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[
"AskScience Cosmos Q&A thread. Episode 10: The Electric Boy"
] |
[
false
] |
Welcome to AskScience! If you are outside of the US or Canada, you may only now be seeing the ninth episode aired on television. If so, This week is the tenth episode, "The Electric Boy". The show is airing in the US and Canada on Fox at Sunday 9pm ET, and Monday at 10pm ET on National Geographic. Anyone can ask a question, but Popular science shows, books, and news articles are a great way to causally learn about your universe, but they often contain a lot of simplifications and approximations, so don't assume that because you've heard an answer before that it is the right one. If you are interested in general discussion please visit one of the threads elsewhere on reddit that are more appropriate for that, such as , in , and in . Please and . We'll be removing comments that break our rules and some questions that have been answered elsewhere in the thread so that we can answer as many questions as possible!
|
[
"Why was the glass block so important in the polarization/electromagnetism experiment?"
] |
[
"More cosmic rays hit near the Earth's magnetic poles than the rest of the planet (hence the auroras usually occurring near the poles). Fortunately the atmosphere stops most of the radiation from reaching the surface. However aircraft flying over the poles can receive significant amounts of radiation, and sometimes when the sun is being more active than usual airlines have to change their routes to avoid dangerous areas. ",
"More info."
] |
[
"Since cosmic rays cause mutations in DNA, and they follow the earth's magnetic field toward the Van Allen Belt, is the spot where it comes down to the earth's surface a dangerous place to be? Can you get cancer if you stay in it too long? Is it a dead zone?"
] |
[
"Can anyone identify this?"
] |
[
false
] |
Approximately ten years ago, I found in a creek bed in Indiana. I've always thought it was a fossil of some kind, but maybe that is just wishful thinking. The cross-section shows structures that do not appear to simply be rock. Perhaps it is some type of worm?
|
[
"You can also try asking at ",
"/r/whatisthisthing",
" "
] |
[
"Check out ",
"/r/fossilID",
"."
] |
[
"My apologies AskScience, this didn't belong here. I reposted: ",
"http://www.reddit.com/r/fossilid/comments/118z9c/huge_worm/",
". Apparently, it's a Rugosa coral."
] |
[
"Is there a limit to the syntactical complexity of languages humans can learn?"
] |
[
false
] |
We're told that babies can learn any human language, but is there a limit to the syntactical complexity of a language? Could I come up with a language so complex that humans are unable to become fluent in it, and if so, does Science have any idea of what those limitations are like?
|
[
"http://en.wikipedia.org/wiki/Ithkuil",
"\n",
"http://www.ithkuil.net/",
"This may be of interest to you. It's a language with essentially no grammatical or syntactic ambiguity. This is achieved through very complex grammatical and syntactic structure. It does, however, apply these rules consistently, so I'm not sure how it would compare to languages like English with textbooks full of rule exceptions.",
"I'm not aware of any fluent speakers.",
"At any rate, clearly there must be ",
" limit to the syntactic complexity of a language learnable by people, since the human mind is finite. The language would have to be ",
" complex though.",
"Also, here's a programming language designed to be impossible to write in. People write in it anyway.",
"http://en.wikipedia.org/wiki/Malbolge"
] |
[
"What an interesting question. I have only some related commentary for you, not an exact answer.",
"Human languages are not arbitrary; the human brain appears to be born with built-in biases that certain syntaxes are okay and others are not. Part of this is called the ",
"language instinct",
". Thus there are correlations that cross most languages. If you wanted to make a language that's hard to learn, you would not just make it complex; you would intentionally violate these human assumptions about what language should be like.",
"That said, it would be trivially easy to create a language \"HardLang\" whose rules exceed the limits of human cognition. For example:",
"In HardLang, the gender of a noun depends on the tense of the 20th-most-recently-used verb.",
"In HardLang, people whose height is an odd number of centimeters must be addressed differently.",
"In HardLang, a completely different dictionary of adjectives applies to each of 200 categories of noun.",
"In HardLang, if the duration of a conversation so far has been an odd number of seconds, adverbs must drop their normal ending."
] |
[
"Personally, I don't think you'd be able to invent a language that no one can learn. language is, after all, simply a set of rules that need to be followed when communicating. Humans are great at learning and adapting to work within sets of rules (normal language, mathematics, etc). It might be extremely difficult for ",
" people to learn, but I doubt you'd be able to invent an ",
"Syntactic complexity can become counterproductive to communication, and so extremely complex languages would not evolve to the point of confusing communication.",
" The irony of my gramatical and syntatic mistakes in this post is not lost on me."
] |
[
"Second attempt. I made an false color image of the moon and asked myself how accurate the data is. [image inside]"
] |
[
false
] |
[deleted]
|
[
"The precise colors you see depend on a lot of things: the atmosphere, the glasses that make up the lenses in your camera/telescope, the efficiency of the detector (and its spatial dependence), the filters, the processing that makes it into a color image, and finally the composition of what you're looking at. ",
"Without calibrating each of those things carefully first, you could still probably distinguish various areas of the moon as having a different composition. If you know the answer beforehand, you might be able to say, \"this is what iron looks like through this system,\" and identify other iron-rich areas, but there's a major complication to that. ",
"The molecular and atomic wavelengths that are the signatures of certain molecules/elements are very narrow. Taking very broadband colors mixes a lot of those lines together, and I doubt you'd be able to differentiate them. So a lot of things that aren't iron could also look like iron through your system. ",
"Ideally, you'd like to take a high-resolution spectrum that has been carefully calibrated all wavelengths, or take narrow band images in particular wavelengths to look for signatures of specific elements/molecules."
] |
[
"I know. Doesn't stay out if you're shooting with a refractor. The question is, does the aberration washes out all the data? "
] |
[
"I know. Doesn't stay out if you're shooting with a refractor. The question is, does the aberration washes out all the data? "
] |
[
"2 x Tesla: 1) How feasible and safe are Tesla's ideas for wireless electricity? 2) How much truth is into that particle beam weapon?"
] |
[
false
] |
[deleted]
|
[
"Tesla, of course, wasn't concerned with such issues, as his plan was to give away electricity for free.",
"Also, regarding the ionosphere stuff, afaik he was merely using the ionosphere to effectively complete the circuit with the ground, not as some magical energy source."
] |
[
"The example of wireless charging is already in use. Over very short distances for very small loads, it's a convenience. Anything farther than that and it becomes a power sucking parlor trick. (not a problem when you're Tesla and have your own generators.)",
"As for particle beams, it suffers from the same basic problem. When using radiation as a weapon, increasing the distance to target increases the energy needed exponentially. It's probably possible (to some degree), but not efficient or useful. Remember that plane that fires a laser? It took 10 seconds of tracking a standstill car just to set its engine on fire. The plane could only fire it once per flight."
] |
[
"There is a whole Hell of a lot of hassle embedded in that \"simply\"."
] |
[
"Should we deposit radioactive waste into the ocean trenches instead of trying to bury it in mountains and caves?"
] |
[
false
] |
My understanding is that the continental drift zones have areas where new 'surface' (even if underwater) is created and old surface is destroyed (subduction). Would it make sense to deposit the radioactive materials into these subduction zones where they will be pulled into the circulating magma? It takes these magma flows millions of years before they resurface. They are exposed to the higher radiation levels of the inner mantle while circulating under the earth's crust.
|
[
"While maybe that would help with the super-long term problem IF it survived long enough to be pulled under (maybe a geologist can tell us how long that would take), the problem with this that jumps out to me is corrosion. If you keep the waste underwater, you're risking corrosion over 10's to 1000's of years, which could release material into the oceans.",
"We need to keep the stuff secure over ",
" times, but maybe ",
" times are not so relevant."
] |
[
"Problems include:"
] |
[
"It is not about the radiation getting past the water.",
"It is about the radioactive materials themselves being carried by prevailing currents and entering the ecosystem."
] |
[
"Why did Eris, the dwarf planet that caused Pluto to get demoted, only get discovered in 2005?"
] |
[
false
] | null |
[
"Are these things just too dim?",
"Yes. Although Eris is the same size as Pluto, it's more than twice as far from the Sun. So not only does it have much less sunlight to reflect, it is much farther from Earth. That made it much dimmer and more difficult to find than Pluto.",
"instead of being able to look directly at it",
"We may be able to photograph planet 9 with one of the world's largest telescopes, but we don't know exactly where it is, so we have to search for it. The sky is big, the planet is dim, and time on these telescopes is limited so the search may take years."
] |
[
"I don't know for a fact but I'd guess it would be due to its ",
"highly eccentric orbit",
". Most of the time it's also further from the sun than any other planet in the solar system, and not on the same plane as the rest of the planets, so you just wouldn't know where to look. Anything smaller than a major planet is really hard to see unless you look directly at it (i.e. already know exactly where it is)."
] |
[
"You might be interested to look at it in terms of angular diameter, which in this context you can think of as how wide a body appears to be in the sky; how much of the sky that body takes up.",
"The Sun is 31′31″ – 32′33″. There's 60 arc seconds (″) in an arc minute (′) and 60 of those in 1 degree, so the Sun takes up about half a degree in the sky. ",
"The Moon is reasonably the same size as you can imagine from looking and from eclipses.",
"Pluto, on the other hand is a tiny 0.065″ – 0.116″, that's a fraction of a 60th of a 60th of a single degree of the sky! The bigger variance is because the distance between the Earth and Pluto is obviously much more variable when compared to the Sun or the Moon.",
"Eris? 0.034″ – 0.089″ - half the apparent size again of Pluto!",
"Planet Nine, hypothetically would be something like 0.015″ – 0.18″. ",
"These things aren't just small, they're really, really, really small."
] |
[
"I read in my astronomy textbook that our observable universe is 14 billion light years. Does that mean 14 billion light years in all directions?"
] |
[
false
] |
[deleted]
|
[
"1) The Big Bang happened here. It happened in Andromeda. It happened in the most distant galaxy we can see. It happened everywhere. It was not an explosion somewhere in space sending galaxies in all directions; it was, and still is, expansion of space itself between the galaxies. The universe is evenly filled with stuff everywhere and always has been (there's no void into which matter is streaming; absolutely everywhere in the universe looks pretty much the same), but the distance between those galaxies increases. ",
"2) Subject to the caveats below, yes. ",
"3) Subject to the caveats below, yes. ",
"4) I've used ",
" in my basic astro classes and I know for a fact it doesn't say that. You're misreading something. In fact we know the universe must extend very far past the observable limit, perhaps even infinitely far. ",
"Caveat: the distances you're quoting are light-travel distances, i.e., distances measured by determining how long it takes light to get to you. Cosmologists actually use metric distances, defined as the number of meter sticks that would fit between you and the object in question. In general relativity, these two methods of describing distance will not yield the same results. So you may see various sources, including other answers here, quote different numbers for the radius of the universe. The reality is that even simple concepts such as distance become difficult and ambiguous when dealing with an expanding universe. "
] |
[
"Saying that there's nothing to see is different from saying that there's nothing there. There's certainly something there; we just can't see it, since light has not had time to get to us yet. "
] |
[
"I read in my astronomy textbook that our observable universe is 14 billion light years.",
"About 14 billion ",
", yes. Not 14 billion light-years wide in radius.",
"Does that mean 14 billion light years in all directions?",
"The short answer is, no, it doesn't. Explaination coming.",
"1)Are we assuming the big bang occurred where we currently are?",
"No, and in fact the big bang didn't occur in any one place, it happened everywhere in the universe simultaneously. It wasn't like an explosion which happened at one point and then everything moved outwards from there. Rather, it was like all of space was really dense and small, and then suddenly it inflated super fast and was suddenly not so dense and very large.",
"More specifically, the expansion that the universe went through is called a \"",
"metric expansion",
"\" and not an \"inertial expansion.\" In an inertial expansion (like a conventional explosion), things near the center gain kinetic energy and move outward inertially from the center. There is a shockwave that propagates out, and the density can't remain uniform. But in a metric expansion, all distances increase simultaneously and the expansion is not due to inertia but rather due to the scale factor of the universe as a whole changing, uniformly.",
"2)If you were to theoretically travel 14 billion light years in one direction, would you not then be 28 billion light years away from the other side of our observable universe?",
"No, you wouldn't, because the universe expands over time and so what ",
" 14 billion light-years of distance became even larger, as time passed.",
"4)If 3 is true, then how can the textbook say that there is absolutely nothing more than 14 billion light years away from us? ",
"If your textbook actually says this, then ",
" (or at the very least, outdated).",
"And actually I am not sure but I have a hunch your textbook is right and you are just reading it wrong.",
"The ",
" of the ",
" is about 28 billion ",
", not light-years. That is equivalent to about 93 billion light-years. I suspect this is where you got the \"28 billion\" number from; it's not just 14 light-years times 2, it's a number with a totally different unit.",
"So, how can this be? How can only 13.8 billion years have passed but our observable universe has a radius of about 46 billion light-years? If light can only travel 1 light-year per year?",
"The answer is expansion. The universe expands metrically (meaning ",
"). For example, let's consider the observable universe when it was only 1 billion years old. And take two objects which are, at that time, separated by, say, 1 billion light-years. Let's say these objects are initially at rest with respect to eachother (which won't actually be the case, but this is an example). If they are at rest together, then they are not expanding inertially away from eachother. But, the universe is still expanding metrically. Which means after some more time has passed (say, 2 billion years), those two objects which were initially at rest are now even further apart than they used to be. They aren't 2 billion light-years apart, but they are more than 1 billion light-years, and they ",
". No forces acted on those objects to drive them away from eachother -- they just ... got further away ",
". In metric expansion, it is the ",
" (called the metric) which increases.",
"So light may have actually ",
" a total of 14 billion light-years since the big bang, but during those 14 billion years, that distance increased metrically from 14 billion light-years to about 46 billion light-years. So even though the light only ",
" 14 billion light-years of distance, it is now farther away than the distance it travelled, because the distance it did travel has expanded.",
"Hope that helps! I strongly recommend you read the Wikipedia article on the ",
"metric expansion of space",
", you will probably find it interesting."
] |
[
"Does the total surface area of two submerged air bubbles remain the same if they merge?"
] |
[
false
] | null |
[
"No. Volume scales with the third power of the radius, while surface area scales with the square of the radius. Merging two bubbles will create a bigger bubble, but the surface area will be less than the sum of the two original bubbles.",
"EDIT: there are some more complications I guess, like the tension in the bubbles being different in a small and a large bubble, but these secondary effects should be small compared to the main mathematical idea."
] |
[
"Solve volume for radius:",
"Plug that into the equation for area:",
"Since we’re interested only in proportionality, a constant ",
" can be defined as 4π (3/(4π))",
" and then omitted:",
"Thus, if the volume is ",
", the surface area increases by 2",
" or ",
". In general, this proportionality is true for all arbitrary 3D shapes, not just bubbles.",
"Edit: Replaced “pi” with “π”. Added italics to variables. Added step showing definition and omission of constant. Fixed equation error caught by ",
"u/lukfugl",
". Fixed parenthetical error in third area equation and constant expression. Clarified language in conclusion, omitting confusing percentage. Added ",
"u/PandaGeneralis",
"'s observation of applicability to all arbitrary 3D shapes."
] |
[
"The shape and conclusion of this is entirely correct. But the volume of the sphere is 4π/3 r",
" , not 2π/3 r",
" . This correction disappears into the constant of proportionality (k) though, which is why the conclusion is still correct."
] |
[
"Why is the Fibonacci sequence so prevalent in nature and space?"
] |
[
false
] | null |
[
"The idea that the Golden Ratio and Fibonacci sequence occurs everywhere in nature and human esthetics is regarded by many as a pure myth: See e.g. ",
"this article",
" by mathematician Samuel Arbesman, and ",
"this one",
" by Prof Donald Simanek. ",
"Here's one",
" that debunks some of the claims in music specifically. ",
"In short, it's everywhere because people are insistent on trying to find it everywhere."
] |
[
"The short answer is that nobody's entirely sure. A good guess is that organic growth tends to be governed by the simplest suitable recursive pattern, and simple recursive patterns tend to produce fibonnacci numbers. To give an idea why this is the case, consider ",
"this",
" pattern of algae growth."
] |
[
"It isn't really, it's just that a lot of people attribute it to random things. See here: ",
"http://www.lhup.edu/~dsimanek/pseudo/fibonacc.htm"
] |
[
"What happens at the atomic level when we touch something?"
] |
[
false
] |
Somewhere I read that we actually can't touch, that it's all the repulsion between the negative charges of the atomic electron clouds. This is hard to accept from a macroscopic viewpoint, for example, every machine would be frictionless. I searched to see if this was asked before. It wasn't, but this is a in other sites. Apparently, I don't know how to search Reddit.
|
[
"Appropriate.",
"As to your question, wikipedia says that \"Friction is not a fundamental force but occurs because of the electromagnetic forces between charged particles which constitute the surfaces in contact. \" So, it's like passing one magnet over another--once they are close enough, it's pretty difficult to do so fluidly. I think it's the same thing with the fields around our atoms--they interact with one another, creating friction."
] |
[
"electrons have negative charge, so they always repel, therefore it should be easier to be frictionless.",
"Layman -",
"You're thinking on a much too small scale. Surfaces aren't perfectly smooth, so you don't have a flat surface of negative charge coming into contact with another negative charge, you have a VERY jagged surface interlocking with another.",
"That said imagine if you do have a perfectly flat floor and a perfectly cylindrical wheel. When you rest the wheel on the floor the wheel creates an indentation in the floor. So now the floor (ignoring the wheel) looks like this:",
"___ ___\n \\__/\n",
"With the wheel filling that indentation. Now as the wheel moves it has to compress more of the floor in front of it:",
"___ ___\n \\__/\n",
"Wheel moves --->",
"_____ _\n \\__/\n",
"This requires energy and thus slows the wheel."
] |
[
"The thing you have to understand is that surfaces (at least ones we tend to deal with) are not smooth down to the atomic level. They're bumpy at a much larger scale - if you put \"flat\" objects together, there isn't a plane you could cut through that would leave all of the first object on one side and all of the second on the other. So if you try to rub them against each other exactly horizontally, you're actually trying to push parts of one object through parts of the other one. That's where a lot of friction comes from. ",
"That friction is largely due to imperfections, but you can't actually make a perfectly smooth surface out of matter anyway, because the charge distribution in atoms is spherical - try making a flat edge out of circles. "
] |
[
"Why is the tibia so close to the skin and not surrounded by muscle/fat like the other bones i.e femur, ulna, and radius?"
] |
[
false
] |
Why do we have no protection for bumping our shins?? Haha
|
[
"Bones usually have 2 main fascial compartments around them. A flexor and extensor, and some have a medial compartment too. There is no real need for a strong dorsiflexion action in the lower leg (bending your foot upwards), the muscles are used mainly for stabilization and so there are no large muscle groups there. Compare that to the other side of the leg where a strong plantarflexion (pushing your foot donwards) action is needed for walking and you have the huge calf muscles.",
"edit: mixed up extensor and flexor in the leg again"
] |
[
"It's also not a good candidate for fat deposits because it requires more energy to move mass at the end of your leg than your thighs or upper body. "
] |
[
"Thank you, this seems to be the most widely accepted conclusion."
] |
[
"Why doesn't ice rotate in a glass of water when the glass is rotated?"
] |
[
false
] |
It seems intuitive that it would--is there some force working against the rotation or just a lack of a force where I am intuiting one?
|
[
"Let's say you put a piece of paper on top of a pool of water. You move the paper - do you expect the whole pool to move with it? Intuitively, you would expect only the water in the vicinity of the paper to move.",
"Likewise, when you twist a glass of water, the walls of the cup only exert force on the molecules at the boundary between the cup and the fluid. This force can be translated to the other parts of the cup, depending on the ",
"viscosity",
". If you had a glass full of honey, and rotated it, the whole mess of fluid would rotate with it because the viscosity is so high. ",
"Also note that if you rotate the cup long enough, eventually the entirety of the fluid will eventually rotate with it."
] |
[
"The ice essentially follows the motion of the water in your glass. When you rotate your glass, you're rotating just that: the glass. The water may begin to swirl as well because of frictional forces between the glass and the water, but these can be small."
] |
[
"Thanks! Great examples--made it very easy to visualize my mistake."
] |
[
"Projecting an image on the moon's surface"
] |
[
false
] |
Could we build a projector capable of projecting an image onto the moon that is visible from Earth (weather permitting)?
|
[
"relevant ",
"what-if.xkcd.com #13",
" comes pretty close to answering your question.",
"basically, don't hold your breath."
] |
[
"Expanding on OPs question, would it be possible to project an image from a satellite to the surface of the moon, viewable from earth? Bypassing weather systems and our atmosphere in the projection phase, the atmosphere would still be a variable in viewing the reflected light. I think it would be fair to assume a high earth orbit of this satellite (>22,236 mi).",
"Edit: a massive stained glass like object in orbit could use light from the sun to position an image on the moon. Although it would only be able to do this when its orbit falls in the path of the light from the sun to the moon, it would not be a constant image."
] |
[
"and we would need to find a material that would not vaporise or a way to dissipate all that filtered energy. Once we have that technology, we could aim the device at the earth and ask for a million dollar."
] |
[
"Vitamin D - When it is sunny, what's the minimum length of time (& skin exposed surface area) needed to get a good amount of it?"
] |
[
false
] |
[deleted]
|
[
"Even when the sky is overcast with clouds, sunlight still gets through, it's a misnomer that clouds completely block the sun. UVB rays are responsible for skin interactions that produce vitamin D. On a completely cloudy day, it is true that up to 90% of UVB can be blocked, but an interesting phenomenon in partial cloudy days is increased UVB, which scientists are still unsure of (possibly UV rays bouncing off the sides of dense clouds, and rays getting redirected as they pass through wispier clouds). ",
"As to your actual question, it really depends on:",
"how much skin is exposed",
"what the current UV index is",
"level of cloudiness",
"Typically, on a sunny day, you only need about half the time it takes for your skin to get pink and begin to burn. I realize this isn't an easy thing to know, but that's the best information I have for you.",
"EDIT: You can still get UVB from the sun in winter, whoever told you that you can't is wrong. In places where it snows, the reflection from snow can actually increase the UVB exposure.",
"Also, I found a ",
"website",
" that allows you to enter all the pertinent information and it will tell you how much vitamin D3 you'll be getting. Cheers!"
] |
[
"You can still get UVB from the sun in winter, whoever told you that you can't is wrong.",
"Hmm, according to ",
"https://www.ncbi.nlm.nih.gov/pubmed/2839537",
" no D3 was produced by people in Edmonton, CA (Which is about the same latitude as me in the UK) from October to March.",
"Edits - and when I enter my details for winter in the website you linked it also says that I need to spend 24 hours outside per day to get enough...",
"Given this, can stores of D3 be accumulated during Summer months to make up for this?"
] |
[
"The conversion to recommended daily dose I've heard from reliable professor in my department is 15-20 minutes of exposure with uncovered face, arms, and neck with no cloud cover at a time of day and year when your shadow is shorter than you are tall. He went through a lot of math and there is some rounding and assumption but it puts it in the ballpark of something people can use and understand in the real world."
] |
[
"How do we know dark matter is actually a thing and not a mistake in the gravitational equations?"
] |
[
false
] |
[deleted]
|
[
"There is a ",
"FAQ",
" on this topic."
] |
[
"TLDR bullet cluster. The bullet cluster is formed by the collision of two large galaxy clusters, and in x-rays, you can see a tangled mess. However, you can directly infer the mass density using gravitational lensing (the bending of light behind the cluster) and doing this you find that the majority of the mass of the clusters passed right through, apparently without interacting. ",
"Also you need non-baryonic matter density in cosmology to explain e.g. structure formation and the fluctuations in the CMB (although, presumably if alternative gravity theories were true, cosmological models would be invalid). "
] |
[
"You're thinking of dark energy. Dark matter shows in situations like the orbits of stars in galaxies where the speeds at which they orbit indicate much larger masses than what we can observe as regular matter."
] |
[
"In babies and small kids what is the reason of timing vaccines with age? Why can't all vaccines be given at the same age?"
] |
[
false
] | null |
[
"Babies survive initially on their mother's natural antibodies (shared through the placenta and then through breastmilk) until the baby itself has developed an immune system capable of protecting itself. The thymus in particular is an organ that needs to develop for a while before it can handle any vaccines. Otherwise, without a functional immune system, the vaccine can just make the baby sick and won't result in the development of any immunity.",
"It then comes down to A) whether the vaccine is attenuated, dead, or a toxin vaccine, which each require the developing body to be a certain age/immune strength to be effective. B) The age of administration of the vaccine is also relevant to the diseases the baby will encounter at that age. Many are given at 6, 12, 18 months etc because babies are very prone to whooping cough, measels, pertussis, polio, with lethal outcomes. On the other hand, the gardasil vaccine isn't really necessary until the child is much older (I think the current age is 12, may soon be 10), because it is unlikely that a 12mo baby will encounter a sexually transmitted virus. ",
"The vaccine scheduled has been refined to make sure the greatest amount of immunity can be achieved at the earliest time possible."
] |
[
"[For context I am a PhD candidate studying newborn immunity]",
"The common and accepted answer is that the newborn immune system is just immature, because it is easy to understand and makes intuitive sense. However, many who specifically study the neonatal immune system (myself included) are trying really hard to convince everyone else that the system is not immature, rather it is distinct and purposefully regulated to function different than adults. There are some cell populations where are seemingly unique to newborns which exist specifically to down-regulate immune responses. It is possible these exist as remnants of the fetus needing to not react to the mother, but the fact that they stick around for a while (at least a month, but it varies) seems to indicate they are not just incidental. Honestly it is a bit of a mystery - if the newborn immune system isn't immature, why is it so much worse at fighting infections? There's no argument there - newborns are objectively susceptible to infection and inflammation. However, the last 30 years of understanding the newborn immune system to be immature has not led to any effective treatments for infectious disease (antibiotics / antivirals are all we've got). In a few instances people have tried to bolster the immune system and it has actually increased mortality, though more often there is no difference (always seems to work in mice though, so do with that what you will). ",
"Anyway I think you hit the nail on the head: I just wrote a whole manuscript arguing that it is too energy intensive to mount adult like immune responses, and here it is in a random reddit comment. Another explanation is that newborns may be hypersensitive to immunopathology (self-harm from their own immune response) so they have to balance between not harming themselves and wiping out whatever pathogen got in there. Yet another possibility is that it is the lack of an established gut microbiome (bacteria that live in your stomach) which prevents newborns from mounting adult-like immune responses.",
"I made a lot of claims here about a relatively controversial subject, if anyone is curious about my sources feel free to message / comment and I will provide links. Alternatively, check out the review I just wrote on the subject where this is all done in a lot more detail and with more evidence - ",
"https://www.frontiersin.org/articles/10.3389/fimmu.2018.01077/full"
] |
[
"Is the immune system simply too complex or energy intensive to exist in babies from birth, or is it advantageous to not have immune response as an infant?"
] |
[
"What is going on with our eyes and brain when we are looking at a TV and see a picture with depth on a 2D surface?"
] |
[
false
] |
[deleted]
|
[
"The main depth cues your brain uses to reconstruct a scene are 2D. Things like the angle a line makes on your retina as it recedes are far more important than binocular depth perception. You can demonstrate this yourself: when you cover one eye, the world doesn't suddenly look flat. ",
"For one eye, it doesn't matter if you're looking at a 3D scene or a 2D rendering of a scene: the image on the back of the retina is the same. "
] |
[
"Interesting, thanks!"
] |
[
"You can demonstrate this yourself: when you cover one eye, the world doesn't suddenly look flat.",
"This is true, but you should try (if you haven't) covering one eye for many hours. It happens slowly, but the world does seem less and less depthful, and after ~8hrs, everything seems weirdly flattened. It's a strange experience, I highly recommend it."
] |
[
"Could Venus have supported life in its past?"
] |
[
false
] |
Do we have evidence that Venus has always been the hellscape it is now or could it have had a milder climate in the past?
|
[
"Whereas we have solid mechanism for how planets loose atmosphere, (",
"https://en.wikipedia.org/wiki/Atmospheric_escape",
"), there are no plausible mechanisms by which a planet could capture the huge amount of gas that the find in venus. Volcanic outgassing and cometary strikes are possible, but venus atmosphere is far out of bound for those to be responsible. So, only planetary formation is left, and thus, Venus has been always the hot at the surface. ",
"HOWEVER! As far as Venus life support goes, Venus actually has the most earth-like conditions outside of earth we know of. Quote Wiki: ",
"At an altitude of 50 kilometres (31 mi) above Venerian surface, the environment is the most Earth-like in the Solar System – a pressure of approximately 1000 hPa and temperatures in the 0 to 50 °C (273 to 323 K; 32 to 122 °F) range",
"Due to that is has been proposed to put huge floating balloon cities in the upper atmosphere. "
] |
[
"Wouldn't it have been possible for the atmosphere to change composition in the past?",
"It's happened on Earth before. Although at 96.5% CO2 the atmosphere on Venus probably always had a pretty high concentration of CO2 and must have been pretty hot."
] |
[
"But but but aren't you guys all assuming that when OP says \"support life\" he's saying \"support Earth-like life\"? I mean, as far as I understand, we don't really know if there are other types of non-Earth-like-life that could exist in Venus' current/past atmosphere...",
"So shouldn't the real answer be in the somewhat like \"maybe, who knows? we don't really know what are the conditions and limits for life, all we know is what we have here on Earth\"?"
] |
[
"If matter can't be created or destroyed, how do pairs of quarks just \"pop\" into existence?"
] |
[
false
] |
I was watching a video on subatomic particles and the narrator mentioned if two quarks get too far apart from one another, an entirely new quark will appear to form two pairs. How is that?
|
[
"matter can be created and destroyed. This is exactly what every nuclear reaction is.",
"In order to separate a par of quarks, you have to put a sufficient amount of energy into them to produce two new quarks.",
"The simplest way is by accelerating things real fast and smashing them into each other. This is exactly what the LHC does, create matter by accelerating protons to extremely high energies and smashing them into each other resulting in a splash of new and interesting particles."
] |
[
"There is energy in the field between the two quarks. As you pull the quarks apart, you are doing work on the system, and so increasing its energy. Eventually that energy is large enough to create a quark-antiquark pair."
] |
[
"False. Antimatter does not have negative mass, but opposite charge. Annihilation of matter and antimatter yield energy equal to that of the combined masses. "
] |
[
"How do fields exert force over distance?"
] |
[
false
] |
[deleted]
|
[
"The charge interacts with the field where it is. The field at that point interacts with the field at a slightly displaced position. And so on and so on until it reaches the other charge.",
"One says that all interactions are local, happening either at the same point or at very close points (mathematically one speaks of the derivative of fields). The field mediates an effective interaction between two charges, which is nonlocal (\"at a distance\"), but the fundamental interactions are all local.",
"Think of it like two balls attached through a spring. The balls can interact at a distance, but this is mediated by all the pieces of the spring, which only interact with their neighbours."
] |
[
"There is no medium, there is an intermediary which is the field. The field is like an infinite collection of degrees of freedom at each point in space. Just to be clear: it is not a mathematical trick, it is a real thing. These degrees of freedom can be excited and they can pass on energy to nearby degrees of freedom."
] |
[
"You've got it backwards: fields are responsible for particles. Each and every fundamental particle (electron, gluons, quarks, etc) has an associated field. These fields permeate ",
", and since they have fluctuating energy the \"empty space\" between planets isn't truly empty at all. In fact, the vacuum is filled with virtual particles popping in and out of existence at all times. The absolute nothingness of space isn't so empty after all.",
"You can think of a particle as an excitation of their respective fields, somewhat like a wrinkle in a blanket. An electron is a wrinkle in the electron blanket. Remember: there's a lot more to it, but it's a good start."
] |
[
"If blood is taken from a human corpse several hours after death, can lab tests detect that the blood sample was taken from a dead person?"
] |
[
false
] |
I'm aware that blood coagulates several hours after death. So does a blood sample taken from a person who has been dead for several hours contain markers that distinguish it from blood taken from a live person (or very recently dead person), and can these markers be detected through forensic testing?
|
[
"Yes there are several markers available. Blood cell morphology is widely used for example. I am no expert on this field - but this paper should answer your questions: ",
"Estimation of post-mortem interval using biochemical markers",
"I uploaded the pdf ",
"here",
". ",
"Some excerpts:",
"Edit: Similar pdf with more info ",
"here",
" "
] |
[
"Not a stupid question at all. I do not have very detailed insights in the blood physiology ... but: Everything in our body is tightly connected. Just look at the ",
"components",
" in our blood. All these components are regulated by enzymes and or channels in the surface of the blood vessels and each of these components have a certain function. This delicate balance will not be controlled anymore after death. A slight pH change, therefore other chemicals and enzymes might dissociate - leading to the fact that the blood cells are not \"controlled\" anymore, so they might degrade as well, etc - you get the idea.",
"Edit: Slight update - of course individual cells will still do their job. And \"just\" because the heart is not beating anymore does not mean everything stops working instantaneously (see reanimation of patients). But as said - the balance of all our components is heavily disturbed if there is no blood flow anymore for example which will quickly lead to a cascade of failures within the body."
] |
[
"I always think of brain death. The brain has only a few minutes of run time once the blood stops flowing or you stop breathing. If you quickly tested oxyhemoglobin of a person's blood sample, you would see it depleted to a point you would know the sample was from a dead person. ",
"I even read excerpts from a 1920's medical book where a researchers was using the decay of oxyhemoglobin to try and determine states of health. He would pass light through your finger and cuff off the blood flow, like they do for finger/toe blood pressure. The spectroscopic changes are what he was observing. This was a forerunner of our modern pulse oximeter."
] |
[
"do electrical circuits overheat in vacuum?"
] |
[
false
] | null |
[
"Yes. Power in a circut is I",
" * R (current squared multiplied by resistance). Unless you're running a DC superconductor, you have some finite resistance, which will produce heat in the circuit.",
"In fact, a circuit is much more likely to overheat in a vacuum than it is in air. This is because vacuums insulate heat. The way circuits can expel heat is by conduction (heat travels through the circuit to the structure it's built on), convection (heat is carried away by molecules that interact with the circuit, like air) and radiation (heat is carried away by photons.) Basic circuit cooling technologies use fans to increase convection. More advanced ones use a combination of conduction and convection by conducting the heat to a surface which gets carried away by a liquid through convection. (Liquids convect more heat than gases). Vacuums have no convection, so you are limited to conduction and radiation."
] |
[
"They're more likely to overheat, yes. Two of the three ways (convection, conduction, and radiation) that heat is dissipated aren't available in a vacuum, leaving only radiation. ",
"It's one of the things the ISS has to deal with-- in ",
"this picture",
", for example, you can see solar panels, and a bunch of white panels. The white panels aren't more solar panels-- those are huge radiators to increase the surface area for radiating away extra heat."
] |
[
"Radiators don't require a medium to transmit heat into. The devices commonly called radiators (in cars, houses) primarily transfer heat by conduction and convection. Radiation is the emission of energy from a material. Energy = heat effectively.",
"A sheet of metal in space, but out of direct sunlight, quite quickly falls to ~3k (if memory serves) as there is no energy input. It loses all its heat by radiation.",
"For an effective radiator design one must consider the Stefan-Boltzmann law, detailed ",
"here",
" . When one considers that free space is around 3k its easy to see how effective radiation can be at cooling, if you can shade them from the sun!"
] |
[
"What exactly are VPN’s and how do they work?"
] |
[
false
] | null |
[
"Imagine you have to do everything by mail, and you don't feel safe sending postcards due to your post office being staffed by your overprotective mother. A VPN is like putting the postcard in an envelope to your buddy who is away at college. Your buddy opens the envelope and resends the postcard. He gets a response via postcard and puts it in an envelope back to you.",
"Now the benefit to avoiding your snooping mother (who is actually an ISP) is obvious, but you often hear things like \"Australian Nexflix has that show, sucks to be in Canada.\" If your buddy (who is the VPN endpoint) is in Australia, how does Netflix know? As far as they're concerned, they're sending stuff to an Australian address.",
"As to how it works, it's mainly software in your PC or your router that's signed up for a service that encrypts traffic and sends it to the designated endpoint. One of the less talked about applications is very common in remote work - Companies set up VPNs so you can connect to all the internal tools as though you're on the company network by setting up endpoints within the company firewall."
] |
[
"All of your traffic that goes to the VPN adapter is addressed to the same destination (the VPN gateway). Inside those packets (encrypted) is another packet with the real destination and contents that you want. ",
"The VPN gateway unencrypts the packet and sends it on its way with a source address that’s part of the network the VPN gateway is in. It does the same for packets headed back to you. ",
"What that means is your traffic is (virtually) inside the network that’s behind the VPN gateway. ",
"Let’s say that that network is your home (many home WiFi routers can run a VPN gateway). ",
"It lets all of your traffic from your laptop that’s away from home get to your home computers without going through the router so things like printer sharing will work without exposing your printer through port sharing etc. It’s as if your laptop was on your home WiFi. ",
"It’s great for things like being on your work network, when you’re not at work. ",
"So why do people like them for “security”?",
"Well, anyone spying on your remote laptop only sees encrypted traffic going to one place (the VPN gateway). It doesn’t know what’s in it, or where it’s going. ",
"The final destination of your traffic doesn’t have to be within that VPN. It could be intended for xxxpirates.net. When the traffic gets to that VPN it would be sent out to that server from the VPN and back to you via that VPN. Anyone wanting to charge someone with piracy would only be able to charge the owner of the VPN (who probably lives outside the US). ",
"Nobody can connect you to that piracy (unless the owner of the VPN decides to turn over their records)."
] |
[
"It's not necessarily that Netflix cares. Region locks are mostly due to distributor restrictions/requirements only allowing certain content to be shown in certain areas, which can be done for a variety of reasons."
] |
[
"Is it possible for a moon's orbital period to coincide with its planet's revolution in a way that causes a \"new moon\" that could last for years?"
] |
[
false
] | null |
[
"In order to remain in a new moon phase the moon would have to be positioned near the Earth-Sun L2 ",
"Lagrange point",
". The Lagrange points are 5 points where a small body can will appear stationary (in a rotating reference frame) with respect to two larger bodies that are orbiting a common center.",
"If the moon were perfectly positioned in the L2 point then it would be in a permanent eclipse (maybe only a partial eclipse, depending on the geometry), but it could instead have a ",
"Lissajous orbit",
" around the L2 point, where it would move slightly but basically always be in a new moon phase. However, this isn't stable forever.",
"EDIT: evensevenone pointed out that I got new moon and full moon mixed up. However I think everything I said is still correct, just replace L2 with L1 and lunar eclipse with solar eclipse."
] |
[
"Doesn't the instability also mean that a moon would never form at L2 in the first place?"
] |
[
"That would make sense, however the Moon is also slowly moving further away from the Earth. Perhaps given enough time (and nothing else interfering, which I'm sure is highly unrealistic) it could drift into an L2 orbit?"
] |
[
"Is it possible to change polarity of a film of some sort using voltage or current?"
] |
[
false
] |
Im thinking something like when youre holding up two 3d glasses and when you tilt one 90degrees and it turns dark, achieving the same tilt but using current or something like that. This feels like material science, which is why I ask here :)
|
[
"What you are describing is exactly how a ",
"LCD display",
" works. \nIn this video someone creates his own LCD display and goes in depth about the process to make it work.\n",
"https://www.youtube.com/watch?v=d4QFNWBSZYg",
"In short, a LCD display consists of two polarizers, and a liquid in between that changes the polarity of the light depending on it's on/off state. "
] |
[
"This. Same goes for self-dimming mirrors in cars (which are basically one giant pixel over the whole mirror) and the clever window blinds on the Boeing 787."
] |
[
"Would you care to elaborate on the blinds used in the 787? Is it also 'one giant pixel'?"
] |
[
"A facebook \"friend\" is trying to sell these things but I've told him there's no way they can possibly work: USB to 110V AC converters."
] |
[
false
] | null |
[
"Your suspicions are correct, there's no way to boost 5v DC @ ~1A to 110-120v AC with anything approaching useable current. You could cheat for a very short time with a gargantuan capacitor bank but that's clearly not the case here.",
"e: Don't hair dryers draw >1kW? 10-15A on AC sounds about right. And max USB power is somewhere around 5W..."
] |
[
"The DC to AC part is not the unbelievable part.",
"When a USB port supplies 10 Watt of power it is considered a lot (e.g. iPad charging)",
"Even if you could manage a lossless conversion from 5V DC to 110V AC (which you can't) you would be worlds away from powering a hair dryer."
] |
[
"So report him. Facebook has pretty clear rules about scams and spam."
] |
[
"Do all photons in sunlight have the same energy?"
] |
[
false
] | null |
[
"No, sunlight is black body radiation. It emits photons with a huge range of energies, some more common than others. IIRC it emits more green photons than any other. The atmosphere blocks most of the range, but what gets through are mostly the photons with energies that our eyes are able to detect. Red photons have lower energy than green photons which have lower energy than blue photons. When our eyes see a range of colors spanning the visible spectrum, our brains interpret it as white light (the sun appears yellow due to our atmosphere interfering)."
] |
[
"It is very rare that I find someone admit the sun is white, not yellow. Thank you!"
] |
[
"Hm, all you need is to show them a picture of the sun from the space station!\n",
"http://www.nasa.gov/mission_pages/station/multimedia/gallery/iss036e002224.html#.VEl8o_ldWy8",
"Although the sun is even pretty white when it's high in the sky from earth."
] |
[
"How did HIV/AIDS pass onto humans?"
] |
[
false
] |
[deleted]
|
[
"Current understanding is that it transferred from monkeys (in the form of SIV) to humans (as HIV) when humans ate infected monkeys. SIV and HIV are close. There has been a bunch of research into their relationship: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2739573/"
] |
[
"Not ate but hunted. Ingesting HIV is a very minimal chance of transmission; ingesting SIV through cooked bush meat would pose a negligible risk of zoonosis."
] |
[
"Specifically, the point at which the highest chance of infection would have occurred was during butchering when the human would have been exposed to a large amount of internal fluids (blood and otherwise) from the monkey but none of it would have been cooked yet."
] |
[
"Is it possible to be motionless in space? That is, not hurtling around a sun or through a galaxy or any sort of velocity."
] |
[
false
] |
Since motion is really just relative, I imagine there would be no way of knowing if you're motionless or not? Assuming it is possible though, I think it would be interesting to sit motionless and watch giant systems fly around at astronomical speeds.
|
[
"It's a matter of definition. What does it mean to be motionless? It means two independent things. First, it means that you're not experiencing any acceleration. Acceleration is a real thing, and it can be measured with a purely local experiment, so that's easy to rule out. The second part is that it means to have no velocity relative to something else. What's the something else? Pick whatever you like.",
"In practice, it turns out that we can get away with just the first part of the definition. As long as you're not accelerating, whether you're moving relative to something else doesn't matter at all. The laws of physics in our universe dictate that you can't tell the difference between being unaccelerated and being motionless with a local experiment, so it's a distinction without a difference."
] |
[
"Thank you for the reply, btw it was your comment about faster than light travel that spurred me to think about this and want to ask questions. I appreciate that you take time out of your day to entertain questions from the internet :)"
] |
[
"In the whole scheme of the universe no. Relative to an object, yes. Check out this thread:",
"http://www.reddit.com/r/askscience/comments/el5e0/can_you_make_yourself_completely_motionless_in/"
] |
[
"What is a classical analog in science?"
] |
[
false
] | null |
[
"Can you give the context for where you saw this?"
] |
[
"In the article titled \"A water wave analog of the Casimir effect\"."
] |
[
"Then the article is probably talking about quantum effects. A “classical analog” to a quantum effect is a similar example to the quantum effect which happens in classical mechanics."
] |
[
"Is there a spot in the universe where The Big Bang happened? And if so, where is it now?"
] |
[
false
] | null |
[
"Is there a spot in the universe where The Big Bang happened?",
"Yes.",
"And if so, where is it now?",
"It's everywhere in the universe now. The \"spot\" where it happened covers the whole universe."
] |
[
"You're thinking of the universe as a sphere that has expanded from a central point of origin; it's not. The ",
" universe looks like a sphere because we can only see a finite distance in any given direction. But there is exactly zero reason to think that the universe stops there -- in fact, the CMBR (being more or less uniform throughout the observable universe) would suggest that space just keeps on going.",
"You know in Blade Runner or any CSI when they stand in front of a screen dramatically instructing the image to \"enhance\"? The image isn't literally growing larger from it's centre -- rather, over time, one blurry pixel increases slowly in fidelity until the distance between it's constituent objects becomes large enough to identify them as such. (sort-of)Similarly, the universe is less expanding over time as it is just slowly increasing the distance between everything until you move from a single blurry-bang-pixel to a universe where all the atoms have enough space between them to form galaxies and people and whatnot. ",
"So, you've got an infinite-size picture that is being slowly enhanced at all points. Science!"
] |
[
"You're thinking of the universe as a sphere that has expanded from a central point of origin; it's not. The observable universe looks like a sphere because we can only see a finite distance in any given direction.",
"I don't see what the observable universe has to do with anything. In the expanding sphere model, the radius of the sphere represents time and the surface area represents space. The big bang had a central point of origin, t=0. It also occurred everywhere in space as the universe was a point at that time. ",
"Is that not the expanding sphere model you know of?"
] |
[
"Is there such a thing as \"economic momentum\" and if so can it be measured, or can it be used to predict economic behavior?"
] |
[
false
] |
I'm wondering if the natural laws of physics apply to man-made systems, in this case, whether Newton's First Law of Motion (paraphrased), where a body will remain in a given state until acted upon by an external force, can be applied in some fashion to economic systems. To give an example, say applicable forces are constant (unemployment, GDP growth, national debt, consumer confidence, interest rates, etc.) and as a result economic conditions will be in some state. Then a crash happens, such as 2008 / 2009 (as a result of applied forces). It seems to me that no matter how much effort is poured in to getting the economy back on track, the economy will have gained a certain amount of negative momentum which will have to be overcome with sufficient force to (ideally) reverse economic direction. It also seems that this cannot be done overnight simply because the forces would have to be (impossibly?) tremendous.
|
[
"Economics and Newtonian physics can share only the most shallow analogy. Using one to make conclusions and predictions about the other (and attempts to control) is more or less pointless.",
"You ",
" make strong analogies between economics, turbulence, weather patterns, and certain types of noise in electronic systems."
] |
[
"The phenomena of social and industrial inertia could be seen to combine as economic inertia, or momentum as you say, but such an analogy to the laws of physics is only effective to a point, as you cannot draw conclusions beyond your understanding of economics based on a relatively more expansive knowledge of physics."
] |
[
"As you mentioned before with your example of Newton's first law of motion; trade and foreign investment could be seen as an \"outside\" force that causes motion in stagnate economic factors such as GDP growth (though foreign investment isn't usually factored into GDP for the client country) or unemployment. But to your main question, economic momentum could be measured in several ways-- consumer spending, investment, real GDP growth, to name a few. "
] |
[
"Can butterflies remember being caterpillars?"
] |
[
false
] |
During the metamorphosis of insects it seems their cellular structure is completely reorganised. How much of the memory of the individual survives this? For example, if you "trained" a caterpillar or conditioned it to respond in a certain way would the resulting imago remember this conditioning?
|
[
"Yes, and it's actually quite amazing that it happens at all. The caterpillar's body breaks down to reorganize into it's adult form yet does retain memories. This was discovered using your example, conditioning. Caterpillars were conditioned to avoid a scent and remembered it as adults. However, it seems events are more likely to be remembered in older caterpillars than younger ones. "
] |
[
"Thanks for this. It makes one wonder how the memory is stored and retained under these circumstances."
] |
[
"Not all of the caterpillar's tissue is reorganized. Some structures, including the gut and respiratory system, are conserved during metamorphosis. The brain may also be conserved, which would explain why butterflies can remember some things they learned as caterpillars. Here's the article with MRI scans showing how these structures persist:",
"http://phenomena.nationalgeographic.com/2013/05/14/3-d-scans-caterpillars-transforming-butterflies-metamorphosis/",
"Here's an interview with a scientist who explains that the butterfly brain is visible from the start of metamorphosis. This suggests that the brain is not reorganized, but conserved, with memories intact. ",
"https://evolutionnews.org/2012/01/peering_into_th/"
] |
[
"How do scientists give mice cancer for study purposes?"
] |
[
false
] | null |
[
"You introduce genes that lead to guaranteed tumour development into the germ line of a mouse species, then continue to breed that line. The initial process can be tricky and expensive, though this may have changed in the past five years or so since I've done it."
] |
[
"They breed mice with a predisposition to cancer.",
"http://www.vetmed.ucdavis.edu/Animal_alternatives/cancer.htm"
] |
[
"Certain scientists use mice which have been specifically engineered to be immunodeficient, such as mice which do not have a thymus, due to a mutation in the FOXN1 gene. (",
"Nude Mice",
"), or mice which have severe combined immunodeficiency (SCID), where the entire immune system is non-functional, due to the inability of the body to generate antibody diversity. In such mice, there is no issue of tissue rejection, and can be used to grow human tumors by simply injecting them into the desired location.\nThe same effect can also be achieved if the tumor being injected is syngeneic to the mouse strain being used. "
] |
[
"Why did the sea faring dinosaurs go extinct?"
] |
[
false
] |
I was hiking with my 9 year old son along the York River and we came to a place called Fossil Beach. This led to a discussion about how the ocean used to cover much of the land we live on and one question led to another as they often do with 9 year olds. Then he asked me "why did the dinosaurs in the ocean die?" He understands that it was probably a meteor or some similar cataclysmic event that caused the extinction of most of the land dinosaurs (yes, except the ones we now call birds). But would that affect the reptiles in the sea as well? My layman thoughts are that the extinction event would not have really affected the aquatic food chain. If there was some Dino-pandemic on land it would not have affected the aquatic reptiles. I just can't think of an event that would cause the demise of creatures on the land and in the sea as well. Educate me so I can look really smart to my son. ;)
|
[
"Not a direct reply to your question, but if you want all the smarty sounding bits for your son, there were no seafaring or flying dinosaurs (excepting birds). Rather those which we typically think of as such were reptiles.",
"To your direct question, it is theorized the extinction event massively depleted plankton which would substantially affect ocean food chains, due to an extended climactic change as a result of the theorized impactor and subsequent dust cloud.",
"(If you really want to blow his mind, the dimetrodon was a synapsid, a precursor to modern mammals, and not closely related to dinosaurs at all)"
] |
[
"Plankton forms the basis if the food web in the ocean. They are green plants that photosynthesis sunlight for energy and are in turn eaten by larger animals, which are in turn eaten by carnivorous animals. When the comet hit that \"killed\" the dinosaurs it didn't directly kill them all. What it did do was inject enough dust into the atmosphere to block sunlight, both for photosynthesis purposes and as a heating mechanism. For both land plants and plankton this meant sudden climate change, less light, more cold. Since the darker and colder conditions last several years (or longer) its a massive impact. Most of the green plants die. The animals sustaining themselves on it eventually die. Their predators eventually run out of dead and dying herbivores and die too. ",
"In short the same mechanism that killed the dinosaurs kill the oceanic reptiles, sudden climate change killed their food source."
] |
[
"And we know that the mammals were best prepared to survive the change on land.",
"Is there evidence of a giant die-off in the ocean at this time? Is it even possible to even have records like this in the ocean? ",
"It seems a failure of plankton would be catastrophic to all sea life. If we take today's sealife and look backwards, do we sea an evolutionary convergence to this time?"
] |
[
"Why is it that different substances burn different colours?"
] |
[
false
] |
I have an extremely basic knowledge of chemistry but just enough to know that sodium salt burns yellow and potassium salt burns purple, and I was wondering why this is the case and also why they don't all just burn the same colour.
|
[
"Fun little fact this process is responsible for the colour in fireworks typically elements such as sodium magnesium potassium added to the firework to give distinct colours"
] |
[
"When a substance burns, it is clearly at a very high temperature. These high temperatures excite the electrons in that substance from the 'normal state' (called the ground state) to an excited state. ",
"Electrons prefer to be in the state of lowest energy, so shortly after the heat excites them from the ground state to the excited state, the electrons will drop back to the ground state. In order to drop back to the ground state, electrons have to give off an amount of energy equal to the difference in energy between the ground and excited states. Electrons can give off energy in a few different ways, one of which is the emission of light.",
"Different substances have different 'energy gaps' between the excited and ground state, so they will emit light at different energies when dropping back to the ground state. For light, E = hc / λ, where E is the energy of the light, he hc term is just a constant, and λ is the wavelength. From this equation you can see that energy is inversely proportional to wavelength. Since the light emitted by different substances have different energies, they must have different wavelengths, so they're perceived as different colours by our eyes.",
"One final note I'll add in is certain structural features of compounds are known to significantly influence the 'energy gap' between the excited and ground states of its electrons. For instance, extended resonance decreases the size of this gap (so the light emitted becomes more red), as does the presence of polar groups. Compounds that emit light in the visible range are known as [chromophores](http//",
"www.innovateus.net/science/what-chromophore",
"), and they are used in a wide variety of applications including dyes and acting as pH indicators, and are integral parts of the photosynthesis pathway."
] |
[
"Thanks for the answer, this is exactly what I wanted to know thanks."
] |
[
"What is the margin of error when launching a satellite into orbit? If too high it drifts off to space and too low it crashes to earth. How much difference are we talking about?"
] |
[
false
] |
Also, how is the Lagrange's points found?
|
[
"The other comment is correct, but I'd like to add: speed is even more important than distance.",
"The margin of error is not much. A satellite in a typical orbit at 400 km must move at 7.67 km/s. If my math is correct just 0.1 km/s less than that would cause it to reeenter the atmosphere and burn up. On the other hand, if its speed is exceeded by 0.3 km/s then it may reach the altitude of the proton belt, causing it to experience harmful radiation.",
"A 41% excess (11.2 km/s) means reaching escape speed and getting indefinitely far away from Earth."
] |
[
"Thanks so much!"
] |
[
"If too high it drifts off to space",
"This height is ",
" high, as in about 1,000,000km. All satellites are within the orbit of the Moon as far as I'm aware, and in that region of space those satellites will stay there for up to millions of years.",
"Too low is typically about 300km. For example, the ISS is 416km to 425km high. "
] |
[
"Is there a direct link between the growth of facial hair and baldness in men?"
] |
[
false
] |
I was reading up on why my beard looks so awful and it seems that facial and body hair is stimulated by the conversion of testosterone into DHT. As far as I know, the effect of DHT on hair follicles is the primary cause of male pattern baldness. Is there any basis for assuming that men with better beards are more likely to experience going bald? I guess I'm most interested in the underlying chemistry that may be involved. As an aside, if anyone knows the science behind why my beard is so patchy I'm definitely curious. I can grow the hair on my chin like a champ but the rest is just peach fuzz.
|
[
"In my case the hairs on my head realize they have turned gray, and commit suicide by jumping..."
] |
[
"I have a personal theory, that each hair is an individual and intelligent entity. The hair on top of the head does not stop growing and fall out, it just migrates downwards due to milder climates and a more interesting view.",
"There is no scientific content in my theory. "
] |
[
"I'm glad to hear someone else thinks the same way as me :)"
] |
[
"If a human were to be cloned, would the clone have identical fingerprints?"
] |
[
false
] | null |
[
"https://medlineplus.gov/genetics/understanding/traits/fingerprints/",
" ",
"Fingerprints are only partially genetic. They are also influenced various epigenetic factors in the womb.",
"",
"The basic size, shape, and spacing of dermatoglyphs appear to be",
"\ninfluenced by genetic factors. Studies suggest that multiple genes are",
"\ninvolved, so the inheritance pattern is not straightforward. Genes that",
"\ncontrol the development of the various layers of skin, as well as the",
"\nmuscles, fat, and blood vessels underneath the skin, may all play a role",
"\n in determining the pattern of ridges. The finer details of the patterns",
"\n of skin ridges are influenced by other factors during fetal",
"\ndevelopment, including substances taken during pregnancy and the",
"\nenvironment inside the womb. These developmental factors cause each",
"\nperson’s dermatoglyphs to be different from everyone else’s. Even",
"\nidentical twins, who have the same DNA, have different fingerprints."
] |
[
"Worked in a data center with biometric access (fingerprint and retina scanner), over the course of a couple of weeks where I put in a whole lot of new Ethernet cable, the ludicrous amounts of velcro I used for cable management wore my fingerprints off to a degree where the biometrics didn't recognize my fingerprints anymore (my fingers didn't look smooth, but definitely ragged enough that I'd say there were no more fingerprints), a month later, without registering new prints, fingerprint access began working again.",
"My conclusion is that your fingerprints don't change significantly by being regrown."
] |
[
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3338710/",
"This study shows that identical twin fingerprints differ, but not as much as they differ from the fingerprints of a non-twin. ",
"Since identical twins possess the same genetics, it is reasonable to assume that other forms of cloned genetics would lead to similar results. ",
"No, cloning someone would not likely lead to both people having the same fingerprints."
] |
[
"Is it possible to transform matter into anti-matter?"
] |
[
false
] |
If so what does it take? I'd assume lots of energy input? If not, why not? Thank you.
|
[
"To be pedantic, those conservation laws are actually ",
"violated by non-perturbative processes",
". In the standard model, these processes convert three baryons into three anti-leptons (so I guess this helps answer OP's question). The rate of these processes are totally negligible at current energies/temperatures, but in the early universe they should be important, so cosmologists need to take this into account for how matter formed."
] |
[
"It is possible to use matter to create anti-matter and vice versa through high energy interactions such as at accelerators, and nuclear decays.",
"An example of nuclear decay producing anti-matter is positron emission from beta decay.",
"Accelerators also produce anti mater by colliding matter particles at high energy to produce new particles and the matter and anitmatter can then be separated.",
"Anitprotons at CERN are produced by 26GeV protons impacting on an iridium rod and then magnetically separating the products.\n",
"https://en.wikipedia.org/wiki/Antiproton#Modern_experiments_and_applications",
"But there is no known way to take a particle and directly convert it into its antiparticle."
] |
[
"You can create matter-antimatter pairs from a collision between two particles, but if we define baryon (lepton) number to be the number of baryons (leptons) minus the number of antibaryons (antileptons), these quantities will always be conserved. So if we have a proton and an proton collide, then initial baryon number is two, so the end result of the collision could have be three baryons and one antibaryon; four baryons and two antibaryons; two baryons, two leptons and two antileptons, etc, but we always need the same number of matter particles to be created as antimatter particles. So if you create an antimatter particle, you must also create a matter particle. ",
"This isn't the entire story though. The symmetry which gives these conserved quantities turns out to be anomolous, which means it the quantities are not strictly conserved. At todays energies, the quantities will be conserved in any reaction we see, however in the very early universe when the temperature was incredibly high (before the electroweak phase transition), baryon number was not a conserved quantity. "
] |
[
"Are all the stars in the sky within the milkyway?"
] |
[
false
] |
Someone once told me or i heard it somewhere, that all the nstars visible with the naked eye at night are all contained in the milkyway. Is this true? I don't know how to verify this.
|
[
"Yes and no. All the individual stars you can see are within the Milky Way Galaxy. Most of them are fairly close, within 10,000 light years, in a Galaxy 100,000 light years across. But even most of our own galaxy appears as a single cloud in the night sky; no discreet, individual stars are visible. Likewise, you can see the Andromeda galaxy with the naked eye, and thus all of the stars it contains, but the whole trillion of them appear as a faint smudge."
] |
[
"Yes, you can see other galaxies sometimes with a good telescope, but you can't see the stars in them."
] |
[
"All of the answers here are correct, but I'd like to point out another thing:",
"The galaxy is filled with dust and gas which blocks out the light of many stars on the other side of the galaxy! So, the stars that you do see are mostly localized to our general part of the galaxy!"
] |
[
"Are there observable relativistic effects due to the speed of the solar system orbiting the galaxy?"
] |
[
false
] |
I saw in the New Scientist (25th June) that the solar system travels at 200,000km/s relative to the galaxy centre. This seems surprising close to the speed of light. Do we see relativistic effects as a result? For instance, do we see stars near the centre age more rapidly than models predict, or planets orbit stars faster than expected?
|
[
"I saw in the New Scientist (25th June) that the solar system travels at 200,000km/s relative to the galaxy centre",
"Whoa that's too big. That's like 2/3 ",
". You might have the units wrong, it's closer to 225-250 km/s (about 500,000 mph). While these may seem like hilariously high speeds, they're still paltry compared to the speed of light - 300,000 km/s. This means the sun moves at 0.07% of the speed of light around the galaxy. ",
"A good number for checking relativistic effects is the gamma factor - it's just a number that tells you how relativistic you are. For example, at speeds of 0.86 c (which means 86% of the speed of light) you'll have gamma=2, which means lengths are halved by length contraction, and times are dilated doubly. Higher relative velocities means higher gammas. ",
"For the solar system, gamma is about 1+10",
". Basically, this motion is almost utterly indistinguishable from Newtonian (nonrelativistic) mechanics."
] |
[
"Sure.",
"For example, ",
"this jet",
" from galaxy M87 is about 5000 light years long, and is relativistic.",
"We also observe cosmic rays and neutrinos (albeit in fancy expensive detectors) every day which are moving close to the speed of light. ",
"Of most interest to you is probably hypervelocity ejections. In interactions with supermassive black holes in galactic cores, stars can get accelerated and flung out of the galaxy with velocities equal to a substantial fraction of the speed of light. ",
"This paper",
" discusses the theory of it, and predicts that with appropriate conditions stars can be ejected with velocities up to a third of the speed of light."
] |
[
"If the acceleration is mainly by gravity and reasonably uniform - yes. It is spatially non-uniform acceleration that rips things apart. "
] |
[
"Since time is not absolute, does it make sense to describe the age of far away galaxies in years?"
] |
[
false
] | null |
[
"It turns out the effect isn't that big in most real-life situations, but there is a convention we can use if we really want to be more careful when we talk about time.",
"Time runs at different rates depending on the relative velocities of objects, and also based on the strength of gravity fields. However, you have to be going pretty close to the speed of light (relative to some other observer) to experience time at a significantly different rate, and you have to be basically right next to a black hole or neutron star for gravity to make a big difference. While we do experience time at different rates, for the speeds that most galaxies & stars are moving at, this comes out to a tiny fraction of a percent. It's usually way finer than the precision we have in measuring distances anyway, so it really doesn't matter, and we can basically assume that time is pretty much simultaneous everywhere - we don't care about a few days out of a few hundred thousand years.",
"But if we want to be more precise, we use the cosmic microwave background as a base. The CMB is moving relative to us at a very consistent velocity, and it is very uniform across the observable universe. So it's a convenient frame to use if we want to define a convenient \"universal\" time frame. It isn't ",
" universal - it's just fairly constant over a very large volume of space, and that makes it a useful convention."
] |
[
"That's the age as seen by an observer far away."
] |
[
"Something else worth mentioning is that scientifically, the \"age\" of a galaxy is somewhat important in understanding it's properties, and in studying the way galaxies form and evolve over time. ",
"However, the time units used are practically irrelevant. You could make up some new unit of time if you want, and it doesn't even necessarily need to be based on \"seconds\". You could make up a unit that's like \"the reduction factor in star-formation from the initial burst\", and compare all galaxies on that metric, and still test a lot of interesting math and physics. Because of the way galaxies typically evolve, that metric would be a noisy proxy for \"time\".",
"FWIW galaxy ages are typically stated in billions of years, in my field anyway. It's the unit of time where most galaxies are a number like 1,2 or 3, etc, so you don't need a bunch of zeroes or scientific notation.",
"In a similar way, it's why we use units of \"log() solar masses\" to measure galaxy mass; we calculate how many equivalent Sol's worth of mass are in the galaxy, and take the log, and then we get \"normal\" numbers to work with.",
"Basically, there is a tendency for scientists to mess with the units until the parameter they are working with is of order 1, with some useful scatter that they can use to look for correlation with other parameters."
] |
[
"Is it possible to change our brain chemistry at will?"
] |
[
false
] |
[deleted]
|
[
"Directly? Absolutely not. You can't say to yourself: \"I'm going to reduce the level of cortisol being secreted by the hypothalamic-pituitary axis and thereby lessen my stress response.\"",
"Indirectly? Certainly. Deep-breathing techniques are a wonderful tool often used in Cognitive-behavioral therapy to teach people how to slow down and calm themselves when they are getting worked up and anxious. But, again, this doesn't mean that you can sit in a room and will your brain to alter it's chemical make-up. The brain was simply not evolved with that level of control. You can change your behaviors and the way to you think (again, through evidenced-based therapy) to change the way you feel, but none of this goes down to the micro-level of consciously changing your neurotransmitters. It's much more macro.",
"Does this make sense?"
] |
[
"Directly? Absolutely not. You can't say to yourself: \"I'm going to reduce the level of cortisol being secreted by the hypothalamic-pituitary axis and thereby lessen my stress response.\"",
"Indirectly? Certainly. Deep-breathing techniques are a wonderful tool often used in Cognitive-behavioral therapy to teach people how to slow down and calm themselves when they are getting worked up and anxious. But, again, this doesn't mean that you can sit in a room and will your brain to alter it's chemical make-up. The brain was simply not evolved with that level of control. You can change your behaviors and the way to you think (again, through evidenced-based therapy) to change the way you feel, but none of this goes down to the micro-level of consciously changing your neurotransmitters. It's much more macro.",
"Does this make sense?"
] |
[
"See, LSD. Or any kind of drug for that matter. "
] |
[
"In neuron depolarization, why does the cell use two types of ions (Na+ and K+) if they are both positive? Why not just use one type?"
] |
[
false
] |
Is it because one type is faster than the other at crossing the membrane? Or is it just because there is more sodium available in our diet?
|
[
"Na is being pumped out of the cell and K is being pumped in. There is a high concentration of Na outside the cell and a high concentration of K inside the cell. However for every 3Na coming out of the cell 2K are coming in. So more positive charge leaving the cell than entering. This difference of charges generates the electrical impulses leading to nerve impulses. "
] |
[
"This generally applies to all membrane potentials, not just to neuron depolarization. Basically, what it comes down to is that using multiple ions (Cl is also involved, as is Ca in some cases) gives the cells better control over the membrane potential; with multiple ions, you can have multiple signaling pathways that can give you complex action potential shapes, as well as complex external regulation of muscle/neuron activity.",
"Perhaps the most prominent example of this is in cardiac cells, where ",
"interplay of three different ions",
" gives rise to a complex mechanism for regulation of not just the rate at which the heart beats, but also regularity of the heart rhythm, as well as strength of heart contractions. "
] |
[
"As for the \"why\" part, it is very difficult for a cell to have such complex properties of action potential by controlling only one ion. Getting more ions involved allows it to control the process in a more automatic fashion. You can eat with only one hand, but using both hands makes it much easier.",
"First, potassium ions are more capable of crossing the membrane without ion channels involved in depolarisation due to its lower charge density and potentially leak channels. This is partly responsible for hyperpolarisation, one of many circuit-breakers for membrane depolarisation.",
"Second, sodium channels act in a chain-reaction fashion whereas potassium channels generally don't, which leads to \"threshold voltage\" requirement to prevent spontaneous reaction.",
"Third, sodium channels inactivate rather quickly but potassium channels do not, and this is responsible for refractory periods having two phases (absolute and relative) instead of one. Without absolute refractory phase, cells will be firing action potential way too often. Relative phase allows cells to still transmit signals if sufficient depolarising stimulus is given."
] |
[
"Has the growing % of the population avoiding meat consumption had any impact on meat production?"
] |
[
false
] | null |
[
"This site",
" has the answer.",
"It's just throwing numbers at you, so I just glanced at it, but meat consumption seems to be growing everywhere. World meat consumption is increasing like crazy, European meat consumption a little less, but still growing.",
"Is anyone from ",
"/r/dataisbeautiful",
" around?"
] |
[
"No.",
"For every member of the first world who decides to eschew meat, there is a population increase of much more than that.",
"Even discounting the population growth's effect on meat production, per capita the figure increases to grow. Worldwide, per capita meat consumption increased from 41.3 kilograms in 2009 to 41.9 kilograms in 2010. (",
"Sources regarding this figure vary",
") So even if a growing percent of the population in your country/part of the world is avoiding meat consumption, the ones who are left more than make up the difference. "
] |
[
"It is worth mentioning that the rise in vegetarianism is mostly happening in Western countries which, collectively, are a small portion of the world population. Meanwhile, meat consumption is growing in developing countries - so all that is really happening to meat production is that they are selling to different people."
] |
[
"Why do you need to take malaria pills BEFORE you travel?"
] |
[
false
] | null |
[
"General rule of pharmacokinetics, start with high dose, probably double what the goal is. This gets the drug passed \"first pass\" which is removal by liver and kidney, but leaves \"target\" dose in the blood stream. Then keep dose steady, which takes a little while to reach equilibrium since the bodies natural response is to clean things up. If you have to be exposed, you want it to be in this \"steady\" state when there is adequate supply in the blood to adequately fight off the invading condition. You don't want a inconsistent amount in the blood leaving yourself susceptible to infection. Once the risk has cleared, the dose is stepped down, for one of two reasons, 1) to fight off any small lingering amounts of whatever the drug is for 2) some drugs cause shock to the system if not stepped down (prednisone and most steroid based drugs) and slowly let the body clear it with little to no repercussions from taking the drug. Hope that helps. "
] |
[
"Health care professional here. The reason for taking it before you leave is to build blood levels to the point of being effective before you enter the malaria risk zone. It also helps to assess for serious side effects, particularly with mefloquine, although it's obvious to me that you're taking Malarone. "
] |
[
"Questions like this need to be directed at your doctor. We can't offer any advice about medication on ",
"/r/AskScience",
"."
] |
[
"Why is there a launch window for a geosynchronous orbit."
] |
[
false
] |
I just watched the SpaceX launch attempt, they had some issues, and the next launch window is in three days. If the satellite was being launched in a geosynchronous orbit, why does it matter when they launch it? (please excuse my KSP based understanding of orbital mechanics)
|
[
"That only means that the Falcoln 9 will only get the satellite to GTO, and the satellite will do a final burn at apoapsis to get into geosynchronous orbit."
] |
[
"Possibly, I don't know the details of the mission plan. It might be longer because of terrestrial constraints like resetting the rocket and launch pad."
] |
[
"the thing that doesn't make sense to me: if it's a geosynchronous orbit, wouldn't launching the satellite at any hour of the day put it in the same place?",
": satellite, not salivate, damn spellcheck :)"
] |
[
"What is the evolutionary reason for Australia's many poisonous critters?"
] |
[
false
] |
What is the evolutionary reason why Australia has so many poisonous snakes, spiders, jellyfish etc.?
|
[
"Evolutionary biologist and herpetologist here! I can answer the reason for the venomous snakes. ",
"The reason for the amount of venomous snakes has to do with evolutionary history. Essentially, Australia was first colonized by sea snakes (family Elapidae -- a family of venomous snakes -- the same family as cobras, mambas and coral snakes) before \"regular\" generally harmless snakes (family Colubridae). Over millions of years these elapids have out-competed and evolved to fill the niches that would normally be filled by colubrids. So whereas most continents have (generally) harmless colubrids -- like garter snakes, rat snakes etc. -- these same ecological roles are performed by elapids, which tend to have very potent venom. Their venom did not evolve because of a specific need in Australia, but instead is leftover from their evolutionary history. (Of course, co-evolution with Australian animal resistance to the venom has probably made some species more potent over the years.) It's quite a remarkable example of biogeography and convergent evolution if you ask me.",
"Here",
" is a paper describing the bigeography of elapids corroborating this statement.",
" Cobra-relatives got there first and filled the ecological roles that are usually filled by non-venomous snakes on other continents. Evolutionary history is the answer!",
"The same is true for marsupials. Marsupials colonized Australia before placental mammals could. Coming to an ecological open landscape, they speciated rapidly and filled the niches that are normally filled by placental mammals in other parts of the world. But, they don't have venom, so this is more of an aside.",
"edit: wording and TLDR"
] |
[
"Chris Lavers covers this question in ",
" which is a very readable book about how animals use energy and how basic physics and maths alter animal forms. ",
"A paraphrased, vaguely remembered summary of that chapter is: Australia is geographically old (all the rocks near the surface have been near the surface for a very long time) so it's been leached of nutrients over time. Lots of the good stuff has been washed into the sea, and no new good stuff is churning up from below. That means there's less nutrition for tasty animals to eat, and thus fewer tasty animals for predators to eat. So, it makes sense for predators to be venomous, because it means a chance encounter with a prey animal is more likely to end up with the prey animal dying, for less effort expended by the predator. This gives venomous creatures a decided edge, hence the selection towards Australia's current existence as a giant rocky smorgasbord of sudden death.",
"I don't think that answers all the questions though."
] |
[
"Not complete conflict. First of all, my answer only applies to snakes. SMTrodent and ymersvennson's answers explains why venom has persisted over time and why it would be advantageous for venom to evolve in the first place. Indeed, his answer is a good explanation for why venom may have evolved independently in Australian insects or jellyfish (assuming their taxonomic most common ancestor did not have venom), but in terms of snakes, the deeper answer lies with their evolutionary history. The venom may have persisted and grown stronger over time due to the answer that SMT rodent and ymersvennson gave, but even the first snakes to colonize Australia were venomous; the trait did not evolve independently due to the climate or geology of Australia.",
"Again, this is true for snakes -- not the other venomous animals of Australia."
] |
[
"Why do the veins of the arms pop out as they grow more muscular?"
] |
[
false
] |
I do realise that this may have an obvious answer, but can anyone with the knowledge behind it chime in? Also, isn't it a disadvantage from an evolutionary point of view for this to happen? Aren't they more likely to be damaged or avulsed as this happens?
|
[
"It has more to do with body fat percentage than muscularity. As body fat decreases, the space between skin and muscle decreases and vascularity become completely visible. "
] |
[
"Do larger and more fit muscles have a higher demand for blood (i.e. than their wimpy counterparts), and would the body compensate by increasing the size of the blood-vessels that supply them?"
] |
[
"Good question, some body builders look like they have abnormaly huge vains"
] |
[
"What is the lowest possible atmospheric pressure a human could survive in?"
] |
[
false
] |
[deleted]
|
[
"Humans begin so suffocate at around .16 pO2...at lower pressures, pulmonary gas exchange no long occurs at a sufficient rate to support respiration.",
"So, if you are in a 1/6th atmosphere environment of pure oxygen, your the alveoli in your lungs could still function. I suppose with acclimation you could lower that a little bit.",
"I would imagine there would be a numble of other physiological effects, the nature of which I could only speculate. Heat exchange, evaporative cooling, rapid, shallow breathing...probably not great for you in the long run. "
] |
[
"I found ",
"this",
" and ",
"this.",
" I think it has some answers."
] |
[
"Perhaps the partial pressure of Oxygen on the top of Mt Everest would be a start."
] |
[
"What limits observation outside the \"observable universe\"?"
] |
[
false
] |
[deleted]
|
[
"The speed of light.",
"The observable universe is defined as a sphere, centered on the observer, with a radius equal to the speed of light times the age of the universe, in comoving coordinates. (That last bit is to deal with the metric expansion of the universe.)",
"People who say \"universe\" when they mean \"observable universe\" should be tortured slowly in front of a warmly applauding audience. I know no greater sin, personally.",
"As to your other questions, the only possible answer is \"maybe.\" Right now, the universe appears to be expanding at a rate that exceeds the rate at which the edge of the observable universe is receding from us. Therefore, it's possible that distant galaxies will dim to invisibility and eventually leave observable universe. But it's not possible right now to say that conclusively, because we cannot predict what the scale factor of the universe is going to do in the future. It could continue to increase monotonically at a constant rate, it could accelerate, it could even stop growing entirely and slam to a halt right ",
" and we wouldn't know it in our own lifetimes, or realistically probably not even within the lifetime of our own ",
"Things happen slowly in our cosmos, on the scales we humans are used to thinking about. A billion years is ",
" to the universe."
] |
[
"As the universe expands and more and more space between galaxies is created, will there come a time where our galaxy will be isolated to the point where no observation outside of our galaxy is possible? If humans had evolved 5 billion years later on Earth with all other factors being equal, how would our \"image\" of the universe be different?",
"If I recall correctly Lawrence Krauss talks about these questions toward the end of this ",
"video",
"."
] |
[
"The fact we haven't been able to find traversable worm holes."
] |
[
"How do you calculate the total % chance of 2 things happening?"
] |
[
false
] | null |
[
"The product (0.05)*(0.15)."
] |
[
"wow thats super simple, lol thank you\n so the chance of breaking through both walls would be .75%?"
] |
[
"Yes."
] |
[
"What happens to the body when you fast?"
] |
[
false
] |
Specifically fasting for daylight hours (like in Ramadan). How does the body change and adapt. How long after the fasting stops does the body take to adapt back? One process I've heard that takes place is that due to glycogen leaving the liver and muscles that insulin tolerance resistance drops. How long does this last, and other processes?
|
[
"With daylight fasting the changes aren't actually that dramatic. We have enough glycogen stores to tide us over for about 20-24 hours, so upon fasting, we just begin to catabolise glycogen. This provides the glucose which then fuels the rest of us.",
"The more dramatic metabolic change happens with longer periods of fasting. Once we finish our glycogen store, we begin to burn fats. For the majority of tissues, this isn't a problem. We break down the fatty acid chains and feed acetyl CoA directly into the Krebs Cycle. The brain, however, can only metabolise glucose, so we need to start using gluconeogenesis, using glycerol sourced from lipids (freed from the lipid structure by fatty acid oxidation). Eventually, once the fat stores are used, we begin to metabolise protein which is bad news for a number of reasons! But these are only relevant in considerably longer starvation periods. ",
"We restore our glycogen stores remarkably quickly, essentially the limiting factor is blood glucose concentration - so if you \"sugar load\" after fasting, your stores are replenished within a matter of hours. ",
"I'm not sure about insulin resistance - I'll have a look and get back to you."
] |
[
"The brain, however, can only metabolise glucose",
"Actually, the brain is capable of metabolising ketone bodies as well, and these are the key to long term starvation survival in (most?) mammals. I think there's also some evidence that the brain might be able to use lactic acid, but I don't have sources on hand.",
"Essentially the brain can't break down fats through beta oxidation (the process by which the rest of our bodies 'burn' fat), but if you're deriving the majority of your energy from fat (i.e. you're starving and burning body fat) then the liver enters ketogenesis, converting fatty acids to ketone bodies. These ketone bodies are plasma soluble and can be used by the brain.",
"So once you run out of glycogen stores, you'll begin breaking down a lot more fat. The beta oxidation cycle gets overloaded (not enough oxaloacetate and other intermediaries) and the liver begins turning fats into ketone bodies, which fuel the brain. Even with gluconeogenesis and protein stores, we only have enough available glucose to last for maybe a week or two without food at a 'normal' (i.e. roughly 120 g glucose per day) rate of brain glucose usage.",
"Ketone bodies are actually fascinating things, and there's emerging evidence now that they may be useful in treating certain neurological disorders, including Alzheimer's and epilepsy.",
"Brain Metabolism During Fasting",
"Resistance to Symptomatic Insulin Reactions after Fasting"
] |
[
"Although this is a totally unhelpful answer - it depends how fat you are!"
] |
[
"What would a very powerful electromagnet do to the human body?"
] |
[
false
] | null |
[
"This is a very interesting question that I have discussed with colleagues but I don't know if anyone has really tested since the ethics are a bit... unsettling. ",
"From what I understand, as long as you have no ferromagnetic objects in your body, even very powerful DC magnetic fields won't really affect you. But things change when you are dealing with dynamic fields, such as those used in MRI imaging. ",
"Peripheral nerve stimulation in MRI machines",
" is widely reported and documented, and increases in severity as field strength is increased. 7T MRI are generally considered ",
"safe for human use",
", with peripheral nerve stimulation minimal below 7T. 7T-15T are not used on humans, but are ",
"sometimes used in research on animals",
". >15T there is a risk of brain damage or death due to electromagnetic effects on electrical signals in an animal's brain. We know that some very simple animals like frogs can survive and even float around via diamagnetic levitation in ",
"higher static fields up to 16T",
", but the effects on more complex animals are not known, and the fields used to levitate frogs were static rather than dynamic. ",
"As of 2003, the FDA specifies",
" the criteria for ",
" and 4 Tesla for neonates....increased magnetohydrodynamic effects and human response to increased fields. Transient phenomena reported in association with patients moving in high fields include slight nausea and vertigo, headache, tingling/numbness, visual disturbances (phosphenes) and pain associated with tooth fillings.",
"The thing is: the higher the field strength, the better resolution you can obtain. And therein lies the paradox: observing the brain in sufficient detail affects the brain's processes. "
] |
[
"Strong static magnetic fields usually aren't an issue for living tissue. Magnets have very little effect on people since we are mostly water. 7 Teslas or below is considered pretty safe for MRI machines. Like others have mentioned, the main issue I've heard of is from the dB/dt, or change in magnetic field w.r.t. time. This can cause issues with nerves, potentially causing central nervous system issues in the 8+ Tesla range. MRI machines usually don't go above 15 Tesla fields, max.",
"",
"The main risk of electromagnets is probably trauma associated with foreign metallic objects maiming you. Imagine getting hit by a screwdriver flying at 50 mph. Or...imagine a metal hospital chair slamming into you and pining you to the side of an MRI machine, crushing limbs in the process.",
"",
"For \"non-quickly\" changing magnet to actually do anything to your body, it would be primarily interacting with the water that makes up 70% of humans. At around 15 Teslas you can float small critters like frogs, so you get a force on the body (and ",
" nerve stimulation?). Even the magnets at CERN don't get much stronger than this.",
"",
"To get a noticeable effect, you have to go bigger. ",
" (Off an order of magnitude, 50-100 apparently is what we can do without trashing the equipment, normal conductors can be larger) Those could potentially do some damage, probably major brain damage. Since it is extremely difficult to make fields very large, there haven't been any biological testing in this respect. There have been some suggestions in papers that fields as low as 50 Tesla could be seriously damaging or lethal to humans, but of course it hasn't been tested...primarily due to the extreme difficulty in creating fields this large.",
"",
"If you jump up to cosmological scale, something like a Magnetar would completely mangle us if we got anywhere near it. But it's magnetic fields are in the ~100,000,000,000-ish Tesla range. Magnetic fields aren't really effective on a lot of materials."
] |
[
"If we have crazy futuristic superconductors, we could get 100-1000 Tesla magnets.",
"Superconductors have a limiting field strength, normal conductors have not. The strongest fields we can produce are from normal conductors (~100 T short-term without destroying the equipment, and ~50 T long-term)."
] |
[
"Which constellations would differ if viewed from Mars or is the difference in viewing angle too slight to detect any difference at all?"
] |
[
false
] | null |
[
"Considering Earth all by itself pretty much answers this question. ",
"In January and in July the Earth goes one-half of its orbit around the sun, making it 298,000,000 kilometers from its starting point more or less (and not counting the sun's movement as it traverses around the Milky Way galaxy). We don't see any perceptible changes in the constellations for those ones that are in our sky in both months.",
"The average distance from Earth to Mars is about 225,000,000 km, which is a little shorter. And the furthest from Earth to Mars, when those two are on opposite sides of the Sun, is about 400,000,000 km.",
"So, no perceptible change between Earth and Mars constellation views because we don't see it already on dates that are six months apart."
] |
[
"You have to go way further than Mars to see any difference in constellations. Even going to the next nearest star, Alpha Centauri, will only alter the night sky slightly. There are some computer programs which have the nearby stars in 3d, rather than a 2d skymap, and let you travel around the galaxy so you can see how the sky would look like. I recently answered a similar question and took some screen shots with ",
"Celestia",
". See the pictures ",
"here",
". ",
"In the first two images, you can see how Sirius and Procyon mostly have moved a bit as we go from the Sun to Alpha Centauri. Also Pollux. And the Sun itself appears left of Cassiopeia, nicely continuing the zigzag pattern. There's a couple other small changes too, but for the most part the sky looks pretty much the same. The last two pictures are also quite similar, I can only spot small differences here and there. The bright extra star in Taurus is Proxima Centauri, these pictures are from the vicinity of Alpha Centauri.",
"The point being that for the apparent position of stars to change significantly, you need to travel a distance comparable to how far they are. Most visible stars are much further than the 4 light years to Alpha Centauri, so most stars don't appear to move much at all."
] |
[
"There would be no perceptible difference. Most of the stars we see in constellations are dozens or hundreds of light years away, so a change in distance of order 1 AU would be far too small for us to notice. It would be a bit like looking at a mountain tens of kilometers away and moving your head an inch or two to the side. The image of the mountain would look no different."
] |
[
"How can any animal withstand 497 atmospheres?"
] |
[
false
] |
Specifically, the deep-ocean who lives comfortably 16,400 feet down where (I calculate) the pressure is about 7,200 psi. Even though he's only 7 inches long, still, normal only has a compression strength of 6,000 psi. How can this even be possible?
|
[
"The pressure on the inside and outside of the fish is equalized. If you take a pressure vessel full of air and submerge it to the bottom of the ocean, the vessel must resist the entire pressure difference. If you open the vessel and let water inside, the pressure on the inside and outside is now the same, and the vessel does not need to support any load.",
"We breath air in our lungs, so when we dive deep into high pressure water the air in our lungs and the strength of our bodies is the force resisting the water pressure. If a fish can extract oxygen out of the water without actually making little air pockets, there is no low pressure zone to be crushed. Humans could potentially use a method called ",
"liquid breathing.",
" and dive very deeply without the use of a pressure suit."
] |
[
"Because the interior of the fish's body is also pressurized to that same level.",
"We do the same thing with air. Your body is currently subjected to the equivalent of about 20 tonnes of pressure from the Earth's atmosphere, but you don't feel it because your body is pressurized to that same level. The fish just takes that principle to a further extreme."
] |
[
"Thank you, and that seems pretty obvious now.",
"Still -- it seems miraculous..... And I wonder, do you think that the extreme pressure at ocean depths would mimic the effects of gravity? Would these fish \"weigh\" more.... would their time move slower? I wonder if anyone has ever tested that notion"
] |
[
"How did the first single celled organism come into existence?"
] |
[
false
] |
Had this question thrown at me today in a Religious Studies class (essentially philosophy and ethics) and I couldn't answer it. But I know there has to be someone out there with a good idea of the current theories surrounding this issue. Thanks!
|
[
"Well it doesn't just happen. ",
"First the universe must create enough carbon, and organic molecules to make their dispersal around the universe high enough for conditions where more complex organic compounds can form. This happens through fusion, fission, and the processes of element creation in the cosmos. ",
"Then, when the conditions are favorable on a planet that has a large amount of these processes that are conducive to a stable state, the complex organic molecules can undergo a process where one compound replicates itself through the intake of outside chemicals. ",
"When the replication starts, it is random, and through enough replications this process can change, these changes may change the original reaction;(IE expanding to an area where secondary reactions occur because of the first), or it may move the reaction into areas that are more favorable. (expanding into areas where volatile compounds are energized by the chemical changes). This happens enough times, and we get Airplanes. ",
"That's science, that's a fact. I am out.",
"Edit- and then I came back! adjusted some punctuation, gave it some paragraphs, that sort of thing."
] |
[
"This lecture",
" is fantastic. It is much more detailed than the other video linked here.",
"I would highly suggest watching the whole series. If you're not planning to work in the life sciences then this course will give you everything you need to know about evolution and ecology and it's understandable by all."
] |
[
"Could you go into more depth on one of the more likely theories perhaps? How do things like this just happen?"
] |
[
"Can we predict coronal mass ejections?"
] |
[
false
] | null |
[
"I'll take your question to be 3 parts.",
"Can we predict coronal mass ejections?",
"Generally speaking no. We have a very difficult time definitively predicting that an active region on the Sun will produce flaring activity and/or coronal mass ejections beforehand. Our best indicator is whether the active region has already been producing flares/CMEs, to see if the the magnetic flux in the region is still pretty mixed, and then assume it has a good chance of producing more.",
"Can we predict whether a CME will strike the Earth?",
"Yes! There are multiple spacecraft dedicated to observing the Sun, specifically monitoring for space weather sources. These observations are fed into predictive space weather models which then predict impacts at Earth. The one most relevant for CME impact at Earth is the ",
"WSA-Enlil model",
", maintained by the Space Weather Prediction Center (SWPC), operated by NOAA. Essentially, Enlil models plasma flow from the Sun, taking relevant plasma physics into account.",
"If yes, how do we respond/prepare?",
"A large CME hitting Earth and being able to deposit a lot of its energy into the magnetosphere, and eventually creating geomagnetically induced currents (GICs) is close to a \"doomsday\" scenario. A well placed CME could knock out the entire North American power grid, destroy the electrical systems of a large number of cars, and damage any number of other electrical systems (your computer being charged via power cable may be fried, for example). A lot of this depends on the orientation of the magnetic field in the CME and the orientation of the long conducting components of electrical systems. Now, obviously, this is all bad, so how do we prepare? The answer is that all major electrical companies actually subscribe to reports from SWPC on space weather events. In the instance that a large event is expected to hit Earth, measures can be taken to reduce the impact. The key thing for the power grid is taking transformers off the grid as much as possible, which may mean choosing to manually power down the grid for a short period by disconnecting transformers. Since transformers are expensive and can be destroyed by GICs and there aren't a lot of spares just sitting around, it is important to protect them. As for other impactors, flight paths will be redirected away form the poles as the radiation environment can reach dangerous levels. Also astronauts aboard the ISS will go into a region of the ISS and shield themselves with large water containers in order to better protect themselves from solar energetic particles."
] |
[
"destroy the electrical systems of a large number of cars",
"How would this happen if a car is not connected to a long conducting cable?",
"close to a \"doomsday\" scenario. ",
"The case study of the 1989 solar storm is probably informative here.",
"It was estimated to be about 60% as strong as the dreaded Carrington event (600 nT vs. estimates around 1000 nT for the 1859 event). The biggest effect was that it knocked out power in Quebec for 9 hours; relays were tripped due to fluctuating voltage, creating the blackout before transformers could start failing. Also note Quebec was particularly susceptible given its high latitude, unusually long power lines, and unusually low magnetic permeability bedrock."
] |
[
"It depends. I believe it might be possible to predict them a few hours to a few days beforehand. But anything more will not work . For example people believe ",
"Carrington level event",
" happens once in 150 years so. But there isn't much data to prove that and there isn't much consensus (I was at a talk about this recently). My understanding of why its difficult to make these predictions months in advance is this. Think of the Sun as a sphere of water sloshing around. You can imagine how chaotic things are and its not too hard to see how difficult and computationally expensive any prediction and simulation is. Now replace water with plasma and add strong magnetic field and you have magneto-hydrodynamics equations which are notoriously difficult to solve, even with the best supercomputers."
] |
[
"Will a new planet eventually form in our solar system's asteroid belt?"
] |
[
false
] |
[deleted]
|
[
"No. Also the mass of all the asteroids together is ",
"about 4% of the mass of the Moon",
" - pretty small. "
] |
[
"About one third of the mass of the asteroid belt is contained in ",
"one object",
"."
] |
[
"The asteroids are too spread out as well as not enough. For a new planet collisions would have to be common. "
] |
[
"Matter can be converted to energy. Does the opposite also happen?"
] |
[
false
] |
I know of many processes where matter is converted to energy, but I can't think of a single one where the opposite happens. Is the amount of matter in the universe in a constant decline or is energy turned back into mass somewhere? It seems like a very basic question so excuse me if this is common knowledge. I honestly don't know and I have no idea how I would google something like this.
|
[
"Let me clear a misconception: energy is not a thing, energy is a number that tells you about a \"conserved quantity\" in your system. You cannot \"create\" energy, energy is there all along.",
"What E = mc",
" tells you is this: when you have a particle at rest, it has an intrinsic amount of energy, just by the fact that it has mass. In newtonian mechanics this didn't happen, all the energy in your system could only come from movement, velocity... but in relativity, mass is in fact needed to account for energy.",
"What a nuclear bomb does is the following: there are bound states of matter - like a very heavy atom. When you measure the mass - rest energy of the atom, most of what accounts for this mass is the potential energy of what keeps the atom together. When you smash it, this potential energy is converted into kinetic energy of the things that were bound together, and you have a chain reaction. Most of the decay products happen to be high energy radiation.",
"Now you ask the question: can you have a bunch of stuff with very big kinetic energy that can be converted into something that's very massive but slow? Yes. For instance, the universe was once dominated by radiation (very fast, light particles) that were transformed into the kind of matter that we see today. see ( ",
"http://en.wikipedia.org/wiki/Radiation-Dominated_Era",
" ) "
] |
[
"Just to be more precise, the full equation is actually:",
"E",
" = (mc",
" )",
" + (pc)",
"in which ",
" stands for momentum. When you have a reaction of this kind, you start with a massive slow particle, ",
", and end up with a fast light particle, ",
". You do not create energy. ",
"Your confusion regarding gravity is because what causes gravity in general relativity is not the rest mass, but the whole energy of the system. see ",
"this"
] |
[
"Thanks for you answer. And happy cake day!"
] |
[
"If a normal/healthy person started to take anti-depressants, what would happen? Would they feel happier then normal?"
] |
[
false
] | null |
[
"Anti-depressants aren't pills you take that make you happy. They are not like fun drugs where you pop a few and get all dopey. They work to regulate and restore balance to a chemical imbalance in the brain, over a long period of time. Usually AD have to be take for about 6 weeks before they even start to have the desired effect. If someone who has a chemically balanced brain starts taking a medicine that ups the neurotransmitter count, then they can become depressed since their brain chemical balance is now ",
" ",
"This was a very rudimentary way of explaining it, but I hope it helps"
] |
[
"Depression involves a decrease in positive emotions and an increase in negative emotions ( ",
"source 1",
", ",
"source 2",
" ). Antidepressants, when effective, reverse these effects, sometimes increasing positive emotions and consistently decreasing negative emotions ( ",
"source 1",
", ",
"source 2",
" ). I haven't seen support for the idea that antidepressants cause blunting on the positive end of the emotion spectrum. ",
"To answer the OP, I've seen ",
"this study",
" on SSRI use in healthy subjects. It found that SSRIs reduced negative emotions even in healthy subjects."
] |
[
"Not sure where you're getting your info from, but Xanax isn't a selective serotonin reuptake inhibitor, it isn't even an antidepressant. ",
"It's a benzodiazepine, basically a mild tranquilizer used to treat anxiety disorders. It would not be used to treat depression, since it is actually a depressant itself, and it is also habit-forming. "
] |
[
"Heart diseases - what is the difference between hypertrophy, cardiomyopathy, cardiomegaly and dysplasia?"
] |
[
false
] |
I understand that heart muscle is thickened/enlarged in all these cases, so why are there so many distinctions? Would anyone explain to me the differences in the simplest possible way? I got interested in this, but I'm a total layman in medicine or biology. Thank you.
|
[
"Hi, these are all terms that may be used to describe varying heart adaptations and/or pathologies",
"Hypertrophy: this technically refers to excessive growth of an organ. For the heart, this typically refers to extra muscle growth. This can lead to decreased cavity size due to thickening of your hearts walls (concentric hypertrophy) or dilation of heart cavities (eccentric hypertrophy)",
"Cardiomyopathy: This is an umbrella term given to a group of chronic heart diseases, which are ultimately characterized by some form of heart remodeling due to some cause. The most common is dilated cardiomyopathy in which the chambers of your heart are dilated (eccentric hypertrophy), but can be also due to long-term concentric hypertrophy (restrictive cardiomyopathy), infiltration by foreign substances (like iron or abnormal proteins), or several other causes.",
"Cardiomegaly - A somewhat generic term describing enlargement of the heart, but not necessarily indicating why. There are many possible causes.",
"Dysplasia: this term is used when you take a biopsy of tissue and look at the cells under a microscope and identify the presence of abnormal cells that seem to be growing rapidly. Some common features include high rates of mitosis, irregular cell shape/sizes, irregular nucleus shapes/sizes, and irregular patterns of invasion of surrounding structures. Depending on the context, this can be benign, precancerous or cancerous."
] |
[
"Adding on to this: ",
"Cardiac Hypertrophy isn't necessarily bad. You mention two types, and endurance exercise induced Eccentric Cardiac Hypertrophy is not only about the dilation of the heart cavities, but also proportional increases in left ventricular wall thickness. Together, these enable significant increases in stroke volume, which in turn enable significant increases in cardiac output for ANY heart rate (compared to pre-training levels). This is a very desirable training effect that has no appreciable downsides that I'm aware of."
] |
[
"Spot on. Eccentric hypertrophy is commonly seen in aerobic athletes, concentric in weight lifters, and a combination of concentric/eccentric for athletes who do both (most common). This can be dangerous in rare pathological circumstances but is otherwise a normal and healthy physiologic response to exercise."
] |
[
"What happens when a photon hits an electron but doesn't excite it?"
] |
[
false
] |
[deleted]
|
[
"'Hitting' an electron isn't really a thing, neither the photon or electron are small hard spheres. ",
"The photon is a change in the electrical (and magnetic) field and the electron is a charged particle that responds to it. The end result can be that the photon just passes without any change, that the electron is excited if the photon has sufficient energy, or that the photon gets scattered (the scattered photon may also have higher or lower energy than the original photon)."
] |
[
"It's not little pieces of something. (Neither is an electron, which is also a fundamental particle) There's no 'shell' around these things. They're particles, but in the sense of quantum mechanics, which doesn't imply they have a size of its own. "
] |
[
"It's not little pieces of something. (Neither is an electron, which is also a fundamental particle) There's no 'shell' around these things. They're particles, but in the sense of quantum mechanics, which doesn't imply they have a size of its own. "
] |
[
"Why does cancer form in organs but not in your arms or legs?"
] |
[
false
] |
I've never heard of leg cancer or finger cancer. Maybe they exist but ya idk.
|
[
"There are. Bones have things like osteochondromas, osteoblastomas, osteosarcomas, ewing's sarcoma, osteiod osteoma, chondroblastoma, etc. Skeletal muscles have rhabdomyosarcomas. Smooth muscles have leiomyomas and leiomyosarcomas. Your nerves can get shwannomas. Your skin can get melanomas, basal cell carcinomas, and squamous cell carcinomas. This isn't even half of the list. And don't forget about metastases. The reason you don't really hear about them is because arm and leg cancers mostly fall under sarcomas which are cancers of connective tissue. These account for <10% of cancers while carcinomas account for >90%."
] |
[
"Rhabdomyosarcomas can develop in the muscles, so potentially you could."
] |
[
"Cancer forms in your tissues. You won't get \"calf cancer\" but you might get skin or bone cancer located in the lower region of your leg. Theoretically you could have abnormal cell growth and division anywhere in your body, but some cancers are more frequent than others. Which is why we often tend to relate cancer to major organs. But in reality this can occur anywhere in your body where there are cells."
] |
[
"Why can a probability distribution (like the Cauchy distribution) not have an average, and what does that mean in the real world?"
] |
[
false
] |
I'm a computational mathematics student whose finishing my master's degree, so I'm actually pretty familiar with the math of the Cauchy distribution not having an expected value or a variance, but I can't really interpret what that means in practice. To simplify, let's consider a random variable X whose probability density function is f(x) = 1/(4x ) if |x|≥1 and f(x) = 1/4 otherwise. Doing the math, you find that this is in fact a probability function, but its mean and variance are undefined (they both simplify to +∞-∞). What does this mean, exactly? Say for example that a machine draws a number x with the probability of X. Someone offers me a bet where I win or lose x dollars depending on the number x that is drawn from the machine. Should I take the bet? And what if I get x+1 dollars if the machine draws a number x? Or x+10 ? And what if I'm allowed to keep betting as long as I'd like? What happens if I try averaging out all the numbers that the machine spits out? Does it simply not converge?
|
[
"As your number of drawn values increases, the average would converge if there was a defined expected value. That's kind of what an expected value is, the expected mean is an ensemble-averaged quantity. So if you have numbers drawn from a true Cauchy distribution, then the more you draw, the average will not converge to any value. Your example is a little bit funny though because you can figure out the probability within certain ranges, and you do know things like the median drawn value, so whether you take the bet or not depends on the specific conditions."
] |
[
"So-called \"power law\" distributions like this one come up quite a bit in practice, especially in some models of node sizes of social networks. ",
"The idea is that there could be a probability distribution describing the numbers of friends an average person has that does not change much as the social network grows. As facebook has gone from 5000 people to 1 billion, the number of friends of people in my network has not changed by much. However, if we look at people at the very top end, or even try to average across the whole network, growth is unbounded. Take Katy Perry, who has 64 million twitter followers, for example. There are various models of network growth that converge to power law distributions. Whether or not real-life networks have this behavior is up to debate and statistics, and it certainly doesn't make much sense to talk about taking bets according to such a distribution."
] |
[
"A bet is considered fair when one party pays the expected value to receive the random variable. By cutting off the tail of the Cauchy distribution you can see that its mean must be greater than any positive number, in other words it is not merely undefined but infinitely large. Therefore if X is a sampled value, for any x, if you receive X - x repeatedly, your winnings will eventually diverge to positive infinity.",
"On the other hand, variance is also infinite, so you could lose arbitrarily large amounts before exceeding any given amount. I'd have to do some analysis to be sure how this works, but typically one uses variance to do this analysis and we don't have one...",
"Finally, when we talk about bets we are mapping from numbers to dollars to \"value\", assuming this all works linearly (e.g. $10 is half* as good as $20). It is up to debate whether $10",
" is a meaningful number of dollars and whether or not it is 10 times better than $10",
" For all these reasons, I don't think it's particularly fruitful to try to understand this distribution in terms of bets. "
] |
[
"Can cats/dogs recognize other animals in photos?"
] |
[
false
] |
Inspired by post. I get the feeling we're anthropomorphising it, but who knows?
|
[
"There is some weak evidence for dogs recognizing faces from photographs:",
"Study focusing on visual tracking and controlling for animal's background ",
"http://link.springer.com/article/10.1007/s10071-013-0713-0?no-access=true",
" ",
"edit: (",
"more detail on this study",
")",
"Study with indirect evidence, testing for if dogs match owner's voice with photos of owners: ",
"http://link.springer.com/article/10.1007/s10071-006-0025-8#page-1",
"Also, it seems fairly plausible to hypothesise that the visual system of both canines and felines plays a sufficiently important role in their undomesticated behaviours that they would have, at the very least, basic object recognition for hunting purposes, seeing as scent and hearing aren't targeting systems, only tracking systems. This lends credence to the idea of being able to visually identify rough animal groups, although no weight to the hypothesis that it's possible to recognise individuals. ie the cat might recognize that it's seeing a dog that is vaguely visually similar to the one it knows, but if presented with an array of similar looking dogs, might not be able to identify which is the one without the scent and motion cues.",
"It would be interesting to see if crows are able to recognise individual humans from photos, as it's fairly well documented that they can recognise individual humans in live interactions."
] |
[
"I'd like to see more studies on crows and magpies as well, also targeting raccoons and flying foxes. I didn't find any research on these animals."
] |
[
"The New York Times published an article a few years ago about facial recognition in crows, and also group memory of recognized 'enemies'. The story is here: ",
"http://www.nytimes.com/2008/08/26/science/26crow.html?_r=0",
" and comes from the University of Washington. Not sure if there is a corresponding article from an academic journal on that study too."
] |
[
"Is the vascular system of women better than men?"
] |
[
false
] |
Considering that they have to replace the lost blood periodically, is their vascular system flush with fresher blood? I heard that it is good to donate blood because it stimulates the marrow into producing more blood.
|
[
"I heard that it is good to donate blood because it stimulates the marrow into producing more blood.",
"Your body is constantly producing and destroying blood cells on a daily basis. "
] |
[
"I heard that it is good to donate blood because it stimulates the marrow into producing more blood.",
"It's good to donate blood because it saves lives. But a healthy person's bone marrow will be constantly producing blood cells no matter what. A red cell only lives about 3-4 months, so they are constantly being recycled and replaced.",
"There is a medical condition called ",
" in which the body makes too many red blood cells. People with that condition need to have regular bloodletting (seriously!) to avoid complications. But that is pretty rare, and it's not the same thing as regular blood donation."
] |
[
"is their vascular system flush with fresher blood?",
"Not really, no. Women who have menstrual cycles are more likely to have iron deficiency anemia, though.",
"I heard that it is good to donate blood because it stimulates the marrow into producing more blood.",
"That's wrong and I've heard smart people say it as well. Smart people who presumably aren't anemic on purpose.",
"EDIT: I should say it does stimulate the marrow. But it stimulates the marrow because there are not enough blood cells. It's like saying getting a leech treatment is good because it stimulates the blood."
] |
[
"How does light transfer energy without having mass?"
] |
[
false
] |
Since it's something we deal with everyday it feels intuitive that sunlight causes things to warmup. How does it do that exactly? How does something with no mass effect things that do?
|
[
"Light is an electromagnetic wave, which is essentially an electric field and a magnetic field that dance around around each other, and self sustain each other, as the wave moves through space. ",
"These electric and magnetic fields actually carry energy in them! This is demonstrated better nowhere than the capacitor and the inductor, which are electronic devises that store energy in their respective electric and magnetic fields. The energy stored in these fields is what you feel when light from the sun warms your skin. "
] |
[
"The whole \"relativistic mass\" thing is an outdated way of looking at things. I believe that the preferred way of thinking these days is that photons have no mass, but they ",
" have momentum."
] |
[
"The whole \"relativistic mass\" thing is an outdated way of looking at things. I believe that the preferred way of thinking these days is that photons have no mass, but they ",
" have momentum."
] |
[
"Do human antibodies bind to animal cells? I see that in ANA tests they use rat cells. are they transgenic mice? or just regular mice."
] |
[
false
] | null |
[
"The body only really makes antibodies against stuff it has actually encountered. So a human would only have antibodies against animal stuff that has come into contact. Under normal circumstances that might be a bit of hair and the like, rather than more intact/living cells or their nuclei (what ANA tests for).",
"An ANA test on human blood will usually be ELISA and not have anything to do with animal cells. They will probably use secondary antibodies from some animal (mouse, rat, rabbit, whatever floats your goat) just to bind to and detect human antibodies. You wouldn't be mass producing those antibodies in animals though, rather you'd generate some clonal cell lines."
] |
[
"Wait but they used to use animal cells? ",
"https://www.hopkinslupus.org/lupus-tests/lupus-blood-tests/",
" 'usually sections of rodent liver/kidney or human tissue culture cell lines' What I mean to say is, do human cells and rat cells share the same antigens. Thanks for replying btw"
] |
[
"I don’t know about ANA tests in particular, but nuclear proteins in general tend to be highly conserved (I.e. similar across a wide range of species). This makes sense because the basics of DNA replication and RNA production are virtually identical across hundreds of millions of years of evolution. Wikipedia’s article on ",
"conserved sequences",
" notes that many of them are the “",
"”."
] |
[
"Is our emotional response to certain colors caused by nature or nurture?"
] |
[
false
] |
[deleted]
|
[
"As in all things psychology, the answer is both. Take the color red for example. Researchers measured hormone levels of women every day for 1-2 months, took their picture, and independent people rated how attractive they were. They found that women wear red almost 2-3x more often when they're going through the first few days before ovulation, aka when they are most fertile. It has been suggested that possibly, we (men) have learned that red coloring on women = fertility, and it is a subconscious cue for us to want to mate. ",
"Does this effect hold up across cultures?"
] |
[
"As in all things psychology, the answer is both. Take the color red for example. Researchers measured hormone levels of women every day for 1-2 months, took their picture, and independent people rated how attractive they were. They found that women wear red almost 2-3x more often when they're going through the first few days before ovulation, aka when they are most fertile. It has been suggested that possibly, we (men) have learned that red coloring on women = fertility, and it is a subconscious cue for us to want to mate. ",
"Does this effect hold up across cultures?"
] |
[
"Women wearing red 2-3x more often while ovulating is interesting and possibly useful to know scientifically, etc., but it tells us nothing about genetic/environmental causation, because either genetic factors OR environmental factors could very easily be used to explain that. ",
"You would need results that are unambiguously only explainable by one or the other and ideally which make falsifiable predictions exclusive to one or the other as well (which is usually difficult or impossible in most cases, since genes can interact with their immediate cellular environment, which interacts with its immediate organ environment, etc. etc. bidirectionally on a continual basis. But that's still what you would need for such claims)"
] |
[
"Would there be negative side effects to de-desertification of the Sahara?"
] |
[
false
] | null |
[
"Of course. The Sahara and it's surrounding environment are far from lifeless and the ecologies are adapted to the current state. Furthermore,there are many unknowns in the way this might affect weather patterns around the world. There would most certainly be effects and they would be disruptive - not to say they would be all bad, but they would require some degree of adaptation. Because of the scale of the Sahara and the complexity of climate, the effects would be very difficult to predict. For all we know, a desert might develop somewhere else. "
] |
[
"You'd kill the amazon rain forest. Dust from Bodélé and elsewhere in the Sahara blows across the Atlantic Ocean and fertilizes the Amazon. ",
"http://m.theatlantic.com/technology/archive/2012/08/today-in-astonishment-the-amazon-rainforest-gets-half-its-nutrients-from-a-single-tiny-spot-in-the-sahara/260655/"
] |
[
"This is along the lines of what piqued my curiosity. I understood vaguely that we kinda sorta thought sand storms actually spark hurricanes in the atlantic as well."
] |
[
"What gas has the strongest color?"
] |
[
false
] |
[deleted]
|
[
"Iodine",
" has a strong magenta colour as a gas. Scroll down for a photo. This is the first I could think of. "
] |
[
"Could you explain further? What does \"strongest color\" mean, and in what way do gases \"have\" colors?"
] |
[
"They do have colors. I just wasn't sure if you were referring to maybe absorption or emission spectra instead of reflection spectra or what have you. Ignore my silliness.",
"I don't have the requisite knowledge to answer your question, but I can tell you a few things you need to consider controlling for in a hypothetical experiment. Either pressure or molar concentration will affect the amount of light absorbed, not sure which (these are not the same but are related by temperature). Your question is better if these variables are controlled for."
] |
[
"What is the minimum number of sides on a rubik's cube that must be known, after randomizing, to successfully solve it?"
] |
[
false
] |
In the case of more than one unknown side, each unknown can either be opposite or adjacent to each other.
|
[
"Exactly half the possible configurations can actually be reached. If you know everything about every piece but one edge, you can deduce the orientation of that edge, but there's no information beyond that.",
"It may or may not be solvable with five sides known. You might have a green/red edge and a green/yellow edge with the red and yellow edges on the unknown side, making them indistinguishable. But if that side is solved, you'll know it's solved because none of the unknown edge pieces can be confused with each other. Also, the face piece is known since it's the only one not accounted for, and if you know two sides of a corner piece, you know the third side.",
"If there are two unknown sides, if they share an edge there's a completely unknown edge that could be confused with anything, so it's impossible. If they don't share an edge, I'm not sure how to prove it but I'm pretty sure there's too many unknown edges so there will always be ones that can be confused with each other."
] |
[
"Do you mean \"the smallest n such that for every legal Rubik's cube state, there exists n faces which provide enough information to determine a solution\", or do you mean \"the smallest n such that there exists n faces such that for every legal Rubik's cube state, these n faces provide enough information\"?",
"In the latter case, the answer is n = 6 (i.e. all six faces are necessary). Five faces do not suffice; while any five faces would give enough information to determine all the corner cubies, this is not true for the edges. Consider the state given by (L' R F2 R2 D2 R2 B' R2 D2 R2 F2 L R' U'), where the four edges on the U face are flipped. If every face but the U face is visible, it is indistinguishable from (L R F R2 U2 R2 U2 R2 U2 F' L' R'), where the four U edges are still flipped, but have also been rearranged.",
"In the former case, the answer is still n = 6. Consider the superflip state where all twelve edges are flipped (L2 F' L2 R2 F L2 F' L2 B2 U2 L2 F' L R' U' R2 U2 B F' R' D' U'); any choice of five faces would lead to the same situation as described above where the permutation of the edges on the unseen face is not uniquely determined.",
"(Alternatively, if we're allowed to continue looking at our n chosen face(s) during the solve itself, then the answer is simply n = 1, because we can always use preliminary moves to move every sticker into view to determine the identity of every piece.)",
"On the flip side, contrary to ",
"/u/DCarrier",
"'s answer, there ",
" states that are solvable when four visible faces are given. One such example is (L F2 L U B D2 U2 F' D' F' R2 D' U L'), where the U, F, L, R faces provide enough information to reconstruct the whole state. There is no state solvable with only three visible faces, because for any choice of three faces, there will be at least two completely invisible edge cubies, the orientations of which are not uniquely determined. (Edit: I missed out some edges that made my example state have at least three solutions, thereby invalidating my claim. I still believe there are states solvable with only four visible faces, but I've not managed to find any correct example yet.)"
] |
[
"None, if it was randomized to solved (despite how improbable, that is the minimum)"
] |
[
"Can you get diabetes from eating sugar supplements."
] |
[
false
] |
The idea being that when you eat a sugar supplement, for example when drinking a diet fuzzy drink, your body produces and releases enzymes into the digestive system to break up the sugar molecules. But because these sugar supplements are not sugar and as a result do not consume the enzymes; The body reacts to the large amounts of enzyme being left in the digestive system with not producing as much enzyme the next time sugar is consumed. Does this phenomena exist and can it lead to diabetes or any other sort of permanent disease?
|
[
"There's no known negative side effects in humans of ingesting a reasonable amount of artificial sweeteners. Type 2 diabetes is thought to be caused by environmental factors like diet, but it is related to having a large waist with lots of belly fat. It is characterized by an insensitivity to insulin, where the hormone does not have much effect on lowering blood sugar where the high levels of abdominal fat are though to cause the insulin insensitivity. ",
"The digestive enzymes that metabolize sugar in the gut are not consumed in the process, and as far as I know the body does not regulate enzyme secretion by observing how much excess enzyme was left over from previous meals. "
] |
[
"Show me the data. I'm willing to bet all you have is correlation. ",
"Fat people tend to drink diet soda, fat people tend to have diabetes."
] |
[
"Yes, when I used the word supplement I actually meant replacement so that naturally occurring sugars would be replaced with artificial sweeteners.",
"English is not my native tongue, have mercy on my soul dear scientists."
] |
[
"Is it possible to build a van sized vehicle propelled by an electric motor powered by rooftop solar panels given present-day technology?"
] |
[
false
] |
It's a pipe dream but I've always wanted the ability to just get in a car and roadtrip to, for example, the Grand Canyon and not have to worry about paying for gas or a hotel room. I'm just looking for any possible way that I can have a vehicle large enough to fit a mattress in the back that I can drive around in powered only by the sun. If I have to stop and let the thing charge every hour, fine, I can deal with that. Is there enough power generated by present-day solar panels that I could pull this off and get to minimum highway speeds?
|
[
"This question is fairly common on this subreddit. I answered something similar ",
"Here",
". The specific result was that you need 35x the area of a normal car ",
" to get around 20hp. If you are willing to drive one hour a every day and a half, you can have ~20hp by covering the entire area of your car in solar panels. You probably need a pretty slippery car to get to 20hp, but if not you can always double the power for half the time.",
"Edit: clarification"
] |
[
"covered in current tech solar panels to get around 20hp",
"To make matters worse, it can only get about five times better. Current off-the-shelf consumer single-junction PV is about 20% efficient at the upper end of the market. And you can't get more than 100%-- that's all the energy available for even a perfect panel. Granted, 100hp would be a massive improvement-- but that's still subject to the 1h of driving per 36h of sitting limit. ",
"It's not entirely useless to put them on electric cars, but at least for now, it's much more cost-effective to put them on fixed rooftops where you can plan for angles and shade, have space for many times as many panels, and don't have to worry about putting your expensive PV at risk of chips and cracks from high-speed driving.",
"Hell, even covering parking spaces with them makes more sense, because a parking space is two or three times the surface area of a car due to all the extra depth and width for door opening and whatnot."
] |
[
"There was, but the panel was not large enough to run heat or a/c-- it only ran a small vent fan to circulate hot air out of the car.",
"Amusingly, when I tried to buy one here in Arizona in 2010 (seemed like a perfect fit for a sunny place with 125F heat), the dealership warned me against it because it's too hot here, and there was some sort of thermal protection circuit that prevented the fan from running if it was too hot. Showed me multiple examples on his lot... fans would run in the morning, but as soon as the day warmed up, they'd stop, just when you needed them most.",
"It's possible they've fixed this since then-- I haven't been in the market for a car since then, and kinda stopped paying attention. "
] |
[
"What is the minimal amount of social interaction needed to not lose sanity?"
] |
[
false
] |
[deleted]
|
[
"I'm not an expert on this topic, but I spent 6 weeks with absolutely ZERO contact with humans years ago while camping in northern Alberta, Canada. (Note: I wasn't lost or stuck, I did this on purpose!)",
"By the end, I was having full conversations with myself, and even arguments. I was also having vivid dreams were I did nothing but talk to people the whole time. I didn't ",
" crazy or anything, but I did find myself filling the silence by talking to myself and also singing a lot.",
"When I finally re-joined civilization I was able to converse normally and didn't seem \"crazy\" to anybody (at least, my friends never pointed out that I was being weird). ",
"So I guess my answer is: Longer than 6 weeks :)"
] |
[
"No. The only things I had were a 8'x8' blue tarp, a large axe, about 200 feet of nylon rope, a small metal pot (with a long handle), a fishing pole (with 3 hooks), a bar of soap, and 10 lbs of brown rice in a water proof container.",
"Clothing wise: A winter jacket (rated to -40C), three sets of wool socks and the jeans and T-shirt I was wearing.",
"Nature was nice enough to provide a lake full of delicious fish, and a forest full of delicious ferns and berries. And it was summer :)"
] |
[
"Zero. Read ",
"The Island of the Blue Dolphins",
". It is a well written famous children's book based on the true story of an Aleutian woman stranded on her home island, alone, for 18 years. While she was not able to effectively communicate very well with anyone after the ordeal due to language barrier (there were no survinvg members of her home), she was clearly not insane.",
"Edit - Answer was in regards to sanity. Mental health is another issue and debatable.",
"Edit 2 - Also see the documentary \"Alone in the Wilderness\" (amazing documentary) about ",
"Richard Proenneke",
". This guy makes survival shows look quaint. He lived for like 30 years alone and isolated in rural Alaska, seeing people like 3-4 times a year."
] |
[
"Can a central force produce different closed orbits?"
] |
[
false
] |
I saw on and was interested in the mechanics of a geocentric solar system. Could a central force produce two different closed curve orbits other than a circle and ellipse? Could an object subject to a central force orbit the source of the force on a cardioid, or any other closed curve, for example?
|
[
"The following statements should answer all of your questions.",
"In general, the bound orbits of a point mass in a central force field are not closed. (Note, however, that circular orbits do exist for all ",
" central force fields. ",
" See ",
"this post below",
" for some clarity on that point and click through the deleted post.)",
"For any central force, if a bound orbit exists then it lies in an annular region. That is, the orbit lies between a minimum distance (such points are periapsides) and a maximum distance (such points are apoapsides) from the center of the orbit.",
"The only central force fields for which all bounded orbits are closed are the potentials U(r) = kr",
" (the simple harmonic oscillator) and U(r) = -k/r (Newtonian gravity) for some k > 0. In both of these cases, the bound orbits are ellipses. (So nothing exotic like rosette patterns.)",
"For all other central force fields, the bound orbit (if it exists) is partially described by the apsidal angle, the angle between successive apsides."
] |
[
"Here's a nice web applet that lets you play with different central force laws. ",
"Demo for Newtonian gravity",
" (F = -GM/r",
"Demo for 2D harmonic oscillator",
" (F = -kr)",
"General demo",
"Enjoy!"
] |
[
"The only central force fields for which all bounded orbits are closed are the potentials U(r) = kr2 (the simple harmonic oscillator) and U(r) = -k/r (Newtonian gravity) for some k > 0. In both of these cases, the bound orbits are ellipses. (So nothing exotic like rosette patterns.)",
"Is this related to the fact that these two potentials are more symmetric than the other central forces? The ",
"derivation of Bertrand's theorem",
" on Wikipedia makes it look like an ugly accident, and doesn't give me any intuition, whereas I know that the harmonic oscillator and Kepler potentials are special for having extra conserved quantities in addition to angular momentum. Is there some way to see the result through symmetry?"
] |
[
"Why do we fall asleep when we are bored?"
] |
[
false
] | null |
[
"the question implies this is not the case and wonders why boredom makes someone who has gotten plenty of sleep tired and what purpose it serves"
] |
[
"That's because the question is wrong. ",
"\"If you believe that boredom, a warm room, or a heavy meal causes sleep, you are completely wrong! If boredom, a warm room, or anything else seems to cause you to feel drowsy, you have a sleep debt and you need to be stimulated in order to stay awake.\""
] |
[
"How do you know that the sleepiness comes from boredom and not prior sleep deprivation?"
] |
[
"Whenever I read a story about a school or something installing a windmill for the purpose of powering the building, I always hear something about selling the excess power to the power company. How exactly do they do this?"
] |
[
false
] |
I mean, do they just charge up batteries and send them over? Sorry if this is the wrong subreddit, figured this was my best bet.
|
[
"Typically a wind or solar system will be used to charge a bank of batteries for power on-site. These systems can be connected (by a professional!) back to the grid, and when your batteries are fully charged and your source of electricity is generating more power than you need, your meter will actually run backwards. (Most installations of this sort will require you to remain a customer of the utility, as you will unlikely be able to cover your power needs 100% of the time.)",
"There's plenty of information on the specifics of selling power back to utility companies, and generally the rates are not favorable to consumers, so it's rarely the primary purpose of installing alternative electrical system."
] |
[
"Many properly constructed solar houses actually produce more energy than they need and the owner of the home actually recieves a check from the power company.",
"What typically happens is the power generated by the mechanical motion of a turbine or from a solar array is just wired into the grid, allowing power to be drawn by the homeowner and used onsite with excess being used by others.",
"If said house does not produce more than they use for the month, then they are only charged by the power company for the amount that had to be generated by the company, as the homeowners generated power allowed for the otherwise generated power (from the company) to go to some other customer."
] |
[
"Net Metering",
" allows electricity generated onsite to run the electric meter backwards if more is being generated than is needed (and thus being sent to the grid as a result). When the power company comes and reads the meter at the end of the month, they'll credit you the appropriate amount of money if the meter indicates that you generated net power since the last billing cycle. Smart meters take this a step further and figure out how much you get credited in real time, as overall demand fluctuates during the day."
] |
[
"Would a live stream of a clock travelling at near the speed of light appear to be ticking slower to someone stationary on earth?"
] |
[
false
] |
Or say an astronaut is going 25,000 miles per hour (I think that's the fastest any human has travelled). He has a stopwatch that shows time to many decimal points and a camera pointing at the watch. To an observer on earth watching a stream from the camera would the watch appear to be ticking slower than a similar watch in the observer's hand? New to relativity and trying to get my head around it.
|
[
"Yes, although at 25,000 mph, just barely.",
"Let's instead look at a clock travelling .866c with respect to us. If we kept a telescope trained on that clock, and we kept an identical telescope next to our telescope, we'd notice that our clock ticked twice for every single tick of the travelling clock. Time is passing more slowly for the clock that is travelling. If we had a bit of radioactive material with a half-life of one hour next to our travelling clock, we would notice it took two of our ours for half that material to decay. If we had a mouse along with that clock and radioactive material, we would notice that the mouse lived twice as long as our mice back home.",
"These effects would be negligible for something travelling 25000 mph. If an object traveled at 25000 mph for a year of ship time, we would observe it taking a year and 1/50th of a second to make the trip."
] |
[
"we'd notice that our clock ticked twice for every single tick of the travelling clock.",
"As it happens, this isn't what you actually ",
". The Lorentz factor tells you how much time \"really\" passes on the two clocks, ",
" accounting for the speed of light delay in the signal. To answer the question of what one ",
", you need to have more information about the direction of motion.",
"The two simplest cases are those in which the traveler is approaching or receding radially with no lateral motion. In the approaching case, you ",
" the moving clock as running fast, while in the receding case it appears to be running slow (by a factor different from the Lorentz factor).",
"Here",
" is the spacetime diagram for an approaching clock, and ",
"here",
" is the diagram for a receding clock. In both cases the green line is the stationary observer, the red line is the clock traveling at 0.6c to make my life easier, and the yellow lines represent light pulses sent out every second as measured by the moving clock (the spacing is 1/4 second vertically and 1/4 light-second horizontally). Note that when the clock is receding you see the pulses come at two-second intervals, and when it's approaching you see them at half-second intervals."
] |
[
"Fair enough. I should have said, \"moving tangentially.\""
] |
[
"When neurons are transmitting messages, why don't the messages go through each and every neuron exactly how it was received initially?"
] |
[
false
] |
Sorry if the title doesn't make too much sense, I'm learning about action potential in Psychology and don't understand the transmission of the messages. What I do get is how the messages travel through the axon via chemical polarization and depolarization, albeit some of it is a bit fuzzy, and from what I've learned on Khan Academy & my textbook is that the messages are sent from one neuron to the next etc..., over long distances. So when I get poked with a needle on my finger, why do I only feel pain on my finger not all the way up my arm? From what I know I would assume that that same "pain" message is being sent from my finger to my spine to my brain? What is the message being sent? I know that it's electrical based through chemicals, but does the message change as it goes through more and more neurons? Would the dendrites not have as much stimulations as the number of neurons between it and the neuron initially struck be lesser because of the increased distance? It would great if you could cover the basics of action potential to clear anything up which I'm misunderstanding if I am, today's my first look at the topic and I've only put an hour or two into it, so I can't say I know a lot about it.
|
[
"Your general idea of how an action potential works seems correct. A chemical message in the form of a neurotransmitter signals the dendrite of a nerve to begin an electrical signal (in the form of ions flowing across the neuron's membrane). If that signal is adequate (close enough to the axon hillock or followed by enough other signals) an action potential propagates down the axon and results in neurotransmitter release which signals the next axon, and so on.",
"As to how this carries ",
", that's more complicated. Neuronal transmission is not a 1:1 phenomenon; that is to say, one neuron firing upon the next will not necessarily cause the next neuron to fire. Whether the next neuron fires depends basically on how much stimulation it gets: how many neurons dump neurotransmitter onto its dendrites, how close together in time these signals are, and how close spatially they are to the origin of the axon. If the summation of incoming signals is high enough, the neuron exhibits an action potential and releases neurotransmitter onto the next neuron.",
"Now, to your specific question. The reason we know that a pinprick occurs on our finger is due to somatotopic organization within the brain. Neurons that sense input from the skin of your finger are kept separate from neurons that sense input from skin on other parts of your body, and as they synapse and project up into your brain, that separation is retained. Inside the brain, the information is projected onto a specific part of the somatosensory cortex that is responsible for processing information only from that particular piece of skin. You can look up sensory homunculi on google to see what part of the brain handles what part of the body."
] |
[
"I'm unclear what you mean by \"Neuron arrangements\" but I'll interpret as how the neurons are connected to each other in space. The answer is, in as far as we know yes. How neurons are wired together through the formation of synapses, the strengthening of synapses or the weakening of synapses, in what is termed synaptic plasticity, is how information is stored in our brain. ",
"The second part of your question is also true. A second order of synaptic plasticity exists which is termed metaplasticity (the term coined by Cliff Abraham and Mark Bear). After a bought of neuronal activity, the neuron has a modified threshold for further plasticity. Plasticity is a change in synaptic strength, this process describes a change in the change of synaptic strength and hence meta-plasticity.",
"Source: Second year neuroscience masters student holding first class honours in neuroscience."
] |
[
"An axon hillock is the point of the neuron at which the axon connects to the cell body.\nTo expand on the relevance of the action hillock in this discussion:",
"Action potentials travel through a neuron in the form of an electrical charge. The charge across the neuron is not equal. Input from the axons of other neurons impacts the chance of producing an action potential differently dependent on where on the neuron the message is received. An action potential will only be created if the charge of a neuron at the axon hillock reaches the cells tipping point. This is easier to achieve if the synapse of a previous neuron is close to the axon hillock of the next neuron than if the synapse is further away because only at that point does the voltage need to reach the tipping point.",
"In the case of an action potential being received at the dendrites of a neuron as opposed to the cell body or closer to the axon hillock, the voltage of the cell has to change all the way through the cell to the axon hillock to create an action potential. Since synapses connected closer to the axon hillock have less of a distance to travel, it requires less of a signal (voltage change or amount of inputs from other neurons) in order to create an action potential.",
"source: third year undergraduate psychology student. Some of this information may be simplified or slightly inaccurate. "
] |
[
"If space is expanding, are more units of space being made, or are they getting \"bigger\"?"
] |
[
false
] |
My knowledge of quantum field theory is very tenuous and high-level - I have basically no clue about the underlying math here - but my rough understanding is: So if space is expanding, are more quanta of space being created? Or is existing space stretching in some way? IE - is the ratio of quanta of space to the size of the universe steady or changing? Either way, doesn't this mean that more energy is being created out of nothing? How does that work? Or am I off the mark with the space quanta thing?
|
[
"If you draw a sphere in space by putting test masses (at \"rest\"), or galaxies, all around its surface, then as the universe expands there are more cubic meters inside the sphere as time goes on.",
"But, a few remarks on your other comments:",
"- We do not as yet have evidence that space itself is quantized. That probably requires a unification (theoretical and experimental) of gravity and quantum mechanics.",
"- There is the possibility that the \"dark energy\" is indeed a \"vacuum energy\", ie intrinsic to space and quanta, but that's at the conjectural level since any computation gives a energy density (for the dark energy) that is 10^120 off the real answer. Even in cosmology, that's a miss. But yes, in that model, there's an energy density associated with every cubic meter of space, and as space expands there's more energy. It turns out that that's okay in General Relativity, because there is no requirement that the global energy be conserved in GR.",
"- The expansion of the universe is not \"due to dark energy\"... but we think that the acceleration of that expansion (ie speeding up with time) is due to dark energy.",
"- I believe (but would appreciate expert backup on this) that *if* space is quantized, then the expansion of space would require more bits of quantized space to be created, rather than expanding the size of the quantized bit. The latter idea seems like it would require time-evolution of fundamental constants in physics, which would lead to terrible time-dependence of all sorts of phenomena, which I very strongly suspect we can rule out given our observations of phenomena from long long ago (ie very distant objects, the plasma of the CMB, etc)."
] |
[
"Jumping in on that last point - the current fashion in quantum gravity is to consider the total number of bits of information that can be stored in a finite volume of space (which is surprisingly thought to be finite even if space itself is not quantized). As a given volume of space expands, more information can be stored in it, so in this sense the number of \"bits\" is indeed growing in a finite volume universe. I'd probably consider this still in the realm of conjecture due to the lack of direct experimental probing of the Planck scale, but theres a ton of mathematical evidence that this is quite likely the case."
] |
[
"I love arguments based on information theory - thanks for adding that! But surely the number of bits that can be added depend on the \"size\" of the bit, and it seems like you're assuming that is fixed in meters, yes?"
] |
[
"How is the \"power\" of dish soap measured? How can a company claim one of its products is \"3 times as powerful\" as another one?"
] |
[
false
] | null |
[
"Soap works by forming something called a miscelle. It's basically a ball where all the dirt and grime sticks to the middle, the hydrophobic part, and the water touches the outside hydrophilic part. When you use soap, you're not killing any bacteria or dirt, You're just making tiny dirt bubbles and washing it away.",
"I would say that if soap has the ability to make more miscells, as it has more lipids, it's likely to be a better, more powerful soap. As you wash it down with other fillers or water it becomes less powerful.\nEdit- I've added a ",
"picture",
" to help you understand the soap at the molecular level "
] |
[
"...you're not killing any bacteria...",
"Well, you absolutely can and will kill bacteria with a surfactant like soap. Not all bacteria are equally susceptible, but many are.",
"I would say that if soap has the ability to make more miscells, as it has more lipids, it's likely to be a better",
"Increasing lipid fraction of surfactant does not necessarily decrease CMC, nor does it necessarily make higher # density miscellar solutions. It's the interplay between the hydrophobic and hydrophilic parts, the relative size, and the shape of the surfactant molecule that will make variously sized and shaped miscelles and therefore affect the ability of the soap to extract dirt."
] |
[
"Soaps are basically surfactants. They remove dirt by lowering surface tension of water and forming emulsion with dirt. There are various parameters of soap efficiency. In case of dish soaps, the efficiency is usually determined by testing the amount of dishes cleaned by a particular amount of soap, foam test, CMC, surface tension test, anti-microbial test, etc. From all these tests statistical average is drawn and compared against the competitors. However the actual power of soap depends on many factors, and the statement of by how many times one soap is powerful might just be a marketing strategy."
] |
[
"What causes an allele to be dominant or recessive?"
] |
[
false
] | null |
[
"The dominance of different alleles of a gene is largely determined by the nature of the protein that it encodes. For example, defects in structural proteins generally manifest as dominant traits because being heterozygous results in defective protein synthesis, which disrupts the native healthy protein. On the other hand, defects in enzymes tend to be recessive because there is a certain amount of compensation, such that heterozygotes may be asymptomatic (aka gene dosage effect). These rules do not always hold (eg haploinsufficiency with familial hypercholesteremia), but are useful generalizations. ",
"Here's my attempt to simplify the above via analogy:",
"So think of structural proteins (very simplistically) as bricks. The allele (B) codes for a normal brick, while the allele (b) codes for a brick that is spherical instead of rectangular. You can have BB, which makes the wall all rectangular and normal, or you can have bb, which is just a pile of spheres. What about the heterozygote? Bb will lead to half normal bricks and half spheres, which ultimately does your wall no good. In this scenario, the heterozygote still has a loss of function, so we think of that trait as 'dominant'.",
"Now think of enzymes (very simplistically) as trucks carrying cargo from point A to point B. Again, you can have working trucks (T) or broken trucks (t). Having only working trucks (TT) is great - everything gets delivered on time. Having only broken trucks (tt) is bad. What about the heterozygote (Tt)? Well it depends on how much cargo you need to deliver! If you have a low cargo day, then the number of working trucks you have may be sufficient. In this case, the heterozygote is not affected, so we think of the trait of 'recessive'."
] |
[
"the genetics of eye color is actually quite complex, at least 15 genes are involved",
"Although, for a thought experiment, lets assume its one gene:",
"BB = make brown pigmnent",
"Bb = make brown pigment",
"bb = make no pigmnent (unpigmented irises are blue)",
"In this case, blue eyes are classically recessive (although this is NOT how human eye color is acutally determined)"
] |
[
"Since this is a science thread, let's not call alleles genes.",
"Genes cannot be dominant/recessive, but alleles can. Similarly, you cannot have or not have a gene, but you can have one allele or another. "
] |
[
"Do we perceive in 1, 2 or 3 dimensions?"
] |
[
false
] |
I read somewhere that each of our eyes see a 2D image and the brain combines those images that are from different perspectives to create a 3D representation via adding perception of 'depth'. This seems to make sense as illustrated from this . If i look at the corner a, i can intuitively say it forms a right angle. However if i take that same angle and represent it independently of the drawing (b, now looking like a 2D object), i can say it takes on an angle of ~135 degrees. Perspective b is the 2D image one eye gives us, and by combining the perspective from both eyes, we can form the 3D perspective a. But here lies a conundrum. Do we see in 2D or 3D? a and b are exactly the same, but from different perspectives can be thought of as different angles, b=135 degrees if there is no depth, and a=90 degrees if there is depth. I've heard an argument along the lines of, we perceive in 2D and infer approximate 3D, because if we perceived in 3D we would be able to see the back of an object. But i'm not really sure of the grounds for that argument. However recently i watched a video from minutephysics titled In the video he says "Mathematicians have shown that it's possible to fill up 2D or 3D space using a 1 dimensional space filling curve". My questions are as follows 1.) How can 2D or 3D space be represented as a 1D space filling curve? 2.) If it's possible that we live in 1D space, how do we prove that we actually live in 3D space? or can we not? 3.) How accurate (as described above) is the argument that we don't perceive directly in 3D but infer it from 2D 'slices'?
|
[
"In regards to your diagram, the only reason we can perceive that angle as 2 \"different\" angles is due to three-dimensional perspective. Perspective B is NOT a 2 dimensional image. You're viewing it from a different place of reference, indicating 3 dimensional perspective. True 2 dimensional perspective would only allow you to perceive the edges of other objects. "
] |
[
"Thanks for the response.",
"as in, the light emitted or reflected from things in the world around us enters our eyes and is focused on the retinas of our eyes, which are 2-D structures. ",
"What do you mean the retinas are 2D structures? are you saying they don't have width? ",
"The rods and cones in our retinas each end up sensing light that came from a specific direction, which means a 2-D projection of the image from the outside world.",
"So light is hitting this 2D surface (our retinas) and if we could somehow look at that imagine at a particular instance from 1 eye, would you say it would look like a photograph?"
] |
[
"| What do you mean the retinas are 2D structures? are you saying they don't have width?",
"They line the inside of the back of the eyeball: two dimensions. It's not like the whole\neyeball is filled with layer after layer of photoreceptors or anything, so not three.",
"| So light is hitting this 2D surface (our retinas) and if we could somehow look at that imagine at a particular instance from 1 eye, would you say it would look like a photograph?",
"Yeah, pretty much (ignoring the fact that the retina is probably\nnot a very good projection screen, and looking in from the outside\nmeans looking through the lens of the eye, which is going to distort\nwhat you see from the outside, but it's the exact same principle\nas how a camera makes a photograph)."
] |
[
"Would the night sky look very different on a planet orbiting proxima centuari compated to ours?"
] |
[
false
] | null |
[
"Alpha Centauri would be extremely prominent at magnitude -7 or so. Not as bright as our Moon but still dominating the night sky when visible, and clearly visible even during the day (assuming similar or better atmospheric conditions).",
"At a typical separation of around 0.1 degrees a human eye could see it as binary star."
] |
[
"It would depend a lot on the exact stars, but only moderately different. eg: there's a new fairly bright star somewhere around Cassiopeia (Sol), and Sirius would have moved a lot, but Betelgeuse very little and Deneb not at all."
] |
[
"One significant difference is that the Sun would appear as a 1st magnitude (+0.5) star in the constellation Cassiopeia. Observers there would see it as the brightest star in the W of Cassiopeia, which would appear only slightly distorted from its appearance on Earth.",
"Sirius, the brightest star in Earth's night sky would be slightly dimmer from Proxima as it's an additional 1.5 ly distant. Canis Major, the constellation in which Sirius resides would be distorted beyond recognition in Proxima's sky. ",
"Procyon, another relatively nearby bright star would also be less bright from Proxima due to increased distance."
] |
[
"Question on the motion of dark matter"
] |
[
false
] |
[deleted]
|
[
"Well, it interacts gravitationally. So it can be attracted by the gravitational field of, for instance, a billion stars."
] |
[
"There's nothing in principle saying there couldn't be, but it depends on what exact particle the dark matter turns out to be. If there were, then in all likelihood most of it would have long ago annihilated away, just like the rest of the antimatter did."
] |
[
"The smart money is on dark matter consisting of the lightest neutralino, which theory predicts should be a Majorana fermion — that means it's its own antiparticle. If that's the case then yes, neutralino-neutralino annihilations can occur. But the rate of annihilations will be much less than it would be for, say, a cloud of electrons and antielectrons, because neutralinos are uncharged and thus aren't attracted to each other electrostatically.",
"Searches are underway right now for evidence of cosmic neutralino annihilations. But those events are expected to be very rare, so it'll be a while before those searches tell us anything one way or the other."
] |
[
"How legitimate are the results of Harvard's \"Eating ANY red meat leads to higher risk of premature death\" study?"
] |
[
false
] | null |
[
"Actually, that looks awfully solid. The biggest red flag to look out for with these sorts of broad cohort studies is any kind of variable between the groups that are extraneous to the one being tested. They controlled for a ton of variables:",
"We simultaneously controlled for intakes of total energy, whole grains, fruits, and vegetables (all in quintiles) and for other potential nondietary confounding variables with updated information at each 2- or 4-year questionnaire cycle. These variables included age; body mass index (calculated as weight in kilograms divided by height in meters squared) (<23.0, 23.0-24.9, 25.0-29.9, 30.0-34.9, or 35.0); race (white or nonwhite); smoking status (never, past, or current [1-14, 15-24, or 25 cigarettes per day]); alcohol intake (0, 0.1-4.9, 5.0-14.9, or 15.0 g/d in women; 0, 0.1-4.9, 5.0-29.9, or 30.0 g/d in men); physical activity level (<3.0, 3.0-8.9, 9.0-17.9, 18.0-26.9, or 27.0 hours of metabolic equivalent tasks per week); multivitamin use (yes or no); aspirin use (yes or no); family history of diabetes mellitus, myocardial infarction, or cancer; and baseline history of diabetes mellitus, hypertension, or hypercholesterolemia. In women, we also adjusted for postmenopausal status and menopausal hormone use.",
"Pretty extensive, and that's not even the entirety of their controls. I'm impressed. Obviously the big step is to demonstrate some sort of mechanism explaining the observation, but the data and the analysis are solid if you ask me."
] |
[
"It's a good study for how large it is. I'm not necessarily debating their findings, but self-questionnaires on diets are commonly flawed (especially in a case like this where diet questions were taken so infrequently). ",
"(speculation) Additionally, if you think about the average diet, those that are unlikely to eat red meat and have good recollection of their diets are probably more likely to be health conscious (or at least diet conscious).",
"I'd love for this to be examined in greater detail to elicit a possible cause or link."
] |
[
"Did they control for total carbohydrates and refined carbohydrates? ",
"Most red meat in North American society comes with a hearty helping of carbohydrates. You wont see many steaks without potatoes, or burgers without buns. It would be interesting to see if they were able to control for this.",
"I would read the paper myself, but I don't have my university sign-on anymore to get publications. :("
] |
[
"Store data in living DNA?"
] |
[
false
] |
Is there any wasted space in the DNA code of living things? and Given a file format that used DNA, could one for example, store a message in DNA that would propagate to offspring?
|
[
"Is there any wasted space in the DNA code of living things?",
"Yes, but not as much as you think. ",
"The Encode Project",
" recently found that about 18% of your DNA regulates the 2% of your DNA that manufactures proteins. And this definitely isn't the complete picture. While we do have a lot of junk that is leftover from the evolutionary process, we are still studying the human genome.",
"Given a file format that used DNA, could one for example, store a message in DNA that would propagate to offspring?",
"A T C G are the base codes in DNA. Using a ",
"http://en.wikipedia.org/wiki/Quaternary_numeral_system",
" we could easily convert this to binary and it would actually be a pretty good way to store information.",
"However, since the DNA would be non-functional.... it would definitely undergo mutations. This isn't extremely corruptive and the same thing can happen to bits in other storage medium, but I speculate that DNA would undergo this at a higher rate. Their are many ways to repair corrupted data in computer science, but only to a certain extent.",
"It would last a long time, but is that enough time for it to propagate uncorrupted to offspring? That I don't know. Maybe someone with more knowledge in genetic mutation could comment."
] |
[
"A good estimate of DNA mutation rate is 2.5 mutations per 10",
" bases per generation. Over evolutionary time (millions of generations), of course, there would be an unacceptable loss of integrity in any single copy. ",
"However, if you inserted your message into lots of species with long generation times (not bacteria), you could align all these imperfect messages and infer the original message to high accuracy for a very long time. Scientists using 20 genomes can reconstruct, with ",
"99% accuracy",
", the genomic sequence of the Boreoeutherian mammalian ancestor that lived >70 million years ago. My hunch is that once you are talking about using DNA as a storage medium for tens of millions of years, your problem isn't the degradation of the sequence due to the molecular clock, but it's the extinction of most or all of the lineages you embedded the message in."
] |
[
"There are large segments of the genome (up to 90%) that don't code for expressed genes, but the exact biological role of this \"junk DNA\" isn't fully known.",
"Craig Ventner, who created an organism with an artificial genome, ",
"encoded a lot of information",
" in the genome of a bacterium."
] |
[
"Why is it so drastically easier to tear a piece of tape, or a bag of chips once it already has begun tearing?"
] |
[
false
] |
Just a thought that popped into my head while messing around with some tape at work today.
|
[
"Here's a good article: ",
"http://en.wikipedia.org/wiki/Stress_concentration"
] |
[
"This is also the case for faults on the earth. If you have a homogeneous material (well, as homogeneous as it gets on Earth), then you will be spreading out the stress throughout a specific area of the tectonic plate. However, once you introduce a fault (due to either a previous weakness being exploited, or the stress becomes so much that somewhere has to break), then a lot of the stress will then be concentrated on that fault, thus causing it to move. It's the path of least resistance. "
] |
[
"The stress will concentrate at the ends of the propagating fracture."
] |
[
"How can there be matter (low density plasma) in outer space? Why doesn't gravity pull it towards stars or planets?"
] |
[
false
] | null |
[
"The answer is simpler, with no need to invoke cosmology or general relativity.",
"If you have a gas in a potential (such as one caused by gravity), and each gas particle is undergoing thermal motion, there will be a distribution in gas density where gas is more likely to be found deeper in the potential, with very sparse density higher up in the potential. This is what we observe: sparse gas (or plasma) far from stars.",
"Heuristically, one could compare the root-mean-squared velocity of a proton at interstellar temperatures (~200 m/s) to the escape velocity from a star at a distance of a lightyear (also ~200 m/s) and see that they are similar."
] |
[
" but I think I have enough background knowledge to help here.",
"First, the universe is not at equilibrium. It was once thought that eventually everything either a) had enough kinetic energy from t=0 to continue forever [that is, the universe was expanding beyond the escape velocity of the universe itself] or that it would eventually collapse back down on itself due to gravity. The latter is what you're describing. The thing is: we haven't had enough time for this to happen. A lot of math was done to try to figure out which would happen (or, a third option: the universe would eventually stop and remain in balance forever) These were the \"death models\" of the universe. The big rip and the big crunch.",
" as scientists have confirmed the existence of dark energy, or the tendency for spacetime to expand on its own. There's now a new factor at play in addition to gravity and kinetic energy. This expansion of space itself, since it increases with space itself, is a positive feedback loop. So as we now see it, even at t-> infinity, gravity will not pull everything back together. Dark energy will eventually make every bit of matter arbitrarily far away from every other bit of matter.",
"Second, there's radiation pressure. Fusion releases energy as it's converted from mass, and that energy (photons and particles with a LOT of kinetic energy) pushes away from the objects that release it. These objects also tend to be massive: stars. So stars (or, precisely, their mass) contract spacetime [gravity] but at the same time push stuff away from themselves [radiation pressure, solar wind, etc]. Every once in a while, this energy release is extreme- a star will go supernova and fling large atoms, some of which can only be formed this way, into the interstellar regions of space. The kinetic energy of these nuclei can get them far enough away from other matter that they are not immediately pulled together by gravity/Coulombic forces.",
"I leave any additional explanation to properly tagged scientists.",
"EDIT: clarified a few things, also adding this ",
"depressing link"
] |
[
"The interstellar medium is mostly plasma, and it generally orbits around the Galactic center in more or less the same way that stars do. It ",
" being pulled by gravity. Individual stars' gravity is pretty weak outside of their immediate system, and they generally have stellar winds that push gas away as well."
] |
[
"Some of the spacecraft rendezvous have been compared to firing a rifle on the east coast and hitting a small target on the west coast. What would comparable with New Horizons?"
] |
[
false
] |
After 9+ years and X millions (or billions) of miles traveled New Horizons will end up within just a few thousand miles of the surface of Pluto. What would be a comparable accuracy scaled down to a a distance/accuracy on Earth?
|
[
"The goal in the New Horizons mission is to hit a region that's ",
"60 miles by 90 miles",
" at a location that's about ",
"32 AU",
" or 3 billion miles from Earth.",
"Hitting that region at a distance of 3 billion miles is like sending something from NY to Paris and having it land right in the recipient's hand."
] |
[
"Thanks, that is the type of analogy I was thinking of."
] |
[
"I can assure you NH ",
" perform a gravitational slingshot with Jupiter and the Earth-Jupiter segment was ",
" straight (though pretty elliptical)"
] |
[
"If future data from the LHC and ILC suggest that our universe is metastable, what does that mean for the future of the universe?"
] |
[
false
] |
1) What does "metastable" mean in comparison to unstable and stable? Why is this related to the properties of the Higgs Boson and Higgs Field? 2) If it is metastable, what kind of event could cause it to suddenly want to seek a lower energy state? 3) How fast would this "new physics" bubble expand once it reached a lower stable energy level? 4) Would this be compatible with life chemistry as we know it? If the bubble hit Earth, would we just simply stop existing? Bonus Question: If the Higgs Field were to simply disappear in an area of space, would W+, W−, and Z bosons become massless and completely change the weak force? Does this have anything to do with a vacuum metastability event?
|
[
"While the previous comments give some partial answers, there are still some unanswered questions in your post, so let me jump in. ",
"First, the metastability of the vacuum is ",
". As you might know, the Higgs field is a scalar field which means that it is described by some number at every point of spacetime. The Higgs field is the only scalar field in the standard model (all the other fields consist of a number and a direction associated with every spacetime point) and this allows for a very fruitful possibility: while the symmetries of our universe forbid all other fields to have non-zero values in vacuum (which is roughly the state of minimal energy), the Higgs field is allowed to have a so called vacuum expectation value (vev). This vev is put into the standard model by hand, meaning that it is already present at the classical level, when you don't consider quantum effects. By doing so, you arrive at a classical vacuum configuration that describes our universe very well.",
"\nIt just so happens to be the case that quantum effects can drastically change the vacuum structure and for the experimentally measured parameters of the standard model, this indeed happens. If you consider the standard model as a quantum field theory, the classical vacuum configuration which describes our universe very well turns out to be some excited state while the true vacuum state is a different one. This true vacuum differs from the false vacuum in only one respect: in the size of the Higgs vev.",
"\nThe predicted Higgs vev of the true vacuum is many magnitudes bigger than the classical value, in turn implying that in the true vacuum all particles are magnitudes more massive. ",
"So after roughly describing the scenario let me adress your first question. ",
"1) In this context, metastable does not mean what the other commenters described. Instead it means 'unstable, but with a lifetime that's bigger than the age of the universe'. So in some sense this means that it is unstable but in a way that might still allow for the model to be a consistent description of nature. Look at it like this: if you predicted the lifetime of the current state of the universe to be, say a few thousand years, than your model if clearly at odds with the observed age of the universe of 13 billion years. Therefore, measurements that'd put the standard model in the unstable part of its parameter space would rule it out experimentally! Luckily, actual measurements put it in the metastable region, at the boundary to the stable region - with absolute stability still not ruled out due to measurement uncertainties. As I've argued above, vacuum stability depends critically on quantum corrections to the Higgs field which come from all particles that couple to it, with effects proportional to their mass. Therefore, the most important influence comes from the heaviest particle of the standard model, the top quark. Since the energy of the classical vacuum is also important in determining the stability, another important property is the Higgs mass. Stability is therefore often discuased in terms of those two parameters only, which is strictly speaking an oversimplification, but sufficient in large parts of parameter space.",
"All the other questions are very well answered by ",
"/u/ashpanash",
"."
] |
[
"All of this is very fun speculation, but it's just speculation based on our current models of the universe, which are well understood to be incomplete. Still...",
"1) It means roughly what you probably think it means - it's in a stable configuration but there are other potentially stable configurations it could take, which would presumably manifest as lower energy states.",
"2) No idea.",
"3) Back of the envelope calculation says 'at the speed of light' but it's really uncharted territory.",
"4) Again, uncharted territory. But presumably, no, it wouldn't be compatible with life chemistry ",
". Doesn't preclude other configurations of which we are unaware. ",
"And also, presumably, yes. If it hit earth, everything we understand would stop existing in its current form.",
"Bonus: It's more complicated than this - the Higgs field is a scalar doublet that interacts with the more fundamental electroweak fields in interesting ways. The W and Z bosons as well as the photon would cease to exist as we understand them, instead there would be four different massless bosons. Also, what we consider a right-handed electron would be a different particle than the left-handed electron (along with some funky neutrino physics too). As for how the Higgs relates to a potential vacuum metastability event, as far as I know, ",
". But you can build toy models where the Higgs field is metastable and it's a good analogy for a more general vacuum metastability."
] |
[
"Thanks for the great explanation in how the Higgs Field is related to this!"
] |
[
"Is there currently a reliable way to extract or isolate DNA in a prokaryotic cell without damaging it?"
] |
[
false
] |
[deleted]
|
[
"yes. either shearing or sonication will break up cell walls in the presence of a detergent. then using correct buffers, it is possible to solubilize dna molecules while precipitating out other cellular material and separating solubilized dna from cellular debris by centrifugation. once dna is isolated, it can then be precipitated and concentrated by addition of ethanol to a concentration greater than about 75 percent. once the dna is precipitated and collected by centrifugation, it can then be purified by suctioning off the supernatant, and resuspended in distilled water or tris-EDTA solution.",
"voila: purified dna from prokaryotes. i do this often with e. coli."
] |
[
"Did you mean without damaging the DNA, or without damaging the cell?"
] |
[
"Without damaging the DNA or without damaging the cell?",
"Anyway, there's a technique called SCODA that uses rotating electric fields to isolate DNA. It's pretty effective."
] |
[
"If I were to make an radio transmitter that broadcast at between 430 and 790 THz, would it emit light that I can see?"
] |
[
false
] | null |
[
"Electromagnetic waves at those frequencies are no longer called radio waves, so this wouldn't be a radio transmitter; it would be something that emits light. ",
"Radio and light (and microwaves and IR and UV etc.) are just names we give to different portions of the electromagnetic spectrum. For example, if you designed something that can emit electromagnetic waves that can be tuned from 10",
" Hz to 10",
" Hz, it would move from emitting radio waves at one end on up to UV light at the upper end."
] |
[
"Pretty snobby for being wrong.",
"To be fair, technically you are correct, it would emit light, thus making it \"a lightbulb\". However, the mechanism behind how and why light was emitted would be completely different. It would be novel, not like any light bulb today. In short, you completely missed the point of the question.",
"Incandescent bulbs have their filaments heated until the thermal radiation emits visible light. Similar to a stove top. The hotter something is, the higher the frequency of thermal radiation. Fluorescent lamps use electricity to excite the electrons of the gasses inside, and when they return to lower energy levels, light is emitted.",
"However, if you could drive an antenna at that frequency, it would indeed emit visible light ",
". The challenge is driving a circuit that fast, which is basically only possible for nano-scale sized objects. I believe I have read a paper about researchers trying to do just that, nano-scale visible light antennas. You could google around for some info.",
"I'm not sure how it would look though. I imagine since the wavelength is so small, it would look like a little point of light in some pure color. Just a guess though."
] |
[
"Pretty snobby for being wrong.",
"To be fair, technically you are correct, it would emit light, thus making it \"a lightbulb\". However, the mechanism behind how and why light was emitted would be completely different. It would be novel, not like any light bulb today. In short, you completely missed the point of the question.",
"Incandescent bulbs have their filaments heated until the thermal radiation emits visible light. Similar to a stove top. The hotter something is, the higher the frequency of thermal radiation. Fluorescent lamps use electricity to excite the electrons of the gasses inside, and when they return to lower energy levels, light is emitted.",
"However, if you could drive an antenna at that frequency, it would indeed emit visible light ",
". The challenge is driving a circuit that fast, which is basically only possible for nano-scale sized objects. I believe I have read a paper about researchers trying to do just that, nano-scale visible light antennas. You could google around for some info.",
"I'm not sure how it would look though. I imagine since the wavelength is so small, it would look like a little point of light in some pure color. Just a guess though."
] |
[
"How long would it take to hard-boil an egg on Mount Everest?"
] |
[
false
] |
[deleted]
|
[
"The egg requires heat to be cooked, it doesn't actually boil. Boiling water is a lower temperature when it is at a lower pressure, so the egg would exist in lower temperature water, so it would cook slower or not at all depending on the pressure."
] |
[
"The increased altitude won't (shouldn't) really affect how long it takes to cook the egg, merely whether it is possible to cook the egg at all. It simply boils (heh...) down to asking:",
"As you increase altitude, the pressure at which liquid water boils will fall. You can see this on a ",
"phase diagram of water",
". At sea-level, the pressure is 1 bar so the boiling point of water is 100 deg. C. The altitude of Everest is ~8.848 km at which altitude the pressure is ",
"33 kPa or 0.33 bar",
". At this pressure, the boiling point of water is about 65-70 deg. C*, reading off the phase diagram (according to ",
"this",
" page, it's 67.5 deg. C. or 153.5 F).",
"What temperature is required to cook an egg? ",
"This page",
" tells us that the egg white will become a tender solid at 150 F and that the yolk will still be a little soft, not solidifying until 158 F. ",
"Here",
" we see that we would have to keep the egg at this temperature for at least 12 minutes to kill off most of the Salmonella bacteria. So it doesn't sound as though you can quite cook an egg on the top of Mount Everest, but if you can keep the water boiling long enough you can at least make it safe to eat!"
] |
[
"Pressure cookers are generally set to about 14 PSI, so you could hard boil an egg in a pressure cooker at any elevation, assuming you can provide the heat needed. An electric hot plate should do the job at near vacuum. Will be an interesting experience opening it though."
] |
[
"Does a fetus dream?"
] |
[
false
] | null |
[
"I googled because I thought this was interesting and it seems like the answer would be yes, since we typically define the dream-state as occurring during ",
"REM-sleep",
". I'm not an expert in this though "
] |
[
"I got the same thing. 85-95% sleep, and spdcukstion",
"What I did find interesting is that a fetus will lick the uterine wall and touch its hands and the umbilical cord."
] |
[
"So is a fetus conscious in the womb? I always assumed it was asleep or something."
] |
[
"What happens when water vapor evaporates from a cloud?"
] |
[
false
] | null |
[
"First of all, water vapor can't evaporate. It's already vapor. Get it? Clouds are made of droplets and crystals (ice) or at least that's the white thing you see when you look up at the sky. \nIt just goes back into the air. Temperature does not change as a result of this. Rather, water drops/crystals turn into water vapor because temperature raises and the maximum amount of water vapor that can be dissolved by air increases. "
] |
[
"Thank you for the response! I was asking myself this question a few days back, and I realized that I did not know the answer. I suppose I did not consider the idea that water vapor can not evaporate. Thanks again!"
] |
[
"It evaporates and the humidity increases in the surrounding air. This will also cause a slight decrease in the temperature of the air, but like, a tiny fraction of a degree C since clouds are very low density structures."
] |
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