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[
"Is there any merit to the arguments presented at this link \"Why the Big Bang is Wrong\"?"
] |
[
false
] | null |
[
"No, there is no merit to this whatsoever. The author uses old controversies which were solved back in the 60s and 70s, and combines them with a general misunderstanding of astrophysics in general. (Not wanting to pull out the argument from authority or whatever, but it does say at the bottom \"John Kierein has a BS in Physics from Notre Dame\"... this guy really doesn't have any advanced astrophysical education). ",
"[...] there are many objects observed that are older than the time from the big bang, which is variously estimated to be from 10 to 15 billion years ago, with the best estimates being 10 billion years using trigonometry rather than cepheid variable brightness.",
"This is really dated information. We now know with good accuracy that the Universe is 13.7 billion years old, and we have refined our stellar evolution models (using updated physics and better computing power), and no stars seem older than that. (Also, trigonometry was ",
" used to measure the age of the Universe, I'm not sure where that comes from).",
"Stars and globular clusters in our galaxy are thought to be older than 15 billion years and there seem to be similar stars that are seen in galaxies that are many billions of light years away from us and thus apparently formed closer to the time of the big bang.",
"Same as above. This was realised as being incorrect many years ago.",
"Measurements of the uranium content of stars has produced a minimum age of the universe of at least 12 billion years, whereas the best direct measurements of Hubble's constant produce an age of 10 billion years. The iron content of quasars is much too great for their age.",
"That's fine now, with the correct age of the Universe.",
"Even though supernovae are thought to last only fraction of our sun's lifetime, it is highly improbable that there is sufficient time for these cycles to have occurred since a big bang.",
"He's pulled this out of thin air... where are the models/calculations that suggest that it is 'improbable'? What does 'improbable' mean in this context? This is entirely made up. Sloppy, silly thinking like this casts doubt on his whole argument. Anyway, stars massive enough to go supernovae have short lifetimes, on the order 10 million years. That's enough time for 1000 generations so far. ",
"Similarly, our galaxy is rotating at a speed that only permits from 45 to 60 rotations since the big bang, which (according to Mitchell) is not a long enough time for it to achieve its spiral shape.",
"Again, this is ",
" outdated. Back in the 70s/80s, work by Lin and Shu (amongst others) showed that spiral arms are emergent density waves, so galaxies don't act just like little catharine wheels winding up.",
"There are some very large chains of galaxies spread throughout the universe.� It is believed these large structures, like the \"great wall\", would require many hundreds of billions of years to form.",
"This is, yet again, just made up, and is totally unsupported by anything in the literature. \"It is believed\"? Come on. ",
"Galactic redshift surveys show a regularity in the spacing of galaxies a quarter of the way to the time of the supposed big bang. This is totally different from a big bang expectation which would have them closer together as they get closer to the time of the big bang.",
"The link he provides is broken, so I can't check what he means by this. I'm not sure, because when we look at the distant Universe, we ",
" see galaxies are more densely packed than at the present day, evidenced by their high rate of merging/colliding.",
"How do galaxies collide if they are flying away from each other?",
"This is getting silly at this point - saying something like this really belies his profound lack of understanding. The speed of recession is proportional to the distance, so for small distances the random motions are much greater than the expansion speed. So galaxies can collide easily. ",
"Mature galaxies are found near the time of a supposed big bang that have not had enough time to develop.",
"This is a minor point from 2004, which caused galaxy evolution models to be updated. Calling this 'evidence against the Big Bang\" is wrong, to say the least.",
"... I don't have the energy to continue, the lines of argument are getting weaker as we go down the page. To sum up, then, no. This isn't a good argument. "
] |
[
"The comparison with refraction and gravitation bending light without blurring is just stupid. Neither works via the Compton effect. Even colored glass isn't colored because of Compton scattering, it is because some light is absorbed.",
"The 'proof by picture' argument isn't that convincing either. Those stars are visible through the cloud similarly as the glass, it is because the photons we see didn't interact with anything at all, neither being absorbed nor being Compton-scattered.",
"I am too lazy right now to calculate what the deviation of light would be if it were compton-scattered.. But i am sure it would be large enough to blur stuff, if the photon only enters a telescope 1mm off, the overall effect would be to blur, so the average angle change must me less than 1mm/billions of lightyears. (in radians)",
"Can't really say much about those proper motions..",
"I can't really say much about if things appear older than they should be, but the comparison with the age of the Earth isn't a realistic one; larger stars burn up faster than smaller ones, and the density being higher early on, one would also expect more large stars in this case.",
"Lastly, it is curious these people are writing books instead of writing papers.."
] |
[
"What he's really arguing is that red shift should not be used as evidence for the big bang. When we came up with these ideas red shift was the primary evidence for the Big Bang. You'll notice that the paper ",
"he cites",
" is from 1968 and the other work he cites doesn't reference much past the late 70's. Currently there is much more evidence for the Big Bang that doesn't rely on red shift. ",
"The reason that the Big Bang is the most accepted theory is because there's the most observational evidence for it. It could be wrong, but the evidence is stacking in its favour."
] |
[
"Design method for analog filter with maximally flat group delay of a chosen value with design pass band?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"/r/HomeworkHelp",
"guidelines.",
"If you disagree with this decision, please send a message to the moderators."
] |
[
"Hi,",
"thanks for looking at my comment. This is not a homework question.... As I stated I'm looking at a possible equivalence between filter design and a research problem I am working on. I had hoped someone with experience in filter design would be available to discuss optimization strategies and equivalence. Such discussions on this forum have been very fruitful for me in the past. I would appreciate it if you would reconsider your decision."
] |
[
"I did look at the text of your post so please do not presume I have not. The guideline also covers general project assistance. In any case, your question is rather broad and open-ended and so should go to ",
"/r/AskScienceDiscussion",
". If you can narrow the question appropriately then feel free to resubmit that.",
"In addition, future correspondence should be dealt with as was stated in my post:",
"If you disagree with this decision, please send a message to the moderators.",
"You can send a message via the sidebar."
] |
[
"How big would a building have to be to cause a change in the Earth's momentum?"
] |
[
false
] |
Here's my thought: we keep building bigger skyscrapers. How big would one have to be to alter Earth's orbit? And what might happen if it did?
|
[
"rmhism is correct, you can't change the Earth's orbit with terrestrial things.",
"However, a tall and massive enough skyscraper could change the Earth's ",
" (not orbit) by changing its moment of inertia because of the redistribution of weight. This could give something like a wobbliness to our rotation. However, we're talking more massive than we could probably ever care to undertake - remember, there are mountains far bigger and more massive than anything we've built, and that's child's play compared to the size of the Earth so even they don't do anything to the Earth's rotation."
] |
[
"It will never alter the earths orbit (the orbit of the center of mass, that is) since there is no external torque. To change angular momentum, the only way possible is to apply an external torque. All the forces that will be needed to build a skyscraper are internal to the system. "
] |
[
"No, it affected rotation. Not orbit."
] |
[
"What do you think will be the first major vindication/discovery of the LHC in CERN?"
] |
[
false
] |
Creation of a mini black hole? Uncover a Higgs particle? Who decides what experiments are going to be done using the facility? Is it a for profit entity where you can pay to use the collider or what?
|
[
"There are four detectors, and two types of collisions. "
] |
[
"Creation of a mini black hole? ",
"No.",
"Uncover a Higgs particle?",
"Maybe.",
"Who decides what experiments are going to be done using the facility?",
"There are two experiments that they do proton-proton collisions and gold-gold collisions. When you say that two different scientists are doing two different experiments with with the LHC that means that they are looking at the same data but looking for different things in the data, eg The higgs or black holes. However, they do have to decide how much time to spend on protons an how much time to spend on gold, I think the decision is made by the director of the CERN laboratory.",
"Is it a for profit entity where you can pay to use the Collider or what?",
"No, CERN is an international interjurisdictional entity created by the governments of several European nations. It would be really expensive to pay for anything the LHC does and it would be of little commercial value."
] |
[
"Isn't it a bit more than two experiments? Atlas, Alice, CMS, LHCb?"
] |
[
"What are the physics of an explosion in space?"
] |
[
false
] |
I remembered an episode of mythbusters that disproved the movie notion of explosions forcefully pushing people off their feet and away from the blast. Would the same be true for an explosion in space (e.g., a star going supernova)? Would the explosion be enough to push something (e.g., ship, planet, etc.) away, or is any movement solely due to a change of gravitational forces?
|
[
"\"Explosions\" are not a class of one single type of phenomenon. Explosions in the atmosphere tend to have a vaguely similar effect since one of the primary ways they propagate their energy is via shockwaves in air. And since they're highly energetic and generally dangerous to humans we lump them into one category.",
"In space that isn't there, so the nature of the explosion is very important. ",
"For example, C4 exploding in space would result in rapidly expanding gases and a bit of light, and all the products of the explosion (which is just a really fast chemical reaction) would quickly cool.",
"A nuclear explosion in space (such as if a nuclear warhead was detonated in space) would release most of its energy as light (i mean broad spectrum EM radiation, not only visible light). With nothing to push against there would be no pressure wave or anything like that. ",
"A supernova is a different beast, since the explosion is actually caused by a prior implosion, when radiation pressure from nuclear reactions in a star are insufficient to stop its collapse. In this event a large amount of matter and energy is ejected. If enough matter from a supernova were to hit a planet near the nova, I'd be willing to bet that it could be accelerated to escape velocity under the right conditions. I'll let the experts speak to that.",
"My point was just that \"explosion\" is too vague a term in this context."
] |
[
"That makes sense. I'm a complete novice/layman with this, so I appreciate the explanation "
] |
[
"When you say \"space\", do you mean outside of Earth's gravity well, just outside the atmosphere, or maybe something else? \"Space\" is kind of a vague term.",
"A force acting on matter can propel it, even ever so slightly. Enough force can move anything. Gravity is the dominant force for celestial movement, but other forces exert small but non-zero force on the planets.",
"Supernova can accelerate planets above escape velocity, from what I understand. I'll do the math in a bit. "
] |
[
"Do dogs have the capacity to understand that if I step on their paw that it was an accident?"
] |
[
false
] |
Or, from their point of view, do I just hurt them and am immediately after really nice to them with petting and talking to them for an unrelated reason?
|
[
"Folks, we don't allow speculation here. Answers need to be based on scientific information."
] |
[
"There is no evidence that dogs are capable of that type of reasoning. Dogs fail the mirror test for self awareness. Dogs fart and it surprises them, and they chase and bite their tail, which also surprises them. It is known that dogs don't associate punishment with prior behavior. ",
"http://www.dogtraining.helentaylordorset.co.uk/punishment.htm",
" "
] |
[
"Oh man, that isn't he answer I was hoping for, but I'd rather have the truth than be ignorant with this kind of thing. Thanks for the response! "
] |
[
"If you quantum entanglement two atoms, and one is sent into a black hole, is there observable changes in the atom outside of the black hole?"
] |
[
false
] | null |
[
"No. Entanglement doesn't work like that. You can observe a correlation between 2 entangled particles by comparing results of experiments on each of them, but observer A doing something to particle A does not cause particle B to behave in a way that is observably different to observer B alone. It is only after they compare notes do they observe correlated outcomes."
] |
[
"Ok so since u could no longer get any data from the one in the black hole you would have no way of knowing?"
] |
[
"Right."
] |
[
"Would a typical modern adult human who'd never seen or heard of a snake before instinctively know it was dangerous and which end to be worried about?"
] |
[
false
] |
I think that's the whole question, but please ask any questions for clarification.
|
[
"Monkeys are instinctively afraid of snakes, even captive-born monkeys that have never seen one (",
"http://www.pnas.org/content/110/47/19000",
") but I can't find a source for apes. However, the part of the brain in the macaques that responded so strongly to the snake images is conserved across primate species, including humans. I'd say it's likely. ",
"Edit: link was borked, fixed now"
] |
[
"I don't remember where I read it, so take that for what it's worth, but I read about a study that was done that showed snakes were the number one predator humans could spot. Even out of periphery, we can spot them better than anything else. "
] |
[
"I saw the same thing, but it included spiders. They did a test where they put a collage of all kinds of animals together and asked the person to find animal x. They consistently found the spiders and snakes quicker than everything else."
] |
[
"If you have an orgasm in your dream, do the same brain areas get activated as though you were having the orgasm while completely awake?"
] |
[
false
] | null |
[
"If science was driven by what we deemed useful, we wouldn't have the x-ray, data transmission over wires, or hell, the microchip. "
] |
[
"If science was driven by what we deemed useful, we wouldn't have the x-ray, data transmission over wires, or hell, the microchip. "
] |
[
"If science was driven by what we deemed useful, we wouldn't have the x-ray, data transmission over wires, or hell, the microchip. "
] |
[
"What exactly happens when you get executed by hanging? Technically speaking."
] |
[
false
] | null |
[
"It depends. There are four different kinds of hanging: suspending, short, standard, and long. Suspending is putting a noose around someone and then lifting them up which strangles them. \nA short drop is when you are on and object and that object is removed, leaving you dangling there.. The drop isn't enough to break your neck so you are again strangled.\nThe standard drop is the more popular (obviously) and was developed in Britain in the mid 1800s. The victim would be on a platform about 6 feet in the air and the platform would release, breaking the victim's neck, causin instant paralysis, etc. Because of this instant breaking of the neck, tho was seen as more humane which is why it was widely accepted in the world.\nThe long drop is nearly the same as the standard except calculations were used to make the noose as short as possible but still be able to break the neck. This was developed shortly after the standard. The problem with the standard is that all of the victims suffered the same drop and if there was that great of a distance of a drop for the wrong size person, the person would be decapitated (which if it's a public execution, it would be quite gruesome)."
] |
[
"Sorry for the wall of text. I'm on my phone and I tried to space them out but it seems that that had failed"
] |
[
"It depends. There are four different kinds of hanging: suspending, short, standard, and long. Suspending is putting a noose around someone and then lifting them up which strangles them. ",
"A short drop is when you are on and object and that object is removed, leaving you dangling there.. The drop isn't enough to break your neck so you are again strangled.",
"The standard drop is the more popular (obviously) and was developed in Britain in the mid 1800s. The victim would be on a platform about 6 feet in the air and the platform would release, breaking the victim's neck, causin instant paralysis, etc. Because of this instant breaking of the neck, tho was seen as more humane which is why it was widely accepted in the world.",
"The long drop is nearly the same as the standard except calculations were used to make the noose as short as possible but still be able to break the neck. This was developed shortly after the standard. The problem with the standard is that all of the victims suffered the same drop and if there was that great of a distance of a drop for the wrong size person, the person would be decapitated (which if it's a public execution, it would be quite gruesome).",
"Hopefully this is what you were looking for."
] |
[
"Are there any known objects in our galaxy that are moving near the speed of light?"
] |
[
false
] |
[deleted]
|
[
"Not even close. The fastest thing I can find is ",
"S2",
" moving at 5,000 km/s or near %2 lightspeed."
] |
[
"That's pretty fast, and it's a large mass. I can imagine an asteroid size mass being gravitationally slingshotted by that to much higher speeds."
] |
[
"Pulsars rotate at decent fractions of it. "
] |
[
"How are 25nm transistors made."
] |
[
false
] |
I'm aware of the process of photo-lithography whereby the surface of a substrate is etched using ultraviolet rays. However 25nm is smaller then the wavelength of ultraviolet light, wouldn't this cause issues and if so how are 25nm transistors made.
|
[
"The wavelength of UV lasers used in the current 22 nm process is 193, (DUV or \"deep\" UV). The inability to create a spot smaller than the wavelength is called the diffraction limit, and roughly speaking the formula is D = .61 lambda / n sin theta. D is the spot diameter, lambda is the wavelength, n is the index of refraction, and theta is the acceptance angle (related to the size of the lens). If everything else is held fixed, we can increase the index of refraction by using ",
"immersion lithography",
". Outside of changing the spot size, you can use some other process techniques: ",
"http://en.wikipedia.org/wiki/Computational_lithography",
" ",
"http://en.wikipedia.org/wiki/Multiple_patterning"
] |
[
"nanoelectronics PhD student here\n25nm or smaller features can be accomplished via a combination of tricks, one of which is the reduction of features AFTER lithography. photolitho will give you a minimum linewidth of, say, 60 or more nm, but you reduce it by etching isotropically underneath a hardmask. You don't gain anything in density (because the intervals between lines is the same), but it's still good. Furthermore, the combination of features reduction with multiple exposures helps in getting the best of both worlds (small features AND density). \nOther tricks you can use is spacer lithography (promising for top-down nanowire devices), or e-beam lithography (but the throughput is not as good)"
] |
[
"Coherent Extreme Deep Ultraviolet (EUV) lllumination, Calcium Floride optics and Interference Lithography are all used to create 25nm aerial images in very expensive photoresist. The exposed resist undergoes photolytic changes that allows it to dissolve in a 'developer' solution. This pattern in the remaining photoresist is then transferred to the silicon substrate by way of plasma etch processes.",
"EDIT: BTW, the photoresist exposure needs to be performed in a vacuum, EUV is attenuated in the presence of air."
] |
[
"Say you took our universe and cleared out all matter except for two electrons, placed 1 light-year apart. They would repel, right? Can someone give some details as to the mechanism?"
] |
[
false
] | null |
[
"The quantized field is ",
" using virtual photons. They don't 'just appear'; they don't really exist. It behaves ",
" they existed. (but that's only one way of describing the quantized field) Electrons are ",
" constantly emitting photons in all directions. If they were emitting real, detectable, photons, they'd be termed 'real' photons, not 'virtual' ones. The 'quantum foam' is (AFAIK) just an interpretation that Wheeler made; it's not part of quantum field theory.",
"QFT gives a more detailed and accurate description of how electromagnetism works at the quantum level. But virtual particles and such are ",
" a mechanism; they're a visualization of how the calculations are done. They don't actually explain anything about why the EM field exists or why charged particles ineract with it. It's a way of representing the state of the field. ",
"Indeed, quantum field theory doesn't really say much more about the how-and-why of how electromagnetism works than classical electromagnetism does. Certain particles have a property of electrical charge, and through it, they couple to the electromagnetic field. A charged particle giving off virtual photons doesn't really say much more than a charged particle being surrounded by an electrical field. ",
"All we can say is that we've since discovered analogous fields that describe all other forces and particles, except for gravity."
] |
[
"Well, for starters the most well-known QED effects, the Lamb Shift and Casimir Effect (ironically, both are often cited as 'proof' of virtual particles) were both predicted and calculated well before that whole formalism was developed. Then there's the whole starting point of S-matrix theory, and much development in non-perturbative field theories, which is however not my area of expertise. (What ",
" though, is non-relativistic many-body theory, where it's quite abundantly clear that perturbation theory is merely one way of solving the problem, and the virtual states there are never portrayed as some kind of objective physical thing. Nobody has the impression that Hugenholz and Goldstone diagrams portray any kind of 'event' or process, even though they're direct analogues of the Feynman diagrams people often construe as such. Not that I mind people talking about them ",
" they were real, as a visualization technique. I just don't agree with the philosophical leap from that to them ",
" real.)",
"Conservation of energy and four-momentum isn't violated; it's conserved at every vertex in the Feynman diagram. Virtual particles certainly ",
" to violate energy conservation, but this is only a problem if you consider them to be real things, rather than just terms in your calculation that'll eventually sum up to the right result where energy is indeed conserved. To me, this is another argument for why they're ",
" be considered real, if anything. (The whole 'justification' for that which I've heard from time-energy uncertainty, is ",
" hand-wavy, as the whole time-energy uncertainty is very hand-wavy in general. When was it ever used in a truly rigorous context?)",
"I'm not saying that non-perturbative theories can do exactly everything PT can, and equally well. It's the dominant method for good reason. But the fact that a particular series-expansion approximation method works well is no kind of evidence that the terms of that expansion having some 'deeper' physical meaning. "
] |
[
"Well, for starters the most well-known QED effects, the Lamb Shift and Casimir Effect (ironically, both are often cited as 'proof' of virtual particles) were both predicted and calculated well before that whole formalism was developed. Then there's the whole starting point of S-matrix theory, and much development in non-perturbative field theories, which is however not my area of expertise. (What ",
" though, is non-relativistic many-body theory, where it's quite abundantly clear that perturbation theory is merely one way of solving the problem, and the virtual states there are never portrayed as some kind of objective physical thing. Nobody has the impression that Hugenholz and Goldstone diagrams portray any kind of 'event' or process, even though they're direct analogues of the Feynman diagrams people often construe as such. Not that I mind people talking about them ",
" they were real, as a visualization technique. I just don't agree with the philosophical leap from that to them ",
" real.)",
"Conservation of energy and four-momentum isn't violated; it's conserved at every vertex in the Feynman diagram. Virtual particles certainly ",
" to violate energy conservation, but this is only a problem if you consider them to be real things, rather than just terms in your calculation that'll eventually sum up to the right result where energy is indeed conserved. To me, this is another argument for why they're ",
" be considered real, if anything. (The whole 'justification' for that which I've heard from time-energy uncertainty, is ",
" hand-wavy, as the whole time-energy uncertainty is very hand-wavy in general. When was it ever used in a truly rigorous context?)",
"I'm not saying that non-perturbative theories can do exactly everything PT can, and equally well. It's the dominant method for good reason. But the fact that a particular series-expansion approximation method works well is no kind of evidence that the terms of that expansion having some 'deeper' physical meaning. "
] |
[
"If I had a vine and split it into 5 strips and wove those strips into a rope, would the rope be stronger, weaker, or the same strength?"
] |
[
false
] |
Say there you had a vine and you were able to break it up into 5 even strips that run the original length. If you then took those 5 strips and wove them together, would the new rope be stronger because of the interweaving, weaker because the size of the strips, or the same strength because it is essentially the same as when it started?
|
[
"Stronger, but shorter due to the weaving, regardless of weave pattern."
] |
[
"Weave pattern will also increase the cross sectional diameter, increasing strength."
] |
[
"yep, that's why it's shorter."
] |
[
"Why does rocket exhaust sometimes look like this."
] |
[
false
] |
[deleted]
|
[
"Those are Shock Diamonds, which are a complex phenomenon resulting from supersonic flow in air:",
"http://en.wikipedia.org/wiki/Shock_diamond",
"You don't always see them because they need specific conditions to form, or at least to be visible, including excess fuel in the exhaust stream. "
] |
[
"It's called ",
"Nozzle Overexpansion",
", and it can even happen with high speed aircraft. Rockets and high speed aircraft are typically designed to travel at very high altitudes. ",
"Since it is taking taking off at a hight it's not designed for, there is a bit of inefficiency. This inefficiency causes the exhaust to form an ",
"oblique shock wave",
" giving us the diamond pattern.",
"Interestingly, this is one of the reasons why space rockets have ",
"multiple stages",
". Each stage is designed for a different level of atmosphere, and no overexpansion is present. "
] |
[
"The expansion of the gases out of the nozzle are designed to have a relatively perfect expansion at x back pressure. That back pressure varies based on altitude, so at points in the flight path the C-D nozzle is working at lowered efficiencies. This causes the flow to either over or underexpanded, and once outside the nozzle the exhaust pressure has to reach ambient. At supersonic speeds over expanded flows create oblique or normal shock waves to reach ambient pressures, and the waves create a pattern of oblique shocks and expansion waves resulting in a pattern like this.",
"Rockets have multiple stages for several reasons, one being so each stage can have a C-D nozzle designed for ambient air pressure at it's operating altitude. If you had one stage your rocket would be operating at lower efficiencies for the majority of the flight path."
] |
[
"Why does evolution produce such complex creatures?"
] |
[
false
] |
I'm not sure if I'm phrasing this right. What I want to know is why there aren't just bacteria, instead of complex multi cellular organisms like mammals and reptiles. Aren't bacteria a lot better at reproducing than large organisms? What advantage do larger, more complex organisms have compared to small bacteria?
|
[
"How complex are organisms supposed to be ? You could equally ask why aren't organisms way more complex than humans and dolphins ? We don't know, but it seems that it's the level of complexity associated with the amount of energy the earth receives. Maybe if the sun were brighter everything would get more complex."
] |
[
"that's actually what happend early in evolution! for like 3 billion years there was only colonies of bacteria on earth but for some reason it wasnt sustainable for bacteria to just keep multiplying. there was a phase change - the internal structure of modern cells suggests that there have since been numourous symbiotic relationships formed in which one kind of cells that was living close to or inside another cell, becomes an organelle of that cell, for example. when such higher-level relationships form there's no going back and hierarchy upon hierarchy forms until you get the high complexity of modern cells. it's a result of cells living in high densities with more energy flowing through the system than it can absorb - something has the give to maximize the flow of energy. ",
"edit: spelling & grammar appaulling this morning! "
] |
[
"efficiency through outsourcing is one thing, e.g. each of our\ncells contains mitochondria which are little cells with their\nown DNA, they make ATP which powers\nour cells. The reason it's more efficient that way is that each kind of cell has its neiche and is specialized. when a cell has to do many different thing it cannot be good at all of them; but colonies of specialized cells living in symbiosis can reap the common benefit of each other's particular abilities. \nanother benefit is diversity of functions. when cells evolve down a narrow path they enter new areas in function space which wouldn't happen if they had to generalize, because if you are being pulled in every direction you dont go anywhere. \nthe whole picture has been replicated in the medium of human culture, suggesting that specialization and symbiosis are evolutionary principles which would shape any evolutionary system "
] |
[
"How stable are the Lagrange points?"
] |
[
false
] |
We know that L1, L2, and L3 are inherently unstable, whereas L4 and L5 are stable. But how much does it take to actually affect the equilibrium of an object in an unstable Lagrange point? Let's say we have a ship parked at L1 between the Sun and the Earth. Now if this ship was to move a little closer to the Sun, its gravitational pull would obviously pick up, and the ship would inevitably fall towards the sun. But how much instability are we talking about? Astronomical scales are pretty huge in general, but how much displacement would it take to affect the ship's equilibrium? Is it in the order of the meter? Kilometer? Megameter?
|
[
"This image is great for this",
". The height of the striped surface indicates the energy due to the gravitational force + centrifugal force, as seen in the rotating system where we consider the earth and sun to be stationary. The force is the gradient of this surface, a steeper slope indicates a stronger force (the direction of the force is downhill). L1, L2, L3 are unstable because any object that starts near them will quickly fall in or out, because a small change in position produces a small change in slope, and the force due to that slope just keeps adding up. ",
" deviation from the exact center of the L point would exponentially grow until the object falls off the point. L4 and L5 are stable because small changes in position don't affect the slope very much, so the force has much less effect and can be countered by the coriolis effect. ",
"The real reason that L4 and L5 are stable is the coriolis effect, not shown in this diagram. Because the orientation of the diagram itself is changing over time (after all it's attached to a rotating system), the straight path you'd expect from a moving object looks curved. To model the system with Newtonian dynamics we invent a coriolis force that accounts for this curving of a path that would otherwise be straight. So even if the object veers slightly off of the L4/L5 point, the rotating reference frame will steer it around in a circle that stays close to the L4/L5 point. "
] |
[
"L1, L2, L3 are unstable because any object that starts near them will quickly fall in or out",
"That is a great diagram, but I don't think this is the right way to think about it. Objects in orbit don't \"fall down the hole\": because of the Coriolis effect which you mentioned, they move along the curved purple \"topo lines\", maintaining a constant height in the diagram.",
"L4 and L5 are stable because as you can see, the equipotential lines in that region are small ovals: an object displaced slightly from L4 or L5 will move in little ovals but won't go far from L4 or L5. An object displaced from L1, L2, or L3 will either make big circular loops around the planet, big circular loops around the moon, or follow a long \"horseshoe\" path, going from the leading side of the moon around the back of the planet to the trailing side of the moon and back again. (There are a number of bodies in the solar system that actually do this.)",
"https://en.wikipedia.org/wiki/Horseshoe_orbit#/media/File:Lagrange_Horseshoe_Orbit.jpg",
"So definitely, use that diagram to understand the stability of Lagrange points, but think of motion ",
" the purple lines, rather than downhill."
] |
[
"At an inherently unstable point, any displacement will affect the equilibrium. The only difference is how rapidly displacement increases, which depends on the mass of the orbiting object as well as the magnitude of the initial displacement. "
] |
[
"Is there or has there ever been an important role in our body for hiccups?"
] |
[
false
] | null |
[
"The first air-breathing fish and amphibians extracted oxygen using gills when in the water and primitive lungs when on land—and to do so, they had to be able to close the glottis, or entryway to the lungs, when underwater. Importantly, the entryway (or glottis) to the lungs could be closed. When underwater, the animals pushed water past their gills while simultaneously pushing the glottis down. We descendants of these animals were left with vestiges of their history, including the hiccup. In hiccupping, we use ancient muscles to quickly close the glottis while sucking in (albeit air, not water). Hiccups no longer serve a function, but they persist without causing us harm—aside from frustration and occasional embarrassment. One of the reasons it is so difficult to stop hiccupping is that the entire process is controlled by a part of our brain that evolved long before consciousness, and so try as you might, you cannot think hiccups away.",
"Excerpt from the Smithsonian Magazine ",
"EDIT: ",
"Journal article published in ",
" on the subject",
". "
] |
[
"Oh my god - this is the most bullshit thing I think I've read on Reddit (and I occasionally frequent ",
"r/brickporn",
"). This theory was proposed a while back by some sleep researchers - not a fuck was given!",
"The more accepted (read: medical) explanation is that hiccups are diaphragmatic spasms, and they serve a very important pre-natal role: hiccups allow unborn infants to exercise and build their breathing muscles before exiting the womb and without inhaling amniotic fluid.",
"PLEASE - if you read this, upvote so more people don't read the mess outlined above! Remnants of an amphibian breathing aparatus, ancient muscles - come on!"
] |
[
"Here's the journal article that I believe you are referring to",
". As far as I can tell it appears valid. As a note, this is a hypothesis, not a fact. ",
"EDIT: According to recapitulation theory the hiccup is evolutionarily antecedent to modern lung respiration. Additionally, they point out that hiccups and amphibian gulping are inhibited by elevated CO2 and may be stopped by GABAB receptor agonists, illustrating a possible shared physiology and evolutionary heritage. ",
" ",
"There could be some overlap with these two articulations."
] |
[
"Is it theoretically possible to create a human from DNA alone?"
] |
[
false
] |
[deleted]
|
[
"No, not really. Human DNA is just the carrier of the bulk of the information. There are numerous other ingredients needed to make a human being - epigenetic information inherent in the uterine environment and the sequence of steps undergone by a fertilized egg; additional DNA carried in mitochondria; additional symbiotes like our gut and skin bacteria; etc. DNA isn't so much a blueprint as a really, really messily written recipe that relies on a lot of obscure ingredients assumed to exist in the reader's kitchen. "
] |
[
"To add onto what was said, the other thing many people fail to understand is that \"environment\" can be on a very very small scale as well, not just the general surroundings of an organism that we tend to think of. For instance, maternal mRNAs and proteins are directly provided by the mother for the developing oocyte, so these proteins are not encoded by the DNA of the developing offspring.\n",
"http://en.wikipedia.org/wiki/Oocyte#Maternal_mRNAs_and_Proteins",
"This could still be considered an environmental effect and not a genetic one, because these mRNAs and proteins are not directly coded for by the offspring itself."
] |
[
"I'm sure they could. But there's a lot hidden in the \"sufficiently advanced\" part of that sentence. "
] |
[
"Why are atoms preferentially made up of electrons instead of another charged lepton?"
] |
[
false
] | null |
[
"Because the other charged leptons are unstable. ",
"Higher-generation leptons can decay into lower-generation leptons through the weak force. For example, the μ decays into electron + ν_μ + anti ν_e. You can tell it's a weak interaction because neutrinos show up. The muon neutrino is there to carry away the \"muoness\" of the original muon, which is a conserved quantity, and the electron antineutrino is there to balance the \"electronness\" of the newly created electron, which is ",
" a conserved quantity.",
"So forgetting about the neutrinos, you can have",
"τ -> μ or e",
"μ -> e",
"Also, the τ can decay, still through the weak force, into a number of pions from 1 to 4 (hadronic decay) + a tau neutrino to carry away the \"tauness\", and this is actually the most common way for it to decay.",
"Nevertheless the μ lepton is relatively long-lived and in precision experiments it has been possible to create muonic atoms where the μ substitutes for the electron. The lifetime is enough for some atomic transitions of these muonic atoms to be measured and the muonic hydrogen atom essentially looks like a rescaled hydrogen atom. Basically ",
" of what you already know about the hydrogen atom can be applied to muonic hydrogen by substituting the electron mass with the muon mass in the formula.",
"(Or better, with the reduced mass for the muon-proton system. The proton : muon mass ratio is around 10, so you cannot neglect the backreaction of the muon on the proton like you did for the electron)."
] |
[
"For anyone who doesn't know the numbers, I just wanted to add that \"relatively long-lived\" means that muons live an average of two microseconds. From a particle physics perspective that's pretty long."
] |
[
"The reason electrons and protons (and neutrons in nuclei) dominate the amount of matter has to do with the ",
"totalitarian principle",
": any process which can occur (is not forbidden by some conservation law) eventually will occur.",
"There's nothing preventing the higher-mass leptons from decaying into electrons and neutrinos. But electrons simply have nothing to decay into while conserving charge, so they are stable."
] |
[
"I asked once already, but no one answered. If my kid is vaccinated, I have nothing to worry about. Right?"
] |
[
false
] | null |
[
"Vaccines are not 100% effective, though some have really high protection rates of 90%+. Various vaccines have different rates of protection (you'd have to look up the rates for each one), and there are also biological factors that come into play such as weakened immune systems. Vaccines are to a large degree a teamwork effort. Everyone depends on everyone else to get them so that we all enjoy the best possible reduction in the spread of diseases. ",
"If everyone around the child is vaccinated then there isn't much else you can do. If that's the case then I wouldn't worry. Vaccines are generally pretty amazing if everyone has them. "
] |
[
"For the most part, yes.",
"Your kid is most likely one of the lucky 98% who properly develop immunity after vaccination, so he/she should be protected.",
"For some, the immunity doesn't build up properly, which places them at risk if they come in contact with infected people, this is why the \"herd immunity\" thing is still important and vaccination is not a purely personal choice.",
"As long as the vaccinations are current (some need to be refreshed regularly), you have done all you can."
] |
[
"I can't find the specifics, but some people have 'low blood titers' meaning that their body does not develop very many antibodies when they are vaccinated.\n",
"https://answers.yahoo.com/question/index?qid=20080909135601AAo0c3o",
"\n",
"http://www.motherjones.com/environment/2015/02/open-letter-parent-unvaccinated-child-measles-exposure"
] |
[
"How much water does our skin absorb during a 5 minute shower. I'm sure there are a few different variables, but my sister-in-law was trying to convince me that it could be up to 8 cups which seems ridiculous to me."
] |
[
false
] | null |
[
"Your skin does not absorb water, and is in fact very resistant to water movement in both directions. The wrinkling effect is an internal mechanism which increases your grip in wet environments, caused by the contraction of blood vessels and regulated by the sympathetic nervous system."
] |
[
"It is my understanding that human skin is waterproof and therefore NO water is absorbed during a shower. Otherwise, how can we swim without getting waterlogged and sinking until we drown? And wouldn't waterborne diseases just enter our bodies through our skin? I am pretty sure that skin is resistant to water. "
] |
[
"Totally blew my mind when I found out that wrinkling is a nervous system response. Some paralyzed people lose that ability!"
] |
[
"Why are the primary colors for paint different from the primary colors for computers?"
] |
[
false
] |
In art class in elementary school I learned that the primary colors were Red, Yellow, and Blue. Later, I learned that computer colors are made of Red, Green, and Blue. Furthermore, we used the RGB color wheel in Chemistry in high school, which is apparently the standard ( ). I'm guessing the difference has to do with the difference between paint and light, but can anyone elaborate further or provide a link?
|
[
"Because the difference between ",
" and ",
" light. Also, your eye sees in RGB, but CYMK (Cyan, yellow, magenta, black) is whats used for printing.",
"When mixing dyes, you can create any color using RYB. These is because dyes mix in a way that one color is indistinguishable from the other. Dyes are made with subtractive primary colors (CYM + K or RYB). Dyes are reflected light and thus your eye only sees one wavelength of light.",
"Stuff like screens use ",
" light. Here, your eye sees the 3 different wave lengths and there is additive mixing. When mixing light, you use percentages like dye, but they're expressed differently. 100% Red/Green/Blue gives you only that color. 100% Red and 50% Blue gives you purple."
] |
[
"Best way to explain this is...",
"Paint and objects in the world remove colors. This means that they absorb all colors except the one that they reflect. A plant isn't really green, for example, because it absorbs all colors except green which it reflects. Paints work the same way by \"sucking up\" all colors except those that they reflect. When you mix red paint and green paint, only a few colors are left and it appears as a muddy brown. Keep adding colors and you get close to black.",
"Flashlights and CRTs (monitors, or TVs) create light: that is, they don't absorb, they shine. They aren't removing light... they are adding light to the environment. The result is new color and when those colors add together, you produce new shades. RGB can produce almost all colors that people can see.",
"In the end, the two models aren't too different: RGB vs RYB. CMYK is quite a lot different, but it's simply a more accurate version of RYB."
] |
[
"Hi, not an expert, but if you look up ",
"additive color",
" and ",
"subtractive color",
" on Wikipedia, you'll get a good explanation. ",
"Short summary is that when you shine a red torch and a blue torch at a white wall, you are adding the frequencies to produce purple.",
"When you paint a white wall with red paint, you have a surface that reflects all frequencies (white) that is covered with a substance which filters out (subtracts) all frequencies except red. "
] |
[
"How does center of mass/gravity work and how can you manipulate it?"
] |
[
false
] |
[deleted]
|
[
"That's a vague question, what exactly do you mean?"
] |
[
"Like the definition of the center of gravity, how it works(properties), how you could manipulate the center of gravity (as in the location with forces and such). It is rather vague, but I kind of want a big answer, if that isn't too much of a hassle."
] |
[
"Like the definition of the center of gravity",
"The proper term of it is actually \"center of mass\".",
"It's the location in an object where its mass is evenly distributed in all directions. If you could put your finger ",
" an object to its center of mass, it would balance perfectly on your fingertip in any orientation. Also, for certain objects, it's possible for the center of mass to be ",
" of the object. For instance, in ",
"this video",
", the center of mass of the two forks is somewhere in a line extending directly up through the vertical toothpick.",
"how you could manipulate the center of gravity",
"The only way to manipulate the center of mass is to change the distribution of mass in the object. You could take some material away, add material, or deform the object."
] |
[
"Micro-fusion for spacecraft propulsion, is it possible? "
] |
[
false
] | null |
[
"Great question! Unfortunately I did not work on this project directly, but close friends of mine did conceptual work on something very similar.",
"The basic idea was to use muon-catalyzed fusion. I'm not a particle physicist so I don't know the details, but essentially muons can serve to make fusion much \"simpler\" by facilitating it at much lower temperatures. As far as I understand, this has been shown to work.",
"The problem is that muons are very short lived and can take an immense amount of energy to generate. Therefore you need an extremely large device to create the muons (particle accelerator); and then to make use of them before they decay, you need fuel in an extreme region of the plasma phase that has never been produced before (to my knowledge).",
"Beyond the power source itself, the question arises: \"What do we do to convert all that power to some form of propulsion?\". You could use the direct products of the fusion for the highest performance, but this would require massive amounts of deuterium or tritium. Even if you had those, you would have a very hard time ducting the products into some form of propulsion (getting them all going in the same direction) as they would melt any material.\nThe other option is to just use the heat of the reaction to heat a different gas (likely hydrogen) and use that as the propellant. In this case you wouldn't actually be performing incredibly better than an ",
"NTR",
" which has already been developed and tested.",
"The fusion concept was developed by a group at my work for use in space propulsion. Due to the size requirements of the accelerator and the phase requirements of the fuel it was ruled as an extremely advanced concept. It would require dozens of scientific breakthroughs over 100+ years for it to be feasible.",
"Sorry I can't give more detail, but like I said, it wasn't my project."
] |
[
"I wonder if recently developed tabletop laser driven accelerators could help create muons for use in this case? (see ",
"http://www.nanowerk.com/news/newsid=22491.php",
")"
] |
[
"Hmmmm....I don't know. I know my colleagues did extensive research on technology for muon production, but I don't know if they came across this or if this serves their needs. If I remember, I will ask my friend the next time I see him. "
] |
[
"How does our body know when we need to drink water?"
] |
[
false
] | null |
[
"A previous comment is correct that thirst regulated by osmolarity sensors associated with the hypothalamus, but I want to provide some more detail about that mechanism because it is really cool. ",
"You actually have an osmolarity sensing organ in your brain called the organum vasculosum of the lamina terminalis (OVLT). This is a structure that is adjacent to the fluid-filled ventricles of the brain and has a minimal blood-brain barrier - so it can interact with blood vessels and sense the osmolarity of the blood. This sensor is also adjacent to the hypothalamus - so it can interact with brain regions that control thirst.",
"It is well understood that cells will change their volume when challenged with an extracellular solution that contains too much or too little salt. This is also true of cells in the OVLT as they experience extracellular salt changes in the blood and cerebrospinal fluid. The OVLTs express mechanically activated ion channels that respond to these changes in cell volume, which essentially stretches or shrivels the cell membrane. This generates an electrical signal that can be transmitted to neurons in the hypothalamus.",
"",
"Source:",
"https://jasn.asnjournals.org/content/18/12/3056"
] |
[
"Resuming it, our hypothalamus has a group of neurons that work as an 'osmolarity sensor. Mainly focusing on sodium levels, the more concentrated the blood, the thirstier you are, since it assumes you are lacking water to make your blood go up in concentration.\nIf I recall correctly, there's also ADH (antidiuretix hormone) involved, not sure if directly in the thirst feeling. Those neurons are also known as thirst center, you can search a bit about it, I'm sure you'll find some neat stuff!"
] |
[
"Actually no, it's not. This is a structure inside the brain, and the brain itself doesn't actually have any pain sensors. However, the membrane which attaches your brain to the inside of the skull (the meninges) does. When you're dehydrated, your brain shrinks in volume and puts tension on this membrane, which gives you that dehydration headache. It's also the reason moving your head quickly when you're dehydrated aggravates the headache."
] |
[
"Evolution of Galaxies that have no Super Massive Black Holes in their centers?"
] |
[
false
] |
It's still fascinating to me that such a HUGE galaxy like the , which is 10 times wider than our galaxy, does not have a Super Massive Black Hole (SMBH) in its center. Will it form a new SMBH under gravity or will it eventually "dissolve"?
|
[
"Ooch, this is a tough topic. We don't actually know exactly how SMBHs form. While we know that galaxies tend to have mass concentrations in the centre, so it seems likely that having all that mass in a small space will give you an SMBH, the exact process is unknown, and why some galaxies have SMBHs and others don't is still a matter of active research.",
"But to answer your question: it looks like galaxies form their SMBHs fairly early on, so this galaxy will probably just stay as it is.",
"Galaxies also don't ever split up. There's just not enough energy for anything more than a bit of gas and the odd rogue star to escape. Instead, galaxies tend to merge with each other, building up into progressively bigger galaxies.",
"If this galaxy merges with another galaxy that has a SMBH, then the SMBH will \"sink\" to the centre of the new galaxy, and you'll have a single galaxy with an SMBH in the centre. That's the most likely way to \"gain\" an SMBH at this point."
] |
[
"As a counter-example - ",
"M33",
" is a nice spiral galaxy that doesn't have a black hole either.",
"Elliptical galaxies may actually be ",
" likely",
" to have bigger SMBHs than disc galaxies."
] |
[
"From what I read from NASA this galaxy might already be a result of 2 merged smaller galaxies and their SMBHs got slingshot away hence the absence of central SMBH. The diffuse core makes me think that the bulge's stars are expanding due to lack of gravity. Yes I also think that SMBHs exist in the early stage which makes the A2261-BCG really mysterious. :D"
] |
[
"Do planets fall out of orbit just as our satellite fall out of orbit?"
] |
[
false
] |
I know that satellites we put in space eventually fall out of orbit over time. As well as debris. Does this go the same for planets? Obviously the star in a system may probably collapse before a planet ever were able to be swallowed into it but I just saw an article on Facebook about the satellites falling out of orbit and burning up in the atmosphere I wondered if planets did the same.
|
[
"Satellites in LEO (low earth orbit) are still in a very thin atmosphere and thus experience drag and eventually slow down enough to start descending, hitting thicker atmosphere and then burning up. The planets generally aren’t considered to be in the suns atmosphere, although the planets do experience ‘solar winds’"
] |
[
"Thanks! That’s what I thought but I still read somewhere that even though space is a vacuum there’s still particles in the deepest parts of space. At least within our solar system. I knew satellites decayed cuz of the thin atmosphere. But I figured maybe the same was with the planets and sun"
] |
[
"It is so thin that it doesn't matter over the lifetime of our solar system. Mercury, Venus and probably Earth will eventually fall into the Sun as it expands and the drag gets significantly larger.",
"The orbits also lead to the emission of gravitational waves. While this is an even smaller effect, it is one that will keep active even after the Sun becomes a white dwarf. If there is nothing else disturbing the orbit of the remaining planets before (the more likely case) all the planets will fall into the Sun in the ",
" distant future."
] |
[
"Why are carbohydrates considered bad by some?"
] |
[
false
] |
The underlying philosophy of some diets, like the keto- paleo- and to a lesser extent the 'slow carb diet', is all based on the assumption that carbs are bad. What, scientifically speaking, makes carbs bad? Is there a distinction between good carbs and bad carbs?
|
[
"The references in this section on Wikipedia: ",
"http://en.wikipedia.org/wiki/Insulin_resistance#Management",
"provide some good peer reviewed sources on both the effects of and treatment of insulin resistance."
] |
[
"The references in this section on Wikipedia: ",
"http://en.wikipedia.org/wiki/Insulin_resistance#Management",
"provide some good peer reviewed sources on both the effects of and treatment of insulin resistance."
] |
[
"Sugars from fruits are also carbohydrates. But compared to simpler sugars like glucose, fructose (the sugar in most fruit) takes longer to break down in the liver and therefore doesn't go all into your blood at once. This is compounded by the fact that fruit also contains a lot of fiber, which means even slower digestion."
] |
[
"When trying to build muscle, people often recommend eating lots of protein. Proteins are made of amino acids, so is it possible to get the same effect by just ingesting amino acid suppliments? Are there any advantages/disadvantages?"
] |
[
false
] | null |
[
"1) Practicality. The cost of getting aminos through supplements vs whole proteins would be astronomically higher.",
"2) From a scientific standpoint the breakdown of proteins in whole food to aminos is facilitated by metabolic trickery that allows amino acids to enter the cell with relative ease. On their own, quite a few aminos would not be able to traverse the membrane. ",
"As an analogy, someone once asked why you couldn't simply ingest ATP for your energy needs. ATP is a very highly charged molecule. It dislikes nonpolar compounds. This precludes it from effectively getting across the oily, nonpolar membrane of the cell efficiently."
] |
[
"This is kind of silly. Do you realize how many different amino acids are in protein? It would be WAY more expensive to get them individually than to get either cheap meat or protein powder.",
"You may be thinking of BCAAs, which are pretty common and not too expensive. ",
"Even still, my ON 100% Whey was $50 for 73 servings of 5.5g of BCAAs (plus all the other amino acids in protein). ON BCAA powder is $30 for 67 servings of 5g of BCAAs. Unless you have a specific reason for going with the BCAAs, the powder is a better deal."
] |
[
"More simply put, how are you going to initiate protein synthesis without a pool of excess aminos in the first place? Leucine's mechanism of action parallels insulin, but again, all totally worthless if you don't have the substrate in the first place."
] |
[
"Is there such a thing as a mathematical discontinuity in nature?"
] |
[
false
] |
I know that due to the existence of vacuums or near vacuums, material discontinuities can exist, but can a mathematical discontinuity exist as an observable, physical manifestation? One potential example I can imagine would be the singularity of a black hole, which is a 4-dimensional asymptote as gravitational pull approaches infinity, but this is purely speculative since current methods have no way of proving the theory.
|
[
"One example where discontinuities pop up in nature is phase transitions. Depending on the specific phase transition you're studying, you might find that things like the entropy, density, heat capacity, etc. are discontinuous across the transition."
] |
[
"Except, if you remember your stat mech, real phase transitions don't exist in nature. Only infinite systems have true transitions."
] |
[
"A shock wave from a supersonic aircraft or projectile is close... typically it is modeled as a discontinuity, but in reality there is a finite transition (a similar sort of issue relating to the phase transitions discussed above)."
] |
[
"Does an organism with a \"fast metabolism\" have any benefits over an organism with a \"slow metabolism\"? Or vice versa."
] |
[
false
] |
[deleted]
|
[
"For your basic question, it would depend on the situation. If it's winter, or somewhere that being eaten is not something very imminent, then having a slow metabolism would be helpful. But if you are, let's say, in the savannas of Africa, with mild seasons and sufficient grass, water, etc, then having a high metabolism would give you speed, focus, and awareness.",
"So, Johnny would have more energy and focus, but would end up being hungrier."
] |
[
"It depends what the body is doing with that energy. On a cellular level, that increased metabolic rate might mean that bacteria 1 can produce new cells faster than bacteria 2. Or it just might mean bacteria 1 is less efficient, perhaps because it is using nitrate as an electron acceptor instead of oxygen.",
"Without a really REALLY complicated metabolic breakdown, its pretty hard to say.",
"On a more basic level, is food scarce and Tom just gets hungrier and hungrier, or is food plentiful and Tom wants to lose weight?"
] |
[
"Basal Metabolic Rate is not just some number you are gifted with, it changes based on your muscle mass and how much you use your muscles (exercise / fitness level). Somebody with 10% higher BMR than another is likely stronger and in better shape. The muscles that he has that burn the extra energy will certainly give him an advantage when he is hunting, fighting, or possibly trying to attract a mate. But if there is a famine the person with lower BMR will have a survival advantage because they require less food initially.",
"I think your initial premise is not fair. If you have two people who are both 6'0, 170 pounds, 8% body fat and one of them has 10% higher BMR, these people will not be \"equal\" as you imply. There will almost certainly be some physical differences in strength and/or endurance. Those advantages would be the noticeable benefit, but he will pay a long-term price due to a higher calorie requirement."
] |
[
"Suppose for a second you had a 2 light year long rod, if you pushed one end, would the other end move at the same time?"
] |
[
false
] | null |
[
"For your rod to be infinitely stiff then by that you are already surmising that all motion exerted on one end of the rod is immediately communicated to the other end through the bonds between their atoms; ie faster than light. ",
"In effect what you're saying is \"If I have something that travels faster than the speed of light, will it move faster than the speed of light?\" The answer is, of course, yes. "
] |
[
"In a universe where special relativity is correct, you cannot have any material that is infinitely stiff."
] |
[
"If i remember correctly, if you pushed it from one end, the force of the push you make would propagate through the material (any material) at the speed of sound.. therefore the other end wouldn't move until the movement got there"
] |
[
"Carbon dating (and presumably other isotope techniques) rely upon a constant background ratio in the atmosphere. Was this background ratio always the same?"
] |
[
false
] |
I don't know much about isotope aging techniques, but this in response to comment thread. As I understand it, to date items via isotope dating, we compare the current isotope ratio to what the background/atmospheric level is. My issue is, how to do know that the background level was the same 20,000 years ago, 100,000 years ago, or 4.4 billion years ago in the case of the linked article which used Uranium, I believe.
|
[
"For Carbon dating, the background ratio of C-14 (the radiogenic one which decays) has not stayed the same. This is because of the way C-14 is produced, namely an interaction between a nitrogen atom and a cosmic ray. The flux of cosmic rays reaching the earth's surface fluctuates over time, and thus the production rate of C-14 varies over time, so finally the ratio of C-14 to C-12 incorporated into something alive varies over time. The ",
"wikipedia article",
" on carbon dating actually lays this out reasonably well. For this reason, radiocarbon dates need to be ",
"calibrated",
" to this variation in the ratio. To do this, radiocarbon dates are measured for things of known ages. This has been primarily done using tree rings using a technique called dendrochronology. As you likely know, trees produce rings annually. So one can start with a very large, old living tree and examine it's rings, date the interior one with radiocarbon, count the rings to get an independent estimate of the age and then use that to calibrate the radiocarbon date. The other awesome things about trees, is that the characteristics of the rings (width, etc) vary by the growing conditions that year producing a unique pattern through time depending on changing conditions. So, you can find an old dead tree, which has some period of overlap with your live tree in the same general area (experienced the same growing conditions) that you can identify from the patterns in the rings to extend you record back. In a very simplistic sense, you do this a lot with lots of trees and you're able to reconstruct back pretty far. Old timbers in ancient buildings have actually played a big role in extending these records back, if memory serves. Other things are used as calibration as well (see the link above). This calibration gets us back to 26,000 years. The other important thing to point out, is that while this calibration helps to make dates very accurate for things less than 26,000 years old, it also shows that the variability in the C-14 to C-12 ratio is not that huge, so using it for things older than 26,000 is still acceptable, though there is more error associated with those measurements. Also, radiocarbon is not much good past ~45,000 years due to the relatively short half-life or C-14.",
"For Uranium-Lead (U-Pb) dating, background levels don't matter (they've been always been changing because no isotope of Uranium is stable). In a simple scenario, there we measure the amounts of the parent (U-238 or u-235) to daughter (Pb-206 or Pb-207) and the main concern is whether the thing in which we are measuring our ratios has behaved as a closed system (no extra radiogenically produced lead added or lost)."
] |
[
"Awesome! Thanks!"
] |
[
"The best geochronological method is U-Pb in zircon crystals. It's efficacity is unaffected by atmospheric composition, as neither Pb nor U are even trace components of the atmosphere and the magmatic systems which produce dateable zircon crystals are sequestered from the atmosphere."
] |
[
"Is West Nile Virus still an issue?"
] |
[
false
] | null |
[
"West Nile Virus first appeared in North America in 1999. In 2015 it is endemic across most of North America. While it doesn't make the news very often, the CDC still monitors it. ",
"HERE",
" is the 2015 Surveillance data from CDC. ",
"HERE",
" is a map of lab verified human disease in 2014. As an example ",
"HERE",
" is a map of my state (LA) for 2014. Most human disease occurred Jul-Sep, mosquito season!."
] |
[
"In some parts of the world, mosquitoes could give you or your child malaria, dengue virus and other quite serious diseases. In North America, the diseases (like West Nile Virus) are less likely to cause serious disease in an otherwise healthy person. However, the risk is not zero. People can reduce the risk by using staying indoors when mosquitoes are especially active and by using a DEET-based bug repellent."
] |
[
"In some parts of the world, mosquitoes could give you or your child malaria, dengue virus and other quite serious diseases. In North America, the diseases (like West Nile Virus) are less likely to cause serious disease in an otherwise healthy person. However, the risk is not zero. People can reduce the risk by using staying indoors when mosquitoes are especially active and by using a DEET-based bug repellent."
] |
[
"Plasma: how can the same phase of matter seem so eclectic in its behaviour?"
] |
[
false
] |
Are different types of plasma as uniquely behaved as they seem, or is their apparent broad categorization justified? I don't know if this question is naïve, and I am a layman. Lightning, stellar surfaces, fire, aurora, etc. are all categorized as types of plasma, or at least partially so, but behave and appear quite differently. Does this mean that the phase is just a general term for ionized energetic gases, or that they're more similar than they seem to the untrained eye, with concise explanations for the different behaviours? For instance, why doesn't lightning ever follow the convection rules of how fire spreads, or why doesn't fire get conducted into bolts? Shouldn't all plasma transfer energy similarly? The question stems from other phases: liquids and other phases have recognizable and consistent patterns of behaviours. Plasma seems to be more indie. Sorry for the long post. It feels like I'm just missing one or two simple pieces to make sense of it. Searching the Web just led to overcomplicated papers or TV sales.
|
[
"The definition of plasma is straight-forward: it is a gas of charged particles, typically free electrons and positively charged ions. In principle, you can get exotic plasmas (I've heard about electron-positron plasma, and you can also get 'cold' plasma), but I will not discuss those further here.",
"Plasma can exist in a wide variety of physical conditions, which means you can get a lot of different behavior and phenomena, as you point out. Plasma can be low-density (e.g., interstellar space) or high-density (stars). Plasma is very sensitive to electric and magnetic fields: it conducts electricity very well (as we see in lightning), and it interacts strongly with magnetic fields (it can be confined, like in the stellarator that made news recently, or it can drag magnetic fields with it, like in the solar wind). The physical processes that occur can change a lot depending on whether there is a strong electric or magnetic field, how hot the plasma is, and how dense.",
"In plasma physics (which I've taken a few courses in, but don't consider myself a true expert), there are several key parameters that are used to determine what processes are important. The one I know most about is called 'plasma beta', and is defined as the ratio of the thermal energy/pressure to the magnetic energy/pressure. If beta is large, there is more themal/kinetic energy than magnetic energy, so the motion of the plasma will control the magnetic field. If beta is small, then the magnetic field is strong and can confine and control the motion of the plasma. There are similar parameters that compare the plasma to the electric field, or compare the large-scale motion to the thermal energy, etc. With these parameters, plasma physicists can immediately estimate what processes will be important in a given situation. For example, if the electric field is weak compared to kinetic energy, we can immediately know that the electric field will not dominate the behavior of the plasma."
] |
[
"The term 'plasma' refers to an ionized gas where the kinetic energy of the particles far exceeds their Coulomb potential energy. This seemingly innocuous property leads to a lot of complexity in behavior, as ",
" processes, involving large numbers of particles acting in concert and interacting with the self-consistent electric and magnetic fields, dominate the dynamics. ",
"Complexity also derives from plasmas being able to support a large number of different normal modes (waves). These waves can interact with one another as well as with groups of particles in the plasma (wave-particle interactions), whereby some plasma particles can \"surf\" on the waves. ",
"Because 'plasma' refers to a vast array of different media, the behavior can be widely different depending on the setting. It can depend on, e.g., the ratio of kinetic energy of the particles to the energy of the magnetic field (a quantity called \"beta\"), the ratio of plasma collision rates to the frequencies of the different modes, the ratio of the thermal velocity of different groups of particles to the phase velocities of waves, the ratio of the plasma particle thermal speeds to the speed of light, etc. ",
"The upshot is that calling something a plasma doesn't really say much with respect to figuring out how the medium will behave. You need to specify quite a bit more. "
] |
[
"The definition of plasma is straight-forward",
"Your definition is incomplete, unfortunately. It's also required that the plasma coupling parameter (the ratio of potential to kinetic energy) is small. Otherwise, you're dealing with what's called strongly coupled plasma, which, despite its name, isn't really plasma. It's more a Coulombic liquid. "
] |
[
"Why does silly putty behave differently when placed under pressure?"
] |
[
false
] |
For example, it shatters when or when . What happens on the molecular level that causes an otherwise soft, highly malleable material to become hard and shatter? As an aside question, from what I can tell, a combination of water and corn starch produces a similar effect, hardening when under sudden pressure, . Is this the same mechanism at play here?
|
[
"Silly putty is a fun type of fluid because it's viscosity isn't constant. ",
"Viscosity",
" is a property of a fluid that determines how it responds to a stress, basically, how much it will flow if you push on it a bit. ",
"Newtonian fluids",
" have a viscosity that is constant relative to the applied stress on it. Water is an example of a Newtonian fluid. Silly putty is an example of a Non-newtonian fluid, in particular it is a shear-thickening fluid: when you apply a stress to silly putty its viscosity goes up! ",
"Both cornstarch&water and silly putty are shear-thickening fluids. In the case of cornstarch&water, the shear-thickening occurs when clusters of the cornstarch agglomerate due to the shear. When suspended in water, each cornstarch particle is basically like a tiny sphere that floats around. ",
"Itai Cohen's",
" group at Cornell does some research on this. For silly putty, the microscopic details are similar, but not exactly the same. In this case, the shear-thickening is due to jamming of the interpenetrating PDMS polymers. If you stress the silly putty slowly, the tangled mess of spaghetti (PDMS) has time to untangle and flow. They're both types of jamming, but slightly different."
] |
[
"Good question!",
"There are three different parts to your question that I would like to address separately. First is how pressure matters here. Pressing on a fluid, or on a wad of silly putty is one way to stress it. The force you are applying to the volume by pressing is perpendicular (also called 'normal') to the area experiencing the pressure. But you can also ",
" a fluid, if you're not pressing perfectly normal to its surface. This shear stress, while not changing the pressure of the fluid underneath it, is perfectly capable of inducing a change in viscosity. When you shear, the layer closest to the applied force moves at the same speed of the shear you're applying, the layer just under it wants to go a bit slower, and the layer under that wants to go a bit slower. So you've got these layers moving at different speeds, and if you shear fast enough in a shear-thickening fluid, the polymer/beads/dice/whatever in the fast-moving areas jam against the particles in the slower moving areas and now all of a sudden you have structure in your fluid that is resisting the shear more than before.",
"To summarize this first part: it's not just squishing that can cause a change in viscosity, shearing can too.",
"This brings us to the second part; what forces are at play that can cause this jamming, are there hydrogen bonds? This really depends upon what's being jammed. If you have a polymer like PDMS, the hydrogens are on methyl groups bonded to silicon, which isn't super electronegative, so hydrogen-bonding isn't going to be a dominant force between chains. For a tangled mess of polymer chains, it's just their tangling that causes the jamming. For the most part, the chains repel each other or don't interact much at all, besides not wanting to overlap (which, incidentally is caused by electromagnetic repulsion). For cornstarch and water, the particles suspended in the fluid are really big spheres (hundreds of nanometers to microns, compared to 10's of angstroms for the polymer chains), that may have some small amount of charge keeping them dispersed in solution. In this case, the particles don't attract each other at all, it's just that they can't get past each other when sheared too fast that causes the jamming. ",
"To summarize this second part: even particles that don't attract each other can jam. The forces at play in jammed systems ",
" involve attractions like hydrogen bonding, van der Waals forces, depletion interactions (my favorite!), charge-charge attractions/repulsions, or dipole-dipole interactions, but they don't need to.",
"Finally, the key to this is the geometries of the constituent particles when they're stressed. These geometries may not optimize minimum potential energy in every case (in fact, they most likely do not), but the fact that something about them prevents them from rearranging when stressed makes them resist stresses more. In shear-thinning fluids, the opposite is the case; you can see alignment of particles in different shear layers that then slip past each other more easily!",
"phew, that was a mouthful."
] |
[
"You're exactly correct. Both are Non-Newtonian fluids, or a fluid without a constant coeffeciant of viscosity. As pressure is applied, the viscosity changes.",
"\nCheck it out!\n",
"http://youtu.be/3zoTKXXNQIU",
" "
] |
[
"Why is there so many variations of f1 cars/planes/rockets? Wouldn't a 'perfectly' aerodynamic shape exist?"
] |
[
false
] |
In the sense that out of all the permutations you could design something, surely there is just one particular way which would have the perfect shapes to create the right lift/drag/aerodynamics where it is needed?
|
[
"There's an old credence used by engineers to describe these questions. Think of finding the \"perfect\" design for anything as finding the perfect spouse. Science would dictate, with a given amount of variables, that one could find the theoretical perfect spouse. A man/woman that perfectly satisfies every one of our hopes, dreams, and desires.",
"The fact of the matter is, nobody has the time, money, or knowledge (or a combination thereof) to pursue the matter. So what we do is use the information at hand, along with some cost-effective research, to determine the best design that we can reasonably accomplish with the resources available to us.",
"Science would dictate that there is a perfect solution to everything. Unfortunately, the perfect solution is never attainable, and that's why you need engineers."
] |
[
"To build on this metaphor, for aircraft, its even more complicated. Now instead of trying to find your perfect spouse, you're trying to find one person who will be the perfect spouse for say... five very different people.",
"Since we demand very different things from our different type of aircraft (their general commonality is just that they can take-off, fly, and land), different solutions exist for each. You may have noticed how most modern jet fighters look kinda similar, and most passenger jets look pretty similar. That's an example of solutions to different problems. Jet-fighters must be fast and nimble (and capable of breaking the sound barrier!), while passenger jets must have range, capacity, and be economical (and hopefully not break the sound barrier!). "
] |
[
"Oh boy! My specialty is aerodynamic design optimization! Incoming rant.",
"surely there is just one particular way which would have the perfect shapes to create the right lift/drag/aerodynamics where it is needed?",
"Problem number 1 in optimization: define what \"optimum\" actually means. What do you mean by \"perfect\", say for a wing? Is it the maximum ratio of lift-to-drag? Is it the maximum lift? Is it the smallest weight? Is it the cheapest to build? Easiest to manufacture? Most efficient at high speeds? At low speeds? Most maneuverable? Most stable? I'll try and cover two things to consider: (1) all aerodynamic design is inherently built upon trade-offs between different characteristics for different conditions, and (2) even if you determined exactly which characteristics you want an aerodynamic shape to have, actually finding a shape which matches those characteristics exactly is a problem ranging from extremely difficult to completely impossible.",
"In designing something like an aircraft wing, everything is a tradeoff. You can minimize drag by making it very thin, but the wing needs to support the weight of the entire fuselage, so you need to be able to fit large structural elements in it. Aerodynamicists would rather get rid of the whole fuselage because it just creates drag, and weight engineers would love to get rid of the stupid landing gear, but then it probably wouldn't be too good at transporting things. ",
" (MDO) is incredibly complex, and airplanes are a great example of this. You want to go faster so you put on a bigger engine, bigger engine means it's heavier, heavier means you need more structure and more lift and more fuel, more structure means even heavier still. You also need to be able to physically manufacture aircraft, and you'd like to do so in an assembly-line fashion, so you really want your aircraft to be able to perform lots of different functions. I could design one passenger aircraft that's amazing at transporting 200 people 200 miles, and I could design a different aircraft that's amazing at transporting 200 people 2000 miles, but it'd probably be better if I just designed one aircraft that's pretty good at both.",
", since that's sufficiently complex without going into MDO stuff. Let's focus on airplane wings. A very long narrow wing (\"high aspect ratio\") is much more aerodynamically efficient (less drag for the same amount of lift) than a short, stubby wing (\"low aspect ratio\"). But when you have a very long wing, turning the aircraft is much harder due to angular momentum conservation; conversely, a short stubby wing is far easier to turn, but less efficient. Compare the wings of the ",
"U2 plane",
", meant to fly very long distances efficiently but not be very maneuverable, compared to any ",
"fighter aircraft like an F22",
" which is designed to be highly maneuverable. The leading edge of the U2 wing is very straight, whereas the leading edge of the F22 is swept back at a very high angle. This is because the U2 was optimized to fly at subsonic speeds, and the F22 at supersonic speeds. ",
"A result of this is that the F22 performs poorly in subsonic flight. It's wing and control surfaces are very poorly designed for subsonic flight, and it becomes very unstable, has bad lift and drag characteristics, etc. Something like a U2 would have terrible drag problems if you attempted to strap on huge engines and fly it supersonic. One could make an F22 that's better at flying supersonic, but make it even worse in subsonic. But you have to be able to fly subsonic to take off and land, so there's a compromise here.",
" In doing optimization problems, you have a desired set of characteristics (like max lift-to-drag ratio) and a set of contraints (like the wing must be at least X\" thick to accommodate structure). It's entirely possible for a designer to specify desired traits that are physically impossible to achieve.",
" One way to check is to physically build a model and test it in a wind tunnel. Fabricating and testing takes a long time, and you could easily have to test thousands or millions of shapes to get at one that satisfies what you want. Another way to check (what I do) is computational fluid dynamics; Determining just the lift and drag characteristics of an aircraft body accurately enough to assess the design can take thousands of CPU hours. And again, you'd have to test potentially thousands of them.",
" The equations governing aerodynamics are the ",
"Navier-Stokes equations",
", whose general \"solutions\" currently are limited to computationally expensive numerical approximations. The question of designing an aerodynamic body with desired characteristics is far more expensive than simply solving Navier-Stokes, because you're posing a question on an equation that is an initial boundary-value problem (IBVP) where you don't a priori know the boundary conditions, but have to solve for them. You're trying to invert a non-linear operator. There are really neat methods for approximating this efficiently, if you're up on your functional analysis."
] |
[
"Do sunsets look like sunrises?"
] |
[
false
] |
Could one tell if a picture displays sunset or sunrise without knowing when and where it was taken? Also for a video played backwards or forwards?
|
[
"To some extent, ",
" so - sunsets tend to be more colourful, owing to slight changes in atmospheric condition in the evening compared to the morning. The sun itself, of course, is emitting exactly the same light, and the amount of air that sunlight needs to pass through likewise remains the same. However, increased activity on the ground during the day throws more particulate matter (dust, pollution, haze etc.) into the lower atmosphere, as can the heat of day result in an increase in low atmospheric water vapour levels.",
"Molecules and small particles in the atmosphere change the direction of light rays as they hit, ",
"causing them to scatter",
", and this scattering affects the colour of light that we see coming from the sky. Furthermore, warmer air has a ",
"slightly different refraction index",
" than cooler air, which can likewise alter the direction of light, and therefore colour.",
"It seems to be the case then that higher levels of vapour and particulate matter in the warmer atmosphere during sunset mean light is scattered slightly differently, and colours towards the red end of the spectrum will occupy more of the sky (during the night, particles settle and water vapour condenses - hence morning dew and a less jazzy sunrise) - all depending, of course, on what's happening on the ground during the day.",
"Otherwise, I'd imagine all else being equal, sunrise and sunset are nigh on indistinguishable."
] |
[
"So, you're saying as a side benefit of pollution we'll get prettier sunsets until we start heading down the other side of the curve and blocking out the sun with smog."
] |
[
"Even those probably won't compete with the amount of particulate matter thrown into the atmosphere by e.g. ",
"volcanoes"
] |
[
"If people can eat frozen fecal pills to transplant healthy microorganisms to the intestine. Could kissing someone with a healthy mouth flora replenish your own?"
] |
[
false
] |
I have heard of doctors giving fecal transplants. Im wondering if the same idea could be applied with saliva and for the mouth. So can kissing someone healthy benefit your own health?
|
[
"In short, we don't know enough yet to know. But as someone who actually does this type of research, I've asked very similar questions. What you're talking about is essentially a probiotic, but for other parts of the body, instead of the gut which we generally associate with probiotics. We know the mouth is coated in bacteria (actually, so is every surface of your body that is in contact with the outside world, including from your mouth to your anus, and also down into your lungs). We are also now associating shifts in bacterial communities (dysbiosis) we disease in locations other than just the gut. Hypothetically, we could use a healthy source of inoculation (say saliva) to help reseed a disrupted community (like is done with fecal transplants for C. diff patients).",
"The catch though is that we don't really know yet what a healthy mouth (which actually has a lot of different communities) really looks like microbially speaking. We don't know how resilient those communities are. Nor do we know what aspects of disrupted communities cause problems, or if the problem happens first which then disrupts the community."
] |
[
"Oral flora is less likely to be involved in illness, so replacing it is a lot less important.",
"As someone working in this field, I strongly disagree with your last sentence. We know that changes in oral and respiratory bacterial communities (The word flora should die a fiery death! We aren't talking about plants!) are associated with a number of diseases. I'm more familiar with the respiratory ones, as that is closest to my area of research. We see changes in these communities associated with cystic fibrosis, asthma, smokers, sinusitius, and recurrent tonsilitis (sp?). But much like the gut, we don't know which comes first, the change in community followed by problems, or problems that then cause the change in the community."
] |
[
"Oral flora is less likely to be involved in illness, so replacing it is a lot less important.",
"As someone working in this field, I strongly disagree with your last sentence. We know that changes in oral and respiratory bacterial communities (The word flora should die a fiery death! We aren't talking about plants!) are associated with a number of diseases. I'm more familiar with the respiratory ones, as that is closest to my area of research. We see changes in these communities associated with cystic fibrosis, asthma, smokers, sinusitius, and recurrent tonsilitis (sp?). But much like the gut, we don't know which comes first, the change in community followed by problems, or problems that then cause the change in the community."
] |
[
"Would putting a polymer composite into an ultrasonic cleaner damage the materials the piece is made of?"
] |
[
false
] |
For example, if part of the piece was a rubber below its glass-transition temperature, and the other piece was a hard piece of plastic. You know, like the rubber ring around a coffee mug cap that helps seal the liquid inside. Yes, I'm going to gently clean my coffee mug cap inside an ultrasonic cleaner with soapy water for fun. But this really does apply to science in general, I've always been curious how gentle these are on different types of materials. I'm afraid to put my finger in one with the machine turned on.
|
[
"I know that anecdotes are frowned upon in this subreddit, but there isn't much literature on cleaning coffee mugs with lab equipment. So without further ado, I present a list of things that I have successfully cleaned in an ultrasonic cleaner:",
"Hard rubber stoppers",
"Soft rubber septums",
"Borosilicate glassware",
"Polyethylene glassware",
"Natural cork",
"Quartz tubes",
"A human hand",
"Extrapolating from these materials, I think your coffee mug will be okay. But there's only one way to know for sure..."
] |
[
"I think anecdotal evidence for a question like this is quite alright. My question both has both a silly side and a serious side.",
"Polyethylene glassware",
"Poly (polymer) and glass are contradicting to me, initially! Is the polymer considered glassware because the polymer is amorphous instead of a crystalline or semi-crystalline polymer? I've only had a basic material science course that all engineers take.",
"But there's only one way to know for sure...",
"Science! ",
"I'm no stranger to my own experiments",
" for the sake of AskScience's knowledge. My guess is that if there would be damage, the damage would accumulate over time and not be apparent right away."
] |
[
"I clean my polycarbonate lensed, metal framed glasses in my ultrasonic clean with no ill effects to them."
] |
[
"Will all the Lithium-ion batteries we keep in our attics ignite eventually?"
] |
[
false
] |
Won't each one of them ignite as soon as their protective layer fails to keep the oxygen out? Or do they somehow "disarm" themselves over the years?
|
[
"Why in the world would you store lithium batteries in a place that has such extreme temperature swings? The short answer is that they won't do a thing if you store them in the discharged state. If they're being stored fully charged, there is the possibility of rupture and fire, especially when they get very hot. "
] |
[
"They can still catch fire in the fully discharged state. If the seal gets compromised and air gets in, it can cause the lithium to react, heat up, and then catch fire.",
"In addition there are many different ",
"lithium chemistries",
". The ",
"lithium thionyl chloride primary cell",
" is more dangerous in the mostly discharged state, Because the reaction leaves sulfur behind, which can react violently with the remaining lithium, if it gets too hot or is mechanically damaged.",
"So the answer depends a lot on many various factors."
] |
[
"That's true, but OP asked about lithium ion batteries, which generally refers to a battery with lithium cobalt oxide/graphite electrodes, or something similar. At no time does lithium enter the metallic state, unlike lithium anode batteries."
] |
[
"If dark matter generates a gravitational field, and dark matter can 'clump' like ordinary matter, can dark matter collapse under its own weight like regular matter to make a dark-black hole?"
] |
[
false
] |
[deleted]
|
[
"dark matter can 'clump' like ordinary matter",
"No, it cannot.",
"Regular matter - there's gravitational attraction, and then there's friction (collisions) between particles. Gravity pulls everything together, and then friction slows particles down (relative speed decreases) so that they can \"clump\" together. This is how you get planets, asteroids, etc.",
"Dark matter - truth be told, we don't know much about it, but it does not appear to experience friction as far as we can tell, either with itself or with regular matter. For that reason, it will probably never make \"clumps\". Particles of dark matter (if they exist as such) will be drawn together by gravity, but then they will just zoom right past each other.",
"I did some numeric simulations for particle collectives under mutual attraction, years ago. Without friction, it's just a big swarm that keeps roiling over and over. Kind of fun to watch, but it doesn't really do anything.",
"With dark matter, you may get such swarms arbitrarily big, maybe as big as a galaxy. This is because the only significant interaction that DM seems capable of is gravity; there might be exceptions, but those are probably exceedingly rare (some experiments are being worked on to hunt for such rare occurrences).",
"If DM falls into an existing black hole, it's likely that the BH won't treat it any different from regular matter. It gets swallowed up, and its mass is added to the BH. But this is a bit speculative, since we haven't seen DM from up close.",
"TLDR: It doesn't clump."
] |
[
"Dark matter is different from normal matter than in that it doesn't interact with itself using all of the other forces (only gravity and weak interaction).",
"Normal matter can properly form planets and stars because it can bind together using the other forces. Dark matter doesn't have this property. It is attracted to itself by gravity, yes, but ",
"gravity is very very very weak",
" compared to other forces. ",
"Further, when normal matter falls into a black hole, ot very rarely does so by falling in a straight line. Space is mostly space, and the odds of going straight into a black hole a very small. What usually happens is ",
"an accretion disk is formed",
".",
"This accretion disk is really important. The bits of matter than circle in an accretion disk around a black hole can knock into each other and ",
". Thus they spiral in. ",
"This works for normal matter but not dark matter",
"This ",
"paper goes into it in a bit more detail",
", but essentially while it is possible for dark matter to fall into existing blackholes if it happens to be on a direct path, it seems very unlikely that dark matter will spontaneously create black holes at anywhere near the same rate as \"normal\" black holes."
] |
[
"You have it backwards. Everything not evident by ",
" significant interactions is simply ",
" dark matter."
] |
[
"Is it possible to dive so fast you can turn upwards and exit the water?"
] |
[
false
] |
I dove from small heights in the past, about ten feet or so, and as soon as I hit the water I bent my body upwards, did a vertical U-turn, and exited the water before stopping halfway out. Well, I guess it was more of a J turn... Is it physically possible to dive from a high enough place that you can use that speed, turn upwards and leave the pool completely? If yes, video please? To make my original question clearer allow me to paraphrase WazWaz's definition: The angle with which you enter doesn't really matter to me, as long as you enter the water completely, and use the entry force to exit the water completely, even if it is a centimeter off the water surface.
|
[
"Terminal velocity for a skydiver is about 195 km/h. Most of that energy would be absorbed by the water upon impact, not giving enough time to turn your angle back upward to exit. Mythbusters did an episode of shooting bullets into water. Most of them stopped moving in the water after a couple feet (especially when shot at an angle.) I believe your body's energy would have similar effects. "
] |
[
"To clarify, it is completely possible to have enough downward momentum to turn it back upward while moving through a fluid; this is how gliders work. However, due to the limits of terminal velocity and the high surface tension and viscosity of water, most of the momentum would be absorbed on impact and in the ensuing drag.",
"EDIT: Thanks for pointing out, I neglected to mention that the forces at work between a glider and a human are DRASTICALLY different, so comparing the two is a bit like comparing apples and oranges. "
] |
[
"That is the weirdest most interesting explanation of lift I've ever heard. But your premise is false. This is essentially an energy problem that you could theoretically work out by KE + PE + losses = const. Lift and flight in general is much more complex than that. ",
"In reply to the OP: ",
"The limiting factor here is the speed you can attain just before contact with the water without killing yourself. The highest (safe) diving boards you'll find are about 10 metres. Freefalling from those you'll hit about 45km/h at the water. Your total energy at the water surface for that velocity (using the surface as the datum) is 7.4kJ (75kg person). Assuming coming clear of the water is a 1 metre jump out of it, you do have enough energy to get out of it, but you must account for the losses. ",
"You basically need to do some computational fluid mechanics to find the losses in the water so I'll leave that to someone with more time!",
"edit: I had originally made a stupid mistake and came to a more interesting definite no answer. But it was wrong ;)"
] |
[
"If we were hit today by an asteroid similar to the one that killed the dinosaurs, would the human race survive?"
] |
[
false
] | null |
[
"Here is a ",
"good discussion",
" of the effects caused by the Chicxulub impact. The effects are complex and do not depend solely on the size of the impactor. Factors like the target (rock vs. water), type of rock (sulfur-rich, for example), and location on the globe also play important roles. It is the secondary effects, not the impact itself, that would pose the greatest hazard to humankind."
] |
[
"I don't think its the kinetic energy that will kill us, but the ensuing ice age."
] |
[
"The human race could not be very easily assumed to be doomed by a single shot of one asteroid; however if the single asteroid is accompanied from debris it collected from other collisions previously accumulated through smashing into smaller but still significant asteroids in a larger swarm that would strike around the world rather than just as one block.",
"To kill all the humans with rocks from space, you need a lot of big ones, not just one gigantic one with the kinetic energy of a group of merely giant ones. ",
"*Humans are also tricky, if we can see the rocks coming we might be able to deduce and set up a network of defences to destroy and divert the rocks before they collide with certain targets. ",
"I assume you ask this question because you seek to apply it later. \nTake heed, you must sabotage the humans defences from the inside before calling down your heavenly powers...."
] |
[
"Why do arm hair and leg hair stop growing at a certain length?"
] |
[
true
] |
[deleted]
|
[
"What is the speed of dark?"
] |
[
"Hair Follicle Cycle",
"And jeez, this has to be the most common question here, besides the speed of light ones."
] |
[
"7"
] |
[
"Have we hit a sort-of dead end in cosmology?"
] |
[
false
] |
We know a lot about how/when the universe started, but we still don't know it started. Time itself started with the universe so what came makes no sense, but obviously something caused it to happen! According to my understanding, we didn't know earth wasn't flat for atleast about 2000 years, when finally by the 15-1700s it was established once and for all. But all that time we had a good idea how world around us worked (like buoyancy and parabolic motion due to gravity etc. to name a few things). Then came optics/radioactivity/electromagnetism/relativity/quantum mechanics that fundamentally changed our picture of universe. Presently we're in the same situation again, we know a lot about how the world work and yet no clue why it all started in the first place. Now that I think about it, will this series of "why"s ever end? Will we ever have a complete answer? If not us, will any life/organism/sentience/consciousness/thing be able to get to the complete answer? Is it like a puzzle that'll take to solve? What if forever isn't enough?
|
[
"First, many ancient societies and most educated people in the age of exploration (ie prior to and contemporary with Columbus) knew the earth wasn't flat. You can show it isn't without needing to circumnavigate the thing. The Greek's size estimate is actually fairly close even. ",
"To be honest, cosmology is a field just getting started. I mean physics has been around since Newton, but the big bang's only on the order of 50 years old. I've heard many people claim that rather than a dead end, we're just beginning a new golden age of astronomy and cosmology. We don't yet know what some things are, but we know that the effects are there, so we know there should be a lot of exciting discoveries ahead. ",
"As to whether we'll ever know \"why\" in some philosophical sense... well it's just that isn't it? Philosophy. If we can't scientifically speak of what \"caused\" the primordial conditions of the universe, then we're free to speculate philosophically, and even to allow our science to inform that philosophical speculation. But it just is one of the limits of science. If you can't measure a thing, then it's not a scientific concept.",
"But also, I should point out, that physics is littered with examples of things that happen ",
" There just ",
" a formal definition for cause in science. It's a useful fiction to keep track of relationships in time between things, but it's not really needed. And certainly if there is no \"before\" you can drop the idea altogether as there aren't any time ordering relationships to keep track of."
] |
[
"but obviously something caused it to happen",
"why?",
"According to my understanding, we didn't know earth wasn't flat for atleast about 2000 years",
"Your understanding is wrong; Eratosthenes accurately calculated its radius in Hellenistic era."
] |
[
"So, as a cosmologist, I can say for certain that we haven't hit a dead end. There are lots of efforts ongoing to probe the inflationary epoch, which occurred in the first 10",
" seconds of the universe. That probably won't answer why the universe started, but it might shed some light on theories that try to do just that. There are lots of theorists, for example string theorists, trying to pick at the \"Why\" question, or at least unpack it, disassemble it, and explicate it. Hopefully they will be getting more clues as time goes on.",
"Precision cosmology is a young science. One question that you might ask, perhaps a better question is, Has the \"golden age of cosmology\" come to an end? That's a more widely discussed question. Between COBE, WMAP, and the Supernova work demonstrating the acceleration of the expansion of the universe, we've had a really good couple of decades. Some astrophysicists feel that all the important solvable questions in observational cosmology have been solved and it's time to move on, but I disagree.",
"I think the most exciting results in observational cosmology in the next few years will be from CMB polarization experiments (like Plank) and from 21 cm tomography."
] |
[
"Is the normal force \"real\"?"
] |
[
false
] |
That is to say, is it a force that is distinguishable from the force "pushing" something against another, or is it something that isn't real but makes our model work.
|
[
"The normal force is real. At root, it's one way the electromagnetic force can manifest."
] |
[
"You need to be very careful discussing normal forces and third law pairs as there are a lot of misconceptions in this area, for instance people thinking the normal force and the force due to gravity are a third law pair (equal and opposite) which is very much not the case as can be shown by looking at what happens to the normal force if the table is inclined with respect to the force due to gravity. "
] |
[
"it seemingly (from my limited knowledge of physics) only results from the application of another force.",
"Well that's also true. If you weren't being pushed into the table it would exert no force back on you; you'd be just hovering over it slightly without putting any pressure on it. Normal forces are 'contextual' in that way, where they aren't something an object is constantly generating no matter what happens. It's not ",
" in the same way that gravity is, but it's certainly a real force.",
"To be more precise the electrons in the table are always repelling your own, but the force drops to almost nothing if you're not within an atomic distance of each other. So from a large-scale perspective it looks like a force is just turning on and off very suddenly."
] |
[
"If you put a large number of charged particles (say, electrons) into a star, what would happen?"
] |
[
false
] |
From what I understand, the electromagnetic force is much stronger than gravity. The only reason we don't see its effects on a cosmic scale are because protons tend to find electrons so the charges all balance out. However, if you were to manipulate a star so that its electromagnetic field was as strong or stronger than its gravitational pull, would it behave any differently? Also, what would happen if you tried the same thing on a black hole?
|
[
"This occurs in neutron stars. Neutron stars have huge magnetic fields (10",
" G compared to 0.5 G for Earth). As these magnetic fields sweep through space they induce huge electric fields parallel to the surface of the star. For an electron this electric force is about 10",
" times greater than the gravitational force. This causes charges to be ripped from the surface of star into space. These charges create large region of dense plasma that surrounds the star called the ",
". Inside this region the plasma co-rotates with the star out to a point where the plasma would have to move faster than the speed of light to continue co-rotating. This boundary is called the ",
".",
"The details of the magnetosphere complicated. The important thing is that it emits high energy radiation that sweeps around like a lighthouse as the neutron star spins. We see these as pulses in our telescopes, hence the original name pulsars. "
] |
[
"That's not the ",
" reason why electromagnetism sort of \"self-regulates.\" Apart from the fact that most matter is electrically neutral, energy-dense electric fields will tend to radiate away their charge via spontaneous pair production.",
"Once you cram enough energy into an electric field, it becomes favorable for particle-antiparticle pairs to appear. The one with identical charge to the charge of the field will be pushed away from the source of charge by the electrostatic force, while the one with opposite charge will be attracted. In this way, the charge will be effectively radiated away until the energy density of the field drops to the point where pair production is no longer energetically favorable."
] |
[
"I'm disappointed that no one has ever told me how awesome neutron stars are. Thanks.",
"How is it that neutron stars have such a strong charge? Does the total charge of the star plus the magnetosphere cancel out? If not, what happened to the extra charge?"
] |
[
"How much does the centrifugal force of the earth’s rotation counteract gravity at the surface? If the earth wasn’t rotating, how heavy would a kilogram be at sea level?"
] |
[
false
] |
I was reading about how the Gault asteroid is spinning so fast the surface material overcomes gravity and escapes. This made me wonder about the earth’s rotation and how much centrifugal force is acting against the earth’s own gravity. Would it make any measurable difference if there was no rotation? Would it be so much that we’d all be squashed by our own weight?
|
[
"At the equator, where the centrifugal force is maximal in magnitude and directed straight upwards, the magnitude of the centrifugal acceleration is 0.3% of the magnitude of the gravitational acceleration at the surface of the Earth.",
"So an object in this situation is 0.3% \"lighter\" than it would be if there were no centrifugal force."
] |
[
"The centrifugal acceleration (in m/s",
") of a rotating object is w",
"r where w is the angular speed (in radians per second) and r is the radius of its rotation (in meters). Earth does a full rotation in one day, which is 2pi radians in 86,400 seconds or an angular speed of 7.27x10",
" rad/s. The radius of the earth at the equator is 6,378 km. This means an object at the equator has a centrifugal acceleration of 0.0337 m/s",
", which is about 0.3% of the acceleration of gravity at the surface, 9.81 m/s",
". In order for centrifugal acceleration to equal gravitational acceleration at the equator, the earth would have to have an angular speed of 0.00124 rad/s, which corresponds to a day that is 5,066 seconds long, or about 1.4 hours.",
"Edit: I used w for simplicity's sake, the actual symbol is a lowercase omega which looks a little like a w."
] |
[
"If you want to measure the mass of something with an accuracy better than 0.3% you have to calibrate your scale to the place where you use it."
] |
[
"Does Earth appear as a bright light to other planets in space, like Jupiter and Saturn do in our night sky?"
] |
[
false
] |
[deleted]
|
[
"have you never heard of the pale blue dot. that's a picture of earth from the satellite \"Voyager 1\" (I'll have to double check that) orbiting Saturn.\nits a barely visible dot from orbit so no interference ",
"Edit: ",
"Link to picture",
"\nalso it is from voyager 1"
] |
[
"We may look bright in the Mars and Venus skies, but I'm not so sure about how bright we are to Jupiter and Saturn. Look at how big they are compared to us and only appear as dots in our sky."
] |
[
"The brightness of a planet as viewed from another planet depends on a few factors. The first is phase angle. This is the angle between the light source and the observer, with the planet of observation at the vertex. The body will be brightest at a phase angle of zero degrees (think full moon), and dimmest at 180° (like new moon).",
"A second factor is obviously distance, as greater distances correlate to lesser apparent magnitudes.",
"Third, the albedo, or reflectiveness, is important.",
"Earth would not be visible with the naked eye from Jupiter or Saturn, but is quite bright from inner solar system planets.",
"You can find the apparent magnitude of earth from various planets here:",
"http://en.wikipedia.org/wiki/Extraterrestrial_skies",
"(Along with more interesting facts about the view fun rise planets)",
"Edit: phone ate most of my original reply, retyped it."
] |
[
"Do lines of latitude and longitude move?"
] |
[
false
] |
Systems like GPS and Google Maps can give you lat-lon coordinates of features on the Earth down to several decimal places. I'm assuming they're using some kind of reference geoid. But do the actual lines of latitude and longitude move around with the earth's precession and nutation? Do the north and south pole, where the axis of rotation intersects the surface, move around? Also, what about continental drift? How much does that put GPS off by?
|
[
"Do the north and south pole, where the axis of rotation intersects the surface, move around?",
"Yes, they certainly do.",
"Polar motion is observed routinely by very long baseline interferometry, lunar laser ranging and satellite laser ranging. Current and historic polar motion data is available from the International Earth Rotation and Reference Systems Service's ",
"Earth Orientation Parameters",
".",
"Polar motion is compised of three major components: a free oscillation called ",
"Chandler wobble",
" with a period of about 435 days, an annual oscillation, and an irregular drift in the direction of the 80th meridian West.",
"This slow drift, about 20 m since 1900, is partly due to motions in the Earth's core and mantle, partly to the redistribution of water mass as the Greenland ice sheet melts, and to isostatic rebound, i.e. the slow rise of land that was formerly burdened with ice sheets or glaciers."
] |
[
"Continental drift is on the order of centimeters per year, which is enough to require compensating for now and then. But this isn't really lines of latitude and longitude moving, just the position of objects on the planet moving.",
"It's also possible for the rotational axis to shift relative to the surface, something called \"true polar wander\", and this would presumably drag latitude and longitude with it, but so far as I can tell we haven't measured any such wander with current instruments, and at most it probably couldn't be more than a fraction of a degree of wander every million years."
] |
[
"The Earth's axis of rotation relative to an inertial reference frame (e.g. stars far away) changes with a 26,000 year cycle, but its rotation relative to the landmasses is more stable: ",
"https://en.wikipedia.org/wiki/Axial_precession"
] |
[
"If the y chromosome is human specific what causes the differentiation of male and female apes?"
] |
[
false
] |
I guess I just want my confusion cleared up on this article about the y chromosome Adam... Was the y chromosome due to the fusion of apes 24 chromosomes into our 23? Here's the article:
|
[
"The Y chromosome originally evolved from an autosome which acquired sex-determining characteristics. Apes also have X and Y chromosomes; in fact, many vertebrates do - mice have XY (male) and XX (female), birds have ZZ (male) and ZW (female). ",
"Some vertebrates don't have their sex determined in this way. Often, environmental facts play a major role such as the temperature-dependence of sex determination in crocodilians.",
"This",
" is a great place to start for getting your head around the origin of the Y chromosome. Fascinating stuff."
] |
[
"They didn't ",
" to be, but evidence suggests (according to Wikipedia) that they lived within a few ten thousands of years of each other."
] |
[
"So by y chromosome adam do they mean the point at which sex was not determined by environmental factors and instead the y chromosome was the deciding factor? Thank you for the link by the way!"
] |
[
"Why is it that after staying up all night and feeling tired, you become more energetic, passing a certain interval of time."
] |
[
false
] |
Additional quesiton: Why is there a sweet spot of sleep deprivation where one is more likely to be creatively inspired.
|
[
"The reason one begins to feel better towards the end of the night is due to the circadian rhythm in alertness. The body contains a circadian clock that promotes sleep during the night and wakefulness during the day. As the next day begins, that circadian wake promoting signal also begins, which partially counteracts the increasing sleepiness with time spent awake.",
"The same is true if people are kept awake for several days. There is an overall decline in alertness from day to day, but also a circadian rhythm in alertness within each day.",
"I don't know of any scientific evidence to support the idea that sleep deprivation increases creativity. Experiments that have measured performance on tasks designed to measure creativity have shown impairments due to sleep loss, e.g., ",
"http://www.journalsleep.org/Articles/110604.pdf"
] |
[
"To add onto OP's question. Why is it when morning comes around again often headaches will set in"
] |
[
"I can't give a simple answer to that anecdotal observation. The relationship between sleep and headaches is complex. Headaches have been associated with both reduced and extended sleep. The physiological mechanism by which sleep deprivation induces headaches is still not known. We do know that sleep has effects on both the brain and overall vascular function.",
"Additionally, prolonged wakefulness can lead to eye strain or light sensitivity, so headaches in the morning following sleep loss could be as much to do with the morning light exposure as the sleep deprivation itself."
] |
[
"I wear glasses. Why did the optometrist not give me super vision?"
] |
[
false
] |
The other day I was sitting at the traffic department to have my drivers license renewed. Part of the renewal process requires me to have an eye test. I wear glasses and was tested both with, and without, my glasses on. Without my glasses I failed the test, but with my glasses on I tested as having 6/6 (or 20/20) vision. Later I wondered what these numbers meant so I read up a little on the internet and discovered that there are a great many people who have vision significantly better than 20/20 visual acuity. For example apparently used to have a remarkable 20/10 vision. So my question is, why did my optometrist issue me with glasses that only gave me 20/20 vision. Why not better? Why can't I have super vision?
|
[
"The best your optometrist can do is to make sure the image on your retina is perfect. That's why they correct the geometrical defects of your eye. But there can remain some imperfections: shape of the cornea, size of the eye, shape of the retina, etc. And it doesn't change the \"resolution\" of your retina (how many photoreceptor cells you have).",
"Buying an expensive objective won't make your camera perfect (but it can help)."
] |
[
"They're called multifocal inraocular lenses. If you win the \"I got cataracts lottery\" and have good insurance or have a fair amount of cash you can get back to the vision you had when you were young. ",
"Now go away. I'm not telling you any more of our rich people secrets"
] |
[
"Optometrist here. LASIK works by reshaping the cornea so that light rays will focus on the retina. \"Age related degeneration\" also known as presbyopia is due to the lens losing its flexibility because of free radical damage (aging). There is nothing wrong with the muscle (ciliary body). It is still doing its job put the lens just simply won't change its shape to cause accommodation. We have nothing to cure presbyopia. The lens is avascular so we can't get any medication to it via the blood stream. We also can't give it anything via an injection because if you even brush up against the lens it will get a cataract. "
] |
[
"A lot of things in this new video by minutephysics don't seem logical to me, can anyone explain some things for me?"
] |
[
false
] |
So in made by minutephysics in combination with Vsauce, there were a couple of things that, although I am a layman, didn't seem very logical at all. A) 1:28 - 1:52 I have the smallest problem with this bit, but he says "you could float freely around with no sense of up or down". 1, once you reached terminal velocity in such a tunnel, you would have almost no sense of up or down, correct? 2, you wouldn't be able to "float around freely" because you have nothing to push off of and, presumably, no device to thrust you. (mostly just a minor nitpick) B) 2:55 - 3:06 He says "gravity from the different parts of the spherical shell would perfectly cancel out, and you'd float freely about inside..." In the drawing, the stick figure is closest to the top left of the drawn circle. If this were the case, wouldn't the side closest to you have the strongest gravitational pull on you, pulling you toward the edge of the interior of the sphere? C) 3:20 - 3:35 Hey says "Back outside of the earth, we wouldn't really notice much difference, at least, not from a gravitational perspective. Falling things would still accelerate at 9.8 m/s a [thrown] baseball would follow the same trajectory, and the moon would follow the same orbit around the earth" First off, wouldn't gravity on the outside of the Earth be much, much weaker, considering the insanely large amount of mass the Earth would lose if it were hollowed out, thereby causing things to accelerate towards the Earth much slower, baseballs to fly further, and the moon to cease orbiting the Earth and start going in a straight line, as the Earth's gravitational field would now likely be far too weak? I would appreciate some answers to these questions, because looking at what minutephysics is saying with what I have learned in high school physics and science classes throughout my life, it seems like they are just sort of spouting BS. Thanks, to anyone who takes the time to answer.
|
[
"A) For starters, they've assumed no air resistance, and therefore no terminal velocity. I agree with your second point - it's a minor nitpick - and they're really just trying to point out the lack of a net force acting on the person. \"Freely\" in this sense doesn't mean \"at will.\" It just means with no resistance.",
"B) The stick man ",
" closer to one side to another, and this means that the mass on that side will exert a stronger gravitational pull. ",
", notice that there is less mass on that side - because he's closer to that side! So having more mass on the far side actually cancels out the stronger attraction on the near side. This is the ",
"shell theorem",
".",
"C) They've stated that they'll make the Earth hollow, but it \"weighed the same,\" which can be interpreted as \"having the same mass,\" therefore having no effect on gravitation.",
"Also, check out ",
"this thread in r/sciencefaqs",
" for an overview of ",
"gravity trains",
"."
] |
[
"With the first one I just got a bit annoyed that they showed the stick figure almost swimming about. I feel sort of dumb for having missed that it was supposed to weigh the same. It took me a minute to understand what you were saying for C, but I get it now, and it's sort of interesting. Wouldn't you sort of drift towards the center though?"
] |
[
"For the case of being inside a hollow sphere?"
] |
[
"When something is heated by induction, is it only metal that is heated?"
] |
[
false
] |
Because induction heating is so efficient and precise I am curious if there is a place for it in industrial fields, specifically quickly heating (cooking) a large amount of something
|
[
"only effects ferromagnetic metals, and in so far as they are below the curie point for said metal. This makes melting metals basically impossible",
"I'm not an expert, but I don't think this is correct. See ",
"this",
":",
"... eddy currents (also called Foucault currents) are generated within the metal and resistance leads to Joule heating of the metal.",
"Eddy currents can, however, be generated in any conductor ... Induction heating has been used to heat liquid conductors (such as molten metals) and also gaseous conductors (such as a gas plasma) ..."
] |
[
"only effects ferromagnetic metals, and in so far as they are below the curie point for said metal. This makes melting metals basically impossible",
"I'm not an expert, but I don't think this is correct. See ",
"this",
":",
"... eddy currents (also called Foucault currents) are generated within the metal and resistance leads to Joule heating of the metal.",
"Eddy currents can, however, be generated in any conductor ... Induction heating has been used to heat liquid conductors (such as molten metals) and also gaseous conductors (such as a gas plasma) ..."
] |
[
"Sure, ",
"induction furnaces",
" aren't uncommon in foundries these days.",
"A pretty cool (although not that common) application is ",
"levitation heating",
", which uses the same high frequency magnetic field to induce a current and levitate the object being heated.",
"You could use induction heating with anything that's a conductor. But in practice it's probably just metals, since there are few non-metallic bulk materials that are good conductors."
] |
[
"What medical uses does the decay of radioisotopes have besides treating certain forms of cancer?"
] |
[
false
] | null |
[
"The entire field of ",
"nuclear medicine",
" is involved with radioisotopes in medical applications - not just in treatment, but in imaging as well."
] |
[
"While not treating a disease, ",
"PET scanning",
" uses a variety of radioisotopes for diagnosis, research, and medical imaging."
] |
[
"Radiation is used extensively in imaging. Apart from that, there are several non-cancer diseases we can treat with radiation. Most of them are similar to cancer, in that they involve excessive cell growth. Radiation can be used to prevent ",
"keloid scarring",
". It is often given after traumatic pelvis/femur injuries to prevent ",
"excessive bone growth",
". It can also treat ",
"Dupuytren's contracture",
"."
] |
[
"If an Astronaut would take his iPhone into Space, how would the different sensors react?"
] |
[
false
] |
How would the accelerometer, magnetometer and especially the gyroscopic sensor work or not work and why?
|
[
"There is a difference between how the gyroscope works on Earth and in space. On Earth the gyroscope will record one turn every 24 hours (of the casing about the gyroscope). In orbit the iPhone will maintain the same orientation, and this turn wouldn't get recorded. This is all assuming that neither device is handled at all.",
"I doubt that would actually affect anything... I can't really think of an application where that 1 turn per day would matter... but it would be a measurable difference. "
] |
[
"The gyroscope would work as it doesn't depend on gravity. The accelerometer would work unless it's to determine which way is up or down as it doesn't experience proper acceleration in free fall. ",
"I'm not too sure of the magnetometer. "
] |
[
"Oh yes thanks for that. I forgot to consider the rotation itself. "
] |
[
"How long does it take for cellular damage to result from total hypoxia"
] |
[
false
] |
I see a lot of people talking about choking fetishes that some couples enjoy, wherein pressure is used to restrict the breath until the other becomes either light-headed or completely loses consciousness. They had standard warnings involved that you should be careful with 'breath play', but nothing other than that. That got me curious and I was wondering how much of this 'breath play' is too much and can very short (5-10 seconds) periods of unconsciousness due to lack of oxygen be harmful?
|
[
"I know that in the event of a stroke it usually takes 2-4 minutes for ischemia to do permanent damage to the cells (Glucose, however, again in the case of a stroke, takes only seconds to deplete and cause damage). If it takes a few minutes for oxygen depletion to actually kill brain cells getting NO perfusion, I would assume that cells deprived for a short period of time, such as in the case of \"breath play\" would not cause any permanent brain cell damage in otherwise ideal conditions, and that most damage done to cells in the body from momentary lack of perfusion would only cause a hiccup in full function.",
"However, I feel as though being choked on a fairly regular basis could cause stress and damage to the major blood vessels being constricted in the neck, elevating a risk for unstable plaque, or distention, or vasospasms, or even burst vessels and hemorrhaging pretty much anywhere in the body from hypertension caused by this additional stress on the cardiovascular system.",
"So I don't know that I'd peg the lack of oxygen for damage caused by choking someone as the reason, but I do believe there are a good number of other reasons why this could be harmful to the body, particularly if you're not the epitome of healthiness (good genes, good diet, good immune system, strong body, etc.).",
"The body is a wonderfully strong and durable thing, so I wouldn't say that doing this ",
" kill you, but it has a small risk of doing so and thus my not technically professional advice would be to not choke someone you like."
] |
[
"The answer depends on the cell type. To the best of my knowledge, neurons (the cells that make up much of the brain and the activity of which results in conscious experience) are some of the most susceptible in the body to short term hypoxia. 5-8 seconds is enough to induce unconsciousness, hence the effects of the \"chocking game\" and the phenomenon you speak of. Anywhere from 15-30 seconds of hypoxia is enough to eliminate electrical activity in neurons, and more than a minute of neural oxygen deprivation can lead to cell death. Whether these activities induce enough neural hypoxia to lead to these \"typical\" outcomes is debatable. I don't know of any studies using models that closely resemble the activities your talking about, and there might be protective mechanisms that are not present in the studies which yielded the results above. Bottom line: short term hypoxia is no biggy and the longer neurons are deprived of oxygen the worse. Most other cell types can withstand fairly long bouts without arterial oxygen supply."
] |
[
"Great response, thanks!"
] |
[
"How can sensitivity (d') increase and bias (C) increase in a memory paradigm?"
] |
[
false
] | null |
[
"Increase over the course of what? Like if you do two sessions of a memory experiment and find that people are better the second time around?"
] |
[
"I'm measuring an independent variable. Let's say it is height: as people get taller, they increase in both sensitivity and bias to remembering a certain type of apple (also made up). ",
"Conceptually, how can people both be biased to saying yes to red apples, but also more sensitive to red apples? Also, how do I interpret these people?"
] |
[
"That's the whole point of signal detection theory - sensitivity and bias are separable. In your example, maybe people encounter lots of red apples during their lifetime so they become expert apple detectors and can recognize them much more easily. They also become biased to \"see apples everywhere\" so even when they didn't see one, they think they did."
] |
[
"Reading the post about Uranus and it’s 90 degree axis - Why do planets rotate to start with?"
] |
[
false
] | null |
[
"Planets rotate because of the Conservation of Angular Momentum. The gas and dust that forms planetary systems has some net rotation to it before it starts contracting. There are a lot of reasons for this, but basically it's very hard to not have angular momentum. If any particle moves in a way that's not directly toward or away from the center of mass of the cloud, then the cloud has angular momentum. ",
"Since, like normal momentum, this must be conserved, as the gas contracts and forms stars and planets, these objects must also spin. Some of this angular momentum goes into the revolution of the planets around the central star, but some of it also goes into the rotation of the planets themselves. "
] |
[
"its like dropping a ball and expecting it not to roll some distance from where it lands. possible but almost never happens."
] |
[
"Perhaps an explanation of 'angular momentum' is in order?",
"Consider two small objects in stable orbits of different radii, about a central body. \nThe object with the smaller radius orbit will be moving faster about the center than the one with the wider orbit.\nAs the two approach each other, and gravity draws them together, \n(envision a string drawing them together), that difference in speed must appear as a rotation of the new single object."
] |
[
"Do people in the International Space Station experience day and night? Or is it continuously one or the other?"
] |
[
false
] | null |
[
"The orbital period of the ISS is about 96 minutes, so they experience multiple sunrises and sunsets per day. I'm not sure what kind of toll that takes on the circadian rhythm and how they combat that, though. I'm an orbits guy, not a bioastro guy!"
] |
[
"yes, they experience day and night. Of course, its also orbiting very fast (about 1.5 hrs per orbit), so one \"day\"/\"night\" only lasts a short time",
"edit: ",
"check out the map"
] |
[
"You can take a look at ",
"this ISS activity log",
" to get a general idea what a day's work looks like aboard the ISS. As you will note, sleep time is regularly scheduled from 9:30PM to 6:00AM (times are in Greenwich Mean Time), with some padding on either side for \"pre sleep\" and \"post sleep\" activities and a small bit of staggering for different crew groups to rotate in and out of shared facilities (bathrooms, etc). During most missions the majority if not all of the crew keep the same working and sleeping hours.",
"As it has been mentioned, the ISS experiences 16 sunrises/sunsets a day, so in order to facilitate natural sleep cycles as best as possible, \"Day\" and \"Night\" are simulated according to GMT with appropriate covering of windows, dimming of light sources, etc. You can read more about it in ",
"this posting from ISS Science Officer Ed Lu",
"."
] |
[
"If time is stopped at the speed of light, than is time existent for light itself?"
] |
[
false
] | null |
[
"There are no inertial frames where the photon is at rest, so it doesn't make physical sense to ask what happens when you reach light speed or what a photon experiences in its rest frame, because in all rest frames, massless particles including photons move at ",
". Asking \"does time stop at the speed of light?\" is essentially the same as asking \"in the inertial frame of a photon, does time stop?\" and the answer is \"there are no inertial frames of photons where ",
"=0, so it doesn't make physical sense to ask this question\"."
] |
[
"No. Because the photon is a massless particle, it ",
" move with speed ",
". Unfortunately, there's no 'if's' here, massless particles are required to move at speed ",
"."
] |
[
"No. Because the photon is a massless particle, it ",
" move with speed ",
". Unfortunately, there's no 'if's' here, massless particles are required to move at speed ",
"."
] |
[
"What is that 'curtain' of gaseous stuff that we usually see falling down the sides of a rocket during launch ?"
] |
[
false
] |
If you look closely at rocket launches (Saturn V or maybe other rockets too) you will find some kind of a curtain of gaseous stuff falling over its sides. Till this day, I have no idea what that is :( Photo: and I have this nagging question ever since I was a kid (now I am 30 but no answer in sight). I am hoping someone here can answer my question. Thanks!
|
[
"ice- most modern rockets are hydrogen based. And are propelled by large amounts of liquid oxygen in hydrogen, making the surfaces of the rocket very cold before launch, enough that ice forms on the surface, which then falls off during launch. "
] |
[
"Thanks!!! Now I know :)"
] |
[
"If you really want to know more than you've ever known before about the shuttle and its launch then watch the 45 minute long documentary ",
"Ascent - Commemorating Shuttle",
". ",
"It's shuttle footage hand picked by shuttle engineers and narrated by shuttle loving engineers.",
"\nDownload a HD copy, the footage is amazing and much of it \"never before released\" with amazing discussions of how to make a camera that can survive the backthrust of a launching shuttle and handle the massive dynamic range of near dark to light from several thousand degrees of burning exhaust."
] |
[
"General questions about Multiverse Theory and related concepts"
] |
[
false
] | null |
[
"Your 3rd point is your only actual question:",
"CMB Cold Spot - what about this spot shows imprints/evidence of another universe?",
"Simple quantum fluctuations are likely sufficient explanations for the CMB fluctuations, and thus, ultimate formation of galaxies. You should understand the basic idea of quantum uncertainty, that you can't know the position and velocity of a particle exactly. During the early universe, these uncertainties were on the scale that they could cause those fluctuations. Gravity magnified those fluctuations. Quantum decoherence is perfectly random as far as we can tell. Therefore the fluctuations are a product of random quantum fluctuations.",
"When people talk about imprints from another universe, they probably are implying fluctuations beyond the randomness. You can't credibly disagree with the quantum randomness. It played a role without doubt. People just hope that we might see ",
" signal hidden in there. Experimental evidence hasn't proved these ideas 100% wrong, but it might eventually.",
"On your point 2:",
"the number of black holes a universe has indicates how much more down the evolutionary line the universe is.",
"No it doesn't. The universe has many more black holes now than it did 13 billion years ago. So that's probably not making a universal statement about our universe.",
"If the universe came about through black hole evolution line, then where does the \"line\" begin? It's a circular existentialist argument, like all existentialist arguments.",
"Black hole universe evolution can be useful to explain how certain properties of a universe evolved. Nonetheless, it doesn't make the universe ideal for life, only ideal for black holes. Anthropic selection is for life, and it may actually fight with black hole evolution. There's no guarantee that black holes and life like the fine tuning. Because of this, black hole universe evolution has a problem in that it doesn't have a problem to solve in the first place. It may still fit into the picture, but it should appear confusing with our level of knowledge."
] |
[
"the number of black holes a universe has indicates how much more down the evolutionary line the universe is.\nNo it doesn't. The universe has many more black holes now than it did 13 billion years ago. So that's probably not making a universal statement about our universe.",
"This was actually something I learned directly from the Black Hole course I took, so I'm guessing its a theory you don't agree with?",
"Your 3rd point is your only actual question:",
"Well I made it pretty clear at the beginning of the post that I was asking for expansions of these concepts as I only had a surface understanding of them.",
"Other than that thanks for the input."
] |
[
"You could make the argument that a large number of black holes indicates that the universe is further ",
", meaning optimized for making black holes. But that doesn't reflect the number of universes that came before it. By chance, one line got might have gotten really good really fast."
] |
[
"A question about earth pre- Pangea."
] |
[
false
] |
I recently read an article( ) and I was confused about this specific part: "It appears that Kenorland broke up around 2.6 billion years ago, creating a massive spike in rainfall. This in turn caused a decrease of greenhouse gases like carbon dioxide" My question is why would the breakup of a supercontinent such as Kenorland cause a spike in rainfall?
|
[
"Since no one will have an actual answer for this I will try and take a stab at it. PhD in Mechanical Engineering, so not exactly a layman, but feel free to correct me geologists and climatologists.",
"Weather is very dynamic, and geographical features play a major role in the local environment. For example, the Himalayas separate India and southeast Asia from China. Because of this moisture has a very difficult time getting over the mountains, in India you have a tropical jungle, on the other side you have a desert. Imagine the Himalayas are removed, now there would be nothing trapping the moisture and the rainfall would most certainly increase in the part of China that is normally cut off. However, this would probably balance out, a decrease in rainfall in India and Southeast Asia and an increase in China.",
"Now, in order to increase global rainfall, and not just locally, some sort of new geographical feature should account for it. In the case of a continent breaking up a new shallow sea could be formed between the two continents. A shallow body of water will be much more prone to evaporation than say the ocean. It is possible that a large shallow sea was created and the evaporation rate of water into the air was greatly increased due to this shallow sea that was not present before."
] |
[
"Well the hotter a liquid is the faster is evaporates. With a smaller body of water the water will evaporate quicker. The more shallow the water the easier it is to heat it up."
] |
[
"In addition, the Himalaya only cuts off a relatively \"small\" part of the global landmass, central Asia. But it seems likely that in a \"supercontinent\" much of the inner landmass would be dry deserts of one kind or another. ",
"With the breaking up of such a supercontinent not only would there be direct-effect shallow seas (land 'rips' open and seawater rushes in), but also indirectly, by exposing the formerly dry lands to rain you will have lots of new lakes etc forming over time where previously only dry depression areas existed."
] |
[
"Are there examples of evolutionary change or adaptation in humans evident from the last few thousand years?"
] |
[
false
] |
From the peppered moth to the tawny owl, we see examples of rapid evolution. Though I'd expect nothing of the speed of these two creatures evolutionary adaptation, I'm wondering if there have been any examples of evolutionary adaptation that can be seen in humans in the last few thousand years(I'll keep that time frame relatively vague to account for my lack of knowledge of how detailed our records are of these characteristics depending on how far back we go in time, though clearly we needn't too much "recorded" data to surmise a species' believed anatomy considering our hypotheses about so many other animals).
|
[
"Lactose tolerance in Europeans and North Africans, which apparently developed in both populations independently of each other and obviously after the domestication of cows, so some time in the last 10000 years. The idea is, that being able to use milk as a food source gave you a survival advantage when there food was scarce.",
"Also alcohol intolercance in Asians, also a result of the agricultural revolution, so also in the last 10000 years. The idea is, that fermented rice is rather bad for you, so people who were super sensitive to it, wouldn't eat it, and thus stay healthier.",
"If I was evolution, I'd have created a resistance against the toxic parts of fermented rice, but there you see how 'blind' evolution is, it's not looking for the best solution, it runs with whatever works."
] |
[
"It doesn't even run with \"whatever works.\" It runs with \"can I still reproduce successfully with this mutation.\""
] |
[
"Another one is resistance to malaria disease. ",
"https://malariajournal.biomedcentral.com/articles/10.1186/1475-2875-11-349",
"“The first generally recognized evidence for genetic resistance to malaria in humans was in 1954 [7] for sickle-cell haemoglobin heterozygotes AS. Overall, the “malaria hypothesis” of Haldane that some human diseases such as thalassaemia are polymorphisms and provide heterozygote advantage because of the trade-offs between the advantages of resistance to malaria and negative effects due to the disease, is now widely accepted but the exact means of disease resistance have often been difficult to elucidate.”"
] |
[
"I wear glasses for distance, but if I look through a tiny hole in my fist, I can make things come into focus. What's going on?"
] |
[
false
] |
[deleted]
|
[
"optometrist/vision scientist here. this is called the pinhole effect. light coming from 'straight ahead,' or incident to the lens does not get diverged from it's path. if you can eliminate off-axis, or non-incident light, you get a fairly clear image without having to change the optics (i.e. don't need your glasses as much). you can actually make a cheap effective 'pinhole camera' which is easy enough to google."
] |
[
"To add to hokieod's answer, this is also used as a test as to whether someone has reduced visual acuity due to an uncorrected refractive error (nearsighted, farsighted, astigmatic) or if their reduced visual acuity is due to an organic cause."
] |
[
"Yes, and astigmatism. "
] |
[
"In space disasters (ex: Challenger), when they mention remains, what was actually left?"
] |
[
false
] |
Rather morbid, but I've always been curious as to what was left of the occupants of Challenger, Columbia etc. Tangentially, what actually killed them, was it something like fire or oxygen deprivation?
|
[
"The publicly released reports state that several of the Challenger crew managed to activate their emergency oxygen supplies after the orbiter breakup, and may therefore have remained conscious until impact, unless the cabin was spinning ast enough to cause a blood-deprivation blackout. They would have been killed by the tremendous deceleration forces, which were sufficient to shatter the crew cabin into fragments. ",
"The human remains would be similar to those seen in commercial aviation accidents, where the cabin hits water or terrain at several hundred miles per hour. Extremities are separated from the torso, broken apart at the joints, or, depending on impact force, into even smaller fragments. Torsos can be pulped, with all internal organs ripped loose from their attachment tissue, and again, can be fragmented, depending on the impact force.",
"Needless to say, it usually requires forensic anthropology or genetic analysis to identify remains."
] |
[
"Depending on the type of spacecraft failure that results in death, not much in the way of remains can be left over. Here below is a link to a NSFL image from the Soviet archives, showing the remains of Cosmonaut Vladimir Komarov, whose Soyuz 1 capsule suffered multiple failures - both while he was on orbit and during re-entry. \n",
"http://imgur.com/ltxMD",
"Komarov survived re-entry interface, but his Soyuz capsule parachutes then failed to deploy properly, resulting in his capsule smacking into the ground at a horrific 200+km per hour, killing him instantly. In this case, Komarov's remains after impact were burned badly by the subsequent fire that was caused by the impact of his capsule with the ground.",
"For the STS-107 Columbia disaster - where the orbiter broke up at high altitude during re-entry - the occupants were killed very quickly (certainly before they hit the ground). The STS-107 orbiter crew module broke up in such a way that the astronauts aboard would have had their pressure suit clad-bodies subjected to hypersonic entry conditions very early on into the break-up. We know that none of Columbia crew even had their helmet visors down and locked at the time of breakup (or after), demonstrating that the forces and environmental conditions they were subjected to rendered them unconscious very quickly and killed them well before impact with the ground. In the case of Columbia, the orbiter breakup forces were great enough to actually dismember the astronauts and tear their bodies (and suits) apart as they separated from the remains of the orbiter, decelerated, and plummeted to Earth. ",
"Here is a link to the NASA archive PDF of their \"Columbia Crew Survival Investigation Report\", which is one document that goes into some detail about the last moments those astronauts aboard STS-107 experienced - ",
"www.nasa.gov/pdf/298870main_SP-2008-565.pdf",
"When it came to the Challenger disaster, where the shuttle and booster configuration disintegrated early into the launch phase, the crew were most probably still alive (though maybe not all conscious) at the time of impact with the water, as they were contained within the crew compartment and flight deck, which essentially remained intact (though unpressurized) during its break-away and freefall into the Atlantic. Most of the physical damage to the astronauts bodies in that case were caused post-mortem by sea life and water exposure, rather than being a result of the failure itself. "
] |
[
"Only Challenger. Also, they probably would not have been conscious. They would have lost consciousness due to oxygen deprivation quite quickly.",
"There is no way that the Columbia crew survived the initial breakup of the orbiter given the speeds they were traveling."
] |
[
"Have Noticeable Earthquakes Become More Frequent?"
] |
[
false
] |
I was tinkering with some data here (for fun): Note that I'm aware that I'm looking at data for 23 years of a planet much much older than that so the sample size isn't even great. Based on the number of global Earthquakes in 3 categories (magnitude 4.0+, 5.0+ and 6.0+), can we say though that there will likely be more of these noticeable Earthquakes over the next 10 years? Statistics is more of my strong suit than seismology - is this question not even valid (are past trends of Earthquakes not predictive of future events)? I also noticed that there seems to have been a substantial jump in the number of 4.0+ recorded Earthquakes from before 1994 to after 1994. This is in spite of the fact that ("Starting in January 2009, the USGS National Earthquake Information Center no longer locates earthquakes smaller than magnitude 4.5 outside the United States, unless we receive specific information that the earthquake was felt or caused damage."). Is this because we're using better tools now, are detecting in more places, or has there legitimately been more Earthquakes after that point consistently?
|
[
"To a first order, numbers of earthquakes of different magnitudes are well explained by the ",
"\"Gutenberg-Richter Law\"",
". If you take a look at that page (or look other things about this relationship) you will see there is some slop in that, especially in regards to the \"b value\", which is an empirical constant that varies a bit depending on environment.",
"That all being said, we know there can be temporary departures from those relationships. As best we can tell, we seem to be in one of those departures at the moment, or at least that's what this ",
"recent paper suggests",
" or ",
"here is a more boiled down version of the same result",
". This paper however also suggests that the apparently elevated rates of occurrences of large (M >5.2 in this study) are mostly driven by aftershocks related to isolated great earthquakes (M > 8) and if you filter those events out, the strange statistics largely disappear. There seems to be something funky going on for smaller magnitude earthquakes, but this could be because of issues with catalogs (mainly whether they are complete, which is a similar problem you were encountering in your simple analysis).",
"To get at the bigger part of your question, as a general rule, we think that patterns in past earthquakes are a good predictor of future patterns of earthquakes, however, this is predicated on having a good and representative record. The \"seismic cycle\" for most faults or sections of major faults (cycle of strain accumulation, earthquake rupture, and re-accumulation of strain) usually is on the order of 100's or 1000's of years, so the instrumental record is usually insufficient to really understand the history of seismicity and future risk. Paleoseismology (building records of past earthquake histories by various means such as trenching across a fault or indirect methods like both historical and geologic records of tsunamis, damage, etc) thus is an essential part of accessing risk and building histories of earthquakes to really understand long term (and more representative) patterns of earthquakes.",
"If you want to play some games with seismic data, you'd be better served to consider longer and global datasets, like the one hosted by the ",
"International Seismological Centre",
"."
] |
[
"You should look into the concept of induced seismicity as it explains the increase in smaller magnitude quakes (~mag 4). The most common cause of these small quakes is fluid injection for industrial wastewater (primarily off of oil/gas operations). The exact cause of the slip is somewhat case dependent but is in general due to changes in the stress state across faults. Also, like you mentioned, we are getting increases in the number of global seismometers so its inevitable that we will be able to see more earthquake events...but it doesn't take too many global stations to detect and resolve the larger events. In order to understand the increases in seismicity, I recommend refining your investigation by magnitudes. I imagine that you will see a significant increase around the mag4 range and not much change at all in the frequency of the bigger events. "
] |
[
"I appreciate the info!"
] |
[
"Shouldn't a black hole have only as much gravity as the star that formed it did?"
] |
[
false
] |
A question fueled by Dr. Who. Where does the extra mass come from that makes a black hole so dense if it was only made from a single star?
|
[
"Black holes have ",
" mass than the star from which they formed. As a general rule of thumb, when a star undergoes the kind of supernova that can create the pressure necessary to make a black hole, about three-fourths of its mass is blown off out into space. A twenty-solar-mass star becomes a five-solar-mass black hole. In general. Ish. Roughly."
] |
[
"1) Yes. 2) They have no extra mass, only higher density."
] |
[
"Not all stars are capable of forming black holes. They have to be above a certain mass."
] |
[
"My physics teacher reckons the \"heavy and light objects fall at the same rate\" demonstration only works below certain heights. Is there any truth in this?"
] |
[
false
] |
I'm a trainee teacher, and I was doing a subject knowledge lesson in Physics today. The tutor told us about a demonstration showing that objects of different mass hit the ground at the same speed, using an empty whiteboard marker and one filled with sand. Pretty standard. However, he cautioned us that if we did the demonstration from higher than the classroom ceiling (say, the roof of a 5-storey building), the demonstration wouldn't work - and the heavier pen would actually hit the ground first. We pushed him to explain, but all he could say is that it wasn't to do with drag or air resistance. Then he got distracted by a helicopter (don't ask). Is there any truth in this? Is it possible that he WAS thinking about air resistance? Or is there any other explanation?
|
[
"Air resistance will definitely cause things to fall at different rates, and have different terminal velocities - although that has more to do with the shape than the mass.",
"But he is absolutely incorrect in saying that, in the absence of air resistance, heavier things will start falling faster if you drop them from high enough. Gravitational acceleration can easily be shown to be independent of mass in a first semester physics course.",
"Gravity: F = GMm/r",
"\nNewton's Law: F = ma",
"Setting them equal, because the force of gravity is the force causing acceleration, gives:",
"GMm/r",
" = ma",
"m cancels, so",
"a = GM/r",
"Independent of the mass of the falling object, m."
] |
[
"My physics teacher tried to demonstrate a way to neglect air resistance.",
"He dropped a textbook and a sheet of paper separately. Of course, the textbook hit the floor first as the paper drifted down on light air currents.",
"Then, he put the paper on top of the textbook and dropped them both, so as to situate the sheet in an air pocket created by the book which would reduce most of the air resistance. The textbook hits the floor and the paper is on top of the textbook the moment it hits the floor.",
"Now, obviously, it's not a perfectly controlled environment, but it demonstrated the point fairly clearly with the resources on hand."
] |
[
"A better demonstration would be crumpling the paper and dropping it independently, because placing it against the book does like you said, the paper is caught against the book because of air pressure as the book falls."
] |
[
"Is there a known gas that burns without creating visible light?"
] |
[
false
] | null |
[
"Yes, hydrogen glows mostly in the infrared and UV spectrum when it burns, but it emits almost no visible light. Furthermore, water vapor resulting from the combustion also glows in infrared and UV due to thermal radiation, but since it is (almost) transparent in the visible spectrum, ",
"Kirchoff's law",
" determines it will not emit meaningful amounts of visible light.",
"Here's a picture of the Space Shuttle Main Engine: ",
"http://www.rocket.com/files/aerojet/images/media/spaceshuttleemain3.jpg",
"Yes, it's burning, but you can almost not see it at all. The white patch at the left is a ",
"shock diamond",
"."
] |
[
"Because they are \"single use\" the Delta IV first stage motors have an ablative inner nozzle lining that contains carbon which slowly burns away as the engine runs.",
" The Space Shuttle main engines are intended to be re-used and so do not have coatings that are meant to be burned off during operation."
] |
[
"The video you linked is about Apollo 11. That was a Saturn V rocket, which burned RP-1 (very refined kerosene) in its first stage. Certainly a kerosene flame won't have the same properties as a hydrogen flame.",
"For the Delta IV, ",
"/u/Guysmiley777",
"'s answer is correct."
] |
[
"Will opening a door darken a room?"
] |
[
false
] |
Suppose you are trying to sleep in a small room with several doors and a lamp. It is hard to fall asleep because of the brightness of the lamp. Will opening the doors "darken" the room (the rooms on the other side of the doors are dark)? Will some of the photons now travel to the other room as opposed to bouncing off the walls in your room?
|
[
"Furthermore, turning your lamp off will eventually darken the room as the photons are absorbed into the materials that they collide with."
] |
[
"After using the internet for years upon years... I still can't tell if this is a joke, science, or both."
] |
[
"One extra note: everything depends on the reflectivity of the door in comparison with the reflectivity of the room behind the door. It the door would have a reflectivity of 0%, and absorb all the light falling on it, then opening the door would lighten up the room.",
"Practical: if the door is made of a pitch black material or paint, and the room behind it has white walls, then opening the door would lead to more light being eventually scattered back into the room."
] |
[
"What's the smallest possible number of fundamental units, and what would they be?"
] |
[
false
] |
I know the SI system has 7, but I was thinking and realized that distance and time are actually the same, aren't they? And a mole is just a numerical multiplier, right? So, how few units could you end up with?
|
[
"Mass can be expressed in units of distance (Schwarzschild radius).",
"That's fantastic! I never thought about that!"
] |
[
"Mass can be expressed in units of distance (Schwarzschild radius).",
"That's fantastic! I never thought about that!"
] |
[
"In principle, you can have only one unit. ",
"The idea is that some fundamental constants are actually just proportionality factors, so you can just set them as 1. These are the speed of light, Planck's constant and Boltzmann constant. So distance and time are the same, which are inverse mass, energy, frequency and temperature. Of course you still need to express these in terms of a length/mass scale, and if you agree on one length scale (as cosmologists like to use, Planck length), then you can reduce your units to 0."
] |
[
"If the centre of the Milky Way happened to contain a Quaesar, would it have affected anything here on earth? Would it just be a brighter light in the night sky, or would it perhaps have more affected significantly the evolution of life?"
] |
[
false
] | null |
[
"It's possible that the centre of the Milky Way ",
" \"active\" at some point - like a low-level quasar. The centre of the galaxy is still obscured by dust, so all the bright visual-light radiation would still be dropped down into infrared and you still wouldn't see much. The effects on the structure of the galaxy would be fairly subtle and complex - e.g. it might slow down star formation a bit because the gas (especially in the middle) is a little bit hotter and less likely to cool and condense into stars. But for the solar system, the Sun is by far the most dominant thing going on, so it wouldn't really make a huge difference to humanity."
] |
[
"A cursory read over the wikipedia page that you linked to seems to imply that the Yarkovsky effect is only important \"in relation to meteoroids or small asteroids.\" I have very little knowledge about astrophysics, so I'm not sure that one can extend that principle to entire galaxies. Do you have any information to support that?",
"Also, you say, \"Humans as they are now probably wouldn't be able to live on a planet where Earth it is currently situated relative to the center of the galaxy.\" What is this sentence trying to say? If the galaxy spiral were smaller, but earth stayed at the same distance from the galactic center, then the planet couldn't support life? Do you have any sources on that?"
] |
[
"No, most celestial bodies have a prograde motion, so the force would accelerate these objects outward. However, the Yarkovsky effect is reduced even further on a star, which does not radiate inbound EM waves the same way that solid objects do. Asteroids also expel gases in response to the solar radiation, so that adds force to the heat emissions.",
"I think the bigger issue here is the amount of X-ray and gamma radiation.",
"Are you referring to the concentrations of various elements when you mention the position of the Solar System in the Milky Way?"
] |
[
"When you touch something, do you feel it in your brain or your body?"
] |
[
false
] |
[deleted]
|
[
"Short answer: It's your brain. You can stimulate the brain's sensory parts directly and create \"fake\" sensations that are felt out in the body. ",
"Longer answer: The brain works together with the body to generate your sensory experience. The specialized neurons in your skin translate various forms of touch (pressure, vibration, temperature, pain) into neural signals that travel to the brain and are interpreted there. ",
"The destination in the cerebral cortex for neural signals that have to do with touch on the skin is the ",
"postcentral gyrus",
", also known as the primary somatosensory cortex, or S1. The primary somatosensory cortex has a map of your entire body, meaning that signals from different parts of the body are fed to different parts of the somatosensory cortex. ",
"Here's an image showing that map",
". The guy on the right is called the \"homonculus\", or little man, and he has his parts exaggerated to show which parts of the body take up the most real estate in S1. For instance, the hands have disproportionate amount of space devoted to them because they are so sensitive. ",
"If you stimulate S1 with electrical current, the person will feel something in the part of the body corresponding to the location you stimulated. So touch localization is encoded by the brain using, at least in part, the maps in S1. ",
"Wilder Penfield",
" became famous for doing these kind of stimulation studies on people during brain surgery and mapping out the sensory and motor cortices. ",
"Edited to fix links."
] |
[
"Thanks for the answers. ",
"So really, our brain is virtually creating sensations in a 3D space. If you close your eyes and someone pokes your hand, your brain produces a sensation that would seem to be in that exact spot. It's kind of like virtual reality..."
] |
[
"This is part of your Somatosensory system. Neurons in your body pass feedback to the brain which translates that and lets them know it's feeling something. ",
"Your brain can absolutely mix up feelings. It's actually pretty common. Phantom Limb Syndrome is a phenomenon where amputees will still claim to experiences tactile feelings, usually of pain, where the limb used to be. Wikipedia states that 60-80% of amputees claim to experience some degree of phantom limb. ",
"Your brain can also make up feelings. If you think strongly that you should be feeling something, chances are, your brain will translate that into tangible feedback. Studies show that the brain's imagined pain and physical pain are actually identical, so if you ",
" you're in pain, you ",
" in pain. "
] |
[
"How does the body determine what it is going to be allergic to? And what stage of development does it occur?"
] |
[
false
] |
[deleted]
|
[
"To add to the great points above, the body doesn't determine. It's random chance, genetics, and (bad)luck. Some allergies are mediated by what are called innate immune cells, e.g. Mast cells, that produce histamines (which is why you need anti-histamines). Other allergies/autoimmune disorders are mediated by adaptive immune cells like T-cells. In this case by random combination you produce a receptor (protein) on the surface of these T-cells that can recognize things like Gluten as \"foreign\". This is what happens in Celiac Disease. ",
"Remember, the fundamental function of all of these T-cells is to make an immune response so as to kill \"foreign pathogens\". Normally when you are developing as a foetus/ infant T cells that recognize such proteins as well as proteins made by the own body (\"self\") are killed off to avoid this exact problem. But this process is largely imperfect, and sometimes by chance you have a good number of Gluten-specific T-cells that survive and can later cause the allergy/autoimmunity. Then there is also the issue of \"mimicry\". For eg. Let's say Gluten protein sequence has a partial \"match\" with some other virus' protein. Your T-cells don't know the difference and start attacking your own cells thinking it's the virus. ",
"In all these cases, you have a combination of genetic predisposition and bad luck that can cause it. Hope this helps. Let me know if you need some sources. ",
"EDIT: \nSource 1: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3306175/",
"Source 2: Good examples of Celiac's triggers including antigen mimicry.\n",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3818716/",
"Source 3: Non Ig-E Allergies ",
"https://aacijournal.biomedcentral.com/articles/10.1186/1710-1492-2-2-78"
] |
[
"It is my understanding that mast cells and T-cells are present in most forms of allergic responses, and they are better classified as IgE vs non-IgE responses. Am I missing something?"
] |
[
"Correct me if I'm wrong but I believe it works by your immune system attaching to 'Invaders'. A leaky gut would be the most common place through which we get the stuff in. With about 70% of the immune system around the gut, it is the first place where particles are detected that don't belong in the body. With a bad digestion and leaky gut you get particles in that otherwise would never be able to enter. The immune system will develop binding proteins to tag the foreign particles. The tag is like a key for a lock, unfortunately some of these locks look very similar to other locks (cells/proteins that are part of our own body) so they get tagged too. The immune system then distroys the tagged elements. Not all allergies are noticed though. I also don't know why but sometimes there is also a delay of a couple days in reaction.i believe it depends on what part of the immune system is responsible (igg, igf etc..)\nNot a very sciency explanation but that is what I've understood so far."
] |
[
"Why are there so many differences (racially, linguistically, etc.) between India and China?"
] |
[
false
] |
For countries that are so close to each other it seems odd that the racial differences are so pronounced. Does it have to do with the mountains dividing them?
|
[
"The Himalaya Mountains separate India from China. That mountain range is ",
". It is easier to cross oceans than the Himalayas."
] |
[
"We both speak a phonetic language, have similar diets, and they have intertwined history. India and china really have none of those in common not even a war."
] |
[
"Melanin/Race falls under Biology",
"Linguistics falls under Soc./Poli-Sci/Econ./Arch./Anthro./etc"
] |
[
"[Physics] What is the highest angle from the horizontal a standard road automobile (IE: Honda Accord or something similar) can drive up without sliding down or flipping?"
] |
[
false
] |
I'm aware there are a lot of contributing factors (coefficient of friction, tire quality, material of the road being driven on) but if there's a somewhat general answer, I'd love to hear it.
|
[
"You can do a loop without flipping:",
"http://scienceblogs.com/dotphysics/2009/08/31/5th-gear-loop-the-loop/"
] |
[
"This is a good point that displays the complexity of the question."
] |
[
"There are a number of factors in play here that I don't see being addressed. A car's traction is based on friction between the tires and road. This, in turn, is based on the vehicle's wheel size, the coefficient of friction between the tires and road, and whether you've already lost traction or not (Wheels spinning vs. gripping on the ground changes the coefficient of friction). Due to the coefficient of friction being a factor, you must also consider what the road's comprised of, whether it's rained recently or been sealed, etc. The wheel size is important because it defines how big an area the vehicle's weight is distributed over, therefore how much force is applied at a given point under the tire. For example, if a car has wheels twice as wide, there's half as much force per unit area under the tire, with all else remaining constant.",
"So we have a specific road material under constant conditions with a given wheel size and number of wheels, and given tires. This gives you your available traction on a flat plane. If you multiply the vehicle's weight by the sine of the road angle, with a large enough angle the road traction will be less than the weight, and you'll slide.",
"If the vehicle's engine is underpowered, you'll have difficulties which may include rolling backwards while in gear before you cross that threshold, but that depends on a number of factors internal to the car. ",
"If the vehicle is front wheel drive, due to the weight distribution on the axles on a slope the drive wheels will have less traction than the rear, and you may lose traction earlier than the above estimate.",
"Whether or not you'll tip over depends on the vehicle's center of mass, and the physical dimensions between the COM and the point at which the rear tires contact the ground. If the slope is large enough that the COM is more than 90 degrees (directly) above the contact patch, you will flip over. COM should also include the mass and position of all passengers etc. ",
"You may be able to look up your car's center of mass specifications. Generally speaking, cars have a lower COM due to lower ground clearance and design differences. Trucks tend to have more ground clearance and different structure, and typically have a higher COM.",
"I'm offering a lot of generalities here, but some googling should supply you with the hard data you'd need to prove this for yourself. Your question seemed theoretical to me, so I've responded in kind."
] |
[
"What's new in Fluid Dynamics?"
] |
[
false
] |
I'm an undergrad applied math major and a professor recently sent me a link the DARPA's 23 Mathematical Challenge questions. Question #4 was looking for a fluid mechanics for the 21st century. The problem description implied the limits of the classic Navier Stokes Equations in dealing with things like foams and liquid crystals. Are researchers trying to develop a new unified fluids theory? Does the classical study of fluids really break down theoretically, or is it just a matter of not being able to solve the equations? Also a questions about the researchers themselves. I know fluids is kind of a cross disciplinary subject, but what departments are pushing this sort of research, is it mainly Math, or physics, or ME departments?
|
[
"I work in a field called nanofluidics where we study the behaviour of fluids in regions under 100 nanometers. The whole field is only about ten to fifteen years old. This is related to microfluidics and the \"lab on a chip\" paradigm.",
"Before that I studied the dynamics of oscillating bubbles, which is also fluid mechanics. A lot of complex simulations go into modelling two phase systems like bubbles in water.",
"Before that I studied perfect fluid solutions to Einstein's equation, which involves fluid mechanics but not so much as it involves general relativity."
] |
[
"How did you define a bubble? Was any bubble shaped interaction between two fluids fair game? i.e. letting out a breath under water, or maybe olive oil and water. Or were you more concerned with soap type bubbles?"
] |
[
"I was keeping them spherical. A spherical cavity of gas inside a liquid. ",
"This does not have to be the case",
". The bubbles I was studying were very small so surface tension forces dominated."
] |
[
"How do bacteria gain immunity on antibiotics?"
] |
[
false
] |
I read that microbes can and will be able to adapt immunity to antibiotics at a matter of time. Is this also the same at alcohol and soap?
|
[
"Good explanation but there are a few errors.",
"Bacteria that are already resistant to antibiotics are present everywhere, even on your hands right now. Using antibiotics kills more of the non resistant strain allowing the resistant strain to dominate.",
"Bacteria can evolve to have anto biotics resistance but that is a very rare event. A new mechanism may emerge in the near future but that is very unlikely. All the antibiotics we have today have already existed for thousands of years so have the corresponding resistance genes in the bacteria.",
"Bacteria are not antibiotic proof. Resistant bacteria will still die but are just not as susceptible. So taking anti biotics reduces the viability of both resistant and nonresistant bacteria allowing your immune system a better chance of winning over the infection. If this was not the case, taking anti biotics would be completely useless and it would just replace non resistant bacteria with resistant ones.",
"There are bacteria that are somewhat more resistant to alcohol and other bacteriacidal agent like triclosan and chlorhexidine. What happens is that they have some mechanism to pump out unwanted distances. They make it a little harder to kill them but ultimately bacteriacidal agents destroy the physical structures of bacteria so that's pretty much no way to become resistant against it like they do with anti biotics"
] |
[
"Thanks for explaining!",
"I'm not sure if that's beneficial and I don't know if there is any research about that because the effect of soap/sanitizer works so damn effectively against almost every variety of bacteria. So weakening the concentration/potency of the soap is basically just testing \"how can we mix our soap efficiently so that it can still break the cell wall of these bacterias?\""
] |
[
"So bacteria have 2 ways of storing their genetic information: the chromosome, in the nucleoid region and plasmids scattered throughout the cytoplasm.",
"By using antibiotics, we are basically exerting evolutionary pressure on the bacteria in question. Through random chance, some individuals possess mutations that shield them from antibiotics and therefore survive. Since bacteria show not only lateral, but also horizontal gene transfer, they can basically \"hug\" each other and exchange useful information stored in their plasmids, or even pick up useful skills from dead bacteria, quickly spreading immunity throughout an entire population.",
"We already know alcohol-resistant bacteria, and by using soap and hand sanitizers, we are exerting evolutionary pressure on them, so yes, it is plausible."
] |
[
"Are there any substances that can induce a delayed mental illness state when exposed to?"
] |
[
false
] | null |
[
"What do you mean by \"mental illness state\"? Many recreational drugs including alcohol take some time to \"kick in\" to have metal effects"
] |
[
"Akin to exhibiting a schizophrenia or bi-polar where there was none previous to exposure"
] |
[
"Not really, no. The closest might be some drugs producing auditory hallucinations perhaps."
] |
[
"Do bigger cars have an advantage over smaller cars when the driver hits a deer?"
] |
[
false
] | null |
[
"I couldn't find the height of the CR-V grill so based on the picture and height of the tire (215/70R16 is 27\" tall) it looks to be around 40\". White-tail deer shoulder height is 21\" to 47\". The CR-V would hit the body of the tallest deer, and the altima would hit the legs and probably end with the deer through the windshield. "
] |
[
"You could look at this from a simplified conservation of momentum point of view.",
"Basically, the heavier the car you're in, the less you are going to slow down after hitting the deer. Assuming it's over the same amount of time (Which has a lot to do with how much the hood of the car compresses, and some other factors) the bigger car would experience a lower acceleration, which would tend to mean a lower risk of injury. ",
"On a frictionless surface, a 1000 kg car going 40 mph would slow down to ~36.4 mph after hitting a 100 kg deer, while a 2000 kg car going 40 mph would only slow down to ~38.1 mph. ",
"You can model this with (mass of car) x (initial speed of car) + (mass of deer) x (initial speed of deer*)= (mass of car + deer) x (final speed of car) assuming the collision is inelastic. I'm also assuming that the deer isn't moving at the start. ",
"Of course this is a very simplified scenario, and the real answer depends a whole lot of other factors that would vary from car to car, but I think that in general you would be safer in a larger car. "
] |
[
"head on? who hits deer head on? you smack them in the side."
] |
[
"Why is botulism toxin (botox) able to be injected despite being so incredibly toxic to humans?"
] |
[
false
] |
Also, what makes it so potent compared to other compounds like Sarin or VX?
|
[
"Part one of your quesition: It is injected in very very dilute concentrations, into peripheral facial muscles.",
"To answer the second part of your question:",
"Sarin and VX are chemical warfare nerve agents. Botulism is an organic compound [Edit: meant to say toxin]. [edit: Nerve agents are organic as well, but synthetic].",
"Since the effects of Botulism were already somewhat explained by Alexander, I'll tell you about nerve agents, since that is something I am a bit more familiar with.",
"Nerve agents work as acetylcholinesterase inhibitors. Acetylcholine is sent from nerve transmitters to nerve receptors telling whatever muscle they are attached to fire or activate. Then acetylcholinesterase \"clears it out\" stopping the nerve impulse. Nerve agents inhibit this action by \"blocking\" the acetylcholinesterase (by forming a molecular bond with it) from performing their functions. This why typical nerve agent symptoms include twitching, tingling, runny nose, lacrimation, self urination and defecation, convulsions and death. The muscles continue to receive the impulse, because the acetylcholine was never removed.",
"This was kind of an over-simplified explanation, but I hope it helped some.",
"The potency is determined by LD50 or the dose necessary to be lethal to 50% of the unprotected affected population. The amount of nerve agents that need to be absorbed, while fairly minute, to cause death in the average person is significantly less [edit: that should say more...] than the amount of botulism needed. As to the exact reason for this, I can't really say without layman speculation (which I am about to do). I would assume the amount of a specific nerve agent needed (although minute) to cause enough effects to cause death is less [edit: more... again] than the toxin, as long as the toxin makes it to the heart and lungs where it has a paralytic effect.",
"As an aside, Soman is by far the scariest of the nerve agents. It ages, or bonds to the acetylcholinesterase extremely quickly, making most of the standard nerve agent antidotes fairly ineffective unless administered immediately.",
"Edits: I was tired and miswrote a few things. fixed in brackets."
] |
[
"It's not just the dose, it's also the distribution. Botox is injected locally to exert its desired paralyzing effect. Injecting botox into the bloodstream would result in a much more deleterious outcome. Lidocaine would be another example. Inject it locally, fantastic anesthetic. Administer it systemically, and it acts as on the heart as an antiarrythmic. "
] |
[
"It's the dose that makes the poison. Nicotine, atropine, and scopolomine are nasty poisons at doses that mean you wouldn't want to eat the nightshade family plants they come from. But we use all of those drugs medicinally, albeit at much lower doses."
] |
[
"Why does a sugar-free energy drink actually taste sweeter than a regular energy drink?"
] |
[
false
] | null |
[
"Sugar-free drinks contain artificial sweeteners (for example aspartame or stevia). If these are present in sufficient quantities, the drink will taste sweeter than its sugar-containing equivalent."
] |
[
"No, on the contrary. The sweetness of a drink doesn't determine how (un)healthy it is. In general, sugar has a number of known negative health effects, affecting risk of obesity, diabetes and dental issues.",
"Artificial sweeteners don't have those effects on health. Artificial sweeteners are considered food additives and are therefore regulated by (supra-)national health / food-safety agencies (EU: EFSA, US: FDA). While there have been some that are worried about negative health effects of artificial sweeteners (primarily aspartame), scientific studies have yet to find conclusive evidence that validates these concerns."
] |
[
"No, on the contrary. The sweetness of a drink doesn't determine how (un)healthy it is. In general, sugar has a number of known negative health effects, affecting risk of obesity, diabetes and dental issues.",
"Artificial sweeteners don't have those effects on health. Artificial sweeteners are considered food additives and are therefore regulated by (supra-)national health / food-safety agencies (EU: EFSA, US: FDA). While there have been some that are worried about negative health effects of artificial sweeteners (primarily aspartame), scientific studies have yet to find conclusive evidence that validates these concerns."
] |
[
"Does binocular dysfunction also cause loss of 3D thinking, and not just stereopsis?"
] |
[
false
] | null |
[
"By 3D thinking do you mean something like mental rotation? If so, then the answer is no (",
"Klein, 1977",
"). People can get spatial and depth information from other cues."
] |
[
"Always makes my day to see my supervisor get referenced in the wild! I had no idea he had written on this topic. Coincidentally we're currently stewing up a study on depth effects in a Posner-esque cueing task."
] |
[
"I mean... what you're basically asking is, \"if someone has no senses that can perceive in three dimensions*, will they lack an ability to ",
" in three dimensions?\"",
"The answer is that we don't perceive in three dimensions. Our eyes perceive in two dimensions, which we then manipulate to give an illusory composite that approximates seeing in three dimensions. Our brains then stitch those experiences together with other experiences to perceive three spatial dimensions and a temporal dimension, giving us a perception of a four dimensional universe.",
"The brain is not somehow incapable of doing what it was built to do just because you took a sense away. We're still intelligent beings who understand the world IS three dimensional spatially and thus we can mentally put together lots of, say, monoptic views of the world to give a mental three dimensional image."
] |
[
"If you mix pure Hydrogen and pure Oxygen, do you get Water or Hydrogen Peroxide?"
] |
[
false
] |
Since both Hydrogen Peroxide and Water and composed of both H and O, would you end up with one or the other? or would you have both becoming products of the reaction?
|
[
"In a combustion reaction between hydrogen and oxygen, water is the product, as it is the lower energy product compared to hydrogen peroxide. Even if hydrogen peroxide is formed, it will decompose into water and oxygen."
] |
[
"See ",
"the Wikipedia page",
". The method either involves the use of other compounds, or the use of a catalyst to avoid the high energies associated with combustion."
] |
[
"Hey thanks bud. So since combustion is the reaction for water, what method would a chemist use for H2O2?"
] |
[
"Could I go far enough underground to survive a wayward gamma ray burst?"
] |
[
false
] |
If a nearby star went nova and splashed Earth with a wash of gamma rays, could I find a mineshaft and survive? I realize the likelihood of such an event occurring is low and all that jazz.
|
[
"No. This is because the gamma ray burst wouldn't ever directly affect you even if you were standing outside at the time.",
"The problem is that they would cause a chemical reaction in the upper atmosphere changing molecular nitrogen into nitrogen oxides, depleting the ozone layer and exposing the surface to solar and cosmic radiation. This would affect phytoplankton and reef communities, severely impacting the marine food chain.",
"So finding a mineshaft isn't going to protect you from starvation."
] |
[
"I'm not 100% sure that Phage0070 is correct about gamma rays from a ",
" supernova not making it through the upper atmosphere, although he very well could be. I tried to do some rough calculations to check his assertion but I got lazy when the numbers I needed weren't conveniently available. I happen to be studying the physics behind your question as part of a detector course in my PhD, so I will endeavour to introduce you to it:",
"There are three ways photons can lose energy as they pass through matter:",
"1) ",
"The photoelectric effect",
"2) ",
"Compton scattering",
"3) ",
"Pair production",
"For energetic photons (such as gamma rays), pair production is the dominant process and you can relate the intensity of a beam of photons that has travelled some distance x through a material to its original intensity via a decaying exponent: e",
", where mu is the absorption coefficient of the material. This is where my back-of-envelope calculations fell apart, as I'm not sure what the absorption coefficient of the upper atmosphere would be, nor am I sure what a reasonable intensity is for gamma rays from a local supernova! ",
"In any case, it seems to me that a sufficiently intense gamma ray burst could get through the upper atmosphere. The same argument goes for hiding in a mineshaft, although I can only imagine the absorption coefficients of soil and rock are higher than that of air/the upper atmosphere, so if you go deep enough you should be able to avoid the gamma rays.",
"Interestingly enough, we did briefly discuss how to survive a supernova in my class (you can't), and the bad news is that for a \"local\" supernova, the intensity of extremely energetic neutrinos output by the supernova is so high that even if the gamma rays don't kill you, the neutrinos will.",
"Edit: Typos, clarity."
] |
[
"This is the type of thing you can look up in the particle data book. ",
"Dry air has a radiation length",
" of about 300 m at 1 atm. The density will be lower at higher altitudes, so the radiation length will be higher but let's just keep that in mind for now.",
"The mean free path for a high energy gamma ray to pair produce is 9/7 of a radiation length. So let's say 400 m. Now, you can go up about 5 km before the density of air is halved. So, since the thinner air means a longer radiation length, we've got roughly 10 mean free paths, just from the air closest to us.",
"That means something like 50 out of every million high energy gamma rays will make it through the atmosphere. The rest are going to pair produce and make EM showers."
] |
[
"Did eyes evolve only once on Earth? Is there something about the small band of \"visible\" light that makes it optimal for eyes to evolve to see? Or is it just a coincidence that most animals see in the same spectrum?"
] |
[
false
] |
I have heard of animals that see infrared & ultraviolet. But they all see (or so I think) the same frequency of light we see. Would an alien eye be more or less likely to see nothing in our "visible" band of light because it sees a higher or lower frequency? If eyes evolved once, it may be that the commonalities are just happenstance and not due to some inherent quality about the small band of frequency of light we can see.
|
[
"\"eyes\" evolved independently in an enormous number of species.",
"Or more accurately, the basic parts of an eye developed waaay long ago in the species that formed the base of a lot of different genetic trees.",
"Long before the dinosaurs, or before most mammals existed.",
"And this has to do with what the most basic form if the eye is, a cell that can determine light from dark is to most people an \"eye\" and that has evolved near the base of almost every family tree.",
"It evolved because the sun is the basis of almost all life on Earth.",
"From that simple beginning most animals have developed eyes as at least a secondary sensory organ.",
"But those eyes are well different from each other, some only see certain colors, some see movement, some work in low light, some are farsighted etc etc.",
"The basis of all of them is pretty similar, because the base evolved we'll before \"human\" and \"cat\" evolved to be separate.",
"The original mammal had something that we might recognize as \"eyes\" and those formed the basis of what all the mammals (well, the vast majority) would modify into the eyes they have today."
] |
[
"Great answer. The Sun gives off most light in the visible spectrum ",
" water (where most early animals lived) is transparent in the visible spectrum."
] |
[
"You're a bit confused as to what \"frequency\" means. Frequency is the reciprocal of wavelength, and we use wavelength for light, because frequency is very clumsy when you get into petahertz.",
"Visible light runs from roughly 800 nanometers to 450 nanometers. As light gets shorter wavelength (higher frequency) it becomes more energetic, to the point where UV is energetic enough to be mildly hazardous in natural doses.",
"A human retina can see near-ultraviolet (to about 390 nm), but it's filtered out by the lens and cornea. People who've had their lens replaced can see some of the patterns in flowers invisible to the general population.",
"Visible light has a very special place in the EM spectrum, so biology, even alien biology, would probably use it somehow. It's short enough wavelength to resolve fine detail, most gases and liquids are transparent to it, but it's not energetic enough to cause chemical damage to a biological detector (e.g. a retina). These are the result of laws of physics, which are the same everywhere.",
"Infra red is absorbed quite strongly by many chemicals by vibrating their bonds (IR spectroscopy works this way), including chemicals in the air and water, so it doesn't pass through air or water very well. Ultraviolet is not only hazardous, but also exhibits very extreme scattering in air. In the same way the sky is blue due to Rayleigh scattering of blue light, UV is scattered even more. This is why insects (and hawks) use it only for relatively short range vision: UV has a lot of \"glare\" about it thanks to atmospheric scattering.",
"Light in biology is so useful that photoreceptors evolved multiple time (even plants have them) although all true eyes in vertebrates have the same ancestral structure. It's so useful it was never lost but at the genus level in specific habitats, like blind cave fish."
] |
[
"How does radiation cause cancer?"
] |
[
false
] |
I've been reading about Chernobyl and it made me wonder. Also, how does it cure cancer? Are there different kinds of radiations? Thanks
|
[
"Ionizing radiation damages DNA. When DNA is damaged, 1 of 3 things can happen.",
"1) The DNA damage is repaired, and the cell returns to normal",
"2) The DNA damage is unrepaired, and the cell dies.",
"3) The DNA damage is unrepaired, but the cell survies with altered (mutated) DNA.",
"In normal cells, the most often result is 1 - DNA is repaired. In cancerous cells, since they are dividing very rapidly, they are more likely to be in a phase of the cell cycle where DNA damage is difficult to repair. This is why radiation preferentially kills cancerous cells.",
"Number 2 is called \"acute\" damage. It usually results cell death within hours or days. When we deliver radiation to a tumor, we are giving enough radiation to trigger acute damage to the cancer. ",
"Number 3 is a much more rare event, but it can happen in any cell, cancerous or not. These mutations are what leads to cancer developing, if those mutations are in genes that control cell division or other related factors.",
"So radiation can treat cancer due to the acute damage it causes to dividing cells, but it also has a chance to alter the cell instead of kill it. "
] |
[
"Thanks so much, and finally one of my askscience questions got answered. That makes sense what you said and it's makin me want to do more reading up on it. Thanks askscience"
] |
[
"You can try ",
"a quick search",
" as well to show the many times this question has been asked and the excellent answers those questions received."
] |
[
"Can elephants breath through their mouth ?"
] |
[
false
] | null |
[
"Yes! Elephants can and do breathe through their mouths, just as most other mammals do.",
"Human newborns (can after a few months but prefer to use nostrils even after, comment below with source), horses (unless there are issues, see comment below), rodents and rabbits cannot, for example. They are referred to as obligate nasal breathers (human babies are a weird category here). ",
"Elephants can also breathe through their trunks and do this while swimming, keeping their mouths closed. I knew this but finding a source to back this up was surprisingly difficult. Here we go with the textbook ",
".",
"A few articles about elephant breathing and their respiratory systems:",
" - Science Daily",
" - BBC News",
" -Eureka Alert",
"Edit - A few people asked about horses and rabbits, I have links in my replies to their comments below. Please check those out before asking the same question again."
] |
[
"Just want to say that it’s awesome that you took your time to search and site your sources. Thank you!"
] |
[
"You should never just take someone's word for it, and it's part of the sub-rules. :) ",
"I'm happy to find sources, I ended up reading a lot about elephant anatomy in the process. For example, they do not have a pleural cavity as most mammals do. The pleural cavity allows lung volume to change with the thoracic cavity volume. An elephant's lungs are actually attached to the chest wall, so inflating the lungs is reliant on chest musculature not negative pressure like our lungs. ",
"While I knew the basics, this deep dive has been an excellent learning experience for me as well!"
] |
[
"It looks as though new SSD technologies will be nearly as fast and durable as DRAM. Can we expect fundamental changes to how operating systems handle storage as a result?"
] |
[
false
] |
An awful lot of the way we work with data seems to be built around the concept of slow serial IO; read()ing records into buffers a chunk at a time, rewinding file pointers, etc - as it has been since the days of magtape. What happens if and when it's safe to assume that all your data is random-access and equally fast; when the file the buffer, and there's no advantage to copying it out? Do you foresee a day when file pointers are just pointers? Will we be executing code directly off 'disk'? Will exec() become a JMP? It strikes me that there's a hell of a lot of potential optimisation there, though it would involve some serious ripping-up of paradigms. I'm not even sure the concept of filesysystems as we know them makes a lot of sense in that context... Is this something anyone's currently pursuing, or is it fundamentally a Very Bad Idea?
|
[
"Hm. Intel are claiming that their new '3D Xpoint' nvram is 1000x more durable than current offerings, and 1000x faster also.",
"The cheeky buggers made a prototype SSD in a DIMM form factor... which is what prompted my question.",
"Thanks for the info on XIP; that's just what I was after."
] |
[
"As far as I know SSD durability is going the other way.",
"But it does seem like the move towards SSDs is moving us towards the times before mag tape where everything was in memory. SSD could eventually be regarded as an extension of memory space.",
"It seems as though people are already experimenting on what's called execute in place with SSDs ",
"https://en.wikipedia.org/wiki/Execute_in_place",
"Also, I assume, for embedded applications, devices like GPS, or other similar devices have been working this way for probably a decade or more.",
"One thing that sticks out is the emphasis on filesystem journaling, which as far as I can tell is made obsolete on an SSD. The purpose of the journal is to arrange the filesystem log so that it can be read sequentially. Something that serves no purpose on an SSD that I can see. It's just a waste of space, write cycles, and other resources."
] |
[
"It's been possible for a long time to use normal pointers when writing to files. Using mmap you can map a file to a memory area and write to it using pointers.",
"\n",
"https://en.wikipedia.org/wiki/Mmap",
" ",
"There will most likely be something like a file system in the future also. Sharing files between applications requires some function to locate files, and that is the file system. It may not look exactly like it does today though."
] |
[
"Is there a physical limit on how big a kite could be?"
] |
[
false
] |
Would the mass of the kite eventually be unable to be supported by the wind?
|
[
"The biggest kites I have heard of are used for pulling cargo ships. If the ship is sailing with the wind they can release a kite that is attached to the bow and It helps pull the ship along and get better gas mileage. Google \"Kites pulling ships\" or just check out some of thes pictures and Diagrams.",
"http://www.sott.net/image/image/5865/Kite-ship.jpg",
"http://inhabitat.com/transportation-tuesday-wind-powered-cargo-ship-takes-sail/wp-content/blogs.dir/1/files/beluga2.jpg",
"http://assets.inhabitat.com/wp-content/blogs.dir/1/files/2011/03/skysails-2-537x301.jpg",
"http://www.nature.com/news/2008/080208/full/news.2008.564.html"
] |
[
"definition of a kite",
"This reminds me of an apocryphal story about a paper-plane competition: the winner balled up their paper and threw it."
] |
[
"Would the mass of the kite eventually be unable to be supported by the wind?",
"No, not really. Theoretically floating structures can be built of almost ANY SIZE. For example Buckminster Fuller proposed floating spherical cities. ",
" with thousands of people living in them a mile or two wide which would float around the world in the air.",
"And the craziest thing about them is that technically they ",
" work.",
"http://en.wikipedia.org/wiki/Cloud_Nine_(tensegrity_sphere)",
"http://www.alternatehistory.com/discussion/showthread.php?t=242891"
] |
[
"Were there any mp2 files, what about an mp5? Where does the 3 and 4 come from?"
] |
[
false
] | null |
[
"MP2 is MPEG1 Audio Layer 2. The others are:",
"MP1: MPEG1 Audio Layer 1",
"MP3: MPEG1 Audio Layer 3",
"MPEG refers to the Moving Picture Experts Group that developed the various video compression standards in use. Today the most common is probably MPEG4, although there are others in common use as well, like MPEG2 and H.264.",
"There is no MPEG3 and there is no MP5, but there is an MP4a."
] |
[
"To go one further, mp1 is a simplified version of mp2 (computationally more efficient, lower fidelity), and mp3 shares the core psychoacoustic trick to reduce bitrate as mp2 but with higher precision, followed by a second lossy coding trick based on pure mathematics, and the lossy signal is finally compressed using a lossless encoding scheme on top. ",
"Originally mp3 wasn't computationally efficient enough for encoding and decoding for broadcast, essentially it was only good for reducing file size. Eventually purpose built microprocessors for encoding/decoding mp3 got cheap enough that it obsoleted mp1 and mp2. ",
"The actual mp3 algorithm is really cool. It's a combination of psychoacoustics, classic information theory, and a dope math phenomenon. "
] |
[
"A ",
"container format",
", most commonly used to store audio, video, and certain sorts of metadata like subtitles, EXIF tags, still images, etc. It's part of the ",
"MPEG-4",
" specifications.",
"An audio coding format for digital audio, which uses a form of lossy compression. It was defined by the MPEG-1 and MPEG-2 Audio Layer III standards. It builds on the insight that losing some information from an audio stream results in imperceptible differences in playback quality.",
"Another (lossy) audio coding format, which preceded mp3, and was defined by MPEG-1 Audio Layer II and MPEG-2 Audio Layer II standards. See ",
"here",
" for a high-level description of how it works.",
"A simplified version of MPEG-1 Audio Layer II, for applications which can tolerate lower compression efficiency (i.e. higher storage requirements) in exchange for a less complex (and thus possibly faster) (de-)compression algorithm. The concerns behind the creation of MPEG-1 Audio Layer I are now obsolete."
] |
[
"Is there a genetic upper limit for size? For example, can we selectively breed largeness in dogs to get them to the size of bear?"
] |
[
false
] | null |
[
"An organism's size is determined by its growth rate, the rate at which certain structures like growth plates ossify & fuse, and the ability of its body to handle the biomechanical and nutritional stresses of a larger size. Really large animals need much stronger hearts to deal with the increased circulation required, stronger bones and muscles (obviously), and a lifestyle that allows it to obtain enough nutrients to sustain its massive body.",
"In principle there's no hard reason why a dog couldn't be bred to be the size of a bear. However, it would require a lot of novel mutations and a great deal of time. Additionally, the final result would have very different behavioral patterns from their dog ancestors."
] |
[
"Chickens are bred to be extremely large aren't they? To the point where they can barely even support their own weight."
] |
[
"It's not exactly a genetic limit in a hard sense, but dogs can't be bear sized, because their various organs and nits are meant to be a certain size. Above a point, pumping blood becomes difficult without the sort of adaptations and changes you would find in other animals of a comparitive size.",
"You can see this in humans. Particularly tall and large people have a lot of joint problems and a higher tendency for heart problems.",
"If you wanted a bear sized dog you would need to do a lot more than breed for some kind of gigantism trait."
] |
[
"How is autism diagnosed in adults? Is it being overdiagnosed?"
] |
[
false
] | null |
[
"The two main reasons that an adult may be diagnosed is that they've had difficulties that have not been identified until that point, for example a person might have an intellectual disability diagnosis but then gets hospitalized as an adult and there is a thorough assessment where ASD is diagnosed.",
"OR the person's ASD is relatively low level, what used to be called Asperger's and they've been functioning for a long time with no diagnosis.",
"Over diagnosis.",
"Kind of controversial, there is a lot of focus on increases in diagnosis over the last couple of decades, but there isn't much evidence of over-diagnosis. In my experience the risk is more for missing a diagnosis there doesn't seem to be a population of non-ASD folk with wrongful diagnosis.",
"Is there any research regarding the pros and cons of being diagnosed?",
"Hard to find research on the topic because how do you objectively assess not being diagnosed right?\n Again in my experience, its highly dependent on the individual(s) and the context. For most people a diagnosis is a relief because it provides coherence for the difficulties the person experiences. I think there is this view among relatively \"normal\" folk that a diagnosis is 'finding out your crazy' whereas a more accurate portrayal is being are suffering or having difficulties which prompt a diagnosis. Don't get me wrong there is stigma still.",
"So the main pros of being diagnosed is having a point of call for a problem, it can open doorways to support and funding and a term to communicate difficulties to others in a helpful way. In the case of ASD this is really useful because once you have that diagnosis it provides a lot of guidance around how to work with it",
"The main cons, are self and other stigma, and that diagnosis doesn't necessarily provide as many answers/solutions as one might hope! "
] |
[
"Autism is now often diagnosed in childhood but there is greater awareness now than there was decades ago. \nAutism is a spectrum disorder - some kids are diagnosed very young, some are not diagnosed until much later.\nIt is not unusual for a child to be diagnosed and then for a parent to recognise the behaviour traits as traits they have, and then the parent to be diagnosed."
] |
[
"Autism is diagnosed usually at a young age of about 1 year old. Symptoms include unusually antisocial behavior, and fits when one day is dissimilar to another, such as a daily routine being ruined. ASD doesn't usually present itself later in life."
] |
[
"Is infinity possible in the real world?"
] |
[
false
] |
I know the concept of infinity is useful in calculations, e.g. limits, but is there any sort of physical measurement or "meaningful calculation" that can yield infinity as a result? By meaningful calculation, I mean one that uses real data from real objects/particles , not a hypothetical spaceship.
|
[
"I know the concept of infinity is useful in calculations, e.g. limits, but is there any sort of physical measurement or \"meaningful calculation\" that can yield infinity as a result?",
"No by definition. Physical measurements can only suggest infinities, they cannot measure them. The reason is that measurements produce numbers, and infinity is not a number.",
"It's easy enough to say, \"this measurement implies infinity.\" But it's not possible to say \"This measurement is infinity.\" Infinity is not a measure of things, it is a notion about things.",
"Another comment:",
"I know the concept of infinity is useful in calculations, e.g. limits ...",
"The limit's purpose is to avoid infinity, not embrace it. The only reason the limit exists is because we cannot treat infinity as a number."
] |
[
"If you have a particle at a point, how many paths can it possibly take to move to another specified point ? You'll find an infinite number of paths, but in practice its impossible to differentiate a lot of these paths because of the limitations of whatever measuring apparatus you use. If we had measuring apparati of unlimited accuracy we could probably find infinites everywhere o_O",
"That made very little sense..."
] |
[
"If the universe if finite (and I'm pretty sure that it is), than nothing that has finite size, mass, etc. can occur an infinite number of times or it would be larger than the universe.",
"You can make intangible things infinite (particle paths, etc.), but nothing physical, that I'm aware of, can be infinite."
] |
[
"Are there any colors that remain difficult to produce as dyes in modern times?"
] |
[
false
] |
In Medieval England, it seems that dark blue, purple, and red dyes were difficult to make because few sources produced the colors. Was that just because these sources didn't exist in England at the time, or are they just naturally difficult colors to produce?
|
[
"I’ve no clue about dyes, but you might find this interesting. ",
"The range of colours produced by any technology is the “gamut”. As I understand it, every tech we have has a gamut that is smaller than human vision, in that, no matter how much you paid for that monitor, there are colours it can not display. ",
"I have to assume that this applies to dyes even more than $30,000 monitors."
] |
[
"Thank you for the info!"
] |
[
"Oh, wow. I didn't think anything like that still existed. Thanks for the info!"
] |
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