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[
"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, rotating black holes that will actually occur."
] |
[
"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 ",
" to occur in males, however, it's likely that some selection can take place in utero."
] |
[
"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 the likelihood of a boy child is increased, while if the pH is left more basic, girls are the result.\"",
"However, they continue later on to point out that the difference is exceedingly small, but non-zero."
] |
[
"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 calculations."
] |
[
"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 figured it our yet. This happened before, e.g. with the MD5 checksum algorithm. "
] |
[
"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), find z\" is still a hard problem. "
] |
[
"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) representations. These are guided by various optimality schemes or neuro results and have some promise to make things like auditory scene analysis more powerful."
] |
[
"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. There are a few issues that need to be considered.",
"For example, the amplitude in your spectral representation has to be positive. It is possible your noise estimate may be a little too high at some instance so subtracting it from the current value results in a negative. To get around this you can simply clip the value at zero, or some threshold slightly higher than zero. If your noise estimate is too low, on the other hand, you make get small peaks in your spectrum. These sound like brief musical tones when played back, and so are referred to as musical noise.",
"Here are ",
"spectrograms of a clean signal, corrupted with 5dB white noise, and enhanced using spectral subtraction",
". The musical noise is evident as \"blotches\" in the background.",
"EDIT: I should have mentioned that spectral subtraction isn't a fantastic enhancement method, but it is one of the simplest to understand conceptually."
] |
[
"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', everything else is background. This allows you to separate components of the audio.",
"http://en.wikipedia.org/wiki/Computational_auditory_scene_analysis"
] |
[
"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 nuclear fuel, a lot of which was spread around the surroundings when the (non-nuclear) explosion blew the roof of the containment hall off."
] |
[
"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:",
"http://www.todayifoundout.com/index.php/2013/10/can-people-live-hiroshima-nagasaki-now-chernobyl/"
] |
[
"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.",
"And the answer is, with an ",
" high degree of certainty, that the universe is spatially open, flat and infinite. (Those are all effectively synonyms in this context.) That means if you traveled in a straight line in space, you would ",
" end up back where you started, but rather you'd just keep going on forever.",
"Now, I've been getting more than the usual amount of hate mail today anyway, so I doubt my saying this will help at all. But I'll say it anyway: Can we ",
" that this is correct? Of course not. But again, we are ",
" certain that what I just said is true. It's on par with asking how sure we are that the sun is lit by nuclear fusion, or that the Earth does not have a core of solid custard. No one will ever be able to ",
" things like that with their eyes, ears or hands. But we are as certain of the correctness of our inferences as it's really reasonable ever to hope to be."
] |
[
"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 expanded.",
"If the universe is infinite, then we'd see the entire night sky filled with stars... no?",
"No. That's called ",
" It's usually stated like this: In an infinite universe, every ",
" you can extend from the centre of the Earth out into space must eventually intersect a star. Therefore the sky should be blindingly bright.",
"But the paradox is resolved by the fact that not every ray you can extend out from the centre of the Earth intersects a star ",
" The universe is only about ten billion years old; only objects which lie within a certain distance can be seen, because light from any more distant objects hasn't yet had time to reach the Earth."
] |
[
"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 keep you from falling out of trees. It doesn't help you when thinking about cosmology. So it turns out that those questions are simply ",
" There is no \"outside\" the universe; the concept of \"outside\" does not apply to the universe. There is no \"before\" the Big Bang, because the concept of \"before\" does not apply to the Big Bang.",
"I know that's hard to accept, if you're fixed on imagining that the universe is just like the world around you only bigger. But it's true."
] |
[
"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 action is unknown. Iodine rapidly penetrates into microorganisms (76) and attacks key groups of proteins (in particular the free-sulfur amino acids cysteine and methionine [184, 267]), nucleotides, and fatty acids (15, 184), which culminates in cell death (184). Less is known about the antiviral action of iodine, but nonlipid viruses and parvoviruses are less sensitive than lipid enveloped viruses (384). Similarly to bacteria, it is likely that iodine attacks the surface proteins of enveloped viruses, but they may also destabilize membrane fatty acids by reacting with unsaturated carbon bonds (486).",
"The tldr is that iodine probably interferes with various proteins' behavior, and it's not terribly specific to any particular proteins, just to some building blocks that exist in many proteins. Proteins need to bond to themselves in order to fold into the right shape, and usually bond to other things in order to do whatever it is they do, and iodine gets into and messes up those bonds. (The free-sulfur amino acids are important for bonding.)",
"This makes it a good disinfectant in part because it's very broad-spectrum — it's not interfering with some specific process that some germs might not have, it's interfering with some basic mechanisms that are used all over the place by earth life."
] |
[
"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 the chemical structures of bacteria?"
] |
[
"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 surface (i.e. uplift along the course of the river forming a dam, subsidence of areas along the river forming a depression), but any changes that influenced the river course would likely be relatively temporary. Natural dams formed by earthquake ruptures (or landslide deposits) are not stable. As the newly impounded water rises, the dam material will become saturated leading to instabilities (e.g. ",
"sapping",
"). Even if it survives until the water level rises to the top of the dam, once the water level over-tops the dam, rapid erosion of the blockage will remove it."
] |
[
"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 earthquake had uplift of ~10 m and subsidence of ~3 m",
"). And even if there was exceedingly large magnitudes of subsidence, it would take something akin to a megathrust event to produce a rupture long enough to have any (even minimal effect) over the distance between the Gulf of Mexico and New Madrid. Using the 1964 quake again, that ruptured a fault length of ~900 km, but uplift/subsidence would have been minimal as you approached the tips of the rupture and generally maximum uplift/subsidence is going to be near the center of the rupture, so even if you had a 900 km long rupture, centered at New Madrid and aligned perfectly to extend toward the Gulf, it would only get ~450 km away from New Madrid (still ~200 km shy of the Gulf Coast), not to mention the fact that by the time you gt to the tip of the rupture, there is no displacement. So no, the scenario is in no way feasible."
] |
[
"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 distinct way so that each piece you solve exactly sets up the next one appropriately.",
"For instance, here's the webpage introducing probably the best-known blindfold method: ",
"the Pochmann method",
". In this method, you basically start out by finding a piece you want to move into an appropriate location. You then move it there, careful to affect the rest of the cube as little as possible (of course, you must also move the piece that's currently sitting at the destination, and perhaps a couple more pieces somewhere else, but leave the rest of the cubies as is). The algorithm works in such a way that the piece that was at the destination is now where your other piece started! Therefore, you now repeat this process for the new piece. Repeat this (with minor caveats) for each edge and for each corner, and eventually you're done!",
"So what exactly needs to be memorized? Just the destinations of your pieces. A typical example, taken from the site, would be memorizing something like ",
"FR - UL - FD - DB - DR - UF - LB - UB - DL - FL - BU - stop - UB - RD - UF - UR - DL - RB - FR - LD - BL\n",
"(where F = front, B = back, U = up, D = down, L = left, R = right) or some color coded equivalent.",
"This is not hard to do using either the ",
" (come up with a story based on the text -- see the link for an example) or simply by lots of practice."
] |
[
"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 variants which are slightly different proteins made from the same gene, but that's getting above my level knowledge. There is some evidence these have different effects and there are some compounds which bind selectively to one or the other:",
"The ability of mu opioids to differentially activate splice variants may explain some of the clinical differences observed between mu opioids.",
"This article examines how differential activation of splice variants by mu opioids occurs through alternative mu-opioid receptor binding, through differential receptor activation, and as a result of the distinct distribution of variants located regionally and at the cellular level.",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4616723/",
"But you also have kappa and delta opioid receptors. Some opioids act both at the MOR and KOR/DOR. I believe most of the morphine-like (non-synthetic or semi-synthetic) opiates bind only weakly to these, for example morphine binds at least 20x better to MOR than KOR or DOR. ",
"Activating or inhibiting the function of these receptors has various effects which can be quite different from what MOR agonists do, for example KOR agonists can produce dysphoria and hallucinations.",
"The main compound in Salvia binds to KOR, for example. ",
"https://en.wikipedia.org/wiki/%CE%9A-opioid_receptor",
"https://en.wikipedia.org/wiki/%CE%94-opioid_receptor"
] |
[
"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://www.agencymeddirectors.wa.gov/calculator/dosecalculator.htm",
"Not to say that they are exactly identical though. At the bottom of the page you can see in small text:",
"Equianalgesic dose ratios are only approximations and do not account for genetic factors, incomplete cross-tolerance, and pharmacokinetics.",
"Pharmacokinetics refer to how the drug is metabolized, different opioids can be metabolized by different enzymes, and every patient is different in terms of how 'strong' each of their metabolic pathways are. Also some opioids have metabolites which have their own effects. ",
"Oxycodone can be oxidatively demethylated to oxymorphone which is a more powerful opioid. In most patients the levels of oxymorphone are only around 10-15% of those of oxycodone, but in patients with a certain CYP 2D6 enzyme genotype, it can be closer to 50% which would make the overall drug effect stronger. ",
"Also you should keep in mind that the placebo affect can be very strong, you may get better effects out of the oxycodone because it is newer to you and you are expecting it work better. As crazy as it may sound, your anticipation and expectation has a huge real impact on how the drugs work."
] |
[
"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 potential deals with these other receptors, so in that sense they are interesting."
] |
[
"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 have to have infinite energy. The \"everywhere stretch\" is definitely a more meaningful name than the Big Bang, seeing as it was indeed a stretching of the entire universe."
] |
[
"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 from the \"Big Bang\" first cause.",
"As far as I know, this isn't the case. The total universe is believed to be open, and infinite in extent. The energy ",
" is finite, but the spatial extent isn't. Integrate energy over all space, and you get infinite energy. No problems with that.",
"the expanding universe behaves as if expanding from after an explosion.",
"Eh, not so much. The current models aren't really anything like explosions. They explicitly deal with an expansion of space.",
"As applied by astro-/physicists, a singularity describes that single point i.e. tiny",
"Can do. It's the most common usage, referring to black holes. But the term comes about because of a mathematical singularity in the models. Essentially the point where the equations give an infinity, and a big hint that the equations aren't valid in that regime.",
"tiny (smaller than state of Rhode Island) size from which the universe expanded",
"The ",
" universe was at one point that small. The overall universe was probably infinite.",
"There are two types of 'infinities' being mixed in use here. [...]",
"Haven't a clue what they're on about here. There ",
" different classes of infinities, but your friend isn't really making much sense with the rest of the paragraph.",
"I do not recall reading any scientists or philosopher who held that the universe eternally existed.",
"They exist. Can't name many - not my field. But I know that Penrose has been looking at cyclical ideas - frankly he sounds like a nutter to me, but he isn't alone in thinking about the possibilities.",
"But by the laws of physics, cannot have an eternal existing universe.",
"We don't know this. This is ludicrously strong claim considering that it isn't really known what the laws of physics are as applied to the extreme conditions at the 'beginning'.",
"I don't know what your friend does, but if I would bet quite a bit that they're not a cosmologist."
] |
[
"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 believed to be the causative organism of the flu (hence the name) because it was frequently recovered from flu victim's bodies on post mortem. At the time, viruses were unknown. ",
"more",
"More to the point, many symptoms that you experience of the flu which are painful and/or unpleasant are actually symptoms of your own immune reaction against the flu, ",
" the virus itself. Excess production of nasal mucus (leading to runny nose, sneezing, sinus headache, sore throat from post nasal drip, etc) is an attempt to wash the pathogen out of the upper respiratory tract. The body will raise its core temperature in an effort to kill the pathogen (leading to fever and chills).",
"On a molecular level, cells which are infected with influenza will produce large amounts of signalling molecules such as cytokines, which act to stimulate an immune response. This immune response is uncomfortable but necessary in order to kill the virus and recover from infection.",
"It's worth mentioning that this very immune response can be turned against you. It's believed that the reason the 1918/1919 Spanish Flu pandemic was so virulent and deadly even in healthy people was that it resulted in an ",
"stimulation of that same immune response. The cells which were infected produced so many cytokines and other pro-inflammatory chemicals that the resulting immune response caused massive tissue damage and death. ",
"source, of course"
] |
[
"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 reason why Ebola has never taken hold outside of Africa. But it's part of a bigger picture- Ebola is endemic to an area that is extremely rural and impoverished. There isn't much travel in and out of these communities so Ebola outbreaks will consume the community but never make it out. Also, Ebola is pretty well understood as far as transmission goes and we know to implement quarantines quickly to prevent the spread of the virus. We also are better equipped to prevent the nosocomial infections which used to decimate African hospitals which lacked the knowledge or ability to institute contact precautions."
] |
[
"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 occasionally or b) some other idea that wasn't theorized yet.",
"So, the SETI guy (Jason Wright) is putting up an alternative theory (which he is working on writing a paper for): that it's an alien megastructure. Alien megastructure, IMO, is going to be a hard theory to disprove because there's always room for \"we haven't imagined the right type of megastructure to produce this result, because we're not as advanced as they are\". Now, we could theorize on a couple specific megastructures (like Dyson Sphere) and make predictions of those and either confirm or rule them out. As another comment points out, Dyson Sphere probably doesn't match the data (should emit low energy radiation and shouldn't have any variation in the output). Of course, if we continue to rule out specific megastructures, we should continue to keep aliens far down on the list of possible ideas, and try to come up with new physics that can possibly explain the data and test those theories.",
"Edit: ",
"Jason Wright just published this to his blog",
". It's a good read. tl;dr - \"Tabby’s team tentatively settles on a plausible but contrived natural explanation for it: a swarm of comets recently perturbed by the passage of a nearby star. I would put low odds on that being the right answer, but it’s the best one I’ve seen so far (and much more likely than aliens, I’d say). If I had to guess I’d say the star is young, despite all appearances. I can’t back that up.\" Also, the British Tabloids are dumb."
] |
[
"Straight from the abstract: ",
"By considering the observational constraints on dust clumps orbiting a normal main-sequence star, we conclude that the scenario most consistent with the data in hand is the passage of a family of exocomet fragments, all of which are associated with a single previous breakup event. We discuss the necessity of future observations to help interpret the system. ",
"There's two big challenges to the analysis, first, the lack of excess infrared signal puts some severe limitations on what could be causing the dips, for instance an oddly shaped protoplanetary disk is disfavored. The second is that a predicted dip (from debris of a possible planetary collision) might or might not have occurred in April of 2015, but the system was unobserved—so there's a lack of data going on here too. They recommend further observation. ",
"Observations of KIC 8462852 should continue to aid in unraveling\nits mysteries. First and foremost, long-term photometric\nmonitoring is imperative in order to catch future dipping events. It\nwould be helpful to know whether observations reveal no further\ndips, or continued dips. If the dips continue, are they periodic? Do\nthey change in size or shape? On one hand, the more dips the more\nproblematic from the lack of IR emission perspective. Likewise, in\nthe comet scenario there could be no further dips; the longer the\ndips persist in the light curve, the further around the orbit the fragments\nwould have to have spread. ",
"http://arxiv.org/abs/1509.03622v1",
"All of this is more reasonable than aliens. This isn't my field, but I will say the drop in flux is kinda nuts, I was under the impression \"common\" exoplanet transits produced drops of only on the order of a ",
" percent and not the massive drops of 15 and 22% observed here. Any exoplanet people willing to chime in on that?",
"I'm not an expert in what a Dyson sphere or alien megastructure would look like spectroscopically, but I'm pretty sure the lack in IR would also be a huge problem for that idea too. The star's energy has to go somewhere and unless the aliens figured out how to hijinks thermodynamics, a megastructure should glow in IR."
] |
[
"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 a 1% drop. For an Earth-sized planet passing in front of a Sun-sized star, you're talking about 1/100th of 1%.",
"That's what makes a 22% drop in flux really, really unusual. A sort of \"smoke screen\" of gas and dust from a family of comets could do this, though, since a single comet alone can easily produce a dusty coma as large as Jupiter."
] |
[
"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 visible to larger area in the receiver).",
"In practical cameras you need a bigger hole to allow more light in. To get focused picture with larger hole you need a lense to focus the light so that light from one spot in the target only hits one spot in the receiver. However a lense focuses light from points in some specific distance blurring everything else in the process. Like ",
"this",
". So you need to adjust the lenses to choose the distance that is in focus."
] |
[
"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 photography is literally painting with light, that's usually (but not always) a bad thing.",
"So, enter lenses. Convex lenses intrinsically ",
". They make incoming light rays converge towards the ",
"focus",
"), or image point. This turns out to allow much more light in, but to still form a ",
"real image",
" of whatever's on the other side. But, there's a catch. If you change the subject distance, the distance at which a focused image is projected also changes. So in order to be able to image subjects both near and far we need to physically move the lens either farther from or closer to the imaging surface. This is exactly what happens when a camera focuses.",
"There's another way to focus, and that is by physically adjusting the ",
" of the lens, changing its ",
". This would naturally be a bit tricky to do with glass lenses, but it is exactly how our eyes focus, the lens being more of a squishy organic blob than a rigid object.",
"In a camera, it is useful to be able to control the ",
"depth of field",
", the range of distances where the subject can be said to be in an acceptably sharp focus. For instance, in a group portrait everyone's face should be in focus, and in a landscape photo everything should typically be sharp. This is achieved by including a mechanical ",
"aperture diapraghm",
") whose opening can be adjusted by the user or by the camera automatics. The smaller the aperture, the greater the depth of field, but the lower the amount of light gathered, as indicated in the first paragraph.",
"Lenses with large maximum apertures are popular and sought after not only because they can be used in a dimmer light, but precisely because of their shallow depth of field that permits ",
" for instance, in a portrait the subject's face is in sharp focus, but the background elements fade into blur. The aesthetic quality of the background blur is often referred to with the Japanese loanword ",
".",
"Here's a really nifty ",
"simulator",
" that lets you play around with how optics work. To get started, you can download the following and try them out in the simulator:",
"Pinhole",
"Large aperture",
"Small aperture",
"Note that these examples use an idealized \"thin lens approximation\". You can also create more realistic lens shapes with the tool (Glasses>Free-shape) and see that in reality it's quite a bit trickier to get light to focus neatly at a single point, which is why real-world photographic lenses typically consist of several individual lens elements, up to twenty or so."
] |
[
"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 rocket engine from the ground up is very hard. The math to predict weather is indeed more complex than calculating orbital trajectories. See ",
"here",
" under \"Turbulence\", then problem is a great unsolved one in physics and one of the ",
"millennium prize problems",
"."
] |
[
"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 forecasts are generally quite accurate. ",
"There's a perceptual bias here; you're more likely to remember the one time the forecast was off by a bit and it ruined your baseball game or picnic, and ignore the 20 days leading up that event where the forecast was correct. "
] |
[
"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 are a simple Brayton cycle and stoichiometry. Stoichiometry can get complicated fast, but they were able to ignore all the radicals and focus purely on input and output. The Brayton cycle was used only to drive the turbopumps. There was some complexity added on top, such as using the fuel for the bearing fluid, but the basics could be done today by an undergraduate.",
"The real fun was in the bell design. The first tests had a simple bell of inch-thick stainless steel. It disintegrated in less than a second. They didn't have the math to accurately model what the combustion gasses would be doing, much less how the fuel and oxidizer would mix, so it was just a process of trial and error to fix the worst issues one at a time. Different flow rates, different hole patterns on the baffle, different ridges separating the hole patterns on the baffle, stoichiometric gradients (to form cooler gasses against the bell)... Eventually they reached a point where they could put gunpowder charges inside the bell behind varying thicknesses of covers (so that they would go off randomly) and the created shocks would stabilize harmlessly in a system that once spontaneously--and catastrophically--generated its own."
] |
[
"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'd guess that shaving a mile or two off the several hundred miles of altitude required wouldn't have that much of a benefit.",
"That said, there are a few proposals that involve using some other mechanism besides rockets to get some of the initial height. Back in the 50's, NASA tried ",
"launching suborbital rockets from high-altitude balloons",
". I would imagine the main problem is that typical rockets are very, very heavy and would require extremely large balloons. There are also more exotic proposals like the ",
"launch loop",
", which relies on building a permanently supported structure about 50 miles high, above most of the earth's atmosphere."
] |
[
"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 save you some fuel."
] |
[
"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 has a lot of complicating factors.",
"Alternatively, you could just determine it experimentally. Get a squeegee or sponge and outline different control areas to measure the condensation from. You measure different surfaces at different intervals (for example, four control surfaces and you measure one at 15 minutes, 30 minutes, 45, minutes, and 60 minutes, and then repeat on different areas of the tank) and then plot it out. "
] |
[
"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 Reynolds and Prandtl numbers. what correlation you use depends on all of these factors. There are 20 different possibilities, but yes, your system is probably describable mathematically."
] |
[
"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 water (plus rust and bacteria so it looks extra gross in the tank) and office personal don't understand where it came from. Normally the tank would have been cleaned and refilled within a week or so but since it got to sit for so long a lot of condensation built up inside. Was hoping there was a formula or perhaps a rule of thumb we could use to prove our theory."
] |
[
"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 energy is negative.",
"2) Yes, but you'd need a sufficiently large region much bigger than the size between galaxies.",
"3) Yes - but it only becomes evident on very large scales. Since it is so homogeneous, it is also quite dilute on scales where lots matter is.",
"4) ",
"Cosmological constant",
"Though a good talk for laypeople, I have a few problems with Krauss's talk. Namely - since the FRW metric doesn't have time translational symmetry, there isn't actually a conserved energy in the universe, so it is meaningless to talk about the energy of the universe. It only becomes useful when using Newtonian approximations. Secondly, although the universe appears to be close to flat, we don't actually know if it's perfectly flat or not, and it being perfectly flat is central to his argument."
] |
[
"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 short of it is, it's not real motion."
] |
[
"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 proportional to its mass and this number is negative. also assume m1 = m2. so G1 = G2 = -mk. and the total gravitational potential energy is GT = -2mk. however, ",
" that individual gravitational potential energies would exactly be cancelled by the energy due to mass ET = 2mc",
" so we are at zero total energy. ",
"2) two objects have velocities, therefore they have kinetic energies, and kinetic energies are positive. further in an accelerated expansion the total kinetic energy is increasing indefinitely. what is going to cancel this excess positive energy? gravitational potential energy between two objects cannot cancel, since it decreases as the distance between the objects increases (due to U = -Gm",
"what is the resolution in this case?"
] |
[
"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, and it's basically at the point of diminishing returns for a lighter-than-air craft.",
"At these altitudes, air is about 1/1000th as dense as at sea level, so there's just very little overhead for lift in terms of buoyancy. I would speculate that going beyond 200,000 feet in a full-sized gas balloon is probably impossible.",
"Note that Earth's atmosphere, though very tenuous at these altitudes, extends FAR beyond this altitude. The top of the thermosphere is over 10 times higher and the upper bounds of the exosphere are about 200 times higher than the record unmanned balloon. There is absolutely no way a lighter-than-air ship can get near these altitudes."
] |
[
"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 something in orbit is traveling REALLY fast sideways, it's trajectory keeps it from hitting Earth as it falls around Earth.",
"Here's the XKCD that is usually linked as the answer: ",
"https://what-if.xkcd.com/58/",
"And lastly, rocket propellant as actually more effective (higher specific impulse) in a vacuum than in atmosphere, so your last point is reversed."
] |
[
"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 motor run.",
"When the motor is starting up, you have an rotation rate that is varying in time, so theres an coil in there, and some magnets around, and the flux through the coils due to said magnets is changing. This induces an EMF in the coil due to lenz's law of induction, and this EMF happens to be opposite to the current applied. People call this back EMP because it has a polarity opposite to the applied EMF and behaves like an apparent resistance to the applied current."
] |
[
"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, the total length of all blood vessels in the body, laid out end to end, would be about a hundred thousand kilometres long.",
"From the capillaries, nutrients and oxygen can pass into the interstitial fluid between the cells and diffusion makes them available for uptake."
] |
[
"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 atteches the molecule to its membrane and sucks it in."
] |
[
"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 of the map of on top of an artist rendition of the structure of the galaxy. The thing on the right is the center of the galaxy. We're about 2/3rds of the way out. So, we've gotten a sizable fraction of the Milky Way covered. The far side of the Milky Way is a little bit harder, partially because of pulsars being fainter with distance, partially because of scattering of pulses by the gas in the interstellar medium, which makes the pulses not very distinguishable as pulses.",
"Do they have a general frequency or other features that sets them apart?",
"I assume you're talking about the pulsars now. Pulsars have their own spin periods/frequencies which are unique and very easy to tell apart because you can figure them out with extremely high precision. Also, they have their own ",
"pulse shapes",
", which are fairly stable and are kind of like a unique fingerprint for each pulsar. However, this might only work specifically for a single observer. If another observer somewhere far away could see the pulsar, they might ",
"look different",
" depending on how the line-of-sight intersects the pulsar's emission beam. So, that might not be as good for using on a galactic scale unless you could model that shape in full 3D, and not just a slice like we at the Earth see.",
"This is a few years old now, but you can see the ",
"general coverage of pulsars",
" we know about in the plane of the Milky Way. The total number right now according to the ",
"ATNF Pulsar Catalogue",
" is 2525."
] |
[
"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 could figure out where you were if you could sift through hundreds of billions of stars, but obviously this would be ",
" harder. Galaxies also do not have these same \"frequencies\", what would they be frequencies of? They are collections of stars and gas and dust, what is oscillating?",
"You might be able to make a map of ",
"quasars",
", looking for specific features in their spectra or in their time variability, but this is again much harder and probably a lot less robust than with pulsars. Might eb more doable. If you were capable of detecting supermassive black hole binaries (sort of a binary quasar) at the centers of merging galaxies, you would have certain periodic information about how they are orbiting, both observed in light and maybe in ",
"gravitational waves",
", but observing GWs are again much harder (only recently in human history have we been working to directly detect them)."
] |
[
"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 getting ",
"ALMA",
" data and this will greatly help. What then happens is that we attempt to reproduce these observations with simulations.",
"But no, we cannot directly see it. And I even doubt that ALMA would be able to resolve an Earth, we could perhaps see the effects of an earth in the disk, but never the planet itself. It's just too small. "
] |
[
"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 pre-amputation. It would end up being your normal blood volume minus the blood usually present in the lost limb.",
"Blood pressure is regulated by pressure receptors, particularly the carotid sinus in your neck. Amputating a limb would only affect blood pressure in the very short term (due to blood loss, etc.). After a day, if you are eating and drinking, your blood pressure will be the same as it was before the amputation.",
"The things that decrease are your blood volume and your cardiac output. Both of these make sense: you don't need as much blood to fill your smaller arterial system, and you don't need to pump as much blood to fewer limbs."
] |
[
"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 telescope time is very limited and heavily contested."
] |
[
"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 around a titanic planet when we don't know they are there in the first place?"
] |
[
"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 substances, and IIRC correctly those containing aluminum are more prone to heating than others.",
"Fun fact - some types of glass can experience thermal runaway in a microwave, and heat until the point that they melt. "
] |
[
"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 winter I believe Ice crystals in the air at high altitudes magnify the effect by reflecting more light."
] |
[
"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 expect to see deaths occurring in populations with a below average immune response (ie, the old and the very young). Not this virus! Healthy people DROWNED in the detritus left by their own immune system. Also the young and old died in the usual numbers."
] |
[
"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 of immune cells and their activating compounds (cytokines), which, in a flu infection, is often associated with a surge of activated immune cells into the lungs. The resulting lung inflammation and fluid buildup can lead to respiratory distress and can be contaminated by a secondary bacterial pneumonia -- often enhancing the mortality in patients.\""
] |
[
"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 rates of star formation than the periphery. This means (1) that it will have a higher rate of supernovae, and therefore possibly lethal levels of radiation, and (2) that the average stellar metallicity (proportion of elements heavier than helium) will be higher, because you have more intermediate- and high-mass stars to produce heavy elements, die off rapidly, and eject those elements into the interstellar medium (through planetary nebula formation or supernovae) to enrich future generations of stars. Higher-metallicity stars are more likely to develop an excess of gas giants, which could interfere with the orbits of terrestrial planets and/or starve them of material as they form, ",
"like Jupiter may have done to Mars",
". Said terrestrials - if they form too late to wind up as the cores of gas giants - will probably be larger and denser than Earth too, which could mean that their gravities and atmospheric pressures would be too high to prevent life from occurring.",
"On the other hand, the outer regions of the galaxy will be much more diffuse (reducing the chances of star formation, which is often triggered by nearby supernovae) and metal-poor. While we know of some very metal-poor stars with planets, such as ",
"Kapteyn's Star",
" (two known \"super-Earth\" planets, detected last year) and possibly ",
"Groombridge 1830",
" (no planets detected yet, but a close-orbiting gas giant is a likely explanation for its \"superflaring\" behaviour), the overall chance of planetary formation is heavily influenced by metallicity. Basically, low metallicity means that there's less material available to form planets, which means that there's not only less terrestrial planets available, but also less gas and ice giants, which can perform the valuable service of shielding those terrestrials from comets.",
"This leaves you with a region where life should stand more of a chance of forming, and if such a region exists, then we're ",
"in it",
". Keep in mind that the concept of a galactic habitable zone, and exactly where it should lie, is still disputed though (although everyone probably agrees that the galactic centre is a no-go zone)."
] |
[
"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 planets supporting life would be wiped clean every billion years or so, perhaps preventing technological civilizations from arising.",
"A short paper concerning this: ",
"http://arxiv.org/abs/1409.2506",
"In the sense that by habitable you mean habitable for technological civilizations, then I would say yes there are habitable zones for galaxies (at the very least because we live in one)."
] |
[
"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 the galaxy than others. Here's a recent paper on it:",
"http://arxiv.org/pdf/1107.1286v1.pdf"
] |
[
"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 are typically ARM-based, not x86 architecture, and the ARM architecture is very well adapted to power savings. They also usually operate at lower voltages, and they often include the capability to shut down and/or reduce the voltage of some parts of the chips whenever this is possible. A typical smartphone SoC will dissipate no more than 800mW. Also, one of the major power consumption contributor in a system is the screen, which is smaller in the case of a smartphone. That's the hardware part of it.",
"The software also plays a major role. OS written for smartphones and tablets make heavy use of the low-power capabilities of mobile processors. For a moderate usage of your phone, such as playing a Youtube video, the processor may actually be asleep up to 80% of the time (sorry, I could not find a reference available to the public for that). Asleep means your SoC power consumption is in the range of 100uW to 10mW, depending on a number of parameters.",
"As a reference, the total sustained power consumption for a smartphone platform is no more than 3 to 4 Watts for very heavy usage (multiple channels encode/decode + heavy computing + 3D processor active). To be compared to ",
"10s of Watts",
" for the lowest performance netbook. There is no need for a fan to dissipate that much heat."
] |
[
"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 greater computing and storage abilities however."
] |
[
"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 following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"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 quite certainly in the \"abstract thinking\" group, I have met many people who aren't, and they are none the worse for it. It just means they're good at something else that I'm not. It just so happens that our economy currently favors the abstract thinkers and rewards them with higher salaries for something that may just be a natural ability.",
"Either way: I believe anyone who's ever done a university-level math class could quickly tell that they fell into one of two camps: either they \"got it\", or they didn't, and in the second case, no amount of studying would make them \"get it\", and their best outcome would be passing the test by memorizing lots of special cases.",
"What I want to know is: has this phenomenon been scientifically studied, and if so, where can I find this study?",
"EDIT: maybe I should read your link first before commenting. Looks interesting. brb",
"EDIT2: Nope. While definitely being an interesting read, this article only argues that\n\"virtually everyone has the capability to achieve [...] an understanding of arithmetic procedures, algebra, geometry, and probability deep enough to allow application to problems in our daily lives.\"",
"I don't doubt that. But it's not what I was looking for. "
] |
[
"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 quite certainly in the \"abstract thinking\" group, I have met many people who aren't, and they are none the worse for it. It just means they're good at something else that I'm not. It just so happens that our economy currently favors the abstract thinkers and rewards them with higher salaries for something that may just be a natural ability.",
"Either way: I believe anyone who's ever done a university-level math class could quickly tell that they fell into one of two camps: either they \"got it\", or they didn't, and in the second case, no amount of studying would make them \"get it\", and their best outcome would be passing the test by memorizing lots of special cases.",
"What I want to know is: has this phenomenon been scientifically studied, and if so, where can I find this study?",
"EDIT: maybe I should read your link first before commenting. Looks interesting. brb",
"EDIT2: Nope. While definitely being an interesting read, this article only argues that\n\"virtually everyone has the capability to achieve [...] an understanding of arithmetic procedures, algebra, geometry, and probability deep enough to allow application to problems in our daily lives.\"",
"I don't doubt that. But it's not what I was looking for. "
] |
[
"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 also extremely valuable, if not indispensable, in computer science in general and software design in particular. "
] |
[
"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 the same in any direction you look. There is no curve to be seen, except for the curve away from you that creates the horizon line, which is the same in every direction... Though closer than on earth. ",
"To see the horizon curve like you are thinking you would have to leave the surface enough to perceive the moon or planet as a separate ball."
] |
[
"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 beyond the horizon.",
"For reference, here's ",
"Plato",
". The four larger craterlets on the crater floor have diameters of about 2-2.5km (so the crater wall would be discernible in those)."
] |
[
"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 beyond the horizon.",
"For reference, here's ",
"Plato",
". The four larger craterlets on the crater floor have diameters of about 2-2.5km (so the crater wall would be discernible in those)."
] |
[
"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 long it might take a hypothetical enemy to guess the key through trial and error. Historically, the hard part has been securely exchanging keys, and this was a very difficult problem to solve",
"The big breakthrough was the development of asymmetrical encryption techniques in the 1970s, where you can reveal the encryption key publicly, but since the decryption key is different (and you can't practically figure out the decryption key from the encryption key), having the encryption key doesn't let someone read encrypted messages sent to you. Asymmetrical encryption takes more effort, so you just use it to transfer a key for symmetrical encryption, which you then use to relay your longer messages."
] |
[
"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 ",
".",
"The recipient then publishes the public key in some well known manner. Maybe on their website. Maybe in a ",
", a piece of software whose job it is to distribute keys. Maybe on billboard in the middle of town. Whatever. It doesn't matter if this key is intercepted because, as its name implies, it is meant to be public.",
"The recipient keeps the private key to themselves. As its name implies, it should not be shared with others. It must remain secret.",
"The mathematical relationship between these keys is such that anything encrypted with the public key may then be easily decrypted with the private key. (And it is infeasible to decrypt it without the private key.)",
"With that setup, consider how we might send an encrypted email. One choice would be for the sender to obtain the recipients public key, encrypt the email, and send the encrypted version to the recipient. This approach would work but has some issues.",
"First, this sort of encryption, called ",
", is fairly computationally expensive.",
"Second, what if you want to send the email to multiple recipients? Do you encrypt it multiple times with each recipients key? That would mean the actual message size gets multiplied by the number of recipients.",
"A common solution to both of these problems is, instead, for the sender to first generate a symmetric key, most commonly using ",
"AES",
". This is referred to as a ",
", in that it will only be used for this one email session. The sender encrypts the email using the session key, and encrypts the session key with the recipients public key. The encrypted session key and the encrypted email are bundled up and sent to the recipient. The recipient uses their private key to decrypt the session key, and the session key to decrypt the email.",
"This solves the performance problem because only a small session key is encrypted using asymmetric encryption, while the much larger email is encrypted using relatively fast symmetric encryption.",
"If the email is sent to multiple recipients, you can encrypt the session key multiple times, once with each recipient's public key. You still need to include all of these encrypted copies of the session key in what you send, but that is much more efficient than having multiple copies of the email."
] |
[
"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 the key again. 11 xor 10 is 01.",
"In this case the encryption and decryption algorithms are literally identical, which explains why they're called \"symmetric.\" Real-world symmetric encryption algorithms like AES are not necessarily like this, but they're still referred to as symmetric if they have this key structure (there is only one key used for both encryption and decryption)."
] |
[
"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. listening to music can be very rewarding). See ",
"this page",
" for a collection of excellent papers on the relationship between music and emotion by a preeminent researcher in the field. My key point is this: ",
" There is no evidence that music can do anything to you physiologically except trigger emotions.",
"Let's talk about brain waves. Of course music affects the amplitude and frequency of brain waves. ",
" that you perceive or sense affects the frequency and amplitude of brain waves. Brain waves (as measured by EEG -- electrodes on the scalp) are an extremely coarse reflection of ongoing activity in the brain. Thus if something triggers a response in your brain, it will be reflected in the EEG. ",
"But ",
"! Some brain waves look really fast and messy, they must happen when your brain is doing something really frantic! ",
" Different neural circuits in the brain have different resonant frequencies. Visual cortex tends to oscillate at 10Hz when it's not doing much (the alpha wave). Just closing your eyes will trigger massive alpha oscillations. Motor cortex tends to oscillate at ~20Hz when it's sending signals to your muscles (the beta wave). Making a tight fist will trigger massive beta oscillations. The hippocampus (seat of episodic memory) tends to oscillate at 8Hz (the theta wave). And pretty much every part of the brain has some resonance at ~40Hz (the gamma wave) that appears to be associated with ongoing processing. There's nothing magic about the relationship between brain waves and mood or brain waves and music.",
"Let's talk about memory. I'm in agreement with your statements here. It does appear that rhythmic, repetitive structures are much easier to memorize than non-repeating structures. This is one of the leading theories for the evolution of music: the propensity to enjoy repetitive structure encouraged the persistence of culture and ideas across many generations in pre-literate societies. ",
"And then there's this:",
"Another key to the order in music is the music being the same and different. The brain works by looking at different pieces of information and deciding if they are different or the same. This is done in music of the baroque and classical periods by playing a theme and then repeating or changing the theme. The repetition is only done once. More than one repetition causes the music to become displeasing, and also causes a person to either enter a state of sub-conscious thinking or a state of anger. Dr. Ballam goes on to say that, \"The human mind shuts down after three or four repetitions of a rhythm, or a melody, or a harmonic progression.\" Furthermore, excessive repetition causes people to release control of their thoughts. Rhythmic repetition is used by people who are trying to push certain ethics in their music. \"",
"What a load of bullshit. This is just embarrassing."
] |
[
"\"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 enhances the ability to learn. ",
"... ",
"..Many revealing scientific experiments, studies, and research projects have been performed to try and discover the extent of the power of music. Up until 1970, most of the research done on music had to do with studying the effects of the beat of the music. It was found that slow music could slow the heartbeat and the breathing rate as well as bring down blood pressure. Faster music was found to speed up these same body measurements.",
"The key component of music that makes it beneficial is order. The order of the music from the baroque and classical periods causes the brain to respond in special ways. This order includes repetition and changes, certain patterns of rhythm, and pitch and mood contrasts. One key ingredient to the order of music from the baroque and classical periods is math. This is realized by the body and the human mind performs better when listening to this ordered music.",
"One shining example of the power of order in music is King George I of England. King George had problems with memory loss and stress management. He read from the Bible the story of King Saul and recognized that Saul had experienced the same type of problems that he was experiencing. George recognized that Saul overcame his problems by using special music. With this story in mind King George asked George Frederick Handel to write some special music for him that would help him in the same way that music helped Saul. Handel wrote his Water Music for this purpose.",
"Another key to the order in music is the music being the same and different. The brain works by looking at different pieces of information and deciding if they are different or the same. This is done in music of the baroque and classical periods by playing a theme and then repeating or changing the theme. The repetition is only done once. More than one repetition causes the music to become displeasing, and also causes a person to either enter a state of sub-conscious thinking or a state of anger. Dr. Ballam goes on to say that, \"The human mind shuts down after three or four repetitions of a rhythm, or a melody, or a harmonic progression.\" Furthermore, excessive repetition causes people to release control of their thoughts. Rhythmic repetition is used by people who are trying to push certain ethics in their music. \"",
"-",
"Source",
" ",
"Be warned: that site is not a scholarly article and there is a fair bit of subjectivity. The sources it cites are not easily accessible online and are from the 80s and 90s. ",
"this",
"this",
" ",
"As far as whether or not listening to music can \"cause\" beta waves... let's just forget about that. As far as I'm concerned right now a beta wave is only a brainwave that has been measured to a specific frequency that makes it a beta wave. I'll let the neuroscientists cover those questions. ",
"Music obviously causes a variety of responses physiologically and psychologically, but lets get to the original question posed by OP, ",
"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? ",
"more specifically the title: ",
"...could music in a way also be changing our brains to explore tasks differently? ",
"As much as it makes me wonder... Has anyone really been far even as decided? ",
"There's great reading on music and the brain over at the Phychomusicology journal.",
" I'm going to copypasta myself from another comment I made in a hope that you will be inspired to go do some reading on the subject over just taking my comment at face value.",
"There's an article on how musicians and non-musicians react to music, and it talks about how there's a 300ms response (a P3 brainwave) after you hear a sound that is essentially your brain referencing and refreshing the data to a previous memory - so when you hear music, your brain kicks on a type of updater of your \"working memory\". When your brain processes music, the sensory information has to go from short term to long term memory, and that same sensory input gets checked against long term memory as it enters short term memory.",
"Musicians have a reduced response as they are much more familiar with specific notes, showing it is easier on their brains to recognize what they are hearing vs. trying to identify what is being heard. How can that help the gamer? Will a gamer-musician have a different response than a non-musically inclined one? Sadly, the main conclusion to the article is focused on the future research possibilities and the lack of current research. There's also major complications in what music to use - things that may be too simple for the musician but to complicated for the neuroscientist. That article is ",
"here",
", titled \"Neural Basis for Music Cognition: Neurophysiological Foundations\" "
] |
[
"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 the person to match his/her movements. This interpretation doesn't necessarily require neuroplasticity--that is, this can be implemented in a purely feedforward system.",
"Drawing on the idea of music as complex but pleasing distractor, music can compete with other unwanted stimuli or internal states (e.g. pain). Hence, it's not surprising that music can make exercise more tolerable/enjoyable and that music can be used to reduce post-surgical pain.",
"Some would argue that music may be helpful for people with Alzheimer's because it contributes to reminiscence, but that's probably just because of how strongly we link music to life experiences and events.",
"I'm sorry that this isn't a more exciting answer. The reality is often simpler than it looks. :("
] |
[
"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 depends on the type of atom, the chemical properties, ..."
] |
[
"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, such as heat.",
"I'm fairly sure this is how it works, but could someone please verify or correct me?"
] |
[
"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', in other words, transmitted by atoms/molecules bumping into each other: Thermal conduction!",
"So even when light is re-emitted, part of the energy has often been lost as heat. For instance when you see a white shirt turn violet under a UV bulb, that's because the invisible UV light is getting re-emitted as less-energetic, visible violet light.",
"Anyway, for a solid material, there's a very large number of possible levels, so in practice most things absorb across the all (or almost all) of the visible spectrum. So it's really less a question of whether the light ",
" be absorbed and more a question of whether it's ",
" to be absorbed.",
"See, besides having different states, you also have different transition probabilities between them. It's not enough that the light has the right energy for the transition; it's still a matter of chance whether or not it gets absorbed and the transition occurs. Some transitions are 'forbidden', which means 'extremely unlikely'. You can see that with phosphorescent ('glow-in-the-dark') objects. When exposed to light, they phosphorescent objects get excited into a higher state that requires a 'forbidden' transition to occur for them to re-emit the light and return to their ground states. Which is why they can continue to glow for hours (whereas with a non-forbidden transition, the light gets re-emitted on the order of picoseconds).",
"So, since things absorb light with different probabilities at different wavelengths, the reflected and re-emitted light has a different color than the incoming light. And so you have color.",
"If you look at a gas, rather than a solid, it's typically a much smaller molecule. And it doesn't have many other molecules around it. That causes it to have fewer vibrational/rotational states compared to a solid. (When molecules are near, their combined energy states is far more than just the sum of their individual ones) So there are fewer possibilities for absorption then, and gases ",
" usually absorb all across the visible spectrum. In fact, as you've probably noticed, it's relatively uncommon for gases to have color. And it's more common for liquids, and for solids it's uncommon for them ",
" to have color.",
"Finally, you might wonder how/why we have distinct states, and why they have different transition probabilities. There's an answer to that, but it's a bit difficult to explain, since it's all quantum mechanics. In fact, it's the original problem that that lead to the development of quantum mechanics. As coin-coin said (and what I said now) the basic parameters are the chemical composition, the aggregation state and/or what the 'environment' looks like for the molecules. The same molecule can have different colors as a gas, liquid and solid, and it can have different colors as a solid, for different arrangements of the crystal structure. Color (and radiation absorption in general) is fundamentally connected to all chemical properties. (which is why spectroscopy in all its forms is a very useful tool for chemists) There's essentially no property of molecules that ",
" have an effect on it. ",
"Well, there's one though. Isotope composition, i.e. the mass of the atoms (rather than the charge) usually has little effect on color, because mass only affects vibrational/rotational states (electrons \"don't care\" about how fast they move, because the electrons move much, much faster), which at room temperature are mostly in the infrared. It's only when combined with an electronic state transition it's in the visual range. ",
"Offhand I can only think of one example: Water, which is blue. (No really, water is intrinsically a very, very pale blue, but not to be confused with the reason bodies of water ",
" blue, which is a different thing) But heavy water is colorless."
] |
[
"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 burn rate between tokes. ",
"Wet cigarette smell might have to do with the ammonia in the cigarette which is there to control the delivery of the 2 mg of nicotine. ",
"Source: chem MSc, drug/med Chem lectures, smoker!"
] |
[
"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 neuroblastoma; a correlation between serum BPA levels and prostate size; suppression of DNA methylation; multiple studies suggesting reproductive and sexual behavior changes; and many more.",
"Note that these changes have been detected at low levels in animal studies (as low as 0.025 ug/kg/day- that's at the double-digit part per ",
" level), and these levels are 3 orders of magnitude lower than what the EPA considers safe (to 50 ug/kg/day). Moreover, these levels are ",
"easily exceeded,",
" and levels of BPA have been quantified in multiple studies, indicating that there are ample sources (environmental and dietary) to demonstrate there could be cause for concern. The National Toxicology Program has expressed some concern about the compound (particularly with respect to children), none of it with respect to acute toxicity. The concerns all revolve around damage to the developing child. Meanwhile, there are lingering questions about what xenoestrogens do to adults.",
"Apparently, there are improved manufacturing techniques, and polycarbonate can now be produced without remaining BPA. There are also a number of substitutes in the field, and I am sure than in 5-10-20 years, we'll be questioning the safety of these as well.",
"My advice would be to stick to glass if you're concerned about BPA."
] |
[
"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 temperature the migration of BPA was independent of whether or not the bottle had been previously used. Exposure to boiling water (100 °C) increased the rate of BPA migration by up to 55-fold. The estrogenic bioactivity of the BPA-like immunoreactivity released into the water samples was confirmed using an in vitro assay of rapid estrogen signaling and neurotoxicity in developing cerebellar neurons. The amounts of BPA found to migrate from polycarbonate drinking bottles should be considered as a contributing source to the total “EDC-burden” to which some individuals are exposed.",
"From J Sep Sci. 2009 Nov;32(21):3829-36.\n",
"PC bottles were heated in a water bath and in a microwave oven at four different temperatures (37, 53, 65, and 85 degrees C). The higher the temperature, the more the BPA was released, and after a few heating cycles, the released concentrations became constant. At normal use, i.e. at 37 degrees C, concentrations are ca. 10 ng/L. No significant difference was noted between water bath and microwave heating illustrating that migration of BPA is mainly temperature dependent.",
"From Food Chem Toxicol. 2009 Feb;47(2):506-10. Epub 2008 Dec 24.\n",
"Estimated mean (standard deviation) intake of BPA was 1.1(0.839) microgram/day.",
"From Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2008 Jul;25(7):904-10.\n",
"Migration of bisphenol A into water ranged from <0.1 to 0.7 microg l(-1). There was no correlation between the amount of residual content of bisphenol A in the bottles and the migration of bisphenol A into water. Furthermore, there was no correlation between the amounts of bisphenol A in consecutive migration extracts. Data show that during three microwave-heating cycles of a baby bottle made from polycarbonate, microwave radiation had no effect on the migration of bisphenol A into water from polycarbonate."
] |
[
"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 maintain the fluid in a liquid state. Imagine you fill a container with water at constant temperature, leaving a little space at the top. Then you instantly suck all of the air out and cover the top. In order to maintain an equilibrium, some of the water will evaporate to fill that space. When you measure the pressure of the system at its new equilibrium, you will notice that it equals the vapor pressure of water at the original temperature. ",
"Another way to look at it is that ",
" describes the boiling point. If the pressure acting on the fluid is less than the vapor pressure, the fluid will vaporize (a.k.a. boil).",
"This leads to an interesting phenomenon when you try to accelerate a liquid: ",
". You can examine this in a simple manner using Bernoulli's principle (where P, Q, and G are the static pressure, dynamic pressure, and hydrostatic pressure contributions, respectively): ",
"Let's simplify a little by assuming no body forces. Consider ",
". Consider ",
" The equation becomes:",
"Recall that dynamic pressure, ",
", is a function of velocity (",
"). As you increase your fluid velocity (when accelerate through a converging-diverging nozzle), ",
" rapidly increases while ",
" rapidly decreases to balance the equation. ",
"Eventually, you will reach a point in which the fluid is moving so quickly that the static pressure at the throat becomes lower than the vapor pressure (i.e. ",
"). This velocity is far lower than that of the speed of sound in water. At this point, the system can no longer reliably maintain the water in liquid form and begins to vaporize: you have reached the point of inception of cavitation. Vapor bubbles begin to spontaneously form, impeding the flow of liquid water. ",
"Obviously, this is the point at which the assumptions of the Bernoulli's principle (due to compressibility) and isentropic relations (due to two-phase flow) break down. In practice, you will likely never be able to reach the sonic velocity of liquid water because it will become water vapor. Neither can you reach the sonic velocity of the gas because the gas expands, increasing increasing throat pressure (i.e. ",
") - condensing/preserving the liquid. Therefore, the production and collapse of the vapor bubbles surges in an unsteady fashion, maintaining the throat pressure near the vapor pressure. ",
"The phenomena and effects of cavitation are quite complex to determine, even by today's standards. There is a whole field of investigation/research into cavitation and two-phase flows. ",
"The study (and prevention) of cavitation occurs in a lot of naval and flow systems engineering. For example, cavitation can occur on marine propellers or in piping. The collapse of a cavitation bubble releases a lot of energy, which both causes damage to the components and contributes to noise output.",
"In terms of direct application of cavitation, cavitating venturis have been used for many years as critical flow metering devices. Although the underlying fundamental phenomenon is not well understood, the point of cavitation also happens to be the condition at which a liquid system \"chokes\" - achieves its maximum flow rate (analogous to a sonically choked CD nozzle flow). ",
"In biology, you see cavitation being applied by pistol/mantis shrimps. When they strike, their claws move extremely quickly and create a cavitation bubble. The energy released when the bubble collapses stuns their prey. ",
"A short overview of cavitation",
"Cavitating Venturis: ",
"Choked Flow Analogy for Very Low Quality Two-Phase Flows, NASA, 1966",
"Sample manufacturer \"About Cavitating Venturis\" Product Page",
"A humorous, but factual, overview of the Mantis Shrimp"
] |
[
"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 so much for the incredible info!"
] |
[
"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, marine thrusters, and the like would see enormous benefit in doing so. Then again, I don't think I'd want to be anywhere near supersonic rain droplets...",
"Of course, we aren't sure if there is even a way to get rid of cavitation. It obviously hasn't been made easy or possible so far. There are a lot of different factors at play here, namely those revolving around compressibility and phase changes."
] |
[
"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 very smooth transitions of slowly raising and lowering each between the pure color nodes to create real transitions. AKA 1,0,255 is almost exactly red but just a little blue and thus will look very very close to red.",
"Now this is how our eyes see color not necessarily having a pure violet laser looking smooth against a pure red. There you really are only getting two discrete frequencies of light."
] |
[
"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) colour model as Diracdeltafunct explained we can arrange colours in whatever way we want."
] |
[
"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 that we see that as completing the color wheel. Looking at the pairings of rods that produce different colors: Red (R) -> Yellow (R+G) -> Green (G) -> Cyan (G+B) -> Blue -> (B) -> Magenta (R+B) -> Red (R)."
] |
[
"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 escape, it's just an idea of how long the energy that the photon is carrying bounces around inside the sun before flying out."
] |
[
"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 stellar structure. ",
"This article",
" describes the matter in some detail."
] |
[
"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. But fluorescent yellow can additionally convert the energy in the blue part of the spectrum, as well as any UV, and concentrate that energy in the yellow range, making it brighter than a normal yellow object.",
"This is the same phenomenon as in a fluorescent lamp where the phospher coating on the inside of the glass absorbs ultraviolet created by the mercury arc inside and converts it to visible light that is emitted through the glass."
] |
[
"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 those cells. "
] |
[
"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 neutrons.",
"As you make bigger and bigger nuclei, they get less and less until they don't stay together long enough to really be thought of as \"one nucleus\".",
"Cosmologically, however, if you are in a very strong gravity field, you can hold nuclei together would otherwise fly apart. This is a neutron star, which can be compared to a giant atomic nucleus.",
"However, even neutron stars have ",
"size limits",
". Too big and they collapse into something else. (Expected to be a black hole.)",
"So even if such extreme circumstances, there is a limit."
] |
[
"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 the basics of number theory. ",
"That there can be countable things or no countable things... So this doesn't help, cause it's possible for these person's to count, it's just challenging. ",
"This is like seeing impaired, not blind. Though it does make me wonder if this argument is even germain to my point. Because just because some people are blind doesn't mean there's nothing to see."
] |
[
"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; only in advanced cryptographic applications or very long monte carlo simulations can it prove problematic.",
"That said, quantum random number generators really are ",
" random. It's tough to think about, because our intuition for the real world so totally fails at the level of the very small, but quantum mechanics is very thoroughly probabilistic. Though it's ",
" that the result of a quantum mechanical event (e.g. the determination of a spin) ",
" be deterministic, this would require a hidden variable that we so far have not been able to detect. It turns out that these \"hidden variable\" theories don't really agree with the way reality seems to function--they violate either causality or locality. Until a ",
" breakthrough occurs in quantum mechanics, we can continue to use quantum random number generators as sources of truly random numbers."
] |
[
"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 you need random numbers. Rolling a die, for example, is random enough for Dungeons and Dragons players, but if physics is deterministic then it's still not true randomness.",
"Example time: Ask your pet random number generator for 16 random digits.",
"If it returns 0000000000000000, it's a shitty RNG. Or it's a very good RNG, and you got the one-in-10",
" roll where it gave 16 zeroes in a row. But that's unlikely.",
"If it returns 2114292167718531, it's pretty close to true randomness. I don't see a pattern among those digits at all.",
"If it returns 1298704356129870, it starts repeating after 10 digits. Maybe not true randomness, but there are situations where this doesn't matter too much - like if you only really need a single 3-digit number, or you only need to be sure that all 10 digits appear equally often.",
"If it returns 2104031911030232, it's not giving any numbers larger than 5 (except for that stray 9). It's not uniformly distributed, but if there's no way for someone else to accurately guess the next number it might still be very useful for secret codes.",
"Now, while you can't tell me whether, say, 4 is a random number, you can tell me how likely each of the four RNGs above are to give an 4 as their next digit, what proportion of the digits they give are 4s, how likely they are to give two 4s in a row, and so on. True random numbers don't have a pattern, but what counts as a \"pattern\" depends on what you want the random numbers for.",
"(PS: Lossless data compression, like that used in ZIP files, allows you to fit the same data into less space. It works because the data people want to compress isn't random; it has lots of different patterns, usually all at once. Data compression systems express these patterns using less space; instead of \"0000000000000000\" one might just say \"16 0s\". Fully compressed data has no patterns at all; it is indistinguishable from random data. Conversely, truly random data can never be compressed. The two concepts are pretty tightly linked in information theory.)"
] |
[
"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 because they're only \"responsible\" for their own survival, and not their neighbors or the community of cells as a whole."
] |
[
"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 floor (rim) and walls. But think about one particular instant in time: the air is moving in a ",
" tangent to a circle above the station floor. It can't continue moving in that straight line because it will hit the floor, so it will be forced back toward the center either by the floor itself or other air piled against the floor.",
"Now if you have a helium balloon among the air, it will also get pushed inward by the air surrounding it, but because it has less mass than the same volume of air, the corresponding inward acceleration will be higher than for the air. Thus it accelerates inward.",
"The actual direction of \"in\" changes as the station rotates though, so there will be an additional apparent acceleration from the point of view of the station to lead the rotation, so the balloon's path will tend to curve forward some. This is the Coriolis force.",
"edit: forward."
] |
[
"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 pressure differential. The same thing happens in a car as it accelerates/decelerates, or when a car goes around a curve/turn."
] |
[
"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\" presents a good cause for alarm.\nThe danger triangle can be traced from one corner of the mouth, over the bridge of the nose, and down to the opposite corner of the mouth. Any time infection in this area occurs, there is the very rare but very real risk that the infection can spread to the brain."
] |
[
"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 tremendous amount of variation within every population. "
] |
[
"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 tremendous amount of variation within every population. "
] |
[
"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 this foot image but simply because I haven't seen anything as to it's validity. I don't know where the image originated, but I've never seen anything linking foot shape to ethnicity."
] |
[
"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 been measured, but is predicted to exist. Same thing for dark matter."
] |
[
"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 stand out:",
"Giordano Bruno has an interesting history",
"Eimmart A",
"From what I can tell, a major crater formation that would change the appearance of the moon viewed with eyes would generate a great deal of meteors on Earth, like when comet debris hit Earth. I do not know enough obscure history, but if a major crater formed while there were literate humans on Earth, then maybe they would have recorded that as some great mystical event. ",
"So in short, my best guess is that major crater formation that would alter the view of the moon during human civilization is unlikely, but possible.",
"My guess is that light pollution from cities are a bigger difference in how the moon appears to us and to Ceasar."
] |
[
"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 then after a minute of that video (so about the dinosaur extinction) it would have shifted by a few thousand kilometers, less than the perigee-apogee difference."
] |
[
"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” particles can’t occupy the same space at the same time. That’s a bad condensation of it, but it’s the best I can do in a sentence.",
"EDIT - If anyone is up for some light reading, here are the original papers by Dyson and Lenard in 1967 and 1968. ",
"Stability of Matter I",
" and ",
"Stability of Matter II",
". The sequel really does live up to the hype.",
"Tell your mom she asks brilliant questions."
] |
[
"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 them closer to each other) requires more energy, which gravitational potential cannot provide.",
"If this sounds very confusing, that's because it kinda is, but the name of this extra energy term is the exchange interaction, which Wikipedia probably does a better job of explaining than I can. "
] |
[
"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 orbital trajectories in general relativity) terminate at the singularity. It means that stuff just piles up at that point. By conservation of mass/energy, the mass/energy of the particle that went in is now a part of the singularity, and thus the black hole. "
] |
[
"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 ball of stuff, the event horizon is a point in the object's gravitational field which is too \"steep\" for light to cross out of.",
"The actual \"ball of stuff\" - if you can even call it that - is at the singularity, which is a single point far away from the event horizon. The more mass there is concentrated at the singularity, the stronger the field around it, so the farther the event horizon will be."
] |
[
"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 mechanisms, but in general, these proteins will be expressed in ",
". That is, there are more of them in some places, and less of them as you get farther away from their source. In this way, cells can tell how far away they are from specific points, and alter their gene expression accordingly. ",
"A protein that is only expressed along the midline will help nearby cells (which will receive a lot of stimulation from it) start along the pathway to becoming vertebrae, whereas cells that don't sense so much of it will instead activate other genes, perhaps turning into limb buds. The left and the right sides will ",
" be similarly far away, and so similar developmental processes will create limbs on both sides. ",
"So, it's not about telling cells they should start making a left arm, but rather letting those cells know they're in the right place with the right potential to form ",
" arm. There will ideally be other cells receiving the same message on the right side. This is why it is much more common for a genetic defect to affect both sides similarly: a defective morphogen won't work on either side. But accidents of development can occur due to chance environmental causes, and this is what's more likely to be responsible for a defect on just one side of the body."
] |
[
"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 vessels clamp off, limiting blood loss). This is mediated by neurogenic reflex mechanisms and enhanced by secretion of local factors such as endothelin, a potent vasoconstrictor. ",
"These effects are temporary, and bleeding would quickly resume without the coagulation cascade. Injury to the blood vessel wall exposes the clot-promoting subendothelial extracellular matrix beneath, causing platelets to activate and pile up at the site of injury. Platelets recruit more platelets, forming a temporary hemostatic plug.",
" or ",
" is also exposed at the site of injury. This acts with factor VII to trigger the clotting cascade, which ultimately leads to polymers of fibrin cross-linking throughout the clot, stabilizing it further. ",
"Now that blood loss is controlled, healing can begin. Superficial wound healing occurs in three phases: inflammation, proliferation, and maturation. The aforementioned clot acts as a scaffold for migrating cells, which are attracted by factors released at the site of injury. Within 24 hours or less, neutrophils arrive at the site of injury and start clearing out cellular debris and any invading bacteria.",
"Fibroblasts migrate in within 24-72 hours along with new vascular endothelial cells, recruited from the bone marrow by ",
" (VEGF) release. New, small blood vessels can start to form at this time, in a process known as angiogenesis. Gradually the neutrophils are replaced by macrophages - these guys are the key players in tissue repair. They clean out debris, fibrin clots, foreign material; they also promote angiogenesis and new ECM deposition.",
"Now this is the process for smaller vessels, but penetrating trauma to larger vessels follows this same process. If you accidentally needle someone's carotid while trying to insert a central line into their jugular, holding pressure for ~10 minutes or so will allow the puncture to clot off, and eventually new ECM and endothelium is laid down. In this case, new endothelial cells don't have to mobilize from the bone marrow - often the injury is small enough to allow regrowth of endothelium from local precursor cells.",
"In larger injuries to blood vessels (like if someone gets shot directly through their aorta) usually require surgery to correct, as the wound is too large to properly clot, and the injury may quickly become incompatible with life otherwise. "
] |
[
"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 0V to 2.44mV (2.44mV peak-to-peak).",
"If your input signal is 4.8mV peak-to-peak, you get a steppy square wave out - you get a 1 (01b) out of the ADC at 2.44mV, and a 2 (10b) out at 4.88mV. ",
"Each 2.44mV you increase the input signal gets you another higher number out. If you use the first two bits of the ADC fully, you get 0 to 3 out of the ADC - but that requires 7.32mV peak-to-peak. The first three bits, 0-7, requires 17.08mV. Four-bit resolution gets you 0-15 out, and requires 36.6mV in. ",
"As you input signal increases in amplitude, you use more and more of the ADC's range - until, at a full 12-bit resolution (10V peak-to-peak input signal), you get a signal out that looks a lot like the sine wave you put in originally. It has steps from 0 to 4096, but not such huge steps that you can't get a good approximation of the analog signal.",
"So when you amplify the input signal, you are not changing the ADC range at all - you're simply using more of the available range, which means you get an output that more accurately reflects the input - it looks more like a sine wave and less like a square wave.",
"For the resolution, if you define 0-4096 as 0-10V, your resolution is 2.44mV/bit. BUT if you start with a 1V signal, amplify it by 10, and then define 0-4096 as 0-1V, your resolution is suddenly 244uV/bit - a 10x increase. If you define 0-4096 as 0-10mV (with the same circuit plus a 1000x amplifier), your resolution just went to 2.44uV/bit."
] |
[
"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, Ring 2, etc. which allow for different types of software to run with different hardware permission levels. The ring-level is managed exclusively by the operating system during events like context switches.",
"(No) However, in practice this is generally not done. Linux and Windows both only use two permissions levels- Ring 0 for kernel mode and Ring 3 for user mode. ",
"(Yes) Instead, OS designers have long opted for the interrupt service routine (ISR) approach. When an interrupt occurs the processor always transfers execution to a known memory address in the kernel, which is where the ISR is located. This piece of code is responsible for figuring out what interrupt was requested, who requested it, and whether or not the performed action should be accomplished.",
"This means that any software can trigger as many interrupts as they want, entering kernel mode whenever they want, but those interrupts are always handled by the operating system. If you trigger an invalid interrupt, or an interrupt you don't have permission for, then the OS decides not to handle it. So while a program can trigger a switch to kernel mode, it doesn't do anything unless the OS decides it's OK to process the interrupt."
] |
[
"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, and from a security perspective you've already won."
] |
[
"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 it, it will just trigger an access violation.",
"Does x86 itself have some concept of its current access mode and some sort of encryption key or whatever required to enter / exit that mode?",
"Programs can always go to a ",
" ring (the higher the ring, the less privileged it is) but going to a ",
" ring can only be done via hardware-gated mechanisms such as interrupts. The current access mode/ring is part of the current execution state of the CPU. It is well aware of the current access mode and gates access appropriately."
] |
[
"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/mnist/",
").\nAs you can see on the link, the accuracy also depends on the size and specific structure of the network. One of the most precise networks (error percentage of 0.35) requires 6 layers of 784-2500-2000-1500-1000-500-10 neurons. Though you could also get a relatively high accuracy with just 800 hidden neurons.",
"Keep in mind that this dataset is relatively simple, and most likely you would use a neural network for much more complicated tasks, which are not necessarily image based. Though it still puts it into perspective of how the accuracy scales with size.",
"Also note there are, today, many different types of neural networks capable of computing specific tasks with a smaller number of neurons to at higher accuracy. An example is Convolutional Neural Networks, fine-tuned for recognizing features in images.",
"Edit: in regards to the connections, in this case every neuron in one layer is connected to every neuron in the next layer. However that depends on the type of neural network."
] |
[
"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 out modeled exactly like the brain. In the brain, number of connections and number of neurons play a reasonable role in determining how good it is at doing something. In machine learning, not so much. In deep learning, it’s one of a huge number of hyperparameters, and it’s not even one of the more important. The particular example you gave has a pretty intricate model that really can be expressed by X number of neurons. It doesn’t really give you much perspective anymore. "
] |
[
"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 out modeled exactly like the brain. In the brain, number of connections and number of neurons play a reasonable role in determining how good it is at doing something. In machine learning, not so much. In deep learning, it’s one of a huge number of hyperparameters, and it’s not even one of the more important. The particular example you gave has a pretty intricate model that really can be expressed by X number of neurons. It doesn’t really give you much perspective anymore. "
] |
[
"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 time you looked at them.",
"There are many other examples, and lots of cool optical illusions based on them.",
"I imagine much of what you see when you close your eyes is a side effect of the predictive/illusory nature of the visual system."
] |
[
"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, you can consider that the beams are not emitted at all in that direction and must either interfere constructively elsewhere or not emitted at all (cancellation at the source)."
] |
[
"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 describing the idea of the ",
"graded profile in detail",
". What this really means is that on average, a river tends toward a state where it erodes down at the same rate the rocks beneath it are moving up (and/or it moves as much sediment as it deposits in any given place for rivers in more passive landscapes) and the slope that develops at any point along the river is the slope necessary to maintain this erosion rate, given the amount of water (which varies as a function of position within a river system, less at the headwaters and progressively more downstream as the accumulation area increases). What this implies is that a river will not erode below its base level*. So, the only way you would get a canyon below sea level is if the base level of the river that cut that canyon was below sea level (e.g. an internally drained basin that lies below sea level).",
"*Because AskScience readers love technicalities, the technical exception to this statement would be ",
"submarine canyons",
", which are canyons below the surface of the ocean cut into the continental shelf and typically form down slope of the mouth of a subaerial river (and thus by definition are canyons below sea level). However, it is important to note that these features are primarily formed by ",
"turbidity currents",
" and thus represent a very different erosional process than a subaerial river and it's not really correct to consider these as canyons occupied by rivers in any formal sense."
] |
[
"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 idealized canyon with a narrow bottom and vertical walls, like the ",
"Zion Narrows",
". This canyon cannot be infinitely deep. The further you go underground, the hotter the temperature and higher the pressure. This makes rocks more fluid, so they will squeeze into any convenient void. At a certain depth, they will squeeze the canyon walls until you no longer have a canyon. Hopefully you're not there when this happens.",
"At what depth do the rocks start deforming? Our deepest drill hole, the ",
"Kola Superdeep Borehole",
" in Russia, made it to ~12 km before the (unexpectedly) hot rocks made the well sides collapse inwards. The Kola site was chosen for its cold, ancient shield rocks- in most places, the collapse will happen at much more shallow depths.",
"In general, rock deformation ",
"starts at about 5 km below the surface",
". All metamorphic rocks come from deeper than this. Given that a canyon is a lot bigger than a borehole and thus less stable, 5 km is a good estimate for the depth limit. Add a couple km if you dig it in old shield continental crust, or subtract a couple if you dig in oceanic crust, where 5 km would almost take you to the mantle! If you're digging underwater, add another ~1.5 km for buoyancy. In total, given the right location and an endless budget, you could probably dig an underwater canyon ~8.5 km deep.",
"To check my work, how does a 5 km aboveground limit compare to the deepest canyons on Earth? Surprisingly similar! Yarlung Tsangpo Canyon in Tibet, sometimes called the ",
"deepest canyon in the world",
", is 5.1 km deep. This canyon doesn't have vertical walls, so it could still be deeper and stay stable. In general, the limit to natural canyon depth on Earth is not rock deformation but sediment deposition. The deeper the canyon, the more rocks and sand will deposit there- making it shallower. Weird tectonic circumstances eons ago might have made a canyon so deep that deformation ",
" the limiting factor to that canyon's depth, but we don't see any of those today.",
"If you want an 8.5 km underwater canyon, ya gotta dig it yourself."
] |
[
"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 unpractical. The better is an indirect light-sound conversion. \nExample from the tip of my head: phototransistor as the conversion medium to control sound generation of a speaker connected to current source."
] |
[
"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 looking at socioeconomic groups that don't have access to good screening, concludes that the increase can NOT be explained by better screening. Screening plays a role though.",
"For anyone that wants to look at cancer incidence data, ",
"this",
" is a good website. You can see that, from 1975, the age-adjusted incidence rate of melanoma for people over 50 has risen by roughly 400% (under 50 shows a ~60% increase since 1975). I'll note that I'm not sure if \"age-adjusted\" means that they correct for increases in lifespan.",
"There doesn't seem to be much consensus as to what is causing the cancer increase. "
] |
[
"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 much less intense.",
"Today, people like to go to the beach at high noon to work on their tan. This means a very high UV exposure, and since tanning is presumably an irregular activity, there isn't much skin protection already present. We explicitly visit the beach to cook ourselves with the sun's rays. Hence, higher skin cancer rates.",
"The solution? Stay inside and keep reading reddit, I suppose."
] |
[
"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. However, if you pressurize carbon to several hundred atmospheres, and then heat it, you can get liquid carbon along a narrow pressure range.",
"Of course, there ",
" more than three phases, and the exotic ones don't show up in all materials, to my knowledge: Superfluids, for instance, require low temperature and a liquid state, but some materials are solid at low temperature, even at very low pressure.",
"Because He-3 and He-4 remain liquid even at T=0K, they ",
" form a superfluid state.",
"Here's a question I don't know the answer to: ",
" and low temperature, does He-3 form a solid?",
" Both He-3 and He-4 have solid phases:\n",
"http://www.physics.udel.edu/~glyde/Solid_H13.pdf",
"At p>~1000-1500 Bar, both He-3 and He-4 form FCC crystals, at T>15K, and HCP, at T<15K and p<1000 Bar. At p~25 Bar and T~1.5K, He-4 forms BCC, while He-3 forms BCC at p=50-125 Bar and T<3K. "
] |
[
"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 expansion was constant then the light from a star sufficiently far away will never reach us."
] |
[
"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 expansion was constant then the light from a star sufficiently far away will never reach us."
] |
[
"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 trees, brains cells need to be constantly \"watered\" with neurotransmitters and other chemicals like neuronal growth factors (e.g., BDNF) in order to survive. Depression deprives them of these chemicals, so they wither up and die in many parts of the brain. ",
" As brain cells begin to wither up and die, certain parts of the brain begin to shrink. These changes are often so dramatic that we can see them on ",
"brain imaging",
". Probably the most famous example is the hippocampus, which begins to shrink after a few weeks of untreated depression. ",
" Brain cells that talk to each other a lot form stronger connections, while brain cells that never talk to each other lose their connections. (As a common saying goes, \"Fire together wire together; use it or lose it.\") In depression, parts of the brain that we don't want to be talking to each other are forming extremely strong connections (LTP), while the opposite is happening in parts of the brain that we do want strong connections between (LTD). Some examples are extreme LTP in the ",
"lateral habenula",
", or extreme LTD in some cells in the ",
"prefrontal cortex",
". ",
" all of these changes are reversible with treatment. As the neuroscientist I ",
"quoted",
" above went on to say, ",
" Different antidepressants have different mechanisms, but all are known to reverse or prevent these changes in the brain. Even therapy helps prevent this damage, and some rapid-acting antidepressants can even reverse these changes almost ",
"overnight",
". "
] |
[
"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, from situational to widespread CNS disorders (NT/receptor concentration/regulation issues) to whole-life experiences to protein and cell-specific (something like diabetes, maybe involving death or autoimmunity to specific cell types) issues, all altering brain function in significant but different ways?",
"It just seems like there's such a wide range of issues in depression that maybe not all known problems present in all known patients, and I'm wondering if that's any bit useful in narrowing down precisely what's going on with particular patients, and if a potential therapy will be more or less likely to work.",
"Also, is there any attempt to move towards a more objective, testable method of diagnosing depression in clinical settings, or is it likely to remain kind of symptom and self-reporting based until cheaper/practical/useful tests are called for and developed?",
"Finally, what does the short to medium term future for depression treatment hold? Are there major advances on the horizon, potentially, or does it look like a long haul to more effective therapies, barring some major, unpredictable discovery?"
] |
[
"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.wikipedia.org/wiki/Common_descent"
] |
[
"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 following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"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, and other variables, a and b that can be written using x and y, you can substitute to see what the graph turns into. ",
"If we have x",
"-y",
"=4, a hyperbola, and have a=x-y, b=x+y, then ab=(x-y)(x+y)=x",
"-y",
". This means that a=x-y, b=x+y turns the hyperbola ",
"x",
"-y",
"=4",
" into the hyperbola ",
"ab=4",
". ",
"The biggest difference between these two examples is that the change of variables a=x",
", b=y",
" is not reversible. If I know a and b, I cannot say what x and y are. If a=4, b=9, I could either have x=2 or x=-2 and y=3 or y=-3. This means we'll be taking a higher degree object, like a circle, parabola, hyperbola, and turn it into a lower degree object, like a line. Additionally, I cannot get any a and b from this transformation, there is no x and y so that I'll have a=-1, for instance. What results is then a line segment. A line because we're reducing the degree from 2 to 1, and a segment because I don't get all a and b through this transformation.",
"But the transformation a=x-y and b=x+y is reversible and it can give me all possible a and b. If I know that a=1 and b=3, then I must have x=2 and y=1, there's no other option. If you give me ",
" a and b, I can find you an x and y that give me them. Because of this, under this change we'll get the same \"shape\" we had before, and we'll get all of it! Those two hyperbolas are essentially the same thing, just placed on the plane differently.",
"An interesting transformation you can do is take a hyperbola like x",
"-y",
"=1 and do the transformation a=1/x and b=y/x, this means that x=1/a and y=b/a and so the curve becomes (1/a)",
"-(b/a)",
"=1, multiply though by a",
" gives 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, with the two points (0,1) and (0,-1) missing. This means that a hyperbola is just a circle with two points taken out or, equivalently, a circle is a filled-in hyperbola.",
"You can do this to a parabola as well: if we let a=2y/(x(1+y)) and b=(1-y)/(1+y), then this will turn the curve y=x",
" into the circle a",
"+b",
"=1. We can cheat a little so that when y=0, x=0 we'll have a=0 (this is okay because we can take limits as long as we know that we approach (0,0) along the curve y=x",
"). In this way, the only point on the circle that we're missing is the point (0,-1), as this is the point that (a,b) approach as (x,y) approach infinity.",
"This means that Hyperbolas are just circles with two missing points, Parabolas are circles with just one point missing and Ellipses are just stretched circles. In other words, we can use coordinate changes to show that ",
" (plus or minus one-or-two points). There is a field of math, called Projective Geometry, where we include extra points at infinity, and in this geometry parabolas have one extra point and hyperbolas have two extra points. So in Projective Geometry, all conics are circles in the strictest sense.",
"I may have gone off on a tangent, but there's no general theorem that tells us what kind of object we'll get under a transformation. But we can say that under rational changes of coordinates, we'll change one algebraic object (conic, line, or higher order) into another one (or at least part of another one). These kinds of transformations are called ",
"Regular Functions",
" and play a very important role in some very deep math, in the subject of ",
"Algebraic Geometry",
". A simple exercise in Algebraic Geometry is working with conic sections, which are examples of ",
"Algebraic Varieties",
". Regular Functions working on Projective Varieties behave particularly nicely."
] |
[
"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 (i.e., cells removed and put into cell culture) is more contentious.",
"Inasmuch as we don't have many plants more than a thousand years old- a bristlecone pine at 5,064 is the current known record-holder- as individual organisms (meaning we ignore clonal plants like the Pando quaking aspen), it suggests immortality in plants is rare, if it is possible.",
"It is conceivable that certain plants whose mode of vegetative propagation is like that of ",
"water hyacinth",
" (i.e., vegetative proliferation) or ",
"Azolla",
" could be largely if not entirely clonal and therefore difficult to estimate how \"old\" they truly are. Those plants could conceivably be immortal if they are allowed to continue to proliferate, and any seedlings were culled."
] |
[
"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 elements are made. You won't always see it but on some periodic tables (like the one above my bed :D ) there is a notation to denote ",
"synthetic elements",
", and they're all huge. There is an exception but I can't remember the details and ill get back to that with an edit later. ",
": The element I was thinking of is ",
"Technetium",
", which has no stable isotopes; all are radioactive.",
"The thing stopping them making even heavier elements is stability. Neutrons (basically) help to stabilise nuclei, preventing the electronic repulsion between protons from overcoming the 'strong force' (one of the four fundamental forces), presumable by getting between them and reducing the repulsion (since electronic repulsion increases exponentially as distance decreases) See ",
"here",
". Disregard the units, I just pulled that from google images; just notice that the repulsion increases as distance decreases.. At some point (number of protons, that is), you require so many neutrons that the atom becomes unstable and begins to undergo radioactive decay. There is a theoretical \"island of stability\" at which very heavy (I think ~ 140 protons) atoms are known to be stable. ",
"I'm redditing on the phone now. Let me shower and ill provide some references and images. :) ",
": Putting the neutron:proton, island of stability graphs here for coherence of the above passage. ",
"Here",
" is a graph showing the relationship between protons and neutrons. Notice the number of neutrons required to stabilise a nucleus increases exponentially with regard to the number of protons. Also, the reason the red dots in the middle don't form a perfectly straight line is because there are isotopes of many elements (differeing ratio of n:p, thus different location on the graph).",
"Now ",
"here",
" is the wiki article for the island of stability. It explains the topic better than I could."
] |
[
"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 the pressure upon your eye, and thus slightly changes the curvature of your cornea (The outer clear layer of your eye). This changes the refractive properties of your eye (keep in mind light is refracted not just at your lens, but also at your cornea. this is how LASIK surgery works, by minutely changing the curvature of your cornea).",
"I have a feeling Staus' explination may be true too, and this might be a combination of both effects."
] |
[
"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 spatial resolution and intensity for improved focus. ",
"Edit: I remembered another example that works on this principle - point-and-shoot digital cameras. They have a tiny lens and chip (basically the same as a tiny pinhole) so everything from really close to really far away is in focus basically all the time (depth-of-field is the photography term). Contrast this with an SLR or even medium format camera with a very wide aperture - the depth-of-field is very short. You can play the same trick with your eyes. "
] |
[
"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, all of it will be used up and water remains. From this you can deduce that in water there are twice as many hydrogen atoms as oxygen atoms.",
"Alternatively you can apply a high voltage to water and break it into its constituent gases and come to the same conclusion."
] |
[
"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, son.",
"http://en.wikipedia.org/wiki/Electrolysis",
"EDIT: I am 99.99% sure both hydrogen and oxygen were known before there was an atomic theory. And their properties were well described also. \"Hydro-generater\" and \"Oxide-generator\". So in a way, they new about atoms because they knew about the properties of these gases."
] |
[
"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 related maladies.",
"But just being at 300m can be fatal...the air becomes so thick that the effort merely to breath becomes exhausting. Without excellent cardiovascular fitness, the effort of breathing tires you so you breath harder, tiring you further, breathing harder, until you succumb to hypercapnia (exceess CO2 in the blood).",
"David Shaw",
" dies this way from exerting himself trying to recover the body of another diver at 270m. "
] |
[
"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 principle, so \"nuclear force\" is actually the sum of the residual strong force and the fermionic exclusion force."
] |
[
"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, when nuclei get too big, the electromagnetic repulsion of the protons will overcome the residual strong force, producing less stable nuclei). ",
"Maybe your teaching was speaking about interactions between atoms, like the ",
"Lennard-Jones potential",
", but the origin of that potential is the electromagnetic force and not the strong force. "
] |
[
"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 its focal point, essentially every \"plane\" on the reflector is normal to the direction of the beam going to or coming from the focus. ",
"So imagine it this way: If you have an octagonal ring of mirrors, you can look in 8 different directions from the center and see specifically one reflection in each direction. If you bump that up to a dodecagon, you'll see ",
" 12 distinct reflections. As the planes get thinner and thinner, you begin to lose surface area that can reflect the whole image back to the focus. Eventually, in the case of the ring, the surfaces get infinitesimally thin and you're left with a sliver of a reflection in every direction you look in. The result is an amorphous, but continuous, smear of color, almost as if someone covered you with some sort of transfer material and rolled and dragged you around the interior surface of the ringed mirror.",
"A lightbulb at the center of such a reflector would see nothing but a band of continuous light all the way around, but it would be very different for any person observing from a point not at the center."
] |
[
"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 equations, exact equations, linear equations, etc. There may also be so-called ",
" which may be exploited to reduce the order of the differential equation, which often makes finding a solution much easier. (Exploiting energy conservation is an example of this last method.)",
"For a force law of the form ",
"(",
") = k(",
" - ",
")/|",
" - ",
"|",
" (e.g., gravity), there are well-known analytical solutions in terms of conic sections, and these solutions are examined in more detail in a first- or second-year mechanics course.",
"For general force laws, there is no known method to find an analytical solution (and there may not exist such a solution in terms of elementary functions and their integrals). So we have to use numerical methods to solve the equation approximately. There are many such numerical methods, which vary in accuracy, robustness, and complexity. The basic numerical methods (e.g., Euler's forward different method) are covered in a course on differential equations. More specialized methods are covered in a course on numerical analysis.",
"Finally, sometimes we are not able to find an analytical solution but we don't really care. For many problems we may only want to find the solution \"for small angles\" (or some other approximation) or we may only want to know some general dynamics about the long-term behavior of the system. Questions like that can often be more easily treated not by appealing to Newton's second law directly. For instance, if a system can be described by a suitable ",
", then we can extract a lot more information, particularly about the fundamental symmetries of the problem.",
"In high school or introductory physics, a problem like a rocket launched from Earth would most likely be treated using energy conservation. You can perfectly well answer questions like \"what launch speed is required to get the rocket to a certain height?\" without having to find a full analytical solution for the rocket's trajectory."
] |
[
"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 fluids to mechanical to chemical reaction rates."
] |
[
"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 transparent to visible light are fairly transparent to wifi, like wood. ",
"Oddly brick is fairly transparent to wifi in a way stone and concrete are not. "
] |
[
"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 lot of vital functions like breathing, swallowing and cardiovascular tone), your brain will stop telling the rest of your body to breathe.",
"So, even when oxygen in the blood drops (hypoxia) and carbon dioxide builds up (hypercapnia), opiates inhibit the signals that would normally stimulate your brain to tell your body to breathe faster and harder.",
"Opiates will not directly cause your heart to stop, but respiratory depression definitely will.",
"Edits for clarity"
] |
[
"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 activate the diaphragm muscle to contract(breath in). ",
"In even larger doses, the heart can stop as well, though most people die from suffocation rather than their heart stopping. ",
"Don’t do drugs, kids. "
] |
[
"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 gut that prevent the C. botulinum from taking hold. ",
"You may be familiar with botulism as a problem in food canning or ",
"botulinum toxin",
" which is used medically (and cosmetically) as Botox."
] |
[
"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 light. And particles with imaginary mass, called tachyons, travel on ",
" paths, which are paths through spacetime that correspond (in some reference frames) to travelling through space but not through time. (In other frames, these look like paths moving faster than light.)",
"These correspond to the three different types of path that are possible in spacetime - paths that look like moving just through time, paths that look like moving just through space, and lightlike paths that act as the dividing line between them. A physical particle can't change from one type of path to another - if you're on a timelike path, you'll always be, and similarly for the other kinds.",
"The reason we travel only one direction in time, and can't just turn around, is because - you can convince yourself of this - the only way to change direction in spacetime would involve, at some point, becoming spacelike, which isn't allowed."
] |
[
"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. That ties in with the laws of thermodymaics. We don't remember the future because entropy is increasing with time. Think about it this way: if you were moving backwards in time you would have no way of knowing. So \"movement\" doesn't really make sense."
] |
[
"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 transmission pipelines."
] |
[
"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 bacteria die every day in the ocean from viruses. Their immune responses are very weak while we have dedicated armies of specialized cells for protecting us. ",
"Humans are among the top class, it's jsut we live in a world with a LOT of things that try to infect us."
] |
[
"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 nitpick about precise definitions and things."
] |
[
"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 oscillator (its quantum depending only on the frequency ω of the system).",
"Coming back to quantum fields, if you consider a field in a box, its frequency ω depends on the size of the box, just as the particle in a box and its energy. However, the Hamiltonian (i.e the energy) of a field in any system is the same as that of a quantum oscillator. This means that the energy is quantized, and each quantum (ħω) is a particle. What this means is the field is always quantized (i.e. it has an integer number of particles), but the energy of the single particles themselves may depend on the boundary conditions, and if there are no boundaries the particles are free to have any energy. "
] |
[
"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 approaches infinity?"
] |
[
"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 the internal resistance changes with the amount of alcohol gas detected. When the internal resistance changes, there's a proportional change in voltage across the load resistor (RL). The arduino board reads the actual voltage across RL. ",
"The unit of measurement is voltage, measured across RL. ",
"There are two ground connections because one is for the heater, one is for the resistor.",
"You need six pins because two are for the heater. The other four belong to the internal resistor (two on each side, one side is A, other side is B). There are probably two connects on each side of the resistor because of the expected current to operate the sensor.",
"Learn more about resistors in series and you will understand, this is very simple."
] |
[
"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 observatory and why it was placed at the South Pole at their web site given above."
] |
[
"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",
"The high Antarctic plateau provides a superlative environment for the measurement of the faint light from distant stars and galaxies. This is on account of the extremely dry, cold and stable air. This permits more sensitive observations to be made, across a wider wavelength range, and with sharper imaging precision, for telescope in Antarctica than if placed in any other location on the surface of the Earth. Constructing a telescope to take advantage of these conditions, however, is a formidable challenge on account of the extreme environment and the logistical difficulties that working on that continent poses. No optical telescope larger than 60cm has yet been operated on the Antarctic plateau through winter months."
] |
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