title list | over_18 list | post_content stringlengths 0 9.37k ⌀ | C1 list | C2 list | C3 list |
|---|---|---|---|---|---|
[
"How can a black hole have a spin?"
] | [
false
] | I've read that black holes are defined by 3 properties: mass, charge, and spin. My question is, since a black hole's mass resides in a singularity which is infinitely small and pointlike, how can it be said to have angular momentum? I know angular momentum is conserved, but in other words, if a rotating object's angular momentum is defined by its speed and moment of inertia, how can an object with a diameter of zero be said to be spinning? For that matter, as the black hole is forming and the moment of inertia shrinks, shouldn't its speed become infinite when the singularity forms? I'm not terribly great with terminology and I may have that wrong, so let me ask it another way: I've read that rotating black holes drag space itself as they rotate. But with an infinitely small and "featureless" singularity, exactly what is it that's doing the dragging? | [
"Strictly speaking, only a non-rotating black hole has a point singularity. A ",
"rotating black hole",
" has a ",
"ring singularity",
". Realistically, all black holes are rotating, but it's a lot easier to understand ones that aren't so we often assume they don't."
] | [
"Oh yeahhh. I never even thought of that. As far as we can tell, all stars rotate, right? And during collapse, any angular momentum will be conserved, making the rotation much faster. So a non-rotating black hole is more of a simplified model then something we actually expect to encounter?"
] | [
"Yeah. And for some reason I don't understand, charged black holes are a slightly better model of rotating black holes in some ways while still having the same symmetry that makes non-rotating ones easy to study. As a result, we look at charged, non-rotating black holes in order to understand the non-charged, rotat... |
[
"Can humans be genetically predisposed to giving birth to males over females and vise versa? If so is it caused by the man, woman, or both?"
] | [
false
] | null | [
"Humans ARE predisposed to giving birth to males at a ratio of 1.06:1. The ratio comes closer to 1:1 when we only consider people in their mid-20s to 30s.",
"Interestingly the sex chromosomes are at ",
"war",
" with each other -- each trying to be preferentially transmitted over the other. In mammals, this ... | [
"True answer, but most people with sex chromosome related disorders are sterile, so really nobody is beyond independent assortment."
] | [
"Technically, yes. According to ",
"http://scienceline.ucsb.edu/getkey.php?key=3062",
"\"However, there are some basic differences between x and y carrying sperm that do have an influence on sexual selection.",
". There have been experiments to show that if the pH of the uterus is changed to more acidic, then... |
[
"My understanding is that both Sodium and Chlorine by themselves are dangerous (explodes in water and is toxic, respectively). If that is true, why is dissolved sodium chloride (salt) perfectly safe? Why don't the dissolved ions have the same properties as sodium and chloride separately?"
] | [
false
] | null | [
"But they aren't electronically identical. The spacing of the orbitals is different. ",
"But yeah, that spacing is dependent on the charge in the nucleus, so OK, the nucleus matters. But the electronic structure matters much more."
] | [
"The form of chlorine which is dangers is ",
"chlorine gas, (Cl2)",
" which has very different properties from the ",
"chloride ion. (Cl-)"
] | [
"The nuclei don't matter in chemistry. Only the structure of the electrons. ",
"Sodium and chloride ions have totally different electronic structures than neutral sodium and chlorine atoms, and subsequently behave totally differently."
] |
[
"Do any compressible liquids exist?"
] | [
false
] | I learned recently that the reason why falling long distances into water hurts/kills is that water is non-compressible. Does a liquid exist that could provide more cushion/compressibility when struck with a lot of force? | [
"By definition, no. As I understand it, if a liquid is compressible it is called a gas. If a gas is incompressible it is called a liquid."
] | [
"I heard it as \"if it fills it container\" it's a gas. I expect that in practice most fluids that don't expand to fill their containers will indeed be nearly incompressible though."
] | [
"Supercritical fluids could be cool to read up on... they can go through a wide range of temperatures and pressures without any distinct phase change. I would imagine most supercritical fluids are compressible. ",
"Really, everything is compressible. But in the case of water, it's pretty negligible for most ca... |
[
"Don't checksums prove that some problems are easier to verify than to solve?"
] | [
false
] | [deleted] | [
"The problem lies in that for many NP problems, for example a lot of cryptographic algorithms, there is no mathematical proof that they can't be broken within polynomial time. To our current knowledge, there might be an efficient way of finding an input which produces your desired checksum and we just have not figu... | [
"This happened before, e.g. with the MD5 checksum algorithm. ",
"MD5's collision resistance is broken, but there isn't yet a practical attack on its preimage resistance.",
"That is - it is very easy to find x,y such that MD5(x) = MD5(y). We don't yet know how to easily \"reverse\" MD5: that is, \"given MD5(z), ... | [
"It's not hard to find a solution to a checksum. You can't find the original solution, but that's not what P vs NP is about. For example, if I know the digits add to 7, then 7 has that checksum. It's not the only thing that has that checksum, but it's a solution to the problem \"Find a number with the checksum 7\".... |
[
"Does our sun have any unique features compared to any other star?"
] | [
false
] | null | [
"It's the only star humans have ever discovered that sustains life on one of its satellite planets :)",
"But seriously though, our sun is incredibly typical when it comes to stars. It's mass is a little bigger than average, but there are tons and tons of other stars that are very similar to ours."
] | [
"One thing that does set our sun apart though is the fact that it is not a part of a Binary system which kinda makes it an 'anomaly' of sorts. This is only speaking statistically as lots of stars the size of the Sun usually have a friend they hang out with."
] | [
"\"More than four-fifths of the single points of light we observe in the night sky are actually two or more stars orbiting together.\"",
"http://www.space.com/22509-binary-stars.html",
"Don't know how reputable of a source it is though."
] |
[
"AskScience AMA Series: Speech Processing"
] | [
false
] | Ever wondered why your word processor has trouble transcribing your speech? Why you can't just walk up to an ATM and ask it for money? Why it is so difficult to remove background noise in a mobile phone conversation? UncertainHeisenberg, pretz and snoopy892 work in the same lab, which specialises in processing telephone-quality single-channel speech. I am a third year PhD student researching multiple aspects of speech/speaker recognition and speech enhancement, with a focus on improving robustness to environmental noise. My primary field has recently switched from speech processing to the application of machine learning techniques to seismology (speech and seismic signals have a bit in common). I am a final year PhD student in a speech/speaker recognition lab. I have done some work in feature extraction, speech enhancement, and a lot of speech/speaker recognition scripts that implement various techniques. My primary interest is in robust feature extraction (extracting features that are robust to environmental noise) and missing feature techniques. I am a final year PhD student working on speech enhancement - primarily processing in the modulation domain. I also research and develop objective intelligibility measures for objectively evaluating speech processed using speech enhancement algorithms. I'm working to create effective audio fingerprints of words while studying how semantically important information is encoded in audio. This has applications for voice searching of uncommon terms and hopefully will help to support research on auditory saliency at the level of words, including things like vocal pitch and accent invariance—traits of human hearing far more so than computerized systems can manage. | [
"\"Is there\" is almost always answered: yes. Our brain does it so there's sort of an existence proof that it's possible. We don't currently do a great job at it computationally though. There's some interest in finding more fine-grained (an not necessarily auditory-lossless, maybe just semantically lossless) repres... | [
"In addition to what ",
" mentioned, spectral subtraction is arguably the simplest method to understand for removing noise in the spectral (frequency) domain. Spectral subtraction estimates the noise level at each frequency, and simply subtracts these values from the measured amplitude at any given point in time.... | [
"Computational auditory scene analysis is one method used for this sort of thing. Obviously filtering the speech normally will result in a loss of speech information if the sounds you are trying to filter are at similar frequencies. ",
"CASA gives you a mask that says 'these frequencies at these times are speech'... |
[
"How are Hiroshima and Nagasaki habitable and Chernobyl won't be for another 20,000 years?"
] | [
false
] | If all of those places had lethal amounts of radiation released into the environment, how are the Japanese cities habitable today? | [
"Both bombs over Japan were air bursts, and air bursts doesn't cause significant local fallout (meaning very little to no remaining radioactivity). Also, Little Boy was loaded with a core weighing ~63 kilograms, Fat Man had a core weighing 6.2 kilograms. Reactor 4 at Chernobyl was loaded with several metric tons of... | [
"Quantity of radioactive material released and location of release: Hiroshima had a couple of pounds released in the air and Chernobyl had many tons released, many underground. Stuff in air blows away, versus the Chernobyl spill made the ground radioactive.",
"This article appears to answer your question exactly:... | [
"why did little boy have such a larger core? Because it used a different element?"
] |
[
"If you traveled in a straight line in space, would you eventually end up back where you started?"
] | [
false
] | In my searches I have encountered both answers. I haven't specified a speed though I understand this might be important. I presume there are competing theories out there, so maybe this boils down to which is the currently the most accepted. Edit: Wow, thanks for all the replies, this has cleared a few things up for me. | [
"What you're referring to goes by a few different bits of technical jargon in the literature. It's the question of whether the universe is ",
" or ",
" whether it's ",
" or ",
" whether it's ",
" or ",
" These all mean the same thing. They're just different ways of talking about the same question.",
"... | [
"How can it be infinite if it's expanding?",
"Consider the real number line. Identify two points on that line, say two and five. How far apart are they? Three.",
"Now multiply the whole line by two. Your two points now lie at four and ten. How far apart are they? Six. The number line, which is infinite, just ex... | [
"This is one of those cases where your intuition fails you. Yes, intuitively it's obvious that if the universe is a volume, there must be something ",
" that volume, and if the Big Bang happened at some time there must have been a moment before that moment.",
"But remember that your intuition is highly tuned to... |
[
"Why is iodine used as a disinfectant? I've looked for information online but several articles say its \"unknown.\" Why is iodine a good disinfectant?"
] | [
false
] | null | [
"Answer: ",
"Here's a review article on modes of action for various biocides including iodine",
". Here's what it says about iodine, and it has tons of citations if you want to dig deeper:",
"Similar to chlorine, the antimicrobial action of iodine is rapid, even at low concentrations, but the exact mode of ac... | [
"Thank you for this, I still love that \"unkown\" is still in the description. This is one of the most informative responses so far."
] | [
"Do the disinfectant properties of chlorine and iodine have something to do with the fact that they are in the halogen group, and bond with things easily, because they only need 1 more electron to form a full shell? So if I'm understanding correctly, they'll just bond with practically anything and this breaks down ... |
[
"Could a New Madrid fault line earthquake create a drop in elevation?"
] | [
false
] | Could a big earthquake cause the area to sink and reverse the flow of the Mississippi and create a sea or bay of sorts? | [
"I'm assuming this is in reference to the New Madrid earthquake sequence in 1811-1812, which among other things, ",
"temporarily dammed portions of the Mississippi river, causing it to flow backward/pool up",
". Another large earthquake sequence in the New Madrid zone could cause similar effects to the land sur... | [
"The New Madrid area has an average elevation of 80-90 meters above sea level and is over 650 km from the Gulf (longer if you were thinking along the course of the Mississippi River). No earthquake is going to subside an area 80+ meters in a single event (even a megathrust event, e.g. ",
"the M9.2, 1964 Alaska ea... | [
"So you're referring to an uplift causing dams. But is it possible that an intraplate fault could drop the area a few hundred feet causing an infux of water from the Gulf?",
"The area isn't at a very high elevation."
] |
[
"How do people solve a rubik's cube blindfolded? Do they actually memorize the location of every piece?"
] | [
false
] | null | [
"Do they actually memorize the location of every piece? ",
"Kind of. Ultimately, they have to memorize enough information to be able to recreate the cube state, but most blindfold methods have you memorize the sequences in which you solve pieces, and the method prescribes that the pieces are to be solved in a dis... | [
"Yeah, I've heard that you don't have to be a genius and that you just need a lot of practice and a method. Maybe it is kind of like how people can learn to play chess without looking at the board as a result of playing for years."
] | [
"To add onto this, they assign letters to each location, which makes turning the locations into words/sentences much easier.",
"Source: I can solve one blindfolded in around 4 minutes."
] |
[
"Do different opioids bind to different opioid receptors or are they all the same?"
] | [
false
] | I think I sort of worded the question wrong so I’m sorry. I know that norco and percocet are both opioids but if I take a bunch of norco and build that tolerance up a lot isn’t the tolerance for percocet still at the start? Does the oxycodone in percocet bind somewhere different in the body than the hydrocodone in norco? I’m prescribed both but I’ve been on norco longer and my tolerance is very clearly higher than it is for percocet and I’m just wondering how it all works in the body. Sorry I’m terrible with words | [
"The 'main' opioid receptor is the mu (greek letter) opioid receptor, MOR for short, it is responsible for sedation, euphoria, pain-killing effects, decreased respiratory rate, constipation, and pupil constriction, and all classic opiates/opioids bind to it, so in that sense you are correct. ",
"It has splice var... | [
"Generally the cross-tolerance between different opioids is very strong or very 'complete', meaning that usually switching opioids does not really get rid of your overall tolerance. A physician may just use a conversion chart to directly change a given dose of oxycodone to a given dose of hydrocodone. ",
"http://... | [
"No problem. From the perspective of a doctor treating a patient with opioids you don't really need to know too much about all those detailed molecular mechanisms, but it is interesting!",
"Some of the research into trying to treat opioid dependency or addiction or to create new painkillers with less addiction po... |
[
"Where do atoms come from?"
] | [
false
] | null | [
"Matter can be created and destroyed."
] | [
"I always learnt that matter can neither be created nor destroyed, but changed from one form to the other. Is that false?"
] | [
"He is talking about \"created from an equivalent energy\" and \"destroyed into an equivalent energy\". You are thinking of \"energy cannot be created or destroyed\". Matter is a form of energy."
] |
[
"How accurate is MinutePhysics explanation of the expansion of the universe?"
] | [
false
] | seen here: I ask because this has always been one of those subjects (like when people talk about the universe vs the observable universe) that seem to change depending on who's talking about it and even if they're prominent physicists. I've been told that the "Everywhere stretch" idea wouldn't work because it implies the universe has infinite energy when in fact it has a finite amount. So what's going on? | [
"I've been told that the \"Everywhere stretch\" idea wouldn't work because it implies the universe has infinite energy when in fact it has a finite amount. So what's going on?",
"The universe is thought to be infinite in size, and if that's true, it will have infinite energy. But even a finite universe wouldn't h... | [
"The video seemed pretty spot on to me, though I'm not a cosmologist.",
"Regarding (a): The idea of \"Everywhere Stretches\" is an eternalist point of view of the universe thus suggesting there is an infinite amount of energy in the universe. We know there is a finite amount of energy in the universe, that is fro... | [
"Why must an infinite universe in size mean that it has to have infinite energy?"
] |
[
"Why does the flu hurt us so bad if it needs our cells alive to reproduce?"
] | [
false
] | Seems counterproductive of it to destroy what it needs to reproduce. Edit: Thank you for all the replies. I learned that it's our immune response that does the most harm in the form of collateral damage. | [
"You're right- a virus or any other parasite is not really a great parasite if it kills its host outright. The flu itself causes some tissue damage, but people who die of the flu almost always die of pneumonia or some other secondary infection. In fact, a bacteria called Haemophilus influenzae was originally believ... | [
"Viruses like Influenza only use their hosts to reproduce and spread. As long as the initial infecting virus was able to reproduce and spread, it couldn't care less if the host dies or becomes mortally ill.",
"http://news.bbcimg.co.uk/media/images/65434000/jpg/_65434255_270c6881-bbd8-4217-8846-1e4446ee5537.jpg"
] | [
"Sure. The longer the host remains alive and shedding viruses the more new hosts it can infect. But as I mentioned in an answer above, even spreading to one new host is considered reproductive success for viruses. It's natural selection on a much simpler level than for living organisms.",
"That is ",
" of the r... |
[
"Before the media blows up reporting on how we've found a Dyson Sphere what does the paper for KIC 8462852 actually say?"
] | [
false
] | [deleted] | [
"Short version: this paper is saying \"there are a bunch of theories, all of them fail one metric or another except this one low probability theory\" (Edit: that theory is not aliens either; still natural).",
"That's all the paper says. Solutions to that paper would be: a) the low probability thing happens occasi... | [
"Straight from the abstract: ",
"By considering the observational constraints on dust clumps orbiting a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet fragments, all of which are associated with a single previous breakup event... | [
"I was under the impression \"common\" exoplanet transits produced drops of only on the order of a few percent and not the massive drops of 15 and 22% observed here.",
"Even a few percent drop in flux is pretty unusually massive. For a Jupiter-sized planet passing in front of a Sun-sized star, you'd expect to see... |
[
"Would a regular clock be affected by gravitational time dilation?"
] | [
false
] | null | [
"Yes, it works the same for any kind of clock."
] | [
"Ok, so for example in a quartz watch, what component would gravity work on? The vibrations of the crystal which are then translated by the microchip and turned into seconds?"
] | [
"Gravity doesn't pick a component of the clock to work on, it's slowing down time itself. It doesn't matter what you use to measure time intervals, different observers will get different results due to the presence of the gravitational field."
] |
[
"Why do cameras need to focus? Why can't everything be in focus at once?"
] | [
false
] | null | [
"Technically with an ideal ",
"pinhole",
" camera everything is in perfect focus. Ideal pinhole camera however would have infinitely small hole so it's not practically possible. In a non ideal pinhole camerea everything is blurred proportional to the width of the hole (because every point in the target is visib... | [
"Everything ",
" be in focus at once if you make the aperture (the opening that lets light in) small enough. That is, if you have a ",
"pinhole camera",
" with an opening very small relative to the distance to the subject. But a tiny aperture means a tiny amount of light getting inside, and given that photogr... | [
"There are cameras that can effectively put everything in the field of view in focus without the disadvantage of a small aperture. See \"plenoptic camera\" or \"light field camera\". They are not common."
] |
[
"I'm watching Bill Nye on Netflix. He just said that the math it takes to predict weather is more complex than the math that put Man on the Moon. Is this true?"
] | [
false
] | Seems possible, since weatherman are wrong so much, but figured I'd asked the true professionals~ edit: sorry if I tagged it incorrectly, there's quite a few categories I could see this question fitting into. | [
"In terms of calculating orbital trajectories, putting a man on the moon requires only basic Newtonian Mechanics, and the math is very simple. But the full process of getting a man to the moon involves incredibly difficult engineering problems and a lot of trial and error, because, like the weather, modeling a rock... | [
"Seems possible, since weatherman are wrong so much",
"They're really not, unless you wish to single out broadcast meteorologists. ",
"Randy Olson, motivated by Nate Silver's chapter on forecast accuracy in his book, looked at the calibration of precipitation probability forecasts",
" and found that NWS forec... | [
"While precisely modeling a rocket is hard, it is also not necessary to design the rocket. I had the opportunity to learn principles of design from an engineer that worked on the F-1 engine, and he discussed it at length.",
"The initial design stage is actually pretty simple, in engineering terms. The foundations... |
[
"Why don't they launch satellites/shuttles from high altitudes?"
] | [
false
] | Less distance to travel to orbit, less fuel costs? | [
"In addition to other people's replies, it takes energy/fuel to get the heavy components to the top of the mountain."
] | [
"If you mean launching them from mountaintops or something, it wouldn't actually save that much fuel. The vast majority of the energy used to launch a spacecraft into orbit goes toward accelerating it to the incredibly high speed required to stay in orbit. (About 90%, if I recall correctly.) Of the remaining 10%, I... | [
"There's a reason that the shuttle launch site is in Florida: we wanted to put it as close to the equator as possible. The equator of the Earth is about 26 miles farther from the core than the north pole, so you gain some height there. More importantly, the equator is moving about 1000 miles an hour, which does ... |
[
"Is it possible to calculate the rate of condensation given a surface area?"
] | [
false
] | Having an issue at work and worked with calculating rates of condensing steam but is there a formula that can be used to figure the rate of condensation that would occur given a surface area of steel (a tank) and relative hummidity and temperatures? | [
"Analytically, nothing immediately jumps to mind. You could possibly figure it out if you knew the ambient humidity and you had a steady-state heat transfer rate between the surface and the air, but the heat transfer rate is going to be tricky to figure out analytically because you're dealing with convection, which... | [
"yes, but this is one of those \"too many unknowns\" to answer directly. the roughness of the surface is one the biggest factors here as it determines nuclelation sites for condensation. Then, is it drop wise condensation or falling film condensation? The degrees above boiling at your operating temperature and your... | [
"I like the analytical idea but a little hard to do where we are in the field. Without giving away to many details, long story short, tanks were cleaned and dry 6 months ago and then closed other than a 6\" vent line for a 60k gallon tank. A few days ago we open the tank back up to fill it with brine and there is w... |
[
"some questions on the talk \"A Universe From Nothing\" by Lawrence Krauss, discussing dark energy and the flat space."
] | [
false
] | so i was watching talk delivered by Lawrence Krauss and he is basically saying that the cosmologists believe that the geometry of space is flat (probably since the inflationary models of the big bang predicts it being so). to confirm this people sent out probes to measure the "mass density" (including the dark matter) of the universe and found out that it is 1/3 of the mass density required for a flat universe. then Krauss goes on to talk about another experiment in which the geometry of the space is determined by observing the "clumpiness" of the shapes observed in the early universe (i.e. cosmic background radiation), and according to said experiment the universe is now determined to be flat with one percent accuracy. so his explanation to this obvious discrepancy is as follows: and he goes on with explaining the evidences of accelerating expansion of the space, i.e. the farther away galaxies are escaping faster than expected. and then says: therefore Krauss concludes that 1) the universe is flat 2) largest energy in the universe, 70 percent, resides in empty space. 3) also in this case the total energy in the universe adds up to zero (since the gravity can have negative energy?), and in quantum mechanics something can arise from the nothing, hence the name of the talk: "A Universe From Nothing" finally, my questions: 0) do you think my understanding of the situation is correct? 1) 2) if we assume that the universe is homogeneous in all directions, isn't it the case that all sufficiently large regions of the universe should have zero energy in total? in our case, this sufficiently large regions are the spherical regions with a radius equal to half the average distance between the galaxies. focusing at one of these patches/regions alone, how can you demonstrate that the total energy adds up to zero? 3) 4) what are some good candidates for "the source of dark energy" residing in the empty space? | [
"1) The potential energy of something is how much work it would take to get in into that state, if you bring in everything from infinity. For a gravitationally bound system - work is required to get it out of the state rather than bring it into the state, since gravity is attractive. Hence, gravitational potential ... | [
"I have had it told to me in this subreddit several times that metric expansion is not the same as the galaxies gaining velocity and accelerating away.",
"If it was, I believe you would get different measures of the kinetic energy of a galaxy depending on how far away it is, which can't be true.",
"But the shor... | [
"can you explain this in terms of two objects surrounded by the vacuum and separated by a long distance. they are also escaping from each other with some velocity (you can assume that they are accelerating too). ",
"lets count the energies:",
"1) lets say the gravitational potential energy of each object is pro... |
[
"Theoretically, how high could a balloon like craft go?"
] | [
false
] | Assume the "basket" would be a pressurized vessel, possibly the weight of 2-3 cars. The balloon can be filled with, and made out of, anything. I'm hoping for as close to the edge of the atmosphere as possible. | [
"The record for manned and unmanned gas balloons is about 136k ft and 174k ft. However, these balloons didn't have the massive payload you have assumed. To get such a large payload into the upper stratosphere would require a much larger balloon, but it's theoretically feasible. Getting much higher is very difficult... | [
"That type of question is asked around here a lot - usually in the form of \"Why don't we launch rockets from balloons?\" or \"...from mountaintops?\"",
"The problem is you're thinking about getting into space from the wrong perspective. Gravity in orbit is not much lower than gravity on the surface, but because ... | [
"Interesting! Thank you, I was wondering if using balloon power to get to an area of low gravitational force, then some propellant to escape that force was a feasible idea. It seems unlikely. Now that I think about it, the propellant world probably work less in the low pressure anyway =/"
] |
[
"How do SONAR systems actually produce such loud noises?"
] | [
true
] | [deleted] | [
"They use an array of giant transducers. When electricity gets passed through them, they vibrate and produce the “ping” that gets transmitted into the water. They are so loud that from the inside of the ship or sub, it sounds like a sledgehammer hitting the side of the ship."
] | [
"It can be painfully loud. Environmentalists and ecologists are concerned that sonar usage can disorient (and through follow-on effects, kill) marine wildlife.",
"You can find videos of sonar pings on the internet. First result for me on Youtube:",
"https://www.youtube.com/watch?v=EAqUelpwEl8"
] | [
"It can be painfully loud. Environmentalists and ecologists are concerned that sonar usage can disorient (and through follow-on effects, kill) marine wildlife.",
"You can find videos of sonar pings on the internet. First result for me on Youtube:",
"https://www.youtube.com/watch?v=EAqUelpwEl8"
] |
[
"Can anyone explain to me what a back emf is and how it works? Start simply and work up. Taking a power electronics module and can not get my head around what is happening."
] | [
false
] | null | [
"A motor (a really simple one) is a bunch of coils wrapped around a tube, surrounded by magnets (or the other way round with magnets on the axle and coils on the outside). You send current through the coils and the force acting on the coils due to the presence of magnet (or vice versa) makes the axle spin and the m... | [
"Ok that actually has cleared it up for me a bit. thanks"
] | [
"For reference: ",
"Faraday's Law"
] |
[
"How does our digestive system distribute nutrients to specific parts of our body? [Human Body]"
] | [
false
] | Like when we eat certain food, how does our body know where to send protein to certain organs, or iron to blood, etc. How are nutrients segregated or filtered then assigned to specific areas? | [
"Everything goes into the bloodstream from the intestines. The body doesn't direct the nutrients to soecific locations, it's the other way around - individual cells pick out of the bloodstream whatever they need."
] | [
"The main arteries aren't all there is. Smaller arterioles branch off from them, and those again branch into a very fine network of capillaries. That network is so fine and widely distributed that everything is in diffusion range from at least one capillary. To give you a perspective of how vast that network is, th... | [
"All your cells have ability to recognise the protein sctructle of certain molecule. Your microvilluses suck up all the nutrients to your blood and lymph system. The lymph system delivers the fat and ADEK vitamins back to your blood. So basically all your nutrions are in your blood. When a cell needs something, it ... |
[
"I recently learned about the pulsar map. Could we make such a map on a galactic level?"
] | [
false
] | Are galaxies, on a very big scale, easily recognizable from each other? Do they have a general frequency or other features that sets them apart? | [
"Are galaxies, on a very big scale, easily recognizable from each other? ",
"For some, yes, but overall probably not. For ",
"spiral galaxies facing us",
", I'll let you be the judge. The same goes for ",
"ellipticals",
".",
"Could we make such a map on a galactic level?",
"Here",
" is a rendition o... | [
"Ah, I see. Almost certainly not. In the galaxy, pulsars are rather unique among stars, so a closer analogy to what you're asking to do is sort of like trying to figure out where you are based on all of the stars in the Milky Way. If you knew enough properties about them and their positions, then possibly you coul... | [
"I see I wasn't very clear with my question.",
"I wanted to know if we could make a map using the 12 closest galaxies to help identify our galaxy. ",
"Or if galaxies as a whole have distinguishable frequencies...",
"Thank you for that very in-depth answer so far, great information!"
] |
[
"solar flare myth?"
] | [
false
] | null | [
"in 1859 they used it to send telegraph messages without powering the wires"
] | [
"in 1859 they used it to send telegraph messages without powering the wires"
] | [
"in 1859 they used it to send telegraph messages without powering the wires"
] |
[
"Is there any place in the universe where we can observe (potentially) earth-like planetary formation?"
] | [
false
] | Was reading today about the formation of the earth. I was curious to see if we can observe the same processes elsewhere in the universe. Thanks! | [
"The formation happens on a timescale of ten million years, so no, we cannot directly observe it.",
"We can however observe ",
"protoplanetary disks",
" in which planet formation is on-going. We can observe these at different disk ages and in doing so get an idea of the entire process. We have just started ge... | [
"Saturn's moon Titan is believed to have early-Earth conditions, it hosts a dense nitrogen-rich atmosphere and lakes of liquid hydrocarbons/methane on its surface.",
"It's really a fascinating thing, we've had one Huygens probe that piggybacked on Cassini visit its surface, I'd love to see another mission."
] | [
"I'd love to see another mission.",
"The ",
"TiME mission",
" has been proposed for the past couple of NASA funding cycles - this would put a boat on the hydrocarbon seas of Titan. It still hasn't been approved yet, but keep your fingers crossed as the mission proposal becomes more mature."
] |
[
"Will you have/require a lower blood pressure after having a limb amputated? Would it change based on the limb that was amputated?"
] | [
false
] | I'm thinking that it would take less energy to send blood to a non-existing appendage. | [
"Blood volume is regulated by the kidney. It can detect the amount of blood flow passing through it and adjust accordingly. After an amputation, the kidney would sense an increased blood flow and reduce the blood volume. After a day with no limb, your blood volume would normalize to be slightly less than it was ... | [
"Good call. I guess they don't have to add as much blood during the surgery (assuming its a controlled environment). I guess the body just learns that it doesn't need to produce as much blood right?",
"Would this person have less white blood cells too and have trouble fighting off disease and infection?"
] | [
"Good to know!"
] |
[
"How can we know about a 20-mile wide Kuiper belt red object (MU69), but just now be \"discovering\" two new moons over Uranus?"
] | [
false
] | null | [
"These \"moons\" are expected to be only 2-9 miles wide and as they are still about half as far away as MU69 they might still be way fainter depending on their albedo (reflectivity). MU69 was only discovered when Hubble was used to especially look for potential candidates for New Horizons. Space is big and telescop... | [
"Science is conducted by scientists who compete for grants and lab time. Whatever their experiment is will directly affect what sort of results are found. We don't 'neglect' anything at all, rather try to pay attention to everything, one thing at a time. How are we supposed to know to look for 2 mile radius rocks a... | [
"Some links for context:",
"MU69",
"New Uranus Moons"
] |
[
"Why do some ceramic mugs get hot in the microwave and others don't?"
] | [
false
] | null | [
"Microwaves operate on the principle of dielectric heating - essentially they vibrate polarized molecules within food (or whatever else you've put in your microwave) by applying high-frequency non-ionizing radiation. Some substances are, by nature, more prone to heating by this process. Ceramics are among these su... | [
"I thought he answered that. Microwaves heat by vibrating polarized molecules. Some substances are more prone to heating by this process. Ergo, some substances consist of more (and/or more strongly) polarized molecules that are better at absorbing microwaves."
] | [
"I have found that they may have chips and or cracks and that lets moisture into the ceramic after a while, which heats up..."
] |
[
"Why are the clouds in this image so bright at night? (Image from Mt. Wilson Solar Tower cam at time of posting)"
] | [
false
] | that's the image and is the source. I'm thinking it could be due to light pollution but surely the lights cannot make the cloud glow that brightly. The only time I saw something that bright at night was during the | [
"It's an extremely long exposure, so the lights are over-exposed."
] | [
"I have seen that effect to a lesser degree in winter over small towns in northern Sweden. Basically city lights get reflected back and fourth between the snow and coulds and create this otherworldly orange glow. A city has quite a lot of lights and the right cloud cover can really light up because of it. Also in w... | [
"That makes sense. Thank you."
] |
[
"What caused the spanish flu outbreak in 1918 to be one of the deadliest outbreaks ever? What made this version of the flu so deadly vs other flus?"
] | [
false
] | null | [
"There were multiple factors at work. Here are two that come to mind.\n1) WWI - many thousands of soldiers living in close proximity to each other. Sick soldiers get packed into infirmaries like sardines and the virus is spread by either direct contact or by medical staff.\n2) Immune reaction - usually, you would e... | [
"1.2) medical infrastructure was destroyed or needed for soldiers, people were weakened from the war and so on."
] | [
"The virus triggered an overreaction from the immune system of a healthy, young individual. This is called a cytokine storm. This source (",
"https://www.sciencedaily.com/releases/2014/02/140227142250.htm",
") defines the results with respect to flu rather clearly:",
"\"A cytokine storm is an overproduction o... |
[
"Are there 'habitable zones' of galaxies?"
] | [
false
] | null | [
"Simple answer: Probably.",
"Longer answer: Probably, and it's got to do with a number of factors.",
"In the case of spiral galaxies (which are younger and experience more star formation than most lenticular, elliptical, etc. galaxies), the core is very star-dense relative to the rest, so it will have higher ra... | [
"Probably? An interesting thing some astrophysicists have looked into is the fact that galactic gamma ray bursts have the ability to sterilize planets in more or less one shot. In the inner portions of the milky way, due to the greater density of stars (and thus supernovae), there is a much greater likelihood that... | [
"Sort of. There's no well-defined zone that we expect to be habitable while the rest of the galaxy is not. But there are some differences between regions of the galaxy due to density of stars, frequency of supernovas, and metallicity that makes us think habitable planets are somewhat more common in some parts of th... |
[
"How come even my smallest low end netbook produce so much waste heat and have loud fans running when a more powerful smartphone produce less heat and lack fans?"
] | [
false
] | null | [
"All components in a smartphone are heavily optimized to minimize power consumption. This includes using flash-based mass-storage instead of hard disks (typically not SSD but eMMC), and low-power memories such as LPDDR2 and LPDDR3 instead of DDR2/3. The processors are also designed to reduce power consumption. They... | [
"On a ",
" level, \"computers\" produce more heat when they're using more power. Your smartphone is most likely better optimized to use less energy to do the same tasks, so it's not going to heat up as much. Good hardware isn't only fast, it's efficient. "
] | [
"Well your smartphone doesn't contain as many moving parts.",
"For starters, it has solid-state memory instead of a spinning hard drive.",
"Also, smaller components use less power and therefore produce less heat. ",
"If you were to compare a smartphone with a contemporary laptop, the laptop would have far ... |
[
"Why does a computer need to calculate all the interactions, movements, outcomes of different things when in reality particles interacting don't calculate anything but just move according to different forces?"
] | [
false
] | null | [
"Hi sander2525 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 foll... | [
"I'm not sure I understand the question. The computer is simulating those interactions; in the real world, they are actually happening..."
] | [
"If I'm thinking more about this then I start to understand also, that I am asking the wrong thing. ",
"I would actually like to know if it would be possible to have a simulation as real as our reality or is there something besides processing power that sets the limit on how realistic we can make the simulations?... |
[
"Not everyone has the mental capability to learn the type of abstract thinking required for being good at mathematics. True or false?"
] | [
false
] | Dear AskScience: I believe I read about a scientific study some years ago that claimed to prove that not everyone has the right brain structure required to engage in the kind of abstract thinking that is required in disciplines like Mathematics and Computer Science. Specifically, I believe that the "type of thinking" was even defined as the process of being able to take one type of abstraction (say, using a variable to stand in the place of a number) and apply another one on top of that (say, a function), and being able to deduce the rules that would apply to this operation (i.e. applying a function to a variable). If memory serves me right, it was shown in that study that if a person was able to process the above, they were also usually able to learn higher-order abstractions (e.g. functions applied to functions), but if they had systematic problems with this concept, they were never able to "get it". Does anyone know of this study? Was there actually one? Is the above an actual scientific fact or did my brain just trick me into making it up to feel better about it's capability to solve abstract problems in order to console myself for its shortcomings in dealing with other human beings? | [
"Arithmetic procedures? On what level though? Basic arithmetic is quite a different beast than is, say functional analysis.",
"Just to be very clear here: I do not want any of this to seem like trying to classify people in categories in order to pass judgement on their value. While my experience shows me that I'm... | [
"Arithmetic procedures? On what level though? Basic arithmetic is quite a different beast than is, say functional analysis.",
"Just to be very clear here: I do not want any of this to seem like trying to classify people in categories in order to pass judgement on their value. While my experience shows me that I'm... | [
"The abstract thinking skill in looking for is the ability to infer a set of rules from the behavior of one class of elements (e.g. arithmetic on simple variables) and apply it to another, slightly more complex one (e.g. functions). ",
"Maybe the focus on mathematics was a but misleading - this is a skill that's ... |
[
"Is anything in the universe stationary?"
] | [
false
] | Or is everything always moving about another point | [
"it depends on your reference point"
] | [
"All motion is relative. Any object can be taken as stationary and the motion of other objects in relation to it can be taken as moving."
] | [
"no, it could not be said (correctly anyways) that the sun orbits the earth. linear motion is what is relative. If an object is moving in a straight line at a constant speed, then in that object's reference frame, it is you that is moving."
] |
[
"If you were standing on the moon's surface, would you be able to see the horizon curve?"
] | [
false
] | If not, how small would a planet/moon have to be to be able to notice a curve of the horizon? | [
"It depends on how you mean it. You will see the horizon, just as you do on Earth. But, just as on earth, if you are standing on a smooth plane (IE: ignore hills and mountains and such) the horizon will be the same height in any direction you look. This is because the ball you are standing on curves away from you t... | [
"Horizon distance = sqrt[(Moon Radius + Eye Height)2 - (Moon radius)2] = approx. 2.64km.",
"A consequence for the curious: if you were to stand at the center of any of the larger craters (diameters from tens to ~100km), you wouldn't know you were in a crater. The crater walls (mountain ranges) would be far beyon... | [
"Horizon distance = sqrt[(Moon Radius + Eye Height)2 - (Moon radius)2] = approx. 2.64km.",
"A consequence for the curious: if you were to stand at the center of any of the larger craters (diameters from tens to ~100km), you wouldn't know you were in a crater. The crater walls (mountain ranges) would be far beyon... |
[
"Fever dreams: why does a fever cause long, bizarre dreams?"
] | [
false
] | Also, why does it seem like you can wake up, be aware of your surroundings, but still not realize it's a dream and fall back into the dream almost immediately? I've fallen sick, and somehow spend over 4 hours thinking the entire air force was inside my body last night. I know it's over 4 hours, because I occasionally managed to check the time. | [
"I wasn't on any medication. "
] | [
"I wasn't on any medication. "
] | [
"elaborate"
] |
[
"How does Symmetrical Encryption really work?"
] | [
false
] | I get that one key is able to both encrypt and decrypt, but I can't find an explanation as to how that flies practically. Let's say you send e-mails using Symmetrical Encryption. Do you have a different key for every e-mail that's sent? And how are those keys exchanged with no possible interception? | [
"Symmetrical encryption relies on both parties having the same key. You can choose a new key as often as you want. You certainly need a unique key for every different person you're sending messages to. You probably want to change your key for a given person every so often. How often is going to depend on how lo... | [
"Typically for something like encrypted email, the recipient generates a pair of mathematically linked keys. Traditionally this has been done using the ",
"RSA",
" algorithm, though newer methods based on elliptic curves is gaining popularity. One of these keys we call the ",
", and the other we call the ",... | [
"One very simple example of symmetric encryption is to have a key the same length as the data (possibly by repeating a smaller key), and just xor the data with the key.",
"Suppose my data is binary 01 and my key is 10. After encrypting, my ciphertext is 11.",
"How do I decrypt it? Simple - just xor it with th... |
[
"With neural plasticity in mind, there is a very common practice in gaming where players listen to high bpm music to increase reflex time, could music in a way also be changing our brains to explore tasks differently?"
] | [
false
] | I am very interested on a cultural level also, and any examples anyone wants to throw at me. I have heard many cases in how people tend to explore things through music, I know a lot of artistic people wouldn't seem to function without music. And if anyone has exercised to music it is a less painful experience, at first. I guess in a way you can put it as, is being partly consumed by something you enjoy repeatedly doing, help explore common tasks differently? | [
"This is a lot of silliness mixed with a sprinkling of truth. Music can certainly trigger strong emotional responses and thus parasympathetic (causing reduced heart rate and blood pressure) or sympathetic (causing increased heart rate and blood pressure) activity. Music can also trigger dopamine release (i.e. liste... | [
"\"Responses to music are easy to be detected in the human body. Classical music from the baroque period causes the heart beat and pulse rate to relax to the beat of the music. As the body becomes relaxed and alert, the mind is able to concentrate more easily. Furthermore, baroque music decreases blood pressure and... | [
"You know, I'm very skeptical that high bpm music decreases response time because distractors (like music) tend to have detrimental effects on most performance tasks. Read up on dual tasking and the attentional bottleneck for more info on this. ",
"One possibility is that the music just provides a metronome for t... |
[
"What causes certain substances to refract certain wavelengths of light?"
] | [
false
] | What chemical properties make a red apple appear red instead of blue? What decides which wavelength of light is absorbed and which wavelength is reflected? Edit: I meant reflected in the title and description. Thanks Coin-coin | [
"That's not refraction. Refraction is the change in direction at the interface between two materials. You're talking about absorption and reflection.",
"It's a matter of energy levels of the electrons. Depending on the different available levels, electrons can or cannot be excited by a given wavelength. This depe... | [
"The color that a naked human eye sees is the result of reflected light, that is, light which is not absorbed.",
"Absorption of light (for instance, light from the sun) takes place when the energy of a photon is taken up by matter. The energy is transformed from electromagnetic energy into other forms of energy, ... | [
"Basically. Although it's not just the electrons but also the vibrational and rotational states of the atoms/molecules. Usually, absorption of light causes both an electronic and vibrational/rotational excitation. Since the latter degrees of freedom correspond to motion, that energy can be lost 'non-radiatively', i... |
[
"Why does lighting a cigarette cause a constant amber instead of a a flame?"
] | [
false
] | Why can't I actually just light a cigarette on fire (like I could light a stick on fire and cause a dancing flame)? Second cigarette related question....why do wet cigarettes smell stronger/worse? I just smoked a cigarette in the rain and it got a few drops on it. Now I'm noticeably smellier than usual. | [
"It has to do with the design of the paper in the cigarette. There is a surprisig amount of engineering wit cigarettes. The paper contains a chemical called titanium oxide which controls and sustains the burning of the paper. Also on the paper are 'burn rings'. These rings are spaced along the paper to slow the bur... | [
"yes, true. an amber-tipped cigarette would be interesting though. no flame on these cigarettes....but the weird part is when you light it, it permanently encases nearby mosquitoes."
] | [
"I think the word you wanted was ",
"ember",
" not amber. =)"
] |
[
"What are the risks associated with microwaving plastics?"
] | [
false
] | Are certain plastics more prone to leeching into the contents when this happens? Where does cling wrap fit in? | [
"Specific health effects ",
"include:",
"Endocrine disruption; obesity; neurological disorders, particularly in the developing fetus; dopaminergic system disruption; blocking thyroid receptors; breast cancer (note that neither the FDA nor the IARC has evaluated BPA); promotion of growth and metastasis of neurob... | [
"From Toxicology Letters, Volume 176, Issue 2, 30 January 2008, Pages 149-156 doi:10.1016/j.toxlet.2007.11.001: ",
"Using a sensitive and quantitative competitive enzyme-linked immunosorbent assay, BPA was found to migrate from polycarbonate water bottles at rates ranging from 0.20 ng/h to 0.79 ng/h. At room temp... | [
"I thought the issue wasn't ",
" ",
" as much as they're carcinogens and/or cause birth defects."
] |
[
"What happens if we force water through a supersonic nozzle (converging/diverging flow) to accelerate it to Mach 1?"
] | [
false
] | Do we see Mach 1 at the throat like in a supersonic wind tunnel and then expansion to create supersonic flow past it? Will the incomprehensibility mean that nothing extraordinary happens? | [
"If water were a perfect, compressible fluid, then accelerating water to Mach 1 and beyond would be exactly as you described, much like how you would for a gas.",
"In real life, however, all liquids have a something called vapor pressure, ",
". This pressure describes the equilibrium pressure required to mainta... | [
"What an excellent reply! That all makes a lot of sense. I assume if you accelerate a flow without such a loss of pressure than you could possibly accelerate it past Mach 1? I don't see the application of doing so with such a high Reynolds number fluid, but cavtiation issues would probably still exist.",
"Thanks ... | [
"Well, it would have a lot of benefit if it could be done. Although gasses and liquids are different states of matter, both are \"fluids.\" ",
"If you could accelerate a liquid in the same manner as a gas, you could impart a lot more momentum at once given the same pressure differential. Rockets, jet engines, mar... |
[
"Why do opposite ends of the visible spectrum seem to blend into each other?"
] | [
false
] | As my understanding of light serves me, the electromagnetic spectrum looks something like . Specific colors within the part which we call the "visible spectrum" correspond to specific frequencies/wavelengths. On this spectrum, light with less energy is more red, and light with more energy is more violet. Why, then, are we able to arrange these colors in such a way that they blend continuously into each other, ? It seems like the two colors which represent light on opposite sides of the spectrum should appear to be, in a sense, opposites. | [
"Imagine all colors are in R,G,B (red green blue) every color can then be represented by a linear combination of each. We represent this as 3 8 bit integer values 0-255.",
"Pure blue is 0,0,255\nPure red is 255,0,0\nPure green is 0,255,0",
"Because its just a linear combination of those numbers you can make v... | [
"Mostly because the spectrum doesn't have a whole lot to do with the colour wheel. The spectrum, as you say, is just all the colours that correspond with specific frequencies/wavelengths. Other colours can be formed by combining light of different wavelengths together.",
"By using the RGB (or whatever else) colou... | [
"Look around 12 and 13 on your color wheel. Magenta colors like that don't exist as a single frequency of light on the EM spectrum. There's a clear difference between violet on the spectrum and red; the colors in between come as a result of mixing red and blue light.",
"It's an oddity of human color perception th... |
[
"Why does it take 10,000+ years for a photon to go from the core of the sun to the outside?"
] | [
false
] | I apologize if this has been asked before. I've heard that it takes millenia (or more) for a photon to go from the core of the sun to get to the outside of the sun. Why is this? What are those photons doing in there? Are they moving? If they are moving, are they just going in circles or something, and if so, why? If they're not moving (or for some reason moving slower than photons on Earth) what causes them to go so slow? | [
"The last time this was answered, the answer was the the individual photons themselves were not that old, but that they are generally absorbed and re-emitted by atoms in the sun for a very, very long time before managing to escape and not be re-absorbed. So it doesn't literally take that long for a single photon to... | [
"I'm far from a plasma expert, but I do work with radiative transfer simulations in highly ionised gas. For much of the volume of the sun, everything will be fully ionised. So the predominant mode of interaction will be scattering rather than absorbtion."
] | [
"This is indeed true regarding the scattering.",
"The exact answer is a little hard to compute because the mean free path for photons varies significantly from the inner portion of the sun (where it's of order 100 microns) to the outer (where it's more like 0.3 cm) and we have uncertainties in our models for stel... |
[
"What makes a colour \"neon\"?"
] | [
false
] | Is there a special ingredient in neon yellow or neon orange dyes or colours that makes them particularly glowing? | [
"A so-called neon dye or paint is actually fluorescent, which means that it can absorb a short wavelength photon, such as UV or blue, and emit a longer wavelength photon, such as yellow or orange. A normal yellow object can only reflect a small range of the spectrum of light contained in the light illuminating it.... | [
"Colors that are called \"neon\" are actually fluorescent colors. They are made with pigments that reflect invisible ultraviolet light at a longer wavelength that humans can see. The makes items colored with that pigment appear brighter than the items around them because they reflect more visible light."
] | [
"Yes—mostly correct. The fluorophores actually absorb the UV photon and re-emit a whole new photon at a longer wavelength."
] |
[
"Why don't I crush cells when I sit down?"
] | [
false
] | When I put all 160 pounds of me on my rear cells or even foot cells why don't they burst? It just seems like they are so fragile, how do they withstand so much pressure? | [
"If you were to put all 160lbs on one cell, it would make sense that the cell would burst. However, that's not what's happening when you sit down. There are thousands, if not millions of cells supporting your weight. The force experienced by each cell is negligible because your weight is distributed between all tho... | [
"The best way I can explain this however dumb an analogy this might be.. if you lay down on a bed of nails, why aren't you impaled? Because the weight is distributed through all of the nails, you are fine. Those nails are far fewer and much larger, than your butt cells or your feet cells."
] | [
"Bed of nails is actually a good example of cell strength, in so much as the cells surrounding the tip of the nail are strong enough to not let it penetrate. "
] |
[
"Is there an upper limit to the number of protons/neutrons you can have in one nucleus?"
] | [
false
] | null | [
"Yes, but the value of the upper limit depends on the circumstances.",
"The heaviest completely stable nucleus is lead-208. Everything with more than 82 protons or 115 neutrons is unstable and decays eventually. But many are stable enough to last an appreciable amount of time; e.g. U-238 has 92 protons and 146 ... | [
"What about the \"island of stability\"? Isn't there a theoretical spot somewhere above the end of the periodic table in which atoms once again become stable?"
] | [
"Yup. In fact, we already have one such element (Ununoctium), but haven't yet synthesized the potentially stable isotope of it to be sure if it really will be stable."
] |
[
"Is there such a thing as people who can't conceptualize number?"
] | [
false
] | null | [
"https://en.m.wikipedia.org/wiki/Dyscalculia"
] | [
"So that's difficulty understanding numbers and counting. But it doesn't seem to say inability all together. It's interesting... ",
"I am trying to argue that math is real philosophically. One argument that I use is that I was hard pressed to think of anyone or any animal unable to grasp the idea of a number or t... | [
"Sorry, that link has an additional link inside to ",
"https://en.m.wikipedia.org/wiki/Acalculia",
" which might be closer to what you are asking about directly in your post text. I'm not sure I exactly follow what you are asking about in this comment."
] |
[
"What are the requirements for a number to be truly random?"
] | [
false
] | Does such a thing even exist? I imagine the only thing that would make a random number generating process truly random would be if there are unknown or unpredictable inputs. For example each time you throw dice you might shift them around in your hands, throw them with a different force and there might be environmental effects that change the outcome such as different surfaces, air resistance, etc. But if there were a computer that could sufficiently track and account for ALL the variables involved in a the throw I would think it'd be able to predict the exact outcome. So is the only thing that makes a number random the fact that there are unknown inputs or an intractable process? I've heard of quantum random number generators being truly random, but is that only because we currently don't completely understand quantum physics? If we knew all there was to know about the process of quantum events would these numbers cease being truly random or are they somehow inherently random even if we knew all the inputs? and if so how is that the case? To me it seems like there could be no such thing as truly random and the only way we emulate it is by hiding inputs or processes in generating the number from the observer, but if the observer were aware of all the inputs and processes it'd be impossible to create a truly random number. sorry if i'm all over the place, i was just randomly reflecting about the thought earlier. | [
"You're very perceptive. Pretty much all of the numbers generated currently by computers are the result of algorithms that produce a long chain of numbers that ",
" to be random, but will eventually repeat if you keep running it for long enough. This is plenty random for almost everything we need in everyday life... | [
"The criteria for \"true randomness\" depend on what you want the random numbers for - Monte Carlo simulations are one thing, cryptography is another - but they can be summed up like this:",
"The question is, what counts as a \"pattern\"? Unfortunately there's no simple answer to that; it depends entirely on why ... | [
"The superdeterminism debate is a heated one in physics, but until we have a valid Theory Of Everything I think it is premature speculation to say quantum random number generators are ",
" random in the strong sense."
] |
[
"Can a single celled organism get cancer?"
] | [
false
] | [deleted] | [
"No. \"Cancer cells are defined by two heritable properties: they and their progeny (1) proliferate in defiance of the normal constraints and (2) invade and colonize territories normally reserved for other cells.\" (Essential Cell Biology, Garland Science, 2010)",
"A single-celled organism thus can't get cancer b... | [
"They CAN however mutate in a way that cancer cells come from though, through some sort of copying/translating error in DNA/RNA synthesis which can also cause the cell to die. It's not cancer but it's a fatal mutation. "
] | [
"Thank you. "
] |
[
"When you're using centifrugal force on a space station ( or ship ) to simulate gravity. What would happen to a helium baloon when you let it go?"
] | [
false
] | Just watching Babylon 5 which takes place on a spinning space station I saw a new years celebration where they used a helium balloon to lift a small "Happy new year" banner. And I wondered if that would actually work. | [
"Yes, the balloon will rise, though not in a straight line due to the Coriolis force. Here's an intuitive explanation for why it rises:",
"Imagine looking into the station from outside, along its rotation axis. The air inside, at least near the edges, is rotating along with the station due to friction with the ... | [
"Here is a site that answers you perfectly: ",
"http://webassignwired.webassign.net/2012/09/26/physics-experiment-helium-balloon-in-a-car/",
"What happens is that there is a small pressure differential between the edge of the station and the centre of rotation, and so the balloon will \"rise\" against that pres... | [
"Unfortunately the video in the link doesn't work because it's marked as private."
] |
[
"Questions about nose picking and other socially unacceptable habits"
] | [
false
] | Is there a reason we do them even though they're socially unacceptable? Are there any inherent risks or health benefits to habits like nose picking? In a general sense, how do habits like these form, and how can they be unlearned? | [
"Risks: Small but real risk of infection, which in turn ",
"can spread to the brain.",
"Nose picking (rhinotillexomania) can lead to infections in the nose, which is situated very close to the brain. They share the same blood supply. Getting an infection anywhere in the area doctors call the \"danger triangle\"... | [
"But why do we do it?",
"I always wonder this, same with scratching an itch. I know the itch scratching is overloading the nerve's itch signals with pain, but why is that our evolutionary instinct."
] | [
"Just a natural habitat most likely linked to removing blockages, and irritants or contaminates trapped in the mucus. "
] |
[
"Can you really tell ancestry by looking at someones foot?"
] | [
false
] | null | [
"I second this notion. While I've never heard of this specifically, human phenotypic traits are usually polygenic, so they're a combination of multiple genetic, epigenetic, and environmental factors. Trying to trace a particular anatomical feature to a geographic origin is sketchy at best, as there's likely to be a... | [
"I second this notion. While I've never heard of this specifically, human phenotypic traits are usually polygenic, so they're a combination of multiple genetic, epigenetic, and environmental factors. Trying to trace a particular anatomical feature to a geographic origin is sketchy at best, as there's likely to be a... | [
"The above is all true, however from an osteological perspective there are generalities that can manifest in the skeleton which from a legal perspective can be used to positively identify the ancestry or \"race\" of an individual e.g. nasal aperture, femur curvature, eye orbit angle. I've also been skeptical of thi... |
[
"If the universe will eventually run down and all motion cease, how can its expansion be accelerating?"
] | [
false
] | [deleted] | [
"Magic.",
" Physicsy magic, so the worst kind. "
] | [
"Because expansion is not 'fueled' by motion of stuff in any sense; rather it is an expansion of space itself. All the stuff, including matter and radiation, is just coasting along more or less with space."
] | [
"the universe in not \"coasting\". that would imply acceleration is 0. Space is expanding and the \"standard model\" of physics states that dark energy is responsible for it. The standard model is the widely accepted theory of the universe (e.g. it's not string theory or super symmetry). Dark energy has not bee... |
[
"How much has our view of the Moon changed throughout human history? When I look up am I seeing the Moon as it appeared, more or less, to William the Conquerer? Caesar? King Tut?"
] | [
false
] | Follow up, how far back in time would you need to go before our view of the Moon was noticeably different from the modern day? | [
"One thing that in principle can be different is the crater patterning. However, it seems unlikely that has changed in any meaningful degree in human history.",
"Certainly not all craters have been dated, but a decent number has. You can access a crater Excel sheet ",
"on this page",
". I shortlist two that s... | [
"You wouldn't notice it over the span of the entire human history. Even per 10000 years, that's less than half a kilometer. The moon's orbit varies by 40 thousand kilometers between perigee and apogee every two weeks.",
"You might start noticing movement if you make frames of a million year's change, and even the... | [
"The moon is slowly moving farther away from the earth. But for humans to notice you'd have to span out 10,000 plus years at a time. NASA claims its about 3.8 centimeters a year. Definitely not noticeable in one's lifetime."
] |
[
"My mum had the question \"Why don't the atoms of a liquid fall through the gaps between the atoms of the containers?\""
] | [
false
] | null | [
"It is not electrostatic repulsion as some have suggested. If that was the case, you would see behavior similar to Rutherford scattering. It is because of sometching called the Pauli Exclusion principle, which is curious aspect of nature that is central to quantum mechanics. It basically says that two “identical... | [
"It's not the molecules which are equal, but the electrons in the molecules (which also are responsible for holding said molecules together and for most of chemistry)",
"This means that electrons bound to water molecules and electrons bound to the plastic will tend to repel, as trying to confine them (bringing th... | [
"How does “two “identical” particles can’t occupy the same space at the same time” relate to the question? Are the two particles part of water, plastic or two of any particles between plastic and water (in this case). "
] |
[
"How do/can black holes \"grow\"?"
] | [
false
] | Perhaps this has been answered here or elsewhere, but I can't seem to find a clear answer. Maybe this is a dumb question, and maybe I've already read the answer before and forgotten, but: How is it that black holes can "grow" by consuming matter/mass? If matter beyond the event horizon is "gone" (though, I guess Hawking radiation would suggest otherwise?) why should the ingestion of matter after creation of the singularity cause the black hole to "grow" or otherwise become more dense? It makes sense to me that the aggregation of massive objects would do so, but does a singularity have mass, in the traditional sense? I guess what I'm struggling with is the idea that such mundane rules could apply to something so seemingly peculiar - is it just that simple, or is the actual phenomenon also appropriately exotic? | [
"Are you asking about a mechanism?",
"Because if so, they just ",
" by conservation of mass/energy.",
"When matter (or energy, such as photons) cross the event horizon it is absolutely doomed to end up at the singularity. That's just the way spacetime works in the black hole. Basically, geodesics (which are o... | [
"The event horizon isn't a physical surface like the surface of a massive object. When you add gas to a star it gets bigger because it's a big ball of plasma and you're just physically increasing its volume (for some stars, others will compress further due to the added weight). An event horizon isn't the edge of a ... | [
"Somewhat related, I understand that due to relativity an outside observer will not see something cross the event horizon. Can this be taken to understood that it can't \"grow\" after the initial formation? (at least to the outside observer)"
] |
[
"Biological symmetry and DNA: Are repeated body parts coded for once or multiple times?"
] | [
false
] | In the case of a starfish, does the DNA essentially say, "Here's how to build an arm, now repeat 5 times?" And if so, are mutations affecting only one arm extremely rare? | [
"You're right to think that this would be redundant. Body parts (and at much smaller levels, tissues, cells, and molecules of proteins) are not individually coded for in this way. ",
"Rather, the genome encodes developmental genes that pattern the body from the earliest stages of development. There are many mecha... | [
"This is super interesting. Any chance you could recommend a book or something to read more about it? "
] | [
"Endless Forms Most Beautiful, by Sean B. Carroll - I had to read it for a course on developmental biology, and it was helpful without getting too technical. "
] |
[
"What happens to an injured blood vessel?"
] | [
false
] | What happens after a shot, bruising, etc. Does the blood vessel clot and then heal up, or are they replaced by new blood vessels? | [
"Let's say someone gets shanked in their leg during a street fight and compromises a small artery. For simplicity's sake we'll ignore other aspects of the trauma and focus on the arterial injury.",
"Immediately after the injury, hemostasis occurs. This is begun by a brief period of ",
" (basically, small vess... | [
"Thanks!"
] | [
"Yeah, science bitches!"
] |
[
"Regarding Amplifiers"
] | [
false
] | So I'm reading about programmable gain amplifiers and A/D converters, and the text said that amplifying "a low level signal by 10 or 100 increases the effective resolution by more than 3 and 6 bits respectively." The example given is that, for a 12-bit A/D converter, any signal below 2.44 millivolts on a 10 volt range will go undetected. But if you amp the signal by 1000 before the conversion, the resolution could be increased to 2.44 microvolts. Can someone show me the math behind this and why the resolution would increase? | [
"Try ",
"this picture",
". Although this only shows a 3-bit ADC, the theory translates directly. ",
"If your input signal is a single-bit resolution, you get a square wave out of the ADC: 0 or 1 are the only two possible options. This is the case if you have an input signal, in your example, which varies from... | [
"No think about it. Your resolution is always 2.55 microvolts but if your signal goes up to 2.6 microvolts then the ADC will only read 0 or 1. Increase the voltage and you get more possible values."
] | [
"Perfect answer. The last paragraph was exactly what I was looking for."
] |
[
"How do kernel programmers access software interrupts while writing code in C?"
] | [
false
] | Additionally, is there any mechanism in place to prevent someone from writing an ordinary program that, when compiled and run in user mode, prevents it from hijacking this same functionality and entering kernel mode? | [
"Additionally, is there any mechanism in place to prevent someone from writing an ordinary program that, when compiled and run in user mode, prevents it from hijacking this same functionality and entering kernel mode?",
"Yes, No, and also yes. ",
"(Yes) CPUs support permission levels such as Ring 0, Ring 1, Rin... | [
"Yep. Memory is typically divided into \"kernel space\" and \"user space.\" The memory management hardware will block access to kernel space when in protection ring 3 (user mode), generating a segfault on a modern machine.",
"If you're already broken that barrier, then you have write access to the entire kernel, ... | [
"There are no instructions that work in user-mode that allow you to manipulate the MMU. Simple as that. There are no magical registers.",
"Unless the kernel is ridiculously-poorly implemented, the page directory and such are going to be mapped as kernel-only, so if your user-mode application tries to manipulate i... |
[
"How many neurons does an average modern neural network have?"
] | [
false
] | [deleted] | [
"Generally it heavily depends on the complexity of the \"decision\" or classification that the neural network needs to make. To try to put it into perspective, one very used open dataset that I previously used to test the implementation and accuracy of my neural network, is MNIST (",
"http://yann.lecun.com/exdb/m... | [
"What I meant was, the beginning of neural nets was formed very much like the brain, stemming almost directly from feedforward neural control. People discovered very quickly that brain models break down. The first example of this was the perceptron activation function. Mathematically, things don’t necessarily work ... | [
"What I meant was, the beginning of neural nets was formed very much like the brain, stemming almost directly from feedforward neural control. People discovered very quickly that brain models break down. The first example of this was the perceptron activation function. Mathematically, things don’t necessarily work ... |
[
"Why don't you see a solid shade of black when you close your eyes, even in complete darkness?"
] | [
false
] | null | [
"Close your eyes and rub them really hard",
"Don't do this. You could damage your eyes. Pressing gently is enough to generate the effect."
] | [
"Close your eyes and rub them really hard",
"Don't do this. You could damage your eyes. Pressing gently is enough to generate the effect."
] | [
"Much of what we 'see' is actually just what your brain thinks is there. For example, we have very bad colour vision in all but the centre of our field of view. The sensation of colour vision in your periphery is a clever trick pulled off by your visual system, which keeps track of what colours things were last tim... |
[
"Destructive Interference and Conservation of Energy"
] | [
false
] | Let's say that one was able to aim two beams of polarized light of the same wavelength but 180 degrees out of phase with each other. From my limited understanding, the electric and magnetic fields should cancel out, but then where does the energy go? EDIT: I meant 180 degrees out of phase, woops. | [
"Wherever there's destructive interference, there's constructive interference. Every point in space where the field value goes to zero is accompanied by another point in space where it goes to twice what it would otherwise have been. So the books balance."
] | [
"I guess I was thinking about two waves that look like ",
"this",
" coming at each other, but completely out of phase. Would that be an un-physical picture?"
] | [
"It is not clear if you mean that the beams travel in the same or opposite directions. If opposite directions, you get a standing wave where the fields cancel only at the nodes, every half wavelength.",
"If in the same direction, the phase must be 180 degrees to have a cancellation. As other contributors noted, y... |
[
"How deep below sea level could a canyon theoretically get?"
] | [
false
] | Would it get too unstable at some point and collapse in on itself? | [
"Assuming this is a canyon cut by a river, no more below sea level than the base level of the river (i.e. the elevation of the body of water the river flows into). Rivers tend toward an equilibrium condition referred to as a 'graded profile'. Here is a ",
"graphical representation",
" and a classic paper descri... | [
"I like the other answers, but they don't answer this interesting question; \"how deep could you dig a canyon on Earth before it collapses?\" This is similar to the popular question \"what's the highest possible mountain?,\" answered very well by ",
"/u/CrustalTrudger",
" ",
"here",
".",
"Let's imagine an... | [
"I'm thinking that maybe the question was about deep-sea trenches rather than a true canyon."
] |
[
"Can light make a sound?"
] | [
false
] | Is it possible to turn on a light with such intensity as to cause a vibration that could be heard? I figure light is made of particles and sound is just compressions of matter. So could light possibly make a sound? | [
"There are a few effects involving the ",
"interaction of sound and light",
". One of these is the photoacoustic effect, where light causes something to expand which causes it to emit sound."
] | [
"I know that by light you probably mean visible light, but low frequency electromagnetic radiation can make ferromagnetic materials vibrate due to ",
"magnetostriction",
". The sound produced is called ",
"Mains hum",
" and you can hear it around transformers."
] | [
"Light produces pressure, however very minimal (near µPa from Solar light IIRC). So probably you could generate a sound by:",
"1° Illuminating a membrane with a super powerful light emitter.\n2° Alternating on/off frequency to match an accoustic frequency (20-20 KHz).",
"However it's pretty useless and unpracti... |
[
"Why are we seeing increased rates of skin cancer in young adults when they are generally spending less time outdoors than before?"
] | [
false
] | Hopefully this doesn't violate the "No Medical Advice" rule, but I wondered about this since I just had my second biopsy for skin cancer at the humble age of 22 (think we got everything out, knock on wood). After doing some googling on skin cancer in youth it seems that rates have increased recently, moreso in women than men. Many experts attribute this to intentional tanning, but I wonder why we didn't see these high rates of skin cancer before when kids would work outside much more often. Have we just gotten better at detecting it or is there something else at work here? One thing I was thinking of is maybe this new generation doesn't spend as much time outside as previous ones and therefore is more easily susceptible to UV radiation. | [
"One big theory is that the increase is due to better screening. If we get better at looking for something, and spend more effort trying to diagnose it, we will find more of it. Much like autism.",
"However, ",
"this study",
" (pdf warning) puts the melanoma incidence increase at 3.1% per year, and by looki... | [
"In the past, working outside was a more regular activity. Youths working in sunlight tended to already have a built-up tan and they would also wear protective clothing (shirts, jeans, hats) rather than stripping down to a bathing suit. Work would also be done at times such as morning and evening, when the sun is m... | [
"Your second biopsy for skin cancer? Wow.",
"\nI had my first at 19, I'm 20 now. I really hope I'm never going to get it again. Good luck with that. Do/did you get into the sun often? "
] |
[
"Does every element have a solid, liquid, and gas form if brought to the correct temperature?"
] | [
false
] | I know that different elements have different threshold temperatures which determines their state, but do all elements have the three standard states available to them? | [
"Barring weird exceptions due to quantum mechanics (looking at you He-3), yes, you get all three, but you must vary both temperature ",
" pressure. For instance, at atmospheric pressure, carbon only has a solid and a gas phase: if you heat carbon enough, it will sublimate and turn to gas without turning to liquid... | [
"Excellent reply.",
"OP, google \"phase diagram\". Or read this:",
"http://en.wikipedia.org/wiki/Phase_diagram"
] | [
"Yes H3 is solid at low temperatures above 33 Atmospheres. See ",
"http://hep.ph.liv.ac.uk/~hock/Teaching/2011-2012/8-liquid-helium-3-handout.pdf",
" for a nice phase diagram. Didnt know that either until a few minutes ago ;)"
] |
[
"What happens to the light of a star so far away that it is moving away from us faster than the speed of light? Does that light eventually reach us?"
] | [
false
] | null | [
"Due to Hubble expansion, stars far enough away are receding faster than the speed of light. In fact they are not just receding, but accelerating away, such that some stars that we currently can see will eventually disappear beyond the Hubble limit. ",
"Source",
"Edit: In answer to the OP's question, if expansi... | [
"Due to Hubble expansion, stars far enough away are receding faster than the speed of light. In fact they are not just receding, but accelerating away, such that some stars that we currently can see will eventually disappear beyond the Hubble limit. ",
"Source",
"Edit: In answer to the OP's question, if expansi... | [
"What do you mean \"if the expansion was constant\"?",
"I'm having trouble understanding the cambridge paper linked above. It says we can observe galaxies that have and always had recession velocities greater than the speed of light. :/"
] |
[
"Does persisting depression damage the brain?"
] | [
false
] | null | [
"Yes, but these changes are preventable and can be reversed with treatment. Here are a few examples: ",
" Brain cells look like little trees under a microscope, and depression makes them lose their branches. To quote a ",
"neuroscientist",
", ",
" ",
"Depression kills your brain cells",
". Just like tre... | [
"According to what we know now, are there different causes for depression? Like, LTP in the lateral habenula sounds like it may be sufficient to cause depression on its own, but will it always present with LTD in the prefrontal cortex? It seems like depression may be a clinical diagnosis with a range of causes, fro... | [
"Fascinating insight, thank you! Seems like there is good news with antidepressant use, contrary to what many people think."
] |
[
"Was the development of life on Earth a one-time event?"
] | [
false
] | If life first developed from some sort of primordial soup approximately 5 billion years ago, how do we know that these types of conditions don't exist all over the place (here on Earth), for example in thermal vents in the ocean, or tidepools, and are creating new life all the time, or even occasionally? Was the jump from non-life to life on earth a one time single event, or does it happen all the time, or somewhere in between? | [
"There is a small fraction of amino acids that are used to build proteins in all life, and they are all left-handed isomers. If life wasn’t descended from the same tree, you would expect different amino acids to be used and for right-handed isomers to be used in some life.",
"More examples:",
"https://en.m.wiki... | [
"Left handed and right handed isomers refer to different versions of the same molecule. They work the same, but the 2 isomers have 3D structures that are mirror images of each other. The names left and right are used to distinguish between the 2 types."
] | [
"Or a new kind of life could have started forming but been totally out competed for resources by existing life."
] |
[
"If you hold off going to the bathroom, does your body still absorb nutrition from the waste after you feel your body trying to have a bowel movement? 🚽"
] | [
false
] | null | [
"Hi Fwest3975 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... | [
"Human body"
] | [
"‘Human body’"
] |
[
"Is there any theorem in mathematics that states axis conversion for graphs(see details)?"
] | [
false
] | eg: I'll take a simple case, if there is an equation x + y = 4 then when the axis of the graph are x and y the points form a circle but when the axis are x and y then it is a straight line with some restrictions. Here, it is easy to decide if it is a circle or a line but most of the times it is tough, so is there a theorem that defines the relation between two or more different types of axis and relates them. | [
"You're just doing a change of variables. If we put a=x",
" and b=y",
", then the circle x",
"+y",
"=4 becomes the line (segment) a+b=4. Since a and b are squares of other numbers, we can only look at solutions a+b=4 for both a and b positive.",
"But if you have a general equation in variables x and y, a... | [
"The latter is definitely a hyperbola, right? Am I going crazy?"
] | [
"1-b",
"=a",
", and moving the b to the other side gives 1=a",
"-b",
". This change of coordinates changes the hyperbola x",
"-y",
"=1 into the circle a",
"-b",
"=1",
"1=a",
"b",
" , right`?"
] |
[
"Why do my ice cube trays flash with light when I crack them in the dark?"
] | [
false
] | If you haven't tried this, you should. Simply crack a fresh tray of ice cubes in the dark. You will notice that they create a flash of light when they crack. It is pretty cool - yet, I can't find a good scientific explanation for it. | [
"Fractoluminescence",
"*edit for better link"
] | [
"Its also possible to see flashes of blueish light from Scotch Tape by quickly unrolling it in a dark room. If done in a vacuum, the ",
"X-rays",
" generated are strong enough to develop an X-ray image on photographic paper."
] | [
"Ben Krasnow has a video demonstrating both effects in a vacuum chamber."
] |
[
"Do plants die of \"old age\"?"
] | [
false
] | null | [
"There are plants that are ",
"indeterminate,",
" meaning that they will continue to grow until external forces kill them. But there are many plants that are annuals or biennials or ",
"semelparous,",
" and therefore clearly not \"immortal.\" Whether these plants would be immortal under certain conditions (... | [
"Is it possible that some of those plants are indeed immortal, but once they get into the time frame of thousands of years they have to deal with weather pattern changes and since they can't move they die because their locations are no longer ideal for them?"
] | [
"Also things like 1,000 year floods, fires, earthquakes, tsunamis and other rare events."
] |
[
"Exactly how do scientist create new chemical elements, and what stops them from creating atoms with any number of protons?"
] | [
false
] | [deleted] | [
"Source: undergrad medicinal chemist, took some physical chemistry modules in 2nd year. ",
"I know little of the details of the fusion but I do know they fuse elements such as Nickel (rather heavy elements) to make these ",
"SHEs",
" (Super-Heavy Elements), and AFAIK that's how the heaviest, synthetic element... | [
"Pretty much, you can set up a reactor and throw a bunch of money at it to obtain a few grams of unununium, but you better play with it quick because it will decay in less than a minute and you'll probably have cancer when you are done."
] | [
"Pretty much, you can set up a reactor and throw a bunch of money at it to obtain a few grams of unununium, but you better play with it quick because it will decay in less than a minute and you'll probably have cancer when you are done."
] |
[
"Why does squinting slightly improve your vision?"
] | [
false
] | null | [
"Staus' explanation is interesting, and not one that I have heard. It does sound somewhat plausible.",
"Keep in mind that I am not an optometrist, but I do teach anatomy and physiology, including of the eye, in extensive detail.",
"The explanation as I learned it in medical school is that squinting increases t... | [
"It's the same reason that a pinhole camera works. By collecting the light that passes through a small aperture, the intensity of high-angle light rays is greatly reduced. These high-angle rays contribute more to the blurriness when not quite focused than the low-angle rays. ",
"Basically you end up trading sp... | [
"To me it does. Try it. ",
"If I stare at some distant text, and narrow my sight using my hands or pieces of paper, my sight also improves. Not just in bright light. In fact I don't see any more improvements with squinting."
] |
[
"HOW do we know water contains 2 Hydrogen bonds and 1 Oxygen Bond."
] | [
false
] | I know its true, and it makes sense and everything but HOW did someone find this out? Is there an experiment or was it deduced through logic? | [
"You mean atoms?",
"Anyway, if you have two equal volumes of gas at equal pressure and temperature, you know they have the same number of molecules. If you mix equal amounts of hydrogen and oxygen together and combust it, there will still be hydrogen remaining. But if you have twice as much hydrogen as oxygen, al... | [
"To prove it, you split water apart through electrolysis then prove that the gases had identical properties to oxygen and hydrogen through controlled experiments, most likely through other chemistries. This would also prove that the molar ratios are 2:1. ",
"But the 2:1? You already know that from the gas law, s... | [
"Interestingly, there is recent evidence that water acts not as a single H2O molecule but as a working group of like 20 of those."
] |
[
"At what depth in the sea would the pressure kill a human?"
] | [
false
] | [deleted] | [
"The current record for scuba diving is 330m, but dives over 200m are rare and dangerous...Guinness no longer publishes records because so many people have died.",
"The main danger is the ascent...a diver might spend 20 minutes going down, then 12 hours coming back up to avoid the bends and other decompression re... | [
"Dammit, I meant 1.4 furlongs.",
"Now they are going to kick me out of the US."
] | [
"THANK YOU for using the metric system."
] |
[
"Why is the strong force repulsive at small distances?"
] | [
false
] | I'm an A-level student so don't throw too much maths at me but the other day my physics teacher said that at very close proximities the strong force acted to repel particles instead of attract them. Why? | [
"If I understand correctly the force that binds nucleons together (",
"nuclear force",
" but often inaccurately called \"strong force\") is indeed repulsive at very short distances; otherwise nuclei would just collapse entirely. The mechanism behind this is actually a force arising from the Pauli exclusion prin... | [
"My favourite ",
"link",
" for \"why\" questions, especially of this nature.",
"Also the Strong force itself isn't repulsive over short distances, just an effective description of it for use between nucleons is."
] | [
"To my knowledge it's not. The strong force itself binds quarks together so tightly that it is impossible to observe a free quark (the strong force between two quarks does not decrease with distance). The residual strong force binds nuclei together and has a limited range, but it is also never repulsive (rather, wh... |
[
"What would you see in the middle of a ring of mirrors?"
] | [
false
] | If you were to have a giant ring of mirrors set up, so that there were no corners between them (so effectively a giant ring shaped mirror), and then stand in the middle of it, what would you see? I can't my head around this and I can't figure out if you would see one reflection of yourself, or a reflection of yourself everywhere. If it's the second option, what would that even look like? | [
"Lighting design engineer here. We work with parabolic reflectors all the time. They try to focus light (information) from a source and put it into a specific direction. All parabolic surfaces, however, have a focus at which point rays of information will converge. With a perfectly circular surface concentric with ... | [
"I briefly considered breaking out the 3D modeling but my example would have paled sharply in comparison."
] | [
"I briefly considered breaking out the 3D modeling but my example would have paled sharply in comparison."
] |
[
"How do we solve problems that don't have constant acceleration?"
] | [
false
] | [deleted] | [
"Calculus! Lots of it.",
"We solve Newton's second law which is a second-order ordinary differential equation. Solution methods for finding analytical solutions for several sub-classes of such equations are typically covered in a course on differential equations. Such sub-classes of equations include separable eq... | [
"This is literally why calculus was invented! If you’re at all interested in physics you should take it. Algebra-based physics sacrifices a lot to accommodate students’ math skills: the real universe is built out of calculus."
] | [
"One method that's often used is you arrange your equation in such a way that you 'guess' something 'close', and calculate some 'difference'. You solve the same equation over and over until this 'difference' gets really small. This is the current way that almost every complex engineering problem is solved from flui... |
[
"What specific behaviors cause increased degradation of lithium ion batteries?"
] | [
false
] | We all know that using a lithium ion battery causes it's capacity to decrease over the years. But I am interested in better understanding how different usage patterns impact the speed of this degradation. I've read some about the chemical mechanisms that cause this problem, and I've read several articles on "best practices" for battery health, but I still do not feel like I have a good understanding of everything. For example, suppose we need to use 20% of the energy of a battery. Is it best for the long term health to only charge the battery up to 20%, and then drain it to 0%, and then back to 20%? Or is it better to go from 100%-80%-100%? Or is the optimal thing to split the middle and go from 60%-40%-60%? I have also seen it mentioned that charging batteries more slowly improves their lifespan. Is this solely because of reduced heat, or is that still true even if temperature is removed from the equation? I have also seen many mentions of "deep cycles" being bad for the battery, meaning that multiple smaller discharges/recharges in a row are better than a longer discharge. Does this mean that, in the previous example, using the battery from 100%-80%-100% every day is worse for long term battery health than doing four sets of 100%-95%-100% every day? While I would certainly appreciate any well-informed answer to the above questions, what I am ultimately searching for is a better understanding of the subject that would allow me to answer such questions myself. | [
"Because battery life in hours is an important marketing metric and battery life in years is not"
] | [
"If I buy a pricey phone or car, should I expect the charging system to actually change to ~85% and tell me it's 100%?"
] | [
"If I buy a pricey phone or car, should I expect the charging system to actually change to ~85% and tell me it's 100%?"
] |
[
"Does transparent material like glass affects wifi as much as non transparent wall?"
] | [
false
] | null | [
"Things are transparent to different wavelengths of light. You have seen glass that is transparent to green but not red or plastic that doesn't let through blue or whatever. Wifi is just another color of light. ",
"That said glass is pretty transparent to wifi, as is plastic, but also things that aren't transpare... | [
"If you have enough wood it'd eventually stop the signals but yeah, wood is pretty transparent. ",
"On the flip side we can see visible light through water real well but wifi is stopped very quickly by water. If you put a router underwater it'd have a range of only an inch or two. Water absorbs wifi real well. "
... | [
"Oddly brick is fairly transparent to wifi in a way stone and concrete are not.",
"Why's that?"
] |
[
"What physically happens to the body in a morphine overdose?"
] | [
false
] | I know that its used in regulation to negate pain but what physically happens to a body when a large amount of morphine is given to kill someone. | [
"This isn’t quite right. It does relax muscles as well, but the respiratory depression you’re talking about is central. The kind of action you’re talking about is neuromuscular blockade, which opioids can’t do.",
"Because there are a lot of opioid receptors in the brainstem (a part of your brain that controls a l... | [
"Painkillers (such as morphing, heroin, OxyContin, etc) relax muscles as well. In large enough doses, the person is literally unable to move a muscle, voluntarily or otherwise. ",
"This means that the diaphragm, which is the muscle used to breathe, cannot contract. The person suffocates because the brain can not ... | [
"Because it’s not like they know they’re suffocating...they’re in an opium dream where everything feels wonderful and then they just drift off to death. "
] |
[
"Why shouldn't you give babies honey?"
] | [
false
] | null | [
"Honey contains ",
"Clostridium botulinum",
" spores which can give rise to ",
"infant botulism",
", which can lead to short-term paralysis (",
"floppy baby syndrome",
"). Why don't adults get botulism from honey? It isn't completely understood, but one theory is that adults have more bacteria in their ... | [
"The great thing about asking these questions is that they share interesting insight with other people who may not have otherwise pondered the topic."
] | [
"The great thing about asking these questions is that they share interesting insight with other people who may not have otherwise pondered the topic."
] |
[
"In spacetime continuum, why are we only able to move forwards in time, when we can move in any direction in space?"
] | [
false
] | null | [
"This is a deep and interesting question. The short answer is that it's because we're made of massive particles. Massive particles travel on ",
" paths, which are paths through spacetime that go forward (or backward) in time. Massless particles travel on ",
" paths, which correspond to travel at the speed of li... | [
"Why do you expect directions in space and directions in time to behave exactly the same? They are different - it is not an accident that they have different names."
] | [
"The answers bringing up the laws of thermodynamics are not complete. The answer to your question is that there is no \"movement\" through time, as such. The state of the universe is different at any particular point in time from any other point. The illusion of movement is a result of the way our memory works. Tha... |
[
"Would this rollercoaster kill its occupants? I saw it on reddit a few days ago and wanted to know if it was true or not."
] | [
false
] | [deleted] | [
"The designer claims it would subject the riders to a sustained 10 Gs over 1 minute."
] | [
"The designer claims it would subject the riders to a sustained 10 Gs over 1 minute."
] | [
"I was under the impression that it took several minutes of oxygen deprivation to cause permanent damage, much less death, of your brain."
] |
[
"Is there a limit to how high birds can fly? What's the determining factor?"
] | [
false
] | null | [
"Very interesting study",
". One very interesting thing about these birds is that there lungs don't function like ours, with repetitive inhale-exhale-repeat. The air actually flows through their lungs in a more continuous flow. "
] | [
"Like a jet engine?"
] | [
"From ",
"wikipedia",
":",
"A Rüppell's vulture was confirmed to have been ingested by a jet engine of an airplane flying over Abidjan, Ivory Coast on November 29, 1973 at an altitude of 11,300 m (37,000 ft).",
"That's a sad way of realizing how high they can fly."
] |
[
"Why have humans not evolved to develop a more robust defence system against disease-causing microorganisms, even when they are one of the leading causes of human deaths?"
] | [
false
] | null | [
"Microorganisms are evolving too, and they're faster because there's more of them and they reproduce more quickly.",
"Also, we're ",
" them evolve more quickly by providing evolution pressure through the overuse of antibiotics and hand sanitizers, plus our global transport infrastructure providing global rapid ... | [
"Our immune system is incredibly robust. We fight off continuous infection each day, every hour and minute of it. There are always viruses and bacteria trying to kill us and they get a few cells worth of damage done before we take them out. Compare that to a bacterium in the ocean. Estimates are that 30% of bac... | [
"Not on the same time scales. \nA human generation is roughly 20 years, a virus, 12 hours, bacteria minutes."
] |
[
"Is there any place in the universe where there is literally zero gravity?"
] | [
false
] | I get that we couldn't go there and observe it, as our being there would create a gravitational field. | [
"you could have a point in space where the net gravity is zero. Kind of like the tunnel through the center of the earth problem everyone always talks about. but this point in space would be infinitely small and as you moved away from this point, the gravitational fields wouldn't cancel out anymore. "
] | [
"In what way does that answer say that there is a center to the universe?",
"They said that if you were between objects, the gravitational forces would cancel out."
] | [
"Gravity as a force has (as far as we can tell) an infinite extent, so the gravitational field of every single mass in the universe has an effect at every other position in the universe.",
"So the answer to your question is 'no' by the general laws of gravity, though it may be possible to say 'yes' if you want to... |
[
"Why are quantum fields quantized?"
] | [
false
] | I know it may sound silly, but for example, if you put an electron in a box it will have only permitted energies depending on the size of the box. If the electron was free, it could have any energy. So my question is, what makes an excitation on a quantum field (particles) quantized? | [
"“Quantization” in QFT doesn’t refer to energy, it refers to the fields. The fields are quantized in that it can only be excited with discrete numbers of particles. If you want, it’s the “amplitude” of the field that’s quantized."
] | [
"As you said, a particle in a box is quantized and its quantum depends on the size of the box (i.e. on its boundary conditions). However, this is not true in general as there are systems which are inherently quantized, without introducing any boundary conditions. One of these systems is the quantum harmonic oscilla... | [
"However, this is not true in general as there are systems which are inherently quantized, without introducing any boundary conditions. One of these systems is the quantum harmonic oscillator",
"Isn't the \"boundary condition\" in this case the requirement that the wave amplitude approach zero as displacement ap... |
[
"How does an ethanol gas sensor work from both a chemical and a circuitry perspective?"
] | [
false
] | I am trying to program an ethanol gas sensor as a personal project and I am a little stumped in a few places. I was originally creating a CO2 sensor, but the parts never came in so I had to make due with the ethanol sensor I already had. for the model I'm using and for how I'm programming the arduino board. My questions are as follows: what unit of measurement is the sensor outputing to the arduino board, what is the purpose of the resistor when there is already a direct connection to the ground, and why are there 6 pins. Ultimately I would like to calibrate the sensor so I can use it to measure different concentrations of ethanol, so I am very interested in understanding the complete inner workings of this device. Any help at all would be greatly appreciated. I am in third year of an undergraduate chemistry specialization if you are wondering what level of science I can comprehend. | [
"That is a really bad data sheet. ",
"Here's another one",
".",
"First off, there's a heater you don't really care about, it's there to keep the sensor at a constant temperature to avoid miscalibration.",
"Basically, the sensor itself is a variable resistor, controlled by alcohol concentration. The value of... | [
"If he was an electronics tech or engineer yes, but sounds like he's a stuggling chemist who needs a little theory to get started."
] | [
"You don't want to let the guy work it out for himself at all?"
] |
[
"Would it be worth it to place telescopes at the poles?"
] | [
false
] | null | [
"For every completely dark day, there's a \"white night\" where observing would be impossible. The costs associated with building a telescope at the pole are high, and you're at sea level instead of at a high altitude, so you get lots of distortion from the atmosphere."
] | [
"As a side note: The ",
"IceCube Neutrino Observatory",
" ",
" located at the South Pole. The detector is referred to as a neutrino telescope, though it is not a telescope in the conventional sense of using lenses or mirrors to focus something, and it detects neutrinos, not light. You can read about the obse... | [
"There are plenty of telescopes already at the South Pole: ",
"http://en.wikipedia.org/wiki/Category:Astronomy_in_the_Antarctic",
". That page doesn't seem to list any ",
" telescopes, but some of those exist and more may follow: ",
"http://www.phys.unsw.edu.au/jacara/Papers/pdf/rsnsw_pilotretrospective.pdf... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.