral genome is just stuffed into the available capsid and there's no real ""counting"" system established for how many spike proteins are on it." +1290 Where does the flu virus go when it's not flu season? What is the reservoir it uses to come back from each year? 554 https://www.reddit.com/r/askscience/comments/bfufvx/where_does_the_flu_virus_go_when_its_not_flu/ 1555885352 bfufvx Medicine 2019-04-22 1:22:32 Sick people. Flu season is just the time of year when the rate of infection by flu increases ~1,000%. But all year long it’s still steadily transmitting itself from person to person, there is no flu off-season unfortunately. Flu is global, so it's always influenza season somewhere. When it's summer in the Northern hemisphere, it's winter and flu season in the Southern hemisphere. In the brief periods between peak flu season in the Northern and Southern hemispheres, the virus is still circulating in tropical and semitropical regions. +1462 Is constant light exposure beneficial to plants, or do they also require periods of low light? 553 https://www.reddit.com/r/askscience/comments/ds5a02/is_constant_light_exposure_beneficial_to_plants/ 1572986738 ds5a02 Biology 2019-11-05 23:45:38 "The concept you're referring to is [Photoperiodism](https://en.wikipedia.org/wiki/Photoperiodism) + + +Depends on the plant, and the phase of growth that plant is in. Some plants do just fine with 24/7 light and can benefit from no darkness. + + +Other plants, particularly those that flower in the fall, are dependent on changing day/light periods to trigger blooming. + + +Many of those plants will still be fine under 24/7 light but will stay in a vegetative state, growing, but not producing fruit or flowers." An additional point for clarification: many of you may remember hearing about the light and dark reactions of photosynthesis, but these are now commonly referred to as light dependent and light independent reactions. These two crucial sets of reactions can both operate during exposure to light, so at least in this sense, plants are fine. Just wanted to share just in case that's in the back of the mind of anybody who hasn't had a biology class in a while +1463 How far back in time would a modern English speaker have to travel before not being able to understand anyone? What about other modern language speakers? 551 https://www.reddit.com/r/askscience/comments/d54wym/how_far_back_in_time_would_a_modern_english/ 1568660707 d54wym 2019-09-16 22:05:07 "Old English was the language spoken before the Norman Conquest (1066), and would be completely incomprehensible to you other than a few words that have remained, see [Beowulf](https://www.poetryfoundation.org/poems/43521/beowulf-old-english-version). Middle English was spoken between 1066 and about 1500, and varies a lot within that time period and from region to region. Take two pieces from the late 14th century: [Sir Gawain and the Green Knight](https://quod.lib.umich.edu/c/cme/Gawain?rgn=main;view=fulltext) which is a little better than Old English, but not really, and [The Canterbury Tales](https://chaucer.fas.harvard.edu/pages/general-prologue-0) which is getting close to modern English. *Sir Gawain* was probably written in a dialect from the northern Midlands, while *The Canterbury Tales* was written in the dialect spoken in London at the time which clearly was a more direct predecessor to modern English, though it's deceptive because vowels were pronounced differently in Middle English. From the 1400s to the 1600s the [Great Vowel Shift](https://en.wikipedia.org/wiki/Great_Vowel_Shift) and a general trend towards standardized spelling swept across England, leading to the modern language. The works of Shakespeare and the King James Bible are the best examples of early modern English, though they are sometimes erroneously called ""old English."" Of course the language continues to change but other than using a few words differently or not understanding the slang of the period/region you would understand just about anything from about 1600 on, possibly 1500 if you're in the right place." "A Mandarin Chinese speaker would be able to read most of the way back to the beginning of writing (especially a person familiar with calligraphy), but unless they were familiar with the exact provincial dialect of wherever they were sent, they wouldn't understand much (or possibly any) of the spoken language. If the time traveler were from Nanjing and thus natively familiar with Nanjing Mandarin, and with approximately the same difficulty as modern Americans find in trying to talk to modern Scottish people, they might be able to communicate with a government official after Ganhua/官话 (the ""court language"") began to be required of Imperial officials in the 1400s. + +Putonghua (standard mandarin) as the national language is a very modern invention, dating from after the Communist takeover. Prior to that nearly everyone spoke a local dialect of a local language, and a majority of the eastern provinces spoke (and still natively speak) dialects of Chinese languages that are not Mandarin, such as Wu (which includes Shanghainese) or Yue (which includes Cantonese)." +1812 How did people find out about the Earth’s core and if other planets have a core? 538 https://www.reddit.com/r/askscience/comments/l9me22/how_did_people_find_out_about_the_earths_core_and/ 1612128227 l9me22 Earth Sciences 2021-02-01 0:23:47 "Others have mentioned the importance of earthquakes and magnetic fields. I want to add some info on those and add another key factor: planetary shape and gravity. + +1) **Seismic waves** (earthquakes) are used to probe the interior of a planet. Some seismic waves will travel through solids, but not liquids, so a liquid core will block these waves from traveling from an earthquake on one side of the planet to seismic sensors on one side. More elaborate analysis of seismic waves can detect changes in the type and density of solid materials, detect a solid inner core inside the liquid outer core, and so on. + +A problem with seismology: you can only analyze seismic waves if you have a sensor on the surface of the planet, which means you have to land a delicate instrument on it. We have good seismic data for the Moon, inconclusive data for Mars, and nothing for Venus or Mercury or any of the outer planets and moons. + +2) **Magnetic fields** are useful but ambiguous. Strong planetary magnetic fields are created by having an electrically conductive liquid in a rapidly spinning planet. However, that liquid doesn't have to be iron (the giant planets Jupiter and Saturn, the field may be created in high-pressure liquid metallic hydrogen), and if a planet *doesn't* have a magnetic field, it's hard to say whether that's because its core is not liquid, not conducting, or not spinning fast enough. + +3) **Gravity and Shape**: Centrifugal force causes spinning planets to flatten out from a perfect sphere into an ""oblate spheroid"": they're a little bit wider across the equator than from pole to pole. The amount of flattening depends on whether the planet's mass is spread evenly through it or not. A planet that's all the same density throughout will be more squashed, a planet with a heavy core covered by a lightweight crust will be more spherical. It's easy to measure the shape of the planet, by either taking a picture with a camera or measuring its gravitational pull on a spacecraft: from that you can infer how much mass is concentrated at the center, though you can't get any detailed structural info." "Several different things allow us to constrain what's inside the planet: + +1) Density. Because of the Earth's gravity, we know how much matter must be inside of it. But pretty early on, we noticed that the surface of the Earth is way too light to explain how much gravity there is— so we knew that the inside of the Earth must be much more dense, on average, than the outside. Specifically, the density of rocks on the Earth's crust is around 2.5 times as dense as water, but based on gravity, we know that the entire Earth in total is about 5.5 times denser than water. So we know that the inside of the Earth must be quite a lot heavier than the rocks we see on the crust. + +2) Earthquakes. When an earthquake happens, ripples of shaking spread out away from the epicenter. As the shaking passes through different materials in the earth, the shaking is affected by the properties of the material— how heavy the material is; how much it resists or permits being deformed and in what way; how quickly the shaking is transmitted through it. We can use seismometers to measure the shaking far away from the earthquake, after it has passed through a lot of rock, and see how the shaking has been affected. + +If you do this with a lot of earthquakes and a lot of seismometers, over time, you can build up a big map of all the features inside the earth that affect the shaking waves that pass through them. From this, we can very clearly see the various layers of mantle and core, because the boundaries between them bend the shaking waves in much the same way that water or glass bends light! Also, the core of the earth doesn't transmit certain kinds of shaking because it's made of liquid, and liquid doesn't ""hold together"" if you shear it, so shaking that involves shearing (rather than squeezing) simply doesn't make it through liquid layers. So if we plot where all the shearing-waves wind up, we can see a big ""shadow"" cast by the liquid core on the other side of the Earth from where the earthquake is! + +3) Moment of inertia. Differently-shaped objects have different resistance to being turned (think of an ice skater bringing their arms in or letting them out; it changes how fast they are spinning). We can examine the detailed motion of a planet, and in combination with information about its total mass, and small variations in gravity (which we can measure from satellites), we can figure out how the mass of the Earth is distributed radially. Specifically, the more mass is close to the core, the less the Earth resists turning motion, like the ice skater. The moon also slightly tugs on the Earth (via the tides), and this affects its turning movement very slightly. By very carefully watching how the Earth and moon move relative to each other, we can figure out what the moment of inertia must be in order to explain the movements we observe. This works for other bodies in the solar system too. Knowing the moment of inertia allows us to better constrain our guesses of what could possibly be inside a planet." +1291 1000kg of cotton, 1000kg of nails, or both? 532 https://www.reddit.com/r/askscience/comments/auykbe/1000kg_of_cotton_1000kg_of_nails_or_both/ 1551181751 auykbe Physics 2019-02-26 14:49:11 "Sounds like a crap science teacher. How crap of a teacher he is depends on what year your class is and what foundational knowledge you are supposed to have at this point. + +If you want to screw with him, ask what the speed is. Engine size also matters, as does the configuration of the truck bed. Is it segmented? Can the nails move around? Is the cotton compressed? I would bet that the answer would vary considerably with a traditional engine vs an electric truck. He can say it doesn't matter all he wants, but if he is going to play games, he needs to give you more info. + +With the information you have, and under the assumption that you aren't in university, I'd argue that ""same time"" is a fairly safe answer. + +​ + +Edit: Unless he's being completely ridiculous and going with something like ""the cotton would all blow out of the truck bed as the truck accelerates"" which is an assumption you can't make (shaped of truck bed) from the information given." "My comment is that he should have framed the question in an answerable way. Or at least prompted you all to ask the questions you needed to. The point of being a teacher is not too show superiority over your students but to help them to, hopefully, exceed your ability. + +For what the question is worth, I've heard it in a different form which is: what weighs more, a ton of bricks or a ton of feathers. And of course the answer is neither, they weigh the same. And the answer to your teacher's question is that, all else being equal, the trucks would tie the race." +1130 If it were possible to put a pipe straight through the earth, from north to south pole and you dropped a ball down the pipe what would happen? 518 https://www.reddit.com/r/askscience/comments/9fp68d/if_it_were_possible_to_put_a_pipe_straight/ 1536900524 9fp68d 2018-09-14 7:48:44 "Ignoring air resistance and assuming the earth is a homogenous sphere, + +The force F acting on the ball while within the earth is described by: + +**F** = -GMm/R^(3)**r** where r is the distance from the centre of the earth to the ball. + +For those that have studied springs, this equation is of the form: + +**F** = -k**r** where k = GMm/R^(3) + +Or equivalently: + +**a** = -ω^(2)**r** where ω^2 = k/m = GM/R^3 + +ω is the angular frequency of such a system, and is also given by ω = 2π/T where T is the period of oscillation. + +Given those equations, we can calculate T to be: + +T = 2π(R^(3)/GM)^(1/2) ~= 84 minutes. + +That's the time it takes to fall right through the earth and come back to its starting position. Coincidentally, that's also the time it takes to make a full orbit at the surface of the earth (it's not exactly a coincidence, since simple harmonic motion along one axis is simply circular motion projected onto that axis). + +Since there is no air resistance, the ball will fall right through to the other side, reverse direction, then fall back to its starting point indefinitely in simple harmonic motion. + +If there is air resistance, the amplitude of this oscillation will decay exponentially and eventually the ball will come to a rest at the centre of the earth. " "Surprise answer: if there is air in the pipe, the ball will not make it to the center of the Earth because at some point (probably in the mantle) it will float on the increasingly dense air in the pipe! The air will not just provide resistance; it will provide buoyancy as well. + +​ + +First, our assumptions: + +* The air in the pipe is open to the free atmosphere and is therefore at 1 bar at sea level, and follows the ideal gas law at the depths that we're looking at. +* The pipe is strong enough to withstand the crushing pressures of the deep Earth (which will be higher than the air pressure, at least in the depths we're looking at). +* The air in the pipe is somewhere between atmospheric temperature and the temperature of the rock right next to it. Let's be generous and say that the air is at the temperature of the rock. Most importantly, the air can't be way, way hotter than the surrounding rock. + +Just like ordinary holes in the ground like mines or caves, air pressure will increase exponentially the farther down you go according to p = 101 kPa \* e^(z/H), where z is the depth and H is the ""scale height"" of the atmosphere. H is proportional to absolute temperature (H = R\_air\*T/g); in the atmosphere H is around 8 km, but in the mantle T might be around 2500 K, so H would be around 73 km. *(R\_air is the gas constant for air that shows up in the ideal gas law, about 287 J/(kg\*K).)* Let's be generous and assume H = 73 km everywhere. g, the gravitational acceleration, varies with depth within the Earth, but we're looking at relatively shallow depths (around 10%) so let's assume g is constant. + +​ + +So, p = 101 kPa \* e\^(z/70 km), and from the ideal gas law, *density* *= p/(R\_air\*T)* = 101 kPa/(R\_air \* 2500 K) \* e^(z/70 km)= 0.14 kg/m^(3) \* e^(z/70 km). This means that the air becomes denser than a baseball (\~650 kg/m^(3)) around 600 km depth, and denser than a bowling ball (\~1300 kg/m^(3)) around 650 km depth (for reference, the outer core is at about 2900 km and the center of the Earth is at \~6370 km) (which quite shallow in the mantle). At this depth, the ball will be of neutral buoyancy; it will sink a little beyond that depth due to its momentum but then rebound to its equilibrium position, just like a piece of wood tossed into a pond. + +​ + +If you somehow managed to keep the air temperature at a normal surface temperature (say, 17 deg C), the air would be way denser all the way down the pipe and the ball would start floating between 50-60 km depth. + +​ + +Edit: minor changes for clarity." +1501 "How do plants protect their DNA from the sun? Do they ever get ""skin"" cancer?" 518 https://www.reddit.com/r/askscience/comments/fzbvtd/how_do_plants_protect_their_dna_from_the_sun_do/ 1586627961 fzbvtd Biology 2020-04-11 20:59:21 "There are protective esters that serve as sunscreen for the plant, effectively filtering out the spectrum of ultraviolet-B Ray's. Depending on the plant species and the climate around it, chlorophyll is accumulating and being utilized while also producing proline (for example) to help protect the plant against extreme wavelengths it's being exposed to. + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3730951/" "Plant's DNA gets damaged quite often from UV light. The most common damage is the thymine dimer: [https://lh3.googleusercontent.com/proxy/aoSL4qJgH8XblnJ\_BqA2eGPGQ9h1nQd2NvaUTl6IxxZUT3Lx33WwiWvCHKr\_SJQBqSRWpVnJgdXc9V2jms6I105pejBTmod0MZlR0xUTm-W2HPROswRA3BUHKQiulQ](https://lh3.googleusercontent.com/proxy/aoSL4qJgH8XblnJ_BqA2eGPGQ9h1nQd2NvaUTl6IxxZUT3Lx33WwiWvCHKr_SJQBqSRWpVnJgdXc9V2jms6I105pejBTmod0MZlR0xUTm-W2HPROswRA3BUHKQiulQ) + +Lucky, mechanisms to repair these damage such as excision repair or photoreactivation repair exist; the latter being unique to specific plants and prokaryotic species. (Ironically the photoreactivation repair uses light to repair DNA damaged by light) + + [https://www.ncbi.nlm.nih.gov/books/NBK9900/](https://www.ncbi.nlm.nih.gov/books/NBK9900/) + + [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC218148/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC218148/)" +1292 Can someone explain why Saturn has a hexagon at its uppermost pole? 516 https://www.reddit.com/r/askscience/comments/biikbr/can_someone_explain_why_saturn_has_a_hexagon_at/ 1556500724 biikbr Astronomy 2019-04-29 4:18:44 "This [paper from nature in 2006](https://www.nature.com/news/2006/060515/full/news060515-17.html) explains it really well. + +The TL;DR is that the hexagon will form naturally in a spinning fluid provided the spin is the correct speed. + +[This article](https://phys.org/news/2010-04-fluid-clue-saturn-hexagon-video.html) has a short video." "Short answer: nobody knows for sure. But here's a likely hypothesis that comes from Harvard: + +Essentially, think of Saturn as a bunch of liquid in a globe, and the globe is spinning. (Gas is a fluid, and the scale is big enough that this makes a decent toy model) The water at the very top is gonna be moving slower than the water that has to go all the way around the outside at the middle/equator. + +Normally this wouldn't be too much of a problem, but the ""liquid"" in Saturn's atmosphere is actually bands of different types of gas. What we see as the Hexagon is the boundary between two of these bands. The difference in thicknesses (viscosities) and speeds of these two bands creates turbulence where they meet. This spawns mini-vortices just south of the barrier (in the less viscous gas). + +These mini-vortices space themselves out evenly, and due to the magic of fluid mechanics, they push the boundary between the bands north a little bit wherever they are. This makes the polygon pattern. The folks at Harvard were able to get triangles and octagons too, with the right conditions. But the conditions on Saturn are just right to make a hexagon. + +Source: 4 years of physics and astrophysics at uni + +Edit with the actual source: http://adsabs.harvard.edu/abs/2010Icar..206..755B + +Turns out it was actually Oxford scientists. Misremembered." +1131 Why do some parts of the eyes not need blood vessels? 507 https://www.reddit.com/r/askscience/comments/9jlh5u/why_do_some_parts_of_the_eyes_not_need_blood/ 1538126627 9jlh5u 2018-09-28 12:23:47 "The cornea and lens both lack blood vessels, since they need to be clear for good vision. + +The cornea (front window of your eye) is only about 0.5 mm thick, enabling it to get the oxygen it needs via diffusion (the front half gets oxygen from the outside air, and dissolved O2 in the tear film. The back half gets its O2 from dissolved O2 in the aqueous humor). + +The lens is not nearly as metabolically active as the cornea, so its oxygen needs are much lower. The oxygen it needs, it gets via diffusion from the aqueous humor (eye fluid)." "As nuclear Cadillacs said.... I would add that the vitreous jelly that constitutes the largest part of the eye (from a volume standpoint) embryologically was a vascular structure. That allowed the eye to develop in utero when it's metabolic demands were higher and all parts of the eye needed more blood flow. But in order to have a clear medium for light to travel through, those vessels regress, leaving a virtually clear cavity through which light can travel. There are disease states associated with failure of this process (eg persistent hyperplastic primary vitreous). + +One other interesting fact is that despite having some avascular parts, there are other parts of the eye with incredibly high blood flow. The choroid which supports the outer third of the retina has the highest blood flow density of any tissue in the body as well as the highest oxygen tension." +1293 Is there are maximum of brightness that light can reach? 498 https://www.reddit.com/r/askscience/comments/b3q8oa/is_there_are_maximum_of_brightness_that_light_can/ 1553173199 b3q8oa Physics 2019-03-21 15:59:59 "As far as I can tell, there is no clear cut upper ceiling limit for the brightness in light. But there is a lot of nuance to explore so let's ask three questions: + +1. Does the light ever get so bright that it interacts with itself through gravity? + +2. Does the light ever get so bright that it interacts with itself through electromagnetism or another fundamental force? + +3. Does the answers in the above two questions depend on whether or not the light beams are parallel or if they have some intersection angle between them? + +Before we begin we can note that in principle I can Lorentz-boost myself into any reference frame giving a single photon as much energy as I want. In that sense, there is truly no upper ceiling. But real light is a multitude of photons so let us continue. (**Edit:** For the purposes of our discussion, brightness means intensity of light or power/area. From a photon perspective that means the same intensity can be reached from a lot of low energy photons or a few high energy photons.) + +For now let's restrict ourselves to a beam of light that is moving parallel, in other-words, if nothing else happens the rays in the beam will never intersect. It turns out that a beam of light does distort space-time. However, the space-time deformation produced by massless objects, like light, aren't in any way like the bending of space-time caused by masses, which give you Newtonian gravity. Rather the gravitational field of a light beam is a kind of gravitational radiation called ""plane-fronted gravitational waves."" + +These solutions were initially worked out using ""linearized general relativity"" which makes gravity act in a similar fashion to electromagnetism. However it was later found that these solutions were actually exact for full general relativity which is wonderful because it lets us talk about very high intensity light. As a strange aside, this solution is also the same solution for a black hole traveling near (in the limit of) the speed of light relative to an observer. Plane-fronted gravitation waves traveling in the z-direction have the line-element, + +* ds^(2) = (c^(2)dt^(2)-dx^(2)-dy^(2)-dz^(2)) + A(cdt-dz)^(2) + +where A is related to the intensity of the light. This is the equation for a small straight line in space-time which is similar to Pythagoras's theorem. Think of ""dz"" as a small change in the z-direction. The first part of the metric is just normal flat space-time, the second part is the interesting part, + +* ds'^(2) = A(cdt-dz)^(2) + +This basically tells you that the ""plane"" which is [normal to the direction of travel](http://mathworld.wolfram.com/NormalVector.html) is special in some way. It turns out that it is only in this plane that spacetime is deformed. The interesting consequence of this is that since the space-time deformation also travels at the speed of light and only exists attached to the beam of light, any light sent after the first beam cannot interact with the original beam. In other words, light beams do not make gravitational wakes like a speed boat in water. Another feature is that the gravitational fields of parallel light beams (say A1 and A2 intensities for beam 1 and beam 2) simply add together and do not otherwise influence each other's motion. This means parallel beams of light do not interact. + +Now the second question. I won't go through the details like I did for gravitation, but in short parallel light beams do not interact with each-other through electromagnetism either. This is true in both the classical theory (where electromagnetism is linear and even non-parallel light doesn't interact) and the quantum field theory (QFT) called quantum electrodynamics (QED). + +The third question is where all the fun happens then. Nonparallel light beams, and most especially intersecting light beams do interact! Gravitationally, nonparallel beams will attract each other and the attraction is strongest when they are moving in opposite directions (aka antiparallel). In other-words, the beams will not move in straight lines, but along a curve. (**Edit:** This is not too surprising considering just special relativity where the invariant mass of two nonparallel light beams is nonzero. This mass, made purely out of massless light, then naturally should gravitate. This invariant mass is also relevant in particle production from light described further down.) In fact, there is a situation called a ""Kugelblitz"" where if the nonparallel beams are confined to a small enough space, an event horizon forms around them trapping them in a newly formed black hole whose mass is given by the energy of the trapped light. As an aside, hypothetically a quantum theory of gravity may lead to higher order interactions, but those are not well understood as we do not yet have a complete theory of quantum gravity. + +Electromagnetically, as far as I can tell, only the intersecting light beams has been explored. I am unaware of research along the lines of simply nonparallel beams. The self-interaction of light through electromagnetism is only a quantum effect and not present in the low energy limit (read: long distance) which explains why this is the case. Even in QED we don't expect nonparallel beams to interact, we need them to get close enough to ""count"" as a collision. There are two main avenues of studying light self-interaction in QED. The first is called the [Breit–Wheeler process](https://en.wikipedia.org/wiki/Breit%E2%80%93Wheeler_process) process which is the production of an electron-positron pair via colliding light. You can make other particles too, but the electron-positron process is favored because it is the lowest mass particle pair. The second process is light-light scattering where two photons will bounce off each other and travel in new directions. The best measurement for this actually was just released [a few days ago](https://home.cern/news/news/physics/atlas-observes-light-scattering-light) done using lead-lead collisions at the LHC. + +All this nonparallel stuff is what might limit the max brightness of a beam. Any scattering due to gravitational attraction or QED light-light scattering will defocus a beam of light and any pair-production will sap away energy from the beam as well. This means the stability of our light beam, and our ability to keep increasing the brightness depends on our ability to keep the light perfectly parallel. + +Anyway the fruit of all this is that we are now prepared to discuss the original question: **Can you have a flashlight producing an arbitrary brightness?** The answer is no, but I have no Earthly idea what that max brightness would be. It would be incredibly high. No beam of light is perfectly parallel (because any real process which produces light does so with an angular distribution) which means at sufficient intensities, the beam will at some point be reduced in brightness due to the production of particle pairs, scattering which disperses the beam even further lowering the brightness and even potentially producing a black hole. Exactly which process is important first depends on the wavelength, and therefore the energy, of the photons in your light beam. + +Here's a smattering of literature on the topic. + +* Bonnor, W. B. ""The gravitational field of light."" Communications in Mathematical Physics 13.3 (1969): 163-174. https://projecteuclid.org/download/pdf_1/euclid.cmp/1103841572 + +* Aichelburg, Peter C., and Roman Ulrich Sexl. ""On the gravitational field of a massless particle."" General Relativity and Gravitation 2.4 (1971): 303-312. https://doi.org/10.1007/BF00758149 + +* Tolman, Richard C., Paul Ehrenfest, and Boris Podolsky. ""On the gravitational field produced by light."" Physical Review 37.5 (1931): 602. https://doi.org/10.1103/PhysRev.37.602 + +* Wheeler, John Archibald. ""Geons."" Physical Review 97.2 (1955): 511. https://doi.org/10.1103/PhysRev.97.511 + +* d’Enterria, David, and Gustavo G. da Silveira. ""Observing light-by-light scattering at the Large Hadron Collider."" Physical review letters 111.8 (2013): 080405. https://doi.org/10.1103/PhysRevLett.111.080405 + +* ATLAS collaboration. ""Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC."" Nature physics 13.9 (2017): 852-858. https://doi.org/10.1038/nphys4208 + +* Krajewska, K., and J. Z. Kamiński. ""Breit-Wheeler process in intense short laser pulses."" Physical Review A 86.5 (2012): 052104. https://arxiv.org/abs/1209.2394 +" "As far as I am aware, it is theoretically possible for light to get so bright, that it puts so much energy in one spot, that it forms a kugelblitz (black hole). So, the limit on how bright light can get, would be the point at which the light (which is energy) becomes so dense, that it forms a black hole. + +This video by sci-show will explain it better than I can: + +[https://www.youtube.com/watch?v=gNL1RN4eRR8](https://www.youtube.com/watch?v=gNL1RN4eRR8)" +1464 "What does ""turns per armature"" mean in an electric DC motor?" 494 https://www.reddit.com/r/askscience/comments/cz3k0y/what_does_turns_per_armature_mean_in_an_electric/ 1567509935 cz3k0y 2019-09-03 14:25:35 "Turns is number of times the wire used to make up the winding is wrapped around each armature. The armature is the part of the motor that produces the power; this can either be a winding that the rotor spins around (External rotor motor) or the armature itself can be ~~the part that spins wrapped~~ around the rotor (Internal rotor motor). + +Edit: here is a site with a couple of good diagrams: [https://www.motioncontroltips.com/external-rotor-motor-basics-design-applications/](https://www.motioncontroltips.com/external-rotor-motor-basics-design-applications/) + +Edit 2: Number of turns per armature can affect motor performance in a number of ways. The more turns there are generally the smaller the wire gauge to accommodate this; smaller wire gauge = higher resistance (Impedance if AC motor) of wire meaning the motor spins slower ~~and produces less torque~~. On the other hand, thicker wire gauge means lower resistance so higher power motor. + +It's not quite as clear cut as that though as you have to take into account is number of poles on the motor and type of magnets used for the rotor. + +If anyone else wants to correct me or add further info go ahead please, motor theory hasn't been something i have looked at for a long while. + +Edit 3: because brain fart, lower turns is less torque, higher turns is more torque, not what i initially put, also changed IRM and ERM description at top as fluffed that aswell, need coffee." "There is a certain amount of airspace around each stator ""tooth"". You need to fill that airspace with as many copper wire wraps as will fit. You can use many turns of thin wire, or fewer turns of thicker wire, or...any variation between the two extremes. + +The more turns you use (*high turn-count, low Kv), the lower the shaft RPMs you get per volts that you apply. Few turns of fat wire is a high-Kv. This is a ""fast"" winding, and you get higher RPMs per volt. + +Many motors wind ""in hand"", meaning it is easier to wrap thin wire, but to get a fast winding, you bundle several small diameter wires, so they act like one fat wire. Therefore, you cannot tell the Kv by simply counting the strands around each tooth, you must determine if it is one continuous thin wire that is very long, or several thin wires with attached ends, with each being shorter than the wire in the low Kv." +1997 Why are radiators below windows? 489 https://www.reddit.com/r/askscience/comments/rb1lrd/why_are_radiators_below_windows/ 1638890769 rb1lrd Physics 2021-12-07 18:26:09 Heating the glass to room temperature also prevents condensation on the glass. Condensation will rot your traditional wooden windows, and a large picture window can distill a problematic volume of water if not heated correctly. "It's to prevent draughts in the room. If you put your radiator on the opposite side of the room to the window, the window is a cold surface so air cools and drops to the floor, the radiator is a warm surface so air heats and rises. This sets up a circular pattern in which cold air drops, flows across the floor (making your feet cold) the warms on the radiator rises and flows back across the ceiling, then cools on the window, drops to the floor etc. + +[https://wpcdn.bestheating.com/info/wp-content/uploads/2016/10/natural\_convection\_diagram.png?strip=all&lossy=1&quality=70&resize=590%2C351&ssl=1](https://wpcdn.bestheating.com/info/wp-content/uploads/2016/10/natural_convection_diagram.png?strip=all&lossy=1&quality=70&resize=590%2C351&ssl=1) + +If you have a radiator under the window, these effect broadly cancel each-other out and it heats the air more evenly with less air movement and less draughts. + +EDIT: To the people who keep messaging about my spelling of draught. I'm British, please leave me alone. [https://dictionary.cambridge.org/dictionary/english/draught](https://dictionary.cambridge.org/dictionary/english/draught)" +1896 Does Mars have caves and if we discover a large enough cave system on Mars, how deep would we need to go to reach a hospitable temperature? 485 https://www.reddit.com/r/askscience/comments/o1zuxt/does_mars_have_caves_and_if_we_discover_a_large/ 1623943465 o1zuxt Planetary Sci. 2021-06-17 18:24:25 [It has lava tubes](https://en.wikipedia.org/wiki/Martian_lava_tube). Don't know about the temperature. "There's a lot to unpack, but let's try. +>Does Mars have Caves? + +Almost certainly it does, but there multiple types of caves and the type of cave you're thinking of probably doesn't exist. +Cave Types: +1)Limestone caves carved by co2 disolved in water (carbonic acide) trickling through them eroding chambers in the limestone. +2) Lava tubes - lava flowing down a slope forms a hard outer crust and continues to flow on its interior, finally draining out, leaving a hollow tube +3) Ice Caves - water flowing under a glacier erodes the ice, leaving chambers in the ice in a sort of combination of 1 & 2 above + +I think you're probably thinking of type 1 above since by their nature, types 2 & 3 are limited depth beneath the surface and are not going to increase in temperature with depth. + +More to the point though, it is doubtful Mars has the kind of deep limestone deposits that formed on earth as a consequence of life. The presence of limestone on mars would in fact be an almost smoking gun for life having existed; and to be deep enough to form caves, there would have to have been a both a lot of life and it would have had to exist for a long time (long enough for thick deposits of carbonate to have accumulated into thick sedimentay layers). Most theories of a warm wet mars have a limited lifetime of conducive environment for life: 100-200 million years. Consider that life existed on earth for billions of years before it became prolific enough to create limesone, it seems unlikely there are significant deposits of limestone on mars + + +---EDIT--- +Markup formatting correction, spelling, punctuation" +1609 AskScience AMA Series: We are statistics professors with the American Statistical Association, and we're here to answer your questions about data literacy in an age of disinformation. Ask us anything! 484 https://www.reddit.com/r/askscience/comments/hrljbe/askscience_ama_series_we_are_statistics/ 1594810847 hrljbe Mathematics 2020-07-15 14:00:47 [deleted] "What are the most common red flags to spot manipulated data? +How do we combat our own personal biases when we see data we *want* to be true? +(TYSM for being here!)" +1465 What does it mean physically that the Weak force and electromagnetism become one force at a certain energy? 478 https://www.reddit.com/r/askscience/comments/dsr8d6/what_does_it_mean_physically_that_the_weak_force/ 1573095217 dsr8d6 Physics 2019-11-07 5:53:37 "This article makes sense to me: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/the-known-particles-if-the-higgs-field-were-zero/ + +The situation he calls ""If the Higgs field were zero"" is how things were before the Higgs field turned on (aka. above the electroweak unification energy) and the article explains how the Higgs field interactions hide the symmetry of the underlying fields and give us what we see now." "Forgive me if this isn't the sort of answer you're looking for: + +1. The weak and em forces are modeled by quantum field theories (QFT's). One of the main ideas is that matter particles carry some sort of ""charge"": em - electric charge, weak - weak isospin. These particles interact with one another by exchanging a force carrying boson: em - massless photon, weak - massive W+,W-,Z bosons (The first two are electrically charged, the Z is neutral). +2. Above a certain energy, the two forces are unified in the sense that both are modeled by a single QFT. Here we have two types of charge: weak isospin and hypercharge. We also have 4 massless force carrying bosons that facilitate the interaction: W1,W2,W3,B. It is at low energy that the systems lose the symmetry of this QFT, interact with the Higgs field and reduce to the forces above. In particular, particular linear combinations of the bosons above become the photon, W+,W-,Z with the latter three gaining mass." +1294 Excess Leptin, is that a thing? 476 https://www.reddit.com/r/askscience/comments/b7obfo/excess_leptin_is_that_a_thing/ 1554042467 b7obfo Human Body 2019-03-31 17:27:47 Leptin to fat is like insulin to sugar. What happens when you eat in excess is that leptin is overwhelmed and you develop leptin resistance. Anorexia is a mental disorder where you have body dysmorphia and think you're fatter than you are. There are people who don't eat enough, but they usually don't starve to the point of danger, it takes a lot of deliberate starvation which would cause stomach pains among other symptoms, many associated with low blood sugar, even in the presence of a leptin deficiency. +1698 Are we just lucky that covid does not have a higher mortality rate or is this because more deadly infectious diseases are less common? 474 https://www.reddit.com/r/askscience/comments/jvif4e/are_we_just_lucky_that_covid_does_not_have_a/ 1605571403 jvif4e COVID-19 2020-11-17 3:03:23 "Higher mortality diseases get quarantined more aggressively. + +If COVID had a 15% case fatality rate and most survivors were left permanently disabled, Wuhan would have been in hard lockdown four weeks earlier. Similar actions were taken when Africa had an ebola outbreak. + +Because the disease is 80% 'less deadly' than that, it was able to slip out of the origin region and into nearly every country on Earth. + +It's also an evolutionary advantage for diseases not to kill their host. It simply makes them better at spreading, and this creates a tendency for viruses to mutate to become less lethal. This is why the 2018 flu virus was much less deadly than the 1918 one, despite the 1918 one being an evolutionary ancestor of the 2018." "While a super high lethality rate would have caused the virus to quickly burn out, something in the 10-20% range easily could have spread out of control. What every commenter I have seen here is forgetting is that COVID-19 can be transmitted asymptomatically for up to 12 days. SARS, which had a lethality rate of around 10%, was contained because only symptomatic individuals were contagious. If SARS could have spread through asymptomatic carriers, it is unlikely it could have been stopped before spreading globally. + +So yes, we are lucky COVID is not more lethal." +1897 Does anything have the opposite effect on vocal cords that helium does? 466 https://www.reddit.com/r/askscience/comments/p86d5h/does_anything_have_the_opposite_effect_on_vocal/ 1629469820 p86d5h Human Body 2021-08-20 17:30:20 "The other noble gases can be inhaled just like helium - neon, argon, krypton, and xenon are all available. + +Helium and neon both have similarly higher pitches. Argon is close to normal; slightly deeper. Krypton is significantly deeper and Xenon makes you sound like a creepy, evil villain. + +I don't know if youtube links are allowed, but a dude named Cody (Cody'sLab) has a cool video where he inhales all of these in order, as well as showing relative density by having them all in balloons. Here's the link: https://youtu.be/rd5j8mG24H4" Yes. It’s called Sulfur Hexafluoride (SF6). Sound travels slower in denser gasses and SF6 is 5x more dense than air so it makes the sound waves move slower through the gas which makes your voice deeper even though your vocal cords are still moving at the same rate. +1898 How does the immune response that causes hay fever differ from the immune response that is utilised by COVID vaccines? (And why don't antihistamines affect the latter?) 464 https://www.reddit.com/r/askscience/comments/o1ue31/how_does_the_immune_response_that_causes_hay/ 1623927181 o1ue31 Medicine 2021-06-17 13:53:01 The answer is in the word. Anti-histamine inhibits histamine (inflammatory protein) from being released by specific immune cells, mainly granulocytes (basophils, eosinophils, neutrophils). Vaccine immune response is focused more on lymphocyte specialization, sensitizing B-lymphocytes to antigens which then become plasma cells that produce antibodies to previously encountered antigens. Of course this is a very simplified explanation of immunology. "I would reframe it as the antihistamines are treating the symptoms of an unwanted immunogenicity, specifically the inflammatory cascade. The underlying immunogenicity is still there, usually IgE in the case of pollens, you're just tuning down part of the nonspecific defense. + +That cascade is beneficial for certain things, like protecting an open wound, but it can actually be harmful for other diseases including Covid. At least some portion of severe Covid patients develop systemic inflammatory responses that were damaging lung tissue and driving mortality." +1899 Nowadays, dogs get vaccinated for several different fatal diseases. In the past, did lots of dogs just die of them? 448 https://www.reddit.com/r/askscience/comments/p8djsg/nowadays_dogs_get_vaccinated_for_several/ 1629492167 p8djsg Biology 2021-08-20 23:42:47 "Yes. You see massive spread of disease in wild animal colonies. While i dont have much experience with wild dog packs, i am working with a cat colony now. The colony has an outbreak of leukemia that has been killing one every month or two. Flv is a vaccinatable virus in cats. Without human intervention and vaccination it has caused many deaths. I have not worked with packs of dogs, only a stray here and there but it would work the same way. + +A side note. Human Culture even without vaccinations makes a huge difference. Owning one or two animald that live inside helps curb disease. In a lot of countries dogs are kinda treated like cats and allowed to lretty well run wild which doesnt help stopping spread of disease." "Yes. Some vaccinations for cats and dogs lower risk of diseases that are not necessarily highly fatal (Bordetella, feline herpesvirus), are not necessarily fatal but hard to detect before there is serious damage (leptospirosis), but several are for fatal diseases (canine distemper, parvovirus, feline panleukopenia, feline leukemia, rabies for both). Vaccination isn't 100%, so we do have dogs and cats who still die of rabies, puppies who die of parvo, and kittens who die of feline leukemia and panleukopenia; even if they receive treatment after diagnosis (notably, rabies has no treatment). + + +It is difficult to assess how common some of these diseases were/subsequent fatality at that time, given that veterinary medicine has generally lagged behind human medicine, and that a certain loss of pets or livestock without clear explanation was more or less acceptable. Think of how we reference to ""dying of old age"" or ""failure to thrive,"" or TBH for people the generic term of ""sudden infant death syndrome."" None of these descriptors are actual explanations, but in time could find what the various causes were. There were times where a ""new"" disease was found, and initially there is a panic about a new disease emerging, but it turns out we were probably just more capable of diagnosis - this happened with feline leukemia in the 80s (there was also an initial fear that, since this was a retrovirus as is FIV, that it could affect humans; it's can't) or for a non-infectious condition, feline hyperthyroidism. It wasn't assumed that those diseases were there all along and there was an attempt at explaining where these diseases could have come from, but realistically they were there, it was just there was a technology and social shift that allowed their diagnosis. Unwell barn cats are less likely to just be abandoned, drowned, or euthanized now - and so we end up diagnosing feline leukemia (FeLV). Similarly, with more indoor and well-kept cats, more cats started living to the age where they could develop hyperthyroidism, *and* their owners were willing to pay for the labwork to diagnose it." +1466 Will endangered animals, if saved from extinction through Human Intervention, face the threat of inbreeding and recessive genes? 438 https://www.reddit.com/r/askscience/comments/d0v2vt/will_endangered_animals_if_saved_from_extinction/ 1567857269 d0v2vt Biology 2019-09-07 14:54:29 "They already do. Tiger populations in Asia, for instance, are extremely fractured because their territories are separated by human development. As a consequence, problems resulting from inbreeding are very common. + +There's a lot of species that are still doing fine in terms of numbers but are threatened because their population is spread apart and isolated to the detriment of the gene pool." "This is one of the reasons why zoos are incredibly important and ultimately beneficial to the health of a species. By engaging in ""breeding programs"" they're able to provide each other with mating animals that will most effectively produce a genetically diverse population. + +The same exists in other areas of conservation. For example, the present stock of American Bison is so heavily polluted by cattle genetics that every animal has to be tested at the Nature Conservancy's Nachusa Grasslands reserve in Illinois to determine their authenticity as pure bison. Using this knowledge they can then trade bison with other reserves to introduce new genetic material. This not only helps to reduce the potential for poor diversity, but also dilution of the genetic material that makes the species itself. + +Prior to the advances in genetic testing that we have today, the inbreeding problem was a much bigger issue. It's still a problem in wild populations where bottlenecks are common in highly threatened species that are impacted through natural occurrences. With advances in gene editing it may be possible to subvert this problem all together, but then of course you open up the issue of authenticity. + +Wildlife conservation is a much muddier and challenging task than it might seem to an outside observer." +1813 Can a photon release a portion of its energy? 431 https://www.reddit.com/r/askscience/comments/lt0e0o/can_a_photon_release_a_portion_of_its_energy/ 1614354412 lt0e0o Physics 2021-02-26 18:46:52 "This can only happen when the photon interacts with something else, and it's impossible (and frankly meaningless) to tell if the photon after the interaction is the same one or a different one with lower energy. +If a wave bounces off a wall, is it still the same wave? Maybe so, maybe not. A wave isn't an object in itself, but rather a moving pattern of excitation in a field." ">Can a photon release a portion of its energy? + +Yes, it can. For example, Compton scattering." +1610 Are there diseases which can transfer from plants to animals? 361 https://www.reddit.com/r/askscience/comments/h8601d/are_there_diseases_which_can_transfer_from_plants/ 1592048613 h8601d Biology 2020-06-13 14:43:33 It's rare but it can happen. One particular example I can think of is Pseudomonas aeruginosa infection. It's a Gram Negative bacteria causing a soft rot in plants and in humans it is most commonly associated with Pneumonia but it can invade any tissue. This doesn’t quite match but it’s kind of spooky to me; the prion responsible for causing chronic wasting disease (CWD) in ungulates (deer. elk, etc) can lay dormant on plants and leaves for years until it’s ingested. +1998 AskScience AMA Series: I am a medicinal chemist and pharmaceutical scientist at the University of Florida who is an expert on Kratom, which is currently under investigation as treatment for opioid withdrawal syndrome. AMA! 352 https://www.reddit.com/r/askscience/comments/q2i2q2/askscience_ama_series_i_am_a_medicinal_chemist/ 1633518055 q2i2q2 Medicine 2021-10-06 14:00:55 Please do not answer any questions for our guest until the AMA has concluded. Our guest will begin answering questions at 1 p.m. ET (17 UT). Please remember, [r/AskScience](https://www.reddit.com/r/AskScience/) has strict comment rules enforced by the moderators. Keep questions and interactions professional and remember, **asking for medical advice is not allowed**. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). What class of drug is kratom? What’s the moa? +1132 How is it possible that we can sleep too much? Shouldn't we wake up the moment our body has rested enough? 351 https://www.reddit.com/r/askscience/comments/9eb9x5/how_is_it_possible_that_we_can_sleep_too_much/ 1536477655 9eb9x5 2018-09-09 10:20:55 "Sleeping in a room with no windows and poor ventilation can mess with your body’s perception even when sleeping. External signals can be a large part of waking up (ever go camping and wake naturally with the sunrise?). + +Depression can easily have large effects on motivation to get up and out of bed, leading to chemical and electrical signaling in your nervous system outside of the normalcy you’d find in a natural circadian rhythm for a healthy person. + +Poor diet and exercise can contribute to oversleep as well if your body can not rest and repair as it would with proper nutrition and a previous day’s activity wearing you out. + +Sleep is very complicated and individual if you are having sleep issues I would recommend asking your GP and considering talking to a specialist." "Well, the mechanics of sleep aside, remember that a lot of the questions concerning *""why can't our bodies do this or that?""* can be answered with the following: **did it have some survival advantage that led to greater mating opportunities** or **prevent those with said traits from reaching breeding age**. + +Remember that you are a product of a long and unbroken chain of surviving organisms stretching back tens of millions of years, who's adaptions have led them to find sufficient food and successfully breed. ""Good enough"" is the motto of natural selection. + +So, would the ability to precisely wake up the moment our bodies had rested enough have some major utility? The process of waking from an unconscious state to an alert one is already fairly fast, but what if it were faster and more precise? If an individual had a combination of genetic traits that led him to be able to wake up every so slightly sooner once he was fully rested, would that organism have a selective advantage over his immediate rivals insofar as mating is concerned? + +The answer is likely *not really*. Therefore our evolution never trended towards it. And so long as our bodies get roughly sufficient rest. And so long as our bodies wake up when there are perceived threats (flight or fight), then it's good enough and no more precise adaptions would be observed in that area." +1814 How do we know if sound cames from behind or from front? 346 https://www.reddit.com/r/askscience/comments/la21s1/how_do_we_know_if_sound_cames_from_behind_or_from/ 1612182775 la21s1 Human Body 2021-02-01 15:32:55 "The ear is shaped in a very funny, but very specific way. The shape of the ear makes sound very slightly different, depending on front or back, or even above and below (specifically not left and right, funny enough, but that's why 2 ears are nice). The way you tell is more trained than an actual knowledge. The sounds you hear from behind are always very slightly muffled, but your brain recognizes them as sounds it's heard before and makes them sound normal, but ""from behind"". This also helps explain why sounds you don't normally hear can be hard to pinpoint the location of. Your brain's spacial mapping plays a big role in how you hear sounds." "To add to the other to level reply, you also integrate (combine) senses to process information. This means that if you see something that should make noise it will help you locate the source of the sound, if you don't see the source your brain might interpret that information to indicate out is behind you. + +Also, sound sources are almost always moving relative to you. This means that you also have movement information that can add into the equation." +1133 Is there a limit on how many stars could be in one solar system? Currently world building for a story, and wondering if a planet could realistically exist in a system more 3+ stars, and if so, what effects could that have on its climate and seasons. 328 https://www.reddit.com/r/askscience/comments/9gr2s5/is_there_a_limit_on_how_many_stars_could_be_in/ 1537239711 9gr2s5 Astronomy 2018-09-18 6:01:51 "For stars, only two-body orbits are stable. Small objects can work in a three-body system (e.g. the Trojan and Greek asteroids), but stars are too massive for that to work. + +However, you can *nest* two-body orbits to get more stars in a system. If you have two stars orbiting around each other, then the third star could be so far away from the system that those two stars effectively feel like one body, and you get a stable orbit. Alternately, the third star could be so close to one of the stars that they feel like one gravitating body to the other star. You can keep on going like that to add more and more stars to the system. Similarly, planets will have stable orbits if they are either so close to one star that they can stick to the star and follow it around, or so far from the whole star system that it all just feels like a single big messy star that they can orbit around. + +[Nu Scorpii](https://en.wikipedia.org/wiki/Nu_Scorpii) is a *septuple* star system. It consists of a 3-star system and a 4-star system orbiting around each other. The 3-star system consists of a 2-star binary and third star. The 4-star system consists of a 3-star system orbiting with a fourth star, and that 3-star system consists of a binary star and a third star. So that's the sort of hierarchy you have with multiple star systems." "There's already a book like that out there called Nightfall, written by Isaac Asimov and Robert Silverberg. It's about a race of beings that live in a world with 6 sun's, and though I don't remember how that works (I can't remember how in-depth they got with it exactly), there was always at least one sun shining on a side of the planet at a time. + +The story specifically revolves (heh) around an event that occurs every once in a very long time (I want to say every 14k years or so, but I'm not for sure on that) that it's a one-sun day and some outer planet/asteroid/whatever eclipses that one sun for one full rotation of the world. Basically everyone goes absolutely crazy, because this world's life evolved always exposed to sunlight, and civilization has to begin again. + +Heck, I took my user name from a character in that book: Siferra 89, an archeologist partly responsible for this weird discovery right before it happens. " +1815 Could we eliminate the Flu if we all got vaccinated for the flu and wore masks during flu season? 328 https://www.reddit.com/r/askscience/comments/lwt1ri/could_we_eliminate_the_flu_if_we_all_got/ 1614775539 lwt1ri Medicine 2021-03-03 15:45:39 No, there are large reservoirs of flu in bird and swine populations. It’s probably more helpful to think of “flus” not “flu”. Being vaccinated against one or a few doesn’t do much if you get exposed to a different strain. Each year health authorities try and predict which strains will be the major ones. "The 'flu' has a number of variants that infect species besides humans (swine and avian flus come to mind). Also flu viruses mutate a bit so human flu vaccines are tweaked most years to better combat that year's flu. + +Because there are other hosts and new varieties, we probably won't be able to eliminate the flu totally with current vaccines and safety precautions like masks. We may be able to limit its spread and impact symptom-wise." +1816 AskScience AMA Series: We are rare disease experts and directors with the NIH, ask us anything! 327 https://www.reddit.com/r/askscience/comments/lqgs7a/askscience_ama_series_we_are_rare_disease_experts/ 1614081620 lqgs7a Medicine 2021-02-23 15:00:20 A reminder to all that [asking for or giving medical advice](https://www.reddit.com/r/AskScience/wiki/quickstart/commenting) is not allowed on this subreddit. "Hello everyone, thank you for joining the Reddit AMA for rare diseases. To start, we’d like to provide the U.S. definition for a rare disease (as defined in the Orphan Drug Act of 1983, and the Rare Disease Act of 2002): In the United States, a rare disease is defined as a disease or condition that affects fewer than 200,000 people in this country. Rare diseases are sometimes called orphan diseases, and we tend to use “rare disease” and “orphan disease” interchangeably. + +A few FAQs: + +* Most rare diseases are genetic disorders, typically affecting a single gene. +* At the current time, there are about 7,000 different rare diseases, each affecting only a few hundred to a few thousand people (sometimes fewer). As we continue to uncover the [underlying genetics of more rare diseases](https://www.omim.org/), the number of known rare diseases increases by about 200-250 diseases each year. +* Only about 5% of rare diseases have an FDA-approved treatment. (The FDA estimates about 450-500 drugs and biologics are approved to treat a variety of rare diseases) +* NIH devoted around $6 billion to rare diseases research in Fiscal Year 2019. This research is very diverse, ranging from basic science to translational science to clinical trials in a broad array of diseases and conditions. +* The [National Center for Advancing Translational Sciences (NCATS)](https://ncats.nih.gov/) within NIH has identified rare diseases as a priority research area. Some examples of NCATS-supported rare diseases research programs include: + * The [Rare Diseases Clinical Research Network (RDCRN)](https://www.rarediseasesnetwork.org/). + * The [Genetics and Rare Diseases Information Center (GARD)](https://rarediseases.info.nih.gov/). Did you know GARD can accept individual inquiries for rare diseases questions and concerns? You may contact a GARD information specialist at 1-888-205-2311, or [online](https://ncats.force.com/gccinquiries/GccInquiryFormEn). + * The [Therapeutics for Rare and Neglected Diseases program (TRND)](https://ncats.nih.gov/trnd). TRND works with companies, academic centers and patient groups to further preclinical development of candidate therapies, with the goal of moving these candidates toward clinical trials. + * The [Platform Vector Gene Therapy program (PaVe-GT)](https://pave-gt.ncats.nih.gov/). PaVe-GT is a new program whose goal is to try to develop 4 gene therapies for 4 diseases in parallel to try to improve the efficiency of gene therapy development. + * Please visit the [NCATS website](https://ncats.nih.gov/) for more information. + +Rare Disease Day at NIH will virtually take place on March 1. Please join us! [Registration is open](https://events-support.com/events/NIH_Rare_Disease_Day). +\- Dr. Anne Pariser, NCATS ORDR Director" +1502 Is there any known correlation between a person's average body temperature and their susceptibility to disease? 321 https://www.reddit.com/r/askscience/comments/g16d62/is_there_any_known_correlation_between_a_persons/ 1586874030 g16d62 Human Body 2020-04-14 17:20:30 "Simply put, pathogenic species for humans tend to thrive on the lower end of human body temperature. At higher temps, pathways needed for homeostasis become unstable for small organisms like pathogens, stamping out infections. That's why sick people tend to develop fevers. At too high of a temp tho, the body itself cannot regulate homeostasis, and weakens, which can lead to issues that increase susceptibility to infections. Lower body temps don't really kill pathogens, so while it isn't necessarily a disadvantage, the peaks of the susceptibility curves lie at the extremes of human body temps, with you probably wanting to lean on the warmer side. + +Extra stuff: During an immune response, inflammation causes pyrogenesis in the body (in the form of increasing cellular metabolism, since metabolic rates are correlated with body temp) that disrupts small-scale functions. Of course, at high enough temperatures, this begins to chain into disrupting large-scale functions that the human host needs to survive, so fevers are good for your immune defense but only so much. + +People at lower body temps normally would have to burn up a lot more energy to reach the same fever temperature since they would need to make up for that few extra degrees. This actually puts a lot of strain on the body's thermoregulation and homeostatic systems, which can cause a lot of issues. A big one is that most people who were operating at a lower body temp had a low resting metabolic rate. This usually coincides with something like malnutrition, comorbidities, homeostatic dysregulation, or even just old age- all of which make one more susceptible to diseases in a multilateral manner. This means if you're cold, you can't just huddle up in a blanket and except to lower susceptibility, but there is indeed a relationship between temperature and infection" "Interesting question. + +Found this: [https://academic.oup.com/cid/article/31/1/148/318030](https://academic.oup.com/cid/article/31/1/148/318030) which discusses baseline temp variations between young/older patients, and effects of blunted febrile response, + +and this [https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.2539](https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.2539) in which daphnia were exposed to a known pathogen at varying temperatures, + +and this, [https://www.frontiersin.org/articles/10.3389/fmicb.2015.00700/full](https://www.frontiersin.org/articles/10.3389/fmicb.2015.00700/full) which discusses the different stategies of cold blooded pathogens, and also compares the to the the very different strategies used by pathogens affecting warm blooded creatures." +1503 Seasonal flu has a basic reproduction number (R0) of 1.3 and COVID-19 has a 2-2.5. What factors dictate the difference between these diseases in terms of spread? 319 https://www.reddit.com/r/askscience/comments/g1pq4y/seasonal_flu_has_a_basic_reproduction_number_r0/ 1586947988 g1pq4y COVID-19 2020-04-15 13:53:08 "R0 is the average of how many people one infected person would spread the disease to in an 100% susceptible population. So very similar to infectivity of a disease, not how many viral particles are needed to infect one person. + +Stuff that affects a diseases R0 = how long you can be walking around spreading the disease before you get too sick to leave home, whether it makes you sneeze and cough or not, how well the pathogen can infect your cells (this would be affected by a virus' spike protein binding adherance to human cell receptor like you mentioned), lots of other facts. Also affected by climate (people are more social in different weather), social factors (cities are dense, public transport can be an infection hub, good hygiene reduces spread of disease). + +That is why it is quite hard to measure R0 in a real life pandemic." "Just to emphasise what those numbers imply - if each person infects 1.3 people, then a single person will, after 10 transmissions, have infected 1.3^10 = 13.8 people. + +If each person infects 2.5 people, then each person will, after 10 transmissions, have infected 2.5^10 = 9,500 people. + +If R0 is more like 3, then 3^10 = 59,049 people. That's not a typo - that's the power of exponential growth." +1467 What is the strongest evidence for the existence of the Oort Cloud? 317 https://www.reddit.com/r/askscience/comments/cze3l3/what_is_the_strongest_evidence_for_the_existence/ 1567560595 cze3l3 Astronomy 2019-09-04 4:29:55 "Evidence in solar system dynamics is usually given of the form ""if this has happened, then this must have happened"" + +If we see a huge crater with an ejecta blanket around it, we must be looking at the site of an ancient impact, for example. This isn't an explanation of what an impactor would be or anyone's personal feelings. + +What we see in evidence for the Oort cloud is from several avenues of investigation. We know short period comets, those which have a period of less than 200 years, tend to be aligned with the plane of the solar system (their inclination is low). They did not come from a cloud, but instead from a belt - the Kuiper belt. + +Long period comets, those we see in thousand-year orbits, come from random parts of the sky, their inclination is random. Knowing a longer orbital period is a much more distant aphelion, and the comets move more slowly at aphelion, so long period comets will dwell at aphelion, so forming the appearance of a cloud of them. This is fairly basic orbital mechanics, and very well understood. + +The next bit of evidence comes from Late Heavy Bombardment. This was discovered during the Apollo missions, although the Soviets learned about it from their robotic sample returns too. The age of the oldest lunar material was significantly younger than anyone could account for. It was 3.8 billion years old, and nobody could tell us why. + +This was the case until the Nice models, which showed that, in the early solar system, Uranus and Neptune swapped places during a period of instability caused by Jupiter and Saturn in a 2:1 resonance. Neptune crashed through the early (and very dense) Kuiper belt, scattering everything around, losing its own moons, capturing Triton, capturing Pluto and the plutinos, forming the scattered disc... Yet interactions from Neptune would indeed scatter objects around, and even to very high aphelia, but would only rarely give them enough energy to escape, so these highly scattered objects remained gravitationally bound. + +Couple these scattered objects with the ones scattered during plantetary formation, then add in the effects of galactic tides, and their mutual gravity, and we get a slow, but steady, decline in aphelia and rise in perihelia: Their orbits tend to drift toward being circular. This, then, is the Oort cloud. + +You won't see any physical evidence, there are no stone tablets or walking trees saying ""I am Oort"". The formation happened billions of years ago and we can't time travel. + +What we can do, however, is predict its existence and then go to find it. Sometimes this happens quickly: Le Verrier predicted Neptune, and it was rapidly found. Sometimes slowly: Gerard Kuiper had an inkling that there may be a belt just outside Neptune (he didn't do any dynamics work on it, though), from early work done by Leonard (1930), Edgeworth (1943) and Cameron (1962). Nobody actually found one until 1992, when 1992 QB1 was discovered and, six months later, 1993 FW. + +Oort cloud objects will be significantly more difficult to observe than the Kuiper belt is." "I'm a final year Physics student so I'm sure there are much more qualified people here than me to answer your question, but to my knowledge there is one main reason for the existence of the Oort cloud - and particularly for distinguishing asteroids originating from the Oort cloud from those orginiating from the Kuiper belt and that is: + +1. Asteroids originating from the the Oort cloud enter our immediate solar system from a wide range of angles; they can effectively appear at any point in the sky whereas Kuiper belt asteroids tend to appear at relatively small angles to the ecliptical plane (the plane in which the planets orbit as well as the Kuiper belt). The fact that certain asteroids appear to be coming from all directions suggests we are surrounded by a spherical source of these asteroids. Therefore where we first see an asteroid in the sky gives us a big clue as to where that asteroid originated from. + +2. The time periods (the time it takes to complete one full orbit) of asteroids that originate in the Oort cloud tend to be much longer than those that come from the Kuiper belt. Oort cloud asteroids tend to have time periods longer than 200 years or so (some of them being much longer than that) whereas Kuiper belt asteroids tend to have time periods of much less than that. Longer time periods suggest these asteroids are coming from further away and while it doesn't necessarily suggest we are surround by a shell of these rocks, it certainly suggests the source of these rocks is much further away from us than the Kuiper belt. + +I would guess that also the metal/silica and hydrocarbon composition of the asteroids in the Oort cloud would be quite different from those in the Kuiper belt due to the differences in their age at formation but I'm afraid I don't know of any evidence to support that. + +Interestingly, I would presume that there are some asteroids that have entered our solar system from interstellar space - asteroids that are not bound by the gravitational pull of any particular solar system, and simply drift through space - but it is difficult to be sure of the origins of an asteroid if an orbit cannot be determined. + +NB. This was typed on my phone so apologies for any typos or grammatical mistakes." +1134 Questions about black-hole mergers? 313 https://www.reddit.com/r/askscience/comments/9e3ifx/questions_about_blackhole_mergers/ 1536404354 9e3ifx Physics 2018-09-08 13:59:14 "So the short answer is that there is no exact solution to the Einstein field equations involving two black holes (and there probably never will be). This means that we wont know the exact form the geodesics will take. + +But we can make solid guesses and do numerical calculations. The best source for these considerations I have found is [here](https://arxiv.org/abs/1010.5260). However, this review focuses mainly on the gravitational waves produced by these mergers. It does, however, consider your final question in one of the last sections. In general, the amount of electromagnetic radiation given off will depend on the size of the hole and the presence of an accretion disk or other matter between the holes. Also, this radiation is expected to arrive at the same time as the gravitational waves since they both travel at the speed of light. Any deviation from this would be evidence for some speculative physics theories like de Sitter Relativity or Causal Dynamical Triangulation. Also, keep in mind that since light always travels the same speed it will not be ""accelerated"" like you mentioned. It can experience red- or blueshift though. + +Also, we can make some good guesses about the geodesics, and the paths of light, that occur in this system. There will not be any (observable) figure 8s since if it is meaningful to say they occur it would be within the event horizons of the merging black holes EDIT: this is not true, I don't know if there would be any stable photon orbits and what they would look like. Also, a lot would depend on the size of the holes since for supermassive black holes the local curvature outside the event horizon is extremely close to flat. This means that if not for the presence of other matter you would not experience any trauma from being between the two edges of the event horizons, no matter how close they were, and you wouldn’t necessarily see any extreme optical phenomena when you look away from the holes. But from other perspectives or smaller black holes, there would probably be some very weird and extreme gravitational lensing. Light sources behind a single black hole will appear from a distance as an [Einstein Ring](https://en.wikipedia.org/wiki/Einstein_ring). But from behind the merging black holes, they might make an [Einstein Cross](https://en.wikipedia.org/wiki/Einstein_Cross) or even something weirder since the distribution of matter is elongated but in a more interesting way. + + +" Is there a brief amount of time where the merged black hole is not spherical? Once the event horizons merge, how long does it take for the mass to be transferred into one sphere? If one or both black holes are spinning, does that have a major effect on the collision? +1900 If Hailey’s comet loses ice to form its tail, how many years will it take for the comet to erode into nothing? 307 https://www.reddit.com/r/askscience/comments/nzy81l/if_haileys_comet_loses_ice_to_form_its_tail_how/ 1623708005 nzy81l Planetary Sci. 2021-06-15 1:00:05 "Comet Halley seems to lose mass at an approximate rate of 0.5% every perihelion passage (Whipple 1951; +Kresak & Kresakova 1987). At this rate, the comet might be +severely diminished or even vanished in about 15,000 years. + +[Source](https://arxiv.org/pdf/1409.7762.pdf)" "This is a really great question because asking it led us to discover most of the solar system! For many years, astronomers had a paradox: comets have relatively short lifespans of maybe millions of years maximum, and the solar system is billions of years old; however, there are still observable comets! The answer, as reasoned by Ernst Öpik and then more famously by Jan Oort, is that there is a vast collection of objects that we can't see that occasionally get bumped into the periodicity that we see for comets like Halley. + +Research has ~~shown~~ suggested that the number of these objects range in the billions, meaning most of the things in the solar system are in what we call the Oort cloud! And because it takes up the sphere 0.03 to ~~3.2~~ .8 (ish) light-years from the sun it's the vast, vast majority of solar system by volume. + + +[https://solarsystem.nasa.gov/solar-system/oort-cloud/overview/](https://solarsystem.nasa.gov/solar-system/oort-cloud/overview/) + +​ + +edit: 3.2 light years was a ridiculous estimate! The Oort cloud is not experimentally confirmed, although presumed by most scientists. It's exact nature is hotly debated." +1135 If a spacecraft was to use a magnetic field to protect its passengers from cosmic radiation decently as well as the Earth protects us, how would we generate it (method, power source, etc.) and how strong would it have to be, assuming a ship that is not much larger than the ISS? 306 https://www.reddit.com/r/askscience/comments/9jfikj/if_a_spacecraft_was_to_use_a_magnetic_field_to/ 1538073817 9jfikj 2018-09-27 21:43:37 Earths the magnetic field is pretty weak, about .3 Gauss, it is only able to protect us from energetic charged particles because it is so vast - it needs to act over extremely long distances to deflect particles by small angle changes. I haven't done the math but if it scales linearly you'd need about 10^6 times more field to act over the small scale lengths of a vessel. This puts us around the 100 Tesla range and you'd need the field to extend somewhere on the order of a meter. This is about the same as the 2012 record set by the national high magnetic field laboratory. Given that I suppose its possible to generate such fields with current technology but a space application would have to be at least decades off. "The best solution is not to use a magnetic field, but an electric one. We can generate these fields at a much higher strength with less power and they have no effect on humans (unlike magnetic fields which long term exposure results in some weird and possibly hazardous effects). Furthermore, electric fields do not need poles and you can face them in any direction. If you were to face one out it would slow down any particles approaching the spacecraft. + +We would only place these at key points such as the windows to living areas etc, and use clever design such as location of onboard water to provide some passive protection." +1817 Is there a system of geographical coordinates in space? 301 https://www.reddit.com/r/askscience/comments/lxu933/is_there_a_system_of_geographical_coordinates_in/ 1614889390 lxu933 Astronomy 2021-03-04 23:23:10 "There is, and it's called the ICRS (International Celestial Reference System). It is an idealized set of coordinates, the current realization of which is called the ICRF (International Celestial Reference Frame) version 3. + +Astronomical reference systems are based on the celestial sphere, which is the backdrop of very remote galaxies and other radio sources that are for all practical purposes so distant as to be effectively motionless. If you can fix a set of three orthogonal axes with respect to this sphere, and define its center, then you're done. + +The center of the ICRS is the barycenter (center of mass) of the solar system. This is quite close to, but not exactly at, the center of the Sun. + +The two biggest features on the celestial sphere for Earth astronomers are the ecliptic and the equator. The ecliptic is the circle on the celestial sphere that the Sun traces out over one year. It is the projection of the orbit of the Earth onto the 'universe'. Likewise the equator is the projection of the plane of rotation of the Earth. If you label their intersection (the vernal equinox, which is where the Sun is around March 20th) as the positive x-axis, and define that positive z is in the direction of angular momentum of Earth, you've basically captured the idea. This is called equatorial coordinates. + +Now this is tied to the rotation of the Earth, which is not as stable as first thought, which means this coordinate system moves. That's not good. The ICRS directions we use today are more or less 'frozen in time' on January 1, 2000, with a slight offset to account for the fact that we have better measurements since then. + +The ICRF itself is defined as a list of coordinates of some very distant radio sources which can be pinpointed to very high accuracy: + +https://hpiers.obspm.fr/icrs-pc/newwww/icrf/icrf3sx.txt + +Other reading: + +https://en.wikipedia.org/wiki/International_Celestial_Reference_System +https://en.wikipedia.org/wiki/International_Celestial_Reference_Frame +https://en.wikipedia.org/wiki/Equatorial_coordinate_system + +Actual astronomers feel free to arrest me on inaccuracies." "There is no unambiguous ""this place but 6 months ago"". Such a description would need an unambiguous definition of ""at rest"" (staying at the same place), which does not exist. Something that's at rest for one observer will move for another observer and vice versa. Both views are equally valid. + +All the coordinate systems we can introduce are arbitrary. The ICRS discussed by /u/TheBB uses the barycenter of the Solar System as reference. In that case Earth is ~300 million km away from the place where it was 6 months ago (twice the Earth/Sun distance). Similarly, you could use the barycenter of our galaxy as reference. Then Earth would be ~3 billion km away from where it was 6 months ago (largely from the Sun's orbit in the galaxy). You could also use the barycenter of the Andromeda galaxy, or any other reference you like, and you'll get a different answer every time." +1901 Why do teenagers need the covid-19 vaccine? 301 https://www.reddit.com/r/askscience/comments/p82v6x/why_do_teenagers_need_the_covid19_vaccine/ 1629456944 p82v6x COVID-19 2021-08-20 13:55:44 "> it doesn’t stop transmission + +It makes it less likely. A method doesn't need 100% success rate to be useful. + +Teenagers can get sick, and even die, from COVID. It's not as likely as for old people but the risk is there and you can reduce it." "> Mom is anti-vax so all I get is it will shorten life expectancy. + +There's no evidence to support that. Even if it were true, and I'm confident that it's not, it'd be decades before we could say that for certain. + +Also, it's worth noting that the whole anti-vax movement was basically kicked off by something published by a guy who we now know made up his results. Even then, his intention wasn't to discredit vaccinations in general, but the MMR vaccine, so he could sell the alternative he was working on instead. + +> ...my mum says as a teenager I would not be ill with covid? + +There have been numerous cases of teenagers (and children) dying from the virus. You're less likely to die than an adult, but it can happen, even if you don't knowingly have any other health problems. Well over 300 minors have died from it in the US alone. + +https://www.bbc.com/news/av/uk-england-birmingham-55071614 +https://www.nytimes.com/2021/06/04/health/coronavirus-teenagers-hospitalizations.html + + +> ...why is england mandating that teenagers get it? + +Even if you don't get ill, if you've had the vaccine you'll probably be able to pass the virus on for a shorter time if you're vaccinated than if you're not. So it does help stop the spread a little, and also it turns the tiny chance of a teen dying from it into a minuscule one. + +So, a little bit to protect you, but mostly to stop you from infecting (and potentially killing) others. Which to be honest, is the main reason even for adults, if they're healthy. + +I'm 42, and like 95% of why I got the vaccine was to try and reduce my chances of passing it on. +I know someone whose dad died when both parents were more-or-less isolating to avoid the virus. Literally the only person he'd been in contact with since about three weeks before falling ill was a visit from his daughter a few days before he fell ill, and she had no symptoms. Getting the vaccine is very little effort, but it seriously reduces the chances that I have to live with knowing someone probably died because I passed the virus on to them." +1611 AskScience AMA Series: My name is Dr. Rosalba Bonaccorsi, and I am an interdisciplinary scientist and astrobiologist at the SETI Institute's Carl Sagan Center. AMA! 294 https://www.reddit.com/r/askscience/comments/hwdog8/askscience_ama_series_my_name_is_dr_rosalba/ 1595502049 hwdog8 Planetary Sci. 2020-07-23 14:00:49 What do you think is the biggest spin-off of your research, that we all take advantage of? What kind of setup are you using to simulate the Enceladus plumes? Are you actually trying to simulate the physical process of a plume or simulating the chemical environment of such a plume? +1699 AskScience AMA Series: My name is Franck Marchis, and I am a Senior Planetary Astronomer at the SETI Institute and Chief Scientific Officer at Unistellar. AMA! 285 https://www.reddit.com/r/askscience/comments/jv5lyu/askscience_ama_series_my_name_is_franck_marchis/ 1605528034 jv5lyu Planetary Sci. 2020-11-16 15:00:34 Amazing. Thank you for this. Obvious question: what it the most interesting or promising thing you have encountered thus far in the project? Have you found any aliens yet? +1902 AskScience AMA Series: We have 60+ years of experience with renewable energy & the energy transition. Ask us anything! 273 https://www.reddit.com/r/askscience/comments/o0bncs/askscience_ama_series_we_have_60_years_of/ 1623754820 o0bncs Engineering 2021-06-15 14:00:20 What someone with a STEM background, but no experience in the field itself, can do to help with the development of such technologies? What do you say to oil and coal producing nations, states, or provinces (or those engaged in massive deforestation) who use the argument “renewables need steel (or other materials)” to be made as reasons to continue opening new mines and leases? Certainly the decisions made today on things like mines have impacts that last decades, but the decisions are made using short term viewpoints… how does the world overcome this? +1468 Which planet is the most visible from another planet in our solar system? 263 https://www.reddit.com/r/askscience/comments/dhn7hx/which_planet_is_the_most_visible_from_another/ 1571038259 dhn7hx Astronomy 2019-10-14 10:30:59 "Venus as seen from Mercury. Venus is close to the Sun and bright, you can have it in full sunlight when seen from Mercury, and it is very close. + +Venus would reach an apparent magnitude up (down?) to -7.7. + +https://en.wikipedia.org/wiki/Extraterrestrial_sky" "Without a doubt, Venus observed from Mercury. Venus at opposition would-be fully illuminated disc, on average a mere 31 million mi away. + +The brightest planet observable from Earth is also Venus. But it achieves this maximum brightness while in a crescent phase (about 27% lit), and about 45 million miles away. + +With 4 times more illuminated area, and ⅔ the distance, I'd expect Venus to appear 4^(1.5^2) = about 22 times brighter (abt 3.4 magnitudes) from Mercury than at its max brightest as seen in the skies of Earth." +1469 Can someone explain the spontaneity of time symmetry breaking in the Lukin and Monroe time crystal experiments? 222 https://www.reddit.com/r/askscience/comments/doxk82/can_someone_explain_the_spontaneity_of_time/ 1572388553 doxk82 Physics 2019-10-30 1:35:53 A priori, continuous time translation symmetry is broken by the drive to a discrete time symmetry with period T. To say that the remaining discrete time translation symmetry is spontaneously broken is to say that the Hamiltonian (which governs the evolution of the system) still has time translation symmetry with period T (i.e. H(t+T)=H(t)), but the *state* of the system only obeys a lower symmetry, in this case |\psi(t+NT)>=l\psi(t)>. We then would say that the time translation symmetry with period T was spontaneously broken to a time translation symmetry with period NT. +1136 What was ocean weather like when Pangea was all together? 219 https://www.reddit.com/r/askscience/comments/9ibs6u/what_was_ocean_weather_like_when_pangea_was_all/ 1537735607 9ibs6u Earth Sciences 2018-09-23 23:46:47 "The formation of supercontinents has several direct and indirect impacts on the global climate. + +Geometry of the huge global Panthalassa ocean basin and high sea level would favor tidal strength of less than half of its present-day value ([1](https://www.sciencedirect.com/science/article/pii/S0012821X16307518), [2](https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017GL076695)). The distinctive equatorial configuration of Pangea and its comparable hemispheric distribution of land-masses are thought to have given rise to an intense seasonal reversal of winds, termed the 'Pangean mega-monsoon' ([3](https://www.sciencedirect.com/science/article/pii/S0031018210001434)). + +Construction of Pangea also had a profound impact on the deep carbon cycle because it played a dominant role in determining volcanic fluxes (CO2 source) and weatherability (CO2 sink), which is why a greenhouse climate much hotter than today ensued after the peak of supercontinent formation. The high-latitudes in particular were up to 40°C hotter and ice-free - something current generation climate models are unable to convincingly replicate. A vigorous ocean heat transport was invoked to explain the polar amplification of warming ([4](https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2013PA002535)), however, physical arguments suggest that ocean circulation should be more sluggish during ice-free hothouse states. + +On the other hand, elevated greenhouse gases are known to shift storm tracks of tropical cyclones poleward ([5](https://www.nature.com/articles/nature13278)) and there is geologic evidence that cyclone strength was amplified during greenhouse climates ([6](https://pubs.geoscienceworld.org/gsa/geology/article-abstract/29/1/87/191983/temporal-variation-in-the-wavelength-of-hummocky?redirectedFrom=fulltext), [7](https://www.sciencedirect.com/science/article/pii/S0012821X15003532)). It has therefore been suggested that turbulent upper ocean mixing and polar cloudiness by stronger cyclonal activity represent a major driver of global climate during the Mesozoic and help explain the structural differences in climate between today and past warm intervals ([8](https://journals.ametsoc.org/doi/10.1175/2007JCLI1659.1))." "Due to Panthalassa (the ocean surrounding Pangea) not having any surface to break its momentum in the parts far from land, massive waves would form. Air in wet climates, especially oceans, is obviously humid, so the regions of Panthalassa that recieve more sunlight would be very warm, with the regions that recieve less being, of course, colder. This large area of differing temperatures would result in powerful winds, creating even larger waves, and the warmer regions would suffer powerful tropical storms. This would result in life that had existed in the oceans staying close to the bottom, just like marine life today does during hurricanes and tsunamis. + +Regarding Pangea, the coastline would be very active, but the tides would dissipate due to the resistance from the rising ground near the shore. It’s possible the large tides are the reason as to why life had evolved to live on land, they were forced to. In the same way monkeys evolved to climb trees to escape predators, Tiktaalik had also likely evolved to survive longer after being beached." +1818 Why do young, healthy people have more intense vaccine reactogenicity but get less sick when they catch a virus? 215 https://www.reddit.com/r/askscience/comments/lsbir8/why_do_young_healthy_people_have_more_intense/ 1614273201 lsbir8 COVID-19 2021-02-25 20:13:21 Because young healthy people have stronger immune systems. The “vaccine reactions” are not directly due to the vaccine (this is true of all vaccines) but symptoms caused by the immune system “turning on” in response to the vaccine and develop that future protection. For the same reason, a young healthy person with a strong immune system will generally be able fight off the virus faster/stronger so won’t get as sick. "It all comes to a concept called immune senescence. As we get older our bodies start to get weaker, and our immune system less capable of producing a effective response to a foreign agent. The key difference between a vaccine and the virus is that the former is designed to cause a immune response, and the latter to infect an individual. So when a young person gets a shot, it will have a immune response (that doesn't mean that he will develop symptoms mind you), but the virus may not be strong enough to cause illness in such individual. An older individual may not be able to have a response either to the shot or the virus, each will have it's own consequences. If he can't elaborate a immune response against the agent in the vaccine it will not develop immunity for it and if can't defend itself against the virus it may develop the illness. It's also why we don't vaccine immune compromised individuals, as they will not develop an immunity in most cases. + +​ + +EDIT: Fever and other phlogistic symptoms are consequence of the immune response, that itself can be caused by a virus, vaccine or a myriad of things. Usually you will not develop a fever if you don't have the apparatus for it. + +PS.: It's a COMPLEX subject and my comment is just a really simple overview, made worse for the fact that my english is not that sharp." +1137 How do we know that gravity's effect on time dilation is not an artifact of the effect that gravity has on the electrons orbiting the cesium atom used in atomic clocks to detect time dilation? 214 https://www.reddit.com/r/askscience/comments/9hxx53/how_do_we_know_that_gravitys_effect_on_time/ 1537601334 9hxx53 Physics 2018-09-22 10:28:54 "It doesn't matter if you use cesium or any other clock. *All* processes are influenced. And we did measure this with a large variety of clocks and clock-like processes. + +Edit: See [this follow-up comment](https://www.reddit.com/r/askscience/comments/9hxx53/how_do_we_know_that_gravitys_effect_on_time/e6gcd91/) for measurements." "I this is really hard to explain because 1 second taking 1.2 seconds makes no sense to us and it just doesn't happen anywhere on Earth the only time you see extreme examples of it happening is in physics textbooks. In real life it's more like gps satellites being a tiny fraction of a second off. But everything will happen slower. If you take a person or a radioactive sample to a place were relativity says time should pass 2x slower then in the standard reference frame a identical radioactive sample will have double the half life. The person will live 2x as long as the other person. + +https://www.aanda.org/articles/aa/full_html/2018/07/aa33718-18/aa33718-18.html#S7 + +I think this is one of the best real life examples of general relativity from June 2018. The basic of it is that they observed a star zooming around our galaxies center black hole at 25% of the speed of light. The velocity of the star after the encounter does not line up with Newtonian mechanics which assumes time passes at an constant rate. But if you calculate the velocity according to general relativity, by assume that time passed slower for the star when it was moving at it's fastest then the value for the final velocity of the star lines up exactly with the observed velocity of the star after the encounter with the black hole. + +The only way it's possible for that star to have the orbit it currently has is if the 12 second we saw it take for the star to swing by that black hole somehow only was 10 seconds for the star. " +1138 How did HIV/AIDS virus originate? Was there someone like patient zero? 207 https://www.reddit.com/r/askscience/comments/9h4cpk/how_did_hivaids_virus_originate_was_there_someone/ 1537356750 9h4cpk 2018-09-19 14:32:30 Radiolab did an episode called Patient Zero where they get in to this [pretty in depth](https://www.wnycstudios.org/story/169879-patient-zero/). IIRC, they don't really know who patient zero is as HIV is a result of a random mutation that unfortunately allowed it to infect humans. "There are several known strains of HIV. Two are closely related to SIV from particular groups of chimpanzees, and a third is related to SIV found in Gorillas. [The NIH has a a summary of HIV’s origins with citations.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2935100/#!po=23.3333) + +Chimps seems to have acquired it from other monkeys. It appears to be endemic to African monkeys. + +It probably spreads to human hunters via blood-blood contact. + +HIV doesn’t tolerate being out in the open air for long. It’s very unlikely that it would become “airborne”, but I’m no expert. + + +Just imagine all those researchers wandering around Africa collecting samples of chimpanzee poop so we can study HIV. What a job." +1470 If every cell in the human skin is replaced every couple of years, why don't scars heal? 207 https://www.reddit.com/r/askscience/comments/d4b0j5/if_every_cell_in_the_human_skin_is_replaced_every/ 1568495053 d4b0j5 Human Body 2019-09-15 0:04:13 "Your skin has a few different layers. The top layer is the epidermis, which is composed of both dead cells (the very top part) and living cells that constantly divide and replace the ones on top. The layer under that is the dermis, and it contains living cells but is mostly a kind of web of structural proteins--mainly collagen. +See here for a simple illustration: https://www.skininstitute.co.nz/wp-content/uploads/2017/07/shutterstock_layers-of-skin_blog-post.jpg + +If you have an injury to your epidermis, you don't form a scar because the living cells at the bottom of the epidermis reproduce and replace the lost cells quite easily. + +Scars are what happens when you get damage to the underlying connective tissue. Your bodies response to that is (simplified) to recruit a bunch of collagen producing cells to the area after the immune cells have finished cleaning up any debris and/or pathogens. These cells produce tons of collagen, but produce it in a stiffer, more regular pattern partially because this helps to pull the two sides of the wound closer together. + +Although u/TheGentlemanDM is correct that initially you get a big growth of blood vessels into the damaged area to supply all the ""repair/cleanup"" cells with nutrients and provide them with a way to get to the area, after a couple weeks those new vessels die off and you're left with a big area that's mostly collagen. + +For a metaphor, imagine you have a house and a tree falls and crushes part of the roof and one room. It's not a big problem to just rebuild those walls/windows/roof, because the rest of the house is still standing fine. A scar is like if the whole house gets destroyed by a tornado, and after cleaning up all the debris, they decide to just pave it over with concrete because it's cheaper/easier than rebuilding the whole thing." """Scars form at any injury site that takes more than three or four weeks to heal. The body produces collagen fibres in a criss-cross pattern. The normal shedding process of skin doesn't affect scars because it only involves the migration of the epithelial cells from the base of the epithelium to the surface."" Quoted from BBC Science Focus Magazine." +1139 Why do salt crystals form in almost perfect cubes? 205 https://www.reddit.com/r/askscience/comments/9ga51a/why_do_salt_crystals_form_in_almost_perfect_cubes/ 1537100371 9ga51a 2018-09-16 15:19:31 "Crystal shape is defined by the packing of the individual atoms/molecules that make up the substance the crystal is made of. Ice is made up of the packing of water molecules, rock salt is technically called [halite](https://en.wikipedia.org/wiki/Halite) and is the results of close packing of sodium and chloride ions. + +In the packing structure of halite the sodium and chloride ions sit in a three dimensional grid. In this grid each chloride is surrounded by six sodiums and each sodium is surrounded by six chlorides. This is what is known as a [cubic crystal system](https://en.wikipedia.org/wiki/Cubic_crystal_system#Rock-salt_structure) and is what determines the shape of the crystal when it grows." "I think you really have two separate questions here: why are salt crystals cubic, and why did my scenario result in fewer, macroscopically large crystals vs a flatter layer of many more finer crystals? + +I'll answer the latter question and leave the first one to someone else. Crystallization from solution entails a competition between the nucleation of new crystals and growth on existing crystals (along with other processes). The rate of these processes depends on the supersaturation of the solution in different ways. (Approximately speaking) high supersaturation favors nucleation and lower supersaturation favors growth. Slow evaporation results in low supersaturation. Thus, growth dominates and there are fewer and larger crystals instead of the many small crystals you'd expect if there was more nucleation. + +Slow evaporation is a common technique for scientists that are trying to grow large crystals, e.g. for crystallographic characterization. + +Edit: last couple sentences in the first paragraph edited for clarity" +1612 How do companies get the viruses for vaccines? 200 https://www.reddit.com/r/askscience/comments/h0pgwp/how_do_companies_get_the_viruses_for_vaccines/ 1591839659 h0pgwp Medicine 2020-06-11 4:40:59 "Essentially yes. We can already grow cells in labs and have many ""cell lines"" (cells that all come from one lineage and can essentially be propagated indefinitely, in one way or another). In general, they'll add virus to a susceptible cell line being grown in a dish and let the virus infect + kill the cells. For viruses, these are probably mammalian cells... and given that they would then normally have an immune system they're usually pretty susceptible, and a company will obviously pick a cell line that maximizes production (given some constraints, ie such as try to avoid human cells where possible). + +As to how they get the virus itself, either a university or research institution such as a hospital or government lab will give it to them. If not, and if it cannot be purchased commercially, theoretically you can introduce the viral DNA using various existing biotechnology techniques to get it to start replicating. Once it does it's far more trivial, because it's a virus that replicates itself. To be clear, the virus consists of its genetic material and a limited set of proteins encoded by this genetic material that are required to enter the cell and hijack cellular processes to create these same proteins from the genetic material, and to copy the genetic material. These proteins and genetic material will self-assemble before release, and go on to infect other cells and repeat the process exponentially." One of the ways you make vaccines is to make the viruses grow in, and therefore adapt to, other animals. You make flu vaccine by making the virus grow in chicken embryos. So that naturally makes more viruses then you put in and you only need a very small sample of the human virus to get started. For some more modern vaccines like the HPV vaccine the virus's shell is made by GMO yeast from the genetic sequence. So you don't need to get the live virus. One of the newest methods of making vaccines is called an RNA vaccine. In those kinds of vaccines your own cells are taught to make pieces of the virus but not the whole thing. Those cells then show their new proteins to your immune system which learns to attack them. +1999 Any news about the antibodies created when infected with the new Omicron variant? Since it has multiple mutations, are the natural antibodies from Omicron effective in fighting the earlier variants? 200 https://www.reddit.com/r/askscience/comments/rbuc6i/any_news_about_the_antibodies_created_when/ 1638978979 rbuc6i COVID-19 2021-12-08 18:56:19 Pretty sure we’re still waiting for research to be completed on these questions. We’ve only been aware of this variant for less than three weeks. Guaranteed someone is researching this now, but it’ll take a minute for enough data to be collected for them to be able to draw any firm conclusions. Tests for naturally acquired antibodies effectiveness typically lag tests for vaccine effectiveness simply because it is easier to test vaccine effectiveness. The reason is that you can control variables easier with a consistently produced vaccine versus a virus in the wild. I would imagine this information will be available in the months order of magnitude and not weeks. +1140 Do Insects have a sleep schedule? 188 https://www.reddit.com/r/askscience/comments/9gqaj7/do_insects_have_a_sleep_schedule/ 1537233409 9gqaj7 Biology 2018-09-18 4:16:49 Yes! If we are referring to the taxonomic class within *Arthropoda*, insects are known to undergo a period of less activity, with intermittent periods of higher activity. Insects can be diurnal, nocturnal and crepuscular(active at dawn and/or dusk). "Abstract from Shaw et al, *Science* (2000): + +> Drosophila exhibits a circadian rest-activity cycle, but it is not known whether fly rest constitutes sleep or is mere inactivity. It is shown here that, like mammalian sleep, rest in Drosophila is characterized by an increased arousal threshold and is homeostatically regulated independently of the circadian clock. As in mammals, rest is abundant in young flies, is reduced in older flies, and is modulated by stimulants and hypnotics. Several molecular markers modulated by sleep and waking in mammals are modulated by rest and activity in Drosophila, including cytochrome oxidase C, the endoplasmic reticulum chaperone protein BiP, and enzymes implicated in the catabolism of monoamines. Flies lacking one such enzyme, arylalkylamine N-acetyltransferase, show increased rest after rest deprivation. These results implicate the catabolism of monoamines in the regulation of sleep and waking in the fly and suggest that Drosophila may serve as a model system for the genetic dissection of sleep. + +To sum this up, not only do insects (in this case fruit flies) sleep, their sleep is quite like mammalian sleep, both in overt structure (""schedule"": they have regular wake/sleep cycles, sleep debt, decline with age, etc) and in its molecular mechanisms; other research has shown that it has similar genetic basis and similar neural mechanisms." +1141 Is it possible to know if a molecule is harmful or not by only looking at its structure? 182 https://www.reddit.com/r/askscience/comments/9ds34x/is_it_possible_to_know_if_a_molecule_is_harmful/ 1536306773 9ds34x Chemistry 2018-09-07 10:52:53 "We can mostly tell whether things are corrosive, flammable or explosive by looking at their structure. But telling whether or not they are poisonous or otherwise bad for our health is difficult. + +There are definitely some things that will be an immediate sign that something is likely to be bad for our health such as organic heavy metals, organic halogens or organic sulphur compounds. But even these have exceptions. + +And even for compounds that do not have obvious signs a lot can depend on how the compound is going to metabolize inside of our bodies which can't really be predicted all that well and has to be tested. + +But I'm only a chemist, for a more detailed answer we'd need a toxicologist." "I've worked in this area for over two decades. + +First there are chemical substructures that can be deemed mutagens (e.g., many aromatic amines); then there are ""reactives"" that are harmful (e.g., sulfonyl-chlorides); then there are known poisons (from Hg and CO to strychnine and designed chemical warfare agents, such as ""Novichok""). + +*So, as long as you catalog these, you can train computers to recognize them.* + +Then there are software based companies that predict toxicity - [Lhasa Ltd](https://www.lhasalimited.org/), [Leadscope](http://www.leadscope.com/) and [MultiCASE](http://www.multicase.com/) come to mind. However, do keep in mind that there is always uncertainty related to predictions, especially about the future (aka new chemicals). + +Other computational substructure filters, such as [FILTER](https://www.eyesopen.com/filter) (unwanted reactive species) and [BADAPPLE](http://pasilla.health.unm.edu/tomcat/badapple/badapple) (unwanted scaffolds) fulfill different (still comptox) related functions. + +The entire field of Computational Toxicology has now been [recognized](http://www.toxicology.org/groups/ss/ctss/) as an area of active interest by the [SOT](https://www.toxicology.org/index.asp) (Society of Toxicology), and a [dedicated journal](https://www.journals.elsevier.com/computational-toxicology) has been launched by Elsevier in 2016. + +Many experienced (I'd say 15+ years) medicinal chemists can look at the 2D structure of a molecule and intuitively know these molecules may be harmful. However, that skill is not universal, since it is humanly not possible to recognize every harmful (poisons, venoms, mutagens, carcinogens, etc.) chemical. + +Using that entire catalog of toxic substances plus chemical similarity & substructure recognition trained software is what most scientists who want to address this question use. + +Last but not least, recall the words of [Theophrastus Bombastus Paracelsus](https://en.wikipedia.org/wiki/Paracelsus): *Sola dosis facit venenum* ""[Only the dose makes the poison](https://en.wikipedia.org/wiki/The_dose_makes_the_poison)"" After all, even water (not to mention distilled water!) and salt (NaCl) are harmful when rapidly ingested in really high doses. + +**TLDR: Yes - mostly with appropriate software.**" +1471 Why are lunar landers wrapper in golden foil like material? 180 https://www.reddit.com/r/askscience/comments/cypen0/why_are_lunar_landers_wrapper_in_golden_foil_like/ 1567433241 cypen0 2019-09-02 17:07:21 It's for insulation, like mylar, which looks silver. It protects the instruments from extreme temperatures. "The gold foil is reflective, so most of the suns radiation, is reflected instead of absorbed, which is important because there’s no atmosphere for heat to be conducted/convected away from the spacecraft like there is on earth. + +This basically means that spacecraft won’t over heat, and also means the craft doesn’t develop a large temperature gradient, which can be very dangerous. I think the Chinese jade rabbit rover wasn’t adequately covered in parts which lead to its eventual demise." +1472 How violent/rapid was the separation of Pangaea? 179 https://www.reddit.com/r/askscience/comments/dnyn3o/how_violentrapid_was_the_separation_of_pangaea/ 1572206673 dnyn3o 2019-10-27 23:04:33 Explained in very simple terms: Look at the Afar region of East Africa as a modern day example. It is a very, very slow process that takes millions and millions of years. There is no ‘crack’ as you might visualize it - it’s more of a slow spreading apart, like taffy getting pulled. Eventually it gets so thin that lava begins to erupt and, because it sits so low, will get filled with water. So no, there is no big crack that separates the plates, and the separation itself was not violent (geologically, at least) or rapid at all. "Continental rift zones exist today and give you a good idea what things would have looked like in the early stages. + +​ + +[https://www.nationalgeographic.com/news/2018/04/east-african-great-rift-valley-crack-spd/](https://www.nationalgeographic.com/news/2018/04/east-african-great-rift-valley-crack-spd/)" +1613 After a couple months of the pandemic, can we know which epidemiological models have performed 'well'? 178 https://www.reddit.com/r/askscience/comments/hkt0b6/after_a_couple_months_of_the_pandemic_can_we_know/ 1593817886 hkt0b6 COVID-19 2020-07-04 2:11:26 [This website ](https://covid19-projections.com/historical-performance/) tracks historical performance of several models every week. Their performance comparison methods and code is also open source. "To judge the accuracy and effectiveness of individual models you would have to look at what the models predicted over the past few months and how the predictions fared compared to the reality. If you (or someone with time and data) did this then you could get a sense for how far ahead each model was accurate. + +Almost all models will be accurate for 1-3 days into the future. It's the 4-30 days into the future that are tricky. You could judge how good a model is based on how many days on average its forecasts were in agreement with the actual numbers. A better model might be accurate 7 or 8 days out. While a less accurate model would only be accurate 3-4 days out. Really good models could get 15+ days out with accuracy. Special shocks (changes in social distancing and shutdowns) will throw most of them off." +1473 Voyager 2 has reveled that the interstellar medium near the heliopause has a temperature of around 30,000-50,000K (29,000-49,000C). How and why doesn't Voyager just melt with such tempatures? 168 https://www.reddit.com/r/askscience/comments/dsqd1m/voyager_2_has_reveled_that_the_interstellar/ 1573091059 dsqd1m Astronomy 2019-11-07 4:44:19 "Most of the gas in space really is quite hot. Most of the volume of the ""interstellar medium"" - the gas distributed within a galaxy - is an ionised plasma at around 10,000 K. In intergalactic space, the gas is a hot blob of plasma that has largely been ejected from galaxies through supernova explosions, so it's at ~1,000,000 K. It's only really in dense cool molecular clouds that you get to room temperature or below. + +*But* this is an extremely thin gas, and it doesn't transfer heat to solid objects very efficiently, because the rate of collisions is so low. On a human scale, it doesn't feel like a gas/plasma at all, but more like an insulating vacuum. How much a probe heats up or cools down comes down to: how much heat does it produce, how much heat is lost through radiation, and how much heat is gained from radiation. You get heated up by nearby stars and your own internal power source, and cooled down by thermal radiation. + +Once you are far away from the Sun, you really don't get don't get much heat at all from the background of Milky Way stars. So the general tendency is to cool down - you emit more radiation than you receive. This is quite a slow process: for a human in a space-suit it's slowed down by your body converting food & air into heat. A human in a space-suit without heating might die of hypothermia, but it'll be over days - they won't be snap frozen like in Mission to Mars. For a probe or satellite, you can even get the opposite problem - the power source might be producing too much heat, and you need to think about how to design it to make sure it cools down. + +**tl;dr** interstellar space is full of hot gas that feels cold, but not *that* cold." It's the same reason as why you can put your hand inside a hot oven without feeling anything but a vague drying sensation, but if you grab a hot tray, you'll be burned. The heat that is conducted to an object depends on both the temperature of the surrounding matter, and the amount of matter the object comes into contact with. In space, while the matter is very very hot, there's hardly any of it, so Voyager just doesn't receive much heat. +1142 Does lemons prevent the binding of caffeine & tannin in tea? 167 https://www.reddit.com/r/askscience/comments/9fgapj/does_lemons_prevent_the_binding_of_caffeine/ 1536828267 9fgapj Chemistry 2018-09-13 11:44:27 "As far as I am aware, the citric acid only interacts with the tannins and not the caffeine. +In hard water areas the tannins oxidise to for what is known as tea scum. The addition of a slice of lemon disrupts this process so it no longer forms. This also affects the harshness of the stains formed on the surface of the cup. +Caffeine content is also affected by the type of tea used and the hardness of the water. +From what I know I don't think you can ever calculate the amounts of citric acid needed exactly as a tea brew contains far too many compounds to fully quantify it all. +Culturally in Britain lemon is put in tea like Earl Grey to enhance the flavour. It is not necessarily to change the caffeine content. " "Reducing the pH makes tannins less soluble because they are acidic. Lower pH means less deprotonation of the tannins making them less soluble in water. It would be very hard to quantify this without knowing levels of tannin (and tannin is an undefined mixture). + +Ca2+ won't really oxidize tannins because you'd need a rather strong oxidizer for that which Ca2+ is not, but it can undergo interactions, possibly precipating out negatively charged tannin as was mentioned. +" +1143 Has natural selection lead to animals having a better ability to cross the road than the animals in the early 1900s? 163 https://www.reddit.com/r/askscience/comments/9kb50p/has_natural_selection_lead_to_animals_having_a/ 1538350347 9kb50p 2018-10-01 2:32:27 "Some birds that nest in bridges and overpasses have experienced a shortening of the average wingspan. Shorter wingspans allow them to maneuver quickly in small areas and avoid being hit by cars. + +https://www.sciencenews.org/article/shorter-winged-swallows-evolve-around-highways" [deleted] +1474 Humans use titanium dioxide for so many things, what will happen when we run out of it? 162 https://www.reddit.com/r/askscience/comments/dqf3za/humans_use_titanium_dioxide_for_so_many_things/ 1572666045 dqf3za Earth Sciences 2019-11-02 6:40:45 "It is very unlikely we could ever deplete the supply of titanium. + +https://en.m.wikipedia.org/wiki/Titanium + +Titanium is the ninth-most abundant element in Earth's crust (0.63% by mass)[22] and the seventh-most abundant metal. It is present as oxides in most igneous rocks, in sediments derived from them, in living things, and natural bodies of water.[5][6] Of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titanium. Its proportion in soils is approximately 0.5 to 1.5%.[22]" "I can speak for the FnB industry in some measure where substitutes are being sought and used. My hunch is that if other industries find substitutes, running out of TiO2 wouldn't affect as much. Further, thanks to the current slowdown and the US China trade standoff, the overall TiO2 market seems to be headed for a slowdown, postponing the depletion. + +Essentially, substitution (and/or process modifications) would be key to offsetting any after-effects of TiO2 depletion. + +For what's being done by at least one player in FnB, check here: https://sensientfoodcolors.com/en-us/research-development/two-new-solutions-replace-titanium-dioxide/ + +Hope this helps." +1819 What percentage of genes are purely human? 161 https://www.reddit.com/r/askscience/comments/lu1no5/what_percentage_of_genes_are_purely_human/ 1614473926 lu1no5 Biology 2021-02-28 3:58:46 "It’s hard to know for sure. We don’t have a solid count for how many genes humans have to start with because there is some discussion about what counts as a gene, and not all sequences that could be considered a gene have been fully studied. Out of the 20,000-25,000 genes in our genome, 23 have been identified only in humans and not in any other currently living animals. + +https://www.theatlantic.com/science/archive/2015/10/the-mystery-of-human-only-genes-and-why-theyre-a-bit-like-oreos/410206/" "There are maybe 6 genes that are only found in humans. That's about 0.002% of the human genome. +But the answer is more complicated than that. What makes us human is not just the genes but how they are regulated. We share 98-99% genes with chimps but when looked closely the genomes are all filled with structural rearrangements. This results in a very different regulatory system in both. So the actual similarity may be 60-70%." +1144 Why do our teeth not heal or regenerate when cracked or broken? 151 https://www.reddit.com/r/askscience/comments/9j3y4g/why_do_our_teeth_not_heal_or_regenerate_when/ 1537978506 9j3y4g Human Body 2018-09-26 19:15:06 The cells (ameloblasts) responsible for forming the outer, white layer of protection on our teeth (the enamel) die when the tooth erupts into the mouth. So while the enamel can become demineralized and remineralized like most hard tissues, it cannot form any new enamel whatsoever. The insulating layer just underneath (dentin) does have some slight self-healing properties but even that has severe limitations. "Well, looks like I'm up to bat. + +Teeth are organs that have several mechanisms by which they can restore damage or even lost tissue. The pulp can create tertiary dentin either as a defense mechanism or a restorative measure in some cases, this includes some types of micro-fractures and abrasions. + +The cement and enamel on the other hand, have no such direct mechanism. They are not vital tissue and have no method of ""reproducing"" or ""regenerating"" themselves.... that being said, enamel has the capacity to engage in an ongoing remineralization process in which the enamel matrix will ""adsorb"" and ""bond"" with certain minerals to create substitute for natural dental tissue (Ex: Flourhydroxyapatite) which is not ""regeneration"" or ""healing per se, more like crude but functional patchwork, this is one of the methods by whcih a tooth can stave off major forms of damage, by dealing with the many micro-fractures that our teeth can suffer, which can eventually lead to a full blown transverse or linear fracture. + +All of that being said; + +Lacerations in the skin do not fully heal or regenerate. Scar tissue is not the same as the original tissue that it substitutes. + +Broken bones never actually ""heal"", it's more like they settle back in place. The segmented portions will forever be weakened due to an increase in rigidity. + +>Why is it that teeth do not regenerate whatsoever? + +They do, just that most dental tissue simply does not have reproductive capacity or the ability to generate new dental tissue. + +Sources: **Roijas Garzas Dental Anatomy**, **Dental Histology and Embryology by Jose Alfonso Castillo** , but tldr, I am a dentist and can confidently state that these things are true." +1504 Does distributed generation (e.g. rooftop solar) on a power grid reduce transmission demand? 150 https://www.reddit.com/r/askscience/comments/ejylqu/does_distributed_generation_eg_rooftop_solar_on_a/ 1578154950 ejylqu Engineering 2020-01-04 19:22:30 "Yes, sort of. +Electricity takes the path of least resistance, from the (rooftop PV) inverter into the service panel, where it will first (try) to power any loads inside the house itself (replacing 'utility' power). + +If there is not enough demand in the house then it will leave the premises and (try to) power the neighbour's house, etc, until eventually it will reach a neighbourhood substation and (tries to) power the next street. + +The 'electrical' load on the transmission(+distribution) will be lower, but because rooftop PV is not 'dispatchable' (doesn't have a throttle and is subject to clouds) the operators in the grid control room have to work harder to 'balance' the grid at large." "Potentially power factor correction can be a huge deal. +Power factor correction is needed when voltage and current are out of phase on an AC grid. +This means you are not transforming the power from the grid 100% efficiently into something useful (heat if you are boiling water, light if you have a lamp on). + +To try to correct for this inefficiency (which can be caused by a many different things) you either need to use more copper in you wires or put big capacitors in your grid, or both. +You may have seen systems like this: +https://electrical-engineering-portal.com/wp-content/uploads/2015/10/capacitor-banks-pole-mounted.jpg + +Generally speaking, the closer your source is the lower the transmission costs of power. You can get good efficiency over long distances, but it requires some pretty expensive equipment. + +Distributed supplies, such as wind turbines, grid storage batteries and solar cells can help with these issues. + +Long story short: You can spare a lot of expensive equipment if your have a source of electricity close to where it is consumed, which also lowers the transmission inefficiency." +1614 AskScience AMA Series: I'm Will Armentrout, an astronomer at the Green Bank Observatory in the heart of the US National Radio Quiet Zone. Ask me anything! 150 https://www.reddit.com/r/askscience/comments/hvrrkh/askscience_ama_series_im_will_armentrout_an/ 1595415648 hvrrkh Astronomy 2020-07-22 14:00:48 Do you know how the size and restrictions of the National Radio Quiet Zone were determined? Do other observatories have areas of similar restriction? How do you see the future of single-dish observatories in comparison to interferometers? Do you think at some point we will practically only be using interferometers, or will there always be a use for single-dish observatories? +1475 How is water able to stay in gaseous form in air (water vapour) well below its condensing temperature? 149 https://www.reddit.com/r/askscience/comments/dko0ev/how_is_water_able_to_stay_in_gaseous_form_in_air/ 1571597950 dko0ev 2019-10-20 21:59:10 All liquids have what's called a vapor pressure. Essentially, if you leave the liquid sitting open to air it evaporates, often very slowly, until there's a certain concentration (partial pressure) of it in the air. The vapor pressure also depends on temperature, which is why hot air can be more humid than cold air. "When you have less than 100% humidity, water is constantly evaporating. If you leave a glass of water in your house for long enough, it will eventually all evaporate off like you expect. It is just a relatively slow process. The kinetics of evaporating water in the atmosphere is controlled by 2 things + +1. At the boundary layer between the water and air, the air will have a concentration gradient of water vapor. When water evaporates, the air immediately above the water will be saturated with water vapor. Until that water vapor moves away, you will not evaporate more water. You can speed this up by forcing air flow past the surface of the water to pull away the water vapor. This is typically the limiting factor for how quickly water evaporates. +2. Evaporating water takes a lot of energy so as more of it evaporates, the water becomes colder. Eventually you reach a point where you will not evaporate any faster because you water has cooled down to much. We see this with a wet bulb thermometer, which measures the temperature you would get if you wrapped a thermometer with a wet cloth, then spun it around really fast. It is a really important number for designing water cooling towers." +1903 How does thinking about breathing turn it from an automatic to a conscious act? 149 https://www.reddit.com/r/askscience/comments/p86br5/how_does_thinking_about_breathing_turn_it_from_an/ 1629469704 p86br5 Human Body 2021-08-20 17:28:24 "Your fundamental autonomic control of breathing originates from your medulla, where the respiratory centres control breathing. Normally you'll have passive expiration and inspiration. If a stroke was to happen there, you would have to consciously breathe in order to survive also known as Ondine's Curse. + +However, by consciously thinking about breathing. Your brain activates the motor cortex instead and utilises the accessory muscles and diaphragm to contract/relax to breathe, leading to active inspiration and expiration. I assume it's slightly different form of breathing and exertion. + +Fellow redditors, please correct me if I'm wrong! And add more details if anybody knows more!" "An interesting disease related to this is the Ondine's Curse. + +""Ondine's curse is named after a mythical tale in which a heartbroken water nymph curses her unfaithful husband to stop breathing should he ever fall asleep."" (there's probably an opera about this) + +[The Medscape entry](https://emedicine.medscape.com/article/1002927-overview) says: + +>Congenital central hypoventilation syndrome (CCHS), also referred to as Ondine's curse, is a life-threatening disorder manifesting as sleep-associated alveolar hypoventilation. According to American Thoracic Society (ATS) guidelines, a mutation in the PHOX2B gene is required for the diagnosis of CCHS. Treatment is supportive and is based on an assessment of respiratory impairment, cardiac dysfunction, and gastrointestinal dysfunction, as well as surveillance for underlying oncologic manifestations." +1820 Is it a legitimate claim to say that random, erratic weather is a result of climate change? 143 https://www.reddit.com/r/askscience/comments/lrzljj/is_it_a_legitimate_claim_to_say_that_random/ 1614232628 lrzljj Earth Sciences 2021-02-25 8:57:08 "At the general level, you're asking about so-called ""attribution studies"", i.e., can a particular extreme event, or types of extreme events, be attributed to climate change. This is, and has been for at least two decades, an active topic of research (e.g. [Stott et al, 2003](https://www.nature.com/articles/nature03089), [Santer et al., 2009](https://www.pnas.org/content/106/35/14778/), [Stott et al., 2010](https://onlinelibrary.wiley.com/doi/full/10.1002/wcc.34), [Hegerls & Zwiers, 2011](https://onlinelibrary.wiley.com/doi/full/10.1002/wcc.121), [Otto et al, 2012](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011GL050422), [Coumou & Rahmstorf, 2012](https://www.nature.com/articles/nclimate1452), [Otto, 2016](https://www.nature.com/articles/nclimate2971), [Zhai et al., 2018](https://link.springer.com/article/10.1007/s13351-018-8041-6)). If you peruse some of those, you'll see generally we can think about this in two ways, (1) identifying new extremes (i.e., is a particular event actually outside the expected range of these types of events based on past climate data) and (2) attributing a new extreme to climate change, which is often done by seeing if forcing a global climate model with anthropogenic influences (e.g., increases in CO2) produces similar extremes and are not expected without the anthropogenic influence. + +As discussed in more detail in many of the papers above, it is definitely possible to attribute particular extremes, or shifts in patterns of extremes to climate change, e.g., the 2010 Russian heatwave and associated [wildfires](https://en.wikipedia.org/wiki/2010_Russian_wildfires) have been linked to global climate change (e.g. [Otto et al, 2012](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011GL050422) also ref'd above). However, a lot of work goes into tying particular events and/or shift in statistics of types of events to global climate change, so it is reductive (and potentially incorrect) to simply attribute any ""out of the ordinary"" extreme to climate change. Even without global climate change, weather events can be thought of as stochastic, and ""drawn"" from some underlying distribution. For many types of weather events (e.g., precipitation), these distributions appear to be [""heavy-tailed""](https://en.wikipedia.org/wiki/Heavy-tailed_distribution), and specifically heavy right tailed. The practical outcome of this is that large and rare events are to be expected, but by definition do not occur very frequently and so we try to estimate their likelihood and magnitude by modeling the tail of these distributions. However, this exercise is challenging because our records may not be complete or long enough to actually know what the correct distribution is to explain the tail (and also gets into lots of somewhat strange ideas like those of [black swans](https://en.wikipedia.org/wiki/Black_swan_theory) or [dragon kings](https://en.wikipedia.org/wiki/Dragon_king_theory)). E.g., if your record is 100 years long, there's a good bet you have not observed an event with an average recurrence interval of 1000 years, so when this occurs, whether this appears to be ""out of the ordinary"" depends on how you've extrapolated the tail of the distribution. This is independent of climate change, which in detail is potentially changing the nature of the underlying distribution for some types of events in some places, hence the challenge posed by trying to identify whether an extreme event is explained by the distribution of events before climate change or is outside of this distribution (i.e., could be attributed to climate change). + +**TL;DR** With careful analysis, it is possible to relate some specific events or shifts in various patterns to climate change, but because even in the absence of climate change, we expect weather events to have skewed (heavy right tailed) distributions, attributing any apparent ""out of the ordinary"" event to climate change is extremely problematic without the aforementioned careful analysis." "Weather is caused by uneven heating of the earth. The hotter it gets at the equator, the larger difference in potential energy between the equator and polrles, the more energy storm systems will move with. Hot air movibg poleward doesn't imnediately dissolve, it displaces the colder polar air, leading to cold fronts moving towards the equator. + +This is a very very very basic simplification, but it's helpful in understanding why climate change will result in more severe weather, including cold spells." +1476 I’m Christof Koch, President and Chief Scientist of the Allen Institute for Brain Science and author of the new book, “The Feeling of Life Itself: Why Consciousness Is Widespread but Can’t Be Computed.” Ask me anything about consciousness! 142 https://www.reddit.com/r/neuroscience/comments/d9lj5p/im_christof_koch_president_and_chief_scientist_of/ 1569532550 d9q2qb 2019-09-27 0:15:50 +1700 AskScience AMA Series: I'm Emily Calandrelli, I have 4 degrees in science and engineering and I'm the host and co-Executive Producer of Emily's Wonder Lab on NETFLIX - AMA! 138 https://www.reddit.com/r/askscience/comments/isiqk1/askscience_ama_series_im_emily_calandrelli_i_have/ 1600081251 isiqk1 Engineering 2020-09-14 14:00:51 “What is your favorite food?” - my 8yo son who loves your show "My 5 year-old daughter loves your show. When my wife pointed out to her that you were pregnant and ""had a baby in your belly"" my daughter paused for a moment and said ""What kind of baby? Like a science baby?""" +1145 Why does meat from different animals taste different? 137 https://www.reddit.com/r/askscience/comments/9g1dv5/why_does_meat_from_different_animals_taste/ 1537017484 9g1dv5 Biology 2018-09-15 16:18:04 Short answer: there are different proteins in different types of meat. What makes up the diet of the animal can change the fats and chemical composition of the animal too, so even within species you can have different flavors. "Most of the meat's flavor comes from fat, as most of the flavorful molecules are fat-soluble. Those molecules come partly from the diet of the animal. Chicken is so bland tasting, as it doesn't really have much fat, especially in the breasts. That's also why so many other lean meats taste like chicken. + +​ + +It's also quite important to note that much of the flavor you experience is a result of the cooking. Maillard reaction specifically makes meat taste so tasty." +1904 Did the GOODS south image capture colliding galaxies? 137 https://www.reddit.com/r/askscience/comments/o0cs74/did_the_goods_south_image_capture_colliding/ 1623758736 o0cs74 Astronomy 2021-06-15 15:05:36 "Okay, I managed to track them down. + +That image is from high resolution Hubble imagery, but those galaxies are big enough and close enough that they aren't too hard to see. I found them using the 'worldwidetelescope' [here](http://worldwidetelescope.org/webclient/?wtml=http%3A%2F%2Fwwtcoreapp-data-app.azurewebsites.net%3A80%2Fwwtweb%2FShowImage.aspx%3Fra%3D53.1266361292%26dec%3D-27.8031323267%26x%3D640.0%26y%3D390.7836419073964%26scale%3D0.74515395805994%26rotation%3D250.32%26name%3DGOODS%2BSouth%2BField%26imageurl%3Dhttp%253A%252F%252Fesahubble.org%252Fmedia%252Farchives%252Fimages%252Fscreen%252Fheic1620a.jpg%26thumb%3Dhttp%253A%252F%252Fesahubble.org%252Fmedia%252Farchives%252Fimages%252Fthumbs%252Fheic1620a.jpg%26credits%3D%26creditsUrl%3Dhttp%253A%252F%252Fesahubble.org%252Fimages%252Fheic1620a%252F%26wtml%3Dtrue#/place=Open_Collections.GOODS_South_Field.0&ra=3.54558&dec=-27.86169&fov=0.02498). (Yes, that is a giant url) + +That gave me the RA and Dec coordinates, which I used to search the objects on Simbad [here](https://simbad.u-strasbg.fr/simbad/sim-coo?Coord=03+32+44.17+-27+51+42.5&CooFrame=ICRS&CooEpoch=2000&CooEqui=2000&CooDefinedFrames=none&Radius=2&Radius.unit=arcsec&submit=submit+query&CoordList=). + +What I found is there are *two* active galactic nuclei (AGNs) listed there. [This one](https://simbad.u-strasbg.fr/simbad/sim-id?Ident=%405449606&Name=2XMM%20J033244.0-275140&submit=submit) and [this one](https://simbad.u-strasbg.fr/simbad/sim-id?Ident=%40655192&Name=CXOCDFS%20J033244.3-275142&submit=submit). To tell if they're at the same distance, we look at the redshift or radial velocity, which is 0.2781 for one and 0.281 for the other, which is pretty close. + +An AGN is produced when the supermassive black hole in the centre of a galaxy is accreting a lot of gas and has a really bright accretion disc, bright enough to give off a lot of light and heat up the gas around it. They *may* be triggered by merging, because the gas get stirred up by all the crazy gravitational forces and tends to fall towards the black holes. + +They are overlapping galaxies at the same redshift, and both are AGNs, so it does look like they are merging. Of course, at a redshift of z=0.28, we're seeing the galaxies as they were about 3 billion years ago, so they should be merged by now." +1146 If electricity were to be passed through radon, would there be light? 136 https://www.reddit.com/r/askscience/comments/9ji0bq/if_electricity_were_to_be_passed_through_radon/ 1538092189 9ji0bq 2018-09-28 2:49:49 "Yes, it would emit light just like helium, neon, argon, krypton, and xenon. + +The spectral lines of radon are listed here: https://physics.nist.gov/PhysRefData/Handbook/Tables/radontable2.htm + +I'm not sure what visual color the spectrum would correspond to, but probably somewhat reddish due to the strong lines at 705 and 745 nm. + +Also, there's a previous thread: https://www.reddit.com/r/askscience/comments/41rly1/what_color_light_would_radon_emit_in_a/" "It would emit light, but its peaks are in the near Infrared. Under the right conditions, you might see a faint dark red glow. + +​ + +As for the other poster asking for a picture, any picture would not do it justice. A computer screen cannot render this range of red." +1477 How can software perform tasks hardware cant’t? 136 https://www.reddit.com/r/askscience/comments/dj1i9k/how_can_software_perform_tasks_hardware_cantt/ 1571288008 dj1i9k Computing 2019-10-17 7:53:28 "Any computation can be broken into simple steps. Maybe trillions of them, but all simple. The hardware only needs to be capable of the simple operations. The compiler translates high level operations into simple ones. Hardware can of course add features such as multipliers, say, to perform some complex operations faster. + +Volatile is a good example: it's a purely compile time construct. The hardware neither knows nor cares when or whether you access variables or memory mapped registers. It has no idea what variables even are. But the compiler does care, and emits assembler which achieves the desired result." "Software emulation + +If your cpu can do basic mathematical operations then some sequence and combination of those operations would eventually be able to do every computing operation provided it has enough memory. + +For example if your cpu can add but can't multiply in hardware then you can write it in the software such as adding the number of times it needs to be multiplied. E.g 2x5 = 2+2+2+2+2 + +Practically you'd want a cpu that is fast enough to emulate the operations in reasonable amount of time. + +In terms of hardware there is nothing stopping you to say run simulations of galactic collision on your home PC processor but the time it'd take to do it would likely be beyond your lifetime. Nevertheless it's possible with emulation as long as all computation can be broken down to basic mathematical operations (with conditionals and other logic ofc)." +1147 How far can we possibly see using a telescope (in terms of time and space)? 135 https://www.reddit.com/r/askscience/comments/9d3sof/how_far_can_we_possibly_see_using_a_telescope_in/ 1536129240 9d3sof 2018-09-05 9:34:00 "You can actually see further than 13.8 billion light years because the universe is expanding. Light travels at the speed of light, which is one light year per year. So the furthest distance that light can travel in the history of the universe is 13.8 billion light years. But in 13.8 billion years, the universe has expanded a lot. The object that the light came from can be more than 13.8 billion light years away. So we can see objects that are now further than 13.8 billion light years away. Taking this into account, the furthest object you can possibly see is about about 50 billion light years away. + +In practice though, the universe was opaque in very early times, so when we look at very large distances we just see a uniform ""wall"". This is the cosmic microwave background. Note that you don't need an exceptionally good telescope to see that far - the limiting factor in telescopes is more about brightness than resolution, and this background is fairly bright. + +And yes, if you were sitting at a star 200 light years away, you could see Earth as it was 200 years ago, although you'd need a very very good telescope to get enough resolution." "A few years ago I owned a 10 inch reflector telescope. I did some looking around to find the most distant object that an amateur astronomer could hope to see, and found [quasar 3C 273](https://en.wikipedia.org/wiki/3C_273) seemed to be it. + +2.4 billion light years out. + +Then I did some math to put it in perspective. If you created a model of the universe in which the distance from the Earth to the Sun was 1 inch, then 3C 273, in your model, would be past Neptune in the real world. Think for a minute how insanely *bright* that object must be, to be visible at that distance. (If you brought the quasar to about 34 light years from Earth, it would be about as bright as the sun in our sky. For comparison, our sun is about 8 light *minutes* from us.) + +>Say you teleported to some observatory 200 lightyears away and were able to use a telescope to look back at Earth. Say you could also zoom in enough to see cities. + +Someone crunched the numbers on this, I think on Reddit, a little while back. Turns out the size of lens you'd need to be able to do this, would be so massive it would collapse itself into a black hole." +1148 Does the human brain treat its own face differently from the faces of others? 133 https://www.reddit.com/r/askscience/comments/9jhyfi/does_the_human_brain_treat_its_own_face/ 1538091766 9jhyfi 2018-09-28 2:42:46 "This isn't my specific area of research so I might be missing some key findings, but the answer seems to be yes, both behaviorally and neurally, although we also have many of the same processing advantages for very familiar faces (see discussion of this at the end of the post): + +- We're faster at recognizing our own faces compared to either familiar faces (of friends) or unfamiliar faces, even when they are inverted, whereas inverted familiar and unfamiliar faces are equally difficult to recognize ([Keyes & Brady, 2010](http://journals.sagepub.com/doi/pdf/10.1080/17470211003611264?casa_token=pJekisSAb_YAAAAA:aXYwUZE-tUBbluC1ysrgafqHJ6RcWFYXi2jz2ywmEkoYeU03xIwS5kVAwfuVJT2Y3QCsM7L0OZASw4I) <- pdf!). + +- We process highly familiar faces (including our own) more rapidly than those of strangers as measured by response time in a visual search task where you are shown a number of face images and have to say whether a target face is present or not ([Tong & Nakayama, 1999](https://www.researchgate.net/profile/Frank_Tong3/publication/12834940_Robust_representations_for_faces_Evidence_from_visual_search/links/53cfe1420cf2f7e53cf839ca/Robust-representations-for-faces-Evidence-from-visual-search.pdf) <- pdf!). Although more recent work ([Devue et al., 2009](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.147.9671&rep=rep1&type=pdf) <- pdf!) suggests that familiar faces hold attention longer once they are already focused on and make it harder to disengage during a search task so you spend more time looking at them, rather than the effect being due to enhanced processing. + +- Seeing your own face captures your attention while doing another task, but not more so than seeing other, highly familiar faces ([Devue & Bredart, 2008](https://s3.amazonaws.com/academia.edu.documents/42275913/u190843274Devue_Bredart_2008.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1538152206&Signature=cmynWm4ANfg2G8DlYl3LIVRHxOY%3D&response-content-disposition=inline%3B%20filename%3DAttention_to_self-referential_stimuli_Ca.pdf) <- pdf!) + +- We're faster at recognizing frontal pictures of our own face rather than profile pictures. There is no difference in reaction time for unfamiliar faces. This suggests that familiarity with seeing our face from a specific viewpoint affects face processing / representation ([Laeng & Rouw, 2001](https://www.tandfonline.com/doi/pdf/10.1080/713754410?casa_token=vA9QBrEN8KkAAAAA:n8PyrqIWxqEiG9a6Rp4aSWYWxupKDm8aWtIA4CaVBn-xaR4B2c9zP65P8cbHplV7sB-95ozEVEmtQwA) <- pdf! ; [Troje & Kersten, 1999](http://journals.sagepub.com/doi/pdf/10.1068/p2901?casa_token=_67fGuo_hk8AAAAA:BRaWRdpdl_MvUnO1xgAB-VVoQ8J-X6iEeJ2nvujVkAJCu_vvFFfKEI95LQlpLJ7_ZPw6u1mBJAUoOHU) <- pdf!). This is supported by the fact that we think mirrored pictures of ourselves are more representative than non-mirrored, while the opposite is true for pictures of our friends ([Rhodes, 1986](https://link.springer.com/content/pdf/10.3758/BF03197695.pdf) <- pdf!), although it might be the case that we use slightly different cues (e.g. asymmetrical features like moles or hairstyles) for our own faces vs. those of our friends since we sometimes see pictures of ourselves (non-mirror-reversed), but we almost never see mirror-reversed pictures of our friends ([Bredart, 2003](http://journals.sagepub.com/doi/pdf/10.1068/p3354?casa_token=npBN_FHwNlgAAAAA:NnFQTU8j0RS6Rr1DSBFHyqyfVM5VFWMUEAOaTYo--06y3Zijgl2L4kiJd0EWGOZY3PFit9FXUIWNe-o) <- pdf!). + +- Some studies have found unique patterns of brain activation to one's own face vs. both familiar and unfamiliar faces ([Keenan et al., 2000](https://pdfs.semanticscholar.org/4083/3f3e65ed7a910351ddf1c4cded5fb2d4e6d6.pdf) <- pdf!; [Keyes et al. 2010](https://www.sciencedirect.com/science/article/abs/pii/S0278262609001778) ; [Kircher et al., 2001](https://s3.amazonaws.com/academia.edu.documents/43911052/Recognizing_ones_own_face20160320-14736-ipatxt.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1538152568&Signature=D6Mf5DrOLQVgNoLuOn12oOHxYew%3D&response-content-disposition=inline%3B%20filename%3DRecognizing_ones_own_face.pdf) <- pdf! ; [Platek et al., 2006](https://pdfs.semanticscholar.org/1d13/83a6bea09deddfd5a173c829cc607d9a621a.pdf) <- pdf! , [2008](https://www.sciencedirect.com/science/article/pii/S0006899308016648) ; [Platek & Kemp, 2009](https://www.sciencedirect.com/science/article/pii/S0028393208005095) ; [Uddin et al., 2005](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.659.5844&rep=rep1&type=pdf) <- pdf!), particularly in right frontoparietal areas, possibly connected to mirror neuron system (for reviews, see [Uddin et al., 2007](https://pdfs.semanticscholar.org/828a/b00c644ea7f2164b385b6a705567da20891b.pdf) <- pdf! and [Devue & Bredart, 2011](https://orbi.uliege.be/bitstream/2268/85119/1/DevueBredartC%26Cpostprint.pdf) <- pdf!). These areas seem to be specific to self-face recognition, as opposed to being generally related to self-identity (e.g., recognizing one's name) ([Sugiura et al., 2008](https://www.sciencedirect.com/science/article/pii/S1053811908003029) ; [Miyakoshi et al. 2010](https://www.sciencedirect.com/science/article/pii/S1053811910000509)). + +- The right-hemisphere preference is supported by some behavioral work that found that we're faster at responding to our own face when making responses with the left hand (controlled by right hemisphere) rather than the right (Keenan et al., [1999](https://www.sciencedirect.com/science/article/pii/S0028393299000251), [2000](https://www.sciencedirect.com/science/article/pii/S0028393299001451)). Furthermore, modulating cortical activity in areas in the right, but not the left hemisphere using rTMS impairs self-face recognition ([Heinisch et al., 2010](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.665.2609&rep=rep1&type=pdf) <- pdf! ; [Uddin et al., 2006](https://www.researchgate.net/profile/Lucina_Uddin/publication/6420954_RTMS_to_the_right_inferior_parietal_lobule_disrupts_self-other_discrimination/links/00b7d5215b6285dbd9000000.pdf) <- pdf!). However, responses to other familiar faces show a bias for a different visual field than those for self-faces ([Brady, Campbell, & Flaherty, 2004](https://www.sciencedirect.com/science/article/pii/S0028393204000454)), suggesting that perhaps familiar and self-faces are represented separately. + + +Some of the studies linked above suggest that whether the effects are specific to our own face vs. face stimuli to which we've been exposed to many times seems to vary depending on task. Note that this is a little tricky to tease apart when looking at patterns of neural activity: you can compare activity to many different instances of familiar faces vs. unfamiliar faces and show a difference between average response to one vs. another. That would indicate that the difference is not likely due to any one particular face, but is a categorical distinction that we make. That's been found in plenty of studies (see below). It's trickier to do a comparison between one's own face and other faces. If you just have one image of your face, then the difference in response might be due to that particular image, as opposed to a categorical distinction. Even if you have many images of one's own face taken at different times and from different angles, they are still going to be more similar to each other than images of familiar faces of different people, so it wouldn't be surprising if you found a difference in activity. I'm not sure what the best way of doing such an experiment would be. I haven't read all of the papers too closely, so perhaps they control for such things in a way I haven't thought of. " +1478 Since in nuclear fission a very small amount of matter is converted to energy, is it Theoretically possible to create matter from energy and have we done this? 133 https://www.reddit.com/r/askscience/comments/dmr2ly/since_in_nuclear_fission_a_very_small_amount_of/ 1571971169 dmr2ly Physics 2019-10-25 5:39:29 "Yes, creating matter from energy is perfectly doable. + +One example would be particle accelerators such as the LHC. In the LHC, proton beams are accelerated and thereby given a very high amount of kinetic energy. These highly energetic protons collide and produce various new particles. The combination of newly produced particles often has a higher mass than the 2 protons that collided to form them. + +Consider for example the production of a Higgs boson. The Higgs boson was found to have a mass of 125 GeV (giga-electronvolt), while a proton has a mass of 938 MeV (mega-electronvolt) or slightly less than 1 GeV. So the 2 protons that collided to create a Higgs boson have a combined mass far smaller than the mass of the particle that was created. + +And this is possible thanks to the fact that the protons had such a high amount of (kinetic) energy going into this whole mess." "Another example is *pair production*. A high energy photon can, when in the vicinity of a nucleus, turn into an electron and positron or other particle-antiparticle pairs. The photon energy has to be greater than the mass-energy of the particle pair. A photon in empty space doesn't undergo pair production because energy and momentum cannot both be conserved, a nearby nucleus is needed to take up the excess. + +EDIT PS: The photons need to be high-energy X-rays or gamma rays to do this." +1149 What exactly is muscle memory and how does it work? 131 https://www.reddit.com/r/askscience/comments/9ezt2v/what_exactly_is_muscle_memory_and_how_does_it_work/ 1536688511 9ezt2v Human Body 2018-09-11 20:55:11 "Well, to start off, muscle memory is not in your muscles, it's in your brain. Muscle memory is essentially your brain learning what to do to make a certain movement happen. + +When you start off trying to learn a new physical skill, you often know what you want the end result to be (I want the ball to wind up over *there*), but you don't know exactly how to make that happen. You try to make the right movement, and over time your brain learns exactly what sequence of individual muscle movements (and what visual / bodily feedback to use) will produce the result you want. + +Essentially, in the process of learning a motor (movement) skill, your brain creates a new ""program"" that it can run whenever it's needed. When it's time to throw a ball, your brain can activate the ""ball throwing program"" instead of having to consciously figure out exactly what movements to try, like you do when you're first learning." "You know how in pictures of the brain there's this spaghetti-like lump at the back? That's the cerebellum. The cerebellum is a **cybernetic control machine**. I've yet to see a textbook explain how fascinating it really is. Let's take a look. + +​ + +About 75% of your neurons are located in your cerebellum. Some researchers estimate [that it contains 100 billion neurons](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/), all packed into that ball of spaghetti. Because of this, you'd be right in assuming that the cerebellum is the brute-force mechanism of the brain in terms of information processing. + +​ + +So what does it do? + +​ + +I've used the word ""machine"" to describe it, which might sound odd to you. In 1967, a trio of researchers published *The Cerebellum as a Neuronal Machine*. Therein, they argued that the cerebellum was analogous to a computer. This idea has persisted and has been expanded on by others. + +​ + +The cerebellum performs error correction; it reduces the discrepancy between intended and actual movements. When you reach out to grab something, you rely on proprioceptive feedback signals to adjust your trajectory. Motor plans originate in the motor area of the cerebral cortex. Signals are sent down to the spine and to relevant muscle fibers. At the same time, a copy of the motor plan travels to the cerebellum. Signals from the motor fibers head back up to the cerebellum. There they converge. The cerebellum can adjust the movement so that becomes nice and smooth rather than ""jerky"". + +​ + +Now, the motor plans and the error correction is fine and all, but there's an important question we haven't considered: *should* you reach out to grab something? + +​ + +The basal ganglia can be blamed for your habits, good or bad. It is believed to be highly involved in **habit-formation**. What's more, it is thought to evaluate and scrutinize motor plans. + +​ + +The motor cortex is, in fact, at all times inhibited by the basal ganglia. The basal ganglia frees cortical neurons from inhibition when it has been decided that the motor plan is appropriate. In a sense, the basal ganglia is the sculptor of behavior. Actions that lead to good consequences are encouraged (less likely to be inhibited) and actions that lead to bad consequences are discouraged (more likely to be inhibited). + +​ + +As the basal ganglia is involved with value, it has been suggested that its goal is to maximize reward. *Skill* simply means you are able to more efficiently carry out a task, which means you can collect rewards faster. + +​ + +Now, this all seems nice and dandy. There are some issues, however. People with cerebellar ataxia, meaning their cerebellum is screwed up, are just pretty clumsy. They aren't flailing around in misery. When treating Parkinson's disease, DBS is often used to essentially put the basal ganglia out of commission. And it doesn't seem to affect people very negatively. So if these two structures are so incredibly important, why do we seem to manage so well without them? I have no idea. + +​ + +Some researchers argue that the basal ganglia in humans mostly controls the *vigour* of movement. I'm not sure what I think about this idea. + +​ + +One idea I'd like to leave with you with is the idea that automatization of behavior is remarkably similar to organizational structures in human groups. There's a leader, like the prefrontal cortex, that decides on the overall goal and how it should be achieved. The leader shouldn't concern itself with minute details, just the overall progress toward the goal. Similarly, humans tend to ""space out"" when their attention is not required. What I believe actually happens is that attention moves where it is most useful. While lower brain areas steer your car towards your destination, you engage in (relatively) incredibly complex simulations of the future, such as planning what you will be having for lunch. This is beyond the scope of most organisms on the planet. You are acting not on the actual world, but on a model of it that is so exact that you can treat it as a substitute for the real thing. This should blow our minds more than it does. + +​ + +Acquiring ""muscle memory"" is the process of delegating trivial motor activity to subconscious processes so the conscious part can focus on more important issues. + +​ + +/rambling" +1479 "In stars with enough mass to collapse into a black hole specifically, what causes the ""shock wave"" that blows apart the rest of the star in a supernova?" 128 https://www.reddit.com/r/askscience/comments/d45516/in_stars_with_enough_mass_to_collapse_into_a/ 1568467482 d45516 2019-09-14 16:24:42 +1150 Did the advent of the Nuclear Age have a spectroscopic effect on our atmosphere if viewed from another solar system? 127 https://www.reddit.com/r/askscience/comments/9joj38/did_the_advent_of_the_nuclear_age_have_a/ 1538152685 9joj38 2018-09-28 19:38:05 The closest thing you could look for would be the flash itself. It would be nearly impossible to distinguish from the neighboring star, current tech couldn't do it, but it would be the easiest thing to see. there is not going to be enough radioactive isotopes produced to create a spectroscopic signature. "The nukes themselves would be very unlikely to be noticed. The vast majority of the material put into the atmosphere by a detonation is going to be ordinary dirt and dust. Occasional atoms in that dust will have undergone nuclear transmutation into unusual materials, and the bomb components themselves could theoretically be detected, but we're talking about amounts as low as a few pounds distributed across hundreds of miles of atmosphere, and rapidly decreasing to boot. + +One nuclear-age product, however, would have been an excellent sign of intelligent life - CFCs. Commonly used in refrigerators and responsible for the hole in the ozone layer, these chemicals can not be produced by any known natural process. Thousands of tons were released before they were banned, and it takes years for them to break down. Any aliens doing a spectrographic analysis on us at the time would have had a pretty good indication that there is intelligent life on Earth." +1615 Black Lives Matter 124 https://www.reddit.com/r/askscience/comments/gvc7k9/black_lives_matter/ 1591120666 gvc7k9 Social Science 2020-06-02 20:57:46 "**Organizations supporting diversity in STEM:** + +- African American Women in Technology (http://aawit.net/) + +- National Conference of Black Political Scientists (https://www.ncobps.org/) + +- Women of Color Research Network (https://womeninscience.nih.gov/women-of-color/) + +- Women of Color Advancing Peace and Security (https://www.wcaps.org/) + +- Association of Black Women Physicians (https://www.blackwomenphysicians.org/) + +- National Association of Black Geoscientists (http://www.nabg-us.org/) + +- Black Girls Code (https://www.blackgirlscode.com/) + +- National Society of Black Engineers (https://nsbe.org/home.aspx) + +- National Black Nurses Association (https://www.nbna.org/) + +- National Association for the Professional Advancement of Black Chemists and Chemical +Engineers (https://www.nobcche.org/) + +- Society of Black American Surgeons (https://www.sbas.net/) + +- Association of Black Psychologists (https://www.abpsi.org/) + +- Society of Hispanic Professional Engineers (https://www.shpe.org/) + +- American Indian Science and Engineering Society (https://www.aises.org/) + +- National Action Council for Minorities in Engineering (https://www.nacme.org/) + +- Women in Science and Engineering (https://www.wisecampaign.org.uk/about-us/) + +- LGBT+ STEM (https://lgbtstem.wordpress.com/) + +- Out in Tech (https://outintech.com/) + +- Pride in STEM (https://prideinstem.org/) + +- Out in National Security (https://www.outinnationalsecurity.org/) + +**Know of any others? Please leave a comment below!**" "According to Wikipedia, Native Americans are killed most often per capita than any other race in America. + +> The rate of fatal police shootings per million was 10.13 for Native Americans, 6.6 for black people, 3.23 for Hispanics; 2.9 for white people and 1.17 for Asians. + +https://en.m.wikipedia.org/wiki/Police_use_of_deadly_force_in_the_United_States + +When accounting for poverty / wealth, racial bias practically disappears. + +https://replicationindex.com/2019/09/27/poverty-explain-racial-biases-in-police-shootings/ + +If these are accurate, then it brings up a couple of questions to me. Why is there still a large discrepancy in poverty levels in the different races and ethnicities in the US? Why does poverty lead to crime in such a large degree? If reducing poverty reduces crime rates and police homicides, can we decrease the poverty level without dragging the rest of the nation down?" +1505 AskScience AMA Series: I am paleontologist Hans Sues, I study late Paleozoic and Mesozoic vertebrates. Ask Me Anything! 123 https://www.reddit.com/r/askscience/comments/g13hb7/askscience_ama_series_i_am_paleontologist_hans/ 1586862007 g13hb7 Paleontology 2020-04-14 14:00:07 "Just got the most hilarious commentary with the lovely headline ""You are stupid - but Satan loves you"" + +I quote: + +""Just seen you going to answer questions on Reddit about Palizoic and Mezosoic eras being what you claim are 65 to 540 million year ago. + +You're obviously a simpleton but even so you may be able to operate a calculator and work out this equashun: Earthworms build topsoil at the rate of one inch per five years. + +Therefore if Earth was 540 MYO there would be 540 divided by 5 = 108 million inches of topsoil everywhere. + +Clearly there isn't and therefore you head has been stuffed with garbage. + +Darwin actually proved Earth is young and The Flood was a worldwide catastrophe about 4,350 year ago and during the 330 days of downpour, inundations, drain-off and drying all the land creatures were buried in deep sediments that idiots like you label Mesozic, Cretinous etc. + +Mary Schweitzer has had the grace to admit that she know her silly 65MYO dinosaur tissue is wrong but she is going to believe it anyway - so why are you so deluded as to believe there was masses of dinosaurs 540 MYA? + +Instead of prattling nonsense why not do the world a favour and go poking about the secret storerooms and drag out some of those Nephilim giant bones?"" + +This, folks, is why we need to get better science education in our schools!" What is the general feeling about professional fossil hunters in academia? +1480 Is capillary action free energy? 118 https://www.reddit.com/r/askscience/comments/d3u27i/is_capillary_action_free_energy/ 1568401992 d3u27i Physics 2019-09-13 22:13:12 "For capillary action to occur, the liquid in question has to wet the surface of the capillary. So the gravitational potential energy is offset by the energy gained from the wetting of the liquid to the capillary surface. This leads to a quite nice and intuitive mathematical description for the height, h, the liquid moves up the capillary (called [Jurin's law](https://en.wikipedia.org/wiki/Jurin%27s_law)): + +>h = 2 γ cos(*θ*) / *ρ*rg +> +>h = height +> +>γ = surface energy of liquid +> +>*θ* = liquid-surface contact angle +> +>*ρ =* liquid density +> +>r = radius of capillary +> +>g = gravitational constant + +This can be thought of as essentially a ratio of the interfacial energetics (top) and the gravitation energetics (bottom). The greater the affect of gravity, e.g. more dense the liquid or a stronger gravitational field, the lower the height. Counter to this, the greater the interfacial affects the higher the height." In addition to what was already mentioned, you would need to put energy in the system to reverse the process. Right now, you probably have a lot of potential energy with respect so some deep pit somewhere, despite the fact you personally never put in the energy to climb out of the pit (since you never found yourself inside it). You could in theory exchange that potential energy for kinetic by jumping into it, but in the great scheme of things, conversion of energy is not violated. +1701 Why do some vaccines require a booster shot a few weeks later after the first one? 113 https://www.reddit.com/r/askscience/comments/jwruhm/why_do_some_vaccines_require_a_booster_shot_a_few/ 1605744585 jwruhm Medicine 2020-11-19 3:09:45 "In simple terms, the first vaccine exposes your immune system to the virus (or bacteria, etc) so your body learns to fight. Sometimes to have lasting response your body needs a boost (sometimes said to “challenge the immune system”), which primes the immune system creating a more lasting immune response in the body. + +Not all vaccines require boosters; there are a lot of variables involved. When we do research we look at immune titers at several intervals (days, weeks, months) post-dose to see if they drop below the immune response threshold... this tells us if we need to prime the immune system again with a booster." "There's also a fascinating phenomenon with vaccinating infants. If the mother has had exposure to the pathogen in the past, or been vaccinated against it herself, she will be carrying antibodies against that pathogen. During pregnancy, some of those antibodies go through the placenta to the baby, so when it is born it has some protection against the pathogen. This is known as passive immunity. + +Now, the protection isn't as lasting as that the baby would get from its own immune system, but it's better than nothing (get your pregnancy vaccinations ladies!), and gives some protection while the baby's immune system is still developing. + +Because the immune protection is the mum's antibodies, not made by the baby itself, once those antibodies begin to reduce, the baby no longer has any immunity to the disease. But while the antibodies remain, any vaccine delivered is reduced in its likelihood to elicit an effective immune response, as the baby already has antibodies against the vaccine, so the threat is destroyed before the baby's immune system has enough time to process its own response. This is a great thing, because if the baby doesn't have sufficient protection left from the mum to fight off the pathogen, the vaccine will stimulate it to generate it's own response. + +A great example is MMR. It's safe and licensed from the age of 6 months, but it's only routinely given from age 12 months, as circulating antibodies from the mother mean that vaccine given before 6 months, will not provide lasting immunity, so the entire course needs to be repeated at 12 months. If you are in an area with a high rate of measles, you can request the vaccine from as young as 6 months, but you still need the full course later." +1821 AskScience AMA Series: Hi! I am Tel Aviv University cancer biologist, Prof. Neta Erez. I'm developing a novel approach to treating breast cancer. Ask Me Anything! 110 https://www.reddit.com/r/askscience/comments/lws8ge/askscience_ama_series_hi_i_am_tel_aviv_university/ 1614772805 lws8ge Biology 2021-03-03 15:00:05 What would you most like to tell us that no one ever asks you about? Thank you for doing this AMA. I’m a researcher embarking on my first project investigating the microenvironment of aggressive tumors. An overarching theme of such research is to identify “targets for novel therapeutics” as you say. I’ve never actually had the chance to ask anyone about this ultimate goal. Does this mean that your role as a researcher is to elucidate a mechanism in the tumor micro environment, and then some industry folks take on the task of drug discovery to target that particular mechanism? If so, how do we ensure beforehand that this same mechanism isn’t at play outside the tumor microenvironment? I’m curious about the journey from “bench to bedside” in this field. +1481 Why are planets always round? (Not a flat earther at all here btw) just wondering why a planets are not a more random shape? 106 https://www.reddit.com/r/askscience/comments/dlv5la/why_are_planets_always_round_not_a_flat_earther/ 1571811568 dlv5la Planetary Sci. 2019-10-23 9:19:28 "The definition of a planet has a few criteria and one of them is that it has to be round. So if an object isn't a sphere, we wouldn't call it a planet. + +But that's a bit of a lame explanation. The reason why the things we call planets are round (and the reason that we added ""being round"" as a requirement for something to be called a planet) is that a sphere is the most energy efficient state for an object to be in when its own gravity is sufficiently strong. + +So if a celestial body becomes large enough, its gravity will automatically force it more and more towards a spherical shape. Imagine an object that is otherwise spherical, but contains a large mountain-like structure sticking out from the spherical surface. A rock will roll down from this mountain without requiring additional energy input. This rock rolling down the mountain brings the object closer to a spherical shape. But rolling a rock from the surface up the mountain, making the object less spherical, requires some external force. + +So any objects in space that are not spherical are simply too small for their own gravity to pull them together into a ball." "Imagine holding up a magnetic pebble—no matter the shape. Then have another pebble stick to it. Now add a third and ask yourself: where would this go, such that all pebbles attract one another as equally as possible? Would it go on top of the second so as to form a line? No, because it wouldn't stick to the first, so it'll go right next to them both, making a little triangle, so to speak. Now add a fourth, ask your self the same thing, and you'll find that there's a place next to all three, forming a pyramid, and so on. + +You'll find that no matter the shape of your pebbles, if you add enough, by the time you have a bundle the size of your fist, you'll see it take on a spherical shape. It won't be perfect of course, and if you throw it at something it'll bust up, but most things aren't thrown into other things, especially in space. + + +Now let's approach this another way: if you did make a line out of, say, fifty pebbles, and if they would fit in your jacket pocket given the right shape, what shape would that be? As a line, they'd dangle out of your pocket, and as a sheet they might not fit. You'll find that when you try to compress these pebbles to take up as little space as possible, they'll again arrange into an imperfect sphere. + + +As it turns out, particles in terms of gravity aren't biased towards other particles as much as they are in terms of magnetism. The pebbles above very much want to click to the nearest one, but on the scale where gravity is the determining factor everything wants to stick to everything roughly just as much. That's why a pebble rolls down hill: it's much closer to the collection of pebbles that make up the planet than if it were on top of the hill, just like your pebble was much closer to the rest if it completed a triangle of three or a pyramid of four, etc. + + +And that's geometry for ya." +1151 1 Why do pressed/dried leaves retain most of their bright colors instead of turning brown? 105 https://www.reddit.com/r/askscience/comments/9gs8zi/1_why_do_presseddried_leaves_retain_most_of_their/ 1537250744 9gs8zi 2018-09-18 9:05:44 "The pigments in plant leaves are of organic origin. These differ from pigments that are of mineral origin. Most organic pigments have double bonds with delocalized electrons primarily between carbon atoms...such as C=C=C, and the nature of these bonds determine to a large extent the color of the pigment. Mineral pigments derive their color from presence of various metal ions. + +Photons of energy from the sun and oxygen in the atmosphere can break the double bonds between the carbon atoms found in organic pigments. These processes cause the degradation of the various colored pigments. When all colored pigments are lost (e.g., green, red, yellow, etc.) the leaf takes on a brown color. + +Now to your question...the reason pressed leaves, if stored properly , lose very little color is because they are placed in a dark environment and kept away from photons of light energy. The level of oxygen in a isolated box kept in the dark also would lessen, but not completely, thus the reason all pressed leaves do gradually lose some color and begin to fade. I think you can now determine why leaves on the ground all turn brown before winter. " "Leaves, like all biological matter, decompose. This happens in two ways - biological decomposition and chemical degradation. + +Biological decomposition is by far the main component here. When the leaf falls to the ground it is eaten by small invertebrates and microogranisms, fungi and bacteria. These, like all life, are to some extent, dependent on water. Even more so for simpler microorganisms. Water is universal to all life, and a damp, energy rich substrate like a dead leaf will be colonized and eaten (""decomposed"") quickly. + +Take an identical leaf, but keep it perfectly dry - now you have made it significantly more difficult for microorganisms, especially fungi, to colonize and eat. They need the moisture. + +Keeping things really dry is a an age old preservation technique to keep microbes away. + +The second component is chemical degradation. Organic structures are large complex chemical structures. The bonds between them are based on probability, and while it can spontaneusly change into a more simple chemical configuration, it can not change back into a higher energy configuration/more complex (see Entropy). As such, things break down, slowly, by themselves. + +The main culprit is Oxygen. Oxygen is highly reactive. It is why most all life use it as the oxidizer for our fuel/energy source (""food""). Sugar/wood/high energy organic structure mixed with Oxygen, add some heat, and you have a fire. Oxygen is what makes a fire. Our cells burn sugar and oxygen, but we do it in several steps, so we get the energy out in small bursts, not as a run-away fire. So, oxygen reacts with mostly everything, one chemical bond at the time. (Oxidative stress, one of the main reasons we age/wear down). Provide sun-light (high energy radiation), and the process will go a lot faster. UV-B and UV-C is the part of the sunlight that gives you sunburns and skin cancer. It literally breaks down organic molecules, including your skin, and it damages DNA. Oxygen and added energy through sunlight degrades mostly everything. + +So, keeping the leaf dry wards off microbial decomposition, keeping it dark and sealed away from the air protects from the majority of chemical degradation. + +As a side note, the beautiful colors of living leaves indicate that they are able to absorb some parts of the visual spectrum - these pigments are reactive and short lived. They are especially sensistive to degradation, and brilliant colors are a reoccuring theme in nature, in the form of sexual selection - showing off vibrant colors shows of good strong health to a partner. + +Source: I am a biologist (EDIT: spelling)" +1702 Question about whale blow hole muscles: are the muscles designed to keep the blowhole open or closed? Does it take more muscle to open? 102 https://www.reddit.com/r/askscience/comments/kfbrle/question_about_whale_blow_hole_muscles_are_the/ 1608257232 kfbrle Biology 2020-12-18 5:07:12 They are sphincters, much like your arsehole. And also like your arsehole, there is an outer one which is consciously controlled, and an inner one which is unconsciously controlled. So it’s a bit of both really. "Blow holes are specailized nostrils, they are connected directly to the trachea, when they dive it automatically contracts tightly by strong muscles that surround it, so that water cannot get into the whale or dolphin’s lungs. + +When they surface to breath again they forcefully exhale the co2, similar to blowing your nose" +1482 Why does some thunder make a boom sound and sometimes it makes a crack/snap sound? 98 https://www.reddit.com/r/askscience/comments/d9ethw/why_does_some_thunder_make_a_boom_sound_and/ 1569472774 d9ethw Earth Sciences 2019-09-26 7:39:34 """Cloud-to-ground lightning that discharges fairly close to you will produce a sharp clap or crackle of thunder as the strong sonic shockwave from the part of the bolt nearest your position reaches you first. + +A drawn-out, subsiding roll of thunder follows as your ear registers shockwaves from higher and more distant parts of the bolt’s channel. + +If you’re some distance from a thunderstorm, you may only hear rolling or pealing thunder."" + +https://sciencing.com/difference-between-rolling-clap-thunder-6906574.html" +1483 Why does the hair on our heads and faces continue to grow unabated, while our body hair essentially grows to a certain length and then stops? 96 https://www.reddit.com/r/askscience/comments/d0gnbt/why_does_the_hair_on_our_heads_and_faces_continue/ 1567776393 d0gnbt Biology 2019-09-06 16:26:33 Facial hair does not actually grow forever. Every male has a terminal length of facial hair. For some it may only be a quarter inch, for others it may be many feet. But eventually, it stops and will not grow any longer. "All hair follows the same process that your body hair follows, which is grow to a certain length, die and fall out, and then start regrowing a new hair in its place. The reason this is more noticeable for body hair than it is for hair on your head is the maximum length the hair will reach is much longer for the hair on your hair than it is the hair on your body. + +You can equate it to a human needing sleep. We are awake for a certain consistent amount of hours until our body’s need another consistent amount of rest. Hair follicles do the same thing, where the go through a long period of growing, and then a short period of rest (where the previous hair falls out) before it can start growing again. This process goes through three stages. + +The first stage is the stage where your hair is actively growing. The overwhelming majority of your hair will be in this stage, but each hair will be at its own individual place during that process. While each hair will be at different parts of these stages from each other, they will generally all grow at the same rate determined by your genetics. This stage generally lasts 3-5 years. + +Then it goes through a transitional/renewal stage where melanin production and hair growth stops. This lasts a couple weeks. + +Then the final resting stage is when the old hair falls out. This lasts roughly a couple months. Then the first stage starts again and it starts growing. + +Most people keep their head hair and beard much shorter than the maximum length it can grow. Although there is a lot more variance in beard length, ranging from not being able to grow one at all or having it never grow longer than a very short length all the way to being able to grow out a few feet long wizard beard." +1484 When the end of a garden hose is oscillated, the water will make curves in the air. If a laser pointer oscillated fast enough and you had a camera quick enough, would the resulting image show the light behaving similar to the water? 96 https://www.reddit.com/r/askscience/comments/djwjhy/when_the_end_of_a_garden_hose_is_oscillated_the/ 1571445414 djwjhy Physics 2019-10-19 3:36:54 "The water flying through the air isn't actually curving. You're just looking at a bunch of individual bits of water moving at their own trajectory which creates the shape of a curve. If you track one section of water you will see it fly out in a line straight from where the hose ejected it while falling to the ground. + +Your laser pointer would act the same way. You would get the same appearance of a curvy wave of light (assuming there are particles along the way for the light to bounce off of and reflect back to you,) but if you looked at the path of an single section you would see it moving out (at c) in a straight line from where the pointer emitted it." "Yes. + +The effect is known as the *aberration of light* or *relativistic beaming*. The apparent direction of light will change due to relative motion of the source and viewer, resulting in the apparent position of the light source changing. + +(By the principle of relativity, it doesn't matter whether you regard yourself as stationary and the light source as moving, or vice versa). + +Earth's orbital motion around the Sun is fast enough to produce a measurable shift in the apparent positions of the stars, of around 20 arc seconds. (This is much greater than stellar parallax.) This is how the effect was first discovered." +1152 Does the pilot-wave interpretation of quantum mechanics require an absolute reference frame that is incompatible with special relativity? 95 https://www.reddit.com/r/askscience/comments/9h6p4h/does_the_pilotwave_interpretation_of_quantum/ 1537374807 9h6p4h Physics 2018-09-19 19:33:27 "It does require a preferred frame, which means there is only one foliation into spacelike hypersurfaces over which the particle trajectories are actually classically deterministic (which is the essential promise of the interpretation). Working in other frames, the Bohmian trajectories zig and zag in random, unpredictable ways. In particular, this can be understood via working out the pilot wave trajectories in EPR experiments. If one could observe these trajectories, one could use these random zigs to figure out (by process of elimination) which frame was preferred. But it is also a requirement of the interpretation that one can't ever access these trajectories at the level of granularity required to achieve this. So strictly speaking it is not consistent with SR, but the problem can be kept under the rug for practical purposes. Whether this is philosophically acceptable is up to you. And pilot wave adherents tend to be willing to abandon exact Lorentz symmetry as a guiding principle. + +But preferred frame aside, remember that the pilot wave interpretation is also presented in terms of fundamental particle-like entities, while the union of quantum mechanics and special relativity produces quantum field theory, where particles are not really fundamental in this sense. To the extent particles exist at all in QFT, they instead are more like structured patterns in the fields. There is no broadly accepted or worked out pilot wave interpretation of quantum fields, and the idea is not particularly promising. The basic problem is that in QFT there is no analogue of QM's position operator. In QM, particle position can make sense as the defining hidden variable in all cases. In QFT, there is nothing that can perform this role. + +Additionally, there is no known way to do particle creation and annihilation in a classically deterministic way, even in a pilot wave interpretation. So when we demand this other important feature of QFT, the whole endeavor to save classical determinism fails anyway." +1485 How does a computer determine if a given number is larger than another number? 95 https://www.reddit.com/r/askscience/comments/dseuao/how_does_a_computer_determine_if_a_given_number/ 1573038652 dseuao Computing 2019-11-06 14:10:52 "###**TL;DR: they subtract one number from the other and check if the result is positive or negative. If you want more math, keep reading.** + +Typically, a computer will represent binary numbers in a slightly more complicated way than you may have been taught in school. + +Positive binary numbers are simple enough. They work like regular numbers, except you only use ones and zeros, i.e. counting up from zero is 0 -> 1 -> 10 -> 11 -> 100 -> 101 etc. + +Negative numbers are represented a little differently though. Basically minus one is ""11111"", with as many ones as the size of the register. That means that an 8 bit storage will represent negative one as 11111111 while a 4 bit storage will represent it as 1111. Negative two is 1110, three is 1101 and so on. It sort of ""counts down"" (this standard of binary negative numbers is called Two's Complement numbers, and is the most common because of their versatility). + +This means that you can also tell if a number is negative simply by looking at the first binary digit (bit). If the first bit is 1, it is negative. + +This is useful for many reasons. First of all, you can add negative numbers to other numbers correctly. If you add three to negative one with four bit registers, that is, 0011 + 1111, for example, you get 10010. As a computer does not add more bits if the number is bigger, you get something called an ""overflow"", and the computer basically ignores the extra bit at the end, so the answer is still 4 bits. The answer the computer comes up with is, in other words, 0010, which is two. The computer added negative one to three correctly! + +You can also subtract easily. Simply by inverting the number you want to subtract and adding one you can add it and get your answer. Let's try to subtract positive 1 from 3. Three is 0011, and one is 0001. + +Inverting one means you switch all bits to the opposite, so 0001 becomes 1110. You then add 1 and get 1111 (which you may remember is -1, inverting a binary number and adding one is always the same as multiplying it by -1). You can then add this to 0011 and get 0010 once you get rid of the overflow. It worked! + +So what does this have to do with size comparison? + +Well, a computer can easily subtract one binary number from another, and that number will be either positive, zero, or negative. Positive binary numbers and zero always have their first digit as 0, and negative numbers always start with 1, as I've already explained. This means that the computer can subtract one number from the other and immediately look at one single bit (called the sign bit, always the first/most significant one in the memory register) and tell wether this number is zero or greater, or less than zero." "Here is an example of how 2 numbers in binary can be added with the use of logic gates: [https://cdn.instructables.com/FP1/ZI2I/GHX77248/FP1ZI2IGHX77248.LARGE.jpg](https://cdn.instructables.com/FP1/ZI2I/GHX77248/FP1ZI2IGHX77248.LARGE.jpg) + +there you have one number (A) that can be 1 or 0, and another number (B) that can be 1 or 0, and the sum can be 00=0, or 01=1, or 10=2. + +The 0 or 1 can represent low current/high current in the wire. + +And the logic gates work this way: [https://www.youtube.com/watch?v=7ukDKVHnac4](https://www.youtube.com/watch?v=7ukDKVHnac4) + +You could also make a mecánica ""transistor""/logic gate: [https://twitter.com/page\_eco/status/1188749430020698112](https://twitter.com/page_eco/status/1188749430020698112) + +From them you can have two numbers 00101001, 10010111, and subtract them or whatever to get another number, or find which number has the first non zero digit, etc. All with lógica gates (AND, OR, NOT)." +1486 Are fingerprint mutations (such as a random patch of dots instead of lines) common? 93 https://www.reddit.com/r/askscience/comments/dnx1tp/are_fingerprint_mutations_such_as_a_random_patch/ 1572199238 dnx1tp 2019-10-27 21:00:38 It's called dysplasia. It's not very common. It does mess with the ID of your print. There are various causes. Were you born with it like this, or did this develop over time? +1487 How are nuclear arms/weapons safely created and stored to prevent accidents related to arming and detonations? 91 https://www.reddit.com/r/askscience/comments/dob7ra/how_are_nuclear_armsweapons_safely_created_and/ 1572280132 dob7ra 2019-10-28 19:28:52 "You can sort of chunk the history of US nuclear weapons safety into a few broad categories: + +* 1940s through early 1950s: The early weapons were _very dangerous_ once assembled. They had very few safety protections. They could be set off by lightning, fires, what have you. The main safety precaution was that the nuclear core of the weapon could be removed from the non-nuclear components and stored separately. So the odds of them going off were very low, because they weren't assembled until they were intended to be used. So in a sense these were very dangerous weapons (once assembled!), but very safe the rest of the time. + +* 1950s through 1960s: The development of ""sealed-pit"" weapons made it so that the cores were now permanently part of the weapon. Safety procedures were relatively poor but not terrible — there were ""[ready/safe](http://blog.nuclearsecrecy.com/wp-content/uploads/2013/09/Mk-39-ready-safe-switch.jpg)"" switches that would interrupt the firing signal if it was sent inappropriately. They started adding ""environmental sensors"" that would making a firing order unlikely to complete if the weapon wasn't under ""realistic"" war conditions (like falling through the air). They did tests to try and make sure that if one of the conventional explosives did go off, the weapon was ""one-point safe"" and unlikely to generate a nuclear yield. (Not all weapons designs were, and sometimes engineering ""hacks"" were used to make them safer. One warhead had a reel of neutron absorbing material inside of its hollow core that could be withdrawn upon use; it turned out that this made the warheads very unlikely to fire correctly and they all had to be fixed.) This was a time of _many_ nuclear accidents, fortunately none of which generated a nuclear yield. But it came close-enough that people started to worry about it very seriously in the late 1950s, and start creating better regulations and engineering guidelines to make them safer. + +* 1960s to the present: Continual review of weapon safety, integration of technologies meant to make accidental nuclear use very unlikely, such as using insensitive high-explosives that basically won't detonate unless you set them off in exactly the right way. The integration of Permissive Action Links (PALs), electro-mechanical ""locks"" on the weapons, so that unauthorized use can't occur. Better creation of ""strong"" and ""weak"" links to make it so that under adverse circumstances the weapon won't possibly have a nuclear yield. Etc. I don't want to make it sound like everything from the 1960s onward was super safe — some warheads weren't — but they started taking this very seriously and started taking advantage of safety techniques so that they could be pretty sure that no matter _what_ you did to a nuclear warhead, you wouldn't get a nuclear yield unless you were authorized to get one and were using it under the right circumstances. + +For a very readable overview of this history, see Schlosser's _Command and Control_. For a video version, Sandia National Lab's three-part _[Always/Never](https://www.youtube.com/watch?v=DQEB3LJ5psk&feature=youtu.be&list=PLouetuxaIMDrht4F8xiS4AY-oLvCq77aA)_ does a great job of explaining it, with the engineers and physicists who were involved talking about what they did and what they were afraid of happening." "Very simple explanation: + +So the core is required to be compressed in order to achieve a real nuclear blast. The core is a ball of reactive material, like plutonium. It is surrounded by shape charges that blast inward. +Out side of that is material that add to all detonation, but not relevant here. + +In order to to achieve total detention every shape-charge must be activated at the exact same time to press the core as small as possible. + +This requires a timing trigger since the wires aren't all the same length. + +The trimmers are what are placed in the weapons to ""arm"" them. At that point they are dangerous. + + +Before that, if one was compromised it would be a fairly light conventions detonation with some radioactive debris. If that debris is in an underground silo, it's not so bad (from a contamination view) since it's contained. + +There are all sorts of safeguard based on material choice for housing, etc. But basically these things area designed not to detonate without the timing trigger being manually installed and activated." +1822 What's the latency of the Mars rover Perseverance regarding communications to earth / commands from earth? 90 https://www.reddit.com/r/askscience/comments/lr85bn/whats_the_latency_of_the_mars_rover_perseverance/ 1614157162 lr85bn Planetary Sci. 2021-02-24 11:59:22 "The latency of interplanetary communication is limited by the speed of light. The one-way path between Earth and Mars will take anywhere between 3 and 20 minutes (approximately) depending on where the planets are in their orbit. So a the round-trip-time of a message would be between 6 and 40 minutes. + +Improvements to signal processing on either side of the transmission will have negligible impact on the total latency. It's all about the distance and the speed of light, neither of which are things we can change." "While you specifically call out latency, your overall question is whether the *communication* got faster. + + ""Speed of communication"" is the result of two factors: latency and bandwidth. Latency is the speed limit on the highway, bandwidth is the number of lanes. Imagine you have a 1 lane highway that takes 1 minute to drive and a 5 lane highway that takes 2 minutes to drive. More cars get through the slower highway in the same amount of time even though it is ""slower"". + +(Or my favorite example is a pigeon flying with a USB stick tied to its foot versus a person signalling using a flashlight in morse code. The signal flashlight moves at nearly the speed of light, but to communicate the works of shakespeare will take forever. But the pigeon can carry all the works of Shakespeare in one slow flight.) + +It appears the bandwidth of Preserverance Rover to orbiter is 2000 kbps. For reference, Curiousity to orbiter was only 250kbps (if I am reading the articles right.) + +Communication of same amount of info from Rover to Orbiter is faster than same amount of info from Curiousity to Orbiter, but the latency is not faster. + +Edit: Ah, I see you were talking about commands. For a command system to feel responsive, you need a latency of about 500ms or less at most human speed activities. Since the latency is 3 minutes at minimum... Not even close. However, bandwidth does affect the rover's ability to communicate video and sound and other large chunks of data, so the increased bandwidth does affect what we are getting from the rover (not so much what we send to the rover.)" +1823 Why can't we have contagious vaccines? 89 https://www.reddit.com/r/askscience/comments/lqniul/why_cant_we_have_contagious_vaccines/ 1614100402 lqniul Medicine 2021-02-23 20:13:22 "Vaccines aren’t always viruses, we currently several types of vaccines + + +1) killed virus, basically you grow the actual virus then kill it and give it to people dead, this way they react to it without mounting infection. Problem with these is that the killing process can alter the protein so immunity is not perfect + +2) live attenuated: the live virus but has been altered to be weaker, causing the virus to make a reaction but without full blown infection, problem with these is that it can cause disease in immune suppressed people, and can potentially become strong again + +Both these types aren’t as commonly used these days, atleast not for Covid in the western world. + +3) viral vector: a harmless but different virus that has been genetically modified to contain proteins of the virus you want to target, so you get reaction to both the vector and the disease causing virus. I think the Russian and Chinese Covid vaccines are of this type. Problem with it is that if you have the same or similar vector virus in a previous vaccine, your body may kill it too quickly to notice the new protein. + +4) recombinant protein: you create a protein of the target virus in the lab and give it to people, problem with it is that the protein made in the lab may look a little different than the same sequence made in human cells ( it is not just the sequence but also how the protein folds is how the immune system identify them) + +5) the newest type which is mRNA, these are the moderna and Pfizer vaccine, you just get a piece of Viral RNA (made in the lab) which your body takes abs creates the protein out of it probably for a couple days, the advantage here is that you get a more persistent exposure for the target protein and that protein is being made by your cells so it looks more like that produced by the actual virus ( the virus itself replicates by forcing your infected cells to make the new copies) + +Now back your question + +It is theoretically possible to create a contagious vaccine, of the above types 2 and 3 but that is a bad idea fir the following reasons + +A) if the vaccine turns out to cause bad side effects, then your screwed, you just created a whole new disease running around + +B) even a vaccine safe in most people can be unsafe in certain groups, like pregnant women, or immune compromised people, a contagious vaccine will reach them and cause damage there + +C) Your contagious vaccine can mutate in the wild abs loose its effectiveness, the people will be immune to the vector virus and won’t respond well to other vaccines + +D) People need to consent to receiving the vaccine, a contagious vaccine will be forced on others which is unethical" "The current widely-available COVID vaccines are a string of RNA bound in a package that lets it enter your cells and convince them to make a particular protein. + +The COVID virus is a string of RNA bound in a package that lets it enter your cells and convince them to make more of itself. + +A contagious, self-replicating vaccine is literally a virus." +1703 "Why is the mRNA vaccine more expensive than the ""classic"" vaccines?" 87 https://www.reddit.com/r/askscience/comments/kfq15w/why_is_the_mrna_vaccine_more_expensive_than_the/ 1608314175 kfq15w Medicine 2020-12-18 20:56:15 "Just a correction: the AstraZeneca platform is NOT a ""classic"" vaccine platform. AstraZeneca (as are a number of others) are using a modified adenovirus platform and that platform has only been used in vaccine development for about a dozen years. It is highly unlikely that you or any significant number of people reading this have ever received an adenovirus-based vaccine. Edit: here is a good review of the platform: [https://www.intechopen.com/books/adenoviruses/adenoviral-vector-based-vaccines-and-gene-therapies-current-status-and-future-prospects](https://www.intechopen.com/books/adenoviruses/adenoviral-vector-based-vaccines-and-gene-therapies-current-status-and-future-prospects)" "New production lines, paying for R&D, the storage requires colder, more expensive to buy and operate freezers, and therefore more expensive shipping too. + +There's also a level of risk present that many other vaccines don't necessarily face that could also factor into pricing." +1488 "Do blood vessels have a ""preference"" in where (or how) they develop?" 85 https://www.reddit.com/r/askscience/comments/d5thu7/do_blood_vessels_have_a_preference_in_where_or/ 1568786571 d5thu7 Human Body 2019-09-18 9:02:51 "Oh something I can chime in on. (someone more knowledgeable please chime in if you can) + +So I will only speak about blood vessels growing from preexisting blood vessels (angiogenesis) because I have no clue how it works during fetal development. + +Angiogenesis is controlled by various angeogencic proteins, the mechanism I'm not certain of. But essentially cells release these proteins and the blood vessels ""grow towards"" the proteins. + +There is evidence that reactive oxygen species (especially in cancer) have a role to play in increasing the rate of angiogenesis and as a result it has been considered that NoS produced during exercise can increase angiogenesis in an area. Much the same way cancer does. + +So in essence, yes there is a preference, blood vessels will grow with regard to angegenic protein concentrations. + +If you look at cancer, cancer actively increases angiogenesis in order to gather needed resources and one treatment is to reduce this effect by inhibiting angiogenesis some how. + +[Check out the wiki, it's pretty extensive.](https://en.wikipedia.org/wiki/Angiogenesis)" "This is an area of active research. + +I know someone that did a PhD on the subject of angiogenesis. Somehow blood vessels know to grow in certain places and not others, for example they know not to grow across the front of your eyes otherwise we wouldn't be able to see. Therefore there must be some mechanism or mechanisms stopping them from growing in those places. The research was to see what prevents blood vessels growing in front of your eyes in the hopes of isolating the cause and replicating it. Many forms of cancerous tumor are able to encourage angiogenesis to feed the tumor with blood, if we could block it that would be one more tool in our arsenal of weapons against cancer. + +I'm summarising years of someone else's research into one paragraph based on my memory from skimming it at least four years ago, but I think the basic concepts are correct. As with almost all PhD research the conclusion was: ""It might be possible in theory, but we didn't get it to work properly""" +1489 AskScience AMA Series: We're a team of researchers from St. Michael's Hospital, and Peel Regional Paramedic Services in Toronto, Ontario, Canada who specialize in Cardiovascular Health and Resuscitation. 85 https://www.reddit.com/r/askscience/comments/dinnqo/askscience_ama_series_were_a_team_of_researchers/ 1571223602 dinnqo 2019-10-16 14:00:02 The AMA will begin at 12pm ET (16 UTC), please do not answer questions for the guests till the AMA is complete. Please remember, /r/AskScience has strict comment rules enforced by the moderators. Keep questions and interactions professional and remember, asking for medical advice is not allowed. If you have any questions on the rules you can [read them here](https://www.reddit.com/r/askscience/wiki/rules). Hi, I have heard there are differences in symptoms of a heart attack between men and women. Can you describe the similar and different symptoms men and women feel during a heart attack and how someone could identify that they're having one? +1905 Why are liquids almost always shiny/reflective? 85 https://www.reddit.com/r/askscience/comments/o0k1fs/why_are_liquids_almost_always_shinyreflective/ 1623778868 o0k1fs Physics 2021-06-15 20:41:08 "In general, a liquid can not have a rough surface (at small scale, not counting wind, etc.), as the surface tension in the liquid smooths out any irregularities, leaving a locally flat surface. And this ""flat"" surface gives you the shiny (specular) reflection." Liquids tend to have comparatively smooth surfaces when compared to solid surfaces. So you're likely to get specular and not diffuse reflection off of a liquid interface: liquids look shiny. +1906 What happens to a person dying of thirst if they drink seawater? 84 https://www.reddit.com/r/askscience/comments/o13haj/what_happens_to_a_person_dying_of_thirst_if_they/ 1623845761 o13haj Biology 2021-06-16 15:16:01 Our bodies maintain a very narrow range in concentration of sodium and chloride inside (intracellular space) and outside (interstitial space) cells. The only way to maintain this is through the diffusion of water down the concentration gradient. So as soon as the salty water hits the blood stream, your body will move water from the interstitial space into the blood, then water will move from the intracellular space into the interstitial space in order to equilibrate the concentration. This can have deleterious effects on your kidneys as it now needs to remove the excess salt by producing urine, which requires water. So it will further dehydrate you. Your body will also try to compensate from losing all these fluids by constricting your blood vessels to maintain blood pressure which is further damaging your body. Eventually you can go into organ failure, coma, and death. "One job of your kidneys is to get rid of extra junk (like salt or urea) in the blood. Unfortunately they can only produce a certain concentration of urine, so for each gram of salt excreted you need to expend a certain amount of water. Human kidneys only produce a maximum concentration less than that of sea water, so you use more water to get rid of the salt than you gain. Some other animals, such as cats, have far better kidneys and can get away with seawater. Actual marine animals may also have specialized organs for salt removal. + +There was a chap called Alain Bombard who experimented with drinking small amounts of sea water in addition to whatever else he could scavenge (fish blood, some rainwater...) when experimentally ""stranded"" at sea. In his experiments it worked, but he claimed that you needed to start on the seawater before severe dehydration. This is controversial. It *is* widely accepted that you can dilute sea water, say 2:1, with fresh water to extend your supply in many cases." +1704 How are Protons and Neutrons spherical when they're made up of three Quarks? 83 https://www.reddit.com/r/askscience/comments/kfmyro/how_are_protons_and_neutrons_spherical_when/ 1608304650 kfmyro Physics 2020-12-18 18:17:30 "Protons and neutrons are not necessarily perfectly spherical, and you can [calculate how much they deviate from spheres](https://arxiv.org/abs/hep-ph/0101027). + +But anyway, it seems like you're imagining nucleons as looking something like [this](https://media.sciencephoto.com/image/c0382742/800wm), as three discrete quarks with well-defined positions in space. But nucleons are quantum systems, and you can't think about them in that way." "As others have mentioned, the short answer is that they are not spheres. + +However this depends at what energy scales you are trying to probe the nucleon at! At low energies, if you throw an electron at a proton, it will scatter elastically (Rutherford scattering) as if the proton were a point source. + +As you move to higher energies, you are able to probe more details of the structure of the nucleon and will eventually see that not only is the nucleon made up of three valence quarks, but that half of the momentum of the nucleon is actually contained in the gluons which hold the nucleon together (as described by QCD). See [deep inelastic scattering](https://en.wikipedia.org/wiki/Deep_inelastic_scattering?wprov=sfti1) for some details. + +What we think of as the picture of a proton (as u/RobusEtCeleritas showed) is incomplete and highly simplified." +1490 This may sound dumb, but what makes glass shatter, and not split or crack in half? 82 https://www.reddit.com/r/askscience/comments/dncdpq/this_may_sound_dumb_but_what_makes_glass_shatter/ 1572087243 dncdpq Physics 2019-10-26 13:54:03 "Tempered glass shatters into tiny shards; plate glass breaks into large pieces. + +The tempering process cools and solidifies the outer parts of the glass while the inner layer is still expanded and molten. The solidified outer layer prevents the inner layer from shrinking, but the inner layer has to shrink as it cools. This sets up the inner layer under tremendous tension, and the outer layer under tremendous compression. + +This makes the pane stiff, and tough. You can throw a baseball at it, and it won't break. But, if the outer layer is damaged at all, even with a slight nick from a piece of gravel, the internal forces within the pane cause it to simply tear itself apart into tiny shards. + +Plate glass doesn't have these internal forces, so it just breaks into shards wherever the stress exceeds its elasticity." "By ""shatter"" you mean the spiderwebing you see on car windows in an accident? That's an intentional design through a process called ""tempering."" The energy imparted to the window on impact has to go somewhere. It can either be dissipated by propagating the force throughout the glass (the spider web effect) or it can be translated into motion. In that case, the glass becomes two (or more) very dangerous flying shards. + +The shattering effect is because the exterior of the glass is ""compressed"" while the interior is ""stretched"" (tension). This creates a ""pathway"" through the glass for the force to propagate, somewhat like the energy in a lightning bolt follows the ""path of least resistance"" to ground. + +You do see this effect in some static installations, e.g. plate glass in a window. The tempering process is a significant additional cost, and isn't required for situations where impacts are unlikely. + +For more information about how tempered glass is made, see the wiki. +https://en.m.wikipedia.org/wiki/Tempered_glass" +1153 Why aren’t underwater windmills more of a thing? 81 https://www.reddit.com/r/askscience/comments/9czq7k/why_arent_underwater_windmills_more_of_a_thing/ 1536095181 9czq7k Engineering 2018-09-05 0:06:21 "A few reasons, + +1. Maintenance. It's very costly to maintain underwater infrastructure. +2. Corrosion is a big problem in salt water environments. Meaning more maintenance is needed. +3. Biological buildup. Again in saltwater, the blades are going to end up getting fouled by barnacles and other aquatic life making them less efficient over time... also needing more maintenance. +4. Limited useful locations - Tides are predictable, but you need to be in a place like a narrow bay inlet where the water actually flows inland and Outland. Out along most places on the coast, there's not actually a lot of tidal flow, just rising water. An ideal sort of location might be under the golden gate bridge. These high flow areas tend to be murky... complicating maintenance. That useful water flow also complicates maintenance because you can't easily service in high flow times. +5. Lastly transporting that power requires infrastructure either underwater or on the shore. In many of the ideal locations, placing that infrastructure is probably politically complicated. + +Compared to wind turbines, the extra cost makes tidal systems less efficient over time. That's not to say there are no ideal places for it. It's just there are very few compared good wind production areas + +Hydroelectric is more or less the same sort of thing mechanically, but you end up harvesting the potential energy from falling water flowing downhill. Frequently hydro project serves other purposes like flood control, fresh water collection, habitat and recreation. These other factors offset some of the higher capital and maintenance costs. It's also something that can be controlled and called upon in a time of need whereas a tidal system would be more like solar where it is predictable, but not controllable. Wind is neither predictable or controllable." I’ve installed underwater turbines. They make a lot of power at first and then they fall apart. Blades snap, seals flood, nacelles fly off, drive shafts bend...and they’re made sturdily enough. As another commenter said, if the current is strong enough to make the power it’s strong enough to rip them apart. +1491 Allowed electron orbits seem odd and purely a mathematical construction. Are they just theory but reality gives more laxitude to where an electron might be? 80 https://www.reddit.com/r/askscience/comments/d1pizm/allowed_electron_orbits_seem_odd_and_purely_a/ 1568027908 d1pizm Physics 2019-09-09 14:18:28 "If you're a mathematician, I'd recommend reading more rigorous sources than A Brief History of Time. + +Electron orbitals are the stationary solutions of the time-independent Schrodinger equation. + +The electron having negative total energy (where ""zero"" energy is defined by a particle at r = infinity, with zero kinetic energy) imposes boundary conditions which lead to a discrete spectrum of bound states. + +The modulus-squared of the stationary solutions gives the probability density for where you'd find the electron in space if you measured its position." "> Does this mean we limit ourselves further to electron energies that have wavelengths longer than or equal to their orbital circumference so they can intefere? + +Equal or shorter, so you can get constructive interference. But ""wavelength of the electron in an atom"" is not a very well-defined thing, the ""wavelength"" depends on the kinetic energy which depends on the position. + +As a mathematician you can take the Schroedinger equation and find solutions to it - or at least follow the derivation of these solutions. That's the better approach, the wavelength/interference description is a hand-wavy thing for laypeople. The solutions that are eigenfunctions in the resulting space have discrete energies. + +These states are all stable with just the Schroedinger equation because you don't consider any coupling to external radiation. If you add that then everything apart from the ground state becomes unstable, and states with a finite lifetime have some energy uncertainty." +1492 In saving nearly extinct species, are we dooming them to generations of genetic disorders due to inbreeding? 80 https://www.reddit.com/r/askscience/comments/d509wh/in_saving_nearly_extinct_species_are_we_dooming/ 1568638512 d509wh Biology 2019-09-16 15:55:12 "Sometimes. + +Your hypothesis is sound, and there are cases where saved populations have high rates of genetic conditions. The general idea is that is still better than all of them being dead, and that the genetic health of the population can improve over time. + +For many species on the brink, conservation groups and zoos dedicate a large amount resources to finding the best genetic path forward for a species, and to move animals, sometimes around the world to get the best genetic matches for the long term health of the species. + +[https://institute.sandiegozoo.org/conservation-genetics](https://institute.sandiegozoo.org/conservation-genetics)" "Cheetahs survived a severe population bottleneck, likely around the last iceage, and there is very little genetic diversity between individuals or populations. + +​ + +Inbreeding can be a method for removing the genes that cause genetic disorders from a population. + + +oversimplified: The same math that causes negative receives to express in inbreeding also causes offspring that have none of the recessive. The offspring of those without the negative gene will never have it with or without inbreeding. The ones that have the double negative die. The offspring that are mixed will repeat the process and have fewer viable offspring than the recessive free. Ultimately the recessive becomes rare. + + +Inbreeding in domestic animals like dogs only causes problems because of artificial selection. Human intervention of only breeding dalmatians with a particular color pattern prevents kidney disease from being the selective pressure that it would be in the wild and as a result ends up becoming more common." +1493 How does cocaine get into the hair structure through use and environmental exposure? 80 https://www.reddit.com/r/askscience/comments/dagje4/how_does_cocaine_get_into_the_hair_structure/ 1569680223 dagje4 Chemistry 2019-09-28 17:17:03 ">is water soluble, why isn't it coming out in the water? Why is permeating the hair further? + +I can't answer your other questions, but keep in mind there is a lot of water in the human body, inside cells and tissue and bodily fluids etc. Just googling it hair is apparently 10 - 13% water. Might be wrong but I think anything water soluble that enters your bloodstream is liable to be transported to other areas of your body as your blood does its thing, transporting oxygen and nutrients and such." "I can't offer you any solid answers, but just to touch on one point (and this is still basically speculation), crack cocaine (or freebase cocaine) and cocaine hydrochloride are going to behave mostly the same once they have entered the body and become dissolved in blood or other aqueous fluid. + +In that case, the lipophilicity of the cocaine molecules and their tendency to partition into aqueous solution vs. non-polar things like cell membranes or possibly hair is dictated by the pH of the environment which dictates the ionization of cocaine at its tertiary amine. + +Cocaine has a pKa of about 8.6 at its tertiary amine / nitrogen atom, so at physiologic pH of ~7.4, more than 90% of cocaine molecules will exist as the ionized R3-NH+ form which is more water soluble and is less lipophillic. + +I imagine that cocaine molecules are permeating deep enough into the hair that the solvent and water washes aren't reaching them. + +Whether the cocaine was originally crack or cocaine HCl, it should be highly soluble in an acidic (or even pH 7) wash solution since hydrogen ions from the wash will convert molecules of cocaine base into the more water soluble cocaine ion with a salt counterion. So assume the water wash is acidic or neutral pH, I would assume it isn't removing cocaine because the wash isn't able to penetrate fully into the hair. + +EDIT: Also, have you read this? Lots of good stuff in here although it is a bit dated. + +https://www.ncjrs.gov/pdffiles1/Digitization/146672NCJRS.pdf + +Some data about washing on pages 51-55." +1824 Are they searching for a single particle in the search for black matter or is it believed the answer to the unobservable majority of mass within the known universe has multiple solutions? 80 https://www.reddit.com/r/askscience/comments/lsy42h/are_they_searching_for_a_single_particle_in_the/ 1614347630 lsy42h Physics 2021-02-26 16:53:50 "It's unknown whether the missing mass will turn out to mostly be one particle or several or... something else. There are a lot of candidates that are being explored, though. + +Particle physicists have come up with a lot of dark matter candidates. [This](https://arxiv.org/pdf/1707.06277.pdf) paper reviews some of them, and they are a strange sounding bunch: axions, axinos, neutralinos, sterile neutrinos. I'm not going to pretend I know what all these things are; it's not my area. They are hypothetical particles. You could also make a long list of candidates that have been considered in the past but have been since ruled out. Arguably, we've got a better idea what dark matter is NOT than what it actually is. + +Then you have dark matter candidates that aren't particles. For example, [MACHOs](https://en.wikipedia.org/wiki/Massive_compact_halo_object) include things like black holes, brown dwarfs, and neutron stars. They are essentially a grab-bag of hard to detect objects that may nevertheless be abundant in the universe. + +And then you've got other researchers that think the reason nobody has detected dark matter after all these years is because our understanding of gravity needs to be adjusted. These new gravity theories typically fall under the heading of [MOND](https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics). They manage to solve some of the problems of dark matter, but they don't explain everything. Also, general relativity has proved extremely precise in other ways, and observations of the [bullet cluster](https://en.wikipedia.org/wiki/Bullet_Cluster) argue compellingly that dark matter is real and it is a particle. + +I hesitated to add this tidbit because another user took me to task for this the other day, but here goes. I think arguably there has been at least one dark matter particle discovered: the neutrino. They are 'dark' in the sense that they don't participate in electromagnetism, and they have enough mass to contribute non-trivially to the total mass-energy of the universe. Stars make huge numbers of neutrinos as a by-product of nuclear reactions in their core. Stellar neutrinos fill the universe as much as star light does. Neutrinos are passing through your body right now! They go straight through the whole Earth like a 'ghost' particle. They are obviously extremely hard to detect but are nevertheless detected as a regular matter at observatories like [IceCube](https://en.wikipedia.org/wiki/IceCube_Neutrino_Observatory). Maybe one day we'll make a neutrino telescope, and a whole new branch of astronomy will open up. + +All that said, we have known for a long time that neutrinos can't account for the large amount of dark matter in the universe. One of the things that dark matter does is shape the way that large scale formation of structure appears in cosmological models. It was discovered in the 1980s (I think) that the dark matter particle had to be 'cold' (meaning that it moves at non-relativistic speeds) and neutrinos always travel near the speed of light due to their vanishingly small mass. Thus, neutrinos are a type of 'hot' dark matter. This is the reason why dark matter participle candidates have large masses; since they have a large mass, they move at non-relativistic speeds." Check out the [wikipedia article](https://en.wikipedia.org/wiki/Dark_matter#Composition); I've linked directly to a table of hypotheses, some of which are already 'known' components of dark matter (but none of which is known to account for all of it, so far), and some of which are theoretical or hypothetical. +1154 What is the temperature threshold for the release of hexavalent chromium from stainless alloys? 78 https://www.reddit.com/r/askscience/comments/9f78te/what_is_the_temperature_threshold_for_the_release/ 1536754877 9f78te Chemistry 2018-09-12 15:21:17 "I’m a safety guy and I’ve tried to look this up several times with no luck. My gut tells me that cutting stainless mechanically (bandsaw, recip, drilling/milling) does not release hex chrome vapors, but cutting with heat/light does. Melting points of stainless vary by grade. To err on the side of caution, I’ve put cutting with an angle grinder into the heat category, because it can heat up the stainless to a cherry red glow. + +I wish I had a scientific answer for you. If you find something definitive, please pm me. " "It isn’t always as simple as temperature. I’ve done extensive personal sampling of welders doing stainless work. MIG welders are often overexposed to Cr6+ while TIL welders almost never are. So the use and type of shielding gas ad welding type can have an effect on exposure as can the number of amps. + +With vaping, hex chrome will be unlikely to be created because there’s not enough energy to convert Cr2/3 into Cr6+ - vaping wire isn’t melting, just heating up. It takes more energy to do that than just a wire getting hot. + +Having said that, heavy metals ingestion is an issue with vaping as lead, elemental chromium, nickel, and other metals can be carried by the droplets into the lungs. + +According to this article, propylene glycol converts to propylene oxide when inhaled, which is a class 2 carcinogen according to IARC. Another good reason to stay away. + +“Heavy metals include lead, nickel, cadmium, and so on. In 2013, Williams, M. et al. found heavy metals such as tin, nickel, lead, chromium and other nanoparticles in the smoke of E-cigarettes [30]. The inhaled heavy metal nanoparticles can be deposited in the alveoli, inducing lung damage and leading to cough, dyspnea, chest pain, pulmonary edema, acute respiratory failure, as well as carcinogenicity, nephrotoxicity, and neurotoxicity [22]. For example, tin is cytotoxic to human lung fibroblasts [30]. In 2017, Williams, M. et al. continued to study the electronic flue gas sol. They selected 36 kinds of elements to detect, of which 35 kinds were detected in the electronic flue gas sol, while there were only 15 kinds of heavy metals detected in traditional cigarettes. These elements contain a variety of heavy metals, and the concentration is usually higher than that of traditional cigarette smoke [31]. The content of lead and chromium is equal to that of traditional cigarette smoke. Especially the nickel content is much higher than that of traditional cigarettes [30]. However, we still do not know the effects of inhaling heavy metal particles in aerosol on health.” + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5800174/" +1616 How do we have accurate records of hurricanes before satellites? 78 https://www.reddit.com/r/askscience/comments/hwgtk2/how_do_we_have_accurate_records_of_hurricanes/ 1595515299 hwgtk2 Earth Sciences 2020-07-23 17:41:39 Reports from different places at the same time and different times in the same place, from ships at sea as well as land-based observers. Put the data together like pieces in a puzzle. Fill in the holes with educated inference. Going back even further -- paleoclimatology! Using lake cores, geologists can discover hurricanes hundreds of years in the past. Here's an article about it: [https://insideclimatenews.org/news/01102019/hurricane-warm-water-climate-change-history-science-study-sediment-core-donnelly-muller](https://insideclimatenews.org/news/01102019/hurricane-warm-water-climate-change-history-science-study-sediment-core-donnelly-muller) +1825 “James Webb will not actually orbit the Earth - instead it will sit at the Earth-Sun L2 Lagrange point, 1.5 million km away” - What does this mean? 76 https://www.reddit.com/r/askscience/comments/lxlomt/james_webb_will_not_actually_orbit_the_earth/ 1614868008 lxlomt Astronomy 2021-03-04 17:26:48 "The James Webb telescope will not orbit the earth, instead it will orbit the sun. + +Imagine drawing a straight line from the sun to the earth and then extending this line by 1.5 million kilometers. This is the L2 Lagrange point. + +Just as the earth orbits the sun in ≈ 365 days, the James Webb telescope will also orbit the sun in ≈365 days. + +What this means is that at the L2 Lagrange point, the earth will always be between the telescope and the sun. And the distance between the earth and telescope will remain constant so it will always be next to us + +Wikipedia have a nice gif diagram to visually explain this: + +https://en.m.wikipedia.org/wiki/Lagrange_point + +I hope this answed your question :)" "Wikipedia has a good article on Lagrange Points with image references. + +https://en.wikipedia.org/wiki/Lagrange_point + +The short version is that orbital dynamics aren't as cut and dry as ""orbiting the Sun"" being distinct from ""orbiting the Earth""; sitting at a Lagrange Point is about halfway between those." +1155 Would solar systems with young stars have more radioactive isotopes? 74 https://www.reddit.com/r/askscience/comments/9e5ov0/would_solar_systems_with_young_stars_have_more/ 1536426160 9e5ov0 Biology 2018-09-08 20:02:40 "So I can't speak to the your secondary question about mutation rates, but as for your initial question, + +> Would solar systems with young stars have more radioactive isotopes? + +...the answer is definitely yes. + +The main sources of radioactivity on Earth today are primarily Thorium-232, Uranium-238, and Potassium-40. These all have long half-lives of 14 billion years, 4.5 billion years, and 1.3 billion years, respectively. This makes sense, considering that the age of the Earth is somewhere around 4.6 billion years - all the shorter half-life isotopes would have mostly decayed by now. That said, there are definitely shorter half-life isotopes that were really important for the formation of the Solar System as we currently observe it. + +When we look around at the asteroids, we notice that there's a surprising amount of differentiation among them, which strongly suggests their parent bodies had at least partially molten interiors that allowed the different elements to separate out. This is why we see that certain asteroids like [16 Psyche](https://en.wikipedia.org/wiki/16_Psyche) are particularly metal-rich - it's very likely the remnant of an iron core from a forming protoplanet that eventually broke up. + +The problem is that when you carry forward the amount of energy available to initially melt and differentiate these small bodies, the heat from release of gravitational potential as well as the heat from Uranium, Thorium, and Potassium decay simply don't provide enough energy for their cores to melt. However, if you include the heat added by the decay of short-lived isotopes - most notably, [Aluminum-26](https://en.wikipedia.org/wiki/Aluminium-26), with a half-life of 700,000 years - suddenly all the energy equations balance, and we can reproduce the early differentiation of the Solar System on paper." "Short of living in a nuclear reactor, radioactivity from isotopes is not the most likely source of mutation in the evolution of life. Mutation comes from DNA adducts, oxygen, cosmic rays, and errors in replication at rates greater than that of isotopic emission. Further, mutation is the means by which evolution of life occurs. In the short term, mutation may have consequences, but in the long term, it has benefits for survivors. +" +1617 Why does the cosmic microwave background permeate space instead of just the edges? 73 https://www.reddit.com/r/askscience/comments/hv65s8/why_does_the_cosmic_microwave_background_permeate/ 1595333050 hv65s8 Astronomy 2020-07-21 15:04:10 "IN THE BEGINNING the universe was formless and void. More precisely, the universe filled with a hot, dense, opaque, and nearly uniform gas. As the universe expanded, the gas became thinner, until it was thin enough that it went through quite a rapid transition and became transparent. The light from that moment of transition was then able to freely travel through the universe. It is still flying around today, because it only stops when it gets absorbed by something. + +This light travels at a finite speed, and the universe is either infinite in size, or just plain enormous. Either way, 13.7 billion years after the Big Bang, light is still reaching us from this early transition from opaque to transparent - this light is just coming from billions of light years away. Over the future, we will continue to receive light from the CMB, just from further and further away. + +You can flip this around and think of it the other way around if you like. As light travels at a finite speed, the further we look away, the further back in time you are seeing. But eventually you looking far enough back in time that you're seeing when the universe was opaque. This looks like a sort of a solid opaque wall ""behind"" everything else we see - we can't see anything behind that because the gas is opaque. And this ""wall"" is the cosmic microwave background. + +As for why it's microwaves: the gas was actually hot enough to give off yellow-ish light, but the light has been stretched by the expansion of the universe. It's been stretched out from visible light to longer wavelength microwaves." ">Why does the cosmic microwave background permeate space instead of just the edges? + +Because there are no edges. The CMB was emitted from *all points* in the universe, in every direction. + +>When we see light from the CMB, where is it coming from? + +The CMB radiation that *we* see is coming from the [surface of last scattering](https://en.wikipedia.org/wiki/Cosmic_microwave_background), which is the sphere of points in space centered around us with just the right distance such that photons emitted by those points ~13.8 billion years ago are just now reaching us. CMB radiation from points a little further than that will reach us in the future (it's what we will be measuring tomorrow, for example), and CMB radiation from points a little closer than that reached us in the past (it's what we measured yesterday). + +Hope that helps!" +1618 How does a computer know when to shutdown itself due to overheat? 72 https://www.reddit.com/r/askscience/comments/gzp9ge/how_does_a_computer_know_when_to_shutdown_itself/ 1591716348 gzp9ge Engineering 2020-06-09 18:25:48 "Modern electronics run using semiconductor materials. These materials are designed to be conducting part of the time and non-conducting the rest of the time. By applying a voltage, you can force the material to become conductive. The threshold this happens at is determined by the material properties and can be manipulated by doping (adding impurities) into the silicon. Doping adjusts the band-gap, or how easy it is for electrons to move across the material. Modern CPUs are made so it can switch the material very quickly (>10 GHz most of the time) but to do this it becomes more thermally sensitive. + +As the temperature goes up the band-gap gets smaller and so it is easier for electrons to move across the material. If it gets too hot, the band-gap effectively goes away and the material gets purely conductive, short circuits, and releases the ""magic smoke"". + +The motherboard and the CPU/GPU have devices that measure temperature by changing how much voltage the parts output. The BIOS monitors the temperature and will take care not to destroy your computer. The first step is thermal throttling, normally around 90-100°C, where it slows the processor down to try and reduce the temperature. The CPU itself can do this sometimes. If that fails it throws an error, fully halts the CPU, and spins the fans up all the way. You have to power cycle before the BIOS will allow the CPU to start up again. + +GPUs normally have similar protections, but normally they will just turn themselves off or cause a BSOD depending on how it is made. + +You also have to worry about processors getting too cold, but that is a lot harder to do. If the get too cold, they can't conduct at all and just sit there. Most CPUs can operate down to 0°C or 35°C depending on the model and just power them on heats them up considerably." "Computer Science Major Here: + +There is a temperature sensor inside the CPU. The UEFI (or BIOS on older systems) polls the temperature on a regular basis. If a threshold is configured in the UEFI / BIOS, and the temperature has exceeded the threshold, the poweroff signal is sent and the CPU halts operations and the system shuts down non-gracefully. I.E., you're working one second listening to the really loud fan and then suddenly you're staring at a black screen and you've lost all your work. This is the last-resort self preservation system, independent of any software or operating system. + +The Operating System can also monitor the CPU temperature. If it detects the CPU is heating up and getting close to the shutdown threshold, it can throttle the CPU using the ACPI (Advanced Configuration and Power Interface). Throttling in this case is a reference to the throttle of an internal combustion engine, specifically reducing the throttle. In an engine, this causes less fuel to be sent, reducing heat and RPMs. In a CPU the clock frequency is reduced, meaning fewer operations per second are performed and less electricity is sent through the CPU, reducing the amount of waste heat produced. This is a way to reduce heat and not suddenly shutdown the system. + +You may see that some CPUs are marketed as a 4.5GHz Boost or something similar. This just means that the CPU can't run at that speed for sustained periods (typically due to heat) and will eventually (in minutes or seconds) drop down to it's normal frequency to allow heat to dissipate. This primarily is used on laptops with poor thermal cooling systems, but I'm sure there's desktop CPUs that do this as well." +1907 If the earth was hit by another large planetary body early in its life, why is our orbit still relatively circular? 72 https://www.reddit.com/r/askscience/comments/o0cbbe/if_the_earth_was_hit_by_another_large_planetary/ 1623757173 o0cbbe Planetary Sci. 2021-06-15 14:39:33 The other object was orbiting the Sun as well. If something with 10% the mass of Earth approaches Earth with a relative velocity of let's say 3 km/s the impact will change Earth's velocity by 300 m/s, or 1% of its orbital velocity. Earth changes its velocity by more than 1% during each orbit from the small eccentricity it has. "The same can be asked about the Moon's orbit, since the Moon originated from that same early collision with Theia, and now it is also in a nearly-circular orbit! That is due to something called tidal circularization, where the tidal forces of the central body act on the satellite in a way that the eccentricity is decreased with time, and therefore the orbit becomes circular [Source](https://www.researchgate.net/profile/Stanton-Peale/publication/228687644_Origin_and_Evolution_of_the_Natural_Satellites/links/00b4953ad93377c674000000/Origin-and-Evolution-of-the-Natural-Satellites.pdf). I'm not sure if the collision with Theia had a significant effect on the Earth's orbital eccentricity, but, if it did, it could have been circularized again with time due to this effect. + +Another interesting thing is that the Earth's eccentricity varies periodically with time over tens of thousands of years due to the gravitational forces of the other planets, namely Jupiter and Saturn, which is one of the [Milankovitch cycles](https://en.wikipedia.org/wiki/Milankovitch_cycles#Orbital_eccentricity)." +1156 If I were holding a handful of DNA, what would it look like? 69 https://www.reddit.com/r/askscience/comments/9fw49g/if_i_were_holding_a_handful_of_dna_what_would_it/ 1536961331 9fw49g 2018-09-15 0:42:11 [This picture](https://gsw.silverchair-cdn.com/gsw/Content_public/Journal/geology/32/3/10.1130_G19940.1/3/i0091-7613-32-3-241-f01.jpeg?Expires=2147483647&Signature=HSvq0gw~GH6Cz0RIeFVfff5Tr8mje-hKNSfjTenGyWzAA1geN8347GE3KAXVg~4uDe48ptgVWQCnEoydEWVwO8JZi2FnG9o1edmLvaPL2FO0nAfAeKa-U~P0Xi3cCU37q8Zb3NcPluCus2xjaMjoV~pNSQD9t9vqw9AS9zrx1owyseDD1V2r~U~eMQZ1eOrSjod54Bx3xIvpEPYrVgG99KjycKrDA-gONeU0VBnJWH09Wz-k621qv-B3eynDZ6qCupijx7arfJi6GnrYPCIWc2RDpSRdYVcl86rQzd2doy7Z9QyAr6qi361DpxyqG38aGJNbUIp2TbpZTvNjSL07Ag__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA) is in black-and-white, but it would look like a clear, somewhat stringy goo. DNA is about 1.7 times as dense as water, or similar density to rubber, so it would weigh close to whatever a handful of rubber weighs. "I've led my students to extract DNA from strawberries many times. I agree with the ""snot"" comments. Due to the stringy nature of the molecule, DNA will cling to other strands, similar to how grabbing one piece of yarn from a basket pulls along a tangle of other yarn. So If you poke at a glob of DNA, a long string like snot or spit will stretch from the glob to your finger. The color is cloudy white. If you spin it in a centrifuge, you can pack it down into a harder pellet with less water incorporated into it. " +1826 What is the process for decontaminating sites where nuclear waste is present? 66 https://www.reddit.com/r/askscience/comments/lrgux2/what_is_the_process_for_decontaminating_sites/ 1614184192 lrgux2 Engineering 2021-02-24 19:29:52 "1. Measure, measure, measure:. Which isotopes in what chemical form. Whats the environmental matrix (sandy soil, clay, etc.). What horizontal and vertical distribution? What's the water table and surface water conditions, etc. + +2. Stabilize:. Stop it from moving due to wind, rain, ground water flow, etc. Maybe a quickly deployed ground cover like hay and grass seed. Maybe subsurface pumps to keep it from going down into the water table, etc. + +3. Remediate: depends on the details, but could for instance be scrape off the top few inches of contaminated soil and pack into drums. Sometimes the best option is just get it covered in grass and leave it. Drums will be analyzed for content and shipped to a waste storage site, often a carefully prepared area with no chance of ground water contamination." "There's a lot of technical detail, but in the end it mostly boils down to ""collect all the contaminated soil and water, pack it into drums, and take it ... uh ... somewhere else."" + +For water, it's possible to use filtration techniques to reduce the amount of water you need to cart away, but there's really not much you can do to make nuclear waste safe except put it in a drum and wait. + +https://www.wired.com/story/fukushimas-other-big-problem-a-million-tons-of-radioactive-water/ +https://www.tepco.co.jp/en/decommision/planaction/alps/index-e.html +https://www.youtube.com/watch?v=t0sTNLdNhuE" +1705 Why are our fingerprints spirals? 65 https://www.reddit.com/r/askscience/comments/juot2d/why_are_our_fingerprints_spirals/ 1605458613 juot2d Human Body 2020-11-15 19:43:33 Not everybody has spirals. The main 3 recognised patterns are loop, whorl and arch. [here’s](https://www.sciencedirect.com/science/article/pii/S0022202X16004528) a paper on it. No one can answer that because No one knows about regularity of fingerprints, because fingerprints are not genetic. All of your finger and toe prints are formed when you’re rubbing the inside of the amniotic sac. +1827 Is the extra 1 mg in a dose of aspirin really necessary? 65 https://www.reddit.com/r/askscience/comments/la0ce7/is_the_extra_1_mg_in_a_dose_of_aspirin_really/ 1612175966 la0ce7 Medicine 2021-02-01 13:39:26 "I know this is a simple calculation but it's probably not well known why a lot of doses aren't nice round numbers. + +The quick answer is that pharmacists/apothecaries use their own measurement system: https://en.m.wikipedia.org/wiki/Apothecaries%27_system + +1 pound = 7000 grains (5760 troy) + +1 grain = 64.79891 mg (SI) + +5 grains = 323.99455 mg + +323.99455 mg / 4 = 80.9986375 mg + +To answer your question, it doesn't matter. The 324 mg (5 grains) and 81 mg (1.25 grains) are just the doses from old studies/products. (Pre-1971, when the US Pharmacopeia officially adopted the metric system)" "No, it does not matter. The 324mg dose is based on the chewable children's, but a 325mg adult is a negligible increase. The benefit of the children's chewables is that it is absorbed through the mouth instead of swallowed and absorbed in the digestive tract, allowing it to get to work faster. You could chew an adult pill, but it won't taste good. + +Our protocol is 1 adult or 4 children's chewables, but we do not carry adult ASA." +1828 Dumb question but, how is Caesium just chilling in the ocean after the Fukushima Daiichi disaster? 61 https://www.reddit.com/r/askscience/comments/lrneoh/dumb_question_but_how_is_caesium_just_chilling_in/ 1614200471 lrneoh Chemistry 2021-02-25 0:01:11 Caesium *metal* will react violently with water. The caesium found in the ocean are caesium ions in solution. Or if you want to think about it that way, the caesium reacted with something random to form a salt, which then dissolved in water. "The other person already answered, but I guess I can expand a bit. When elements react, the atom of the element isn't destroyed, it only changes its form/configuration. + +Say you have some sodium metal (which also reacts violently with water), and some chlorine gas (extremely toxic and reactive non-metal). If you combine them, they form sodium chloride, also known as table salt. Both the sodium and chlorine are in there, except now as ions. And they dissolve in water too. In fact, about 0.9% of your blood mass is sodium chloride. + +So yeah, likewise caesium is in the form of Cs^+ ion and is swimming in the water. The only way it will disppear is by radioactive decay." +1619 How can DNA code for instinctive behaviours such as building nests, recognising preys, finding the mother's breast...? 60 https://www.reddit.com/r/askscience/comments/hwfajf/how_can_dna_code_for_instinctive_behaviours_such/ 1595509508 hwfajf Biology 2020-07-23 16:05:08 "The genetic element of instinctive patterns of behaviors is generally based on the release of reinforcing neurochemicals like dopamine, oxytocin, etc. When an animal performs a certain type of action they get a release of these chemicals that make them feel better, so they do it more. + +When it comes to your example of birds making nests, the kinds of behaviors that get reinforced will be simple things like finding and carrying long flexible and/or fuzzy material, weaving them through each other, sitting in the middle of it, etc." "My old professor would be so disappointed in me, but I forgot more about this subject than I remember. Behavioral genetics is a fascinating subject. It may be easier to study (and comprehend) if you look at insects, rather than animals that have clear learned behaviors. + +Let's take parasitoid wasps for example: I, for the life of me, cannot remember the name of the species, however, this wasps will sting/paralyze a large spider, lay it's egg(s) in it, dig a hole, and bury the spider. They do the exact same steps every time. In fact, if you move the spider ever so slightly while the wasp digs the hole, it will reposition the spider, and dig another hole. The wasp cannot deviate from it's fixed movements. These types of behaviors are called: fixed action patterns. They are truly genetic behaviors. + +This is about the extent my brain can currently remember. I have a book on behavioral genetics that I could skim through, and get back to you, if no one answers your specific question regarding how DNA can create this." +1620 Does your blood type influence how sick will you get with the common cold? 60 https://www.reddit.com/r/askscience/comments/h0y9x1/does_your_blood_type_influence_how_sick_will_you/ 1591878103 h0y9x1 Medicine 2020-06-11 15:21:43 "Not sure about the common cold, but that is true for the norovirus (also know as the stomach flu) + +The expression, or lack thereof of [H1-antigen on the walls of the small intestine](https://www.mdpi.com/1999-4915/11/3/226) determines whether many strains(currently there are 29 different known strains) of norovirus can bind and infect a person. + +In general, those who do not make the H1-antigen and people with B blood type will tend to be resistant, whereas people with A, AB, or O blood types will tend to get sick, but it will depend on the specific strain of norovirus." "why'd they ignore the chemokine receptors etc, where mutations were far more clearly represented in the sickest? + +​ + +Other than that ABO preference sounds cool." +2000 How does a computer communicate with another one behind NAT? 60 https://www.reddit.com/r/askscience/comments/rblcts/how_does_a_computer_communicate_with_another_one/ 1638947127 rblcts Computing 2021-12-08 10:05:27 "Your understanding is a little incomplete, and correct under certain caveats. For NAT to make sense, the motivation is important. NAT is born out of the requirement to establish IP communication between two address realms which are not distinct (disjoint). For example, end-to-end IP communication is impossible between two hosts between a router (each) which are assigned the same IP address. Why is that use-case important? In some cases, re-using an address range for a subnet means that the limited IPv4 address range can be assigned to more than 2^(32) hosts. In others, unwillingness to set up a network collaboratively. + +What is NAT? it is a mapping of two IP address spaces, or IP address and port spaces. [1] [2] The ~host~ gateway performing address translation typically combines one of four implementation classes (these are historical terms, but useful to understand their different needs). Note that all of them involve a port, which is not an IP entity: + +1. one-to-one NAT; an ""internal"" address and port is mapped to an ""external"" address and port. An external host can thus contact the internal address only at the internal port, by sending packets to the external address and port (*) + +2. ""address-restricted-cone-NAT""; same as one-to-one NAT, except the internal host must have initiated the communication to the external address, at any port + +3. ""port-restricted-cone-NAT""; same as one-to-one NAT, except the internal host must have initiated the communication to the external address and (specific) port + +4. ""symmetric"" NAT; the most wrongly named variation is when an external address and port is used for a singular (internal address, internal port, destination address, destination port) (aka ""flow"") [3]. Communication must be initiated from the internal address and port + +This terminology is no longer used because, as you have probably understood, the possible observed behaviours are largely common between them. Therefore terminology now uses behaviour. [4] [5] + +In all these cases, the NAT gateway rewrites packet addresses and ports according to its mapping. All packets (pertaining to a connection) must be rewritten in order to maintain communication. + +The mapping can be discovered (by hosts initiating communication) or configured statically. + +As soon as a single NAT gateway exists between two hosts, the traversal problem occurs. Note that more than one NAT gateway may exist, so the problem is complex. Because NAT violates the end-to-end principle, and its operation is opaque to the end hosts, cooperation is necessary. + +One solution is port forwarding [6]. Port forwarding (or destination network address translation) solves the problem of exposing a single internal host to external hosts, at a single external port. Packets to the external address & port are always forwarded to a single host and at the same port #. Sometimes this technique is used on an entire host, which becomes exposed, and is referred to as ""DMZ"" (from ""demilitarised zone""). Port forwarding is popular with home setups and it is often a solution/workaround offered for peer-to-peer multiplayer games. Port forwarding is almost always a manual affair. Manual mappings can also be made by employing IGDP [7] + +Another solution is hole punching. [8] Hole punching relies on implicit cooperation between hosts that they will use the same port number(s) on both sides of the NAT. While this is a crucial assumption for connection-oriented protocols, it makes little difference for connectionless ones. Hole punching methods include guessing or inferring mapping assignments by the gateway, when not relying on the aforementioned assumption. This technique is popular with peer-to-peer protocols. + +Another proposed solution is dynamic discovery for the information necessary to perform traversal, by something like STUN [9]. STUN is intended as a way to discover NAT mappings. Once discovered, the host(s) can use other techniques to establish connectivity. It's a fragile and incomplete proposal. + +At this point you may want to hear about some interesting details about NAT. + +* While NAT was 'marketed' as a solution to limited IP address space, this has almost never been the dominant use-case. IPv6 also features NAT, which carries significant concern +* NAT, contrary to what the RFC document claims, is not ""transparent routing"". The changes that are made on packets are not transparent to the endpoints. NAT is a completely opaque proposal, which is the reason most ways to bypass it rely on convention and guesswork +* NAT as described here cannot operate properly on real networks, where protocols in layers above IP carry information about IP (ICMP redirects, for example). The NAT implementation must necessarily takes actions beyond the IP layer. This increases complexity and administrative burden. A trivial example is segment checksums (TCP / UDP) +* NAT has been ""extended"" with features like ""hairpinning"" - allowing access to an internal host from another internal host via the (mapped) public IP address. Consider the one-to-one use-case above (*) where a single web server is exposed, and the internal host wants to access the web server without making changes to the upper layer stacks (e.g. name resolution), or exposing the internal network address +* Some protocols send addresses with their data (FTP, SIP, etc). Those protocols rely on special techniques like STUN, and in some cases cannot work: passive FTP cannot work with two instances of NAT +* UPnP [7] contrary to its claims is a spectacularly and unnecessarily complex set of protocols. Vulnerabilities in the protocols, as well as the implementations, have had spectacularly wide impact (see the Conficker worm) + +[1] https://datatracker.ietf.org/doc/html/rfc2663 + +[2] https://datatracker.ietf.org/doc/html/rfc1918 + +[3] It actually includes the protocol. Remember TCP and UDP port numbers overlap but their use differs + +[4] https://datatracker.ietf.org/doc/html/rfc3489 + +[5] https://datatracker.ietf.org/doc/html/rfc4787 + +[6] https://en.wikipedia.org/wiki/Port_forwarding + +[7] https://www.iso.org/news/2008/12/Ref1185.html + +[8] https://en.wikipedia.org/wiki/TCP_hole_punching + +[9] https://datatracker.ietf.org/doc/html/rfc5389" "NAT traversal and STUN is what you're looking for. The *very short story* is both peers tell a third party who and where they are (some identifier and the public IP:port as seen from the outside. The third party transmits that info to the peers. The peers then talk directly to each other. + +Here is a detailed description of the problem and a solution for hosts behind many NATs and when both peers are behind their own NAT. https://tailscale.com/blog/how-nat-traversal-works/" +1621 Is it possible to have PTSD for something that never happened ? Like when our brain creates false memories ? 57 https://www.reddit.com/r/askscience/comments/h10rw5/is_it_possible_to_have_ptsd_for_something_that/ 1591887149 h10rw5 Psychology 2020-06-11 17:52:29 "Interesting question... technically, no, because in order to meet for PTSD, [according to DSM-5](https://dsm-psychiatryonline-org.proxy.library.emory.edu/doi/full/10.1176/appi.books.9780890425596.dsm07#BABJAEHE), one has to have + +>Exposure to actual or threatened death, serious injury, or sexual violence in one (or more) of the following ways: 1) Directly experiencing the traumatic event(s) + +>2) Witnessing, in person, the event(s) as it occurred to others + +>3) Learning that the traumatic event(s) occurred to a close family member or close friend. In cases of actual or threatened death of a family member or friend, the event(s) must have been violent or accidental + +>4) Experiencing repeated or extreme exposure to aversive details of the traumatic event(s) (e.g., first responders collecting human remains; police officers repeatedly exposed to details of child abuse). + +The last one gets at what we're calling [vicarious trauma](https://tpcjournal.nbcc.org/trauma-redefined-in-the-dsm-5-rationale-and-implications-for-counseling-practice/), which is [definitely a real thing](https://www.humanservicesedu.org/trauma-pst.html) for people who are tangential to trauma routinely (like a welfare worker who sees extreme child abuse). + +We also know that PTSD causes disruption in memory [(wiki here)](https://en.wikipedia.org/wiki/Memory_and_trauma), and the fact that humans constantly [make false memories about ourselves](https://medicalxpress.com/news/2018-09-real-myth-constantly-false-memories.html), and [we can't really distinguish them from true memories](https://www.frontiersin.org/articles/10.3389/fpsyg.2020.00650/full). So I wouldn't be surprised of someone wholly convinced that a false memory of abuse was real could develop PTSD-like symptoms. And for obvious ethical reasons, we can't give people false traumatic memories to test this." "You don't wake up in the morning with false memories of a PTSD event, so ""PTSD for something that never happened"" indicates a symptom of something else, such as a delusional disorder, which would have telltale signs that would eventually be uncovered by clinical interview and throughout the course of treatment. There are hypothetical non-delusional situations that might cause it, such as being told something was done to you while you were unconscious that didn't actually happen, but I haven't seen any actual evidence of this in practice. + +""False memories"" aren't created in a vacuum. You don't wake up one morning with false memories, so you wouldn't wake up one morning with a false memory of PTSD without something else going on. The creation of false memories is a whole other issue that is more complex than just suddenly remembering something that didn't happen. + +Regardless something like ""PTSD for something that never happened"" generally would be a symptom of something else, like a delusional disorder." +1622 When I see a star, did the photons entering my eye actually come from that star? 57 https://www.reddit.com/r/askscience/comments/hu34jc/when_i_see_a_star_did_the_photons_entering_my_eye/ 1595175622 hu34jc Astronomy 2020-07-19 19:20:22 ">When I see a star, did the photons entering my eye actually come from that star? + +Yes. + +>Or were they absorbed and re emitted along the way somewhere, such as in the atmosphere? + +There's a chance they may have [scattered](https://en.wikipedia.org/wiki/Compton_scattering) off of a dust particle in space or (more likely) off of a particle in the atmosphere, but both scattering and absorption/reemission tend to change the direction that light is headed, so ... in general, no, this isn't particularly likely if you're looking directly at a star. + +Now, mind you that all the stars you can see with your eye are not particularly far away. It's not like that light has been travelling for billions or even millions of years. Every star you can see in the night sky is within just ~4,000 lightyears of us, so the light has only been travelling for about that many years. But, you can also see faint light from the Andromeda galaxy despite it being located 2.5 million lightyears away due to its sheer size and light output." [deleted] +2001 If Photons Carry Momentum Despite Having No Mass, Does the Sun's Output Move Planets' Orbits? 56 https://www.reddit.com/r/askscience/comments/rbfm2m/if_photons_carry_momentum_despite_having_no_mass/ 1638928652 rbfm2m Planetary Sci. 2021-12-08 4:57:32 They push, yes, that’s why solar sails work. But the area of a planet compared to its mass means the push is so small it is utterly overwhelmed by all the other things that can push planets around in their orbits. The radiation pressure follows an inverse square law, just like gravity. You can treat it as negligible correction to gravity. Sunlight reaching Earth exerts a force of [550 MN](https://www.wolframalpha.com/input/?i=1.3+kW%2F%28m%5E2+*+%28speed+of+light%29%29+*+pi+*+%28radius+of+Earth%29%5E2), which has to be compared to [3.5\*10^22 N](https://www.wolframalpha.com/input/?i=mass+of+sun+*+mass+of+earth+*+gravitational+constant%2F%281+AU%29%5E2) from gravity. It's effectively as if the Sun would be lighter by ~1 part in 10^14. That ratio is different for other objects as the surface area (->radiation force) doesn't scale linearly with mass (->gravity). For very small objects the radiation pressure can be relevant. +1157 Why is there an EpiPen (and generic alternatives) shortage? 55 https://www.reddit.com/r/askscience/comments/9jxrts/why_is_there_an_epipen_and_generic_alternatives/ 1538234950 9jxrts 2018-09-29 18:29:10 "EpiPens are a medical device. Medical devices don't really have a ""generic"" regulatory option so any company that decides to sell a EpiPen knock-off needs to do all the testing over again except less testing for the drug. + +Moreover, some companies decide to file patents around the device component, so you might not be legally able to make copies. This is what happened to all the asthma inhalers since as soon as the law went into effect banning CFCs in medical devices, Teva Medical filed a patent on propellants other than CFC's in inhalers so a $20 inhaler in the 90's is now $200+ for the same drug and same delivery mechanism. + +*Edit: It looks like I forgot to respond directly to the OP's question. Being a medical device, you can't just build another manufacturing line and say everything is ok. You have to build the line, re-test the line to see if it still makes everything correctly at the extreme tolerances (process validations), and make sure your raw material suppliers don't change their materials on their side and still meet your increased capacity. What usually ends up happening in my industry (medical devices) on shortages are usually due to: (1) One of the key raw material suppliers cannot make enough of a component, (2) Your new or existing line fails process validations/in-process checks, (3) FDA/notified body audit findings triggering shutting down the line, or (4) A massive product recall that is currently in-progress. + +With (3), I've seen the FDA at times try to negotiate with companies not trying to shut down a key product-line, but companies usually end up shutting the line down out of spite and have the physicians & patients file complaints to the FDA. I am personally unsure of which of the reasons are causing EpiPens to be in short supply, but I wouldn't be surprised if it is one of the above causes. " "I think part of the issue has to due to the large demand of epipens, and shortish shelf life (1 year). Basically they couldn't keep up with the demand, and therefore announced months ago about the upcoming expected shortage. + +When they mention manufacturing delays, it's not that the actual process to make epinephrine has become more difficult.. more like ""we had to update all the machinery in the plant"" or ""X machine broke down and we have to wait for parts"" for example. Something happened on the manufacturing side that slowed down production." +1158 The MINERVA rovers show boulders on the asteroid they landed on. Despite obviously lacking erosion due to water or an atmosphere or geological activities, how have these boulders formed? 53 https://www.reddit.com/r/askscience/comments/9jhyr3/the_minerva_rovers_show_boulders_on_the_asteroid/ 1538091834 9jhyr3 Planetary Sci. 2018-09-28 2:43:54 Formed from dust in the early solar system and either never got any bigger than that or (probably more likely) fragmented from a bigger rock due to a collision, before joining the asteroid. The whole thing is just a loosely-held-together ball of debris. +1506 AskScience AMA Series: Hello, we are Dr Kate Woodthorpe and Dr Hannah Rumble from the Centre for Death and Society at the University of Bath. We're here to talk about death, bereavement and funerals during the global Covid-19 pandemic. Please ask us anything! 53 https://www.reddit.com/r/askscience/comments/g2cua6/askscience_ama_series_hello_we_are_dr_kate/ 1587034824 g2cua6 Psychology 2020-04-16 14:00:24 "Hi there, thanks for doing this! I'm guessing that there will or already is a large increase in the number of virtually-attended funerals during the current pandemic. My question is on whether or not there has been any research into the emotional/psychological variation for people due to this virtual attendance versus being able to attend a funeral in person. I realize that's kind of broad and quite possibly unknown thing that has been looked at, and for what I am thinking of I'm going to guess that there probably aren't a lot of studies on the impacts during a pandemic unless perhaps there's information from the Spanish Flu era (or maybe there's been a rise in virtual attendance before COVID-19 anyway?). But, there are always people who simply cannot attend a funeral generally and I'm wondering if there is some known difference in the grieving process just due to a difference inability to find closure or not in being at a funeral in person. + +If I may also ask one more (if this is outside of your area then please feel free to ignore!), do people handle the impact of someone dying in relation to a large group versus an isolated event? That is, during mass tragedies (natural disasters, wars, etc.), is there some difference in how people grieve just on the basis of the person who died being part of a larger tragedy or not?" "How is your industry handling the mass flux, I have heard that some countries are overwhelmed and isnt there concerns about spreading through the funeral process? + +Also in Us and western countries visitation at a funeral home is common, how has/will that change with social distancing?" +1159 Do dark surfaces contribute to climate change? 52 https://www.reddit.com/r/askscience/comments/9c7sso/do_dark_surfaces_contribute_to_climate_change/ 1535846100 9c7sso 2018-09-02 2:55:00 "Yes. They absorb visible light and re-emit the energy as infrared light, which is absorbed by greenhouse gasses. Lightly-colored surfaces, on the other hand, reflect more of the incoming visible light back into space, so that energy doesn't have to find its way through the greenhouse gasses (as they are transparent to visible light). + +For this reason, the melting of sea ice creates a feedback loop. Sea water absorbs a great deal of incident light, especially compared to ice. As the ice melts, the Earth absorbs more of the energy from the Sun, which warms the Earth, causing more ice to melt, causing more absorption of energy from the Sun, etc. This is not the only feedback process involved in the climate (some are positive feedback loops while others are negative), but it is an important one. A negative feedback loop that works the same way is that a warmer Earth leads to more water evaporation, which leads to more cloud formation, which leads to more incoming sunlight being reflected away, thus cooling the Earth back down. How strong each of these various feedback loops is is one large source of uncertainty in modelling the future of climate change. (I want to be clear, though, that uncertainty in modelling the future is not the same as uncertainty in what is causing climate change - carbon dioxide originating from human activity is responsible for increased global average temperatures in the last several decades.) + +We can see this effect in other planets as well. [Venus reflects an incredible 77% of all the light incident upon it](https://i.redd.it/ugexjlyu2oj11.jpg) (compared to Earth's 30%). Venus actually absorbs less energy from the Sun than Earth does, even though it's closer to the Sun! Yet Venus is hot enough that the first several probes sent there melted. Why? Venus has a thick atmosphere, dozens of times as dense as Earth's, and it's almost all carbon dioxide, so that Venus is extremely inefficient at re-radiating the energy it receives from the Sun. The greenhouse effect is strong enough to turn the 23% of sunlight that isn't reflected by the clouds into a hell-scape. " "I only have one thing to add to the great answer given by /u/lmxbftw, which is that the name for what you're thinking about is albedo. Surfaces with low albedo (like asphalt) absorb most incoming energy, while surfaces with high albedo (like snow) reflect most incoming energy. + +One fascinating part of your question is the matter of how trees impact climate change. The naive thought is that forests reduce global warming by consuming carbon dioxide in the air. This is true, but trees tend to have low albedo and absorb a lot of sunlight, since photosynthesis is used to provide the energy needed for trees to live. Thus it becomes clear that trees contribute to cooling in some ways and warming in other ways, and there may in fact be places on Earth where forests may be net-warming features rather than net-cooling. + +[https://en.wikipedia.org/wiki/Albedo#Trees](https://en.wikipedia.org/wiki/Albedo#Trees) + +NASA has done high-resolution measurements of Earth's surface albedo: + +[https://earthobservatory.nasa.gov/images/84499/measuring-earths-albedo](https://earthobservatory.nasa.gov/images/84499/measuring-earths-albedo)" +1160 I know rogue planets (planet-sized objects that don't orbit a star) are theorized in the galaxy but are rogue stars (stars that don't orbit a galaxy) also theorized? Any theories on how prevalent they are? 50 https://www.reddit.com/r/askscience/comments/9hp7a3/i_know_rogue_planets_planetsized_objects_that/ 1537532285 9hp7a3 2018-09-21 15:18:05 Not only are they theorized, but they have been observed. Not only have they been observed, but they are incredibly numerous. It's estimated that they make up ~10% of the mass of the Virgo galaxy cluster. [More reading](https://en.wikipedia.org/wiki/Intergalactic_star) [intergalactic stars](https://en.wikipedia.org/wiki/Intergalactic_star) are known, and a recent study found that there are more of them than previously thought. I cant seem to find that article though. the wiki page I linked has several references though which make for good further reading on the subject +1161 At what point in the atmosphere would a person need a space suit to survive? 49 https://www.reddit.com/r/askscience/comments/9hrnsx/at_what_point_in_the_atmosphere_would_a_person/ 1537547679 9hrnsx 2018-09-21 19:34:39 "It's known as the *Armstrong limit* and it's around 18 km up. At that altitude the air pressure is so low that water boils at body temperature. This includes the moisture inside the lungs that is required for healthy lung function. (But not the blood because that's pressurised inside the body.) + +In practice a pressure suit (or a pressurised aircraft cabin) is needed at somewhat lower altitudes, around 15,000 metres or so, to avoid problems with insufficient oxygen since even 100% oxygen through a mask isn't enough at such low pressures. + +EDIT: But at, for example, the 8000 metre height of the highest mountain peaks, an oxygen mask will suffice, a pressure suit is not required. In fact Everest has been climbed without an oxygen mask, but it's very dangerous. The ""death zone"" cannot be survived for more than a few days without supplemental oxygen." "What if you were to do the opposite? Say you spent a month at 20K+ feet elevation. Then you went directly back to sea level. Would you have to descend gradually, or could you do it immediately via helicopter? Would the sudden ""boost"" of O2 in your lungs make you dizzy? increase athletic performance? " +1829 What is the Dirac Sea and how does it work? 49 https://www.reddit.com/r/askscience/comments/lxbhse/what_is_the_dirac_sea_and_how_does_it_work/ 1614828263 lxbhse Physics 2021-03-04 6:24:23 "The Dirac sea doesn't really exist. + +It comes from Dirac's very valiant attempt at unifying special relativity and quantum mechanics, which demonstrates his astounding genius as a physicist, but has been replaced with a more sophisticated understanding (quantum field theory). + +The idea was that the Dirac equation seemed to predict an unbounded-below energy spectrum. And it's a common fact in physics that physical systems want to minimize their energies. So if you had an electron with some positive energy, it would rather transition into one of those infinitely many negative-energy states instead. But we don't observe that in nature. So one way to fix that is to say that even though there are infinitely many negative-energy states, they're all filled, so that's why the electrons we observe don't transition into them. + +So within this model the Dirac sea is this infinite ""sea"" of filled negative-energy states, and a positron (the antimatter counterpart of the electron) is really just a [hole](https://en.wikipedia.org/wiki/Electron_hole) in the Dirac sea. + +So it's a neat idea, and the Dirac equation is still useful for the fairly limited number of situations where you need to study relativistic fermions, but aren't concerned with particle creation/destruction. But it's been replaced with a better theory: quantum field theory, and particularly quantum electrodynamics. + +An example of a scenario where the Dirac equation fails but QED succeeds is in predicting the [Lamb shift](https://en.wikipedia.org/wiki/Lamb_shift). QED is now the most precisely-tested theory *ever*, so we're pretty confident about it." +1162 What physical features does a polar bears paw have to help grip on ice? And how does it not freeze? 48 https://www.reddit.com/r/askscience/comments/9i4y27/what_physical_features_does_a_polar_bears_paw/ 1537667398 9i4y27 Biology 2018-09-23 4:49:58 """Rough pads give it a nonslip grip, and thick fur between the pads keeps the bear’s feet warm. It uses the sharp, curved claws on its front paws like hooks to climb onto the ice from the water. Polar bears’ claws also help them dig in the ice when they hunt seals."" + +https://asknature.org/strategy/paws-have-non-slip-grip/#.W6cEYulME0M" +1163 Is the large curve of coastline between Florida and the Carolinas in any way related to erosion from centuries of hurricanes? 48 https://www.reddit.com/r/askscience/comments/9fd9p4/is_the_large_curve_of_coastline_between_florida/ 1536798393 9fd9p4 2018-09-13 3:26:33 "I'm more of a science enthusiast, but there is a phenomenon called ""Carolina bays"" that aren't fully understood, which may partly explain the curve. They're oval depressions that run up and down the Eastern seaboard. There's roughly 40-50k of them at least .1 hectare in size +https://www.tandfonline.com/doi/abs/10.1080/15230406.2016.1162670?journalCode=tcag20 + +https://en.m.wikipedia.org/wiki/Carolina_bay?wprov=sfla1 + +Aside from that, the Low Country is very flat, very sandy, etc. The ocean keeps trying to moving the barrier islands (humans are very bent on that not happening), so I wouldn't be surprised if it was just ocean currents that contributed to that shape over time." +1623 Once there's a COVID vaccine, what percentage of the population must be vaccinated to reach herd immunity? How long would this take? 47 https://www.reddit.com/r/askscience/comments/gzf11m/once_theres_a_covid_vaccine_what_percentage_of/ 1591673447 gzf11m COVID-19 2020-06-09 6:30:47 "The percent of the population that needs to be immune for a herd immunity effect depends on the transmissibility of the pathogen. The higher the transmission rate, the higher the percent immune is needed. An extremely transmissible disease like measles needs something like 94% of the population to be immune; a weakly transmissible disease, like some influenza strains, might only need 50%. The equation for the herd immunity threshold is (R0 – 1)/R0 where R0 is the basic reproduction number. + +A good summary is Figure 2 in [“Herd Immunity”: A Rough Guide](https://academic.oup.com/cid/article/52/7/911/299077). + +SARS-CoV-2 is between influenza and measles in its transmissibility. A reasonable guess is that its R0 is around 5, which means you need around 80% immunity for the herd immunity threshold. I’ve seen estimates of Its R0 between 3 and 8, which would correspond to between around 65% and 90%. + +This is obviously simplified and assumes even distribution of immunity and so on. The article linked above covers many of the more realistic and complicated variants that affect it (heterogenous populations, imperfect vaccines, etc etc). + +How long would it take? It will never happen with natural infections, it obviously needs a vaccine. A good comparison might be influenza vaccination, which is the right ballpark - a little less than half the US population is vaccinated against influenza each year, mainly in a couple of months in the fall, and it’s not all that big a deal. There are campaigns for it, but not shut-down-the-city type campaigns. Reaching 65% instead of 40% should be easy. + +After that it gets to be a PR issue, not a scientific or public health issue. The 80:20 “rule” says that if we need more than 80% coverage - which is quite likely - it will be fairly easy to get most of the way there but hard to get the last part. + +On the other hand, it’s likely that immunity will last for several years, so unlike flu you don’t have to go through it over and over, and you have a longer window to get it done. + +But technically, if manufacturing is up to it (and it should be) there isn’t a technical barrier." +1908 When you look at a crescent moon it seems you can see the edge of the darkened portion. Are we really seeing an edge or is our brain just filling out the rest of the circle? 47 https://www.reddit.com/r/askscience/comments/o03muo/when_you_look_at_a_crescent_moon_it_seems_you_can/ 1623724623 o03muo Astronomy 2021-06-15 5:37:03 "Earthshine! + +The Earth reflects enough of the Sun's light that it illuminates the Moon just a little bit. So the side of the Moon facing the Earth is never completely dark, even at ""night"". With a long exposure camera, you can actually take a photo of the crescent Moon and see all the craters and stuff on the dark side, while overexposing the lit crescent. + +There are some nice pictures on the internet: + +https://earthsky.org/astronomy-essentials/what-is-earthshine/ + +https://www.timeanddate.com/astronomy/earthshine.html + +etc" If you've ever been to the countryside where there aren't many street lights, you'll see just how bright the full moon is. Now imagine how bright the Earth must be at night on the moon! That's what you're seeing. It's the Earth's reflecting sunlight back to the moon. +1164 How do trees fight off disease? 46 https://www.reddit.com/r/askscience/comments/9ixjyi/how_do_trees_fight_off_disease/ 1537920811 9ixjyi 2018-09-26 3:13:31 "Trees *do* in fact have an immune system, as all plants do! Plant immunity is an innate immune system, while animals have innate and adaptive immune systems. + +Plant immunity is, in general terms, concerned with detecting pathogenic proteins and/or pathogen-associated molecular patterns that would signal the presence of a potential plant pathogen. + +Once detected, plants activate a number of processes designed to make the plant tissue inhospitable for a plant pathogen. A classic hallmark of plant immunity is the production of reactive oxygen species (or ROS) that will kill pathogens or drive them to dormancy. This is analogous to a fever in animals. + +Another molecular response that occurs in plant immunity is the creation of barriers to the diffusion of pathogens. Deposition of callose - a complex polymer - prevents pathogens from growing or moving freely in the interleaf space. In more serious immune reactions, plant cells around the pathogen will kill themselves in a process known as the hypersensitive response (HR). This denies the pathogen living tissues and nutrients. + +Another important barrier that prevents plants getting sick is physical barriers. The bark of a tree is an excellent barrier, much as our skin is, to prevent pathogens from getting anywhere near the important parts of the tree. This is why the vast majority of tree diseases are seen after the tree is damaged by pruning, weather, or by burrowing insects." +1909 If mRNA vaccines remain proven safe, is it actually necessary to go through new trials each time when vaccinating for a new strain or another disease? 46 https://www.reddit.com/r/askscience/comments/p8vtoe/if_mrna_vaccines_remain_proven_safe_is_it/ 1629567841 p8vtoe Medicine 2021-08-21 20:44:01 "For a completely new virus, sure - you'd definitely need new trials. + +For a modified vaccine targeting a new strain, probably not in the long term (maybe the first few times it's done for a given vaccine). Or greatly reduced compared to the original trials. + +Inactivated virus and protein based COVID vaccines needed full trials despite using well understood production methods and adjuvants, but an updated inactivated or protein based seasonal flu vaccine doesn't need a new clinical trial." In addition to testing for side-effects, clinical trials are also designed to test efficacy. It’s one thing to suspect that coding for a spike protein (for example) will generate a robust immune response when faced with the actual virus, it’s another thing to prove it! (And to figure out exactly how much protection the vaccine provides, for how long, etc.) +1165 Is intelligence hereditary? 45 https://www.reddit.com/r/askscience/comments/9eew9z/is_intelligence_hereditary/ 1536515196 9eew9z Neuroscience 2018-09-09 20:46:36 "Yes it is, to quite a large degree. Geneticists know this in part through studies of twins: identical twins, who share 100% of their genetic variants, have more similar intelligence than fraternal twins who only share 50% of their genetic variants. Estimates of the heritablity of adult intelligence are in the range of 70 – 80%. This means that 70 – 80% of the variation in intelligence within a population is due to genetic differences. (See: https://en.wikipedia.org/wiki/Heritability_of_IQ#Estimates ) + +Researchers know intelligence is largely based on genetic factors, and are currently trying to identify which genes are most important. One of the most recent papers can be found here: https://www.nature.com/articles/s41588-018-0152-6 + +The abstract, for those interested: +>Intelligence is highly heritable and a major determinant of human health and well-being. Recent genome-wide meta-analyses have identified 24 genomic loci linked to variation in intelligence, but much about its genetic underpinnings remains to be discovered. Here, we present a large-scale genetic association study of intelligence (n = 269,867), identifying 205 associated genomic loci (190 new) and 1,016 genes (939 new) via positional mapping, expression quantitative trait locus (eQTL) mapping, chromatin interaction mapping, and gene-based association analysis. We find enrichment of genetic effects in conserved and coding regions and associations with 146 nonsynonymous exonic variants. Associated genes are strongly expressed in the brain, specifically in striatal medium spiny neurons and hippocampal pyramidal neurons. Gene set analyses implicate pathways related to nervous system development and synaptic structure. We confirm previous strong genetic correlations with multiple health-related outcomes, and Mendelian randomization analysis results suggest protective effects of intelligence for Alzheimer’s disease and ADHD and bidirectional causation with pleiotropic effects for schizophrenia. These results are a major step forward in understanding the neurobiology of cognitive function as well as genetically related neurological and psychiatric disorders." +1830 Why is purifying uranium so hard? 45 https://www.reddit.com/r/askscience/comments/laysvo/why_is_purifying_uranium_so_hard/ 1612281234 laysvo Physics 2021-02-02 18:53:54 "> Countries need to spend millions or billions of dollars on centrifuges to get weapons-grade uranium. Since uranium is so heavy, shouldn't it separate out from other elements fairly quickly? + +The first reason is that it is not present in the earths crust as metal. It has reacted, over the years, with other compounds. So you need to chemically leech the metal out of the quartz and rock. + +The second reason is that, now you have (and we're skipping a lot of steps here) solid Uranium metal, the bit your interested in is one [isotope](https://en.wikipedia.org/wiki/Isotope) of it. Isotopes (different number of neutrons on the same basic thing) obviously weigh differently, due to the extra neutrons but neutrons don't weigh much and, given that Uranium is a gigantic atom it already has a lot of neutrons - that means the percentage weight difference is very very small. Call it 1%. + +That's the first step, going from raw ore to uranium metal. It's cost quite a bit at this stage and you have violated some treaties probably. But the next bit takes a lot longer and costs a lot more. + +The different isotopes are very, very similar in weight. You are only interested in one isotope of Uranium, [U235](https://en.wikipedia.org/wiki/Uranium-235) because that one is, for various reasons, useful in bombs and the rest is not. + +Given they're chemically identical you can't use chemical separation to get U235 separated out, the only difference in them is the weight of the nucleus. So you need to magnify the difference in atomic weight in order to usefully refine your feed-stock from being 1% stuff-that-goes-bang to 99%+ and there are several ways of doing this. + +One of those ways to separate the 1% you're interested in from the 99% dross is the [gas centrifuge](https://en.wikipedia.org/wiki/Gas_centrifuge) method, which can be simply explained as ""spin the gas really fast and the heavier stuff will gradually move closer to the outside wall where it can be tapped off"" + +The gas centrifuge approach takes engineering to it's limits. The centrifuges themselves are made of [maraging steel](https://en.wikipedia.org/wiki/Maraging_steel) to withstand the near super-sonic rotational speeds needed to separate the [Uranium hexafluoride](https://en.wikipedia.org/wiki/Uranium_hexafluoride) that the uranium metal is transformed in to for processing. + +All of this takes a lot, megawatts, of electrical power, so when we see people building vast power plants in the desert and setting up access roads for SAM sites around it then questions are asked. + +The gas centrifuge method was sold around the world by a rogue Pakistan scientist called [A Q Khan](https://en.wikipedia.org/wiki/Abdul_Qadeer_Khan) so a lot of countries have, at minimum, the academic knowledge of how to enrich uranium. The know-how gained from actually doing it, though, is rarer. + +Interestingly, South Africa - the only nation to give up a nuke program - did not use the centrifuge method, instead they used the [Aerodynamic process](https://en.wikipedia.org/wiki/Enriched_uranium#Aerodynamic_processes) in which the weight difference is exploited by dual-pathing light and heavy." The issue is not separating uranium from other elements, but separating one isotope of uranium from another (only one of them is useful for making weapons). The difference in mass between these isotopes is very small. +1624 Has the invention of shoes changed the anatomy of human feet? 44 https://www.reddit.com/r/askscience/comments/h89obk/has_the_invention_of_shoes_changed_the_anatomy_of/ 1592062410 h89obk Human Body 2020-06-13 18:33:30 "Short answer, no. +Full foot covering shoes are a relatively new thing, only being around for the last 1000 years or so, and before that any type of footwear was usually sandals or similar or just went barefoot. Once you go barefoot awhile your skin thickens to the point you can walk over stones without an issue." Any variation in physical form must confer a reproductive advantage in order for it to replace another physical form over time. Genetic variation happens, but a wholesale change across an entire species would only occur if the derived form conveyed differential reproductive success compared to the ancestral form. It’s very unlikely that variation in feet due to the constraints of wearing shoes would make one more successful than another in passing along that genetic variation to offspring. +1166 How do sea creatures react to tropical storms? 43 https://www.reddit.com/r/askscience/comments/9ffdpb/how_do_sea_creatures_react_to_tropical_storms/ 1536817303 9ffdpb Biology 2018-09-13 8:41:43 +1831 Do we know the climate of Pangaea? 43 https://www.reddit.com/r/askscience/comments/lry5ww/do_we_know_the_climate_of_pangaea/ 1614227446 lry5ww Earth Sciences 2021-02-25 7:30:46 There are lots of papers (and information in general) out there on the paleoclimate of Pangea, either broadly (e.g. [Parrish, 1993](https://www.journals.uchicago.edu/doi/abs/10.1086/648217)) or those focused on more specific time intervals or geographic locations (e.g. [Kessler et al, 2001](https://pubs.geoscienceworld.org/jsedres/article-lookup/71/5/817)). A great deal of the literature focuses on the so-called [mega-monsoon](https://en.wikipedia.org/wiki/Pangean_megamonsoon), which led to extreme variations between wet and dry seasons within Pangea (e.g. [Parrish & Peterson, 1988](https://onlinelibrary.wiley.com/doi/full/10.1111/sed.12668), [Kutzbach & Gallimore, 1989](https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/JD094iD03p03341), [Dubiel et al, 1991](https://www.jstor.org/stable/3514963), [Kutzbach, 1994](https://pubs.geoscienceworld.org/books/book/430/chapter/3798577/Idealized-Pangean-climates-Sensitivity-to-orbital), [Mutti & Weissert, 1995](https://pubs.geoscienceworld.org/sepm/jsedres/article/65/3b/357/98689), [Selwood & Valdes, 2006](https://www.sciencedirect.com/science/article/pii/S0037073806001436), [Bahr et al, 2019](https://onlinelibrary.wiley.com/doi/full/10.1111/sed.12668)). While there are lots of nuances (and changes through time, Pangea in some form was around through the Permian to Triassic, a span of ~100 million years and details of the climate changed as the geometry of the continents and ocean basins changed), generally this mega-monsoon led to extremely wet summers and extremely dry winters in both hemispheres, respectively (i.e., during northern hemisphere summer, it was very wet in the northern hemisphere and very dry in the southern hemisphere which was experiencing winter, and this reversed when the southern hemisphere began to experience summer). The linked wikipedia article goes into some level of detail, for those not interested in looking at papers. I was able to find lots of information when googling for 'paleozoic climate' and 'mesozoic climate'. I can't type it out at the moment, due to a lack of time, however if you don't get a qualified answer anytime soon, at least you got some of the information right there at your fingertips. +1910 Does organic matter decompose in highly irradiated zones? 43 https://www.reddit.com/r/askscience/comments/p8tciv/does_organic_matter_decompose_in_highly/ 1629559392 p8tciv Biology 2021-08-21 18:23:12 "You can check out the wiki article about Food irridation. It scales from 0.06 kGy to 44.0 kGy. + +44 kGy is like total sterilization. [https://en.wikipedia.org/wiki/Food\_irradiation](https://en.wikipedia.org/wiki/Food_irradiation) + +About the deadwood in Chernobyl that sounds really strange, any source on that? + +Because it is not so radiated that mammals and birds no longer can live there. In fact the wildlife near Chernobyl is thriving, cancer rate might be high though, but the animals are not unable to reproduce. + +​ + +Edit: In general wood IS more resistant to decomposition than flesh and other plant parts due to it contains lignin. Lignin last longer naturally (harder for the microbes to break down) than cellulose, and cellulose last longer than flesh." "Radiation literally destroys stuff on a cellular level. Ionized particles traveling near the speed of like (alpha and beta radiation) or extremely powerful electromagnetic waves (gamma radiation) break apart molecules when they collide. When you imagine a fast zippy thing smacking into a molecule and breaking it in two, that's literally what's physically happening on the atomic level. In the case of, say, Chernobyl, even the people who received excessively lethal amounts of sub-cellular level damage from radiation didn't die from the effects for days to weeks, because there's a big difference between how much of a cell can be damaged before it can't be repaired, and how much radiation it would take to damage the *entire* cell and kill it instantly. + +The amount of radiation that would be required to *maintain* sterility would be truly ridiculous. Intense levels of radiation generally drop off pretty quickly and sterilization by radiation isn't instant, so even in the case of a catastrophic nuclear accident, you're not gonna wipe out microbes and then keep them dead, the most you can do is make the environment slightly unfavorable to them. The same way chemo hinders growth of rapidly dividing cells (cancer and hair, to name two), radiation hinders the growth of colonies of microorganisms. You can imagine that since chemo can be either strong or weaker, the interaction between background radiation and microbe population is also a spectrum. So, there'll be places in chernobyl where decay just happens a little slower, and places where it happens a lot slower, and at no point in time has there ever really been a place (outside the reactor building itself lol) where radiation levels would have maintained a microbe-free environment. + +If you, say, wanted to see a piece of meat not rot due to ultra high radiation levels, you'd need a *lot* of radiation. We're talking being *inside* a nuclear reactor operating at its maximum power output. Any amount of radiation potent enough to sterilize the meat fairly quickly (within 30 seconds or so) would be so intense it'd also physically break down the meat. You'd probably see a color change and a transition from solid to liquid, as well as the meat heating up from absorbing the energy. This is a level of radiation that can't really be created or maintained except in fairly limited volumes, and even if you somehow irradiated a whole football field enough to be *that* radioactive, the levels would be so high that no matter the half life, the field would probably be habitable to microorganisms in a week." +1625 Besides cilantro, are there any other ingredients that have been identified to taste different to people based on their genetics? 42 https://www.reddit.com/r/askscience/comments/hh6f6w/besides_cilantro_are_there_any_other_ingredients/ 1593310258 hh6f6w Chemistry 2020-06-28 5:10:58 "Brussels Sprouts are regulated by TAS2R38, a.k.a. “the brussels sprouts gene”. + +TAS2R38 controls the bonding of a specific chemical called phenylthiocarbamide (PTC). If you have the gene, PTC will be detectable to you. Sprouts and cabbages are laced with PTC. + +I love the story of the sensitivity’s discovery. There were two scientists working in a lab, one was decanting phenylthiocarbamide, and had no idea the other could smell the horrific stench. Intrigued he basically gassed family members until he had a working hypothesis and went from there. While he didn’t have the ability to inspect the genes, it was clearly genetic in nature even in the 1930s." "Every TAS gene is about this. That's the whole point of the TAS(te) classification. + +Tas2 is just a type 2 taste receptor. + +The shape of the question is problematic - almost everything has a slightly variant taste. What you seem to want is night-and-day differences. + +Those ones, like the cilantro, cucumber, and brussels sprout examples so common in here, tend to be that someone has inherited a defective taste gene that fails to pick up a noxious chemical. + +This is actually quite common. One of the human superpowers is we're really, really good at ignoring poison. There's a reason you can't feed your pets half the stuff you eat. + +And so, as our liver ranks, our tongues have learned ""oh, guess we don't have to worry about furolinase anymore"" over the years. + +Those are mutations that lose tongue protections we used to have, but don't need anymore, because what used to be poison has gone through the liver and is now food. And so it should be tasty instead of noxious now, because as animals in the forest, we need all the food we can get. + +Those mutations aren't universally distributed. + +Those foul chemicals you're tasting were dangerous to our weaker ancestors. They're mostly natural pesticides. + +Caffeine, THC, nicotine, opium, capsaicin (hot peppers,) theobromine (tea,) and theoxanthan (chocolate) are all poisons meant to keep insects in check. + +Delicious, delicious poisons." +1832 Which facial features are the most important to the brain when remembering someone? 42 https://www.reddit.com/r/askscience/comments/lxz64b/which_facial_features_are_the_most_important_to/ 1614902732 lxz64b Psychology 2021-03-05 3:05:32 "It isn't quite universal. I recall reading a study that showed we tend to focus on what varies most for our race. Let's make a fake example. + +Let's say group A has more eye variability and group B has more chin variability. + + People from group A will learn to focus more on the eyes and ignore the chin, leading them to falsely think people from group B, with less eye variability 'all look the same' + +People from group B will lean to focus on the chins and ignore the eyes, leading them to falsely thing people from group A, with less chin variability 'all look the same'. + +​ + +I don't recall if they addressed biracial people or studied people adopted into families that are a different race from them." "It varies by region and the races you're used to seeing. If you've only seen one race all your life you have difficulty telling others apart because their facial features are similar and different in ways you're not used to. + +Lots of white suburban people have extreme difficulty telling black people apart for example... not even *racism*, they literally don't know how, which can easily lead to the wrong people getting put in jail, etc. + +I had a lot of difficulty telling asians apart until a relative roped me into watching asian dramas; I still have trouble sometimes, but now I know I don't like asian dramas." +1167 How populated was the earth with Dinosaurs during the Triassic, Jurassic, Cretaceous periods? 41 https://www.reddit.com/r/askscience/comments/9dvftt/how_populated_was_the_earth_with_dinosaurs_during/ 1536334175 9dvftt 2018-09-07 18:29:35 "Well the Triassic was immediately following the Great Dying, 90% of life was gone, so you wouldn’t see much of anything at first. Then you’d see more Lystrasauros (sp?) which weren’t dinosaurs but rather some of the last of the Mammal like Reptiles. They were really the first animals to recover and were everywhere. Then you start seeing a rising group of reptiles, the archosaurs, the precursors to crocodiles on the one hand, and dinosaurs on the other. After that the first small dinosaurs start appearing, as do mammals. At the end of the Triassic there’s another extinction event that kills off the rest of the mammal like reptiles and the large archosaurs, but the dinosaurs thrive and dominate. + +In the Jurassic and Cretaceous they’re ubiquitous." "I hope a real paleontologist can take a stab at an answer. It's a challenging question because only a very small amount of animal life gets preserved as fossils, and preservation depends on a ton of factors, so it's tough to extrapolate from the number of fossils to the number of living animals. + +I'll take a very rough physics stab at the the problem by thinking about energy. To make animals, you need plants. Was the growth rate of plants significantly different in the Mesozoic era? Well, the sun was about the same brightness, so same energy for photosynthesis. The temperature was generally warmer, though, and there was much more CO2 (which plants need for photosynthesis). But on the other hand, grasses had not evolved yet. Grasses are the dominant plant type in many of the places on the modern Earth that have the densest population of wild animals, like the African savannah you mentioned: they use a special photosynthesis system called [C4](https://en.wikipedia.org/wiki/C4_carbon_fixation) that's much more more efficient than other plants. Without them, average plant growth rate would be less. + +So we've got a factor suggesting overall similarity of plant growth (sunlight), and other factors that both increase and decrease it (CO2, C4 evolution). So there's no way to say for sure, but it's reasonable to guess that the plant growth rate, and so the abundance of large animals, might not be too different from what it is in wild ecosystems today. + +Most places in the modern world, you'll see a few small animals (including the descendants of dinosaurs) without having to look very hard, maybe a large plant-eating mammal or two, but big predators are very rare. I doubt the Mesozoic would have vastly more or fewer." +1706 "AskScience AMA Series: I'm a primatologist and conservationist who's seen every genus of primate in the wild and is featured in the PBS/BBS series ""Primates."" Ask me anything!" 41 https://www.reddit.com/r/askscience/comments/jwejij/askscience_ama_series_im_a_primatologist_and/ 1605700829 jwejij Biology 2020-11-18 15:00:29 How many known primate extinctions have there been in the last 200 years? What’s it like being near gorillas? I used to work with some folks from Uganda and they’d tell stories about how powerful gorillas are. Awe inspiring, terrifying or something else? +1911 If we found a way to reverse a hashing function, would that make them ultra-compression algorithms? 41 https://www.reddit.com/r/askscience/comments/o0h3bi/if_we_found_a_way_to_reverse_a_hashing_function/ 1623771098 o0h3bi Computing 2021-06-15 18:31:38 "A hash is **not** meant to produce a unique output for any input, it simply can't. The number of possible inputs is much, much, much larger than the number of unique outputs. This is the *pigeon hole principle*. + +For a good hash function, the output space is so large, that in practice, the chances of having two actual existing inputs with the same output is quite small. These duplicates exist, but finding the collisions is extremely hard. + +In fact, for any file you have, there are billions upon billions (actually much much bigger) of other possible files that would yield the same hash value, but you're just very, very unlikely to ever bump into one." "You could reconstruct _an_ output which produces the same hash, but this is not guaranteed to be the original input. + +There are many possible values of the inputs and many fewer possible values of the hash, therefore multiple inputs _must_ hash into the same hashes." +1168 Why dont more people in the US get illnesses from mosquitoes even though the same mosquito may extract blood from several hosts? 40 https://www.reddit.com/r/askscience/comments/9gfgso/why_dont_more_people_in_the_us_get_illnesses_from/ 1537142514 9gfgso Biology 2018-09-17 3:01:54 "To spread via mosquitos, pathogens need to be pretty specialized. Mosquitos don't take all that much blood from one host, and transfer far less to the next host, so if the pathogen is just in the blood, it's very unlikely that there will even be a single pathogen particle in the transferred blood. + +Vector-borne pathogens, like yellow fever or malaria or dengue, overcome this by replicating in the mosquito and often by entering the mosquito's salivary glands. Mosquitos transfer more saliva than blood, and if the pathogen has replicated there and is present in high concentrations, it's easier to spread. + +But look at the challenges this presents to the pathogen. It has to be equally effective at replicating in a mammal and in an insect. In the mammal it has to spread into the blood and be there in high concentrations, and then it has to follow a completely different pattern in the mosquito. The body temperatures, the receptors, the cell types - everything is different, so the pathogen basically has to carry double sets of everything. + +So just generic pathogens don't do this. In the US, there are a handful of the specialized pathogens that are arthropod-born. West Nile virus is well known. There are several types of viral encephalitis (Venezuelan Equine Encephalitis, Western EE, Eastern EE). There are some tick-borne diseases like Lyme Disease and Colorado Tick Fever and so on. + +Some of the other diseases used to be present in the US, but were eradicated. Malaria was eliminated by the precursor of the CDC in the 1950s. The process reduced the number of the worst types of mosquitos, the ones that spread some of the worst diseases. That's helped as well. + +Currently of course there are some mosquito-born diseases that are trying to move back into the US, as climate change makes larger regions more attractive to the mosquitos. Zika was found in Florida. Chikunungya has been found spreading locally in Florida. " +1169 Because light has momentum, can it move an object with a defined mass? 40 https://www.reddit.com/r/askscience/comments/9fnhdv/because_light_has_momentum_can_it_move_an_object/ 1536885506 9fnhdv Physics 2018-09-14 3:38:26 "Yes. Solar sails have been used to transfer momentum from light to spacecraft. The Mariner 10 used radiation pressure on its solar panels to adjust its attitude, and the JAXA IKAROS spacecraft utilised a solar sail as propulsion. + +The amount of propulsion provided is minuscule, but it would be useful for extremely long journeys. " Because the other comments are focused on space propulsion I will also add that light is used to exert forces on matter at the microscopic scale, ie optical tweezers. Because light has momentum it exerts a force on molecules and can be used to trap and move very small particles. This is a famous technique in biophysics where, for example, you want to measure the mechanical properties of DNA by trapping it and pulling on it with a laser. +1912 Why is the floor of the Uyuni salt desert partitioned into specifically hexagons and no other pattern? 40 https://www.reddit.com/r/askscience/comments/p8ushd/why_is_the_floor_of_the_uyuni_salt_desert/ 1629564364 p8ushd Earth Sciences 2021-08-21 19:46:04 "[Convective currents in the evaporating surface water after rain.](https://www.lindau-nobel.org/blog-from-star-wars-to-geophysics/) + +When it rains, there is a flat layer of salty water sitting above ground. As the water evaporates from the surface, it leaves its dissolved salt behind, which concentrates salt in the very top layer of water. This leaves you with a layer of less-salty water touching the soil's surface, and a layer of saltier water floating on top. + +But the saltier water on top is actually *more* dense than the ligher, less-salty layer of water below. The heavy salty water wants to sink, and the light less-salty water wants to float. Because the surface is so flat and so wide, this creates little 1-2 meter ""convection cells"" in the water, with less-salty water rising in the center, displacing the heavier, saltier water which can sink along the edges of each convection cell. + +If there was only *one* convection cell in one place, this cell would be more like a circle. And as the denser, saltier water flowed down at the edges of that circle, it would deposit a little of its dissolved salt onto the ground. As all the water evaporated, this would create a ""ring"" of salt around the edges of the cell. + +But since there are lots of convection cells, they intersect at their edges, creating geometric patterns much like bubbles create flat geometric edges where they touch one another. At the center of every hexagon (or pentagon, some of the shapes are five-sided) was once an upflow of less-dense, low-salt water, and at the edges are where the higher-salt surface water was flowing away and down. + +The diagram in the linked article may help you visualize this process." "Because even salt knows that hexagons are the bestagons..... + +https://youtu.be/thOifuHs6eY + +More practically, though not unrelated, hexagons are an infinitely stacking shape that has its corners at equal distance from the centre. It also forms easily when a shape regularly contracts towards the centre, as drying objects do." +1170 Why do waves come in sets? 39 https://www.reddit.com/r/askscience/comments/9hiasg/why_do_waves_come_in_sets/ 1537472555 9hiasg Earth Sciences 2018-09-20 22:42:35 Wind speeds are variable in space and time and this produces a spectrum of waves of different periods and wavelengths. The longer period waves travel faster in deep water so the waves will sort themselves out as they propagate away from the source. These waves interact and the waves with the shorter periods are modulated by longer period waves producing wave packets that vary in wave amplitude as U experienced diving with small waves followed by larger waves than small waves. The larger waves occur at the crest of the longer period waves. "There are multiple wavelength and amplitudes of waves in the ocean. When two different wave trains of approximately the same wave length are traveling in the same direction, their wave crests and troughs will move in and out of phase with each other over long distances. A ""set"" is when two waves trains with slightly different wavelengths are in phase with each other just as they reach the shore. The three waves of a set consist of the first, where they're barely out of phase, the middle where they're exactly in phase, and the third where they're starting to separate by still mostly in phase. Obviously the middle wave is the biggest (an often debated point among surfers an which of the three is the biggest). You'll often notice waves just before and after a set are ""doubled"" --ie the waves have moved far enough out of phase that they're perceived as two separate wave crests; but they're close enough together that the trough between them isn't the full trough depth between waves. The second wave of these doubled waves often seems like a bigger, good wave to catch, but is invariably disappointing because you don't get a steep wall as it moves into the first wave. " +1171 Are there any other viable power sources available to us other than electromagnetic induction and photovoltaic technology? 39 https://www.reddit.com/r/askscience/comments/9d5v83/are_there_any_other_viable_power_sources/ 1536149200 9d5v83 2018-09-05 15:06:40 "Fuel cells and thermoelectric generators are two less known ways. Fuel cells generate electricity through reacting oxygen with a fuel, often hydrogen, and have no moving parts similar to a photovoltaic cell. Thermoelectric generators use a strange property of metals called the seebeck effect, where two different metals at different temperatures connected at two points will cause a current to flow though them. + +Fuel cells are really only used for energy storage, because we don’t have an easy source of hydrogen without electrolyzing water, which takes energy. Thermoelectric generators aren’t very efficient, so we don’t use them often either. Though, in space they’re pretty handy because you can put radioactive plutonium pellets in a chamber which heats it up, and the outlet side can be cooled by radiating its heat to space, effectively giving you a constant power source for many years." "Well there are other methods to get power. Most of the ones I am going to list are not really viable, but it doesn't mean it's not impossible in the future or something we want to look at in the future. + +* There is direct chemical electrical production (think a battery), if you can find the raw materials and build the battery it could be a power source. Along those lines in a hydrogen fuel cell, if you can find hydrogen it's possible to be a power source, not just a storage medium. In reality, the chemicals that this requires are very reactive and don't really exist on earth in any significant quantities. +* There are thermocouples that work off the seebeck effect, anywhere there is a thermal gradient you can exploit that for power. This could be replacing the steam and generator bits in a power plant, used to harness solar by just painting one side black and putting the other in contact with coolant, or geothermal, etc. In general this isn't as efficient as steam+generator. +* Static electricity can be used to essentially harness the wind, that is you could fly a piece of plastic off a tower and it would develop a voltage due to the wind over it, and you could get a current between that and ground, this is similar to harnessing lightning (which really isn't viable because it's not controllable and it's far too variable, a wind-static generator would be more controllable and more consistent) +* One of the designs they are working on for fusion is a magnetically controlled reactor, they could compress the fuel with a magnetic field, and let it expand as it undergoes fusion and gets hot, this would push the magnetic field, and that pushing could be extracted though inductors. It would operate like an internal combustion engine, but the piston would be a magnetic field. Ultimately this is still electromagnetic induction, but it's without the spinning electric generator so I think it's worthwhile to mention. +" +1507 Is there a theoretical limit to how much detail we can get from satelital images? 39 https://www.reddit.com/r/askscience/comments/ej6in2/is_there_a_theoretical_limit_to_how_much_detail/ 1578008598 ej6in2 Physics 2020-01-03 2:43:18 "Diffraction puts a (quite) hard limit on the size you can resolve. To distinguish two things (like an ant from the ant next to it) with a separation x from a distance d using wavelength lambda your telescope should have a diameter of d\*lambda/x. Let's take 5 mm for the ants, 400 km for the orbit, and 500 nm for the wavelength, then your telescope needs a diameter of 40 meters. That's the size of the largest optical telescope under construction on Earth (ELT), and much larger than any space telescope under development. You don't need a full mirror that size, an interferometer that has a few smaller mirrors spread out that much can work as well, but this is not easy to build either. + +Atmospheric distortions are another thing to worry about - currently more relevant for space telescopes looking outwards, but on the level of watching ants this might become relevant for the opposite direction, too. + +Google maps uses satellite images for large-scale views and images from airplanes for the higher zoom levels. If you can see people then the image is most likely from an aircraft." +1508 what would happen to a person’s immunity if they were exposed to monoclonal antibody therapy after already developing a natural immune response? 39 https://www.reddit.com/r/askscience/comments/g0s0bm/what_would_happen_to_a_persons_immunity_if_they/ 1586813153 g0s0bm Human Body 2020-04-14 0:25:53 "Not an immunologist but a physician....any antibody that you are providing (monoclonal or otherwise) will then be a supplement to the existing antibody. The difference is that in the case of natural immunity there probably also exist many memory T-cells that can recognize the antigen and stimulate a secondary immune response and plasma cells that can make a lot more new natural antibody, while the monoclonal antibody has to be provided frequently (levels may drop by 50% every 3 weeks). Another issue is that any antibody you provide, if not sufficiently ""humanized"", may generate an immune response against the new antibody itself (eg if from mouse myeloma cells, there may be a response against the mouse immunoglobulin peptide) that can cause major side effects. As monoclonal antibodies are expensive, it may be worthwhile to do seroprevalence testing to see if someone has natural antibodies first. Also, one can develop a vaccine that provides more longer-term immunity (but takes time to develop; hence post-exposure prophylaxis or treatment may include antibodies/convalescent sera)." "The most likely scenario is that nothing happens as long as the mAb is also human derived. If the mAb is better than the natural immune response, it will help in the fight. If it is worse, it will eventually get cleared by the liver as any other antibody. + +The only potential side effects from an antibody therapy come from the antibodies having a cross-reactivity with a different antigen than the intended. If the monoclonal antibody binds to a self-antigen, it might create an autoimmune response. This is usually not the case if the antibody was derived in the same species." +1626 What prevents white blood cells from entering the intestines and attacking the large colonies of bacteria that exist there? 38 https://www.reddit.com/r/askscience/comments/hwbhe1/what_prevents_white_blood_cells_from_entering_the/ 1595489694 hwbhe1 Human Body 2020-07-23 10:34:54 [deleted] Immune cells can react to intestinal pathogens, but they don't actually enter the lumen. There is a special type of immune cell called [Microfold cell](https://en.wikipedia.org/wiki/Microfold_cell), which is embedded into the mucous membrane. It basically takes small samples from the contents of the gut, and passes those samples onto the lymph follicles in the submucosa. The lymph follicles contain lymphocytes (T-cells and B-cells) which can elicit an immune response if necessary. +1833 If a woman ovulated off the right ovary and had an early miscarriage, is she more likely to ovulate off the left ovary in the following cycle? 38 https://www.reddit.com/r/askscience/comments/lsd7hg/if_a_woman_ovulated_off_the_right_ovary_and_had/ 1614277569 lsd7hg Human Body 2021-02-25 21:26:09 A miscarriage shouldn't affect where you ovulate from next. Often at the point of the miscarriage, the embryo has already implanted into the uterine lining so everything that happens after that does not influence the ovulation cycle. Hope this helps answer your question! Side of ovulation appears to be random and has no impact on the hormonal characteristics of reproductive events (see [this study](https://academic.oup.com/humrep/article/15/4/752/706405)). As for early miscarriage, after any pregnancy ends (regardless of its duration), the hypothalamus, pituitary and ovaries (both of them) can take a few cycles to get back to normal. During early pregnancy, progesterone from the corpus luteum (yellow blob of tissue on the ovary that ovulated the egg, at the site where the eggs ovulated from) strongly inhibits all of those organs and keeps both ovaries effectively shut down. As soon as progesterone drops, though, the hypothalamus usually starts back up again pretty promptly, but it can take a couple cycles to get the pituitary and then the ovaries back in gear too - it’s a sequence of events involving all those organs “talking” to each other & it can take a bit of time before the next crop of ovarian follicles reaches ovulatory size. But in theory, the miscarriage shouldn’t have affected the ovary that ovulated that egg, From the ovary’s perspective, all that happened was that its corpus luteum lasted a bit longer than usual, but a corpus luteum should be nothing new for that ovary since a C.L. develops after every ovulation. +1627 If rabies is virtually 100% fatal and humans have a vaccine, why is it not common practice to give every human a rabies vaccine? 37 https://www.reddit.com/r/askscience/comments/hw35l9/if_rabies_is_virtually_100_fatal_and_humans_have/ 1595455271 hw35l9 Medicine 2020-07-23 1:01:11 The rabies vaccine has a pretty high rate of side effects, and for most people it's really not needed. The only people who are vaccinated as a preventive measure are veterinarians, spelunkers (risk of rabid bats), or people traveling to areas where rabies is a problem. If you don't have an imminent need for the vaccine, there's no point in administering it, since the overwhelming majority of people will never need it. And it's 100 effective when administered soon after a bite anyway. "It is recommended by the WHO in areas where the risk is high. A few reasons that it isn't widely recommended in areas where the risk is lower: + +\- Post-exposure prophylaxis is protective (and we'd do it anyway, even if people were vaccinated) + +\- The risk of rabies (in many countries) is very small + +\- The rabies vaccine is pretty expensive + +\- While the vaccine has fewer adverse effects than it used to, it still has a surprisingly high rate of adverse events, so in populations where the risk of rabies exposure is minimal, it may not be worth the risk of vaccinating everyone." +1834 "Some of the most massive craters on the surface of the moon and elsewhere throughout the solar system seem relatively ""shallow"" considering how wide the craters are. What gives craters this wide and flat shape?" 37 https://www.reddit.com/r/askscience/comments/lse7ry/some_of_the_most_massive_craters_on_the_surface/ 1614280123 lse7ry Planetary Sci. 2021-02-25 22:08:43 "The Modification stage of crater formation. See figure [here](https://i.imgur.com/jBKi8pF.jpg) of simple crater formation. + +So long as there aren't huge density differences, the initial excavation from the impact is pretty close to a hemisphere centered on the impact point. However, the resulting crater walls are usually a fair bit steeper than the [angle of repose](https://en.wikipedia.org/wiki/Angle_of_repose), especially for all that newly fractured rock. That material slumps back into the bottom of the crater, leaving behind a wide, relatively shallow depression." "One of the reasons is that if the impact is large enough it'll crack the crust and cause magma to well up and fill in the crater. This is why the larger craters on the moon are darker (the ""Mare""), because they're filled with igneous rock." +1835 Is poison immunity actually attainable by poisoning the body repeatedly? 37 https://www.reddit.com/r/askscience/comments/lcldj3/is_poison_immunity_actually_attainable_by/ 1612460877 lcldj3 Human Body 2021-02-04 20:47:57 "Sometimes, but it depends upon the poison/toxin/venom and how you define immune. That's exactly the process which is often used to produce snake antivenom. People will inject horses with small doses and build up a tolerance, then harvest their blood for the antibodies. Those horses are effectively immune to a normal snakebite. You could argue that a large enough dose would still be lethal so it's not complete immunity, but for practical purposes it is. I have run into stories of at least one person doing this to himself intentionally. + +But you aren't going to be able to build up a resistance to mercury, for instance, because your body can't produce antibodies against it. + +https://www.zmescience.com/ecology/animals-ecology/antivenom-made-precious/" The term for administrating sub-lethal amounts of a poison with the purpose of building up tolerance is called **mithridatism**. In practice it entails a lot of risk and is only effective against certain types of poisons, mostly those that are biologically complex that the liver metabolizes. Essentially this method is conditioning the liver to ramp up enzyme production. This doesn't give you immunity to the poison only increases the amount you have built up tolerance to. Where as poisons like heavy metals will not be metabolized and accumulate, this method will not be effective against these types of poisons. +2002 How can Neuropathy (Nerve Damage) cause Numbness is Some but Pain in Others? 37 https://www.reddit.com/r/askscience/comments/rbu17z/how_can_neuropathy_nerve_damage_cause_numbness_is/ 1638978062 rbu17z Neuroscience 2021-12-08 18:41:02 "Unfortunately I don't have a complete answer for you, but I may be able to point you in the right direction. The following explanation will depend on your Masters background knowledge! + +This may be down to the type of fibre and the spinal cord tract the nerve belongs to. Pain and temperature are handled by the lateral spinothalamic tract, whereas crude touch and pressure are handled by the anterior spinothalamic tract. Pain is also moderated by a variety of fibres depending on the type of pain, and the signals travel at different speeds depending on the type of fibre. Alpha delta fibres handle acute pain (fast signal), whereas C fibres handle dull, throbbing or ""burning"" pain (slow signal). + +As I said earlier, this may not answer your question completely, but hopefully it helped a bit! (Source: my master's degree in physiotherapy!)" A nerve is a bundle of axons. Each axon is associated with a specific neuron. Could be motor neurons or any of the various types of sensory neurons (touch, pressure, pain, temperature, etc).If you damage a nerve, you might not damage all the axons in the nerve. If the axons that were damaged were primarily from pain neurons, you might feel more (or less) pain. If the damaged axons were motor, you might not have any sensory issues, but just have trouble contracting muscles. It’s really all about where the damage has occurred that determines what the symptoms are. +1172 How do we know that quarks are fundamental particles (don’t have a substructure)? 36 https://www.reddit.com/r/askscience/comments/9k32gy/how_do_we_know_that_quarks_are_fundamental/ 1538278127 9k32gy Physics 2018-09-30 6:28:47 We are not sure and there are searches for hints of compositeness. It is unlikely, however. Typically you expect to see a substructure before the involved energy reaches the rest energy of the particle. You see that an atom has a nucleus and electrons with a few electronvolts of energy (ionization), you see that the nucleus has a substructure (protons/neutrons) with a few million electronvolts, you see that the protons and neutrons have a substructure (quarks/gluons) with ~100 million electronvolts - compared to proton and neutron masses of 940 million electronvolts (and more for larger nuclei and atoms). Now we are at trillions of electronvolts and still no substructure of quarks visible. It would need very strange fine-tuning of their components and their binding to create something relatively light that cannot be split even with so much energy. +1173 How much did the Chicxulub crater affect the plate tectonics of North America? 36 https://www.reddit.com/r/askscience/comments/9fgd5e/how_much_did_the_chicxulub_crater_affect_the/ 1536829176 9fgd5e 2018-09-13 11:59:36 "The Chicxulub impactor is not thought to have caused any change in the way plate tectonic processes were operating. + + +Pangea was fully assembled in the late Permian, about 270 million years ago. The breakup process started in the early Jurassic, about 200 million years ago, though this took tens of millions of years. By Late Jurassic the world looked something like [this](https://i.imgur.com/r747mcd.jpg). Sometime in the Early Cretaceous, about 120 million years ago or so, reconstructions look [like this](https://i.imgur.com/EsJxYmO.jpg). All of today's continents are clearly recognisable, though some shuffling about still needed to occur before we have today's map. + +The Atlantic Ocean basin opened up in stages throughout the Cretaceous, so that by late Cretaceous times just before the asteroid hit we have something [like this](https://i.imgur.com/L7XKn0q.jpg). The only things which have yet to occur are further widening of the Atlantic basin, India's collision with Asia, Australia's separation from Antarctica and a lowering of global sea levels. The forces responsible for moving tectonic plates around are linked to production of plates at mid-ocean ridges, recycling of plates at subduction zones, and to a lesser extent the convective drag on the underside of plates from currents in the solid mantle. It's not thought that the end-Cretaceous impact did anything to change any of these, definitely not to the extent that plates configured a certain way or anything. I'm sure there would have been the largest earthquakes the planet has ever experienced when it hit though. " +1174 "How long did it take for nuclear fusion to spread throughout the core of the star on ""ignition""?" 36 https://www.reddit.com/r/askscience/comments/9jun78/how_long_did_it_take_for_nuclear_fusion_to_spread/ 1538205220 9Jun78 Physics 2018-09-29 10:13:40 +1707 How do the Indian-made COVID vaccines differ from their Western counterparts? 36 https://www.reddit.com/r/askscience/comments/kfpcl4/how_do_the_indianmade_covid_vaccines_differ_from/ 1608312085 kfpcl4 COVID-19 2020-12-18 20:21:25 India along with countries like Bangladesh can receive special rights for producing patented medicines for very low cost. This has created a massive and booming pharmaceutical industry in these countries. I remember last time I visited Bangladesh pretty much every town had a pharmacy district with multiple drugstores on the same street. There wasn't a prescribed medicine you couldn't find. This extends to vaccines. +1836 Why are Covid tests least accurate when you’re most contagious? 36 https://www.reddit.com/r/askscience/comments/l9jt3w/why_are_covid_tests_least_accurate_when_youre/ 1612121287 l9jt3w COVID-19 2021-01-31 22:28:07 "> but much higher (up to 100%) earlier in infection + +That refers to 4 days before you show symptoms, at that time you are generally not contagious yet. The false negative rate decreases as you get closer to showing symptoms and then stays relatively low while you are contagious. Direct quote from the source of your first source: + +> Over the 4 days of infection before the typical time of symptom onset (day 5), the probability of a false-negative result in an infected person decreases from 100% (95% CI, 100% to 100%) on day 1 to 67% (CI, 27% to 94%) on day 4." "The antigen test is looking for the virus, which increases prior to the host identifying it. The antibody test is looking for at host defenses to a prior antigen exposure or a current exposure (based on which Ig type you are looking for.) + +So under the right conditions, someone is contagious and shedding viruses before the host is able to identify it, and then it makes antibodies. Once these antibodies are present, so is the virus, and the immune system kicks in to deliver a synergistic attack. The symptoms are the body trying to decrease the total antigens present; coughing it out, pooping it out, and baking it to a crisp. + +The ""Molecular test"" looks for the antigen. If you look for the antibody early in the viral process, it might not have been made yet by the host or too low to be detected." +1175 Is there any circumstance in which the coefficient of kinetic friction is greater than the coefficient of static friction? 35 https://www.reddit.com/r/askscience/comments/9ihv21/is_there_any_circumstance_in_which_the/ 1537795297 9ihv21 2018-09-24 16:21:37 "Well imagine what happen then: + +You overcome static friction so you start moving the object. But you didn't overcome dynamic friction, so you stop immediately. Having static friction35" +1181 As the sun burns, is it losing mass, volume, neither or both? 30 https://www.reddit.com/r/askscience/comments/9cvkf5/as_the_sun_burns_is_it_losing_mass_volume_neither/ 1536067463 9cvkf5 Astronomy 2018-09-04 16:24:23 "The answer is more complicated than the possibilities you provided. + +Do you mean the sun specifically, or stars generally? Because the change in volume is going to vary wildly based on the type of star and which evolutionary phase it is in. + +As for the sun, the light we see is a result of hydrogen fusion. Keeping a long story short, a Helium atom (the end result of the fusion process) weighs less than the sum total of 2 protons and 2 neutrons. The difference in mass is transformed into energy in the process. Some of that energy is in the form of photons. So as the sun emits light, it is technically losing mass. + +On top of that, the sun actually produces a Solar Wind, in which it expels roughly 2-3 . 10^-14 M_☉ (solar masses) per year. + +The sun also loses mass through solar flares and coronal mass ejections, which amounts to roughly one order of magnitude less than the solar wind. + +Other stars, such as Wolf-Rayet stars will lose a lot more mass due to winds. A quick google search gave me [this](https://arxiv.org/pdf/1710.02010.pdf) article, which estimates that very massive stars (60 M_☉) lose around 10^-5 M_☉ per year. There exist even more massive stars (> 100 M_☉), which will lose even more mass by winds. + +As for volume, you'd basically have to read a whole book on stellar evolution by mass to see what happens to which stars in which phase, but suffice to say it's complicated. During the main sequence, most stars will be relatively stable, but many stars undergo big changes in volume over their lifetimes, some even pulsate quite extremely (e.g.: Cepheids and RR-Lyrae stars). + +The sun will be relatively stable for now, then, once hydrogen core burning stops, it will expand and become a red giant. Once Hydrogen shell burning starts, it will pulsate. Once Helium core burning starts it will be relatively stable, until the AGB phase starts, during which it will pulsate some more because there will be an interchange between hydrogen shell burning, helium core burning, both and neither. Once that is done, the outer layers will be gone and a white dwarf remains (which is a size on the order of the size of of Earth). + +TL;DR: it's complicated." "Energy and mass are related. It’s giving off energy as it “runs”, therefore losing mass. Volume is a bit trickier to talk about though. As a star burns through it’s fuel, it can either shrink or eventually expand in to a red giant (pressure vs gravity). + +It’s been far too many years since my astronomy classes though, so I do not remember the maths we did to calculate the destiny of the great Sol. So I’ll leave it for someone else to expound. " +1182 If the brain recovers from depression, than are there obvious before and after structural changes? 30 https://www.reddit.com/r/askscience/comments/9eixre/if_the_brain_recovers_from_depression_than_are/ 1536547248 9eixre Neuroscience 2018-09-10 5:40:48 "Depression isn't a simple thing. It's not even one thing. There's no reason why we should believe the mechanisms involved in the depression of all people are similar. + +​ + +Let's take a look at the most infamous of antidepressants: SSRIs. These drugs work by preventing neurons from shutting down serotonin signals by reabsorbing the molecules. Normally, serotonin is cleared from the synapse (the space between two neurons where communication takes place) by dedicated transporters. By blocking these transporters, it takes more time for serotonin to be cleared. Because of this, serotonin acts on the post-synaptic neuron for a longer period of time, boosting the signal so to speak. + +​ + +We first started specualting serotonin levels could be involved in depression when a drug used for treating high blood pressure, reserpine, seemed to trigger depression in some people. Reserpine blocks the mechanism that transports monoamines (including serotonin) into ""vesicles""--small ""bags"" inside neurons containing signaling molecules that are released across the synapse. + +​ + +There's a strange thing about SSRIs: they don't start working until about two weeks after treating has begun. This is strange, because their effects are present within hours. But then again, neurons have things called autoreceptors. They control how much of a neurotransmitter is present in the synapse and can regulate release accordingly. If the brain is being flooded, they can reduce release via a negative feedback mechanism. The two-week period could correspond to a desensitization of this mechanism. + +​ + +But there are also receptors for the signaling molecules that can be regulated up or down. If there is a lot of serotonin going around, receptors can be downregulated. So it's hard to say what the clinical effects of SSRIs actually are. + +​ + +Then there's the issue of effectiveness. NNT--Number Needed to Treat is a term used to describe the efficacy of a treatment. It's how many patients need to be treated for one of them to improve. This number varies depending on the study, [but this is representative](https://www.aafp.org/afp/2010/0701/p42.html). They found a NNT of 7. 7 patients needed to be treated for 1 of them to improve for other reasons than mere placebo. + +​ + +And for some reasons, SSRIs seem to only be effective at all for severe depression. Mild and moderate depression can be ""treated"" via the placebo effect, but drugs don't seem to help much. + +​ + +Then there are the side effects. About 95% of the serotonin in your body is used to regulate processes in your gut. If you mess with the serotonin system, you will be getting serious gastrointestinal side-effects. + +​ + +Some researchers even believe that SSRIs work by reducing serotonin levels. It's so complicated that it's hard to know what exactly is happening. + +​ + +Tryptophan is the rate-limiting factor of serotonin. This means that it is needed for synthesis and there's no way around it. Lower levels of tryptophan and eventually levels of serotonin will plummet. Tryptophan depletion is a trick that is sometimes used to study the effects of low levels of serotonin. Researchers have found that impulsivity is the most common result. Depression does occur in some people--but it actually only seems to happen to people treated with SSRIs. + +​ + +Then we have different receptors. There are 14 types of serotonin receptors, with 7 major families. The 5-HT1AR is the one that is targeted by SSRIs. It's inhibitory, meaning that it reduces the activity of neurons onto which it is expressed. The 5-HT2A, on the other hand, has the opposite effect: it results in increased activity. The balance between expressions of each receptor can obviously be involved here. And 5-HT2ARs can be located on inhibitory neurons and thus result in inhibition rather than stimulation. + +​ + +There have been studies on the genes coding for the serotonin transporter, the 5-HTTLPR, with research suggesting that differences in this gene can result in a predisposition for depression as a result of stress. But then there are different studies arguing that this is a misinterpretation of earlier studies and that such a link does not, in fact, exist. + +​ + +There have also been a study where mice have been bred so that that normal serotonin signaling in the central nervous system is abolished. These showed no signs of depression; just impulsivity and some increased aggression. + +​ + +And there's the case of how serotonin receptors are expressed on different brain areas in different people. + +​ + +Sure, you could get some fMRI images that seem to show a little different activity in the amygdala and the anterior cingulate cortex and the hippocampus and the basal ganglia and the habenula and the prefrontal cortex and in any other brain area that has been linked to depression, but there's a problem. Let's say you wanted to figure out what is happening in different streets. So you can long-exposure images lasting 12 hours each. You then look at the images and try to find something meaningful to say. This is basically how fMRI works. You see some lights indicating a hub of activity in front of the ATM. That might be meaningful, but it's really hard to say whether it actually is. Because the time scale is off. Things inside cells happen very, very fast. fMRI images are comparatively very, very slow. + +​ + +And we have only talked a little about SSRIs. That's a small piece of the picture, but yet it is very complicated. + +​ + +What I want to convey is that depression is a hugely complicated process. We are very, very far away from understanding it." "The question is legit, but also a little flawed. The brain is not like a mini-me we have inside our bodies. Depression is a big and complex construct with implies many aspects such as the whole physical body, the cognition aspects and the context. Believing that the so called mental illness and the brain are that much connected is a current and popular misconception, probably is due to bad journalism and poor science press on major media. Another problem is that the word *""linked""* can be extremely confusing, we trend to believe that two linked things are directly related, for example one may see that Tibetan monks live a pretty anxiety-free and depression-free life, and also that they do a lot of meditation, that may lead us to make the false connection that they are not depressed because they do meditation (that's the *'post hoc'* fallacy bias). + +So as you ask, yes there are studies that *link* certain aspect of depression on how the amygdala processes stimuli, and the levels of certain neurotransmitters and hormones in the central nervous system (that's not the brain at all). But there are also studies that *link* depression to economic levels and studies that *link* depression to genetic predisposition and studies that link depression with isolation.... + +" +1510 How do ants breathe? 30 https://www.reddit.com/r/askscience/comments/ek8oap/how_do_ants_breathe/ 1578202009 ek8oap Biology 2020-01-05 8:26:49 Insects do indeed lack lungs, and instead have a tracheal system which spreads oxygen around their body (and removes carbon dioxide). Air enters through holes called [spiracles](https://textimgs.s3.amazonaws.com/boundless-biology/figure-39-01-05.jpe) in their thorax/abdomen, and then circulates around to mediate gas exchange. [Here's a neat picture](https://i.redd.it/2cvdggizh1z31.jpg) of a semi-transparent caterpillar where you can clearly see the spiracles and tracheal branches. This is mostly a passive process, but when exerting themselves many insects can also pump their abdomens to move air faster (you've probably seen bees or wasps doing this). Another fun fact is that even though it goes throughout their body, the tracheal system is still part of an insect's exoskeleton, so they replace it when they molt. You can sometimes see the inside-out remnants of the old tracheal system as white strands when they do this, like in [this molting cicada](https://upload.wikimedia.org/wikipedia/commons/e/eb/Cicada_Molting.jpg). "Ants, like a lot of other insects, have a tubular system that allows individual cells to get the oxygen directly from air. You can imagine it like our blood vessels, but instead of heart pumping the blood, it's rigid and just open to the air and ~~molecules just happen to get in there~~ *as* u/amaurea *pointed out insects force air flow through sort of valves and body contractions / expansions.* This is also how ages ago giant insects could live on earth; the atmosphere was denser */ more oxygen rich* than it is now, so more molecules were shoved into those tubes. + + +*Edit: owning up to my mistakes*" +1630 Why are cleft palates, which seems like a really specific condition, so common? 30 https://www.reddit.com/r/askscience/comments/h7vonj/why_are_cleft_palates_which_seems_like_a_really/ 1592004370 h7vonj Human Body 2020-06-13 2:26:10 "When a baby grows in the womb the face actually consists of 5 different growths than then fuse together. The forehead/nose, the cheekbones and the jawbones (which is why when you feel your chin you can feel where the jawbones fused together and why some people have a cleft chin). + +Anyway, if this growth process is inhibited in anyway the face won't close properly and you end up with a cleft palate/cleft lip. Especially since the upper part of the face needs to be a lot more precise than the lower jaw (the lower jaw has a bit of tolerance. I mean, how many people don't have an over or underbite?). + +Heart defects are common for almost exactly the same reason. Growing a lot of independent parts that need to fuse together exactly is hard. + + +P.S: Note that there are many checks and balances in face growth, for example the [IRF6 gene](https://ghr.nlm.nih.gov/gene/IRF6#conditions) that allows the tongue to not attach itself to the rest of the mouth structure by coating the growing tongue with a protein that prevents ""stickiness"". IRF6 malfuction is one of the biggest risk genes for cleft palate." +1709 What would average life expectancy be if there was no healthcare? No doctors, hospitals and modern medicine. 30 https://www.reddit.com/r/askscience/comments/jv6guf/what_would_average_life_expectancy_be_if_there/ 1605532166 jv6guf Medicine 2020-11-16 16:09:26 You would end up with a number that is a little misleading. You know how people say the Romans only lived to 35? The number of young person deaths skews the average way lot. At a guess, in an otherwise-stable society, without doctors, hospitals, and medicine? Plenty of people living into their 60s, lots of people not living past 4 or 5. "The tricky part is that there are times when people are far more likely to die. + +Children below, say, 4 are very vulnerable. Women delivering children also. Young men often died in battle or accidents which also skewed things. + +If you live through those things and have a little luck on your side and enough food and whatever then 60 or 70 wouldn't be unusual. But if you take the average, because so many children died, it's quite low. + +The average adult age at death will be very different to the population average. + +I don't know the exact numbers but if the average age is, for example, 40 that doesn't mean that loads of people drop dead between 35 and 45." +1839 Does regular use of SSRI’s impact overall serotonin or dopamine production? 30 https://www.reddit.com/r/askscience/comments/lsopdg/does_regular_use_of_ssris_impact_overall/ 1614309772 lsopdg Neuroscience 2021-02-26 6:22:52 There are mechanisms for this to occur. For example, some serotonin and dopamine receptors can regulate synthesis and release of their respective neurotransmitters. These are collectively known as “autoreceptors”. So, an ssri, or selective serotonin reuptake inhibitor can lead to increased serotonin levels and possibly autoreceptor activation and inhibition of serotonin synthesis and/or release. However, this varies in different brain areas based on different expression of these autoreceptors. So, the answer to your question depends on where in the brain you look. +1913 What exactly makes the Higgs Boson so special? 30 https://www.reddit.com/r/askscience/comments/nzoeii/what_exactly_makes_the_higgs_boson_so_special/ 1623681891 nzoeii Physics 2021-06-14 17:44:51 "There's a lot to unpack here, and I'm not totally sure if you're asking about the nature of the Higgs boson or how it got its multiple names... so I guess I'll just tell you about both! + +First, it has absolutely nothing at all to do with any God, deity, or religion, and is just a funny name. + +In particle physics, every particle is expressed as an excitation of a field. Photons, for example, are little discrete wiggly excitations of a universe-spanning electromagnetic field. The Higgs boson is, similarly, a little kink in a field that we call the Higgs field. Until this particle was produced and measured at the LHC we weren't actually sure that the Higgs field was really real- producing the Higgs boson in collisions and measuring its mass confirms that the field is real (and knowing its mass and what it decays into tells us some other properties of the field). + +This field is special because it is ultimately the thing that gives fundamental particles their mass. By interacting with this field, particles 'gain' mass. Think of it like a vast, universe-filling ocean of honey that sticks to particles and gives them their inertia. Massless particles, like the photon, do not interact with this field (which is why its massless and always moves at the speed of light!). As you can probably guess, knowing if this is right is a *big deal.* + +The existence of the Higgs field was first proposed in 1964 by a bunch of people pretty much simultaneously (one of whom was Peter Higgs) to solve a problem in particle physics at the time, and it pretty naturally predicted the existence of an associated boson- because if you have a field you get particles from it. The problem was that it was soooo hard to produce this boson experimentally that it became something of a holy grail for particle physicists at the time. Given the religious connotations of 'holy grail', I need to be really explicit that it's not sacred in any way, it's just something fancy and important we quested for. + +In the 90s a physicist named Lederman wrote a popsci book titled 'The God Particle' all about this, which is regarded among physicists as just a sensationalist title to get the public interested and make them want to buy the book (and get some public support for a really expensive accelerator to look for it), and obviously it worked because the name kind of stuck in the media. Funny enough, Lederman has a nice quote about that name- + +> ""This boson is so central to the state of physics today, so crucial to our final understanding of the structure of matter, yet so elusive, that I have given it a nickname: the God Particle. Why God Particle? Two reasons. One, the publisher wouldn't let us call it the Goddamn Particle, though that might be a more appropriate title, given its villainous nature and the expense it is causing. And two, there is a connection, of sorts, to another book, a much older one..."" + +Yeah, it's called the 'God' particle as a PR stunt and because its so *goddamn hard to actually measure*." +1710 Would the antigens produced from the covid 19 mRNA compete for ACE2? 29 https://www.reddit.com/r/askscience/comments/jw5044/would_the_antigens_produced_from_the_covid_19/ 1605658319 jw5044 COVID-19 2020-11-18 3:11:59 "I haven't looked into exactly which part of the spike protein the mRNA replicates, but only one part of the spike protein binds to ACE2 receptor. Targetting anything but the binding domain would not cause ACE2 binding and subsequent inhibition. + +I'm not too sure on the rest as I'm a glycobiologist but have contributed where I can" "If the COVID vaccine caused heart problems, the trials would be throwing adverse events. They are not. Therefore, at a minimum, we know that any adverse impacts must be minimal (by observable fact) before we event consider the bio chemistry. + +Considering biochemistry, the industry is EXTREMELY aware of competing for ligands as an issue since the parexcel disaster in London. + +While I don't know any relevant details for the vaccine, I would be very certain the the proteins encoded by the mRNA will not be ACE2 binding sites, and will instead be other parts the spike structure. Although I am happy to be corrected by an expert." +1511 Does the Earth's magnetic core emit electromagnetic waves as it rotates? 28 https://www.reddit.com/r/askscience/comments/g2igu9/does_the_earths_magnetic_core_emit/ 1587055329 g2igu9 Earth Sciences 2020-04-16 19:42:09 "Yes. Earths magnetic field is due to electric currents caused by convection currents of molten iron at outer core area. Most of it is pointing g up or down. If it was perfectly up and down and perfectly uniform, there shouldn’t be a signal, but since it is not uniform, and since the magnetic Axis is both offset and tilted relative to the rotational axis of earth, there should be some EM waves due to that rotation. + +Edit: I don’t know how significant this source is compared to other sources though." +1631 Why do lung transplant patients have a poorer long-term outlook than other organ recipients? Do we know what causes this? 28 https://www.reddit.com/r/askscience/comments/h11l9q/why_do_lung_transplant_patients_have_a_poorer/ 1591889740 h11l9q Medicine 2020-06-11 18:35:40 +1840 Why is the effective temperature of a black hole inversely proportional to its mass? 28 https://www.reddit.com/r/askscience/comments/lcljz8/why_is_the_effective_temperature_of_a_black_hole/ 1612461340 lcljz8 Physics 2021-02-04 20:55:40 "It's worked out [here](https://en.wikipedia.org/wiki/Hawking_radiation#Emission_process). + +Basically, an observer outside a black hole sees it emitting radiation with a thermal spectrum (characterized by a temperature), but light is gravitationally redshifted as it climbs out of the gravitational well of the black hole. + +Using general relativity, one can calculate the effective temperature of the radiation spectrum as seen by an observer infinitely far away from the black hole, and it works out to be inversely proportional to the mass of the black hole." +1183 What's the reason behind countries choosing different voltage standards? 27 https://www.reddit.com/r/askscience/comments/9gmf28/whats_the_reason_behind_countries_choosing/ 1537205717 9gmf28 Engineering 2018-09-17 20:35:17 "More than anything else, electric systems need to be standardized. Once a country (or a company within a country) decides on a certain system, everyone else has to use the same standard or else bad things (i.e. fire) will result. + +The specific choice of voltage usually had to do with a trade-off between the cost of installing new electric wires and the demand for electricity. Higher voltage systems are able to carry more power with less copper conductor than lower voltage systems. Thomas Edison thought that 110 volts was a reasonable compromise between power and conductor size, and 110 volts happened to work pretty well for Edison's electric light bulbs, which are what most people used electricity for at the time. Everything else built in the US had to be compatible with that 110 volt standard. + +Other countries recognized that 220 volts required less copper, and would therefore result in a cheaper electric grid. They also standardized later than the US, and were able to take advantage of improved techniques and materials that made 220 volt power easier to work with. For those countries the higher voltage made sense at the start, so everything else built in those countries had to be compatible. + +In practice there's not any pressing reason to say that the entire world needs to run the same electric standard, so we just continue with multiple standards. Most electronics are manufactured so they can run on either 110 or 220 volt systems (and 50 and 60 hertz systems), so the point is increasingly becoming moot." +1184 Why haven't we adopted and improved upon Nikola Tesla's designs for wireless charging and power? 27 https://www.reddit.com/r/askscience/comments/9hb1e3/why_havent_we_adopted_and_improved_upon_nikola/ 1537406760 9hb1e3 2018-09-20 4:26:00 "We have. Some applications of wireless power transfer are based on Tesla's ideas. For example induction cooking and wireless charging of various cordless and mobile devices (from electric toothbrushes to smartphones). + +However, Tesla's plans to build a global system for wireless power distribution never came to fruition and the general consensus is that it's simply not feasible and that Tesla greatly overestimated the conductivity of the Earth's atmosphere and underestimated the energy loss with distance." +1185 Does eating lactose while lactose intolerant have cumulative negative effects? 27 https://www.reddit.com/r/askscience/comments/9gktkd/does_eating_lactose_while_lactose_intolerant_have/ 1537194775 9gktkd 2018-09-17 17:32:55 "The lactose itself does nothing in people with lactose intolerance, they just can't digest it. The bacteria that feast on the undigested lactose that enters the intestine cause the problem. +If you don't eat lactose for a longer period you'll have less lactose-consuming bacteria in your intestinal flora. +If instead you eat lactose regularly your intestinal flora will contain more lactose-consuming bacteria. Which will result in a stronger reaction. + +So no real permanent damage but eating lactose will worsen it." "I am lactose intolerant. I find that if I haven't had much lactose recently, I could have 3 slices of pizza and be fine. But if I had 3 slices of pizza yesterday and I have buttered toast today, I feel it. + +So I kinda feel like the lactose level builds up in my system and takes a few days to dip back down. + +Long term effects? None that I know of. Just a pain in the butt sometimes (pun intended)." +1186 Would it be theoretically possible for Earth to generate a permanent hurricane, similar to the red spot on Jupiter? 27 https://www.reddit.com/r/askscience/comments/9fb0hw/would_it_be_theoretically_possible_for_earth_to/ 1536781481 9fb0hw 2018-09-12 22:44:41 The red spot on Jupiter isn't permanent. It's likely been around for more than 350 years, but lately it has been weakening and may be completely gone in 20 years. Earth's longest recorded storm was hurricane John in 1994 which lasted just 31 days. "Hurricanes are powered by evaporation of warm seawater, so the fact that Earth has land puts a pretty strict limit on their lifetime: they drift westward until they hit a continent and die. + +Hurricanes might last much longer if the planet had no land in the tropics, but that planet wouldn't really be Earth anymore." +1512 Do bugs sleep? Plain and simple. 27 https://www.reddit.com/r/askscience/comments/g1gc5t/do_bugs_sleep_plain_and_simple/ 1586906638 g1gc5t Biology 2020-04-15 2:23:58 "Yes. The only living organisms that *don't* sleep (in some form) are the ones who don't live long enough to incorporate the day/night cycle into their lifespans, ~~i.e. Mayflies~~. Plants sleep. Slime molds sleep. Single-celled organisms sleep. The common misconception that ""sharks don't sleep"" comes from the observation that sharks never close their eyes, but as it turns out, sharks don't have *eyelids*." +1841 Once a rocket reaches space and goes in to free fall, how do they get fuel/oxidant to flow downward towards the nozzle without thrust or gravity pulling it downward? 27 https://www.reddit.com/r/askscience/comments/lcnjdc/once_a_rocket_reaches_space_and_goes_in_to_free/ 1612466317 lcnjdc Engineering 2021-02-04 22:18:37 "In the simplest tank design, the propellant is at the bottom, separated by a diaphragm from an ullage volume where a pressurizing gas pushes the diaphragm. + +Pros: very simple and cheap design + +Cons: you lose pressure as the propellant is consumed and the gas expands on an every time larger volume. This can be mitigated if the ullage volume is initially very large, so the gas won't have expanded a lot, but then you'll have the problem that big tanks are massive (in space, you want things to be as light as possible so they can be accelerated easily with little propellant). + +A better design is to keep the gas in a separate small container at high pressure, with a pressure regulator feeding the gas gradually into the tank. Then as the propellant is consumed, more gas flows into the ullage volume and pressure is kept nearly constant without the need for a very large tank. + +Pros: less massive, nearly constant pressure + +Cons: more complex and expensive + +In simple rocket engines (e.g. for attitude control), sometimes these approaches suffice. But when high thrust is required (i.e. high mass flow rate), then the pressure from the gas and diaphragm may not enough to ensure a good flow into the combustion chamber. Then you need turbopumps. They can be powered by the same fuel and oxidizer with a pre-burner." "The third stage of the Saturn V used ullage rockets. It only had to relight once, so it had four small solid rocket motors that would give it a kick forward to force the propellants to the ""bottom"" of their tanks so that they could properly feed the turbopumps. Once the engine's lit, you're good to go. + +After the third stage of the launch vehicle was jettisoned, The Command/Service Module and the Lunar Module had much less mass and were able to just use their reaction control system to provide the thrust to accomplish the same thing. + +In addition, many rockets use separate high pressure helium tanks in addition to some sort of ullage kick to provide a blanket of pressurized gas ""above"" the propellants that provides the motive force to actually get the liquid propellants into the combustion chamber. Helium is generally used because it remains a gas at the same temperature any cryogenic propellants are liquid at, so it won't condense out and get ingested by the engine with likely catastrophic consequences. In non-cryogenic applications it's still a good choice because it remains a gas at lower temperatures than any other gas, thus reducing the heating required to make sure it vaporizes properly when introduced into the propellant tanks. Similarly, it requires less heat to keep it from freezing solid than any other viable choice. In fact, it can't even exist as a solid below something ridiculous like 350 psia, so if you don't exceed that pressure, keeping it from freezing isn't even something you have to worry about. + +So, the kick from the ullage motors or RCS sends the propellant to the bottom, the high pressure gas gets it to flow to the combustion chamber adequately to get a start on the engine, then engine thrust takes it from there." +1842 Why is so much of the American West dominated by coniferous forests? 27 https://www.reddit.com/r/askscience/comments/lc31vl/why_is_so_much_of_the_american_west_dominated_by/ 1612399282 lc31vl Biology 2021-02-04 3:41:22 It's all about water. conifers grow slowly but year-round (different sap), even in winter but very slow. deciduous trees need water during the warm months, and out west it does not rain during the warm months. So deciduous can't compete very well. You are noticing the difference in rainfall seasonality. In the rainy east, deciduous outgrow the conifers because they use cheap, disposable leaves. "Another principal factor is allelopathy (a Greek word meaning ""to cause something to each other""), which - aside from the root system - is a plant's chemical-based offence or defence against competition. In this case species which cover the forest floor with needles are notorious for inhibiting the growth of other species so pine forests are generally less diverse than something like a tropical rainforest." +1843 How were ‘eye floaters’ viewed prior to knowledge of the eye’s structure? 27 https://www.reddit.com/r/askscience/comments/lwo5r9/how_were_eye_floaters_viewed_prior_to_knowledge/ 1614756838 lwo5r9 Human Body 2021-03-03 10:33:58 "From what we have in writing, eye floaters were typically seen as a physical disorder of vision, something wrong with eye itself. In *Places in Man*, Hippocrates wrote that ""the eye is nourished by the purest moisture, from the purest part, the brain."" (He likely was referring to the optic nerve, believing it to be a moisture transport vein.) Eye floaters—which Hippocrates described as ""images of birds or black lenses seeming to fly in front of you""—were inferred to be obstructions or impurities in the moisture carried along this ""vein."" + +The Roman physician Galen wrote \~200 CE that over-dense fluid inside the eye could impair vision, but that if the denser portions clumped together, it would create the illusion of ""small flies"" outside the eye. + +In Avicenna's *Canon of Medicine* from 1025, Avicenna draws heavily on Galen, but also suggests that *some* of these shapes may be actual physical objects that can only be seen by people with exceptionally good vision. But the rest were still understood as some fluid pathology of the eye. + +Probably the most thorough examination of your question was written by H. Plange in 1990, but unfortunately [his article is only available in German](https://docplayer.org/75322891-Muscae-volitantes-von-fruehen-beobachtungen-zu-purkinjes-erklaerung.html). A translation service [might give you the gist of it](https://translate.google.com/translate?sl=auto&tl=en&u=https://docplayer.org/75322891-Muscae-volitantes-von-fruehen-beobachtungen-zu-purkinjes-erklaerung.html)." If you don't get an answer here, you can try /r/askhistorians, /r/historyofscience or /r/historyofmedicine +1187 How can humans share 60% of our genes with bananas? 26 https://www.reddit.com/r/askscience/comments/9cs0ye/how_can_humans_share_60_of_our_genes_with_bananas/ 1536031745 9cs0ye 2018-09-04 6:29:05 "One way to think about it: how much does a smart phone have in common with a refrigerator? Basically nothing, right, they're totally different in size and purpose. But think about it. + +Both contain steel, plastics, and glass. Both have circuit boards. Those circuit boards have fiberglass, copper, gold, and semiconductor chips that contain silicon and plastic. + +Remember, DNA describes *everything*, both the big obvious shape stuff you can see, and the basic chemical structures you can't. The DNA sequences that humans share with bananas include instructions on how to build a cell membrane, how to create the amino acids that form proteins, how to assemble those proteins, how to build DNA itself, how to replicate and maintain it, etc." "[Here's](https://commons.wikimedia.org/wiki/File:Human_genome_by_functions.png) a chart classifying the human genome by gene function. Most genes are concerned with cell-level functions: making proteins, converting sugar to energy, replicating and repairing DNA, etc. All cells need to perform these functions, so it's not surprising that cells from different species would have a similar ""toolkit"" of genes to carry them out." +1188 Are there any drugs that have stopped being used because the disease evolved total resistance to it? 26 https://www.reddit.com/r/askscience/comments/9is1xl/are_there_any_drugs_that_have_stopped_being_used/ 1537881612 9is1xl Medicine 2018-09-25 16:20:12 "There are many examples; here is one: + +1-adamantylamine was once commonly used to treat influenza. Its target is the M2 pore protein of the virus. Over time, the gene for this protein mutated, and now practically all influenza virus is resistant. + +From https://en.wikipedia.org/wiki/Amantadine +>Amantadine is no longer recommended for treatment of influenza A infection. For the 2008/2009 flu season, the CDC found that 100% of seasonal H3N2 and 2009 pandemic flu samples tested have shown resistance to adamantanes. The CDC issued an alert to doctors to prescribe the neuraminidase inhibitors oseltamivir and zanamivir instead of amantadine and rimantadine for treatment of flu. A 2014 Cochrane review did not find benefit for the prevention or treatment of influenza A." "Yes, this is unfortunately quite common, and is an active area of research in both antibiotic and antiviral medications. + +I'm a chemist and actually recently received funding from NIH directly related to this issue. One of the systems our lab studies is the Influenza A M2 protein. We study the structure and function of this protein along with its interactions with antiviral medications. + +The adamantane class of influenza antivirals (amantadine and rimantadine) are one of only two classes of FDA approved influenza antivirals (the other class being neuraminidase inhibitors such as oseltamivir AKA Tamiflu). This adamantane class of antivirals works by blocking the proton channel in the M2 protein. Proton conduction through this channel is necessary for the acidification of the endosome, a key step in the viral life cycle. Interrupting this acidification prevents the production of new viruses. + +[In recent years, greater than 99% of circulating flu viruses are resistant to both amantadine and rimantadine; the CDC no longer recommends their use in the treatment of influenza infections.](https://www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm) This resistance has come about from certain mutations, such as the S31N mutation which affect the binding of amantadine and rimantadine to the influenza A M2 channel. My current study aims to better understand the proton conduction mechanism of this protein and to understand how the interactions of certain adamantane class drugs, which are still effective against these mutants, with the M2 protein differ from adamantane and rimantadine." +1189 How to deal with a person who has a pacemaker and needs to do an fMRI? 26 https://www.reddit.com/r/askscience/comments/9k8om5/how_to_deal_with_a_person_who_has_a_pacemaker_and/ 1538332122 9k8om5 Medicine 2018-09-30 21:28:42 depends on the model of the pacemaker. many newer generation devices are MRI compatible. in more extreme cases—if the device is not compatible and the MRI is absolutely critical, the patient may require a lead and/or generator exchange. "In real life, you work around it. If you look at MRI in general, it increases certainty in some situations, and it's convenient for the patient, but you can formulate a hypothesis and treat the patient without it if you have to. Contrary to our expectations when the technology first rolled out, MRI turned out to have its share of inaccurate results. It's seldom the deal-maker. + +Nobody actually needs a functional MRI. It might be interesting but it's not indicated for any disease state. For standard MRI, you aren't always losing ground by using older technology. For spine conditions, to give one example, you don't gain much with MRI over CT myelography, in fact you actually lose some information. Spatial resolution isn't as good as CT, you don't get the bone detail and you don't get analysis of the spinal fluid. + +One exception to that rule is multiple sclerosis, where MRI has revolutionized diagnosis. In that case, there would be a strong incentive to place an MRI-compatible pacer. Fortunately the age range doesn't usually overlap, people who have MS are usually too young to need a pacemaker. + +There's more than one way to skin a cat, main thing is to have someone in the loop with the physical diagnostic skills and critical reasoning skills to solve the problem. " +1190 It seems just about everyone here is on some kind of antidepressant medication and the majority are American - so are Americans more depressed or do doctors in the USA over prescribe antidepressants? Or is the usage similar in other countries? 26 https://www.reddit.com/r/askscience/comments/9gk27g/it_seems_just_about_everyone_here_is_on_some_kind/ 1537188867 9gk27g 2018-09-17 15:54:27 "I think you have a bit of bias here. I find it incredibly unlikely that even a quarter of reddit users are on antidepressants. + +Of the American population, about 1 in 6 people are on psychoactive medications. There might be some subreddits where this ratio is higher (such as /r/depression, and related subs), but I don't really see any reason to expect that american redditors as a whole deviate from the country norm. + +As an aside, The USA is not even in the top 10 of antidepressant consumption. Iceland has historically been in the lead. " """Just about everyone here"" Where is ""here"" for you? It sounds like your question's premise is based on a small sample set based on personal observation. Before your question is addressed, you should be making sure the premise is valid..." +1632 Why does the comet NEOWISE appear to have two tails? One that bends and is white. The other that is straight and is blue. 26 https://www.reddit.com/r/askscience/comments/hvt2d7/why_does_the_comet_neowise_appear_to_have_two/ 1595421650 hvt2d7 Astronomy 2020-07-22 15:40:50 The blue tail is ionised gas - i.e. charged particles. Charged particles are sensitive to magnetic fields, and these are following the Sun's magnetic field outwards at high speed. The other tail is dust, gas, and vapour being stripped from the comet's halo by the solar wind. This material isn't as bolted onto the magnetic field lines, so it's more puffy, and spreads out as it orbits the Sun. +1711 Do octopuses show reduced cognitive abilities/lower intelligence after losing one or more of its tentacles? 26 https://www.reddit.com/r/askscience/comments/jvtdn1/do_octopuses_show_reduced_cognitive/ 1605621410 jvtdn1 Biology 2020-11-17 16:56:50 "I am pretty sure that is not the case. ""Smaller brains"" is just a term to facilitate human understanding. Ocotopuses dont have something like 9 different thought processes or anything of the sort. These ""brains"" are larger assimilations of neurons, not distinct structures, like this wording suggests. The purpose of those is to speed up the reaction to sensory input, not to think. The arms do have a way to kind of communicate with each other while bypassing the brain in the octopuses head. +This is completely different approach to intelligence compared to our own. +To answer your question: no, octopuses do not lose intelligence when losing an arm. Its likely, that they would not be influenced by it at all, since every arm can perform every task." +1844 There's been a lot of speculation about whether people who have received the Covid-19 vaccine may still spread the virus to others. Is this common for other vaccines? 26 https://www.reddit.com/r/askscience/comments/lbiirs/theres_been_a_lot_of_speculation_about_whether/ 1612338209 lbiirs COVID-19 2021-02-03 10:43:29 "*Most* viral vaccines *do* block transmission, or greatly reduce it - smallpox, measles, mumps, rubella, polio, etc etc. + +Influenza vaccine is not sterilizing, and does allow some transmission even in vaccinated people. (Influenza is always an exception to other viruses. Because it’s an exception, it’s exceptionally important, so people think about flu before they think about measles, mumps, etc.) Even for influenza, though, vaccination greatly reduces shedding and transmission of the virus. + +The odds are pretty good that any effective COVID vaccines will be sterilizing, or close to sterilizing, but we won’t know until the tests are done. Preliminary data from the AstraZeneca vaccine trials strongly suggests that the vaccine either eliminates, or greatly reduces, transmission; so did the Moderna trial. + +This is one of those things where the media have done a terrible job conveying information accurately. We have been through this already several times during this pandemic. Scientists said early on, “We don’t know if the virus induces antibodies,” and there were a million hysterical posts saying “the virus doesn’t induce antibodies!” Then scientists said “we don’t know if the antibodies are protective”, and there were a million people saying “the antibodies aren’t protective!” Then they said “we don’t know if vaccines will work”, and the response was “vaccines won’t work!” Now we're at the point where scientists say, ""We don't know if the vaccines block transmission,"" and there's this rock-solid certainty that the vaccines won't block transmission. I know this is a stressful time, but the fifth or sixth time around this rollercoaster people should start recognizing the pattern. + +Also see these r/askscience threads: + +* [Why can you still infect others with covid-19 after vaccination?](https://www.reddit.com/r/askscience/comments/kn0gb7/why_can_you_still_infect_others_with_covid19/) + +* [Why - despite having millions of people which have already been vaccinated - we don't really know if vaccinated people do transmit covid or not?](https://www.reddit.com/r/askscience/comments/kobgv0/why_despite_having_millions_of_people_which_have/) + +* [How to test transmission of COVID-19 after vaccination?](https://www.reddit.com/r/askscience/comments/knz0rg/how_to_test_transmission_of_covid19_after/) + +* [How common is covid-19 reinfection? Are there any published statistics?](https://www.reddit.com/r/askscience/comments/kgtz3k/how_common_is_covid19_reinfection_are_there_any/)" "There were great comments in this thread, that I think address your question: [https://www.reddit.com/r/Coronavirus/comments/lbjzik/the\_astrazeneca\_vaccine\_is\_shown\_to\_drastically/](https://www.reddit.com/r/Coronavirus/comments/lbjzik/the_astrazeneca_vaccine_is_shown_to_drastically/). + +​ + +>I mean, I know of at least 1 example where a vaccine suppresses symptoms while allowing transmission, which is in the pertussis acellular vaccine. Bordatella can still colonize the nasal cavity of vaccinated individuals, it just does not cause disease due to the type of immunity generated by the vaccine (I believe there are not memory B cells generated in the acellular vaccine?). The whole cell pertussis vaccine prevented transmission and disease, but was not completely safe to administer, so they moved away from it. But a big difference between Bordatella and a virus is that you can have commensal bacteria live commonly in your body on mucosal surfaces without needed to cause infection, where as to replicate, viruses need to Infect your host cells. It seems like the immunity granted by vaccines should target viruses and prevent transmission because of the essentiality of infection to viral proliferation, but I haven't actually looked into it with other vaccines yet. But it does seem intuitive that vaccine should help cut down on transmission. + +u/Loafy20 + +​ + +>The logic behind is that you have different antibodies in your nose than in your blood (IgA vs IgG), and vaccines don't make you build up IgA. So for airborne diseases your nose/throat may be infected and you may be spreading the virus, but the body will fight it off fast enough and soon enough for you to not feel symptoms. So for a few days you may be spreading the virus, but you may not notice it as being sick too much - especially with Covid that spreads asymptomatically 50% of the time. + +u/DoUHearThePeopleSing + +​ + +>There is a huge difference between stopping and reducing transmission. A quite probable scenario is that vaccination prevents infection of lung tissue, but does not prevent an infection of the upper respiratory tract. Given the observed efficiency of the vaccines, they could easily limit the extent of the infection in the mucosae. +> +>Such a scenario would mean a significant reduction in transmission, but not elimination. This is in fact what we find with most respiratory infections. We might be lucky that after a first 'real' infection, localized immunity in the mucosae provides something more akin to sterilizing immunity for subsequent infections. +> +>Finally, given that super-spreaders are the main driver for the pandemic, it is arguably much more important what the effect of vaccination is on super-spreaders. If it stops or greatly reduces the transmission in this particular subset, it is not a problem if the non-super-spreaders don't get sterilizing immunity. The majority of infected never transmit infection even without vaccines. +> +>One theory about super-spreading is that it caused by asymptomatic infection of the lungs. In that case the vaccines would massively impactful - even if they have 0 reduction in transmission from the upper respiratory tract. +> +>TL;DR - we'll have to wait see. It is entirely possible that the effect on transmission is miniscule, but it's also possible that the effect on transmission is much greater than the effectiveness and/or PCR-based studies of post-vaccine transmission indicate. + +u/codergaard + +​ + +>...there's no generic way a vaccine works or generic definition that says the vaccine has to cause strong immunity. +> +>A vaccine is a chemical that preps your immune system for the virus by either using weak virus cells or like with the MRNA vaccines particular mechanism has been targeted that is unique to the virus and can also be used to trigger an immune response. +> +>That absolutely does not mean that you actually get immune from the virus. +> +>You get as immune as your immune system can make you in regard to that virus and the mechanism being used to prep the immune system. +> +>People think that vaccines all generate immunity because you only hear about vaccines for viruses that have been fairly easy to make vaccines for it. We target the viruses that produce the best results and we make vaccines for those. +> +>If we try to make vaccines for every virus you would see the shortcomings of vaccines much more easily but we're all spoiled because vaccine makers have picked off the low hanging fruit first making vaccines look like they always produce sterilizing immunity for life and that's not how they work. +> +>You can look at the varying different vaccines out there like the measles vaccine or the flu vaccine or the rabies vaccine and this coded vaccine then you can see that they're not all the same because it's just how one set of chemicals happens to react with another set of chemicals. There's no guaranteed outcome. There's no guarantee that you can actually train the immune system to get full-blown sterilizing immunity. + +u/GOPisTreason" +1191 To what degree are increases in cancer and terminal illness related to living longer? 25 https://www.reddit.com/r/askscience/comments/9i96r5/to_what_degree_are_increases_in_cancer_and/ 1537716511 9i96r5 Biology 2018-09-23 18:28:31 "Too a large degree: + +""The total number of cancers is projected to increase by 45% from 2010 to 2030, driven largely by the growing number of older adults. By 2030, an estimated 70% of all cancers will occur among adults aged ≥65 years."" + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4544764/ + +Cancer rates when corrected for age are more or less stable, and survival rates are going up. So it's really aging that is the major driving force." "The longer you live, the more time you have to accumulate damage to your DNA that will eventually lead to cancer. A study in 2015 reported that a large portion of cancers can potentially be attributed to ""bad luck"", they found a very linear relationship between cancer type and stem cell division for that cell type. This may potentially be because as stem cells divide more often, they have more opportunities to develop a spontaneous mutation in their genome. Divide enough times, get more mutations, and boom cancer. + +http://science.sciencemag.org/content/347/6217/12 +" +1712 What adaptations do elephant seals have that allow them to dive 2km underwater? 25 https://www.reddit.com/r/askscience/comments/jvazvv/what_adaptations_do_elephant_seals_have_that/ 1605548037 jvazvv Biology 2020-11-16 20:33:57 "Elephant seals have high concentrations of carbon monoxide in their blood which allows for the slow delivery of oxygen to their bodies. +You can read more here + +https://www.sciencemag.org/news/2017/11/killer-gas-aids-elephant-seals-deep-dives + +Also a side note some whales can dive to nearly 3000m." "The deepest diving mammals are actually a type of whale called a [Cuvier’s Beaked Whale](https://en.m.wikipedia.org/wiki/Cuvier%27s_beaked_whale)! + +Pretty close though, the three deepest diving animals are the sperm whale[sperm whale](https://en.m.wikipedia.org/wiki/Sperm_whale), the elephant seal like you said, and then the beaked whale. + +As far as adaptation, I’ll mention that I’m not a biologist, but I do love the science behind this sort of thing. + +It seems that most deep-diving creatures have lots of extra cartilage that allow the pressures of the deep ocean to push in their flexible rib cage and organs without simply collapsing their chest cavities. + +It does seem that all mammals have to be careful in regard to decompression sickness[decompression sickness](https://en.m.wikipedia.org/wiki/Decompression_sickness), but these animals have more well-adapted gas-exchanging capabilities and surface from the deep slowly enough that they are probably fine most of the time. + +With elephant seals, it seems that they have very very well-developed abilities to exchange gasses in their lungs and blood, which means that they use less oxygen and therefore can dive deeply for longer periods of time than most marine mammals. They are also mostly blubber and cartilage, so like the whales, they can more easily withstand the crushing depths. + +Hope this helps! The links have more specific info, particularly the whale ones, as they explain more of the biology behind them. I think we know more about those whales in general because we’ve been (sadly) hunting them for so long." +1845 What kind of tasks are Quantum computers better at compared to classical computers? 25 https://www.reddit.com/r/askscience/comments/lwxko5/what_kind_of_tasks_are_quantum_computers_better/ 1614788039 lwxko5 Computing 2021-03-03 19:13:59 "I guess here you want to differentiate between ""tasks"" and ""algorithms"". + +There's quite a few algorithms where you can prove that a quantum computer will show a significant speedup over a classical computer *if* you can actually build the appropriate-sized, error-corrected quantum device. + +Examples are, as you say, the prime factorization algorithm (though here of course we don't have a proof yet that there's no polynomial time prime factorization algorithm, if I recall correctly). + +Another example is that whole Grover's search algorithm, which you then can extend to the Quantum Amplitude Estimation algorithm, which you can then show will speed up *certain* Monte Carlo type simulations by a *quadratic* factor (e.g. if the classical algo takes O(N) steps to reach a certain accuracy, the quantum algo will only take O(sqrt(N)) steps). (Hit me up if you are unfamiliar with that O-notation.) + +Now these simulations can play an important role in finance, where you need to compute complicated portfolio risk measures based on some probability distributions. Classically you do that with Monte Carlo, and really what a speedup allows you is to do a better job at computing these various scenario risk measures for the same amount of time spent. + +As the other poster says, simulating quantum mechanics is THE killer app for quantum computers. + +Oh one algo that has a speedup but needs a shitload of qubits is the HHL algorithm that allows you to invert a matrix faster than a classical computer could (with some caveats) and of course matrix inversion shows up as a sub-problem pretty much EVERYWHERE. + +To expand on what the other poster /u/EZ-PEAS said about ""clever tricks"": Right now the only large-scale commercial quantum ""computer"" is the D-Wave quantum annealer. This is a special purpose machine that does one thing, and one thing only: Find the optimal solution for a QUBO (quadratic unconstrained binary optimization) problem. If you happen to be able to take *your* actual real-world problem and turn it into a QUBO, you could then use D-Wave to solve your problem. The issue is that most problems are neither quadratic nor binary nor unconstrained. The binary part can be overcome of course via encoding, but the quadratic and unconstrained parts are much harder, and if you happen to manage for *one* version of your problem, chances are your client or your boss or whoever will come and ask for what *seems* like a small modification but now all of a sudden it is *impossible* to model your problem as a QUBO. + +I'd assume similar issues exist with some of the other algos, like Grover, phase estimation etc etc but I'm not *that* familiar with them." "Barring some big change in understanding, the biggest application for quantum computers is going to be to simulate quantum systems. I think there's a lot of focus on things like encryption and optimization because people don't have a good intuitive understanding of quantum systems and why understanding quantum systems is important. + +Supposing a workable quantum computer is made, then simulating quantum systems is going to be the ""workhorse"" application that actually gets people to go out and buy the things. Such a machine would have huge applications for physics, chemistry, biology, materials science, etc. Many cutting edge applications could be impacted: solar panel design, low temp superconductors, protein folding, etc. These are all applications where understanding quantum behavior of a system is relevant. + +Classical computers have a hard time simulating quantum systems. An entangled system with N quantum particles requires 2^N amplitudes to fully describe the state of that system. If you have 20 entangled particles then you have 2^20 amplitudes and you need a few megabytes of memory to store them. If you have 30 particles then you need a few gigabytes of memory. Around 50-60 particles you exceed the memory capacity of the largest supercomputers currently on Earth. At 175 particles you've got more amplitudes than there are atoms in the Earth, and at 1000 particles you've got more amplitudes then you have particles in the universe. + +However, a quantum computer can simulate N quantum particles with N qubits. + +The first and biggest category of quantum computing applications is simply modelling quantum systems. If we only ever got to this first category then it would still be enough of a reason to build quantum computers. + +The second category, which includes factorization, optimization, and everything else, is really just playing ""clever tricks."" I don't mean this in a diminutive way- all of these other applications are based on setting up a quantum system that resembles a real-world problem in some way, and using that as a shortcut around computing the solution directly. They're very clever and useful tricks, but they don't represent a general or scalable way of doing business in the future." +2004 How much of the electricity that a computer uses is converted into heat? And how efficiently does a computer transfer that heat into the surrounding air? 25 https://www.reddit.com/r/askscience/comments/rbazbz/how_much_of_the_electricity_that_a_computer_uses/ 1638915219 rbazbz Physics 2021-12-08 1:13:39 "> I have heard some tech reviewers and outlets claim that all the energy consumed by a computer is converted into heat. Is that true? + +That's correct. Although a tiny fraction of it is converted into light and sound. In a closed room, those will end up absorbed by surfaces and again turning into heat. So effectively all of the electricity used by a computer ends up as heat. + +> A second question is, how efficient is a computer at transferring that heat to the surrounding air compared to a typical electric furnace in a house? + +Eventually, all of the heat generated by a heating device (be it a computer or an actual heater) will be transferred to the surroundings. On short timescales, things like the materials used and the airflow through the device (for example the fans in a computer case) can speed up the transfer of heat, but the rate of heat transfer depends on the temperature difference, so a device that is inefficient at transferring heat will warm up, increasing the rate of heat transfer. In the equilibrium state, if a device consumes 100 Watt of power, it will transfer 100 W of power as heat. How efficient the device is at transferring heat only affects how fast this equilibrium state is reached. + +> That is to say, could I heat a house more efficiently with computers than with your standard electric furnace? + +No, it would be just as efficient." ">Shouldn't some amount of energy go towards computing the information? + +You're correct, there is a fundamental energy cost called the [Landauer limit](https://en.wikipedia.org/wiki/Landauer%27s_principle) associated with (irreversibly) computing one bit of information. The energy cost is due to the change in entropy associated with erasing one bit. The energy cost (k\_B T log 2) scales linearly with the ambient temperature, and at room temperature is about 3×10^(-21) J. + +As a concrete example, the Core i7 processor in my MacBook Pro runs at 3 GHz with 16 double precision FLOPS per cycle and computes about 2×10^(13) bits per second, which is about 60 nW at room temperature. The processor uses 37W, so at most 0.00000002% of the energy is used to compute the information. + +Other than energy converted to light / radio / sound /airflow, all of the other energy of a computer is transferred into heat, and even these categories eventually end up as heat anyway. Your computer is effectively exactly as efficient as converting energy into heat as a standard furnace." +1192 [Earth Sci.] [Physics] Carrying metal objects increases one's risk of lightning strike. Does it have to be exposed? Can car keys or other objects in my pocket make me a more likely target? 24 https://www.reddit.com/r/askscience/comments/9f7phx/earth_sci_physics_carrying_metal_objects/ 1536758572 9f7phx Physics 2018-09-12 16:22:52 "Car keys in your pocket don't do anything. While they are sort of exposed (clothes don't matter much) they are small and close to your body. + +Metals are not magically attracting lightning. They just provide better conductance paths than various other materials. That can increase the risk of a lightning strike following their path a bit. Usually the geometry is more important. Lightning rods get struck often because they are higher than the remaining building and provide a good conductivity over the whole length of the building." +1193 Is the Uncertainty Principle due to the fact scientists do not know enough, or is it genuine chaos? 24 https://www.reddit.com/r/askscience/comments/9ic434/is_the_uncertainty_principle_due_to_the_fact/ 1537738082 9ic434 2018-09-24 0:28:02 "It's not about a lack of knowledge, and it's not ""chaos"" either. It's fundamental to quantum mechanics. Certain observable quantities are ""incompatible"", meaning that if one of them is well-define in a given state, the other necessarily can't be. Position and the conjugate momentum are an example of this." "The Uncertainty Principle is an intrinsic property of *any* wave. It is definitely not just something we can push through if we try hard enough. But the big jump in Quantum Mechanics is that idea that *all* particles are waves, and not just things like light. + +As a side-note, this is very different to ""chaos"". Chaos is really about systems that are extremely sensitive to extremely small changes, so that it becomes impossible to predict the system with any accuracy because you need extremely precise measurements of absolutely everything in the system. So it's a different thing. + +But back to the uncertainty principle: so, everything is a wave. Any wave can be expressed as the sum of simple sine waves of different wavelengths. The simplest wave is just a single sine wave. This wave has exactly one wavelength, but it doesn't really have a *location*. It's a sine wave that goes on forever. Alternately, you can have a wave made up of lots of sine waves of different wavelengths, so that you get an isolated ""wave packet"". [This gif](https://upload.wikimedia.org/wikipedia/commons/c/c1/Wave_packet_%28no_dispersion%29.gif) from wikipedia nicely illustrates what such a ""wave packet"" might look like. Here, it kinda does make sense to talk about the *location* of the wave - it's kinda spread out a little bit, but it does seem to be focused around one general area. But now we don't have just one wavelength anymore - the wave is made up of lots of sine waves of different wavelengths. + +This is the uncertainty principle: a wave is either spread out in space, or spread out in wavelength. The more it's spread out in space, the less it's spread out in wavelengths, and vice versa. + +For a matter wave, the wavelength gives you the momentum of the particle - λ=h/p, where λ is the wavelength, p is the momentum, and h is the Planck constant. So we know that for any wave, the more constrained the position is, the less constrained the wavelength is (and vice versa). For a matter wave, this means that the more constrained the position is, the less constrained the momentum is, and vice versa. And that's the uncertainty principle." +1194 Where does fluid that gets 'locked' into your ear go? 24 https://www.reddit.com/r/askscience/comments/9e3n0m/where_does_fluid_that_gets_locked_into_your_ear_go/ 1536405880 9e3n0m Human Body 2018-09-08 14:24:40 "The ear canal is pretty narrow. Water adheres to the skin on the inside of the canal, and the small opening can allow that adhesion combined with it is own surface tension to create a scenario where gravity is insufficient to cause it to flow out of the canal on its own. + +The action of jumping up and down with one's head turned to the side can remedy this situation sometimes by both momentarily increasing the weight of the water (as you land) and disrupting the surface tension as a result of the abrupt motions. + +It can clear itself on its own for various reasons, from simple random chance to shifts in temperature (which alter the surface tension and changes in the ear canal over time for various reasons." +1195 Why don't neutrons in neutron stars decay into protons and electrons like free neutrons? 24 https://www.reddit.com/r/askscience/comments/9g2sq0/why_dont_neutrons_in_neutron_stars_decay_into/ 1537028941 9g2sq0 2018-09-15 19:29:01 " +There are protons and electrons inside the star but there is a limit. Once that limit is reached there are no more energy levels to accomdate the decay products due to the Pauli exclusion principle. With no where for the products to exist the decay cant occur. + +Hopefully someone else can give you some better details but thats my best understanding. " "There are two things going on here. The first is that your system wants to reach the lowest energy state: in this case, the free neutron decays because a proton and an electron (plus a neutrino) is a lower energy state. The second is the Pauli exclusion principle, which states that two electrons can't be in the same quantum state. + +In a neutron star, gravity is squeezing particles close together. So close, in fact, that the fact that two electrons can't be in the same state becomes a problem, but there is a way around it: you can excite one of the electrons to a higher energy state! And so we do that: as electrons are squeezed tighter together, we just shove them into higher and higher energy states. + +For a smaller star like a white dwarf, this is where things end: the amount of energy gained by squeezing the star smaller is balanced out by the amount of energy required to push an electron into a higher energy state, something known as electron degeneracy pressure. + +In the core of a neutron star, this isn't good enough. As we keep adding electrons into higher and higher energy states, we eventually reach a crucial tipping point: the energy required to put an electron into an even higher energy state is more than the energy difference between a proton + electron and a neutron (+neutrino). When that happens, the electrons and protons start to fuse into neutrons. + +These neutrons don't decay, because to do so would mean they would have to put the electron in that really high energy level, and even if all the excess energy from the neutron decaying went into the electron, there just isn't enough energy available to do that." +1513 What does *actually* affect our eyesight? Reading in the dark? Using screens at a high brightness? Something else entirely? 24 https://www.reddit.com/r/askscience/comments/g1e8vi/what_does_actually_affect_our_eyesight_reading_in/ 1586899579 g1e8vi Human Body 2020-04-15 0:26:19 "Two conditions, myopia and presbyopia, are the only optical problems that typically progress. We know the physiology and reasons why these conditions occur, and they have almost nothing to do with how you use your eyes. + +Given that myopia and presbyopia are almost impossible to stop, human eyes are remarkably stable and predictable and hard to influence. Where your monitor sits or how bright it is, those are a matter of comfort and ergonomics, not the cause of change inside your eye." "Peoples eyes change as they age. Losing the ability to focus up close and becoming less sensitive to light are common changes. Your dad’s eyes are probably a lot less sensitive and he needs a bright monitor to see clearly. + +https://www.allaboutvision.com/over60/vision-changes.htm" +1633 Could you non destructively remove a viruses dna? 24 https://www.reddit.com/r/askscience/comments/h0dffl/could_you_non_destructively_remove_a_viruses_dna/ 1591803628 h0dffl Biology 2020-06-10 18:40:28 "Can you extract a virus’ genetic material while leaving the capsid intact? No.  +I don’t quite know what you mean by the second question. Are you asking whether the empty capsid triggers the immune system? If so, yes. For instance, Gardasil, the vaccine for HPV, consists of engineered, empty capsids." "No. All genome extraction from virus particles is destructive. + +However- if you know the viral genome sequence- you don’t even need the virus in order to make a vaccine. + +This is a technique used by vaccine developers today- you can completely artificially synthesize a viral gene using the published sequence, inject that DNA (more complicated backbone production is necessary obviously, but I’m paraphrasing) into an animal- and the cells will make the protein encoded by the DNA, and the animal will develop an immune response against the original virus. + +Instead of injecting- you can even have the patient administer a solution of DNA molecules from a Flonase type device. Gets a pretty robust response under the right circumstances + +Mucosal DNA vaccination for viral pathogens" +1846 What would happen if a fully vaccinated individual were to contract coronavirus? Would it just feel like a light cold for them or would they literally not get sick at all? 24 https://www.reddit.com/r/askscience/comments/ls00et/what_would_happen_if_a_fully_vaccinated/ 1614234259 ls00et COVID-19 2021-02-25 9:24:19 "The purpose of a vaccine is to prepare the adaptive immune system for an invasion by a pathogen, so that when it arrives it is immediately recognized and destroyed. Symptoms are a result of tissue damage when pathogens destroy host cells far beyond initial invasion. + +If you receive a low load long enough after you have been vaccinated you should experience nothing. A high load or frequent exposures will saturate your immunity and take effect to the extent that such a load would had you not been vaccinated. + +If you are exposed within a short window after one of your vaccinations, your adaptive immune system will be saturated and you will likely be more sick than you would have been had you not gotten the jab. + +Hope this clears things up." +1914 Are there any examples of Binary Solar Systems (two separate star systems in extremely close proximity)? 24 https://www.reddit.com/r/askscience/comments/o05n1z/are_there_any_examples_of_binary_solar_systems/ 1623731195 o05n1z Astronomy 2021-06-15 7:26:35 "There are! + +There's two cases for stable orbits for planets in a binary system. There are ""p-type"" (""planet-type"") or ""circumbinary"" planets that orbit around both stars, from such a distance that the pair of stars feels like just one star. And there are ""s-type"" (""satellite-type"") planets orbit orbit around one star, close enough that the planet and its star feel roughly the same gravity from the more distant star. + +Both of these have been observed! [Here](https://www.univie.ac.at/adg/schwarz/bincat_binary.html) is a catalogue of planets in binary systems. You can turn on ""Show all data"" and sort by ""planet motion type"" and see loads of planets in both P-type and S-type orbits. + +And there are indeed binary planetary systems, such as [this one](http://www.openexoplanetcatalogue.com/planet/WASP-94%20A%20b/) which has a planet around each of the two stars. + +As for the visibility of the second star in an S-type configuration, that can vary a lot. The brightness of a star increases very dramatically with mass - a star that is twice as massive is about 11 times brighter. So it's quite possible to be dominated by the gravity of a nearby small star, but for a more massive distant star to almost as bright (if not brighter), and still have the system be gravitationally stable. Or, the secondary star might be a faint distant red dwarf star that's only visible at night. There's a huge spectrum of possibilities. + +Of course, in a P-type/circumbinary orbit, you can easily see both suns close to each other in the sky, regardless of what the brightnesses are." +1847 Does the shape of our skulls change over the course of our life from things like sleeping on one side more or leaning against hard surfaces? 23 https://www.reddit.com/r/askscience/comments/lwpokv/does_the_shape_of_our_skulls_change_over_the/ 1614763092 lwpokv Human Body 2021-03-03 12:18:12 +2005 How do limpets metabolize iron for their super-hard teeth? 23 https://www.reddit.com/r/askscience/comments/rbn6ad/how_do_limpets_metabolize_iron_for_their/ 1638954306 rbn6ad Biology 2021-12-08 12:05:06 "Dissolved minerals from their food. How do you think we build our bones? 😉 + +And it's not only limpets: some [shrews](https://carnegiemnh.org/shrews-dark-red-teeth/) have iron in their teeth to crush these pesky hard insects, and the most extravagant is the deep-sea [armored snail](https://www.scienceandthesea.org/program/201802/armored-snail). + +https://old.reddit.com/r/NatureIsFuckingLit/ for more cool stuff." The same way we do to make hemoglobin? Aka the iron isn't bound into rocks, it's dissolved into the water. Iron is useful to a number of organisms, so in the ocean iron is often found chelated - surrounded by organic molecules - and can be picked up via filter feeding. They may also get iron from the algae they eat. +1634 "How ""thick"" are lagrangian points?" 22 https://www.reddit.com/r/askscience/comments/h7iydr/how_thick_are_lagrangian_points/ 1591961159 h7iydr Astronomy 2020-06-12 14:25:59 "The actual spot where all gravity is “canceled” is a literal “point,” but the areas around that point (depending on the bodies involved) are nearly “canceled” and are quite large. The L-points associated with earth are nearly a million kilometers in diameter, within which a craft can hang out and use very little maintenance propulsion. The areas get bigger further from the sun: Jupiter’s Lagrange areas are full of freeloading asteroids, and Neptune’s L-point areas are positively gigantic, millions of kilometers in diameter. + +So in answer: they thicc" Theoretically, they are points, so they have a thickness of 0, however if you place the center of mass of a symmetric object at a Lagrange point, then the gravitational forces acting on the object would all cancel to zero +1635 Can you kill a virus? 22 https://www.reddit.com/r/askscience/comments/gzq02q/can_you_kill_a_virus/ 1591718633 gzq02q Biology 2020-06-09 19:03:53 "I think the basis of your question is 'how can something that is not alive be killed'. While viruses may not be considered alive in the same way as animals, plants, etc. they still have organic structures that are needed for them to function. If these are damaged such that the virus cannot function, then it is effectively dead. + +Perhaps we should say viruses are 'destroyed' rather than 'killed'. But it's more a question of language than science. + +Regarding smallpox, I don't know if that particular virus is capable of lying dormant for long periods of time. But, we haven't seen any new cases for decades, so it is safe to assume it has been eradicated." "Virologists usually say you ""inactivate"" a virus particle for this very reason...it's not alive so you aren't really killing it. But you are breaking it so it can't infect anything. + +Not all viruses can stay in the host for many years (actually most can't)...smallpox is one of the ones that can't. For smallpox to persist in a population it has to be constantly infecting new people, like a wildfire that needs new trees to keep burning. That means it's fairly easy for it to be eradicated completely, and we'd notice if it was still around because people would still be catching it." +1713 Are icebergs made of ocean water or freshwater? 22 https://www.reddit.com/r/askscience/comments/jvgu5i/are_icebergs_made_of_ocean_water_or_freshwater/ 1605565989 jvgu5i Earth Sciences 2020-11-17 1:33:09 "Sea ice is frozen sea water where the salt has been forced out as it freezes. Sea ice can freeze to a thickness of 2 - 3 meters but rarely gets thicker than that. Multi year ice May pile up into greater thicknesses of tilted slabs riding on top of each other to the point that some might call it an iceberg...but real icebergs hundreds of feet thick break off from glaciers entering the sea. They come from falling snow piled up year after year on land until compressed into ice. That ice then flows down hill into the ocean where it breaks off into bergs. Real icebergs are freshwater + +----EDIT---- + +Chunks of frozen sea water aka ""sea ice"" are typically referred to as ""ice floes"" rather than ""icebergs""" "Icebergs don’t contain salt, sea-ice (ie. floating ice shelves) do contain a very small amount. + +Rather than getting locked in into water ice, salts are removed as water freezes. This is what creates such high salinity in the waters around the polar sea-ice forming regions and then helps to drive the thermohaline circulation. +It’s slightly more complicated than just saying salt doesn’t freeze though: when [frazil ice](https://en.wikipedia.org/wiki/Frazil_ice) crystals form, salt accumulates into droplets called brine, which are typically expelled back into the ocean and is what raises the salinity of the near-surface water. + +A certain amount of brine droplets do actually become trapped in pockets between the ice crystals however. This brine remains in a liquid state because much colder temperatures would be required for it to freeze. At this stage, the sea-ice has a high salt content. Over time, the brine drains out, leaving air pockets, and the salinity of the sea-ice decreases. Brine can move out of sea ice in diferent ways, mostly it is simply aided by gravity and migrates downward through holes and channels in the ice, eventually emptying back into the ocean. Mature sea-ice is pretty much salt free then, despite forming from seawater. + +Sea-ice is not to be confused with the polar ice caps (on Antarctica and Geeenland) - these have built up from ice precipitated as snow (or occasionally rainfall) and then compacted. The important thing being that this precipitation is formed from evaporation of seawater, which does not include any salts at all because salts have a *much* higher boiling point than water. So the polar ice caps are fresh from the start and have not gone through any brine rejection or salt-draining processes. Most icebergs are formed from glaciers which calve off these ice caps and into the sea, so they are fresh." +1848 Do nuclear submarines use the hydrogen they get from electrolysis or just dispose of it? 22 https://www.reddit.com/r/askscience/comments/lronh0/do_nuclear_submarines_use_the_hydrogen_they_get/ 1614205126 lronh0 Engineering 2021-02-25 1:18:46 The hydrogen is pumped overboard. [This video](https://www.youtube.com/watch?v=g3Ud6mHdhlQ) has a pretty good series of explanations. "One thing that's not mentioned in the adjust very thorough answers so far is that hydrogen is also pretty hard to store. It's very small so it leaks through pretty much whatever you put it in. It's not a question of when it's going to leak, it's a question of how much. + +In normal cases it leaks slowly enough that it's not much of a danger but on a submarine it's possible for it to build up and go boom." +1915 Is there research that indicates that being vaccinated against the seasonal flu is effective in protecting other people who are immunocompromised? 22 https://www.reddit.com/r/askscience/comments/p83b2r/is_there_research_that_indicates_that_being/ 1629458862 p83b2r Medicine 2021-08-20 14:27:42 "The incidence rate of infection for vaccinated individuals is lower than for nonvaccinated. So while a vaccinated person may still be infected with a strain of influenza, the likelihood is lower. If a vaccinated person gets influenza, the vaccine is then likely to help them by lessening the severity of symptoms. So while they could still possibly infect others, they aren't sneezing and coughing everywhere. This helps the people around them too, since it's less likely to be spreading to people in the vicinity. Is it still possible? Yes. Is it much less likely? Yes. The best way to protect others is to get a flu shot. + +Sources: CDC, https://www.cdc.gov/flu/vaccines-work/vaccineeffect.htm +BMC Infectious Diseases (peer-reviewed study from 2017), https://bmcinfectdis.biomedcentral.com/track/pdf/10.1186/s12879-017-2399-4.pdf" "While you can still get the flu if you are vaccinated and you could still spread it if you have it even if you don't show symptoms it is not more likely. There was a blog post that made this claim based on a study published in pnas but the author's of the original paper actually addressed the blogpost and said it was in accurate. Also the CDC still says that it is protective of vulnerable people around you. + +This person probably will dismiss the above but their claim shouldn't stop you from getting vaccinated. + +But please continue to wash you hands and etc to further prevent the spread." +1916 Why don't mRNA vaccines require an adjuvant? 22 https://www.reddit.com/r/askscience/comments/o2tj79/why_dont_mrna_vaccines_require_an_adjuvant/ 1624034051 o2tj79 Biology 2021-06-18 19:34:11 "RNA itself has an adjuvant effect. Biontech mentions it in their presentation. + +It makes sense for the body to defend itself against foreign RNA, before they express any foreign proteins. + +There are so-called RNA sensors which are tightly regulated to prevent sensing of self-RNA. + +Toll-like receptors can sense RNA, there are also pattern recognition receptors in the cytosol." "mRNA vaccines do a really good job of mimicking an actual viral infection because the proteins are expressed inside the cell where they can then be processed and displayed by MHC proteins. + +https://res.mdpi.com/d_attachment/ijms/ijms-21-06582/article_deploy/ijms-21-06582.pdf" +1514 Do other Great apes pee holding their penises with their hands or is that just humans? 21 https://www.reddit.com/r/askscience/comments/g92pc4/do_other_great_apes_pee_holding_their_penises/ 1588000933 g92pc4 Biology 2020-04-27 18:22:13 +1714 AskScience AMA Series: I'm a glaciologist focused on why large outlet glaciers in Greenland are changing. Ask me anything! 21 https://www.reddit.com/r/askscience/comments/iv3y1z/askscience_ama_series_im_a_glaciologist_focused/ 1600426806 iv3y1z Earth Sciences 2020-09-18 14:00:06 "I’ve read about how glaciologists have found that undercut seawater is leading to much faster calving and glacier melt. How much have these processes sped up loss mechanisms in glacier fronts? + +Your paper in Nature discusses how most glacial loss happens due to the retreat of glacier fronts. Is there anything we can do to mitigate this loss? Either technology or process wise. + +Lastly, I’ve heard some climate folks worry about the effects of melting glaciers, specifically those in Greenland, affecting ocean currents. Do you think it is feasible for a melting event to destabilize thermohaline circulation? What would the effects look like on the globe? + +Thanks for doing this AMA and for all the work you’re doing with our glaciers!" So why and how are large outlet glaciers in Greenland changing? +1849 We all know that salt can lower the freezing point of water. Are there any chemicals that can raise the freezing point of water? 21 https://www.reddit.com/r/askscience/comments/lthn4g/we_all_know_that_salt_can_lower_the_freezing/ 1614405463 lthn4g Chemistry 2021-02-27 8:57:43 "Salt lowers the freezing point of water because, for all intents and purposes, it makes a solution in the water liquid phase but does not incorporate itself into the structure of ice. Thus, it increases the entropy of the liquid phase while having no effect on the chemical potential of the solid phase making the liquid phase more thermodynamically favourable at lower temperatures. + +To have the opposite effect, you'd need a material that incorporates itself into the solid ice phase while not forming a solution in the liquid phase. I don't know of any substance that behaves this way." "The are a bunch of articles on the web about how some substances can raise the “freezing point” of supercooled water - testosterone is one example. + +I don’t think this is really what you were asking about though. The idea is that very pure water will not freeze until far below 0°C, due to lack of nucleation sites. Mixing in some substances changes that temperature, which I would not call the freezing point (though the articles do). + +https://sciencing.com/raise-freezing-point-water-5211895.html + +https://www.rsc.org/news-events/journals-highlights/2018/04-april/water-freezing/" +1850 Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology 21 https://www.reddit.com/r/askscience/comments/lreugz/ask_anything_wednesday_economics_political/ 1614178815 lreugz 2021-02-24 18:00:15 What are the most credited economic theories about what caused the Great Depression? How did so many different dialects of Mayan language evolve over a (relatively) short period of time? +1851 Particle size distribution in soil. Gaussian, Power law, log normal? 21 https://www.reddit.com/r/askscience/comments/lxpu2i/particle_size_distribution_in_soil_gaussian_power/ 1614878341 lxpu2i Earth Sciences 2021-03-04 20:19:01 The grain size distribution in soil been modeled as log-normal (e.g. [Wagner & Ding, 1994](https://www.ars.usda.gov/ARSUserFiles/30200525/93-219-J%20%20Representing%20Aggregate%20Size%20Distributions%20as%20Modified%20Lognormal%20Distributions.pdf)), but that doesn't work across the board. Alternatively, [Fredlund et al., 1997](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.462.8211&rep=rep1&type=pdf) came up with an empirical distribution, which may work better in some cases. As an aside, this is specifically for soil and should not be extrapolated to other sediment (e.g. grain size distributions in sediment carried by a river would be different, etc). It depends on the soil. Different soils have different amounts of sand, silt, and clay. Here is one talk on the topic: https://www.horiba.com/en_en/products/scientific/particle-characterization/particle-analysis-webinar-series/soil-particle-size-analysis-and-clay-fraction-extraction/ +1852 Should I still get the COVID vaccine if I’ve already had COVID? 21 https://www.reddit.com/r/askscience/comments/lwq52v/should_i_still_get_the_covid_vaccine_if_ive/ 1614765026 lwq52v COVID-19 2021-03-03 12:50:26 "The CDC has [Frequently Asked Questions about COVID-19 Vaccination](https://www.cdc.gov/coronavirus/2019-ncov/vaccines/faq.html). They say: + +>Yes, you should be vaccinated regardless of whether you already had COVID-19. That’s because experts do not yet know how long you are protected from getting sick again after recovering from COVID-19. + +There's also a somewhat more technical page at [Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States](https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html), where they say + +>Data from clinical trials indicate that mRNA COVID-19 vaccines can safely be given to persons with evidence of a prior SARS-CoV-2 infection. Vaccination should be offered to persons regardless of history of prior symptomatic or asymptomatic SARS-CoV-2 infection. ...Vaccination of persons with known current SARS-CoV-2 infection should be deferred until the person has recovered from the acute illness (if the person had symptoms) ...While there is no recommended minimum interval between infection and vaccination, current evidence suggests that the risk of SARS-CoV-2 reinfection is low in the months after initial infection but may increase with time due to waning immunity. Thus, **while vaccine supply remains limited**, persons with recent documented acute SARS-CoV-2 infection may choose to temporarily delay vaccination, if desired, recognizing that the risk of reinfection, and therefore the need for vaccination, might increase with time following initial infection. + +As that last part suggests, the concern really isn't that infection won't lead to immunity -- scientists are confident that after you're infected, you're immune. The problem is that infection leads to *inconsistent* immunity. A mild or asymptomatic infection still leads to immunity, but it's often much lower than after a more severe case of COVID; and even severe cases might not give a strong, *long-lasting* response in everyone. By comparison, the vaccines *consistently* drive immunity to at least the highest level seen after most infections. So if you're infected, you're very likely protected for some time, but you won't know how long you're protected for. The vaccines all show every sign of giving good, consistent protection that will last for years." "Please explain this to me because I don’t understand. Your body doesn’t constantly produce every type of antibody it’s ever made. So why would this vaccine be any different than say a polio vaccine? It’s not like your body has been consistently making polio antibodies since your vaccine, yet we don’t worry about how the length of that immunity. + +And as for the severity of the covid case, what do they do to the vaccine that drives a higher level of immunity? As far as I know vaccines are either dead versions, a weakened version, or a piece of the virus. So how is this vaccine, which isn’t as high of a dose as a severe infection, going to “drive” a higher level of immunity?" +1917 Did the Spanish flu (1918 influenza pandemic) also have variants? 21 https://www.reddit.com/r/askscience/comments/nzpvnz/did_the_spanish_flu_1918_influenza_pandemic_also/ 1623685828 nzpvnz COVID-19 2021-06-14 18:50:28 [deleted] +1853 The typical number of flu variants and the numbers with COVID-19. Is it unusually high? 20 https://www.reddit.com/r/askscience/comments/lck6o2/the_typical_number_of_flu_variants_and_the/ 1612457895 lck6o2 Medicine 2021-02-04 19:58:15 There are a massive number of variants of influenza. By comparison, the coronavirus is fairly stable. SARS-CoV-2 isn't any type of influenza virus, BTW. And one of the defining characteristics of influenza is the extremely fast rate at which it mutates and adapts, as compared with most other virii. "4000 is the number you get if you put every single mutation that has been found somewhere in a spreadsheet - or [a website](https://nextstrain.org/sars-cov-2/) with [colorful graphs](https://nextstrain.org/ncov/global). Almost all of them are irrelevant for how the virus works, but they are still useful to track how the virus spreads from one place to another. + +If you do the same with the flu then you end up with another huge number. The flu is much less dangerous, however, so the resources spent on tracking individual mutations are smaller. Nevertheless, [here is a colorful graph for influenza H3N2](https://nextstrain.org/flu/seasonal/h3n2/ha/2y) with 1500 recorded mutations. If we would look closer we would find even more. Note that this is only one particular flu variant - there are more." +1854 "What is the difference between ""seeing things"" visually, mentally and hallucinogenically?" 20 https://www.reddit.com/r/askscience/comments/mk3uj2/what_is_the_difference_between_seeing_things/ 1617567110 mk3uj2 Neuroscience 2021-04-04 23:11:50 "Actually the brain is not a passive receptor of information. + +When you get information from the eyes (an electromagnetic signal), it is compacted and sent through the optic nerve to the thalamus. + +There it meets a flow of information from the occipital cortex (where most of the visual areas are). Why is this? so the information from the eyes can be compared to the working model of the real world you are ALREADY predicting. You see with the occipital lobe to say it in a simple way. but it needs to be updated, the flow of information that the optic nerve provides help to update the model you have already in your brain. tweaking it to reflect the information being gathered. + +If we depended completely on the input from the eyes and we were a passive receptor of information the brain would not be structured like this. and we would need more brainpower to process what we are seeing. + +Most of what we see is just an useful representation of the world, but not that faithful. Remember the white with gold / black with blue dress? It has to do with how your brain decides to handle the available information. colors are not real also, it's something the brain makes up. + +Lots of things in our perception are actually illusions. and thats ok. the thing is when you hallucinate you are allowing yourself to process something as an actual perception that should have been inhibited. you have a filter that's not working correctly. Some scientists associate this to an overly active dopaminergic system that's teaching you that certain cognitive processes are reflecting the real world when they are not. it's like the filter has a low threshold to select what is real and what is not when thoughts emerge from what you are watching. the network is being overly active, generating representations that should not be there. + +So to answer the question, the difference is the source. but illusions happen all the time, illusions are part of the visual processing system, but having a visual processing system that is too lax in the control of the network activation, leads you to see even more things that are not there." "Perception is controlled hallucination, [as Andy Clark explains in this video](https://www.edge.org/conversation/andy_clark-perception-as-controlled-hallucination). + +When you look at something, like a painting, you are constantly moving your eyeballs about in visual saccades. Each saccade can be thought of as an experiment. You start off with a hypothesis generated by a predictive model of the world that you've built with experience and you test it against sensory evidence. If there's a match, you don't notice much. But if there's a mismatch, you might sense that something isn't quite right. In science, surprising discoveries result in breakthroughs. Because when you stumble upon something not yet covered by your model, you've stumbled upon something *new*. And your brain, as fine a scientist as any, treats surprises with the same reverence. + +Something very interesting happens when you realize that the proportional influence of the predictive model versus sensory evidence can vary. In psychology, there's a long tradition of distinguishing between top-down and bottom-up processes. The top-down predictive model attempts to ""cancel out"" the bottom-up sensory input. It can only cancel out what it already expects. So the true quantity of interest is always to be found in errors. But what happens if you expand your acceptable error bar? You become more reliant on your predictive model. You start seeing what you expect to see, because the influence of those pesky errors have decreased. You become somewhat detached from reality, if not delusional. And if you shrink the error bar? You will constantly be bombarded by error signals. The tiniest discrepancy from your model predictions will demand your undivided attention. It will be exhausting. + +Dreaming is more like the former, top-down heavy state. It's the flow of unrestrained predictions. It's perhaps interesting to note that in dreams locations and people tend to transform without us realizing it. Which may hint that we rely on error signals as a compensatory working memory mechanism, preventing us from drifting away from reality in waking life. + +Different types of hallucinations may involve different brain areas in different levels of the cortical hierarchy. In the V1, the primary visual cortex, low-level visual patterns such as lines slanted in different orientations are processed. If you're familiar with scintillating scotoma--migraine auras--you may have experience with the feeling of having low-level visual areas invade your visual experience. A wave of excitation spreads across the cortex, activating neurons in such a way that there's no way for the brain to distinguish it from natural activation. + +Your brain is constantly making predictions, so your visual experience is actually of the expected future rather than the actual present. That might sound bizarre, but it's true. We're talking about much less than a second here, but the fact remains. Prediction errors tether you to reality. + +**Further reading:** + +Hohwy, J. (2013). The Predictive Mind. + +Clark, A. (2015). Surfing Uncertainty: Prediction, Action, and the Embodied Mind. + +Rao, R. P. N., & Ballard, D. H. (1999). Predictive coding in the visual cortex: a functional interpretation of some extra-classical receptive-field effects. *Nature Neuroscience*, *2*(1), 79–87. [https://doi.org/10.1038/4580](https://doi.org/10.1038/4580) + +Clark, A. (2013). Whatever next? Predictive brains, situated agents, and the future of cognitive science. *Behavioral and Brain Sciences*, *36*(3), 181–204. [https://doi.org/10.1017/s0140525x12000477](https://doi.org/10.1017/s0140525x12000477) + +Friston, K., Adams, R. A., Perrinet, L., & Breakspear, M. (2012). Perceptions as Hypotheses: Saccades as Experiments. *Frontiers in Psychology*, *3*. [https://doi.org/10.3389/fpsyg.2012.00151](https://doi.org/10.3389/fpsyg.2012.00151) + +Blom, T., Feuerriegel, D., Johnson, P., Bode, S., & Hogendoorn, H. (2020). Predictions drive neural representations of visual events ahead of incoming sensory information. *Proceedings of the National Academy of Sciences*, *117*(13), 7510–7515. [https://doi.org/10.1073/pnas.1917777117](https://doi.org/10.1073/pnas.1917777117) + +Also feel free to join us at /r/PredictiveProcessing to learn more!" +2006 How do microbiologists know whether the virus they discovered is a novel virus or not? 20 https://www.reddit.com/r/askscience/comments/q2g9lv/how_do_microbiologists_know_whether_the_virus/ 1633509265 q2g9lv Biology 2021-10-06 11:34:25 "Modern virology works mainly with DNA or RNA sequencing, which is vastly more sensitive than more traditional isolation or electron microscopy approaches. It's also much more specific, since you can directly compare the genome sequence against the vast databases of previously-sequenced viruses. Simplistically, if you compare to the databases and it's not the same as anything in there, then it's novel. + +Slightly less simplistically, since viruses often mutate rapidly, their genomes are highly variable and you often will not have an *exact* match in the databases. It's still usually very obvious if it's actually a minor variation on a known virus, a new species of a known group, or something even more different. If in doubt, the [International Committee on Taxonomy of Viruses](https://talk.ictvonline.org) has guidelines that can help you. + +It's extremely common to find new viruses, especially in these days of large-scale environmental sequencing (where *most* viruses identified are new), so this isn't a theoretical, abstract discussion. The bigger problem isn't declaring that the virus is new, it's actually understanding what it could possibly be -- many viral sequences are so new and so weird they can barely be identified as anything at all ([“biological dark matter""](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4588555/)). + +>Massive amounts of metagenomics data are currently being produced, and in all such projects a sizeable fraction of the resulting data shows no or little homology to known sequences. It is likely that this fraction contains novel viruses, but identification is challenging since they frequently lack homology to known viruses. + +--[Discovering viral genomes in human metagenomic data by predicting unknown protein families](https://www.nature.com/articles/s41598-017-18341-7.pdf?origin=ppub)." It used to be complicated but these days you just send a sample to a lab that does sequencing and the next day you get an email with the whole genome of the virus. Than you can check that genome against databases +2007 Why are there varying cooking safety temperatures among meats? Don't bacteria die at similar temperatures? 20 https://www.reddit.com/r/askscience/comments/q2ttc1/why_are_there_varying_cooking_safety_temperatures/ 1633555258 q2ttc1 Biology 2021-10-07 0:20:58 "165 F is a temp that kills salmonella quickly. In chicken, the bacteria can exist anywhere in the meat, meaning one must cook all of the meat to that temp, or risk ingesting potentially harmful bacteria. + +Cut beef (steaks) are less likely to have salmonella or ecoli exist within the meat fiber, and would likely have the bacteria present on the surface, so grilling the outer shell of the peice of meat is sufficient for killing pathogens. + +Ground beef must be browned (reach 165 degrees F) because more surface area of the meat is exposed to potentially harmful bacteria. + +Edit: Cleaned up, words." Salmonella or similar are not in the muscles of the living animal, but in the guts. Carefully butchered meat is thus very safe to eat. Cleanly butchering a Chicken in high amounts is harder than cleanly butchering a cow. I mean, Steak Tartare is a thing. food safety guidelines are formulated very conservatively, they usually add a bit to what‘s really necessary. +1515 Do people become immune to CoVid-19 after recovering from it? 19 https://www.reddit.com/r/askscience/comments/g12eo4/do_people_become_immune_to_covid19_after/ 1586856301 g12eo4 COVID-19 2020-04-14 12:25:01 "Absolutely yes. + +There’s been a lot of media fuss about a (non-peer-reviewed) paper that claimed they found 1/3 of recovered people to have low antibody titers. You should look very skeptically at that paper, and even more skeptically at the media response, which draws exactly the opposite conclusion from what this group says - because even this group says that two-thirds of patients had high titers of antibodies against the virus. So obviously, at the very least the majority of recovered people are immune. + +Second, this group is the only group that finds that many people with low antibody titers, which makes you wonder about their testing. Looking at their paper, we see that it’s not peer reviewed (it’s a preview). We also see that they made up their own antibody test, instead of using an agreed standard, and never validate their test to show that it’s actually measuring something meaningful. + +So we can be quite skeptical about this paper (even though, again, it says that the majority of recovered people do have high titers and are probably protected). What do other groups find? + +Other groups do find occasional people with low titers, but far fewer than here. For example, [Severe Acute Respiratory Syndrome Coronavirus 2−Specific Antibody Responses in Coronavirus Disease 2019 Patients](https://wwwnc.cdc.gov/eid/article/26/7/20-0841_article) found that all of 19 tested recoverees were antibody positive, and [Detection of antibodies against SARS‐CoV‐2 in patients with COVID‐19](https://onlinelibrary.wiley.com/doi/10.1002/jmv.25820) found 60 of 60 positive. Another paper I just read but can’t find again found 37 of 38 positive. + +Note: these tests were on symptomatic patients. We know much less about asymptomatic people (maybe half or more of the overall cases may be asymptomatic, or very mild). There’s a little evidence that milder cases have lower immunity, which wouldn’t be surprising. Even so, the expectation is that asymptomatic people, having recovered, would have an even milder and shorter second exposure, and (again, an expectation not something demonstrated) this would likely act as a booster so that subsequent exposures would be even shorter. + +Because I know people are going to parrot the repeat-infection claim, few scientists are convinced that those repeat-positives are truly reinfections. Rather, they’re probably false negative tests taken between two true positives. We know that false negatives are fairly common with the available tests, so this is by far the simplest explanation. + +> There remains a lot of uncertainty, but experts TIME spoke with say that it’s likely the reports of patients who seemed to have recovered but then tested positive again were not examples of re-infection, but were cases where lingering infection was not detected by tests for a period of time. ... Instead, testing positive after recovery could just mean the tests resulted in a false negative and that the patient is still infected. “It may be because of the quality of the specimen that they took and may be because the test was not so sensitive,” explains David Hui ... + +—[Can You Be Re-Infected After Recovering From Coronavirus? Here's What We Know About COVID-19 Immunity](https://time.com/5810454/coronavirus-immunity-reinfection/) + +So to summarize a bunch of other stuff (look through my previous posts for many, many references): + +* even the most pessimistic (unvalidated) tests say most people are immune +* most tests find over 90% of recovered people are immune +* so-called reinfection almost certainly is simply bad tests +* SARS and MERS gave decent to good immunity +* experimental vaccines against SARS and MERS have given great immunity +* convalescent serum transfer gives protection against disease, showing that immunity is protective" [deleted] +1516 Why do some substances like soap foam while others do not? What exactly causes it to foam? 19 https://www.reddit.com/r/askscience/comments/ejyb2l/why_do_some_substances_like_soap_foam_while/ 1578153579 ejyb2l Chemistry 2020-01-04 18:59:39 Foams are largely formed by amphiphile substances, stuff that has polar and nonpolar ends. That ends up with a tendency to form films that roll into bubbles when agitated. In other cases, foams can just be viewed as trapped gas bubbles, such as in a polyurethane building foam. There, the substrate just solidifies around the gas bubbles. "There are additives to make it foam. That’s why you can’t use dish soap in a dish washing machine.. the suds will be too much for the machine. + +I believe the foaming substances are ammonium lauryl sulfate and sodium dodecyl sulfate" +1855 How do antibodies attack coronavirus in the upper respiratory system? 19 https://www.reddit.com/r/askscience/comments/lcfmc7/how_do_antibodies_attack_coronavirus_in_the_upper/ 1612445284 lcfmc7 Biology 2021-02-04 16:28:04 "> So how do the antibodies neutralize the virus in this situation? If the virus is not ""inside"" our body floating around in our blood stream. + +Similar to how your blood stream is not actually 'everywhere' in your body, it still permits nutrients or oxygen to reach each of your body's cells (that require such). Aka, ressources and other 'sub-cellular entities' can pass i.e. from your blood into the cells of your skin (or respiratory system) and in reverse. + +It's weird to wrap your head around, but your blood veins are not 'perfectly sealed'. They're just 'sealed tightly enough' for both the liquid 'blood', *not* the small things within blood. + +Consequently, the virus, and antibodies, can more or less freely reach 'every part of your body', just that obviously some areas are more easy to reach than others. I.e. an airborne virus will much easier reach the respiratory system, and since virus cells (do you call singular viral entities 'cells'?) don't actually possess a GPS + map of your body, they will simply spread to and accumulate in whatever regions they can reach 'most easily at random' (simplification). + +So, yes, there's plenty of 'space' for both the virus and the immune-system to meet even outside the blood stream." "You have small blood vessels, called capillaries that reach all of our tissues, how else would those cells still get their nutrients. These capillaries reach until just under your epithelial cells (those ""exterior"" cells). The very last part can be reached by simple diffusion. All these exterior tissues are obviously the main point where all viruses and bacteria enter our body, thus our immune system is anyway especially present in those tissues, having something like local dependances present within this tissue. So some antibodies and T-cell immunity is even present locally." +1856 How do springs continue to apply pressure over years? 19 https://www.reddit.com/r/askscience/comments/lt3xdo/how_do_springs_continue_to_apply_pressure_over/ 1614363138 lt3xdo Engineering 2021-02-26 21:12:18 "Materials have what is called an elastic limit. + +It is essentially the amount of deformation that a material under force can undergo such that when the force is removed, the material will return to original shape/position/size. + +As long as you don’t exceed this limit, it will continue to bounce back. If you go beyond this you will cause plastic deformation, which happens when you stretch out a spring too far and it doesn’t go back." Count yourself lucky you're not a piano tuner. Their springs (meaning their tensioned strings of piano wire) are under a high load and are continuously relaxing at a glacial rate (in a process known as [creep](https://en.wikipedia.org/wiki/Creep_\(deformation\))), which changes their resonant frequency slightly and puts the piano out of tune (in addition to the effects of thermal expansion and humidity). But the general concept is the same: strain energy is stored in the material from an applied load, and we hope that creep (which becomes nonnegligible only at high stresses and relatively high [homologous temperatures](https://en.wikipedia.org/wiki/Homologous_temperature)) doesn't adversely affect our application. Does this get at what you're asking about? +2008 Does taking mock tests increase mental stamina? 19 https://www.reddit.com/r/askscience/comments/rc25g8/does_taking_mock_tests_increase_mental_stamina/ 1639000899 rc25g8 Psychology 2021-12-09 1:01:39 "Here's a meta-analysis I found on the effects of practice tests. I can try to get you the PDF if its worthwhile + +https://journals.sagepub.com/doi/abs/10.3102/0034654316689306 + +It doesn't include anything about stamina it in, but what we know from social/IO psych about trainings/simulations would definitely argue that that's the case. The more ""naturalistic"" the practice, the easier the translation into the real deal. + +I think too about pacing and tapering (just like athletes would). You want people to be performing at the expected level for a bit before the actual event, then taper down a few days before to give them some energy rebound and decrease natural stress from the grind. + +We also know that snacks and water and things during the break can help with focus. And sleeping!" "Hmmmmm, I’ve never heard this before. + +There are some studies that practice tests assists with retention, like this one: https://journals.sagepub.com/doi/10.1111/j.1467-9280.2006.01693.x + +I’ve never done a timed mock exam, but when I was in high school my math teacher had me study using practice exams. The goal was to get me used to the style of the exam questions and hopefully reduce my test anxiety through familiarity. I’ve looked for studies to support that, but I can’t find anything specific, though I suppose it basically amounts to exposure therapy, which is scientifically supported by fairly strong evidence." +2009 What would happen if protons, neutrons, and electrons kept accumulating in a single atom? 19 https://www.reddit.com/r/askscience/comments/rc5jos/what_would_happen_if_protons_neutrons_and/ 1639011066 rc5jos Physics 2021-12-09 3:51:06 "We actually think this happens, more or less, during the [rapid neutron capture process, or **""r process""**](https://en.wikipedia.org/wiki/R-process) that occurs inside core-collapse supernovae and/or neutron star mergers, and it produces about half of the nuclei heavier than iron in the universe. + +In those environments there are an enormous quantity of neutrons flying around and available for capture. Nuclei will capture more and more of these neutrons until they are radioactive enough to rapidly beta decay, turning neutrons into protons and electrons. In that way all of these particles are available. Each time a proton is made, the nucleus will go up by one element. + +The conditions for this to occur are short-lived, something like one second. It's possible that they end before nuclei run out of appetite, but we know it goes at least past uranium because it's the only astrophysical process that should be able to make it. + +However if the conditions last long enough (or if it's cool enough and there are enough neutrons) then the nuclei can grow well past uranium. They don't do it forever though, because as they get big the nuclei become very easy to fission. There are lots of particles flying around that can rapidly trigger the fission, even neutrinos in the supernova case. So what happens is called **fission cycling**, where the fragments from the fission resume the r process somewhere in the middle, and build up again. They may build up and fission again, perhaps several times before they run out of neutrons. + +We don't know where exactly the end of this process is and fission takes over, because we haven't been able to build those nuclei in the lab and the theoretical calculations are just too complex to actually execute. Any of these nuclei that may have survived at the end of the event should pretty quickly decay into more familiar ones via fission and/or alpha emission. + +[You can read more about the r process and other processes in this old thread.](https://www.reddit.com/r/askscience/comments/1l99tx/how_did_elements_heavier_than_iron_form_given/cbx18lh/)" +1636 Has herd immunity ever been achieved without a vaccine? 18 https://www.reddit.com/r/askscience/comments/gzvi57/has_herd_immunity_ever_been_achieved_without_a/ 1591734781 gzvi57 COVID-19 2020-06-09 23:33:01 """Herd immunity"" is the natural end state of an epidemic disease. It's not like a goal you achieve, it's a description of the population dynamics of a disease organism. + +Take a virus, virus X. A person with virus X, all else being equal, spreads it to three other people on average. Now, imagine a situation where nobody is immune. Each sick person spreads the disease to 3 other people, and the number of people who are sick increases. Now imagine a situation where 1 in 3 people is immune. Each person spreads the disease to three people, but only two of them get it because on average one is immune. The disease spreads more slowly. Now imagine 2 in 3 people are immune. Each person spreads the disease to 3 people on average, but on average two are immune so it on average only spreads to one other person, and the number of people with the disease stays the same. If even higher fraction of people are immune, the disease dwindles and dies out in the population. + +That's herd immunity. + +Infectious diseases naturally tend to reach some level near herd immunity, because herd immunity is the thing that stops the disease from spreading effectively. Go back to my hypothetical example above: first 0% of the population has had the disease, at this point it can spread easily so eventually 1/3 of the population has had it and it can still spread but more slowly and then 2/3 of the population has had it so it stops spreading effectively. + +The thing about herd immunity through disease spread is that it means everyone who is going to get sick has gotten sick, so it's not really an effective way to keep people from getting sick. It's like if your solution to keeping deer from eating plants in your garden was to let them into your garden to eat all the plants they wanted. After they had done that, the only remaining plants would be ones that taste bad to deer, so deer wouldn't eat any more plants in your garden. But it doesn't exactly save the plants that got eaten." "Throughout the middle ages and for a few hundred years after, the Black Death would hit Europe about once every 20 years. My understanding of this cycle is that it was based on herd immunity. The plague would hit the populace hard, until heard immunity kicked in. Over time, the immune die and a new generation who are not immune are born. Eventually, herd immunity disappears and the plague hist once again. Rinse and repeat. + +I'm a history guy, not a medical guy, so maybe I'm off on this. If so, I'd love if an expert could corroborate or correct my understanding." +1637 Lighting a fire on jupiter? 18 https://www.reddit.com/r/askscience/comments/h1840d/lighting_a_fire_on_jupiter/ 1591909796 h1840d Astronomy 2020-06-12 0:09:56 "I'm not sure where you see oxygen? The only oxygen I see is bound in water and CO/CO2. But that is not the same as having oxygen available for combustion. You don't exactly fuel a fire with water. +And in any case, the atmosphere is almost exclusively made up of hydrogen. On Earth Oxygen makes up 20% of the atmosphere and that is oxygen in the form of O2 mainly. This doesn't count oxygen in the form of CO2 or H20." "wikipedia says the atmosphere of Jupiter is about 99% hydrogen and helium, the remaining 1% being traces of methane, water, ammonia, carbon, ethane, hydrogen sulfide, neon, sulfur... and oxygen. Farther into the interior these trace gasses might be up to 5%. + +Oxygen molecules may interact with hydrogen, ""burning"" to form water vapor, but there's definitely not enough loose oxygen floating around to make a planet-wide conflagration. + +There's also the fact that Jupiter gets much less energy from the sun, but I don't know how hot the interior of the planet gets and I'm not qualified to factor that in." +1857 How are satellites electronically grounded? 18 https://www.reddit.com/r/askscience/comments/la5bxu/how_are_satellites_electronically_grounded/ 1612192524 la5bxu Engineering 2021-02-01 18:15:24 "Everyone else is absolutely missing the point. Nearly all circuits in a satellite *are* grounded, just not to the earth. The fact that you are not on earth makes grounding *more* important, not less. Within *seconds* in an space environment you can build up large charges between different circuits just based on the electrical isolation of extremally high vacuum, and the surrounding plasma and high energy particles of space. This is coupled to the problem that the breakdown voltage of the vacuum is *lower* than air. So a potential that would not be dangerous on my lab bench would be very dangerous in space! + +A ground is a reference 0 Volt Potential. Note that it is a reference, not an absolute! Within electrial circuits it is *critical* that any part that talks to another has a common refrence, or is electrically isolated via optical isolators. ( Using LED/Photorecptors to send information ) + +There is absolutely a reference ground between circuits external to the circuit, and they are not allowed to float. Otherwise you would have a nearly impossible task of having circuits talk to each other. Everything would have to be opto-isolated from each other. You could never have any high frequency signals without every circuit turning into a antenna. + +What this reference is is different between different satellites. However be far the simplest ground is the conductive frame of the circuity itself. ( Large complex satellites will use multiple grounds isolated from each other ) + + +Space induces a ton of problems into circuit design. As it is not a complete vacuum you also have to deal with the plasma of high energy particles around you. Your craft can develop high static charges in the frame, or even relative to itself! + +[NASA has an excellent introduction](https://science.nasa.gov/science-news/science-at-nasa/2001/ast13nov_1sidebar) to the problems of charge in space. As the ISS is ENORMAS compared to everything else in space it has the largest problems as well. It has multiple grounding planes, and they can generate massive potentials relative to each other. ( The Solar cells are the main concern ) + +Dr. Robert Frost at NASA has some excellent pictures [here](https://www.quora.com/What-is-used-as-the-electrical-ground-on-the-ISS-What-does-the-ISS-use-as-a-ground-in-space-or-does-the-whole-station-slowly-build-up-charge-If-so-how-does-it-make-sure-the-charge-is-spread-evenly-so-no-arcing-occurs) showing DC arcing damage to the solar array, and discusses how the ISS deals with reducing the potential between different sections of the ISS." "They're not. + +Electronics are likely using the frame itself as the common, which may be at a different potential than the surface of the earth, or not. + +If there was no net charge on the ship to begin with, it won't ""build up charge"" because it's isolated in space. Where would the charge come from? I supposed rare ionized gasses in space? Solar flares? Maybe? + +If you wore socks and dragged them across carpet inside a satellite, you pulled charge from the floor of the satellite into your socks, then to your body. If you touched the metal frame, you'd feel a shock as you give the charge back. The total charge was always constant. It just moved around inside the satellite. + +What grounds the earth?? It's just a bigger satellite." +1858 How realistically viable are mrna vaccines in treating autoimmune disorders? 18 https://www.reddit.com/r/askscience/comments/ltznrq/how_realistically_viable_are_mrna_vaccines_in/ 1614467268 ltznrq Medicine 2021-02-28 2:07:48 "Yes, it’s an area of active research. Of course, with autoimmune vaccination, the goal is to activate the tolerizing components of the immune system, but conceptually many of the same processes are needed (particularly activation of specific T cell subsets, which means delivering the antigen to dendritic cells or similarly antigen-presenting cells). That means that mRNA vaccination has similar advantages (and disadvantages) to conventional vaccination, though obviously since your goal is tolerization instead of activation you can’t do everything the same. + +>…to achieve tolerization, the authors encapsulated an mRNA encoding a myelin antigen in liposomes made of lipids devoid of pro-inflammatory activity. Importantly, the authors have also synthesized the mRNA replacing the nucleotide uridine with 1-methylpseudouridine (m1Ψ), with the result that this m1Ψ mRNA can induce protein translation but cannot engage TLR7. Finally, injection of these liposomes into the blood stream has ensured the uptake by circulating or lymphoid tissue-resident APCs, but avoided the potential tissue-derived danger signals, and draining to the same lymph node as the targeted APCs. This strategy was not only highly effective in treating EAE induced by the very same antigen used to tolerize, but also inhibited EAE induced by a different antigen. + +—[A Tolerizing mRNA Vaccine against Autoimmunity?](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7875549/), commenting on [A noninflammatory mRNA vaccine for treatment of experimental autoimmune encephalomyelitis](https://science.sciencemag.org/content/371/6525/145.long)." "Autoimmune disorders aren't one thing. There are a whole lot of different things going on and it can be very different for different people. + +So not likely that there will be a silver bullet that will help fix everything. + +Specifically inducing tolerance to an auto-antigen seems feasible. The mRNA delivery platform is one way that has promise. + + But it doesn't necessarily address the underlying mechanism that led to the autoimmunity in the first place. + +I'll also add that messing with immune control systems is really hit and miss. It's a whole new area for cancer therapeutics. But it has also badly surprised us a few times. + +The human immune system is really hard to study in vitro and isn't modelled as well in animals." +1859 Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science 18 https://www.reddit.com/r/askscience/comments/lbpctb/ask_anything_wednesday_physics_astronomy_earth/ 1612364418 lbpctb 2021-02-03 18:00:18 Since my posts are oddly not posting, this was my question in mind. If Earth's gravitional pull was weaker could we see parachutes designed for per 2 or more people? [deleted] +1918 Why are there so many vitamin ‘B’ types and how come the numbers skip? 18 https://www.reddit.com/r/askscience/comments/p8cfy6/why_are_there_so_many_vitamin_b_types_and_how/ 1629488671 p8cfy6 Human Body 2021-08-20 22:44:31 "The long-lost B vitamins (no longer labeled vitamins): + +* B4 (also known as adenine) +* B8 (also known as inositol) +* B10 (para amino benzoic acid – PABA) +* B11 (salicylic acid) + +And the regular ones: +* B1 (thiamine) +* B2 (riboflavin) +* B3 (niacin) +* B5 (pantothenic acid) +* B6 (pyridoxine) +* B7 (biotin) +* B9 (folate) +* B12 (cobalamin) + +https://lauriegoldmanmd.com/2020/03/11/long-lost-b-vitamins-b4-b8-b10-b11/" Because of their discovery history it was originally thought to be one b vitamin. Then they started identifying slightly different structures doing different things. They skip numbers because some of them were found to not actually fit the definition of a vitamin +2010 "How genuine is the science in that ""Warp Bubble"" article I've been seeing everywhere?" 18 https://www.reddit.com/r/askscience/comments/rb5o2e/how_genuine_is_the_science_in_that_warp_bubble/ 1638901616 rb5o2e Physics 2021-12-07 21:26:56 "Complete Hogwash. This is from the same engineer who was ""testing"" the non-momentum conserving ""EmDrive"" and claimed it worked to the press. + +They have no test article. + +“We have not manufactured the one-micron sphere in the middle of a 4-micron cylinder.” + +This is silly eye-candy. There is no warp drive." "The math is good, the science is sound. + +BUT... + +The equations only work for physical conditions and forms of matter which are only theoretical and have never, ever been observed, not even hypothetically. Very much like how the square root of negative one works fine in math, but you'll never get a physical representation of it you can point a finger at. + +Until we have negative energy or strange matter in a lab, or at least somewhere we can observe them, it's all purely theoretical." +1638 How would two planets share a moon? 17 https://www.reddit.com/r/askscience/comments/h0asy6/how_would_two_planets_share_a_moon/ 1591795223 h0asy6 Astronomy 2020-06-10 16:20:23 "There's only two way to have a stable system of more than two bodies. + +The simplest is to make it *really close* to acting like a two-body system. For example, multiple objects orbit the Sun because the Sun is so much more massive than the rest of the solar system that you can mostly ignore the effects of other planets, except as a minor correction to be added later. So Earth's orbit around the Sun isn't destabilised by Jupiter. This isn't really ""sharing"" an object though - it's just a stable system. + +You can similarly have a close orbiting binary, with a third object orbiting it from far away. If the binary is close enough, it ""feels like"" one star or planet. So you could have one moon orbiting at a very large distance from a double planet, sharing a moon in this sense. I don't know if this happens in reality for moons around planets - but it is one way how a binary star could have planets. You can also have a planet with a moon orbiting another planet with a moon - or similarly, a star with planets orbiting another star with planets. Again, the moons need to be close enough to the planets that they ""feel like"" one object (or the planets need to be close enough to the star), to make things stable. This doesn't really count as ""sharing"" either - it's just another way for things to be stable in a multiple object system. + +The second option is that there actually are stable points in full three-body systems. These are the L4 and L5 Lagrange points. The other Lagrange points are equilibrium points but aren't stable. Forces add up to zero on L1-L3, but any slight perturbation causes things to fall away from that point. The L4 and L5 Lagrange points only exist if one of the two main objects is at least about 25 times more massive than the other, and the third object has a very low mass. If you satisfy these conditions, then you have stable points trailing in front and behind the orbit of the second massive object. We see this in the solar system, where Jupiter has the Trojan and Greek asteroids trailing in front and behind it. In a sense, these asteroids are shared between Jupiter and the Sun - they aren't totally dominated by the gravity of either one, but are strongly affected by both. + +**tl;dr** A moon could orbit at a large distance from a close binary of planets (although I'm not sure if that would happen naturally), or if one planet is >25x more massive than the other, then they could share small moons or asteroids in the L4 and L5 Lagrange points, trailing ahead and behind the orbit of the smaller planet." "What do you want the moon to *do*, lore and story wise? That's going to determine the setup to tell the story. + +A ""double planet"" can have a common moon. However from each planet, the dominant object in the night sky is the other planet - the shared outer moon is more distant thus appears smaller and fainter. + +Two planets in similar orbits could, in the short term at least, exchange moons. In the long term this is probably unstable though. But if your setting features sufficiently advanced aliens or wizards, then you can have an unstable solar system that's been artificially created. + +The converse, two moons sharing a parent planet, is of course possible. And for moons close enough in, the planet will be the dominant object in the night sky." +1715 Differences between Pfizer and AstraZeneca vaccine? 17 https://www.reddit.com/r/askscience/comments/k6vaw7/differences_between_pfizer_and_astrazeneca_vaccine/ 1607121462 k6vaw7 COVID-19 2020-12-05 1:37:42 "Pfizer and Moderna are based on a new type of vaccine called mRNA. These have never been approved for use in humans before outside of trials. They must be kept at very cold temperatures (-70 and -20 Celsius respectively). The testing of these vaccines has been for roughly 40k people for each company. So far they’ve released safety and efficacy results based on 7 days after the administration of the second dose. The phase 3 trial data has yet to be released in any peer review publications. So far what we know is only from press releases from the manufacturers. The reported side effects are said to be mild compared to the AstraZeneca and Sputnik V vaccines. Medium to long term efficacy and safety of these vaccines are entirely unknown. The uk has approved ‘emergency authorization use’ of the Pfizer vaccine (this is different than normal vaccine approval). They have also granted Pfizer legal indemnity to protect them from lawsuits. + +AstraZeneca and Sputnik V use a previously well known and in-use type of vaccine (called viral-vector, eg. some Hep B vaccinations). They can be stored at normal refrigerator temperatures. AstraZeneca has been tested on roughly 40k people, while Sputnik V has been tested on 20k people. The side effects are said to be often more uncomfortable than the Pfizer and Moderna vaccines - typically headaches and/or soreness at the injection site. They have also only reported phase 3 results from only 7 days after the second dose. They have also yet to release their phase 3 trial data in peer reviewed publications, having only released summaries so far in the form of press releases. The mid and long term safety and efficacy rates of these vaccines is also entirely unknown. The Russian Sputnik V vaccine is approved for use in Russia (possibly a few other countries as well). It is the first vaccine to have been approved for public use, the Russian government having done so based only on phase 1 and 2 testing results. + +All of the vaccines mentioned claim to have 90+% efficacy ratings, which is more than stellar for vaccines in general. However it is widely expected that this efficacy rating will drop once much larger sample groups are known. + +I hope this helps." "Pfizer’s mRNA is new technology basically. They’re injecting a replica of the “covid-19 spike” inside you so your body learns how to fight it. When you do finally get covid-19, your body will now have the weapons to beat this invader before he kicks your ass completely. + +Cost - It also costs about 10x as much as astrazenecas. + +Theres concerns over the long term effects of the mRNA vaccine. That is the only reason South Korea is not going with them. It may be harmless and be Nobel peace prize worthy. We don’t know yet." +1860 How do airplane pilots control lift? Is there a way to vary the lift the wings generate, or do pilots have to slow down up or pitch down when cruising? 17 https://www.reddit.com/r/askscience/comments/lshkuo/how_do_airplane_pilots_control_lift_is_there_a/ 1614289005 lshkuo Engineering 2021-02-26 0:36:45 "MysticAviator mentioned flaps, which change the shape of the wing so that it generates more lift and more drag. + +The old F-8 could rotate its whole wing structure a little bit, which let it land with the fuselage more or less level but the wings effectively ""nose up."" + +The B-52 was designed to cruise a little bit nose-down. Or, rather, it was designed to land with a level fuselage because of how they had to arrange the landing gear, and cruising nose-down was an acceptable side-effect. + +Edit: In both cases they designed the planes this way because military planes face weird and sharp constraints." "The other replies touched on the mechanics of the process some. + +A useful formula: lift is proportional to the sine of the angle at which the air meets the wing, times the square of airspeed (provided that angle is smaller than about 16 degrees.) + +That means that, without changing the shape of the wing with flaps, the wings produce the same amount of lift at 150 knots 12 degrees nose-high, or 180 knots 8 degrees nose-high, or 210 knots 6 degrees nose-high, or 300 knots and 3 degrees nose-high. + +Airplanes are typically designed to be self-stabilizing: setting elevator trim (as /u/mysticaviator mentioned) directly sets the angle of attack and indirectly sets the speed. Adding power results mostly in climbing, only a tiny increase in speed; cutting off the power results mostly in descending, only a tiny decrease in speed. To prepare to land, you reduce speed by increasing the angle of attack, and reduce power even more, so that the increased angle of attack doesn't result in excess lift and climb. + +A very readable and not-too-math-intensive free intro to the physics of flight is John Denker's [See How it Flies](https://www.av8n.com/how/)." +1861 I am considering using electrolysis to remove rust from a pair of antique Wiss Tailors Shears that have a brass shear bolt that is better left in place. Will the presence of brass on the cathode affect the electrolysis process and vice versa? 17 https://www.reddit.com/r/askscience/comments/lqpj3b/i_am_considering_using_electrolysis_to_remove/ 1614105451 lqpj3b Chemistry 2021-02-23 21:37:31 "Project Farm YT did a comparison video with evapo-rust and electrolysis. + +[https://www.youtube.com/watch?v=8dtDLQHjHBc](https://www.youtube.com/watch?v=8dtDLQHjHBc) + +Then someone else did a brass electrolysis: + +[https://www.youtube.com/watch?v=PeGpu0s4b0g](https://www.youtube.com/watch?v=PeGpu0s4b0g) + +Check more info online for details like not using stainless steel for sacrificial anode or not pumping too much electricity through electrodes." "Generally speaking, the brass is not going to be damaged if it's the cathode. You are pumping electrons in so you are effectively giving it cathodic protection against corrosion. + +You will generate hydrogen on the part. For a short time period this is likely fine, if you did it for weeks you might see some hydrogen embrittlement I guess. + +The biggest risk will come from maybe redepositing something that comes off the anode. But you need to scrub it after anyways so that will come off. + +with respect to what /u/Iruton13 said, not using stainless steel for anodes doesn't apply at the scale you are talking about. Maybe it's a thing on industrial scale, but it just means paying for wastewater neutralization. + +https://www.reddit.com/r/askscience/comments/2ta57z/does_using_stainless_steel_as_an_anode_in/" +1862 How does the Sinovac Covid-19 vaccine have such wildly different efficacy rates around the world? 17 https://www.reddit.com/r/askscience/comments/lsr39m/how_does_the_sinovac_covid19_vaccine_have_such/ 1614318395 lsr39m COVID-19 2021-02-26 8:46:35 +1863 How similar are SARS and COVID-19 (SARS-CoV and SARS-CoV-2, respectively), in the disease pathology/mechanisms? 17 https://www.reddit.com/r/askscience/comments/lt1ns3/how_similar_are_sars_and_covid19_sarscov_and/ 1614357797 lt1ns3 COVID-19 2021-02-26 19:43:17 "SARS-CoV-2, like you correctly assumed, is 80% genetically similar to SARS-CoV[\[1\]](https://www.sciencedirect.com/science/article/pii/S2211383520302999). However, the International Committee on Taxonomy of Viruses released a [statement](https://digital.csic.es/bitstream/10261/212994/1/Severe%20acute_Gorbalenya.pdf) on February 11, 2020, stating that based on ""**phylogeny, taxonomy and established practice**, \[the Coronavirus Study Group\] formally recognizes this virus as a sister to severe acute respiratory syndrome coronaviruses (SARS-CoVs) of the species Severe acute respiratory syndrome-related coronavirus and designates it as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)."" (emphasis mine) + +In regards to similarities and differences between the viruses and related diseases, both SARS and SARS-CoV-2 bind to the ACE2 receptor on human cells[\[2\]](https://www.nature.com/articles/nature02145)[\[3\]](https://www.nature.com/articles/s41564-020-0688-y?report=reader). However, SARS-CoV-2 contains a furin cleavage site - a basic region with amino acid sequence PRRAR - in its spike protein that is absent in SARS-CoV. To enter cells, this furin cleavage site is ""cut"" with a furin enzyme which allows the spike protein to be processed by TMPRSS2, a serine protease, before the viral spike protein can fuse with the ACE2 receptor. Data suggests that this furin cleavage site enhances (but is not required for) viral infectivity and transmission[\[4\]](https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1009246&rev=2). + +As mentioned above, both SARS-CoV and SARS-CoV-2 target the ACE2 receptor which is found on cells in a wide variety of tissue types, organs, and organ systems. These include (but are not limited to) the intestines (enterocytes), reproductive system (male and female), the heart and vascular system (cardiac and endothelial cells), lung epithelial cells, the endocrine system, kidneys, and the eyes[\[5\]](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7383091/). **Both viruses target multiple organs and organ systems, though the primary mechanism of infection is through the respiratory system.** When SARS-CoV first emerged in November 2002, it was primarily characterized as an unknown virus causing severe pneumonia in extreme cases. It wasn't until April-May 2003 that it was formally identified[\[6\]](https://www.sciencedirect.com/science/article/pii/S0140673603130772) [\[7\]](https://www.nejm.org/doi/full/10.1056/NEJMoa030781) [\[8\]](https://www.nejm.org/doi/full/10.1056/NEJMoa030747), and not until November 2003 that the relationship between SARS-CoV and ACE2 was published[\[2\]](https://www.nature.com/articles/nature02145), and by that point, SARS was already known as a severe respiratory condition. Additionally, cases of SARS only numbered roughly 8000[\[9\]](https://www.cdc.gov/dotw/sars/index.html) thanks to containment protocols[\[10\]](https://www.cdc.gov/mmwr/preview/mmwrhtml/mm5243a2.htm), limiting the identification of less frequent symptoms. + + +TLDR: SARS-CoV and SARS-CoV-2 have similar names because they are phylogenetically related. They have similar mechanisms of infection, replication, and transmission, though SARS-CoV-2 has evolved to a lower fatality rate but higher transmission rate and longer incubation period than SARS-CoV[\[11\]](https://www.thelancet.com/action/showPdf?pii=S1473-3099%2820%2930484-9) resulting in a fitter virus capable of spreading much more readily than SARS-CoV. Calling SARS a respiratory disease and COVID-19 a vascular disease is an oversimplification of both, as both viruses are capable of infecting a variety of cell types, organs, and organ systems." +1864 Why is the protective factor of covid vaccines and immunity through previous infection different? 17 https://www.reddit.com/r/askscience/comments/lwu8vy/why_is_the_protective_factor_of_covid_vaccines/ 1614779195 lwu8vy COVID-19 2021-03-03 16:46:35 "There's very little published research on the precise protective efficacy of prior infection, but what there is suggests that it's around 95% ([Assessment of the risk of SARS-CoV-2 reinfection in an intense re-exposure setting](https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1846/6033728)) - The same as, or higher than, most of the available vaccines. + +But that was in the context of homologous challenge (that is, people were being exposed to the same strain as they were previously infected with), and was over a fairly short period. + +The COVID vaccines probably have two main advantages over infection (three, if you count the obvious one that you won't get sick and die from the vaccine). First, the vaccine-induced immunity is going to be much more consistent. If you vaccinate 100 people, they'll most have a fairly similar level of antibodies. If you infect 100 people, 20 or 30 of them will be asymptomatic and probably have a fairly low antibody response, 50-60 will get sick but have a pretty good immune response, maybe a dozen will get quite sick and may have a variable immune response. So you end up with a much more inconsistent response. + +What's more, even the good responses to the natural infection are not better than the vaccine response. Most of the authorized vaccines give antibody responses that are consistently as good as or better than the best natural immune responses. + +What does that mean for heterologous immunity (immunity against variants)? We've seen pretty strong hints that what the variants do is raise the threshold of protection. That is, if protection against the same virus needs an antibody titer of (arbitrary number) 1000, then the variants might need 4000. The vaccines give say (and again, these are made-up numbers) an average of 6000, with a range between 4000-8000; so most people are protected against the variants. The natural infections give an average of 6000, but with a range between 1000-8000; most people are still protected, but a fairly large minority are not. + +This is not formally shown, but most of the pieces have been shown - the inconsistent immunity, the 4-fold difference in neutralizing titer, the fact that vaccines give antibody responses equal to or higher than natural infection - so it's likely most of the explanation." "Part of your confusion may be due to a core misunderstanding. + +> if a vaccine with a weakened virus just triggers a complete immune response + +This refers to attenuated virus vaccines, but none of the currently used COVID vaccines use that method. There are two basic methods at work in the vaccines currently being used in the western world, but neither involves an infection with any sort of COVID-like virus: + +* mRNA Vaccines (Pfizer, Moderna): these deliver carefully modified mRNA strings that are basically blueprints for how to build the spike protein that COVID uses to gain access to cells. The mRNA itself causes the immune system to go on alert and look for possible signs of infection. Once the mRNA reaches cells, ribosomes take it up and build actual copies of the protein. Those proteins then get displayed on the surface of the cell for immune cells to pick up and deliver to the cells that initiate the adaptive immune process. This has a number of big differences from the immune response to natural infection, but one of the biggest is that the only thing seen by the immune system is the spike protein. In an actual infection, the immune system will also be sampling the capsid proteins, etc. +* Adenovirus Vector Vaccines (e.g. Oxford/AstraZeneca, J&J): These vaccines involve something like infection by an actual virus but NOT the coronavirus. Instead the vaccines deliver different heavily modified adenoviruses that have all the pieces needed to gain entrance to cells but are stripped of the stuff they need to actually make additional viruses. Instead, they have the RNA needed to make the spike protein used by COVID. Like the other vaccines I mentioned, this results in copies of the spike protein being created and then displayed to the immune system. For these vaccines, the viral vector does invade cells, but at no point is there any viral replication in the recipient. The vector itself is an adenovirus with no resemblance to COVID." +1639 When light goes from a vacuum, into water, then back to a vacuum. At what speed is it now traveling ? 16 https://www.reddit.com/r/askscience/comments/h09uc5/when_light_goes_from_a_vacuum_into_water_then/ 1591791938 h09uc5 Physics 2020-06-10 15:25:38 It’s traveling at the vacuum speed again. There is no energy boost associated with the change back to vacuum; the frequency of the light stays the same. But the phase velocity changes because the index of refraction changes. "Just to add ... the speed of light, either through vacuum or through the medium, is [inversely proportional to the electric permittivity and magnetic permeability](https://en.wikipedia.org/wiki/Speed_of_light#Electromagnetic_constants) of the vacuum or medium. In a medium, these two constants have higher values than they do in free space ... consequently, the speed of light is lower in those media. When light leaves a medium and reenters free space, the local values of those constants reverts back, and so light regains its faster speed. No additional energy is required for this; all light travels at the speed of light (in vacuum and in a medium) regardless of how energetic it is or isn't. + +Hope that helps," +1640 Why doesn’t California get tsunamis? 16 https://www.reddit.com/r/askscience/comments/gz21o4/why_doesnt_california_get_tsunamis/ 1591632101 gz21o4 Earth Sciences 2020-06-08 19:01:41 "Tsunamis are generated by a sudden displacement of water, so in the context of earthquake generated tsunami, the earthquake must cause a vertical displacement of the sea floor to cause a tsunami. This [set of cartoons](https://www.usgs.gov/centers/pcmsc/science/life-a-tsunami?qt-science_center_objects=0#qt-science_center_objects) from the USGS might be helpful. + +For the majority of the length of California, [the plate boundary faults](https://en.wikipedia.org/wiki/Plate_tectonics#/media/File:Plates_tect2_en.svg) (i.e. the San Andreas and associated faults) are (1) mostly onshore and (2) dominantly strike-slip. Faults onshore obviously are not going to tend to generate tsunamis, but even for the portions of the San Andreas system that are offshore, these are not generally tsunamigenic because the [strike-slip faults](https://en.wikipedia.org/wiki/Fault_(geology\)#Strike-slip_faults) move side to side (i.e. they do not produce significant vertical deformation). As you move along California, this changes once you reach the [Mendocino Triple Junction](https://en.wikipedia.org/wiki/Mendocino_Triple_Junction) as north of the MTJ the boundary is now the Cascadia subduction zone which can, and has, generated tsunami in the past, e.g. [this animation of the tsunami associated with the 1700, Mw 9.2 Cascadia event](https://www.youtube.com/watch?v=4W2iUl0VB8c). + +Finally, it is worth mentioning that there is nothing precluding the California coast experiencing a tsunami generated from an earthquake on a subduction zone elsewhere in the Pacific (or other events capable of producing a tsunami, e.g. [flank collapses of volcanic islands](https://pubs.geoscienceworld.org/gsa/geology/article-abstract/32/9/741/103695/Megatsunami-deposits-on-Kohala-volcano-Hawaii-from)). For example, California (and the rest of the Pacific coast of the US) experienced a small tsunami caused by the [Tohoku earthquake](https://www.youtube.com/watch?v=EG507Y40d4U)." +1641 Do we know of any diseases dinosaurs could have been infected with? 16 https://www.reddit.com/r/askscience/comments/hcxfcd/do_we_know_of_any_diseases_dinosaurs_could_have/ 1592700313 hcxfcd Paleontology 2020-06-21 3:45:13 "There are several. + +* Either actinomycosis or trichomonosis (or both) [Common Avian Infection Plagued the Tyrant Dinosaurs](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2748709/) +* Trypanosomiasis [Evidence of Vector-Borne Disease of Early Cretaceous Reptiles](https://www.liebertpub.com/doi/abs/10.1089/vbz.2004.4.281) +* Pathological avian osteopetrosis, possibly caused by a retrovirus [Unusual Endosteally Formed Bone Tissue in a Patagonian Basal Sauropodomorph Dinosaur](https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.22954) +* Infections and abscesses following bites [Possible bite-induced abscess and osteomyelitis in Lufengosaurus (Dinosauria: sauropodomorph) from the Lower Jurassic of the Yimen Basin, China](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5864883/) +* Ticks and lice [Ticks parasitised feathered dinosaurs as revealed by Cretaceous amber assemblages](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5727220/) +* Paget disease of bone, possibly caused by a virus [Paget disease of bone in a Jurassic dinosaur](https://www.cell.com/current-biology/fulltext/S0960-9822\(11\)00881-5)" +1642 Why is string cheese stringy? 16 https://www.reddit.com/r/askscience/comments/h0gogk/why_is_string_cheese_stringy/ 1591813162 h0gogk Chemistry 2020-06-10 21:19:22 "String cheese is basically a type of mozzarella cheese. + +At the factory, when the curd is still hot and the machines (or workers) are manipulating the curd, instead of kneading the curd into itself to form a normal mozzarella ball, they stretch it and knead it into a stick lengthwise, gradually lengthening it over and over, creating many layers. The curd has to have the right moisture content to do this, too moist and it just melts together, too dry and it will not stick to itself even if you press it firmly. + +When the curd has reached the correct consistency they stop and usually put it in a brine solution to absorb salt, then package it. + +When you peel the ends of the cheese, it will break off in strings because those are the layers that the cheese was folded into." +1716 Some COVID-10 vaccine candidates (e.g. Oxford) use Adenovirus as a vector to transport mRNA of Sars-CoV-2's spike protein. What if the recipient of such vaccine had a prior infection of that adenovirus and now has immunity against it, will the vaccine still work? if so, how? 16 https://www.reddit.com/r/askscience/comments/irjbz5/some_covid10_vaccine_candidates_eg_oxford_use/ 1599939940 irjbz5 COVID-19 2020-09-12 22:45:40 "That’s a major concern with adenovirus vector vaccines. There’s evidence it’s a real problem: + +> Before vaccination, 266 (52%) of 508 participants had high pre-existing anti-Ad5 neutralising antibodies (table 1). Participants with low pre-existing anti-Ad5 immunity had RBD-specific ELISA antibody and neutralising antibody levels that were approximately two-times higher than the participants with high pre-existing anti-Ad5 immunity + +—[Immunogenicity and safety of a recombinant adenovirus type-5-vectored COVID-19 vaccine in healthy adults aged 18 years or older: a randomised, double-blind, placebo-controlled, phase 2 trial](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736\(20\)31605-6/fulltext) + +Many groups have taken steps to overcome it by using adenoviruses that humans have not been exposed to. For example, the Oxford group uses a chimpanzee adenovirus, and there are groups using adenovirus serotypes 26 or 35, which are not as common as adeno type 5. + +* [A Novel Chimpanzee Adenovirus Vector with Low Human Seroprevalence: Improved Systems for Vector Derivation and Comparative Immunogenicity](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3396660/) +* [Recombinant Adenovirus Serotype 26 (Ad26) and Ad35 Vaccine Vectors Bypass Immunity to Ad5 and Protect Nonhuman Primates against Ebolavirus Challenge](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3126236/)" "Pre-existing immunity to the adenovirus vector was a major concern in the 2000s. In one of the earliest adenovirus vaccine studies, they found that subjects that had been previously exposed to the vector responded much more poorly than those that had not previously been exposed. [Source](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2711537/). These results were replicated in a number of other disease models. Part of the issue is that your pre-existing immunity essentially clears the vaccine too fast. Generally speaking, the faster a pathogen is cleared, the weaker your lasting immunity will be. + +That being said, in the past decade they’ve developed a number of strategies to circumvent this issue. For example, coating the adenovirus particle in polyethylene glycol essentially masks it from pre-existing antibodies. [Source](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2922072/). Similarly, various methods of encapsulating the adenovirus, for example in lipid vesicles, have been developed to circumvent antibody-mediated immunity. + +Another strategy is to simply use a non-human primate adenovirus strain that isn’t found natively in humans. The problem with this strategy is that if multiple different vaccines use this same strain, then immunization with one vaccine may affect the efficacy of the next. This is the strategy employed by the Oxford vaccine. Not sure if it employs others because I’m not following too closely. + +Yet another strategy is to simply modify the region of the adenovirus vector that your body develops immunity to. [Source](https://www.nature.com/articles/nature04721). + +Anyways that’s about all I know on the topic. Hopefully there was something useful/interesting in there. + +Edit: So to directly answer your question, no this shouldn’t be a concern in the immediate future because nobody should have pre-existing immunity to a chimp adenovirus. However, in the long-run there could be issues if future vaccines choose to use the same adenovirus strain." +1865 What happens when the angular quantum number is greater than 3? 16 https://www.reddit.com/r/askscience/comments/lrvyt3/what_happens_when_the_angular_quantum_number_is/ 1614221328 lrvyt3 Chemistry 2021-02-25 5:48:48 ">The problem is that I'm only taught up to 3 with the f-block. Can someone please explain this? + +When L becomes greater than 3, then you start to fill the [g-block](https://en.wikipedia.org/wiki/Block_(periodic_table\)#g-block). It's predicted to start at element 121, but we've only observed up to element 118. + +>On a related note, what is the purpose of the magnetic quantum number? Does it determine which of the orbitals an electron is in within l? Why are some values of it negative and others positive? + +They represent the different angular momentum projections. If you imagine the angular momentum like a classical vector, it can have the same magnitude but point in different directions. Quantum-mechanically, the possible projections along any axis are quantized. For an angular momentum L there are (2L + 1) possible projections, taking the values -L, -(L-1), ..., -1, 0, 1, ..., (L-1), L. These are the possible values of the m*_L_* quantum number." +1866 Is it possible to be exposed to COVID and develop antibodies (enough to have short term immunity) without ever having a high enough viral load to test positive? 16 https://www.reddit.com/r/askscience/comments/ltth81/is_it_possible_to_be_exposed_to_covid_and_develop/ 1614448540 ltth81 COVID-19 2021-02-27 20:55:40 "When you consider that each test (antibodies, antigens) has variances known as sensitivity (higher sensitivity = higher rates of false positive results) and specificity (higher specificity = higher rates of false negative results) yes, it’s possible. + +But you’re never 100% sure that either test is telling the truth." Due to the type of tests utilized in the US, just about ANY viral load can be detected - even when its, essentially, non-existent. Thats why there is such controversy in the scientific community regarding how this is all being done. +1867 Will corona prevention measures have a lasting impact on generic influenza / flu? 16 https://www.reddit.com/r/askscience/comments/las6h2/will_corona_prevention_measures_have_a_lasting/ 1612259454 las6h2 COVID-19 2021-02-02 12:50:54 "So, these are complicated questions, but I'm going to try and give fairly straight forward answers. Obviously, this means that there will be some simplification, but I'm sure people will elaborate and correct me where it's needed. + +First, yes, there are enough reservoir hosts that people will still get the flu. Both birds and pigs harbor the influenza virus that people get. So we can always get the virus from them. Secondly, influenza has not been eradicated from people. People are still getting the flu this year, and they did last year as well. Since many people are social distancing/wearing masks/practicing good hand hygiene/etc flu cases are reduced but people are certainly still getting the flu. + +Second, it is unlikely that not seeing the flu for 2 years will negatively impact our immune response in the future. First, we should be getting vaccinated, which will protect us from getting the flu. Second, since the flu changes every year (thus the need for a yearly flu shot), our immune system is getting a new version every year. So not seeing it for two years won't affect our antibody titers since those change regularly anyway. Also, our immune system is always primed and ready to go, it doesn't need to see the same pathogen every year to mount a thorough immune response to it. + +There's a great series of podcasts by Vincent Racaniello, PhD, but if you're specifically interested in how our immune system reacts to things I'd recommend his ""Immune"" podcast. They have a whole bunch of episodes on covid and how immune system reacts to both covid and the flu." +1868 Why are certain materials like parchment paper, aluminum foil, etc. not hot to the touch out of the oven while metal and glass are? 16 https://www.reddit.com/r/askscience/comments/ltbuno/why_are_certain_materials_like_parchment_paper/ 1614385452 ltbuno Chemistry 2021-02-27 3:24:12 "Things like aluminum foil are great heat conductors, like metals in general but they are usually very very thin. There is a concept called thermal capacitance that amounts to how much heat can an object hold at a given time. By being so thin and conductive, aluminum foil loses heat quickly after you take it out of the oven. + +Think of something like a big hot potato, which has a high thermal capacitance. The potato holds a lot of heat because of the shape and composition (mostly water). So you have to be careful to not burn your tongue. + +Something like a metal plate sits in between." "1. The more mass an object has, the more heat it will hold, therefore, it will take longer for it to cool down. +2. The more surface area an object has, the faster the heat will escape away from it (that's why [radiators](https://cdn.bestheating.com/media/catalog/product/cache/07469e52453ec3e9e92a88c7a63b12d8/9/4/942205_ls_1000.jpg) are wavy and [electric motors](https://5.imimg.com/data5/QP/UQ/MY-40061069/siemens-electric-motor-500x500.jpg) have a bunch of ribs on them) + +Foil has very little mass because it's thin, and it has a relatively large surface area so it loses heat quickly. That means as you pull it out of the oven, it mostly just cools down before you get the chance to touch it, or at least much faster than a cast iron pan for example." +1869 Do Microbiologists build immunity to laboratory organisms? 16 https://www.reddit.com/r/askscience/comments/l9npma/do_microbiologists_build_immunity_to_laboratory/ 1612131888 l9npma Biology 2021-02-01 1:24:48 "Microbiologist here, I effing hope not! + +If I'm building immunity to any of the lab organisms I work with it means that I'm being exposed to them (they're somehow making it on and into by body). Everything I do in the lab revolves around making sure I don't contaminate myself or my workspace. Everything that may have come into contact with the organisms gets sanitised or sterilised. + +As the risk from the organism increases, so do the measures taken to prevent contamination/infection. For example, when I work with harmless lab stain *E. coli*, I usually work at my bench, don't wear gloves but there is plenty of hand washing, and anything that came in direct contact gets sterilised (like test tubes), anything that may have come into incidental contact gets sprayed with 70% ethanol. As this organism is not pathogenic, the risk is low so that is sufficient. + +Now, if we work with *E. coli* O157, (which is pathogenic and a high risk), it's basically scorched earth. You only work with open culture in a biosafety cabinet, you double glove so you can take a contaminated glove off and still be protected, and everything that may have even had incidental contact gets sterilised including UV sterilisation of the biosafety cabinet. + +For virulent viruses, you might add measures like wearing biohazard suits with their own oxygen supply and you are in an airlocked room with full body decontamination before you come out. + +Essentially, bacteria and viruses are classified into risk levels and the measures in place mean that no one should come into contact with an infectious dose of the organism (or even sub infectious if it's done correctly)." Those who work with pathogenic ones have to work in very controlled environments to avoid any actual exposure. If they did get immunity, it would mean they had got sick/exposed, which in turns would mean the lab would close down because unable to guarantee the biological hazard control measures. +1870 How do sailboats work when the wind is blowing in the opposite direction of travel? 16 https://www.reddit.com/r/askscience/comments/ltd978/how_do_sailboats_work_when_the_wind_is_blowing_in/ 1614390150 ltd978 Engineering 2021-02-27 4:42:30 "You zigzag, called ""tacking"". Depending on the type of boat and sails you might well be able to sail around 45° into the wind because the aerodynamics of the sail create lift rather than just being blown along like a piece of debris. So you sail at that angle for a while then turn 90° so you are sailing 45° into the wind on the other side, and so on." "Well, the hull isn't being blown, the sail is; the mast channels the force to the boat. So, you can adjust by turning the sail to catch the wind by turning them independent of the boat. Hope the mast is good and strong. + +If it is coming literally directly at you, you can do a maneuver called 'tacking' , which is where you adjust the sails one side of the boat and then the other, zigzagging. + +So for example, get pulled northeast, adjust sails, get pulled northwest, adjust sails and NE. You are sailing north still, you mitigate eastward travel with west and vice versa. You just have to switch to maintain it. + +Soo, pretend this punctuation is a boat's course! <>/\\/\\/\\/\\/\\x" +2011 Is there dark matter in our galaxy or even solar system? 16 https://www.reddit.com/r/askscience/comments/rbk09h/is_there_dark_matter_in_our_galaxy_or_even_solar/ 1638942259 rbk09h Astronomy 2021-12-08 8:44:19 "Theory and observation suggests that dark matter seems to form in roughly spherical galaxy-sized blobs. There may be some amount of smaller scale structure, but the most established part is that there's something going on at a galaxy scale - even if you go with modified gravity instead of dark matter, these modifications need to take effect on a galaxy scale rather than a solar system scale. + +The idea is that dark matter particles don't bump into each other, and therefore can't lose energy through collisions, so there's a limit to how far it can collapse. If you start with a uniform soup of dark matter, gravity will cause the dark matter to start to pull together into clumps. As the dark matter is accelerated into clumps, it speeds up. You reach a point where the dark matter's speed balances out the gravity of the dark matter clump, and the dark matter particles are basically all buzzing around in orbit within their common gravity. This balance happens at around the size of a galaxy, and is basically why galaxies are the size they are. + +From observations, it's only on a galaxy scale that we see gravity deviating from what you can explain using general relativity plus the assumption that only visible things like stars produce gravity. So that also confirms the biggest effect seems to be going on at these big scales. + +So yes, there is dark matter spread all throughout the galaxy. + +However, even though dark matter has more mass than the stars and gas and stuff within our galaxy, its *density* is low. Stars and planets form from gas, and gas particles *can* bump into each other and lose energy. This causes gas to settle down into a disc, which is the least amount of motion you can have without breaking angular momentum. The stars then form within this gas disc, to form a disc of stars - although afterwards stars can get stirred up to form a fatter disc, or even a spherical ""halo"". + +So what we have is a huge puffy ball of dark matter, and a thin dense disc of stars. When you're within the stellar disc - as we are - the mass nearby is totally dominated by stars and stuff. Dark matter has a lower density, it's just more spread out, which means that it adds up to more mass overall. + +So yes, while there is dark matter within the solar system - it's spread out everywhere - the mass of dark matter within the solar system is less than the mass of the Sun. + +Additionally, because dark matter is spread out smoothly over such a large scale, even if the density of dark matter was really high within the solar system, it wouldn't affect the Earth's orbit or anything very much. Instead, dark matter pulls the whole Solar System by the same amount - the Earth and the Sun are pulled the same amount - which means that, from within the Solar System, you don't notice any difference to your orbits." +1517 Since many of the COVID-19 cases are asymptomatic, could it be possible that the virus existed before what we are actually being told i.e. Wuhan, through bats? Could it be that the virus was around months or years before the first case started showing actual symptoms and testing began? 15 https://www.reddit.com/r/askscience/comments/g1k261/since_many_of_the_covid19_cases_are_asymptomatic/ 1586920967 g1k261 COVID-19 2020-04-15 6:22:47 "We know based on its genome that it is a brand new virus, emerged in bats, and was transferred through pangolins. At the earliest, it emerged in November 2019. Viruses accumulate mutations at a consistent rate, so the lack of alterations to its genetic code informs us of its age. + +[Read more.](https://www.nature.com/articles/s41591-020-0820-9?utm_source=facebook&utm_medium=social&utm_content=organic&utm_campaign=NGMT_USG_JC01_GL_NRJournals)" +1643 Do monkeys or other apes get chapped lips? 15 https://www.reddit.com/r/askscience/comments/gzfhh6/do_monkeys_or_other_apes_get_chapped_lips/ 1591675237 gzfhh6 Biology 2020-06-09 7:00:37 +1644 How does a cell build a copy of a virus? 15 https://www.reddit.com/r/askscience/comments/gzvcv1/how_does_a_cell_build_a_copy_of_a_virus/ 1591734373 gzvcv1 Biology 2020-06-09 23:26:13 "[Steve mould made an execellent video on Youtube that covers exactly this question.](https://youtu.be/3X6qEE2fHvE) The rest of my comment is a deeper dive into this idea of biology as thermodynamics and not abut viruses in specific. + + +The long and short of how its possible to create sophistication from stochastic processe is that the nanoscale world is very different from our macroscopic world. Those biological molecular animations on YouTube often show the internal parts of cells behaving as highly directed factories, where molecules are created and delivered to exactly where they need to be as though they are governed by some kind of magic, but this is pretty far removed from the truth. + + +Biological reactions are actually mainly just governed by simple thermodynamic princples such as diffusion across concentration gradients (which just happens probabilistically) and the tendency for things to head to equilibriums. Something is to note that once you have enormous numbers then things quickly stop being chance and start being statistics. Given a trillion trials even a one in a billion in will happen about a thousand times plus or minus thirty. A trillion isn't even nessesarily that big given that interactions (sort of) scale quadratically with the number of participants. + + +Another thing thats kind of hard to grasp is just how much thermal noise there is, at body temperatures of around 310K the average water molecule randomly zooms around at ~600 m/s. Considering that cells are microscopic in size this is incredibly fast. With everything undergoing huge amounts of brownian motion net work eventually gets done as long as it is spontaneous (represents a net increases entropy / decrease in gibs free energy). + + +Another caveat of this stochastic nature is that things often aren't done super efficiently or purely in one direction (monotonically). Something like a flagellar motor on a bacteria wouldn't spin perfectly one way, it would instead randomly vibrate back and forth extremely quickly but because some protons are net flowing out of the bactrium due to a concentration gradient it developes a net rotation in one direction. + + +[All of this is pretty well visualized by this video of a simulation of a motor kinesin.](https://youtu.be/JckOUrl3aes). Just to understand a bit of the scale of these things this entire video of part of a step happen in much less then a second. A motor protien actually walks on the order of a hundred or so steps per second." "The genetic material of the virus encodes for a specific sequence of amino acids. This amino acid sequence will fold into a specific conformation, sometimes with the help of other proteins. I think for some viruses these proteins can largely self assemble into the structural components needed. + +However, many viruses actually create their own organelles within host cells to assist with replication. This is a feature of the replication of coronaviruses, and many other +RNA viruses ([review here](https://www.cell.com/trends/microbiology/references/S0966-842X\(14\)00132-2)). This can benefit the virus in many ways. For one, it excludes other proteins that are in the cytoplasm that might interfere. It also creates a higher local concentration of the components the virus needs, allowing for faster assembly. It could also help the virus avoid immune detection by keeping it's components hidden within the organelle. + +Some viruses also have a membrane component. They can achieve this by stealing a piece of the host cell's membrane when the virus buds off, which can also help with assembly. For example, some proteins of HIV get expressed on the surface of the host cell. During budding, the membrane essentially wraps around the core of the virus, so all of the proteins that were on the surface of the cell are now on the surface of the virus. It's a little easier to visualize if you look at a picture, like the one [here](https://aidsinfo.nih.gov/understanding-hiv-aids/glossary/1596/life-cycle)." +1645 Will we see an eradication or serious reduction in other illnesses as a result of social distancing and hand washing and other measures during COVID? 15 https://www.reddit.com/r/askscience/comments/gl4d8q/will_we_see_an_eradication_or_serious_reduction/ 1589670454 gl4d8q COVID-19 2020-05-17 2:07:34 "For viruses that have reservoirs in other species (e.g. birds for influenza) they will certainly be around going forward. + +For those exclusive to humans, elimination would require interventions of sufficient duration and efficacy to result in no hosts passing the virus on to others. This is unlikely, but it is likely to reduce the burden in the short term. + +How quickly a virus comes back in a community will depend on how communicable it is in that specific context (viral factors like number of particles needed to cause infection, population factors like any immunity in the community, number and kinds of opportunities for transmission, what host immune systems look like in that group or subgroup, etc.)" Head lice maybe? I was thinking the other day that with all the schools closed and kids at home with their parents that hopefully individual head lice infestations will be treated and therefore when social distancing ceases there won’t be any headlice left to spread around? +1646 Why are orbits of planets stable over billions of years? How do they not go into the sun or slowly drift away? 15 https://www.reddit.com/r/askscience/comments/h0okjw/why_are_orbits_of_planets_stable_over_billions_of/ 1591836467 h0okjw Planetary Sci. 2020-06-11 3:47:47 [deleted] The moon is moving away from us veeery slowly. It is hypothesized that Pluto was hit and that is why its orbit is so wonky. Also why Uranus is on its side. These things do happen just not something you see everyday +1717 "If you're immune to a virus, does it still ""enter your system"" before your immune system fights it off, or it is blocked from entry/replication entirely?" 15 https://www.reddit.com/r/askscience/comments/jwn6bt/if_youre_immune_to_a_virus_does_it_still_enter/ 1605729741 jwn6bt Medicine 2020-11-18 23:02:21 "While /u/iayork gives a much more nuanced and accurate summary, let me just say this. + +Immunity is an observed characteristic, not a measurable one. And tests are always bounded by upper and lower bounds of a range, not a simple yes/no answer. That's the issue with the PCR tests you are talking about. Where do you set the boundaries? + +So simply, in answer to your first question: +> can you have a true positive in this case because the virus has managed to make it into your system again and PCR tests are overly sensitive and will pick up on even a miniscule trace of virus? + +Absolutely. It's even possible for an over amplified test to pick up on traces from the previous infection. + +Also, over amplification is not the only reason these tests can be wrong. There are many different tests, there are similar viruses, there is mis-handling of samples, there are lab mistakes. + +> could an immune or vaccinated person theoretically have a virus ... but not be symptomatic or infectious because their body already knows how to fight it? + +Abso-fuckin-lutely. + +It is important to remember that asymptomatic and infectious are not the same in any disease vector. But you did say ""or""." "To take the general case, what you’re asking is whether there’s *sterilizing immunity*. That is, is the immunity strong enough to prevent all infectious virus, or is it allowing some replication even if it prevents symptoms? + +It depends. Several pathogens do give sterilizing immunity, some do not. Many of the big names in pathogens like measles and yellow fever do end up with sterilizing immunity. Influenza probably does not: Infecting an immune person with influenza reduces the amount of shed virus enormously (by over 90%, probably) but doesn’t always eliminate it completely. In most cases, actual infection gives stronger immunity than vaccination (so, more likely to be sterilizing) but that’s not necessarily true - it’s quite possible for a vaccine to give stronger and longer-lasting immunity actual infection. + +For COVID-19, we have no idea, because the actual data for vaccines hasn’t been released. With some of the vaccines’ animal data, the vaccine blocked disease without blocking virus shedding, but this was when the animals were given very high doses of virus - far higher than natural amounts. + +In this particular case it’s likely the PCR test was a false positive. We can’t do more than speculate because we don’t know details (and if we did know details, it probably be removed from r/askscience as Medical Advice)." +1718 Where do the seeds for seedless fruit come from? 15 https://www.reddit.com/r/askscience/comments/jvhj5h/where_do_the_seeds_for_seedless_fruit_come_from/ 1605568289 jvhj5h Biology 2020-11-17 2:11:29 +1719 Are they any examples of 2-way predation in biology? 15 https://www.reddit.com/r/askscience/comments/k6wjs4/are_they_any_examples_of_2way_predation_in_biology/ 1607125636 k6wjs4 Biology 2020-12-05 2:47:16 "Ooh, sure! + +[Intraguild predation](https://en.wikipedia.org/wiki/Intraguild_predation#:~:text=Intraguild%20predation%2C%20or%20IGP%2C%20is,from%20preying%20upon%20one%20another.) describes how predators sometimes kill and feed upon each other, usually when competing for shared prey items. The dynamic is often asymmetric, especially among adult animals, with one 'dominant' predator positioned at a higher trophic level, and another 'intermediate' predator, which usually loses out most of the time - think of coyotes and wolves; most often, the wolf gets coyote for dinner, but occasionally the coyotes triumph. + +Intraguild interactions are more symmetric when we take into account age- and size-associated effects however - i.e. many predators will commonly predate juveniles of other predators. Tigers and bears commonly prey on one another's young, whilst on the hypercompetitive African plains, it's no holds barred amongst lions, hyena, wild dogs, leopard and cheetah - all will opportunistally kill and consume juvenile members of the other species. For one, it's a decent meal, but more importantly it reduces competition for shared prey resources. + +In the aquatic realm, it's even more an 'anything goes' type situation. Most aquatic predators primarily select prey based on size (essentially anything that can fit inside their mouths), regardless of trophic level and even species. All planktivorous fish, for example, will regularly feed on any and all juvenile members of other, and even their own, species that they find in the water column. + +So yes, intraguild predation is common, but usually only between adults and juveniles (unless the odds are otherwise disproportionately stacked; e.g. a pack of hyena against a lone lion) - and for good reason: it's far too risky predating on other mature adult predators, and there are no examples, as far as I'm aware, where two mature predator species *regularly* prey on one another. Predators, through evolutionary time, essentially try to max out their offensive stats, whereas prey their defensive. When two fully primed predators are facing off, the chance of life-threatening injury, even if victorious, is therefore so high that evolution selects for behaviours that avoid such interactions. Better to prey on something a little less red in tooth and claw - you might have to deal with their defences, sure, and you'll be unsuccessful much of the time, but at least you won't be, like, eaten back. + +In short: predators rarely pick on something their own size, but regularly snack on one another if the balance is shifted in their favour, as when an adult comes across a juvenile. Between some species, it's usually to reduce competiton, with feeding a secondary objective; in others, it's the opposite. + +___ + +^**Reference:** + + +[^(Polis, G.A., Myers, C.A. & Holt, R.D. (1989)^) ^(The Ecology and Evolution of Intraguild Predation: Potential Competitors that Eat Each Other. *Annual Review of Ecological Systems*. 20, 297-330)](https://web.archive.org/web/20140308021334/http://people.biology.ufl.edu/rdholt/holtpublications/019.pdf) ^(- a pretty good review!)" "As has been mentioned, there's lots of examples where this occurs where big individuals would eat small individuals of the other species. Take fish- loads of fish just gobble the tiny fry (babies) of whatever species of they fit into the size category of a prey item. + +BUT, maybe OP is imagining two kinda equally matched species in a perpetual war where they try and kill and eat each other. You'd be very unlikely to see this kind of thing for a couple of related reasons. + +Evolution favours strategies with a high success rate over those with a low success rate. If two equally matched species are constantly trying to eat each other, the outcome of an interaction is 50/50 that you eat or die. You need to eat lots of times but you can only die once! So this strategy would suck, and animals who picked weaker prey would do better and outcompete those who target their equally matched species. + +Also, this situation where two species are equally matched would be very unstable, so if it ever has evolved, it'd be unlikely to last for long enough for it to exist now, as you're observing. Because individuals vary, so in populations that are on average equally matched, say a mongoose-eating snake and a snake-eating mongoose, there are individuals who would have an advantage or a tactic that wins consistently, like mongooses with resistance to the venom or snakes who hunt by day when the mongoose is asleep. As soon as that advantage appears it'll spread rapidly by evolution and tip the power balance away from equality." +1871 If there is one queen bee or queen ant in a colony that is responsible for laying all of the larvae, is the whole colony genetically identical? 15 https://www.reddit.com/r/askscience/comments/lbf3mt/if_there_is_one_queen_bee_or_queen_ant_in_a/ 1612325111 lbf3mt Biology 2021-02-03 7:05:11 "I can discuss honey bees *Apis mellifera* details on other species, particularly those more distantly related like ants may be different. + +Queens leave the hive soon after they emerge as adults from the pupal stage. They take a mating flight usually a mile or so from the hive to mate in what are called Drone Congregation Areas (DCA). These are areas where drones (male bees) wait for available queens. The drone tend to fly less of a distance than the queens do to these areas so ensure a queen will not mate with her brothers. + +Once at the DCA the queen will be chased by the available drones and mate in flight. Each drone as he mates eviscerates himself and falls away dead. The queen will typically mate with a dozen or more drones and numbers as high as the mid 30s have been recorded. The queen will store the sperm from this flight in her spermatheca for the rest of her life and will never mate again. Typically she makes only one flight but she might make a few if conditions like weather are bad. + +Because she mates with a dozen or more drones each egg she lays has the potential to have any one of those dozen drones as a father providing genetic diversity to the queens offspring. So no her fertilized offspring (all the females) are not all identical. Her male offspring which are fertilized only get their genetics from her they do not include genetics from the drones she mated with. + +Yes being genetically identical can prove to be an issue. The Americas were struck by a pest (varroa mite) in the 90s and feral bee populations collapsed. Studies done with pre-varroa populations and post-varroa populations show a dramatic decrease in genetic diversity as only some of the lines were able to cope with the new threat. Had the populations been identical losing all feral honey bees would have been a possibility. + +This propensity to mate with a lot of drones (and only doing it in flight) to preserve genetic diversity makes breeding honey bees difficult as it is very hard to control that aspect of the genetics. Queen breeders who want specific traits saturate the areas where they are breeding with drones who have the desired genetics to ensure their queens get those genetics for their offspring." "To add a bit to u/svarogteuse's comment, the haplodiploid system of bees and ants does have some unusual consequences for genetic relatedness. Although female workers are the result of fertilization, and so are just as closely related to the queen as any parent and offspring of a sexually reproducing species, males are not. The eggs produced by a queen are products of meiosis, and so are not identical since they can have different combinations of her chromosomes. + +However, since males are born from unfertilized eggs they are already haploid, every sperm they make contains 100% of their DNA. This means that two workers who share the same parents came from identical sperm cells, and so share a relatedness of 75% (compared to 50% sibling relationships for diploid species). Furthermore, this system results in asymmetrical relatedness depending on the focal individual, which gets [pretty complicated](https://nectunt.bifi.es/wp-content/uploads/2014/04/kinkin-e1397086985158.jpg). + +So a bee or ant colony is definitely not genetically identical, but workers are often more closely related to each other than is possible in diploid species (with the exceptions of identical twins and parthenogenesis). Another issue with low genetic diversity in addition to disease and parasite susceptibility is that the sex determination system in hymenopterans is based on the zygosity of a [specific locus](https://www.wikigenes.org/e/gene/e/406074.html), so inbreeding can lead to the production of infertile diploid males." +1872 What exactly caused the Pandemrix vaccine to have links to higher rates of narcolepsy? 15 https://www.reddit.com/r/askscience/comments/lcj0h7/what_exactly_caused_the_pandemrix_vaccine_to_have/ 1612454961 lcj0h7 Medicine 2021-02-04 19:09:21 "You can see in that wiki article that further studies didn't find an association: + + + +>In 2018, a study team including CDC scientists analyzed and published vaccine safety data on adjuvanted pH1N1 vaccines (arenaprix-AS03, Focetria-MF59, and Pandemrix-AS03) from 10 global study sites. Researchers did not detect any associations between the vaccines and narcolepsy. +> +>* Incidence rate study data did not show a rise in the rate of narcolepsy following vaccination except in the one signaling country included (Sweden, which used Pandemrix). +> +>* Case-control analyses for Arepanrix-AS03 did not show evidence of an increased risk of narcolepsy. +> +>* Case-coverage analysis for Pandemrix-ASO3 in children in the Netherlands did not show evidence of an increased risk of narcolepsy, but the number of exposed cases was small (N=7). +> +>* Cases-control analysis for Focetria-MF59 did not show evidence of an increased risk of narcolepsy. + +[https://www.cdc.gov/vaccinesafety/concerns/history/narcolepsy-flu.html](https://www.cdc.gov/vaccinesafety/concerns/history/narcolepsy-flu.html) + +GSK also denies an association and posits that because the risk of narcolepsy is a sequelae of influenza. That is a more likely mechanism especially considering the heterogeneous rates of adverse events around the world. + +https://www.reuters.com/article/us-health-coronavirus-gsk-vaccine-exclus/exclusive-gsk-says-science-does-not-link-pandemic-h1n1-flu-vaccine-to-sleep-disorder-idUSKBN2341HM + +There have been studies into the development of immune responses is a likely causal mechanism for narcolepsy: + +>The known link between narcolepsy and the HLA DQB1*0602 haplotype suggests that narcolepsy can have an immune component—even in the absence of vaccination. Thus, one can envision that some component of the Pandemrix vaccine may stimulate T or B cells that cross-react with HCRT, its receptors or with cells that express these proteins. In fact, one study suggested that narcoleptic patients have T cells that react with both HCRT and with hemagglutinin expressed by the pandemic H1N1 virus (15). This paper was ultimately retracted due to an inability to reproduce the findings. However, subsequent studies suggested a link between vaccination and the formation of antibodies against the HCRT receptor, HCRT-R2 (16). + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5104623/" +1873 Why do viruses have different ways on affecting the human body instead of having the same impact altogether? 15 https://www.reddit.com/r/askscience/comments/lr8paa/why_do_viruses_have_different_ways_on_affecting/ 1614159147 lr8paa Medicine 2021-02-24 12:32:27 "Think of it like a lock and key, the virus has the key and only matches the lock on certain cell types. +On a further note, the different symptoms of different viruses come from the systems they infect. Hepatitis affects the liver, so the symptoms are similar to liver failure. A virus infecting the intestinal tract will cause diarrhea and maybe bloody stills. Lungs cause pneumonia, and upper respiratory infections cause runny nose and stuffy sinuses. HIV affects immune cells, so you get sick easier" "There are many, many ways for parasites like viruses to exploit the host's body (the survival machine built according to genetic instructions of the host) for their own replication. There are different entrances and exit points in the survival machine for the virus to use. + +Take the respiratory system, for example. Viruses which have the adaptation to exploit the host's need to breathe and enter their airways in 'hopes' of finding resources and cells to replicate themselves. Those viruses have the specific adaptations necessary to survive their journey through the air when travelling from host to host, and to bind to molecules found on cells in the respiratory system in order to enter those cells. + +Look at the measles virus, which has obtained an impressive R0 of around 16, i.e., a person infected by the virus infects up to around 16 others. One of the things that make this virus spread so efficiently is that it is aerosolized in tiny droplets expelled by the host's breathing. + +Respiratory viruses may even exploit our respiratory system clearing mechanisms - coughing and breathing. These serve to clear the nasal cavity and the lower airways, respectively. But they come with the extremely convenient side effect of catapulting huge numbers of virions into the air where they can infect others." +1874 Does ice sublimate in freezers? 15 https://www.reddit.com/r/askscience/comments/lqo6eh/does_ice_sublimate_in_freezers/ 1614102048 lqo6eh Chemistry 2021-02-23 20:40:48 "It doesn't sublimate, but it does have a vapour pressure. All condensed phases have a vapour pressure (although sometimes extremely low e.g. most metals) because they must be in equilibrium with the vapour phase. + +More detail: by definition to be in equilibrium two phases must have equal chemical potential. If there is a volume of space that is empty of a given substance, then the substance's chemical potential there is zero. So the condensed phase (which has a non-zero chemical potential) will always evaporate (sublime) some substance into that volume until the two chemical potentials are equal." +1875 Is it possible for an eruption like the one that created the Siberian Traps happen today? Is earth more geologically stable now than it was? 15 https://www.reddit.com/r/askscience/comments/lxnc82/is_it_possible_for_an_eruption_like_the_one_that/ 1614872466 lxnc82 Earth Sciences 2021-03-04 18:41:06 There is nothing explicitly precluding the formation of a [large igneous province](https://en.wikipedia.org/wiki/Large_igneous_province) like the Siberian Traps today, and there indeed have been many erupted much more recently than the Siberian Traps (e.g. the [Columbia River Basalt](https://en.wikipedia.org/wiki/Columbia_River_Basalt_Group), [the Ethiopia-Yemen Basalts](https://en.wikipedia.org/wiki/Ethiopia-Yemen_Continental_Flood_Basalts), [North Atlantic Igneous Province](https://en.wikipedia.org/wiki/North_Atlantic_Igneous_Province), or the [Deccan Traps](https://en.wikipedia.org/wiki/Deccan_Traps), among others). +1876 COVID and Head Lice reduction? 15 https://www.reddit.com/r/askscience/comments/labmg4/covid_and_head_lice_reduction/ 1612207477 labmg4 Human Body 2021-02-01 22:24:37 "Apparently so. At least in Argentina. + +> This obligatory isolation interrupted regular classes avoiding direct contact between children, thus affecting the dispersal route of individuals and the evolution of head louse populations. … Data of 1118 children obtained from 627 surveys were analyzed. As the main result, it was observed that prevalence of lice decreased significantly from before (69.6%) to during (43.9%) COVID-19 lockdown. + +—[Head lice were also affected by COVID-19: a decrease on Pediculosis infestation during lockdown in Buenos Aires](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7787699/)" +1877 How is genetic distance measured? 15 https://www.reddit.com/r/askscience/comments/labidw/how_is_genetic_distance_measured/ 1612207203 labidw Biology 2021-02-01 22:20:03 "Genetic distance is a slightly different (and more complicated) concept from what you're describing. Specifically, it's a measure of the similarity of allele frequencies between populations, and is most commonly calculated based on the formulation by [Nei 1972](https://www.journals.uchicago.edu/doi/abs/10.1086/282771). What it sounds like you're actually asking about is a broader concept of genetic similarity, which is much more loosely defined. In fact, there are several completely different metrics which may be used, and which are not actually comparable. + +In the case of chimpanzees, most comparison numbers are probably calculated in a similar way to what you describe (i.e., literally [comparing sections of the human and chimp genome](https://wp.biologos.org/wp-content/uploads/2018/09/homopangorilla.png), and looking at the percentage of base pairs that are the same). However, similarity differs depending on the scale you're looking at; while about 98.8% of aligned base pairs are identical between humans and chimps, closer to 3% of our genomes differ as a result of insertions or deletions which can't be aligned ([Suntsova and Buzdin 2020](https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-020-06962-8)). And at an even bigger scale, we have different karyotypes from chimps due to the creation of human chromosome 2 from the [fusion of two other chromosomes](http://i.imgur.com/otB1X.jpg). [This video](https://www.youtube.com/watch?v=IbY122CSC5w) does a good job of explaining some of the subtleties here. + +However, another metric you sometimes see is the fraction of our genes can be found in the genome of another species. This metric ignores any non-coding regions of the genome (which make up over 95% of it!) and just uses a presence-absence check of how many of the \~20,000 human genes have orthologs in whatever you're comparing with. This type of comparison is the source behind the common factoid that humans and bananas share 50% of our DNA (which is [not really accurate](https://lab.dessimoz.org/blog/2020/12/08/human-banana-orthologs) even by this method), but does not take sequence similarity at the level of base pairs into account at all, and cannot be compared with it. I'm not actually sure what percent of our genes have orthologs in chimpanzees, but it is pretty certainly over 99%." +1878 Does Photon Redshift (and blueshift) violate conservation of Energy? 15 https://www.reddit.com/r/askscience/comments/lbxbx7/does_photon_redshift_and_blueshift_violate/ 1612384058 lbxbx7 Physics 2021-02-03 23:27:38 "> what exactly would the photon be losing energy to? + +The gravitational field. + +Gravitational potential energy (and, to a lesser extent, kinetic energy as well) is a tricky business in arbitrary spacetimes (no distance parallelism, no covariant expression for gravitational energy density, potential lack of time-like Killing vector fields, Noether's first vs. second theorem, ...). + +While the answer above can be argued to be correct 'morally', due to the subleties involved, one can also reject that perspective and instead abandon energy conservation in the general case of evolving spacetimes." "This is a violation of the traditional way conservation of energy is explained, which is not really a problem with the conservation law, but a problem with the more simplified version we learn (which works for pretty much any reasonable situation we're in). + +The easiest way I know to discuss this is by looking at [Noether's Theorem](https://en.wikipedia.org/wiki/Noether's_theorem). This theorem states that for every symmetry there is an associated conservation law. What does that mean? Take for instance transnational symmetry. That means if I do an experiment *here* and you do an experiment *there*, all else being equal (e.g. in the same gravity and EM field) our experiment will yield the same result. From the fact that translation symmetry exists (translation just meaning I can move my experiment from one place to another) you can prove conservation of momentum (the proof is well beyond the scope of this write-up). + +Now, energy on the other hand, is paired up with time symmetry. That means, if I do an experiment *today* and you do the same experiment *tomorrow*, all else being equal we should get the same result. And for all practical applications, this is true. But, once you start dealing with applications which span local galaxy superclusters (aka- the scale where the expansion of the universe is happening. Our solar system isn't ""expanding"", it is gravitationally bound. But galaxies not in our super cluster are expanding away from us) suddenly time symmetry is no longer true. This is because the place in which you are doing the experiment has changed. + +But this isn't really a fault of conservation of energy, because the conservation law only applies in situations where time symmetry applies. It's just normally we don't mention the full law (sort of like how when teaching momentum, we don't first teach the entire relativistic definition)." +1879 How do we know how well dogs can smell? 15 https://www.reddit.com/r/askscience/comments/ls81dd/how_do_we_know_how_well_dogs_can_smell/ 1614264198 ls81dd Biology 2021-02-25 17:43:18 "I guess by doing experiments. + +Researchers can condition the dogs to get a price when they detect certain smells, and then see how little of the smell they can use and still get the dog to detect the smell. + +They then compare how much dogs need to detect the smell to how much humans need." "Well, of course we can't know for sure because experience is subjective. But we can look at our own noses, how many sensory cells there are, and then look at how much of the brain is devoted to interpreting those sense signals. When we compare those numbers to a dog's, a dog has thousands of times more of both than a human. Perhaps there are diminishing returns, so it could be that they smell 100x better or 1000x better - but it's a lot more. + +We can see proof of this in real life too. Dogs can be trained to recognize certain scents and signal when they find them. We can measure this compared to a human's ability. Something like ""If I have 10 oranges in the back seat of my car, the average human in my front seat will smell them"". But a dog might be able to detect like a .1 oz piece of a orange peel from 50 feet away." +1919 Does orbiting within a black holes ISCO require constant thrust or just additional energy? 15 https://www.reddit.com/r/askscience/comments/o0bpxo/does_orbiting_within_a_black_holes_isco_require/ 1623755068 o0bpxo Physics 2021-06-15 14:04:28 "ISCO is the innermost *stable* circular orbit. You have unstable orbits lower than that where you can orbit just with course corrections. Down to the photon sphere if you increase your speed sufficiently. + +Beyond the photon sphere tangential velocity is harmful - you need constant thrust to keep your distance, and the faster you go in tangential direction the *more* thrust you need." "The ISCO is by definition stable; that is, it does not require thrust to keep its form. + +You can orbit a black hole below the ISCO by supplying constant thrust. This does not contradict the ISCO." +1518 Could an atomic nucleus be donut shaped? 14 https://www.reddit.com/r/askscience/comments/g29gly/could_an_atomic_nucleus_be_donut_shaped/ 1587017788 g29gly Physics 2020-04-16 9:16:28 "Yes, it’s possible for a nucleus to take the shape of a [torus](https://arxiv.org/abs/1807.11646). These are usually excited states with very high angular momenta. + +High atomic numbers and high angular momenta are favorable, because they increase the repulsive contributions to the potential (the Coulomb part and the centrifugal part, respectively)." +1720 Why do some Vaccine's require multiple doses or Boosters while some are one and done? 14 https://www.reddit.com/r/askscience/comments/kfwqmp/why_do_some_vaccines_require_multiple_doses_or/ 1608335309 kfwqmp Medicine 2020-12-19 2:48:29 "It's kinda similar to some petrol engines having a choke to start from cold. Once the engine gets up and running and warmed up, if you shut it down, you don't need the choke to get it started again. + +They're 2 doses of the same thing. The first time your immune system comes in contact with the vaccine it takes a long time to ramp up the response, because the first cells (antigen presenting cells, dendritic cells, monocytes/macrophages) that come into contact with it aren't the ones required to mount the antibody response, so they have to go recruit the proper cells (B & T cells). Those cells then proliferate and differentiate into different types of T & B cells, which are required to mount an effective response towards the antigen, one of which is the plasma B cell which produces the antibodies towards that specific antigen. + +However, these cells all are short lived, and die after a period of time. That's why during the process, so called ""memory"" cells are created, both memory B and memory T cells, that remember antigens which the immune system have come into contact before. In doing so, it vastly reduces the response time needed to ramp up production of the necessary cells & antibodies required for an effective immune response. Because of this it's also able to mount a much stronger immune response. + +This is also why people with allergies to nuts can have a very mild reaction the first time they're exposed, yet end up nearly dying upon repeat exposure. + +As for why some vaccines need multiple doses or boosters - its down to the disease and vaccine being used - some don't produce lasting effects from a single dose. Sometimes a 2nd dose is required to achieve a strong immune response. The immunity can also wear down over time, hence why boosters are given. + +The CDC has a good document that's only a few pages with a bit more detail on how vaccines work. + +[https://www.cdc.gov/vaccines/hcp/conversations/downloads/vacsafe-understand-color-office.pdf](https://www.cdc.gov/vaccines/hcp/conversations/downloads/vacsafe-understand-color-office.pdf)" +1721 At what point does a baby's heart start beating, and how? 14 https://www.reddit.com/r/askscience/comments/irhnok/at_what_point_does_a_babys_heart_start_beating/ 1599934547 irhnok Human Body 2020-09-12 21:15:47 I have answered a similar question like this a couple weeks ago [here](https://www.reddit.com/r/askscience/comments/ic2lqm/what_causes_the_heart_of_a_human_fetus_to_start/). If there's any specifics on top of that, I can try to explain or clarify. +1722 Would the antibodies from the pfizer covid-19 vaccine produce a positive on a covid-19 antibody test? 14 https://www.reddit.com/r/askscience/comments/juuqkb/would_the_antibodies_from_the_pfizer_covid19/ 1605478497 juuqkb COVID-19 2020-11-16 1:14:57 "Generally, we would think yes, and this is what happens for most vaccines. Antibody tests aren’t looking for the virus or vaccine, but instead for your body’s response to it (IgM or IgG antibodies, which your body produces to fight infection). Phase I/II of the Pfizer trial tested for IgG concentration; you can read a write-up of results, including about the antibodies, [here](https://www.nature.com/articles/s41586-020-2814-7) or [here](https://www.pfizer.com/news/press-release/press-release-detail/pfizer-and-biontech-share-positive-early-data-lead-mrna). + +However, not all vaccines elicit equivalent levels of antibodies, and lower levels of IgG may result in a negative antibody test. The official CDC statement is cautious (that vaccination may result in positive antibody tests) because this is a new vaccine (new virus and new type) and much of the data from the trial has not yet been released." "The vaccine only includes the spike protein (and only a segment of it). Viral infection will drive antibodies against many other proteins, such as NP, and there are antibody assays that test for NP as well as spike protein ([Review of Current Advances in Serologic Testing for COVID-19](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7337672/)). Those antibody assays could tell the difference between a vaccinated and an infected person. Presumably once vaccination is widespread such assays will be normal. + +> So once the vaccine is administered, if you are one of the 10% (hopefully only 10%) for which it’s ineffective, a positive antibody test would likely be skipped or ignored until symptoms begin, and you could be spreading during that time. + +Not an issue. That’s not how testing is done. You don’t get antibodies before symptoms, and you can’t use presence or absence of antibodies to tell if you’re currently infected." +1880 Is space-time curved or flat in the centre of the Earth? 14 https://www.reddit.com/r/askscience/comments/ly9c2f/is_spacetime_curved_or_flat_in_the_centre_of_the/ 1614941413 ly9c2f Physics 2021-03-05 13:50:13 "Because there is no net gravitational field at the center (approximating the Earth as spherically symmetric anyway), I would intuitively expect spacetime to be locally flat there. In the case of a spherical shell, this is true and is discussed in [this stackexchange post](https://physics.stackexchange.com/questions/43626/is-spacetime-flat-inside-a-spherical-shell) where they show how the metric tensor (which describes the curvature of spacetime) reduces to that of Minkowski space (i.e. flat spacetime). + +However, for a solid, spherical body, the metric is described by the [interior Schwarzschild metric](https://en.wikipedia.org/wiki/Interior_Schwarzschild_metric). This does not seem to completely reduce to Minkowski space at r=0 (the center of the Earth/spherical body). But for bodies (such as the Earth) with radii significantly larger than their Schwarzschild radius (the radius at which they would collapse into a black hole), spacetime can be approximated as flat to very high precision. + +If there are any GR experts who can chime in, I'd be curious to hear why spacetime would not be flat at the center of something like a neutron star (where the radius is comparable to its Schwarzschild radius). + +Edit: Regardless of the curvature there, the four-acceleration must necessarily be zero to avoid breaking spherical symmetry. In other words, any observer there would be weightless." +1881 What is the advantage of using an adenovirus from chimpanzee compared to adenoviruses from human to develop a vaccine? 14 https://www.reddit.com/r/askscience/comments/lxtedj/what_is_the_advantage_of_using_an_adenovirus_from/ 1614887223 lxtedj Biology 2021-03-04 22:47:03 "One issue with adenovirus based vaccines is that many humans have pre-existing immunity to adenoviruses due to a previous infection. Adenoviruses are common human pathogens, they are one of the causes of the common cold for example. There are also many strains or serotypes of adenoviruses that circulate in humans. + +This makes it tricky when designing adenovirus based vaccines, since if someone has preexisting antibodies against the strain used for the vaccine, their antibodies may neutralize and inhibit the vaccine before it gets in our cells to express the vaccine antigen. Also, immune memory from previous adenovirus infections could result in a stronger reaction against the adenovirus backbone than the vaccine antigen. + +One way to deal with this is to pick a more rare serotype of human adenovirus to make your vaccine, as there should be a lower prevalence of pre-existing immunity to those strains. A different way to deal with it would be to select a chimpanzee strain of adenovirus that doesn't circulate in humans, so we don't have pre-existing immunity to it, but since chimpanzees are so close genetically to humans, the chimp strain should be able to infect our cells (I'm assuming this I haven't actually seen that data). + +Here are some links if you are still interested! + +[Development of novel vaccine vectors: Chimpanzee adenoviral vectors](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6067905/pdf/khvi-14-07-1419108.pdf) + +[Adenoviruses as vaccine vectors](https://www.cell.com/molecular-therapy-family/molecular-therapy/fulltext/S1525-0016\(04\)01342-5) + +Adenovirus based vaccines have been studied for decades, in the early 2000s they were used in a couple of HIV vaccine trials which sadly did not work. However, their effectiveness against COVID19 is very exciting and marks a major strep forward in vaccine design (as do mRNA vaccines)." +1882 Where in the US does the most weathering occur? 14 https://www.reddit.com/r/askscience/comments/lc5n48/where_in_the_us_does_the_most_weathering_occur/ 1612407040 lc5n48 Earth Sciences 2021-02-04 5:50:40 "There are a few different factors that influence weathering rates, the common ones considered are: hydrology (how wet is the area), lithology (what rocks are present and what are their chemistries), physical erosion rates (how fast weathered material is physically transported away from the location of weathering), temperature, and the type/amount of soil present (e.g., [Hartsmann & Moosdorf, 2011](https://www.sciencedirect.com/science/article/pii/S0009254110004389)). That last one can actually be quite important, because as the thickness of soils increase, the weathering rate (which is intimately linked with the rate of soil production) decreases because the soil is ""shielding"" intact rock from the chemical processes that cause weathering (e.g., [Heimsath et al, 1997](https://www.nature.com/articles/41056)). In general, together these factors are controlling the rates of chemical reactions and the elements present in order for those reactions to occur. + +Returning to the question at hand, one can take case studies of how variations in these different parameters result in variations in chemical weathering rates and build a predictive function to extrapolate what the chemical weathering rates would be in places without direct measurements of weathering rates. [Hartman et al, 2014](https://www.sciencedirect.com/science/article/pii/S0009254113004816?via%3Dihub#bb0280) does exactly that to get at global rates of weathering. The key finding is summarized in their figure 1 (a link [here](https://www.researchgate.net/profile/A_Joshua_West/publication/259243854/figure/fig1/AS:297184269488128@1447865659315/Calculated-chemical-weathering-rates-applying-the-island-arc-runoff-lithology-functions.png) that should be beyond a paywall). The top panel is estimated rates of chemical weathering factoring in lithology, runoff, erosion, and temperature. The bottom panel is the same after estimations of the soil thickness are added, so generally one would expect this bottom panel to be closer to reality, but as we add more parameters (which have their own uncertainties), models also get more complicated. + +Caveats aside and using that map in the lower panel, within the US, the highest rates of chemical weathering are actually along the SE Alaska coast (where temperature is low, but rates of erosion are very high, it is very wet, and there are exposures of lots of rocks that are pretty susceptible to chemical weathering) and areas basically in the Ohio Valley (where temperatures are moderate, but it's reasonably wet and there are broad exposures of rock, carbonates, that are susceptible to weathering). As for Florida, comparing the top and bottom panels is instructive. Florida has many of the key ingredients for high weathering rates (wet, warm, and carbonates), but thick soils mean that weathering rates here, while still high, are not expected to the max in the US. Looking globally, one can see that hotspots for weathering vary and there is no specific single predictor (e.g., mountains are hotspots in some places, but not in others, same with tropical climates, etc), but rather the combination of the factors from the beginning that are important." +1883 Does the existence of mental disease common across humans imply that our thought processes are also common? 14 https://www.reddit.com/r/askscience/comments/lbps6j/does_the_existence_of_mental_disease_common/ 1612365509 lbps6j Psychology 2021-02-03 18:18:29 "In the end of the day, what you think of as ""thought"" processes is also nothing but biology. Neurons become active and depending on their activity, they form new connections or break old ones. The expression of receptor proteins rises or falls depending on the need and usage, thus changing the susceptibility of the neurons towards neurotransmitters. + +All of these things are nothing which could be easily influenced by just taking some medication. You have to basically ""rewire"" the brain, which is a slow process, but can be done by actively and conciously altering your physical and mental behaviour. This is basically what psychotherapy does. + +It's something like the brain equivalent of *physio*therapy. Surgery can mend your bones and muscles, but to be able to use them properly again, you will have to train and excercise." "> I understand that we all have the same brain chemistry, so some mental illnesses can be due to altered composition of these chemicals in the brain. + +You're spot on. Because we all diverged from the same population to become the diverse species we are today, brain structures are highly conserved even in great apes - [paper 1](https://www.sciencedirect.com/science/article/pii/S0960982217300209), [figure 1](https://www.google.com/imgres?imgurl=https%3A%2F%2Fwww.researchgate.net%2Fpublication%2F314372936%2Ffigure%2Ffig4%2FAS%3A469978349608963%401489062978115%2FPhylogeny-of-the-neocortical-sheet-Schema-showing-the-layout-of-cortical-areas-in.png&imgrefurl=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FPhylogeny-of-the-neocortical-sheet-Schema-showing-the-layout-of-cortical-areas-in_fig4_314372936&tbnid=mED4wv5pRE7bpM&vet=12ahUKEwidvIzYmdDuAhXFKlMKHXEXDqIQMygDegQIARBC..i&docid=eIIfsCmeuiT1iM&w=689&h=860&q=cortical%20structures%20conserved%20great%20apes&client=firefox-b-1-d&ved=2ahUKEwidvIzYmdDuAhXFKlMKHXEXDqIQMygDegQIARBC), [figure 2](https://www.google.com/imgres?imgurl=https%3A%2F%2Fjournals.plos.org%2Fplosbiology%2Farticle%2Ffigure%2Fimage%3Fdownload%26size%3Dlarge%26id%3Dinfo%3Adoi%2F10.1371%2Fjournal.pbio.3000810.g008&imgrefurl=https%3A%2F%2Fjournals.plos.org%2Fplosbiology%2Farticle%3Fid%3D10.1371%2Fjournal.pbio.3000810&tbnid=wkiIIyd1Vek59M&vet=12ahUKEwidvIzYmdDuAhXFKlMKHXEXDqIQMygKegQIARBQ..i&docid=Af0nIx-BZPlcpM&w=2233&h=1645&q=cortical%20structures%20conserved%20great%20apes&client=firefox-b-1-d&ved=2ahUKEwidvIzYmdDuAhXFKlMKHXEXDqIQMygKegQIARBQ). This is part of why animal models are used, particularly for novel pharmacotherapies. + +>But then tablets/medication alone must be sufficient to treat all mental illnesses. + +Not quite. In theory they are (and one day will be), but we're not quite there yet as a field. We are not sure why some medications work, and still unsure how something like depression arises from the changes we know happen in the brain ([example](https://www.nhs.uk/conditions/ssri-antidepressants/)). We have some good guesses, but they're all theories in progress at this point. The other problem is we're likely not ""carving nature at it's joints."" Depression, for example, is quite heterogeneous, and there is some decent evidence that there are a few processes that can give rise to a similar cluster of symptoms we recognize as a Major Depressive Episode. + +>But that that is not true, as psychotherapy plays a major role in treating the them. So there is a component of these illnesses which is not due to biochemistry, but is 'mental'. + +Indeed! Metacognition is a huge thing in psychotherapy. A lot of therapies rely on teaching people to think about their thinking, and for a variety of reasons, people differ in this ability. Think about something we all do like eating. The concept is universal, the motions are similar, but different people/families/cultures/societies eat in different ways. + +>So, then does it mean that there is some common 'structure' in our mental thought processes (across humans), similar to there being structure in our biological processes? + +Yes! There are pathways in our brain that are involved in disorder processes. [Like alterations in the mesolimbic dopamine pathway can lead to anhedonia](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3181880/). Moreover, different behaviors can often yield similar (enough) results, with some individual differences. For example, if you put someone alone in a cell for 23 hours a day, [you'll get similar results](https://heinonline.org/HOL/LandingPage?handle=hein.journals/wajlp22&div=26&id=&page=). + +EDIT for typos +EDIT2 for broken link" +1884 "What does ""Entropy"" mean?" 14 https://www.reddit.com/r/askscience/comments/l6g1nb/what_does_entropy_mean/ 1611786022 l6g1nb Physics 2021-01-28 1:20:22 "Entropy is a measure of ""how many microstates lead to the same macrostate"" (there is also a natural log in there, but not important for this conversation). This probably doesn't clear up much, but lets do an example, with a piece of iron. + +If you just hold a piece of iron that you mined from the Earth, it will have no, or at least very little, magnetic field. If you take a magnet, and rub it on the piece of iron many times, the iron itself will become magnetic. What is happening? Well, iron is made up of many tiny magnetic dipoles. When iron is just sitting there, most of the time, the little dipoles all face in random, arbitrary directions. You add up all of these tiny little magnetic dipoles and if they are just random, they will, on average, sum to zero. So, no overall magnetic field. + +But when you rub a magnet over the piece of iron, now the little dipoles all become aligned, facing the same direction. Now, when you add all of the individual dipoles together, you don't get zero, you get some number, pointing in the direction the dipoles have aligned. + +So, tying this back into entropy- the non-magnetized iron has high entropy. Why? Well, each of those individual dipoles are one ""microstate"", and there are many, many options of how to arrange the individual dipoles to get to the ""macrostate"" of ""no magnetic field."" For example, think of 4 atoms arranged in a square. To get the macrostate of ""no magnetic field"" you could have the one in the upper right pointing ""up"" the one in upper left pointing ""right"" the bottom right pointing down an the bottom left pointing left. That would sum to zero. But also, you could switch upper left and upper right's directions, and still get zero, switch upper left and lower left, etc. In fact, doing the simplified model where the dipoles can only face 4 directions, there are still 12 options for 4 little dipoles to add to zero. + +But, what if instead the magnetic field was 2 to the right (2 what? 2 ""mini dipole's worth"" for this). What do we know? We know there are three pointing right, and one pointing left, so they sum to 2. Now how many options are there? Only 4. And if the magnetic field was 4 to the right, now there is only one arrangement that works- all pointing to the right. + +So, the ""non magnetized"" is the highest entropy (12 possible microstates that lead to the 0 macrostate), the ""a little magnetized"" has the ""medium"" entropy (4 microstates) and the ""very magnetized"" has the lowest (1 microstate). + +The second law of thermodynamics says ""things will tend towards higher entropy unless you put energy into the system."" That's true with this piece of Iron. The longer it sits there, the less magnetized it will become. Why? Well, small collisions or random magnetic fluctuations will make the mini dipoles turn a random direction. As they turn randomly, it is less likely that they will all ""line up"" so the entropy goes up, and the magnetism goes down. And it takes energy (rubbing the magnet over the iron) to decrease the entropy- aligning the dipoles." "A lot of these answers dance around it but some sort of miss the mark. I’ve found that one of the best simple explanations is that entropy is a measure of the unavailability of energy in a system. Saying things like “disorder” used to be popular but are kind of misleading and many educators are moving away from that term. + +I actually wrote a paper for the American Society of Engineering Education about more effective ways to teach the concept of entropy. There’s a lot of examples that can help you wrap your mind around it + +[I removed this link for privacy, pm me if you want the paper]" +1885 What is the current scientific consensus on willpower? Do we really run out of it? 14 https://www.reddit.com/r/askscience/comments/lsdw60/what_is_the_current_scientific_consensus_on/ 1614279330 lsdw60 Psychology 2021-02-25 21:55:30 "Ego depletion is a resource based theory that basically says we have finite cognitive resources or self control resources, and that by exerting self control we deplete these self control resources. I work in a lab that studies this, it’s a very interesting topic and may not actually be true but a fault of the publication bias. Some recent studies have called it into question. + +Also, willpower can sort of be explained with different motivational theories. Intrinsic motivation has been shown to be more motivating than extrinsic motivators. +If you want to learn more, here’s some resources. + +https://m.youtube.com/watch?v=6yU0QVNwqUo + +https://m.youtube.com/watch?v=HD-dxUZxMcs + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6013521/ + +https://pubmed.ncbi.nlm.nih.gov/9599441/ + +https://blog.hubspot.com/marketing/intrinsic-and-extrinsic-motivation + +https://www.healthline.com/health/intrinsic-motivation" "There's a concept called mental fatigue or ego depletion that captures this well. + +Here's an [article that summarizes it.](https://www.apa.org/topics/personality/willpower) + +Here's a good [link to a conceptual theory manuscript about mental fatigue in Frontiers in Psychology](https://www.frontiersin.org/articles/10.3389/fpsyg.2018.01246/full#h3). + +>Their core idea was that conscious acts of self-control, defined more broadly as volitional action, draw on some sort of limited resource, meaning that even seemingly different unrelated actions share a common resource pool, and thus influence one another. + +There's some evidence a few things underlie it, like resource availability (like glucose) and task demands. Pinning down what ""fatigue"" is and measuring it seems, per the manuscript, somewhat complicated" +1886 If a nursing mom receives the COVID vaccine, will protective antibodies be transferred to the baby via breastmilk, essentially helping to “immunize” the baby who can’t yet receive the vaccine? 14 https://www.reddit.com/r/askscience/comments/lttld7/if_a_nursing_mom_receives_the_covid_vaccine_will/ 1614448848 lttld7 COVID-19 2021-02-27 21:00:48 +1887 How does the asymptomatic rate of coronavirus compare to other illnesses? 14 https://www.reddit.com/r/askscience/comments/l9q57d/how_does_the_asymptomatic_rate_of_coronavirus/ 1612139066 l9q57d COVID-19 2021-02-01 3:24:26 "Just a cursory look at the literature suggest flu has an asymptomatic rate of about 1 in 3: [https://academic.oup.com/aje/article/167/7/775/83777](https://academic.oup.com/aje/article/167/7/775/83777) + +COVID-19 estimates are about 1 in 6: [https://jammi.utpjournals.press/doi/full/10.3138/jammi-2020-0030](https://jammi.utpjournals.press/doi/full/10.3138/jammi-2020-0030)" +1888 Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science 14 https://www.reddit.com/r/askscience/comments/lwvuar/ask_anything_wednesday_physics_astronomy_earth/ 1614783615 lwvuar 2021-03-03 18:00:15 "I did some digging and every source I've found suggests that every planet in a system \*should\* revolve the same way around its star as every other planet present in the system (if multiple). However, I couldn't find anywhere that shows an exception to this ""rule,"" in that it has 1 or more planets revolving anti-directional to the other planets present. (I can, however, find where the star rotates counter to the direction of the revolution.) + +Question 1: Are there *any* known stars that have at least 1 planet revolving anti-clockwise AND at least 1 planet revolving clockwise? (A link would be greatly appreciated!) + +Question 2: Regardless of revolution around the star, can the planets within a system have a rotation that differs from other planets in the system? (IE: Both planets revolve clockwise, but have different rotations around their axes?) **EDIT: I did some more digging and found that Venus has a rotation opposite to the other planets in our system!**" Can planets that consist of primarily one terrain (ocean,desert,arctic etc.) exist in the goldilocks zone and support large multicellular lifeforms (cows for example)? If they can't then are they more likely to be results of climate change or distance from their home star and does that change affect its life support capabilities? +1889 Why are ceramics used for things like heat shielding? 14 https://www.reddit.com/r/askscience/comments/lsl4mq/why_are_ceramics_used_for_things_like_heat/ 1614298848 lsl4mq Engineering 2021-02-26 3:20:48 "There are a few things you want in a heat shield. You want something that can withstand high temperatures, absorb a lot of heat, but also not cook your astronauts. + +Ceramics tend to be very good thermal insulators. They have a high thermal capacity, but do not conduct the heat they absorb very well which is good because you need to keep the heat away from the space craft. So you make ceramic tiles. But since they don’t conduct heat very well, they have no choice but to keep heating up since they aren’t dissipating much heat. + +You solve this by painting them black with a layer of what is essentially glass. This gives the tiles a very high emissivity. Emissivity is a measure of a materials ability to reject heat as radiation. The black ceramic tiles were able to reject up to 90% of the re-entry heating back into the atmosphere. + +So you have 90% being dissipated as IR radiation, and the remaining 10% being absorbed by the tiles and staying there due to the low thermal conductivity. These are simply properties of ceramics that make them desirable as heat shields. You could go deeper, but it’s akin to asking why copper makes good electrical wire. Since radiation is very slow for small temperature deltas it takes a hours to cool all the way to ambient but that doesn’t matter because even though the tiles will still be hot at landing they don’t transfer that heat. + +Let’s say you used a metal heat shield instead. Well metal also has a high heat capacity. But its also an excellent thermal conductor. It will transfer that heat into the aluminum frame of the spacecraft during re-entry, which could damage it. It also means you will be hearing the interior of the craft, since the metal frame is now conducting heat further inward." Because ceramics can be relatively light, absorb tons of heat without melting or cracking, and dissipate heat very well, among other things. Ceramic is just a really non-conductive material that's light enough to be used on large projects like the space shuttle, as opposed to the Apollo-era epoxy heat shields that are heavy and require bits breaking off to function properly (and thus have to be either heavily repaired or replaced after each flight). +1890 Observed Light Speed from a Rocket Never Changes? 14 https://www.reddit.com/r/askscience/comments/lxcnwj/observed_light_speed_from_a_rocket_never_changes/ 1614832365 lxcnwj Astronomy 2021-03-04 7:32:45 "This is basically why time and space have different rules in special relativity. There's a couple of things going on here, but the big thing is that events that are simultaneous in one frame of reference aren't simultaneous in another frame of reference, and the time gap between events can be different in different frames of reference. + +So yeah, you're travelling at 99% of the speed of light away from Earth, and Earth fires a laser at you. From Earth's perspective it takes a long time to reach you, because the distance between the laser pulse and your spaceship is shrinking at only 1% of the speed of light. + +From your perspective, the Earth is moving away from you at 99% of the speed of light, and then fires a laser at you. From your perspective, you are stationary. This laser approaches you at the speed of light, and should reach you quite quickly. For this to add up correctly, what happens is that Earth fires its laser at a different time from your perspective! Earth fires its laser *later*, so even though the distance between the laser pulse and your spaceship is shrinking more rapidly than from Earth's perspective, you still agree about e.g. how old you are when the laser hits you." I'd just add to u/Astrokiwi's answer by mentioning that one consequence will be a BIG red shift on the laser, so that the color you see will be far away from the color fired from earth. The earth also will have this red shift. +2012 Why does a Pfizer booster protect against omicron when the first two doses don’t? 14 https://www.reddit.com/r/askscience/comments/rbssq2/why_does_a_pfizer_booster_protect_against_omicron/ 1638974480 rbssq2 COVID-19 2021-12-08 17:41:20 "A few points: + +1) We are not sure how much a booster will help, but it should help some, just because it will bring our antibody levels back up (they wane somewhat after that second shot, which is normal). These antibodies don't bind as well to omicron due to all the mutations, but they still bind a bit, so having more is helpful. + +2) Antibody levels may stay higher for longer with the booster (per Shane Crotty on TWiV 802). + +3) There is a cool thing B cells do call ""affinity maturation"", where they develop better affinity for antigens with repeated exposure (look up how it works -- it's really neat!). This process can also result in ""guesses"" of new variants, so the body has a chance of better defending itself against things it has never seen before. This may mean the new antibodies after the booster are better at neutralizing. + +4) It's not entirely right to say two doses doesn't protect. We don't know about T-cell response yet, but it is probable that it won't be substantially reduced, as T-cell epitopes are largely the same. It is still possible (I would guess likely) that two doses will provide some protection against severe disease." "What is your source on that? + +The booster is mainly necessary because the immunity of the vaccines reduce over time. The booster boosts it up to similar levels as right after the second shot. But someone who would get their second shot today after their first a few months ago would be just as well protected, I think. + +Edit: spelling." +2013 How long take for an atom whose electrons have ascended to a higher orbit due to light absorption to go back in a ground state? 14 https://www.reddit.com/r/askscience/comments/razpmw/how_long_take_for_an_atom_whose_electrons_have/ 1638885314 razpmw Chemistry 2021-12-07 16:55:14 ">if there is a document with the time it takes for each atom to go from an excited state to a low-energy one. + +It's not that simple. + +For a two-level atom, if you prepare it in the excited state, the survival probability decays exponentially with time, where the timescale of the exponential is the mean lifetime of the excited state. + +So you can't say when exactly any particular atom will make the transition, you just have a probability distribution. + +If there are more two levels in the system and you prepare it in a high excited state, then there are generally multiple branches the atom can decay through to eventually reach the ground state, each transition with its own lifetime. So you'll have a cascade of transitions, each taking some random amount of time." "The tl;dr is that for most common *fluorescent* substances (e.g., fluorescent dyes or complexes, where these things are relatively straightforward to measure), the excited state lifetime is roughly on the order of hundreds of picoseconds to tens of nanoseconds. (i.e., 10^(-10) to 10^(-8) seconds) + +The longer answer is that, as already mentioned, this process is probabilistic, so you can't predict when any given molecule will undergo the transition. And there are many possible transitions from the excited state to the ground state -- ones that involve fluorescence, ones that don't and just produce molecular motion, ones that result in chemical reactions, etc. The lifetime is just an average that is related to the rate constant for that transition. It also depends on conditions like temperature, solvation, presence of other substances, etc. + +Also, we are usually not looking at something simple like an electron going from the hydrogen 1s to 2s orbital, as molecules have more complex molecular orbital structures with many possible transitions. That said, it seems like simple electronic transitions in sodium vapour lamps also have lifetimes in the same range (tens of ns) + +*Phosphorescence* (""glow in the dark"") is a different story and the lifetimes are roughly on the order of microseconds to seconds." +1519 AskScience AMA Series: We are the NASA, ALMA, and university scientists studying comets and asteroids, here to answer your questions about some of our more recent observations on comet Borisov, comet Atlas, and asteroid 1998 OR2. Ask us anything! 13 https://www.reddit.com/r/askscience/comments/g9o4yp/askscience_ama_series_we_are_the_nasa_alma_and/ 1588083922 g9o4yp Planetary Sci. 2020-04-28 17:25:22 Which soon-to-come comet will be visible from Earth with your naked eyes? Is it possible for a large enough comet to have an atmosphere? +1520 If you move a magnet through the air fast enough to create a strong enough changing magnetic flux, can the magnet induce a ring of lightning in the air around the magnet? 13 https://www.reddit.com/r/askscience/comments/fzk5e1/if_you_move_a_magnet_through_the_air_fast_enough/ 1586642815 fzk5e1 Physics 2020-04-12 1:06:55 "Neat question. While presumably you can answer this question using the concept of magnetic flux, my immediate instincts is to consider relativity as the easier avenue to solve the problem. Let's break the question down into steps. Let's talk vacuum first. + +In vacuum, the magnet (if linearly traveling, and the the magnetic dipole is *not* pointing along the direction of travel) would have from your point-of-view a curling electric field around it. Specifically a magnetic dipole would be a magnetic and electric dipole mixture. But relativity is at play here--so your electric-magnetic field mix would become a pure magnetic field in the rest frame of the magnet. Basically--without matter around the magnet, we don't get something interesting. + +Okay let's now talk conductors. A magnet by itself won't produce current alone, you'd need to use a spool of wire or some other conductor which the magnetic is moving relative to. Then you'd induce a voltage in the system and presumably you could engineer a way to create a spark if the conductors had a gap filled by some insulator with a breakdown voltage. + +Now let's talk finally about insulators and therefore air. Air is obviously not a conductor, but an insulator, so charge can't move easily unless their is sufficient voltage to induce a spark. Let's also place our magnet is a vacuum tube so as it moves, it's not hitting the air around it. If the magnetic is allowed to move really fast relative to the air... Presumably you generate a large electric dipole field around the magnet, this should in principle be able to create a spark. + +Edit: Air will spark if the electric field is ~3kV/mm. A fridge magnet has a magnetic field strength of about 100 Gauss. So the napkin equation we're solving is + +* E ~ vB/√(1-v^(2)/c^(2)) + +It turns out (3 kV/mm)/(100 Gauss * speed of light) is very close to 1. So the speed of our magnet is then solved by + +* 1 ~ (v/c)/√(1-v^(2)/c^(2)) + +Solving for v, we get, + +* v ~ c/√2 ~ 0.7c + +So if our fridge magnet was flying through air (without friction which is dubious) at ~70% the speed of light, you'd likely generate sparks as it traveled. Napkin calculation is kinda flawed however for one important reason--the magnetic field was ignored and the magnetic dipole is also going to be enhanced by relative motion as well. As the force, say an electron, feels from magnetic fields goes by vB, and ""B"" here is the boosted magnetic field, then there's going to be some magnetic field strength eventually where electrons are torn off their atoms as well. The generation of this plasma should then occur quite a bit sooner than the above calculation would suggest." "This is basically an ""induction coupled plasma"" generator (except the magnet is being forcefully moved, instead of the ions) + +So the answer is yes, if the magnet moves enough and there is an original ion source" +1521 Small pox was eliminated years ago, but does it or can it still be possible that it is somewhere in nature waiting to make a return? 13 https://www.reddit.com/r/askscience/comments/g2ohrk/small_pox_was_eliminated_years_ago_but_does_it_or/ 1587073789 g2ohrk Biology 2020-04-17 0:49:49 "The only known samples of smallpox are at the CDC and in a Russian bio bank. + +The top comment mentions an old sample in a freezer - worrying. More worrying though, is that chances are pretty good there’s a corpse somewhere in the permafrost in the north with preserved smallpox on it. Ice cores taken from ancient ice have yielded active viruses, though the paper I’m thinking of used amoeba as bait not human cells. + +If you find a frozen body don’t pick its scabs." "They found a lost sample of small pox in the back of a freezer in Maryland. As a species we’re constantly pointing the gun at our own foot locked and loaded. [https://www.nature.com/news/nih-finds-forgotten-smallpox-store-1.15526](https://www.nature.com/news/nih-finds-forgotten-smallpox-store-1.15526) + + +Edit: Maryland" +1647 Why is a swab required to be inserted deep into your nasal cavity to determine a positive or negative covid case, yet it can be spread merely by speaking too close to somebody? 13 https://www.reddit.com/r/askscience/comments/hm9zmw/why_is_a_swab_required_to_be_inserted_deep_into/ 1594050222 hm9zmw COVID-19 2020-07-06 18:43:42 "By speaking, a smaller amount of viral droplets is expelled. This might not be enough to produce an accurate result. The concentration may be too low for the disease to be detected, however it might not be too low to infect a person - remember than not that many particles are needed to start an infection. + +Using a swab, on the other hand, basically guarantees a pristine and trustworthy sample, and it is therefore much more reliable, if a bit uncomfortable. + +Edit: sorry, there were some grammar mistakes" "There are many occasions where you may want to diagnose a patient with early disease (viral load may come up later). A negative result with specimen obtained at the site of (presumed) highest viral load would be much more reassuring than a result obtained from a specimen collected from a less satisfactory site. + +That said, the specimen requirement sometimes makes people avoid sampling because of the discomfort associated. At a time where people will outright refuse even masking, there probably exists a degree of compromise one can make in terms of specimen requirements to increase the uptake rate if wider testing is beneficial to epidemiological management of the disease..." +1648 If there is such a high false positive rate on the antibody tests for COVID-19, how are scientist tracking the accuracy of the vaccine antibody rates? 13 https://www.reddit.com/r/askscience/comments/hu3c7m/if_there_is_such_a_high_false_positive_rate_on/ 1595176386 hu3c7m COVID-19 2020-07-19 19:33:06 "Tests that are optimized for high throughout and quick reads can be less accurate than research-grade tests that have low throughput, individual attention, and that don’t need to have results delivered in days, let alone hours or minutes. + +The vaccine tests use the latter, many of the consumer tests use the former." "antibodies tests are now thought to be 95 percent to 99 percent specific. So “such a high false positive rate” isn’t really accurate. Prevalance also dictates retesting for positive results absent evidence of exposure or symptoms. Control groups for vaccine research will generate more data. Antibody tests in GA are coming back around 5% positive. + + +https://www.thecut.com/article/covid-19-antibody-testing.html" +1723 "Is the weight of a line distributed throughout the line, or is it ""felt"" at every point along the line?" 13 https://www.reddit.com/r/askscience/comments/jwiige/is_the_weight_of_a_line_distributed_throughout/ 1605715721 jwiige Engineering 2020-11-18 19:08:41 "At a theoretical steady-state, the tension in the line at any location is equal to the weight of all the line below that location. So, the entire upper half of the line is overloaded, and liable to break at any location in that half. In other words, it can't actually reach that theoretical steady-state, it's an impossible condition. + +Where would it actually break? Because we can't be in steady-state, let's say we did the experiment by laying the line out horizontally, clamping it between two 100,000 foot long flat surfaces, then turned the clamps upright and released them at t=0. The line would sag slightly as it stretched under the effects of gravity, the tension increasing everywhere. It wouldn't increase linearly with time, nor would it increase linearly with position on the line, but what is true is that the tension would always be higher at any point in the line than every point below it. So the tension would be highest at the top, and that's where it would break, once it had sagged enough to exceed 10 lbs of tension at the very top." "To supplement the good answers so far, this problem can be analyzed using a so-called [free-body diagram](https://en.wikipedia.org/wiki/Free_body_diagram). We consider a small vertical length of line and ask what the relevant forces are that act on it. Well, there's tension at the top, and tension at the bottom, and its weight. When the line is hanging motionless, these forces must add up to zero. Also, the stress is the tension divided by the cross-sectional area, and the line fails when the stress exceeds the strength. + +From this, we can ultimately find that the tension increases linearly as we move up the line and that failure of an ideal line will occur at the highest point. (In reality, the line will snap somewhere below the highest point depending on the variation in strength due to intrinsic defects.) To address your question, if the line snaps at a tension of 10 lbs, for example, you can't hang any more than 10 lbs of line without inducing failure. + +This particular problem is actually well studied in the context of [space elevator](https://en.wikipedia.org/wiki/Space_elevator#Cable_section) requirements. The question is how strong a cable has to be to hang from Earth's orbit and not break from its own weight. The answer is discouraging." +1891 Why don't ripples in a pond propogate at the speed of sound? 13 https://www.reddit.com/r/askscience/comments/lawjqv/why_dont_ripples_in_a_pond_propogate_at_the_speed/ 1612275764 lawjqv Physics 2021-02-02 17:22:44 "Ripples in a pond aren’t sound waves, they’re gravity waves. A sound wave is a longitudinal wave that propagates through a compressible fluid, while gravity waves are not longitudinal, and can occur even in an incompresible fluid. + +You can find more about the dispersion relation and speed of gravity waves [here](https://en.m.wikipedia.org/wiki/Dispersion_(water_waves\)). The speed of the wave depends on whether the water is shallow or deep compared to the amplitude of the wave. But it’s usually much less than the speed of sound through the fluid." "Sound waves are longitudinal waves - compressions along the direction of propagation. Waves in a pond are transversal - the displacement is perpendicular to the direction of propagation. Longitudinal and transversal waves can have different speeds of propagation even within the same medium. + +This difference is used to determine the origin of earthquakes. An earthquake consists of both types of waves, but longitudinal waves travel faster than transversal. By measuring the time delay between the two, you can calculate the distance between the seismograph and the epicenter." +1892 How do muscles store Glucose ? 13 https://www.reddit.com/r/askscience/comments/lbygy0/how_do_muscles_store_glucose/ 1612386845 lbygy0 Human Body 2021-02-04 0:14:05 "Your muscle cells store glucose in larger molecules called [glycogen](https://en.wikipedia.org/wiki/Glycogen)*.* (Your liver stores glucose the same way.) Glycogen is to animals what starch is to plants...it's basically just a bunch of glucose molecules linked together into a larger storage molecule, so that glucose units can be broken off as needed. + +[You actually have quite a bit more glycogen in your muscles](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3248697/) (500g) than in your liver (100g). However, when your liver turns glycogen into glucose, it can release that glucose into your bloodstream...that glucose becomes available to your entire body. Your muscle cells, however, can't pass glucose out of the cell and into the blood...stored glucose (glycogen) is stuck inside each individual muscle cell. So the 500g of glycogen in your muscles is only to fuel your muscle cells' immediate energy needs, while the 100g of glycogen in your liver can help maintain blood glucose levels for your entire body." "Your body will link glucoses together forming carbohydrates. This technically lowers the concentration of glucose since many molecules of glucose make one carbohydrate chain. So when glucose is set to be released if there’s carbohydrates and less glucose, there’s less of a glucose concentration in the cell and so less can diffuse out. Your body can then break the carbohydrates by another mechanism if it needs even more later. This is how say, potatoes do it or else all that glucose would be going everywhere. + +Your pituitary and hypothalamus are going to be regulating your liver. The liver will dump glucose when it encounters growth hormone but for the most part the thyroid will handle most of the metabolism of glucose with the hypothalamus. All your cells have glucose in them at all times and the hormones the thyroid or pituitary releases for insulin is water soluble so it spreads throughout your body very quickly. Glucose runs the ATP gambit and the ATP helps power your muscles contractions. While the glucose is in your muscle cells your muscles are not directly using it to convert it to energy for contractions. All your cells use glucose for many processes but your muscles going to use that energy from the glucose to make ATP and other chemicals like it. That ATP (adenine triphosphate) can then be stored in large quantities in the mitochondria or cytoplasm and that will be used to contract muscles. The glucose helps make atp. + +I commend your teacher for explaining the liver as they should but it’s one of the more complicated systems in your body and it’s probably best if you start with the more simple concepts like electron transport chain and look into ATP and how the mitochondria help to turn glycolysis. Then you can kind of use that knowledge to think about most the organs since they function the same way with minor differences" +1920 How do we know that the neutrinos have spin? 13 https://www.reddit.com/r/askscience/comments/p8wued/how_do_we_know_that_the_neutrinos_have_spin/ 1629571284 p8wued Physics 2021-08-21 21:41:24 "Neutrinos were originally proposed as a way to explain the observed electron spectrum in beta decay: + +n -> p + e + (anti)nu_e + +Conservation of angular momentum for this reaction requires that the neutrino must be a fermion. The proton, neutron and electron are all spin-1/2. So the left-hand side of the reaction is spin 1/2, and the proton and electron together have a total spin of 1, only capable of generating states of integer spin in any given direction. It is therefore impossible for the neutrino to also have integer spin, since you would never be able to get a spin-1/2 state of the system on the right-hand side if that was the case. So the neutrino must have half-integer spin, i.e. it must be a fermion. + +As to why it's specifically spin-1/2 and not some higher half-integer spin, this is more complicated. Fundamental particles in particular have more stringent limitations imposed on their possible spin from things like the Coleman-Mandula theorem, and in general a particle with spin higher than 1 will have unphysical scattering dynamics at high energies unless something very convoluted is done to fix things, that you wouldn't have to do if the neutrino was spin-1/2. The spin-1/2 model is sufficient to explain the data we have, so there's really no reason to have all of that extra complexity." "The mathematics of fermions are very different to that of bosons. The type of measured and observed interactions are entirely different. You could create a checklist of characteristics for observed interactions and cross match it against the known mathematical properties and eliminate obviously failing candidates. + +I think an ELI-15 answer would be that we have a list of known mathematical operators (+,-,*,/,^,etc) and know what they do. If I measure an experiment that I know uses the equation x+y = z and my known input is x and I'm measuring z with an unknown y and get this: + +``` +5 + y = 3i +``` + +then I know that `y` has to be imaginary. + +In some sense, fermions have some similar properties of extending mathematical vectors to their ""square roots"" in the same sense that imaginary numbers extend negative numbers to their square roots. If the unknown particle interaction we're looking at it shows this ""imaginary number"" property, well, it means it has to have an imaginary number in there." +1921 Why does melatonin cause hallucinations? 13 https://www.reddit.com/r/askscience/comments/o0b3he/why_does_melatonin_cause_hallucinations/ 1623752777 o0b3he Biology 2021-06-15 13:26:17 Do you have a link to a study that claims this? "There are literally 3 report of hallucinations in someone taking melatonin in the adverse effects reporting system + +https://www.medsafe.govt.nz/Safety/EWS/2015/melatonin-hallucinations.asp + +Keep in mind that this is a system that just goes - X is one of the things that was around when Y happened. + + +This is very unlikely for numerous reasons. + +1) there have been clinical trials of melatonin for various things and hallucinations were not among the monitored adverse effects. + +2) It is a hugely common OTC supplement - if hallucinations were a thing, then it should be happening more. + +3) the mechanism of action - melatonin has fairly localized effects in the “biological clock” (the SCN of the hypothalamus). It is neither a hallucinogenic or a soporific, rather it is more like a signal that tells your clock it is night. If you are diurnal , that sets into motion the other stuff that would put your to sleep (low noradrenaline, lower cortisol , parasympathetic activation etc). If you are a nocturnal animal, it is party time and you activate cortisol, sympathetic etc. This is not consistent with hallucinations." +1522 Why are master keys able to open different locks? How does that work? 12 https://www.reddit.com/r/askscience/comments/g0yjtr/why_are_master_keys_able_to_open_different_locks/ 1586837269 g0yjtr Engineering 2020-04-14 7:07:49 "I'd recommend [this video](https://www.youtube.com/watch?v=aVPSaKLKHd4) (from about 3:20), it'll do a way bettrer job explaining it than I. + +Essentially, the plug (the part where the key is inserted) of a locked (pin tumbler) lock is prevented from rotating by a bunch of stacks of two pins, cross the line (called the shear line) between the plug and the body of the lock. If the right key is inserted, it pushes each pin stack (against a spring) just far enough that now the interface between the two pins is lined up with the shear line, no longer stopping it from rotating (push it too far the other pin locks it). + +Now, if a third pin (""master pin/wafer"") is inserted into the stack, there are now two interfaces that can line up with the shear line, allowing the lock to open. Now two different keys can open the same lock. + +Now it is just a matter of putting in the right combinations of pins in each lock, making sure that they all work with the master key" "Some locks have rotating disks. +https://m.youtube.com/watch?v=N7lWM_yDxU0 +That video shows the principle of the disks rotating. The locks can be masterkeyed by making at least one of the rotating disks to have more than one slot where the long locking bar can fall. When the slots are aligned (the rotating key aligns them) the bar drops in the groove allowing the cylinder rotate inside the cylinder housing. That rotation opens the lock. + +Locks and keys based on the rotating disks allow multiple levels of master keying. For example key1 can open the outdoor of aparment building, the door of a specific apartment, door of laudry room, recycling room, etc., but not door of electric control room, water control room or any doors of other apartments. While a repairman might get key2 that opens doors of all the common spaces of the building, water and electricity rooms but no apartment doors. And there can be a key3 for the mailman that opens only the outdoor of the building. And key4 that opens every door of that building." +1649 How can the Earth's magnetic field be so weak, yet so large? 12 https://www.reddit.com/r/askscience/comments/htpnef/how_can_the_earths_magnetic_field_be_so_weak_yet/ 1595111707 htpnef Planetary Sci. 2020-07-19 1:35:07 "I believe this has 2 main reasons: + + * The extend of the source + * The energy stored in the field + +MRIs are generated by a machine in a room. The field strength of a dipole falls of proportional to 1/r^(3). Meaning, it falls of very quickly. The field of Earth is generated in the liquid core, a region literally thousands of kilometers across. When the source itself is already that big, the distance over which the field falls of is much larger. That being said, the field on the surface is about 50 times weaker than the field in the core. https://news.berkeley.edu/2010/12/16/earth-magnetic-field/ +The second point is energy. There is a lot of energy in the magnetic field. There is much much more energy in the terrestial magnetic field than in the magnetic field of, say, a MRI." Magnetic force falls off with distance. The Earths magnetic field is ridiculously strong, but it’s generated deep in the core. By the time it is measured on the surface it has already fallen to a fraction of its strength. +2014 How would you slow down a lightsail? 12 https://www.reddit.com/r/askscience/comments/rc21y5/how_would_you_slow_down_a_lightsail/ 1639000661 rc21y5 Physics 2021-12-09 0:57:41 "In short, no, there wouldn't really be a mechanism to significantly slow the probe down. But this isn't as much of a problem as you think. + +Our own Solar System is around 7 light-hours in diameter, so something traveling at near the speed of light would have several hours to collect data, which is definitely enough to do something with. Scale the speed down to 20ish% light speed, and we're talking about a couple days spent inside the Alpha Centauri system." "It depends a lot on the mission in question. + +* Some (small probes) don't slow down meaningfully; it's just a flyby with limited (though we expect still useful) observation window. + +* Some use the light of the star that they're approaching to slow down/orbit. This doesn't really work for laser sails, though does for other designs. It also leads to some weirdness where eg: Sirius is easier to get to than Proxima Centauri. + +* Some really large designs have multiple ""stages"", and detach an outer stage to reflect light back at the inner stage. (The laser is turned back on for this part) I'm unaware of any work that's been done on this since the 1980s, but there might be. + +* Other large designs have additional propulsion options (eg: mag-sails) to slow down." +1523 What was radioactivity called pre-Curie? 11 https://www.reddit.com/r/askscience/comments/ejfgth/what_was_radioactivity_called_precurie/ 1578058494 ejfgth Chemistry 2020-01-03 16:34:54 The term “radiation” already existed, and as far as I can tell the term “radioactive” (or rather the French *radioactif*) was coined in 1898, not long after the phenomenon was discovered in 1896 in Becquerel’s paper entitled “Sur les radiations invisibles émises par les corps phosphorescents” (Of the invisible radiations emitted by phosphorescent bodies). It seems like in the intervening time scientists simply referred to rays or radiation until Curie actually invented a word for the property of spontaneously emitting radiation. +1524 Why do psychiatric medications take so long to become fully effective (six weeks), while many other medications work within minutes or hours? 11 https://www.reddit.com/r/askscience/comments/ejbgjm/why_do_psychiatric_medications_take_so_long_to/ 1578032513 ejbgjm Medicine 2020-01-03 9:21:53 "Neuroscientist here! + +Basically, we don't know. + +The popular notion that SSRIs correct a serotonin 'deficit' is a myth. There is no serotonin deficit in depression. If there were, we'd be able to test for it. There is literally zero actual evidence of a literal deficit of serotonin im depression. That theory was essentially our ""first guess"" at why SSRIs can treat depression, but it was discredited. + +The real answer is probably that SSRIs cause some change in the brain, which causes another change in the brain.... etc., leading to a change that improves depression symptoms. In other words, it's not the direct effect of the drug (which is fast) but a downstream effect of the brain's reaction to the drug (which is slower). + +Look at it this way: developing a tolerance to a drug (which is due to the brain adapting to the drug) can (depending on the drug) take weeks. Now suppose that something about how the brain adapts to SSRIs is beneficial to depression. That's more or less what we think is going on. + +Brains are ludicrously complicated. It's hard to convey exactly how complicated." "If you’re referring to selective serotonin reuptake inhibitors (SSRI’s) for depression the reason it takes 1-2 months is because these drugs don’t directly cause your brain to make serotonin, rather they indirectly block the reuptake of serotonin in your brain allowing serotonin to persist longer whenever you secrete it. The mechanism of action of these drugs are complicated but essentially it’s believed to work at the level of your DNA so it takes time for your brain to stop making serotonin transporters (these are the proteins that decrease the levels of serotonin in your brain) because there are already a lot of serotonin transporters to begin with. + +People with depression have a decreased amount of serotonin in their brain’s and SSRI’s increase the concentration of serotonin indirectly to mimic the levels of a normal individual not suffering from depression. Having a lot of serotonin transporters is normal and SSRI’s lower the number of serotonin transporters to enhance serotonin’s effects. + +Let me know if you have any questions. +TLDR SSRI’s are working indirectly which is why it takes 1-2 months to achieve effects. Most drugs act directly on something which causes a faster response." +1525 Where can one find equations/mathematical description of a non imagining Fresnel lens? 11 https://www.reddit.com/r/askscience/comments/g20bg7/where_can_one_find_equationsmathematical/ 1586983354 g20bg7 Physics 2020-04-15 23:42:34 "You can find one here: + + [https://www.sciencedirect.com/science/article/abs/pii/S0038092X98001431](https://www.sciencedirect.com/science/article/abs/pii/S0038092X98001431)" You would need to look at a really good website on refractive index equations used in predictive Fourier equations for optical engineering. A very good question, why and what is your application? Just wondering. Complex math and the material the optic is made of has to be taken into account. Usually inexpensive plastic and of medium to poor quality . +1526 How does dehydration kill you? 11 https://www.reddit.com/r/askscience/comments/ejnfu0/how_does_dehydration_kill_you/ 1578092786 ejnfu0 Medicine 2020-01-04 2:06:26 "With children, dehydration can cause shock and they can die from this. + +Let me explain. + +Children have proportionately more body water than adults. They need it. If they start running low through fluid loss, say from diarrhea and vomiting, their body will pull fluid from the blood plasma to support their needs. Loss of blood plasma > decreased blood volume > not enough blood to get oxygen to vital organs > hypovolemic shock. This is the same type of shock that you would see in someone who has suffered a trauma or hemorrhage and has lost a lot of blood; it's just that the cause is different. They need fluid, not necessarily whole blood. + +This is why ""stomach flu"" can be so dangerous for infants and small children." "I think I see where the confusion is. If you don’t drink water for about ~3 days you become severely hypovolemic from water loss. +Excluding trauma, bleeding, etc. you lose water 2 ways. There is sensible water loss (peeing and pooping) and insensible water loss (loss of water through sweating and breathing). To a degree your body can control sensible water loss however insensible water loss we don’t have much control over. If your not drinking water for multiple days, then the insensible water loss will catch up to you (in this scenario) and cause hypovolemia. This will present as bone dry skin crusty lips and dried mucous membranes. The decreased volume status in your body causes hypovolemic shock which is a fancy word for your body shutting down. Essentially your brain knows which organs are essential and which ones are not and blood flow to the nonessential organs is cut off to preserve blood flow to the essential organs. Typically your kidneys are the first to go then your stomach and intestines. When your kidneys shut down ammonia and urea (these are the waste products of protein breakdown) build up in your body which causes problems to your heart and brain but probably won’t directly kill you. When your stomach and intestines lose blood supply they can rupture their contents into your abdomen and thorax and this is what probably will kill you. The contents of your stomach and intestines include bacteria that will have field day getting into your blood and replicating basically unopposed because your body is shutting down. This will cause sepsis and ultimately speed up the process of hypovolemic shock. You need to remember the problem is not with hemoglobin/RBC’s, you have plenty of those, the problem is with plasma which is made up of mostly water. Plasma makes up about 55% of blood so that’s why you have decreased blood volume in dehydration. + +Let me know if this helps and feel free to ask questions if something doesn’t make sense." +1527 What happened to the energy released from all the matter/anti-matter annihilation events in the early universe? 11 https://www.reddit.com/r/askscience/comments/g2g0h3/what_happened_to_the_energy_released_from_all_the/ 1587047609 g2g0h3 Physics 2020-04-16 17:33:29 "It is the CMB! You're 100% right! + +But to expand on this, in the very early universe there was enough energy that all the particles (and antiparticles, and photons) could change back and forth between eachother during their interactions. This is a lot like what we do in high energy particle colliders today; smash a proton and an antiproton together with enough energy, and you can get all sorts of other interesting particles out. + +As the universe expanded and cooled the energies of those interactions got lower, and eventually you couldn't make matter-antimatter pairs in the random collisions going on. It's like the energy of your particle collider got turned down. + After that the remaining particle-antiparticle pairs slowly find eachother and annihilate, leaving lower mass particle-antiparticle pairs and photons. + +Eventually, all that's left is the small number of extra stable particles (like electrons, protons, neutrinos...) and CMB photons. The particle-antiparticle pairs (ie not the excess particles) all end up creating photons. We call the excess the ""baryon asymmetry"", and we know how strong it was (ie how many extra particles fractionally there were, over antiparticles) by counting the number density of atoms (aka baryons to cosmologists, because all the mass is in the nucleus), and the number density of CMB photons. What we learn from that is that there are about a billion CMB photons per baryon, so there was about one extra particle in the early universe for every billion particle-antiparticle pairs. So really about 99.9999999% (I hope I counted nines right there!) of the original matter annihilated!" +1650 What is long lasting immunity contingent on, and why are some antibodies “better quality” than others if they all undergo affinity maturation? 11 https://www.reddit.com/r/askscience/comments/hr4go0/what_is_long_lasting_immunity_contingent_on_and/ 1594743430 hr4go0 Biology 2020-07-14 19:17:10 "I don't know what causes the body to maintain some memory cells longer than others (excepting re-exposure to the pathogen), I would also be interested to know. + +I can comment a bit about the quality of antibodies, however. During maturation, the antibodies are selected for their ability to tightly bind to a specific epitope. For the most part, this process is successful and the antibodies produced by the body do bind tightly. However, which epitope they bind on the pathogen can have a large impact. Some antibodies may bind in a region that does not affect the pathogen's function. Alternatively, antibodies might bind a region that has a high mutation rate and therefore can escape binding over time." "The other answer here is correct (antibodies are random, affinity maturation is random under selective pressure, so it's chance). + +I just want to add that not all viruses induce a holistic immune response. What you're referring to is the case where antigen-specific CD4 T cells activate a B-cell (vs T-independent activation), which tends to lead to IgG isotype switching and strong proliferation of B-cells. This is where my understanding becomes weaker and chances are the research becomes less established (ie you should read some reviews). The establishment of memory B cells, afaik, generally relies on follicular T helper cells (as does affinity maturation). Differences in the immune response elicited by the pathogen in terms of it's tissue tropism, the cytokine profile, and immunomodulatory effects of the pathogen can alter the propensity for these steps to occur. Sorry for the hand wavy answer, but basically there's a lot of room for different aspects of the classical, textbook immune response to occur or not occur to different extents based on the nature of the response induced." +1724 How does mercury (Hg) occur in nature? What does mercury-mining look like? 11 https://www.reddit.com/r/askscience/comments/irreh4/how_does_mercury_hg_occur_in_nature_what_does/ 1599969867 irreh4 Earth Sciences 2020-09-13 7:04:27 Mercury can occur as liquid metal (rarely), but as far as I know it occurs more often as cinnabar (I hope that's the correct translation) aka HgS. To obtain pure Mercury (Hg) from that it has to undergo a heated reaction with Oxygen, so it is kind of roasted. "Mercury is mostly mined from ancient hot spring deposits, commonly associated with periods of ancient volcanic or ingenious activity (magmatic rock underground). + +Hydrothermal fluids and Volcanic vapours ascended to the surface, and as it cooled, it deposited Mercury minerals in mineral veins low temperature, about 150 Celsius and lower. The most common Mercury mineral is Cinnabar, Mercury Sulfide, as well as native Mercury. Famous Mercury mines include Almaden Mercury mines in Spain, mined since Roman times, New Idra, California and the Tongren Mercury mines in China. + +Mercury is also produced as a by product of base metal mines, some copper, zinc and lead mines in South America for example contain minerals with traces of Mercury. + +China is the largest mercury producer, over 3000 tons per year. About half the Mercury is mined in Guizhou Provence of South West China, the Mercury veins are dolomite and cinnabar in a sedimentary limestone. The Mercury was recently linked to igneous rocks and volcanic activity. The same volcanic activity produced large gold deposits. + +The Mercury in Guizhou Provence is mainly mined by 100s of small Artisanal mines and they are very polluting, the miners cook the ore in little retorts, burning the ore and liberating liquid Mercury. Some of the Mercury evaporates and pollutes the environment. The Chinese also don't care much about who the sell Mercury to. + +For example, Bolivia had a gold rush that began associated with the financial crisis, it caused unemployment and gold prices to climb, poor headed to the Amazon to mine gold, using Mercury to refine the gold. Peru imported 180 tons of Mercury per year for the mines. + +https://youtu.be/FrHuqT1zpVM + +The last Mercury mines in Spain closed in 2000, due to a price drop caused by cheap Chinese Mercury. + +Here's an old film about Mercury mining in New Idra: + +https://youtu.be/wPYysvKqwus + +Ref.: + +Yin, R., Deng, C., Lehmann, B., Sun, G., Lepak, R.F., Hurley, J.P., Zhao, C., Xu, G., Tan, Q., Xie, Z. and Hu, R., 2019. Magmatic-hydrothermal origin of mercury in Carlin-style and epithermal gold deposits in China: evidence from mercury stable isotopes. ACS Earth and Space Chemistry, 3(8), pp.1631-1639. + +Li, P., Feng, X., Qiu, G., Shang, L., Wang, S. and Meng, B., 2009. [Atmospheric mercury emission from artisanal mercury mining in Guizhou Province, Southwestern China](https://www.sciencedirect.com/science/article/pii/S1352231009000892?casa_token=BPi4MK5O1bgAAAAA:AboJAz236UeNg3E32LzhTictZ32y6H6CtHoMkVGH6YECYm9nOIbdq779zFfBg6szhGuQEmRyYfI). Atmospheric Environment, 43(14), pp.2247-2251." +1725 Can a sun have a ring? 11 https://www.reddit.com/r/askscience/comments/k6y1qv/can_a_sun_have_a_ring/ 1607130819 k6y1qv Astronomy 2020-12-05 4:13:39 "Yes, and our own sun has two! The [asteroid belt](https://en.wikipedia.org/wiki/Asteroid_belt) and the [Kuiper belt](https://en.wikipedia.org/wiki/Kuiper_belt). They happen to be pretty far our from the sun, and may not look like ""classical"" ring systems like Saturn, but consider: + +Asteroid Belt: + +>a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars, that is occupied by a great many solid, irregularly shaped [rock and/or metal] bodies, of many sizes but much smaller than planets... + +Kuiper Belt: + +> a circumstellar disc... Analysis indicates that most Kuiper belt objects are composed largely of frozen volatiles (termed ""ices""), such as methane, ammonia and water. + +Other stars with rings are known. The first seems to have been discovered in the late '90 by You-Hua Chu (University of Illinois). In *Cosmic Catastrophes: Exploding Stars, Black Holes, and Mapping the Universe*, Craig Wheeler wrote (in 2007): + +>You-Hua Chu scored another coup a decade later, at a meeting in Chile to celebrate the tenth anniversary of the discovery of the supernova, when she reported that she had discovered the first star to have rings around it, like the progenitor of SN 1987A. + +SN 1987A was a supernovae that exploded in 1987. The progenitor (the star that actually exploded), Sk-69 20, was a blue supergiant. [Pictures taken from Hubble](https://chem.tufts.edu/science/astronomy/sn1987a.html) showed three rings." [Protoplanetary disks](https://en.wikipedia.org/wiki/Protoplanetary_disk) are basically rings. Just like the rings of the planets have gaps from moons these disks develop gaps from planets. +2015 Is there any validity to the idea that light slows down in medium due to being absorbed and reemited by atoms in the medium? 11 https://www.reddit.com/r/askscience/comments/q21l69/is_there_any_validity_to_the_idea_that_light/ 1633455857 q21l69 Physics 2021-10-05 20:44:17 "If you want to get a group of physicists to fight, get them in a room and ask them why light travels slower and refracts when passing through matter. The fact that there isn't an agreement on the matter might make you say ""oh, so they don't know."" But I would answer ""we do know, there's just multiple ways of thinking about it"" and which one you prefer is likely based on what type of physics you're currently doing. Part of the reason it's hard to give a ""definitive answer"" is because photons are [identical particles](https://en.wikipedia.org/wiki/Identical_particles). + +Identical particles in physics is perhaps a stronger statement than what most people might think ""identical"" means. Identical means asking ""is this particle the same particle as we observed before"" is impossible to answer. If a photon is absorbed and then re-emitted, you can't answer ""is it the same photon or a new photon"" since all photons are identical. They are impossible to label. If a charged particle gains an electron, you can't answer ""the electron which was gained went into a certain shell"" or if it loses and electron saying ""the electron which it lost came from this shell."" You cannot label them, even in principle. + +So, this leads to the fact that you can't even answer ""are the same photons which entered a material the same ones that exited."" You can't track them. + +So, where does this leave us. Well, we do know the simplistic view, thinking of photons as ""point particles"" which get absorbed if they happen to hit an atom, and then re-emitted in any which way, cannot explain [Snell's law](https://en.wikipedia.org/wiki/Snell%27s_law). But Snell's Law can be derived a number of ways. Maxwell's Equations, thinking of light as a wave, can perfectly explain the behavior. Huygen's Principle (the method used in your linked article) does it via constructive and destructive interference. You can also directly calculate it from conservation of momentum and energy. + +So, in field theory (which if you see my flair, you know might be my preference), a massless particle must always travel at 'c' so we distinguish between the speed of light (c) and the speed that a light wave propagates (less than c in a medium). A condensed matter physicists would say, of course a photon can't travel at less than c, but when it's in matter it is a [polariton](https://en.wikipedia.org/wiki/Polariton), which is a quasi-particle, caused by a photon strongly interacting in matter. Physicists more interested in electromagnetism will probably use the Maxwell method. I would say they are all valid. They don't necessarily contradict each other, rather it is multiple ways of describing the same phenomenon. + +Sorry if that isn't the answer you're looking for, and you'll likely get someone who will give you a ""definitive answer"" that is the definitive way of thinking about it in their field, but at the end of the day, we have a collection of models, and our models describe the universe (some better than others)." "I think the other comment does a great job of breaking down different ways of talking about understanding light propagation, so I’m going to talk about what isn’t happening instead. + +You mentioned that if the light was being absorbed it would leave the glass in a random direction. This makes total sense while looking at fluorescent glass for example: light goes in one direction, but comes out in every direction as a glow. But light parring through clear glass is just delayed, not deflected. + +In light absorption in colored glass, we have a different phenomenon. The energy is transferred to some resonant absorber within the glass and stops its propagation entirely. This is distinct from the process of light refraction and propagation, as absorption of light utilizes an imaginary term in the dielectric function while the refractive index comes from a real one. This absorption causes the light to rephrase and sends it hurling in random directions. + +So although you may talk about the light absorbing into the glass as it propagates, it is important to distinguish this nonresonant, non dephasing absorption from classical light absorption by a colored compound." +2016 Why don't we feel air pressure? 11 https://www.reddit.com/r/askscience/comments/ptgjsl/why_dont_we_feel_air_pressure/ 1632345640 ptgjsl Physics 2021-09-23 0:20:40 "Not only is the pressure from all sides, there is also pressure inside your body. So not only is air pushing against you, your body is also pushing back. + +As for the example with your hand on the table, there is actually a way for you to feel that air pressure. Normally, air would be able to get under your hand quite easily and push *up* the same amount you're being pushed down, so you can't actually feel it. But take something like a suction cup, wet it, and stick it on the table. Then, air can't rush beneath, and the (quite strong) force of the air pressure will prevent you from pulling it off. An extreme example of this is the [Megdeburg hemispheres](https://en.wikipedia.org/wiki/Magdeburg_hemispheres), which could not be pulled apart by teams of horses - just through the force of the atmospheric pressure." We don't sense pressure like an actual barometer. Our senses depend on mechanical force causing a stretch or change in position. We don't actually feel the force, we feel the mechanical consequences. So, if our body isn't physically changing shape, we don't feel anything. When we feel pressure, mechanical forces are causing things to stretch and move at a cellular level. We are static at the air pressure we are living in, because the body uses a variety on mechanisms like connective tissue and fluid balance. No change no feeling. But we go under water, or go very high up. We can experience the changes due to pressure. +2017 Why Moderna half dose and not a full dose for the booster? 11 https://www.reddit.com/r/askscience/comments/rb0bws/why_moderna_half_dose_and_not_a_full_dose_for_the/ 1638887152 rb0bws COVID-19 2021-12-07 17:25:52 "Vaccine dosage is based on both laboratory study of how the vaccine works as well as clinical trial data. Drug makers seek to find the optimal balance between desired effects, in this case COVID protection, unwanted adverse effects, use of resources, and cost. You might think that giving twice the dose would be twice as effective (or half the dose half as effective) but it doesn't always work that way. For example, if half the dose gives 90% extra protection but double that gives 95% protection you might go with half because its still very high, but it allows you to double the doses available. And giving 100 people 90% protection vs. 50 people 95% protection would be better. So Moderna and the relevant gov't authorities (the FDA in the US) have looked at the data and determined that for most people a 50% booster dose is sufficient. There are people who can receive a full strength third shot, people who are immunocompromised in some way. In that case the first two doses would be less effective than in a ""normal"" person, so its worthwhile to give them a stronger dose to improve their immune response." its more about public health policy than individual benefits. more shots in arms in a shorter time (ie with less supply bottlenecks) for less cost compared to giving full doses, and less side effects so more cooperation. from an individual perspective a full dose is probably better but the half dose does a good job of boosting immunity too. i don't have the numbers but that was the overview a doctor gave me. +1528 How do auto manufactures avoid RF interference with adaptive cruise control systems? 10 https://www.reddit.com/r/askscience/comments/ejwyog/how_do_auto_manufactures_avoid_rf_interference/ 1578146554 ejwyog Engineering 2020-01-04 17:02:34 "Adaptive cruise doesn’t mean radar. Radar is one approach, but many systems have no radar at all. + +For example Subaru uses machine vision. A pair of forward facing cameras (you can see them in the windshield, to either side of the rear view mirror) take images of the road ahead and the computer uses stereo imaging to determine distance from objects ahead. It’s completely passive, to the point where the cruise control will shut off on a very dark road because the system can’t see anything with any confidence. + +Other companies add LIDAR to actively track nearby objects but as far as I know that’s in conjunction with machine vision. LIDAR is basically radar done with lasers (so light, much higher frequencies than would normally be thought of as RF), and is strictly line of sight with very narrow beams that are scanned rapidly around the LIDAR unit. It’s possible that one LIDAR unit’s bean would strike another unit from time to time, but it’ll just be a short blip of noise. + +All of that said, at least some of the automotive radar units use spread spectrum meaning they are bouncing around between different frequencies very quickly. There may be occasional collisions where multiple radars are momentarily on the same frequency, or where the radar is using the same frequency as something else, but it’s again going to be a very brief blip of noise for both sides." +1529 What does COVID 19 RNA detected on a test mean? 10 https://www.reddit.com/r/askscience/comments/g1p96h/what_does_covid_19_rna_detected_on_a_test_mean/ 1586945699 g1p96h COVID-19 2020-04-15 13:14:59 "SARS is an RNA virus meaning it’s genome is encoded in RNA, not DNA. The test for the virus is to take a swab, usually from the nasopharynx, and extract the RNA from the sample. That RNA will contain predominantly the patients own RNA, but in the case of an infection there will be virus there as well. + +rtPCR is a technique to turn RNA into DNA (more stable, easier to work with) and then amplify a specific sequence you are interested in. In this case, we are interested in the viral genome. + +The lines you describe are the two possible results of the test. Either it’s detected and you are presumed infected, or it is not detected and you are presumed SARS-free. Note, it is possible to get a false negative. + +The result cannot be both. Is there any bolded text in your result?" +1530 Could we give blood transfusions containing Covid-19 antibodies en masse to vulnerable sections of the population for passive immunity? 10 https://www.reddit.com/r/askscience/comments/g0z4j6/could_we_give_blood_transfusions_containing/ 1586839719 g0z4j6 Medicine 2020-04-14 7:48:39 "This is theoretically possible assuming that by “blood transfusions” you meant “convalescent plasma”. In fact, this is already done to many immunocompromised people. However, it is practically impossible. + +The main problem with this approach is the amount of blood that you would need to get to be able to give enough antibodies to every vulnerable person. Convalescent plasma is not prepared from the blood donation of one donor but from thousands of them. The reason behind this is that if you inject too “few” antibodies, they will rapidly be cleared by the liver and you won’t be giving any protection to the receiver." It’s not feasible. Apart from the number of donors you’d need (in [Effectiveness of convalescent plasma therapy in severe COVID-19 patients](https://www.pnas.org/content/early/2020/04/02/2004168117) they used one donor to one recipient), transfused antibodies don’t last long - maybe a week or two - so you’d have to keep doing it over and over, meaning more donors, more transfusions, more chances for complications. +1651 How are viruses weakened for live vaccines? 10 https://www.reddit.com/r/askscience/comments/h017xy/how_are_viruses_weakened_for_live_vaccines/ 1591753226 h017xy Biology 2020-06-10 4:40:26 "There are multiple ways of weakening - or *attenuating* - a virus for use as a vaccine. The most straightforward and historically-used method is by *passaging* (i.e. replicating the virus repeatedly over time using new cells for infection) the virus on a cell-type that is non-human. For example, if you wanted to create a live-attenuated vaccine for SARS-CoV-2, you could - in theory - try replicating it over and over and over again in a civet or cat cell line. Eventually, the virus may adapt to that cell line and lose its virulence against a human host. The key is to identify viral strains that are adapted to the non-human cells, but still maintain some capacity to replicate in a human - otherwise we would never mount an effective immune response to that virus. + +Another newer method is by intentionally introducing mutations into the genome of a virus that result in attenuation in humans. This is essentially directed evolution in the sense that the goal is the same as the prior method - accumulating mutations that reduce its virulence in humans - but more controlled and quicker." +1652 Does the brain use more energy when thinking about something difficult, or is it doing the same amount of activity, just more coordinated? 10 https://www.reddit.com/r/askscience/comments/h7trmg/does_the_brain_use_more_energy_when_thinking/ 1591998090 h7trmg Neuroscience 2020-06-13 0:41:30 "The safe answer is ""yes"" for more challenging mental activity, emotional activity, motor activity, memory retrieval, and other cognitive tasks. Technology such as fMRI uses BOLD as an indicator of oxygen utilization. More highly active brain cells draw more oxygen from the blood supply. It's correlational, however, which guards neuroscientists from asserting cause and effect. However, when you are adept at certain complex tasks that you're used to doing, then it's more automated and can be unconsciously drawn. The latter suggests better economy from existing synapses and the activity of molecular machinery within them." I think it does. I remember reading about researchers trying to figure out what parts of the brain are used for different things - problem solving, recognizing stuff, remembering things. So they inject a volunteer with slightly radioactive glucose, get them to think about different things, and scan the brain to see what parts are active. This seems to me to mean that when someone is working on different problems their brain is consuming sugar at different rates. And I’m no doctor, someone else may have more insight. +1653 Does the influenza virus affect cell size? 10 https://www.reddit.com/r/askscience/comments/gzad25/does_the_influenza_virus_affect_cell_size/ 1591656966 gzad25 Biology 2020-06-09 1:56:06 "It can do both, depending on the timing. + +> The cytopathic effect of influenza virus is seen microscopically in characteristic degenerative changes in the epithelial cells of the bronchial and bronchiolar mucosa. These changes involve all cells of the surface epithelium and often the cells lining the bronchial glands: **swelling of the cells**, vacuolation of their cytoplasm and degeneration of the nucleus proceed to cell loss and frank necrosis + +—[Pathology of the Lungs. Chapter 5 - Infectious diseases](https://www.sciencedirect.com/book/9780702033698/pathology-of-the-lungs) + +But later in infection the cells often undergo apoptosis, which generally includes shrinking of the cell. + +If you’re looking for more info, the key words you’re looking for are “cytopathic effects”." +1654 How do Sperm Whales find Giant squid? 10 https://www.reddit.com/r/askscience/comments/hlqfbc/how_do_sperm_whales_find_giant_squid/ 1593970047 hlqfbc Biology 2020-07-05 20:27:27 "They don't solely eat giant squid- from what we can tell, they require about a ton of food per day, so they eat all kinds of fish and squid. That being said, giant squid are obviously the most well known prey item for sperm whales as far as humans are concerned, and likely a very desirable one for the whales, since its a high payout- one hunt equals a huge, energy rich meal, instead of swimming after numerous smaller things. They find them the way most cetaceans do; with echolocation. They don't have the characteristic ""singing"" that some of their filter-feeding counterparts are known for- instead, their large head (filled with fatty tissue) and their spermaceti organ (where the oil is that whalers seek, mostly in the past but still to a certain degree today) is used to amplify clicking sounds made by their nasal passages and a pair of clappers called ""monkey lips"". It appears that, as the sound bounces back to them, they use a pad of fat in their jaw that is attached to their inner ear to absorb and interpret the sound. They use this same system to make different clicks and sounds to communicate with other whales. Its even come.out fairly recently that they have certain series of clicks to identify different members of their clan- essentially, names. + +As far as hunting though, it can be broken down a little bit- if they send out a ""click"" and it bounces off the hard parts of a giant squid (like its beak), the amount of time it takes to bounce back tells the whale how far away it is. The ""shape"" of the wave tells it how large it is and what shape it is- and if you're a whale that means you now know what it is. Its been determined that they can find a relatively small squid up to a mile away- now imagine it was a big squid, or a school, and you had multiple whales hunting that can all hold their breath for over an hour. While I'm sure its difficult, it doesn't sound nearly as impossible as rooting around in the dark abyss with eyes that rely on light. They can essentially see down there with echolocation. + +We're still learning an awful lot about them (I read a paper about the function of their teeth just last week) so I'm sure that, even in the next 5-10 years, I could come update this answer with more info. Either way, I hope this explains it satisfactorily, but feel free to ask if you have more questions" What happens when the squid realizes a sperm whale is coming for it? Are sperm whales just faster swimmers than their squid or fish prey? I’ve been wondering about this because the fish they eat must not be too small, but not too fast to just swim away. +1655 What is the excess mortality of the pandemic? 10 https://www.reddit.com/r/askscience/comments/htqgxq/what_is_the_excess_mortality_of_the_pandemic/ 1595114857 htqgxq COVID-19 2020-07-19 2:27:37 "Since no one has linked the CDC page specifically addressing your question, here it is: + +https://www.cdc.gov/nchs/nvss/vsrr/covid19/excess_deaths.htm + +There are a lot of excess deaths. + +The 2018 spike is related to the very bad flu season that year." "The NY Times published some estimates of excess mortality a few months ago https://www.nytimes.com/interactive/2020/06/01/us/coronavirus-deaths-new-york-new-jersey.html + +Interesting fact is that there's excess deaths due to COVID-19, but also excess deaths due to untreated heart disease, diabetes, etc." +1726 What is the role of a Staphylococcus culture in artisinal sausage making? 10 https://www.reddit.com/r/askscience/comments/jvuk6n/what_is_the_role_of_a_staphylococcus_culture_in/ 1605625688 jvuk6n Biology 2020-11-17 18:08:08 You know, I can not answer this question but I might suggest you ask over at /r/Charcuterie . It's a good sub and they will know. I do know that it is included in some commercial cultures usually referred to as Bactoferm and sold commercially for making salami. +1727 How exactly is an analog signal encoded onto a laserdisc and played back? 10 https://www.reddit.com/r/askscience/comments/jw3s33/how_exactly_is_an_analog_signal_encoded_onto_a/ 1605654188 jw3s33 Engineering 2020-11-18 2:03:08 It uses pulse width modulation. It is analog in that the lengths of the pits vary in an analog fashion even though they are pits which are either present or not. The pulse width modulation represents an FM signal with 6.75MHz being black and 7.9MHz being white (for PAL, NTSC is a little different). +1728 Are the number of bytes output from a compression algorithm directly proportionate to the number of input bytes? 10 https://www.reddit.com/r/askscience/comments/is6d5e/are_the_number_of_bytes_output_from_a_compression/ 1600029875 is6d5e Computing 2020-09-13 23:44:35 "No, in general it is not. Compression algorithms are more effective when there's more structure in the data. Exactly what type of structure leads itself to be more compressible will depend on the algorithm. + +A simple test you can do is to take a photo file, open it in Paint and save it as Bitmap (.bmp). Then, create an empty image of the same pixel dimensions, but completely blank. Save it ti a new file using the same .bmp file type. Compare the file sizes and note that they are the same. Bitmap files are uncompressed (by default, in theory the file format does allow for some forms of compression). + +Now, compress both files to their own .zip file and compare the file sizes. You'll note that the blank image compresses to a much smaller size than the image containing a photo, despite both input files being the same size. + +The very simple structure of the blank file (""everything is white"") is much easier to compress than a detailed picture." "There is an interesting counterintuitive result: A (non-trivial) lossless algorithm must increase the length for some inputs. This is a direct result of the pigeonhole principle: There is only a finite number of messages not longer than x bits. If you want to compress longer messages to these length then you need to map some shorter messages to longer messages. In fact, a good algorithm will increase the length for *most* possible inputs! + +A good algorithm will shorten the length of typical inputs drastically while extending the length of less typical inputs (which are the majority of all possible inputs) just a bit." +1922 What is the Delta variants mortality? 10 https://www.reddit.com/r/askscience/comments/o2y37z/what_is_the_delta_variants_mortality/ 1624044275 o2y37z Human Body 2021-06-18 22:24:35 "A number of factors to consider here: +1. There will be a delay from new case reporting to hospital admissions to ICU admissions to mortality. Death is a trailing indicator! +2. A large proportion of the UKs population that is most vulnerable have already been vaccinated, meaning that even if they are infected, they are now less likely to require hospital admission, ICU admission, or to die +3. The remaining population that hasn’t been vaccinated are younger and healthier (due to vaccine priority for older and more vulnerable populations) so they are less likely to be hospitalized or die. + +I’ll grab you the data points when I’m off mobile but the question has some suggested answers, but these explanations above are probably more impactful to the observation you’ve made above. + +Edit to add there is no great quality study that I can find that answers your question. A study looking at this question for Alpha is found here: + +https://www.bmj.com/content/372/bmj.n579 + +But I’ve not found something of comparable quality for Delta. May simply be too soon to have the data." ">In the Public Health Scotland/EAVE II study, Cox proportional hazard regression was used to estimate risk factors for the time from test to hospitalisation among individuals who tested positive. Hospitalisation with COVID-19 was defined as any admission within 14 days of a positive test or where there was a positive test within 2 days of admission. The model was adjusted for age and days from 1 April 2021 as spline terms together with number of co morbid conditions, gender and vaccination status. Vaccination status was determined at the data of the PCR test. Individuals who tested positive from 1 April 2021 onwards (until 14 June 2021) were included in this analysis. There was an increased hazard ratio of hospitalisation for those who were S-gene positive compared with those with S gene target failure (1.8, 95% 1.4 to 2.3) + +The previous variant, Alpha / B.1.1.7 / Kent, has a mutation (deletion at 69/70) that results in a false negative for the S-Spike gene in TaqPath PCR machine. This is known a S-gene dropout. The new Delta variant lacks this mutation so it is S-gene positive. That allows health authorities in the UK to track the growth in cases without needing to do full genetic sequencing. + +In Scotland they are seeing people who test S-Spike gene positive (Delta) are about 1.8 times more likely to end up in hospital compared to S gene failure (Alpha). + +This is circumstantial evidence that the Delta variant might cause more severe COVID-19 symptoms than the Alpha variant. If this is the case, it might be due to the P681R mutation, that may boost cell-level infectivity. + +https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment\_data/file/994839/Variants\_of\_Concern\_VOC\_Technical\_Briefing\_16.pdf" +2018 How do scientists determine how many calories different activities burn? And how accurate are the estimates on exercise machines? 10 https://www.reddit.com/r/askscience/comments/q23jlo/how_do_scientists_determine_how_many_calories/ 1633461835 q23jlo Biology 2021-10-05 22:23:55 I think it has to do with measuring the CO2 you exhale when exercising. So you wear a facemask which is connected to a machine which can measure the amount of CO2 you are breathing out and can then estimate the amount of calories that represents while you are running on a treadmill etc. You can also measure power output by a person by using carefully calibrated instruments. Nowadays most competitive cyclists use power meters which measure deflection of a bike part related to your effort. Knowing some other variables like pedal rotation speed and crank length, you can calculate power. If you know how much power a person is generating, you can easily calculate the amount of work or calories they are using. The catch is that you are not accounting for energy spent by other systems of the person. To get the total amount of energy consumed, then a respiration / air exchange study would be better suited. +1531 "How are scientists projecting ""peaks"" of death/infections?" 9 https://www.reddit.com/r/askscience/comments/g0u9x4/how_are_scientists_projecting_peaks_of/ 1586820718 g0u9x4 COVID-19 2020-04-14 2:31:58 [This](http://www.healthdata.org/covid/faqs#differences%20in%20modeling) is the FAQ for one of the groups doing the projection and it has a link to the Github repo that is the exact program they use. It's in python so you should be able to run it on any computer you have access to if you want to see exactly how it works. "They look at historical trends in regions further along the infection curve and use them extrapolate the possible future course in other regions. + +Among the more widely discussed forecasts are those being made by the Institute for Health Metrics and Evaluation (IHME) at the University of Washington’s School of Medicine. The text below isbfrom an [IHME press release](http://www.healthdata.org/news-release/new-covid-19-forecasts-europe-italy-spain-have-passed-peak-their-epidemics-uk-early-its) from April 6: + +""IHME started making projections of the pandemic’s impact in the United States state-by-state on March 26. Today’s announcement is the first set of predictions for European nations and **is based on modeling the peak in death rates and hospital usage in Wuhan City in China, where the virus was first discovered, as well as data from seven European locations that have peaked, including Madrid, Spain; Castile-La Mancha, Spain; Tuscany, Italy; Emilia-Romagna, Italy; Liguria, Italy; Piedmont, Italy; and Lombardy, Italy.** ... + +The analysis is based on an extensive range of information and data sources, including: + + * Local governments, national governments, and the World Health Organization + + * Government declarations on implementation of social distancing policies + + * Age-specific death rate data from China, Italy, South Korea, and the US..."" + +Projections change because the data fed into the models change (more regions included, longer baselines), and the mathematical models themselves are modified to more closely match observed events. + +All of these predictions should be taken with a large grain of salt, as they come with huge but usually glossed over (i.e. ignored) uncertainty ranges." +1532 Why does dehydration cause muscle cramps? 9 https://www.reddit.com/r/askscience/comments/fzq684/why_does_dehydration_cause_muscle_cramps/ 1586666303 fzq684 Human Body 2020-04-12 7:38:23 "It's not dehydration, the loss of fluid, that's responsible for cramping. Instead, it's what happens along with that loss of fluid. + +When you sweat or urinate a lot, you *are* removing fluid from the body. It turns out though that you have a lot of fluid just kinda sitting around between cells, and you can draw on that supply to deal with quite a bit of fluid loss. In fact, if you couldn't rely on that 'interstitial fluid', it would be possible to sweat yourself to death in an hour or so. + +So if it isn't fluid loss, what is it? Well, when you sweat or urinate, you aren't losing *just* fluid - you're also losing other stuff - proteins and ions (electrically charged atoms). The losing of ions is particularly important. Your cells depend on actively transporting ions to create an electrical gradient across the cell membrane - the inside of the cell has one charge, the outside has the opposite charge. That charge difference is very important. For example, nerve signals are sent by removing that charge difference, called 'depolarizing'. When you sweat or urinate, you lose those ions, which means nerve signals can't be sent, for instance. It isn't just nerves that depend on that charge difference, every cell does, including muscle cells. + +So, one way dehydration results in cramping is by interfering with nerve signals - a nerve may not be able to repolarize (or stop sending a signal), so it's telling the muscle 'contract, contract, contract', resulting in a cramp.* + + +*theres a small gap in the explanation regarding the contraction cycle and ATP depletion/necessity to reset myosin heads, but that's getting pretty detailed." +1533 How are viruses kept alive and bred to study them and experiment on them? Especially if they have very specific hosts... and those hosts can only be humans? 9 https://www.reddit.com/r/askscience/comments/g2803j/how_are_viruses_kept_alive_and_bred_to_study_them/ 1587011111 g2803j Biology 2020-04-16 7:25:11 "It’s been possible to grow cultured cells in the lab for decades. HeLa is the best known example, but it wasn’t the first and today there are tens or hundreds of thousands of other cultured cells lines. They are off the shelf products - you can order them from, for example, [ATCC](https://www.atcc.org/en/Products/Cells_and_Microorganisms.aspx), and the techniques for culturing them are generally straightforward. + +That means that you can often grow viruses in a cultured cell line. For example, SARS-CoV-2 and many other viruses grow very nicely in the Vero cell line ([A pneumonia outbreak associated with a new coronavirus of probable bat origin](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7095418/)), which is easy to grow and look after. You can also fairly easily take normal cells from donors (say, from tonsils, or biopsies) and viruses will often grow in those. + +Some viruses also, or preferably, grow in hens eggs that have been fertilized (“embryonated eggs”), which are fairly easy to get (again, off the shelf ordering) and not too expensive. + +If you have a suspected new virus, you’d typically try to grow it on multiple cultured cells, including Vero but usually several others, and you’d probably try normal cells and so on too. + +It’s not invariably successful. Some viruses, like [noroviruses](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5270584/), have been hard to grow on cells, and then labs may spend a lot of time searching for appropriate cell types and methods to grow them. But those are the exception rather than the rule." "That is all correct. +Often in the lab we don't use primary cells (from a donor), but an immortalized cell line because that is more convenient (you can buy the exact same oned again, it's reproducable, ect.). +Immortalized cell lines are often cancer cells that never stop reproducing. A normal cell will only divide itself a certain amount of times, however cancer cells often never stop. Which is the problem for the person with cancer, but in the lab that's great. + +If the virus/bacteria kill their host cells you have to give them new cells “to play with“. Mostly every few days. +That is called cell culture and takes up a lot of time." +1656 Why are bubbles perfectly round? 9 https://www.reddit.com/r/askscience/comments/h7ec7c/why_are_bubbles_perfectly_round/ 1591937809 h7ec7c Physics 2020-06-12 7:56:49 "If just pressure and surface tension are involved, the equilibrium shape is a sphere, because that minimizes the surface area for a given volume. + +If you add other forces, like gravity, the equilibrium shape is not perfectly spherical." If you had a cube-shaped bubble or whatever the more curved parts of it (the corners) would retract inward from surface tension, while the flatter parts would expand. Eventually you would have a round sphere again. +1657 Does immunity from a virus get remembered for longer if a recovered person is exposed continually to it? 9 https://www.reddit.com/r/askscience/comments/hldegf/does_immunity_from_a_virus_get_remembered_for/ 1593907548 hldegf COVID-19 2020-07-05 3:05:48 You did not read that immunity only lasts 3 months. No one knows how long immunity lasts. You read that antibody titers drop off after 3 months. Antibodies drop off after a few months for many viruses. Memory B cells are responsible for long term immunity. "I would be very surprised if there's data that immunity only lasts 3 months. You'd have to get a sufficient number of patients who got COVID in March, at the beginning of this wave, and follow them for 3 months and then have a sufficient number get COVID again. + + +But if your question, if re-challenge with the immunogenic agent will boost your immunity because it will stimulate your body to make the relevant antibodies and those cells get revved up to fight off the pathogen. If you keep getting exposed to it, you'll keep making antibodies to fight it off." +1658 Will related viruses compete with one another in a singular host? 9 https://www.reddit.com/r/askscience/comments/htts1b/will_related_viruses_compete_with_one_another_in/ 1595128848 htts1b Medicine 2020-07-19 6:20:48 "I don’t have much knowledge of virology outside of undergrad, but during viral coinfections you can get different types of interactions between viruses. Here’s a pretty good review for an overview: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6148187/. + +If two viruses infect the same cell, some viruses (observed at least in Newcastle disease virus and FMDV, possibly more) encode certain proteins that make that cell refractory to infection by other viruses. In coinfections, viruses also compete for host cell metabolites, and eventually one is likely to dominate over another. + +At the same time though coinfection could also enhance viral replication, with some examples in the review above. Other viruses also strictly require another virus to infect the same cell in order for them to replicate, for example with hepatitis D virus being a satellite virus that requires the cell to be infected by hepatitis B in order for the viral life cycle to progress. + +Also, for related multi-segmented viruses such as influenza, coinfection can also help generate novel strains by mixing up and packaging their eight genome segments in different combinations. This also tends to be how new influenza zoonoses occur where a new strain gains increased virulence and crosses over to a new host species. There seems to be certain patterns in which segments from different strains tend to be packaged together, but it’s still not super well-understood. + +At a more global level rather than a single cell, competition between different viruses also eventually tend to favour one type of virus to dominate. Can’t find much information so far, but mathematical modeling seems to suggest that fast-growing viruses outcompete slower ones (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4873262/)" +1659 Do people with aphasia experience dreaming differently to normal subjects? 9 https://www.reddit.com/r/askscience/comments/htyaez/do_people_with_aphasia_experience_dreaming/ 1595153768 htyaez Psychology 2020-07-19 13:16:08 "Apparently acquiring aphasia can result in losing dreaming. + +>*Aphasia with reported loss of dreaming* +A W Epstein, N N Simmons. +PMID: 6847970 DOI: 10.1176/ajp.140.1.108 +**Abstract:** +Seven patients who had become aphasic as a result of acute vascular lesions reported a loss of dreaming. The authors conclude that the dreaming process is affected when the left hemisphere neural systems related to waking language are impaired. + +And a thesis from a Univ. of Cape Town graduate student suggested that those who can dream have better language capacity than they do waking. + +>Aphasia and the presence of language in dreams +http://hdl.handle.net/11427/8044 +Theses / Dissertations > Masters +**Abstract:** +A study was done to ascertain the presence of dreams and the quality of language in dreams in patients with aphasia. 24 aphasic subjects were interviewed using Kagan's (1998) Supported Conversation for Adults with Aphasia (SCA) technique of communication. The main hypothesis investigated was that aphasic patients would experience a better quality of language while dreaming than while awake. Severity being kept constant, aphasia in its acute stage displays greater discrepancy between pre- morbid and morbid language abilities than in its recovering, chronic stage. Therefore, a secondary hypothesis was formulated whereby the difference between language in waking life and language in dreams would be more significant in acute aphasics than in chronic aphasics. Thirdly, it was hypothesized that fluent aphasics would experience less dreaming, if any, since posterior lesions have been found to correlate with cessation or reduction in dreaming. Language in dreams was found to be significantly better than language in waking life amongst the 63% of subjects who reported dreaming. Differences in trends between the categories i) acute and chronic and ii) fluent and non- fluent aphasics, that is the second and third hypotheses, did not achieve statistical significance. +**Reference:** +Timol, R. 2005. Aphasia and the presence of language in dreams. University of Cape Town." +1660 Questions about evanescent fields? 9 https://www.reddit.com/r/askscience/comments/gzrfp0/questions_about_evanescent_fields/ 1591722932 gzrfp0 Physics 2020-06-09 20:15:32 "1. There are situations where discontinuous wave models are used. For example, when considering ideal mirrors the wave is discontinuous across the mirror boundary. So we can see that perfect reflection and the evanescent wave solution can both provide solutions to Maxwell's equations. The perfect reflection solution produces a discontinuity, but how can we be sure there isn't such a discontinuity in reality? By conducting experiments. A number of experiments, such as frustrated total internal reflection, show that the evanescent wave model gives correct predictions. Thus, we conclude that the discontinuous model is incorrect (though it is still sometimes used if it makes the math easier and we know it will give the same results, as in the case of the ideal mirror). +2. The second boundary converts the evanescent wave back into a normally propagating wave. This is easy to see as all of the same boundary math works in reverse (just flip the sign on the propagation direction). So we have a normal wave turn into a decaying wave that turns back into a normally propagating wave. + +I haven't done the math in a long time, so I apologize if this is inaccurate. However, from what I recall if you examine the second interface you will get a reflect evanescent wave. This wave will return to the first interface and reflect again and so on. You could follow these reflections indefinitely, or use the homogeneous solutions to Maxwell's Equations in the three regions and the boundary conditions to solve for the limiting solution directly. Either way, you will find that the interference between the two evanescent waves creates a region with E and M fields that are not entirely perpendicular, so there is some non-zero propagation." +1661 What is the current, up-to-date recommendations regarding wearing face masks? Do they protect the wearer against catching COVID-19? 9 https://www.reddit.com/r/askscience/comments/h14x9b/what_is_the_current_uptodate_recommendations/ 1591900045 h14x9b COVID-19 2020-06-11 21:27:25 "[This](https://download.uni-mainz.de/presse/03_wiwi_corona_masken_paper_zusammenfassung.pdf) is a German paper about the efficiency of masks in the city of Jena. The first city in Germany that made masks mandatory on the 6th of april. + +In short: + +- masks are mandatory to wear inside public places +- masks are worn to protect *other* people from your breath and are not worn to protect *yourself* against the virus. You wear them to protect *other* people. Can't say this too often because it's a common misconception. + +- reduced the incidence of Corona about 23% in 20 days from the incidence in the same timespan if Jena would've not made masks mandatory (This cumulative number was calculated) +- reduced the incidence of old people in comparison to the cumulative incidence about 50% +- The cumulative number was verified after comparison eith other German cities. +- daily decline of new infections increased up to 60% + +This study says that wearing masks is in fact very effective." "properly fitted medical masks, with a clean seal on the face, worn properly will protect medical workers from their patients. + +Patients are made to wear medical masks in hospitals/clinics to protect other people from their exhalations. This can be greatly effective since the patient may be to sick to mess with the mask. + +You were told not to wear a mask, for a variety of reasons; but the honest reason has always been: you won't wear a medical mask correctly, and the hospitals need them anyway. + +Now that supplies have recovered a little and economies are reopening its clear everyone needs to wear a mask, but what mask? + +The main point of the mask is to protect people from you! +An improperly worn, non-fitting, contaminated medical mask isn't any better than a 3ply fabric mask. + +Also concider, masks with unfiltered exhalation valves are useless to this system. + +everyone wants you . . . yes you too, to wear a mask because we don't know if you are sick. While your mask may not be suitable in a medical lab, it can catch your spit, caugh, and sneezes. + +That is why they say ""even a scarf is fine"" because we're not trying to protect from some airborne contaminate, we're trying to catch the spit from when people talk. + +edit: Try not to focus on, or try to imagine situations in which someone is spitting in your mouth. The spit/caugh/sneeze is just an easy to grasp illistrarion. A shocking amount of fluid and moisture can be produced by someone while speaking. +Again the mask isn't trying to protect you from the virus its trying to catch the forward ejected fluid from you, protecting people from your fluids. Fluids which would otherwise have been spat out or particalized in the air. + +We all don't need to wear a a hazmat suits if everyone covers their damn mouths." +1662 For how long can a person who is asymptomatic unknowingly spread Covid-19 around their community? 9 https://www.reddit.com/r/askscience/comments/gk9zd1/for_how_long_can_a_person_who_is_asymptomatic/ 1589552457 gk9zd1 COVID-19 2020-05-15 17:20:57 CDC has been unable to culture virus after 10 days of shedding (unpublished data). So possibly no more than 10 days for people with covid-19. Less is known about totally asymptomatic individuals but we think shedding generally begins 2 days before onset of symptoms and for contact tracing we are looking back 5 days before onset of symptoms. So I would guess 2-10 days. +1729 Why particle accelerators are so huge? Wouldn't be possible to crush particles in a smaller and spiral structure? 9 https://www.reddit.com/r/askscience/comments/jurwun/why_particle_accelerators_are_so_huge_wouldnt_be/ 1605469150 jurwun Physics 2020-11-15 22:39:10 "The vast majority of accelerators are not that big (they can fit in a garage). It sounds like you're specifically asking about the few very large colliders around the world. So why are *those* so large? + +You use a collider rather than a fixed-target machine when you want to reach higher energies. Kinematically, the thresholds for interesting processes are lower with a collider than with a fixed target because with a collider, *all* of the kinetic energies of the two beams is available in the center-of-mass frame (because the center-of-mass frame is the lab frame). In a fixed-target experiment, there's nonzero total momentum in the lab frame, so some of the beam energy is ""wasted"" on the motion of the center of mass. + +So you build a collider when you want to study extremely high-energy processes, which generally means you want the beams to have as much energy as possible too. + +And with a collider, you'd prefer it to be circular rather than linear, so the beams will circulate around many times. If the beams circulate some thousands of times before the fill is dumped then each particle has thousands of chances to do something interesting, while in a linear collider it would only have one, so to speak. + +But if you want your accelerator to be circular, you need to steer the beam in a circle. For beams at high energies you do this with magnets. + +The radius of curvature of the accelerator (ρ), the momentum of the beam (p), and the magnetic field strengths of the main bending magnets (B) are all related to each other by + +Bρ = p/q. + +That says that the magnetic field times the radius of curvature equals the momentum per unit charge of the beam. + +So if p is fixed by your desire for maximum energy, and q is fixed by the type of particle you want in your beam, then the radius of curvature of the accelerator is inversely proportional to the magnetic field strength of the dipoles. But field strengths are practically limited by what technology is available. Superconducting dipole magnets for accelerators can currently give sustained fields on the order of ~ 1 - 10 Tesla. So if your dipole field strength is limited, but you want to maximize the energy of the beam, you need to increase the radius of curvature accordingly. That means that the collider ring needs to be bigger. + +If the magnets were stronger, you could have a beam with the same p/q (we call this the ""magnetic rigidity"" of the beam) at a lower radius. But currently we're limited by the strength of the magnets, so we're stuck with these huge rings, *if* we want to reach the highest possible energies." +1730 Are the different regions of the brain separated by actual boundaries, or did we just define them arbitrarily? 9 https://www.reddit.com/r/askscience/comments/jv219y/are_the_different_regions_of_the_brain_separated/ 1605508028 jv219y Neuroscience 2020-11-16 9:27:08 "Some areas have boundaries that are easily distinguishable, say [the cortex to corpus callosum to hippocampus](https://www.researchgate.net/figure/Coronal-section-of-the-mouse-brain-illustrating-the-main-areas-of-the-hippocampal_fig2_23668426), whereas others have more continuous borders that aren't visible by eye or with a sharp change in molecular composition, [such as the striatum and cortex](https://www.researchgate.net/figure/A-coronal-section-at-the-level-of-the-rostral-pole-of-the-mouse-thalamus-showing-the_fig1_47385473). + +A lot of regions are more historic than functionally distinct when you get down to a very detailed level, but convention is slow to catch up to new discoveries. Anatomy does reflect function very well at an overall level though." "How we subdivide the brain and name its components is a constant challenge in neuroscience. + +The first neuroscientists divided the brain **anatomically**, based on its gross (in anatomy, ""gross"" means ""visible to the naked eye"") visual appearance. This is where we get things like the lobes of the brain - frontal, parietal, occipital, and temporal - so-named for the pieces of the skull that cover them, and divided by large grooves or *sulci*. The brain is covered in sulci, but some of these ""wrinkles"" are larger and more consistent across people than others: the big ones are the longitudinal sulcus (which separates the brain in half), the central sulcus (separates the brain front-from-back, separates frontal and parietal lobes), and the Sylvian fissure (AKA lateral sulcus - runs along the side of the brain, separating the temporal from the frontal/parietal lobes). [Here's](https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/LobesCaptsLateral.png/1200px-LobesCaptsLateral.png) a basic image showing the lobes. There's also the [insula](https://i2.wp.com/human-memory.net/wp-content/uploads/2019/10/Insular-cortex-1.jpg?resize=551%2C335) (Latin for ""island""), which is a ""fifth lobe"" that hides underneath the frontal and parietal lobes. + +But anatomy only takes us so far. As we continued to study the brain, doctors such as Broca noticed that lesions (injuries) that affected multiple lobes could have singular effects - Broca's area is a region of cortex containing parts of both the frontal and temporal lobes that is important for speech formation. So we can began regions of the brain **functionally** - i.e. based on what they do - in addition to their gross anatomy + +A little over a century ago, a young researcher began using cutting edged microscopy and visualization techniques to study the **cytoarchitecture** of the brain (literally, ""cell architecture"") - basically the micro-anatomy, the distribution and density of individual brain cells in a specific cortical region. This researcher - Brodmann - identified over 50 regions of the cortex that had unique cytoarchitecture. At first blush most of these divisions looked arbitrary (just look at [this](https://en.wikipedia.org/wiki/Brodmann_area#/media/File:Brodmann_areas_3D.png) map of Brodmann areas overlaid on a gross model of the brain), but upon zooming in and looking at the cytoarchitecture [the boundaries are surprisingly distinct](https://www.researchgate.net/figure/Cytoarchitecture-of-areas-17-and-18-A-and-the-dorsally-and-ventrally-adjacent_fig27_279432787) (this image shows the transition between Brodmann areas 17 and 18, located in our occipital lobe and important for vision; note the change in concentration and size of black dots, which mark cortical neurons). Brodmann areas became the *de facto* means of sub-dividing the brain for decades throughout the early-to-mid 20th century, and it still shapes our terminology to this day. + +As technology continued to improve, we gained a better ability to identify specific molecules (e.g. chemicals, neurotransmitters, proteins, cell markers, specific DNA, etc.) that only belonged to specific sets of neurons, so we could divide the brain **neurochemically**. The brain is very complex and does many different things, and there are hundreds of thousands of molecules that facilitate its functions. A big category is neurotransmitters - molecules that neurons use to signal each other when firing action potentials. We can divide neurotransmitters into two major categories: excitatory (makes neurons more likely to fire) and inhibitory (makes neurons less likely to fire). This is an area I'm not very familiar with so I'll just share [this](https://media.springernature.com/m685/springer-static/image/art%3A10.1038%2Fs41380-019-0406-4/MediaObjects/41380_2019_406_Fig1_HTML.png) image of the major pathways of two neurotransmitters and note that many regions of the brain can be defined by which neurotransmitters they produce and respond to. + +Last example I'll point out is a **functional unit**: e.g. mouse barrel cortices are discrete chunks of sensory cortex in mice, with each ""barrel"" linked to an individual whisker. Barrel cortices are as close to a ""closed system"" in the brain as we can find (speaking generally of course), meaning we can more easily isolate, define, and simulate it since it primarily receives input from one thing (the whisker). This has made barrel cortices a popular target in neuroscience, and there are plenty of figures showing how mouse sensory cortex can be divided into functional ""barrels"" (e.g. [this publication's Figure 1](https://www.pnas.org/content/114/33/8853)). Other examples of functional units include the classic ocular dominance columns, a famous neuroscience experiment where Hubel and Wiesel discovered that the left and right halves of our visual field (i.e. what we see) are processed in the brain in alternating stripes of cortex; in [this](https://www.researchgate.net/figure/Pattern-of-ocular-dominance-columns-revealed-in-a-flattened-representation-of-monkey_fig6_226249123) figure, the dark stripes represent parts of the cortex that receive information from the right eye, and the white stripes receive from the left eye. These columns exist within a Brodmann area and have similar neurochemical makeup, so their main distinguishing factor is where they receive information from. There are also [place cells](https://www.youtube.com/watch?v=lfNVv0A8QvI) in the hippocampus. There is a region of cortex that we believe acts as a ""map"" for our local surroundings; as we pass through an area (such as the center of a hallway), a cell corresponding to that area will become active. This region acts like a smartphone map app: the region (screen) is always the same, but our brain overlays different maps over it based on where we are, similar to how you can move around a map on an app to show different parts all on the same smartphone screen. + +We can continue dividing the brain using all kinds of other criteria. We can divide it based on cellular phenotype - for example Purkinje cells are only found in the cerebellum - or by what part of the [embryonic neurochord](https://en.wikipedia.org/wiki/Cerebrum#/media/File:EmbryonicBrain.svg) the brain region derived from, and so on. + +I'll close by saying that different neuroanatomists will divide the brain based on their questions, speciality, experience, and even their personal preferences and biases. There is no one consensus map of the brain, no universal system for categorizing and subdividing it. Common well-known brain divisions (such as lobes) are based on gross anatomical boundaries, but these are only a crude approximation and are of limited use in modern neuroscience. Therefore, in practice, neuroanatomists use a combination of ""boundaries"" - chemical, anatomical, functional, systematic, etc. - to define their specific regions of interest. Neuroscientists in a common field (e.g. visual system physiology) will often develop a common system, but this will rarely translate well for another field (e.g. systems cognitive processing)." +1731 Could it be possible that someone can't produce antibodies after they are infected with COVID-19? 9 https://www.reddit.com/r/askscience/comments/jut2bw/could_it_be_possible_that_someone_cant_produce/ 1605472848 jut2bw COVID-19 2020-11-15 23:40:48 Well I guess you should change the formulation of the question..the fact that many people do not produce antibodies is the reason why they get sick and potentially die. When you introduce a vaccine this is nothing but a stimulus to organism that hopefully induces it to produce antibodies. The percentage of efficacy is now rated at 90%(Pfizer mRNA vaccine) -biotechnology student Yes being negative in a lab check for antibodies doesn’t mean you are not potentially infected (this is the reason why medical laboratories search for specific SARS cov-2 RNA). When you are not symptomatic it only tells us that virus infection is not causing deleterious immuno-response or maybe the concentration of virus is low( potentially it could not be able to replicate properly). +1732 Would the vaccines being developed for C-19 also work on the common cold corona viruses? 9 https://www.reddit.com/r/askscience/comments/jw6iay/would_the_vaccines_being_developed_for_c19_also/ 1605663585 jw6iay Biology 2020-11-18 4:39:45 "The new vaccines force our body to create a very specific protein that COVID 19 has so the immune system can attack it. In theory, if another common cold virus contains that protein, maybe. + + +I don't know how common that specific protein is among the other related viruses though." "Not really. They may not even work for mutated strains that occur in the future, similar to how we need a different flu vaccine every year. + +What may be beneficial is the ton of research for COVID may help lead to a vaccine for the common cold." +1923 How do vaccines against bacteria work? 9 https://www.reddit.com/r/askscience/comments/nz6ss8/how_do_vaccines_against_bacteria_work/ 1623620636 nz6ss8 Medicine 2021-06-14 0:43:56 "First of all, a search of the [CDC](https://www.cdc.gov/lyme/prev/vaccine.html) reveals that there is no approved vaccine for Lyme disease yet. Did you mean something else? Of the other pesky microbes, neither syphilis nor tuberculosis have ones so far as I am aware. As for other bacteria, it is more important to get vaccinated not so much because our body cannot fight them and get rid of them but that it has trouble doing so for people with weak immune systems eg. Babies and that we want to protect ourselves from ever getting severely ill with them. + +Some vaccines against bacteria work by the addition of something called a conjugate. We basically link an antigen that causes a weak response ( the salient one we want our immune system to recognize and fight) with one that causes a strong response (the conjugate). The adaptive immune system now protects us against both because of the conjugate and activates strongly and produces antibodies that actually target the salient antigen. This is a clever way of 'tricking' the immune system to create a response it would otherwise not be interested in" "Vaccines against bacteria work on the same basic principle as those against virusses. They teach the immune system that it needs to attack certain proteins on the outer wall of virusses and bacteria. The immune system then recognises these, produces antibodies and this way those bacteria and virusses become a target for the immune systems destroyer cells that kill them. + +Lyme is caused by a special bacteria (borrelia) a spirochete that can escape your immune system: 1) it changes its outer proteins all the time so your immune cells don't recognize it anymore (same with vaccine induced antibodies) 2) it can penetrate and hide inside your immune cells making it invisible for your immune system 3) it can go dormant in an inactive state and hide for years in that state. + +So the answer is the same as for H.I.V. (Aids virus) => it escapes your immune system by adapting and evolving all the time which makes it very hard to find a good vaccine." +1924 How effective is the Johnson and Johnson (J&J, Janssen) vaccine against the Delta variant of COVID-19? 9 https://www.reddit.com/r/askscience/comments/o1xiuw/how_effective_is_the_johnson_and_johnson_jj/ 1623937261 o1xiuw COVID-19 2021-06-17 16:41:01 My GP told me today that it's 30% effective against Delta. He basically advised me to stop exercising outdoors because of it. I have found no studies online indicating that number, so I'm not sure where he's getting it. But in his practice (Los Angeles), he is seeing lots of patients who received J&J test positive for the Delta variant. +2019 Are there people who are naturally immune to the flu? 9 https://www.reddit.com/r/askscience/comments/razla8/are_there_people_who_are_naturally_immune_to_the/ 1638884906 razla8 Human Body 2021-12-07 16:48:26 "Immunity implies that you have antibodies against something. Humans are not known to be ""naturally immune"" to any virus. + +However, you can be *genetically resistant* against something. That could be a modification in a receptor that the virus uses to enter the body, that the virus can't use anymore. + +In 2016 a study showed that people in Iran with a certain mutation in the IL-1β-gene were less likely to be infected by Influenza A. IL-1β is a cytokine that helps mobilize your immune system in the beginning of an infection - gives you fever and makes certain immune cells move to places. + +https://pubmed.ncbi.nlm.nih.gov/27155288/" The virus mutates pretty much every year. So we can't say for certain but it's extremely extremely unlikely. Certain body conditions such as how possums have very low body temp making it impossible for the virus rabies to infect them. +2020 Does the spin of atoms have any effect on the macro scale? 9 https://www.reddit.com/r/askscience/comments/q2mby9/does_the_spin_of_atoms_have_any_effect_on_the/ 1633532697 q2mby9 Physics 2021-10-06 18:04:57 This is what causes ferromagnetism, actually. Iron atoms have a large number of unpaired electrons and therefore when large domains of atoms in a piece of iron are spontaneously aligned with each other, they have a net significant magnetization. "Disclaimer: Quantum mechanics is weird. Electrons and nuclei have spins as an abstract property, but under no circumstances do we actually believe they are spinning like a ball. + +The spin direction leads to a magnetic moment. So if all of your spins are pointed up, there will be a strong magnetism to your ball. Probably so strong that it would immediately stick to a passing iron object like a car. + +Another way that we could answer this is, what if electrons and atoms didn't have a spin? If this were the case, matter would be more like what we call a boson, an object with an integer amount of spin angular momentum (or integer multiple of hbar). Light is a boson. Bosons don't really interact with each other in the same way as things like protons and electrons (Pauli exclusion principle), like how light doesn't really repel light but can just pass through it. If matter had no spin, all electrons and protons would fall to their lowest energy level and not repel each other, making matter stop taking up so much space and causing everything to fall apart. + +Short, intermediate-level video on the topic. +[https://www.youtube.com/watch?v=EK_6OzZAh5k](https://www.youtube.com/watch?v=EK_6OzZAh5k)" +1534 Is there folk etymology in sign language? 8 https://www.reddit.com/r/askscience/comments/g5gr5i/is_there_folk_etymology_in_sign_language/ 1587481167 g5gr5i Linguistics 2020-04-21 17:59:27 [deleted] I don't know if this will answer your question specifically, but there's a book called Everyone Here Spoke Sign Language by Nora Ellen Groce about how the early settlers of Martha's Vineyard carried the recessive gene for hereditary deafness. As a result about 1/4 of the population of the island was deaf, and everyone spoke sign language. Even hearing people found it useful, for example seafarers would sign between their boats via telescope when they were far away to shout. This was before American Sign Language existed, so the Vineyarders developed their own sign language largely in isolation. If I remember correctly (been a while since I read the book) a lot of ASL was highly influenced and/or developed from Vineyard sign. +1535 Can cats catch the new coronavirus? 8 https://www.reddit.com/r/askscience/comments/g157ir/can_cats_catch_the_new_coronavirus/ 1586869673 g157ir COVID-19 2020-04-14 16:07:53 There is [some evidence](https://theconversation.com/can-cats-really-get-or-pass-on-covid-19-as-a-report-from-belgium-suggests-135007) that cats [can catch Covid-19](https://www.theguardian.com/world/2020/apr/01/cats-can-infect-each-other-with-coronavirus-chinese-study-finds), and potentially develop symptoms, but experts say that pet cats aren't likely to contribute much to the spread of the disease to people. ">Does it mean that other felines can catch the disease as well? For example, our common domestic cat? + +Yes, [a recent study](https://science.sciencemag.org/content/early/2020/04/07/science.abb7015) found that housecats can be infected, and shed the virus in feces and nasal secretions. + +From the abstract: +> We found that SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and ducks, but ferrets and cats are permissive to infection. We found experimentally that cats are susceptible to airborne infection." +1536 How do patients that have recovered from Covid, test positive again? 8 https://www.reddit.com/r/askscience/comments/fzaqqn/how_do_patients_that_have_recovered_from_covid/ 1586626386 fzaqqn COVID-19 2020-04-11 20:33:06 "The media has made a lot of fuss about this, but few scientists are convinced that those repeat-positives are truly reinfections. Rather, they’re probably false negative tests taken between two true positives. We know that false negatives are fairly common with the available tests, so this is by far the simplest explanation. + +> There remains a lot of uncertainty, but experts TIME spoke with say that it’s likely the reports of patients who seemed to have recovered but then tested positive again were not examples of re-infection, but were cases where lingering infection was not detected by tests for a period of time. ... Instead, testing positive after recovery could just mean the tests resulted in a false negative and that the patient is still infected. “It may be because of the quality of the specimen that they took and may be because the test was not so sensitive,” explains David Hui ... + +—[Can You Be Re-Infected After Recovering From Coronavirus? Here's What We Know About COVID-19 Immunity](https://time.com/5810454/coronavirus-immunity-reinfection/) + +It’s also possible that some are false positives. I don’t know what the false-positive rate is, but given that we’re somewhere around 10 million tests, a 99.9% specificity rate would give us some 10,000 false positives. If some of those were on recovered patients, it would look like a reinfection." +1663 How do birds spot food? Specifically how do they find seeds that have been scattered or in a bird feeder? [Zoology] 8 https://www.reddit.com/r/askscience/comments/h118nv/how_do_birds_spot_food_specifically_how_do_they/ 1591888605 h118nv Biology 2020-06-11 18:16:45 They see food and they go to it. Birds have good vision and hearing so they're able to spot seeds pretty easily and go to it. This is a natural behaviour that most birds have displayed in nature and in urban landscapes (bird feeders). +1664 If something bleaches, where does the colour go? 8 https://www.reddit.com/r/askscience/comments/hc22md/if_something_bleaches_where_does_the_colour_go/ 1592578356 hc22md Chemistry 2020-06-19 17:52:36 "In brief, colour in things like toys, printed objects, hair, etc. comes from molecules that have particular bonding patterns that result in their absorbing certain wavelengths of light. We perceive this as colour. + +When those objects are ""bleached"", those molecules get destroyed (or at least rearranged) so that the bonding patterns responsible for the colour are no longer present." The chemical compounds which previously interacted in the visual range (creating what we perceive and colour) were chemically altered, usually by photochemical reaction with UV light, to become new compounds which do not interact in in this part of the EM spectrum. +1665 How do satellites get power at night? 8 https://www.reddit.com/r/askscience/comments/h927s9/how_do_satellites_get_power_at_night/ 1592170346 h927s9 Engineering 2020-06-15 0:32:26 "The short answer is they use batteries. + +Longer answer, let's do a little math: low-Earth-orbit satellites typically have about 45 minutes of ""day"" followed by 45 minutes of ""night"". A one square meter of high-efficiency solar panel generates about 300 watts of power when in direct sunlight, and so if half of that is used to power the spacecraft and half is used to charge the battery, you'd need a battery that can hold 150 watts * 45 minutes = 100 watt-hours of electricity. + +Lithium batteries have a storage capacity of about 500 watt-hours per liter of battery volume. + +So at the end of the math: for every square meter of solar panel it uses, a satellite needs a battery about the size of a teacup. Not a big problem. + +https://www.sciencedaily.com/releases/2019/03/190328112544.htm#:~:text=Today's%20commercial%20lithium%2Dion%20batteries,400%20watt%2Dhours%20per%20liter. + +https://www.solar.com/learn/space-based-solar-vs-conventional-solar-how-are-they-different/#:~:text=These%20panels%20can%20reach%20up,commercial%20solar%20panels%20can%20reach.&text=Satellites%20in%20space%20are%20also,maximize%20their%20absorption%20of%20sunlight." "Most satellites have pretty low energy requirements. It's not much of a challenge to have some batteries cover that for the 40 minutes or so it's out of direct sunlight. + +[https://en.wikipedia.org/wiki/Batteries\_in\_space](https://en.wikipedia.org/wiki/Batteries_in_space)" +1666 How do survival plans/zoo breeding work for animals groups with long term bonds, like primates? 8 https://www.reddit.com/r/askscience/comments/hvmmyr/how_do_survival_planszoo_breeding_work_for/ 1595389967 hvmmyr Biology 2020-07-22 6:52:47 "Genetically it may be that all of them are very closely related. In rare species of birds SSPs use computer software to ""pick"" the mates so that they are genetically as unrelated as possible. But on an emotional basis I'm not sure of an answer. In the wild an ape leader is challenged by a younger, stronger one. I'm not sure what happens in zoos but it sure it a good question." +1667 I read that Cockroft and Walton split the atom by bombarding Lithium with accelerated protons, producing an end result of alpha particles. Given the result of charged particles, could it be used as an energy source for electricity? If not, why not? 8 https://www.reddit.com/r/askscience/comments/gztgsc/i_read_that_cockroft_and_walton_split_the_atom_by/ 1591728955 gztgsc Physics 2020-06-09 21:55:55 "In principle yes, in practice, probably not for a while at least. + +The reaction Cockroft and Walton observed is essentially p + ^7 Li into 2 alpha particles, [which yields a net energy of around 17.2 MeV per reaction](https://en.wikipedia.org/wiki/Aneutronic_fusion#Candidate_reactions). [The helium 4 nucleus is actually far more stable than both Lithium and some of the Berylium isotopes](https://upload.wikimedia.org/wikipedia/commons/5/53/Binding_energy_curve_-_common_isotopes.svg) so you can actually gain energy from them splitting, unlike most other isotopes lower in mass than iron. So, in an ideal case, you could definitely get energy from the reaction, and in some ways it would be more advantageous than typical deuterium deuterium fusion since most of that energy would be in the alpha particles, which being charged are much more straight forward to extract energy from compared to neutrons (and less messy from a radiation standpoint). This kind of process, where energy from the reaction is deposited mainly in charged particles, rather than neutrons, is called an Aneutronic Fusion process. + +The problem comes when you try to make this into a practical power source, due to several issues. You need to actually start the reaction, which initially requires an energy input, just as you need a lighter to start a fire, and you want this to be low as possible for a given reaction. The reaction also has a finite cross section so not every proton you throw at the Lithium will react, further reducing efficiency, so unless you can generate interactions with sufficiently high energy EXTREMELY efficiently, you won't ever got more power out than you have to put into the system. As it stands we have yet to ever break even with D-D fusion, and this is by far the easiest fusion process to get going when it comes to the cross sections and required plasma temperatures of the reactor (apart from D-T fusion, but that is limited by the availability of Tritium). Other processes will be several or 10s of times more difficult, hence making it a practical energy source is probably not within technological possibility, though there are a number of studies that are exploring the possibilities of using novel schemes. For example: + +https://iopscience.iop.org/article/10.1088/1361-6587/59/2/025011" It could be, yes. Although most attempts at using light charged particle reactions for power are focusing on DD and DT fusion, because hydrogen on hydrogen has the lowest Coulomb barrier. +1668 Crows are all over the world, but where are crows naturally from and what kind of effect did they have as an invasive species? 8 https://www.reddit.com/r/askscience/comments/hbfxg7/crows_are_all_over_the_world_but_where_are_crows/ 1592491454 hbfxg7 Biology 2020-06-18 17:44:14 There are a *bunch* of [different crow species](https://en.wikipedia.org/wiki/Crow) (ravens are in the same genus, they're just big crows) that are native throughout the world. The only species I know of that has really become an invasive problem is the [house crow](https://en.wikipedia.org/wiki/House_crow#Invasive_species), native to Southern Asia and invasive in parts of Europe. It hasn't been much of a problem because competition with native species has kept it in check. I've been reading a book called Crow Planet, where the author asserts that Crows originate from Kazakhstan, and that they have been expanding across the globe alongside our species for millenia. It's a good read: [https://www.amazon.com/Crow-Planet-Essential-Wisdom-Wilderness-ebook/dp/B002GJRYWU](https://www.amazon.com/Crow-Planet-Essential-Wisdom-Wilderness-ebook/dp/B002GJRYWU) +1669 If electric cars are possible, is electric space travel also possible? 8 https://www.reddit.com/r/askscience/comments/hukec6/if_electric_cars_are_possible_is_electric_space/ 1595248214 hukec6 Astronomy 2020-07-20 15:30:14 "Short answer is that yes! and we have been doing that since the late 60's already. + +So I guess before we go into the details it might be interesting to understand why you would want that. If you want to propel yourself in space you need to expel something with mass ([1]). You can think of it as needing something solid to push against. Usually on a rocket engine you use gases. The thrust you get is proportional to how fast the exhaust gas is coming out and how much of it you are ejecting per second. To accelerate this exhaust it takes energy. In fact rocket engines are some of the most powerful machines created for their size. In fact a single space Shuttle rocket engine is producing 5 GW of power, nearly half that of an entire nuclear power plant. So anyway in order to get propulsion in space you need two things: something with **mass** and a source of **energy**. + +The mass part is easy. You just get a tank and put something in it. This mass if often called ""reaction mass"" or propellant. The energy part is harder. There are not that many ways to generate energy that we know of. + +In normal rocket engines the strategy is to burn something. Since this is a chemical reaction we call those chemical engines. However since in space you don't have oxygen you have to bring that with you too. This is how all rockets works. They burn some sort of fuel (hydrogen or kerosene most of the time) which releases a lot of energy in the form of heat. This heat is then used to accelerate the combustion gases to high speed by making them flow through a nozzle. The classic ""rocket bell"" shape is always more of less the same because it's the most efficient way to convert heat into speed. The clever bit with chemical rocket is that the tanks are used to store both the reaction mass and the energy. + +So why would you want to replace that kind of very elegant (and overall fairly simple) system? Well one of the issue is that in space you don't really have petrol stations. So you have to bring all your fuel and oxidizer with you from the beginning. But the more fuel you pack the more thrust is needed to accelerate the spacecraft. Which means you need even more fuel. This is described by the [Tsiolkovsky rocket equation](https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation) which is named after a Russian teacher who already had big ideas about space travel in 1903. This is why rockets are more than 90% propellant by mass at take off. + +To try to cheat the system you can accelerate the propellant to higher speed (remember the thrust is proportional to mass **and** speed). This requires more energy but can save you a lot of fuel. For chemical engines it means you need to find chemical reactions that have the most energy per unit of mass. The highest practical one is hydrogen with oxygen, which is why it is so popular for rockets. With that reaction you top of with a exhaust speed of about 4.5 km/s which is why Tsiolkovsky already mention it in his book. So how can you get to even higher speeds? The issue with chemical reaction is that they have a set amount of energy per atoms. + +One solution that people thought about very early was to use electricity to accelerate the propellant. Tsiolkovsky saw the issue and wrote about it as early as 1911. Goddard, one of the father of rocketry in the US already thought about it in 1906 and patents ideas of electric propulsion for rockets in 1917! Saying that you will accelerate mass to super high speed with electricity is nice and all but how do you do it in practice? + +One easy way is to use electricity to heat up a gas instead of burning it. You can try using resistors (like a toaster oven) but you quickly realize that you can only heat it up so much before the heating elements melt and that in practice you end up less hot than most chemical reactions. Another way you can heat it up is to create an electrical arc through the gas. That way you can get to higher temperatures. This is what we call an arcjet and it can reach exhaust speeds of about 6 km/s before stuff starts to melt, which is not bad. + +But there are even better ways to accelerate thing with electricity. You can use direct electric and electromagnetic forces. However those forces only work on particles that have an electrical or magnetic charge. Gases usually don't really react in any significant way if you apply and electric or magnetic field to them. So you kind of have to mess with them to get them to cooperate. One way is to remove some of their electrons. Plucking one or two of those negatively charged electrons away leaves you with a positively charged atom that we call an ion. In order to remove electrons there are a multitude of ways: you can circulate a high enough current through a gas, hit it with microwaves or RF, get it hot enough... Once you have done that ionization step you end up with a plasma, which is sort of a gas made of positive ions, negative electrons and some leftover neutral atoms. Since the particles are electrically charged this plasma can be manipulated by using electric and magnetic fields. One of the easiest way to accelerate the ions is to have a grid charged very negatively in front of the plasma. If you remember from high school physics, opposite charges attracts each other. The ions in the plasma are attracted to the grid and accelerate towards it, since the grid is full of holes a lot of them miss the grid and are ejected at very high speeds. [Here is what it looks like](https://upload.wikimedia.org/wikipedia/commons/8/8e/NEXIS_thruster_working.jpg) you can see the grid and the blue ion plume. With that kind of systems (adding more grids and other gadgets) you can reach exhaust speed of more than 50 km/s! This is really amazing because it reduces the propellant requirements by a lot. A first version of that grid system was flown in 1964 on a NASA mission called [SERT-1](https://en.wikipedia.org/wiki/SERT-1)! + +There are tons of other electric thruster type, one of the most popular right now are [Hall thruster \(pic from my old lab\)](https://i.dailymail.co.uk/i/pix/2015/10/27/19/2DD846A500000578-3292291-image-a-17_1445975027742.jpg) first developed in the USSR, to [PPT \(pulsed plasma thruster\)](http://www.al.t.u-tokyo.ac.jp/PPT_plasma.jpg) which first flew in space on Zond-1 in 1964 toward Venus, [FEEP thrusters](https://www.researchgate.net/profile/David_Krejci/publication/336578017/figure/fig1/AS:814506347356160@1571204854020/IFM-Nano-Thruster-left-IFM-crown-emitter-during-ion-emission-right-from-Ref-10_Q640.jpg), [MPD thrusters](https://d3i71xaburhd42.cloudfront.net/655b5a72a4c953000134e08f2ed3e46bd4e10eff/109-Figure4-1-1.png)... They all have slightly different ionization and acceleration mechanisms. + +Anyway I guess the question is why don't we use them more often? One of the issue is that they need electrical energy. As explained at the beginning it would take several nuclear power plant to lift the space shuttle at lift off. So it's not really an option when trying to fight Earth gravity. Or at least not until batteries or wireless energy transmission significantly improves. Even in space we mostly only have access to solar power which is not that much. As a result the thrust of those systems is really small. Typically we talk about millinewtons of force, basically the weight of a few sheets of paper. The result is that a spacecraft with an ion thruster will do 0 to 100 km/h (60 mph) in about 3 days... That doesn't sound like a lot but since the propellant consumption is so low it can keep that up for months; in 30 days is will reach 1000 km/h and in a year more than 10 000 km/h! + +So this kind of system is great if you are limited on mass and are not in a hurry. + +Anyway I probably got a bit overexcited since it's rare that I have questions about my specialty. But if you have any follow up questions please don't hesitate, I am on holiday right now and I have a few beers ready. + + + + +[1] I know people will say photon rockets and solar sails, but let's try to keep it simple." "As far as we know (and I mean this very strongly) + +(*I.e. [reactionless drives](https://en.wikipedia.org/wiki/Reactionless_drive) probably aren't possible, and we definitely have no possibility of building one right now*) + +for space propulsion you **always** need to eject reaction mass from your spaceship (e.g. the chemical rockets that we're all familiar with, though there are other and perhaps better ways to do this.) + +**or** + +you need to interact with particles that are moving in space (e.g. [solar sail](https://en.wikipedia.org/wiki/Solar_sail) ) + +**or** + +you need to interact with fields in space (e.g. [electrodynamic tether](https://en.wikipedia.org/wiki/Space_tether) ) + +. + +So one useful possibility is to use electricity to eject reaction mass from your ship, + +but if you're doing that, + +**when you run out of reaction mass to eject, then you need to get more before you can make any more maneuvers.** + +(Newton says [TANSTAAFL](https://en.wikipedia.org/wiki/There_ain%27t_no_such_thing_as_a_free_lunch) )" +1670 How successful is social work and assistance in reducing poverty in the long term? 8 https://www.reddit.com/r/askscience/comments/gyxe5g/how_successful_is_social_work_and_assistance_in/ 1591614753 gyxe5g Social Science 2020-06-08 14:12:33 "Is reducing poverty the goal? Don't social workers help people with bad mental problems, enabling them to live on their own and have a better quality of life? + +​ + +Some people can't contribute to society and are a resource drain, fiscally speaking, that doesn't mean helping them live a better life is ineffective." "It depends on the specific program; some are indeed pretty inefficient and many others don't have the resources to do suitable follow-up to determine whether they have any long-term value. It's hard to measure something like ""reducing poverty"" so as a proxy, most programs measure how much money the relevant government systems are not spending compared to how much the program costs. But some have very startlingly high returns on investment: [Head Start](https://www.headstartva.org/assets/docs/Head_Start_Return_On_Investment_Brief_LAS-yv.pdf) claims a national ROI over time of $7 to $9 per $1 spent; well-run community health programs focused on reducing [community causes of health issues](https://www.healthleadersmedia.com/clinical-care/social-determinants-health-program-generates-roi) such as [homelessness](https://www.healthcarefinancenews.com/news/what-montefiores-300-roi-social-determinants-investments-means-future-other-hospitals) sometimes report up to 200-300% ROIs." +1671 Do manatees get goosebumps? 8 https://www.reddit.com/r/askscience/comments/h789qh/do_manatees_get_goosebumps/ 1591914985 h789qh Biology 2020-06-12 1:36:25 "Not an expert on manatees or anything, but this depends on whether or not manatees have the arrector pili muscle on each of their hair follicles. Humans get goosebumps when the arrector pili on each of our hairs are contracted. + +It is very possible that manatees lost the arrector pili on their hair follicles, as the hair they do have has evolved for a purpose that does not require them to get goosebumps. Goosebumps are a vestigial holdover from when we had thick body hair, as puffing up our hair would help trap warm air, or make us look scarier to threats, etc. Many mammals Puff up their hair in this way. Manatees get warmth in other ways such as a thick layer of blubber, and only have a small number of tiny, thin hairs that cannot trap warmth and don't have much use to have the ability to get goosebumps. the thin and sparsely distributed hairs they do have are used to [detect when something is touching them. ](https://www.hakaimagazine.com/news/shaving-manatees-science/)" Goose bumps are caused by arrector pili muscles, which as far as I can tell are present in manatees (though interestingly, they have been lost in some other aquatic mammals like seals and sea lions; [Yochem and Stewart 2009](https://www.sciencedirect.com/science/article/pii/B9780123735539001243)). So I suppose they might be able to get goose bumps, though I can't find any sources that explicitly document this. It is worth noting that sirenians have some pretty interesting modifications to their hairs though. Specifically, they have no sweat or sebaceous glands, and all of their hairs contain nerves to allow mechanical sensation, effectively making them completely covered in whiskers ([Sarko et al. 2011](https://pubmed.ncbi.nlm.nih.gov/21534996/)). +1672 Why arent't airplanes coating shaped as a golf ball since this expedient improve their aerodinamic? 8 https://www.reddit.com/r/askscience/comments/h80wz2/why_arentt_airplanes_coating_shaped_as_a_golf/ 1592024196 h80wz2 Engineering 2020-06-13 7:56:36 "So there's two types of boundary layers, turbulent and laminar. Boundary layers like to start as laminar then after some distance (due to momentum and energy transfer) the layer transitions to turbulent. Turbulent boundary layers, while larger, have more energy contained and like to ""stick"" to the surface much longer than laminar flow. Golf balls are dimpled to create a turbulent boundary layer around the ball which results in a drastically smaller wake region and increases the range of the ball (when compared to a smooth round ball). + +If i'm understanding the question correctly, you're asking if dimpling the fuselage would be more efficient. Dimpling the fuselage, contrary to conventional understanding, actually increases the drag of the overall aircraft due to the dimples increasing vorticity. The issue with it is that the fuselage is not a primary lifting device, so dimpling the fuselage would have no positive effect on the overall efficiency of flight. Wings do use a similar principle in that some aircraft have what are called ""vortex generators"" which do the same as dimpling the golf ball. The generators incite a turbulent boundary layer on the leading edge of the wing which allows for the air to ""stay attached"" to the upper surface of the wing for a longer distance as compared to conventional laminar flow. + +[Vortex Generators](https://en.m.wikipedia.org/wiki/Vortex_generator) + +[Research on Subject](https://broncoscholar.library.cpp.edu/bitstream/handle/10211.3/185255/KlaibAnthony_McNair2017.pdf?sequence=1)" The other two people have given really good answers on why dimpling doesn't help planes, but a third reason is just that adding dimples to a plane's surface would be a lot more expensive than just using sheet aluminum. +1673 Why can't you get the HPV (gardisal) vaccine after the age of 26? 8 https://www.reddit.com/r/askscience/comments/hwsxmi/why_cant_you_get_the_hpv_gardisal_vaccine_after/ 1595555531 hwsxmi Medicine 2020-07-24 4:52:11 [deleted] +1733 How did nasa know the voyagers left the solar system? 8 https://www.reddit.com/r/askscience/comments/jw8ra9/how_did_nasa_know_the_voyagers_left_the_solar/ 1605672058 jw8ra9 Astronomy 2020-11-18 7:00:58 """The solar system"" here means [heliopause](https://en.wikipedia.org/wiki/Heliosphere), the point where the solar wind of charged particles from the sun tapers off between 75 and 90 times the distance between Earth and the sun. Both Voyagers have tools to measure the solar wind, powered by good old bomb manufacture waste product plutonium-238 and still communicating with Earth even after all this time. + +You could make a case that the solar system includes the truly vast and very widely spaced comets in the Oort cloud, which Voyager 1 will not enter [for 300 years](https://solarsystem.nasa.gov/solar-system/oort-cloud/overview/) and will not exit the outer edge of the cloud for 30,000 years." +1734 How did humans survive for so long without clean water to drink? 8 https://www.reddit.com/r/askscience/comments/jvd734/how_did_humans_survive_for_so_long_without_clean/ 1605554753 jvd734 Human Body 2020-11-16 22:25:53 "A very very large number did die from cholera, dysentery and typhoid among other diseases. + +Partly, we bred fast enough to exceed these deaths. + +Partly, we built up some resilience against these specific diseases. A typical Jogjakarta resident can drink the tap water there without becoming ill - an Australian with no history of exposure to that water would likely fall ill from just half a litre. + +And thirdly, we built up medical knowledge over time. Sometimes, this is presented in a the form of a supernatural or religious edict (e.g. Judaism's concept of 'kosher' food is essentially about 'don't eat food combinations that spoil really quickly'). Other times it's just simple rules like 'drink water from a running source, not a stagnant one'." "Loads of people died from dirty water, and still do even today. If you look at the [WHO top 10 global causes of death](https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death), diarrheal disease is still listed up there in 2016, although it has moved down quite a bit since the year 2000. + +Disease such as cholera, giardiasis, dysentery, and typhoid were all curbed following the [improvement of sanitation practices](https://en.m.wikipedia.org/wiki/1854_Broad_Street_cholera_outbreak) in the developed world, though remain a threat in disaster stricken areas and in developing countries around the world. + +In fact, beer and wine may owe their worldwide popularity to the fermentation process that killed many pathogens lurking in the water, rendering it safer to drink than water that was contaminated by harmful microorganisms. + +So, long story short, many people died until we figured out that we could boil water to make it safe for consumption." +1735 Why are their salts, sucrose and cholesterol in the covid vaccine? 8 https://www.reddit.com/r/askscience/comments/kf822k/why_are_their_salts_sucrose_and_cholesterol_in/ 1608244708 kf822k COVID-19 2020-12-18 1:38:28 "As others have mentioned, salts and sucrose are commonly found in vaccines because they help keep it stable and mimic the blood that the vaccine will be injected into. + +As a microbiologist, perhaps the most exciting part of the COVID vaccine is actually the cholesterol and other lipids that are in it. These lipids are like little packages that deliver mRNA into cells. You can put any mRNA into the packages and have a potential vaccine, pending clinical trials, of course. Just like how you wouldn't open an unmarked package, your cells won't take in just any lipid nanoparticle. The special mixes of lipids that Pfizer/BioNtech and Moderna are using have been optimized to be taken into cells and transfer their payload very easily." "The various salts are in there to balance the pH (edit: also the isotonic balance as pointed out by another user) as closely as possible with human blood, and according to an article I read, the sucrose is there to somehow provide protection during the freezing process. They also add a tiny bit more saline right before injection in order to further balance the pH. + +The lipids, cholesterol, and other fats make up a protective fatty shell (similar to naturally occurring cell walls) protecting the chunks of mRNA. These little protective fat balls dissolve in the body and are expelled or absorbed like any other fatty cells we consume. + +Other than the polyethylene glycol (which is a common food additive) and the bits of mRNA, I don't think there's anything on the ingredient list that isn't naturally occurring in our food already." +1736 "Why do micro-interactions between qubits not ""collapse"" the wave functions (under Copenhagen interpretation) when things like heat and sound can?" 8 https://www.reddit.com/r/askscience/comments/jveco5/why_do_microinteractions_between_qubits_not/ 1605558260 jveco5 Physics 2020-11-16 23:24:20 "What you want from a quantum computer is coherence. Whenever a quantum state interacts with the environment (i.e. becomes entangled with it), it decoheres. A fully isolated system would never decohere, but you could also never measure anything. So what you want to have in reality, is a system that is isolated as much as possible but still interacts with the environment. That way you can apply things like Hadamard transformations (which essentially only rotate a vector in Hilbert space) and keep the quantum state ""alive"" as long as possible. Note that the gate does not collapse anything - it is not a measurement. In the same way an electron flying through a magnetic field will see it's quantum state change, but it won't collapse until you measure it in a detector. After all transfromations are done, you do the measurement that collapses the state at the very end." +1925 Is there a way to predict all the products of nuclear fusion? 8 https://www.reddit.com/r/askscience/comments/o1l5u3/is_there_a_way_to_predict_all_the_products_of/ 1623893830 o1l5u3 Physics 2021-06-17 4:37:10 ">Is there a way to predict all the products of nuclear fusion? + +Yes, just enumerate all possibilities consistent with conservation laws. Any exit channel which can happen, will happen some of the time (although the cross section may be small). + +That alone doesn't tell you anything about how probable each possibility that is. For that, you need cross sections. + +>is there any discernible pattern to predict the products of the fusion of any two arbitrary nuclei, say, oxygen-17 and calcium-44 for example? + +You could write down all possible final states and look up cross sections for all of them. Many (possibly all) of them probably won't have been measured before, and even if they have, not over all energies. For cases that haven't been measured, you'd have to turn to theory to calculate them. + +In practice, for a given energy, there are probably only a handful of possible final states that are of importance, so you'd just focus in on those and forget the other, low-probability reactions." "In practice two heavy elements rarely fuse. Especially in stellar nucleosynthesis. + +""Fusion"" as we refer to it usually just means addition of one of a few really common nuclei or particles. Anything up to an alpha particle can readily fuse in the right conditions, a proton, neutron, alpha, electron, or gamma. This really limits the possible reactions, in fact I can list them! + +(a,p) + +(a,n) + +(a,g) + +(p,n) + +(p,a) + +(p,g) + +(n,g) + +(n,p) + +(n,a) + +And electron capture. + +These reactions can happen on almost any nucleus, though they become endothermic past the iron peak and require extra energy. You can slap these on any isotope, so as an example, 14N(a,p)17O. After that as the other answer states, you have to measure the reactions to know much about probability. Though there are some theoretical formalisms that do an OK job of predicting." +1926 Are we going to need vaccine booster shots? 8 https://www.reddit.com/r/askscience/comments/nzosen/are_we_going_to_need_vaccine_booster_shots/ 1623682943 nzosen COVID-19 2021-06-14 18:02:23 "There are two possible reasons for booster shots: Waning immunity, the rise of variants that are resistant to the first vaccines, and the combination of the two. + +The waning immunity doesn't look like it's going to be a big problem. Vaccinated people seem to have good, solid, long-lasting immunity, extrapolating from close to a year of followup now. Possibly immunity will wane over a longer period -- say, 10-20 years -- so that a booster might be helpful well into the future. That's not a major concern now. + +So far, none of the variants seem to have actually escaped vaccine immunity. People who are vaccinated (at least with the vaccines that give the higher level of protection) have levels of immunity that can still handle even variants that have a degree of escape. That is, there are some variants that need 4-10 times higher levels of immunity to be protected, but those vaccines easily hit that level and exceed it. + +>“They give people a huge amount of antibody, so even if you have a fivefold reduction in reactivity in your serum to some of these variants, you’re still left with a bunch of antibodies that can bind and block” the virus, said Richard Webby, an infectious disease expert at St. Jude Children’s Research Hospital, citing the mRNA vaccines in particular. + +--[Vaccines seem to work well against coronavirus variants. It’s also complicated](https://www.statnews.com/2021/05/13/vaccines-work-variants-complicated/) + +But new variants are continuing to arise, and vaccine immunity is slowly waning. It's starting to seem likely that at some point in the future, the trends of escape variants and waning immunity will cross, and more vaccinated people will be susceptible to re-infection. + +(This isn't likely to be a black-and-white thing. We're not likely to see a variant that is completely resistant to immunity. Instead, we might see something like 60% vaccine efficacy instead of 90%. More people might have low-level infections, while still be protected against severe disease.) + +How long will this take, if it does happen? Part of it depends on the number of new infections -- the more infections, the more opportunities for variants to appear and undergo natural selection. So the faster people worldwide can get vaccinated now, the longer it will take before new escape variants appear. + +Some people are suggesting that this fall may see enough variants to justify boosters (to be fair, these people tend to be executives of the vaccine companies). Others think it might take several years. The present variants have probably moved a little faster than they were expected to -- I think the tentative guess would have been that we'd be a couple years into the pandemic before things like the B.1.617.2 (""Delta"") variant were widespread -- but we are a year and a half in and the vaccines are still hanging tough. Anywhere from 2-5 years wouldn't surprise me. + +The good news is that it looks as if a single booster with a single variant gives really broad, strong immunity against many different variants ([Moderna Announces Positive Initial Booster Data Against SARS-CoV-2 Variants of Concern](https://investors.modernatx.com/news-releases/news-release-details/moderna-announces-positive-initial-booster-data-against-sars-cov)), and even a booster with the original vaccine amplifies immunity to a point that there's great immunity against a wide range of variants ([Vaccination boosts naturally enhanced neutralizing breadth to SARS-CoV-2 one year after infection](https://www.biorxiv.org/content/10.1101/2021.05.07.443175v1)). + +So it seems unlikely that we will need repeated boosters -- just one booster should give wide protection -- and we almost certainly will not need annual boosters; this definitely isn't like influenza. And if and when variants do appear, whether it's 2 or 5 or 10 years in the future, the boosters are already prepared for them. Meanwhile, doing everything we can to suppress current global infections will have big payoffs in the future by reducing the tempo and risk of variants." +2021 Could we take a picture of JWST with Hubble? 8 https://www.reddit.com/r/askscience/comments/rbedxn/could_we_take_a_picture_of_jwst_with_hubble/ 1638925075 rbedxn Astronomy 2021-12-08 3:57:55 It could be *detected* by Hubble very easily, but it can't be *resolved*. That is, it would appear as a point of light, since it would be much smaller than a pixel on Hubble's cameras. +2022 How do deciduous trees exchange gases in the winter? 8 https://www.reddit.com/r/askscience/comments/rb3des/how_do_deciduous_trees_exchange_gases_in_the/ 1638896603 rb3des Biology 2021-12-07 20:03:23 "They slow their metabolism waaaaaaaay down so that they don't need their leaves. Basically, they hibernate. + +This is why pruning on fruit trees is done in winter. The sap is flowing very slowly, so less sap is lost before the cut seals over." Not really. The only reason they need gas exchange is to make fruit, new leaves and stuff but in winter, when they loose it, as someone mentioned above ,they turn down metabolism (note: metabolism is sum of all chemical reactions in an organism.)and thus they don't need to exchange gas as basically no photosynthesis as it already is stocked on glucose converted to scratch +1537 What causes shockwaves to form on an airfoil when the airflow is supersonic? Why does this cause flow separation? 7 https://www.reddit.com/r/askscience/comments/ejtemm/what_causes_shockwaves_to_form_on_an_airfoil_when/ 1578121856 ejtemm Physics 2020-01-04 10:10:56 "Shockwaves form around an airfoil because the flow is disturbed (an obstacle is in the way) and the information can not be sent fast enough (because supersonic flow) to other molecules of air. + +Wikipedia explains it a lot better than I do : +>When an object (or disturbance) moves faster than the information can propagate into the surrounding fluid, then the fluid near the disturbance cannot react or ""get out of the way"" before the disturbance arrives. + +Because of this, the pressure, temperature and density have a huge gradient near the obstacle, creating a shock. After the shockwave, the flow is subsonic." "In supersonic flow, that is when the overall air speed is faster than the speed of sound, shocks will form at the front and back of a wing like [this](https://i.imgur.com/Pt7AeTV.jpg). These are [oblique shocks](https://en.wikipedia.org/wiki/Oblique_shock) and the angle of them will depend on the Mach number i.e. ratio of flow speed to the local speed of sound. The shocks can be thought of as the air not being able to move out of the way fast enough, as pressure waves that allow it to 'know' that the wing is there are moving slower than the wing itself, [like this](https://i.stack.imgur.com/q1g36.jpg). Wings that fly at these speeds are specially designed to ensure these shocks are in certain positions and don't become [detached](https://en.wikipedia.org/wiki/Shock_wave#Bow_shock_(detached_shock)), which would significantly increase drag, and to ensure shocks don't form on the wing itself. A well designed supersonic wing shouldn't have to worry about flow separation as supersonic flow is able to turn with [expansion fans](https://en.wikipedia.org/wiki/Prandtl–Meyer_expansion_fan) rather than separate like subsonic flow. + +Where separation is a concern is in transonic flows, where the Mach number is between around 0.75-1.0. In this regime is is possible for flow to become supersonic as it flows over an aerofoil, and shocks will form at the back of this supersonic region like [this](https://i.stack.imgur.com/aWEWY.jpg). This flow quickly becomes very complicated and the interaction of the boundary layer with the shock is an ongoing area of research. The shock wave can thicken the boundary layer and make it more susceptible to separation later on, or the shock can directly cause separation if it is able to sustain enough flow turning." +1538 If you had an accident and your fingers lose their fingerprints temporarily, would these fingerprints be the exact same when they heal back? 7 https://www.reddit.com/r/askscience/comments/fztuno/if_you_had_an_accident_and_your_fingers_lose/ 1586684298 fztuno Human Body 2020-04-12 12:38:18 "Yes. +there was a famous case of a bank robber caught in the act, who burned all the skin from his fingertips with his welding torch to delete his prints. He wanted to make it impossible for police to track his other break-ins. +Enough of his original prints grew back through the scars to prove his identity." The ring finger on my right hand was trapped in a door when I was 18 months old and is approximately 7mm shorter than the same finger on my left hand. I have a small scar diagonal on that finger which goes right through the centre swirl of my fingerprint. The swirl is almost uninterrupted, there is only a minute distorted line through it where my scar sits but the fingerprint itself is pretty much the same. Only a little stretched with a few millimetres missing so could be comparable with my fingerprints before the accident happened. +1539 How do the vitamin and mineral compositions of vegetables stay so consistent, despite such varied growing conditions? 7 https://www.reddit.com/r/askscience/comments/g2b98v/how_do_the_vitamin_and_mineral_compositions_of/ 1587026872 g2b98v Earth Sciences 2020-04-16 11:47:52 "Macronutrients like calcium don't just randomly enter the plant, they are actively taken up by regulated transport proteins in the root and their cellular concentration is tightly controlled, too. [Thor, 2019](https://www.frontiersin.org/articles/10.3389/fpls.2019.00440/full) provides a short review. + +So, even if there is more than enough calcium in the soil, the plant won't take up more than it needs. If there is not enough, growth will be stunted. An example for a plant disease caused by calcium deficiency is blossom end rot in tomatoes. + +Such a depletion can happen if you grow the same plant in the same soil year after year. It's why we fertilize." "Imagine a drastic shortage of bicycle tires. Do bicycle makers start leaving the front tires off their bikes' front wheels? Do they switch to making unicycles? No; in the short term at least, they make fewer bicycles. If there's a massive surplus of tires the next year, do they make millions of tricycles? Again no. The ratio of metal to rubber stays about the same. + +Most plants operate that way too, rather inflexibly. If an important nutrient is scarce, the plant grows smaller or perhaps doesn't grow at all, but what does grow still has roughly enough of that nutrient. If another nutrient is abundant, the plant cannot do much with it, perhaps can store some of it, but mostly either excretes it or leaves it on the table. + +What may happen is that other plants, plants that have evolved to use more of nutrient A and less of nutrient B, will grow enthusiastically in places where B is scarce and A is abundant, and crowd out a plant that has evolved to need little A and plenty of B. Some parts of the world don't live on sweet potatoes, for roughly that reason. + +Disclaimer: there is far more complexity in real life. I'm just trying to illustrate a general rule, one that probably has exceptions or at least gets bent. Nature is messy." +1540 How the water that we drink is distributed inside our body? 7 https://www.reddit.com/r/askscience/comments/g1mwlr/how_the_water_that_we_drink_is_distributed_inside/ 1586934038 g1mwlr Biology 2020-04-15 10:00:38 "It goes into the stomach, then the intestines, and is absorbed through the walls of the intestines into the bloodstream. Your body is quite good at this, which is why poop (from the end of the digestive tract after the water has been absorbed) is usually solid, while vomit (from the beginning) is liquid. + +Once it's in the bloodstream, it distributes out based on diffusion. About 2/3 of the water in your body is inside of your body's cells. Of the remaining water, 3/4 of it is in the fluid around your cells. The final part, (about 1/12 of the total) is in your bloodstream. + +This is obviously constantly changing, based on sweating, breathing, and eating/drinking...and one of the main things the kidneys do in the body is adjusting exactly how much water is retained by the body vs excreted (as pee). All the blood in the body flows through the kidneys, and they're constantly ""deciding"" how much of the water in it to drain off into the bladder and how much to keep in the bloodstream. Exactly how they do this would take a few hours of university lectures to explain, but there are sensors in your body measuring exactly how much fluid volume there is in your blood and how concentrated the blood is. If they sense anything outside of a very small range, they send chemical signals to the kidneys that adjust." "How much you absorb is going to vary depending on how hydrated you already are. All water that is absorbed will eventually be filtered through the kidneys (unless its used for hydrolysis I actually tried to look up some value for how much that is but couldn't find anything. Its likely out weighted by the water produced by metabolism which apparently can amount to up to 350 milliliters of water a day: [https://www.20questionsaboutwater.com/what-is-hydrolysis](https://www.20questionsaboutwater.com/what-is-hydrolysis) ) + +​ + +Edit\* Found some data: [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4207053/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4207053/) + +See figure 1 + +Average Water inputs: Drinking 1575 mL, Food 675 mL, Metabolic 300 mL + +Average water outputs: Insensible 450 mL, Respiratory 300 mL, Urine 1600 mL, Feces 200 mL + +​ + + [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908954/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908954/)" +1541 Are there any diseases for which a vaccine exists but humanity isn't trying for herd immunity? 7 https://www.reddit.com/r/askscience/comments/g0sx8n/are_there_any_diseases_for_which_a_vaccine_exists/ 1586816130 g0sx8n Medicine 2020-04-14 1:15:30 There are plenty. For example, rabies vaccine for humans goes to people at higher risk of exposure (veterinarians, cavers, etc). There are other vaccines which are targeted at the at-risk population with no aim at herd immunity. "To give one more example: there's a vaccine for exposure to anthrax-based chemical weapons. + +While the mass vaccination programs use safe vaccines, the anthrax one (at least the one that existed ~20 years ago) was not completely safe. It had side effects. Consequentially it was used very, very sparingly." +1542 Since the CoronaVirus has a limited lifecycle outside of human body (up to 3 days on different surfaces) can the masks left unattended be reused? 7 https://www.reddit.com/r/askscience/comments/fubn2w/since_the_coronavirus_has_a_limited_lifecycle/ 1585931907 fubn2w COVID-19 2020-04-03 19:38:27 The newest CDC guidelines contain several reuse strategies, the easiest - if you still have supplies, that is - is to dispense 5 masks/respirators to staff. Have them number them and or the bags they go into, using one mask per day and then placing it into the paper bag (please be careful not to contaminate the inside of the mask). After the fifth day, you start over at mask #1. The research from UNMC suggests that after about 3 days they don't seal well and need to be tossed, but with the rotation that could get you several weeks of use. "It is not ideal to reuse masks, but CDC has released guidelines essentially stating that masks should be stored in a ""clean, breathable container such as paper bag."" [CDC guidelines](https://www.cdc.gov/niosh/topics/hcwcontrols/recommendedguidanceextuse.html) + +Indeed some articles are stating that COVID-19 can live up to 3 days on certain surfaces so that in theory [leaving them to sit out in a well-ventilated area](https://www.insider.com/can-you-reuse-a-face-mask) is a possibility given the shortage. + +Lastly, studies from [Stanford researchers](https://news.stanford.edu/2020/04/01/researchers-show-how-to-decontaminate-reuse-n95-masks/) and others show that treating *N95* masks at constant 158 F (70 C) for 30 minutes can also inactivate viruses (i.e., H1N1/H5N1) without damaging the functionality of the equipment. However, these are all not ideal or ""endorsed"" and must be rigorously followed to ensure effectiveness. + +As it's been pointed out to me, the Stanford study does not include data on heat inactivation of coronaviruses explicitly (rather *E. Coli*), but could be used as by healthcare providers if absolutely necessary. + +Edits: Specified N95 masks from the Stanford study and changed language from ""baking"" to treating at constant temp for further clarification. Also thanks to u/bookerTmandela for clarifying information about the lack of research on heat inactivation of coronaviruses." +1543 If quarks are point-like particles and also probability waves, how are scientists able to differentiate between protons and neutrons or able to add/remove protons or neutrons from the nucleus? Wouldn't the atomic nucleus be a probability-blur of up/down quarks, gluons, and (maybe) mesons? 7 https://www.reddit.com/r/askscience/comments/g1vfx5/if_quarks_are_pointlike_particles_and_also/ 1586968562 g1vfx5 Physics 2020-04-15 19:36:02 "Protons and neutrons have different quark content, therefore they have different electric charges and also very slightly different masses, which is enough to distinguish them. + +It is true that a nucleus is a ""probability blur"", but that does not mean that we cannot add or remove particles from it. We do not pick particles from the nucleus with microscopic tweezers one by one. We rather shoot particles at it with the right energy so that we can break it apart to smaller nuclei and/or elementary particles, or hope that what we shoot ""sticks"" to it." "Protons and neutrons are ""probabilistic blurs"" of quarks over a length scale of less then 1 femtometer, yes. + +They're pretty easy to tell apart because protons have electric charge and neutrons don't. And we are able to add/remove protons and neutrons from nuclei." +1544 AskScience Meta Thread: COVID-19 and reaching people in a time of uncertainty 7 https://www.reddit.com/r/askscience/comments/fjt707/askscience_meta_thread_covid19_and_reaching/ 1584395540 fjt707 COVID-19 2020-03-17 0:52:20 "I was wondering how all of this is supposed to die out? Like lets say 90% of people are in ideal quarantine conditions for a certain period of time and the number of cases steadily drops. + +Even if there are only a handful of people worldwide who are contagious wouldn't that number just spike back up again once we go back to living our lives normally? If so does that mean the only thing that can bring us back to living normally is a very effective treatment option/a vaccine that is at least a year off? + +I apologize if this has been asked before, I tried my best googling/looking through threads and FAQ's on here" "I keep seeing stuff from the CDC saying masks don't work for the general population. Yet the Korean Medical Association is saying to wear masks even if healthy. + +*The Korean Medical Association’s guidelines advise wearing face masks when outside, for sick and healthy people alike, especially in crowded places like public transit.* + +*Choi Jae-wook, a preventive medicine specialist at Korea University Hospital, told The Korea Herald that the Drug Safety Ministry’s revised guidelines, asking asymptomatic individuals not to wear face masks, were “unsupported by medical opinions.”* + +http://www.koreaherald.com/view.php?ud=20200305000800 + +*The KMA also said that not only people who have symptoms associated with the new coronavirus, but also healthy people, should wear the protective masks to prevent any further virus infections.* + +https://www.koreatimes.co.kr/www/nation/2020/03/119_286132.html + +Masks are scarce right now. Is this recommendation not to wear a mask perhaps meant not to cause any sort of panic? The Chinese and the Koreans are beating this outbreak (despite patient 31 in Korea) and if you look at pictures it appears most everyone on the streets is wearing a mask. Why is that? *edit- these two questions are more rhetorical and I am not asking for speculation. It's more of an expression of frustration.* + +I live in the Seattle area and am very well aware *now* of social distancing (what a difference a week makes). I know the line from the CDC on masks but the CDC is not necessarily the end all, be all in medicine and they appear to be conflicting with other associations recommendations on the mask issue. + +I'm not asking for advice here on if one should wear a mask. I'm wondering why there is such a conflict of information on something so potentially profound and important. + +edit- slight tweaks to try to comply with rules + +additional edit- I want explanations for this: + +https://www.researchgate.net/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic + +https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440799/ + +https://www.theguardian.com/world/2020/mar/17/face-mask-coronavirus-covid-19-facts-checked + +https://www.nytimes.com/2020/03/17/opinion/coronavirus-face-masks.html + +https://www.scmp.com/news/hong-kong/health-environment/article/3050689/how-make-your-own-mask-hong-kong-scientists" +1674 In a post covid-19 world, in which we have a vaccine and virtually no one has covid anymore, would we have to worry about new outbursts of the virus, just like there are occasional outbursts of various diseases such as ebola and influenza? 7 https://www.reddit.com/r/askscience/comments/gz3ams/in_a_post_covid19_world_in_which_we_have_a/ 1591636029 gz3ams COVID-19 2020-06-08 20:07:09 "Probably, yes. + +And to be sure, the flu happens all year, around the world. It just flourishes when it's colder, either due to preferential environment or the activities of the population. + +Also, the flu vaccines don't fight all strains, nor are the vaccines permanent. Statistics and analysis predict the strains that might be problematic to drive the seasonal vaccinations. If additional strains of covid-19 that develop or get discovered, there may be that complexity, too." "We don’t know, but perhaps a better comparison would be measles. Most Western countries have *almost* eliminated measles, but there enough reservoirs and low-vaccination pockets that travelers can intermittently trigger new small(ish) outbreaks. It needs constant vigilance from public health orders, but it’s not something that average people worry about on a day to day basis. + +That’s really a best-case (but probably achievable) outcome for COVID-19." +1675 Why can't we throw lightweight things very far away? 7 https://www.reddit.com/r/askscience/comments/h0zc5u/why_cant_we_throw_lightweight_things_very_far_away/ 1591882212 h0zc5u Physics 2020-06-11 16:30:12 "Air resistance, basically. The force of friction depends on the shape of an object and how fast it's going - it doesn't depend on how massive it is. By Newton's Second Law (F=ma), if two objects with the same shape and speed but different masses, the less massive one will decelerate faster. To be the same shape, but have less mass, you typically have an object that's less dense. Things like feathers and cotton wool have lots of empty space in them, so they have a big surface area and feel a lot of air drag for their mass. + +Of course, F=ma works the other way too - heavier objects are more difficult to *accelerate* too, so it takes more effort to throw with your arm. + +Generally, you want something with a bit of weight to it so that air drag deceleration isn't too big, shaped to minimise its cross-sectional area to further reduce air drag, but still light enough that you can get a decent acceleration with the force of your arm. A javelin is a good example - it's very thin, so it reduces the area that's hitting the air." Air resistance has been mentioned, but even in a vacuum there'd be another limit - the mass of your own arm and hand. Even holding nothing there's a limit to how fast you can move your arm. So while you could throw an apple many times the distance you can throw a bowling ball, you won't be able to throw a piece of cotton many times the distance you can throw an apple. +1676 What would happen if all the micro-organisms on and in your body suddenly disappeared? 7 https://www.reddit.com/r/askscience/comments/hr3s2x/what_would_happen_if_all_the_microorganisms_on/ 1594741200 hr3s2x Biology 2020-07-14 18:40:00 "Well, in truth we are not sure about that. + +However, it can be safely said that if you didn't live in a bubble so to speak, the consequences could be terrible, possibly, fatal. + +Excluding the ways our microbiome helps our metabolism and stimulates our immune system, simply by being there, it is preventing other, potentially dangerous microbes from settling in. The sudden loss of this dynamic ecosystem could lead to harmful microbes flooding the body and overwhelming the immune system." "This has been addressed experimentally using [""germ-free animals""](https://en.wikipedia.org/wiki/Germ-free_animal): a laboratory mouse can be delivered by c-section into a sealed, sterile environment breathing only filtered air and eating sterilized food. These mice never come into contact with any microbes during their life. + +Germ-free animals have various medical/scientific uses, but to answer your question a germ-free animal is fine as long as they don't leave their sterile bubble (underdeveloped immune system). Apart from needing vitamin K supplements (normally our gut biota makes vitamin K for us), germ-free animals appear normally healthy with some interesting quirks, for example they have no tooth decay and minimal body odor- both normally caused by bacteria." +1677 Do toothed wales digest bones, if they eat seals? 7 https://www.reddit.com/r/askscience/comments/hv4lsd/do_toothed_wales_digest_bones_if_they_eat_seals/ 1595325032 hv4lsd Biology 2020-07-21 12:50:32 Trying to figure out the answer to this took me to the Wikipedia page on [ambergris](https://en.wikipedia.org/wiki/Ambergris), a hardened slurry of sperm whale bile and squid beaks. Apparently, the squid beaks are normally vomitted before they encounter the hindgut. Surely part of the answer for dissolving bones includes evolving digestive systems that can withstand stronger acids... +1678 Does an ACE inhibitor have an effect on ACE2 receptors? 7 https://www.reddit.com/r/askscience/comments/htsf2m/does_an_ace_inhibitor_have_an_effect_on_ace2/ 1595122965 htsf2m COVID-19 2020-07-19 4:42:45 "Hey, I was actually searching about that to answer a question of my physiology homework. I’ll explain what I understood, someone please correct me if I’m wrong. + +So the ACE inhibitor inhibits ACE, obviously, but what is ACE? The ACE is an enzyme central to a system that helps to regulate the volume of blood. The ACE will convert angiotensin I to angiotensin II, which will activate various mechanisms that will raise your blood pressure. Therefore, the ACE inhibitor is used to inhibit ACE, meaning there will be less angiotensin II available and your organism won’t raise your blood pressure as much as it did. + +Okay, but what does this have to do with ACE2? ACE2 is another enzyme that will break angiotensin II to angiotensin 1-7, countering the ACE effect and helping to reduce blood pressure. The catch is that many studies suggest that your body has a balance of ACE and ACE2 activity. So, when the action of ACE is inhibited, ACE2 is more expressed. + +Considering all that, patients treated with ACE inhibitors probably have a higher quantity ACE2 in their bodies, which means the virus would have more pathways to enter the cells, making them more susceptible to infection and complications. + +However, there is another possibility! It is known that ACE2 has anti-inflammatory properties, so there is another hypothesis suggesting that the increase of ACE2 would be a good thing, protecting those individual from major complications regarding inflammatory responses. + +Also, there are studies that contradict the idea that ACE inhibition leads to increased ACE2 expression, so that’s another important point of uncertainty. + +I’ll try to find the paper I read and link it here + +Hope I could help, stay safe!" +1679 "How long can a body part ""be asleep"" before damage is done?" 7 https://www.reddit.com/r/askscience/comments/h16kat/how_long_can_a_body_part_be_asleep_before_damage/ 1591904961 h16kat Biology 2020-06-11 22:49:21 "Depends on the degree of crush. If you take a pliers to a nerve it will take seconds to irretrievably destroy it. A traumatic nerve injury in a car crash can run the spectrum from very mild to wrecked. + +Most of the time however you squish a nerve a little because you sat on it or rested on it and it starts to tingle. You “shake it out” and it goes away. + +What really changes when this happens is that the local blood vessels get squashed interrupting blood flow within the squished part of the nerve. The nerve then loses its ability to send electrical signals to you up in your brain. You perceive that absence of information as tingles and pain snd so forth. + +By and large those signals are enough to tell you that you’re doing it, or to wake you up if it happens while you’re asleep. + +In my practice I regularly see people - often those who had taken something that would tend to keep them asleep - who have inadvertently smooshed a nerve for even a small number of hours, who will never regain function in the nerve in question." +1680 How does the Maillard reaction brown meats with low carb content? 7 https://www.reddit.com/r/askscience/comments/hu1vbu/how_does_the_maillard_reaction_brown_meats_with/ 1595170986 hu1vbu Chemistry 2020-07-19 18:03:06 "Amino acids are present in all meats, because they're protein. Additionally, all meats contain sugars, as you can see in the link to the chicken breast. + +The Maillard reaction is the reaction between those two chemicals, and so the process works the same for chicken as all other things. It doesn't take much. + +The Maillard reaction is also responsible for browning of other foods, like bread crust." I don't know anything about this reaction so take this with a grain of salt but most extracellular proteins in eukaryotes are heavily glycosylated (and moreso in complex animals). This puts sugars and proteins in close (even intramolecular) contact. I would guess this is why this reaction occurs in e.g. chicken breast. +1681 What causes the symptoms of pox diseases? 7 https://www.reddit.com/r/askscience/comments/gzkdk2/what_causes_the_symptoms_of_pox_diseases/ 1591697962 gzkdk2 Medicine 2020-06-09 13:19:22 The pustules are caused by dead white blood cells, bacteria and tissue accumulating in blisters due to the prolonged immune response against the virus attacking the epidermis. Blisters are caused by fluid accumulation under epidermis. The symptoms are essentially the immune system responding to the virus. In terms of evolution, symptoms could be due to the facilitating of viral spread but there isn't a favourable outcome for this reason in terms of natural selection and virus survival due to most humans gaining lifelong immunity from just one case of chickenpox. However, with a case of chickenpox there is a chance of getting shingles which is from inactive virus in nerve tissue. Due to vaccination, most pox viruses are essentially eradicated. +1682 If fossil fuels once were a part of the carbon cycle, why is it bad when we emit the carbon back into the air? 7 https://www.reddit.com/r/askscience/comments/gzgyt8/if_fossil_fuels_once_were_a_part_of_the_carbon/ 1591681482 gzgyt8 Earth Sciences 2020-06-09 8:44:42 The key here is time / rates. We are extracting carbon (whether that is from coal, which represents fossilized terrestrial plant material, or oil/gas, which represents fossilized photosynthetic marine microorganisms, i.e. algae, etc) that was removed from the carbon cycle gradually over millions to hundreds of millions of years of deposition, and then instantaneously (within the context of geologic time at least) putting it back into the atmosphere. +1683 Is it possible to catch more that one virus in the same time? 7 https://www.reddit.com/r/askscience/comments/h7kvhl/is_it_possible_to_catch_more_that_one_virus_in/ 1591969207 h7kvhl Human Body 2020-06-12 16:40:07 "Yes, absolutely. Different viruses have differnt affinities of cells. You can have multiple viral infection going on at the same time at any point. One of the main causes of death in HIV patients is influenza. + +You have HIV killing off the immune response of the host, giving the flu virus chances to cause more damage. You can have the flu and herpes at the same time, just as general example." It's funny because technically you always have more than one virus at the same time as the virus mutates when replicating. There are some quite interesting articles which say a virus is really 'a cloud' of similar viruses, some of them even new! That's why a virus can slightly differ from 'the same' virus in other region. Also that is why they usually use more than one treatment for a virus so that if some duplicates have developed resistance for a treatment they can't duplicate and therefore make the treatment useless. +1684 Why is the rate of positive COVID-19 tests numbered so differently depending on the day of the week? 7 https://www.reddit.com/r/askscience/comments/hxah12/why_is_the_rate_of_positive_covid19_tests/ 1595626076 hxah12 COVID-19 2020-07-25 0:27:56 Testing in the USA follows a distinctive weekly cycle, with more tests being processed and reported on weekdays and fewer on weekends, producing a jagged shape in the graphs +1737 Does naturally magnetisted magnetite(lodestones) occur on other planets? 7 https://www.reddit.com/r/askscience/comments/irgkrz/does_naturally_magnetisted_magnetitelodestones/ 1599930962 irgkrz Planetary Sci. 2020-09-12 20:16:02 "Probably? + +So, the first question is: what causes lodestone to be magnetized? We don't know. Only a little bit of the magnetite on Earth is actually magnetized, and Earth's magnetic field isn't strong enough to magnetize lodestone. Theory is that it's caused by lightning strikes. + +[https://en.wikipedia.org/wiki/Lodestone](https://en.wikipedia.org/wiki/Lodestone#:~:text=The%20leading%20theory%20is%20that,than%20buried%20at%20great%20depth) + +Do other planets have lightning? Lightning requires an atmosphere around a planet with weather. It seems very likely that those conditions exist elsewhere, although technology doesn't exist to actually detect extrasolar lightning, and even determining if a rocky planet has an atmosphere is a bit dodgy. + +So, there you go." +1738 How are trajectory adjustments made to far earth objects? How long does it take before these probes or rockets respond to commands from earth? 7 https://www.reddit.com/r/askscience/comments/jvxfus/how_are_trajectory_adjustments_made_to_far_earth/ 1605634933 jvxfus Engineering 2020-11-17 20:42:13 "I know a little bit about commanding the mars rover, which is about 3 1/2 minutes away at lightspeed. + +Basically, they schedule a set of commands with stop points for verification of status. + +So the schedule will be like ""Move rover 200m due south, then stop and wait for confirmation, then turn 90deg west, wait for confirmation, then deploy arm"" + +The confirmation points will be where the status of the vehicle is checked with sensors and cameras. Basically, they need to make sure they travelled due south for 200m, and didn't get stuck on a rock, or turned one way or the other by inconsistent terrain etc. + +Communication with further objects like deep space vehicles takes a lot longer, but has the same basic principles. Most really far objects like deep space satellites etc. are largely one way transmitting their data, and don't really get many instructions or change course etc." +1927 Is oxygen percentage the same across all layers of the atmosphere? 7 https://www.reddit.com/r/askscience/comments/o30irx/is_oxygen_percentage_the_same_across_all_layers/ 1624051143 o30irx Earth Sciences 2021-06-19 0:19:03 "To the seawater question, different gases have different solubilities. This relationship is governed by Henry’s Law. + +In terms of temperature, all (I think) gases become less soluble as the temperature increases, because Henry’s constant changes with temp. I don’t remember off the top of my head which (of O2 and N2) has a greater temperature dependence (greater slope)." "[Wikipedia has a graph](https://en.wikipedia.org/wiki/File:Msis_atmospheric_composition_by_height.svg) based on [this model](https://ccmc.gsfc.nasa.gov/modelweb/models/msis_vitmo.php). The first ~100 km are pretty well mixed. Above that single oxygen atoms (instead of regular O2) become important. Go even higher and they get replaced by helium and a bit of hydrogen. + +> Another question is why does seawater have a higher percentage of nitrogen and oxygen? + +Compared to what?" +1928 Why are there no odd number CPUs? 7 https://www.reddit.com/r/askscience/comments/nz1xom/why_are_there_no_odd_number_cpus/ 1623606915 nz1xom Computing 2021-06-13 20:55:15 "It's not required. + +Other than the somewhat pedantic example of single core CPUs, there have been triple core CPUs in the past. The AMD Phenom II line of CPUs included triple core models, for example. + +Often, lower core CPUs are actually models with more physical cores, but where in testing not all cores reach the required level of performance (or work at all). So some cores are disabled to create a lower tier model. The aforementioned Phenom II triple core CPUs were created in this way, as quad cores that didn't live up to specifications and had one core disabled. + +In some cases, if manufacturing yields are high enough and too few chips with these defects are made, a manufacturer might opt to take a perfectly functional CPU and lock a number of cores to sell it as a lower tier unit. This is mostly a marketing decision at this point. + +As for why there aren't more CPUs with an odd number of cores. In some cases the reason might be technical. For example if certain resources (such as cache memory) are shared between multiple cores, it may not be possible to disable just one core, but it becomes an all-or-nothing thing for that set of cores. + +In other cases, it's likely for marketing reasons. There's often not much benefit to be had in diluting the market with too many models. If you're already shipping 6- and 8-core models, adding a 7-core chip in between those two won't help you much and might make your lineup harder to understand by consumers." "The Wii U used a triple-core CPU called ""Espresso"". Espresso was built as a triple-core from the start as can be seen from images of it, it's not a quad-core with a core turned off. + +https://forum.beyond3d.com/threads/wiiu-cpu-espresso-die-shot.53736/" +1929 Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology 7 https://www.reddit.com/r/askscience/comments/o15kdn/ask_anything_wednesday_economics_political/ 1623852019 o15kdn 2021-06-16 17:00:19 +1930 Baking soda and vinegar to clean a drain? 7 https://www.reddit.com/r/askscience/comments/o19qxw/baking_soda_and_vinegar_to_clean_a_drain/ 1623863108 o19qxw Chemistry 2021-06-16 20:05:08 "The point of this mixture are not the pH of the mixture or any reaction of vinegar or baking soda with the clogging material. + +The vinegar protonates the carbonate to carbonic acid, which decomposes to water and carbon dioxide. + +You might remember the latter as being gaseous. + +So, vinegar and carbonate react with each other, gas evolves, pressure builds up (which is why you have to plug the drain), gas *pushes* the clogging material away. + +The actual declogging is purely physical." "I agree. You're not likely to get a perfect mixture so there will be some excess, but mixing bicarb and vinegar is just making expensive salty water. People think foaming means cleaning because soap and detergent form foam, but that's a logical error. + +I have yet to see any justification in chemistry for a bicarb+vinegar mix being more effective than either ingredient alone." +1545 "On the back of my cooking salt, ""Sodium FerroCyanide"" is listed as an ingredient. I've heard Ferrocyanides are safe except in the presence of acids when they give off Hydrogen Cyanide gas. If I cook with this salt and acidic foods or sauces, am I slowly poisoning myself?" 6 https://www.reddit.com/r/askscience/comments/g16nka/on_the_back_of_my_cooking_salt_sodium/ 1586875009 g16nka Chemistry 2020-04-14 17:36:49 "There are two factors at play here. + +One is that the cyanide-iron bond in ferrocyanide salts is very strong, and it takes extended treatment with strong acid to liberate cyanide ion in any appreciable quantity. Even straight lemon juice or vinegar are probably not acidic enough to generate cyanide ion from ferrocyanide salts without a lot of ""cooking"". + +The second factor is that the amount of ferrocyanide in cooking salt is very small -- less than 20 mg per kg of salt (~~2%~~ 0.002% by mass). Given that the minimum toxic dose of cyanide at the low end is 0.5 mg per kg of body weight, and that sodium ferrocyanide is only about ""50% cyanide"" by mass, a typical adult would have to ingest about 3 kg of cooking salt (6.6 lbs) to get a toxic dose -- again, if the ferrocyanide were all converted to cyanide, which it isn't except in extreme conditions. + +So overall, it's nothing to worry about." No, not at all. You basically need to heat it with a strong acid (like hydrochloric acid or sulphuric acid) to free any cyanide from the complex, and even if you did that there wouldn't be enough in there to poison yourself. Also, as far as I know hydrogen cyanide does not accumulate in any way, so you wouldn't be at risk even if you boiled it in strong acid and consumed that over a long period of time. +1546 How does chickenpox continue to survive? 6 https://www.reddit.com/r/askscience/comments/g1xjzf/how_does_chickenpox_continue_to_survive/ 1586974868 g1xjzf Medicine 2020-04-15 21:21:08 There are around 130 million newborns each year. That’s enough to sustain the virus. Chickenpox also leads to shingles in older people. If they had chickenpox as a child they can get shingles. Shingles can cause chickenpox if spread. We’re just now getting to the point of a chickenpox vaccination being relatively common, and there’s a shingles vaccination now. It’ll take a few more generations of preventing shingles and chicken pox to even get close to eradication. And that’s only if ppl get their vaccinations, and get their children vaccinated against chicken pox. +1547 "In almost every nature documentary about venomous snakes/spiders there is a part about how ""even though the snake/spider kills X people every year, his venom may be used to develop new drugs"". Is there any well known drug developed from snake/spider venom?" 6 https://www.reddit.com/r/askscience/comments/g1nole/in_almost_every_nature_documentary_about_venomous/ 1586937797 g1nole Medicine 2020-04-15 11:03:17 "Captocobril - treats high blood pressure; derived from Brazilian pit viper + +Ziconotide - treats severe chronic pain; derived from the cone snail + +Eptafibatide - anticoagulant; derived from the southeastern pygmy rattlesnake - rarely used due to posssible severe side effects + +Exenatide - helps treat type-II diabetes; derived from the Gila monster + +Batroxobin - used in several blood related drugs (both coagulation and anticoagulation as well as a surgical application to aid in healing; derived from two species of pit vipers found east of the Andes" "It’s important to remember that venom is composed of hundreds of components or toxins, each with its own biological activity. There are enzymes, peptides (small proteins) and small molecules. Individually and in the correct dose a toxin can be life saving while the venom can be deadly. + +Of particular interest are neurotoxins such those as found in the venom of many spiders, centipedes, sea snails and certain snakes. Voltage gated ion channels (the cell surface proteins that control neuronal activity) are notoriously difficult to develop effective drugs against. Their extracellular portion (outside the plasma membrane) is very small and structurally very similar among gene family members so if you are trying to drug Nav1.7 for example, which is required for all peripheral nociception (pain sensing), it is difficult to avoid hitting Nav1.8 and Nav1.9 which are involved in pain sensing but also important in a lot of other types of neurons including the involuntary nervous system. + +Neurotoxins which evolved to hit the voltage gated ion channels of insects or other animals often have a high degree of specificity to human gene products. A tarantula toxin can block the Nav1.7 nociceptory channel with better efficiency and specificity than any small molecule drug (maybe new ones have been found, I worked on this 4 years ago)." +1548 Would a neck pillow soften the blow of whiplash or would the lack of free neck movement make the impact worse? 6 https://www.reddit.com/r/askscience/comments/ejdj19/would_a_neck_pillow_soften_the_blow_of_whiplash/ 1578046360 ejdj19 Human Body 2020-01-03 13:12:40 "[HANS system](https://en.wikipedia.org/wiki/HANS_device) + +Minimising head movement will reduce severity of injuries. That’s why we have head restraints (not head rests)" +1549 What causes the peltier effect? 6 https://www.reddit.com/r/askscience/comments/g09raa/what_causes_the_peltier_effect/ 1586743930 g09raa Physics 2020-04-13 5:12:10 "To be more correct, with the Seebeck effect it is the *junction* that is heated. + +Consider with the Seebeck effect that the excited electrons choose conductor A, as this is energetically favourable. + +In the reverse case a current/PD drives the electrons through the circuit. They arrive at the junction and must hop from A to the less energetically favourable B. This requires energy which is pulled from the environment, cooling the junction. If the current is reversed then the electrons fall down the energy jump, releasing energy and heating the junction." "It might be useful to construct in your mind a picture of charge carriers also carrying entropy. + +(A charge carrier is the positively or negatively charged particle—that is, a hole or an electron, respectively—that predominantly moves when a voltage is applied to a material. The interpretation of entropy we want to use is the ""stuff"" that moves when one system heats another; that is, the extensive variable conjugate to temperature.) + +So now a current is coupled to a heat flow. Given this, it might be easier to understand how when a voltage potential is applied to a material, brief heat flow occurs as the charge carriers redistribute (the Peltier effect). When a temperature gradient is applied, a brief current arises, again as the charge carriers redistribute (the Seebeck effect). + +The addition of a second material simply allows either effect to be run continuously. In this case, interesting things occur only if the thermoelectric coefficients are different between the two materials, allowing a current loop to drive directed heating or directed heating to drive a current loop. + +Alternatively, one could just run a current along a length of material and exploit the temperature gradient that arises (the Thomson effect)." +1550 Why do some medicines or doctors tell you that the medicine needs to be taken at a certain moment of the day, like morning or night, what difference would it make if I took them at a different hour than the prescribed one? 6 https://www.reddit.com/r/askscience/comments/g1fogh/why_do_some_medicines_or_doctors_tell_you_that/ 1586904330 g1fogh Medicine 2020-04-15 1:45:30 Usually because certain things need to be taken with food, or need a certain amount of time to kick in, or have side effects that change your energy level. Some medications are also nasty in high amounts - I used to take a lithium base depression med and if I took my morning late and my evening on time, I would swell up like a baloon and get acne. An hour won't make a health threatening difference if you missed your dose time, just don't make a habit of it. u/mlucaswalker is right. I'll just generalize that most of the time it has to do with side effects and level of the drug in your bloodstream. As another example, often once per day blood pressure medicines are to be taken in the evening because having too much of it in your bloodstream can cause you to be dizzy or light-headed - which would be bad for daytime activities. After sleeping, you still have enough in your blood for it to have enough of the desired effect, but with the side-effects sufficiently reduced. +1551 Are all the individual stars we see in the milky way? 6 https://www.reddit.com/r/askscience/comments/g2dju6/are_all_the_individual_stars_we_see_in_the_milky/ 1587038229 g2dju6 Astronomy 2020-04-16 14:57:09 "For the most part! In fact, the farthest star you can see with the naked eye is Cassiopeia, which is 16,000 LY away. For comparison, the Milky Way is over 100,000 LY in diameter. + +If you’re talking about seeing or imaging through a telescope, the answer will be much different :) + +Sources + +https://physics.stackexchange.com/questions/45759/what-is-the-farthest-away-star-visible-to-the-naked-eye + +https://en.m.wikipedia.org/wiki/Milky_Way" "All the stars you can see with the naked eye are in the milky way. If it's dark enough, it's possible to see the Andromeda galaxy and the Magellanic clouds, but not well enough to see individual stars in them. + +With a telescope, it is absolutely possible to see stars in other galaxies." +1552 Can anyone explain how Max plank disproved Rayleigh-Jeans law in the context of the ultraviolet catastrophe in layman's terms? 6 https://www.reddit.com/r/askscience/comments/fzctzj/can_anyone_explain_how_max_plank_disproved/ 1586629293 fzctzj Physics 2020-04-11 21:21:33 "Max Planck didn't really disprove Rayleigh-Jeans law. It was already known that there were issues with the law. + +The law predicted that a black body would emit infinite energy through ultraviolet radiation. Obviously, an object cannot emit infinite energy, so there was a discrepancy between prediction and results. This was referred to as the ultraviolet catastrophe. + +Max Planck postulated that energy was quantized, and this worked out mathematically to fit the data pretty much perfectly. He had no real reason for this insight, but it worked." "Little known fact: the Wien law (exponential decay of intensity towards higher frequencies, valid at high frequency) is older than the Rayleigh-Jeans law (increase in intensity for increasing frequency, valid at low frequency)! + +So, when the Rayleigh-Jeans law was published, it was already known that it can only be valid for the IR range, not for UV/vis. Planck was trying to figure out how to combine the two laws, and while deriving such a function he stumbled upon quantum physics." +1553 Why are noble gases in Group 18 able to bond? 6 https://www.reddit.com/r/askscience/comments/g12ine/why_are_noble_gases_in_group_18_able_to_bond/ 1586856921 g12ine Chemistry 2020-04-14 12:35:21 "Excluding helium, because He doesn't like to do anything unless you subject it to insane pressure and temperature, the other noble gases have been found to not be inert just generally less reactive. Take simple compound like XeF2, the xenon isn't gaining electrons it is just sharing two of its own and each fluorine shares one electron. These 4 elections occupy one bonding orbital and one non-bonding orbital to make the bond and leaves the anti-bonding orbital empty. + + +As for their usefulness, it varies, but as for the example XeF2, its great for oxidation flourination because of the low bond energy of the Xe-F bond and is one of the reactants in the production of the super acid fluoroantimonic acid that can basically protonate anything organic. + +Source: *Acta Chim. Slov.* **2006**, 53, 105–116" "From my understanding (it has been a while), the atoms are in a lower energy state and more stable with complete valence shells. As the noble gases are both neutral and contain full shells in their elemental form, they have pretty much the lowest energy state possible. Amy changes, such as gaining an electron, would increase their energy state and make the more unstable. + +As for uses, noble gases are often used as a sheilding gas in welding. They have other uses, but that is all that jumps to mind." +1554 How do scientists determine r values for infectious diseases? 6 https://www.reddit.com/r/askscience/comments/g05zbg/how_do_scientists_determine_r_values_for/ 1586729589 g05zbg Medicine 2020-04-13 1:13:09 "People throw around R0 values, but usually use them incorrectly. The technical definition of R0 is *“the average number of secondary infections produced when one infected individual is introduced into a host population where everyone is susceptible*” (Anderson R, May R. Infectious Diseases of Humans. Oxford: Oxford University Press; 1992). So you’ll see people saying something like “the R0 will be lower once people are immune”, but that’s misusing the term - once people are immune, there’s no R0 any more. + +It’s true that the value will be different depending on environment and population, etc. You say the “value should vary wildly”, and of course it does. That’s why (1) there are different R0 values estimated by different groups. And (2) that’s why the values are always given as a range. For example, although media quoted a [recent R0 estimate](https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article) as “5.7”, the actual value the authors gave was + +>a median R0 value of 5.7 (95% CI **3.8–8.9**) + +In other words, they would be fairly confident that the R0 is somewhere between 3.8 and 8.9, which is a pretty wide range, and 5.7 is a reasonably probable value from that. + +If you want to see more explanation of how they calculated the number, that paper ([High Contagiousness and Rapid Spread of Severe Acute Respiratory Syndrome Coronavirus 2](https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article)) is worth a read - they explain their assumptions, discuss how different assumptions would change their estimates, and review some of the implications, in a fairly readable way." +1555 How is the Oxford group months ahead of producing a vaccine? 6 https://www.reddit.com/r/askscience/comments/g98iz3/how_is_the_oxford_group_months_ahead_of_producing/ 1588018757 g98iz3 COVID-19 2020-04-27 23:19:17 From the article: ‘scientists at the university’s Jenner Institute had a head start on a vaccine, having proved in previous trials that similar inoculations — including one last year against an earlier coronavirus — were harmless to humans‘ "Important point, I think you might be confused about what ""peer review"" means. Scientists publish their findings in peer reviewed journals, which means you submit your paper to a journal and then usually 3 other scientists working in a similar field review the paper for accuracy, make sure your methods make sense, see if you're drawing incorrect conclusions, etc. Their monkey research findings will be published with these standards. The actual process of designing and undertaking clinical trials, and the methods for determining efficacy and safety, are regulated very tightly by government organizations." +1685 Do spiders take over webs? 6 https://www.reddit.com/r/askscience/comments/gvatc0/do_spiders_take_over_webs/ 1591116321 gvatc0 Biology 2020-06-02 19:45:21 "Argyrodes do this. + +Argyrodes. Spiders of the genus Argyrodes (Theridiidae), also called dewdrop spiders, occur worldwide. They are best known as kleptoparasites: they steal other spiders' prey. They invade and reside in their host's web even though they can spin their own webs. + +https://en.wikipedia.org/wiki/Argyrodes" "Once i witnessed a huge spider getting stuck in the web of a super tiny spider. The big one struggled trying to get out while the tiny one slowly creeped on him, wrapping the legs and, what seemed like, started eating him. +It was horror watching it due to my phobia to spiders." +1686 Why and how do we get moles? 6 https://www.reddit.com/r/askscience/comments/h7f9bj/why_and_how_do_we_get_moles/ 1591942141 h7f9bj Human Body 2020-06-12 9:09:01 It depends on the type of mole, also known as a nevus in dermatology. There skin is a complex organ made of many different cell types. Many kinds of moles are the result of overgrowth of one cell type in that area of the skin during fetal development. Others are caused by the melanocytes putting out more or less melanin in that area than in the surrounding skin. Others can be caused by genetic mutations brought on by UV light exposure. These can potentially become cancerous. +1687 I’m a chemist so I should know the answer to this question but I don’t. Why is Technicium a synthetic radioactive while the two elements above it on the periodic table (Manganese and Rhenium) are naturally occurring elements? 6 https://www.reddit.com/r/askscience/comments/h13mvk/im_a_chemist_so_i_should_know_the_answer_to_this/ 1591896116 h13mvk Physics 2020-06-11 20:21:56 "There's no single reason. Out of the ~3000 known nuclides (at least 7000 are predicted to exist), only a lucky few (less than 300) are stable. + +No element is ""entitled"" to have *any* stable isotopes (except maybe hydrogen, barring proton decay). Although it turns out that most elements up to and including lead do have at least one. Technetium and promethium are the two exceptions. + +A nuclide is theoretically unstable if there exists at least one energetically possible decay mode. (Even if this is the case, it could still be ""observationally stable"", if its half-life is so long that we haven't observed it to decay.) + +But anyway, if you look at all of the isotopes of Tc or Pm, even the ones near the valley of stability, they are unstable to beta decay. What makes the decay energetically possible is the difference in binding energies between the parent and the daughters. The binding of a nucleus is a complicated balance of forces, and it just turns out that every isotope of these elements has an isobar (a nuclide with the same mass number) with a higher binding energy. So in every case, there is a beta decay which is energetically possible." +1688 Why do you see a sort of “motion blur” in real life? 6 https://www.reddit.com/r/askscience/comments/gywuxb/why_do_you_see_a_sort_of_motion_blur_in_real_life/ 1591612130 gywuxb Human Body 2020-06-08 13:28:50 "That is in fact correct! The more technical term is persistence of vision, and it is caused by the photosensitive receptors in your eyes not reacting quickly enough. + +It's also how most dimmable lights work, instead of lowering voltage and reducing efficiency, one can flicker the lights thousands of times a second to produce a dimmer light that we perceive as continuous. It's called PWM." +1689 Is there an estimate for number of infections required for the COVID19 virus to mutate enough to start infecting people with immunity again? 6 https://www.reddit.com/r/askscience/comments/hkornf/is_there_an_estimate_for_number_of_infections/ 1593802664 hkornf COVID-19 2020-07-03 21:57:44 "Asking about this from the viewpoint of number of infections is the wrong metric. You need to think about positive selective pressure, negative selective pressure, and mutation rate. Of those, mutation rate (or mutation count) is the only one that is affected by number of infections, and it’s possibly the least important of the three. + +Coronaviruses mutate fairly fast - much slower than other RNA viruses like measles or influenza, but faster than DNA based organisms. But notice that even though measles and influenza have similar mutation rates, measles is a very stable virus (the vaccine hasn’t changed for decades) and influenza is not (vaccines need to be changed every few years). + +That’s because of negative selection. When measles mutates, it almost always makes the virus worse than before, so the mutation is negatively selected. When influenza mutates, at least on some of its proteins, it’s able to tolerate the changes very well, so there’s not much negative selection. + +So influenza can accumulate mutations because it has a high mutation rate (not all that important), and because the mutations don’t lead to much negative selection (very important). + +But so far, the mutations don’t affect the virus much. All you have a bunch of mutations that are insignificant, neither positive nor negative. + +What happens next is that some mutations get positively selected. In this context, those are the mutations that make the virus able to avoid immunity. + +Why is there positive selection for influenza? Because immunity to influenza is so common. Just about everyone has been exposed to influenza at some time in their life, often multiple times, and in the US nearly half the population is also vaccinated. So a virus that can escape immunity even a little, gets a little positive selection boost. + +It takes several of those mutations - probably around a dozen, all in the right place - to actually become resistant to immunity, not just a little but enough to notice. That’s why influenza viruses take several years - say three to ten years - before they change enough to need a new vaccine. + +Returning to coronavirus. Is there negative selection against mutations? We don’t know for sure, but probably yes, quite a bit. The receptor binding regions that get neutralizing antibodies targeting them need to fit quite nicely to their ACE2 receptor, so they can’t tolerate changes all that easily, let alone the half-dozen or dozen changes it needs to avoid immunity. That’s not to say it can’t, but compared to the wide highway that influenza can stroll down without losing its function, SARS-CoV-2 probably has a narrow, awkward path to go down to avoid negative selection. + +Is there positive selection to avoid immunity? Not really yet. In spite of the large absolute numbers of infections, even in the US a fairly small percentage (less than 10%, maybe less than 5%) are actually immune. That’s not really enough to drive positive selection. + +So it’s reasonable to say that for the next while, negative selection will likely outweigh positive selection on the coronavirus. At some point, enough people will have immunity that there will be positive selection, but even there the virus is likely to be much more like measles (strong negative selection outweighing the positive) than influenza. + +Notice that this isn’t really affected by number of infections, as it is by the nature of the virus protein and the percent of people who are immune. + +It wouldn’t be surprising if in five years, or perhaps ten, the virus does change a little antigenically. Presumably by then we will have vaccines, and it will be as easy (or even easier) to tweak them to match the new virus, so it will likely be a minor thing at that point that may need a booster shot once a decade." +1690 What does the new theory of SARS-Cov-2 being capable of hanging in the air for 16 hours means for containment attempts? 6 https://www.reddit.com/r/askscience/comments/ho5r1y/what_does_the_new_theory_of_sarscov2_being/ 1594310780 ho5r1y COVID-19 2020-07-09 19:06:20 "[Nature Article](https://www.nature.com/articles/d41586-020-02058-1) + +This seems like a good summary, it seems that in enclosed spaces with less ventilation, the virus could be airborne, or at least smaller droplets could spread the virus much further than previously thought. I agree with what was said, perhaps the main route of transmission is via respiratory droplets, in the air or from surfaces, but to a lesser extent aerosols may be responsible, so this is now being considered. Another study that has been discussed on here, suggested that after more data analysis from China, the R0 of the virus may have been 5.7. There have been further interventions since, but it could be spreading via other routes, one concern is that there may be more asymptomatic people accidentally infecting others. We’ll know more as the weeks go on." "Just because the virus is found in airborne particles doesn't necessarily mean the quantity or the quality of virus is potent enough to actually cause infection in significant numbers. + +If it turns out it doesn't pose much of an infection risk, then not much changes. + +If it does pose a clinically significant infection risk, from a practical standpoint, not much actually changes as well. In the community setting, it's already been established that if people practiced appropriate safety measures (physical distancing, avoiding close indoor contact with strangers, washing hands, wearing masks when in close contact, etc..), then the virus could be held at bay. Nothing ""extra"" would be needed to curb any perceived increase in infectivity. It's those who flaunt the guidelines or are too ignorant to follow said guidelines that have result in increased infections. In the hospital setting, not much should change as well, as most physicians already assumed that the virus was capable of being airborne and hospitals should have already been operating under airborne precautions." +1691 How does the body “kill” COVID-19 if the person is asymptomatic and there are no medical interventions? 6 https://www.reddit.com/r/askscience/comments/ho6akf/how_does_the_body_kill_covid19_if_the_person_is/ 1594312539 ho6akf Human Body 2020-07-09 19:35:39 "Your immune system is in all honesty quite powerful. It is also what causes the most damage if it overreacts. Having no symptoms does NOT mean that your body is not fighting the disease. + +Think about what symptoms are. Cough is defined as the expelling of air from the lungs. This is done to clear them, preventing damage, such as fluid buildup in the case of a strong immune response. But in many cases, the immune system does not mount such a strong response, and pathogens are killed without the need for coughing. + +Fever is a way of increasing body temperature to misfit the ideal temperature range of pathogens. But in many cases, that is not needed either." "The symptoms of the this disease ARE merely the result, loosely put, of your body fighting the COVID-19 virus. However not all fights are equal, and asymptomatic people have largely been successful in fighting the disease before it gets to the obvious 'illness' stage. + +Your immune system is fighting things all the time every day. On a 1 out of 10 scale it might (random numbers for illustrative purposes) be putting in an effort of 3 or 4 out of 10 all the time. You dont notice this cos 4 out of 10 has no noticeable affect on your obvious health. However once it gets to 5 or 6 you might still seeing symptoms like temperatures, headaches, body aches etc. Once it gets to 9 or 10 out of 10 then you feel really really ill, not just from the sickness, but from your bodies desperate attempts to survive. + +Everyone who has survived to date has done so because their own body killed the virus, in the end, and possibly with outside help." +1692 Here in Brazil theres been talks that the US bought the rights of a lot of the possible vaccines for COVID-19, is this true and how it affects other countries? 6 https://www.reddit.com/r/askscience/comments/hw36sq/here_in_brazil_theres_been_talks_that_the_us/ 1595455379 hw36sq COVID-19 2020-07-23 1:02:59 "It's not possible to buy all the rights to a vaccine. All countries will still be able to get them and there are companies all over the world developing over [100 different vaccines](https://nyti.ms/2MHNdRL). + +The US probably will have priority over the first doses coming out of the 6 efforts the government is funding though." The US has been pre-ordering early production of many vaccines in the US but those are not exclusive licenses. Brazil has already arranged for the production of at least one vaccine (the Oxford one) at the Fiocruz vaccine lab in Rio. +1739 Does a Neutron have a dipol-moment or at least a temporary dipol-moment? 6 https://www.reddit.com/r/askscience/comments/jwev4t/does_a_neutron_have_a_dipolmoment_or_at_least_a/ 1605702313 jwev4t Physics 2020-11-18 15:25:13 "Neutrons definitely have a magnetic dipole moment, but it sounds like you're asking about electric dipole moments, and that's a [much more interesting question](https://en.wikipedia.org/wiki/Neutron_electric_dipole_moment). + +For the neutron to have an electric dipole moment, time-reversal and parity symmetries would need to be broken. That's just because of how odd-parity electromagnetic moments transform under the P and T operations. If P and T are good symmetries of nature, then magnetic monopole moments, electric dipole moments, magnetic quadrupole moments, electric octupole moments, ... are all forbidden. + +That being said, we know that T and P are both violated in nature. So it's not really unheard of that the neutron EDM could be nonzero. But it must be very small, and currently the most precise measurements are consistent with zero." +1740 What are some really difficult tasks to solve when it comes to distributing billions of doses of vaccines across the planet? 6 https://www.reddit.com/r/askscience/comments/jvd6hv/what_are_some_really_difficult_tasks_to_solve/ 1605554701 jvd6hv COVID-19 2020-11-16 22:25:01 The biggest one I see, aside from the how and when, is the who. Since you can only get people vaccinated as fast as they can be manufactured and distributed, who gets it first. Knowing that people are still dying while this happens, who does it go to first? "Of the two recently announced mRNA vaccines, it is logistics. The Pfizer vaccine needs to be stored at extremely low temperatures -- beyond what common commercial freezers can achieve. So delivery to logistics-handicapped regions (most of Africa), it faces a challenge. The Moderna vaccine must still be refrigerated, but only needs temps achievable by consumer-available freezers. But still, dealing with delays imposed by corrupt governments, lack of transportation, and hours of travel over dirt roads or barely roads to remote villages, will pose challenges. + +Edit: I forgot to include countries where terrorists and militants kidnap and/or kill NGO health care workers." +1741 How does a new recessive gene get spread? 6 https://www.reddit.com/r/askscience/comments/irg5pt/how_does_a_new_recessive_gene_get_spread/ 1599929664 irg5pt Biology 2020-09-12 19:54:24 It's inbreeding. But you're thinking of it short term. Humans are all inbred to hell. However you're often actually talking about distant cousins numerous generations apart. You have to understand that until recent history the likelihood of you marrying someone that wasn't related to you in some way was pretty slim. Not like they had cities all over the world with millions of people in each and the ability to move to hundreds of miles away. +1742 Why do some foods (for example bread) go hard when they go stale while others go soft? 6 https://www.reddit.com/r/askscience/comments/jv56gr/why_do_some_foods_for_example_bread_go_hard_when/ 1605525751 jv56gr Chemistry 2020-11-16 14:22:31 "It is specific to each food. For the example of bread, the change in softness is mainly due to exchanging water with the environment. Amide forms polymeral chains, according to the [Wikipedia](https://en.m.wikipedia.org/wiki/Amide), + +""In primary and secondary amides, the presence of N–H dipoles allows amides to function as H-bond donors as well. Thus amides can participate in hydrogen bonding with water and other protic solvents;"" + +For certain humidity levels, amide chains are broken and soften, if it is too low, it forms larger polymers, which appears to be harder. There is a simple experiment you can do at home. Keep a piece of bread in tied plastic bag and a piece of bread in closed paper bag. You will see the first one will stay more soft for a longer time. This is due to the plastic bag isolating humidity and the paper bag allowing it to be lost ti the air." "It’s the amount of moisture in them to. + +Bread and cake are both moist when fresh whereas biscuits are dry and hard when fresh. + +So, to get some kind of equilibrium, moist things will lose moisture to the air whereas dry things will take up moisture from the air. Unless the atmosphere is very humid or dry in which case the equilibria will tend not to tip so much to the right + +Flour type, amount of sugar, amount of fats, and raising agents may also be contributing factors to how dry or wet something may end up." +1743 The forthcoming 'great conjunction' - does it tell us anything we don't already know? 6 https://www.reddit.com/r/askscience/comments/kfkpvd/the_forthcoming_great_conjunction_does_it_tell_us/ 1608296497 kfkpvd Astronomy 2020-12-18 16:01:37 "Pretty much a curiosity. + +That said, it gives a good way to directly compare the surface brightness and colour of the two planets, since they can be captured in a single image. I'm not sure that's especially useful since this is easy enough to do with a well calibrated camera anyway. + +Great Conjunctions happen every 20 years or so. But this one is particularly close." "There is the novelty element. It is also getting a bit more public attention. Anything that gets people more interested in science of any kind is good. This follows up on the recent Geminids shower that peaked at the start of the week and the solar eclipse that was visible from South America. Conjunctions like this one, along with things like meteor showers, eclipses and transits are great to watch. + +Jupiter and Saturn have been well studied, so there is not much that can be learned by this. It is just a conjunction, with them being apparently close together from our viewing point on Earth. Obviously there is no effect that they will have on each other. So get out, hope for clear skies where you are and enjoy it, along with all the other wonders on view in the night sky." +1744 What actually is a torque? 6 https://www.reddit.com/r/askscience/comments/kf92de/what_actually_is_a_torque/ 1608247923 kf92de Physics 2020-12-18 2:32:03 ">My question is what actually is the resultant vector? We know it is perpendicular and can find the direction, but what significance does that have? How does it help us understand motion? I just don't get it. Does it help predict motion? Am I overthinking it or is it talked about more in more advanced courses? + +**T** = d**L**/dt. + +The time derivative of the angular momentum (**L**) equals the net external torque (**T**). + +You use this to predict how the angular of the object will change, in the same exact way that you use **F** = d**p**/dt to predict how the momentum of an object will change when you apply a net external force **F**." "So I'm interpreting your confusion to mean why are angular vectors perpendicular to the way(s) the object appears to be moving, right? + +The mostly true, but sort of a cop out, answer is, its a notation convention thats not really meant to be taken literally. Its easily one of the less intuitive portions of newtonian physics. Like most physics, its a representation of reality thats useful for modeling reality, but the vector itself isn't a thing thats actually ""real"". Its a way to describe how something moves and how an external force is changing the way it moves. + +But I assume what you're actually looking for is a way to interpret the torque vector thats more intuitive. To do that, lets start with making angular momentum a little more intuitive. Angular momentum of a particle is L = r x p, or the cross product of the position vector with respect to the axis of rotation and the linear momentum of the particle. When you take this cross product, you get the angular momentum vector. Vectors have two properties, direction and magnitude. The direction of the angular momentum vector actually tells you two things. First, it tells you the axis about which the object is rotating. Second, it tells you (via the right hand rule) ""this is the direction this object is spinning"". The axis is the important part - the directionality is mostly just because we use a right handed coordinate system in physics, i.e. a convention. The magnitude is just like the magnitude for momentum. It tells you how much stuff is spinning, how fast, and how far from the axis of rotation. + +So the takeaway here is, angular vectors are directed along the axis of rotation, because thats the most consistent way to describe things that spin. + +So, back to torque. As another commenter said, torque is the change in angular momentum, dL/dt. Lets back up a little from this though, because thats a bit too general - its like telling people F = dp/dt before telling them that F = ma, even though the latter is a special case of the former. Torque is basically ""angular force"", i.e. its a force that acts to make an object spin faster or slower, rather than a force that acts to accelerate its center of mass. In the case of the particle described above, torque = r x F. A torque that makes something spin faster increases the magnitude of the angular momentum vector and acts in the same direction. A torque that makes something spin slower acts in the opposite direction of the angular momentum vector and makes it decrease in magnitude. + +A concept that is a little closer to everyday life is ""leverage"". Leverage and torque kind of go hand in hand - if you have more leverage, it is easier to apply a torque, because you're increasing distance from the axis of rotation (the fulcrum) and so likewise you need to apply less force. This is because, if torque required is constant, and t= r x F, if r is increased, F can be reduced." +1745 If wind is caused by a pressure difference between cold air and hot air, how is it sometimes we feel hot wind like a Sirocco? Shouldn't the wind always be cold? 6 https://www.reddit.com/r/askscience/comments/jvs7k6/if_wind_is_caused_by_a_pressure_difference/ 1605616403 jvs7k6 Earth Sciences 2020-11-17 15:33:23 "It sounds like your confusion is the result of over-simplified explanations you've been given in the past. Wind is not caused by a ""pressure difference between cold air and hot air"". While that might be correct to a very rough approximation in certain contexts, it's not accurate overall. + +So what is wind? Wind is just the movement of air in our atmosphere. It is ultimately driven by two* forces: + +1. Pressure Gradient Force - the difference in pressure between one location and another makes air move from the area of higher pressure to lower pressure +2. Gravitational Force - denser air is pulled downwards stronger than less dense air + + +Temperature and changes in temperature are *related* to these two things, but temperature is not the actual physical mechanism driving the wind. + +To give a specific example: a mantra that is mostly true but very confusing if taken literally in the wider context of atmospheric motions is the idea that ""warm air rises"". This is not strictly true: what *is* true is that denser air sinks below less dense air under the influence of gravity (absent other forces). This means that if you have a uniform region of air (same pressure, same temperature) and you make one part of it warmer, that region will be slightly less dense than the surrounding air. Gravity will pull stronger on the surrounding cooler, denser air, and so the denser air will slide underneath the less dense air, ultimately causing the warmer air to rise. + +So really all that's necessary for wind is that there is either an imbalance in pressure causing air to move from the higher pressure area to the lower pressure area, or there is a region of denser air that is being pulled down, displacing less dense air. There are a whole variety of ways that these situations can come about, which is why the temperature and the wind speed are not really directly dependent on each other at all. + +Let me know if you have any follow-up questions! + +---------- + +^\* ^( There are complications due to the rotation of the earth, the compression and expansion of air as it sinks and rises, and the role of water -- especially in the vapor phase -- but we will ignore those for now.)" +1931 Is misophonia culturally dependent? 6 https://www.reddit.com/r/askscience/comments/o39z7d/is_misophonia_culturally_dependent/ 1624084722 o39z7d Psychology 2021-06-19 9:38:42 "Personal anecdotes and uneducated opinions don't constitute scientific answers. If and when someone leaves an answer that doesn't violate the [rules](https://www.reddit.com/r/askscience/wiki/index#wiki_askscience_user_help_page), it will stay up. + +If you *want* to read unscientific answers to the question, I'd suggest asking it on another sub." A [cursory search for literature](https://scholar.google.com/scholar?hl=en&as_sdt=0%2C44&q=misophonia+culture&btnG=) on the subject suggests that your question hasn’t been studied extensively. There are a few studies of undergraduate populations, but clearly those aren’t necessarily partitioning individuals into defined *cultural* groups. +1932 Why are large parts of Africa and South America not in the range of common house mouse? 6 https://www.reddit.com/r/askscience/comments/o1znrf/why_are_large_parts_of_africa_and_south_america/ 1623942926 o1znrf Biology 2021-06-17 18:15:26 "You should be a bit skeptical of range maps, especially ones with unclear sourcing and especially ones for introduced species and species that tend to live in scattered pockets. That map, for example, claims there are no house mice in Madagascar, but the associated Wikipedia article lists a subspecies living in Madagascar. And a quick googling found me a paper about house mouse in Senegal, which isn't marked on your map + +https://www.fondationbiodiversite.fr/wp-content/uploads/2020/07/Diagne-C.-et-al.-2020-Biol.-Inv.-1.pdf + +House mice seem to have originated in India and spread outward from there. + +https://elifesciences.org/articles/05959 + +While there are some populations living away from humans, for the most part house mice are human commensals and tend to live in cities and farms. They are often not found much away from these areas." "Inhospitable environments with better predators, more competition for food, and dramatically different climates. + +This is speculation but because they’ve invaded west Africa and can’t penetrate central Africa, it has to be one of or most of those reasons." +1933 How improbable was the mass-devastation and series of events that followed the K-T extinction vs. if the asteroid had hit somewhere else on Earth? 6 https://www.reddit.com/r/askscience/comments/o1ytft/how_improbable_was_the_massdevastation_and_series/ 1623940716 o1ytft Earth Sciences 2021-06-17 17:38:36 "The simplest answer to your question is that at the time of the impact, only ~13% of the Earth's surface was covered with deposits similar to the sulfur and organic rich carbonate platform where the Chicxulub impact occurred (e.g., [Kaiho & Oshima, 2017](https://www.nature.com/articles/s41598-017-14199-x)), suggesting that there were a lot of places the impactor could have hit and not produced the same ecological effects. As highlighted in that paper, there were places on Earth at that time that if impacted would have potentially had a greater climatic influence (with maps). + +There is a lot of nuance in this however that is not reflected in your questions (and thus, I suspect, in the video that inspired these questions). To the extent that the impact hypothesis is correct (more on that in a bit), there is still disagreement on what the kill mechanism would have been, which is touched on in the Kaiho & Oshima paper. Some papers focus on the injection of sulfate into the atmosphere from the target rocks being high in sulfur compounds (e.g., [Ohno et al., 2014](https://www.nature.com/articles/ngeo2095)), but an alternative set of papers focus instead on that these target rocks were also very rich in organic rich materials and would have generated significant amounts of soot also injected into the atmosphere and this may have been the primary kill mechanism (e.g., [Kaiho et al., 2016](https://www.nature.com/articles/srep28427), [Lyons et al., 2020](https://www.pnas.org/content/117/41/25327.short)). Either way, these both highlight that where the impactor hit was important and that not all locations would have produced the same result. + +Beyond this, it's also important to realize that while the impact hypothesis is still viable and strongly supported by some, there is a lot of disagreement about whether it was actually the primary (or only) cause of the K-Pg (the more modern name of the K-T) extinction. As I discussed in [an answer a few days ago](https://old.reddit.com/r/askscience/comments/ny2rl4/how_strong_is_the_evidence_for_alternative/), there is a substantial literature arguing that the primary cause of the extinction was the eruption of the [Deccan Traps](https://en.wikipedia.org/wiki/Deccan_Traps), with the impact being something that happened, but not actually important for causing the extinction (e.g., [this series of criticisms of the bolide impact hypothesis](https://science.sciencemag.org/content/sci/328/5981/973.1.full.pdf), [McLean, 1985](https://www.sciencedirect.com/science/article/abs/pii/0195667185900485), [Renne et al., 2013](https://science.sciencemag.org/content/339/6120/684.abstract), [Schoene et al, 2015](https://science.sciencemag.org/content/347/6218/182.abstract), [Tobin et al., 2012](https://www.sciencedirect.com/science/article/pii/S003101821200384), [Keller et al., 2020](https://www.sciencedirect.com/science/article/pii/S0921818120302034)). There also exists a compromise set of ideas whereby it was the combination of the Deccan Traps eruption and the impact that caused the extinction and that neither independently may have been able to cause the scale of extinction event that took place (e.g., [Renne et al., 2013](https://science.sciencemag.org/content/339/6120/684.abstract), [Petersen et al., 2016](https://www.nature.com/articles/ncomms12079), [Schoene et al., 2019](https://science.sciencemag.org/content/363/6429/862.abstract)). + +**In short,** to the extent that you accept that the impactor was the primary cause of the K-Pg extinction, the location of the impact and composition of the target rocks were important for generating enough climatic disruption to feasibly cause an extinction. However, there remains a lot of debate about whether the impact actually was the primary cause, with the Deccan Trap continental flood basalt eruption being a prime alternative candidate, either independent of or in conjunction with the impact. Unsurprisingly, there is a lot more nuance and disagreement in the actual literature compared to what is implied by animated videos aimed at a general audience." "An interesting question - I mean, to add to this, what would have happened if it had hit say the Oklo Reactor? + +I mean I can imagine the impact would basically vapourise what is essentially a boatload of depleted uranium, but would this have made things worse?" +2023 With all the talk of travel at the speed of light, isn't a major concern colliding with objects? 6 https://www.reddit.com/r/askscience/comments/rb2n0j/with_all_the_talk_of_travel_at_the_speed_of_light/ 1638893975 rb2n0j Physics 2021-12-07 19:19:35 "You cannot travel at the speed of light. Relativity makes it impossible. But it's ok, OP's question still makes sense at lower speeds. + +Yes, hitting small objects would be a concern. Actually, two different concerns: + +**Small solid objects such as dust particles:** + +They would behave like micrometeoroids, potentially making craters in spacecraft walls, or even holes if the meteoroid is big enough. + +I can answer this because spacecraft in Low Earth Orbit (LEO) are shielded against micrometeoroids and orbital debris (MMOD). Shields are basically multi-layer plates of aluminium or kevlar, the basic configuration is two layers. The goal is to destroy the incoming object when it hits the first layer, breaking it into smaller pieces or even vaporizing it, so that its remains spread over a larger area before hitting the second layer. Then the second layer has much higher chances of resisting. + +They work nicely in LEO, the ISS can resist impacts of objects up to several mm across, and post-flight inspection of the MPLM modules have revealed several craters showing that the shields worked as expected. (Crater counts have also been used to improve our knowledge of the debris environment, combined with knowledge from the Space Shuttles, NASA's [LDEF](https://en.wikipedia.org/wiki/Long_Duration_Exposure_Facility), and ESA's [Eureca](https://earth.esa.int/web/eoportal/satellite-missions/e/eureca)). + +Still, while MMOD speeds are so fast that make the speed of sound or the speed of a bullet negligible in comparison, they are nothing compared to the speeds that OP may be thinking about. I'm not aware of any designs or research about resisting dust at relativistic speeds, so I'll just say the challenge is orders of magnitude harder than the current LEO debris situation. + +**Protons in interstellar space:** + +While you'd normally ignore them at our usual spacecraft speeds, when you go orders of magnitude faster they become ionizing radiation in a reference frame fixed on your vehicle. They can cause potentially cancerous mutations in humans, flip a bit in a computer's memory, or even burn sensitive electronics when they hit. + +If your speed is contained, the spacecraft walls might be able to stop them. Or you might need some light shielding. But the faster you go, the deeper they can penetrate, so they will become unmanageable if your speed approaches the speed of light. + +There are also alpha particles and some heavier ions in space. They are, of course, a lot worse than lone protons. + +We can compare this to the Galactic Cosmic Rays (GCR) issue. The difference is that GCR are moving fast relative to Earth. They have the same effects on humans and electronics, and GCR energies are high enough to penetrate any realistic shield. Their flux is very low, so they cannot cause radiation sickness, but the risk of cancer in a long term is an issue. Hitting protons in space when a spacecraft moves fast enough would be comparable in energy, but the flux might become much higher. + +**An actual case that has considered this:** + +Project Breakthrough Starshot plans about making nanospacecraft with light sails, and accelerating them using a GW-scale laser to 20% of the speed of light. This is fast enough for the two concerns above to become real. They have actually addressed both points in their website: + +[Interstellar dust](https://breakthroughinitiatives.org/forum/7) + +[Interstellar protons](https://breakthroughinitiatives.org/forum/9) + +Still, they have neglected a large part of the issue, mostly because their concept is about sending a large number of spacecraft (so even if many of them fail there will be lots of others to transmit useful data), and because they are so tiny that the chances of them hitting something are very low. (They even said they can neglect GCR, which would be inadmissible for any other kind of space mission.)" ">With all the talk of travel at the speed of light + +just a little perspective.... + +​ + +this is the ***fastest*** thing ever made by man. it's going to take *years* to build up to max speed. 430,000 miles an hour: .064% the speed of light. + +​ + +https://en.wikipedia.org/wiki/Parker\_Solar\_Probe + +The Parker Solar Probe (abbreviated PSP; previously Solar Probe, Solar Probe Plus or Solar Probe+)\[8\] is a NASA space probe launched in 2018 with the mission of making observations of the outer corona of the Sun.\[3\]\[6\]\[9\] It will approach to within 9.86 solar radii (6.9 million km or 4.3 million miles)\[10\]\[11\] from the center of the Sun, and by 2025 will travel, **at closest approach, as fast as 690,000 km/h (430,000 mph), or 0.064% the speed of light.** + +​ + +...all the talk about light speed is just talk." +2024 Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology 6 https://www.reddit.com/r/askscience/comments/q2l1na/ask_anything_wednesday_economics_political/ 1633528814 q2l1na 2021-10-06 17:00:14 I seem to remember a Scandinavian country doing an experiment with universal basic income. Did that happen, and if so, what were the outcomes? "I'm looking for videos on foundations of mathematics that would be appropriate for a seven year old. Does anyone have any suggestions? + +Also is a question asking for recommended books, articles, videos, etc. on a specific topic appropriate for this sub?" +2025 What's the physical meaning of potential flow in fluid dynamics? 6 https://www.reddit.com/r/askscience/comments/q23nyd/whats_the_physical_meaning_of_potential_flow_in/ 1633462189 q23nyd Physics 2021-10-05 22:29:49 "I think the problem is that potentials (including voltage) are not ""real"" things, the fields that are real here. + +In EM we start with electrostatics, with a constant electric field and no magnetic field. Maxwell equations tell us that this field has no curl, that is, curl E = 0. + +Helmholtz theorem says that a field with no curl can be written as the gradient of some function, which we call the potential function. Due to the nature of the electric force this function is actually related to the energy of the system, so there is a natural interpretation for the potential. + +Helmholtz theorem also says that a field with no divergence can be written as the curl of a vector potential function. This is very useful in fluid dynamic, where the system is represented by the velocity of the fluid in each point of space. In particular, if the fluid is not compressible, mass conservation requires that div V = 0, so the velocity field can be written as V = curl A, for some vector potential function A. + +The same principle from EM can be applied to fluid mechanics if the fluid in question has no curl, as we'll have curl V = 0 and there should be some scalar function f such that V = div f. The difference is that unlike in EM, where the force F = q E, in general there is no force associated with V, so f is not really related to energy. + +I haven't studied fluid dynamics in dept to know the meaning of those potential functions (if any), but hopefully I made things a bit clearer. + +TLDR: although useful, potential functions are actually built to yield these fields under some operation. They can be very insightful, but are not really physical things." ">I have an idea for what voltage means physically -- it's the potential energy per unit charge w.r.t. some predefined reference. But what does this potential function mean physically in the context of fluid dynamics? + +Unfortunately, there's no clear analog in the fluid case. It's simply the function whose gradient is the velocity field (in an Eulerian sense)." +1556 Have artificial flooding patterns negatively impacted bottomland hardwood forest? 5 https://www.reddit.com/r/askscience/comments/g167hg/have_artificial_flooding_patterns_negatively/ 1586873471 g167hg Earth Sciences 2020-04-14 17:11:11 +1557 Does COVID-19 cause a positive test for influenza? 5 https://www.reddit.com/r/askscience/comments/g63pmx/does_covid19_cause_a_positive_test_for_influenza/ 1587571089 g63pmx 2020-04-22 18:58:09 Rapid influenza diagnostic tests are identifying the presence of viral nucleoprotein antigens, that is a specific immune response to influenza. Covid19 swab tests detect the presence of the genetic material, called nucleic acids, of the actual SARS-CoV-2 virus. "Doctors will test a sick person for influenza virus first to rule that out before offering a coronavirus test. They will only test you for corona after it's proven that you don't have influenza. Though these illnesses may sometimes have similar symptoms, the tests are able to clearly distinguish between them. If you tested positive for influenza B, they wouldn't have tested you for corona in January even if testing was available then. + +I had influenza B a few years back, and it was completely incapacitating in a way I'd never experienced. Bedridden for two weeks, terrifying fevers. We've all had the flu before, but some strains are whompers. Glad you made it through. You're likely to have some natural immunity to similar influenza strains for the next year or two, so that's good news. (You should get a flu shot anyway, though.)" +1558 How human milk is made? I mean all the way through: from food to bloodstream to mammary glands 5 https://www.reddit.com/r/askscience/comments/ej5o9z/how_human_milk_is_made_i_mean_all_the_way_through/ 1578004959 ej5o9z Human Body 2020-01-03 1:42:39 You're asking a very broad and comprehensive question that would take at least a couple of semesters of human anatomy and physiology to answer. You are asking about digestion, absorption, circulation, cellular transport, homeostasis, chemical equilibria, energy and work, DNA transcription and translation, biosynthesis, secretion, and the specific anatomy and physiology of several organ systems. An answer that hits all your points would be hundreds of pages long. You might want to try asking a more narrow question that we could answer in a few paragraphs. If you're interested in gaining knowledge about all these topics, I suggest checking out the videos at Khan Academy to start. They are relatively short, 5-15ish minutes, and totally free to watch. "> Also, are there machines which can turn food into bioidentical milk, let’s say corn into human milk or grass into cows milk? + +This part of your question is easy to answer. + +No, there are not. + +Our best attempts at milk-like substances are infant formula. They are good enough for infants to survive on, but there are many differences from the real thing. A close chemical analysis would very easily tell them apart." +1559 Can liquid oxygen be combusted? 5 https://www.reddit.com/r/askscience/comments/g04k35/can_liquid_oxygen_be_combusted/ 1586724739 g04k35 Chemistry 2020-04-12 23:52:19 Only if there is a fuel for it to combust with. Combustion takes both a fuel and an oxidizer, just as wood cannot burn without an oxidizer liquid oxygen cannot burn without a fuel. Mixed with a fuel though, liquid oxygen is explosively combustible. So much so that it’s used as the oxidizer in most first stage rocket engines, in combination with a fuel such as hydrogen or kerosene. Yes, oxygen is only the second strongest oxidizer. Oxygen can be oxidized by flourine into [Oxygen difluoride](https://en.wikipedia.org/wiki/Oxygen_difluoride). There is basically nothing besides flourine that can oxidize oxygen, and nothing at all can oxidize flourine. +1560 How do we know when cosmic inflation began? 5 https://www.reddit.com/r/askscience/comments/g18q7u/how_do_we_know_when_cosmic_inflation_began/ 1586881747 g18q7u Physics 2020-04-14 19:29:07 "Great question. + +We can plausibly trace back in time from where we are now to the time when the energy density was high enough to invoke the (untested) new physics associated with the idea of Cosmic Inflation. We can even say, if that idea is right, about how many factors of 10 space inflated by during that process, or at least set a minimum number on that. And, if we make yet more (untested, and maybe untestable) assumptions about the physics and energy densities of stuff \*before\* inflation started, we can say how much time passed in going from ""t=0"" (ie energy densities associated with the Planck scale) and the start of Cosmic Inflation. Roughly. The number you're quoting assumes the energy density is dominated by radiation, the universe is not too-far from flat at that time (if it were overdense enough, ie too positively curved, it wouldn't reach the conditions required for Cosmic Inflation and would instead collapse) and that there's no new interesting relevant physics at play. All of these are reasonable assumptions, but assumptions nonetheless. + +But, it is certainly possible that our assumptions about that very-hard-to-test time are wrong. So it's quite possible that the number you quoted is wrong, and that something else went on before Cosmic Inflation that changes it. + +And don't get me wrong, I'm very impressed by the success of the paradigm of Cosmic Inflation, ie its predictions and subsequent verifications, but it is also possible that Cosmic Inflation is not right, and that something less standard, like the cyclic/epkyrotic/etc models are right. It's a tough question to answer, which is one of the reasons it's so interesting!" +1561 On a cellular level, how do deciduous plants know what season of the year it is? 5 https://www.reddit.com/r/askscience/comments/g136bm/on_a_cellular_level_how_do_deciduous_plants_know/ 1586860441 g136bm Biology 2020-04-14 13:34:01 "Plants sense light and temperature, though temperature is the large factor which induces many seasonal changes. Different plants rely on different temperature thresholds, and have varying sensitivities and trigger levels to induce these changes. For some, it might be the temperature needs to reach a certain point for several consecutive days, while others may just require a short temperature flux to trigger their seasonal changes. These changes - for example, the leaf out or flowering of a maple tree - are referred to as phenology. + +Using a maple tree example again, when the temperature consistently rests between +5 and -5 degrees celsius overnight, this triggers sap flow because of a change in pressure within the vascular structures (and is why during this short time maple syrup can be produced). Eventually, this range closes, and therefore the nutrients will be able to continuously be moved up and down the tree, from the roots to the branch tips, allowing for leaf out to occur. Similarly, when temperatures drop steadily into the cooler seasons, this triggers the tree to stop producing certain pigments in their leaves (giving us the fall colours) because this means that light is becoming more scarce, and photosynthesis is less beneficial. With only certain pigments present, photosynthesis is reduced/stopped and leaves are more vulnerable to sun damage, causing them to eventually fall off." Sunlight drives the production of sap through photosynthesis. As the days become shorter in the fall and the angle of the sun changes, those plants can’t produce as much food as they can during, say, the middle of the summer. The drop in food production and temperature drop causes the tree to begin becoming dormant. This could take a few weeks before you notice. When leave change color and fall that’s the final step in a process that started weeks before. +1562 The Governor of Louisiana said the antibody test for coronavirus can show results for the common cold coronavirus— can some explain how the test for positive Coronavirus (Covid19) making sure it is not just a common cold? 5 https://www.reddit.com/r/askscience/comments/g2neqo/the_governor_of_louisiana_said_the_antibody_test/ 1587070412 g2neqo COVID-19 2020-04-16 23:53:32 "Antibodies have a variable region that binds to what is called an epitope. The epitope is on a protein, that in this context is called an antigen. Well, there are a few non-protein antigens, but let's just say protein. + +Epitopes are very short regions of the antigen. It can either be a continuous sequence of amino acids, or a plurality of sequences on different parts of the antigen. + +Regardless, antibodies do not recognize a ""coronavirus,"" per se. Rather, a particular antibody recognizes a tiny region of a specific protein of a specific virus. + +If you align the human coronaviruses amino acid sequences, there are many similarities and many differences. There are many potential epitopes that are unique to each individual coronavirus. + +Could an antibody exist in the human population that recognizes both non-SARS coronaviruses and SARS-CoV-2? Sure. This would not be particularly difficult to find out, though, and is part of the normal validation that would go into any government-approved test. In particular, any government-approved screen should return a negative when screened against negative control-positive human serum, and return a positive when screened against control-positive human serum. + +Also, to be clear, this is only regarding the antibody test. The FDA-approved tests for active infection are RNA-based, and are already considered highly specific for SARS-CoV-2." +1563 Is it possible for a tidally locked planet to have a tidally locked moon? 5 https://www.reddit.com/r/askscience/comments/fzjior/is_it_possible_for_a_tidally_locked_planet_to/ 1586640500 fzjior Physics 2020-04-12 0:28:20 "If the planet is tidally locked to the moon: Yes. The Pluto/Charon system mentioned by /u/AsAChemicalEngineer would be an example if Pluto would count as planet. + +If it is tidally locked to the star: No. It would mean the moon orbits in a fixed position relative to the star/planet system which is not a stable configuration for anything that can be called a moon. You can have things 60 degrees ahead or behind in the orbit, but that's not a moon." "Indeed it is possible and our solar system has an example of this: + +* https://upload.wikimedia.org/wikipedia/commons/2/2f/Pluto-Charon_system-new.gif + +Pluto and Charon and mutually tidally locked such that they are always in the same position, facing the same way, in each other's sky. Because Charon's orbit is fairly elliptical, this means if you were standing on Pluto and watching Charon for a full Plutonian day (~6d 9h), you'd see it moving close and farther away like a yo-yo over time." +1564 How do the Andes Mountains affect Chile's vegetation and climate in the North and South? 5 https://www.reddit.com/r/askscience/comments/g09e5g/how_do_the_andes_mountains_affect_chiles/ 1586742549 g09e5g Earth Sciences 2020-04-13 4:49:09 "In general you're correct, precipitation tends to be higher on the windward side of mountains, leading to a [rain shadow](https://en.wikipedia.org/wiki/Rain_shadow) on the leeward side. In terms of the Andes, the important thing to remember is that they are extremely long and oriented in a North-South direction, meaning that they span multiple, major changes in dominant [prevailing winds](https://en.wikipedia.org/wiki/Prevailing_winds). Along their entire length, the western side is the windward side at the extreme southern tip (with the westerlies blowing from west to east), whereas the eastern side is the windward side in the north (with the trade winds blowing east to west). Northern Chile lie in between these, and the area you're talking about is the [Atacama desert](https://en.wikipedia.org/wiki/Atacama_Desert). The hyper aridity of the Atacama is a byproduct of a few interactions, one of the main drivers being the [Humboldt current](https://en.wikipedia.org/wiki/Humboldt_Current) an ocean current driven by the trade winds. The aridity is enhanced in much of the Atacama because it actually lies between two mountain ranges, the Chilean coast range and the Andes so it is further isolated from moisture. + +The nature of the wind currents along the length of the Andes (and distribution of precipitation that results) change fundamentally if you 'remove' the Andes (e.g climate simulations run with various fractions of the Andean topography in [Ehlers & Poulsen, 2009](https://www.sciencedirect.com/science/article/abs/pii/S0012821X09001149)) so the influence of the Andean topography is not just as simple as concentrating rainfall on one side vs the other, i.e. the direction of major wind currents in the atmosphere change and in turn change ocean currents, etc. The Andes are an extreme case because of their length and orientation, but in general, we see similar major changes in wind currents, ocean currents, and precipitation as a result of the presence of large mountain ranges (like the Himalaya) that go well beyond the simple orographic effect / rain shadow." +1565 Is it possible for someone to lose their ability to sleep? 5 https://www.reddit.com/r/askscience/comments/g1yj9x/is_it_possible_for_someone_to_lose_their_ability/ 1586977823 g1yj9x Human Body 2020-04-15 22:10:23 "Yes, it is. You can read up on one of them [here](https://en.wikipedia.org/wiki/Fatal_insomnia). + +TL, DR: It's a rare neurodegenerative disease that will eventually make it impossible for someone to go into the stage of sleep where we dream. There's no known cure and it is, eventually, fatal. + +There are other things that can make it very hard to sleep (most of them related to brain injuries), but those won't neccessarily kill you." +1566 What is the diff. bet. DC and AC Conductivity for Metals Vs Dielectrics, and how do they change with frequency? 5 https://www.reddit.com/r/askscience/comments/g1av47/what_is_the_diff_bet_dc_and_ac_conductivity_for/ 1586888586 g1av47 Physics 2020-04-14 21:23:06 "A point of clarification: DC corresponds to a frequency of 0 (you can imagine it as an oscillating signal that just never oscillates). So there is no ""combined DC and AC conductivity."" Once your frequency is above 0, it is just AC conductivity. + +Also note that, for purposes of electrical engineering, high DC conductivity is the definition of a metal. + +You are correct about the general trends of metals and non-metals. However, I want to note that in general metals tend to be better conductors than non-metals at high frequencies, even though the trend is for metal conductivity to decrease and non-metal conductivity to increase." +1746 What are the purposes of boogers? Why do they form in our nasal cavity? 5 https://www.reddit.com/r/askscience/comments/jvz0nw/what_are_the_purposes_of_boogers_why_do_they_form/ 1605639723 jvz0nw Human Body 2020-11-17 22:02:03 "The mucus and hair in your airways help trap particles in air that would otherwise go all the way to your lungs. By filtering the particles earlier, your immune system doesn't need to clean up all the foreign bodies that have no way our of your lungs. + +Coughing or swallowing mucus and blowing your nose or wiping with a tissue to get rid of boogers are ways for your body to remove those particles once they are trapped. Boogers are a combination of mucus and dust/particles from the air. + +Edit:typos" +1747 Why are sedimentary rock layers clearly defined, rather than being a smoother gradient of colors? 5 https://www.reddit.com/r/askscience/comments/is1b8u/why_are_sedimentary_rock_layers_clearly_defined/ 1600014383 is1b8u Earth Sciences 2020-09-13 19:26:23 "Not all layers in sedimentary rocks are as clearly defined, but your eye will certainly be drawn more towards the ones clearly distinguishable and we tend to use the clear breaks to define ""facies"" which represent signficant changes. Specifically, clear breaks in a set of sedimentary rocks with major color, compositional, or textural changes across them are often reflecting a change in 'depositional environment', e.g. sea level rises and inundates an area leaving a clear break between beach sand (which will become sandstone, so maybe a white to yellow color with a distinctive set of textures developed from wave action) and deeper water muds (which will become a shale, so thinly laminated reflecting less water movement, very fine grained, and black to grey in color). This is often described in terms of [Walther's Law](https://en.wikipedia.org/wiki/Facies#Walther's_Law_of_Facies). But within either of these facies (representing the different environments) there will be lots of gradational changes in texture, grain size, and composition which can be defined as layering as well, thought not as visually clear, but when someone is ""logging"" a section, they might still consider this layering, depending on the level of detail. + +The other important factor is that the stratigraphic record is very incomplete, so many times these clear breaks which define layers represent ""missing time"", either erosional surfaces or hiatuses in deposition. The completeness of the stratigraphic record, and how much time is truly represented vs missing, has been an ongoing question for a long while, e.g. this paper by [Trabucho-Alexandre, 2015](https://sp.lyellcollection.org/content/404/1/251) (with a truly hilarious and instructive abstract). More generally, the presence of a hiatus or erosion (and especially the latter) can make what was a gradual transition from one depositional environment to the next appear abrupt in the stratigraphy as these visually striking layer boundaries about which you are asking. However, especially hiatus can happen in the middle of deposition of a particular facies, which is the origin of the problem (i.e. how do you recognize there is missing time in a monotonous section of the same rock)." +1748 How effective are vaccines? 5 https://www.reddit.com/r/askscience/comments/ivbvx4/how_effective_are_vaccines/ 1600454469 ivbvx4 Human Body 2020-09-18 21:41:09 "Vaccines aren’t 100% effective. They will not guarantee that you won’t get the disease they’re designed for, and they generally don’t protect against diseases they aren’t intended for. + +However, they do reduce the likelihood of a vaccinated person catching the intended disease. Some of the common vaccines are almost 100% effective; it’s how we’ve eliminated polio. Other diseases like the flu are trickier and only run at 40% effective. It depends largely on how the human immune system interacts with the disease. For some diseases, like polio or smallpox, the body’s really good at remembering the vaccine’s signature and will kill any of the associated disease quickly. For flu, there’s lots of slightly different strains, and our body isn’t as good at fighting them, so the immune system might not recognize the specific flu as a bad thing. There are other reasons, but those get extremely complicated. + +But the important thing is how many people are vaccinated. For example, take a disease that, on average, one sick person will transmit it to one non-vaccinated person in a 10,000 person population with 1% with the disease already. It’s gonna get most of the population sick eventually if there’s no vaccine. But if everyone takes a 40% effective vaccine, only a small fraction of the population will get it because the first 100 will only infect 60, that 2nd group only 36, and so forth." "Smallpox you mentioned in your question, so I'll address that as it's a really interesting example of a cost-benefit calculation in vaccination. + +Very few people nowadays are vaccinated against smallpox, because it's no longer a disease that's naturally occurring (it was wiped out in the late 1970's after concerted international efforts that took about 30 years). In its natural state, it was highly transmissible and relatively virulent, killing about three-in-ten people (bear in mind this figure will have been skewed by lower classes of healthcare in much of Africa, Asia and South America, which were the last continents to report outbreaks). An interesting parallel with Covid-19 is that what gets lost in talk about case fatality rates is the impact the disease had on survivors: smallpox forms pustules that eventually scab over and fall or brush off, but leave survivors visibly disfigured (the longer-lasting effects of Covid-19, by comparison, include organ damage and particularly damage to the lungs). + +Officially, only two reserves of smallpox still exist: one at the CDC and one in Russia. The reason for keeping samples is because of persistent concerns around the use of smallpox as a biological weapon. The Biological Weapons Convention (BWC) prohibits the production or stockpiling of biological weapons \*except\* for ""protective"" purposes (""protective"" here meaning research into things like further vaccine development and other safeguards). + +The smallpox vaccine is actually highly effective (around 95%) and can even be given retroactively post-infection (so long as it's given before symptoms present). The last large-scale smallpox vaccination programme I can think of was of American military personnel in 2003 as part of the invasion of Iraq, when the belief/narrative was that Saddam's government could be holding stocks of smallpox as part of its supposed WMD arsenal. + +So, here's the interesting cost-benefit analysis: the smallpox vaccine \*is\* highly effective. But it also has a comparatively high rate of adverse reactions in recipients. It's a live vaccine and does not contain the variola virus (which causes smallpox), but a different pox virus in a small amount that's similar enough for the body to build antibodies against. So, you can't get smallpox from the smallpox vaccine (good), but if you're unlucky you \*can\* get a little sick (nausea, sleeplessness, slight fever - common and bad), sicker (sores, rash, eye damage - rare and very bad) or life-threateningly sick (swelling in the brain, heart damage - extremely rare and extremely bad). + +The US - last time I looked - was the only country in the world to have a smallpox vaccine stockpile big enough for its whole population. Why you don't give these out like flu shots it because of that risk of severe reactions. I had to give in and look at the CDC website for estimated adverse reaction rates, but it's estimated at about one-in-a-thousand for 'severe' complications and one-to-two-in-a-million who would die just from receiving the vaccine. So as a \*very\* broad, back-of-the-napkin calculation, that's 300-600+ dead in the US from the vaccine alone, \~330,000 severe reactions and a third of the population feeling crappy and taking time off work, school etc. Depending on how quickly the vaccine were deployed, you would also see isolated cases/outbreaks of smallpox in the population (though they would be small if the vaccine stockpile is up to date and was deployed effectively). + +So, that's a multi-layered answer to your question about the effectiveness of vaccines: there is a cost-benefit calculation for all vaccinations and multiple human elements that can cause disaster (as we've seen with Covid). **And to be very clear:** I am not suggesting anything remotely anti-vaxx. Cut me and I bleed vaccine. Smallpox is just an interesting case where the dangers of vaccinating against a disease that only exists (officially) in laboratories now are globally accepted to outweigh the risk of an outbreak. Other factors for smallpox vaccine are the relatively short window of protection it gives you (you'll need a booster every three-to-five years) and its prominence in biological weapons research during the Cold War in the Soviet Union (where the primary goal would have been to engineer smallpox variants designed to defeat available vaccines). If there were a smallpox outbreak today, there would be some very big question marks over where on Earth (literally) it had come from and whether the vaccine would be effective, given the general state of disarray of the various weapons programmes during and after the collapse of the Soviet Union (i.e. things going 'missing'). + +A more practical example of effectiveness you didn't mention was the annual flu shot. I've gone on about smallpox now for seven paragraphs, but 'flu shots' aren't effective against all influenza variants - there are just too many for that to be feasible. What goes into the seasonal flu shot is actually a cocktail of different influenza strains currently circulating that epidemiologists predict could be the most damaging. It's basically a very well-informed best-guess involving a network of global monitors, which is why occasionally you see spikes in influenza fatalities in flu season even among people who had flu shots (especially in vulnerable populations). + +tl;dr: 'effectiveness' is a broad term that can be misleading. **That being said: get your shots.** + +[Here is the CDC link for smallpox](https://www.cdc.gov/smallpox/index.html) which should back-up the above novella I wrote for you. + +And [here is a link](https://www.amazon.com/Biohazard-Chilling-Largest-Biological-World-Told/dp/0385334966/ref=sr_1_1?dchild=1&keywords=ken+alibek&qid=1600612016&sr=8-1) to one of the only accounts of the Soviet biological weapons programme, written by a defector named Ken Alibek." +1749 Are trees active during winter? 5 https://www.reddit.com/r/askscience/comments/jvbo9x/are_trees_active_during_winter/ 1605550132 jvbo9x Biology 2020-11-16 21:08:52 If you cut a tree down you see rings, these are growth rings during the winter the tree still grows but it will not grow as much as it would in summer *at least up here in Canada*, the reason the trees drop their leaves in winter is because the leaves take up resources from the tree, the same reason it doesn't produce fruit in the winter is because the tree is conserving all if it's resources to be able to live throughout the winter. +1750 Can DNA still be found in skeletal remains that have been in salt (ocean/sea) water for 20 years? 5 https://www.reddit.com/r/askscience/comments/jutwk3/can_dna_still_be_found_in_skeletal_remains_that/ 1605475624 jutwk3 Biology 2020-11-16 0:27:04 +1751 What is a pill capsule made out of? (the ones that look like plastic) 5 https://www.reddit.com/r/askscience/comments/jwfkmd/what_is_a_pill_capsule_made_out_of_the_ones_that/ 1605705348 jwfkmd Medicine 2020-11-18 16:15:48 "You're probably thinking about gelatin capsules. They last for years if stored properly but dissolve quickly in your stomach. They are very cheap, too. Here's an example: + +[https://www.amazon.com/Empty-Gelatin-Capsules-Size-1000/dp/B000ACUJRW](https://www.amazon.com/Empty-Gelatin-Capsules-Size-1000/dp/B000ACUJRW)" +1752 "Does ""concentration"" have any effect on ability to learn?" 5 https://www.reddit.com/r/askscience/comments/jus89s/does_concentration_have_any_effect_on_ability_to/ 1605470171 jus89s Psychology 2020-11-15 22:56:11 Where to begin... for the brain to actively process information, we need attention, aka concentration. Attention is like a selective filter that lets you choose which information to let in your brain and be processed. The information can then be held onto for a short period (6-9 secs)of time for example while you accomplish a task. This is called working memory. For information to be passed on to the long term part of your memory, the information needs to be maifested/recalled again and again in the working memory with the help of attentional processes. If your attention works precisely and effectively, the process is successful and it is easier to store information in long term memory. There is no uniform definition for intelligence. Depending on the definition of intelligence, stored knowledge can contribute to your general intelligence, so if your storage of knowledge is big that would make you more intelligent. Whether you acquired that knowledge due to good attention or even better education is irrelevant. Some other theories count the working memory (of which the efficacy depends directly on the attentional processes) as a factor of general intelligence. To make things even more complicated, your ability to focus is a *state* that can be manipulated or changes over time, while intelligence is more considered a consistent *trait*, which makes the two hard to compare. So while coffee can increase your ability to process and store information effectively, it doesn‘t increase your overall intelligence, because that kind of manipulation is only temporary. To recall that information you still need attentional processes and like mentioned before, the stored knowledge and working memory are only factors that contribute to the general intelligence. To conclude: while the statement in your post is not completely incorrect, i‘d put the effects on learning up for debate. It certainly has effects, but probably not any effect that would improve the results of studying directly, and certainly not to the extend that it would increase intelligence. +1753 Will COVID-19 vaccine candidates (specifically mRNA) allow us to more quickly suppress or prevent pandemics in the future? 5 https://www.reddit.com/r/askscience/comments/jvd2ml/will_covid19_vaccine_candidates_specifically_mrna/ 1605554381 jvd2ml COVID-19 2020-11-16 22:19:41 "No, the candidates won't. The platform it was created on though, has been in design for years to solve exactly this problem. Next Generation Vaccine platforms differ from classical vaccine in the way we trigger the immunoresponse. In the nature article I linked there is a nice summary of the main methods to trigger a response, but the main point is classical vaccines rely on using parts of the virus to trigger the response, while next generation uses genetic information. + +This alone is fantastically faster technology than 20 years ago, but it also allows us to trigger a response from nucleotides, as opposed to inactivated viruses or designer molecules. The process of purification therefor is infinitely faster, and the same methodology can be applied whenever a new vaccine is needed. All major pharmaceutical companies have their own platform, the machine and algorithm that 'solves' the SPIKE protein key that lets the virus into the cell. + +The common misconception is that we are cracking the code to all viruses. Pandemics will never be solved, only milder and further apart. NG Platforms however will forever change how we approach the challenge, as well as our ability to virtualize viral infections on a cellular level, so much of the grunt work that in the past took time will be done by a computer sequencing DNA. + +Heres another interesting part of the nature article: + +>Nucleic acid-based vaccines can consist of DNA or mRNA and can be adapted quickly when new viruses emerge, which is why these were among the very first COVID-19 vaccines to enter clinical trials. DNA vaccines consist of a synthetic DNA construct encoding the vaccine antigen. For efficient uptake of the construct into cells, injection needs to be followed by electroporation. After uptake into cells, the vaccine antigen is expressed from the DNA construct. mRNA-based vaccines work on the same principle as DNA vaccines, except that the first steps (nuclear translocation of the DNA construct and transcription into mRNA) are bypassed. Self-replicating RNA vaccines are likely to induce protective immunity using a lower dose, because more vaccine antigen is expressed per cell[12](https://www.nature.com/articles/s41563-020-0746-0#ref-CR12). Since mRNA is not very stable, these constructs include modified nucleosides to prevent degradation. A carrier molecule is necessary to enable entry of the mRNA into cells; lipid nanoparticles are most commonly used. Nucleic acid-based vaccines induce a humoral and cellular immune response, but multiple doses are required. + +[https://www.nature.com/articles/s41563-020-0746-0](https://www.nature.com/articles/s41563-020-0746-0)" "It's possible, but we don't know. + +There's no way to predict what the next pandemic will be. If early reports are correct, then SARS-COV-2 has turned out to be a pretty easy virus to vaccinate against. Whereas we've spent over 30 years and ungodly sums of money trying to come up with an effective vaccine against HIV and have not yet succeeded. We still have no vaccines for many of the worst pathogens afflicting humanity. + +mRNA vaccines are unlikely to prevent pandemics of *new* pathogens. Each new vaccine needs to be tested in human populations for safety and efficacy before it can be used on a widespread basis." +1754 Can Defibrillators restart a stopped heart? 5 https://www.reddit.com/r/askscience/comments/jv50wc/can_defibrillators_restart_a_stopped_heart/ 1605524872 jv50wc Medicine 2020-11-16 14:07:52 You are correct, what they are saying in the video is a simplification of a complex situation that is technically wrong. If the patients flat lines (i.e. no electrical activity) then the ICD isn't going to do anything. Your understanding is correct that when a person has a dangerously fast heart rhythm the defibrillator can shock the heart to attempt to stop that rhythm and restore a normal rhythm. Patient education like this is overly simplified to help the lowest common denominator understand what a complex technology or device is going to do. "Since that covered the electrical system of the heart, this will be easier lol. + +So the lines you see on an EKG are just electrical impulses - it doesn’t mean that the heart is actually beating. When you have a bunch of crazy electrical impulses you typically have to correct it with electricity, or “Edison medicine”. Sometimes the heart will still be beating, sometimes it won’t be. Sometimes the shock from the defibrillator or ICD will correct the electrical portion and the heart will start beating normally." +1934 Did cell phone covid-19 exposure notification apps make an impact on getting early notifications or help in reducing spread? 5 https://www.reddit.com/r/askscience/comments/o0z8nm/did_cell_phone_covid19_exposure_notification_apps/ 1623828432 o0z8nm COVID-19 2021-06-16 10:27:12 +1935 What actually kills a plague victim? 5 https://www.reddit.com/r/askscience/comments/p8udy2/what_actually_kills_a_plague_victim/ 1629562973 p8udy2 Biology 2021-08-21 19:22:53 "Plague refers to the bacterium Yersinia pestis. There are a number of different forms a Yersinia infection can take, but they're all caused by the same bacterium. The difference is in how the infection starts, and thus which tissues are primarily infected. In all cases, the infection is quite aggressive, and does widespread damage in many ways, any of which can be deadly. + +Commonly, Yersinia is introduced to a host when they're bitten by an infected flea. Often, these infections will target the lymphatic system, which it uses as a sort of highway around the body. This type of infection is called Bubonic plague, due to the 'buboes' - the swollen (and often haemoraghed) lymph nodes. Widespread tissue necrosis is typical in advanced Bubonic plague, and the resulting organ damage is a frequent cause of death. Secondary infections are a problem for survivors of the primary infection, due to the lymphatic system's role in immunity, but if the primary infection is going to be deadly, it will generally be deadly before secondary infections have a chance to establish themselves. + +Sometimes the infection will take hold in the blood instead, and this is called Septicaemic plague. Blood-borne Yersinia releases endotoxins that cause blood clots. This also causes widespread necrosis, but in this instance due to ischaemia (blocked blood vessels) rather than bacteria attacking tissues directly (though that is also occurring). This also depletes the body's clotting resources, resulting in uncontrolled bleeding. + +The third most common mode of infection is pneumonic plague, in which the lungs are the primary target. Unlike Bubonic and Septicaemic plague, Pneumonic plague is likely to spread person-to-person. Respritory failure is a major cause of death in this instance. + +And, of course, each form of plague can easily become another form. An infection that begins as Bubonic can easily spread to the blood or the lungs. However, due to how aggressive the infection is, the initial mode is often fatal (when untreated) before secondary modes have a chance to really manifest. Similarly, while sepsis is a major concern in any systemic infection, plague tends to work faster than sepsis does." +2026 If photons are quantum particle of electromagnetism, why are electric currents described as electrons flowing from one point to another? 5 https://www.reddit.com/r/askscience/comments/q23rmw/if_photons_are_quantum_particle_of/ 1633462483 q23rmw Physics 2021-10-05 22:34:43 "Electricity and Electromagnetism are related, just like the electron and photon are related, but they are different things. + +[Electricity is the flow of charged particles](https://en.wikipedia.org/wiki/Electricity). It could be any type of charged particles, but commonly it is electrons moving (because electrons are not bound to the atom in metals, they are shared so it is easiest for them to move). But, if you had flowing protons, that would also be electricity. + +The [electromagnetic force](https://en.wikipedia.org/wiki/Electromagnetism) is what causes the charged particles (aka- electrons normally) to move. Charged particles emit an electromagnetic field, and when other charged particles interact with that field, they feel an electromagnetic force. So, when there is a unbalance in charges somewhere, there will be a net force acting on charged particles, and the force will be in the direction to balance the charge (aka- opposites attract. If you have too few electrons somewhere so there is a net positive charge, that will make an electromagnetic force that pulls electrons towards the protons, balancing it out). + +As sort of a side note on electric and magnetic fields. Charged particles emit an electric field, and if the charged particles are moving, they will also emit a magnetic field. But as we know from relativity, there is no absolute measure of ""moving."" So, if I am standing on Earth and see an airplane with a net positive charge flying by, I will see an electric and magnetic field being created by that aircraft. But, for someone on the aircraft, there is no motion to the net positive charge, so there is no magnetic field. Thus, electric and magnetic fields must essentially be the same thing, and which one you measure [depends on your frame of reference](https://en.wikipedia.org/wiki/Relativistic_electromagnetism). (This doesn't really have anything to do with your question, but I think it's neat). + +The photon is the [force carrier particle](https://en.wikipedia.org/wiki/Force_carrier) for electromagnetism. It is what exchanges information between charged particles, which leads to the forces arising. A photon itself does not have any electric charge, it is simply the particle which mediates the interactions between charged particles." +2027 Is there any data on side effects and the gap between first and second dose of mRNA vaccines? 5 https://www.reddit.com/r/askscience/comments/q294sc/is_there_any_data_on_side_effects_and_the_gap/ 1633479385 q294sc COVID-19 2021-10-06 3:16:25 "In terms of side effects the CDC in the USA has a web site called VAERS (Vaccine Adverse Event Reporting System) that is a centralized database of all reported side effects for all vaccines (not just for COVID). The site can be reached here: [https://wonder.cdc.gov/vaers.html](https://wonder.cdc.gov/vaers.html) . It can be a little tricky to navigate because it contains so much data but the site has a guide. You can select what data you are looking for such as including only the mRNA vaccines. From what I have seen the mRNA vaccines have a similar percentage and types of side effects as the ""standard"" flu vaccine. + +In terms of the effectiveness of just a single dose versus both doses there are many studies available on their effectiveness, but very generally from what I have read the Moderna and Pfizer are roughly 50% effective after one dose and over 85% effective after the second." +2028 Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science 5 https://www.reddit.com/r/askscience/comments/rbt6l9/ask_anything_wednesday_physics_astronomy_earth/ 1638975610 rbt6l9 2021-12-08 18:00:10 [deleted] How can snakes shed their skin in a single smooth piece -- if they have scales? +2029 When an unstable isotope decays are the decay products always more stable than the original isotope? 5 https://www.reddit.com/r/askscience/comments/ptm7vb/when_an_unstable_isotope_decays_are_the_decay/ 1632366336 ptm7vb Physics 2021-09-23 6:05:36 "No, daughters can have shorter half-lives than parents. + +>what is it about the weak interaction + +I want to mention that it's a common misconception that the weak force is responsible for *all* nuclear decays. That's not the case; the weak force governs beta decays and electron capture, but not alpha, gamma, etc." +1567 Why are flu vaccines limited to only 3 or 4 strains? Why not compound them from year to year so young people are protected against previous strains? 4 https://www.reddit.com/r/askscience/comments/ejr2f9/why_are_flu_vaccines_limited_to_only_3_or_4/ 1578109203 ejr2f9 Medicine 2020-01-04 6:40:03 Part of it is pragmatic. Manufacturers have to prepare new vaccines every year, with maybe 6 months warning. Preparing flu vaccines means growing weakened versions of the appropriate virus in specially-sourced (pathogen-free) eggs. Each egg only provides a few doses of vaccine, and manufacturers need hundreds of millions of doses. If they doubled the number of antigens in each vaccine by including last year’s variant, they’d need to double the number of eggs they use (and double the square footage of their manufacturing plant, and the number of employees, and so on). If they used all the variants back to say 2010, they’d need to use ten times as many eggs etc - for a virtually worthless payoff, because the strains from 2010 have died out since 2012. +1568 Is it possible for plants to survive in continuous light? 4 https://www.reddit.com/r/askscience/comments/ejpz96/is_it_possible_for_plants_to_survive_in/ 1578104083 ejpz96 Biology 2020-01-04 5:14:43 "Depends entirely on the plant and the light intensity. + +In general, plants do better in alternating light/dark. The dark period helps them process the sugars they produce. Sometimes too much light will burn the plant. There's just too many factors involved. But yes, some plants will do just fine with constant light exposure. Aloe Vera, for instance, will do fine as long as the light isn't too intense and watered properly" "Most younger plants will survive and even thrive. It's in the flowering phase where stuff like blossom drop can happen. + +Some pole beans will fruit for a few weeks and then stop producing beans. Tomato plants can depend n the cultivar. + +Here's a study on 24 hour lighting and plants. + +http://www.globalsciencebooks.info/Online/GSBOnline/images/2010/PS_4(1)/PS_4(1)5-17o.pdf" +1569 When blood is drawn from the body, why is it taken from veins instead of arteries? 4 https://www.reddit.com/r/askscience/comments/g0746d/when_blood_is_drawn_from_the_body_why_is_it_taken/ 1586733748 g0746d Medicine 2020-04-13 2:22:28 Certain blood tests are done via the artery but it's a much bigger deal to do so as arteries are under high pressure. Poke them and they spurt. Penetrating them and then getting them to clot off would take a longer time (on the magnitude of even days)verses a couple minutes with low pressure veins. Lastly veins are very easy to access because multiple veins tend to lie just under the skin. +1570 Does an interferometer add or multiply together signals? Is it either? 4 https://www.reddit.com/r/askscience/comments/fztx7e/does_an_interferometer_add_or_multiply_together/ 1586684671 fztx7e Physics 2020-04-12 12:44:31 "There are a couple things that you could be referring to: + +1) There are a number of trig identities that turn adding two trig functions into multiplying two trig functions. One that you may have seen in class is the beat frequency: Add two waves with similar frequencies, and it becomes one wave with the mean frequency, multiplied by sin(Deltaf\*t) + +2) Cross correlation function multiplies one signal by a time shifted version of another, then integrating, with the largest value indicating the actual time difference." "I recently taught a course on radio astronomy, so this is fresh in my mind. It should be noted that optical interferometry and radio interferometry work differently in astronomy, so what follows applies only to radio interferometry. Sorry for not seeing your question until now. + +Yes, radio interferometry is built around the idea of correlating signals, which is a multiplication operation. So it is a different operation from 'normal'/classical interference, which is addition. But it is very similar in the sense that the output depends on the amplitude and relative phase of both waves, so we use that terminology. In that sense, there are both similarities and difference to classical interference, so using any intuition from classical interference for the behaviour of a radio interferometer should be done with a bit of caution. + +It should be noted that addition of signals, leading to classical interference, is also used in radio astronomy in the form of phased arrays. Phased arrays add the signals from multiple antennas (with time-delays) such that signals from one direction add constructively and signals from other directions undergo partial destructive interference. This gives enhanced sensitivity in the target direction, and improved angular resolution." +1571 What other families of viruses have potential to cause pandemics other than influenza and coronavirus? 4 https://www.reddit.com/r/askscience/comments/g5nzsk/what_other_families_of_viruses_have_potential_to/ 1587504105 g5nzsk COVID-19 2020-04-22 0:21:45 "In 2016, after the Ebola pandemic, the WHO made a list of viruses that should be prioritize because they could be the cause of a pandemic. + +https://www.who.int/activities/prioritizing-diseases-for-research-and-development-in-emergency-contexts" "Diseases to ruin your civilisation 101: + +* Must have high R0: ie. each infectee must infect multiple others. Either be outrageously contagious or have a very long asymptomatic-but-infectious period. If there is existing immunity in the population you must evolve around prior immunity (like flu) or be infectious enough to spread though a disparate vulnerable population (measles, pertussis, chickenpox) +* Be lethal. This conflicts directly with point 1 because dead people are not very sociable. + +Therefore it is hard for any pre-existing human disease to meet these requirements, as high lethality is maladaptive for germs. + +It is therefore most likely for a pandemic to be an emergent zoonotic infection; an animal germ that is newly learning to infect humans effectively. Given that we are then inventing a hypothetical pathogen, you can kind of choose whatever you want as the next pandemic-causer. + +The most probable infections are going to come from diseases whose current hosts are in close proximity to humans (farm animals) or have virulent living conditions (eg. bats). You would also want a germ that targets a receptor that is relatively well-conserved (ie. similar) across humans and the target population -- such as the ACE2 that COVID targets. + +Honestly, nothing is really that probable, which is why lethal pandemics have been rare in history. The only families of germs with proven potential to cause pandemics are those that we have already seen achieve it, so I would say high risk families are flu, coronaviruses and coccobacilli. + +At a lower tier, we may worry about things similar to HIV (Retroviridae), ebola (filoviridae), leprosy (mycobacteria , as is TB) and rabies (Rhabdoviridae); pathogens that are nasty and known or suspected to be zoonotic. However they each have their own impediments to future relatives becoming pandemics, chiefly that they are not sufficiently infectious." +1572 What is the functional reason as to why some leaves are serrated or have different types of margins? 4 https://www.reddit.com/r/askscience/comments/ejw25c/what_is_the_functional_reason_as_to_why_some/ 1578140685 ejw25c Biology 2020-01-04 15:24:45 "Leaf shape genetics is a pretty complex topic. See here for a review: https://evodevojournal.biomedcentral.com/articles/10.1186/2041-9139-5-47 + +In the case of the margin, I found a study on the model organism *A. thaliana* which shows that the serration is due to a self-organizing pattern of the hormone auxin. See here: https://www.pnas.org/content/108/8/3424 + +>Here, we use a combination of developmental genetics and computational modeling to show that serration development is the morphological read-out of a spatially distributed regulatory mechanism, which creates interspersed activity peaks of the growth-promoting hormone auxin and the CUP-SHAPED COTYLEDON2 (CUC2) transcription factor. + +This is similar to a reaction-diffusion system, and in general this kind of system is the source of many types of patterns in biology. But there's an added layer of complexity because the auxin is actively transported by PIN1 (an auxin transport protein). + +>At the heart of the model is a feedback loop between auxin transport by PIN1 (process 1 in Fig. 5A) and polar localization of PIN1 by auxin (process 2). Within each cell, PIN1 is polarized toward the neighboring cell with a higher auxin concentration (up-the-gradient polarization model) (10, 11). Operation of this mechanism requires the presence of CUC2, which enables the reorientation of PIN1 (process 3). Auxin, in turn, represses CUC2 expression (process 4), which yields an interspersed pattern of auxin convergence points and CUC2 activity. In Arabidopsis leaves, which grow primarily at the base, this mechanism produces a basipetally progressing sequence of auxin convergence points separated by CUC2 expression. This pattern controls local rates of margin outgrowth, yielding serrations at sites of high auxin activity and indentations at sites of high CUC2 expression." +1573 What are exosomes? What, if any, relationship do they have with viruses? 4 https://www.reddit.com/r/askscience/comments/g0f2b4/what_are_exosomes_what_if_any_relationship_do/ 1586767181 g0f2b4 Biology 2020-04-13 11:39:41 Exosomes are small membrane bound packages that bud off of the membrane of cells. They can contain many kinds of small molecules from within the cell, and are used by cells to communicate with one another. I don’t know of a specific relationship to viruses, but the process of budding may be similar to how some membrane bound viruses are released from an infected cell. Most of the current research has focused largely on exosomes as (1) Biomarkers of specific diseases or disease severity (2) Potential delivery systems for therapeutic molecules. To be clear - a virus is definitely not an exosome, even though some enveloped viruses are structurally similar because of how they bud from the membrane. A virus is a package of genetic material, and its purpose is replication rather than communication. +1574 How can I develop a fair scoring system for a game with a variable number of players from day to day? 4 https://www.reddit.com/r/askscience/comments/g0q7a6/how_can_i_develop_a_fair_scoring_system_for_a/ 1586807308 g0q7a6 Mathematics 2020-04-13 22:48:28 "One option that you could take is to convert the full match ranking into a set of pairwise match-ups. Then you can apply one of the systems that handles that type of contest. + +So for example, if someone ranks 2 out of 3, that's represented as two head-to-head matches against the other two players: A loss against the player who ranked 1, and a win against the player who ranked 3. If someone ranks 2 out of 4, that's represented as three head-to-head matches, with two victories and a defeat. + +There are a lot of algorithms for ranking players over time based on head-to-head match-ups. The Elo system, developed for Chess, is one of the earlier modern systems and is still widely used. It's fairly simple to understand, so it's worth studying. Many other ranking systems used by video games are often refinements of Elo." You're going to kick yourself when I tell you. Just give each player a number of points per game equal to the number of players they beat. So 5 player game points 4 to 0. Two player game 1 point to the winner, etc. Add a bonus point to first place if you want or stagger the points 1,3,5, etc. If you want to vary the numbers a bit but you get the idea. +1575 How do we know that photons are massless? 4 https://www.reddit.com/r/askscience/comments/g08x0y/how_do_we_know_that_photons_are_massless/ 1586740696 g08x0y Physics 2020-04-13 4:18:16 "Theoretically, it’s required to be massless, so that the Standard Model has the right symmetries ([local gauge invariance](https://quantummechanics.ucsd.edu/ph130a/130_notes/node508.html) of the electromagnetic part). + +And experimentally, the upper limit on the photon mass is being brought closer and closer to zero. The current upper limit is around 10^(-18) eV/c^(2)." "The speed of light in a vacuum seems to be independent of its wavelength (~ photon momentum due to quantum physics) and equal to the invariant speed 'c' of special relativity. + +The electric field of a charge in a vacuum seems to decay as 1/r^2, without any exponential suppression at any distance." +1576 Why is it that we were able to produce a vaccine for H1N1 reltively quickly but it will take much longer for COVID-19? 4 https://www.reddit.com/r/askscience/comments/g1ju89/why_is_it_that_we_were_able_to_produce_a_vaccine/ 1586920039 g1ju89 Medicine 2020-04-15 6:07:19 We already have a mechanism for developing flu vaccines, h1n1 was just a new strain. It's my understanding we don't have any vaccines for any coronaviruses that are closely related to this one, although one for sars was in development. "Not a doctor, but I know a little bit about vaccines. As others have said, H1N1 is just a new strain of influenza for which we already have a number of vaccines. Even so, it took roughly 6 months to develop a vaccine for H1N1 after the outbreak started. Furthermore, most strains of influenza (including H1N1) also respond to Neuraminidase inhibitors (aka. Tamiflu), so there was an existing treatment available from the very start. + +COVID-19 has no known treatment, and this particular coronavirus has a fairly unique spike protein compared with SARS and MERS, so even the experimental vaccines in development for SARS won't really work on COVID. So compared with H1N1 it's really like starting from scratch." +1577 Ask Anything Wednesday - Economics, Political Science, Linguistics, Anthropology 4 https://www.reddit.com/r/askscience/comments/g62tdf/ask_anything_wednesday_economics_political/ 1587568193 g62tdf 2020-04-22 18:09:53 What was Noam Chompsky's major contribution(s) to the field of linguistics? Is there any indication that brain size tracks with intelligence in any meaningful way? Were Neanderthals smarter than humans, whatever that might mean? +1578 Why is there more head loss in a smaller radius bend than a larger radius bend? 4 https://www.reddit.com/r/askscience/comments/g931pm/why_is_there_more_head_loss_in_a_smaller_radius/ 1588002014 g931pm Engineering 2020-04-27 18:40:14 "http://www.thermopedia.com/content/577/ + +That has some pictures of the vortices set up in the (rectangular) pipe. Those happen because aside from the fluid against the outer wall, the fluid only has itself to bounce off of. So the incoming fluid along the inside wall of the bend just flows into the center of the pipe. + +A tighter bend causes higher force which makes the vortices spin faster at the outlet, which represents more energy shifted from forward to spinning motion. + +Ducting the flow in the pipe might fix it." +1755 Why are the two new vaccines for COVID-19 both with mRNA instead of antibodies? 4 https://www.reddit.com/r/askscience/comments/jwcfjj/why_are_the_two_new_vaccines_for_covid19_both/ 1605689669 jwcfjj COVID-19 2020-11-18 11:54:29 "The hundreds of COVID19 vaccines that are in development, and the dozens that are in clinical trials, use all kinds of different approaches from mRNA to recombinant viruses to subunit proteins to inactivated viruses. + +The major advantage of mRNA vaccines is that they can be developed very quickly. That’s why the first two vaccines to reach this phase are mRNA - they are the fastest to develop. + +It doesn’t mean they’re going to be the most immunogenic or more effective or anything like that. Just that by their nature, they’re fast to go from nothing to a finished, validated and tested product. + +In the next few weeks and months, we should start seeing reports for various other types of vaccines, including some that are more conventional and easier to manufacture and distribute. If it turns out that some of these vaccines are as effective as the mRNA vaccines seem to be, it’s likely that they’ll end up being more widely used because of ease of use." Would like to add that for vaccines you don't use antibodies, but some part of a virus being it a whole inactivated virion or some protein on the surface of it traditionally. Antibodies are made as a response to those structures (called immunogens) +1756 Ask Anything Wednesday - Engineering, Mathematics, Computer Science 4 https://www.reddit.com/r/askscience/comments/jwh9sm/ask_anything_wednesday_engineering_mathematics/ 1605711623 jwh9sm 2020-11-18 18:00:23 [deleted] +1757 If regularly donating blood without being re-exposed to a particular pathogen, will circulating antibody levels decline over time? 4 https://www.reddit.com/r/askscience/comments/kez2tt/if_regularly_donating_blood_without_being/ 1608217597 kez2tt Biology 2020-12-17 18:06:37 "Nah. Not really. You lose blood constantly, it just gets recycled internally and/or passed as waste. Antibodies themselves are just these little protein markers that act as cues to the rest of your immune system. They are produced constantly, quasi-randomly, but in low numbers. When they start ""sticking"" to things, your immune system takes notice. It obviously starts attacking the ""flagged"" intruders, but it also starts preferentially cloning the antibody (or rather the cell that produces that antibody). That's really why you get sick at all (at least, among illnesses you've had before). Your body may have the template ""on file"", but it takes a bit to ramp up production." "Yes, circulating antibody levels will decline over time, but I don't think donating blood will be a factor in that. You still have some of the memory B cells, but the longevity of immunity varies depending on the antigen/disease/whatever. Sometimes it's adequate for lifelong immunity; sometimes it fades away enough to become ineffective (thus booster shots for tetanus, etc.). I think I've seen a couple of reports suggesting that COVID19 immunity seems to last around six months? I may be wrong about that. We don't know about the vaccines' long-term effectiveness yet. + +[https://www.sciencemag.org/news/2020/11/more-people-are-getting-covid-19-twice-suggesting-immunity-wanes-quickly-some](https://www.sciencemag.org/news/2020/11/more-people-are-getting-covid-19-twice-suggesting-immunity-wanes-quickly-some)" +1758 Will Covid-19 Vaccination technology work against the common cold coronavirus also? 4 https://www.reddit.com/r/askscience/comments/jvp1l7/will_covid19_vaccination_technology_work_against/ 1605599252 jvp1l7 COVID-19 2020-11-17 10:47:32 The common cold isn't causes by one single virus, but a variety of them producing similar symptoms. A lot of them aren't coronaviruses, but rhinoviruses. Also, seeing the pushback we're already hearing about a vaccine against a sickness that does put people in the hospital and is potentially fatal, I don't think a vaccination against the common cold would have great success. "I was wondering the same. I don't know the answer. My reasoning was: The vaccine learns to recognize the Coronaspike protein. And those spikes are specific to corona viruses. So maybe mRna can also be constructed for other, similar spike proteins. + +That would only affect coronaviruses of course and not other like rhono viruses." +1759 If I understand the mRNA vaccine correctly, the vaccine contains molecules that are able to enter a healthy human cell, and cause that cell to produce the spike protein of the nCOV-SARS2 virus, enabling the body to produce antibodies against the virus. What happens to the cells that are taken over? 4 https://www.reddit.com/r/askscience/comments/jvsclp/if_i_understand_the_mrna_vaccine_correctly_the/ 1605617028 jvsclp COVID-19 2020-11-17 15:43:48 "“Taken over” is not the best way to think of this. The viral mRNA is taken up by the cells, and the ribosomes recognize the mRNA as a sequence which should be translated as a protein and do so. The protein sequence has a “secretion signal” included in it, so the protein is shoved out of the cell so the immune system can see it. + +We don’t think the mRNA should do anything to the cell which translates the RNA, but in this specific case I don’t know that we know. It doesn’t have the other viral signals to make virus, or viral signals which act to fool a cell into putting the viral needs first." "I don't know how many things you know about mRNA but the truth is that it is molecule (actually a category of molecules) that exists inside every living cell. It is responsible for the cell's protein synthesis as it functions as a ""messenger molecule"" that carries information (writen in the DNA) from the nucleus to the ribosomes where proteins are made. + +Every active gene produces a separate mRNA molecule (this process is called transcription) which in turn produces a protein through its translation. So, inserting a foreign mRNA inside a cell doesn't mean taking over it, we just teach it how to produce a new protein. That protein (the spike protein when we talk about the vaccine) is then excreted from the cell and by circulating in our vascular system and tissues, it safely activates our immune system and initiates the production of antibodies for the specific protein." +1760 "Does the fallopian tube bring any interstitial ""junk"" into the uterus, and if so how does the body deal with it?" 4 https://www.reddit.com/r/askscience/comments/jwtk0u/does_the_fallopian_tube_bring_any_interstitial/ 1605750643 jwtk0u Human Body 2020-11-19 4:50:43 "Regarding what could enter the fallopian tubes from outside: Most of the organs in the abdominal cavity are surrounded by the peritoneum (a supportive membrane), so the organs kind of have their own compartment with peritoneal fluid on the inside of their compartment. So the fallopian tubes can bring in some peritoneal fluid but this is completely clean and sterile and should not have or junk in it. + +I think you question is actually better asked the other way around: +How come the bacteria living in the uterus don't get into the peritoneum or abdominal cavity through the fallopian tubes? Normally the uterus has its own microbiome while the abdominal cavity is supposed to be sterile. So I don't think the uterus is at risk of getting infected by the much ""cleaner"" abdominal cavity but the other way around I don't know." +1761 Hookah versus cigarettes in the long term? 4 https://www.reddit.com/r/askscience/comments/jvwscw/hookah_versus_cigarettes_in_the_long_term/ 1605632929 jvwscw Medicine 2020-11-17 20:08:49 "Hookah is no safer for you than cigarettes. Studies show that hookah users may even be inhaling *more* carcinogens that typical cigarette smokers. Furthermore, the water does not filter out toxic ingredients present in the smoke. + +Additionally, the flavorings used in hookah can also cause inflammatory reactions in the lung parenchyma, leading to long term consequences like pulmonary fibrosis and obstructive lung disease. + +The lungs don’t like *anything* in them except air. I would urge you not to smoke, and to encourage others around to quit as well. + +https://www.cdc.gov/tobacco/data_statistics/fact_sheets/tobacco_industry/hookahs/index.htm + +https://www.mayoclinic.org/healthy-lifestyle/quit-smoking/expert-answers/hookah/faq-20057920" +1762 When a massive star explodes, what keeps it bright for months? 4 https://www.reddit.com/r/askscience/comments/jvhn1n/when_a_massive_star_explodes_what_keeps_it_bright/ 1605568655 jvhn1n Astronomy 2020-11-17 2:17:35 "Supernovae will actually get *brighter* after they explode. The outflowing gas is hot and covers a large surface area, so it's quite bright. The nuclear reactions in a supernovae also mean that the supernova remnant is full of radioactive material. This stuff continues to decay, giving off lots of energy from nuclear reactions. This is actually the main source of brightness - a supernova could reach peak brightness *weeks* after the initial explosion, because that's about how long it takes the dominant nuclear reactions (usually Nickel) to run through. + +It gets quite complicated, and there's lot of different ""light curves"" for supernovae (i.e. how bright they are vs time), which depends on their elemental composition, how they exploded, what environment they're in etc. But it's mostly ongoing nuclear reactions that are able to make supernova so bright for such a long time." +1763 With several COVID vaccines on the cusp of being approved for use, the next big step will be mass producing the vaccine. Can Pfizer or Moderna farm out the production of the vaccine to other companies in order to get more vaccine produced more quickly? 4 https://www.reddit.com/r/askscience/comments/k6w0ii/with_several_covid_vaccines_on_the_cusp_of_being/ 1607123776 k6w0ii COVID-19 2020-12-05 2:16:16 "Actually if the information I was given was correct the production of the vaccine was already happening before the clinical trials were finished. Crazy I know but it's part of the process of speeding up the rolling out of such a vaccine. Based on the fact that the clinical trials were looking hopeful mass production had already begun before the end of the final trials. Could have been a massiveee waste if the results weren't good. + +Of course your point still stands that there needs to be a lot more produced if we are to vaccinate enough of the population!" +1764 How can the distance between two objects increase faster than the speed of light? 4 https://www.reddit.com/r/askscience/comments/jvwblq/how_can_the_distance_between_two_objects_increase/ 1605631463 jvwblq Physics 2020-11-17 19:44:23 "> What are some examples of this? + +All things that are farther apart than ~14 billion light years. Their distance increases because space expands in between them. It's not a motion of anything, the speed of light is nothing special here. The larger the distance you consider the faster this distance increases." No information is traveling faster than the speed of light. A shadow cast on the moon can go from one side to another faster than the speed of light. But is doesn't transfer any information with the speed of light. So ye a point kan travel a the speed of light. Wanna know more watch the video of cause about the speed of dark. +1765 How do they determine how many calories any specific food has? 4 https://www.reddit.com/r/askscience/comments/jv1v0x/how_do_they_determine_how_many_calories_any/ 1605507138 jv1v0x Chemistry 2020-11-16 9:12:18 "In short, the food's composition is determined through various means and through knowledge of the caloric content of each of those components, the caloric content of the total food is obtained. + +The food Calorie (big C) is equal to 4.184 kJ, which is the heat energy required to heat up one kg of water one degree centigrade. When discussing food caloric content, the analogy of combustion is often used. This is because the overall reaction of respiration (sugar + oxygen -> carbon dioxide + water) is the same overall reaction as if you had burned sugar in air. However, your body doesn't burn food, and in a combustion reaction, a lot that energy released from the process is 'wasted' to heat the surroundings. Living things draw out the process over several steps instead of one big 'whoosh' to try to extract out as much usable energy as possible. + +One could just burn some food in an instrument in a calorimeter and find out how much heat energy is released from the combustion reaction, and this theoretically would give you an idea of the maximum amount of energy available in the food, but there are a couple big problems with this. The biggest problem is that not everything that can burn can be used by the body for energy, such as fiber/cellulose. The more commonly used approach is to determine the food's composition through varying steps and then use those ""pure"" components energy value to sum up to the energy value of the entire food (for reference, 1g of carbs or protein gives 4 Calories and 1g of fat gives 9 Calories). + +Protein content has traditionally been determined through elemental analysis, which gives the carbon, hydrogen, and nitrogen content of a material through a process of *completely* burning the material and analyzing the products. The majority of the nitrogen content from food comes from protein, so using some estimations, the approximate weight% of protein can be determined in the food. There are various complications with this method including: not everything with nitrogen in the food is protein (though most of it is) and bad actors may add adulterants to increase the apparent protein content by adding in high nitrogen non-food items. + +Fats are usually determined through extracted triglycerides. Since fats are not soluble in water, they can be extracted using an organic solvent. The organic solvent is evaporated, and the fat content of the food is determined. The main source of error here is that there will b some non-fat water-insoluble content, such as cholesterol or various vitamins, but the majority of any fat present will be dietary fat. + +Historically, carbohydrate content has been determined as a ""the remaining difference"" (i.e. initial weight - water - fat - protein - ash = carbohydrates). The water is determined by drying the food and the ash is what remains after the food has been burned to completion. However, this method has a significantly higher error than the estimations used in the determinations of the other components. Carbohydrate determination often requires specific chemical reactions that are specific to certain types of carbohydrate; this allows the analyst to distinguish sugars from things like cellulose. + +Once you know the %weight of protein, fat, and carbohydrate in the food, you can find out the caloric content per unit weight." "The average calories in the four major energy-providing macronutrients (protein, fat, carbs, alcohol) was determined by burning a bunch of different molecules and seeing how much heat it generated. These values were then (**partially**) corrected to account for the actually biologically extractable energy by subtracting away the amount of energy lost in waste matter. This gives the average amount of energy that humans can get from one gram of typical carbs, fats, or proteins. The calorie content of foods is then determined by adding up the amount of carbs, fats, and proteins in it. In some cases where the only things going into the food are basic ingredients like sugar and oil it's very easy to add them up. In most cases you need to do laboratory testing to determine the chemical makeup and figure out what macronutrients are in it. + +This is called the [Atwater system](https://en.wikipedia.org/wiki/Atwater_system). It's important to do it this way, breaking down foods into basic categories of nutrients, since not all organic molecules are digestible. For example, if you burn a strawberry the fiber will also produce heat, but fiber cannot be digested and provides no useful energy to humans. + +It should be noted that nutritional information is just a rough estimate. There's a lot of places where errors can occur. For example, not all carbs have the same energy content but all carbs are assumed to provide the average 4 cal / g. And similarly, not all strawberries are the same and some will have more sugar than others. However, generally the errors due to taking averages everywhere will cancel eachother out over time so that the average provides a good estimate. Whats more tricky to account for is metabolic effects (the thermic effect of food means that although protein provides 4 cal/g, some of this is used for digestion itself and the actual usable energy is lower) or the effect that cooking or otherwise processing food has on its caloric content" +1936 Would a space heater too small for the room use more energy than a heater that is big enough to heat the room or would it all end up the same? 4 https://www.reddit.com/r/askscience/comments/o09er0/would_a_space_heater_too_small_for_the_room_use/ 1623745604 o09er0 Physics 2021-06-15 11:26:44 "Heater B, the one that is ""big enough"" would use more energy in a realistic scenario. + +Lets consider where we need energy for in our heating scenario. First, we need energy to heat the house up to the desired temperature. But when the house is hotter than the outside air, the house will continuously shed heat to the outside air. This heat will have to be replaced, which also uses energy. + +The amount of heat lost is proportional to the difference in temperature between the house and the exterior. This is also known as Newton's Law of Cooling. So if the temperature difference is 10 degrees, the rate of heat loss is twice as big as when the temperature difference is 5 degrees. + +Heater A is not powerful enough to reach the desired temperature (lets call that one T). That means that at some temperature below T, the heat loss from the house to the exterior is equal to the amount of heat produced by the heater. So the amount of energy used by heater A is simply its maximum power multiplied by the time. + +For heater B, it'll run at full blast for a while until the house reaches T. At that point, depending on how smart it is, it'll either turn off completely until the temperature drops sufficiently low or it will run at a lower power setting to keep the temperature more or less constant. + +While the house is at T, it will lose more heat than heater A is able to produce, so in the second case (heater B runs at a lower power setting to keep a constant temperature), heater B will clearly use more energy. In the first case, where the heater turns off for some time, it'll depend on how far the temperature is allowed to drop before the heater turns back on again. If you let the temperature drop far enough, you end up with heater B using less energy than heater A, but also with the scenario where the average temperature in the house will be below what heater A is able to achieve. So you lose the whole point of having a more powerful heater. In reality, the heater would pulse on more rapidly and the temperature would stay much closer to T. + +So in all realistic scenarios, the bigger heater will use more energy when the smaller heater can't reach the target temperature. The fact that the smaller heater has to run at full power the entire time doesn't change this. + +As a corollary, with basic dielectric (space) heaters that simply convert energy into heat at a constant 100% efficiency, it is more energy efficient to let a house cool down when it's not occupied and then to heat it up again than it is to keep it at a constant temperature." "Just in case the purpose of this question is to determine the 'right' size of space heater you want it's worth noting that basically every single space heater is 1500 watt. From the tiny one on your desk with a fan, to the big oil based radiator style, they all are 1500 watt. Which means their energy consumption and heat output are identical. + +At least in the US that is. + +All the stuff on the box about what size of room the device was made for is just marketing." +1937 What does oxidation state mean exactly? 4 https://www.reddit.com/r/askscience/comments/o0dy9h/what_does_oxidation_state_mean_exactly/ 1623762480 o0dy9h Chemistry 2021-06-15 16:08:00 "Use of Oxidation numbers assumes the bonds are 100% ionic, which works out OK for compounds that are actually ionic but can be misleading for covalent compounds. It can be used as a sort of bookkeeping method for covalent compounds, as in the case for redox reactions and tracking oxidation states, assigning oxidizing and reducing agents, etc. + +So in an ionic compound like CaCl2, then the charges of the ions and their oxidation numbers agree. Calcium has 2+ charge and +2 oxidation number; chlorine has 1- charge and -1 oxidation number. + +But in your case assigning oxidation numbers to CO2 is treating it as an ionic compound and that the electrons are transfered, which is not true. Carbon certainly does not actually have a 4+ charge but it does have a +4 oxidation state; it certainly did not lose 4 electrons (it'd be more accurate to say it gained 4, kind of, they are shared so it is still neutral). And neither does Oxygen have a 2- charge but it does have a -2 oxidation state (even though it kind of gained 2 electrons those electrons are still shared so it is still neutrally charged). + +So oxidation numbers treat everything as an ionic bond whether it is or is not; sometimes that is useful, and sometimes that is misleading." +1938 What makes different viruses trigger such diverse responses in our body? 4 https://www.reddit.com/r/askscience/comments/o2mwl6/what_makes_different_viruses_trigger_such_diverse/ 1624015632 o2mwl6 Biology 2021-06-18 14:27:12 "A very simplified answer would be the genetic makeup of viruses are designed to do different things. (Almost like different animal species that are designed for land, water, etc) + +A lot of the time viruses mutate randomly (and quickly) so the effects of infection could vary even if you have the same virus twice. + +Most symptoms are linked to how your body's immune system deals with the threat, or what the virus is tricking your immune system into thinking. Ebola for example is very contagious partly because it makes your body eject all of its fluids that have been infected. Increasing its chances for reproduction. Like how animals by nature want to reproduce, viruses want to do that while also finding new, healthy hosts. It's how those viruses choose to do that, that creates symptoms. + +This is a rough description of how some viruses work. The complexity of the question lies in the fact that with millions of viruses not all of them work the same way." an infection isn't a disease until damage occurs. where this damage occurs usually determines the symptoms: damage to the lungs can result in bronchitis and pneumonia, damage to the larynx can result in laryngitis, damage to the sinuses can result in sinusitis. the specifics of the symptoms depend on how the cell multiplies and what cells it attacks. some viruses can attack multiple cell types while other attack very specific cells. this is determined by the virus capsid proteins, which bind to specific receptors on the surface of the host cell, so whether or not a cell has these receptors will determine whether or not it is a potential host for said virus. +1939 How can certain bacteria and viruses be deadly to one species but completely harmless to another? 4 https://www.reddit.com/r/askscience/comments/o2mscv/how_can_certain_bacteria_and_viruses_be_deadly_to/ 1624015251 o2mscv Biology 2021-06-18 14:20:51 "You could potentially get many answers to this question! One example is if the pathogen's surface proteins recognizing specific cellular receptors that exist on one species but not the other. If they cannot recognize and attach to the cell, they are not infectious. Another variation is the immunity of the species and whether it can keep the pathogen in check. For example, bats have sophisticated anti-viral mechanisms that keep them safe from otherwise deadly viruses (like SARS!). + +Yet another variation is the part of the world the host lives in; many pathogens thrive in a specific environment, so it makes sense that they would adapt to recognize hosts that live in a similar environment. + +The short answer to your question is evolution. The host and pathogen co-evolve together which reinforces their relationship. Occasionally, however, the pathogen can mutate and cross species, like what happened with SIV and HIV." "The shortest and easiest analogy, why do your house keys work on your lock but not others? The key is anagolous to the virus, the lock an animals cells / body + +Locks vary, some more than others, keys were natrually selected to fit those particular locks. + +Sometimes the key is just a notch away from fitting your lock instead of someone else's, that key can natrually change (mutation) and ta da! Now it fits your lock!" +1940 Could seasonal allergy vaccines be created through the same method as COVID vaccines? 4 https://www.reddit.com/r/askscience/comments/nz2sga/could_seasonal_allergy_vaccines_be_created/ 1623609408 nz2sga Medicine 2021-06-13 21:36:48 "Maybe a bit of a misunderstanding of how vaccines and allergies work. Vaccines sensitize your immune system to react very quickly to a pathogen. Allergies come about from your immune system developing a sensitivity to something rather innocuous like pollen. So fundamentally you'd want a reverse vaccine. + +Immunotherapy for allergies involves slowly ramping up a dose of allergen to desensitize your immune system to it over a series of many shots. + +The mRNA-LNP technology could be programmed to create the allergen but your cells would produce a massive dose and just a guess but you would probably get anaphylaxis. + +Getting back to a reverse vaccine, there is some research into how [measles can reset immune memory](https://pubmed.ncbi.nlm.nih.gov/19255001/) but AFAIK there hasn't been much progress. This of course isn't to suggest the hygiene hypothesis for the measles vaccine which was shown not to be the case in the above study and [demonstrated again in other studies.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6190691/)" +1941 Is most melatonin produced synthetically? 4 https://www.reddit.com/r/askscience/comments/p82f2j/is_most_melatonin_produced_synthetically/ 1629454787 p82f2j Medicine 2021-08-20 13:19:47 "Wow dude this reads like a Joe Rogan podcast quote, but yeah it's synthesized chemically basically because economically it's a whole lot more efficient, less variable and more GMP than having to raise and killl a whole cow to get just one tiny molecule. + + +Then again some places in the world still make their melatonin by murdering poor moo moos + +Here's a link: + +https://www.ch.ic.ac.uk/local/projects/s_thipayang/synth.html + + +Yours sincerely + + +A scientist" +2030 How are viruses, such as covid and flu, cleared from long-lived cells like nerve and brain cells? 4 https://www.reddit.com/r/askscience/comments/q2hk31/how_are_viruses_such_as_covid_and_flu_cleared/ 1633515729 q2hk31 Biology 2021-10-06 13:22:09 [Here’s](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2891389/) an article exploring that question. Basically, there are various components of the immune response aimed at inhibiting viral activity, aside from eliminating infected cells. It would seem that the only clear mechanism of viral clearance is the destruction of infected cells, which would mean any neural infection necessarily leads to permanent infection, although many of them can be suppressed to the point of permanent latency, with little to no chance of reactivation. The mechanisms involved probably include local antibody-producing cells, modulations of protein production and virus release, and perhaps some degree of epigenetics may play a part in repressing viral genes. +2031 What is the most habitable celestial body besides Earth? If we had the technology, what would the best celestial body be to move to? 4 https://www.reddit.com/r/askscience/comments/q21e5h/what_is_the_most_habitable_celestial_body_besides/ 1633455283 q21e5h Planetary Sci. 2021-10-05 20:34:43 "rotating habitats inside the holes we’ve drilled in asteroids to mine them + +it protects from radiation, provides the precisely desired artificial gravity, and is way easier to transport to/from than the gravity well of a planet + +plus there’s way more room in the solar system for these habitats than there is on the surface of all the planets" "> SpaceX want to inhabit Mars but as it seems like a hellish place to live, what other celestial body's are out there that are closer to Earth. + +Mars is a hellish place to live, but unfortunately it is the most habitable place in the solar system off Earth. The only places closer are the Moon and Venus. The Moon can be colonized too though it's somewhat more difficult as it lacks many of the raw materials we need and the lower gravity might not be good for us long term. Venus is one of the least habitable places in the solar system." +2032 How come particle accelerator experiments take so long? 4 https://www.reddit.com/r/askscience/comments/q23cqz/how_come_particle_accelerator_experiments_take_so/ 1633461280 q23cqz Physics 2021-10-05 22:14:40 "This isn't something you can just intuit, you need to actually work out the numbers. Running an accelerator is generally expensive, so you need to understand fairly precisely how much time you'll need. And if you're wrong, you could ruin your experiment, or at least waste a bunch of beam time taking extra data. + +There are three things that determine how long your experiment needs to run for: + +1. How many particles can your accelerator put on target/at the collision point per unit time? (The beam ""intensity"" in nuclear physics, or ""luminosity"" in particle physics.) + +2. What fraction of the time will a particle on target do the thing you want it to? (Including what fraction of events of interest will your detectors actually record?) + +3. How many events do you need to detect to reach the desired level of statistical uncertainty on the result? + +Depending on all of those details, you might need a few minutes of beam time, or a few months." "> Does it take 10 years to fire a sufficient number of elementary particles at each other? + +In some cases, yes. Let's look at a specific example: A Higgs boson decaying to two muons (technically a muon and an antimuon). The collision rate and energy increased over time, but most of the data were taken at an energy of 13 TeV and a collision rate of about 1 billion per second (separately for the two largest experiments, ATLAS and CMS). About 1 in 2 billion collisions produce a Higgs boson, so we got one every other second. Due to various other work (upgrades, repairs, ramping up/down the magnets, ...) you get that collision rate for effectively 2 months per year or so, or ~2 million Higgs bosons per year. About 0.02% of all Higgs bosons decay to two muons, so you get 400 of these decays per year. That sounds like a lot - but the production of two muons is an extremely common process. You have literally millions of muon pairs that have nothing to do with the Higgs boson. 400 extra are not sufficient to identify. + +There are studies that were done with the collisions of a single day, but most of them need far more data." +2033 If a concave lens and mirror are kept under water, the focal length of the mirror stays same but changes for the lens. Why is this so? Isn't the physical length the same no matter the medium? 4 https://www.reddit.com/r/askscience/comments/q2zyr6/if_a_concave_lens_and_mirror_are_kept_under_water/ 1633576207 q2zyr6 Physics 2021-10-07 6:10:07 "Focal length isn't a physical length, though. For a lens, it is a function of the change in the index of refraction between media, because a lens works by refracting light. If the index of refraction is the same, then there's no refraction at all and the lens doesn't function. Which you can see if you put a glass lens in water and try to look through it. + +A mirror does not function by refraction, so the index of refraction of surrounding media doesn't change anything about it." "The lens' focal length depends on the refractive indices of both the lens and the surrounding material. The latter is often omitted from formulas because it's close to 1 for air. + +Instead of thinking of it as a lens in water, think of it as a glass lens coupled with other lenses made of either air or water." +1579 Do large amounts of smoke, ash, dust in the atmosphere affect cloud formations? 3 https://www.reddit.com/r/askscience/comments/ejwuf3/do_large_amounts_of_smoke_ash_dust_in_the/ 1578145820 ejwuf3 Earth Sciences 2020-01-04 16:50:20 Absolutely. As a different example, you can often see increased thunderstorms and torrential rains around a volcanic eruption due to the particulates ejected seeding clouds. Australia's bush fires are now so large that they're creating their own thunderstorms. As mentioned above, all the particulates seed new clouds called pyrocumulonimbus. These are causing thunderstorms and lightning strikes which are causing more bush fires. It's a pretty horrible situation. +1580 What is the strange vapour-ish formation sometimes seen under the surface of hot tea without milk? Is it in any way similar to the formations in a cloud chamber? 3 https://www.reddit.com/r/askscience/comments/fsfs4j/what_is_the_strange_vapourish_formation_sometimes/ 1585671334 fsfs4j Physics 2020-03-31 19:15:34 "[see here for a past thread](https://www.reddit.com/r/askscience/comments/1eu9vx/why_does_my_tea_do_this_video_included/) + +Also see [this example](https://www.youtube.com/watch?v=C3_tmNMwB6M&ab_channel=EdCaffyn-Parsons), [this example](https://www.youtube.com/watch?v=NyndU9m0gJM&ab_channel=ConorMcDonagh), and [this example](https://www.youtube.com/watch?v=f7IdB0Smlvs&ab_channel=mrgroable). + +The patterns are tiny fog droplets hovering over the tea. There's a thin boundary of air where the temperature just above the tea is high, and then quickly drops off. That boundary layer behaves very strangely. Droplets form because the layer is so thin that rising hot humid air is launched up into the cooler layer, and floats on the hot layer underneath. The high temperature gradient makes the layer surprisingly resilient, and the sheer number of tiny droplets make it behave like a very thick fluid. + +Tiny gusts of air can disrupt the temperature gradient and cause fog to recondense, but there are sharp edges because of how resilient the layer is. Even tiny variations in the static charge carried by different bits of air can cause voltage differences that create forces across the fog layer, causing it to sink back into the tea. Movements in the tea under the layer can cause changes. There's a bunch of stuff happening." +1581 I'm interested in learning more about viral phylogenetics 3 https://www.reddit.com/r/askscience/comments/fxvuft/im_interested_in_learning_more_about_viral/ 1586450803 fxvuft Biology 2020-04-09 19:46:43 It's not at the core of my field, but when you are dealing with sparse and highly mutating sequences, looking into the structure of the proteins involved tends to improve phylogenetic reconstructions. Fold families and superfamilies are more highly conserved. [Nasir, 2015](https://advances.sciencemag.org/content/1/8/e1500527) has an overview with lots of references that should get you deeper into that rabbithole. ">And do we know anything about relationships between different classifications of viruses? Do they even all share a common origin? + +We unfortunately know very little about the relationships between different groups of viruses, if any exist. Viruses don't leave fossils, and a virus today could easily be 100% different in every way from its ancestor a million years ago. This is unlike cellular life, which has components like the ribosome that are universally conserved. By analyzing the sequence of ribosome genes (and other highly conserved genes), we can piece together a phylogeny of cellular life going back millions and even billions of years. Unfortunately, there is nothing that is even close to universally conserved in viruses, so this sort of analysis is impossible. It is very hard to imagine any way around these problems. + +On a theoretical level, it is considered highly unlikely that viruses share a common origin. On the contrary, it is very likely that entities we would classify as viruses have evolved independently countless times since life began on Earth." +1582 Considering a supernova can lead to the creation of new stars is it not possible that if it was a big bang which created our universe, this event could have been a common supernova on a scale which we are just too small to understand in a universe that is much bigger than we expect? 3 https://www.reddit.com/r/askscience/comments/fz95pe/considering_a_supernova_can_lead_to_the_creation/ 1586623494 fz95pe Physics 2020-04-11 19:44:54 "A supernova is an explosion: it is a star (or stellar remnants like neutron stars or white dwarfs) which explodes and sends material traveling outward through space. It has a meaningful center from which the explosion originated. It creates star formation by adding material to the interstellar medium (the gas & dust between stars) and, crucially, by disturbing and stirring up that interstellar medium. + +The Big Bang was not an explosion. It did not send already-extant matter traveling outward in a radial direction. It was a simultaneous expansion of space itself. It did not have a center-- the whole of space started enlarging. Imagine an infinite rectangular grid of points, each spaced 1 millimeter apart. Now increase that distance to a centimeter, now to a meter, now to a kilometer. No matter where you are, you will see all other points getting farther away from you, but this does not mean that you are uniquely at the center of the event--it's happening everywhere. + +The extremely rapid expansion of space in the early moments of the universe meant that the mass-energy in the universe became less dense very rapidly, so that it could cool down and form things like protons (also known as hydrogen-1 nuclei), which, because the universe was still quite dense and hot by our human standards, could undergo some nuclear fusion and create some helium, the second-lightest element, and trace amounts of lithium. The universe's visible matter (i.e., not dark matter) was composed almost entirely of hydrogen and helium after this fusion ended when the universe was 20 minutes old or so. + +Over time, the universe became cool and low-density enough that it was transparent. This is when the photons that hat been bouncing around in the dense hot opaque primordial plasma soup were able to stream freely in all directions. This is known as the ""surface of last scattering"" and is what we see as the redshifted Cosmic Microwave Background. It's by far the most important observational tool for understanding the early history of the universe, and it demonstrates that the universe was much hotter and denser in the past than it is now. + +After the universe cooled further, the gas could start gravitationally clumping up and forming stars. + +The universe may be infinite or it may be ""finite but unbounded"", like old arcade games where you can go off the left side of the screen and come back on the right side. Either way it's extremely large, so large (and expanding so rapidly) that physical material from an explosion can never travel all the way across the universe." +1583 Where does the capsule of a benign tumor come from? 3 https://www.reddit.com/r/askscience/comments/g0kd3y/where_does_the_capsule_of_a_benign_tumor_come_from/ 1586789371 g0kd3y Medicine 2020-04-13 17:49:31 +1584 Can antibodies be cloned for mass distribution? 3 https://www.reddit.com/r/askscience/comments/g3db3o/can_antibodies_be_cloned_for_mass_distribution/ 1587166937 g3db3o Medicine 2020-04-18 2:42:17 "It’s quite easy to mass produce antibodies. It’s hard to use them as a treatment on a large scale. + +Mass producing antibodies is off the shelf technology. [Monoclonal antibodies](https://en.wikipedia.org/wiki/Monoclonal_antibody) have been around since the 1970s and have been a basic lab technique for forty years. The technology of making them suitable for human treatments has been around for 20-30 years, and there are many humanized monoclonal antibody treatments available for a wide range of diseases. + +There’s also newer technology, maybe 10 years old and just becoming routine, that allows cloning antibodies from humans that have been infected with whatever. + +Certainly at the moment hundreds if not thousands of labs and pharmaceutical companies are preparing monoclonal antibodies against SARS-CoV-2. + +But they’re not a great treatment for infectious disease. They have many of the drawbacks of convalescent serum treatment, as well as some of the advantages (see [Deployment of convalescent plasma for the prevention and treatment of COVID-19](https://www.jci.org/articles/view/138745)). + +Disadvantages: It’s easy to produce them at small to medium scale, but it’s hard to produce them on the truly global scale you’d need for COVID-19. They’re short term treatment only, lasting only days to a couple of weeks. They may prevent people from developing their own, active long term immunity. + +And traditionally, though of course we don’t know for COVID-19 yet, antibody treatment has worked better as a prevention than a cure - once symptoms are well advanced, they don’t work as well. (And since they are short term, it’s hard to use them as a prevention unless you know that this once and once only you’ll be exposed to the virus in 24 hours.) + +They’re likely to see use as a short-term, emergency use treatment in severely ill people until better treatments appear, but it’s unlikely they’ll be useful on any kind of large scale." "Nurse here, that would be a very bad idea. Antibodies are very specific to each individual person. When working correctly your white blood cells would be attacking the virus based off chemical markers from the antibodies. So correct blood type would be the first issue, but there are so many nuances that affect the process that you would be more likely to have the new donated white blood cells attacking all of the host cells (this would cause effects similar to those of AIDS) + +Many people already started developing immunity though, as many peoe did not even know they had it." +1585 How does the test for Covid 19 work? 3 https://www.reddit.com/r/askscience/comments/fzv8os/how_does_the_test_for_covid_19_work/ 1586691481 fzv8os COVID-19 2020-04-12 14:38:01 The most common test is an [RT-PCR](https://en.m.wikipedia.org/wiki/Reverse_transcription_polymerase_chain_reaction). Essentially, you isolate RNA from the sample, convert it to DNA and then amplify a sequence specific to the virus using an enzyme that copies DNA. You can monitor that with a fluorescence marker to see how many copies are made per cycle of the reaction and thus how much there was present in the first place, if any. +1586 Why are some trisomies lethal and some are not? 3 https://www.reddit.com/r/askscience/comments/g1t8bh/why_are_some_trisomies_lethal_and_some_are_not/ 1586961782 g1t8bh Human Body 2020-04-15 17:43:02 It's what the chromosome contains that determine whether an extra copy might or might not be tolerated. In general, the larger the chromosome the more harmful an extra copy is, because there's more genes. If you look at chromosome no.2 it's relatively large, and a trisomy of that would equal fatality. But trisomy 21, (otherwise known as down syndrome), is relatively very small. That being sad, size isn't the determining factor, (trisomy 22 is small but deadly), again it's mainly the genes contained in the chromosome that might be lethal. +1587 Why do quantum processors require WAY more cooling vs conventional computing? 3 https://www.reddit.com/r/askscience/comments/g27mta/why_do_quantum_processors_require_way_more/ 1587009517 g27mta Engineering 2020-04-16 6:58:37 "It's not about the heat, it's about the temperature needed. Classical computers work fine at room temperature and even a bit above. Quantum computers need to preserve the delicate quantum state of whatever their bits use, and thermal fluctuations can easily disturb them. That typically means they need to be cooled down a lot. + +It's like driving a truck through the rain (easy, collisions with raindrops don't matter much) vs. a fly flying through the rain (hard, every collision brings it off track)." "Think of quantum states as dots. At low temperatures, the dots are all separate and can be distinguished from each other. At room temperature, the dots all overlap. To draw parallels to conventional computing, the dots overlapping is like not being able to tell if your transistor is on or off, or if a bit is 1 or 0. + +The cooling in conventional computers serves a different purpose. The chips in the computer heat up due to electrical resistance. You're cooling the chip to keep things running quickly and prevent hot electrons from destroying your transistors. Even at high temps, you can run a conventional computer. The transistors will just have worse performance and will fail sooner." +1588 Are there any inhabited islands in the North Pacific? 3 https://www.reddit.com/r/askscience/comments/g2oa21/are_there_any_inhabited_islands_in_the_north/ 1587073117 g2oa21 Earth Sciences 2020-04-17 0:38:37 "Keep in mind that many of the places you may think are South Pacific islands are actually in the tropical Northern Pacific, such as Hawaii, the Philipines, Palau, Gaum, Micronesia, the Marshall Islands, and many others. + +However, most of the northern Pacific, the areas north of Hawaii, east of Japan, west of North America, and south of the Aleutian Islands of Alaska, has very few land masses. Midway Atoll is one of the few in this area although it's still geologically part of the Hawaiian Islands. There's really not much else." [Aleutian Islands](https://en.wikipedia.org/wiki/Aleutian_Islands)? Not between Hawaii and *Canada*, but North Pacific. +1589 Can a planet have a core made of diamond? 3 https://www.reddit.com/r/askscience/comments/ejferk/can_a_planet_have_a_core_made_of_diamond/ 1578058164 ejferk Planetary Sci. 2020-01-03 16:29:24 Not a core, but a planet with a higher carbon/oxygen ratio than Earth might end up with a mantle composed of diamond and silica carbide. However, these materials are poorer insulators than the silicate-dominated mantle we have, so such a planet would cool fairly rapidly in its interior and lack surface tectonics and volcanic outgassing, which are vital to the stability of Earth's habitable climate. "Cores don’t form due to density differences. You can actually prove this for yourself in your own kitchen. Make a saltwater or sugar water solution, then let it sit for as long as you can. Assuming enough water hasn’t evaporated to saturate it, you’ll find a homogenous solution with no layers on top of each other, even though the density difference between water and the salt or sugar isn’t insubstantial. When planet-building material separates into layers, it does so because of chemistry. + +Different types of materials have different forces that hold them together. Each can interact with its own kind. But if two different ones don’t have a way of interacting with each other, then it will take more energy to separate each from its own kind than combining them could release. Therefore, just like how a ball rolls down a hill, the two will separate, because it takes less energy to keep them separated than to combine them. + +So you’d have to have some chemistry that could force some allotrope of carbon out of a solution into its own physically-separate phase, which would then precipitate to the core. I don’t know that we’ve ever seen such a chemistry. Not only would the carbon allotrope (which likely would not be diamond) to sink to the core, it would have to be denser than rocky and metallic phases, and I don’t know how you’d get that. + +At standard temperature and pressure, metallic iron is about 7.89 grams/cm3. Diamond is 3 something. Granted, neither of these numbers will hold up at the temperature-pressure regime at the core, unknown to any mortal experience. But there’s no reason to believe that carbon could ever overtake iron-nickel metal, which is what normally forms cores in planetary bodies. Hard to reckon with the fact that iron has more protons and neutrons in its nucleus than carbon, no matter how you arrange the atoms. + +The rocky minerals at the deepest parts of planets (just before they transition to the core) are oxides, which may have a median density of 4.65 g/cm3 to a maximum around 11. Again, don’t know if we have any cosmic chemistry that gets carbon denser than that. + +But more importantly, I don’t know how we get any cosmochemistry where graphite, diamond, amorphous carbon, and other allotropes cannot remain mixed with the rocky materials. In fact, graphite appears all throughout the chondrite meteorites that we believe are samples of the type of material solar-system planets formed from. Even in bodies that have undergone differentiation into geologic layers, the carbon doesn’t seem to separate to any layer in particular. For example, graphite shows up in basalt melts on the earth and the moon, where it produces carbon monoxide and dioxide that help propel the magma to the surface by buoyancy. They wouldn’t be there if they were chemically incompatible with the molten silicates. + +Basically, no, I do not think we know of any situation where this could happen." +1590 What’s the difference between a live and dead cell? 3 https://www.reddit.com/r/askscience/comments/ejs6yt/whats_the_difference_between_a_live_and_dead_cell/ 1578114788 ejs6yt Biology 2020-01-04 8:13:08 "Philosophical arguments aside, if you can take a snapshot of a living cell, identify all of its components (proteins, membranes, metabolites, nucleic acids etc etc) and can somehow synthesize them all and arrange them in the same way, voila you get an identical cell. But this is as far from a trivial process as you can get. The field of synthetic biology is trying to tackle this problem as we speak. + +If you want to simplify things a bit and define viruses as living things (for the record, I do not as they can only metabolize via host), you can synthesize viral DNA and introduce them into the appropriate cell and it will happily make many copies of infection-competent viruses that can be further propagated." The obsession with DNA that comes from genetics has completely obscured the fact that all elements of cell biology, from the composition of the membrane to the subcellular localization of specific signaling molecules, are critical to proper function and difficult if not impossible to synthesize from scratch. We do not have the technology. That said - why reinvent the wheel? If it's easy to repurpose existing cells for bioengineering purposes, who would go through the effort of building a fully synthetic one? +1591 How do they figure out the meaning of lost ancient dialects that have just been discovered? 3 https://www.reddit.com/r/askscience/comments/fxj92x/how_do_they_figure_out_the_meaning_of_lost/ 1586395787 fxj92x Linguistics 2020-04-09 4:29:47 "There are a few different levels of difficulty to this, depending on the circumstances. + +1. If we can read the writing system the language is written in, and the language is related to other languages that we've already translated, then it's reasonably easy: we figure out which words in this new language are related to which words in other languages and use context to figure out the rest. It doesn't always cover everything, though, because there might be some words that slip through: in Ancient Greek, for example, which is one of the best-documented ancient languages, we have no idea what [*epiousios*](https://en.wikipedia.org/wiki/Epiousios) means - which is a serious problem, because it's a word that appears in the Lord's Prayer. +2. If we can't read the writing system the language is written in, but the language is related to other languages that we've already translated, then it's somewhat harder. The go-to method is looking for names, then using them to figure out which sounds are which, and working from there until we know which languages it's related to. If you know that *Κλεοπάτρα* is ""Cleopatra"", then you can figure out e.g. Κ = K, λ = l, ε = e, etc., and then fill in the blanks. This is how we figured out [Linear B](https://en.wikipedia.org/wiki/Linear_B). +3. If we can read the writing system the language is written in, but the language isn't related to other languages that we've already translated, then it has to rely a lot on context, and tends to end up with a lot of words whose meanings we can't figure out. Etruscan, the language of the people who ruled much of Italy before the Romans, is one such language. +4. If we can't read the writing system the language is written in, and the language isn't related to other languages that we've already translated, then we have no way of figuring out what any of the words mean, and the language remains undeciphered. The [Indus script](https://en.wikipedia.org/wiki/Indus_script) is an example: we have no idea what the language is, or how to read the writing, so we can't translate it. + +The exception to all of these is a *bilingual text*, i.e., the language we want to translate on one side and a language we already know on the other, both meaning exactly the same thing. We can use the bilingual inscription to figure out words and grammar from the language we want to translate, then use those to work out other texts. Bilingual texts make translation so much easier, even to the point of making previously indecipherable languages decipherable. + +(This last bit is why the Rosetta stone was so important. Egyptian spent several millennia in the fourth category because hieroglyphs fell out of use and, while there is [a modern, surviving descendant of Egyptian](https://en.wikipedia.org/wiki/Coptic_language), it's so far removed from Ancient Egyptian as to be not a whole lot of help. The discovery of a bilingual text made translation infinitely easier, though it still took a good couple of decades of work to crack it.)" "Essentially there are repetitive patterns that are common throughout every type of language humans have ever tried to synthesize. + +So you try to find a language that closely matches the dialect, timeframe, or geographic location and work from there. + +If you are completely blind to the creation of the language you look for commonly used segments which will lead to either consonant or vowel like patterns. + +Then you can determine if the patterns are start/stop sequences or transition sequences. Which are essentially consonants vs vowels respectively. + +Once this has yielded reasonable results and the lines and dashes can be viewed as sentences context starts to kick in. There are ~50 extremely common words used in many languages for building sentences and ideas. + +Conjunctions, prepositions, etc. + +These will be repeated ad nauseam in the text. Find them and try to determine what words are used in context around them. + +And generally isnt used at the beginning of sentences, but it can be used in a list of words and phrases and metaphors. Especially of the language isnt sophisticated enough to introduce commas yet to delineate listed items. + +If the language is extremely primitive, there will only be hundreds to a few thousand additional words to decipher. + +These would be time and geographically based words like dog, hut, yurt, house, food, partner, slave, clothing, owner, master, father, parent, sibling, etc. + +You would probably find a word for river in a dessert text as often as you would find sand in a text from a rainforest." +1592 How does our brain decide how to combine what both eyes see? 3 https://www.reddit.com/r/askscience/comments/fzgm60/how_does_our_brain_decide_how_to_combine_what/ 1586634572 fzgm60 Neuroscience 2020-04-11 22:49:32 If your visual cortex detects a deficiency in sight in a certain eye it can prioritize the other eye to maximize your sight. If you cover your right eye and look around with your left, your vision doesn't look black on the right side because your brain realizes that there's nothing to process from the right, so it'll rely on the sight of the left eye. +1766 Why do vaccines have to be injected? 3 https://www.reddit.com/r/askscience/comments/jvo1ck/why_do_vaccines_have_to_be_injected/ 1605594000 jvo1ck Medicine 2020-11-17 9:20:00 It's more effective that way because it doesn't get destroyed by the digestive system before the body has time to identify it and make antibodies. They do make some vaccinations that can be inhaled but that's not as common, there's also a nasal spray type vaccine. I did see an article last month that they're working on an inhaled coronavirus vaccine though "Your digestive system is very, very, very good at breaking down anything that does into it. Well, not anything, but most biological things. Vaccines don't survive well in the digestive tract. + +More importantly, they would have no way to enter the blood stream. Eventually it will have to get there, but there is not easy mechanism to force something to go through the cells in your gut into the blood." +1767 Is the Palmaris Longus, vestigial or functional? 3 https://www.reddit.com/r/askscience/comments/irm8mq/is_the_palmaris_longus_vestigial_or_functional/ 1599949834 irm8mq Human Body 2020-09-13 1:30:34 I did some lit review into rock climbers a few years back for my masters degree. Iirc, there was an increased prevalence of PL in highly accomplished rock climbers, and it was hypothesized that this was due to an increased peak contraction force in isometric gripping exercises. That being said, the loss of the PL doesn't impair normal function at all, which is why it is considered vestigial. +1768 Why is it so difficult to create a medication that fits its intended molecular target perfectly and only works on its intended target? 3 https://www.reddit.com/r/askscience/comments/irppao/why_is_it_so_difficult_to_create_a_medication/ 1599962766 irppao Medicine 2020-09-13 5:06:06 "One reason is that the same receptor can be used by different cells for different things. Think of it like you have a key that opens your garage, but it also opens your front door. You try to use a ""key block"" that binds to your garage door lock to keep people out. Except it also binds to your front door's lock and now you can't get in your house." Usually there is some or other consensus to be made in the design. You have to keep in mind that designing a highly potent drug to (for example) a specific receptor does not make it a very good drug. It needs to have some good pharmacological and pharmacokinetic properties, not have toxic metabolites and distribute to the right part of the body. Once one of these parameters is unacceptable, changes have to be made to the design of the drug. Which will lead to changes in the other parameters including how good/specific it binds to the target. Because of this you will get binding to other targets, thus get side effects. (And of course if the target itself is distributed throughout the body or is linked to multiple bodily functions) +1769 Are the Sars-Cov-2 vaccine trials collecting other information that would allow us to test the effects of other interventions? 3 https://www.reddit.com/r/askscience/comments/iv9ov7/are_the_sarscov2_vaccine_trials_collecting_other/ 1600447555 iv9ov7 Medicine 2020-09-18 19:45:55 Typically a trial subject would be given guidance on behaviors they should implement. In this case it would likely be: wear a mask in public, social distance, use hand sanitizer, etc. These instructions would be given to both the patients receiving the experimental vaccine and those receiving placebo. This would seek to control for those variables and level the playing field on their effects. The patient would likely have a follow-up visit where they would be asked if they had followed the instructions about wearing a mask, etc. My boss has designed several major clinical trials that have changed medical practice and he likes to talk about it sometimes (if you can believe that). If you have a clinical trial test for too many things, you lose statistical power. For example, if you had 500 people but then separated them into 250 non maskers and 250 maskers you would have half the statistical power. In general it’s better to control for such things and have 500 only maskers or 500 only non maskers. I don’t know which they will be doing in these clinical trials. It’s a good question. +1770 Will having taken the flu vaccine, somehow negatively impact taking the covid vaccine in any way? 3 https://www.reddit.com/r/askscience/comments/jvdxsw/will_having_taken_the_flu_vaccine_somehow/ 1605556995 jvdxsw COVID-19 2020-11-16 23:03:15 "Absolutely not. I can say this with much more conviction than a classical vaccine because the COV-19 vaccine candidates currently do not use any functional units of the virus. Even if the concern was that injecting fragments of a virus would be dangerous it would not apply. + +Another amazing point about New Generation vaccines such as these is that mRNA is rapidly degraded in the body, so the half-life of the injections will be very short. This means that the immunological response won't depend on anything directly from the vaccine, our own ribosomes will be producing the spike proteins and in turn the key that fits the lock by means of antibodies. + +Another user linked this article which has the answers to any other questions you might have, really amazing times we are living in. + +[https://www.nature.com/articles/nrd.2017.243](https://www.nature.com/articles/nrd.2017.243)" "No, not at all! Taking several vaccines simultaneously does not increase the risk of side effects. (https://www.who.int/vaccine_safety/initiative/detection/immunization_misconceptions/en/index6.html) + +The flu vaccine does not contain live viruses so it can't cause infection, and neither can an mRNA vaccine. Your immune system also won't get overloaded. + +EDIT: See comment below." +1771 Could mRNA vaccines cause auto-immune disorders? 3 https://www.reddit.com/r/askscience/comments/jv9l57/could_mrna_vaccines_cause_autoimmune_disorders/ 1605543623 jv9l57 Medicine 2020-11-16 19:20:23 "In a couple of words? + +Not really. + +In a few more words; we wouldn’t be training the immune system into attacking healthy cells because what the mRNA is doing is creating antigens specific to the disease that the mRNA vaccine is being administered against. The immune system checks for cells with those specific antigens in the initial immune response and attacks only those antigen-presenting cells. + +The benefit of using mRNA in this instance is that mRNA has a very short half-life and doesn’t last in the body long. The mRNA in mRNA vaccines won’t remain in the body long enough to really induce any sort of immunogenicity. Long enough to produce antigens to elicit an immune response but not long enough to cause any long term problems. + +This [nature.com article](https://www.nature.com/articles/nrd.2017.243) explains it in more detail." "The cell isn't healthy - it's been ""infected"" hence the viral protein presentation on its surface. The same process happens when you cell is infected with any virus. You get the flu, your cells process some flu proteins and present them on their surfaces for T-cells to recognize. The T-cell dependent response will lead to killing of that cell. So it's the same as getting the infection without experiencing the other unpleasant effects of infection. + +Needless to say, the benefits of vaccination vastly outweigh any potential harms." +1772 Can a vaccine generate more effective antibodies than a person who had an actual infection? 3 https://www.reddit.com/r/askscience/comments/jv03jf/can_a_vaccine_generate_more_effective_antibodies/ 1605499145 jv03jf Medicine 2020-11-16 6:59:05 "Yes because the vaccine is nicer to your body than an infection. Infection is the wildfire. Vaccine is the controlled burn. + +So your immune system is less damaged by a vaccine and can easily contain it. This allows it to protect you better in the future because it remains strong." "This is dependent on what you mean by more effective antibody. Generally, vaccinated individuals have better outcomes than people who become infected without receiving a vaccine. + +Can a vaccine generate higher levels of antibodies than the infection it protects against? Yes, [early data](https://www.nature.com/articles/s41586-020-2814-7) indicates the Pfizer vaccine did for many volunteers. However, this is not the case with many vaccines ([measles](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7158681/) for example). It’s important to note that we consider you protected with a certain antibody level, and higher levels of antibodies don’t necessarily correlate with higher degrees of protection. + +Can a vaccine generate antibodies with less risk than infection? Yes, vaccines are rigorously tested and [safe](https://www.cdc.gov/vaccinesafety/index.html). + +Can a vaccine protect you from severe disease (even if you are infected)? Yes. A great example is the [flu vaccine](https://www.cdc.gov/flu/vaccines-work/vaccineeffect.htm), which reduces the risk of hospitalization, ICU care, and cardiac events among vaccinated individuals who become infected. + +Can vaccines protect you for life? Yes, in many cases, vaccine-derived immunity is lifelong, though this is not true with all [vaccines](https://www.immune.org.nz/vaccines/efficiency-effectiveness) (infection-derived immunity is also not lifelong with some [diseases](https://journals.lww.com/pidj/fulltext/2005/05001/duration_of_immunity_against_pertussis_after.11.aspx))." +1773 Are space-based solar panels different than Earth-based solar panels (and if so, in what ways)? 3 https://www.reddit.com/r/askscience/comments/jv3n8o/are_spacebased_solar_panels_different_than/ 1605516912 jv3n8o Engineering 2020-11-16 11:55:12 "Yes! They are **way way way** more expensive! + +So, for a ground based solar panel what you care about it $ per watt. +So to setup a solar panel for my house I would want the cheapest solution that gets me to 5kW. So I might pay between 2-8$ per watt installed. These panels will be as cheap as possible, with cells under 1$ per watt. This means generally means a polycrystalline solar panel. It is a single layer assembled from many crystals of silicon. Because of the [Shockley–Queisser limit] (https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit) their theoretical maximum efficeny is 32%. [In reality their effiency is between 12-20%](https://www.energy.gov/eere/solar/solar-performance-and-efficiency). + + +Why is this? Because the solar diode needs to be setup to absob Photons, and kick out an electron at a specific voltage. Any Photon that doesn't have enough energy to get to this voltage is lost to heat. Any Photon that has *more* than this voltage loses all extra energy to heat. You only get 1 voltage per layer. + + + +Now for a space based solar panel? Suddenly cost is not relevant. Even if we lauch the absolute cheapest solar panel, the *minimum* price is 10,000$/kg. This so dwarfs the cost of basic solar panels that any weight and efficacy savings is critically important. + +So, how do we get around the SQ Limit? By stacking Layers! Now we can have our high energy photons in 1 layer, then medium energy in 1 layer, and low energy in another layer. This allows us to maximize the efficiency of the solar cell, while exploding the cost! However we can now get efficiency around double that of a basic solar cell, with >30% efficiency possible. + +So a nearly 2x power per gram, what about cost? [Try over 900$ per watt!](http://spaceflight.com/wp-content/uploads/2015/05/201410-6U-20W-Solar-Panel-Datasheet.pdf) for a 3 junction solar panel. Compare this to new single junction solar cells that are [less than 1$ per watt.](https://www.letsgosolar.com/solar-panels/rankings/affordable/)" Besides the other really well thought out response above... solar panels in space are made of completely different materials mostly to survive radiation that would otherwise shorten their lives significantly. The earth's atmosphere neutralizes most of that radiation for solar panels you see on houses or commercial centers, but in space that radiation literally breaks some materials down and in a few years time you would be seeing steady degradation in their performance and you'd be lucky if they are even working by the time a decade is up. The materials they use for space solar panels allow them about the same life expectancy as ground based panels, while also being vastly more efficient and expensive as the other guy explained. +1774 How come incision is made through the back instead of the abdomen when you donate a kidney? 3 https://www.reddit.com/r/askscience/comments/jvayym/how_come_incision_is_made_through_the_back/ 1605547961 jvayym Medicine 2020-11-16 20:32:41 "The kidneys don't actually sit in the abdominal cavity. They are defined as retroperitoneal, which means they are behind the membrane that surrounds and protects the abdominal cavity. They actually sit behind that membrane and against the back ribs. + +Kidney transplantation surgery is actually much harder on the donor than on the recipient, in terms of the actual procedure itself. The kidneys are vital to the body, so they're well protected to prevent them from being damaged. To get at them, you have to go through the back and up under the rib cage. (Non-functional kidneys are not typically removed from the recipient unless it would be dangerous to leave them in - for example, kidney cancer. The new kidney is placed in the right groin area.)" +1775 Why do some liquids evaporate so fast? 3 https://www.reddit.com/r/askscience/comments/jv2mo6/why_do_some_liquids_evaporate_so_fast/ 1605511112 jv2mo6 Chemistry 2020-11-16 10:18:32 "All liquids are in equilibrium with a layer of vapour above it, meaning you have a constant back and forth of evaporation and condensation. The vapour has a particular pressure at any given temperature, and the temperature at which the vapour pressure equals the atmospheric pressure is known as the boiling point. The higher the vapour pressure at any given temperature, the more vapour there is, meaning there is more vapour that can escape. Therefore, the lower the boiling point, the more volatile your liquid is. + +Liquids have different boiling points because they strength of the interactions between different liquid molecules vary. Liquid molecules that cling strongly to each other are less likely to escape into the vapour above it." "Nothing will ever not evaporate to some extent but some have extremely low vapour pressures so will do so only very slowly. + +Examples - Mercury (about 1/10000 that of water), heavy oils and bitumens, concentrated sugar syrup, concentrated sulfuric acid (about 1/20000 vp of water), silicone oils and polyethylene glycols." +1942 If increasing entropy tends to form clumpy formations due to gravity, why is thermal equilibrium void of said formations? 3 https://www.reddit.com/r/askscience/comments/o0n5r0/if_increasing_entropy_tends_to_form_clumpy/ 1623787149 o0n5r0 Physics 2021-06-15 22:59:09 "I think there's some confusion about what entropy is. Entropy is not just described by the distribution of a system's constituents in space. You also have to take into account the distribution of the constituents of a system in the momentum part of the phase space. + +In the end, for a system contracting in an attractive potential, the increase in the entropy associated with the increased kinetic energy/ momentum of the particles out weighs any decrease in entropy from the system occupying a smaller volume." It depends on the size and energy of the system. If the system is so small that gravity is negligible and thing are hot enough then thermal equilibrium is an evenly distributed gas. If things are cold but gravity is weak thermal equilibrium can be some solid/liquid matter and some gas in the rest of the volume. If gravity becomes relevant then thermal equilibrium can be a planet and radiation in the vacuum around it. +1943 I saw a weird rainbow ring around the sun today and I don’t know what it was? 3 https://www.reddit.com/r/askscience/comments/o2y7hn/i_saw_a_weird_rainbow_ring_around_the_sun_today/ 1624044594 o2y7hn Earth Sciences 2021-06-18 22:29:54 "This might be a [sun halo](https://en.wikipedia.org/wiki/22%C2%B0_halo) due to atmospheric hexagonal ice crystals. + +Light passing through two interfaces at 60 degrees to each other (as in a hexagon) cannot be deflected any less than 22 degrees (with respect to the horizontal incident light beam). So there is an absence of light inside the halo for angles smaller than 22 degrees." +1944 Why does stalling occur in aeroplanes? 3 https://www.reddit.com/r/askscience/comments/nyx061/why_does_stalling_occur_in_aeroplanes/ 1623592985 nyx061 Engineering 2021-06-13 17:03:05 ">I understand that an aeroplane's wings generate lift by making the air travel a greater distance on top than on the bottom in the same amount of time, effectively increasing air velocity on the top, making for a lower pressure relative to the air pressure on the bottom. + +This is not the case. The equal transit time hypothesis (that the air on top has to go further than the air on bottom in the same amount of time so it can ""meet up again"" at the trailing edge) is false. In fact, the air moving over the top of the wing moves substantially faster than required to meet the air flowing over the bottom of the wing. A parcel of air split by the wing does not join back up again. + +>I also know that at too high an angle of attack coupled with too low an airspeed, the air separates from the top surface of the wing. + +Stall has only a very small dependency on airspeed, and is essentially only a function of angle of attack. ""Stall speed"" is a misnomer. You can stall going 300 knots just as you can stall going 100 knots. The reason ""stall speed"" exists as a term is because pilots care about the answer to the question ""how slow can I be going before it is impossible for the aircraft to generate enough lift to support its own weight in level flight?"" The answer to that question is the smallest speed at which 1/2 * ρ * V^2 * C*_L_* = W (where ρ is air density, V is airspeed, and C*_L_* is lift coefficient, and W is the aircraft's weight). C*_L_* can be increased by increasing angle of attack as V goes down, but eventually it reaches a maximum, which is defined as the stall angle of attack. Stall speed, then, is the solution of that equation where C*_L_* = C*_L,max_* + +>Part of me understand that if there is no airflow, and therefore no faster airflow and lower pressure, on the top of the wing, lift will decrease. However, at the same time, if the plane is moving forward and the air is failing to make contact/follow the top surface, would that not in effect be creating sort of a vacuum would be at an even lower pressure than if there was fast airflow? Would that not in itself create more lift? + +There *is* airflow over the top of the wing; it's just that the airflow no longer smoothly follows the surface of the wing. Recirculation currents happen that fill the void below the separated flow. [You can see separation beginning to occur around 1 minute into this video (which also includes proof that the equal transit time hypothesis is false)](https://www.youtube.com/watch?v=6UlsArvbTeo). You can also see it [on this video of a real aircraft](https://www.youtube.com/watch?v=WFcW5-1NP60) -- notice that when the wing is stalled, the pieces of yarn flop around and sometimes point in the direction of travel of the plane. This airflow is oscillatory, but the averaged velocity of air in the separated region near the airfoil is lower (and therefore the pressure is higher) than it had been before stall. + +(As a matter of fact, for many airfoils some degree of separation near the trailing edge occurs before the maximum lift coefficient/stall angle of attack is reached. This is because the increased speed of the attached flow due to increased AOA compensates for the inability to turn the flow near the trailing edge, up to a certain point.) + +It's probably more productive for you to think of lift generation in terms of ""turning the airflow"". A plane flies because its wings redirect the air downward, which produces an upward force on the wings. Most of this turning is actually done by the upper surface of the wing, which is why when the flow stops following the wing, it leads to a loss of lift. Relative to atmospheric pressure, the pressure decrease over the top of the wing is larger than the pressure increase over the bottom of the wing. + +>I addition, I know that gold balls aren't smooth because a smooth surface would cause the airflow to not follow the surface around the ball far enough back. This results in the trailing-side of the ball having a very low pressure which greater accentuates the force acting against the direction of the ball. Would this not apply to an aeroplane's wings, where the top of the wing is analogous to the trailing-side of a smooth golf ball? + +It's true, golf balls are dimpled because they operate in Reynolds numbers where [a rough surface has lower drag than a smooth surface](https://en.wikipedia.org/wiki/Golf_ball#/media/File:Drag_coefficient_on_a_sphere_vs._Reynolds_number_-_main_trends.svg). Broadly speaking, this is because the dimples ""trip"" the flow to turbulent. The turbulent flow has higher average velocity close to the surface than laminar flow would, and more energy -- so the overall flow is better able to withstand the adverse pressure gradient that would otherwise cause flow separation. In other words, you're trading more drag inside the boundary layer for making sure that the flow beyond the boundary layer keeps flowing smoothly instead of completely separating from the golf ball and devolving into chaos. + +[Many aircraft use the same principle to improve high angle of attack performance, in the form of vortex generators.](https://en.wikipedia.org/wiki/Vortex_generator) The vortices generated do the same thing as the dimples on the golf ball -- they make sure the boundary layer has more energy so the flow doesn't separate. + +For aircraft, there are [even more exotic concepts like active boundary layer control](https://hal.archives-ouvertes.fr/hal-01590680/file/article.pdf) where either suction or blowing (or in principle both) are applied to control boundary layer energy and separation. For suction, for example, there is a pressure rise at the leading edge of the airfoil as the flow hits the wing -- having active suction to decrease the pressure there can decrease overall drag. For blowing, blowing air into the boundary layer near the trailing edge can inject energy (like the dimples) and delay flow separation, increasing maximum lift coefficient." ">I understand that an aeroplane's wings generate lift by making the air travel a greater distance on top than on the bottom in the same amount of time, effectively increasing air velocity on the top, making for a lower pressure relative to the air pressure on the bottom. + +First off, [that's false](https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html). + +>I also know that at too high an angle of attack coupled with too low an airspeed, the air separates from the top surface of the wing. + +That's partially correct. But an aerodynamic stall occurs when an airfoil stops producing useful lift, which can result from too little air flow (dynamic pressure) or due to too high an angle of attack. It doesn't require both. And a stall doesn't require the air flow to separate from the wing. + +*Edit: Part of the above section can be semantically debated. Too little dynamic pressure results in lift being reduced to the point that it can't overcome gravity. This is the stall speed. But it's not* technically *an aerodynamic stall without flow separation. I thought I should clarify.* + +>...creating sort of a vacuum would be at an even lower pressure than if there was fast airflow? Would that not in itself create more lift? + +There's far more to this than I could get into typing on my phone. + +But in short, lift has multiple components, and one of those is the turning of the airflow by the top of the wing, and imparting it with a velocity that is, in part, directed downward." +1945 Why do Side Bands exist in AM radio? 3 https://www.reddit.com/r/askscience/comments/o3703q/why_do_side_bands_exist_in_am_radio/ 1624072954 o3703q Engineering 2021-06-19 6:22:34 "AM just works by multiplying the signal by a constant-frequency cosine wave. So if the signal you're trying to transmit ranges from, say, 0Hz to 20kHz, you should intuitively expect the modulated signal to spread out by roughly the same 20Khz. + +In fact, the spread is ± 20Khz, for a total of 40Khz. This is ""because of the math"". Specifically, + +cos(αt)cos(ωt) = 1/2 [cos((ω-α)t) + cos((ω+α)t)] + +So if ω is our fixed frequency, say 30Mhz, and α is one of the frequency components of our signal, say 10Khz, then the output for that component will be the sum of two cosine waves, one with frequency 30Mhz - 10Khz, and the other with frequency 30Mhz + 10Khz. + +Now sum that over all the other frequency-components of the original signal, and what you get is an output wave whose components range from 30Mhz - 20Khz to 30Mhz + 20Khz." "You have your carrier frequency, say 1mhz. + +This is a sine wave at 1mhz. + +A spectrum analysis would show a spike at 1mhz. + +When you amplitude modulate it, with say your voice, + +you no longer have the simple, single spike. + +You have harmonics above and below 1mhz. + +These are the upper and lower side bands. + +These show up as a mixture of the 1mhz +- the frequency of your voice. + +It's kind of like beat frequencies. + +https://youtu.be/rmvDu6EY2lE?t=19" +1946 If you are allergic to one vaccine are you likely allergic to all vaccines? 3 https://www.reddit.com/r/askscience/comments/p83bxi/if_you_are_allergic_to_one_vaccine_are_you_likely/ 1629458970 p83bxi Medicine 2021-08-20 14:29:30 "Most vaccine reactions are reactions to components of the vaccine like stabilizers or preservatives rather than the actual immunogen (the virus, protein, mRNA, or toxin that the vaccine is inducing an immune response to). PEG, which is a component of the COVID-19 vaccine that some people are allergic to (1 in 760,000) is a stabilizer. A lot of influenza vaccines contain a small amount of the protein albumin as a stabilizer, which is found in eggs, so you may recall being asked if you are allergic to eggs before getting the flu vaccine. + +So if a person is known to have a PEG allergy, it would make sense for them to avoid the COVID-19 vaccine, and if someone knows they are allergic to eggs, they may be advised to avoid the flu vaccine. (I say “may” because current flu vaccines contain a very small amount of albumin, too low to trigger an allergic response in most people.) But often when a person has a bad reaction to the vaccine, it’s not apparent which component in the vaccine caused it. Since a lot of these vaccines share these components, it’s possible, even likely, that a person who is allergic to one vaccine will be allergic to another. Usually if a patient has a severe reaction to a vaccine, they would be sent to an immunologist for more extensive testing to determine which specific component they are allergic to. They would then be advised to avoid vaccines with that component. If it’s a common component, that may mean avoiding numerous vaccines, but not all. Different types of vaccines (mRNA; live, attenuated virus; heat-killed virus) will have different stabilizers and solubilizers, so it is highly unlikely you would be allergic to something that is contained in all vaccines. + +PEG is the component that 1 in 760,000 people are allergic to, like you mentioned. As far as I know, it is not a common component of vaccines other than mRNA vaccines. So if you had a previous vaccine allergy, PEG is not likely the trigger, and determining whether you would be allergic to future vaccines really depends on identifying the specific component that caused the reaction." "No. Different vaccines are made with different components. The two-step process you describe is the COV-19 shot, which is based off of messenger RNA technology, which has never been available to general public before. Experimental versions of vaccines based on this technology have existed for almost 3 decades, but the body of research on their effects is not nearly enough for the technology to be called ""mature"". + +The tech behind this is distinctly different from something like your seasonal flu shot, which relies not on gene therapy, but on introducing a relatively benign variation of the virus in order to ""train"" your immune system to fight it better. Therapy like this has existed for over a century now. + +Besides being based on different technologies, vaccines can also be made to combat different viruses, which might require different environment in stasis and consequently - different vaccine components. + +For all these reasons, it's not likely that when allergic to one type of vaccine, a person would be allergic to all types of vaccines." +1947 Can't we include multiple virus traits rather than just the protein spikes in the Covid vaccines? 3 https://www.reddit.com/r/askscience/comments/p8vinv/cant_we_include_multiple_virus_traits_rather_than/ 1629566821 p8vinv COVID-19 2021-08-21 20:27:01 Not really. Although not a cell, the virus has a membrane, just like cells. Only the membrane (and everything on it) can be detected by factors external to the virus (e.g white blood cells). So we want these cells to detect something on the membrane of the virus, that's unique to it. For COVID, these are the spike proteins. What we can try doing is adjusting our vaccines to cover the different spikes (or other proteins, if there are such) on the variety of the COVID variants. Potentially, but a big part of why the spike protein was chosen was because so much of the work had already been done for related viruses. That meant adapting the technology to COVID-19 was extremely rapid, which was a high priority. Don’t forget that spring last year we were being regularly told that it might be several years before we had a working vaccine. The fact that we got something that works so well, so quickly is a testament to how thoroughly the groundwork had been laid. +1948 Is it possible to directly demonstrate that electrons have mass in an educational context without abstract mathematics? 3 https://www.reddit.com/r/askscience/comments/o00kaq/is_it_possible_to_directly_demonstrate_that/ 1623714855 o00kaq Physics 2021-06-15 2:54:15 There are ways to directly measure the speed of an electron. That the speed is less than c means it must have mass. But appreciating that requires some understanding of relativity, which it sounds like you're trying to avoid. To demonstrate that they have a non-zero mass you don't need an explicit calculation. There is some force, there is some acceleration, m=F/a neglecting relativistic effects. +1949 Are there different types of magnetic fields? 3 https://www.reddit.com/r/askscience/comments/o3fjwp/are_there_different_types_of_magnetic_fields/ 1624107520 o3fjwp Physics 2021-06-19 15:58:40 "> Are there different ""frequencies"" in magnetic fields such that the measurement of one field might not get affected by the other? + +Nope! In a sense, the universe has *one* magnetic field. While you're used to thinking about 'this magnetic field around this bar magnet' and 'this other magnetic field around this refrigerator magnet' those are really just the 'contributions' of those two magnets this one magnetic field. This is what we mean when we say magnetic fields are in a superposition- at any point in space, you feel the contributions of every magnetic thing all at once, and that information (about all the little magnetic contributions from this or that) is kept in the magnetic field. In your compass example, at no point does the second magnet and the field around it cease to exist or reach your compass, it just gets far enough away that the interaction between the compass needle and the earth's field dominates. + +It's in many ways similar to gravity. The earth or sun's gravity doesn't just stop if you go far enough away from the solar system, and your local experience is governed by whatever strong gravity source is closest to you. Electromagnetism is very different than gravity in a lot of ways, but the same general principle holds. Magnets are the same way, but for practical purposes you don't need to take into account all these contributions to the magnetic field (from the sun, or the magnets owned by a guy in Dusseldorf, or from the gas in the galaxy)." "> Are there different ""frequencies"" in magnetic fields such that the measurement of one field might not get affected by the other? + +I'm not sure if you mean ""frequencies"" literally. Your compass obviously cannot pick up high-frequency magnetic fields – it's easy to generate magnetic fields that alternate millions of times per second (just send a high-frequency current through a coil of wire), your compass probably cannot spin that fast." +1950 What components of 21st century technology predispose them to eventual failure? 3 https://www.reddit.com/r/askscience/comments/p88096/what_components_of_21st_century_technology/ 1629474875 p88096 Engineering 2021-08-20 18:54:35 "First, be very sure that you're not engaging in selection bias. We have lots of TVs, VCRs, and Commodore 64's laying around that still work from the 70's and 80's, but the reason they're still laying around is because those are the ones that work. The VCRs that broke in 1985 all got thrown away in 1985, and it may be the case that VCRs as a whole aren't particularly more robust. Anyone who used one of these devices back in the day remembers having to clean heads, open up and clean out destroyed tapes, their kid shoving bread in the VCR slot, etc. + +That said, there does seem to be a perception of reduced quality. My personal belief is that there are a few different factors all coming together. It's not actually the components themselves, but rather the design philosophies of the people making the product. It's also more complicated than ""make crap as cheaply as possible."" Several big advances in recent history, hitting different industries at different times, have lead to a perception of less robustness since around WW2. These are: value engineering, better analytical methods, and an increased complexity in the systems we use. + +Value engineering, put simply, is making sure that you're not putting in more time and effort than you need to based on the desired quality of product. This doesn't mean cutting corners, but it can mean reducing the quality of individual components to be in line with the overall expectation. A part that used to be made out of metal might be substituted for a plastic part, for example, if the engineering analysis says the plastic part does the job just as well. In an analytic sense this shouldn't represent a decrease in quality, but by replacing a metal part with a plastic part you've perhaps introduced a new failure mode that didn't exist before. + +Analytic methods have also gotten amazingly better, particularly with the advent of computer simulation techniques. The basic ideas have not changed, but for example a modern desktop computer can run reasonably complex finite-element models informing the design of everything from cars and planes to bridges and buildings. Now, in an engineering context this means more precision is available to product designers, and I contend that this actually leads to a reduction in overall quality. + +When a specific part is designed it has a list of requirements that it must meet. It has to have a certain strength, it must resist certain kinds of forces, etc. When you have more accurate simulation and design software, what this means is that you can get a lot closer to those tolerances than you could before. If the spec said that it withstands 1000N of force, then back in the day they'd come up with a stamped metal part or a milled metal part, or a few others based on the kinds of manufacturing capacity they had available, and then pick the cheapest option that met the spec. However, ""overbuilding"" was inherent just because they lacked the analytic capacity to drill down on every single part, so the part might actually hold 2000N instead of 1000N just because it wasn't worth anyone's time or effort to really optimize this one piece. + +These days we do have that analytic capacity, aided in large part by computers and better manufacturing techniques. If the part spec says 1000N capacity, then a good computer design tool might get that down to 1100N and call it a day. The modern part still meets the requirement, but the individual part is able to be designed and made to a tolerance that is much closer to failure than the older part. There's nobody at any point saying ""let's build cheap crap"" but the modern version might have significantly less headroom than the older version, and the result is an overall less robust product. + +Lastly, modern devices are legitimately more complex than the devices we were making in the 70's, 80's, or at any other time in history. You can build an entirely analog VCR, which ultimately has one or two motors, some switches, a dozen or so moving parts, etc. Many old VCRs have a wiring diagram on the inside cover so you can diagnose and make your own repairs! By contrast, a DVD or Blu-Ray player is an entirely digital device with hundreds of individual electronic components, and then also microprocessors that might have thousands or millions of their own components (transistors). + +What this means is that the level of complexity can predispose the product to failure, and not the individual components. You could very well have more reliable components (as is typically the case when you look at analog vs. digital) and the overall system reliability goes down because the digital version has so many more components. + +For example, you might have one device with 10 components where every component has a mean time to failure of 1000 hours. You might have a digital device with 1000 components and every component has a mean time to failure of 10,000 hours. Each individual component is 10 times more reliable, but there are 100 times as many components, so the overall system is less reliable. + +Lastly, you didn't ask this, but you do have to ask whether this is actually a bad thing or not. Nobody at any point is trying to cheat anybody, we're just building more complex products closer to their design spec than we ever have before. This does have a lot of impacts on the environment, on culture, etc. But is it a bad thing? + +One thing I'll point out is that a VCR in 1985 might have cost you $300, which is $776 in 2021 dollars according to the BLS. A mid-range TV might have cost $500, which would be $1,293 today. The Commodore 64 went on sale in 1982 for $595, which today would be $1,722. + +It's also the case that our modern equivalents of these devices have gotten substantially cheaper and have not gone up with inflation. A capable Blu-Ray player today is less than $100. A mid-range TV can be had for $300. You can find whole laptops for a few hundred dollars, and if you spent $1,700 you'd be getting a really nice product. + +So it's hard to argue that modern engineering is getting it wrong. We don't want to live in a world where a TV costs $1500 but lasts for 40 years. How many people would still willingly use a 40 year old TV today if they had one?" "I don;t know if they do. I had a tv power supply fail after 11 years and taking the main board with it. I sourced the exact same model TV and that's now 14 years old. My PVR is 10 years old. I'm typing this on an 11 year old laptop. + +I did dispose of a broken monitor last year. 12 years old only and the backlight failed. + +​ + +What I do find is that when things break they are now very difficult to fix yourself." +1951 How is Alzheimer's diagnosed? 3 https://www.reddit.com/r/askscience/comments/nzonqr/how_is_alzheimers_diagnosed/ 1623682617 nzonqr Medicine 2021-06-14 17:56:57 "I’m not a specialist in this and I don’t know if this helps at all, but I work in healthcare and in hospitals all over my city for around 6 years. I personally have never seen Alzheimer’s as a diagnosis, instead it is always listed as “dementia” which is the broader term for disorders causing memory problems. + +If I remember correctly, the only true way to diagnose Alzheimer’s is through the testing of brain tissue after someone is deceased. Until there is physical testing on the brain, you can guess that it may be Alzheimer’s by determining what disorders it isn’t, but it’s just a guess based on elimination of other options. + +Again, I may be 100% wrong about everything I’ve stated. Just repeating the limited information I know or have heard in a clinical setting." +2034 Do Antibiotics Reduce Vaccine Efficacy (E.g. the Pfizer vaccine)? 3 https://www.reddit.com/r/askscience/comments/q2eipa/do_antibiotics_reduce_vaccine_efficacy_eg_the/ 1633500980 q2eipa COVID-19 2021-10-06 9:16:20 ">**How long after receiving a COVID-19 vaccine can I take an antibiotic safely?** + +>There is no influence or interaction between antibiotics and COVID-19 vaccines, so when indicated, antibiotics may be taken at any time relative to COVID-19 vaccine administration. + +--[National Foundation for Infectious Diseases](https://www.nfid.org/infectious-diseases/frequently-asked-questions-about-covid-19-vaccines/)" +2035 Are people who have already had covid or been vaccinated, more likely to be asymptomatic? 3 https://www.reddit.com/r/askscience/comments/qkqppj/are_people_who_have_already_had_covid_or_been/ 1635809028 qkqppj Biology 2021-11-02 2:23:48 "Yes we have extensive proof that vaccines make you more likely to be asymptomatic if you get it and it makes less likely for you to get it in the first place. + +As far as previous infection, theoretically possibly yes. But I don’t think we have evidence of that as much as vaccines." "Absolutely. But more importantly, we are engaging in a bit of bias with our testing samples across the US. Unvaccinated people are going to be tested far more frequently than the vaccinated. In fact, at the beginning of 2021, people were so set on the [vaccine being a silver bullet](https://www.cdc.gov/mmwr/volumes/70/wr/mm7013e3.htm) (we said it reduces your chance of INFECTION by 90%) that the vaccinated wouldn't even have to get tests to enter hospitals (as opposed to all the unvaccinated). One could argue that a if a population is tested more often (we can say 3x, 5x, 10x, whatever you feel is correct) they will be more likely to find a positive result (even if the person is asymptomatic). + +Now, to be fair, natural immunity does wane over time. [They say that your natural immunity will likely wane within 16 months.](https://thehill.com/changing-america/well-being/prevention-cures/577541-unvaccinated-people-should-expect-to-catch-covid) However, you'll also note that the pandemic has been around for a similar amount of time. [And natural immunity seems to give you a broader base immunity against COVID, variants, and even SARS](https://www.science.org/content/article/having-sars-cov-2-once-confers-much-greater-immunity-vaccine-vaccination-remains-vital) toward the [Delta variant than the vaccine.](https://www.cnbc.com/2021/07/23/delta-variant-pfizer-covid-vaccine-39percent-effective-in-israel-prevents-severe-illness.html) And of course, to keep up your immunity with the vaccine, you'll need that booster every 6-8 months. + + +Side Note: Does anyone else find it weird that the boosters were given resistance at first when Pfizer and Moderna were pretty clear at the outset that boosters would absolutely be needed at the 6 month mark? Like, we all knew that several months before the vaccine was even out, and then we all pretended to be shocked." +2036 Does polypropylene contain phtalates? If they do, how are they released into the environment? 3 https://www.reddit.com/r/askscience/comments/q28sad/does_polypropylene_contain_phtalates_if_they_do/ 1633478192 q28sad Chemistry 2021-10-06 2:56:32 "Oh man I've waited for this one. Phthalates are used as Plasticisers for PVC only. + +PP isnt super brittle so it doesnt need the Plasticising like PVC does. + +Pthalates are also used in makeup, detergents, shampoos and some other things. + +There is a study done on Pearl Oyster farming equipment using Polypropylene material claiming that Pthalates came off the test samples. Looks pretty shocking until you look at the control seawater from the same area that the test samples were taken and it is higher in most test chemicals. Not a good sign for the degradation of our oceans :( + +You're safe with PP, we should be using it as a PVC replacement for a lot more..." +2037 If I shoot a jet of water at an object, it will have less force if the object is already moving away from me, due to relative velocity. What if the thing I'm shooting is light? Will it get the same force regardless of the relative velocity? 3 https://www.reddit.com/r/askscience/comments/rc0u3c/if_i_shoot_a_jet_of_water_at_an_object_it_will/ 1638997154 rc0u3c Physics 2021-12-08 23:59:14 "The quick answer is 'no.' As the ship picks up speed and move away from the light source, that light source will impart less momentum on the solar sail than it did when the sail was at rest. The reason is due to [redshifting](https://en.wikipedia.org/wiki/Redshift). + +If you are moving in relation to a light source, that light will shift in color. If you're moving away from a light source, the light will shift to be more red (get a longer wavelength), and if you're moving towards it, it will shift towards the blue (get a shorter wavelength). The most famous place we see red-shifting is when we observe galaxies, and we see far away galaxies are more red-shifted than close galaxies. This shows us that the universe is expanding, and that the further things are away, the more they are red-shifting. However, a more practical example of this is just how radar's measure speed- radars measure the [Doppler effect](https://en.wikipedia.org/wiki/Doppler_effect#Radar) of the object it is tracking, and can tell the speed by how much the light has shifted from what was emitted. + +So, as you are moving away from the light source, picking up speed, the photons hitting your sail will be red-shifted (meaning, they will have a longer wavelength). And we know that the momentum of a photon is [inversely proportional to the wavelength of that photon](https://en.wikipedia.org/wiki/Photon#Physical_properties). So, as the wavelength increases, the momentum of each photon is less." +2038 Does Jupiter not technically orbiting the sun also make it not a planet? 3 https://www.reddit.com/r/askscience/comments/rbstru/does_jupiter_not_technically_orbiting_the_sun/ 1638974565 rbstru Astronomy 2021-12-08 17:42:45 "Note that the IAU definition does not exactly match what astronomers actually call a ""planet"" in practice, even in formal journal articles and conferences. For instance, a planet is formally defined as orbiting the *Sun*, which means that exoplanets (i.e. planets around other stars) are technically *not* planets. But if you go to an exoplanet conference, people will refer to exoplanets as ""planets"" and nobody will correct them. So what the IAU technically says on this isn't super important. + +But anyway, here is the formal definition from the IAU: + +>(1) A planet^1 is a celestial body that + +>(a) is in orbit around the Sun, + +>(b) has sufficient mass for its self-gravity to overcome rigid body forces +so that it assumes a hydrostatic equilibrium (nearly round) shape, +and + +>(c) has cleared the neighbourhood around its orbit. + + +>(2) A ""dwarf planet"" is a celestial body that + +>(a) is in orbit around the Sun, + +>(b) has sufficient mass for its self-gravity to overcome rigid body forces +so that it assumes a hydrostatic equilibrium (nearly round) shape^(2), + +>(c) has not cleared the neighbourhood around its orbit, and + +>(d)is not a satellite. + + +>(3) All other objects^(3), except satellites, orbiting the Sun shall be referred to +collectively as ""Small Solar System Bodies"". + +Footnote (1) is: + +>The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. + +So there's no ambiguity - by the IAU definition, Jupiter is a planet, because it is listed as one of the eight planets in the official resolution. + +You are right that no clarification is given for (1a) - what does it mean for something to be in orbit around something else? Is the Earth in a sense, orbiting the Moon, because our planet is moving in a little circle each month? The most common answer is ""no"", but for such a formal definition, it really doesn't tell us much. A similar issue - and this is a bigger one - is that no clarification is given for (2c) either. Jupiter has two sets of asteroids - the Trojans and Greek ""camps"" - that orbit 60° in front and behind in its orbit, within the Jupiter-Sun L4 and L5 Lagrange points. Jupiter hasn't cleared its orbit - in fact, its big enough that its gravity has created little stable spots for asteroids to collect in. So (2c) can't quite be taken literally either, without further clarification." "There's a language semantics shift here. When someone says ""What it's orbiting"" they don't mean what barycenter point in space it's orbiting. They mean what object it's orbiting. The denser an object, the less likely the barycenter will be ""inside"" it." +2039 Do sharks hurt their own stomach with their teeth during gastric eversion? 3 https://www.reddit.com/r/askscience/comments/rc3i83/do_sharks_hurt_their_own_stomach_with_their_teeth/ 1639004828 rc3i83 Biology 2021-12-09 2:07:08 +1776 What is the evidence that viruses are alive? 2 https://www.reddit.com/r/askscience/comments/jvd8ps/what_is_the_evidence_that_viruses_are_alive/ 1605554892 jvd8ps Biology 2020-11-16 22:28:12 +1777 Is there a way of removing a recessive lethal gene from a population just by crossbreeding? 2 https://www.reddit.com/r/askscience/comments/jvuzhp/is_there_a_way_of_removing_a_recessive_lethal/ 1605627117 jvuzhp Biology 2020-11-17 18:31:57 "You mean breed the disease out of the population or the gene? + +Of course it's possible to do either. If you know which pigs are the carriers (heterozygotes), remove them from the breeding pool. Then by the next generation there will be no more carriers and you won't have to worry about it (assuming it's not a mutation that can easily arise de novo). That assumes that you have enough non-carriers to sustain the population. + +If you just want to breed the *disease* (not the gene) out of the population, then you just don't let carriers breed with each other. You'll still have carriers but you won't have homozygotes with the disease." "To do this without molecular tech and no a priori knowledge of the genotype of your pigs, you'd need to keep track of the pedigree of the pigs for many, many generations to be sure none are carriers. Pigs with no diseased ancestors for many, many generations are likely healthy, but even then, it's not a sure thing. + +What would be faster is forcing the pigs to inbreed for a few generations. Pair off breeding pairs in your starting generation, then only allow the offspring of individual breeding pairs to breed within their lineage. That way, no new genetic material is entering the line. You're just reshuffling what's already there over and over again looking for evidence of the disease. After a few generations of inbreeding (number of generations necessary depends on the number of babies born in each generation), if NO pigs in the lineage are born with the disease, you can assume that the lineage doesn't carry the gene and go back to breeding the pigs from healthy lines without restriction." +1778 Are there any positive effects of climate change? 2 https://www.reddit.com/r/askscience/comments/irh285/are_there_any_positive_effects_of_climate_change/ 1599932593 irh285 Earth Sciences 2020-09-12 20:43:13 Hello! This is more of a discussion-based question, so it’s better suited for /r/AskScienceDiscussion. Thanks! +1779 What is the most effective way to vaccinate a large percent of a population in order to stop a disease? 2 https://www.reddit.com/r/askscience/comments/iskr47/what_is_the_most_effective_way_to_vaccinate_a/ 1600089778 iskr47 Medicine 2020-09-14 16:22:58 The CDC & NIH commissioned the National Academies of Sciences, Engineering and Medicine to do a report to assist policymakers with this question. NASEM's Committee on Equitable Allocation of Vaccine for the Novel Coronovirus circulated a discussion draft for public comment last week. The initial proposal is a 4 phase program that starts with health care workers, first responders, people who are medically at high risk, and nursing home residents (about 15% of the pop.). 2nd phase is for teachers & essential workers, people with mod. risk conditions, lower risk elderly, and people who live in crowded facilities (shelters & jails), about 30% of the pop. Third and fourth phase are essential workers and kids, then finally healthy low risk people. In the US, given the prevalence of anti-vaxxers? Probably tactical teams equipped with dart guns and helicopters... +1780 Why is Haumea elongated, shouldn't it just be squished on the poles? 2 https://www.reddit.com/r/askscience/comments/jvcl9q/why_is_haumea_elongated_shouldnt_it_just_be/ 1605552936 jvcl9q Astronomy 2020-11-16 21:55:36 A slower rotation leads to a simple bulge. But if you increase angular momentum eventually such an elongated shape becomes an equilibrium. +1781 After hearing about how human hearing is logarithmic, A question for the scientists out there. If you want something to sound twice as loud, how much louder does the power have to be multiplied by? 2 https://www.reddit.com/r/askscience/comments/jwuase/after_hearing_about_how_human_hearing_is/ 1605753390 jwuase Psychology 2020-11-19 5:36:30 "Approximately 10 times the power. + +[Double or twice the loudness = factor 2 means about 10 dB more sensed loudness level (psycho acoustic)](http://www.sengpielaudio.com/calculator-levelchange.htm) + +Double or twice the voltage = factor 2 means 6 dB more measured voltage level (sound pressure level) + +Double or twice the power = factor 2 means 3 dB more calculated power level (sound intensity level)" "Hearing is not logarithmic. How loud something IS measured via a logarithm. I’m not sure if your question is congruent. + +To double the sound pressure (SPL), you’ll need to increase the dB level by +6." +1782 Does forest fire smoke particles affect how or where lightning strikes during a lightning storm? 2 https://www.reddit.com/r/askscience/comments/iv3o4g/does_forest_fire_smoke_particles_affect_how_or/ 1600425395 iv3o4g Earth Sciences 2020-09-18 13:36:35 +1783 How different was this world ecologically, about 2000 to 2500 yrs ago? 2 https://www.reddit.com/r/askscience/comments/jujv3d/how_different_was_this_world_ecologically_about/ 1605435793 jujv3d Earth Sciences 2020-11-15 13:23:13 +1784 When a gravitational wave front passes through a particular point in space, does the passage of time change even minutely for an instant at that point? 2 https://www.reddit.com/r/askscience/comments/jw2jc2/when_a_gravitational_wave_front_passes_through_a/ 1605650287 jw2jc2 Physics 2020-11-18 0:58:07 +1785 Ask Anything Wednesday - Engineering, Mathematics, Computer Science 2 https://www.reddit.com/r/askscience/comments/jwhf5b/ask_anything_wednesday_engineering_mathematics/ 1605712115 jwhf5b 2020-11-18 18:08:35 +1786 COVID test before COVID vaccination? 2 https://www.reddit.com/r/askscience/comments/jvcaej/covid_test_before_covid_vaccination/ 1605552020 jvcaej COVID-19 2020-11-16 21:40:20 "I don't believe that'd be necessary. You can get a vaccine when infected by the same pathogen (done all the time with tetanus, though that is the exception rather than the rule). Testing people would add a whole another layer onto the already enormous logistical challenge of vaccine delivery. + +When fighting a virus, most of the symptoms are actually caused by the immune system's response to the virus, meaning your body is often the culprit in infection and vaccination (in fact even moreso in vaccination). + +As WHO notes, for example, being vaccinated against multiple diseases simultaneously does not increase the risk of side effects. (https://www.who.int/vaccine_safety/initiative/detection/immunization_misconceptions/en/index6.html) + +Now if you were thinking of the fact that the immune system is weakened during infection, that's not a concern either when using mRNA vaccines as they do not contain live pathogens able to cause disease. + +Hope this answered your question!" +1787 How is effectiveness of vaccines calculated for viruses that leave 80% of infected asymptomatic? 2 https://www.reddit.com/r/askscience/comments/jvqh3g/how_is_effectiveness_of_vaccines_calculated_for/ 1605607280 jvqh3g COVID-19 2020-11-17 13:01:20 "The efficacy of vaccines being trialed is calculated by comparing the number of cases in the placebo group to the number of cases in the vaccine group. + +If the placebo group has 100 cases and the vaccine group 20 (with both groups of equal size), then the point estimate of the efficacy would be 80%, corresponding to an 80% reduction in case count. + +Note that the trial protocols of the frontrunner candidates all define a ""case"" as someone who has covid-19 symptoms and tests positive. Since the trials don't proactively test volunteers, they don't find asymptomatic cases. + +It is therefore possible that a vaccine doesn't necessarily prevent infection, but reduces it to a point where it resolves asymptomatically in almost all people. Further trials may determine how good the vaccines are in preventing infection & disease spreading." +1788 If going from a liquid state to a solid state is considered freezing, is cooking an egg considered freezing it? 2 https://www.reddit.com/r/askscience/comments/k8sero/if_going_from_a_liquid_state_to_a_solid_state_is/ 1607384002 k8sero Chemistry 2020-12-08 2:33:22 +1789 Why does masturbating make a smell in your room? 2 https://www.reddit.com/r/askscience/comments/k6yptp/why_does_masturbating_make_a_smell_in_your_room/ 1607133276 k6yptp Biology 2020-12-05 4:54:36 "> I think she knows + +[She *definitely* knows.](https://youtu.be/D9qOUDHgzpM?t=18) + +> Is it the semen that is released? + +This. Sperm cells account for only ~1-2% of ejaculate mass, the rest is a chemical and nutrient soup - containing all sorts of amino acids, sugars, enzymes, hormones, immunogenic agents, and other compounds - all there to help feed and maintain the sperm on their journey, or otherwise alter the vaginal environment to support their objective. In the latter regard, many of these compounds (e.g. [putrescine](https://en.wikipedia.org/wiki/Putrescine), also associated with bad breath, and [spermine](https://en.wikipedia.org/wiki/Spermine)) have an alkaline pH (~7.2-8), which helps neutralise the acidic environment of the vaginal tract (~3.8-4.5). Healthy vaginas are chock full of *lactobacillus* bacteria which produce lactic acid as a by-product of their metabolic processes, and unless dealt with, this acidic environment can denature proteins present in the sperm cells, killing 'em before they've even had a chance to proverbially storm the beach. + +So yeah, by default, your load will smell a bit like mild bleach / ammonia / chlorine owing to it's alkaline nature. Other compounding factors include diet (e.g. heavy garlic or asparagus nomming, apparently), presence of infection, and hygiene (especially if uncircumcised). Sweat is similarly mildly alkaline, and you getting all worked up and sweaty while you spank yer' monkey only adds to the delightful aroma. Furthermore, compounds in both semen and sweat can interact to further elevate pungency if mixed and/or dried. Mmm, sweaty, crusty socks, anyone? + +**TL;DR:** Vaginas are [hostile environments](https://www.youtube.com/watch?v=MoAUfnKcA3I&list=PL_93VFgaAAMwX4ojyGlPuPthXYmQWLD_7), and sperm need every little helping hand to survive the onslaught they can expect there. The smelly alkaline compounds in your load are one of the many seminal miracles that help them on their quest. God speed, little swimmers! + +**P.S.** Keep yer' willy clean, promptly mop up your mess, and open the windows. If you don't do it for yourself, at least do it for your poor mum. + +___ + +^(**References & Further Reading:**) + +[^(Haugen, T.B. & Grotmol, T. (1998)^) ^(pH of human semen. *International Journal of Andrology*. 21 (2)^), ^105-108](https://onlinelibrary.wiley.com/doi/pdfdirect/10.1046/j.1365-2605.1998.00108.x) + +[^(Linhares, I.M., Summers, P.R., Larsen, B., Giraldo, P.C. & Witkin, S.S. (2011)^) ^(Contemporary perspectives on vaginal pH and lactobacilli. *American Journal of Obstetrics and Gynecology*. 204 (2)^), ^120.1-120.5](https://www.sciencedirect.com/science/article/pii/S0002937810008768?casa_token=-Veg2KJjhwMAAAAA:f_7Jjg32Dt87NhsT78PvLdUxyoEqwQssi-EZQvFc9HokxvSBL_mO7jxkNGNRPma_tViu26ZjZg) + +[^(*Wikipedia* article - Human Semen / Composition)](https://en.wikipedia.org/wiki/Semen#Human_semen)" +1790 How can I persuade my 93 year old Grandmother that if she is offered the Pfizer vaccine, she should at least consider it? Am I wrong to want her to not be diametrically opposed to the idea? 2 https://www.reddit.com/r/askscience/comments/kfx753/how_can_i_persuade_my_93_year_old_grandmother/ 1608336931 kfx753 COVID-19 2020-12-19 3:15:31 +1791 How cold can a lithium ion battery get before it causes permanent damage or permanent loss of performance? 2 https://www.reddit.com/r/askscience/comments/kf1ip3/how_cold_can_a_lithium_ion_battery_get_before_it/ 1608225163 kf1ip3 Engineering 2020-12-17 20:12:43 I believe you want to keep them above -20 C, as below that you can start to freeze out some components which can cause permanent damage. "MEchanical engineer here, working on Lithium HV batties. +Typically cells for automotive can be stored down to around -20C, however, they don't work very well below 0C. There's also increased risk of 'dendrides', or lithium deposits that crystallize in the electrolyte and can piece the boundry layer between cathode and annode. This can result in a short circut and either cause the cell to end up 'dead' or worst, can cause it to have a thermal event , aka explode. + + +Usually when in a vehicle, the thermal control system, usually being water based, will have a preheater in it, and this'll cut in through the BMS monitering to prevent the pack from getting too cold in the first place, though this only really works in a water / glyco cooled battery. + + +Best advice, for tools, is bring the batteries in at the end of the day and keep them by the door, or at least in a thermally insulated pack perhaps if you need to leave them out in the vehicle if you work in a partically cold area." +1792 "How are winds ""made""?" 2 https://www.reddit.com/r/askscience/comments/irjkmz/how_are_winds_made/ 1599940732 irjkmz Earth Sciences 2020-09-12 22:58:52 Sun warms air, air expands, pushes other colder air out of the way to make room for higher energy warm air. This happens on an extremely large scale so you can see how sometimes wind can get real big and fast when you have a planet worth of air all swirling around getting heated and cooled constantly. "Horizontal winds are caused by pressure differences on that horizontal surface. The air wants to move from the high pressure to the low pressure. However, because the earth is spinning, there is a pseudo-force called coriolis force which makes the wind turn to the right in the Northern Hemisphere or left in the Southern Hemisphere. This causes the wind to actually go perpendicular to the pressure gradient (as long as you're not too close to the ground), which is why the low pressure regions don't fill in quickly. + +Vertical winds are caused by a parcel of air being warmer then the air surrounding it so that it's positively buoyant, causing it to rise, or cooler so that it's negativity buoyant, causing it to sink." +1952 Why limit household water consumption during droughts? 2 https://www.reddit.com/r/askscience/comments/nyx3mn/why_limit_household_water_consumption_during/ 1623593294 nyx3mn Earth Sciences 2021-06-13 17:08:14 "First off, this doesn't actually reflect the type of water usage typically targeted during these type of restrictions. For example, if you look at the [type of restrictions](https://www.mercurynews.com/2021/06/07/drought-emergency-heres-a-list-of-water-restrictions-that-may-be-coming-to-santa-clara-county/) being put in place in some counties in California right now, these are limiting usage of water for non-essential activities where most of the water is used outside and where most of this water will end up evaporating. For example, lawn watering, car washing, filling swimming pools, etc. While some of this water will runoff and may end up back in the treatment plants and/or infiltrate and recharge the ground water, the vast majority of this water will end up being evaporated and effectively lost (in a local/regional sense, obviously the water will precipitate somewhere). + +Coming at this from the literature (this is AskScience after all), the answer to the question of ""Why limit household water consumption during droughts?"" is simply because it works at reducing water usage. Specifically there is abundant evidence that restricting municipal water use in a variety of ways are quite effective at reducing over all water usage (e.g., [Haque et al., 2014](https://ascelibrary.org/doi/full/10.1061/%28ASCE%29WR.1943-5452.0000423), [Low et al., 2015](https://onlinelibrary.wiley.com/doi/full/10.1002/wat2.1087)), whether those restrictions are more long-term, e.g., promoting water efficient appliances or fixtures and/or through water pricing (e.g., [Suero et al., 2010](https://ascelibrary.org/doi/full/10.1061/%28ASCE%29WR.1943-5452.0000182), [Cahill et al., 2011](https://ascelibrary.org/doi/full/10.1061/%28ASCE%29WR.1943-5452.0000225)) or from drought specific restrictions on activities like lawn watering (e.g., [Anderson et al., 1980](https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-1688.1980.tb02443.x), [Kenney et al., 2007](https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1752-1688.2004.tb01011.x))." "You have some seriously incorrect assumptions in this question. + +First, water reclamation is nowhere near 100% or even near 50%. As of 2015, California was [using \~40 million acre-feet](https://pacinst.org/wp-content/uploads/2020/06/PI_Water_Use_Trends_June_2020.pdf) of water per year and [reclaiming \~715,000 acre-feet](https://www.waterboards.ca.gov/water_issues/programs/grants_loans/water_recycling/munirec.shtml). It is absolutely not a ""closed cycle"" in any way. + +Secondly, no reclaimed water is used for household consumption, at least in California. It is not considered drinkable." +1953 Why do quarries have such clean and translucent water years after water bodies start appearing in them, while a swimming pool will turn into a nasty green swamp full of algae in a single summer if it isn't treated? 2 https://www.reddit.com/r/askscience/comments/o3exm1/why_do_quarries_have_such_clean_and_translucent/ 1624105619 o3exm1 Biology 2021-06-19 15:26:59 "Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s): + +* A good home for this question is our sister subreddit /r/AskScienceDiscussion. It might be too open-ended or speculative for /r/askscience. /r/AskScienceDiscussion is also a better place for advice on education, book suggestions or general questions about working in STEM. Please feel free to repost there! + + Please see our [guidelines](http://www.reddit.com/r/askscience/wiki/guidelines#wiki_asking_askscience)." +1954 If two people were driving towards eachother in separate cars, what speed would they be able to get up to and high five eachother without getting seriously injured? 2 https://www.reddit.com/r/askscience/comments/nww0g4/if_two_people_were_driving_towards_eachother_in/ 1623352844 nww0g4 Physics 2021-06-10 22:20:44 +1955 Theoretically, would it be possible to load the COVID-19 vaccine into a tranquillizer dart and instantly vaccinate someone? 2 https://www.reddit.com/r/askscience/comments/o0kdmo/theoretically_would_it_be_possible_to_load_the/ 1623779781 o0kdmo COVID-19 2021-06-15 20:56:21 +1956 What determines the heat of combustion of a fuel (hydrocarbon)? 2 https://www.reddit.com/r/askscience/comments/p8bqyr/what_determines_the_heat_of_combustion_of_a_fuel/ 1629486445 p8bqyr Chemistry 2021-08-20 22:07:25 Roughly, this has to do with the energy contained in the bonds of the fuel versus the energy contained in the bonds of the combustion product. Most of the bond energy difference between these will be released as heat into the system +1957 Why do electrolytes help keep us hydrated? 2 https://www.reddit.com/r/askscience/comments/o1pm48/why_do_electrolytes_help_keep_us_hydrated/ 1623908248 o1pm48 Biology 2021-06-17 8:37:28 "Electrolytes (different salts, basically) are in sports drinks etc not because they keep you hydrated, but because you lose salts in your sweat, and it needs to be replaced. You need small amounts of sodium, potassium, etc in order for many biological processes to work correctly, including nerve impulses and muscle contraction. This is called [hyponatremia](https://www.mayoclinic.org/diseases-conditions/hyponatremia/symptoms-causes/syc-20373711). If you are working hard and sweating a lot, and only drinking pure water, eventually you well get muscle cramps, nausea, headache, dizziness. In extreme cases you can have seizures or go into a coma. + +Note that this only really applies when (1) you are sweating excessively, for instance during a long workout or extended exposure to high temperatures, and (2) you are drinking only water. Most of the time, you will get all the salt you need from your diet, and won't need to supplement with extra salts like from sports drinks" +1958 How does the trinucleotide repeat in Friedrich’s Ataxia cause altered expression of frataxin? 2 https://www.reddit.com/r/askscience/comments/o00lwt/how_does_the_trinucleotide_repeat_in_friedrichs/ 1623714995 o00lwt Biology 2021-06-15 2:56:35 "Hi, back then at the university I did research the structural behavior of chromosomes having an excessive gcc triplet expansion. This causes the fragile x syndrome which is similar to Friedrichs ataxia. It is assumed that the silencing of the gene is caused by heterochromatine formation, which might be caused by the attachment of heterochromatine inducing proteins in the triplet expansion area. Methylation might further enhance this problem. I tried to make this loops visible using fluorescent markers, but resolution was too bad, so not really successful. +So , at least 2012 the cause of the gene silencing was not really known." "I am not an expert in trinucleotide repeat expansion disorders, but maybe I can shed a little light on the underlying mechanisms. If you want a nuanced answer you are going to need an expert. + +Most trinucleotide repeat expansions can form secondary DNA structures, this is what the r-loops and triplexes you are referring to are. These can cause problems in transcription for all sorts of reasons, but thinking of it as a tangled knot in the DNA is not altogether wrong. We have all sorts of these structures identified, but GAA is special because it is purine-rich, so the nucleotides with two rings are one strand and the nucleotides with one ring are on the other. Really this just impacts the sort of secondary structures it will form with itself, one of which is that triplex. The r-loop is the RNA going back and binding with the DNA, muddling things up. + +All of this creates a problem of chromosomal fragility. These repeats can expand, contract, and break, which can be difficult for the cell to fix. Often times the cell will look at the sister chromosome to figure out how to fix a break, and having a long section of repeats makes this difficult to do correctly and increases the chance something will go wrong. This is a huge problem if you do not want cancer, stopping these sorts of breaks and fixing breaks correctly is central to your body preventing it. + +So, when the DNA breaks or is unstable the cell will change the way it has bundled the DNA to try and limit the damage. This is great if you want to prevent cancer, but it is problematic when the damaged area is in a place you want to be expressed. So the repeats are causing problems for the DNA, making the cell lock them down reducing expression of the gene they are in, and causing the disease. This is what you were referring to with chromatin changes and DNA methylation. + +A quick google search says that the approach to fixing this would be to try an prevent those secondary structures that are causing damage. So if you could stop the r-loop from forming (DNA-RNA interactions) you could maybe increase expression and stop some of the expression changes. [One approach](https://www.nature.com/articles/ncomms10606?origin=ppub) would be to put in some nucleotides that bind to the RNA and prevent that structure from forming." +1959 CureVac's mRNA vaccine was 47% effective. Is it materially different than Pfizer and Moderna? 2 https://www.reddit.com/r/askscience/comments/o1ign1/curevacs_mrna_vaccine_was_47_effective_is_it/ 1623885480 o1ign1 COVID-19 2021-06-17 2:18:00 "The actual recipes of these vaccines are proprietary, so it's difficult to know exactly how different they are from each other. + +That said, moderna and pfizer seem to be much more efficacious against the variants than 47%. + +> Pfizer was 87 to 89.5 percent effective against the Alpha (UK) and 72.1 to 75 percent effective against Beta (South Africa) *via [NYT](https://www.nytimes.com/2021/06/16/health/covid-vaccine-curevac.html)* + +See replies +~~Notably, though all three of these vaccines contain mRNA for the SARS-CoV2 spike protein, there are also other 'supporting' ingredients which may be different. For example, just injecting straight up mRNA doesn't work because it gets broken down before it can even enter our cells[[1]](https://www.nature.com/articles/nrd.2017.243). There is a lot of variability in mechanisms/reagents used to actually get the mRNA into a cell before it gets degraded. My guess is that this is where the differences between the efficacy of the vaccines lie.~~" +1960 Why can't I remember what I was thinking about in my head but can remember what I said while talking to myself? 2 https://www.reddit.com/r/askscience/comments/ogcf1j/why_cant_i_remember_what_i_was_thinking_about_in/ 1625766469 ogcf1j Neuroscience 2021-07-08 20:47:49 "Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s): + +* This subreddit does not provide [medical or safety advice] (http://www.reddit.com/r/askscience/comments/s4chc/meta_medical_advice_on_askscience_the_guidelines/). Please see our [guidelines](https://www.reddit.com/r/AskScience/wiki/quickstart/guidelines#wiki_no_medical_advice). If you have concerns about your or someone else's health, you need to speak to a medical professional. + +* Questions based on personal anecdotes or isolated events tend to invite speculation and more anecdotes, which are not allowed on /r/AskScience. + +For more information regarding this and similar issues, please see our [guidelines.](http://www.reddit.com/r/askscience/wiki/guidelines#wiki_avoid_questions_about_personal_or_isolated_events.) + + + +If you disagree with this decision, please send a [message to the moderators.](https://www.reddit.com/message/compose?to=%2Fr%2Faskscience)" +1961 are you absorbing a dangerous amount of carcinogens through your feet while running on the concrete street in a suburban neighborhood? 2 https://www.reddit.com/r/askscience/comments/o18rwt/are_you_absorbing_a_dangerous_amount_of/ 1623860641 o18rwt Biology 2021-06-16 19:24:01 +1962 What is the purpose of nasal congestion during infection? 2 https://www.reddit.com/r/askscience/comments/o224p3/what_is_the_purpose_of_nasal_congestion_during/ 1623949491 o224p3 Human Body 2021-06-17 20:04:51 "Mucus has two roles, the first is its originally intended role by the host, to protect us from virus. The second is a hijacked role by the virus taking advantage of mucus production for its own nefarious purposes. + + +* Mucins have been revealed to play an integrated role in the host response to pathogens, both before and during the immune response, and the absence or distubance of this role can be highly detrimental to the host. + +* Mucus appears to be an important physical barrier to protect the host from influenza viruses. + +* Despite the importance of mucins, current understanding of their functions is limited, which is partly due to the complexity of mucus and its interactions. + +^ source https://www.cell.com/cell-host-microbe/pdf/S1931-3128(16)00038-X.pdf + +Additionally, mucus _also_ serves a hijacked role by the virus to spread itself through the host's sniffling, coughing, and sneezing onto nearby hosts. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7462404/" "There are some interesting and related answers in this old question: https://old.reddit.com/r/askscience/comments/343mbf/why_does_only_one_nostril_become_clogged_with/ + +Interesting to know, but not related to being sick, ""You have more accurate smelling when you have a low airflow nostril for more volatile compounds."" so that could be one advantage of the [nasal cycle](http://en.wikipedia.org/wiki/Nasal_cycle)." +1963 It has been told that utilization of Thorium for creation of nuclear weapons is quite hard, but why is it exactly hard to do so if we can utilize several materials to make it reach critical state? 2 https://www.reddit.com/r/askscience/comments/o0aaku/it_has_been_told_that_utilization_of_thorium_for/ 1623749508 o0aaku Physics 2021-06-15 12:31:48 "Let's look at the alternatives first: + +The conceptually easiest approach is to take natural uranium, a mixture of 0.7% U-235 and 99.3% U-238, and to remove most of the U-238. Once you have something like 90% U-235 you can make a bomb out of it. Both uranium isotopes have a very long half life (that's the reason they are still there) and they mainly decay via alpha decays which are easy to shield. You can safely hold them in your hands. + +Nuclear reactors typically use a lower enrichment, something like 5% U-235 and 95% U-238 (some reactors run on natural uranium). Some of the U-238 gets converted to plutonium-239, which can be used for weapons. But if you keep it in the reactor some of that is further converted to plutonium-240, which is really bad for nuclear weapons. It often releases neutrons on its own, which might trigger the chain reaction too early. You also get some Pu-241 which is annoying with its short half life. To get plutonium for nuclear weapons you need to exchange the fuel rods often. Both plutonium have a much shorter half life than the two long-living uranium isotopes, but the main decay mode is again alpha decay. + +Thorium on its own can't be used for a fission chain reaction - a nuclear reactor needs to convert it to uranium first. That's mainly U-233 but with some U-232 mixed in. The latter has a decay chain that includes strong gamma rays, which makes the spent fuel awkward to work with. Bad for people running reactors, bad for people trying to make an improvised nuclear weapon out of it. Bad for the nuclear weapon itself, too. [Here is an overview](http://fissilematerials.org/library/sgs09kang.pdf)." +1964 Are we inside a Computer Simulation? 2 https://www.reddit.com/r/askscience/comments/o3liag/are_we_inside_a_computer_simulation/ 1624124592 o3liag Computing 2021-06-19 20:43:12 +1965 Just curious, why does it seem like we only use the RT PCR test to diagnose COVID-19 when other infectious diseases like the flu uses other diagnostic methods? 2 https://www.reddit.com/r/askscience/comments/p8q49a/just_curious_why_does_it_seem_like_we_only_use/ 1629546780 p8q49a COVID-19 2021-08-21 14:53:00 +2040 What are dreams and why do we see them while sleeping? 2 https://www.reddit.com/r/askscience/comments/q21xwf/what_are_dreams_and_why_do_we_see_them_while/ 1633456906 q21xwf Biology 2021-10-05 21:01:46 +2041 What organism(s) could be considered to have the most efficient circulatory system? What makes one system better or worse than another? 2 https://www.reddit.com/r/askscience/comments/rb869u/what_organisms_could_be_considered_to_have_the/ 1638907586 rb869u Biology 2021-12-07 23:06:26 "Presumably different organisms have different constraints on their circulatory systems. + +(""Better for X"" isn't ""Better for Y"".) + +E.g. Crocodilians have a circulatory system that's a little different from ours, + +but it works for the lifestyle that crocodilians live. + +\- https://en.wikipedia.org/wiki/Crocodilia#Circulation + +Similarly for every other organism." +2042 Weird question but is the mylohyoid muscle denser or less denser than the digastric muscle? I've been researching this for a while now 2 https://www.reddit.com/r/askscience/comments/raxhof/weird_question_but_is_the_mylohyoid_muscle_denser/ 1638877977 raxhof Human Body 2021-12-07 14:52:57 Literally think you’d have to run your own research study to figure it out. I highly doubt any study has ever specifically determined the density of either of them. For one, I can’t think of a reason it’d be important to know. Second, as far as I know there would be no reason to think they were different. Third, it’s going to be different between individuals. If one muscle has more slow twitch fibers, it’d be ever so slightly less dense than the same exact size muscle with more fast twitch. I’m definitely curious why you’re asking though. +2043 Do natural endorphins act quicker than morphine does? Why or why not? 2 https://www.reddit.com/r/askscience/comments/q2kwls/do_natural_endorphins_act_quicker_than_morphine/ 1633528365 q2kwls Medicine 2021-10-06 16:52:45 I don’t think any exogenous chemicals can get to their molecular target as fast as an endogenous chemical impulse. The first has to travel through the bloodstream at the speed of the heart beat, then cross cellular barriers to be utilized. The speed of a chemical impulse is super fast, a small percent of a second. Both are fast enough when you’re the person experiencing it. +2044 Will we have to keep getting booster shots till the end of life every 7-9 months? 2 https://www.reddit.com/r/askscience/comments/rbxky1/will_we_have_to_keep_getting_booster_shots_till/ 1638987865 rbxky1 COVID-19 2021-12-08 21:24:25 +2045 Does birds come from different dinosaurs or is it just one? 2 https://www.reddit.com/r/askscience/comments/rb1xs9/does_birds_come_from_different_dinosaurs_or_is_it/ 1638891681 rb1xs9 Paleontology 2021-12-07 18:41:21 "\- It might be that all birds are descendants of one species of non-bird dinosaur. + +\- It might be that all birds are descendants of a small group of closely related species of non-bird dinosaur. + +We're finding new species of ancient birds and bird relatives every year, and still trying to sort out how they're all related. + +. + +The ""raptor"" dinosaurs are cousins of birds, but we know now that these dinosaurs really had feathers, not bare skin like the ones shown in the Jurassic Park movies. + +\- [Wrong](https://i.pinimg.com/originals/ec/ef/f0/eceff06b3ad537e5320962bf4c3b8909.jpg) + +\- [Right](https://upload.wikimedia.org/wikipedia/commons/thumb/e/ed/Dromaeosaurs.png/2560px-Dromaeosaurs.png) + +We think that the ancestors of birds were like small raptor dinosaurs that spent a lot of time in trees. (Again, we keep discovering new species in this group every year.) + + +\- https://en.wikipedia.org/wiki/Bird#Dinosaurs_and_the_origin_of_birds + +\- https://en.wikipedia.org/wiki/Origin_of_birds + +\- https://en.wikipedia.org/wiki/Paraves + +." +2046 What does the most up to date studies say about the efficacy of Remdisivir? 2 https://www.reddit.com/r/askscience/comments/rb3jic/what_does_the_most_up_to_date_studies_say_about/ 1638897189 rb3jic COVID-19 2021-12-07 20:13:09 "General consensus is that there is essentially zero evidence it helps to treat Covid. + +Below is a formal release from the World Health Organization: https://www.who.int/news-room/feature-stories/detail/who-recommends-against-the-use-of-remdesivir-in-covid-19-patients + +Edit: One thing to keep in mind is that research is ongoing. If you want to keep up to date on the latest research I would suggest setting up a google alert for it." +1966 Daughter was exposed today, I'm due for 2nd shot tomorrow, what to do? 1 https://www.reddit.com/r/askscience/comments/n24hro/daughter_was_exposed_today_im_due_for_2nd_shot/ 1619819981 n24hro COVID-19 2021-05-01 0:59:41 +1967 If we are able to find something faster than the speed of light, would it be possible to see through a black hole's event horizon? 1 https://www.reddit.com/r/askscience/comments/n23cf2/if_we_are_able_to_find_something_faster_than_the/ 1619816522 n23cf2 Astronomy 2021-05-01 0:02:02 +1968 Has there ever been an effort to brute force all possible physical formulas and sort out the ones that fit observations? 1 https://www.reddit.com/r/askscience/comments/n24q6n/has_there_ever_been_an_effort_to_brute_force_all/ 1619820662 n24q6n Physics 2021-05-01 1:11:02 +1969 Does eating snow/ice dehydrate you? 1 https://www.reddit.com/r/askscience/comments/n25gae/does_eating_snowice_dehydrate_you/ 1619822987 n25gae Human Body 2021-05-01 1:49:47 +1970 Could we pump the ISS full of heavy gas? 1 https://www.reddit.com/r/askscience/comments/n23ppr/could_we_pump_the_iss_full_of_heavy_gas/ 1619817601 n23ppr Physics 2021-05-01 0:20:01 +1971 After a night drinking does adding a little bit of salt to your water help you hydrated better? 1 https://www.reddit.com/r/askscience/comments/n23qfa/after_a_night_drinking_does_adding_a_little_bit/ 1619817656 n23qfa Biology 2021-05-01 0:20:56 +1972 After getting vaccinated, is it OK to relax a little on the hand sanitizer and social distancing? 1 https://www.reddit.com/r/askscience/comments/n25it3/after_getting_vaccinated_is_it_ok_to_relax_a/ 1619823217 n25it3 COVID-19 2021-05-01 1:53:37 +1973 How will the vaccines eradicate the virus if it only midi gates the virus? 1 https://www.reddit.com/r/askscience/comments/n25jkl/how_will_the_vaccines_eradicate_the_virus_if_it/ 1619823288 n25jkl COVID-19 2021-05-01 1:54:48 +1974 Relativity Theory; Gravity Warps Space? 1 https://www.reddit.com/r/askscience/comments/n26r79/relativity_theory_gravity_warps_space/ 1619827375 n26r79 Planetary Sci. 2021-05-01 3:02:55 +1975 Why haven’t any species of vertebrates evolved to be immortal? 1 https://www.reddit.com/r/askscience/comments/n27hev/why_havent_any_species_of_vertebrates_evolved_to/ 1619829964 n27hev Biology 2021-05-01 3:46:04 +1976 mixing solid & liquid and the potent of .8 ml ? 1 https://www.reddit.com/r/askscience/comments/n27hon/mixing_solid_liquid_and_the_potent_of_8_ml/ 1619829989 n27hon Chemistry 2021-05-01 3:46:29 +1977 Why is the color blue so hard to recreate compared to other colors? 1 https://www.reddit.com/r/askscience/comments/n29avj/why_is_the_color_blue_so_hard_to_recreate/ 1619836633 n29avj Chemistry 2021-05-01 5:37:13 +1978 Relative descent direction inside a black hole's event horizon? 1 https://www.reddit.com/r/askscience/comments/n28pey/relative_descent_direction_inside_a_black_holes/ 1619834335 n28pey Physics 2021-05-01 4:58:55 +1979 Why do I feel such a weird tingling sensation when something occurs near the center of my forehead? 1 https://www.reddit.com/r/askscience/comments/n2bb9b/why_do_i_feel_such_a_weird_tingling_sensation/ 1619843960 n2bb9b Human Body 2021-05-01 7:39:20 +1980 why am i suddenly a napper ? 1 https://www.reddit.com/r/askscience/comments/n2bz1c/why_am_i_suddenly_a_napper/ 1619846740 n2bz1c Human Body 2021-05-01 8:25:40 +1981 What would happen to the pyramids if you nuked them? 1 https://www.reddit.com/r/askscience/comments/n2c7pe/what_would_happen_to_the_pyramids_if_you_nuked/ 1619847852 n2c7pe Physics 2021-05-01 8:44:12 +1982 Why is it important to sterilize glass jars before using them? 1 https://www.reddit.com/r/askscience/comments/n2ejui/why_is_it_important_to_sterilize_glass_jars/ 1619859273 n2ejui Biology 2021-05-01 11:54:33 +1983 Evolution of Immortality 1 https://www.reddit.com/r/askscience/comments/n278a8/evolution_of_immortality/ 1619829025 n278a8 Biology 2021-05-01 3:30:25 "Thank you for your submission! Unfortunately, it has been automatically removed because you did not include a question mark ""?"" in your title. We require post titles to be phrased as questions so that our panelists and visitors can more easily know what each thread is about. Please feel free to re-submit with a title that contains a question mark. Thanks for understanding. :) + +*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/askscience) if you have any questions or concerns.*" +1984 How did scientists/doctors figure out that there are different blood types? 1 https://www.reddit.com/r/askscience/comments/n2aibp/how_did_scientistsdoctors_figure_out_that_there/ 1619840682 n2aibp Biology 2021-05-01 6:44:42 +1985 My parent has a rare genetic disease, I have my raw DNA data file. Is it possible to decifer it myself to know if I inherited the disease? 1 https://www.reddit.com/r/askscience/comments/n2c5ie/my_parent_has_a_rare_genetic_disease_i_have_my/ 1619847579 n2c5ie Human Body 2021-05-01 8:39:39 +1986 Are people with square jawlines more likely to have a cleft chin, and if so, why? 1 https://www.reddit.com/r/askscience/comments/n2cqg5/are_people_with_square_jawlines_more_likely_to/ 1619850325 n2cqg5 Human Body 2021-05-01 9:25:25 +1987 Daughter was exposed today, I'm due for 2nd shot tomorrow. 1 https://www.reddit.com/r/askscience/comments/n24fx5/daughter_was_exposed_today_im_due_for_2nd_shot/ 1619819815 n24fx5 COVID-19 2021-05-01 0:56:55 "Thank you for your submission! Unfortunately, it has been automatically removed because you did not include a question mark ""?"" in your title. We require post titles to be phrased as questions so that our panelists and visitors can more easily know what each thread is about. Please feel free to re-submit with a title that contains a question mark. Thanks for understanding. :) + +*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/askscience) if you have any questions or concerns.*" +1988 win a amazon gift card 1 https://www.reddit.com/r/askscience/comments/n2divg/win_a_amazon_gift_card/ 1619854144 n2divg Economics 2021-05-01 10:29:04 +1989 What are the challenges with inventing a commercially compostable plastic? 1 https://www.reddit.com/r/askscience/comments/n2fhdj/what_are_the_challenges_with_inventing_a/ 1619863827 n2fhdj Chemistry 2021-05-01 13:10:27 +1990 What will happen to us if the birth replacement rate keeps falling? 1 https://www.reddit.com/r/askscience/comments/n279wb/what_will_happen_to_us_if_the_birth_replacement/ 1619829194 n279wb Social Science 2021-05-01 3:33:14 Such hypothetical / speculative / open-ended questions are better suited for our sister-sub /r/asksciencediscussion. Please post there instead. +1991 Farmed vs wild caught. Which is the better choice? 1 https://www.reddit.com/r/askscience/comments/n2fle3/farmed_vs_wild_caught_which_is_the_better_choice/ 1619864390 n2fle3 Earth Sciences 2021-05-01 13:19:50 +1992 How many lives stand to be saved by the COVID vaccination programme? (Upper and lower bounds) 1 https://www.reddit.com/r/askscience/comments/n28mq3/how_many_lives_stand_to_be_saved_by_the_covid/ 1619834034 n28mq3 COVID-19 2021-05-01 4:53:54 Questions based on discussion, speculation, or opinion are better suited for r/asksciencediscussion. +2047 Why do we only listen to pro-vaccine doctors on getting the COVID vaccine? 1 https://www.reddit.com/r/askscience/comments/pfn5g0/why_do_we_only_listen_to_provaccine_doctors_on/ 1630473168 pfn5g0 COVID-19 2021-09-01 8:12:48 +2048 How long could a human continuously walk before they die? 1 https://www.reddit.com/r/askscience/comments/pfnqt4/how_long_could_a_human_continuously_walk_before/ 1630475888 pfnqt4 Human Body 2021-09-01 8:58:08 +2049 By the law of conservation of matter doesn't it mean that we are all technically immortal, technically? 1 https://www.reddit.com/r/askscience/comments/pfkyjg/by_the_law_of_conservation_of_matter_doesnt_it/ 1630464730 pfkyjg Physics 2021-09-01 5:52:10 +2050 How come I can eaten rotten fruit but I can't eat rotten meat? 1 https://www.reddit.com/r/askscience/comments/pfkuid/how_come_i_can_eaten_rotten_fruit_but_i_cant_eat/ 1630464324 pfkuid Biology 2021-09-01 5:45:24 +2051 Is it possible for a person, or any conscious being, to cease to exist? 1 https://www.reddit.com/r/askscience/comments/pfkkuo/is_it_possible_for_a_person_or_any_conscious/ 1630463353 pfkkuo Physics 2021-09-01 5:29:13 +2052 Since the flavor of meat can change based on the animals' diet, and our human smell/odor can also change based on our diet, how long does it take to modify your scent through eating certain foods (or not)? 1 https://www.reddit.com/r/askscience/comments/pfex0g/since_the_flavor_of_meat_can_change_based_on_the/ 1630444087 pfex0g Biology 2021-09-01 0:08:07 +2053 There is a marketing tactic where vendors will make something 9.99 or 19.98 instead of 10.00 or 20.00. What is this called? And has there ever been a study that attempts rank the perceived value of numbers in this marketing context? 1 https://www.reddit.com/r/askscience/comments/pfh5bu/there_is_a_marketing_tactic_where_vendors_will/ 1630451277 pfh5bu Psychology 2021-09-01 2:07:57 +2054 Why is immunity from the virus not the same or better than the vaccine? 1 https://www.reddit.com/r/askscience/comments/pfmkjs/why_is_immunity_from_the_virus_not_the_same_or/ 1630470731 pfmkjs Biology 2021-09-01 7:32:11 +2055 Would a very hot knife cauterize a wound on the way out if it was hot enough? 1 https://www.reddit.com/r/askscience/comments/pfjy2l/would_a_very_hot_knife_cauterize_a_wound_on_the/ 1630461093 pfjy2l Chemistry 2021-09-01 4:51:33 +2056 How come bacteriophages evolved such complex structures while most viruses infecting plants and animals are simpler? 1 https://www.reddit.com/r/askscience/comments/pfkd3s/how_come_bacteriophages_evolved_such_complex/ 1630462577 pfkd3s Biology 2021-09-01 5:16:17 +2057 Can somebody explain this passage? 1 https://www.reddit.com/r/askscience/comments/pfo3yk/can_somebody_explain_this_passage/ 1630477601 pfo3yk Biology 2021-09-01 9:26:41 +2058 Science series from 1955-70s from a college professor? 1 https://www.reddit.com/r/askscience/comments/pfgeec/science_series_from_195570s_from_a_college/ 1630448778 pfgeec Astronomy 2021-09-01 1:26:18 +2059 Why was this thread locked? 1 https://www.reddit.com/r/askscience/comments/pfi99c/why_was_this_thread_locked/ 1630455063 pfi99c Social Science 2021-09-01 3:11:03 +2060 "Can we use existing technology to ""tag"" asteroids to create an asteroid monitoring system?" 1 https://www.reddit.com/r/askscience/comments/pfho8d/can_we_use_existing_technology_to_tag_asteroids/ 1630453067 pfho8d Astronomy 2021-09-01 2:37:47 +2061 Why is Wave?can't get the fundamental. 1 https://www.reddit.com/r/askscience/comments/pffenx/why_is_wavecant_get_the_fundamental/ 1630445606 pffenx Physics 2021-09-01 0:33:26 +2062 When food goes right “through you”, (as in, instant diarrhea), does that mean your body didn’t absorb many of the calories or nutrients? 1 https://www.reddit.com/r/askscience/comments/pffps7/when_food_goes_right_through_you_as_in_instant/ 1630446570 pffps7 Human Body 2021-09-01 0:49:30 +2063 Will covid mutate forever or is there a limit to it’s mutation capabilities? 1 https://www.reddit.com/r/askscience/comments/pff1g9/will_covid_mutate_forever_or_is_there_a_limit_to/ 1630444478 pff1g9 COVID-19 2021-09-01 0:14:38 +2064 If the majority of the Earth's population was gone, but there was no physical damage, how long would the internet last? 1 https://www.reddit.com/r/askscience/comments/pfjn6b/if_the_majority_of_the_earths_population_was_gone/ 1630460022 pfjn6b Engineering 2021-09-01 4:33:42 +2065 What would happen if you took one of every vaccine? Super immunity? 1 https://www.reddit.com/r/askscience/comments/pflcb9/what_would_happen_if_you_took_one_of_every/ 1630466119 pflcb9 COVID-19 2021-09-01 6:15:19 +2066 Should we avoid having PVC products in the house, or are the toxicity claims nonsense? 1 https://www.reddit.com/r/askscience/comments/pfpyj1/should_we_avoid_having_pvc_products_in_the_house/ 1630486768 pfpyj1 Chemistry 2021-09-01 11:59:28 +2067 In the absence of healthcare resources, what would the SARS-CoV-2 infection fatality rate be in high-income countries? 1 https://www.reddit.com/r/askscience/comments/pfqsgj/in_the_absence_of_healthcare_resources_what_would/ 1630490754 pfqsgj Medicine 2021-09-01 13:05:54 +2068 According to google, tardigrades are 1mm long, and wikipedia says 1.5mm is possible. Why have i never seen one except in what looks to be electron microscope photos? I can see a single milimeter on a ruler clearly and have see tinier insects such as fleas. What gives? 1 https://www.reddit.com/r/askscience/comments/pfqgkg/according_to_google_tardigrades_are_1mm_long_and/ 1630489161 pfqgkg Biology 2021-09-01 12:39:21 +2069 What could we expect if suddenly a fish species became as intelligent as humans? 1 https://www.reddit.com/r/askscience/comments/pfv0k1/what_could_we_expect_if_suddenly_a_fish_species/ 1630506436 pfv0k1 Biology 2021-09-01 17:27:16 +2070 "Why after osseointegration skin does not ""stick"" to an implant?" 1 https://www.reddit.com/r/askscience/comments/pftvud/why_after_osseointegration_skin_does_not_stick_to/ 1630502821 pftvud Medicine 2021-09-01 16:27:01 +2071 If an object flew ≤1% faster than light, could one ever see that object? 1 https://www.reddit.com/r/askscience/comments/pfvcxp/if_an_object_flew_1_faster_than_light_could_one/ 1630507511 pfvcxp Physics 2021-09-01 17:45:11 +2072 How do generic sequencers distinguish between the kinds of genetic material in a sample? 1 https://www.reddit.com/r/askscience/comments/pfx08d/how_do_generic_sequencers_distinguish_between_the/ 1630512442 pfx08d Biology 2021-09-01 19:07:22 +2073 How can we expect to control weather (so as to be Type 1 civilization in Kardashev scale) if we can't even predict weather accurately beyond few weeks? 1 https://www.reddit.com/r/askscience/comments/pfxv9m/how_can_we_expect_to_control_weather_so_as_to_be/ 1630514947 pfxv9m Earth Sciences 2021-09-01 19:49:07 +2074 What is the difference between battery warranties? 1 https://www.reddit.com/r/askscience/comments/pfy2z1/what_is_the_difference_between_battery_warranties/ 1630515556 pfy2z1 Chemistry 2021-09-01 19:59:16 +2075 Why the electron revolve around the nucleus? Why it doesn’t fall? 1 https://www.reddit.com/r/askscience/comments/pfx5y1/why_the_electron_revolve_around_the_nucleus_why/ 1630512914 pfx5y1 Physics 2021-09-01 19:15:14 +2076 Why don’t we understand dna? 1 https://www.reddit.com/r/askscience/comments/pgtqo9/why_dont_we_understand_dna/ 1630626999 pgtqo9 Biology 2021-09-03 2:56:39 +2077 Mouthwash vs Brushing 1 https://www.reddit.com/r/askscience/comments/pg36ea/mouthwash_vs_brushing/ 1630530601 pg36ea Medicine 2021-09-02 0:10:01 "Thank you for your submission! Unfortunately, it has been automatically removed because you did not include a question mark ""?"" in your title. We require post titles to be phrased as questions so that our panelists and visitors can more easily know what each thread is about. Please feel free to re-submit with a title that contains a question mark. Thanks for understanding. :) + +*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/askscience) if you have any questions or concerns.*" +2078 Is it possible to build immunity to nettles stings ?? 1 https://www.reddit.com/r/askscience/comments/pgsnhz/is_it_possible_to_build_immunity_to_nettles_stings/ 1630623223 pgsnhz Biology 2021-09-03 1:53:43 +2079 What are the chance of being reinfected with COVID if you've been vaccinated and had a breakthrough delta infection? 1 https://www.reddit.com/r/askscience/comments/pg5v0g/what_are_the_chance_of_being_reinfected_with/ 1630539317 pg5v0g COVID-19 2021-09-02 2:35:17 +2080 Is there a study that shows the level of spread of COVID between the unvaccinated and the asymptomatic vaccinated? 1 https://www.reddit.com/r/askscience/comments/pg2e7r/is_there_a_study_that_shows_the_level_of_spread/ 1630528219 pg2e7r COVID-19 2021-09-01 23:30:19 +2081 Why would children, who as I understand it, generally have a stronger and more flexible immune system, be at higher risk than adults from a vaccine that has no virus in it? 1 https://www.reddit.com/r/askscience/comments/pgkr6n/why_would_children_who_as_i_understand_it/ 1630598393 pgkr6n COVID-19 2021-09-02 18:59:53 +2082 How exactly are complex instinctual animal behaviors hard wired into their brain and/or DNA? 1 https://www.reddit.com/r/askscience/comments/pgkuv3/how_exactly_are_complex_instinctual_animal/ 1630598690 pgkuv3 Biology 2021-09-02 19:04:50 +2083 Why aren't the bacteria in our microbiome antibiotic resistant? 1 https://www.reddit.com/r/askscience/comments/pgl30v/why_arent_the_bacteria_in_our_microbiome/ 1630599386 pgl30v Human Body 2021-09-02 19:16:26 +2084 Human mixed with plants? 1 https://www.reddit.com/r/askscience/comments/pglehd/human_mixed_with_plants/ 1630600366 pglehd Biology 2021-09-02 19:32:46 +2085 Mars domes filled with CO2 argon bottom? 1 https://www.reddit.com/r/askscience/comments/pfomox/mars_domes_filled_with_co2_argon_bottom/ 1630480036 pfomox Physics 2021-09-01 10:07:16 Such hypothetical / speculative / open-ended questions are better suited for our sister-sub /r/asksciencediscussion. Please post there instead. +2086 What would happen if I was to make an explosion inside oobleck? 1 https://www.reddit.com/r/askscience/comments/pgkcjt/what_would_happen_if_i_was_to_make_an_explosion/ 1630597078 pgkcjt Physics 2021-09-02 18:37:58 +2087 AZ question: Does the likelihood of uncomfortable side effects decrease as age increases? 1 https://www.reddit.com/r/askscience/comments/pfhv2f/az_question_does_the_likelihood_of_uncomfortable/ 1630453739 pfhv2f Medicine 2021-09-01 2:48:59 +2088 Why exactly can't humans and monekys interbreed and how much dna % is required between different species for the interbreeding to produce an offspring? 1 https://www.reddit.com/r/askscience/comments/pgkwgb/why_exactly_cant_humans_and_monekys_interbreed/ 1630598828 pgkwgb Biology 2021-09-02 19:07:08 +2089 Unique and/or interesting studies about the development of life? 1 https://www.reddit.com/r/askscience/comments/pglqe9/unique_andor_interesting_studies_about_the/ 1630601374 pglqe9 Psychology 2021-09-02 19:49:34 +2090 Can waste dumped in the sea cause underwater landslides or tsunamis? 1 https://www.reddit.com/r/askscience/comments/pgpiao/can_waste_dumped_in_the_sea_cause_underwater/ 1630612859 pgpiao Planetary Sci. 2021-09-02 23:00:59 +2091 In the course of evolution, what was the first animal to experience an orgasm during sex? 1 https://www.reddit.com/r/askscience/comments/pguxan/in_the_course_of_evolution_what_was_the_first/ 1630631461 pguxan Biology 2021-09-03 4:11:01 +2092 What kind of couch will not generate static? 1 https://www.reddit.com/r/askscience/comments/pguxii/what_kind_of_couch_will_not_generate_static/ 1630631484 pguxii Physics 2021-09-03 4:11:24