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[
"Was the speed of light ever measured on actual speed or only based on wavelength?"
] |
[
false
] | null |
[
"Like, what do you mean only based on wavelength?",
"Foucault and Fizeau measured it in the 19th century by shining it off a distant mirror and back through a rapidly rotating cog."
] |
[
"The experiment iorgfeflkd mentions doesn't have anything to do with wavelength. It measures how long it takes light to get to the distant mirror and back. That's directly measuring speed."
] |
[
"The original experiment uses a multifaced rotating mirror. Lets say its 12 facets. A light beam is focused on the spinning matrix of mirrors. This causes a flashing beam to spin off. On a mountain 20 miles away is a reflecting mirror similar to the ones used by surveyors. ",
"Lets say the operator can change the speed of rotation of the mirrors. (the real experiment moved the telescope). That way the returning light beam will only be acquired when the beam has rotated 360/12 or 30 degrees. If the distant peak is 20 miles away the path is 40 miles. With light travelling 186,000 miles per second it can bounce back and forth 4650 times a second. For the second facet of the mirror to reflect the light it has to rotate 1/12th of a turn or 387.5 rpms. ",
"If light travelled at different speed for each wavelength the telescope would see a spectrum reflected based on different speeds. They didn't. Similar tests were done with light from stars looking for delays based on wavelength. In free space there is none."
] |
[
"Do dogs understand accidents?"
] |
[
false
] |
If you're running around with a dog or playing a game or something involving a lot of physical activity and you wind up kicking the dog or hitting it in some way does the dog understand that you weren't trying to hurt it? is what made me wonder; the dog kind of gets tangled up with the players but seems cool with it.
|
[
"The real question is whether dogs are capable of understanding human intention and if they possess theory of mind. They are certainly evolutionary masters of understanding human facial expressions and tone of voice (intelligence varying by breed of course)."
] |
[
"Having accidentally kicked/smacked the dog several times I can conclude that he is either stupid, or very forgiving of my accident. I make full well he knows it was a mistake with lots of pets after."
] |
[
"I think it's more the intent they pick up on things like voice tone and body language. When I step on my pug's paw and say how sorry I am in a higher pitched \"cutesy\" tone and pet him, he's fine. But dogs who are hit and yelled at in a lower threatening tone tend to cower and fear. "
] |
[
"What is the purpose or function of DNA laddering when apoptosis is triggered in a human cell?"
] |
[
false
] |
In my biochemistry class we are learning about the process of apoptosis. In the intrinsic apoptosis pathway, cytochrome c is released into the cytosol from the mitochondria, along with other proteins like apoptosis inducing factor (AIF). We learned that AIF goes into the nucelus to trigger DNA laddering, Cytochrome c is already triggering a caspase cascade to cause apoptosis. I know it is helpful for scientists to recognize whether a cell has undergone apoptosis or necrosis, but is there a physiological purpose for the laddering?
|
[
"This is a great question. ",
"Unfortunately, I don't know the answer. But I did some reading. Before I did that reading, my first guess was that it helps neighboring cells digest the remnants of that dead cell (it's easier to take in and recycle small pieces of DNA than an entire genome's worth). I didn't find any literature to support that. ",
"What I did find was some research on DNA fragmentation as part of anti-cancer program. If you scroll down to the ",
"perforin/granzyme Pathway",
" section here, you'll see that immune cells can trigger apoptosis in cancer cells through secretion of a number of different proteins. These proteins cross into the targeted cancer cell; one of them, granzyme B, induces apoptosis through the mitochondrial pathway, while another, granzyme A, initiates DNA degradation. ",
"I guess the thought is that chopping up a cell's genome is a good way to kill it. If someone more knowledgeable than me wants to chime in and correct me, please do. "
] |
[
"I don't know either, but would guess it helps prevent anti-apoptotic gene expression and induces DNA damage-gated apoptotic pathways. The process might also have something to do with mobilizing histones. These are all guesses. "
] |
[
"Thanks for your response. What are the DNA-damage gated apoptotic pathways? I'd be curious to look more into them."
] |
[
"Are there example of inter-species cooperation in nature?"
] |
[
false
] |
Humans have domesticated animals rather successfully and often those animals get along rather well, without which, traditional farming would be much more difficult. Additionally, I keep seeing examples on reddit of animal which would in nature most likely never interact socially getting along quite well (mostly cats and dogs). Is this a result of domestication or is this a natural occurrence as well? Edit: I realize I seem to have been misunderstood. My question was more about inter-species friendships, such as between a dog and a cat, or a cat and a pet rodent of some sort.
|
[
"There are many examples of this. It's called a symbiotic relationship, synergy, or mutualism. A great example of this is the relationship between the nitrogen fixing bacteria, Rhizobium, and any legume, such as pea plants and clover. The legumes provide a stable environment for the bacteria inside their root nodules, whilst the bacteria fix the nitrogen in the soil so the plant can use it.",
"A more visible example is the relationship occasionally seen between small predators, such as a Lynx and birds of prey. The bird spots the prey for the Lynx (the bird usually scares it away on its own, whilst the Lynx has trouble finding it) then the lynx hunts and kills the prey and they both share the meal."
] |
[
"It has happened in ants, some species of ants farm aphids as a food source. ",
"http://en.wikipedia.org/wiki/Aphid#Ant_mutualism",
"Edit: Also some other cases if you are interested: ",
"http://en.wikipedia.org/wiki/Mutualism_%28biology%29"
] |
[
"Cleaning Fish!\n",
"http://en.m.wikipedia.org/wiki/Cleaner_fish"
] |
[
"Which would be better to extinguish a household fire: tap water or a carbonated beverage?"
] |
[
false
] |
Given the various fluids available in the home, which is ideal for dousing flames with assuming no extinguisher is available? Water, soda, beer, mineral water? I would assume that carbonated beverages would outperform normal water, but beverages with sugars in them like soda and beer would add fuel to a fire. Any experimental evidence out there for this sort of thing?
|
[
"There wouldn't be a difference -- fires are extinguished by depriving the fire of heat and or oxygen (both required for combustion). Both water, distilled water, mineral water, carbonated water, and even boiling water, all achieve this goal."
] |
[
"Water and mineral water would be functionally equivalent, because there's not that much difference between them, and those differences wouldn't do much to affect fire suppresion. Soda and beer make me curious because they might have an ingredient that acts as a surfactant, which would allow greater penetration into different surfaces and would likely improve their fire extinguisher capabilities, similar to how fire fighters sometimes mix detergents with water to make foam to fight some kinds of fires. I doubt there's much of an advantage (if there is one), however. "
] |
[
"If by mineral water you mean still mineral water, I agree. What about bubbly mineral water? Wouldn't the carbon dioxide help to smother the flames?"
] |
[
"Hydrophobic Effect?"
] |
[
false
] |
Hello , Studying for my biochem exam and this has been bugging me all semester. Why does the hydrophobic effect exist? More specifically, what are the physical and chemical reasons that hydrophobic substances are soluble in hydrophobic solutes and not in hydrophilic ones, and vice versa? I've taken orgo and gen chem, but have never really asked why this occurs.
|
[
"Because the water molecules can't hydrogen bond with the hydrophobic compound. The water molecules want to participate in hydrogen bonds as much as possible. If you put something in there that they can't hydrogen bond with they want to be around that compound in such a way that they hydrogen bond with other water molecules as much as possible.",
"This hydrogen bonding causes them to form a \"water cage\" around the hydrophobic compound. This cage is a highly ordered structure and when looking from the perspective of entropy is a huge decrease in entropy of the water molecules involved. ",
"Think of it like building a cage around a lego structure with knex. You can enclose the same amount of lego volume with fewer pieces of knex if you have the lego all in one big block than you would if you had the same amount of lego but in a bunch of tiny blocks.",
"If the hydrophobic compound clumps together the entropy of the water increases. Volume increases by a cubic power and surface area increases by a squared power.... so the volume of the clump of hydrophobic material gets much larger but its surface area doesn't increase nearly as quickly.... ",
"This means the hydrophobic compound, when all clumped together, holds much more material but makes a smaller surface area relative to the volume than if the hydrophobic compound was spread out evenly in the water. This smaller relative surface area means that less of the water has to be involved in forming the highly ordered \"water cage\" surrounding the hydrophobic compound. ",
"TL;DR: Increase in entropy. "
] |
[
"The energy explanation is a common misconception. See ",
"Wikipedia",
" and in particular the citation to the ",
"."
] |
[
"For a more in-depth reading, see: ",
"http://en.wikipedia.org/wiki/Hydrophobic_effect#The_origin_of_hydrophobic_effect",
". "
] |
[
"Why does asphalt appear to be reflective when parallel to your line of sight?"
] |
[
false
] |
When looking at asphalt when it matches your line of sight, why does it appear reflective, almost like a liquid?
|
[
"What you're looking at is actually what's defined as a mirage. ",
"Normally, light waves from the sun travel straight through the atmosphere to your eye. But, light travels at different speeds through hot air and cold air.",
"Mirages happen when the ground is very hot and the air is cool. The hot ground warms a layer of air just above the ground.",
"When the light moves through the cold air and into the layer of hot air it is refracted(bent).",
"A layer of very warm air near the ground refracts the light from the sky nearly into a U-shaped bend. Our brain thinks the light has travelled in a straight line.",
"Our brain doesn't see the image as bent light from the sky. Instead, our brain thinks the light must have come from something on the ground."
] |
[
"No, it is because of refraction of sunlight through layers of air which are at different temperatures, as ",
"u/Jak03e",
" said"
] |
[
"To break it down even further, waves travel at different speed when traveling through mediums of different density. Sound waves can travel through air or water or solids. But they travel faster through denser materials. When a sound wave hits a change of desinty (a shout encounters a cave wall) a good amount of the wave is reflected back. ",
"The same thing is happening with light between the more and less dense boundaries of air temperature layers. It is a light \"echo\" that causes reflection or in this case diffraction. "
] |
[
"how do the lungs get rid of solid stuff I inhale? (like dusts for instance)"
] |
[
false
] | null |
[
"The cells in the linings of the trachea and the bronchi have very small hairs called cilia. Furthermore, there are goblet cells in the lining which produce mucus. All the stuff that gets into the lungs gets trapped in the mucus. The cilia then move the mucus up to your throat where you then swallow it or spit it out. The carrying of the mucus to your stomach is a process which is happening all the time without you knowing."
] |
[
"Don't forget dust cells!",
"Those little guys are great at eating up all of the stuff you don't want floating around...I know all too well. "
] |
[
"Awesome, although a little gross :)\nThanks!!"
] |
[
"Does the concept of quantum tunneling translate into chemical reactions?"
] |
[
false
] |
Basically, does the idea of a particle tunneling through a barrier have any relation to reaction thermodynamics? For example, two elements react to form a molecule. For the reaction to occur, some amount of energy is required. Is it possible for the reaction to proceed through some "tunneling" mechanism by which the product is produced without making it over the energy barrier? Without the use of a catalyst or something along those lines, could the reactants "tunnel" through the energy barrier and form the product anyway?
|
[
"yes.",
"There are even some reactions which occur in the body that require tunneling of hydrogen ions (protons) to proceed. Hydrogen tunneling is responsible for some DNA mutations, and is needed in the active sites of some enzymes.",
"I found ",
"this paper",
" whose introduction goes over some of the evidence for quantum tunneling being important in many biological reactions."
] |
[
"Adding on, Quantum tunneling can occur with reactions involving heavy atoms too. This occurs when the energy barrier is very high (relative to kT) and \"thin\",meaning there is only a small atomic displacement is required to proceed past a transition state (the top of the barrier). ",
"Here",
" is a nice example of a ring expansion reaction where carbon tunneling results in a rate that is 10",
" greater than would be expected from a classical barrier-crossing mechanism at 8 K.",
"Warning: you will need to create a free account to read the article if you don't have institutional access to Science."
] |
[
"It is certainly possible for quantum tunneling to occur in reactions. One of the most important reactions for living - hydrogen fusion in the Sun - occurs at its current rate because of quantum tunneling. There is a function called the Gamow peak that describes where the amount of particles at a particular energy (described by a Maxwell-Boltzmann distribution) and the probability of quantum tunneling at a particular energy combine have the highest chance of occuring; without quantum effects, the effective temperature/energy of the hydrogen particles would have to be much higher to fuse. The University of Tennessee Knoxville describes the Gamow peak in more detail: ",
"http://csep10.phys.utk.edu/astr162/lect/energy/temp-press.html",
"EDIT: Quantum tunneling in solar fusion is a nuclear reaction, rather than a chemical reaction. Thanks to ",
"/u/nottherealslash",
" for pointing this out.",
"Quantum mechanics is important in the Sun's fusion because the Sun's density and size give many more chances for quantum tunneling to happen, as opposed to fusion that could be done on Earth. So, while quantum tunneling may be important in chemical reactions, it may not be that pronounced without as extreme of conditions. "
] |
[
"If light moves at a constant speed, how is it that a prism separates the different wavelengths and slows each wave down?"
] |
[
false
] |
Does this mean light speed is a variable thing? Does Einstein's bike light experiment fall apart if you were to be biking through a medium that acted on light the same as a prism?
|
[
"The point is the \"speed of light\" is a bad name. It is the speed that light happens to travel at in vacuum but it isn't fundamentally a property of light, but of spacetime.",
"You can go faster than the speed that light travels in a material. You get something analogous to a sonic boom. See ",
"here"
] |
[
"It's not true that all light travels at the same speed in a given medium. Refractive index can depend on wavelength."
] |
[
"That is how I always thought it went. But I was watching the Cosmos with NDT yesterday and he mentioned that Newton looked at light through a prism and noticed that some wavelengths of light move through \"faster\" than others in a prism. He should have clarified that different wavelengths move through the prism differently than others."
] |
[
"Is the amount of information in the universe constant?"
] |
[
false
] |
If it is, is also the information itself in the universe constant? ie. information cannot be lost and gained at the same time for a net of 0?
|
[
"Then you have a universe that's only deterministic in one direction of time. You can't backtrack the game. I wouldn't call that a perfectly deterministic universe. But, yeah, that's true. I should probably have been more careful in my wording. "
] |
[
"The universe being deterministic might be at odds with the Copenhagen Interpretation. Then again, it's just an interpretation."
] |
[
"The real reason is the Bell inequality, which has been tested experimentally and thus ruling out all hidden variable theories.",
"This is absolutely incorrect, Bell's Inequality (nor any other test) rules out hidden variables. It just lays conditions on what must be the case if hidden variables do exist (i.e., they must be non-local).",
"As much as I find it intuitive to say that quantum events (like decay of a radioactive element) are indeed random, there is nothing that ",
" that. For example, Bohmian Quantum Mechanics, although not terribly popular, is one example of a consistent hidden variable interpretation of physics."
] |
[
"Can chickens (gallus gallus domesticus) survive by themselves in nature?"
] |
[
false
] |
I’m wondering if chickens could survive by themselves in nature? Has the domestication really affected their habits or are they still close enough to their wild ancestors so to survive in nature? Thank you very much!
|
[
"There are places where \"wild\" chickens exist. ",
" Some of the instances listed include feral chickens in urban or semi-urban settings, but some are almost entirely undeveloped areas."
] |
[
"It would depend on the local predator population. For example, if there are enough foxes in the area, they would easily wipe them out. "
] |
[
"pretty much any predator could tackle a chicken.. "
] |
[
"[Mathematics] Is there a formula to how many perfect shuffles it takes for a certain amount of cards to go back to order?"
] |
[
false
] |
I was playing with some cards. I wanted to know how many perfect shuffles it takes for cards to go back to order. I then started with a low amount of cards and did more and more. but didn't do more than 14. A perfect shuffle is taking half the cards and then putting one behind the other if i have 4 cards- 1 2 3 4 (works best with even number of cards) i take 1 and 2 and shuffle them. 3 1 4 2 then again till it goes back to order. *number of cards, number of shuffles *2 2 *4 4 reverses order after 2 shuffles. *6 3 *8 6 reverses order after 3 shuffles. *10 10 reverses order after 5 shuffles. *12 12 reverses order after 6 shuffles. *14 4 *why does 14 cards only take 4 shuffles?
|
[
"If you want to know the number of shuffles needed for larger decks you can look ",
"here",
". Like ",
"/u/DCarrier",
" mentioned this is related to finding the multiplicative order of a number in modular arithmetic. This is called the ",
"discrete logarithm",
" problem and it's hard enough that it's used for cryptography, so I doubt there's a nice formula for it."
] |
[
"This does not answer your question, but you may still find it interesting. There is a ",
"numberphile",
" video about how many shuffles you need for a \"perfect\" shuffle. ",
"I think actually they mention your problem as well, but I can't remember at this point. "
] |
[
"A perfect shuffle of ",
" cards moves card ",
" to 2",
" (",
"mod",
" ",
"). So you need the smallest ",
" such that 2",
" ≡ 1 (mod ",
"). Using ",
"Euler's theorem",
", we can say that this is true for ",
" = ",
"φ(",
")",
". It's not necessarily the smallest value, but the smallest value must be a factor of that.",
"So, if you have p",
"p",
"p",
"...p",
" cards, the answer is guaranteed to be a factor of (p",
"-1)",
"(p",
"-1)",
"(p",
"-1)",
"...(p",
"-1)",
".",
"We shuffled a bit differently though. The way I did it, you need an odd number of cards, and the card in the zero position never moves. So I think we'll be the same if we ignore that card. 0, 1, 2, 3, 4 becomes 0, 3, 1, 4, 2, so ignoring the zero card it's 3, 1, 4, 2, like you got. So I just need to add an extra card.",
"If there's 14 cards, then it will repeat itself after φ(15) = (3-1)(5-1) = 12 shuffles, so the shortest number of shuffles must be a factor of that. It happens to be four.",
"To my knowledge, there's no good way to figure out how many shuffles it will take besides checking all the factors of the resulting number."
] |
[
"Is there a limit to our intellects?"
] |
[
false
] |
I remember reading a scifi story many years ago called "Breeds there a Man" which put forth the idea that some ideas are so foreign to our ability to deal with and comprehend that it would literally kill people who had to deal with those ideas. I've also read in places that theoretical mathematicians are known to have a high rate of suicide compared to other scientific disciplines. As for me, I had to give up studying cosmology as a hobby as the ideas put forth in it would literally trigger severe panic attacks in me. So, my question is: Is there a limit to our intellects? Is there a point where the attempt to learn more of reality is not just beyond our knowledge but beyond our ability to stretch mentally to that point? Or, to put it in the classical sense. Are there some things "Man was NOT meant to know." Thank you.
|
[
"What you are describing has nothing to do with intellect. It has to do with open mindedness and your cultural upbringing. If you can't deal with what cosmology has to tell you then I am guessing you were brought up to believe the universe is nice and neat and conflicting evidences unsettles you. Your intellect has nothing to do with it."
] |
[
"to me, saying there are things that man was not meant to know doesn't mean anything. I do think there are things we will never know (not because we can't comprehend an answer, but just cuz we have no way of experimenting on it), but i dont think the universe would give much of a fuck if we found out."
] |
[
"right, i like to think information about the universe can be put into 3 buckets (not counting stuff we think we know but is wrong):",
"the known known- This is stuff we know.",
"the known unknown- This is the stuff we don't know, but are able to ask the question.",
"the unknown unknown- This is the stuff that we know so little about that we don't even realize that we don't know something - we don't even know enough to ask the question. for example, the composition and nature of dark matter in the 1920's was an unknown unknown because we didn't even realize there was a problem with the amount of matter in the universe. This is now a known unknown. (notice the only examples of unknown unknowns are in the past, because we don't know any current ones - that's the point)"
] |
[
"How deep do Ocean currents go? Do they affect the water at the bottom of areas like the Mariana Trench?"
] |
[
false
] |
I was wondering if the water that sits at the bottom of some of the deepest trenches ever circulates with the rest of the water above it. Or is the water that's down there now, the same water that's been down there for thousands of years?
|
[
"Ok, my time to shine, hopefully. The deep ocean circulation of water is in fact dominated by a gradient in seawater density. The waters of the ocean are not all homogenised or mixed like one would expect, in fact, they are separated by differences in density based on the overlying waters they were sourced from, and can be categorised as 'water masses'. These differences in density are caused by a difference in the temperature (the colder, the denser) and salinity (the saltier, the denser) of the source waters where they were formed. So when you have a situation where the water that forms above is denser than the water formed previously below, it sinks, and we get what we call in the business 'downwelling'. This only happens at a few points in the sea, most notably the Labrador Sea and some places in the Antarctic. So this really dense water sinks and sinks until it reaches a density that it can no longer sink past. So what happens now? The water is still forming above, so it has to keep moving! As such, it moves horizontally throughout the ocean (on the density isocline). What we have here is something called the 'Thermohaline circulation', and it actually links all the waters of the world oceans together. Here is a ",
"diagram",
". ",
"Hope that explains your question a bit! ",
"Knowledge base (not source): Current PhD student in Oceanography, coming from a Masters in Ocean Sciences.",
"EDIT: Thanks for the gold fellow fan of the ocean! ",
"EDIT 2: Absolutely astounded by the wonderful amounts of interest my fellow Redditors seem to have in ocean science! Oceans are really important so I'm glad I could help raise interest! I live in Europe, so it's my bed time unfortunately, but if any more questions appear overnight I'll do my best to answer them."
] |
[
"Hello! Thank you for contributing to askscience. ",
"I'd like to invite you to fill out a short application to get flair on askscience. This will put a colored tag with your field of research next to your username on any comments you make in askscience, allowing readers to identify you as an expert in your field.",
". ",
"The only requirements are graduate training in the sciences and a comment history in askscience demonstrating your expertise (your comments from this thread likely suffice). This requires no personally identifying information. If you have any questions feel free to ask :D"
] |
[
"Good question. Off the top of my head I believe the residence time for water in the conveyor belt is within the area of around 3000-6000 years (definitely that order of magnitude). I'd have to check the literature though!",
"EDIT: ",
"/u/sverdrupian",
" (nice username, very oceanographic!) has provided with a better source of around 2000 years for the North Pacific and 800-1000 years for the Atlantic."
] |
[
"Questions about M-Theory"
] |
[
false
] |
So I just watched some videos on M-Theory on youtube and I find it quite interesting. Though they don't fully explain everything in the M-Theory so I have some questions: They say the big bang was created by two membranes (universes?) colliding. But if they collide wouldn't that mean that a new membrane would have to form for our new universe to form (a new membrane = a new universe?) What is the 11th dimension? They said it was everywhere very small across but infinitely long. This still doesn't answer the question about when everything started. If it comes down to that time was the first dimension and everything has existed infinitely then it's just as good as an explanation as the original big bang theory. Thanks.
|
[
"Okay, so... first... these are all just interesting ideas. They're in a grey area between hypothesis and theory. The math somewhat checks out, but is exceedingly ambiguous. And there's no data to support it. The math checking out gets it out of \"crackpot\" physics territory, but it's still not proper \"science\" yet.",
"Anyway, Brane cosmology posits that there are these separate regions of space-time in some higher dimensional \"container-space time\" (my wording, not official). And when two of these branes bump, they release ",
" into each other. So our brane colliding with another provides the energy to the big bang.",
"Where do the branes come from? We don't know. It may be that we cannot possibly know due to the laws of physics that govern them.",
"Compact dimensions: Imagine an ant on a wire. For us far away, the ant appears only to move back and forth along the wire. But for the ant it has an additional \"degree of freedom\" of its motion. It can move ",
" the wire as well. So if that ant starts moving randomly, some motion will be along the wire, and some motion around the wire. Now it turns out that if it was restricted to only \"along\" the wire, its motion along the wire is different than this 2-D freedom it has \"along\" and \"around.\" So that's the idea about these \"compact\" space-time pieces. At every place in space-time, there are very very subtle ways you could move around. But you can't go very far along that path. Imagine the scale between you and a proton. Now apply that scale to the proton and you're still ten thousand times larger than the lengths supposed for these dimensions. But what they do is they allow for different kinds of vibrations. If I have a string I can shake it up and down. Or I can twist my wrist and send a kind of \"spiral\" wave down the string. There is one degree of freedom in the first kind \"up/down\" and two in the second kind \"up/down, left-right.\""
] |
[
"well the point is that we can only see the ant move around it by blowing up the image, by zooming in. From sufficiently far away, the wire looks like a 1-dimensional thing with only the property of length. So the idea is similar to our using particle accelerators to measure very small distances. If we had a sufficiently powerful accelerator we could in fact \"zoom in\" close enough to see the motion \"around the wire\" as it were. The problem is, that with present technology, such an accelerator would be on the scale of our entire solar system."
] |
[
"there are two things with the \"brane\" kind of thinking. The strings themselves are 1-D \"things\" in their Calabi-Yau manifold, but then the cosmos, spacetime itself is a 3+1D \"brane\" in a higher dimension space that is divided into other subspaces that may or may not have the same division of dimensions as our brane."
] |
[
"How much blood can the human body regenerate in one day?"
] |
[
false
] |
Couldn't find the answer anywhere online. This question assumes the body is under ideal conditions - adequate nutrients, water, etc.
|
[
"The process of making blood is called haematopoiesis. It is estimated that the body produces around 10",
" new red blood cells per hour in the steady state, i.e. when blood is being broken down naturally and new blood is being made (you have 5 * 10",
" per litre of blood). Red blood cells last about 120 days and there is a daily turnover of about 0.8-1%. (Note these figures are from different sources and may not perfectly match but are probably accurate within an order of magnitude)",
"Red cell production can be significantly increased if blood is being lost. ",
"[To be continued]"
] |
[
"(Sorry, had work.)",
"Turns out this has been studied quite a bit, particularly with regards to managing patients before and after surgery. \nIn the post above I mentioned that red blood cells are continously turned over so new blood is being produced all the time. This can be increased if blood is lost at a higher rate or there is an increased need. The main signal known to drive this is a hormone called erythropoietin (EPO) that is produced in the kidneys.",
"The limiting factor seems to be the supply of iron. A normal healthy person will struggle to produce blood at 3x the baseline rate. The theoretical maximum is apparently around 4x if someone is stimulated with EPO. There's a disease called haemochromatosis where the body has too much iron and these patients can produce new blood at up to 6-8x the baseline rate. ",
"So if we estimate that 1% of your red blood cells are being replaced each day normally, if you needed to you could probably regenerate up to 3-4% or even up to ~6-8% if you aggressively supplemented iron.",
"Ref: ",
"http://bmsg-ucth.org/Bloodless%20Medicine%20(Goodnough%20et%20al)%2003.pdf",
"There are probably better attempts to quantify this in the field of autologous blood donation if you wanted to do some more reading. I'd try google scholar. "
] |
[
"Thanks, this answered it perfectly. "
] |
[
"Question from my father: What would happen if temperature suddenly dropped below freezing during fog?"
] |
[
false
] |
Imagine if you're standing in fog, and you couldn't see more than 5 meters in front of you. What would then happen if the temperature suddenly dropped to less than 0 degrees Celsius?
|
[
"Hard Rime",
". No it's not some new form of gangster rap. It actually happened a winter or two ago here in Iowa, and it was one of the most beautiful things I've ever seen."
] |
[
"Freezing Fog Explained"
] |
[
"On a related note, this is why it is dangerous to fly through a cloud when the local air temperature is below zero. Ice deposits on the wings can easily form and they will severely degrade performance. "
] |
[
"Are the properties of antiparticles that are opposite from their non-antiparticle counterpart's properties all vector quantities?"
] |
[
false
] | null |
[
"Physics"
] |
[
"Physics"
] |
[
"No. In fact, none of them are. They’re all scalars."
] |
[
"If I had a stick that was one light year long?"
] |
[
false
] | null |
[
"Please see the FAQ"
] |
[
"I did before I posted, did I do something wrong?"
] |
[
"https://www.reddit.com/r/askscience/wiki/physics/rod_speedoflight"
] |
[
"Why is it that in the center of galaxies I see in pictures there is a huge amount of light?"
] |
[
false
] | null |
[
"The black holes at the centers of galaxies are very small compared to the galaxies. The most massive ones are only the size of our solar system. The bright regions at the centers of photos of galaxies are produced by the multitude (tens of billions) of stars near, but not exactly at, the center."
] |
[
"I looked it up ",
"here",
" (an OSU astronomy course). It says:",
"Because stars are so closely packed together near the galactic center, the night sky for inhabitants there would be spectacular. Near the galactic center, the average distance between neighboring stars would be only 1000 AU (about a light-week). If the Sun were located within a parsec of the galactic center, there would be a million stars in our sky with apparent brightness greater than Sirius. The total starlight in the night sky would be about 200 times greater than the light of the full moon; you could easily read the newspaper at midnight, relying on starlight alone.",
"FYI: Barbara Ryden is the author of a very good undergraduate cosmology textbook."
] |
[
"If we were a star near the center of the Milk Way core, what would the night sky look like? Would it be as bright as day time? How close would the nearest stars be?"
] |
[
"When someone in the family got sick, could everyone else be vaccinated based on that dead virus/ flu? Could this be done every time someone got sick?"
] |
[
false
] | null |
[
"Hi SaveFerris9001 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"‘Biology’"
] |
[
"Biology"
] |
[
"Is reflected sunlight \"different\" than direct sunlight?"
] |
[
false
] |
While discussing gardening options with my wife, I got to thinking about ways to create more "direct sun spots" in our yard. We have a long fence with great soil and space, but it becomes shaded (by the fence) late in the morning. One thought I had was to install a mirror to reflect the sunlight at the shaded spots, creating more light for the plant. We actually have a great spot to do this about 30-40 feet from the shaded area, along a parallel fence. My question stems from the concern that this either wouldn't help that much (if the sunlight diffuses from the glass/silver reflection, loses some property that photosynthesis requires, etc) or even cause damage (for example, magnify/amplify the light in some way). It seems like the reflected light would be "close enough", but I was curious for a scientific reason to confirm or deny it. Thanks!
|
[
"http://en.wikipedia.org/wiki/Polarization_(waves)#Propagation.2C_reflection_and_scattering",
"Reflection can polarize light, and it's possible for different wavelengths to be reflected with differing efficiencies, but photosynthesis uses visible wavelengths, so a normal mirror should be fine, and I don't think the polarization shouldn't matter either. ",
"Is this for flowers, bushes or grass?"
] |
[
"Thanks. I did some quick research and stumbled across that. Can't ",
" trust Wikipedia, so I thought I would ask as well. (Not that random internet strangers are always super trustworthy either, but...)",
"It will mainly be used for vegetables in raised boxes, possibly some bushes (raspberries/strawberries). I guess flowers as well being some of the plants are flowering. "
] |
[
"Well, I do have an alternative solution for you",
"http://www.motherearthnews.com/organic-gardening/vegetables-to-grow-in-shade-zm0z11zsto.aspx",
"\n",
"http://bloomiq.com/content/shade",
"Plants that do well in the shade are probably going to work out better than trying to use mirrors. They'd likely end up having to track the sun anyway."
] |
[
"Could a moon have its own moon?"
] |
[
false
] |
[deleted]
|
[
"I can believe it. Instead of using reddit's search, you should just use google with a string like this: site:",
"www.reddit.com",
" inurl:",
"/r/askscience",
" and whatever you want to find.",
"\nIt's more effective, in my experience."
] |
[
"Again, tried to search and it returned nothing in this subreddit. Regardless, thank you for the info and the downvote. I'll be deleting this now. Bye."
] |
[
"Again, tried to search and it returned nothing in this subreddit. Regardless, thank you for the info and the downvote. I'll be deleting this now. Bye."
] |
[
"How do relativistic effects impact fast rotating pulsars?"
] |
[
false
] |
Some pulsars, like are rotating at almost 25% the speed of light. Given that the object is only 16km across that means there is a huge differential between the seed of the core, and the speed of the surface of the pulsar. In what ways do time dilation, frame dragging, and other relativistic effects impact the pulsar and its behavior?
|
[
"He's asking about the difference between this pulsar on its equator and its core, not asking for a comparison to other pulsars."
] |
[
"Additional question here; what about the difference in velocity between the poles and the equator. Will time dilation have an effect on the crust given the velocity differential? "
] |
[
"It seemed to me that they were asking about fast rotating pulsars versus others as per the title. In any case, that's a tough problem to answer. Unlike with rotating black holes, solutions to rotating neutron stars in general relativity are still an ",
"open problem",
" though I do recall seeing some people claim rather complicated solutions recently but I can't find the paper. For rough numbers, I suggest seeing other ",
"/r/askscience",
" answers previously posted, such as this one ",
"here",
" of via ",
"physics stackexchange",
". For something like ",
"frame dragging",
", the angular momentum comes into play so it depends on both the speed but also the mass/radius, which aren't known so it can't be compared to other neutron stars anyway."
] |
[
"How fast does electricity move in a wire?"
] |
[
false
] |
I know that in theoretical DC circuits, when I connect the battery, all the electrons begin motion at the same time and a current is created. But this can't be the whole picture or I could transmit information faster than the speed of light.
|
[
"all the electrons begin motion at the same time and a current is created",
"This is wrong. Direct Current (DC) is a useful approximation, not a physical reality. No circuit is ever exactly DC all the time. When you connect the wire to the battery, the fact that you have gone from zero current at one instant of time to non-zero current at another instant of time means that the current is changing, and is therefore not DC. This changing current causes changing electromagnetic fields that flow through the circuit at the wave speed (in a crude sense, it's the speed of light in the material, which is less than the speed of light in vacuum). These waves - and associated fluctuations in electrical current - travel through the circuit, scatter off circuit elements, and quickly dissipate and settle down to the constant field state. In a very small amount of time, the transient electrodynamic effects go away, and the circuit acts more and more like an ideal DC circuit. In others words, the instant that you connect a wire to the battery, you do not have a DC circuit. Only after some time, when the fields have had a chance to flow through the entire circuit, and the electrical current has had a chance to settle down to its equilibrium state, do you have direct current."
] |
[
"About two-thirds the speed of light, give or take. The actual speed of the electrons is much, much, much slower though, on the order of like a millimeter per second."
] |
[
"Can you source this?"
] |
[
"Is the expansion of the Universe considered a \"force\"?"
] |
[
false
] |
I understand that there are fundamental forces governing the Universe, but what about the fact that it's expanding? How it that taken into account?
|
[
"No, it is not.",
"The whole \"fundamental forces\" notion is, to put it bluntly, a lie we tell children. It's not actually a very good description of reality.",
"To the extent that metric expansion is a consequence of anything one might be inclined to think of as a \"fundamental force,\" it's gravity."
] |
[
"When you say it's possible to know truth, what do you mean?",
"I meant what I said. This is not a late-night drunken argument about philosophy. I said exactly what I meant to say.",
"How do you know that we aren't living in a simulated world, or even that we aren't simulations ourselves?",
"Because there is no evidence of such. ",
" was a ",
" you know.",
"But then you've got to ask what is meant by 'simulated' versus 'real'...",
"No, you really don't.",
"Look, I'm going to say this bluntly. I want you to take that as a sign of respect; your time is as valuable as my own, so I will not waste it by mincing words.",
"You seem to be having trouble with the whole \"science\" thing. This is fine; science if not for everyone. But it ",
" what goes on here. So please refrain from trying to drag this forum into the muck of navel-gazery. Questions like \"what is real\" are silly and have no place here.",
"Thanks for understanding."
] |
[
"A clearer pedagogical distinction between simplifications and truth would not be unwelcome."
] |
[
"Could we clean the atmosphere using plants?"
] |
[
false
] |
I am wondering what the limitations on the Calvin Cycle are and why it has not been up-scaled artificially to help clean out some of the CO2 in the atmosphere? Its been a while since I've learned about it, but I thought that many pollutants can be taken care of but the cleaning leaves a large amount of CO2 in the air. Then I just recently learned about the Calvin Cycle. I had originally thought that photosynthesis was needed to fix CO2, but I guess it isn't? So what are the limitations on the Calvin Cycle?
|
[
"We don't really have the technology to accurately reproduce photosynthesis. We have approximations using biomimetics, but nothing matching the complexity of the Calvin Cycle just yet. The CC is not the first step in photosynthesis, and it is not very easy to mimic. ",
"RuBisCO is a fairly slow-acting enzyme comparatively, and we don't really have artificial molecules that can fixate the carbon as they aren't stable aerobically. The technology we do have mostly reduces CO₂ into CO, which isn't very useful because it needs to be reduced further and hydrating them is also difficult. We are more efficient at harnessing light to separate water, but haven't been able to incorporate all of the steps into a replication of photosynthesis."
] |
[
"What if we took the Calvin Cycle out of the plants, and beefed it up artificially? So instead of all of those plants, we just have massive reactors of some sort."
] |
[
"2 reasons this isn't likely possible.\n1. CO2 isn't the only greenhouse gas, there are many, namely methane (CH4).",
"So in conclusion, theoretically, sort of, but in reality, not now, and probably not for a long time."
] |
[
"Why doesn't glue harden while in the bottle?"
] |
[
false
] |
[deleted]
|
[
"Type of glue here is essential for the explanation; but I'll take a few examples. ",
"Superglue; cyanoacrylic, actually initiates bond with water molecules. So being in an air-tight container extends the life significantly. So without the water molecules to bond to the glue won't react and create the bond. (This is why the stuff sticks to fingers so fast.",
"Wood glue, elmers glue, and the like use PVA. -- it works by forming a chain (polymerization) when it dries. The solution is usually water, so while in the container the un-evaporated water keeps the chain reaction from happening. ",
"Rubber Cement -- works like the PVA, its dissolved in a solvent such as acetone. This solvent evaporates and creates the polymerization bond. So once again, a sealed container keeps it from evaporating."
] |
[
"There are several types of glue.",
"Solvent-based. The glue is dissolved in some liquid, like water or acetone. This is most kinds of \"cement\", and wood glue. It cures when the solvent evaporates. If it's in a bottle, the solvent cannot evaporate, and the glue remains liquid.",
"Catalyst-based, external catalyst. This is silicon glue, and superglue. It hardens when moisture from the air gets into it. No moisture, no hardening. That's why it's safe in a bottle.",
"Catalyst-based, two-parts. This is like epoxy resin: you mix the resin with the hardener (catalyst). As long as you keep them separate, it remains liquid.",
"Note: The term \"catalyst\" is not used here in the strict chemical science sense. A true catalyst would remain unchanged at the end of the reaction (like when platinum is used as a catalyst to make high-octane gasoline). In the cases above, the \"catalysts\" become part of the final product at a molecular level. Thanks to ",
"/u/FatSquirrels",
" for the correction."
] |
[
"In your #2 and #3 cases there are no real catalysts with the chemical definition (not consumed). For cyanoacrylate the water is an initiator but a water molecule is consumed to start each polymer chain. With two part epoxy the hardener is an epoxide opener, often a multifunctional molecule that binds several different chains from the resin together by cross linking. ",
"In both cases that \"catalyst\" material is consumed and the reaction would not progress in any circumstances without it. A catalyst by definition is not consumed (or is regenerated) and only makes the reaction easier or more likely to happen under certain conditions. As such it is important to realize that those molecules are integral parts of the final products and not catalysts beyond the colloquial definition.",
"Sorry if this sounds pedantic, but I want to make sure people who come here for information understand the correct definitions we chemists use."
] |
[
"How come people with diabetes are more vulnerable to CoVid-19 than healthy people?"
] |
[
false
] | null |
[
"Not entirely understood - but largely thought that it’s related to the pro inflammatory state that diabetes facilitates. This should also be looked at as, most likely, a gradient effect. Those with more controlled and less severe disease at lower risk of complications versus poorly controlled severe chronic disease states. We are still in early stages so definitive data and evidence is severely lacking.",
"Also important to remember that presence of comorbidities is no guarantee of poor outcomes. Many folks with cardiovascular disease, diabetes, pulmonary disease, cancer, and even centarians are surviving and doing well despite being infected. Conversely, some young and otherwise healthy folks do poorly."
] |
[
"Here's one reason....and I've been trying to get this info out for weeks.",
"Human pathogenic coronaviruses (severe acute respiratory syndrome coronavirus [SARS-CoV] and SARS-CoV-2) bind to their target cells through angiotensin-converting enzyme 2 (ACE2), which is expressed by epithelial cells of the lung, intestine, kidney, and blood vessels.",
"The expression of ACE2 is substantially increased in patients with type 1 or type 2 diabetes, who are treated with ACE inhibitors and angiotensin II type-I receptor blockers (ARBs).",
"Hypertension is also treated with ACE inhibitors and ARBs, which results in an upregulation of ACE2.",
"ACE2 can also be increased by thiazolidinediones and ibuprofen. These data suggest that ACE2 expression is increased in diabetes and treatment with ACE inhibitors and ARBs increases ACE2 expression. Consequently, the increased expression of ACE2 would facilitate infection with COVID-19. We therefore hypothesise that diabetes and hypertension treatment with ACE2-stimulating drugs increases the risk of developing severe and fatal COVID-19.",
"https://www.thelancet.com/journals/lanres/article/PIIS2213-2600(20)30116-8/fulltext#coronavirus-linkback-header",
"Link sharing in the reddit app is broke!!"
] |
[
"Does it also have more of a negative effect for people with hypoglycemia without diabetes?"
] |
[
"Is there any evidence FOR Applied Kinesiology?"
] |
[
false
] |
[deleted]
|
[
"No, no, no I didn't mean that. I meant don't take one piece of evidence that argues in favour of it, and discount a mountain of evidence that discredits it.",
"This isn't my field, and I don't know much about it, but from the cursory reading I have done it is an alternative medicine, and I understand that several mainstream medical organisations discount it. For example the American Academy of Allergy, Asthma and Immunology and the American College of Allergy, Asthma and Immunology stated there is “no evidence of diagnostic validity” of applied kinesiology.",
"Further the American Cancer Society ",
"has stated that",
" \"...results showed that applied kinesiology was not an accurate diagnostic tool, and that muscle response was not any more useful than random guessing.\"",
"This touches on medical questions so I would always ask a doctor for their advice on it. But, it seems pretty clear to me that several mainstream medical organisations see it as a waste of time. You would need to find some pretty strong evidence to discount their research - one or two pieces here are there aren;t sufficent and to do otherwise is to cherry pick."
] |
[
"Remember not to cherry pick - a cardinal sin in science. If you test something enough times with enough variables, you may be able to see some effect but you need to look at the totality of the evidence to get an overall picture. ",
"Relevant xkcd"
] |
[
"As a neat psychological trick, muscle response works relatively well for many people. Especially if the questions are surprising. It gets weird when kinesiolgy starts to claim that \"body knows\" what it wants and we can figure things out by just asking it. It seems to me that their diagnostic is just like quija board. "
] |
[
"How are wind chill and the \"feels like\" temperature measured?"
] |
[
false
] |
I've repeatedly heard people disregard the "feels like" temperature, is there any merit it that?
|
[
"\nAt any time, the human body produces heat through metabolic processes. If our skin was coated in a perfectly insulating layer, we couldn't cool, we would overheat and die. Fortunately, heat dissipates from our bodies so we feel comfortable.",
"How does the skin primarily cool? That is known as convection. A moving fluid (air in our case) absorbs heat and each molecule of air, now warmer than before, transports the heat away. ",
"If the air is stagnant, the air layers touching our skin heat up first, and dissipating heat is dependent on the layer closest to our skin slowly passing the heat further away from us. This is pure conduction, the heat transfer process that describes heat transferring through a metal beam. Convection is proportional to the temperature difference. A greater temperature difference corresponds to a higher heat rate transfer.",
"If there is a strong wind, the layer closest to our skin is constantly replenished with cool air. If the wind is too strong, the loss of heat is greater than that supplied by our bodies metabolic processes and we lose heat, feeling cold.",
"Convection is proportional to the temperature difference. So q=h*(Ts-To) where q is the heat transfer rate due to convection, h is the coefficient of convection, Ts is the temperature of the skin, and To is the temperature of the ambient air.",
"\nWhat is important to the average person is how cold the weather will feel if they go outside. If I'm going for a 10 minute walk, I don't want to dress for 60 degree weather if my body will perceive it as 40 degree weather due to the wind.",
"As a result, we \"ignore\" the convection and calculate what temperature, assuming stagnant wind, would cause the same heat loss, q, as occurs with convection.",
"That temperature determines what the wind chill is."
] |
[
"Cold still air cools you off at a certain rate. The colder the air, the faster you cool off. ",
"When cold air is blowing over you, it cools you off faster than if it is not moving, thus if -10c air was blowing by you at a certain speed, it could be equivalent to the heat loss produced by colder air that is still, say -14c. The air is actually -10 but cools you off at a rate equivalent to if it was -14. ",
"The same concept applies to high humidity, which prevents you from cooling off in hot weather and makes cold weather seem cooler. ",
"Hope that helps"
] |
[
"If you're interested in the actual formula, the Nation Weather Service uses the Standardized Wind Chill Temperature Index. Their formula is ",
"WC(F)=35.74+0.6251T-35.74(V",
" )+0.4275T(V",
" )",
"Where T=temperature in F and V=wind speed in MPH. You can see more information here: ",
"http://www.nws.noaa.gov/om/windchill/"
] |
[
"Careers in SCIENCE!"
] |
[
false
] |
I graduated university in 2006 with a Sociology degree , and I've spent the past 5 years bumming around America and Asia traveling and working. Since graduating (unfortunately it came all too late) I have become very interested/semi-well-versed in the hard sciences, (specifically conservation biology and environmental science), have done a ton of research with universities and post baccalaureate programs in order to start school again January of 2011. First time around I was as cliche of a college kid as it gets. All I wanted to do was party and try to get laid (an often futile pursuit). But now, after years of science interest, I can't see myself doing anything else for a career. Is I will have to re-learn a lot of math and work part-time, try for scholarships, and take out loans. I will be 28 when I start. In your professional advice, is this a viable career option based on the kinds of jobs/hiring trends in your various jobs? I assure you I'm very dedicated and will bust my ass to make the Deans list every semester this time around, and will probably go to graduate school afterwards. I need some moral support to push me into this (if you have any to give) given that all my friends have mostly settled and are working on their families at this point. Much appreciated!
|
[
"I started my PhD at 28 after knocking around a few years. It was hard getting back into the swing of things, but it can be done. Go for it. ",
"Hopefully by the time you get out we'll be on the other side of this current funding hell."
] |
[
"I did it, just as you did: Anthropology BA to a PhD in Biology (starting when I was 30).",
"It was a fun but long, impoverishing journey. Rather than give you the details of how I did, I will tell how you how I knew to do it. I found a great grad program in the internet in what I wanted to go into (it was Experimental Pathology at Yale University) and made an official appointment to talk to the director of the program (I lived very close to Yale at the time). He seemed impressed by my enthusiasm, but not by my lack of degrees and experience. He told me how to mold myself into the student for the program: lab experience, courses, amazing GRE scores. It took me probably 2.5 years, but I did it! I was one of the most enjoyable and liberating times of my life (except for the poverty part :) because it was the only time I didn't feel like a slave to a job or to a degree program, I was just studying/doing exactly what I wanted. I took all the courses that had previously terrified me (like statistics and organic chemistry), and did very well because I was more mature than the other kids who had to split their time between being wild college kids and their classes. (I never applied to the original program, because my interests had shifted by the time I was ready, but I am eternally grateful to that professor.)"
] |
[
"I don't have anything constructive to add, but I just want to commend you for following your dreams. I've recently realized that I don't want to be writing code, I desperately want to be teaching. Now I'm just trying to gather up all the brass required to construct myself a set of giant balls like yours."
] |
[
"Has Lamarckian evolution been completely disproved?"
] |
[
false
] |
I've always thought the experiments, cited in basic science classes, that refuted Lamarckian evolution were flawed. Epigenetics point to the possibility of at least something vaguely Lamarckian, is it possible or does any respected scientists believe that Darwinian evolution could be influenced even minutely by Lamarckian principles?
|
[
"This is only a real problem with advanced organisms. ",
"Horizontal gene transfer",
" certainly plays a role in things like bacterial evolution."
] |
[
"The problem is with the mechanics of reproduction. There is no mechanism for the body to 'edit' the DNA of egg or sperm in order to transmit the acquired adaptations to the next generation. Of course we now know the role of DNA, etc., which was not the case when Lamarckism was in its heyday. "
] |
[
"Yes, however, nothing more complex than prokaryotes can accomplish that, so it is safe to say that Lamarkism is not a viable model for evolution."
] |
[
"What was the evolutionary pressure that created the hyoid?"
] |
[
false
] |
The hyoid is the only bone in the biddy not directly connected to the skeleton. It is located in the throat and aids in swallowing and tongue movement. All other bones are connected (the neck bone's connected to the shoulder bone, the shoulder bone's connected to the arm bone) but the hyoid only connects via muscles and ligaments. Where did this bone originate in the fossil record, and what was it selected for?
|
[
"While unsure of the exact process of how it helps, it directly relates to language and our ability to speak. While at one time i did know the answer to this question, unfortunately, I have since forgotten. ",
"Fun fact I learned from Wikipedia and then confirmed a while back: ",
"Due to its position, the hyoid bone is not susceptible to easy fracture. In a suspected case of murder, a fractured hyoid strongly indicates throttling or strangulation. However this is not the case in children and adolescents, where the hyoid bone is still flexible as ossification is yet to be completed."
] |
[
"Ah thanks, good call. I still do think the hyoid differs from those tho in it's singularity, although it is still symmetrical in shape"
] |
[
"Ah thanks, good call. I still do think the hyoid differs from those tho in it's singularity, although it is still symmetrical in shape"
] |
[
"Will the recent supernova in the \"Cigar Galaxy\" (M82) have any direct affect on earth?"
] |
[
false
] |
With this supernova being approximately 12 million light years away from earth and the closest supernova in proximity to earth to date, I'm mainly asking this question in regard to the incredibly large amount of neutrinos that will be flooding the space around earth. Here's the article I was reading that sparked my question: Thank you :)
|
[
"No real effect (other than astronomers pointing their telescopes in that direction). Neutrinos for most practical purposes do not interact with matter. A light year of lead ",
"would only stop about half",
" of the neutrinos trying to pass through it. ",
"To have any noticable effect on life on Earth a standard sized supernova ",
"has to be within about 100 lightyears",
". 12 million is far too far away."
] |
[
"This is not the closest supernova in proximity to earth, by far. Naked eye supernovas have occurred within our own galaxy, for instance ",
"Kepler's Supernova",
", less than 1% of the distance to this supernova. ",
"Supernovas expected to have some influence on Earth are in the range of 100 light years, maybe up to a few thousand light years. This supernova is in an entirely different galaxy, much too far away to have an effect. "
] |
[
"It's the closest known supernova only in the last 10 years. A supernova goes off in our galaxy (about 100 times closer) about once per century."
] |
[
"Could the Earth and Moon be considered a binary planetary system?"
] |
[
false
] |
I've done a little bit of research, and I've learned that if a systems barycenter is outside a planet, its sattelite gets promoted to planetary status. Pluto is smaller than the Moon, and it's theres a dwarf planet. There has been talk that Ceres can be a planet. So if the moon can't be a planet, it coud atleast be a dwarf planet, right?
|
[
"What we call a \"planet\" or a \"dwarf planet\" is just a matter of how we define those terms. While there is some logic to the definitions, in the end they're just words we made up that we linked to definitions that we made up.",
"One of the requirements for being a planet is that the object should be the dominant gravitational body in its orbit. The Earth meets this requirement, but Pluto does not, because the orbit of Pluto is shared by various other Kuiper Belt Objects. We say that Pluto has not \"cleared the neighborhood around its orbit\" (which is the phrasing used by the International Astronomical Union in its definition of what a planet is).",
"The definition of a dwarf planet explicitly requires the object to not be a satellite of a larger body. This would exclude the Moon from being a dwarf planet, even though its size would make it so if it were not in orbit around the Earth. Objects that are large enough to be a planet (or dwarf planet), but don't meet the other requirements are sometimes called \"planetary mass objects\".",
"But all of this is based on the definitions adopted by the IAU. People are free to disagree with these definitions (and some do) and therefore have different ideas on how these objects ought to be classified. Ultimately it's just words and the label we stick on objects like Pluto, Charon or Ceres doesn't change the physical properties of them."
] |
[
"It should be important to note that the barycenter of the Earth-Moon system is ",
" within the Earth, as well."
] |
[
"But the word planet is inherited from the Ancient Greeks and carried over by Renaissance/Enlightenment scholars. It really is a holdover from a time when we didn't understand what the various things orbiting the sun were. In my view, it's totally ludicrous that a body like Jupiter is given the same category name as a body like Mars. Mars has much more in common with Ganymede or Io or whatever. But it's a matter of tradition."
] |
[
"Do silver polishes remove the silver oxide or completely or just remove the oxygen?"
] |
[
false
] |
Same with copper polishes, etc. Are they removing the oxygen from the surface or the whole outer layer? Would leaving the silver in the polish eventually dissolve the silver?
|
[
"Polish doesn't dexoidize a surface, it's made up of fine, sharp granules suspended in a thick fluid that it doesn't dissolve in. when you polish something, those granules scrape off the outer layer of the material when you polish something. the finer the grains, the smoother the shine"
] |
[
"If you did this with a wire running from the tarnished silver to the aluminum instead of just touching them together you'd have a crude battery. Chemical change is indeed taking place."
] |
[
"What about reactions like this: ",
"http://scifun.chem.wisc.edu/homeexpts/tarnish.html",
"\nNo abrasion involved."
] |
[
"Given that there are many unexplored cave systems under our very feet, is a \"Journey to the Center of the Earth\" type scenario possible?"
] |
[
false
] | null |
[
"Geological Engineering Student checking in here. ",
"Short answer - No. ",
"One of the most simple analogues to the earths structure is an egg. If we were to shrink the earth down to about the same size, the crust would be about the thickness of an egg shell. ",
"Expanded out to the size of our earth, the thickness of the crust varies from as little as 5km at the bottom of the ocean where it is thinnest, to about 35 km at it's thickest. This means that all those unexplored cave systems are contained within that band of hardened rock. ",
"Once you get below the crust, you hit something called the Mohorovičić discontinuity (MOHO for short). This is a boundary between the crust and the mantle. Below that, the magma (which is molten rock) behaves like silly putty, and as you go deeper it becomes more hot and fluid. ",
"In addition to the fact that caves don't go down all the way to the earths core, temperature plays a large role in this question. We simply do not have the materials that would allow us to withstand the several thousand kilometer trek through ~2000ºC molten rock. ",
"As a final note, the amount of pressure that whoever was down there would be subjected is almost incomprehensible. Gigapascals of pressure would be acting on all sides of a vessel, and would likely crush it even before it had the chance to melt. ",
"But HOW do we know all of this then? It turns out earthquakes are actually useful. There are seismic monitoring stations all over the earth, and we can basically pinpoint an earthquakes depth and location with a fairly quick calculation. ",
"Once people started doing this regularly, they noticed 2 important things. That there are 2 primary types of waves that are travelling through the earth, and that they arrive at different times and locations. ",
"Through trial and error and some wonderful hypotheses and some horrifying math we have been able to figure out the density of the earths layers, and also approximately where their boundaries are, and also can verify that they are not solid. ",
"I hope this answers your question! "
] |
[
"In actual fact an egg shell is about 3.5 times thicker than the crust in that scenario. "
] |
[
"Caver/geologist here.",
"Along with red_polo's explanation, eventually, you hit water. Even ",
"Krubera",
" ends in a sump.",
"There's the possibility these caves could be pushed even further with advanced diving gear, but all caves pinch out eventually.",
"Interesting note: at Devil's Hole in Death Valley, there's a desert hole pupfish that lives in the water there. It only lives in the top couple of feet of water, but the hole goes to tremendous depths. The hole goes to at least several hundred feet, and one or two divers who went in (illegally) never came back and their bodies have never been recovered."
] |
[
"What prevents birds from reaching the sizes that pterosaurs did?"
] |
[
false
] |
Title more or less. Reading up on how a doubling of bird weight requires 2.25 more muscle power and how wingbeat frequency decreasing as well gives a limit to bird size. Is just the difference in the morphology of the two groups responsible for the size difference?
|
[
"Mainly because of their anatomy, which led to different launching strategies. ",
"Pterosaurs (probably) used a quadrupedal launch, while birds use a bipedal launch. What that means is that a large pterosaur on the ground used its wings to push off; not by flapping, but using them as powerful front legs. Their hind limbs did relatively little work pushing off. In contrast, of course, birds use their hind limbs to push off.",
"That means that for pterosaurs, the same muscles that were used for flight were also used for launching -- they're double duty. For a bird, the powerful muscles that are used to push off and locomote on land are just dead weight once they're in the air. The bigger a bird gets, the more dead weight from its legs it has. ",
"A critical hypothesis for giant pterosaur flight concerns recent interpretations of their launch strategy. This idea is that pterosaurs – probably all of them – took off from a quadrupedal start, not a bird-like bipedal one. ... Firstly, the main launch limbs of flying animals are - above body masses of 500 g - stronger than their non-launching counterparts, and scale with more pronounced positive allometry (Habib 2008). This reflects launch being the most demanding part of flight. Look closely at a launching animal (high speed video helps) and you'll see that flight does not begin with a flap, but a leap: something like 80-90 % of launch effort stems from a powerful jump initiated by the main launch limbs. This explains why birds have proportionally robust and strong hindlimb skeletons but relatively slender wing bones: as they increase in size, their legs must become proportionally stronger to initiate flight at greater masses (Habib 2008). Pterosaurs, in contrast, show the opposite condition: their forelimbs are larger and stronger than their legs, with this relationship increasingly pronounced in larger species.",
"--",
"Why we think giant pterosaurs could fly",
"That article is long and detailed and explains much more about the quadrupedal launch hypothesis, including a long list of the peer-reviewed articles working out the details. An older, more simplified version is in the Scientific American (",
"How Giant Pterosaurs Took Flight",
").",
"There's a ",
"youtube animation of pterosaur launching",
". "
] |
[
"Climate plays no part in this hypothesis, nor (to forestall the usual incorrect claims) does oxygen level. Oxygen levels were not particularly high during the very long reign of the pterosaurs, and over the 150 million years or so that they lasted they saw all types of climates. ",
"Mike and I predicted that giant azhdarchids were supreme soarers, easily able to sustain long-distance gliding even at body masses of 180-250 kg (Witton and Habib 2010). Predicted giant flight velocities exceeded 90 kph and, in that 90 second flapping burst, giant azhdarchids would cover several kilometres - plenty of distance to seek areas of uplift such as deflected winds or thermals. Having located these, azhdarchids could easily adopt energy-saving soaring to recover their flight muscles, their glide ratios being consistent with those of large soaring birds such as storks, Procellariiformes and raptors. Mike has presented calculations that these giants would have sufficient on-board energy resources to travel the planet, their speed and flight range being sufficient to ignore most geographical barriers. ",
" Sure, if you did change these parameters you might make the job easier, but the giants already have very strong flight performance without it. ",
"--",
"Why we think giant pterosaurs could fly"
] |
[
"No, it doesn’t follow. Birds would probably be way better off if they had quad launching, but they can’t get there from here. There’s no plausible path from their current anatomy to one that uses quad launching. ",
"It’s like mammal lungs vs bird lungs. Bird lungs are way better, but mammals don’t have any way to get bird-like anatomy from where they are now. ",
"(Bats, which can use a quadrupedal gait on land, may be closer than birds to being truly gigantic fliers, except they have those sucky mammalian lungs that don’t let them get as efficient as birds. Evolution is terrible at this sort of thing.)"
] |
[
"Whenever plastics do degrade, what do they degrade INTO?"
] |
[
false
] |
[deleted]
|
[
"It depends on the plastic. They can be very different and you can't really generalize.",
"On one end of the scale, think of polyethylene or PVA. They break down into very digestible fragments that aren't much different from what you get when a (plant or animal) wax breaks down.",
"On the other end of the scale, there are plastics like PTFE (teflon) or other heavily halogenated polymers which are much more xenobiotic. (There's not much fluorine-carbon chemistry in nature.)",
"Most plastics are somewhere in between, and although they will ",
" break down all the way, they may have some toxic chemistry along the way which can be harmful to wherever it accumulates."
] |
[
"Most Plastic Material are made of organic compounds. That means it can be broken down into basically carbon dioxide similar to the material most Plastic is made of: gasoline. More problematic are probably the additives in plastic materials. The bacteria which is digesting it is also breaking it down to carbon dioxide. "
] |
[
"On one end of the scale, think of polyethylene or PVA.",
"It is interesting that polyethylene exposed to sunlight (the UV) gets crosslinked into a much harder plastic and more easily cracks into smaller pieces. It does take a few months though. Just leave a polyethylene milk bottle out in the sun for about 3 months. Then try to bend it like before."
] |
[
"What is the function of eye color?"
] |
[
false
] |
Does the color of one's eyes effect anything? Post-question TL;DR: There is no real reason for eye colour. It might have some protection from the sun, but more likely its a trait that was neither wanted nor unwanted. In old times, eye colour was used as a paternity test (brown eyes parents wouldnt have a blue eyed child).
|
[
"Eye color is complex genetically but ultimately comes down to the amount of melanin in the pigmented layer of the iris. People with lighter colored eyes have less, people with darker eyes have more.",
"As others have said, it's likely that the pigmentation does (or did at one time) have some protective effect for the eye, either by limiting entry of light, by blocking UV, or both. Melanin in your skin is there to protect your skin from damaging radiation and it's likely that the melanin in your eye does the same thing. ",
"If you look at the historical distribution of eye color, those with lighter colored eyes come from northern regions (Northern Europe, Scandinavia) and eye color becomes progressively darker on average as you travel south. Given the significant year-round cloud cover in Northern Europe, it would be a good hypothesis that large amounts of melanin would be less important in those areas. There may be some small reproductive advantage as well, as unusual or particularly vivid eye colors may play a part in attracting a mate... but that's just speculation."
] |
[
"This image",
" explains how melanin in the front and back epithelia of the iris and the structure of the stroma create eye color."
] |
[
"OK for something like this, you have to ask yourself: do people of different eye colors appear to have any different ability to see or function with different levels of light? Is this difference enough to make a difference in survivability?\nLearn some elementary population genetics. When you understand what |s| !> 1/(2Ne) means, then you can start calling me wrong."
] |
[
"Are there any cons of not getting your exact blood type as long as it's compatible?"
] |
[
false
] |
I've always been AB+ but never donated blood since my veins are thin and there are so many compatible for my blood type so I never saw the benefit. Is getting ab+ better somehow?
|
[
"While the most negative effects will not appear (ie there will not be agglutination of the donor blood creating clots and leading to death) there will still be some, likely subclinical, negative effects. Blood is a tissue and thus houses some immune system cells, specifically some cells that are designed to determine if cells are self or nonself. This leads to a condition, more prominent in organ transplants, known as graft-vs.-host disease; literally, your immune system attacks the nonself cells and the immune system cells present within the donor blood will attack you. However, with the limited immune system components found in blood, this would probably not be a problem. This is why blood can be donated with less specificity than other tissues such as bone marrow even though both are tissues. Bone marrow has a higher composition of immune system cells (specifically the precursor cells)."
] |
[
"I'm not worried at all, I was just wondering if, someone is AB+ if there are any benefits of getting AB+ blood over A+ or B+ or O+, Does our body have to produce extra antigins? "
] |
[
"I'm not worried at all, I was just wondering if, someone is AB+ if there are any benefits of getting AB+ blood over A+ or B+ or O+, Does our body have to produce extra antigins? "
] |
[
"What happens to the antibodies for a specific virus in a person if said person is infected by another virus?"
] |
[
false
] | null |
[
"The human body produces lots of different types of antibodies! Each one is specific to its own antigen (foreign matter/pathogen that attaches to the antibody) so you can imagine the variety our bodies need to produce.",
"If you want, I can take some time to explain how our body makes such a wide variety.",
"We have these white blood cells, specifically B cells (or B lymphocytes, and they are responsible for making antibodies. ",
" B cells can differentiate into plasma cells and memory cells. ",
"Your body is full of naive B cells - they have antibodies as receptors on their cell surfaces but have not yet come in contact with their antigen yet (you haven't been exposed to, say, Alpha yet). Once that specific B cell comes in contact with that specific antigen (you got infected with Alpha) the B cell can proliferate and become memory/plasma cells. How this is triggered is explained below. In this case, your antibodies against Polio aren't effective against the Alpha virus.",
"Plasma cells will start making free antibodies - the same type that was on the original B cell surface and release these into the body. Antibodies can coat the pathogen and make them more susceptible to attack by killer T cells or induce complement (an immune response with various effects).",
"Memory cells, on the other hand, stay in your body even after the antigen is cleared so that next time you're exposed to that antigen, your body can react more effectively and faster.",
"Anyway, I know you were asking specifically about viruses. Viruses usually invade other cells, or are engulfed by immune cells (such as T cells and macrophages). T cells and macrophages can also engulf dead/infected cells. They then break down the virus and present a piece of it, like a protein of the virus, to a B cell. And voila, your immune response is activated! ",
" your body makes a myriad unique anitbodies, each one responds to a different pathogen.",
"Source: immunology ",
" - so if there is someone more knowledgeable in this field, please correct me if I'm wrong!",
"Edit: cleared up a few words + thanks ",
"/u/onyablock",
" for correcting me!"
] |
[
"This is a good intro explanation, only thing I would correct is that there are many many types of B cells. Not just 2 types.",
"For example antibody producing B-cells are technically B-2 cells, a subset of B-cells."
] |
[
"So essentially, the immune system can multitask pretty well?"
] |
[
"If the speed of light varied regionally across the universe would we be able to tell?"
] |
[
false
] |
My limited understanding of such things suggests that we get most of our cosmological data by interpreting electromagnetic radiation. These signals can only be received by us if its speed is fast enough in relation to its distance from us. But this speed seems to have a limit. If this is not a universal limit would we be able to tell with our current technology?
|
[
"The speed of light isn't just the arbitrary speed at which light happens to travel. It represents something much more fundamental than that. It is the constant which gives us the very relationship between space and time. RobotRollCall posted the ",
"world's best reddit comment",
" talking about this, check it out!",
"Massless particles like photons always travel at the speed of light (in a vacuum). Things with mass never can.",
"Everything we know, both experimentally and theoretically, suggests the the speed of light (denoted ",
") is constant for all times and in all regions of space. Because c interrelates space and time themselves, a variable c might have awkward effects on things like causality (i.e.: effects coming after their cause, and not before).",
"When you ask, ",
", I think the answer is, if this were the case, we would indeed have made observations which contradicted theories involving a constant c, and which would have been better supported by a theory involving variable c. Observation, experiment and current theory all support the idea of a constant c."
] |
[
"I think that any variation in electromagnetism that would change the speed of light would also change the emission lines of faraway stars, which doesn't happen."
] |
[
"The world's best reddit comment just blew my mind. It is now the first reddit comment to end up bookmarked on my computer."
] |
[
"What type of genetic mutation causes Phenylketonuria (PKU)?"
] |
[
false
] |
I've searched all over the web trying to find the answer to the question and I can't find anything decisive. Does anyone in the field of biology or medicine know what it is?
|
[
"Phenylalanine hydroxylase",
", and both need to be mutated. The gene causes phenylalanine to be converted into tyrosine, so you have a buildup of phenylalanine and a lack of tyrosine (and I think the buildup of phenylalanine is the toxic component)."
] |
[
"The gene only encodes the enzyme that does the work. But yes, with a malfunctioning gene (\"both\" referring to the alleles of the gene), the enzyme isn't produced, and tyrosine isn't converted from phenylalanine."
] |
[
"To be clear, you mean: \"the gene converts phenylalanine into tyrosine; ",
" you have a buildup of phenylalanine and a lack of tyrosine...\", Right?"
] |
[
"Where do texts go when the recipient is in Airplane Mode?"
] |
[
false
] |
If someone sends me a text whilst my phone is in Airplane Mode, I will receive it once I turn it off. My question is, where do the radio waves go in the meantime? Are they stored somewhere, or are they just bouncing around from tower to tower until they can finally be sent to the recipient? I apologize if this is a stupid question.
|
[
"The radio waves themselves aren't stored, nor do they go anywhere.",
"Your phone is constantly pinging cell towers and communicating with your cell network. If your phone is not connected to the network, then the texts go into a holding queue on the towers/servers. Same as your voicemail notifications when you miss a call without signal.",
"Once your phone pings the network again, it will start running through that backlog of whatever was received. ",
"It is only at that point that the radio waves, so to speak, would be sent out."
] |
[
"So, there is a piece of equipment that manages the SMS messages called a SMSC. It's not free... the towers don't queue the messages, rather the SMSC puts the messages in a delivery schedule that attempts to send to the phone, if it doesn't get a positive response it tries again shortly after. The cycle continues until successful receipt. The delay between attempts increases after every fail."
] |
[
"Most carriers also only hold your message for a certain amount of time. If your phone is off/no connection for 3 days, my carrier will auto-purge your messages. "
] |
[
"Are women who put eyeliner on the waterline of their eyes potentially doing long-term damage to their eyes?"
] |
[
false
] |
I've heard that in the short-term it can lead to infections or irritation, but, since it is essentially rubbing dyed wax into the area surrounding your eyes, can it have long-term effects?
|
[
"Sharing eyeliner can lead to infection, however using eyeliner on the waterline shouldn't cause infection unless you improperly store/use your make-up. Most eye make-up has preservatives that will retard the growth of bacteria. ",
"It can, however, irritate your eyes and tearducts. Also, people who are allergic to certain materials common in make-up (nickel, fragrances, etc.) can have reactions.",
"This",
" is a University's Department of Ophthalmology's page about make-up and eye safety. "
] |
[
"Using makeup behind the insertion of the eyelashes puts it right at the opening of Meibomian glands. If you have anterior or posterior blepharitis, putting make up on in this zone can aggravate these conditions, leading to chronic conjuntivitis, styes and chalazions. "
] |
[
"For those of you wondering, comments that violate the ",
"AskScience guidelines",
" are often removed. If you have questions or concerns, please do not respond to this post, but feel free to ",
"message the moderators.",
" ",
"Have a wonderfully scientific day!"
] |
[
"Say you are outside in a parking lot, which is worse for you, second hand smoke or the car exhaust?"
] |
[
false
] | null |
[
"A recent study compared the effects of three continuously lit cigarettes",
"The flaw in these studies is that the overwhelming majority of second hand cigarette smoke is ",
" the smoke coming off the end of a lit cigarette, but rather the large volume of smoke sucked through the filter and into a set of human lungs before being blown out into the air. Even if you assume that the filter and lungs remove ",
" from the smoke, the drafting effect of drawing on a lit cigarette causes it to burn significantly hotter, which shifts the smoke content towards lighter compounds.",
"Not saying secondhand smoke is ",
", mind you, just that simplistic studies where they allow three cigarettes to smoulder in an enclosed room reveal little about to composition of real-world second hand smoke."
] |
[
"A recent study compared the effects of three continuously lit cigarettes",
"The flaw in these studies is that the overwhelming majority of second hand cigarette smoke is ",
" the smoke coming off the end of a lit cigarette, but rather the large volume of smoke sucked through the filter and into a set of human lungs before being blown out into the air. Even if you assume that the filter and lungs remove ",
" from the smoke, the drafting effect of drawing on a lit cigarette causes it to burn significantly hotter, which shifts the smoke content towards lighter compounds.",
"Not saying secondhand smoke is ",
", mind you, just that simplistic studies where they allow three cigarettes to smoulder in an enclosed room reveal little about to composition of real-world second hand smoke."
] |
[
"New research is showing that microscopic iron particles found in car exhaust are contributing to it's toxicity. Car exhaust contains microscopic iron particles able to penetrate cells and in conjunction with polycyclic aromatic hydrocarbons can generate large amounts of radicals through redox cycling of the iron."
] |
[
"Do other countries have their own versions of the DSM-IV?"
] |
[
false
] |
Or do other nations subscribe to the same definitions of mental illness as the American Psychiatric Association?
|
[
"Many countries use the ",
"ICD system",
" put together by the World Health Organization. China has the ",
"CCDM",
"."
] |
[
"Ah-ha! Thanks!"
] |
[
"For billing purposes, the ICD coding system is being used in many American psychiatric capacities. The diagnostic criteria are largely based on the DSM(for psychiatry). Note: the ICD contains not just psychiatric disorders, but also classifications for all medical issues."
] |
[
"What colour is a mirror?"
] |
[
false
] |
[deleted]
|
[
"The same color as a window."
] |
[
"Also, probably ",
"this color",
"."
] |
[
"Also ",
"this colour",
"."
] |
[
"How do we know that there is asymmetry between matter and antimatter in the universe?"
] |
[
false
] |
[deleted]
|
[
"The intergalactic space is not totally devoid of matter, and if there were matter-antimatter interfaces in the observable universe we should be able to observe gamma rays resulting from annihilation events with distinct wavelengths. Furthermore, it is not at all clear how such clearly-defined boundaries between matter and anti-matter regions could form in the first place."
] |
[
"There's enough intergalactic gas and dust that you would expect to observe annihilation processes at the boundaries. This is something the AMS detector on the ISS has set limits on. Also galaxies collide with each other fairly regularly."
] |
[
"Other people have commented on the fact that if there were galaxies far off made of antimatter, we would see evidence of mass annihilations. While this is sufficient, I'd like to explain something else called CP-Violation, which is the reason such a symmetry exists in the first place.",
"Before, we used to think that the universe and the matter/energy it contains were symmetric under certain discrete transformations. These transformations were C (charge conjugation, aka matter to antimatter), P (parity, aka flipping something upside down), and T (time reversal). If the universe respected all these transformations (C and P in particular), then matter and antimatter would behave identically according to physical laws. ",
"This was not to be. Chien-Shiung Wu discovered that the weak interaction (through beta-decay) violated P-symmetry. Soon C-symmetry and T-symmetry were also found to be invalid under the weak interaction. CP-symmetry, which is symmetry under the combined transformation of charge conjugation and parity switching, was a promising symmetry for a short while. If CP-symmetry held for all interactions, any matter-producing process would have to progress at the same rate as its conjugate antimatter-producing process.",
"This was not to be. James Cronin and Val Fitch discovered that the decay of neutral kaons violated CP-symmetry. CP-symmetry implies the conservation of a CP-number, a quantity associated with a certain quantum state of a particle. When these kaons began to decay and split into pions, it was noticed that this particle process violated CP-number conservation—the CP-number before was not the same as the CP-number after. ",
"This is a very simplistic picture of the experiment that proved CP-violation, and does not go into the details of how the mixing of the kaon states led to CP-violation. It's interesting reading, however.",
"Essentially, CP-violation implies that matter and antimatter do not behave identically under all physical processes—there is an asymmetry. Physicist Andrei Sakharov outlined conditions for the birth of a matter-filled universe like our own, and two important conditions are a baryogenetic process (something that results in a net gain of protons and neutrons, as of now no such process exists according to baryon number conservation) and CP-violation (so that said baryogenetic process can produce a net gain of matter instead of antimatter).",
"However, the amount of CP-violating processes we have discovered only accounts for a tiny fraction of the universe's matter excess. That's why the search for CP-violation is so important, because it can help explain this asymmetry."
] |
[
"Why are yawns contagious?"
] |
[
false
] | null |
[
"Contagious yawning in gelada baboons as a possible expression of empathy",
"edit: formatting links on mobile feels like wrangling a baboon"
] |
[
"Hi - link shorteners trigger our spam filter. If you need to post a long URL, you can use the following format:",
"[text](link)\n",
"Thank you!"
] |
[
"Hi - link shorteners trigger our spam filter. If you need to post a long URL, you can use the following format:",
"[text](link)\n",
"Thank you!"
] |
[
"What causes my hands to sweat when I carry coins?"
] |
[
false
] |
I was carrying coins today and noticed that hand was sweating more than the other. This happens every time I carry coins. It has happened with Canadian and US Currency.
|
[
"An interesting aside, that I, at least didn't know till recently. The characteristic 'coin' smell that we've all experienced after carrying coins/handling them, appears to not come from the coins themselves, but rather from a reaction between sweat and the metal in the coins, which creates ferrous ions that then react with chemicals on our skin to produce the aldehydes and ketones that produce the odor. See ",
"here",
" for more details. "
] |
[
"I think this may be confirmation bias.",
"Also when carrying coins (or anything) your fist is mostly closed, trapping the sweat evaporating from your hands, creating a humid environment.",
"EDIT: bad wording."
] |
[
"I wish you had given more of an explanation in your reply.",
"Despite being ",
"/r/askscience",
" and wanting scientific replies, in my opinion lap-dog-ish replies are the worst thing to ever happen to this subreddit, the worst thing that can happen, aside from bad knowledge being spread.",
"If you agree, just upvote if you know the subject, if not and with good scientific reason, just downvote. Otherwise leave it alone and let those more knowledgeable make the choices.",
"Just be a bystander if you aren't qualified.. you might learn something."
] |
[
"What are ten scientific facts that you feel everyone should know?"
] |
[
false
] | null |
[
"I cannot represent all sciences as a biologist, but I think one thing is very important for everyone to understand, evolution is a concrete scientific theory, where are there are really no other viable alternative hypotheses. We can demonstrate it with selection experiments in the lab, we apply the concept to antibiotic resistance in bacteria, the fossil record supports it, as well as the fact that all life operates on the central dogma of biology (RNA-DNA-Protein). Also, one more thing, evolution does not mean \"progression.\" Evolution is simply genetic change over time, which can lead to an increase or reduction in complexity depending on which is more fit. Best example is parasitic worms, they lack much of the abilities their free-living cousins have, but they don't need it for their life history, so we've seen a reduction in overall complexity in such taxa."
] |
[
"In no particular order:",
"1) Evolution and common descent. Understanding its basics, not merely parroting stuff like \"our grand-grand-grandparents were monkeys\". In particular, everyone should read Richard Dawkins' ",
"2) The ",
"second law of thermodynamics",
" and ",
"entropy",
"3) Conservation of energy",
"4) Qualitatively, but as clearly as possible, basics of special and general relativity.",
"5) That the world revolves around the four basic interactions: electromagnetic, weak force, strong force and gravity.",
"6) More than a fact: basic chemistry. What are the elements, how an atom works, how do they bind together, etc.",
"7) Big Bang and basics of cosmological evolution",
"8) ",
"Noether's theorem",
". It's something I have a qualitative understanding myself, but it is one of the most awesome things ever. Symmetries = conservation laws.",
"9) The concept of ",
"energy landscape",
" -that is, why stuff happens.",
"10) In general, the time and size scales of things, from elementary particles to the Universe."
] |
[
"I wish everyone could understand that evolution doesn't aim for anything."
] |
[
"Are divorce rates lower for couples who are matched using compatibility tests (e.g. eHarmony)?"
] |
[
false
] |
Obviously personality/compatibility tests can be helpful in narrowing down a pool of potential mates/SOs, but is there any evidence that being a more "compatible" match means you'll get along better over the course of a marriage (or other long-term relationship)? What about "opposites attracting"-- where does that fit in?
|
[
"Regarding the \"e.g. eHarmony\" aspect, there's good evidence that those sites don't provide any actual benefit.",
"Here are some articles about that, each of which references scientific work on the subject:",
"Dating Site Matches Not So Scientific",
"UCLA Professors Say eHarmony Is Unscientific and Its Customers Are 'Duped.' Here's Why.",
"The Pseudo-Science Behind Dating Websites Is Total Crap",
"The latter two both reference a paper \"Online Dating: A Critical Analysis From the Perspective of Psychological Science,\" by a team of five scientists."
] |
[
"Everything has to do with science."
] |
[
"Everything has to do with science."
] |
[
"Why can't some people do the Vulcan salute?"
] |
[
false
] |
For some people, it is quite literally impossible to do. For example, Zachary Quinto had to have his fingers together to do it in Star Trek. Is there some difference in hand muscle development or coordination that some people lack? Did they never develop some motor pathway in the brain that prevents them from doing so?
|
[
"Fun fact: the \"Vulcan salute\" is actually an old [Jewish blessing](en.wikipedia.org/wiki/Priestly_Blessing). It's called the Birkat Kohanim (Priestly Blessing) and is normally done with both hands. Leonard Nimoy is from a Jewish family, and he thought that the action looked suitably mysterious to be part of Vulcan culture."
] |
[
"Source/expertise?"
] |
[
"They are physically capable, but it lies in the way in which our mind works. Our mind learns movement in series and uses \"short cuts\". Instead of it controlling an individual muscle the mind will move several at a time to form coordination. When growing they probably did not develop the neurological sequence to spread their fingers without activating other muscles. "
] |
[
"Are there examples of vaccines that have been denied approval by the FDA for failing to meet safety standards? If so, how often does this occur?"
] |
[
false
] |
I recently had a discussion with somebody who is afraid to get the covid vaccine. Her argument was essentially that big pharma is more concerned with profit than public safety (as evidenced by the opioid crisis) and that the FDA has been corrupted by regulatory capture. Therefore, we should not trust that the new vaccines are safe. So I figured that If I could find examples of vaccines that had been screened out by the FDA process, this might demonstrate that the FDA hasn't just been greenlighting vaccines/medicines to benefit big pharma. With that said, I had a hard time finding such examples (but I also wasn't sure where to look). Are there any prominent instances of vaccines that failed the screening process or that were pulled from the market by the FDA soon after release? If so, how often does this happen?
|
[
"The most obvious example is RotaShield, a rotavirus vaccine that was introduced in 1998 and withdrawn in 1999 (",
"Withdrawal of Rotavirus Vaccine Recommendation",
"). It caused intussusception in infants at a frequency of roughly 1-5 per 10,000; the increased risk was identified within about 6 months of the vaccine being introduced, and the vaccine was no longer in use well before the official withdrawal. ",
"It’s worth noting that withdrawing the vaccine certainly led to the deaths of far more infants than the intussusception would have caused, because the vaccine was highly effective and would have prevented the hundreds of thousands of annual hospitalizations, and scores of deaths, caused by the virus. ",
"This is extremely well documented. A handful of references to start -",
"Rotavirus vaccine withdrawal in the United States; The role of postmarketing surveillance",
"Intussusception among recipients of rotavirus vaccine--United States, 1998-1999",
"Another example is the link between one particular brand/subtype of influenza vaccine and narcolepsy (",
"Incidence of narcolepsy in Norwegian children and adolescents after vaccination against H1N1 influenza A",
"). The increased risk here was even lower (less than 1/10,000) and was identified, and the vaccine voluntarily withdrawn, even faster, within a few months. In this case, since other influenza vaccines without this risk could be used, removing the vaccine didn’t lead to increased disease."
] |
[
"About one in every 5,000 discovered drugs will make it to market.",
"It should be made clear that this isn't 5,000 individual drugs that are carefully hypothesized and synthesized by researchers. It's the result of a shotgun-style approach to generating new drug compounds where you throw everything at the wall and see what sticks. Robotic manufacturing facilities churn out thousands of candidate formulations in micro wells, and some tests are applied to try and predict which ones will be strongly biologically active.",
"This is called ",
"High-Throughput Screening",
"There are human researchers involved in deciding where to \"point the shotgun.\" It's not a totally automated process. But, the FDA is not failing 4,999 carefully managed research projects."
] |
[
"I can’t speak for vaccines specifically, but biopharmaceuticals in general:",
"About one in every 5,000 discovered drugs will make it to market. There are a TON of regulatory steps involved and it usually takes over a decade from start to finish. Generally, potentially dangerous drugs won’t ever reach the point of human trials, unless there are extreme extenuating circumstances.",
"If you only count drugs that make it to human trials, the success rate is about 15% FDA approval. Most of these unfortunate 85% are rejected not due to obvious safety concerns, but because the FDA doesn’t find the statistical health benefits strong enough to justify the risk of approval.",
"I believe vaccine approvals work a bit differently, because so many of them (like the flu vaccines) are just followups to previous vaccines with slight adjustments. Somebody else may be able to respond with info specific to them."
] |
[
"Is it possible that there could be larger astronomical structures than superclusters inside our universe?"
] |
[
false
] | null |
[
"Yes, ",
"Galaxy filaments",
", aka \"Great Walls\". The most known example is the ",
"Great attractor",
"."
] |
[
"Beyond galaxy filaments there does not appear to be many larger structures. This is occasionally called the ",
"End of Greatness",
".",
"The largest observed structure is the ",
"Hercules-Corona Borealis Great Wall",
", which appears to violate the End of Greatness as it is more than 10 billion light-years across. There are a few more such structures but not enough to give a definitive answer."
] |
[
"Oh, right. Thanks. And what about larger than that?"
] |
[
"Chemistry :: What molecule has the highest variety of component atoms? Is it stable near humans?"
] |
[
false
] |
And where might it be found? According to boron could just keep incorporating more matter as it "grows". Boron, however, is an element and if you remove everything with which it might react, it's still boron. I mean a molecule in the smallest amount at which it retains its identity. edit to try to clarify the question. CO2 has two different types of atoms, as does HO. Glucose has three: C,H, and O. Is there a molecule that incorporates more than 1/2 of the periodic table? One that incorporated all 92 natural elements?
|
[
"There are no molecules that incorporate the whole of the periodic table, or even a modest fraction of it... There are ",
"some ceramics",
" that can have ungodly numbers of different atoms and they're high temp superconductors (though, I'm not sure if the two are related). BSCCO is probably the most atomically diverse \"molecule\" I have seen... but the world of ceramics is a big place and I've not seen much of it."
] |
[
"I reckon you could synthesize an organic compound with more than BSCCO. For example ",
"this surface grafted",
" group has 6 different atoms (not including titanium, which is a fairly covalent bond). It wouldn't be much harder to get some sulfur or perhaps some other halogens involved."
] |
[
"I'm not sure I understand the question, but ",
"metallocenes",
" can incorpoate a fairly wide array of atoms.",
"A typical metallocene has two carbon rings of five members each, which are aromatic when in contact with a metal ion. Almost like a metal sandwich, with something resembling benzene as the bread. I'm not an organic chemist, but I think some examples from this class of compounds aren't very picky as to which metals out of the periodic table they're willing to chelate, meaning there are dozens of options as to what that particular atom is, in an otherwise unchanged molecule. (Elements of different groups end up in different ionization states, naturally, giving the overall molecule a variety of states of charge.)",
"A different interpretation of your question might point us toward the ",
"alkanes",
". Methane is familiar, and maybe ethane, probably propane and butane. You've heard of octane, though people usually use it to represent other chemicals nowadays. Higher alkanes include petroleum jelly and paraffin wax, and a lot of the food-safe plastic in your house. The list goes all the way up to ultra-high molecular weight polyethylene (trade names including Spectra and Dyneema), which can have a molecular weight as high as 6 million. It makes better body armor than Kevlar, due to a greater strength-to-weight ratio and better (complete) resistance to salt water.",
"It's technologically possible to produce alkanes of most any length.",
"Interestingly, UHMPE is made using a catalyst that is based on a metallocene."
] |
[
"Why is it easy to pull out individual scalp hairs but not clumps?"
] |
[
false
] | null |
[
"Or the difference between sliding two pieces of paper apart vs pulling apart two phonebooks shuffled together."
] |
[
"The former. Consider a multi-strand string (or rope) with very fine individual strands. You can easily break a single strand - but not a thick string or rope. As an alternative, think of tearing up a single sheet of paper versus tearing up a thick phone book."
] |
[
"This is a great example!"
] |
[
"Will it ever be possible for humans to recreate extinct animals?"
] |
[
false
] | null |
[
"Yes its possible. And its been done once already with the ",
"Pyrenean ibex",
".",
"Sadly, the ibex was born with a lung defect and died 7 minutes later. Thus, becoming possibly the only animal to truly go extinct ",
"."
] |
[
"Cloning is our best bet. We have intact DNA from frozen, very well preserved animals like the mammoth and smilodon. This DNA may be able to be cloned and carried through gestation by a closely related animal."
] |
[
"Highly relevant link!",
" Turns out Russian and South Korean scientists are planning on cloning a mammoth. I have no idea how this is going or even if they've started on it yet. Here's the brief explanation from the article:",
"So how exactly does one go about cloning a woolly mammoth? The scientists plan to replace the nuclei of elephant egg cells with those of a mammoth, producing embryos with mammoth DNA. Then, those embryos will be planted into the wombs of elephants for delivery. The mammoth cells would come from internal organs, skin, bones and blood. Finding well-preserved tissue with an undamaged gene will be the most difficult task, the researchers told the AFP"
] |
[
"What exactly does 'freeing megahertz of spectrum in a band' mean?"
] |
[
false
] |
I was reading an article about how the FCC freed 100 megahertz of spectrum in the 5 gigahertz band to make public WiFi faster but I don't get what that's supposed to mean. How exactly do they free it up?
|
[
"I don't know the specific bands, so ignore the numbers:",
"The FCC allocates certain sections of the band to certain uses. If you try to use a part of the band not allocated to you, it will get interference, and if they track your transmission you can get fined / arrested for it.",
"So previously, lets say 5.0 gig - 6.0 gig was reserved for military use. Trying to use any of it for public wifi would result in breaking the law, and interference.",
"By changing the band to 5.1 gig - 6.0 gig and \"freeing\" 100 megahertz, it tells the military to stop using 5.0 - 5.1, thus freeing it from interference, and then that band is clear and legal to use for public wifi. ",
"Its all regulatory. "
] |
[
"To expand on this, the added 100MHz will allow for greater variations in the modulation of the transmitted signal which will result in greater speed as well as more use of those bandwidths without congestion. Data signals transmitted wirelessly rely on some form of modulation, which means that the frequency gets shifted in some way from the main carrier frequency. The specifics for data transmission vary based on the kind of signal being transmitted (wifi, cellular, etc.) so I will not give specifics, but the basics are not too difficult to understand.",
"Lets say that for each person connected to wifi, there is a specific pattern or key associated with them. Naturally, with a fixed bandwidth, there will become a point where no more users can be added without reusing that pattern/key (key is not technically what it is, but bear with me for the sake of argument). Each \"key\" is associated with a specific kind of alteration/modulation of the main signal, so by adding more bandwidth (ie allowing more alterations/modulation to the main signal), there can be more users using the same connection at the same time without any interference. In addition, the speeds will be much faster because more combinations can be used to represent specific bits of data, resulting in more information being transmitted in each packet."
] |
[
"Oh wow. That was pretty simple. Thanks a lot!"
] |
[
"Is drinking ice cold water any better/worse for your body than drinking room temperature water?"
] |
[
false
] |
I've heard that drinking very cold water helps you burn more calories since your body has to expend energy to heat the water. Is there any truth to this? If not, does ice cold water affect our bodies any differently than comparatively warm water?
|
[
"Well, raising 1ml of water 1 celcius requires 1 calorie (not to be confused with Calories or kcal). So drinking a litre of water at freezing requires 37,000 calories to raise to body temperature. ",
"I suspect that the reason the studies ",
"/u/SciencePatientZero",
" cited don't see those 37 Calories being expended is because the body is already producing heat and that rather than producing more heat to counter the body just conserves what is already being made better. "
] |
[
"I have asked a similar question to a Dr, his reply was that this is a standard first year residency question. That there is so little difference between the energy used to heat the water and the energy conserved from not having to cool the body that the correct answer is \"none.\""
] |
[
"While there doesn't appear to be an entirely conclusive answer, a few studies suggest that drinking cold water does actually increase energy expenditure.",
"This study",
" finds that drinking 7.5 mL/kg body weight of water cooled to 3 degrees celsius causes about a 4.5% increase in energy expenditure over 60 minutes. Quoting:",
"Drinking distilled water at room temperature did not increase energy expenditure. Cooling the water before drinking only stimulated a small thermogenic response, well below the theoretical energy cost of warming the water to body temperature.",
"Most likely, that water actually is warmed to body temperature within 60 minutes. My only guess as to why the energy expenditure didn't increase enough to account for this is that other energy expenditures may have been transiently reduced, but I can't speculate as to where those tradeoffs might occur.",
"Another study",
" used a higher 'dose' of water, 10 mL/kg, in obese children, and found a 25% increase in resting energy expenditure, lasting over 40 minutes. Whether the difference in magnitude of effect between the two studies relates to the different doses, different patient populations, or different measurement techniques are hard to say. Nonetheless, there does seem to be some evidence that drinking cold water actually causes a transient increase in body energy expenditure, though likely not enough to count as a diet plan!",
"As far as other health effects of cold water, I'm not able to find much. Mostly, I see some persistent commentary suggesting that cold water can 'solidify digested fats', leading to all sorts of consequences like weight gain and cancer. There's a good summary ",
"here",
" from Snopes. While it doesn't look like any studies have been conducted to prove that this doesn't happen, there certainly have not been any scientific studies suggesting that it does. While it may seem logical at first glance, these negative effects are mostly attributed to fat solidification in the intestines. The common counterargument I'm seeing, and one that makes a lot of sense, is that it's very unlikely the intestines would ever contain a significant amount of cold water. Any cold water ingested will stay in the stomach for a while, where it will likely warm significantly. Overall, I'd say there's no good evidence suggesting any strong positive or negative effects of drinking cold water."
] |
[
"Does relativity mean that as temperature increases, the mass of the particles also increases?"
] |
[
false
] |
If temperature is related to average velocity of molecules, does that mean that gasses gain mass as they heat up?
|
[
"It's best not to look at the \"increased mass\" of individual particles, because that effect doesn't really exist, but rather at the energy of the whole system. If the system increases in energy, its mass increases by E/c",
" . So when a liter of water increases by ten degrees, its mass increases by about 465 picograms."
] |
[
"Basically it comes from the fact that relativistic momentum is ymv where y is the Lorentz factor. You can demand that momentum must always be mv, and thus redefine mass to ym. However, this new mass doesn't really have much meaning, it can't be measured, and you get scenarios where an object will accelerate with different masses depending on which way a force is being applied relative to the velocity. It is more correct just to treat the relationship between velocity and momentum as nonlinear, and treat rest mass as just rest frame mass."
] |
[
"No, it's just an outdated pedagogical tool. "
] |
[
"Do the strings in string theory have harmonics?"
] |
[
false
] |
In simple terms they seem to resonate much like guitar strings and following the properties of sounds waves; would these strings have a first harmonic, second harmonic, etc.?
|
[
"Absolutely. The spectrum of excitations is a little more complicated than for a guitar string, but the basic idea is the same."
] |
[
"Yes. The lowest order modes correspond to the ordinary particles. The harmonics would correspond to very massive particles (starting at something like 10",
" proton masses). We've never seen, or been in a position to see, such highly massive particles, but they are a prediction of string theory. "
] |
[
"Does the 'harmonics' if you will, or in other words the frequency or way it vibrates actually give rise to higher umm.. forms of matter I guess you could say, or is this property simply a side effect of being a 'string'? In other words are we, and everything in existence, possible just a sequence of vibrations? Sorry if I described that very badly, I don't know what I'm talking about after all."
] |
[
"Where does the mass from radioactive decay go?"
] |
[
false
] |
What happens to the mass if mass is always conserved?
|
[
"Mass is not conserved, energy is. The energy from the lost mass of the mother isotope goes into the kinetic energy of the decay products."
] |
[
"Remember, by Einstein's equation, E = mc",
" matter and energy are fundamentally the same thing.",
"In radioactive decay, matter isn't ",
" it is ",
" into energy. "
] |
[
"I always find it easier to think there is only energy. There is a reason we always talk about the mass of particles in eV. "
] |
[
"Why are earthquakes in the eastern United States felt for such long distances?"
] |
[
false
] | null |
[
"It's because the bedrock, in general, has far fewer faults for the energy to dissipate across. On the West Coast the bedrock is heavily fractured with many (active) faults all over the place. When an earthquake occurs there it is not usually felt very far away because the energy released by the quake is quickly taken up by neighboring faults. On the East Coast, which is a passive margin rather than an active one, there are far fewer faults to absorb the energy released by any earthquakes. Also, the bedrock on the East Coast is older and goes much deeper than it does out West so it can transmit seismic waves across longer distances unimpeded. ",
"Edit: I should mention that there are plenty of old faults in the Eastern US. However, most of them have not moved in so long that they are strongly locked in place and would not be reactivated by the occasional moderate earthquake. Edit 2: spelling."
] |
[
"Yes there is."
] |
[
"The NMSZ is a failed rift that is capable of producing powerful quakes, the most recent of were a series of three between December 1811 and February 1812. ",
"Rifts are zones where the crust is being pulled in opposite directions and they tend to precede continental breakup.\nAs the name implies, a failed rift is one where rifting began but then, for whatever reason, stopped before it really got going. In cross-section it looks ",
"like this",
". ",
"Since the area is heavily faulted in an area that otherwise has very few active faults, much of the stress that accumulates in the region will most likely be released by a rupture in that fault zone. It is a totally different tectonic setting than, say California. However, the quakes produced by the NMSZ tend to be much more damaging because they travel further (as we have seen) and because they tend to rupture fairly close to the surface."
] |
[
"If blood rushes to your head when you are upside down, why doesn't the blood rush to your feet when you stand straight up?"
] |
[
false
] |
Human Body
|
[
"There are valves in your veins and arteries that prevent incorrect flow of blood. Think of it like a backflow preventer in a piping system.",
"Your heart pushes blood up toward your brain on the upbeat, then on the downbeat the valves close up to prevent blood from dropping due to gravity while the heart fills up again. Because this happens quickly, we don't really notice the changes unless we do something like check our pulse.",
"If you turn the veins and arteries upside down, then gravity allows the valves that should be closed to stay open and the valves that should be open to stay closed. This causes a relative draining or pooling of the blood compared to a proper state.",
"Arms and legs, which \"normally\" face down to the ground, get slightly less blood at the extremities, while your head, which normally faces up, gets more."
] |
[
"It does tend to, but in most cases your blood pressure quickly adjusts and distributes the blood properly. Sometimes people can have ",
"postural hypotension",
" where they may even black out from standing up."
] |
[
"So this is why my arm 'stings' when throwing something very hard? Centrifugal force in 'normal' direction but with too much pressure on those valves?"
] |
[
"How does the International Space Station have internet access?"
] |
[
false
] |
Cmdr. Chris Hadfield's is pretty famous now, and he's done on reddit. There are posted from there all the time. There's not a wire coming from the ISS, is there? That doesn't make any sense. And there's no way wireless could reach that far... How does it work?
|
[
"Let's clear a couple of things up first.",
"The internet doesn't need to use one specific technology to work. Indeed even on Earth computers are connected by fiber optic cables, phone lines, coaxial cable, cell phone networks, twisted pair (ethernet), and the list goes on. Pretty much anything that moves data between two computers can be used.",
"Obviously there are no wires connected between ground and 400 km high space station moving at 7600 m/s.",
"But when you say \"there's no way wireless could reach that far\" you probably mean a very specific kind of radio more formally called IEEE 802.11. This is what you can buy on Amazon or whatever to run a wireless network in your home or office. The distance limits of IEEE 802.11 are almost entirely artificial. They make the transmit power very low so as to not interfere with everyone else in your neighborhood or with more important radio transmissions.",
"So how does NASA do it, specifically? They just piggyback the internet on their existing radio infrastructure. Almost all the high bandwidth communication with the ISS is done through a system called the Tracking, Data, and Relay Satellite System, or TDRSS. This can support a very large amount of raw data, whether that be videos of experiments, telemetry or, the internet.",
"There are 3 big TRSS satellites much, much higher than the ISS spread out in geosynchronous orbit so that at any point in time the ISS can see at least one. Then there is a dedicated ground station that connects to each TDRSS satellite. There is fiber from the ground station to mission control and special computers to unpack the data as in comes in. So the internet on station looks like this:",
"ISS -> TDRSS -> Ground station -> Fiber -> NASA Servers -> Regular internet",
"And then back again, of course. Yes this is slow, but not that much slower than, say a not-very-good coffee shop internet connection; at least a few hundred milliseconds of latency."
] |
[
"I don't think they have internet access the way we do. It's most likely coming from their direct connection with Nasa via whatever communication method they use."
] |
[
"Interesting. It's hard to know how fast it 'feels', not having been there myself :)",
"At least part of the slowness is by [NASA's] choice. TDRSS Ka band in single user mode bandwidth is ~180 Mbps. They don't actually use all of that on ISS all the time, and certainly not all of it on the internet."
] |
[
"If the Earth spins 360 degrees in a day, how many times does it spin in a year?"
] |
[
false
] |
I'm not necessarily trying to account for leap (years/seconds/arbitrary time periods) but rather are we counting this time from an inertial reference plane, with respect to the sun, or days are utterly irrelevant and we only should count in seconds. I was doing a calculation to win a bet and I realized I was unclear on some rather basic facts of the way the world actually moves. Are years calculated from an inertial reference frame or from galactic center? Are galactic orbits calculated from an inertial reference frame or from ...? !
|
[
"Relative to the stars, it takes the earth roughly 23 hr and 56 minutes to make one complete turn. This is, in effect a rotation of 360 degrees. It's called a ",
"sidereal day",
"\nNow because the Earth spins and moves about its orbit around the sun, with respect to the sun, it actually takes a bit longer to make one turn so that the sun is in (approximately) the same position in the sky. This requires the Earth to rotate slightly more than 360 degrees and takes almost exactly 24 hours and is called a Mean Solar Day."
] |
[
"No. Imagine if the Earth was not rotating in reference to the sun, only revolving in orbit. Then the day would appear one year long. The extra rotation that you get from the orbit is already included in the ~365.25 days."
] |
[
"... so a solar year is ~366.25 sidereal days and ~365.25 Mean Solar Days? So, if someone was applying Newtonian mechanics to the orbit of the Earth, one should use Sidereal Days as it is as close to an inertial frame as we can get?",
"Thanks. That helps a great deal.",
"!"
] |
[
"How far from the sea do you still need to be worried about salinity for agriculture?"
] |
[
true
] |
[deleted]
|
[
"It's not a defined distance. If you live in a delta where groundwater is being depleted, you might get saltwater seeping in for miles. Or if you are on a cliff top in a wet area, you might not have anything to worry about right up to the edge of the cliff overlooking the sea.",
"Generally speaking if you are literally getting salt spray hitting your crops, that's bad. Beyond that...it just depends on the water table and risk of flooding and rainfall and a bunch of other factors."
] |
[
"Here's an article on the subject. Anywhere we irrigate clay soils where the water evaporates rather than drains will eventually become too saline. It is thought to have been a factor in the decline of Mesopotamia, and is happening in California's central valley right now.",
"https://www.recare-hub.eu/soil-threats/salinization#:~:text=The%20excessive%20use%20of%20water,clay%20texture%20of%20the%20soil",
"."
] |
[
"In Western Australia, the entire agricultural region hundreds of kilometres inland is being poisoned by salinity. Their problem is that early farmers cleared all the trees, and that caused the water table to rise. Old salt deposits in the ground are then dissolved and brought to the surfacw, where the salt precipitates out.",
"Have a look at the West Australian Wheat belt on Google Earth. It's pretty depressing."
] |
[
"Where can I find online summer classes or camps for my child that focus on science and math?"
] |
[
false
] | null |
[
"It would help a lot if you could tell us what she’s interested in and what she already knows. Another big help would be to know what you and any other parental figure(s) are comfortable with as far as science and mathematics goes. Also remember to come back if she’s getting stuck on understanding something for a while!"
] |
[
"This is a little tricky. I’m not really familiar with the US curriculum. I know quite a few good resources for geometry, calculus and trig but I’m not so sure for algebra (which is close to a requirement for most of the former). I’ll have a think and come back to you on that, it’s probably also super helpful for everything I’ll say below.",
"I don’t personally know about any summer schools/camps for that age range, hopefully somebody else will come along with them.",
"For some book recommendations if she’s enjoying the theory of everything (though I don’t recall if they’re all age appropriate so please check yourself):",
"Black holes and time warps by Kip Thorne",
"Also “The science of interstellar” by same",
"The uncertainty principle turned up to 11 by Philip Moriarty",
"Why does E=mc",
" by Jeff Forshaw and Brian Cox is very good",
"On a separate topic entirely Chaos by James Gleick is a wonderful read",
"I’m sure there are many others I’m forgetting.",
"If I or anybody else comes up with a good recommendation for algebra and she gets through that, 3blue1brown has a few excellent series of YouTube videos on calculus, Fourier transforms and the uncertainty principle (which will pair nicely with the uncertainty principle book). Though we’re getting rather ambitious.",
"Sixty symbols and numberphile are also very good and the second in particular I think does a good job of getting across how mathematics is more than just running through problems by rote, in a way that’s largely quite accessible. ",
"Long term to really understand these topics takes some quite advanced mathematics. As I said I don’t know exactly what the curriculum looks like in the US but for quantum mechanics end of high school/early college maths should be about right and for black holes, the majority of physics majors will never even see the required mathematics. So encouraging any interest she has in mathematics as well as the physics will help her a lot"
] |
[
"I recommend posting to ",
"/r/asksciencediscussion",
" or perhaps there is a camp or even science camp specific sub"
] |
[
"Why don't we ever seem to get sick from two things at once?"
] |
[
false
] |
I guess what Im trying to say is, lets say I have the Flu....or a Cold or w/e bug/virus is going around. How come in my weakened state that im not infected by a ton of other viruses. It "seems" like it'd make you MORE prone, but I dont think I or anyone i've known has ever gotten sick by more than one thing at a time. Is there any reason for this? Or is it just because our immune system is in overdrive mode?
|
[
"Alot of bacterial infections, especially upper respiratory infections, are often preceded by a virus infection. ",
"The virus can disturb the local immunity in the mucosal membranes and make it easier for bacteria to colonize and start an infection. In these cases you´re maybe not always \"sick\" from two things at once, but you would be infected by two different pathogens at once. You could for example get a simple cold first (the virus) and about week later develop sinuitis (the bacteria)."
] |
[
"Its worth pointing out that when you have an cold or flu, your immune system is not compromised, but in hyper drive. Although physically you feel weak, you are not more vulnerable to other infections.",
"It is your immune system that causes [typical] symptoms, not the bug basically. (not an expert, 4th week in med school)",
"edit: in [] thank you ameisen. ",
"edit 2:I have been superseded; an actual expert ",
"OV_IS"
] |
[
"Spot on.",
"It 'looks' like the virus because the shot will contain things called antigens, these are what the body uses to recognise a virus or other disease causing micro organism. So when the body sees the antigen again it will recognise it and be able to coordinate a response quicker.",
"A bit like a policeman knocking on your door showing you a picture of a thief, so you wont let him in. "
] |
[
"Does mental maturation happen separately to the physical changes of puberty?"
] |
[
false
] |
I was wondering because in high school there were some boys who were 15 years old but they still looked like young children, and they also acted like them. Once they finally went through the main stages of puberty their personalities also changes.
|
[
"So this is outside of my wheelhouse as I'm not a developmental psychologist, but I've taken several graduate level development classes and I have a book in my office on lifespan development so I can try to synthesize an answer from it. Disclaimer, I am relying on the authors as experts and these many not be the only theories of development.",
"The book is ",
"\"Lifespan Development: Resources, Challenges, and Risks\" by Hendry and Kloep originally written in 2002",
". ",
"So the question is basically asking if an individuals personality changes due to the changes an individual experiences during puberty. As a result, individuals who look like they have not hit puberty have not had these personality changes occur. The book has a short section on how puberty specifically affects development.",
"One of the major changes that comes with puberty is the changes we all experience to our body. So we get taller, our arms get longer, and we generally feel weird and awkward. All of these changes force adolescents to examine their own body as they're becoming more aware of their outwards appearance for several reasons. One of these reasons is this is when our reproductive organs are maturing and we develop much of our sexual identity. As we begin to notice the bodies of our peers maturing and feeling sexually attracted to them, we also self-reflect on what our own body looks like and how others may view it as being attractive or not. You could argue (although i'm not sure this is what the authors are getting at) that this self-reflection goes beyond just body image to how you're perceived by your peers. So changes in personality occur because we're more aware of how others perceive us than we are before puberty.",
"There are also all sorts of social pressures that come with puberty. As you begin wanting to date and have relationships with another individual you're changing and modifying your social structure as well. So you're reaching out to new individuals to join your social group (through a relationship) and you're doing more social activities as you go out on dates. In addition you're also supporting those around you who are attempting similar things as adolescents typically have to rely on each other for support in developing their sexual identity. ",
"To answer your question, I would argue (based on reading this chapter) that the people who have not hit puberty yet may not have these shifts in their body and their social structure that force them to self-reflect and empathize with others, which is why they appear to not have gone through the same personality maturation process as their older looking peers.",
"EDIT: There are lots of other changes going on during adolescents as well, but I don't know how strongly they're tied to puberty. Example, there is other discussion in this thread about how the frontal lobes of the brain continue to develop and mature well into \"adulthood\" and these changes really begin in adolescents. I don't have a source to say these changes in the frontal lobes (and other changes) happen because of the same hormonal changes that cause our bodies to grow to look older as mentioned by the OP, so I have avoided discussing those changes in this post."
] |
[
"/u/Jstbcool",
" has a great response to this. I in a PhD program for School Psychology, so I figured I would add some things. To begin with, we need to think about development through two different lenses: 1) physiological /neurological, or \"what is actually physically happening in the body\" as well as 2) behavioral/social-emotional or \"how are we interacting with our environment\".",
"As for the physiological/neurological piece, essentially, our bodies and brains don't all mature at the same rate, in the same way, at the same time. Just like the way our arms may grow long before our legs do, or breasts develop before others, the brain also \"matures\" during this time, filling in myelin coating/white matter. In fact, many of the immature or risky behaviors that teens undertake have been attributed to an inequality in brain development. The Nucleus Accumbens is fully matured by the teen years, and is associated with pleasure seeking, addiction, and instant gratification, all the while the Prefrontal Cortex, the center of the brain responsible for executive functioning, planning, decision making, etc is still underdeveloped. These two out of balance leads to rash and \"immature\" behaviors. See here:",
"Chein, J., Albert, D., O’Brien, L., Uckert, K. and Steinberg, L. (2011), Peers increase adolescent risk taking by enhancing activity in the brain’s reward circuitry. Developmental Science",
"All that said, these developments in the brain don't all necessarily correspond directly with physical maturity either. Our brains may develop at a faster rate than our height, our arms, or our hormone levels. ",
"In addition, our environment plays a huge role in determining our behavior. Despite an underdeveloped body, a child still has the ability to develop behavioral maturity before their body \"looks like an adult\", but like Jstbcool said, these changes often come hand in hand due to the confluence of social pressures, hormones, and self-perception/identification.",
"Ronald Dahl writes on the integration of behavior and neurology during puberty here:",
"DAHL, R. E. (2004), Adolescent Brain Development: A Period of Vulnerabilities and Opportunities. Keynote Address. Annals of the New York Academy of Sciences, 1021: 1–22. ",
"Hope this helps!"
] |
[
"There is a part of your frontal lobe (I am totally blanking on the name, only human brains have it) that isn't myelinated until people are in their 20's. Myelination of that part of the brain is also DELAYED 5 years for people with higher IQs.",
"So, just from that fact alone you could surmise that physical and mental maturation are dissociated. However, that doesn't mean that the 2 aren't somewhat yoked. Just like Jstbcool, I'm afraid I don't have the expertise to really answer whether puberty is associated with a large change in mental maturation, only to say that your brain keeps changing and \"maturing\" well after puberty."
] |
[
"how would we perceive the universe if...."
] |
[
false
] |
During my physics lesson today we were talking about the speed of light and the distances light has to travel before we can see it. I then started thinking about what we would see an object in space as if we were to move towards or away from it at light speed or close to it. Would we see a blur of that object as we receive the light from it at an accelerated rate, or would it be like watching it age as if watching a sped up film. TL:DR how would we see objects in space if we moved at it at light speed?
|
[
"If you are moving towards it the light would blue-shift. If away it would red-shift.",
"And yes, it would appear to change its passage through time. For instance, if you watched someone fall into a black hole (which due to gravity has the same effect on time as accelerating to high speeds) you would never see the person cross the event horizon. They would seem to move through time more slowly (for a distant observer watching). That is to say you would see their clock tick ever slower. Eventually, to the distant observer, the person would seem to stop then fade away as the light from them was red shifted to ever greater degrees eventually leading them to seem to disappear.",
"Note for the person falling into the black hole their clock seems to tick normally and they will pass the event horizon to their doom. This is why the passage of time is relative to the observer. To one it seems normal, to another watching that person it may seem to tick faster or slower. Neither person is \"right\" (or rather they both are)."
] |
[
"so if you were to move away at light speed would you be seeing the object at a single point of its life. Also thanks for this answer it helped a lot"
] |
[
"Yes.",
"If someone was moving, relative to you, at something very close to the speed of light, then to you it would seem they are almost frozen in time (their clocks would be ticking but very slowly). ",
"Indeed this is a way to \"time travel\" that actually works. If you want to see what the year, say, 3000 looks like get on a spaceship and accelerate to near light speed. The acceleration and deceleration would take a couple years (to you) but when you returned it would not be 2014 but the year 3000 (assuming you calculated it all out right and moved at the right speed...could be more or less depending on how fast you went). Your 988 year trip would take, to you, a couple years. To those on earth the trip to the year 3000 would take 988 years.",
"This is a one-way trip though. You cannot come back to what would now be your past and are stuck in the year 3000."
] |
[
"What happens to the electrons of the original atom after nuclear fission?"
] |
[
false
] | null |
[
"The electrons follow the protons, and go with the atoms that were a product of the fission reaction. In the case of ",
" U splitting into krypton and barium, 36 of the uranium's 92 electrons end up in krypton, and the other 56 end up in barium. This means you get two neutral atoms."
] |
[
"what about alpha decay?"
] |
[
"A short answer: Some tag along with the fission products, some are shaken free.",
"A more detailed answer:",
"The fission products are heavily ionized — On a quick literature search, it seems to me that, for example, uranium-235 fission products would have an average ionic charge around 20 ",
"(source)",
". This is because the fission products shoot off the common center of mass so fast that the least bound electrons are basically left behind. So after the fission, you have heavily ionized and likely very unstable fission products quickly decaying towards more stable isotopes, free electrons that have been \"shaken off\", and possibly some free neutrons."
] |
[
"Do rainforests at higher latitudes have shorter trees because of higher wind speeds?"
] |
[
false
] |
According to a Wikipedia article on tropical rainforests climates, "When tropical rainforest climates are more dominated by the Intertropical Convergence Zone (ITCZ) than the trade winds (and with no or rare cyclones), so usually located near the equator, they are also called equatorial climates. Otherwise, when they are more dominated by the trade winds than the ITCZ, they are called tropical trade-wind climates. In pure equatorial climates, the atmospheric pressure is almost constantly low so the horizontal pressure gradient is low. Consequently, the winds are rare and usually weak (except sea and land breezes in coastal areas) while Does this mean that in places such as Central America, Hawaii, and the Philippines, which have rainforests that are farther from the equator, (above 10 degrees North latitude) the trees are generally not as tall? Source: Wikipedia article "Tropical rainforest climate"
|
[
"This is definitely on the edge of my expertise and I will happily defer to any more plant science adjacent folks out there with relevant details, but this seems largely based on some flawed premises and/or misunderstanding of the term \"impoverished\" as used in this context. If we consider global estimations of canopy height (i.e., how tall trees are) as presented in any number of publications (e.g., ",
"Simard et al., 2011",
", ",
"Zhang et al., 2015",
", ",
"Lang et al., 2022",
"), we can see some broad latitudinal patterns in average canopy heights, but (as well illustrated by the graphical abstract figure of Lang) these are not simple, especially if you consider the maximums, i.e., mean heights generally peak around the equator, but max heights are actually greater in the mid-latitudes and there are local differences in mean (like those in the southern mid-latitudes) that approach the means seen in the equatorial regions. Probably the most relevant answer comes in the Zhang et al., 2015 paper, which directly addresses latitudinal patterns, i.e., that they exist and generally suggest a decrease away from the equator, but (1) highlight there is a lot of variability in this and (2) the patterns that do exist largely reflect changes in water-energy details, i.e., how much precipitation vs potential and actual evapotranspiration occurs. Thus, generally, average wind speeds are not really a huge factor in this, though average wind speed does factor into ",
"some calculations of potential evapotranspiration",
", but again more in the sense of changing the water balance through evaporative potential (and things like mean annual temperature, etc are going to generally be a larger factor), not through a direct wind forced cap on the height of trees."
] |
[
"If you look at the Zhang et al., paper (or summary), their data suggests that in mid- and low latitudes water is the limiting factor on canopy height where as at high latitudes, temperature (as a proxy for energy in the form of sunlight) becomes more important as a limiting factor. So really, it pretty much comes back to kind of the classic concept of a limiting factor/nutrient and whether sunlight or water is the limiting factor is roughly correlated with latitude, but with a lot of potential for local variation."
] |
[
"Does this basically just mean 'it's sunny near the equator, and there's generally a lot of water available there, so trees tend to be taller there, but not always'?"
] |
[
"If a person were to suddenly be on Mars without a spacesuit or helmet, how long would they live (assuming it's a place they wouldn't freeze to death)?"
] |
[
false
] | null |
[
"Mars' atmospheric pressure",
" at the surface is about 0.6% that of Earth at sea level, and then it's only 0.13% oxygen. So you'd last 4 or 5 minutes, about the same as anyone who is deprived of oxygen."
] |
[
"It would be harsh, but survivable. You would quickly sunburn, it would be painfully dry, and it sounds like there's no pressurization in this scenario, which means you'd probably experience swelling, you'd get the bends, and you could have ear tube pressure problems.",
"Water in your mouth and eyes would boil. \"Painfully dry\" is an understatement.",
"And, shortly after noon, the temperature would start falling, and within a few hours, it would be below freezing. You would literally watch your life drain away as the thermometer mercury drops."
] |
[
"No.",
"http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970603.html"
] |
[
"Is it possible, for an intelligent civilization, to detect stars from their planet if they can never see them through the naked eye?"
] |
[
false
] |
Hypothetically, if there is a planet which revolves around a star/stars such that there is never any portion of the planet in complete darkness i.e. there is no concept of night on such a planet. If there are intelligent beings on this planet, would they be able to detect the presence of other stars from the surface or would they conclude that the universe is just their planet and those heavenly bodies which can be seen or whose gravitational effects can be observed/calculated? I got this question while reading Nightfall by Aismov, haven't completed it yet.
|
[
"Since stars emit a wide range of electromagnetic radiation (not just confined to the visible spectrum), I would think that there is a very good chance an intelligent life form would be able to detect them, given enough time. How long that would take would depend on what senses these being have. ",
"In the case of beings with similar senses to humans, since even primitive humans are able to detect the light from stars, we knew of them early on. However, if the atmosphere were too thick to see them, we would have to evolve enough to invent machines that detect their emissions. "
] |
[
"I think yes, if they realized that there might be something to look for! I would think they would need tools beyond the human eye to detect the radiation of the stars in daylight, but it should be possible. Not all radiation is visible light anyway.",
"Here is an example of star-related things that can be observed in daylight:",
"http://en.wikipedia.org/wiki/Radio_astronomy"
] |
[
"What would make them go looking for something else. I am making assumptions here, but on earth we know about stars and other planets because our ancestors could see the night sky and chart out the pattern etc. However, in a world where nothing is there to observe(seemingly) what can make the inhabitants go looking for it?"
] |
[
"Can thunder come without rain?"
] |
[
false
] |
[deleted]
|
[
"Yes. On very hot dry days in the desert and dry planes you can get heat lightning which causes thunder. In addition, if you want to get technical, you can have a thunderstorm in the winter with snow instead of rain as well. "
] |
[
"This is a tad misleading. ",
"The term \"heat lightning\" implies that you can see lightning, but not hear the thunder. It's also not a type of lightning, but rather a very distant strike. ",
"You also need clouds to have lightning, it doesn't appear out of thin air. Lightning can strike clear air FROM a \ncloud, but it still needs a storm to source its energy from. There is a term that is used called dry lightning where lightning occurs with an active rain storm, but the rain evaporates or sublimates before reaching the ground (virga)."
] |
[
"Good to know! Thanks for the clarification. Its much appreciated. "
] |
[
"Why don't our fingerprints change when our skin cells fall off?"
] |
[
false
] |
Is it possible to change them at all? I know you can temporarily remove them with an iron, but when they grow back are they the same?
|
[
"Just to clear up though, you can get your prints burned off. I have a ring shaped burn on my thumb from when I was a kid and it interrupts my fingerprint."
] |
[
"How deep is this layer? I once sliced off a bit of my finger with a razor blade and put it back on with a bandaid and it mostly healed back up. Now that part of my fingerprint is a bit misaligned."
] |
[
"How deep is this layer? I once sliced off a bit of my finger with a razor blade and put it back on with a bandaid and it mostly healed back up. Now that part of my fingerprint is a bit misaligned."
] |
[
"Why is the speed of sound significant with regard to aerodynamics?"
] |
[
false
] |
Why does the speed of a sound wave through air have any relationship or bearing on a completely different type of object moving through the same medium at the same speed?
|
[
"Why does the speed of a sound wave through air have any relationship or bearing on a completely different type of object moving through the same medium at the same speed?",
"You can think about it in the rest frame of the object instead. If the object is moving at the speed of sound in the rest frame of the air fluid, then the fluid is moving at the speed of sound in the rest frame of the object.",
"The speed of sound is the speed at which disturbances naturally move through a fluid, so it follows that if you move something faster than the speed of sound through the medium, the behavior of the flow will be fundamentally different than if the motion is subsonic.",
"Fluids are often treated as being incompressible to simplify the equations of motion, but when you have Mach numbers nearing 1, you can no longer assume that the fluid is incompressible in general."
] |
[
"The speed of sound is how fast air molecules can pass on information. Up until that point the air molecules get information about the object before it arrives and can start moving out of the way. When something transitions across that speed, the way it interacts with the air around it changes. "
] |
[
"When moving at high mach speeds air can't wrap around the wings and provide lift. At low mach speeds the wing can slice through the air like a knife. When traveling supersonic the wings will compress the air and create a bow wave which creates a V-shape pattern behind the airfoil just like a boat creates in the water. ",
"Instead of neatly slicing through the air causing huge ripples and shock waves creates a lot more drag and not to mention basically all your lift is gone. ",
"http://www.rroij.com/articles-images/IJIRSET-177-g003.gif",
"Mcrit is the point where airflow starts exceeds the speed of sound anywhere over the wing. Since normal wings relies on air moving faster above than below the wing you really need a completely different type of wing design if you want to travel supersonic. Subsonic you can use wings to create lift, supersonic all you care about is reducing drag because your wings will be generating more Parasitic drag than actual useful lift at that point. ",
"Once you dealt with wing drag and not relying on lift anymore then at even higher speeds actually getting airflow into the engines start becoming a problem. Normal Jet engines are designed to speed up the air entering the engine and at supersonic speeds and that's the complete opposite of what you want to do at supersonic speeds. The fuel and the air and needs time to be injected, mixed, ignited. To operate the engine core also needs to maintain a very high pressure. At supersonic speeds you want to slow the air down as much as possible inside the engine so it can be compressed and accelerated to an even higher speed at the exhaust. ",
"We can actually make engines that work great at supersonic speeds but the problem is mostly how do you get to supersonic speeds when those great engines don't work when traveling below the speed of sound? "
] |
[
"Why do so many destructive pathogens exist? Wouldn't one that does no harm to the host's body be more likely to reproduce and spread?"
] |
[
false
] |
[deleted]
|
[
"Because they haven't evolved to coexist with the host (yet). ",
"There are 10x as many bacterial cells in the human body than human cells. These bacterial are beneficial to us, and we are beneficial to them.",
"http://en.wikipedia.org/wiki/Human_microbiome"
] |
[
"Part of the reason is the definition of \"pathogen\" -- if it does absolutely no harm it probably wouldn't be called a pathogen. One example of that is ",
"gut flora",
".",
"Another part is that if a pathogen mutates a new strain that is less harmful to the host, this will most likely happen inside a particular host. That particular host will now be carrying two strains of the pathogen, and simply being less harmful does not increase the chances of the second strain reproducing and spreading -- it will still have to compete for resources locally with the more harmful strain. The \"not killing your host\" evolutionary pressure does not have a significant effect within the context of a single host."
] |
[
"That's a slightly different issue though. Retrotransposons and other repetitive elements were active long before human evolution so cannot be thought of as pathogens or even alive. They were viral in origin but at this point they are an integral feature of the genome. "
] |
[
"Does centrifugal force come into play on the surface of a planet and affect your weight? What if you were on the surface of a pulsar?"
] |
[
false
] | null |
[
"Sure. But the difference between the gravitational force and the centrifugal force is huge. For a 80kg person, the gravitational force is about 780 Newtons, while the centrifugal force on earth is about 0.003 Newtons."
] |
[
"It’s bigger (and bigger than 1 N), but still much lower than gravity, of course. "
] |
[
"It’s centrifugal force we’re after, though. The centripetal would point inwards, like gravity. Centrifugal force makes sense in a rotating frame of reference. "
] |
[
"We know the universe is expanding, but I've heard the universe is expanding faster. Does that mean galaxies and other planetary objects are expanding at a faster rate with each second?"
] |
[
false
] |
If so does that mean it will surpass the speed of light?
|
[
"Yes, and in fact things about 13 billion light years are already receding faster than the speed of light.",
"This does mean eventually we won't see other galaxies or even other stars and will think we are all alone "
] |
[
"Wait, faster than the speed of light? Can you elaborate? I thought that was impossible. "
] |
[
"No object can move faster than the speed of light.",
"When space is expanding, no object is moving faster than the speed of light, it is space itself that is expanding. There is no limit to the speed of the expansion, because locally still everything is moving at sub-light speeds.",
"Imagine you are running on a rubber sheet... you have a maximum speed, but if you are far from a distant object, and the sheet is pulled really hard, you might move away faster than your maximum speed, even though locally you are only jogging. (or standing still) "
] |
[
"If you wanted to you could break multiplication, division, subtraction, square root, average, mean, and modulus down into solutions which only use addition. Does this hold true for higher mathematical functions? Can all of math be reduced to addition?"
] |
[
false
] |
[deleted]
|
[
"Depends how you define it. A ",
"turing complete",
" programming language can perform multiplication. ",
"Brainfuck",
" is one such language, with only the ability to add 1 and subtract 1, yet multiplication can be performed with the correct algorithm. And any program could technically be ported to it.",
"We have programs that can calculate π, e and multiplication out to infinite digits given infinite resources. The programs needed to do this are of finite length. That program therefore represents π*e, in a more formal mathematical sense, I can convert my brainfuck program into lambda calculus without using multiplication (since lambda calculus is also turing complete)."
] |
[
"I think it may be true only for whole integers."
] |
[
"I'm pretty sure that 1 and 2 are positive integers, and division is on the list. We could require both inputs and outputs be positive integers, but the resulting arithmetics would be incomlete, like operators would have \"oops, cant do that\" too often.",
"However, there is a ",
"comment",
" above about Turing-complete programming language, that should do the trick. And, according to ",
"Church–Turing thesis",
", any possible calculations could be done that way. "
] |
[
"Is it theoretically possible to create a laser that emits radio waves?"
] |
[
false
] |
Can we, for instance, create a laser that emits radiation in the Citizen's Band as defined by the FCC (27 mhz)?
|
[
"The first lasers were initially called ",
", because ",
"microwave amplification by stimulated emission of radiation",
" came first.",
"Modern masers can be designed to generate electromagnetic waves at not only microwave frequencies but also radio and infrared frequencies. "
] |
[
"In principle you could, but",
"The energy transition involved would be relatively low energy, and thus likely subject to a lot of disturbance (noise) due to thermal energy in the gain material.",
"There's no need to do so since we can create oscillators from ICs or discrete components at these frequencies very easily. Such \"lumped element\" oscillators are likely smaller in size and lower in cost than a laser/maser at the same frequency would be.",
" to clarify, masers are very well known at frequencies from about 1 GHz and up. My comment #1 applies mainly below 1 GHz. My comment #2 nowadays applies at maybe up to 25 GHz (although there may be advantages to masers over other types of oscillators for certain applications in the 1 - 25 GHz range)."
] |
[
"Yes, I'm aware of the existence of masers. ",
"But OP specified 25 MHz. Do you know any practical maser at that low a frequency?"
] |
[
"Is there any evidence that individually targeted advertising is any more effective than traditional ads?"
] |
[
false
] |
For all the data that tech companies are supposedly collecting on us, it doesn't seem like the ads I'm shown are really any more relevant to me than Old Media advertising. If anything, it sometimes seems like they're working against themselves. Like, you search the word "lawnmower" once to double-check how it's spelled (don't judge me), and suddenly your feed is flooded with ads for lawnmowers. For all the money and effort that must have been spent on building this system of targeted ads, is there evidence to suggest that it actually pays off?
|
[
"It depends on a few things according to a ",
"2014 study",
". Apparently smaller businesses do better with targeted ads, while bigger/household-name businesses may do worse. \"Doing good\" here is defined by the revenue stream."
] |
[
"That's not what I asked, though, is it?"
] |
[
"That's not what I asked, though, is it?"
] |
[
"Is the heat death of the universe inevitable?"
] |
[
false
] |
If no, i'd like to hear what are the possible holes in the theory.
|
[
"Downvoting guideline: downvote only those comments which detract from the discussion (distracting memes, off-topic jokes, pseudo-scientific mumbo-jumbo, and anti-science rhetoric)."
] |
[
"Downvoting guideline: downvote only those comments which detract from the discussion (distracting memes, off-topic jokes, pseudo-scientific mumbo-jumbo, and anti-science rhetoric)."
] |
[
"Remember where you are posting.",
"The problem isn't that you made a joke. The problem is that you made joke without giving a useful answer to the OPs question. Funny is a good thing, it isn't necessarily what we want to see as the top comment on a thread. This subreddit has tough guidelines because its existence depends on the ",
" quality of the comments.",
"This is the advice that I keep in the back of my head:",
"If you cannot clarify your answer in excruciating technical detail, don't answer at all. This is to reduce layman speculation, which is generally not helpful."
] |
[
"So; asteroid hits the Earth, wiping out the dinosaurs. We can see the crater even today, but my question is: what happens to the enormous asteroid?"
] |
[
false
] | null |
[
"It got evaporated, some pieces flew back into orbit and others are in the K-T or now known as the K-Pg boundary. A thin layer of dust that can be found all around the globe. The metal iridium which is used in cellphones was a key element of this astroid and can be found in this layer. No bigger fragments can be found because a. it impacted at such a high velocity that nothing of any reasonable size could withstand and b. Any fragment is about 66mio. years old below new layers of rock or underwater finding it would be near impossible like a needle in a hay stack"
] |
[
"Massive is a relative term, here is a ",
"quick sketch",
" of the Asteroid (50km diameter) and the Earth (12000km).",
"As you can see the asteroid is barely visible on that scale. So as Yamialone already said, it's all around you, well below in a tiny layer called the KT boundary. Which we can make out mostly because it's material that isn't found on Earth all that much."
] |
[
"The Moon's composition matches the Earths because it formed from material blown off the Earth by a Mars size impactor. ",
"As the nebular cloud from which the Earth and asteroids coalesced there was some sorting of material so objects formed further out do not have exactly the same composition as those formed closer in. Asteroids don't have the same composition as the Earth, just like Mercury doesn't (higher percentage of heave metals) and the gas giants (largely hydrogen) don't as they all formed at different distances from the Sun. ",
"Also once these objects cooled from a molten state there was further sorting of material. When we talk about the amount of Iridium on Earth vs an Asteroid we are talking about the amount near the surface of the Earth not the body as a whole as much of the Earth's Iridium sunk to the center in the molten stage."
] |
[
"If someone lived in space their whole life, how would their body be different?"
] |
[
false
] |
Assuming they were first born on earth (as I don't think hox genes would work right in zero-G). A particular thing that just struck me was that obesity wouldn't cause the same, if any, problems.
|
[
"They would need to spend a significant amount of time exercising to prevent muscle atrophy (and even then they would not develop the same level as the average person).",
"Astronauts that spend long periods of time in space lose bone mass; on average 1% loss for every 3-4 months spent it space. They can regain this mass on return to Earth (or to similar gravitational conditions).",
"There are also concerns with gas exchange, assuming one undergoes similar methods astronauts currently do when engaging in spacewalks. Their suits are filled with 100% oxygen and kept at a pressure of 1/3 Earth's atmosphere. When a normal pressure environment with nitrogen is reintroduced, one must undergo a process similar to deep sea divers to avoid decompression sickness (or compression sickness in this case).",
"Relevant Wikipedia Link"
] |
[
"It's not my field, but I know that the spine compresses because we stand vertically."
] |
[
"It's not my field, but I know that the spine compresses because we stand vertically."
] |
[
"Medical Research Community - culture of authoritarianism?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines",
"/r/AskScience"
] |
[
"Yeah, sorry, reading the guidelines afterwards I realized it would not fall within the same.",
"Any recommendation on where would be a good location to post this kind of question to the scientific community?"
] |
[
"I'm afraid i'm not too sure, I don't have a good overview of other subreddits."
] |
[
"If we can observe sub atomic particles spontaneously generating in a vacuum, can we use them as a source of energy?"
] |
[
false
] |
I suppose what I'm asking is: If we can observe subatomic particles, such as a positron or electron, spontaneously appear in a vacuum, is it possible to create a stream of these and use them as a source of energy?
|
[
"We can't observe subatomic particles spontaneously generating in a vacuum. We can construct theoretical models where they do, but we can't ",
" them, and conservation of energy means we can't use them."
] |
[
"That's one (oversimplified) way of explaining the mechanism, but we could never observe it happening. When we observed the particle that was left in space, it wouldn't be half of a virtual pair anymore; it would be a real particle."
] |
[
"Not in the way you're describing, no. These particles come into and out of existence by \"borrowing\" energy from the vacuum via the uncertainty relationship and create particle-antiparticle pairs which then promptly recombine and vanish. In order to separate the particle and antiparticle, you have to put energy into the system, so you won't get anything constructive out as far as energy goes.",
"The ",
"Casimir force",
" is due to the force virtual particles exert on two sheets of metal placed very near each other. The idea is that the number of possible wave-functions that fit between the plates is less than the number of wave functions that fit outside the plate, so the plates are drawn together. This effect can be seen macroscopically and is why boats that transfer goods to one another can't get too close or they'll be sucked together and collide. ",
"There is no evidence to suggest we can get any useful energy out of the Caismir effect.",
" I didn't mean to imply that the caismir effect was responsible for drawing boats together, i meant that the concept of integer number of waves fitting between boats was analogous to the caismir effect."
] |
[
"are we aware of any major evolutionary groups that went extinct?"
] |
[
false
] |
so i was just thinking about how monotremes have an extremely low number of species, they could have very easily gone extinct before modern history. in which case we would possibly have had no idea they ever even existed. so my question is, are we aware of any similar groups that did go extinct? and how different were those animals from their closest related group?
|
[
"Oh yes, quite a few.",
"Consider ",
"Anomalocarids",
" for instance - we're not even sure what their closest relatives were, but they were probably some kind of early arthropod. Imagine sleek, sort of squid shaped soft-bodied predators, with an undulating series of fins to propel them. Two stalked eyes, a pair of segmented grabbing appendages on either side of the mouth, and the rather unique mouth system ... a buzzsaw-like cookie cutter vaguely shaped like stacked pineapple slices. If they had survived, they would be their own thing, siding somewhere along crustaceans and insects in the tree of life.",
"The fossil record if full of such groups at various taxonomic levels; look up trilobites, cystids, blastoids, conularids and placoderms for other examples."
] |
[
"It might help to mention ",
"index fossils",
" like ",
"ammonites",
" which are used to identify geological layers. "
] |
[
"Multituberculates are a good mammal example."
] |
[
"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?"
] |
[
false
] | null |
[
"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.",
" 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."
] |
[
"Your comment about gyroscopes is close (and is true for a large number of spacecraft), but is not quite right for the ISS. What you've described here is control via ",
"reaction wheels",
", which are rotors that are fixed to the body and exert control by varying their speed. What the ISS uses is ",
"control moment gyroscopes",
" (CMGs), which are rotors that have fixed speed and exert control by varying their orientation. CMG control laws are substantially more complicated than reaction wheel control laws, but CMGs tend to allow you to exert higher torques than reaction wheels.",
"Edit: for everyone whose curiosity was piqued by this discovery, I highly recommend this ",
"coursera course",
" on spacecraft attitude dynamics and control"
] |
[
"The Cygnus spacecraft can also be used to raise the ISS’s orbit. Back during the OA9 mission they did a 49 second burn to raise the ISS 92m. I worked on that mission!"
] |
[
"Why didn't Einstein tell us that things in the distance actually keep getting smaller as they get further away?"
] |
[
false
] | null |
[
"Do you mean visually like ",
"linear perspective",
"? This has been incorporated into art for centuries."
] |
[
"I'm not quite sure what you mean. What things gets smaller as they move farther away?"
] |
[
"I'm not quite sure what you mean. What things gets smaller as they move farther away?"
] |
[
"What is happening when certain rabies victims get hydrophobia?"
] |
[
false
] |
Rabies begins with flu-like symptoms which can progress to other symptoms such as partial paralysis, anxiety, insomnia, confusion, agitation, abnormal behaviour, paranoia, terror, hallucinations and delirium. It also causes hydrophobia, and I understand that this is linked to victims being unable to swallow and experiencing pain when trying to do so, however I've watched some youtube videos of victims with hydrophobia and they seem to be experiencing a real fear/panic when water is brought near them, more so than would be expected as a reaction to potential pain caused by swallowing. How can the effects of the virus on the nervous system manifest itself in this way i.e. causing hydrophobia and anxiety, paranoia and terror as well. Also can you tell me about any other microbial diseases that result in these kinds of effects on the brain?
|
[
"Lots of illnesses can have neurological effects, it's likely that the hydrophobia of rabies is linked to actually transmitting the disease by slobbering on other animals. For a real mind fuck, look up Toxoplasmosis. It's a parasitic protozoan that lives its life in a cat's gut, and is present in most all cats. It's in cat poop, and if that cat poop is eaten by a rodent (not uncommon), then it will migrate to the rodent's brain and cause a few effects. It will degrade the rodent's fear response, and make it attracted to the smell of cats. That way, it will get back into a cat's gut and be able to complete it's life cycle. All this is known and well documented. What's less understood is how it affects human brains, though since all mammal brains are biochemically ",
" similar, it's not unreasonable to believe it could have the same affect on humans. It's not a testable hypothesis, but it is true people infected with Toxo are 250% more likely to die in a car accident, among other weird things. It's my personal position that cats are as popular a pet as they are because many people are infected with Toxo, and that makes them like cats. "
] |
[
"I have recently read a very good article about toxoplasmosis but I don't want to face up to the possibility that my cat might be affecting my behaviour. He already causes me to have full conversations with him, give him cheese and also sometimes lies in wait on the top of the stairs as a trap, but I'm sure he still loves me: ",
"http://www.theatlantic.com/magazine/archive/2012/03/how-your-cat-is-making-you-crazy/8873/"
] |
[
"Here ya go:",
"hydrophobia (hdr-fb-)\n1. Abnormal fear of water.\n2. Rabies.\nWord History Hydrophobia is an older term for the disease rabies, and it means \"fear of water.\" Because of this name, many people think that rabies makes one afraid of water. In fact, this is not the case (although rabies does cause mental confusion of other kinds). The name hydrophobia comes from the fact that animals and people with rabies get spasms in their throat muscles that are so painful that they cannot eat or drink, and so will refuse water in spite of being very thirsty.",
"http://www.thefreedictionary.com/hydrophobia",
"http://www.youtube.com/watch?v=OtiytblJzQc"
] |
[
"Why do neutrophils have multi-lobed nuclei?"
] |
[
false
] |
Currently learning immunology and my professor doesn’t have a good answer. Is there a functional reason or is it just “because that’s how they are”?
|
[
"No one really knows.",
"One idea is that it helps the cells be more flexible so they can move around and squeeze into tight tissue spaces to do their job. A large round single nucleus would be a hindrance.",
"However, there are other cells that move around that don't have multi-lobed nuclei, so, it's probably not strictly necessary for this function."
] |
[
"They become more lobulated as they age, yeah? Like banded neutrophils are young vs. mature segmented neutrophils."
] |
[
"The definition of a mature polymorphonuclear cell is that lobulation, as you said - anything that isn't pinched is a band or earlier. What I always found interesting is that other PMNs, like eosinophils and basophils, aren't usually as multi-lobed. Mast cells even less so.",
"But AFAIK, once matured, segs don't become \"more\" segmented. And immature granulocytes shouldn't be in peripheral blood outside of a few early-released bands or infection."
] |
[
"What do we use as a metric?"
] |
[
false
] |
This post got me wondering what we use as a metric, or if there is one that we do use. Does c increase/expand as space does?
|
[
"The metric is a function that tells you how distances between points depend on space and time. ",
"The metrics that physicists are interested in are solutions to The Einstein Field Equations, which is the central set of equations in General Relativity. Unlike in Newtonian physics, in GR the distances between objects (in space and in time) depend on the distribution of matter and energy. In the equations, the metric (which is actually 10 independent functions of space and time) is the variable we are usually trying to solve for, just as we were trying to solve for position as a function of time in Newtonian mechanics.",
"The speed of light, c, does not change as space expands. In fact, c is just proportionality constant of space to time that allows you to define \"distances\" in spacetime."
] |
[
"The ",
"FLRW metric",
" describes the expansion of the universe. c is a constant."
] |
[
"For things within the solar system, we often use Schwarzschild or Kerr. For radiative processes, it's often Minkowski with some linear perturbations.",
"Anti-de Sitter is used a lot because of the AdS/CFT correspondence."
] |
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