title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"Does the nature of an event change if observed?"
] | [
false
] | A friend of mine was trying to explain quantum theory to me. There was one thing that really stuck out to me; (I am paraphrasing and may be a little off here) he told me that scientists did some sort of test firing photons at a couple pieces of paper. It had a certain pattern every time, but when they tried to replic... | [
"Observation means \"measurement,\" which means \"interaction with other particles.\"",
"Observation does ",
" mean \"scientists watching it.\""
] | [
"I believe it's a modification of the Double Slit experiment for the testing of Quantum Theory. Since I'm no good at explaining it myself, ",
"here is an article regarding the experiment your friend is talking about.",
" Hope that helps!",
"Edit: sorry, I realized I didn't even answer your question: ",
" yo... | [
"It does not. The manner in which wave-functions collapse can be predicted with extreme accuracy, and the scale at which these things matter is all but irrelevant for the lives humans live. You could throw a rock far into space, where nothing is around to interact with it except the distant light of stars, and it w... |
[
"Why (and how) is it possible to build muscle localized but not burn fat?"
] | [
false
] | I know: different processes, different tissues, different functions. I was wondering if someone could provide a more detailed explanation about this, in case there is any. Thanks! | [
"Muscles grow based on stress applied to them. The harder and more frequently you load them, as long as you aren't overloading, the larger and stronger they will grow. There are two competing processes going on in muscle and bone tissue: breakdown and regrowth. Exercising triggers healing processes that favor regro... | [
"Because the form that fat is stored in adipose tissue is a very effective storage form of energy, but not a very useable form of energy. To use an overly contrived analogy - pretend you want to build a house in a neighborhood, it's easy to choose the location for that house. Building that house will take a lot o... | [
"Wow, thank you for clearing that up for me..im trying to get rid of my man boobs by only doing push ups and other work outs that focus on the chest..would you recommend just doing cardio training to lose the fat?"
] |
[
"Has anyone ever studied total internal reflection of waves that are not EMF waves, for example, through water? Is it possible to exhibit this behavior?"
] | [
false
] | null | [
"Pretty much yeah. Although there isn't any perfect Total Internal Reflection for EMF waves either, if you read the specs on a fiber optic cable it'll tell you how much signal loss you'll get."
] | [
"Do water waves refract across barriers? Yes - water waves do cause oscillations in the materials surrounding the body of water. If water were vibrating very quickly, you would hear a sound coming off of it."
] | [
"Here is an example of the use of total internal reflection with ultrasound: ",
"http://www.ncbi.nlm.nih.gov/pubmed/1858525"
] |
[
"Does the brain control every process of your body?"
] | [
false
] | Or do organs run pretty much autonomously? Does it depend which organ? Does the brain tell the intestines to move food through? Tell kidneys to process urine? Hair folicles to grow hair? | [
"Processes such as the reflex arc occur without the involvement of the brain, although they are still a part of the central nervous system. In situations where your reflexes kick in (Touching a hot stove, pin prick on your finger... etc.) The sensory nerves in the area affected will send a signal to the spinal chor... | [
"This is a somewhat difficult question as there is a large gray area. ",
" ",
" ",
" ",
"Overall, the brain does not \"control\" every organ in the body. Most of these organs can function autonomously. However, the brain does exert significant regulatory functions on most, if not all, organs via direct nerv... | [
"True, but in other reflex arcs (eg. Babinski, Hoffman's) the brain overrides the reflex and the presence of the reflex represents pathology of the spinal cord or brain. ",
"Not true about the pin prick or hot stove. These senses need to make it to the brain to be registered as bad. For this reason if someone get... |
[
"Why do we need to fall asleep to not feel tired? Why doesn’t a conscious prolonged rest provide us with enough energy for the following day?"
] | [
false
] | null | [
"First, in the interest of full disclosure, nobody knows for certainty\nSecond, we don't just get tired when we don't sleep - especially for long periods of sleep deprivation, there is paranoia, personality changes, a disintegration in biological rhythms and many other seriously bad things.",
"Also it is not beca... | [
"The simple answer is that even a \"resting\", but conscious, brain is going to look very different, in terms of overall activity patterns observed, from a brain that is in one of the various sleep states (ignoring REM). We don't have a complete understanding what promotes the recovery from e.g. the feeling of drow... | [
"But if we were in a completely relaxed, but conscious state (no movement, little energy used, low heart rate, etc) could it simulate sleep enough to break down those enzymes? ",
"What is it about sleep specifically that causes the breakdown to happen more efficiently than consciousness?"
] |
[
"Do animals demonstrate traumatic responses to \"sexual violence\"?"
] | [
false
] | I've read that much reproduction in the animal world is what we would consider rape if they were humans. I was wondering if there are any studies that examine the response of females before an after forces reproduction / "rape". (I put the phrases "sexual violence" and "rape" in quotation marks because I don't want to ... | [
"The other poster is correct that we cannot measure subjective experience in non-human animals. That said, however, we ",
" indeed see trauma responses in mammals (someone else will have to contribute for other animals) in response to situations that humans would consider \"sexual violence\".",
"As an example o... | [
"You are asking what an animal subjectively feels in a specific situation. There is really no way to conclusively answer this. ",
"A few considerations: ",
"In most of human culture, our sexuality holds a very particular place, central to our privacy which is why we react so strongly when those borders are tr... | [
"You presume that animals feel an orgasm, and that they enjoy it. We don’t know that. ",
"Most animals only exhibit mating behaviour when in oestrus, for example. Males then only seek out females who are in oestrus. There may be pleasure involved but we cannot be sure as we are talking about qualia. ",
"And n... |
[
"Why is it that if pencil lead is made of graphite, and graphite is electrically conductive, we can't just draw circuits on paper and put real batteries and circuit components onto the pencil lines to create working electrical circuits?"
] | [
false
] | I saw this video on Circuit Scribe just now and I was wondering about tihis question. Can anyone help me out here? Thanks! :) | [
"This is absolutely possible. It's even rather easy to demonstrate at home with a 9 V battery and an LED or two.",
"Graphite isn't the world's best conductor, however. It has an electrical resistivity of around 10",
" Ω m, compared with around 10",
" Ω m for copper."
] | [
"Relevant video",
"Just make sure the lines are nice and thick."
] | [
"There are also special pens for drawing in conductive ink, in case you'll want something that works better."
] |
[
"What happens to the \"useless\" neutrons once 2 atoms collide and form a new one + what effects does it have on its surroundings wherever it goes?"
] | [
false
] | null | [
"What do you mean by “useless neutrons”?"
] | [
"Hummm, the neutrons that aren't part of the atom's nuclei resulting from its fusion? I've heard a teacher saying that when there is nuclear fusion (when to different atoms collide) in some cases, some neutrons end up not being part of the resulting atom. Its claim was made in regards of the way super-heavy-element... | [
"In a fusion reaction used in superheavy synthesis, the projectile and target coalesce into a highly excited compound nucleus, which boils off neutrons, charged particles, and gamma rays as it de-excites."
] |
[
"How do we know what the ratio of a parent isotope to the daughter isotope was in the past?"
] | [
false
] | Radiometric dating is done by comparing the current ratio of the radioactive isotope to its daughter and determining the change from the sample. How do we what the original sample was if we also seem to know that it was different than what we have today? | [
"You can also follow the ",
"decay sequences",
" and start with the present concentration of all the daughter isotopes. then work your way back to any point in time.",
"Like this for ",
"Thorium 232",
"."
] | [
"It depends on what element you're measuring. If we're talking about carbon-14, it's pretty simple. 14C is formed from nitrogen present in the atmosphere because of cosmic radiation. Now cosmic radiation is pretty constant, so the ratio of 14C to 12C remains pretty fixed in the atmosphere. As long is something is '... | [
"Thanks for the links!"
] |
[
"What caused this huge GDP per capita boost in 2002-2008?"
] | [
false
] | Hi guys, I am 22 yo dude from Bulgaria who was looking at GDP per capita for Bulgaria, Serbia and Romania, but later on I checked for Germany and US as well. During the period of 2002-2008 there seems to have been a hugely massive economic boost to The Balkans in particular but other countries as well, and currently fo... | [
"This is the right answer. All the countries of Eastern Europe experienced a huge economic collapse in the early 1990s with the fall of communism in the region and the collapse of Russia as a trading partner. As they integrated with the European community, the saw spectacular growth, which brought them almost -- ... | [
"This is the right answer. All the countries of Eastern Europe experienced a huge economic collapse in the early 1990s with the fall of communism in the region and the collapse of Russia as a trading partner. As they integrated with the European community, the saw spectacular growth, which brought them almost -- ... | [
"By what I am seeing when googling \"gdp per capita Bulgaria\" or pretty much any Balkan/East European country - there doesnt seem to be any drop from 2001"
] |
[
"When perfect destructive interference happens between a pair of waves, where does the excess energy go?"
] | [
false
] | If there was a perfect case of destructive interference where two waves canceled each other out exactly where does the energy that the waves used to carry [E = hf] go to? My guess is that it is dissipated as heat to the general area that the interference happened, is this about right? | [
"The waves won't cancel out over ",
", if you have two spatially separated sources."
] | [
"Then you don't have energy to begin with. You can pick any point in space and arbitrarily say that ",
" is the source of two perfectly destructive waves of energy ",
", where E is ",
". You can ponder where 2E went, but it's a meaningless scenario. The world just doesn't work that way - that system is equiva... | [
"This. The energy will be present in the regions of space where the waves constructively interfere. At no point is energy 'annihilated' or something when there is destructive interference, it is just a redistribution to other areas."
] |
[
"How are photons created? If I am in a dark room and turn on a light, where do the photons come from?"
] | [
false
] | [deleted] | [
"Photons are generally created/destroyed when the energy of an electron changes. In general, electron+photon=more energetic electron. So if you hit an electron with a photon, you would \"excite\" the electron and make it more energetic. Likewise, an energetic electron might be unstable and become non energetic by r... | [
"It's an excitation of the electromagnetic field, so you could say that. These excitations sometimes exhibit particle-like behavior instead of wave-like, which is where quantum shenanigans shenanigize. "
] | [
"Feynman used the analogy that emitting a photon is like speaking - it's not like you have a word bag and when you say a word, eventually you reach a point where you can't say that word anymore. Similarly, photons don't come from somewhere. Just as a word is an excitation of air, photons are an excitation of the el... |
[
"What is the name of the phenomena where you are more likely to notice something because you encountered it before?"
] | [
false
] | For instance, you may come across a really random word and then the next day you hear someone use it. Or perhaps you noted a number and now you are seeing it everywhere. It seems to defy coincidence. | [
"Baader-Meinhof Phenomenon",
"? Although I'd go with pyxlated's reply above."
] | [
"Within Confirmation bias, it is a type of low level ",
"Selective perception",
" known as perceptual vigilance."
] | [
"Within Confirmation bias, it is a type of low level ",
"Selective perception",
" known as perceptual vigilance."
] |
[
"What is the proportion of the size of blackhole's event horizon compared to the volume of mass that created it?"
] | [
false
] | As in, how much bigger/smaller is a black hole than the star that it was born from (accounting for the lost mass during the super nova, if possible) | [
"The volume of a black hole is not well-defined",
", so this is not an answerable question."
] | [
"It appears to me that there is a way of answering your question. While a black hole itself isn't well understood, and the singularity does not have size, the event horizon is well characterized by general relativity. I believe from reading your question, this is what you were asking anyways.",
"Unfortunately t... | [
"Thank you, valuable information in there "
] |
[
"Why is \"proximal\" and \"distal\" used when \"superior\" and \"inferior\" already exists?"
] | [
false
] | null | [
"I'm not sure what the point of reference is. If it is with respect to the center of your body then that just means that your knee is closer to your center than your ankle."
] | [
"Proximal means closer, superior means above. Distal means farther, inferior means below."
] | [
"ohh so when I say \"the knee is proximal to the ankle\" what I'm actually saying is the knee is closer to where the leg attaches to the body? "
] |
[
"Is there a better liquid/gas to use in turbines than water and steam?"
] | [
false
] | In most power plants, something is used to heat up water, convert it to steam, which then runs turbines and is condensed back down into a liquid to begin the process a new. I can understand why water would be used, it's plentiful, and non-toxic, but is there a liquid or gas that can expand more rapidly, and thus creat... | [
"Yes - some concentrating solar systems use Pentane instead of water because it transitions to gas at a lower temperature, allowing more efficient use of low-heat energy sources. In a typical thermoelectric plant however, really only deionized water is economic at that scale.",
"http://en.wikipedia.org/wiki/Orga... | [
"Also, that stuff (plants using photosynthesis and what not) is actually less efficient than our current technology"
] | [
"The term you're looking for is ",
"working fluid",
". Which working fluid is used, depends upon the temperature range. The list also includes liquid metals (sodium, lead) and liquid salts (Lithium Floride) for very high temps >400C."
] |
[
"When a storm like Irma is at sea, what's happening below the surface?"
] | [
false
] | How is the biosphere effected? Do fish just swim deeper and go about their regular life? EDIT: I can't wait to get home from work and read all this awesome science, to the scientists and field experts just joining, many of the comments in this thread are new and more specific questions | [
"Meteorologist here. I cant speak much to biology but tropical systems like Irma cause significant mixing of the surface waters through localized upwelling and freshwater mixing from rainfall. They leave behind cold wakes where you can see the warm water has been mixed with deeper cooler water. I would imagine this... | [
"I have so many questions to add to this. ",
"How big do the waves get with +295km/hr winds? Are there boats there right now? How big does a boat have to be to sail through a storm like that? What happens if there's an oil rig there? Would a submarine notice the storm? How deep would it have to go? Does cool stuf... | [
"Coral reef tank hobbyist here. One thing to remember is that the wave action on the surface only affects the water underneath for 1/2 the wave length and even then it is greatly diminished the deeper you go. That said, the ecosystems depend on occasional storms to distribute bio-matter like eggs plants and coral s... |
[
"What is the lowest level of life for which behavioral learning is possible?"
] | [
false
] | I'm not talking about getting stronger, like a physical adaptation, but behavioral change, like learning where the food is and going back there frequently. For example, is the behavior of a fly controlled by nothing more that genetics and environmental cues, e.g. smelling food? If it is governed by some kind of learnin... | [
"Almost all invertebrates can do simple learning. Fruit flies, sea slugs, and pond snails, for example, are all capable of operant conditioning (= modifying their behavior due to learned associations.) Even flatworms can do some very simple learning - you can train them to turn toward or away from light to search f... | [
"Fungus can be taught to solve a maze",
"."
] | [
"Excuse the pedantic correction, but slime molds are actually no longer classified as fungi; they're now considered protists. Gotta love phylogenetics!"
] |
[
"Why is gluten intolerance a new phenomenon / on the rise?"
] | [
false
] | Wheat was the food staple of Europeans for most of history, and its been only recently (about the last 2 generations) that so many of us suddenly seem unable to process it properly. What in our biological make-up could be causing this sudden rise in intolerance of a once critical food? Have there been any studies point... | [
"The modern Chorleywood process of bread making (which allows a shorter fermentation and is faster/cheaper) is implicated in IBS symptoms ‘. In conclusion, breads fermented by the traditional long fermentation and sourdough are less likely to lead to IBS symptoms compared to bread made using the Chorleywood Breadma... | [
"It is also possible that the increase in the prevalence of celiac disease may be due, at least in part, to improved diagnosis and awareness of the condition. In the past, celiac disease was often misdiagnosed or not diagnosed at all, so it is possible that there were more cases of the condition that went unrecogni... | [
"There are two things that most likely contribute to this. First is what ",
"u/mindgame_26",
" noted: what used to kill people doesn't kill people, so they're more likely to pass on their genes resulting in an increase in the number of people with gluten issues.",
"The second is increased diagnosis of gluten... |
[
"If E=mc², does energy have gravity?"
] | [
false
] | I know for most classical measurements like gravities of astronomical objects, energy would be nearly inconsequential to the equation. But let's say there's a Neptune sized planet in deep space at nearly absolute zero, if it had a near-pass with a star and suddenly rose 200-400 degrees K, would that have any impact on ... | [
"The short answer is yes - the rise in temperature would affect the apparent gravity by a little bit. How little? Well, math!",
"Let's take your Neptunian planet, and raise the temperature by 300K instantly. Now the mass of Neptune is ~10",
" kg, and if we roughly assume its all hydrogen (in reality its about 8... | [
"Yes. Relativistically, gravity is determined by the ",
"stress-energy tensor",
", which considers mass, pressure, and momentum. It turns out that for non relativistic objects, mass dominates.",
"In case you want to know the effect quantitatively, the first correction to Newton's law is replacing the mass of ... | [
"Absolutely. Mass and energy are two sides of the same coin, and so both gravitate. In fact, for the first 80,000 years or so of the Universe's history, light's gravity was far more important than all the gravity due to matter, and this caused the Universe to expand at a different rate than later on when matter was... |
[
"Why aren't asynchronous processors a viable replacement for synchronous processors?"
] | [
false
] | As a computer scientist, I've always been fascinated by the idea of a clock-less processor, but I have very little knowledge of electrical engineering, so I've never really understood why they're not considered a viable replacement for modern synchronous processors? Is there some inherent flaw in making a circuit witho... | [
"Two big things:\n1) More space is required due to completion signal detection circuits.\n2) Synchronous designs are easier to test.",
"That's really about it. Most of the other reasons we don't make them is no one is trained to make them and none of the design programs are built around asynchronous designs."
] | [
"If you drop the global clock, you need synchronization logic between each stage of the pipeline. This takes a lot of space. Asynchronous processors do have uses though. Global clocks cause spikes of electromagnetic interference, so asynchronous circuits usually have drastically reduced EMI and much more stable ... | [
"A clock-less processor would mean an analog processor. ",
"No it wouldn't. An analog processor would operate on continuous data (that cannot be separated into indivisible bits). A clockless processor could still operate on discrete data, and could even do so in discrete operations -- it's just that the time th... |
[
"If rogue waves occur in the ocean, and rogue sound waves also occur?"
] | [
false
] | To my knowledge a rogue wave occurs when lots of smaller waves converge in the right way. My question is, does this happen with sound waves? Could a loud booming sound occur at random from the confluence of many low amplitude waves? | [
"Theoretically yes, small amplitude sound waves can converge to form a large amplitude wave. In practice however this is ridiculously unlikely, and even less likely that it will occur somewhere that it can be heard."
] | [
"If a rogue sound wave propagates in a lonely forest, and nobody is near by to hear it, does it make a sound? "
] | [
"The scales are just really different:",
"The lowest audible sounds are around 20 hz, which means that at a given point, the wave will crest 20 times per second, and the frequencies only rise from there. On the ocean, the frequency would be less than a hundredth of that rate.",
"You need two waves to be somewha... |
[
"How is deep/machine learning different from a bunch of if-else statements?"
] | [
false
] | null | [
"The fundamental difference between if-else and AI is that if-else models are static deterministic environments and machine learning algorithms are probabilistic stochastic environments. Deterministic systems can do well in clearly defined and well-bounded situations, but the primary magic of ML is the ability to g... | [
"At a fundamental level it isn't. In both cases you are executing a computable function and all trained models can be rewritten using other programming constructs. In fact, when executing a trained model your computer is literally executing code that resembles \"if-else\" statements. ",
"The real juice of ML isn'... | [
"So we have then a little bit of: calculus, geometry, linear algebra and programming all mixed into one?"
] |
[
"How has industrialization and the industrial revolution affected Natural selection?"
] | [
false
] | I read about the moths in England but I was wondering how industrialization has affected natural selection either positively or negatively. | [
"Lots of animals have benefited by cities. The species that benefit tend to be omnivorous and generalists, meaning they have multiple ways of surviving and are not restricted to one habitat type or food type. Some great examples: rats, mice, crows, racoons, pigeons, starlings, house sparrows, opossums, gulls, grey ... | [
"how industrialization has affected natural selection either positively or negatively.",
"This is not a meaningful way of phrasing this. ",
"Industrialization and the industrial revolution change the details of the environment that organisms have to cope with, but they're still experiencing natural selection fo... | [
"There is no such thing as positive or negative effects on natural selection. Changing the environment to a city will impact selection, but it is simply favoring those species which are advantaged in the new environment."
] |
[
"What is the mechanism behind the acceleration of the expansion of the universe?"
] | [
false
] | I know it's Dark Energy causing expansion, why is it causing acceleration? | [
"Because it was introduced with that property.",
"You are reversing the logic. We observe the universe, and we observe the expansion, so we try to find a model that fits to this. Dark energy is such a model, and of course it is accelerating the expansion - otherwise it wouldn't be a model to describe the accelera... | [
"Dark Energy is not causing expansion. In a universe without Dark Energy there would still be expansion, it would just be slowing down. Dark Energy is causing the ACCELERATION of the expansion.",
"The mechanism for the expansion is the gravitational influence of energy density on energy density given the initial ... | [
"The universe just might have a very clear center, with the motion of all matter moving away from it. If so, the relative motion experienced by every observer within, if moving in a very simple pattern, could create the illusion that we are sitting at center, when we aren’t, or we could be, who knows. This pattern... |
[
"Why time goes slower when you're near a massive object? (a black hole for example)"
] | [
false
] | [deleted] | [
"to my understanding time is purely an intellectual concept (as it is, in days, years, etc.)",
"Those are the units of time. They are made up by humans. But time it self is purely physical concept.",
"If you where close to a black hole (ignoring stuff like spagethification), you wouldn't noticing any difference... | [
"Time goes slower close to massive objects because that is what gravity is/does. ",
"Is it because the light is bended somehow by the object and arrives at an external observer slower?",
"No. Its not an illusion, time actually goes slower. Closer to a massive object.",
"There is a number of things that we gen... | [
"Time goes slower because masses bend spacetime in GR. The only way you can truly understand this is by understanding the mathematics of general relativity. However we can try to get some intuition by means of an analogy. Imagine an elastic sheet with one direction indicating time and other indicating one dimension... |
[
"Why is the English alphabet organized the way it is?"
] | [
false
] | Or any language for that matter. I realize there is coorelation to the Phoenician alphabet, but is there any other reason behind why we go "a,b,c,d,...."? | [
"As you alluded to, we (English/Germanic/Romance) get it from the Romans. They got if from the Greeks and Etruscans. The Greeks got it from the Phoenicians. Probably etc.",
"There may have been a logical order to it originally. It might have just sounded nice and therefore memorable in the order it was written. T... | [
"The letters that are common/analogous to both the Latin and Greek alphabets are in the same order. Take a look at this pot:",
"https://en.m.wikipedia.org/wiki/File:NAMA_Alphabet_grec.jpg",
"The Romans added and subtracted a few letters here and there, and slotted them into this older Greek order. You can see t... | [
"To answer this question you would need to look at where the alphabet came from. The first alphabet dates back to approximately the 18th century BC near the ",
"Sinai Peninsula",
" in Egypt. We know that \"... early alphabetic writing spread to the Southern ",
"Levant",
" ..., and was in use by ",
" the ... |
[
"MechE's: Gear design question"
] | [
false
] | null | [
"Gear design is actually a rather large, complex topic. I'd suggest you start out by reading the ",
"Wikpedia page",
" and ",
"Engineer's Edge",
". You can also search youtube for videos on \"gear design\" or \"mechanical elements\". And of course there are numerous ",
"textbooks",
"."
] | [
"Nice try. -His real TA"
] | [
"Nice try. -your TA"
] |
[
"How do the poisons of Poison Dart Frogs kill?"
] | [
false
] | So, after I learned the basics about Poison Dart Frogs, I got really interested in how exactly their poisons kill us. Right now my knowledge is limited to Batrachotoxin, but If you can teach me about Epibatidin or Pumiliotoxin I would also be grateful. I know the basics ; their Batrachotoxin bind to the Na -channels, a... | [
"I actually had to look this up. I was getting prepared to correct you in a very stringent manner (AKA call you a dumb ass), because I though Batrachotoxin BLOCKED Sodium channels (Most of those toxins do, eg tetrodotoxin, saxitoxin etc). But it turned out I was the dumb ass, and you are exactly correct.",
"Thou... | [
"Thanks for the explanation, you perfectly explained my main question :)",
"But I have follow up questions;",
"This",
" article states that BTX is binding to PHE1236 via π-π stacking. How exactly are they binding? Are there just Van-der-Waals powers and Hydrogenbridges which hold these together?",
"And if... | [
"It's probably not a single interaction that contributes to binding. For example, ",
"this paper",
" makes a case for electrostatic interactions being significant.",
"How exactly are they binding?",
"The authors are making a case for ",
"pi stacking",
". Some aromatic molecules (or portions of molecul... |
[
"When will we see the next significant comet with the naked eye?"
] | [
false
] | [deleted] | [
"No for fucks sake! Never ever look directly into the sun (ever), it can damadge your eyes irreparably. And since Venus is very small, you won't see the little dot anyways.",
"Build a projector (i.e. a sheet of paper behind a teleskope) or buy some good filters. ",
"http://solar-center.stanford.edu/observe/",
... | [
"No for fucks sake! Never ever look directly into the sun (ever), it can damadge your eyes irreparably. And since Venus is very small, you won't see the little dot anyways.",
"Build a projector (i.e. a sheet of paper behind a teleskope) or buy some good filters. ",
"http://solar-center.stanford.edu/observe/",
... | [
"You didn't miss much. ",
"Halley's in 1986",
" wasn't a great show because its orientation was not favorable for viewing from Earth. We really don't know when the next great comet display will occur. But if you are willing travel, you'll have a better chance of seeing one. For example, Comet ",
"C2006 P1",
... |
[
"New Horizons was launched on Jan 2006 and passed Mars on April 2006 - why, in weightless space, can't we make a shuttle arrive just as quickly - instead of ~150-300 days?"
] | [
false
] | I dont understand why a satellite can do this but a shuttle can not. With the exception of escape velocity (which will take more fuel for a shuttle) once you pass the outer layers of our atmosphere you are weightless - why cant we achieve that speed? Is it because of the suns gravity - and that the shuttle is bigger? | [
"Being likely far more massive, both become more expensive actions, and the more fuel required to do either action increases the weight even further.",
"For reference, New Horizons was launched on an Atlas V 551, which is the most powerful version of the Atlas V (it has 5 solid rocket boosters attached to it). Th... | [
"once you pass the outer layers of our atmosphere you are weightless - why cant we achieve that speed?",
"Weightlessness is a state achieved when no force other than gravity is acting upon you. When a vehicle is accelerating/decelerating, that force will be acting upon you, and you will not feel weightless. You w... | [
"The shuttle is bigger. A LOT bigger.",
"New Horizons is a very light spacecraft-- about the size of a grand piano, launched from a very powerful rocket. It was the combination of the two that made it travel so fast, faster than anything else humanity had ever launched. New Horizons does not have enough propel... |
[
"If higher spatial dimensions could be visualized, then would all of their axes be perpendicular to each other?"
] | [
false
] | If I were an N dimensional hyper-being with a protractor, and I measured the angle between ever pair of the axes of the N dimensions, would all of the angles be 90 degrees, or is there a more abstract notion of what it means to be perpendicular in higher dimensions? | [
"Two vectors are orthogonal if their dot product is zero. This matches the familiar notion of perpendicularity in two and three dimensions. ",
"So, yes, the coordinate axes are all orthogonal to each other in any number of dimensions. "
] | [
"Linear independence is not enough to guarantee orthogonality. A set like {(1,0), (1,1)} forms a linearly independent basis for R",
", but the axes are definitely not perpendicular."
] | [
"The dimension refers to the definition of a certain manifold. Manifolds are generalizations of objects like spheres, cylinders, projective planes, etc. They don't look globally look like Euclidean space so there's no notion of global coordinate axes. So it really doesn't have to so with what I wrote in the top le... |
[
"Let's say I poured 100 gallons of water into the Mississippi River at its headwaters in Minnesota. How much of that water actually makes it to New Orleans, 2500 miles later?"
] | [
false
] | Let's say I poured 100 gallons of water into the Mississippi River at its headwaters in Minnesota. How much of that water actually makes it to New Orleans? The only factors that I can think of that would lead to water loss would be evaporation and osmosis into the groundwater. Is there any way to quantify what perce... | [
"and nobody around here would ever drink from it",
"You may think that, but your water company seems to think otherwise: ",
"http://www.swbno.org/documents/reports/2011_qualitywater.pdf",
"\"Our source water is the Mississippi River, a surface water source...\"",
"In all likely hood you have been drinking M... | [
"The only factors that I can think of that would lead to water loss would be evaporation and osmosis into the groundwater. ",
"Sure, if you ignore all the people that take water out of it. ",
"Communities up and down the river use the Mississippi to obtain freshwater and to discharge their industrial and muni... | [
"Excellent point. I'm in the lower Mississippi, and nobody around here would ever drink from it, at least if they wanted to stay healthy. I didn't think of that."
] |
[
"If all humans vanished at this instant, what human created process/invention would continue functioning the longest and why?"
] | [
false
] | null | [
"Hypothetical questions like this would be more appropriate for ",
"/r/AskScienceDiscussion",
"."
] | [
"Xposted. Thanks"
] | [
"Hi the_boddu 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 follo... |
[
"Effect of Obstacles such as wood and glass on Radio waves"
] | [
false
] | I conducted an experiment to find which obstacle affect most on radio waves. I used 3 obstacles: wood,cement brick and glass. I placed these obstacles between a remote control car and its remote and measured the time car takes to complete a particular distance. my results showed that wood showed most interference and g... | [
"I'm confused about your experiment. The car's speed should not have much to do with the signal it is receiving, unless it is just not receiving a signal at all and isn't moving forward.",
"Where the obstacles the same thickness? Were they the same in every dimension? If not, then your experiment is invalid for t... | [
"No one has mentioned this but are you sure the car is radio controlled?",
"Most RC cars are infrared and this changes the question a good bit. Please clarify if you are assured that your RC car is not IR and is indeed radio controlled. Often this is associated with the original cost of the RC car, more expensive... | [
"It would depend on a few things that you have not measured. It would depend on the frequency of the radio wave (The wavelength ), as well as the size of your obstacles. ",
"This is where the two come together; If you have an AM Radio wave at 1MHz, with a wavelength of 300m, and it is passing by an obstacle that ... |
[
"How do authenticators (2-step authentication) actually work?"
] | [
false
] | I've been curious about how to build an authenticator (e.g. Google Authenticator, Battle.net Authenticator, etc.) I understand the basic ideas, that a server and your device both have a pseudo random number generator seeded with the same value; but how do they not get out of sync/resync (e.g. If your device is unpowere... | [
"There are two methods, both using ",
"Hash-based message authentication codes (HMACs)",
". The first algorithm, called HOTP, uses a counter to generate the code and increments the counter when a password is used. The other method, called TOTP, is pretty much the same except the current time is used instead of ... | [
"Right. I'll make sure to never take my Blizzard authenticator with me on ISS trips. "
] | [
"I suppose there is a pseudo random number generatr which just spits out the next \"random\" number each time you need to authenticate. The server just does the same then. It only needs to sync once at the beginning, with both getting the same seed, will always spit out the same numbers then."
] |
[
"How can 2 black holes possibly merge? Wouldn't one black hole have to \"pull something\" into itself? But if the other blackhole doesn't give up matter... then there is nothing to \"pull in\"?"
] | [
false
] | [deleted] | [
"Layman here - My biggest roadblock to understanding black holes for a while was the overloaded term 'matter'. When talking about black holes, there are no fermions inside the event horizon, 'matter' and 'mass' refer to the energy content of the singularity.",
"Experts - do I have this right?"
] | [
"There's no matter to grab onto. ",
"This is the mistake in your thinking.",
"The mass that falls into a black hole still affects the outside universe via gravity. If our sun magically poofed into a black hole the earth would continue to orbit it same as it is now. The mass of the sun would be present in the ... | [
"They are \"falling\" into each other. I suppose you could say the smaller one is falling into the bigger one if it helps you think about it but that is not a distinction worth making for this. Each one attracts the other under the same rules of gravitational attraction followed everywhere else in the universe. ... |
[
"Particle and radioactive decay"
] | [
false
] | I might have asked this question before, but I don't understand decay processes. First, I understand what it means that radioactive decay is spontaneous. However, my brain still takes issue with that whole thing. I guess the key is to say that any unstable particle doesn't really have a way of knowing how old it is, an... | [
"Say you've got 100 dice laid out on a table. At the end of each hour, you're going to roll all of them and then remove all the ones that land on 1. Say you start at noon, and so at 12:59 you roll all 100 and on average one sixth of those land on 1, and you remove those from the table, leaving 100 * 5/6 dice. Th... | [
"And since the only assumption ikacer made about the way the atoms decay is that the probability of decay (per unit time for a single nucleus) doesn't change over time, this shows that the exponential distribution is the ",
" continuous distribution that satisfies this condition.",
"If the atoms decayed in some... | [
"And since the only assumption ikacer made about the way the atoms decay is that the probability of decay (per unit time for a single nucleus) doesn't change over time, this shows that the exponential distribution is the ",
" continuous distribution that satisfies this condition.",
"If the atoms decayed in some... |
[
"Are there studies of animal geniuses - animals that have intelligence far beyond what is considered to be average for their species?"
] | [
false
] | [deleted] | [
"Wikipedia has a brief ",
"section",
" on this. ",
"Hopefully someone else can help more."
] | [
"Please keep top level comments scientific. Also he is asking if there are exceptional cases of intelligence among a species, not asking if a species as a whole is intelligent."
] | [
"Please keep top level comments scientific. Also he is asking if there are exceptional cases of intelligence among a species, not asking if a species as a whole is intelligent."
] |
[
"If dividing by zero is undefined and causes so much trouble, why not define the result as a constant and build the theory around it? (Like 'i' was defined to be the sqrt of -1 and the complex numbers)"
] | [
false
] | null | [
"There are number systems which do just as you describe. Here are two (I don't know of others) such examples of this:",
"https://en.wikipedia.org/wiki/Projectively_extended_real_line",
"https://en.wikipedia.org/wiki/Riemann_sphere",
"The latter is the extension by defining z/0 in the complex plane.",
"A lot... | [
"There are many good answers already, but I think there's a simpler one that has to do with inverses.",
"An inverse is a sort of mathematical undo, it reverses the action of some function.",
"Instead of thinking of division and subtraction as operations, think of them as inverse multiplication and addition.",
... | [
"Another system that works out just fine is what comes out of ",
"Graphical Linear Algebra",
". There, if you try to divide by zero, you end up with another object, which is labeled ∞. But then as it turns out there are two other “infinities” that show up if you play around with 0 and ∞, which show a bunch of c... |
[
"Why do big cats like lions have round pupils and domestic cats have slits?"
] | [
false
] | null | [
"http://www.reddit.com/r/sciencefaqs/comments/ljrpm/why_do_some_animals_have_slit_pupils/"
] | [
"Not all big cats have rounded pupils just to be clear.",
"The reason for this difference is one group of cat evolved for daytime hunting while another evolved for nighttime hunting. The round pupil is better for the day while the slits of nocturnal hunters catch light better. "
] | [
"Wow cool!"
] |
[
"Why don't solids merge when pushed against each other?"
] | [
false
] | Torn paper I can understand. But what about two crystals? As far as I understand, they're perfect molecular arrays. Let's assume that they are. When two of those are pushed together, what keeps them apart? Or would they actually merge if pushed hard enough? | [
"That's a good question.",
"Most crystal surfaces have an atomic-scale reconstruction, though -- that is, the atoms in the few layers closest to the surface rearrange themselves due to the presence of the surface. Take diamond, for instance. Do you think that all the surface atoms are just sitting there with two ... | [
"Some can. If you take 2 pieces of gold leaf and stick them together, you will end up with 1 piece of gold leaf. It is called cold (or contact) welding. The 2 materials have to be the same though."
] | [
"Solids can most easily be thought of as a mesh of molecules. They are solid becuase this mesh has formed in a stable and strong way. Even the molecules on the edge of the solid are still locked in very neatly and tightly to all the others inside it. Therefore, there is no reason that merely placing another solid n... |
[
"What would be the psychological effects of prolonged (weeks, months) sensory deprivation?"
] | [
false
] | [deleted] | [
"If you are talking complete sensory deprivation, it could not be possible without complete starvation. ",
"It is often noted that those who are within the likes of an induced coma provide their own 'subconscious' sensory processes in a dream like state to combat any possibility of complete loss of senses."
] | [
"It is often noted that those who are within the likes of an induced coma provide their own 'subconscious' sensory processes in a dream like state",
"Interesting - I wonder if that's what normal dreams are for? Perhaps part of the brain keeps wanting stimulation after a while, hence the constant cycle between REM... | [
"Would an IV be any different than feeling an itch on your skin and scratching it? And what about hair follicles? Do those just stop itching?"
] |
[
"Is there evidence that markets without strong intellectual property laws produce fewer creative goods?"
] | [
false
] | I have heard that places like China often ignore copyright and patents on products. Is there evidence that shows that these countries produce less original work? As an example, do countries without strong copyright enforcement write fewer books? Do books that are written still make any money? Is there production of mus... | [
"This TED talk",
" discusses evidence from the fashion industry regarding creativity without strong intellectual property protection.",
"Fashion is still a highly creative industry despite lacking strong intellectual property. But once consequence of the lack of patents is that designers plaster their logo all ... | [
"Related: historian Eckhard Höffner claims the contrary, that the rapid growth of German Industry at the 19th century was due to lax copyright laws, leading to more books written and read (see ",
"this media report",
"; some anti-copyright texts on the web seems to be based on it, like ",
"this",
")",
"I ... | [
"Great example, thank you!",
"Fashion has a low cost of creation compared to a big budget film or a new drug. I wonder to what extent this scales up to higher developmental costs.",
"One of the points made was that the copies can be inferior to the original, how do you feel this applies to exact copies like boo... |
[
"What determines which electrons are boosted to a higher orbital when atoms become excited?"
] | [
false
] | I know when you give an atom energy, electrons can go to a higher orbital that has more energy because the electrons express the energy change in atoms, but which electrons change orbitals? | [
"First of all, there needs to be an energy level with the correct energy difference for the light's frequency: E_final - E_initial = h*frequency of light. Also, there are often constraints on how the angular momentum or other quantum numbers can change called ",
"selection rules",
" which constrain which transi... | [
"We can't tell the exact electron that makes the transition, but we can narrow it down. With various high resolution spectroscopic techniques, eg XPS, we can tell the exact transition which narrows it down to one of the few electrons in that shell."
] | [
"We can't tell the exact electron that makes the transition, but we can narrow it down. With various high resolution spectroscopic techniques, eg XPS, we can tell the exact transition which narrows it down to one of the few electrons in that shell."
] |
[
"How do we know a fundamental particle decaying into another does not reflect/show that it is not actually a fundamental particle?"
] | [
false
] | null | [
"It's not what it decays to that tells you about compositeness. What ",
" tell you about compositeness is the form of the probabilities for the processes (such as cross-section for scattering, and decay width for decay). Typically you can predict almost exactly these probabilities if you assume the particles are ... | [
"What we use to know if a particle is fundamental is not particle decays--we use scattering experiments--slamming particles into each other. If the particles have an internal structure the \"explosion\" pattern of bits and pieces will be much different that if the particle behaves as a point (and is thus fundament... | [
"In essence, yes--although weakly interacting particle (like neutrinos) can be lurking. So based on our current understanding we can \"Sweep\" for new particles. ",
"I think the upper limit right now is around 10 TeV. In reality since the particles are generally (thank you for point this out in the replies) pr... |
[
"Are there any planets found that have rings that spin perpendicular to its axis of rotation?"
] | [
false
] | null | [
"No, none of the planets in our solar system have this and we aren't able to closely study the ring systems of exoplanets yet. ",
"That said, it's possible. If a moon that orbits retrograde to the rotation of its planet (like Triton) were to break up for one reason or another, it could form a ring system that orb... | [
"Probably not originally a moon at all. Triton resembles Kuiper belt objects, and our best guess is it came from there. In order for a planet to capture a moon the size of Triton is has to slow down a LOT. We used to think it hit something else passing by Neptune or collided with an existing moon of Neptune's, but ... | [
"and we aren't able to closely study the ring systems of exoplanets yet. ",
"We probably found a ring system around ",
"J1407b",
" - but we didn't even see the planet yet, studying the rotation of either is beyond our current capabilities."
] |
[
"If friction is only equal to the Normal force multiplied by the coefficient of friction, it implies that size of the surface area in contact has no effect. Then why do sports cars have fat tires and big brake disks?"
] | [
false
] | I'm studying engineering and this has been bugging me since school science. | [
"Few things:",
"Often the larger area has a second purpose. For brakes this would be spreading out the heat produced by friction.",
"Tires slipping on pavement are exceeding the sheer strength of the rubber. That's why you see tire marks on the road as a tire skids to a stop. The sheer strength of a tire ",
... | [
"I am not satisfied with the heavy wooden box vs a cart example. ",
"The cart is easier to move because of the rolling motion of the wheels. I don't think this has anything to do with the contact area being less.",
"Let's assume that the wheels of the cart are locked so that they don't roll. Even though the c... | [
"I am not satisfied with the heavy wooden box vs a cart example. ",
"The cart is easier to move because of the rolling motion of the wheels. I don't think this has anything to do with the contact area being less.",
"Let's assume that the wheels of the cart are locked so that they don't roll. Even though the c... |
[
"Would a d.c supply and an a.c supply of the same quoted value supply the same power to a given resistor?"
] | [
false
] | [deleted] | [
"Depends on how the value is quoted. If the value is RMS voltage, then yes (long-term average), since the power dissipated in the resistor is proportional to V",
" . If it's peak voltage, then no."
] | [
"We actually quote the AC voltage value in RMS for that exact purpose, its the DC equivalent for resistive load."
] | [
"To add to this: most common real-world devices do use the RMS voltage."
] |
[
"Do different intensities of light travel different distances? For example would my phone light travel as far as the light emanating from a star?"
] | [
false
] | null | [
"Yes, and no. ",
"Light can go indefinitely. You phone light could go 1000s of light years away. The intensity though decreases as that of an surface area of a sphere though. Imagine drawing on a ballon and then inflating it, lights fades like this. So yes, any light source can go on for infinity, though it's int... | [
"Awesome explanation, thank you so much!"
] | [
"Photons are photons. However, emitted from a source they spread out with distance and so appear fainter the farther away you are... the more photons emitted and/or the tighter the focus the more \"visible\" the light will be at all distances."
] |
[
"Does the saturation of one substance in water affect the amount of a different solute that can be dissolved in that same cup of water?"
] | [
false
] | For example, if I brew a pot of coffee, some of the coffee grinds are obviously absorbed by the water, this creating coffee. But, does that mean my cup of coffee will be able to dissolve less sugar (or some other solute) than a regular cup of water would (assuming all other things are equal)? Or is the amount of sugar... | [
"Yes, there can be overlapping influence. One example is the ",
"common-ion effect",
". For instance, adding sodium chloride to water reduces the solubility of silver chloride in that solution because it already contains chloride. "
] | [
"Solubility of a particular substance can also be affected by the ",
"ionic strength",
" of the solution, meaning dissolved solutes can have an effect beyond chemical equilibrium."
] | [
"In general, for any solvent to dissolve anything, at least a single layer of solvent molecules on the surface of each solute particle has to be available. Usually, more than a mono-layer is needed. So yes, in general, solubility depends on what is already dissolved in the water.",
"However, coffee is probably a ... |
[
"What SI units are used to measure the highest levels of ionizing radiation?"
] | [
false
] | Hi, everyone! So, I'm a volunteer firefighter with an interest in hazardous materials response. One of the aspects that I've always wondered about is the radiological side of things. I've done extensive research into nuclear disasters such as Chernobyl and Fukushima and have always pondered this question. I'd greatly a... | [
"As you've probably found, there are lots of different units for radiation and the unit used will depend on the exact situation and equipment being used ",
"For the purposes of health and safety the relevant quantity is \"effective dose\" and the SI-derived unit is the sievert (Sv). An older unit still often use... | [
"So there are two SI units (gray, Gy; and sievert, Sv) and two US units (rad and rem). A gray is one joule of radiant energy deposited per kg of stuff irradiated, and 1 Gy = 100 rad. ",
"Sv and rem multiply the dose by some factors that depend on what kind of radiation it is, because alpha, beta, and neutron radi... | [
"Don't forget becquerels (Bq), decays per second"
] |
[
"Why does the immune system fail to fight off some infections?"
] | [
false
] | I am not talking about HIV or any diseases that attack the immune system. Is it just because the rate of reproduction is faster than the speed of the immune system's defense? | [
"Some microorganisms have developed ways to bypass the immune system. Some bacteria are intracellular and thus harder for the immune system to target, others produce toxins that effectively kill lymphocytes. There are many ways for the microbes to trick the immune system."
] | [
"Infections occur when an organism successfully bypasses the physical and immunological barriers, and starts to multiply.",
"1",
" So in a way, having an infection in the first place is a result of the microorganisms multiplying faster than the body's defences can manage. They manage this due to certain propert... | [
"Thanks a lot! Really helps."
] |
[
"Do cellulose based plastics pose any of the same hazards as petroleum based plastics?"
] | [
false
] | If not, is the only reason for not switching to primarily cellulose plastic money? | [
"Cellulose-based plastics were some of the first \"plastics\" discovered. Although there are constant innovations, the cellulose backbone just doesn't work in all the situations we need it to. That's why we made others. Further, many of them are not biodegradable and most require petrochemicals to make anyway."
] | [
"License plate nerd here. Illinois made them until 1948. I have also heard many stories of animals eating them off cars. They were more like a heavy fiberboard material rather than what we would think of today as plastic (they were more similar to the temporary cardboard tags some states issue, but thicker and wat... | [
"License plate nerd here. Illinois made them until 1948. I have also heard many stories of animals eating them off cars. They were more like a heavy fiberboard material rather than what we would think of today as plastic (they were more similar to the temporary cardboard tags some states issue, but thicker and wat... |
[
"If we can see stars and galaxies like they were billions of years ago, shouldn't we be able to see either the beginning of time or the end of the universe if we zoom in far enough?"
] | [
false
] | [deleted] | [
"There's no need to zoom in. We can easily see light from the very first moment when the universe became transparent, it turns out this is just the cosmic microwave background."
] | [
"This is not correct, light gets dragged along with space-time, leading to gravitational red-shifting. The Cosmic Microwave backround is emission coming from the moment the universe became transparent (and thus light could travel from one region of the universe to another)."
] | [
"This is not correct, light gets dragged along with space-time, leading to gravitational red-shifting. The Cosmic Microwave backround is emission coming from the moment the universe became transparent (and thus light could travel from one region of the universe to another)."
] |
[
"Can a photon collide with another photon?"
] | [
false
] | null | [
"Yes, although it's a purely quantum effect that doesn't happen in classical electrodynamics, and it's been difficult to observe experimentally, see ",
"here",
". For low-energy photons however, to a very good approximation, photons pass through each other without interacting."
] | [
"I have zero experience with nonlinear optics, my only expertise is through the lense of quantum field theory."
] | [
"/u/Sirkkus",
"' answer is correct, but there's another way to answer your question. ",
"In free space, light waves normally travel through eachother without interacting, but light waves can interact if they are traveling through matter. In practice, this means that you can send two colors of light into a cryst... |
[
"Is there a massive black hole in the center of the universe where the big bang occurred?"
] | [
false
] | A friend claimed their are credible theories that state there is massive black hole in the center of the universe that serves as the "opposite and equal reaction" to the big bang. Is this true? | [
"Nope.",
"The cool thing is that (according to the benchmark model of cosmology supported by all astronomical observations made so far) there is no single place in the universe where the big bang occurred - everywhere is where the big bang occurred.",
"How is this? The big bang was not an 'explosion' in the sen... | [
"This is something that i have had a lot of trouble understanding, and the \"ant analogy\" makes perfect sense. This also seems to make sense when I hear things described such as \"the expansion is accelerating\".",
"So, it is kind of like when you pinch and expand your fingers in an image on an iPad? Every exp... | [
"Check 'A Universe from nothing' by L. Krauss on youtube"
] |
[
"Watson and Crick"
] | [
false
] | I recently read The Double Helix for genetics, and was wondering how they were able to derive the structure from the X-ray crystallography images they had at their disposal. | [
"Here's a great guide in the DNA learning center that goes through, step by step, how to interpret the diffraction spectrum of B-form DNA:\n",
"http://www.dnalc.org/view/15014-Franklin-s-X-ray-diffraction-explanation-of-X-ray-pattern-.html",
". ",
"It's the iconic crystallograph made by Rosalind Franklin, whi... | [
"They had much more information at their disposal such as the relative chemical composition and the identity of the nucleotides involved, the fact that nucleosides (nucleotide + sugar) can be found. The crystal structure helped them deduce the chemical structure based on their knowledge of the parts. It's kind of... | [
"There are also conflicting accounts of the involvement of LSD, particularly by Francis Crick."
] |
[
"What is the fastest you can move from one side of a city to another?"
] | [
false
] | null | [
"Hypothetical questions are not suitable for /r/askscience",
"."
] | [
"That exact link points out that an example of a good question is \"If a body was left on the moon, how long would it take to decompose?\" which no different from my question. Both wonder what ",
" happen if this ",
" regardless of the fact that it hasn't occurred thus far. My question requires no speculation, ... | [
"It's listed as a better question simply because it attempted a clarification of an actual physical process. Also note:",
"Either case might need to be removed at moderator discretion.",
"In other words, you can simply just ask inquire about the maximum acceleration the human body can endure. As you yourself wo... |
[
"Can a bluetooth device tell how far away another bluetooth device is?"
] | [
false
] | The UK gov have made an app, which will apparently detect if you've come in contact with someone carrying covid-19, and alert you to isolate etc.. Can bluetooth/telephones even do this to any kind of accuracy? Or is this literally if it detects a bluetooth from another car on the m25, it'll register as a hit.. | [
"If you are referring to the bluetooth radios in two phones, held at random orientations, and at random proximity to other objects, then the measure of received signal strength (RSSI) is not sufficient for accurate distance measurement."
] | [
"the app is mostly for contact tracing rather than determining distance. if person a got tested and was positive, person b will get an alert telling them their phone detected the others phone at x point so you may have been exposed. its still useful for that purpose."
] | [
"Not really. The emission is not isotropically and neither is the reception efficieny. Bluetooth can be reflected off walls and other things (air ducts are amazing to transmit RF signals).",
"You can program something that acts like this would work (although I don't know, which phones let you access signal streng... |
[
"Why do most animals have their eyes, nose, and mouth clustered together in roughly the same way as other species?"
] | [
false
] | Why are the eyes usually horizontally aligned, with a nose centered on the face and a mouth slightly below? What are the benefits of this over say having the eyes and the mouth on opposite ends of the body? | [
"This doesn't answer ALL the factors you asked about but:",
"You're right, the typical configuration isn't the ONLY solution to the above (and other) requirements riddle, but it's a pretty darn good solution - and evolution is ",
" much a fan of \"if it's good enough, that's good enough\"."
] | [
"Just to add; you’re generally able to identify whether an animal is a hunter or prey by the position of their eyes. ",
"A hunter will have two eyes facing directly forward. This allows for binocular or stereoscopic vision, which allows an animal to see and judge depth, something having two eyes is important for.... | [
"The things he listed are second degree advantages, the ability to function paralysed would not be selected for from an evolutionary standpoint.",
"",
"Evolution happens in degrees. For example digestion. The first tube worms had a simple gut that ran from the mouth at the front to the anus at the back. As evo... |
[
"We know that certain stars are \"hundreds of millions of light years\" away, but how do we know this?"
] | [
false
] | Clearly we do not have a meter stick that is hundreds of light years long. So what technique do we use to measure these great distances? Does it have something to do with radio waves, or colors? | [
"We have many methods depending on the distance of the object. For close objects we can bounce radio waves off of them, for more distant ones we can use something as simple as geometry. ",
"Here's a diagram of one of the methods we use",
" that relies on a phenomenon called ",
" which we can use for most mid-... | [
"AU (Astronomical Unit) is a measurement of length equal to the mean Earth-Sun distance, which is exactly 149,597,870,700 meters (92,955,807.273 mi)"
] | [
"First, using Parallax as the Earth orbits the Sun can work for measuring absolute distances to nearer stars. ",
"Then you note that Type 1a supernovae have a predictable brightness. Measure brightness, get ",
" distance. ",
"Use parallax to measure distance to a type1a supernova and you have a \"fixed candl... |
[
"How do car and cd scratch removers work?"
] | [
false
] | [deleted] | [
"If the surface of a cd is scratched deeply enough to damage the actual stamped or burned pattern, you're out of luck. If, however, the scratches are superficial and only disrupt the reading of the tracks, you can attempt to improve readability by grinding off a tiny layer of the surface, so that it is smooth again... | [
"CD scratch removers operate the same way that windshield cracks are removed: they're in fact filled in by a clear polymer (in the CD's case, probably the same polymer that makes up the clear part of the disc). The surface is made smooth again, and your CD (or windshield) looks brand new!",
"The data on a CD is s... | [
"As you may imagine, CD drives use light to read the CDs, so if the clear plastic that covers it is scratched, you can try to fill the scratch or grind a bit the plastic to even out the surface. Like a prism, if the surface isn't even enough, the light will bounce to somewhere else.",
"Same thing with the car pai... |
[
"Why do I get that high pitched ringing in my ear occasionally?"
] | [
false
] | null | [
"It's probably a mild case of ",
"tennitus",
". Nothing to be too concerned about, unless it becomes so constant that is is distracting and affecting your quality of life. Don't let the wiki article scare you too much: While it can be a symptom of the listed illnesses, it's more likely that you just have some m... | [
"It's called auto-acoustic-feedback and it is really cool. Basically though, your cells themselves are making noise in your own ear."
] | [
"We don't do that in this subreddit."
] |
[
"How is body temperature controlled?"
] | [
false
] | The body regulates it's temperature, right, we all know that. But surely apart from the sensors on the skin, there must be an internal thermometer? Where/what is this? Secondly, how is the body temperature calibrated? How does it know when it's cold and hot? And more importantly what cold IS and what hot IS? | [
"It's the hypothalamus.",
"http://en.wikipedia.org/wiki/Hypothalamus",
"The body wants to maintain a homeostatic environment as much as possible and utilizes thermoregulation to do so... In short, controlling vasodilation and the body's metabolic rate have a LOT to do w/ it.",
"http://en.wikipedia.org/wiki/Bo... | [
"don't forget that our bodies enzymes have an optimal temperature, and if it exceeds that threshold they denature"
] | [
"Pay attention to his last link. The rest is distraction."
] |
[
"Are there any specific instructions for what astronauts are supposed to do in the event of something catastrophic happening on earth?"
] | [
false
] | null | [
"I was unable to find any information for you, but I have submitted this question to ",
"Ask NASA",
". I will post when I receive a response.",
"edit: ",
"the email I sent",
"edit2: (2/27/12) They never emailed me back..."
] | [
"I'm not sure what the people in space are supposed to do, but I do know there are instructions for people in ",
"submarines",
" in the event of a nuclear catastrophe.\n*EDIT: For those of you who like ",
"radio",
", here's a short discussion of the implications of this letter. There's also a ",
"link",
... | [
"No protocol, but given the specifics of the ISS, the crew will be 6 people, 2 Souyz vehicles docked at the station. Food won't be a problem for about 1 year given that something like the ATV just docked, and they do have fuel to stay on orbit (as they are LEO they have to constantly boost the orbit) for about 2 ye... |
[
"Questions about inertia and gravity"
] | [
false
] | My questions are as follows: * Question 1 :Do astronauts experience inertia in space, or is inertia purely related to gravity? * Question 2 :Recently, a new possible life-sustaining planet was discovered, Kepler 22, which is said to be considerably larger than Earth. If humans could ever travel the 600 lightyears to ge... | [
"1) Inertia is related to mass. If it has ",
"mass it has inertia",
". It's where the equation F=ma comes from.",
"2) Depends entirely on the mass and size of Kepler 22. ",
"F = G",
"m2/r",
"."
] | [
"For 1) you never feel inertia, but you will always feel a change in inertia (A force). And yes, you are always experiencing it, as it is one of the fundamental properties behind mechanics. (anything moving has and experiences it) (Note, I am talking about inertia as it applies to momentum. If you wanted to talk ab... | [
"Inertia is a property of mass with respect to an objective reference frame. All mass has inertia, regardless of where it is. ",
"The force of gravity you feel on a planet's surface is the sum of the gravitational acceleration due to the planets mass, and the rotational acceleration due to its spin (provided yo... |
[
"Since almost all European vineyards graft on to American rootstock which is resistant to phylloxera, if one didn't do this, would there still by phylloxera around to constitute a threat anymore?"
] | [
false
] | I guess the answer is probably that they eat other stuff too, but what though? And I guess by that same token, if there as a natural resistance formed in rootstocks in the Americas, how did the phylloxera survive over there to theoretically have managed to become accidentally imported to Europe? | [
"Resistant means that American rootstock tolerate phylloxera feeding on them. It does not mean that phylloxera can't or won't feed on them. ",
"As far as I am aware, grape phylloxera only feed on roots from the Vitis genera of plants (grapes). America has multiple species of native grapes, nearly all of which are... | [
"Grape vines do also have a production lifespan (production does start to drop off after a few decades)",
"Notably, old vines have fewer grapes, but the quality is higher. Young grapes actually need to have a lot of the fruit removed so that the plant puts more energy (sugar and flavour) into the remaining fruit.... | [
"Also worth noting that Australia has the oldest Syrah and Grenache vines in the world, as our crops weren't affected by phylloxera. Another reason we're strict on border entries."
] |
[
"Optical Physicists: How do you collimate the light out of optic fiber?"
] | [
false
] | If we have a 200 µm, 0.22 NA optical fiber, how do we pick an Aspheric Condenser Lens that will make our spot size roughly 400um? | [
"Thanks drzowie, projecting a 400um fiber tip using 2f of a lens is a great idea! Thanks for the insight!"
] | [
"Cool, I'm glad it worked for you!"
] | [
"You can't.",
"That is, you can't develop a fixed spot size by collimating the beam. The emissivity (brightness per unit are per unit solid angle) is constant, so even if you collimate your beam will subtend a finite solid angle.",
"The narrower the exit cone from the fiber, and the larger the final beam you'r... |
[
"Would babies grow to walk if everyone around crawled?"
] | [
false
] | I was bike riding the other day and passed a toddler running down his driveway and i thought to myself - Would babies learn to walk if everyone in the world was crawling? Crawling is somewhat natural, but i will assume walking is more natural and is self learnt? | [
"EDIT: Looks like feral children can walk, so it appears that walking is instinctual and not socially derived. My bad! I got some bad information."
] | [
"Genie",
" was able to walk, and pretty soon at that. We don't know how much practice she got from before the abuse, but it appears she was chained up her whole life. Yet she was able to walk just fine afterwards. Whereas she never was able to speak competently.",
"It seems to me that humans are naturally ab... | [
"Compelling argument."
] |
[
"Would it be possible to kick-start a brain when they are in a vegetative state? I would expect it to be a bit similar to the use of defibrillators."
] | [
false
] | null | [
"Maybe... but it isn't at all like defibrillation. Using magnetic pulses, there are some who hypothesize that we can \"stimulate\" neural functioning/regeneration. Still needs a lot of research.",
"http://www.coma.ulg.ac.be/papers/vs/Lapitskaya_TMS_2010.pdf",
" ",
"http://www.sciencedirect.com/science/arti... | [
"A brain is way more complicated than a heart and I don't think a defibrillator would work on a brain, even supposing the brain is not damaged. In order for someone to go into a vegetative state, a big part of the brain needs to be damaged beyond repair. Whereas a heart is just muscle which contracts in synchrony, ... | [
"Well a defibrillator actually stops the heart from fibrillating - essentially an arrhythmic spamming of the heart tissue. Since the brain isn't fibrillating in vegetative state (or ever) it isn't really applicable. The brain doesn't have a unique \"simple\" circuit like the heart does, but rather billions of small... |
[
"Ive heard that our universe is \"infinite\", if so, how can it also be expanding?"
] | [
false
] | null | [
"Check out ",
"these past posts",
" - this is a frequently asked question.",
"The short answer is that \"expansion\" doesn't have to be measured from the limits of the universe. All that means is the distance between two comoving points increases over time.",
"The analogy often used is this: imagine you hav... | [
"Good question. The expansion doesn't mean that the Universe is some box which is getting bigger, it means that the distance between any two points is increasing. Obviously if we measure that our galaxy and other distant galaxies are moving apart in a particular way, it doesn't matter whether the Universe is infini... | [
"There are a few facts that make the scientific community conclude this.",
"The known universe is expanding. The parts we can observe directly or indirectly. This has more to do with the limits of the speed of light than anything else.",
"The galaxies that make up the universe also appear to be moving away from... |
[
"When did we discover that the human body produced electricity?"
] | [
false
] | Any other details on this, like who and how, would be welcome. tia. | [
"We don't really produce electricity, we produce action potentials that travel along a nerve.",
"I am not too knowledgeable about all of this, but I believe one of the key moments was the ",
"giant squid axon",
" discovered at Woods Hole. Squids have a really large axon that travels down their body, and this ... | [
"I forgot about the frogs. I would suspect that someone noticed salty water could make muscles twitch as well, but I have no idea where to start looking."
] | [
"It goes back even farther than that. ",
"Luigi Galvani",
" (whose last name you might recognize) found that electricity could cause muscle contractions with his famous frog leg experiments back in the 1700's. Though he certainly did't have a complete explanation for this."
] |
[
"What is it that is \"oscillating\" in a light wave? Do light waves actually \"look\" like a sine wave?"
] | [
false
] | In a way, sine waves seem like a poor visualization of light. I'll use sound waves as an analogy to clarify my question. We use a sine wave on a cartesian plane to represent the variation of air pressure that we detect as sound. But of course sound waves don't go "up" and "down" perpendicular to their axis of propagati... | [
"It is the electric and magnetic fields that are oscillating. For a perfect plane wave, you could, indeed, represent both the electric and magnetic fields as a travelling sine wave."
] | [
"A sine wave is an accurate representation, but there is no \"wobbling\". I think the disconnect here is that you are thinking of a sine wave as something that goes \"up and down\", whereas it is more accurate to think of it as a function that increases and decreases. What is different about a light wave at diffe... | [
"The principle behind the workings of a Faraday Cage isn't that photons are somehow blocked by the physical structure of the cage, but rather with how the electromagnetic field interacts with a conductor. The EM field will cause free electrons in the cage to behave in a manner so as to make the enclosed field 0. ",... |
[
"Probability: Is rolling a double statistically similar to rolling a single die to match an arbitrary number?"
] | [
false
] | null | [
"In two rolls, there are 6 doubles and 36 possible rolls, so 1/6 chance of getting a double. For one roll that must match a given number, there is a 1/6 chance of getting that number. So yes. They have the same exact chance."
] | [
"I'll rephrase that a bit to tie the dice more closely together: The first die is how we determine the arbitrary number to match on the second die."
] | [
"Another way to look at it, the number rolled on the first die is irrelevant, we only care if the second die matches the first. Therefore the odds of rolling a double are equal to the odds of rolling any single result on the second die."
] |
[
"IS it possible for an amateur to build a planar array detector for a radio telescope to show positions of sources without scanning?(plans? Links?)"
] | [
false
] | IS it possible for an amateur to build a planar array detector for a radio telescope to show positions of sources without scanning?(plans? Links?) Basicly I want to see strong sources of radio waves in the sky without scanning the antenna. The planer array would be at the focus of a parabolic dish just as a light detec... | [
"Oh, you are asking for a CCD equivalent of for radio waves to get multiple pixels of the sky? This is basically not possible because radio waves are too big. The way radio images are made is by sampling one pixel at a time. Aricebo (the telescope Janus fell into in Goldeneye) had only one pixel for a really lon... | [
"Well, you can look at what is directly above you without scanning. You would just need to build some dishes, attach them to computers, write software to interpret the signals, and finally visualize the data somehow to see what is overhead!"
] | [
"yes. but that gives you a single point in the sky.(which you can scan or waite for the rotating earth to scan and then assemble electronically.",
"I am looking for a pixel array image of the sky."
] |
[
"What is the nueroscience behind LSD visuals?"
] | [
false
] | [deleted] | [
"Have a read of ",
"this free text-book",
". It has a few chapters on visuals. MAPS also has some ",
"excellent research",
" into all sorts of interesting things. "
] | [
"This is an active area of research, so I can't give you definite answers...but best guesses. ",
"Like you mentioned, most of the hallucinogenics involve interactions with the 5-HT2 receptor variants. These are scattered about the brain, but their actions have a large effect in the cerebral cortex. This is wher... | [
"I thought I saw someone in askscience a few days ago that talked about how people who have a 'better sense of direction' get less intense visuals, perhaps due to a higher degree of communication between those cells, but unless I come back with a paper take that with a grain of salt"
] |
[
"How do animals that live in totally different environments look similar, like scorpions and lobsters?"
] | [
false
] | null | [
"Arthropoda in general is an immensely diverse field and has a huge diversity of forms, so you're bound to find some with similar body plans. But how they evolve to that can be tricky, confusing, and misleading if they have evolved similar structures.",
"I'm assuming you mean why do scorpions and lobster have 8 ... | [
"This is the stuff I love. I was reading this going \"Huh!\" and \"Hmm...\" the whole way! You guys are awesome."
] | [
"Can you clarify? To directly answer your question, it's because ",
"scorpions and lobsters",
" share a distant ancestor; they're related, so they look similar to each other. ",
"That relationship (and their appearances) has everything to do with ",
"Parallel Evolution",
"If they were different species a... |
[
"Did locusts exist in hordes before agriculture?"
] | [
false
] | It seems like it would make sense that they evolved hordes after available food became concentrated (ie farms). | [
"When they're concentrated like that a \"swarm mode\" triggers. There's this entomologist who rubbed a locust's legs with a brush for 3-4 hours and it started to change colour. The swarming seems to be triggered by an already large population and coming into contact with other locusts continuously over a relatively... | [
"Is it really too short of a timespan when you consider these factors?",
"Yes. It's thought that swarming locusts migrated to the US about 6 million years ago. Studies on the phylogeny indicate some swarming & non swarming species have a common ancestor."
] | [
"It takes two weeks for grasshoppers to become adult and capable of reproducing. With such a short span of time between generations, it would make sense for grasshoppers to also adapt to the environment faster. Animals that live for a longer time have more stable environments and as such take longer to adapt to cha... |
[
"Where can I find a graph depicting the rate of information\\knowledge collected throughout human history?"
] | [
false
] | [deleted] | [
"This is trickier than at first blush, because we don't have as good a view into the past as we do the present, and when we do know about them, the past is often incommensurate with the present. That said, I recommend reading ",
", which provided the most detailed summary of the advancement of knowledge I've cam... | [
"You're going to run into some real problems with this.",
"People have tried to graph the progress of human knowledge, often using patents, computing power, etc. ",
"These graphs can be accurately made for something like computing power and Moore's Law, but for the grander historic view it's very subjective. ",... | [
"Your best bet would be to look ",
"here",
", which has a wide variety of charts of that nature. Measuring stuff like that is very hard though, because you're comparing very different things in most cases."
] |
[
"[Physics] when a star dies the explosion creates heavier element like gold and platinum. Is it possible to estimate the amount of a perticular element a star will make when it dies?"
] | [
false
] | null | [
"Absolutely, but its difficult. As others in this thread have said the yield of a specific isotope in a supernova will be a function of things like the starting composition of the star, the distribution of that composition and the degree of mixing between layers in the star, the time dependent temperature and densi... | [
"You are asking what I consider to be the single biggest open question in nuclear astrophysics. ",
" ",
"Let's start at the beginning. ",
"In (possibly) supernova, and (probably) neutron star mergers, there are a lot of hot protons and neutrons getting thrown out. These protons and neutrons clump together to ... | [
"a kilo, or a ton, or a megaton of gold",
"All of these are infinitesimally small amounts compared to the amount generated. It is likely a large number of orders of magnitude more than a megaton.",
"The earths crust has 0.004 ppm of gold in it and from google we can at least get an estimate that it weighs on th... |
[
"How do we know that the brain stops developing at 25?"
] | [
false
] | Is it around the same age for all people, even those with brain conditions? When was this number discovered? | [
"This is not true. The brain is continuously developing and changing through the course of a human being's existence. For instance, there are documented phenomena such as adult neurogenesis wherein certain portions of the brain continue to generate new neurons and connections well into adulthood."
] | [
"They mean the development/maturation of the prefrontal cortex, I imagine."
] | [
"But the major process of synaptic pruning runs into the mid-20s. After that, you can still have some neurogenesis and synaptogenesis and pruning, but it's not on the same scale.",
"https://www.newscientist.com/article/dn20803-brains-synaptic-pruning-continues-into-your-20s/"
] |
[
"Was there a notable difference in oxygen percentages in ancient human history (like 100,000 yrs ago) vs the ~20.9% of today?"
] | [
false
] | I was talking to someone about atmospheric oxygen levels, algae and land plant life are currently experiencing some issues, and apparently human brains die at around 19.5% oxygen (this part has been dealt with in the comments as incorrect information, thank you) I had mentioned this and they argued that oxygen levels w... | [
"The 19.5% seems wrong to me for death. I’m pretty sure humans can function at much lower oxygen percentages down to 15% or so and not die. Also, the body can slowly adjust to lower available levels. Otherwise people in Denver couldn’t live at 6000 feet. ",
"I’ve not run across an oxygen level vs history chart bu... | [
"Yes oxygen levels have varied, and your 19.5% level is wrong. Human lungs can extract oxygen down to about 10%, as has been found numerous times in many mining accidents. At levels lower than 16% we start to struggle, at levels below 12% we start to pass out. Levels below 10% are not survivable beyond several mi... | [
"Most of it came from marshes, bogs and swamps.",
"It was also much hotter and wetter back then. Lots of low, wet areas for marshland to form."
] |
[
"Could carbon dioxide ever freeze out of the air?"
] | [
false
] | Carbon dioxide has a melting point of -57C and a sublimation point of -79C. The coldest natural temperature recorded on earth was -89C. At this temperature could carbon dioxide naturally "freeze out of the air" and condense on the ground? | [
"The coldest natural temperature recorded on earth was -89C",
"Yes this is true, and at Standard Temperature-Pressure this is cold enough, but this recorded temperature was also at Vostok, Antarctica which is at 3288m elevation, meaning the air pressure is slightly lower. The sublimation point of -79C is only tru... | [
"CO2 is about 0.04% of the atmosphere so its partial pressure is about 0.4 mbar. You would need to get well below -100C before any CO2 will be coming out of the atmosphere."
] | [
"So when I'm reading a Temperature-Pressure Diagram, is it only the partial pressure of the substance in question that matters?",
"I was going on the assumption that since it's just mixed in with air, the entire mixture is at 0.54 atm or ~547 mbar.",
"This is by no means my area of expertise."
] |
[
"What is the environmental impact of lithium mining?"
] | [
false
] | Lithium ion and lithium polymer are the most common batteries used today in EVs. With the increase in EV production, how does lithium mining’s carbon footprint and overall environmental impact compare to traditional petroleum based cars? | [
"Carbon emissions due to lithium mining are from high energy usage. Batteries right now have a very high carbon footprint because they are mostly build with chinese coal power. Using regenerative energy sources instead can reduce these emissions significantly. While reducing fossil fuels carbon emissions is extreme... | [
"While the initial carbon footprint of EV is supposedly higher due to their batteries, the batteries don't need to be replaced every few days like a tank of gasoline. Over the life of the vehicle, EVs are still better, though not the end all solution. Battery recycling needs to get better and spread. Charging of EV... | [
"And there are a few places where they want to actually generate geothermal energy while mining lithium.",
"Look up the Salton Sea in California. They think they can get lithium out of the superheated salt brine and use the heat to generate electricity. ",
"It was talked about in a podcast (How we Survive by Mo... |
[
"Why is it recommended to eat a lot of fruit, but it is not recommended to eat a lot non-fruit sweet snacks? Is fructose better than other kinds of sugar?"
] | [
false
] | null | [
"And the aspect of fiber comes to mind. Fruit has fiber which is very much needed for the digestion process. A bar of chocolate - not so much."
] | [
"And the aspect of fiber comes to mind. Fruit has fiber which is very much needed for the digestion process. A bar of chocolate - not so much."
] | [
"It's all the other things besides sugar that is why it's recommended. Eating whole fruit also comes with fiber and various vitamins and the like. ",
"Fructose by itself is suspected to be not very good for the human body.",
"https://en.wikipedia.org/wiki/Fructose#Potential_health_effects"
] |
[
"How do topical creams affect bacteria etc below the skin after they've dried?"
] | [
false
] | I read about a chemical in anti-acne cream I use, Benzoyl peroxide, and that it primarily works by killing bacteria under the skin, but I have to ask how does this work after its dried onto my skin? Is it because the skin absorbs a certain amount as it dries? If that's the case, why does it keep working after the ointm... | [
"Benzoyl peroxide is an oxidising compound, it’s best thought of as chemically disrupting bacteria. The ointment is only actually typically between 2.5 and 10% benzoyl peroxide, this is only sparingly soluble, so needs to be carried in something else for you do be able to put it on at the correct dose. It’s this ... | [
"Like all oxidising compounds it’ll react with pretty much any organic material available. Including your own skin, that’s why it provokes irritation sometimes. Once it’s reacted it ceases to work, and so you need to keep putting it on to get an effect. It’s a rate related thing, so you need to follow the instruct... | [
"If it’s good while dried why do the instructions have you apply it multiple times?",
"How does the chemical above the skin reach the bacteria under it if the hardened ointment isn’t physically reaching through the layers of skin? In other words how does it reach the bacteria without physically going deep enough ... |
[
"Does everyone have the same number of muscle cells?"
] | [
false
] | Currently in a human biology course, we learnt that past a certain point, myocytes can no longer divide and their number stays stable. My question is, assuming none of the muscle cells would die, would their number be the same for everybody? If not, is this difference linked with different body types (e.g. people who g... | [
"Not at all. Muscle cells can under go hyperplasia (increased cell number) and dystrophy (ie. muscular dystrophy which can be caused by a loss of muscle cells.",
"Depending on the use and disuse of the muscle, either of these can occur. Although, in terms of hyperplasia, muscles generally under go hypertrophy (in... | [
"Interesting. In which cases can hyperplasia occur?",
"Also, I'd like to reformulate my question to be sure of the answer : Do all of us have the same amount of muscle stem cells to begin with?"
] | [
"Most likely not. There are so many factors during development that really depend on the environment, and the genetics off the individual that can influence the numbers of cells.",
"Hyperplasia tends to result from imbalances of growth signalling, and can cause a lot of problems within the body, and can even be a... |
[
"Books on cosmology?"
] | [
false
] | null | [
"There's quite a good episode of BBC horizon that came out recently called 'how big is the universe'. it's on iplayer if you are in the uk or can get access to it."
] | [
"Thanks for the suggestion.\nI´m in Sweden though, But I´m sure i can find it somehow."
] | [
"What level of mathematics are you at? If you have a decent background in calculus and diff eq, Barbara Ryden's intro text is a very easy read. (Even without the math, you'll get something out of it.)",
"http://www.if.ufrgs.br/oei/santiago/fis02012/Introduction-Cosmology-Ryden.pdf",
" (5 MB .pdf)",
"For more... |
[
"Can anyone help answer this special theory of relativity problem from my friend on Facebook?"
] | [
false
] | A friend of mine asked this question on Facebook and we have no answer. Hope someone here can help. "So I've been thinking a lot about special relativity lately, and I seem to have stumbled across a paradox that I simply can't make sense of, so maybe one of you can help me. According to Einstein's Special Theory of Rel... | [
"I'm going to stop you here:",
"Spaceship A is going to experience a time dilation factor of 707.10695795%. That means, while the crew will only experience 1 year, by the time they get back to Earth, over 700 years would have passed for people on Earth.",
"This is incorrect. If they are travelling that fast, us... | [
"I hate to break this to you, but your friend doesn't know what he's talking about. Like, he has very little idea of how special relativity works. In fact, he doesn't even know how speed works because he keeps saying the slower one is faster.",
"Let's look at the situation again. Let's say there's a beacon that i... | [
"Lorenz factor has to do with matter compression, its a non issue.",
"Wow, this guy really doesn't know the first thing about Special Relativity. (Or even how Lorentz spelled his name)",
"The Lorentz factor is a term that appears in every equation of SR."
] |
[
"Using copper instead of ice in a cooler?"
] | [
false
] | If you froze copper piping and placed it in a cooler/ice chest instead of ice, would it last as long/work as well as normal ice? | [
"Even if we say the ice does not even melt it is much better than copper. Copper has a heat capacity of 0.385 J/g/K while ice has one of 2.11 J/g/K (",
"source",
"). This means that you need 2.11 / 0.385 = 5.5 times as much copper as ice to cool your drink the same amount."
] | [
"Ice cools well because of the heat required to change state from liquid to solid. Cold metal doesn't have that.",
"If the copper were cold enough such that it's potential energy equalled that of ice, it would be the same "
] | [
"Awesome. I was too tired to look up the heat capacity of copper vs ice."
] |
[
"Why are smaller animals more resistant to ionising radiation?"
] | [
false
] | null | [
"As far as I'm aware, we still don't ",
" know.",
"Compared to humans, we've known for some time that insects are generally more resistant to ionizing radiation, and multiple hypotheses have been proposed to explain this radioresistance.",
"For a long time it was thought that because actively dividing cells a... | [
"Thanks for this very comprehensive answer "
] | [
"I remember a genetics tutor I had talking about this. Someone had asked him some speculative question about organisms in higher radiation environments and whether they'd evolve faster and his answer was along the lines of \".... probably not, organisms seem to be able to dial up or down their DNA repair mechanisms... |
[
"In movies, there's frequently a standoff with two people pointing a gun at each other. Is human reaction time quick enough for the second person to get their shot off before dying if the first fires and hits them in the head?"
] | [
false
] | null | [
"Really depends on the guns and distance involved.",
"From one source, we see bullet speeds ranging from ~180 m/s (.38 special) to ~1200 m/s (.22 swift) (Petzal, 1992).",
"Eckner, Kutcher, and Richardson (2010) found that people respond to visual stimuli at ~270ms, but earlier studies found reaction times close... | [
"The danger doesn't really lie in the guy recognizing he's been shot at and shooting back ",
", it's that he shoots at you ",
" he's been hit, either from a spasm or voluntarily if you fail to kill him on your first shot. "
] | [
"Thanks! So, considering that many of these scenes have them considerably closer for dramatic effect, the logical move in most of these scenes would actually be to shoot."
] |
[
"Could you ride a bike down a really steep incline faster than you could free fall at terminal velocity?"
] | [
false
] | null | [
"Plus at those speeds you would need a spoiler or something to get you some down force so you can continue to get traction."
] | [
"Plus at those speeds you would need a spoiler or something to get you some down force so you can continue to get traction."
] | [
"Hmm, let's look at friction and power consumption. The slope has an angle alpha against the horizontal direction. If we move at the same speed as terminal velocity of a free falling biker we have mg of air resistance by definition. Countering that is gravity, F_g = mg sin(alpha) and our biker. In the easiest case... |
[
"Question about gravity and the expanding universe"
] | [
false
] | We live in an expanding universe, so I don't quit understand why galaxies collide. Would somebody please tell me how gravity comes into play in an expanding universe. Also, if gravity means that everything pulls on everything else, why is the universe expanding, and why is the rate of expansion increasing? | [
"Sure, good question. The answer is that the expanding universe requires tremendous distances to overcome gravity. ",
"Over short distances, gravity wins out. This is why Andromeda will be colliding with us in the not so near future. However, gravity is only so strong. The force of gravity dies out according to a... | [
"Good answer, but I just want to point out that dark energy and the metric expansion of the universe are two different effects both causing the universe to expand. Even if there were no dark energy, the universe could still be expanding. The effects of dark energy were only discovered about 10 years ago. We've k... | [
"The universe started expanding with the Big Bang, so I suppose you could say that whatever caused the Big Bang (still not really understood yet) caused the metric expansion. The gravitational attraction of all the stuff in the universe is actually slowing that down, but dark energy, which is a uniform negative pr... |
[
"What does the edge of the universe look like?"
] | [
false
] | [deleted] | [
"To the best of our knowledge, there is no edge. The universe either extends forever in all directions (this is the more likely case based on observational data) or is curved back around on itself in some way such that there isn't an edge (like the surface of a sphere or donut). While it's possible that there is an... | [
"Now, if you try to look as far as possible, you would come to the point where the \"time delay\" (not sure how to call it) is longer than the time our universe actuallay exists letting you see our universe how it was in the very first moments.",
"Not really. The furthest back you could see would be the surface o... | [
"Bu what could be interesting is that, if we could build a telescope able to let us see as far as we want to, we allthough could not do so. This is so due to the limited speed of light. Probably you know that everything you see is that thing from the past. For example you only see the sun how it looked like (approx... |
[
"Do people of different races have stronger immune systems?"
] | [
false
] | Human body, medicine | [
"Hey ",
"u/MattClarke123",
", that is a very complex question. Because it is mutable, the strength of a person's immune system has a lot to do with their environment (if \"strength\" is taken to mean ability to respond to the particular pathogens to which they are exposed). Meaning, my immune system may be perf... | [
"There's a popular theory right now that Europeans tend to have immune systems that are more resistant to AIDS than Africans, and that this is largely due to natural selection that took place when various epidemics such as the black plague swept through Europe. Supposedly about 10% of Euros have a mutation in the C... | [
"Yes! I think this is so interesting! ",
"Here is one such study,",
" that was done in the Hutterite population by investigators at the University of Chicago (I actually worked with this lab for a bit during my PhD at UofC). "
] |
[
"Are all living beings descended from a single, first living being?"
] | [
false
] | It seems to me that for a living organism to spontaneously appear among non-living matter is an incredibly rare occurrence that might only happen once in a million years here on Earth. Suppose that event did happen and the single living cell managed not to die and divide enough times that it produced a considerable num... | [
"There wasn't a spontaneous bang-heres-an-organism. The beginning was an ill defined mess of poorly self-replicating molecules."
] | [
"not unless you call the very first replicating molecules \"alive\", which I probably wouldn't (no more than I would call viruses alive and they are doubtless at least as complex as - and I expect far more complex than - the first replicators)",
"Replicating molecules would have gone through many stages of increa... | [
"I think what confuses people is that something being alive or dead are fundamentally arbitrary categories. Our definitions of life have mainly come about because of the medical benefit of categorizing things as living or dead. Life and death itself is a human construct and fundamentally nothing is truly alive or d... |
[
"What are the dangers of long term and continual inhalation of sulfur hexafluoride? (The gas that gives you a deep voice when inhaled.)"
] | [
false
] | First, the why: It's for a character we've developed for a performance group that would be served wonderfully with the deep voice that inhaling this gas gives you. There's plenty of information online about inhaling this gas in small doses, such as standing on your head to flush out your lungs and what not, but what a... | [
"I am not a doctor. This is not medical advice.",
"You might want to mix your gas with 21% oxygen. That way you won't asphyxiate. ",
"The ",
"MSDS",
" lists it as nontoxic, so you don't have to worry about acute toxicities."
] | [
"the gas is generally inert, it doesn't really react with anything. wikipedia says that as long as the gas is 20% oxygen (not 20% air, 20% oxygen), then you will not suffocate. having said that though, breathing large volumes of sf6 is not very smart. don't do it."
] | [
"If you have to ask, it's a terrible idea. Buy a voice modulator. "
] |
[
"What stops the atom from exploding outward since most of the space surrounding it is most space?"
] | [
false
] | I have heard that the space around an atom between electron orbitals is exactly that, space. So what are the forces that keep an atom together and stops it from wanting to fill that space by dispersing? | [
"stable atoms have electrons orbiting in stable orbits. It is similar to how we have a moon orbiting Earth, there were many other celestial objects that hit Earth and will hit Earth in the future, but the Moon is pretty stable.",
"This is really not a good way of explaining how an atom is structured. If this were... | [
"stable atoms have electrons orbiting in stable orbits. It is similar to how we have a moon orbiting Earth, there were many other celestial objects that hit Earth and will hit Earth in the future, but the Moon is pretty stable.",
"This is really not a good way of explaining how an atom is structured. If this were... | [
"You are contradicting yourself there.",
"On the one hand you say, that the electron has to be accelerated in order to stay in the vicinity of the nucleus, but on the other hand you acknowledge that accelerated charged particles emit energy.",
"\nThose two statements are not compatible. If both of them were tru... |
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