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[
"What caused the big bang?"
] |
[
false
] |
I have heard tons of conflicting theories on this and don't have enough mathematical skill to perform meaningful research on my own yet. So what was the prime mover or ignition, or what was the most probable cause? Edit: Thanks everyone! Extremely clarifying.
|
[
"We don't know.",
"Our models of physics begin with the big bang - they describe the bang and its consequences but not anything prior to - or outside of that bang.",
"To the extent that such things are unobservable by us there is no constraint on what can be hypothesised. "
] |
[
"Causality isn't a rigorous part of physics. Many, nearly all, processes follow causal rules, and that's why we assume it generally describes reality. But not everything does. Nuclear decay is thought to be acausal (without cause) and other quantum precesses as well. The big bang itself could very well be acausal as well."
] |
[
"pretty much because our present rules of physics do not have any \"cause\" to the decay. They are simply ",
" to happen, and because they increase entropy, they ",
" happen. I wrote more about it here:",
"http://www.reddit.com/r/askscience/comments/iallj/15_questions_evolutionists_cant_answer/c229j74"
] |
[
"What would happen if the two plates that are used to produce the Casimir effect were charged?"
] |
[
false
] | null |
[
"Then there'd be a much greater force between the plates, and it would be hard or impossible to measure the contribution from the Casimir effect."
] |
[
"Oh wow now that you say that I can see why because the electrons would be attractive as well. I was wondering if people have tried different geometries instead of a simple plane? Like for example what if a person blocked 3 sides of the 2 planes and scaled it such that certain selected wavelengths were allowed between the plates. I guess I'm just not really sure if light when it's in wave form is considered a 2 dimensional object or a 3 dimensional object?"
] |
[
"Light is definitely a 3D phenomenon, but the Casimir effect is easy to derive in the case of infinite, flat planes, in which case the problem is effectively one-dimensional. And people want to measure that situation so that it can be compared to the prediction that's easy to derive analytically. I'm sure people have studied other geometries both theoretically and experimentally. But the infinite plane geometry is what's usually covered in quantum mechanics courses."
] |
[
"Why do people and their houses all have different somewhat distinct smell?"
] |
[
false
] |
You know when you walk into someone's house and it just...smells like them? What is that?
|
[
"Ah, finally something I can answer with science, sort of. I mean the best science one can afford on his own in such a case as a 15 year old at the time I did this. ",
"I actually wondered about this as a child. I was split between two houses, my mother's and father's, pretty much every week, each time I'd return to one, I'd smell the familiar smell of the house I was returning to. I'd go shopping with both my mom and dad when they went for groceries. My dad and mother both used different detergents, both in washing machine and dishwasher. So one week, I decided to grab different brands than they usually chose and place it in the cart instead, they'd not mind me changing things up, cos they just grabbed their usual out of habit, no actual preference I don't guess. My mother's house had a good bit of potpourri which I was easy to identify in the smell, however it always had some other undertones which I felt may come from the detergents. Well... I was right. The next week there was a distinct new smell to both houses. Remember, people wash clothes, hang them in closets, place coats on coat racks, bedding in each bedroom and so on. The dishes are washed and there is a good bit of nice smelling humidity that pours out of that dishwasher as they finish.... I'm not sure if this really changed much, but I could very well smell the undertones of the clothes detergent in the house. This obviously doesn't account for it all, as there are multiple things that will affect it. Both my mother and cousin's houses had a smell undertone that was similar, I attributed this to the hardwood floors that both had in various rooms. ",
"But back to detergent. My roommate switched to something new earlier this week and I can still smell the hint of it in the air, whereas the other other we used before I'd long forgotten the smell of. You say it smells like \"them\" and this too could be attributed to clothing detergent which lingers on people's clothing well into their wearing them. I'm sure other things exist that can be attributed to such smells, but clothing detergent seems to be a big modifier of it. ",
"Anyhow, while this isn't the best of scientific experiments, it was the best I could do at the time when I was a younger teen. I felt it adequately answered some of the questions about that for me. "
] |
[
"Upvote for having the passion as a 15-year-old to conduct an experiment in your own free time knowing there was not due-date or grade involved. "
] |
[
"I was a strange child. Me and my brother both... When we were younger than that we spent hours and days, completely determining the password structure from the original metal gear NES game. We knew exactly when every aspect of the password did, could start a game in any location, with any chosen number of ammunition / equipment and so on. I was like 12 and him 9 or so. We did this well before we even finished the game. That required tons of experimentation. Although not particularly \"science\" in the standard sense. I still have the little notepad with all the hex codes used by it and the definitions around here somewhere, I saw it a few months ago when I was cleaning up in a box with some old stuff. ",
"Like I said, weird child."
] |
[
"Does glycogen require insulin to be used?"
] |
[
false
] |
[deleted]
|
[
"In short, no; you're right in that the breakdown of glycogen happens inside the cell, so you don't need insulin to facilitate glucose uptake from blood.",
"If you want more:",
"glycogen only requires glucagon to be used. Insulin is not necessary, because the particular muscle uses its own glycogen to produce usable glucose.",
"Glucagon is the hormone that stimulates the breakdown of glycogen into glucose.*** (See edit)",
"Glycogenolysis (breaking down glycogen) happens within the muscle cell, so the glucose that is formed by the breakdown process remains inside the muscle cell. That particular cell then uses that new glucose. This is particularly relevant in fast twitch muscle that gets most of its energy from glycolysis (breaking down glucose) and subsequent fermentation to lactic acid.",
"Insulin actually has the opposite effect, and stimulates the building of new glycogen (after glucose is brought into the cell en masse by a process stimulated by insulin).",
"Cells have constitutive ability (via GLUT1 transporter) to intake glucose from the blood, so insulin isn't absolutely necessary at all times for the uptake of blood glucose. Insulin's primary function is to induce membrane expression of GLUT4, which massively increases the amount of sugar cells take in from blood, for when your sugar levels are high.",
"GLUT1: ",
"https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/glut1",
"\nGLUT4:\n",
"https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/glut1",
"\nGlycogenolysis:\n",
"https://en.wikipedia.org/wiki/Glycogenolysis",
"Edit: the breakdown of glycogen that happens due to glucagon happens mostly in the liver. The way I wrote it makes it seem like it stimulates glycogenolysis in the muscles- that's mostly the effect of epinephrine. Glycogenolysis in the liver does lead to glucose secretion into the blood, which then circulates to the muscles that might need it. It can then be absorbed by GLUT1 or GLUT4, but since insulin levels are low, it will likely be through GLUT1.\n",
"https://www.ncbi.nlm.nih.gov/books/NBK22429/"
] |
[
"Muscles glycogen doesn't contribute to blood glucose directly, it does indirectly cause when glycogen is broken down inside the muscle into glucose it prevents glucose uptake from blood thus raising blood glucose but this isn't an important determinant of blood glucose levels. Muscles use their stores of glycogen for themselves to breakdown and use for energy when needed."
] |
[
"Glycogen is converted to glucose in the liver and then released into the bloodstream. Cells outside of the liver cannot convert glycogen into glucose, they can only convert glycogen into glucose-6-phosphate (a glycolysis intermediate) and then send it through the rest of the glycolysis pathway, generating some ATP in the process. Converting glucose-6-phosphate to glucose is a backward step in glycolysis that requires an enzyme only found in the liver. ",
"Cells don't actually need insulin to take up glucose, insulin just upregulates levels of GLUT4 in muscle and adipose tissue."
] |
[
"How, mechanistically, does water pressure increase at greater depths?"
] |
[
false
] |
Most people know that water pressure increases with your depth below the surface. In fact, the pressure reaches ~6 atmospheres at only 50 m of depth. I understand from a force-balance point of view why this must be the case- the water below must support the weight of the water above. However, I do not understand this increase in pressure from a molecular point of view. My understanding is that water is largely incompressible, so the density is effectively constant. Lets also assume, for the sake of argument, that the temperature of the water column is constant. Pressure is effectively just the consequence of water molecules striking the walls of a container. However, since temperature (which reflects the kinetic energy of the particles) is constant with depth, and so is density, you have the same number of particles moving at the same average speed at both the shallow and deep depths. So how does the deeper water have a greater pressure?
|
[
"You seem to be thinking of liquid water on the molecular level as if it were an ideal gas, where the molecules are free to shoot around ballistically with some kinetic energy and only interact when they collide with each other. This picture is wrong. As a liquid, the water molecules are packed in against each other (that's what makes the water incompressible) and stick to each other through temporary, ever-changing bonds. The water molecules in the bulk are free to slide past each other, but they are not free to shoot off in their own. In solids and liquids, a mechanical force is not transmitted via the kinetic energy of freely shooting molecules colliding into each other. Rather, a mechanical force is transmitted through the electromagnetic bonds that join the molecules. In this way, pressure, temperature, and density are not related to each other in liquids and solids the same way as they are in ideal gases. ",
"Perhaps this oversimplified picture can help: think of atoms as bowling balls. If the bowling balls are widely spaced (this represents a gas), then you can only transmit a force through a group of balls by throwing one ball against another, which then flies off and hits another ball, etc. However, if all the balls are placed right close to each other in a line so that they touch, you can knock the first ball in line and get the last ball to move without the middle balls hardly moving at all."
] |
[
"On a molecular level each molecule has a downward force equal to it's mass times gravity which is what causes pressure at depth. In a gas you have a density change based on pressure and temperature."
] |
[
"The density of water increases with pressure at fixed temperature. The statement that water is incompressible is an approximation. Often it is a good approximation, but it is still an approximation. The fact that water is nearly incompressible implies that a finite change in pressure will lead to a small change in density. And while small, you need to take this change into account if you want to understand things at the kinetic (molecular) level."
] |
[
"How come we can move in space at varying speeds, but we can only move in one direction at a constant pace in time?"
] |
[
false
] |
Sorry if this question is too metaphysical for . But what is time? Why is speeding up, slowing down or going backwards in time not the same thing as speeding up, slowing down or going backwards in space?
|
[
"This may not be an exact answer to your question, but according to the theory of relativity, everything in the universe is moving at constant velocity ",
" (the speed of light) through 4-dimensional spacetime. This means that an object that is stationary in space (relative to an observer) is moving at ",
" through time, but an object that is moving through space at velocity ",
" must slow down in the time direction to ",
"-",
" so that the constant spacetime velocity is conserved. Extrapolating from this, we see that an object moving at ",
" through space is ",
", as strange a concept as that may seem. In order to move backward in time, you have to travel faster than ",
", which is believed to be impossible because relativity also states that objects with mass can ",
" travel at ",
" because that would require infinite energy (the faster you go the more energy you have). This also has the consequence that massless particles (like photons) ",
" travel at ",
" through space and do not 'experience' time at all.",
"As for the question \"what is time?\", yes I'm afraid that is a bit too metaphysical for me to answer."
] |
[
"We do move at different speeds in time. If you are moving at some speed with respect to me, I perceive your time as passing slower with respect to mine.",
"But I feel the essence of your question is, \"Why is time different from spatial dimensions?\" As discussed above, you CAN change your speed in time, but not your direction. Why is that? ",
"We describe time as a \"timelike\" dimension, and spatial dimensions as \"spacelike,\" and we can distinguish them by their sign in the metric. A metric is a version of the Pythagorean theorem, and we use a version of it in spacetime, except we use \n s",
"=x",
"+y",
"+z",
"-t",
", \nwhere s is the interval between two events. Notice that we are subtracting time off, instead of adding it. This difference is what defines \"timelike\" dimensions as opposed to \"spacelike.\" So your question becomes, A) Why are there 3 spacelike dimensions and only one timelike dimension, and B) Why can I never travel backwards in a timelike dimension?",
"The wave equation in a space is closely related to the metric. For example, in spacetime, the wave equation for a function U becomes \n 0=(d",
"U/dx",
")+(d",
"U/dy",
")+(d",
"U/dz",
")-(d",
"U/dt",
")\nDo you see how the metric is connected to this wave equation? ",
"Now we can finally discuss why we observe a universe with three spacelike dimensions and one timelike - because if there was any other arrangement of dimensions, there would be no observers in that universe to observe them in the first place. This is called an anthropic argument and it works like this. If the number of spatial dimensions was >3, then no orbits would be stable - neither the orbit of Earth around the sun or the \"orbit\" of electrons around nuclei. Intelligent observers would not be possible. With multiple dimensions of time, the wave equation becomes a generalization of the ",
" which means that future events are unpredicatable without knowing the specific path a particles proper time takes through the timelike subspace. A curious exception occurs at 3 timelike dimensions and one spacelike - such a universe is predictable but all massive particles would travel faster than light.",
"So for the second part of the question, why can you never travel backwards in a timelike dimension? Let's consider how we travel in spacelike dimensions. As you travel, you can pause at any point and rotate. What kind of rotations can you perform? Well you can turn right, turn left, turn around... any point on a sphere, right? These are all the valid rotations of space. ",
"The valid rotations of spacetime are called Lorentz transforms and none of them can reverse a timelike dimension. There's something called a lightcone that you just can't rotate through, which prevents you from \"rotating\" forward time into backward time, for exactly the same reason you can't travel the speed of light."
] |
[
"No, the \"rotation taboo\" (the fact that Lorentz transformations can't reverse a timelike dimension) holds just as well inside a black hole.",
"The difference is that, within the event horizon, the timelike dimension is not time. (Remember that \"timelike\" just means it has a negative coefficient in the metric.) It's actually the dimension of space that corresponds to your distance from the black hole singularity. So inside the event horizon, instead of being unable to change forward time into backward time, a Lorentz transformation is unable to change motion toward the singularity into motion away from the singularity."
] |
[
"Why can vaccinated people no longer donate convalescent plasma that can be used to treat Covid patients?"
] |
[
false
] | null |
[
"Can you include links to the Red Cross policy?"
] |
[
"https://www.redcrossblood.org/local-homepage/news/article/covid-19-vaccination-guide-blood-donation.html",
"third heading down.",
"The news report in question",
"I recognize that the person posting the news report is anti-vax, and I'm not at all advocating for it. I'm just referring to the report itself (which I can't seem to find), not what she's saying about it. My motive is to clear this up, and understand what is actually being referred to, and to get an actually scientific explanation about what they mean by \"wipe out,\" because that feels way too oversimplified to me."
] |
[
"Seems like a bureaucratic rather than a scientific question."
] |
[
"I’ve read somewhere that candles can burn hotter than lava, is this true? and if it is, why?"
] |
[
false
] | null |
[
"It is true, but it shouldn't be all that surprising: compared to combustion reactions (which are actively producing a ton of energy due to chemical reactions) lava is relatively sedate, and is only hot because it was recently in contact with a whole bunch of other hot stuff (Earth's interior). ",
"Lava can be different temperatures depending on the exact composition and how it is released, but it can be as low as 650˚C (1200˚F) all the way up to more than 1200˚C (2100˚F). ",
"The hottest part of a candle flame, however, where the vaporized wax is combining quickly with oxygen and releasing energy that heats its surroundings, is ",
"1400˚C (2550˚F) or higher",
". And this isn't even that hot ",
"compared to other flames",
". Extremely energetic reactions, like ",
"thermites",
", can burn at over 2500˚C, or 4600˚F...lava doesn't even hold a candle to those temperatures (ba-dum-tss)"
] |
[
"As very usefully quantified by the ",
"view factor",
"."
] |
[
"As very usefully quantified by the ",
"view factor",
"."
] |
[
"What is the distinction between \"particles spontaneously pick their state when observed\" and \"we don't know what state a particle is in until we observe it?\""
] |
[
false
] |
Why do we say that particles "pick their state?" How do we know they weren't like that before we looked?
|
[
"I am sorry, I should have started with: \"You are being nit-picky about OP's phrasing, when it's functionally equivalent to other phrases describing the phenomenon he is referring to\".",
"Can you answer any of his questions?"
] |
[
"How do we know they weren't like that before we looked?",
"Well what you're describing falls under something called \"hidden variable theory\" But let's talk about some general things first.",
"1) you only know what happens ",
" observations. Anything between observations is pretty much outside the realm of science to answer. But we can have some pretty informed ",
" as to what happens.",
"So let's suppose we have a particle pass through a single slit. The slit is vertically oriented, therefore it measures the particle's position along the ",
" axis. Any particle passing through the slit has been \"observed\" to be at some position, x with some error dx (the width of the slit, eg). Now we don't know what happens to it, but then it strikes a back wall, leaving some impact (perhaps making the wall glow there, or the particle is itself light, or electronic detection or something).",
"What you'll find is that the particle impacts ",
" along that horizontal axis. There was some uncertainty in their ",
" at the first measurement when you asked \"where they were.\" And that uncertainty in momentum means they spread out on the back wall. ",
"So from that first slit, we realize we can't tell directly what momentum the particle has until we see it impact the far wall, and then can measure the momentum. ",
"So then the question is... does that particle have that momentum when it leaves the slit, or does it only \"realize\" one momentum state after it's hit the wall behind it? (or one of the many other quantum interpretations here)",
"Broadly we can divide these guesses as to what happens between observations into 2 camps (this need not be the only way to divide them, but it's the one most relevant to this question). One camp says ",
". The other camp says ",
". ",
"And then we come across Bell's theorem. This theorem states that the first camp can be right, but if it is, then information about measurement setups must be able to travel faster than light somehow. Or the second camp can be correct, that quantum properties are truly in superpositions until measurement, but information doesn't travel faster than light. But you can't have both hidden variables (the first camp) and the speed-of-light limitation on information. ",
"And here is where it's up to you to decide which you prefer. A lot of scientists will keep the locality (that information is speed-of-light limited) because ftl information ",
" be information going backwards in time in a different reference frame. And others will discard locality and keep hidden variables. There's no way, scientifically, to distinguish which one is correct yet."
] |
[
"Basically, observation in this context means forcing the system into a single state."
] |
[
"If the length of vocal chords determines how deep a person's voice is, how big would a giant have to be before his voice would be too low to hear?"
] |
[
false
] |
Let's assume average, modern human proportions hold up as the giant increases in size and the normal stresses applied by physics wouldn't cause his bones to be crushed under his own weight or something. Human beings can hear down to about 20 Hz. So how big would a giant have to be before the length of his vocal chords caused his voice to be so low that we couldn't hear it anymore.
|
[
"The average adult male vocal chords are somewhere between 17 and 25 mm in length. However it's not just the size of the vocal folds that influence the range in frequency, the thickness of the folds, as well as genetic factors which can change the actual layered makeup of the folds themselves play a part as well. According to some sources there have been people who have been able to verifiably produce frequencies as low as 8 HZ! But this isn't so important to your question if we're looking at an average human being / an average giant. If we accept that the larger vocal chords produce lower notes (which is true) then we can say that an average man with 25 mm vocal chords would be feasibly capable of producing the lowest pitch reasonable for the average (25 mm vocal flap) human voice: 60 HZ. The average man is 5 foot 9 inches or 175.26 centimeters. So for every division we make in HZ we multiply in human height, right?? 20 goes into 60 a convenient 3 times. So I guess the giants height would have to be something like 17 feet 3 inches and he would have 75 mm vocal flaps. As far as weight and width and all that (which I guess would be important) I don't know. This is all assuming we take our 5'9\" man and 'giantize' him with all the same proportions. Weird question, glad I'm done thinking about it."
] |
[
"It doesn't scale this way, for a variety of reasons:\nFirst, just like on a guitar, the length of vocal chords is not the only factor at play. Tension plays a big role too. You have to reduce the tension to emit lower notes, and when the tension is weak, the emitted energy is reduced. Because of physiological constraints, it's unlikely the vocal system would scale linearly, and that longer vocal chords would ultimately lead to a more profound bass voice.",
"More to the point, human voice is not a pure frequency. It has harmonics (multiples of the fundamental frequency), and even multiple transient waves. When speaking in very low tones, much of the energy goes into the harmonics, and therefore, we hear the tone even though the fundamental is below our hearing threshold. Our perceptual system reconstructs the missing fundamental from the ratio of the harmonics.",
"Digresssion: as an example of non-harmonics, vowels are actually chords emitted by the vocal system and the difference between 'i' and 'a' is actually the ratio between two formants. Those who have learned to sing in dual-voice (like Tibetan monks or the Bass singer of Camille) have learned to \"hit the right vowel\" all the time.",
"Lastly, if you want, ",
" can emit very low pitches: just wobble a continuous sound. Of course what you hear is something like a high pitched sound with a vibrato. Vibrato/Tremolo is actually what infra-sound hears like.",
"You can play with those concepts using ",
"HighC",
"The HighC scale is continuous from ultrasounds to infrasounds of a period of several minutes. It makes it very easy to perceive the transition between infrasound and sound, as well as measure your hearing threshold in pitch (mine is 14.5kHz)."
] |
[
"60 Hz is quite low. That's lower than C two octaves below middle C. I can say with certainty that the average man is not a basso profundo. 100-120 Hz is much more reasonable.",
"Edit: Your math is very interesting though! Also, I pulled up a chart. 60 hz is between a very low Bb and and B. Definitely outside of the average range of even the majority of developed singers. I'm guessing this means that a giant would probably need to be 5 times taller instead of three, so ~30 feet tall?"
] |
[
"Why are some people more susceptible to mosquito bites?"
] |
[
false
] | null |
[
"I have been convinced my entire life that they 'like' my dad more than me. However, I am forced to admit that this is purely anecdotal, and I suspect is mainly just me falling victim to personal biases. I suspect a bunch of ",
"Selective Perception",
", mixed with a healthy does of ",
"Confirmation bias",
", with some ",
"Cherry Picking",
" thrown in for good measure. ",
"I'd love to see some actual data on whether mosquitoes are more attracted to certain individuals. All I have is anecdotal stuff....",
": So it turns out that they apparently go for some people over others for a ",
"variety of reasons",
". Apparently they like the way we ",
"smell",
"- though I'm simplifying- what they really like are the odorants you produce. These chemical markers can change due to a variety of reasons. Some apparent things that make you tasty to the little suckers are:",
"Your blood type",
"Whether you have been boozing",
"If you're pregnant",
"If you're working out",
"and apparently ",
"your genetics",
"Maybe my anecdotal experience was right, for once."
] |
[
"I'm not sure. I would like to see a more thorough answer to this question before I'm satisfied. When I go camping with my family, my parents and brothers all get devoured, but I'll only find one, maybe two, bites. Perhaps you're right, but I can't even find any red dots from bites. Meanwhile, the others are practically polka-dotted. Very strange."
] |
[
"I'm not sure. I would like to see a more thorough answer to this question before I'm satisfied. When I go camping with my family, my parents and brothers all get devoured, but I'll only find one, maybe two, bites. Perhaps you're right, but I can't even find any red dots from bites. Meanwhile, the others are practically polka-dotted. Very strange."
] |
[
"What does it mean that quantum information cannot be destroyed?"
] |
[
false
] |
This as the top of seems to suggest that according to quantum theory, information cannot be destroyed. What does that mean? Is the universe rewindable in some way? Didn't I learn in physics class that a wavefunction 'collapses'? That sounds like the sort of process where information would be lost. I am guessing there is more going on here, and it has something to do with entanglement, but I am not really sure what.
|
[
"Quantum mechanics has a property called ",
". Unitarity says that as a quantum system evolves in time, it does so in a reversible way. Thanks to unitarity, two different initial states cannot evolve into the same final state.",
"When a measurement is made in quantum mechanics, we assert that something non-reversible (and non-unitary) has happened. Collapse of the wavefunction is one language used to explain what happens. The problem is that this would imply that what goes in in the measurement is not governed by the laws of quantum mechanics. So what a good theory of measurement still awaits us.",
"But even without this resolution, if we look at a quantum system in which no measurements are made, then unitarity should be upheld, and thus no quantum information destroyed."
] |
[
"Many Worlds has unitary measurement, because measurement is just entanglement of the measuring device with the system."
] |
[
"Yes, this was one of the motivations behind Everett's Relative-State formulation of quantum mechanics (which is the original version of what's typically called Many Worlds)."
] |
[
"If the gravity of the moon is strong enough to create tidal waves, why doesn't it lift up things like tree leaves or small animals?"
] |
[
false
] | null |
[
"Surprisingly no one has gotten the right answer to this yet! Mass plays a role in tidal forces but what's really important is more often size, not mass. The reason you have a tide at all is the difference in the pull of the tidal body from one side to another. We get a tide on the earth because the side of the earth on the opposite side from the moon experiences less gravitational pull from the moon than the near side that is close to the moon. This makes a net force on the object which stretches it out toward and away from the object generating the tide. Not everyone realizes this but there is actually a high tide on the side of the earth close to the moon as well as the side on the far side from the moon. Low tides are at 90 degrees from the moon on either side. ",
"The only time tidal forces can act on small objects is when the masses involved are extremely compact. Spaghettification in a black hole is actually caused by tidal forces. Basically your head and feet are getting a high tide while your waist is getting a low tide!"
] |
[
"This is right. When I teach it, I draw a diagram that looks something like this...",
"W E W - - - - - M",
"Water = W\nEarth = E\nMoon = M",
"The moon pulls hardest on the close water since it is closest The moon pulls the close W off the E and it pulls the E off the far W. On my whiteboard, of course, the diagram has shapes and texture. ",
"The answer has nothing to do with the mass of the objects getting pulled. The answer is that there is a difference in the moon's pull on either side of the earth. Water close to the moon gets pulled away from Earth while water farthest away from the moon gets the Earth pulled away from it. ",
"EDIT : Added the ",
"image",
".\nNew Edit : Thanks for the gold! I hear \"thank you\" so rarely that your gesture really made my day."
] |
[
"It does lift those things up! The surface of the Earth will vary in distance from the center by about a meter every twelve hours due to tidal forces acting on it. Trees and small animals ",
" lifted up, but so is the ground beneath them.",
"You can maybe (depending on how much unnecessary technical language you can swallow) learn more in this hard-to-follow ",
"wikipedia article about these so-called \"Earth Tides\""
] |
[
"What's the difference between a regular quad core PC and a workstation with two dual cores?"
] |
[
false
] | null |
[
"It depends so much on the architecture of the chips being used that it's hard to make any firm statements.",
"In a ",
" general sense, the memory hierarchy is going to work differently. The memory hierarchy goes from the lowest level of data storage, the registers, which hold the data that the processor can work on, and goes all the way up to hard drive storage. At each stage capacity increases and speed decreases. Usually it's something like",
"registers > L1 cache > L2 cache > L3 cache > main memory (RAM) > non-volatile storage",
"Each core will have its own registers and L1 cache. L2 caches are often shared between two cores on quad core machines, whereas on dual-core each core often has its own L2. The L3 is often shared across all cores, but all of this is architecture specific so there are no hard rules (except each core having its own registers and L1).",
"So, one difference is that a two-CPU workstation will usually have 2 L3 caches and 2-4 L2 caches, whereas a quad core will typically have one L3 and 2 L4's. That obviously means more space, which means that data can get to the cores more easily. Often the bottleneck in a computing task is not how fast the cores can chug through the data, it's that the data can't get to the cores fast enough.",
"Again, though, this is heavily architecture dependent, and I hesitate to even say that this is a definitive advantage that the workstation has over the quad-core. It's an advantage the workstation ",
" have, but is not going to be true for all workstation v. quad core comparisons."
] |
[
"Economics. Render farms proves that they can do it. There is nothing physically preventing Nvida, Intel and game designers from making a game just for millionaires that would require 100 titan X's. ",
"I mean, they do a limited run sometimes of 1500 or 3000 dollar graphics cards that are just 2 top of the line gpu's on the same card. This is just a case of the people who want it, cant afford it, and the people who can afford it, dont want it. "
] |
[
"Most of the things millionaires would want to do (watch a real-time render, 1000K videos, super high resolution video games, etc...) are actually quite hard to parallelize. A video game, for instance, can split its load between four processors easily (two for render, one for physics and one for gameplay/audio for instance), but beyond that the communication time and memory sharing problems would get really bad."
] |
[
"What is the most advanced artificial intelligence that we have created so far?"
] |
[
false
] | null |
[
"Netflix, Google, and the like—",
"Or, for something more research-y and interesting take a look at ",
"LDA",
", ",
"Kalman filters",
", or hybrid processes.",
"More specifically, AI doesn't exist in the way scifi makes it out to. Not today, and not yet foreseeably. Though we believe theoretically that it's possible to construct a brain-like computer, research today tends to be heavily attracted to reverse engineering small neural circuits and developing mathematics to study generalized inference and prediction problems. It's almost always highly domain/task specific and attempts to make it more \"advanced\" are done by fusing simpler techniques together.",
"It turns out this stuff is all really quite exciting anyway—it dives right at the mathematical structure that underlies patterns and their understanding, things that we sort of assume the brain must be doing somewhere or another.",
"Take note however that the most impressive \"strong AI\" mimicry so far was IBM's Watson beating humans at Jeopardy. While their system ",
" quite impressive, it relied on a great deal of \"overfitting\" such that Watson was really good at playing Jeopardy, but probably not that great at doing anything else."
] |
[
"IBM's jeopardy computer ",
"that's being tuned to help in healthcare",
" ranks pretty high for some definitions of 'intelligence'. It's probably the most hyped AI computer these days.",
"Some interesting discussion about ",
"chat bots aproaching the ability to pass the Turing test appeared on /r/programming/ here",
" a couple months ago.",
"My wild speculation is that the most advanced ones are in some wall street high-frequency-trading systems that are kept as trade secrets."
] |
[
"It's certainly the most publicised. ",
"A couple of genuine questions here, I'm not having a go:",
"What other AI projects are you aware of?",
"Would you consider pose estimation on the kinect (working out where your arms and legs are; which is which; and who they belong to) to be AI?"
] |
[
"What exactly happens to blood as gas exchange happens in the lungs, what organic chemistry is happening - does the pH change?"
] |
[
false
] | null |
[
"You’re blood transports CO2 mostly as carbonic acid (H2CO3) since it’s more soluble than CO2. In high CO2 conditions (like the muscles) the blood will get slightly more acidic as CO2 waste is converted to carbonic acid, that acid then ends up in the lungs where equilibrium shifts (since there is less CO2) and carbonic acid is converted back to CO2 and you exhale it.",
"Here is what it looks like"
] |
[
"Cool. I was reading about the bicarbonate exchange today",
"I’m just interested in hypoxia and hyperoxia ",
"How do lung tissues respond to these situations?"
] |
[
"The lungs shouldn’t really experience hypoxia in a healthy individual unless they are traveling to high altitude, because of course they have the most readily available access to it. Do you mean how the rest of the body reacts to hypoxia?",
"Our bodies can rapidly tell how much CO2 is present based on the pH. Most short term responses to hypoxia will really be through pH changes from CO2 buildup. However over longer periods transcription factors called hypoxia inducible factors (HIFs) can alter gene expression to respond to hypoxia. Normally HIFs are degraded in the presence of oxygen and so they aren’t able to alter gene expression. Because of this HIFs shouldn’t really be active in the lungs, but they are important in other parts of the body. For example in the kidneys HIFs can increase erythropoietin (EPO, the same stuff Lance Armstrong doped with) production which signals for more red blood cells to be made. In the muscles they might signal for angiogenesis to increase the blood (and therefore oxygen) supply. ",
"Not as sure about what happens in hyperoxia. But my guess is a large response to all the additional reactive oxygen species being made. These can be problematic as they damage cells and their DNA. In extreme cases the ROS can kill cells, it’s basically like pouring peroxide into the lungs/tissues."
] |
[
"Why is CMB in every direction?"
] |
[
false
] |
The cosmic microwave background radiation (CMB) is observable in every direction. It is the radiation emitted by the opaque plasma that existed after the big bang that is now reaching us 13 billion years later. if we are still moving away from the origin of the big bang, surely after 13 billion years we would have exited the bounds of the plasma cloud that sources the CMB. Is this true? If so, why is the CMB in every direction? Wouldn't it be like looking at the earth from above the surface, filling a little or a lot less than half the sky?
|
[
"if we are still moving away from the origin of the big bang",
"That's your problem. We aren't moving away and there wasn't an origin point. All of the universe expanded in all directions at the same time and there is no no center of the universe. It's counter intuitive I know but this guy explains it pretty well.",
"https://www.youtube.com/watch?v=pAMpdiBKen8"
] |
[
"Try not to think of the big bang as an explosion that threw everything out. It's an expansion of space. Think of a galaxy as a raisin in a piece of raisin bread that is rising. As time goes on, you see the other raisins moving away, but you're all inside the bread.",
"All matter in the universe used to be compressed plasma. The further out you look, the further back in time you see. So wherever you are, the observable universe is a sphere centered on your current position with the CMB as your horizon."
] |
[
"So, the matter in the observable universe is not an arc of the surface of a sphere, like the pressure wave of an explosion?",
"It is not.",
"So, is it uniform roughly in every direction?",
"Right.",
"And when people talk about us being on the surface of an expanding balloon, they are only referencing the stretching of a 2d surface as metaphor for the 3d expansion of space?",
"The surface is the whole universe in this analogy. The radiation moves within this surface."
] |
[
"Reddit, what's the science behind speeding up the \"fizz down\" of soda by sticking your finger in it?"
] |
[
false
] | null |
[
"the oil from your skin lowers the surface tension of of the bubbles, causing them to fizz down"
] |
[
"The way I have been told, oils on your skin reduce the surface tension of the liquid, causing the bubbles to burst. While ",
"this does have scientific grounding",
", I am unable to find a reliable source specifically addressing the soda- or beer-bubble case."
] |
[
"Sticking your finger in a soda increases the surface area onto which bubbles can form. In a soda, bubbles cant spontaneously form, they must begin at some type of surface nucleation point, typically the side of the glass or a scratch on the glass. Your finger provides many of these, and fizzing occurs. This is also the basis behind the diet coke and Mentos experiment. The Mentos, as it dissolves, creates billions of nucleation points from which the bubbles can form on, and causes the huge release of gas from the liquid. "
] |
[
"Are there similarities between native Alaskan languages and languages native to northeastern Asia?"
] |
[
false
] | null |
[
"Maybe. The ",
"Dene-Yeniseian Hypothesis",
" proposes a relationship between the Na-Dene language family of North America and the Yeniseian language family of Siberia. The Na-Dene family is very large and diverse, extending from Alaska to the southwest United States, and includes such languages as Navajo and Koyukon. See ",
"Campbell 2011",
" for a summary of the arguments for and against this relationship."
] |
[
"Eskimo-Aleut is almost entirely located in North America, but a few Yupik languages (a subfamily) are spoken in Siberia.",
"The Dene-Yeniseian link is a hypothesized language family that is gaining acceptance among linguists, though is not considered \"proven\" as of yet. The Dene branch (called Na-Dene) is a family of languages spoken throughout much of Canada and significant parts of the United States. Yeniseian languages are spoken quite far into Russia, amid central Siberia.",
"A very controversial macro-family is the Dene-Caucasian family, which includes a great many language families of Asia and two language families of North America. It has a small but vocal group of supporters.",
"Those are the nuts and bolts. To list out all the similarities would take, well, a book-length effort. If you wish to learn more, I suggest you start Googling these bad boys."
] |
[
"Yes, in fact Yupik live in both Siberia and Alaska--and they all speak similar languages. "
] |
[
"How do dyes that excite at the same wavelength emit different intensities?"
] |
[
false
] |
I feel like I am missing something obvious but just can’t wrap my head around it right now. I am using Alexa-546 for Cysteines and Alexa-546 for Lysines, yet when I excite them, Cysteines is giving me an intensity of about 4000 AU and Lysines is 12000 AU
|
[
"I'm assuming that you're labelling amino acids in a protein, and that the final concentration of fluorophore in each case is identical (i.e. same amount of protein and same number of labelled residues in each case).",
"Fluorescence quantum yield depends on the environment the fluorophore is in. Anything that causes nonradiative deexcitation will lower the fluorescence quantum yield; this is known as fluorescence quenching. There are many mechanisms by which this can occur: intersystem crossing, vibrational relaxation, Förster resonance energy transfer etc. It could simply be the case that when put on the cysteine, the fluorophore ends up in an environment where it is more strongly quenched than when it is on the lysine. I found ",
"this paper",
" which explores quenching of Alexa dyes by natural amino acids, you may find it helpful."
] |
[
"The two dyes have the same fluorophore but differ in the reactive group attached to the linker. ",
"This is Alexa 546 NHS ester",
", used to label amines. ",
"This is Alexa 546 maleimide",
", used to label cysteines. I'm not sure where you got yours from but ThermoFisher sells the NHS ester as the triethylammonium salt, whereas the maleimide is sold as the sodium salt. I doubt the counterion matters much so differences in fluorescence intensities from each dye will be down to differences in the dyes themselves. Presumably the NHS ester is somehow causing more quenching than the maleimide group, but why this is so, I can't say for sure."
] |
[
"I did both labeled to a protein (with same amount of prot and labels) and just free dye in solution",
"Thank you for all the information though! "
] |
[
"Why is hydrogen bonding only possible with hydrogen?"
] |
[
false
] |
I know this may seem like quite a self-explanatory question, but why not an atom that is even less electronegative than hydrogen, such as boron? Is it due to its size? Shielding effect of inner shell electrons? Charge density? Any answer would be greatly appreciated. Thanks!
|
[
"Because hydrogen is the only element that normally bonds with the 1s valence shell. On can thing of hydrogen bonding as being due to polarization of the electron cloud by proximity of a more \"electron loving,\" or electronegative in the jargon, element. This leaves an electron deficiency on the part of that shell opposite the electronegative element. That local region of relative electron deficiency can be stabilized by non-bonded electrons from another element, i.e. by hydrogen bonding. Now if you were to think about this with a 2nd period and onward element you do get polarization of the valence electron cloud and it does lead to some region of electron deficiency that can have some stabilization (for related example see the Burgi-Dunitz trajectory ",
"https://en.wikipedia.org/wiki/B%C3%BCrgi%E2%80%93Dunitz_angle",
"). However, in heavier elements, you're dealing with orbitals which are further away from the nucleus, and the lower shell electrons further screen the positive charge therein. That means that while a similar interaction does occur, it is usually far weaker (>10x). Since hydrogen bonds aren't normally that strong in the first place, these weaker interactions are of a similar order of magnitude to dipole-dipole interactions, van Der Waals interactions, etc. and get lost in the wash so to speak."
] |
[
"The shielding effect of electrons was the right answer. ",
"Or rather the entire lack of. If hydrogen is covalently bound, then - that bond requires hybridization of the orbitals of that hydrogen with the atom it belongs to. \nThat means it’s density function is mostly between the hydrogen and the other atom. ",
"So basically it works because there’s just that one electron. ",
"So then the proton, on the but side, is completely exposed. Things like oxygen that have extra spin paired electrons that need to get out of the way, typically shy away from the bond the oxygen bond. (Take an orange, and try and stick 4 tooth picks in it, each as far as possible from the other three- and you get the general idea). These negative bits are attracted to the positive exposed butt end of hydrogen and makes hydrogen bonds. There are generally stearic effects that keep the pairs from getting too close and so it remains a weak bond (in the case of organic chemistry). You can see what happens if that stearic effect isn’t there if you watch someone throw elemental sodium or other 1st Column elements into water."
] |
[
"It is possible to have other atom to participate in \"hydrogen-like\" bonding. Halogen atoms do this quite often. There are electostatic interactions between an electronegative atom (usually N or O) and a halogen atom covalently bonded to another electronegative atom. Those types of bonds are called halogen bonds",
"https://en.wikipedia.org/wiki/Halogen_bond"
] |
[
"In what ways/methods did humans change bananas from their natural form and why?"
] |
[
false
] |
I've seen it mentioned multiple times that the current image of a banana is vastly different from what their natural state is. While I understand the basic mechanics of how this can happen, I don't understand why it was necessary. Basically I'm looking for a rundown on the domestication and cultivation of bananas...
|
[
"Wikipedia's page on Banana's",
" is pretty detailed about the development of modern cultivars. ",
"Probably the biggest difference between the Cavendish banana's you're familiar with and their wild ancestors is that the Cavendish has tiny seeds. You can't actually plant a cavendish and grow another tree. The seeds are too small, plus the fruit ripens without being fertilized as well. Cavendish bananas can only reproduce asexually through cuttings taken by humans. That's about as far from \"wild\" as you can get for a plant! All this, just so you don't have to spit out seeds when eating a banana! ",
"The next biggest difference between the Cavendish and more \"wild\" varieties of bananas is sweetness. Try a \"cooking banana\" or plantain sometime. Although equally far from being \"wild\", they can give you an idea of what a banana not specifically bred to be sweet and eaten raw might taste like. Plantains are ",
" very tasty if consumed raw even though they look just like a Cavendish. ",
"The Gros Michel cultivar used to be as ubiquitous as the Cavendish is now, but a fungal disease that is now prevalent in most places where banana's are grown wiped the Gros Michel out, finishing the job in the 1950's. The Cavendish is resistant to that disease, so it has replaced the Gros Michel. There's no guarantee that some other disease won't eventually wipe out the Cavendish and force us to adopt another commercial cultivar. The downside to asexually propagating a cultivar across the globe is that there's absolutely no diversity in commercial banana plants. If something comes along that can kill one Cavendish plant, it could easily wipe them all out. "
] |
[
"thanks for the thorough reply! That last paragraph is really interesting. So if a disease wipes out the Cavendish plant, would we have to basically restart the process?"
] |
[
"The Gros Michel is still out there, but just very rare. Some who have tasted it say it's ",
"better than the Cavendish",
", which does kind of make sense. Banana growers didn't want to grow the Cavendish while the Gros Michel was still viable. If the Cavendish is wiped out by something, we'll likely be stuck with a different cultivar that isn't quite as easy to grow or quite as tasty. ",
"The Cavendish is currently being threatened by a similar fungal disease, but there are ongoing efforts to ",
"genetically modify the Cavendish to be more resistant",
". If these efforts succeed, perhaps eventually the Cavendish will be wiped out by the return of the Gros Michel instead of by disease!"
] |
[
"What's happening at the molecular level when a metal is heat treated?"
] |
[
false
] |
What exactly changes in the metal's molecules or structure that stops it from going back to the way it was when it cools off?
|
[
"There are a few different kinds of heat treating that can be done to either soften or harden different metals. In each case you are looking to alter the crystal structure of the final cooled metal. The solubility of different chemicals in the bulk metal will also change at different temperatures.",
"At different temperature ranges different crystal structures will form. If a metal is heated or cooled slowly enough it will flow through a series structures that is the same going in either direction.",
"But if the metal is cooled quickly different frequently crystal structures will form than if it is cooled slowly as the atoms don't have time to rearrange themselves in the preferred fashion. In this case the metal atoms are trapped in the new structure as the cold atoms don't have enough energy to rearrange themselves like they could when they were hot. They essentially become trapped in position when cold.",
"The rate of cooling is very important, and the time taken to go past certain critical temperatures will effect the type of crystals that form, and the time spent at each temperature (heating or cooling) also effects the size of the crystals in the metal. A metal is rarely one solid crystal but is instead formed of a complex crystalline microstructure. In heat treatment the grain of the metal is often discussed and this refers to the size, type, and orientation of the crystalline microstructure that determines many of the properties of the metal.",
"As an example of why solubility is important high temperature iron can absorb more carbon than low temperature iron, so when it is cooled if the amount of carbon in the higher temperature iron is above the solubility limit of the low temperature iron it will attempt to precipitate out of the crystal structure of the iron. The rate of cooling, and the total amount of carbon present will determine what kinds of structures form. Tubal Cain's Workshop Practice Series Volume 1: Hardening, Temperng, and Heat Treating (",
"amazon link",
") gives a great treatment of this in the first chapter discussing the formation of the different perlite, austenite, and martensite structures under different carbon contents and cooling rates.",
"Wikipedia's Heat Treatment and Carbon Steel pages are less clear on what is going in these processes but still give some good information if you slog through the terminology, and is online for free rather than $10-$30 for the book."
] |
[
"Thanks for the explanation. Also, I'm curious what did the pan end up looking like?"
] |
[
"Probably one of the most common problems with warped cookware is the bottom will no longer be flat. This means concave portion will all the grease/oil will coalesce. There are some ",
"methods for flattening a warped pan",
" but if I remember we just bought a new one. "
] |
[
"What force(s) keeps magnets from sliding down a tilted/vertical surface if it's not friction?"
] |
[
false
] | null |
[
"If the objects in your diagrams are meant to have 0 net force, then clearly ",
" cannot be normal to the surface."
] |
[
"If ",
" is normal to the surface, there is a net non-zero force along the surface. So as I said, if the net force on the object is ",
", then ",
" clearly cannot be normal to the surface. "
] |
[
"If ",
" is normal to the surface, there is a net non-zero force along the surface. So as I said, if the net force on the object is ",
", then ",
" clearly cannot be normal to the surface. "
] |
[
"Can quantum teleportation allow for faster than light communication?"
] |
[
false
] |
For example, suppose particles A and B are entangled. Leave A on Earth and send B to a point light years away. Couldn't both sides manipulate their particle to communicate instantly with the other? Obviously there would have to be a communications protocol, but in this simple example, something like Morse Code would do. If it's not possible, what factors would be prohibitive?
|
[
"No. You can't manipulate the state of the entangled particle like that; doing anything to the particle breaks entanglement."
] |
[
"No, this effect cannot be used for FTL communication. The big thing is that if either Alice (or Bob) does something reversible to her qubit, it doesn't effect Bob's qubit. Taking for example the usual entangled pair, |00> + |11>, in which both Alice and Bob measure the same bit, if Alice does a bit flip, the state is then |10> + |01>, and so they measure different bits. Note that Bob's qubit hasn't changed, and all that is different is that Alice and Bob will measure different bits.",
"No matter what Alice does, when she measures her qubit she will get a random bit, and when Bob measures he will get a random bit. Its only after comparing the two measurements that they will be able to tell if Alice did a bit-flip. This comparison requires classical communication, and so is limited by light. Basically, this entanglement allows for FTL correlations between the qubits, but this correlation cannot be used for communication.",
"As an aside, the actual quantum teleportation protocol, in which a quantum state is transmitted from Alice to Bob, does require classical communication."
] |
[
"Flipping your particle does nothing to affect the particle on Alpha Centauri, other than break the entangled state."
] |
[
"Hey AskScience, how come electrons never seem to crash into protons if they attract each other? What would happen if they did?"
] |
[
false
] |
[deleted]
|
[
"The sun and the earth also attract each other, but they don't appear to crash into each other either. Same thing with protons and electrons.",
"Also because of quantum mechanics the electron is actually spread out, so even if it doesn't have any angular momentum, it's charge cloud surrounds the proton. But there is a non-zero probability that you can find the electron inside the proton."
] |
[
"Wish I could answer it myself, but ",
"this",
" seemed to adress just about all of your question! "
] |
[
"It can happen in certain unstable atoms. It's called electron capture and it results in the proton turning into a neutron and the electron turning into a neutrino."
] |
[
"What's the property of mass that affects its acceleration?"
] |
[
false
] | null |
[
"I can think of no better answer than \"because that's what mass is.\" Mass is what makes this hard to accelerate."
] |
[
"I think his point was that why is gravitational mass = inertial mass.",
"To which there is no good explanation, except that it is observed."
] |
[
"Einstein was among many who have been stumped by this one. At this point, we just chalk it up to being part of an observed, if unexplained part of relativity, called ",
"The Weak Equivalence Principle",
" "
] |
[
"does this phenomenon have a name? briefly before sunrise in southern Australia the sky will act like a UV light and cause things to glow"
] |
[
false
] |
[deleted]
|
[
"Are you sure that it doesn't happen in america? According to wikipedia, due to the longer path length the effect of rayleigh scattering will remove short wavelengths more noticeably, so this would likely lessen the flouresence that is being exhibited rather than increase it.",
"Based on this, I would think that it is still flourescing, but the effect is drowned out after sunrise."
] |
[
"At any rate, the phenomenon you described would fall under fluorescence, or biofluorescence: ",
"https://en.wikipedia.org/wiki/Fluorescence#Aquatic",
"Also, you might want to look into bioluminescence, however these organisms do not require UV to stimulate light emission. In addition to deep sea fish, there are bacteria that are quite visible near the ocean surface that also exhibit bioluminescence.",
"\n",
"https://en.wikipedia.org/wiki/List_of_bioluminescent_organisms"
] |
[
"At any rate, the phenomenon you described would fall under fluorescence, or biofluorescence: ",
"https://en.wikipedia.org/wiki/Fluorescence#Aquatic",
"Also, you might want to look into bioluminescence, however these organisms do not require UV to stimulate light emission. In addition to deep sea fish, there are bacteria that are quite visible near the ocean surface that also exhibit bioluminescence.",
"\n",
"https://en.wikipedia.org/wiki/List_of_bioluminescent_organisms"
] |
[
"Is it possible to create a laser (laser-like phenomenon) with something other than light (photons)?"
] |
[
false
] |
For instance, could one make an 'electron laser', where you 'stack' a bunch of electrons' wave functions atop one another? I vaguely feel like 'exclusion' means it could only works for bosons rather than fermions (assuming I remember my physics correctly), but I am curious about laser-like machines that 'shoot' things other than light (both in theory and in practice). I tried to search for similar questions, but the nearest thing I could find was:
|
[
"There is something sort of equivalent in Bose-Einstein condensates called an atom laser: ",
"http://en.wikipedia.org/wiki/Atom_laser",
"There's something called an electron laser but it's not what you're describing. It's a way of using electrons to create a \"laser beam\" of x-rays."
] |
[
"SASERs (Sound amplification by stimulated emission of radiation)",
" are the \"acoustic analog' of a laser. ",
"In a SASER device, a source (e.g. an electric field as a pump) produces sound waves (lattice vibrations, phonons) which travel through an active medium. In this active medium, a stimulated emission of phonons leads to amplification of the sound waves, resulting in a sound beam coming out of the device. The sound wave beams emitted from such devices are highly coherent. "
] |
[
"All the particles in a laser beam are in the same quantum state. The exclusion principle makes this impossible to do with electrons (or any other fermion). As ",
"/u/iorgfeflkd",
" points out atom \"lasers\" have been made from Bose-Einstrin condensates."
] |
[
"[Earth and Planetary Sciences] - Are there Hadley/Ferrel/Polar-like cells ABOVE the Tropopause?"
] |
[
false
] |
As far as I can deduce, Hadley, Ferrel and Polar cells are all located below the Tropopause - the Trop being their upper limit. Want I want to know is whether cells exist above the Tropopause. I'm assuming that there must be because there always seems to be some sort of "gear" action going on in the atmosphere - where a circular motion of air is balanced out by an opposing circular motion. High pressure systems are balanced out by low pressure systems, and Hadley's are balanced out by the adjoining Hadley and a Ferrel. So is there a balance above the Troposphere? I mean, if there is a wind blowing below the Trop, then surely there would be a wind blowing the same direction above the Trop?
|
[
"As far as I understand, there are no such organised large-scale circulation cells above the tropopause.",
"To understand why, think of the three cells we have. If the Earth is not rotating, we would have one giant cell, rising at the tropics (due to intense solar heating) and sinking at the poles. But because the Earth is spinning, this cell breaks up into three separate cells (there are three because of the rate of rotation of the Earth; if it was faster, there would be more cells).",
"So why does the rising air stop at the tropopause? At the tropopause, there is a strong temperature inversion. That is to say, temperature increases as we go up in altitude. This inversion cap inhibits any rising parcel of air to penetrate far into the stratosphere (in general, any air parcel reaching that height does not have much energy to go further anyway). That is why the circulation is limited to the troposphere."
] |
[
"There is air above the stratosphere, but I've not heard of any organised circulation cells like those in the troposphere. That is to say, there are no regular patterns of motions that exist in the stratosphere (as far as I know).",
"This of course does not mean that there is no motion. There will be winds that forms due to regional fluctuations and changes with varying conditions. I'm afraid it is beyond my expertise on stratospheric dynamics."
] |
[
"Oh I get you. I didn't think of starting with that model.",
"Though to be honest, if there is air above the Trop then there must be some airflows above it as well? Surely there is a wind there. Which way does it flow? Why does it flow in that direction?"
] |
[
"Why don't humans have a mating season, or do we?"
] |
[
false
] |
[deleted]
|
[
"Do you have a source for this? Agriculture is quite recent, from an evolutionary perspective."
] |
[
"Most of Africa has very mild seasonal changes so it was better to just reproduce whenever we can. ",
"Women have periodic (heh) fertility/infertility but don't go in and out of estrous. Pheromones don't reveal fertility very strongly either, men don't respond much to pheromone changes that still exist. This is probably because sex has evolved to have stronger social value in humans than other animals. "
] |
[
"Could you give an example of the mild remnant? Everyone seems to be more easily sexually excited during Spring. Or is that the result of a Social process, rather than a biological one?"
] |
[
"Would the global spread of solar panels lower temperatures globally since heat is being converted to electricity instead of being reflected?"
] |
[
false
] | null |
[
"Averaged over the entire earth, not really. The energy that was converted to electricity doesn't disappear; it'll eventually be released, and almost all of it will end up as thermal energy again. For instance, maybe it turns into chemical potential energy in an electric car's battery, then into kinetic energy when the car accelerates, and then finally into heat in the air as the car does work against air resistance. ",
"Ultimately it has to end up either as heat or as some form of potential energy, and since we have a finite capacity to store potential energy, eventually the energy input and the heat output balance out.",
"If anything, solar panels would very very slightly ",
" the global temperature, because solar panels are dark, and we'd be absorbing slightly more solar energy that would otherwise have been reflected into space. (Of course, I'd expect this to be overwhelmed by the fact that we'd be pumping less CO2 into the atmosphere.) It's also conceivable that a gigantic solar farm could alter climate patterns on a local basis."
] |
[
"it'll eventually be released, and almost all of it will end up as thermal energy again",
"Yup, someone asked a professor at my college almost this same question. We got the roof, and parking lots covered by panels. Professor said the majority of that energy went to the air conditioning."
] |
[
"So.. oil spills are good for the environment? I'm on it. Wish me luck."
] |
[
"Habituation and sensitization: how are their causes different?"
] |
[
false
] |
They seem to be opposites, but from what I can tell have the exact same cause which is "repeated administrations of a stimulus". How are their causes different?
|
[
"I apologize for the late reply! The processes yielding these results on a macroscopic level are really beyond my realm of knowledge, and I really don't want to confuse you with any speculation. Best of luck!"
] |
[
"If you mean biochemically then ",
" is due to phosphorylation of potassium channels, in response to serotonin from a neighbour ",
", which yields longer depolarisation and a greater influx of calcium which in turn yields a greater neurotransmittor release ==> greater signal. ",
" if I recall is due to the synaptic vesicles running out (rate of release > rate of production) yielding less neurotransmittor release to the same stimulus.",
"If anyone has a more correct answer or sees errors, feel free to correct me!"
] |
[
"Do you know, what is the difference in what the organism actually has to experience for either process to occur? From what I can gather, both occur due to exposure to stimuli. Is there anything that makes them different in this sense?"
] |
[
"What differentiates the \"start\" end of a DNA strand from the \"end\"? Is information ever encoded in both directions on a strand of DNA?"
] |
[
false
] | null |
[
"DNA is double stranded. If you read along both strands one is running 5'->3' and the other is running 3'->5' (also referred to as Watson and Crick strands (at least in yeast)). Both strands can have DNA encoding for proteins. So you can have:",
"5'---start....end-------3'",
"3'----------------------5'",
"or",
"5'----------------------3'",
"3'---end......start-----5'",
"The systematic naming system in yeast specifies which strand the gene is on: YDR348",
" is on one strand and YLR206",
" is on the other strand. Sometimes genes will overlap. ",
"SGD",
" shows a chunk of a yeast chromosome. The red lines are known protein coding sequences. Some run in one direction, some in the other. "
] |
[
"I was just trying to diagram this out to explain. So yes, genes can be encoded in both directions. You can also add another layer with non-coding RNA transcripts, as these can overlap genes but in an opposite direction."
] |
[
"It is still in the 5' to 3' direction as the strands of DNA are antiparallel:",
"5'-ATGTCACCCGGGAAATTTTGACAT-3'",
"3'-TAGAGTGGGCCCTTTAAAACTGTA-5'",
"See how there is a start codon (ATG), some random codons, and then a stop codon (TGA) reading the top strand forward and the bottom strand backwards leading to two different mRNAs?... always reading 5' to 3'"
] |
[
"Does the “attention” (as in point of focus) lag behind when you move your eyeballs?"
] |
[
false
] | null |
[
"not very much. it depends on what exactly you're doing.",
"there's a good theory of \"attention remapping\" described here: ",
"https://www.sciencedirect.com/science/article/pii/S1364661310000288",
"it seems that from the moment you begin (unconsciously) planning an eye movement, the visual system begins the work of \"remapping\" attention from the current retinal position of an object to the expected post-movement position. (btw we're talking a time scale of ",
" here - all of this stuff is happening on-line and extremely quickly)",
"it's not a perfect process and like everything it takes some time. it's possible to induce strange illusions by moving a target at just the right moment during a saccade, making it feel like it's in a different position than it really is, or that it has different qualities than it really has. but for the most part it all works very smoothly, which is why you don't usually notice your eye movements (you make around ",
")."
] |
[
"Our eyes can only see when they're not moving. When you move your eyes, the brain receives a very blurry image, which you don't actually see. Instead, when the eyes arrive, the brain fills the period when they were moving with the new image.",
"See here for a more detailed explanation: ",
"https://en.wikipedia.org/wiki/Chronostasis"
] |
[
"i don't think this is true, especially the 'filling in' part. illusory filling-in is a very specific kind of process that is not a normal part of vision.",
"'saccadic suppression' is a concept many still believe in, the idea that during a saccade (eye movement) visual perception is completely suppressed. but I think it's a mistaken idea. there is evidence that vision works perfectly normally during saccades, e.g:",
"https://www.frontiersin.org/articles/10.3389/fpsyg.2011.00247/full",
"https://www.jneurosci.org/content/33/3/1211.short",
"The reason we don't ",
" during saccades is simply what you point out: the image is blurred (and also extremely brief, on the order of a few milliseconds). there's nothing much to see and so we don't notice it, but there's not really any special process or mechanism that suppresses or \"covers it up\"."
] |
[
"How does reproducibility happen in very expensive experiments?"
] |
[
false
] |
[deleted]
|
[
"Similar to cheap experiments. A few examples:",
"The ",
"LHC",
" has four big experiments. Two of them are large general-purpose experiments, ATLAS and CMS. They have the same physics goals, but a different design and they are run by independent collaborations. If one of them finds something new the other one can check this claim (or, more likely, is working on it already and has to finish the publication). ALICE is an experiment dedicated to lead-lead collisions - and ",
"RHIC",
" in the US can do very similar measurements. LHCb is an experiment specialized on matter/antimatter differences. Here ",
"Belle II",
" in Japan can do similar measurements, and ATLAS and CMS can check some measurements that Belle II cannot.",
"It is very rare that a measurement can be done exclusively by a single experiment. Typically there is at least a second experiment that can contribute. Not with the same sensitivity, but enough to serve as cross check. In the rare cases when there is no such experiment then it is likely that another experiment will be built if the first one claims to find something surprising.",
"For instance, if a sensor was malfunctioning in a space probe - and some conclusion was made from the results, how would they be falsified?",
"There are many cross checks to catch malfunctioning parts. Even within experiments scientists try to measure the same thing in multiple independent ways, and monitor if everything is working. Most of the time is spent on these things - make sure that everything is understood."
] |
[
"and RHIC in the US",
"\"Relativistic Heavy Ion Collider\" just to satisfy my curiosity. What speed qualifies as relativistic?"
] |
[
"They reach up to gamma=100, or 99.995% the speed of light. That is clearly relativistic."
] |
[
"How close are we to being able to directly interface with computers?"
] |
[
false
] |
I remember an where everyone had a computer implant installed at birth that allowed them to directly access their version of the internet. I'm wondering if it's at all likely that I will see anything similar to this in my lifetime.
|
[
"I will be a 4th year undergrad studying Molecular Biology and following that up with Graduate school in Biomedical Engineering. I'm extremely interested in Brain-computer interfaces or Brain-machine interfaces (it's why I'm studying what I am).",
"The short answer is far away.\nThe longer answer is there are many different interfaces being developed but there are many aspects to a successful interface all of which have serious hurdles on them. ",
"On a biological side we don't know precisely how much of anything happens in the brain, at least not once you start talking about a complex system like integrating data from the internet into evolving thoughts and conveying that information to others. The neural networks involved in, say, writing a memory into someone's brain, or reading a memory from a brain are not currently well enough understood to really do anything productive with. ",
"Japanese researchers have, however been able to predict what someone is seeing via MRI, after some calibrations",
"\nOther experiments have also shown that MRI can be used to predict what sort of object a person is thinking of or other sorts of binary choices.",
"On a hardware side chronic implants are pretty bad news because eventually the brain will grow scar tissue over the electrodes and you will lose signal. Or the brain or the electrode will shift slightly, and in any case you will have some kind of wire passing through the skin if you don't have wireless transmission. That's for a cortical electrode. The brain is a big place. The only way (probably) to come close to reaching all the corners of it to have full access to its nooks and crannies that you might want a neural interface with is to run the wires through blood vessels which reach to every corner of the brain, and since the blood vessels get very small and very fragile probably the only way to do this would be to use self-assembling conductive materials.\nSince chronic implants probably aren't what jo everyman wants (who wants brain surgery to use your computer? not me. Not until it's damn good.) lots of work is going into using EEG to read the brain's activity. EEG is MUCH MUCH less precise than electrodes inside the brain. You can at best look at effects from thousands of cells rather than single cells or very few. ",
"So that's probably enough... Here's a great radio show about neural prosthetics. ",
"http://www.abc.net.au/rn/allinthemind/stories/2011/3278072.htm",
"robotic exoskeletons relying on muscle activation in non-handicapped or only partially handicapped (weakened) people are also being developed.",
"John Doghue's lab showed years ago that a monkey with a motor cortex electrode could control a robotic arm. here's an article about him: ",
"http://www.guardian.co.uk/science/2011/apr/17/brain-implant-paralysis-movement",
"K I hope I helped. If you have more questions feel free to ask me. It will probably inspire me to read more which I always should be doing!"
] |
[
"I use a keyboard. It works well."
] |
[
"I even use a mouse sometimes. It's pretty reliable."
] |
[
"How does a heating coil work? Why does it not electrocute you when you touch it?"
] |
[
false
] |
Okay, so I know that a heating coil (like on a stove) works by sending electricity to the coil. The coil itself is a resistor of some type... electrons collide instead of conduct and heat is released. So why do you not get a shock when you touch a heating coil? And then why do you get a shock if say dropped in water (like a hair dryer).
|
[
"It's deceiving because a typical heating coil on, say, a stove top typically has three layers - the inner metal coil (to conduct electricity and generate heat), a layer of ceramic insulation around that (electrical insulation), and then a metal sheath around the insulation. So even though what you see is a metal coil on your stove top, it doesn't pose an electrical risk.",
"Interestingly enough, even if you were to touch a current-conducting coil, it wouldn't necessarily shock you. The reason for this is because the electrical resistance of the coil is much lower than your body, so electricity still prefers the metal wire to your hand. In order to short the current, it would have to go through your body, down through your rubber shoes and into the ground - a much higher resistance path than the metal wire. Now if you were standing barefoot on a metal plate when you touched it, you might feel a shock... but then I would probably ask what you were doing barefoot with live electrical wire. ",
"Edit - As a couple others have mentioned, there's a bit more to handling voltage sources that I've left out, such as how close you are to the hot (higher potential) end when you touch the wire. In a wall outlet, for example, the two connections are at 120 V and ground. If these are connected by a simple wire then the voltage is dropped evenly along the length of the wire. So if you touch the wire near the 120 V end, then 120 V is what your body will feel (which will hurt, a lot). If you touch the wire closer to the 0 V end then you likely won't feel anything.",
"I should have been more clear in my initial explanation, I just didn't want to get too sidetracked talking about voltage sources. Please don't handle exposed electrical parts unless you know what you're doing."
] |
[
"PLEASE don't go touching exposed coils either directly or with conductive tools while they are powered. Saying that the electricity prefers to go through the coil is misleading. If you touch the coil close to the end connected to the active you are still going to have most of the voltage across your body. This is going to have the same effect as sticking a knife in an outlet. "
] |
[
"I want to reiterate again what has been said by a few. According to Ohm's law, the amount of current that will pass through your body in a household shock is dependent on TWO and ONLY TWO things. Your impedance presented to the circuit and the voltage across your body. Sticking a fork in an electrical socket is EXACTLY THE SAME as sticking a fork into the prong of a live burner. \nAlso all this mumbo jumbo about getting lucky and hitting the \"ground\" side won't help you on a range. Here in the US electric ranges run on 240 VAC which is produced by having +120VAC on one side and -120VAC (180 degrees out of phase) on the other. There is no \"neutral\" end of a burner. ",
"Also, there is a reason why there are both neutral and ground conductors in a household electrical system. Since neutral conductors are carrying current, it is possible for stray voltages to appear due to voltage drops from the resistance of the wire or connections. Also, if due to some fault the neutral conductors path to ground is impeded, there is likely to be 120V sitting on it coupled through a load, causing a shock hazard. Just because you see neutral, don't assume it is at ground. Never touch ANY conductors in a live circuit without proper insulated tools and training. ",
"I have been shocked by 120VAC a couple times. It hurts. Every time. As a friend of mine used to say \"Once is an accident, twice is stupidity, third time's a fetish\"",
"[edited for grammar]"
] |
[
"r/AskScience, how far from having a functional energy shield are we?"
] |
[
false
] |
As an enthusiastic sci-fi fan, my superior knowledge clearly states its theoretically possible :P Seriously now, regarding real-world experiments have there been any developments in this particular subject? : energy shield, force field, deflector shield, etc... think Dune, Independence Day, Stargate, Star Trek, ...
|
[
"Actual Star Trek force fields aside, there are already uses of 'energy shields' today. Many modern tanks include one of many forms of ",
"reactive armour",
". This type of armour reacts to incoming projectiles in a way that reduces their impact on the tank.",
"The closest to a force field is electrical reactive armour, which is in active development in several places. This consists of two thin metal plates with a strong charge between them. When a projectile pierces the plates, it completes the circuit. The current flowing through the projectile then vaporizes or melts it, before it can penetrate the conventional armour behind. Not quite a force field, but still cool."
] |
[
"I think he's talking about something immaterial but can block projectiles and energy from penetrating."
] |
[
"I'm sorry, I assumed the concept of a force field would be universal given its popularity. To be honest, having to explain the concept - especially in this subreddit - is somewhat puzzling.",
"As Beemecks said, some kind of energy field that effectively blocks projectile and energy from penetrating it's interior. In popular films and games, it is used as an armor."
] |
[
"Does cyanide *actually* smell like almonds, or is that just an artifact of cyanide classically being extracted from almonds?"
] |
[
false
] |
I always thought that cyanide smelled like almonds (and vice versa!), but it turns out almonds contain amygdalin, which breaks down into benzaldehyde and cyanide (and sugars) -- and of course culinary almond extract isn't cyanide. Clearly the cyanide isn't the only thing responsible for the smell, and maybe it doesn't itself smell of almonds at all! In that case, I guess my question is really about the history of cyanide preparations. Why would they leave in the benzaldehyde? I suppose it could be for safety (like odorants added to natural gas), but if it's being made for legit organic chemistry uses I could see impurity being an issue, and if it's being made for poisoning people then safety probably isn't the primary consideration. So where does cyanide get the reputation for smelling like almonds?
|
[
"Cyanide smells like ",
", which is not at all the same thing as a normal almond. This is because bitter almonds actually contain some cyanide. All commercially available almonds are sweet almonds, so the vast majority of people wouldn't know what bitter almonds smell like."
] |
[
"Oh, interesting! Any idea if the smell is at all similar?",
"Someone else pointed out that there are cyanide-producing millipedes that smell like (sweet) almonds -- are they producing both benzaldehyde and cyanide? If they produce amygdalin, this would make sense..."
] |
[
"the following chemicals all smell very similar:"
] |
[
"Are brain games effective?"
] |
[
false
] |
In this doucumentary ., A guy sets on a journey to change imporve is brain with help of couple of scientist,first he goes by imrpoving his attention span by juggilng then he goes to next exercise called double decision . The scientist helping with him, claims this would help a tons imrpoving certain aspect of brain. how true is it?
|
[
"The brain works just like a muscle. You can train by exercising. Once you stop exercising the effect goes away. ",
"I’ve done it myself. Did a programme and after a while I could reproduce/remember 16 numbers after a few seconds of exposure. Once i stopped with the programme I very quickly couldn’t do it anymore. So unless you learn skills you’ll be using daily in your worklife it’s not very effective."
] |
[
"Building off of ",
"/u/Nunc27",
"'s post.",
"The more you do something, the better you get at it. Your brain is a series (or web) of connections. The more the connections are used, the stronger the links become. This is called ",
"Hebb's Rule",
", which is basically the leading theory as to why the brain works the way it does. Think about how, if you walked the same path through a jungle over and over, that path would become more trodden, each time making it less difficult to walk that path, both because it's cleared out and because you know your way.",
"The way these bonds are strenghtened is called ",
"synaptic plasticity",
". Basically, the structure of the neurons involved change structurally to allow for easier connections. It can do so in a number of ways and I won't get too much into the biochemical nature of it here.",
"EDIT - to answer your post, it seems that brain games are good at making you better at brain games, so long as you continue them. ",
"Paper 1",
"; ",
"Paper 2"
] |
[
"I don't know about modern games, but in the 90s, the Tetris effect has been studied extensively. The short conclusion is that after some practise in playing Tetris, some brain areas become less active, some more, indicating brain efficiency, which is related to intelligence (since Tetris involves planning, visuo-spatial, and other brain tasks). But no, there doesn't seem to be an overlap between brain areas becoming less or more active, and the brain areas needed to play Tetris, so brain efficiency does not appear to be related to increased grey matter.",
"https://en.wikipedia.org/wiki/Tetris_effect"
] |
[
"How do supercomputers run so much hardware in parallel?"
] |
[
false
] |
[deleted]
|
[
"There are two main ways it's done.",
"The first is something similar to what you're describing. A bunch of processors linked together with custom hardware, basically creating one giant motherboard (though it does a lot more work than a standard motherboard.)",
"The second is by taking separate server racks of standard computers and tying them together with a high speed network (generally fiber). In this way, there are many separate processor/motherboard pairs that work independently but communicate over the network.",
"I think most modern supercomputers are a combination of the two. They build large racks that can hold a lot of processors (similar to the first type I described), then they tie all of those racks together with a high speed network."
] |
[
"The formal dividing line between these two classes of systems is how memory is arranged. (This is sometimes referred to as the \"size of the coherence domain\".) When a processor modifies a location in memory, can a different processor directly read the new value? These are referred to as \"single-image systems\" or \"shared memory systems\". This is the first class of system you described and they're actually making a bit of a comeback. Since the system automatically handles communication, they make programming a fair bit easier.",
"The Cray XC systems are a distributed shared memory system and one is currently #6 on the Top500 list. People seem to really like this machine from an ease of development standpoint.",
"Alternatively, you have \"message passing systems\" or \"clusters\" where a CPU has to make an explicit request for another node's data ",
" a node has to push data to other nodes.",
"Most of the systems on the Top500 list look like this, however you're right that these systems are in reality all combinations of the two models. Each node is almost always itself a multi-core shared memory machine itself."
] |
[
"You can think of a supercomputer as a bunch of small computers on a network working together. Supercomputers are typically composed of a bunch of identical systems. A simple example is a Beowulf cluster. (",
"http://en.wikipedia.org/wiki/Beowulf_cluster",
")",
"Programming supercomputers so that all the small computers can be doing useful work at the same time can be a challenge, and how it's done depends on the problem that you want to solve.",
"http://en.wikipedia.org/wiki/Supercomputer"
] |
[
"Stars related question"
] |
[
false
] |
I've never posted here before, but since I work night shift, I've been wondering this for a while. (And this may be terribly worded, if any of you need clarity, feel free to ask.) Since the universe is expanding and whatnot, and even though it takes many years for us to see the light of the stars (unless we use telescopes and the like), why doesn't it look like the space between stars (or constellations) is also expanding? We've had the same constellations for centuries.
|
[
"Are the constellations permanent?",
"Ancient astronomers often spoke of the \"fixed stars,\" which maintained permanent positions in the sky. And, indeed, the stars do seem almost fixed in place; the patterns they form look much the same today as they did when the constellations were first named nearly 3000 years ago. But the stars are all moving relative to the Sun, most with speeds of many kilometers per second. Because they are so very far away, it will take thousands of lifetimes to see significant changes in the star patterns. But, over time, they will change. Because of the motions of the stars within it, for example, the handle of the Big Dipper will, in about 50,000 years, appear significantly more bent than it is today (see figure at left). We will, no doubt, keep the same names for the constellations, even if the stars change their positions. Constellations are, after all, products of human imagination, not nature.",
"Taken from - ",
"http://www.physics.csbsju.edu/astro/asp/constellation.faq.html#permanent"
] |
[
"The universe is expanding, but this expansion is only important on a very large scale. If we look at galaxies billions of light years away from us the effects are obvious (they're all moving away from us, at a speed proportional to their distance), but the motion of nearby galaxies (within a few million light years) is hardly affected, because at that scale their individual motion and gravitational forces between nearby galaxies is much more important. So the nearest large galaxy to our own, Andromeda, is actually moving toward us. On the scale of distances to the stars we see in the sky, which is hundreds to thousands of light years at most, expansion really isn't relevant.",
"But of course, the stars in our sky are still moving. Each has its own orbit around the galaxy, and they're all moving relative to each other, typically at a speed of dozens of kilometers per second. So why don't we notice the constellations change? Simply because they are very, very far away. They may be moving many kilometers each second, but even the nearest stars are many trillions of kilometers away. So we'd have to wait thousands of years to see any significant change in the constellations.",
"We can measure the proper motion of nearby stars with photographs of the sky taken through telescopes years apart, but this motion is too small to be apparent to the naked eye. The nearby star Arcturus, for example, moved only half a degree--the width of the full Moon--in the last 1800 years. And here's how much the Big Dipper will change in the next 50,000 years:",
"http://cseligman.com/text/sky/bigdipperchange.jpg"
] |
[
"http://cseligman.com/text/sky/bigdipperchange.jpg",
"->",
"The address you entered is not a valid page name.\nUse one of the links above to reach your destination.",
"But when I paste the URL into the address bar, I get a picture. Midnight blue background, white drawing."
] |
[
"Are there any combustion-like reactions that don't involve oxygen?"
] |
[
false
] |
There's the "fire triangle", and how combustion is defined as a reaction between oxygen and another substance. So would combining any other set of substances/compounds elements produce a similar result? By that I mean light, heat ect. Everything you might think of when you hear "fire".
|
[
"Absolutely. Fluorine is another powerfully electronegative element that starts extremely vigorous fires with a wide variety of substances. Plenty of light, plenty of heat, and plenty of terribly poisonous and corrosive by-products, just as a bonus."
] |
[
"Yes, halogens are a good example, specifically fluorine and chlorine. An example being a reaction between sodium metal and chlorine gas. The sodium, acts like a \"fuel\" and the chlorine acts like an oxidizer, because technically, it is. An oxidizer, which gets its namesake from oxygen, is very electronegative and will bond with atoms that have free electrons. ",
"On the other hand, some compounds which could be considered the \"fuel\" are so reactive, they will \"burn\" in pure nitrogen."
] |
[
"Is chlorine trifluoride what you meant? I wasn't able to find anything on difluoride.",
"But I did find ",
"this",
". It's in French and rather old, but they show what happens when chlorine trifluoride contacts (in order) Plexiglas, a rubber glove, clean leather, not-so-clean leather, a gas mask, a piece of wood, and a wet glove.",
"Edit: ",
"Apparently",
" iron and chlorine gas can be reacted to make iron(II) chloride: Fe(s) + Cl2(g) --> FeCl2(s). Completely oxygen exclusive! And a complete lack of PPE in that video too...."
] |
[
"Are there any foods we eat today that are genetically unaltered from our ancient ancestors?"
] |
[
false
] |
I have a friend who used to say, "Strawberries are proof god loves us and wants us to be happy." I countered that strawberries have been genetically engineered for hundreds of years to produce the fruit we enjoy today, but that got me thinking, are there any foods in our modern diet that we haven't changed to make them better/tastier/more nutritious? The only thing I could think of was honey and wild game, but was interested in a more concrete list. Edit: Not sure if this should be flaired for biology or anthropology, sorry.
|
[
"Even honeybees are probably different that their wild ancestors. IIRC domesticated bees are calmer than their wild cousins. Your guess at wild game rings true of course. I'm sure many of our garden crops, mint and some onions come to mind, are not altered much and can grow wild. Rhubarb grows wild where I live, though I doubt it is native that does indicate at least hardiness. Crops that cannot live without human intervention, maize for example, are highly genetically altered from their wild counterparts. "
] |
[
"What humans have done to plants and animals, until very recently, has artificial been selective breeding. This affects the plant's or animal's genetics over time, just as selective breeding in captive wolves created the cocker spaniel, but it isn't really the same thing as \"genetically engineered.\" It's a hit-or-miss process, you keep the successes and throw away the failures. ",
"If you want a good explanation of how artificial selective breeding works, watch the documentary \"Botany of Desire\" on YouTube or Netflix. It's about four plants that humans have cultivated and completely changed, and how the plants have spread across the globe. Two of them are apples and potatoes, and they show some of the thousands of (smaller and uglier) natural varieties that grow in their original home environments (Kazahkstan and South America), where people still eat them, but you'll never see them at your grocery store. The berries you find growing in the woods are sometimes native and natural, but just as often they are invasive plants brought from another part of the world, and in doing so changing their taste, color, structure, or other epigenetic factors. Blackberries are native to California where I live, but most of them in the woods around here are the Himalayan variety, imported for people's gardens. The \"heirloom\" vegetables that are popular now are no more natural than the almost-tasteless Granny Smith apple. Like the Cornish Game Hen (\"invented\" in Rhode Island in Connecticut in 1955), which is just a chicken less than 5 weeks old, the active ingredient is marketing. ",
"There are 450 native bee species in my county, and none of them live in big hives or produce huge quantities of honey. The European honey bee, which was managed and controlled for centuries by European apiarists, came over with the European colonists (and the crops that needed the bees to pollinate them). They only slightly resemble their wild ancestors, and are nothing like our local bees. And because they are one single species, they are now dying by the millions from a fungus. It might be because we modified them and then exposed them generation after generation to a toxic soup of fertilizers and pesticides, but more research is needed. It's almost certainly a combination of factors. Meanwhile my local bees are doing fine. ",
"Sometimes we are so used to the human-manufactured result that we don't know what the original (natural) thing looked like. Carrots are orange now because the orange carrot was created to honor the Dutch royal family (William of Orange) hundreds of years ago. Wild bananas are about 70% large seeds, but the only ones we eat are seedless. Think about that; how can a seedless plant survive? The seedless banana was created in 1838 on a plantation in Jamaica,and all new banana trees are planted from shoots off existing trees, not seeds. ",
"Corn is my favorite example. It's a grass, which is obvious when you compare the leaves to bamboo (another grass), and its original ancestor (teosinte) from Mexico had a few seeds that fell off if you brushed against the bush. This is good for the plant, but not so good for people who eat the seeds, so farmers planted a few seeds from the plant with the biggest biggest seed-bunches for millennia until they had ears with lots of seeds protected by a husk of heavy leaves. There are caves in Mexico where there are corn cobs going back several thousand years, getting smaller in size the older they are. ",
"Horses big enough to carry a human were entirely the result of humans breeding the biggest with the biggest, until about 900 BC they were big enough to carry people. Look at the oldest carvings and paintings on middle eastern pyramids and tombs, and the horses are tiny things, teams of them pulling chariots. ",
"The Russians set up a program to raise foxes in captivity (for their fur), and accidentally created a tame subspecies of fox that loves people, has floppy ears and curved tails, and acts like a dog. They did this by feeding the foxes that responded well to people, and skinning the others to make fur coats.",
"So, complicated. Purely natural foods are few and far between, but almost all of the modern varieties produce more calories per acre, are safer to eat, and are nicer to look at. But it's good to look back and remember what our ancestors used to eat."
] |
[
"A lot of berries grow wild, ie wild strawberries, raspberries and blackberries. So if you ever collect or eat wild berries then that would be an example of a food that hasn't changed. In terms of what you can buy from the supermarket, I think most foods have changed at least somewhat from domestication. Strawberries are very different from their wild counterparts, blackberries and raspberries are pretty similar though. In terms of animal products, fish and seafood is an obvious one, but you might be counting that as wild game. There is some farmed fish though, there are currently breeding programs for them, but they would be less altered than other domestic animals.",
"Part of your question is a bit misinformed though. Most of our breeding has not been done to make foods more tastier or nutritious, its mostly to make the bigger, less prone to spoiling or damage and have longer shelf lives. Wild strawberries taste much better than domestic ones. A lot of vegetables have been bred to be better tasting though, by breeding for a reduced amount of bitter tasting natural pesticides. "
] |
[
"Why/how do benzodiazepines and Z drugs/sleeping pills cause damage when used long term?"
] |
[
false
] | null |
[
"Both drug families target the same binding site of GABA(A) receptors and potentiate GABA responses. This causes an enhancement of inhibitory signals in the neural circuits. As a consequence, there are less action potentials and thus we get relaxed and less responsive at sensible doses. ",
"In a healthy individual there is a fine balance between inhibitory and excitatory signals that shape communication between neurons. As said above, benzos or z drugs mess with that balance. There is no issue when people consume it rarely at recommended doses. However, when used long-term, the neuronal plasticity (the neurons' architecture which includes for example how many receptors are present at its surface) changes to achieve a balance again. Especially the impact of those drugs on dopaminergic neurons mess with the reward system and can such cause dependency. ",
"When consumed at elevated concentrations, Benzodiazepines and (probably) Z drugs target other receptors and binding sites as intended. For example, they bind to sites on the GABA(A) receptor that are usually targeted by anaesthetics. At this point major neuronal pathways get inhibited which regulate perception of pain, awareness (consciousness), control of muscles and breath. Especially latter can be lethal of course."
] |
[
"They disrupt stages of sleep, decreasing REM sleep. ",
"Also chronic Benzodiazepine use increases risk of Dementia, 50% in 1 study. ",
"https://www.huffpost.com/entry/this-is-your-brain-on-dru_b_439577/amp",
"https://www.bmj.com/content/345/bmj.e6231#:~:text=Results%20of%20a%20complementary%20nested,1.95)%20compared%20with%20never%20users",
"."
] |
[
"How long after cessation would it take for the brain to recover from this (specifically high doses of z class for several years)?"
] |
[
"How does this work?"
] |
[
false
] |
If magma is lava that is under ground, does a volcano spew out magma or lava? When does magma become lava?
|
[
"By definition, melted rock beneath the surface is called magma. Once it erupts, it is called lava. The distinction is largely semantic and done for convenience (i.e. by describing it correctly as either magma or lava, you are conveying extra information in terms of its location), though there are some true differences. For example, magma will have varying amounts of dissolved gases (water, CO2, etc), many of these gases escape in the eruption process (as pressure decreases) so lava tends to have less volatile content than magma. Similarly, by virtue of it being at the surface, lava is cooling rapidly compared to magma and will contain progressively more (small) crystals as it cools. You could also view the distinction as an extension of the way we classify igneous rocks, specifically the division between extrusive and intrusive. Chemically, a ",
"basalt",
" and a ",
"gabbro",
" are nearly equivalent, but we classify and name them differently because one is extrusive and one is intrusive (respectively) and as a result, the size of the crystals within the rocks are very different. To return to the lava/magma distinction, basalt crystallizes from a ",
"mafic",
" lava, gabbro crystallizes from a mafic magma."
] |
[
"Once it's at the surface, it's lava. It doesn't specifically refer to contact with air (i.e. if it's erupted under water, still lava)."
] |
[
"Thank you!"
] |
[
"Specific question about electromagnetic attraction and Coulomb's law."
] |
[
false
] |
Imagine I have two positively charged point masses (mass A, mass B, each with a charge of 1 C, mass of 1 kg) at rest on a surface. The masses are separated by a distance of 1 m. The surface is frictionless. According to Coulomb's Law, the Force of A on B should be the opposite of B on A, and should have a magnitude of ( )/ Assuming qA = qB = 1 and r = 1, |F|= . So this is all neat and dandy if we look from the inertial frame of reference of A, as B experiences a force of , and if it has a mass of 1 kg, B moves with an instantaneous acceleration of m/s away from A. Similarly, from the reference of B, A has an acceleration of m/s But what if we use the table as a stationary frame of reference, a frame that does not move with A or B? In this case, A and B both repel each other and move away equally from a central point defined as the midpoint between the two masses (0.5 meters from each mass's starting position). EDIT: Forgot to make this clear, lol. Sorry, my bad! Anyway, what I meant to ask: So which is right? The frame of reference of the table, where each charge speeds away with an acceleration of k m/s , and if we convert this to one of the charge's frame of reference, the other charge speeds away at 2k m/s ? Or, do we start initially from the frame of reference of one of the charges, calculate the other charge to be moving away at k m/s and leave it at that? The conflict is with one method (originally using the table's frame then converting to the charge's frame) you end up with one charge stationary and the other accelerating at 2k m/s With the other method (initially using the charge's stationary frame) you end up with one charge stationary and the other accelerating at only k m/s
|
[
"Thanks. The stationary frame is ALWAYS right because it is an inertial frame. In the moving frame, you have to add a ficticious force, which will give you the correct 2k result.",
"(This is related to Einstein's postulate that an accelerating reference frame is indistinguishable from a gravitational field.)"
] |
[
"What's the question, exactly?",
"The table frame is definitely correct, since it's an inertial frame. When you go to an accelerating frame, you have to add ficticious forces to make things work correctly.",
"EDIT: Oh, also in a moving frame, electric and magnetic fields partially change into each other, depending on the speed."
] |
[
"Sorry about that, question fixed!"
] |
[
"How is the analog signal from a HDD read head processed before it is digitized?"
] |
[
false
] |
Doing a simple estimation, a hard drive might be able to read 128 MB/s. Maybe it has 4 platters, giving each read head a reading speed of 32 MB/s, or 256 Mbit/sec. So this would be a 256 MHz signal coming from the read head, but of course it's not a clean digital signal. Some of the magnetic domains might have lost some of their alignment making their signal weaker, and in any case everything would bleed together a bit, right? What does the signal from the read head look like, and how is it processed to become digitized? Furthermore, how does the HDD even know where the read head is in terms of the circumference of the platter?
|
[
"Hard drives use some form of ",
"Forward Error Correction",
" with ",
"Soft Decision",
"; in some cases, ",
"Reed-Solomon",
", with ",
"Viterbi decoding",
" is used. Reed Solomon may be popular, but there are other forward error correction schemes in use such as ",
"Turbo coding",
" or ",
"Low Density Parity Check codes",
".",
"First, forward error correction - you take the data that you want to store, run that data through some algorithm that generates extra data (adding redundency), and then write the whole thing to the disk. When you then try to read that block off the disk, if some of the original bits are in error, then you can use the redundant bits to try to figure out what the original message was.",
"Soft decision uses the analog nature of the media to represent the bits, instead of actual ones and zeros - so I say that bit 1 is a '1' with 80% probability, then bit 2 a '0' with 30% probability, etc. This information goes into the error correction logic to increase its error correction performance because it can use the probability information to figure out what is the most probable output code.",
"For example, lets say we had a really simple system - we have 2 bits of original data, and we simply duplicate it 2 times. ",
"If you receive '00 01 00', then as a human you can probably figure out that the most likely values for the original data was '00'. ",
"If you receive '01 00 00', same answer.",
"If instead gave you a value where the second bit was in question: '00 01 00' with probabilities ",
"{ 99, 10, 90, 99, 80, 05}",
", then you would might say that the most likely value for the original data was '01' - the second bit is '1' because one indication for the second bit's value has 99% probability of it being a 1, while the other two indications say '0', but with 10% and 5% probabilities.",
"Viterbi decoding combines this idea of the probability of the bit being one value or another, along with the structure of how the forward error correction data is generated, and attempts to guess the correct data.",
"Reed-Solomon is one widely-used forward error correction scheme, and is based on the mathematics of finite fields, also known as galois fields.",
"The original inspiration for reed solomon was to represent the original data as a polynomial. You could then plot that polynomial, then sample that polynomial in as many extra spots as you want, and then transmit all of extra samples. ",
"For instance, lets say we want to transmit one bit ",
". We could then agree that when we want to transmit ",
"a =1",
", we would send a whole bunch of points sampled on the parabola ",
"y = (1) * x^2",
". If we wanted to send ",
"a=0",
", we'd send a whole bunch of points sampled on the parabola ",
"y = (-1) * x^2",
". If i send you 6 points ",
"{-13, -5, 10, 0, -5, -8, -13}",
", you'll notice that a couple of those points don't exactly agree with a parabola, but they fit the curve well enough that the curve generally fits the pattern of ",
"-1 * x^2",
" and so the transmitted bit was a 0.",
"A decent, practical paper to read to understand Reed-Solomon and Finite fields was written by the BBC:\n",
"https://downloads.bbc.co.uk/rd/pubs/whp/whp-pdf-files/WHP031.pdf",
"If you're feeling very curious, I have written an implementation of Reed-Solomon (without soft-decision) in C#:",
"https://github.com/antiduh/ErrorCorrection/tree/master/ErrorCorrection",
"The fun starts in ",
"GaloisField.cs",
". Also check out ",
"Encoder.cs",
" and ",
"Decoder.cs",
". Those files have almost as many comments as they do code, and my implementation uses a lot of the conventions followed by the BBC paper I linked above."
] |
[
"Q: What does the signal from the read head look like? \n A: An analog signal, or more simply, something like a sound wave. :)",
"Q: How is it processed to be digital?\n A: First, understand the data flow: Head(s) > Preamp > Controller Read Channel > HDD Controller Interface > Host Interconnect. ",
"When it's originally read, it's an analog signal. The preamp, typically on the actuator to limit distance to the heads, performs the signal clean-up, then passes this analog signal to the Read Channel, which will convert it to a digital signal. When a write is performed, reverse this process, and the digital signal is passed from the Controller to the Read Channel, which then converts the digital signal to analog. The analog signal is passed to the preamp/heads to commit the write to disk. The conversion itself just takes the Digital AC signal and spits out an Analog AC signal, by way of using a series of alternating current transitions... ",
"Q: How does the HDD know where the head(s) are relative to the platter(s)?\n A: The platters all have 'spokes' (or more appropriately called servo fields), somewhat like a bike wheel, which are pre-defined spaces along the tracks and between the data sectors. When the heads pass over these spaces or fields, the Controller calculates the heads position on the platters, relative to which track, sector, and block the servo field was detected.",
"Tada!",
"Edit: Correction in terminology of Q#3 summarization (changed reads to head(s), silly auto correct)."
] |
[
"Thank you, finally a detailed answer that doesn't gloss over the fact that there's a great deal of math that goes into deciding which bits are ones and which are zeroes. It's not just a bit-at-a-time threshold decision. "
] |
[
"My understanding is that light waves extend forever. If so, are the periods constant, or does it increase infinitely?"
] |
[
false
] |
[deleted]
|
[
"I'm not sure I completely understand your question, but I think this will mostly answer it. The closer you are to a source that radiates photons, the more photons you'll get hit by. That's why a light source seems more intense the closer you are to it -- it's not because the individual photons lose energy on the way to your eye but because your eye gets hit with more of them."
] |
[
"For an object of set size, the closer you are to a light source the more light you receive. Think about how object appear smaller as they become more distant; given a set energy output per exposed area, more distant objects would have less energy distributed over their surface."
] |
[
"Light is conserved, it just gets spread out (like butter scraped over too much bread!) over a larger area the farther you get from the light source.",
"Consider a light source, be it a campfire or a star. It's putting out a constant amount of energy per time. Now imagine a sphere that just encloses the light source. Each element of surface area on that sphere is going to receive some amount of light from the light source. Now increase the size of that sphere by a factor of ten. The surface area of the sphere will increase by 100x, but the total light hitting it will remain constant, meaning that each surface area element will be receiving 1/100th as much light as before."
] |
[
"Linguists: How do you think the internet will effect the evolution of language?"
] |
[
false
] | null |
[
"I haven't finished my degree in Linguistics yet, so take what I say with a grain of salt, but I think I can give you an idea.",
"First, the most immediate thing the internet is doing is expanding our vocabulary. In English, for example, our propensity for making verbs out of nouns has put \"to unfriend\", along with many others, in ",
"some dictionaries",
". Extant words have also had their uses expanded for the internet (e.g. \"surfing\")",
"Beyond what we already see, I think it's a bit challenging to predict what exactly the internet might do to language. First, let's understand that the internet is just one facet of globalization which has already had some very visible effects on language. For example, China's sprawling economy has doomed small languages like ",
"Shanghainese",
" to obscurity, if not extinction. Another interesting case study is India. (",
"Here",
"'s a good article if you want to read more in depth.) After gaining its independence, the country recognized English as an official language for government proceedings, and today English has become even more than a ",
" for India. Among Hindi speakers, and I'd assume others, it's become commonplace to mix English phrases into speech even with another native Hindi speaker: one of India's most popular songs of all time, ",
", has English in its title.",
"Globalization can work and clearly has worked against language diversity, and frankly I'd be hard pressed to think of a way it could be of benefit to an endangered language. So, I personally think that the internet will not help with the trend towards homogeneity we've been seeing. ",
"Here",
" are some opinions from people of varying authority on the matter if you want to read more.",
"In terms of development ",
" languages beyond expansion of vocabulary which we've already discussed, I think the internet will serve to actually prevent significant change from occurring in grammar and conventions. The internet gets rid of so many barriers—distance, physical dividers (mountains, water), etc.—that have historically given groups of people enough room to develop changes in their language. For example, after the fall of the Roman Empire, standard Latin turned into Spanish, French, and the other Romance languages. That happened over a period of scores of years, and though it's impossible to predict what technology might bring in the coming decades, I'm willing to bet a good amount of money that we will ",
" again see a change in language on the scale of Vulgar Latin's now that the Information Age has dawned.",
"I hope you got something out of that, or at least that I was coherent. Time to get some sleep."
] |
[
"I came here to say what the above two posts have already said, but I'm going to take it a step further.",
"I focus on Asian languages, and I lived in South Korea for a while. South Korea is an example of an extremely closed society that's been opened via internet connection. Despite their own private sector of the internet, and the cultural significance of their language, it is dying due to the influence of major trade languages and the ever-creeping virtual globalization of our society.",
"I see this happening over the next two centuries:",
"Minor languages fall out of use and eventually die out completely. Regional dialects no longer exist due to the removal of regional barriers in mass communication. (We've already seen a homogenizing of dialects due to mass communication).",
"Those minor languages that do live on, will be increasingly reliant on cybernetic enhancement (Translation aids) in order to communicate and operate in an increasingly virtual economy. The cultures slow to give ground to the rising tides of change will not be able to beat it back, because with each generation, internet presence will edge closer to residence.",
"The major trade languages are going to be determined by economic influence and content development. English has secured its foothold due to mass of audience. Chinese looks to be securing an economic foothold in the next century, and Arabic looks to be on the way to securing a major economic foothold. Russian will likely carry on as a dying trade language for several decades, but will likely be superseded by English.",
"Common access portals and common trade languages are going to influence political alignment over time. Meaning simply, the cultures that adopt a specific trade language are more likely to unite with other cultures who have as well. Borders will melt quite a lot due to language flux. In the end, we're going to see three or four major superpowers, likely english-speakers in the west and through western europe. Chinese (via pinion, mostly. Even short-form Hanja is likely to go out of style due to technical issues.) speakers in the east and south pacific as well as most of current Russia, and Arabic speakers through the remaining bits of Russia, large swaths of Africa, eastern Europe, and through large sections of the pacific. While I can't be certain about economic and political events past the next year or so, the certainty that these will be the major trade languages and physical territory of them seems to be a safe bet to hedge.",
"Within individual languages, they are going to start evolving faster, and simplifying for mechanized use. Meaning, we're going to start considering how to adapt our language to software, not just adapting our software to language. Many grammar patterns will be lost, and some of our text-based inflection is going to see standardization through stylized representation. (As in, size and print-style is going to see a move into all written language.)",
"Memes are going to continue to evolve, and have increasing impact and cultural recognition in our society. Not only this, but ideas are going to be communicated and mutate at a much faster rate. Languages themselves won't change nearly as much, except that they will be streamlined and homogenized.",
"The next major frontier in our evolution is our adaptation to the virtual world. Meaning simply, all changes to our language will be direct results of changes in our technology, and nothing else.",
"Edit: We're also likely to see the adoption of tokens or counters within language. Korean language is one of the most suited for computerization of any language on the planet. Counters and tokens are going to make their way into languages permanently as we become an increasingly technologically connected world. They aid in speech recognition and lexical translation tools immensely. English in its current form is not compatible with the future because of the lack of proper or standardized tokens. In the end, there's no choice whether to adopt them or not."
] |
[
"It's a system for identifying a subject, object, or verb within a sentence, or declaring association between numbers.",
"In English, sentence structure is mostly SVO (Subject, verb, object.). But it gets complex fast.",
"Consider the following sentence:",
"Sally went to the store.",
"Sally (Subject) went (verb) store (object).",
"Now let's mix it up a bit:",
"Sally, the girl wearing the trenchcoat, went to the store down off parks and fifth the other day around five o'clock.",
"Now, this is a lot more complex. You have made the sentence a lot more information dense.",
"Sally (subject), went (verb), store(object)",
"the girl (subject) wearing (verb) the trenchcoat (object)",
"store (subject) implied is (verb)",
"And then you have two descriptors for time and place.",
"In English, you can jumble the sentence around a bit, and it'll still grammatically make sense. There is no set order to sentences, making it extremely difficult to parse via machine.",
"Korean solves this with two approaches: A rigid grammatical structure, tokens, and counters. Counters are only used for numbered objects. You apply them after a number to give further context to the number. We use them in english for units of measurement, but I simply say:",
"There are 21 cars in that parking lot.",
"Korean, allows you to essentially say:",
"21(counter) that parking lot. (implied is based on tense. No need for specific location, as the location is already marked.) Based on the counter you use, you can specify people, cars, etc. Different counters are used for different objects. A general counter syllable (gae) is used to reference inanimate objects. Specific counters (cha, ja, mari) are used for cars, people, or animals respectively. You never actually say people, but the counter syllable you use implies people when in use with a number.",
"Tokens, on the other hand, come after a word in a sentence to denote function. Verbs use a universal conjugation, and always come at the end of a sentence or phrase. They are marked by their location, or by their conjugation, which also serves to differentiate intonations or tenses.",
"Tokens are also used to differentiate the subject from the object (ga for subject, rlul for object). Locations are noted with (ey or ey sa) to denote to, from, or at a place. While times are noted by (shi and bun for hour and minute counters. General non-numeric times are noted the same as places.)",
"This continues until you have several thousand different counters for different uses, however, it is all highly efficient and logical. It does stunt the complexity of a language quite a lot, but using simplistic languages, it's still very possible to express complex ideas. The complexity of the codification doesn't indicate the complexity of the expression.",
"Why do I see this being adopted? Databases and lexical association software are literally becoming the future of communication. Without these, we're going to stagnate as a species, and the complexity of language is a barrier to their development. Meaning simply, tokens in language, or a stunted economy. Economics wins every single time."
] |
[
"Why can we NOT drink seawater to survive?"
] |
[
false
] |
I know we can drink small amounts of seawater but why is it we cannot drink it to survive. We require trace metals, minerals, ions etc. that can be readily found in seawater and yet when we drink it we instinctively spit it out and feel a stomachache afterwards. We also cannot survive solely on DI water, since it has none of the trace metals, minerals, ions we require and instead we must eat food to obtain these micronutrients. Yes, seawater will dehydrate you but can you not simply drink more?
|
[
"The problem with seawater is not trace minerals and metals, but rather the >3% salt content. Your body needs to maintain a certain percentage of electrolytes, and doesn't have a good way to absorb only the water and not the salts from sea water. The result is that you'll need more and more water to offset the increasing amounts of salt in your body, resulting in dehydration."
] |
[
"No, drinking more saltwater won't eventually help because that water isn't going to make it into the cells due to osmotic pressure.",
"Imagine a fish tank, and in the middle of the fish tank is a wall that divides it. One side is filled with salt-water and the other side has freshwater. The dividing wall is \"semi-permiable\", which means only water molecules can go through, but salt won't. There will be a pressure, or a tendency for water to go toward the salty side, trying to dilute the salty side."
] |
[
"On a side note, the reason that sea gulls can drink sea water is because they have nasal \"salt\" glands that assist their kidneys by concentrating salt into a 5% salt solution and secreting it."
] |
[
"What is the largest feasible size of space station that could currently be put into orbit and maintained?"
] |
[
false
] |
[deleted]
|
[
"Define feasible. You're pretty much only limited by the amount of money and resources you want to spend building and maintaining it, but the ISS already represents an absolutely staggering investment, at an estimated cost of somewhere well north of ",
"$100 billion dollars",
".",
"Edit: Apparently $100 billion on reddit is like the equivalent of twenty cents. Whatever you think of the budgetary priorities of the USA/the world, the ISS is remains one of, if not the, most expensive objects ever built."
] |
[
"So I don't know exactly how to answer op's question, but I do know that answer to this: yes, I have seen our moon.",
"OK, jokes aside, the reason the moon isn't ripped apart is, in layman's terms, because it's much further away from the earth than a station in LEO. I believe the prevailing theory behind Saturn's rings is that they were created by moons or comets, captured I'm orbit around Saturn, which were slowly pulled apart by tidal forces to form the flat rings we see today. ",
"There is a certain orbital radius (I looked it up bc I couldn't remember the name, it's called the Roche Limit), within which an object only held together by gravity(a.k.a. moon) will be torn apart. Ours is obviously orbiting outside this limit.",
"Edit: so, the wiki page for ",
"the Roche Limit",
" has info on how to calculate the limit for a given body at a given radius, maybe somebody can do the math using a rigid body in LEO."
] |
[
"So I don't know exactly how to answer op's question, but I do know that answer to this: yes, I have seen our moon.",
"OK, jokes aside, the reason the moon isn't ripped apart is, in layman's terms, because it's much further away from the earth than a station in LEO. I believe the prevailing theory behind Saturn's rings is that they were created by moons or comets, captured I'm orbit around Saturn, which were slowly pulled apart by tidal forces to form the flat rings we see today. ",
"There is a certain orbital radius (I looked it up bc I couldn't remember the name, it's called the Roche Limit), within which an object only held together by gravity(a.k.a. moon) will be torn apart. Ours is obviously orbiting outside this limit.",
"Edit: so, the wiki page for ",
"the Roche Limit",
" has info on how to calculate the limit for a given body at a given radius, maybe somebody can do the math using a rigid body in LEO."
] |
[
"How accurate are our methods for dating life/rocks?"
] |
[
false
] |
i.e., Carbon-14 dating, Potassium-Argon Dating, Argon/Argon dating, other methods of dating.
|
[
"Very accurate, although the level of accuracy will vary with the preservation quality of the sample, the sensitivity of the machine being used, the concentration of the necessary isotopes int eh sample, the size of the sample, and whether the material being dated has undergone any form of chemical or physical alteration such as metamorphosis during its history. Error bars of less than 1% of the calculated age are not uncommon (e.g. 1,000 years +/- 10) for carbon dating. The oldest dated terrestrial material on earth was a zircon measured with U-Pb dating at 4,404 ± 8 Ma (0.2% error)."
] |
[
"Thanks for the reply-- do you have any recommended reading? I've found it surprisingly difficult to find some articles on the subject. Google has been failing me. ;;"
] |
[
"Depends what it is you want to know really. The reference list from the wiki page on radiometric dating is probably as good a place to start as any. ",
"http://en.wikipedia.org/wiki/Radiometric_dating",
"It's a technical process though, so it basically only really gets properly discussed in the scientific literature. And I certainly wouldn't consider myself an expert in dating methodologies."
] |
[
"If all movement is relative, is there a cosmic constant zero angular velocity?"
] |
[
false
] |
I'm a layperson when it comes to physics, so bear with me. One of the things hammered into my head in physics class is that all motion is relative to whatever reference frame you happen to be using. But why, then, do we feel centrifugal force if we're spinning around an object, but not if that object is spinning and we're remaining still? For example, if a spaceship tried to orbit the Earth at a high velocity, it would be flung away from the Earth. But if the ship stood still above the Earth and the Earth began to spin very quickly, the ship would simply fall toward the Earth. Seen from the ship's reference frame, both of these events look the same, but have different outcomes. What causes this difference? Thanks!
|
[
"Velocity is relative, and there is no way to tell how fast you are moving. We cannot feel the motion of the planet even though we are flying through space at a very high speed.",
"Acceleration, however, is not frame independent. That is to say, you will be able to tell if you are accelerating because you will feel a force acting on you. you can feel the force of acceleration when you slam on the gas pedal on your car. ",
"Circular motion requires acceleration. Think about the feeling you have when your car goes around a tight curve. Even though you might be going at the same speed, you can feel a force being acted on you.",
"A body in motion will just keep going straight onwards if nothing acts on it. But, in your example, gravitational field pulls the spaceship around in a circle. The force of gravity acting on the spaceship keeps it in orbit, but only if the ship is moving at the right speed, as you noted."
] |
[
"(Not a physicist) Because one thing is inertial motion, and another thing is ",
" motion. Inertial motion is completely reative to the frame of reference. Acceleration is ",
" relative in the same way."
] |
[
"two observers in inertial reference frames will measure the same acceleration of an object. being in different inertial reference frames is like being off by a constant and measuring acceleration is taking the derivative so the constant goes away"
] |
[
"Why don't Cats need haircuts?"
] |
[
false
] |
[deleted]
|
[
"I don't know exactly how I would source this, but hair and fur work the same way - they both go through periods of 'growth' and 'rest', called the anagen and telogen period respectively. After a while the hair falls out and then the process begins again. The only real difference between humans and short haired animals like cats is that their hair grows and falls out on a much shorter cycle, so it never gets a chance to grow longer. Humans actually have a finite hair length too, but it varies between individuals and is usually longer than is comfortable so most people never get to that point. :)"
] |
[
"Could it be because we were covered in hair at one point and now most of it is centralized in one location on the body? ",
"No because we have pubic hair still and this grows to a rather short lenght compared to the head. And human males grow beards too.",
"The best answer really is \"we don't know.\""
] |
[
"Short answer: We have no idea.",
"There's no real determined reason to confirmed idea as to why humans have long hair other than perhaps, it looks nice. ",
"Sexual selection, cultural influence, we don't really know."
] |
[
"Is there more oxygen in water or air?"
] |
[
false
] |
Is assume there is more O2 in air but if you took the oxygen from H2O, does it add up to more oxygen than total oxygen in all the molecules in air? Also, would be possible to make a device to harness the oxygen in H2O to breathe it? ( I'm imagining some fancy little device you put in your mouth and then you can breathe water. )
|
[
"I am not sure of the question, but if you mean whether an equivalent volume of air or water holds more oxygen, the answer is (under typical conditions assuming the dissolved oxygen is at equilibrium with the air) the air. Oxygen only dissolves to the extent of a few milligrams per liter of water (around 8mg/L at 20C). On the other hand, the density of air is around 1200mg per liter. Since the air is about 23% oxygen by mass, this means there is approximately 276mg of oxygen per liter of air. "
] |
[
"Do you mean like...if you somehow split the H2O and got all the oxygen out of it, would there be more from that than there is in the air?",
"Yes. Much more. Pure water has a molarity of roughly 55, so if you somehow split that all up you would end up with roughly 55 moles of O per liter. Oxygen is about 16 g/mole, so this gives you 55 * 16 == 880 grams of Oxygen per liter of water.",
"u/High-Curious",
" already provided us with the amount of oxygen in air, about 276 mg oxygen per liter of air. 880 g/liter is much more than 276 mg/liter, so yes, there is a greater total weight of oxygen atoms in water than in air."
] |
[
"In addition to this, the total amount of oxygen in the air vs. in the water on Earth (roughly):",
"Water:",
"880g/l --> 8.8x10",
" kg/km",
"\nTotal Volume of Water on Earth: 1,386,000,000 km",
"\nTotal Mass of Oxygen in Water: 1.22x10",
" kg",
"Air:\n276mg/l -->2.76x10",
" kg/km",
"\nTotal Volume of the Atmosphere: 17,300,000,000,000 km",
"\nTotal Mass of Oxygen in Atmosphere: 4.76x10",
" kg",
"So interestingly, there is more oxygen in terms of volumetric density, but four times as much oxygen in the air if one is to estimate the total amount in the world.",
"Please correct my often fallible math. I was just doing some quick calculations with Wolfram Alpha, and there is bound to be a mistake somewhere."
] |
[
"If quartz oscillates at an exact frequency, how can an atomic clock be any more accurate?"
] |
[
false
] | null |
[
"All clocks have sources noise at some fundamental level and we have a variety of ways of measuring the stability. For crystals, there are a ",
"number of effects",
" which alter the frequency on both short timescales and long timescales. A good way to think of short timescales is with the precision of a tick of a watch, i.e., how well can you measure when a tick occurs. For long timescales, you can think about the fact that for a watch you have to reset it every month, let's say. In a month, it might be 60 seconds slow or 60 seconds fast; it's random. But a month plus one day from now, it won't go from 60 seconds fast to 60 seconds slow. If it's 60 seconds fast, it might be 59 seconds fast (from now) or 62 seconds fast, something close to that value. There's some correlation between the offset between days. However, one month from now, the ticks of your watch are basically the same as they are today. So that's how you get the different timescales of noise occurring and how they can be different for one another.",
"One way to measure the stability of a clock is with a quantity called the ",
"Allan variance",
". In the second plot, you can see the frequency stability, represented in some deviation (an error) as a function of the frequency (or in this case time, so its flipped). Most clocks have this characteristic shape. You have some noise sources on short timescales leading to increased error and some noise sources on long timescales again leading to increased error. This kind of plot tells you how much error there is at a given frequency/timescale.",
"I work in pulsars and so here is a plot of the Allan variance for ",
"two famous pulsars",
", which act as astrophysical clocks. You can see the characteristic curve for one of them but not the other. That doesn't mean it doesn't exist, just that we don't have data sets that are long enough. PSR B1937+21 is a better clock (lower sigma_z, i.e., lower error) at short timescales but on the long timescales PSR B1855+09 is a better clock though maybe at some point we'll see it turn up.",
"Atomic clocks look quite similar similar but while the curves may look qualitatively the same, where the minimum occurs can be very different as there are many different kinds of atomic clocks. So, some are more stable on short timescales, some are more stable on long timescales. But all are basically better than the kind of stability you can get with a quartz clock.",
"EDIT: Typos."
] |
[
"One month is enough to see a difference between quartz and atomic clocks. ",
"\"a typical quartz clock or wristwatch will gain or lose 15 seconds per 30 days (within a normal temperature range of 5 °C/41 °F to 35 °C/95 °F) or less than a half second clock drift per day when worn near the body.\" ",
"\"The most accurate clock ever built only loses one second every 15 billion years. Scientists have a set a new record in accurate timekeeping, creating an atomic clock that won't lose or gain a second in 15 billion years — a time span greater than the estimated age of the Universe.\" The UK primary frequency and time standard says - \"At this frequency uncertainty, the NPL-CsF2 is expected to neither gain nor lose a second in about 138 million (138 × 106) years.\"."
] |
[
"Quartz's oscillation frequency is exact to a certain number of decimal points. After that, not. ",
"Atomic clocks are accurate to more decimal points. ",
"After a thousand or a million years, those decimal points start to matter. "
] |
[
"If we copy a brain into a computer, will it still forget things?"
] |
[
false
] | null |
[
"Neuroscience"
] |
[
"Neuroscience"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"guidelines.",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Why do herbs taste good to us, in spite of having no nutritional value?"
] |
[
false
] | null |
[
"Well it's not particularly that they do not have a high nutritional content, it's that the standard consumption amount is less than 5 grams. If you take almost anything and reduce the sample size to 5 grams you end up with a bunch of zeros on the fact sheet.",
"Most herbs have your standard leafy green goodies - several minerals and a couple vitamins such as A, K, and folate."
] |
[
"A 3g serving of raw chives has:",
"Vitamin A 131IU 3%",
"Vitamin C 1.7mg 3%",
"Vitamin K 6.4mcg 8%",
"Folate 3.2mcg 1%"
] |
[
"Where did you find this? I wan't to know the nutrition facts of cannabis."
] |
[
"Why do different molecules diffuse evenly across a vacuum?"
] |
[
false
] |
For example: You put in nitrogen and oxygen on separate sides of a container. Why is the density of oxygen and nitrogen relatively equal everywhere?
|
[
"They're not necessarily evenly spaced, just randomly distributed."
] |
[
"Entropy. If you look at the number of ways to arrange all the molecules, and consider the number of ways you can rearrange the molecules so that they are partitioned to the number of ways you can rearrange them so that they're mixed, the number of mixed ways is much, much, much greater. If all the molecules are moving around randomly then at any time they will be in one of those random configurations. The probability that they are in a mixed configuration is just much, much, much greater than the probability they are in a partitioned configuration.",
"In order to overcome this there needs to be some sort of energetic benefit to partitioning the gasses, such as an extremely strong gravitational field, or lowering the temperature so that the molecules attract each other into liquids or solids."
] |
[
"I think you're asking why diffusion occurs along each molecule's partial pressure. i.e. if you have oxygen and nitrogen at equal pressures on separate sides of a container, why do they move? ",
"/u/iorgfeflkd",
" was saying that molecules disperse randomly in a space. Consider each molecule independently. Oxygen diffuses throughout the container and Nitrogen diffuses throughout the container, regardless of what the other molecule does. "
] |
[
"What happens when magma meets an oil reservoir?"
] |
[
false
] |
I've always wondered why we've never experienced the crisis of losing an oil reservoir due to magma finding its way in. I've accepted that there would be no catastrophic explosion due to lack of oxygen, but what does happen? Does the heat 'cauterize' some of the oil, blocking the magma off? Does the magma slowly eat its way through the reservior, boiling it into a useless sludge?
|
[
"First, I need to clarify what an oil reservoir is. It is ",
" a big underground cavity filled with oil - that's a common misconception. Oil is stored in tiny pore spaces between sediment grains, and in order to be extracted, there must be connective spaces between those grains. Thus, an oil reservoir is a ",
" and ",
" rock or sediment layer, and it must be under a non-permeable layer that prevents the oil from rising to the surface and dispersing.",
"Magma doesn't just introduce heat into the scene - it usually applies pressure on the surrounding rock as well. If it cracks the cap rock sufficiently, the oil will rise up and travel to shallower layers of rock or possibly the surface. If oil is heated for an extended period of time it turns to natural gas, but that would depend on how fast the magma encroaches on it."
] |
[
"Also, for magma to exist in a sedimentary basin, usually a high geothermal gradient would need to exist. This would mean accumulations of oil could be found at shallower intervals. \nGenerally, you won't find magma in similar locations or depths as oil, which is why it's an uncommon occurrence. "
] |
[
"Minerals are (in an over-simplified way) the chemicals that make up crystals that comprise rocks. Oil is found in sedimentary rocks - that is, rocks comprised of grains of sediment, from whatever source, that have bonded together through pressure and heat. There are no specific minerals that accompany oil.",
"That said, oil is usually found either in sandstone or in shale. Sandstone is usually comprised primarily of quartz, a little feldspar and various clay minerals. Shale also contains quartz and feldspar, but it usually contains lots of micas as well. All of these are among the most common minerals in the Earth's crust, so you still couldn't reasonably say that oil is \"associated\" with any particular minerals."
] |
[
"How to get a standard deviation greater than value for a nonnegative number?"
] |
[
false
] |
I have seen in multiple presentations the author present a value of something that can't be negative (cost of healthcare, moles of product formed, survival time, etc) that will have a standard deviation that is greater than the value itself. While this isn't an issue for something that can be negative, what does this mean if you can only have a positive value?
|
[
"When a standard deviation is presented like this, it's usually meant to represent some kind of confidence interval for the value of some estimated parameter.",
"A 90% confidence interval tells you that 90% of identically-constructed intervals would be expected to contain the true value of the parameter, for example.",
"When you're doing a parameter estimation near a hard boundary (for example, if the parameter can't possibly be negative, or must be less than 1, etc.), it's probably more proper to set a one-sided ",
" rather than a two-sided ",
".",
"So if I have a parameter p (which must be positive), rather than saying that p = 3 +/- 5 in a 1-sigma interval, I would say something like p < 6 in a 1-sigma limit. Don't pay too much attention to the numbers I chose, they're just made up for the sake of the example. But there are statistically rigorous ways to calculate confidence intervals and limits, and when you have a situation like you've described above, it's probably better to report a limit."
] |
[
"Purely from mathematics: {1,1,1,1,6} has a mean of 2 and a standard deviation of sqrt(5) which is larger than 2 even though all values are larger than 0.",
"If you use these numbers to estimate a parameter that cannot be negative then see the other comment."
] |
[
"The standard deviation has a mathematical definition: it's the root of the mean of the squares of the distances between samples from the distribution and the mean of the distribution.",
"The normal distribution is characterised by only two variables: the mean and the standard deviation. Because many distributions caused by natural processes follow the normal distribution approximately (",
"Central limit theorem",
"), this makes the standard distribution a useful statistic to report.",
"However, some distributions are ",
" normal distributions. That mean that they are characterised by different parameters than the mean and the standard deviation alone. Then you can still calculate the standard deviation, but you cannot use the standard distribution to get your percentiles (like 95% lies within the mean plusminus 2 SD)."
] |
[
"Why are single-poled magnets physically impossible?"
] |
[
false
] | null |
[
"As others have said, magnetic monopoles are not physically impossible, just unobserved. What is worth knowing is not only are they physically possible, they are a natural consequence of most grand unified theories that combine the electromagnetic, weak, and strong forces into a single over-arching force. Thus, there is actually some reason to expect that there are monopoles.",
"Does it make sense for them to exist and for us not to have seen them? Actually, the answer is yes. If grand unification is correct, monopoles would have formed in the extremely early universe (grand unified monopoles are very, very massive -- 10",
" proton masses or more), but then inflation would expand the universe so much that the monopoles would be diluted, so that there would be around one monopole only in the entire observable universe.",
"Dirac observed back in 1931 that the existence of magnetic monopoles would explain electric charge quantization (that every particle's electric charge is an integral multiple of some basic unit charge). Interestingly, grand unification explains charge quantization as well on grounds separate from the presence of monopoles -- but magnetic monopoles appear, too, which would provide a second line of argument."
] |
[
"Great answer!"
] |
[
"Not impossible, ",
". If they existed it would make some scientific theories a bit mathematically tidier."
] |
[
"How long did non-avian dinosaurs survive after the asteroid hit?"
] |
[
false
] |
I’m sorry if this is worded poorly, but I’m wondering how long the non-avian dinosaurs survived after the initial impact. Were they gone within a few days, or were there small populations that stuck around for a few years? Thanks!
|
[
"The fossil record doesn't have the resolution to say anything about that definitively. There's been a bit of debate lately over the exact timing of the extinction, the impact, and some volcanic events occurring around the same time, all of which are measured with errors or 10s to 100s of thousands of years.",
"But to engage in some speculation, it's pretty likely that a substantial amount of these dinosaurs survived the immediate aftermath of the impact, especially far from the impact site. Most the extinction occurred in the subsequent \"winter\" caused by the ash and dust, as plant life died out and ecosystems collapsed. Some species may have even survived through this period (and a subsequent period of high temperatures and climate instability due to CO2 released from the fires) but had populations too small or scattered to sustain themselves, and gradually died out."
] |
[
"There have been some dinosaur fossils found in rocks from the Danian age (64-66 mya) of the Paleogene period. These are mostly thought to have been reworked from underlying (older) sediment from the very end of the Cretaceous 66 mya. That is, natural forces such as erosion removed the fossils from where they formed and they were redeposited. One of the more promising candidates for Paleocene dinosaurs is in the Ojo Alamo Formation, which has rock layers from both sides of the Cretaceous-Paleocene boundary. Some dinosaur fossils, such as a hadrosaur femur, have been found in the early Danian/Paleogene part (~65 mya). Even so, this is a highly debated topic and at most would indicate the last dinosaurs died within a million or so years after the end of the Cretaceous.",
"https://www.researchgate.net/publication/282238650_Dinosaurs_that_did_not_die_Evidence_for_Paleocene_dinosaurs_in_the_Ojo_Alamo_Sandstone_San_Juan_Basin_New_Mexico",
"https://www.researchgate.net/publication/296486608_Evidence_for_Paleocene_dinosaurs_in_the_Ojo_Alamo_Sandstone_San_Juan_Basin_New_Mexico"
] |
[
"Did someone specifically claim to find something 1 million years after the extinction, or is this just someone rounding to the nearest 5 million year mark?"
] |
[
"Why can't we feel the acceleration of the universe?"
] |
[
false
] |
If the universe is expanding at an accelerating rate, why can't we sense it speeding up?
|
[
"The expansion of space is not the same as movement through space."
] |
[
"We don't sense gravitational acceleration from the sun, the moon, Jupiter, or local galaxies.",
"For the other question: I can't quote well on my phone so try reading the first paragraph here:\n ",
"http://en.m.wikipedia.org/wiki/Metric_expansion_of_space"
] |
[
"It's too tiny. It gets completely overwhelmed by all the other forces when you're looking at anything smaller than a galactic cluster."
] |
[
"Is it possible to use a flow of positive nuclei/protons instead of electrons to form an electric current?"
] |
[
false
] |
[deleted]
|
[
"Yes, of course. Some common examples in which the current is a flow of positive charge are:",
"action potential of a neuron: positively charged sodium and potassium ions",
"electrolytic solutions (e.g., salt water): negatively charged chlorine ions (which are not electrons) and positively charged sodium ions",
"non-neutral plasmas of (positively-charged) ions: the ions can be any of a very wide variety of species (positron beams and proton beams are especially common)",
"In simple terms, the flow of ",
" collection of charged particles is an electric current. These particles need not be electrons. I think that the idea that electric current must be the flow of electrons comes from two facts:",
"In a metallic solid (like a wire), the electrons are free and the protons are bound to the nuclei. So an applied electric field will cause the electrons to move, but not the protons.",
"Protons are about 2000 times more massive than electrons. If we consider a collection of both protons and electrons at rest and then apply an electric field, the electrons are going to experience 2000 times the acceleration of the protons. For short time scales, the protons remain at rest and the electrons are the particles that flow."
] |
[
"I think that your answer, while technically correct in its way, doesn't answer the actual question being asked.",
"On the contrary, I answered exactly what the OP asked. I gave three examples in which electric current is not the flow of electrons. The examples, respectively, were that of (1) the flow of positively charged atoms, (2) the flow of both negatively and positively charged atoms but not electrons alone, and (3) the flow of positively charged subatomic particles, protons and positrons being the prime examples.",
"Finally, I explained why the misconception that electric current is the flow of electrons only is so common. The explanation goes to the part of the OP's question, \"instead of electrons\". To wit, ",
"In a metallic solid (like a wire), the electrons are free and the protons are bound to the nuclei. So an applied electric field will cause the electrons to move, but not the protons.",
"Regardless, we could always move to a reference frame in which the electrons are at rest and the protons are moving. In this frame, the current is carried by positive charge. (Of course, the electric and magnetic fields are not the same as in the \"lab frame\".)",
"So I am confused by your objection. Electric current is not limited to the flow of charge in a wire or other metallic solid."
] |
[
"I am afraid you are completely wrong. ",
"There are many materials that can transport protons. Nafion is widely used in the industry.",
"https://en.wikipedia.org/wiki/Proton_conductor"
] |
[
"Does the Monty Hall Problem apply here?"
] |
[
false
] |
Does the Monty Hall apply in the following situation? If not, how is it different from the classic Monty Hall problem? Let's say 3 runners of equal ability are going to race. They are called Alvin, Simon, and Theodore. At the beginning of the race, I bet on Alvin. 6 miles into the race, a bear appears on the track and eats Simon. The betting office announces the chance for me to change my bet at this stage. Should I switch my bet to Theodore?
|
[
"No. But I can re-word it so that it does. ",
"Three runners are running a race. You are the gambler, and I am the race coordinator. While you think the runners are equal, I have given one of the runners springs in their shoes so that I know they'll run faster. After you place your bet, I place a piece of meat into the pocket of one of the racer's you didn't pick and one who doesn't have springs in their shoes (so, if you pick the winner, I have two options, but if you don't pick the winner, I have two options). ",
"Then, half way through the race, I release the bear and that bear eats the person who had meat in their pocket. I then say \"would you like to change your pick?\" Then, the answer should be \"yes.\"",
"So, what is different in these cases? Well, the big difference is, I've chosen so that the winner is never the one eaten. In your case, the person who would have won could have been the one eaten. And I know you said \"they're three equal runners\" so you'd think the springs in the shoes didn't match your description- but that's actually the whole point. The host of the show has to know who the winner was before he can go on."
] |
[
"After a runner gets eaten, the odds go from 1/3 to 1/2. The randomness in who gets eaten makes it impossible to discern any information, and the randomness in who wins makes it impossible to divide the runners into two groups."
] |
[
"i see two main problems with your scenario:",
"1) the information in the Monty Hall problem is set and known in advance (to the show, not to the contestant). the grand prize is behind one of the doors at the beginning. in your race scenario, the winner is not set and not known beforehand.",
"2) the Monty Hall problem works because information is added when the door is opened. the show knows where the grand prize is and the show chooses which door to open, and deductions can be made from that due to the rule that they will not open the door with the grand prize behind it. ",
"in your race problem, no information is added when the runner is eaten, and that makes sense since at that point no concrete information is known."
] |
[
"When I was younger, I placed an ice cube in a pot of very hot oil. At first nothing happened, but when I nudged the pot, the oil exploded violently. What exactly happened?"
] |
[
false
] |
[deleted]
|
[
"After reading ",
"https://redd.it/414a29",
" and the respective top comment i think the theory with superboiling water is pretty likely.",
"The only other thing i could imagine is a occurence of the ",
"Leidenfrosteffect",
". The oil would need to be really hot though to make it work with an ice cube. Shifting the pan would then result in oil actually covering the icecube to trigger what you described"
] |
[
"Initially the water around the ice melts and becomes cold water. This sinks below the ice to the bottom. Then at some point the water at the bottom will have heated up enough to boil and will do so violently from below the oil. It may be that your pot was so clean that the water had no impurities to boil off of and got super heated. The nudge would have given it a start and caused a lot of it to flash boil at once causing the explosion. I hope you were not looking into the pan at that point...."
] |
[
"I think there is a bit more to it than just that, water itself and hot oil don't mix well as it is. The temperatures are hot enough that it rapidly heats the water, making it steam. Which needs a significant more amount of space. It's more likely the ice, while melting, was able to form a barrier of lower temperatures around it, but when nudged the hot oil and thawed water mixed rapidly causing the said explosion. "
] |
[
"Why is it hotter in my house at night than during the day?"
] |
[
false
] | null |
[
"We can't really comment on anecdotes / isolated incidents without resorting to speculation which we try to avoid."
] |
[
"Okay. Should I delete this then?"
] |
[
"Already removed."
] |
[
"What does it mean when people say we've mapped the entire human genome, and how come we don't know what genes cause what if we have?"
] |
[
false
] | null |
[
"It means we know the sequence of the genome (to a degree of certainty) but we don't know what sequence means what. A somewhat similar analogy is : Think of it as a computer program code. We have pages and pages of code, module after module, each of which refers to other modules, etc. Imagine you just come across this code, but you have no idea what it does. Now, you've basically found out all the different lines of code, as in you see all the lines in english before you. But you have no idea what module does what. And you can't figure out what each module does without running it, right? (In fact, that's why you look at people with one/two modules defective (genetic disorders), and thus say \"aah, so this module is responsible for this function\". See what I'm driving at? ",
"So basically, we've mapped the code sequence-> we can read the code. We have no idea what all the code means. "
] |
[
"We make meaningful guesses all the time. But that's exactly what they are- guesses, until you can prove them, which in science is by cause-effect relations. i.e. Knock out/in the gene and see what happens. i.e. Disable a module--- see what happens, then re-enable it,(by a third party/accessory module) and see if the lost function is replaced. Thing is-- this takes a shit ton of time, as you can imagine. \nThat said, we're getting there. The other issue here is that, we can figure out which genes are \"used\" and which ones aren't, and a huge portion of our current genome is basically unused/switched off.",
"\ni.e. around 60% (IIRC) of our program modules are basically disabled, and yet we function so frikkin awesomely. One can only guess what these 60% unknown modules do. "
] |
[
"I am a programmer so this made perfect sense! thanks for your response. How far would you say we are from figuring out what each gene \"does\"? Is it even possible ot make a meaningful guess at this point? "
] |
[
"Why is rabies (nearly) invariably fatal?"
] |
[
false
] |
[deleted]
|
[
"You pretty much nailed it - once it's too late for the vaccine to work (around the time symptoms appear, sometimes longer), you're screwed. Rabies has a particularly nasty way of telling the brain to shut the body down. Nobody knows why our immune system can't fight the disease before it reaches the CNS. Perhaps because it has not alerted the immune system to its presence yet.",
"Edit: As far as not being favorable for transmission because it kills the host, it balances this out by having such a long incubation period, and by causing the host to engage in behaviors that allow it to spread."
] |
[
"Rabies is the type member of the ",
"Rhabdoviridae",
" family of viruses. It infects skin cells from an animal (usually dog) bite, and from there it infects nerves. It travels through the nervous system until it eventually reaches the brain causing severe encephalitis and eventually death. ",
"Interestingly, this progression is extremely slow, which is why we can wait until after infection to administer the vaccine. This is the only instance where vaccine administration is used as a therapy instead of preventative. ",
"During the course of infection, different organs are also infected through the nerves that enervate them, including the salivary glands. This means you can get virus produced in the saliva before the virus infection has reached the brain.",
"Rabies isn't necessarily any more deadly than any other disease or virus. Ebola and Herpes B are also nearly universally fatal. This high degree of lethality is common when viruses jump species. ",
"Virus-host interactions are complex relationships. The virus absolutely requires a host for reproduction and transmission, as they are obligate intracellular parasites. As such, they need to be virulent enough to invade a host, evade any immune responses and enter a cell. However, then also need to exit the cell and infect new hosts. If the current host dies before the virus is transmitted, the virus fails. So, there is a careful balance between virulent enough to infect, but not so virulent as to prevent transmission. The longer a virus and host evolve, the better adapted they become to each other. An excellent example of this is Herpes simplex 1 (HSV1), which causes cold sores in the mouth. Nearly everybody is infected with HSV1, and by a very early age. In general, it causes little more than an occasional nuisance. The virus survives and we survive. Rabies is different, it kills, but slowly, and it is infectious before the host dies. "
] |
[
"From an evolutionary standpoint, being 100% deadly is unfavorable as it makes viral transmission more difficult.",
"Take into account that something can be invariably fatal and still very transmissible if it takes a long time to kill someone or is very easily transmitted. Untreated HIV is invariably fatal, but it spreads easily enough anyway, and ebola kills pretty quickly but spreads very easily.",
"Secondly, and I can't say I know it to be otherwise, but 100% fatal in humans doesn't mean 100% for everything."
] |
[
"Is there a limit to the size of a star?"
] |
[
false
] |
I mean, is it possible for a star the size of a galaxy or bigger to form without collapsing into a black hole? EDIT: Wait, no. What I meant was, is it possible for a star the size of a galaxy to exist?
|
[
"I believe the limit is around 150 solar masses for stars formed in the last 10 billion years. I know there is one exception to this but that was recently discovered and IMO has a very good chance of being downgraded in mass.",
"I am not really sure exactly what the reason for this limit is. I know a fair portion of it comes from the Eddington Luminosity (you can look it up on wiki), which is essentially the point where radiation pressure (pushing outward) is equal to gravity (pushing inward). Once that point is overcome, the star is blown at least partially apart as radiation pressure exceeds gravity.",
"I also know that stars which formed early in the universe, when the metal (in astronomy, that means anything other than hydrogen and helium, which is what the universe started with after about the first second) content was very low, are thought to be far more massive than the sun because of low metal content. They have never been observed so it's not confirmed, but it's thought by many astronomers that masses were typically in hundreds of solar masses. These old stars are called population III stars, you can also look this up. Why low metal = large mass, I do not know yet.",
"/senior majoring in astro"
] |
[
"Incorrect, this limit just refers to the max mass for an astral body before gravity overtakes electron degeneracy pressure and collapsing begins.",
"Take a glimpse at this ",
"article",
"."
] |
[
"The bigger they are, the shorter they last."
] |
[
"Can single enantiomer medicines spontaneously switch to the other chiral form, making them toxic?"
] |
[
false
] |
Someone got it in my head that this just happens over time and that this is why old medicines should be thrown away. I think most are mixtures of enantiomers, but with some only one form is beneficial and the other is detrimental. Naproxen is my example for this as one enantiomer is a commonly used NSAID and the other is a liver toxin. So the question is: Do these chemicals spontaneously switch? Would leaving them in a hot car, keeping them beyond expiration, or some other simple storage mistake possibly kill you or make your medicine toxic?
|
[
"Short answer: Yes, but it depends on the drug in particular. If this process, presents a real hazard the drug in question usually doesn't make it to market. It can happen over time, elevated temperatures, moisture, acidic or basic conditions can make it happen faster. Really depends on the drug though. ",
"Long answer: Chirality comes (...most of the time) from a carbon atom that has 4 distinct things bonded to it. For each carbon atom like this - called a stereocenter - there are only two possible ways to arrange the four things bound to it, we call one arrangement 'R' and the other 'S'. ",
"R and S centers can interconvert, but it requires breaking chemical bonds. The most common ways this happens is when an H atom leaves (making an achiral intermediate) and then comes back on in such a way to form the other configuration. If this happens at some, but not all of the stereocenters in the molecule, you get a diastereomer; if all of them do it, you get the enantiomer. "
] |
[
"I am in no way an expert on this, but many years ago I did a small bit of work on ",
"voriconazole",
", which has a mildly toxic enantiomer in which the methyl group and the H across from it swap places.",
"\nAnyway, as far as I can remember, the enantiomer is a product of the final part of the synthesis being carried out at a slightly higher temperature and I don't think that the correct enantiomer could just change into the toxic one due to something as simple as incorrect storage."
] |
[
"Just adding the classic example of chiral conversion in ",
" causing massive issues: Thalidomide. After intake, the conditions of the human body are sufficient to allow thalidomide conversion from one chirality to the other resulting in the birth defect side effects."
] |
[
"Could the milky way have already collided with another galaxy like 6 billion years ago?"
] |
[
false
] |
Or heck, at any point. What if we, millions or a few billion years ago already merged with another galaxy? Could we tell it happened to our galaxy if our galaxy already fully formed with the other and assumed its new shape?
|
[
"Actually, it seems likely that ",
"the Milky Way collided with a dwarf galaxy somewhere between 6-10 billion years ago",
". After tracking 7 million stars with data from the Gaia satellite, astronomers found a lot of metal-rich stars near the galactic center with eccentric orbits, a pretty good sign that we slammed head-on into a dwarf galaxy and captured its stars. The same team ",
"also found evidence of at least eight globular clusters",
" that may have tagged along with the dwarf galaxy and also merged with our own.",
"As to how this collision affected our own galaxy: ",
"Our current Milky Way has a \"thin disk\" of stars aligned very closely with the galactic plane, and a thicker \"thick disk\" more populated with older stars",
". It seems like the collision scattered some of the old \"thin disk\" and created the \"thick disk\", throwing old Milky Way stars above and below the galactic plane. But the gas brought along with the dwarf galaxy helped re-form the Milky Way's thin disk and triggered a new round of star formation.",
"Beyond this major collision, the Sagittarius dwarf galaxy has been regularly crashing into the Milky Way, ",
"swinging above and below our galactic plane and piercing the Milky Way disc three times in the last 6 billion years",
". Some astronomers believe the Milky Way's spiral arms may be the result of these repeated Sagittarius-punctures, and have even speculated that ",
"the formation of our own solar system may have been triggered by Sagittarius passing through",
"."
] |
[
"Taken from ",
"FutureTimeline.net",
":\n“Our galaxy is surrounded by dozens of smaller dwarf galaxies. These will occasionally pass through the disk of the Milky Way, disrupting both it and the incoming satellite. One such collision occurred in roughly 100 million BC. This was confirmed by observations of 300,000 nearby stars, whose motions indicated a reverberation or \"ringing\" like a bell. The stars were found to be moving up and down at speeds of 20-30 kilometres per second while orbiting the centre of the galaxy at 220 kilometres per second.",
"It would take a further 100 million years (from the time of this observation) for this motion to stabilise and for the Milky Way to stop reverberating. By now, the north-south asymmetry has disappeared and the vertical motions of stars in the solar neighborhood have reverted back to their equilibrium orbits.”"
] |
[
"Don't stars migrate out as they age?"
] |
[
"Why are prions so hard to destroy?"
] |
[
false
] |
Most proteins denature below boiling temperature. Prions, as far as I know, are just a type of protein. Is there a specific reason why prions are so hard to destroy? And is it in any way linked to the diseases they cause? Or is it just pure coincidence?
|
[
"Prions are proteins folded into special configurations that are extra stable. ",
"They’re folded into alternating rows and form sheets—think something quilted into a big square blanket. There’s a high amount of cohesive forces in between each row, so it’s held together quite well and takes an extremely high temperature to overcome those forces.",
"The shape of these sheets also makes it amenable to “crystallization” where one protein stacks on top of another very well, and they form large aggregates, and this is what causes prion diseases.",
"It basically all results from what is the lowest energy configuration."
] |
[
"my rudimentary understanding is that they are essentially a special case of denatured protein whose shape \"breaks\" other proteins of the same kind, in the same way. Or put another way, prions are proteins that have denatured in a particularly unfortunate way, and this particular structure happens to be stable enough that it proves very difficult to further break it down."
] |
[
"Well, \"hard\" is relative.",
"They are in a highly energetically stable molecular configuration, and a lot of the things we are used to doing to prevent the spread of disease -- boiling water, cooking food, sterilizing equipment -- doesn't reach the required energy level to overcome that stability. That's why all these common denaturing techniques don't work on them.",
"But any molecule will break apart if you heat it up enough. Or subject it to enough ionizing radiation. The problem with prions is not finding a way to destroy them. It's finding a way to destroy them that can be done as part of some kind of routine sterilization practice.",
"Like.. if you heat them up to 2000C you will destroy them. Unfortunately you are now talking about the equivalent of kiln-baking. You are going to destroy everything else too, pretty much. Or at least melt a lot of it.",
"Or fry it in high-intensity UV light for a few hours. That will destroy prions. But that too is not a great protocol for routine use.",
"The problem as I see it is that it's hard to destroy prions in a way that is practical, that we could develop and refine as a technique that anyone can easily employ under normal conditions and have confidence that it worked."
] |
[
"Is there a 4 dimensional analog to a sphere like a tesseract is for a cube?"
] |
[
false
] | null |
[
"One of the first things you learn in college is that you didn't learn anything in highschool."
] |
[
"Yes, the sphere ",
", which is the ",
" sphere (embedded in Euclidean four-dimensional space), is the set of points (",
", ",
", ",
", ",
") such that",
" + ",
" + ",
" + ",
" = 1",
"Similarly for higher number of dimensions."
] |
[
"Sorry, I didn't mean high school geometry. I was thinking of introductory courses in differential geometry."
] |
[
"To eliminate the need for an extra day every four years, why couldn't we just redefine the second?"
] |
[
false
] |
Since we need (approximately) one extra day every four years to keep our calendar in sync with our orbit, why couldn't we just multiply (four years +1/ four years) 1461 / 1460 = 1.0006849315... to each existing second? After four years' time we'd be enough later to eliminate the need for the leap day, right? Obviously all GPS satellites/world clocks/etc would have to be adjusted but that seems like something that could be done. I know this is missing something but that why I'm here!
|
[
"This would mean a day is not 24 hours any more. So each day, \"midnight\" would slip a little bit. After 2 years, \"midnight\" would be in the middle of the day!",
"The fundamental issue that can't be solved here is there are not an integer number of days in a year."
] |
[
"The ratio of Earth's orbital period to its rotational period is not an integer. That is why we have leap years, not because of units. If you don't do this, the solstices and equinoxes start moving through the calendar, and we try to avoid that."
] |
[
"There's not a whole number of days in the year, yet a day will always begin when the sun comes up and end when it goes down. So instead of slipping in the extra time into each day, we save up a day's worth and use it all at once every four years. "
] |
[
"Why, in layman terms, was the black body problem so important in quantum physics?"
] |
[
false
] |
I am reading about it, but I cannot make sense out of it. Why quantization was so controversial? What was the problem really? I know high school physics, so not so layman.
|
[
"Black bodies at thermal equilibrium emit radiation. The spectrum of the emission at low frequencies is predicted by the ",
"Rayleigh-Jeans Law",
" and is dependent only on temperature. You can use this law to calculate wavelength (or frequency) of the emission. The black body problem refers to the prediction that as frequency approaches infinity (or wavelength approaches zero), the energy a black body emits approaches infinity. The implication being ",
" matter hotter than absolute zero would instantly radiate all its energy to reach absolute zero. Obviously this prediction is not observed in nature. ",
"Planck made a very unusual assumption to address this problem. He assumed the energy of emitted radiation is quantized in discrete packets. This was controversial because there was no observed evidence (at the time) that this was true and it flew in the face of the understanding of physics of his time. However, by making this assumption, Planck was able to derive the correct function for spectral emission. Planck's assumption is incompatible with classical physics which treats physical quantities as continuous. Plank himself and many of his contemporaries regarded this treatment as a mathematical construct and not a true representation of nature. ",
"Ultraviolet Catastrophe",
"Historical context"
] |
[
"Yes. Planck thought it was only a mathematical trick, but actually he accidentally invented quantum physics. The photoelectric effect is a great example for the quantisation of light."
] |
[
"A bunch of folk around the same time were shooting light at metal.",
"They found that given a certain colour of light, electrons were stripped off of metal.",
"They assumed that increasing the intensity of light will lead to those electrons to leave the metal faster, or for another colour to be able to strip electrons too.",
"In reality they found that electrons ONLY were stripped if light was a certain minimum frequency. Furthemore, they found that increasing the frequency led to the electron to be emitted faster.",
"Einstein saw both studies published, and connected the two, earning the nobel prize for mathematically describing the particle nature of light."
] |
[
"Has it been proven we live in a deterministic / probabilistic universe?"
] |
[
false
] |
As I understand it, a lot of processes on the atomic scale seem to be totally random, for instance radioactive decay. This is then used as proof that the universe is probabilistic, i.e. that anything can happen in the future. But has it ever been definitively proven that these processes are indeed random. I could imagine that at the moment we just do not understand why an atom will decay into another at some time, but that a reason does exist. Following, if all molecular / atomic / sub-atomic processes are deterministic, would that imply that the universe is deterministic? And that everything that will happen in the future is already set in stone?
|
[
"I would say that IFF all molecular/atomic/sub-atomic processes were determined to be deterministic then that would imply that the universe as a whole is deterministic. ",
"What you are talking about is the hidden variable theory of quantum mechanics, which states that while we may be unable to predict with perfect accuracy certain quantum events, there may be hidden variables which we cannot observe that govern all things deterministically.",
"However, the ",
"Bell theorem",
" states that no theory of hidden variables can reproduce the predictions of quantum mechanics. In my opinion this theorem and its supporting evidence essentially disproves determinism on quantum levels."
] |
[
"no. The heisenberg uncertainty principles says that ",
" and in particular the product of their RMS spreads is ~hbar/2. It doesn't have anything to do with measurement."
] |
[
"I don't think the Bell theorem excludes the possibility of a deterministic universe for two reasons:"
] |
[
"Are humans the only species that commit suicide?"
] |
[
false
] | null |
[
"It's not clear what 'commit suicide' means.",
"For example, there are many species where reproduction leads to death - so individuals 'voluntarily' do something that leads to the death of the individual but that propagates the species. Is that 'committing suicide'?",
"Is whales beaching themselves 'committing suicide'?",
"When honey bees leave the hive to forage, it means they're not long for the world. Is that 'committing suicide'?"
] |
[
"The parasites the other redditor mentioned are certain species of Nematamorph worms, but they aren't the only parasites that cause this kind of \"suicidal\" zombieism.",
"\nA really interesting one makes tiny fish in marine estuaries go to the surface and flash their shiny sides at predatory birds. The birds are the final hosts and the parasites want to get inside the birds. ",
"I hear this example and the others I see a lot are things like honeybees. ",
"I find it very difficult to call either of these animals suicidal. That would imply some kind of intent.",
"\nRealistically the parasites have effectively killed the host, so that's not suicidal.",
"\nAnd I think you'd be hard-pressed to show any intent to die in the honeybees at all, they just want to hurt someone. ",
"The last one I've seen less frequently is male insects and spiders that \"sacrifice\" themselves as a meal to the female.",
"\nAnd again, I think it's very hard to call that suicide. It's much more accurately described as 'semelparity'. Which just means that the animal reproduces once and then dies.",
"\nThat would be suicide as much as the salmon spawn would be mass suicide. ",
"So those are the examples I see and I think they all pretty well fail to accurately describe suicidal behavior. "
] |
[
"Here",
" is what wiki has to say on the matter. It is up in the air but there are plenty of well documented instances where animals have harmed or killed themselves, seemingly out of stress or depression. It seems like we don't have enough information at the moment to tell if the animals are acting on the same emotions as humans and if there is truly intent involved, so it might depend on the definition of suicide."
] |
[
"Is there a spot where the big bang happened? do we know where it is? Is it the center of the universe? If you go there, is there a net force of zero acting on you in all directions ( gravity)"
] |
[
false
] |
EDIT: Wow thanks for all of the answers and the support, this is my most popular post yet and first time on trending page of this sub! (i’m new to reddit)
|
[
"The big bang happened ",
", right where you're sitting now included. The universe doesn't have a center; instead, ",
" is equally the center. When we talk about the universe expanding, what we mean is that ",
" is expanding, not that the universe is expanding into something or away from a center point.",
"This is a difficult point to grasp, but it helps if you remember that the universe may well be infinite - it's only the ",
" universe that's finite, and that's because of two things: 1) light takes time to travel and 2) the universe hasn't always existed. There's more universe further out, ad infinitum, but the light from those parts hasn't had time to reach us yet. The stuff inside the universe is being carried away from the other stuff inside the universe as space itself expands, like a baking cake carrying raisins inside further away from other raisins as it rises. "
] |
[
"thank you for this reply, this is very helpful. one question. by “everything expanding” do they mean galaxies are getting farther apart, or so they mean that everything is getting bigger, you, me, all atoms? "
] |
[
"You would think that if you took into account the motions of all the galaxies that you'd be able to calculate a \"center.\" Say, for example, you had a small explosive surrounded by glitter. If you set the explosive off and tracked all the glitter, you could calculate where the explosion was. That's NOT how the universe is.",
"See, EVERYTHING in the universe is moving away from EVERYTHING ELSE, pretty much equally. There is no \"direction\" that things are moving away... to. It's very hard to visualize. ",
"I'll do my best to come up with a visualization.",
"Imagine you're in a kids ball pit. That ball pit is infinitely wide and deep, it has no sides. Suddenly, all of the balls grow. (While you do not.) It's clear that the center of the balls are getting further from each other, but there is no \"direction\" in which the balls are expanding. They're only getting bigger. At the beginning, you could reach maybe a few hundred balls with outstretched arms, but as they grew, you could only reach 100, then 50, then 10, and eventually you could only reach one or 2 balls with outstretched arms. That's kinda like what the universe is doing. Everything is \"growing\" (expanding) and getting further away from everything else. "
] |
[
"If the US one year gave its defense budget of $750 billion to science, what discoveries might we expect in the following 20 years?"
] |
[
false
] | null |
[
"This isn't an answerable question, I'm afraid. The only possible responses would be pure, pointless speculation."
] |
[
"Kurzweil's reputation among scientists is … well, let's not mince words, shall we? He's worse than useless."
] |
[
"But if Galileo could have predicted Newton, we wouldn't have needed Newton."
] |
[
"How are wall-to-wall buildings demolished?"
] |
[
false
] | null |
[
"Explosives are used far less often than TV would lead you to believe. Jackhammers mounted on excavators are far more common and more controlled than explosives. Explosions are cool but the exception not the rule."
] |
[
"Usually, the non-load-bearing walls are removed. Then the inner load-bearing. Then the outer shell walls."
] |
[
"What do you mean by \"wall-to-wall buildings\"? "
] |
[
"Does quantum physics solve the problem of determinism/free-will?"
] |
[
false
] | null |
[
"somehow gives the universe a probability/in-determinant quality at the sub-atomic level... and that therefore there's a real chance that we have real freewill.",
"If your actions are determined by random fluctuations of particles, how is that free will? In other words, how does your question differ from \"",
"\" ",
"Deterministic systems can have pseudo-randomness in them that makes them work as if they had random component in them. It can be indistinguishable from real randomness for all practical reasons concerning cognitive functions. Brain is so complex system that it would probably work the same way if the noise that affects it would be only classical noise instead of quantum noise. ",
"As far as I see, physical determinism versus randomness has nothing to do with free will. Free will is concept that was born when people still believed in the soul. What happened \"inside the soul\" was considered free will and what happened outside it was not free will. Today when we don't believe in the soul anymore, the concept of free will is not reasonable unless we use it interchangeably with randomness. Universe is not totally deterministic, so our behavior is not completely determined by past events from past, thus we have some amount of randomness within us. ",
"There can be noise and randomness in our cognition but it's very likely not instantaneous. If quantum effects affects our actions, it might take time ( seconds or minutes) until it shows up in our actions. "
] |
[
"The issue of free will comes up when you consider the ramifications of a deterministic or random system.",
"If it is determined, then you could not do otherwise, and are therefore not free. If you are not free then you are not responsible for your actions.",
"If it is random, then it is not by your choice that anything happens, because then it wouldn't be random, so again you are not free, and therefore not responsible."
] |
[
"I think there's also the issue of distinguishing between determinism and mere causality. Determinism means that something has a cause (or network of causes) which can theoretically be determined through measurement. Causality just refers to events having causes, regardless of whether they are deterministic. ",
"The issue here is that you don't really need to prove determinism in order to disprove things like libertarian free will. The principle of causality itself is sufficient for such purposes. If we accept that events have causes (even very loose causes, such as the case with systems that behave probabilistically), then libertarian free will has to be thrown out. There's no way for some little homunculus inside your brain to just \"make a decision\" that excludes external causes and effects."
] |
[
"Why does touching an electric stove top while it's on burn you instead of electrocute you?"
] |
[
false
] | null |
[
"No... this is very incorrect. A quick google search says an electric stove coil on high produces somewhere in the range of 2000 watts of heat. If you're running off of 120 volts thats 16.7 amps which by any reasonable household definition is a lot. ",
"It is amperage that kills you, not voltage",
"This is a huge simplification of a complex topic. A 500,00 volt tazer can stop your heart (death) and a 24 volt potential across your body can create large currents resulting in burns or worse.",
"More to the point, using your logic, it doesn't matter how much current is flowing through the coil, if you touch it and can be shocked then presumably you have a conducting path from the mains voltage source in your house (120, 480, etc) to your body which can most definitely kill you (if you don't believe me try sticking a fork in the wall (don't do this)). ",
"/u/serious-zap",
" is correct, the coils are insulated so you can't touch any metal that is at a nonzero potential. ",
"Also the coils in a stove are low resistance, not high. To generate 2000 watts of heat from 120 Volts you need a resistance of 7.2 ohms which is quite low. High resistance result in less heat being dissipated for equal voltage drops through over resistor, if the supply was somehow constant current (its not) then higher resistances would result in more heat."
] |
[
"Because the thing is ",
".",
"There is a wire through which electricity flows, then a layer of non-conductive material and then an outer metal layer.",
"A properly functioning stove top element will not have electricity going through its outer metal part.",
"If you think about it, if electricity was flowing through it, as soon as you put a metal over it, it could allow the electricity to bypass most of the heating element through the pot/pan etc."
] |
[
"This is definitely the correct answer, I just wanted to say that even if it wasn't insulated, if you touched the element, you would be fine (as far as shock goes). Current has a much better time going through the heating element than it does you.. Your body resistance is pretty wicked high in comparison, you wouldn't take very much.... probably. Naturally this isn't backed up.",
"https://www.youtube.com/watch?v=ut5DXxK1dvk"
] |
[
"How intelligent are spiders?"
] |
[
false
] |
Can spiders be trained to do tasks like lab rats? Do they possess any qualities that can be attributed to having some form of intelligence?
|
[
"Greatly varies, and we can say with certainty that most spiders are not intelligent, but there are some remarkably intelligent, even problem-solving spiders: ",
"Check this out",
"."
] |
[
"Is what just an assumption? If you're talking about their intelligent hunting behavior, no, it's not assumed, it is observed."
] |
[
"If I can add to the question, do we know how spider plans its web? I imagine it must asses the place, decide whether it is good or not, check the distances, corners, eventual obstacles, etc. Is it all just trial and error or there's actual thought process?"
] |
[
"Is it possible to create visible light?"
] |
[
false
] | null |
[
"A superposition of UV and IR won't result in light which is the difference in frequency between them.",
"However there are nonlinear optical media which ",
" change the frequency of the light you send into it."
] |
[
"Thanks for you answer! May I ask you about these optical media ? What are they ?"
] |
[
"There are many different kinds, but ",
"this",
" is a good starting point to read up about them."
] |
[
"What would happen if I started to rotate a 100,000km rod at 1 round per second?"
] |
[
false
] |
Made out of the strongest lightest material possible. The perimeter is larger than the speed of light per second.
|
[
"You couldn't make it go at one round per second. No matter how much energy you put into accelerating the rod, the most outer part would still move at some subluminal speed. As you put more and more energy into the system the outer part rotates closer and closer at the speed of light but it never can reach it.",
"Mind that a rod can also never be perfectly rigid as a solid consists out of atoms that interact with each other at the speed of light. If you do something with one end of the rod it can only affect the other end after a delay equal to the distance of the two points divided by the speed of light."
] |
[
"Won't the atoms interact with each other at the speed of ",
"? The movement at one end would translate through the rod at the speed of sound, effectively leading to the motion not having any effect for a long, long time."
] |
[
"Won't the atoms interact with each other at the speed of sound?",
"Principally yes, but then again you can come up with weird scenarios where the e.g. ",
"the group velocity of your phonons becomes faster than the speed of light",
". Of course information can still only be transferred at subluminal speed.",
"With saying that atoms can only affect each other at most at the speed of light you are always on the save side - de facto it will usually be significantly slower."
] |
[
"Is it possible to build a truly empty box?"
] |
[
false
] |
I mean a box that is not just devoid of air or even matter but no photons, neutrinos, nothing. Not even EM fields. One obvious problem would be the inside edges of box would occasionally decay and release photons into the box but could they be somehow prevented from travelling too far inside by a large gravitational or EM field outside of the box? What's the most empty anything could conceivably be?
|
[
"You can't have no EM field. Electromagnetism exists, you have to deal with it. The only thing you can have is the EM field at the lowest possible value. That's what physicists call \"vacuum\". But even in the vacuum, you still have some energy and some quantum fluctuations. Vacuum is not empty."
] |
[
"I don't think so; you would probably have always ",
"virtual particles",
"."
] |
[
"Best not to think too hard about \"virtual particles,\" frankly. They don't actually exist. They're just mathematical objects that we use to describe the state of a ",
" The field is the real thing; virtual particles are something we made up to do maths with."
] |
[
"Why are there no green stars?"
] |
[
false
] |
according to the Hertzsprung-Russel Diagram green is not a part of the stellar spectrum. why?
|
[
"Because a blackbody that's hot enough to have its peak emission in the green part of the spectrum emits enough orange and blue light relative to green such that it looks sort of like white light. ",
"pic"
] |
[
"http://en.wikipedia.org/wiki/File:Solar_Spectrum.png",
"The suns blackbody actually peaks at green(ish).",
"As iorgfeflkd said the visible range is very narrow so any blackbody is going to have is going to have a broad range of emissions that make it appear as white. Its actually neat to note that the eye is most sensitive to green corresponding well with the peak emission of the sun(just a neat evolutionary side product)."
] |
[
"Stars emit light over a range of frequencies depending on their temperature.",
"The distribution of the radiation is skewed towards high frequencies (shorter wavelengths), but after a point, drops off suddenly, like ",
"so",
".",
"When the output peaks at lower frequencies, you only see reds and yellows, the infrared is invisible.",
"When the output peaks at medium frequencies, green might be the brightest, but there are enough reds and yellows and blues to wash it out into white.",
"When the output peaks at higher frequencies, the blue and violet dominate, and the invisible ultraviolet doesn't interfere.",
"So basically, green gets stuck in the middle, with both the reds and blues interfering with our perception of it. Red and blue, in turn, are next to colors we can't see, so they come through stronger."
] |
[
"Why do flames flicker at a relatively consistent rate?"
] |
[
false
] |
In the following paper, one can see that different flames flicker at 10-12Hz. However, I cannot understand the paper itself. Could anyone simplify why it's the case that seemingly unrelated types of flames flicker at a really specific frequency? Chen, T., Guo, X., Jia, J. et al. Frequency and Phase Characteristics of Candle Flame Oscillation. Sci Rep 9, 342 (2019).
|
[
"They're not unrelated types of flames, they're groups of candles. In other words, the buoyancy jets formed by the flames have very similar temperature gradients. Candle flames are driven by buoyancy associated with density differences between the hot flame and combustion products and the surrounding atmosphere. The vertical velocity of the flame creates a shear velocity gradient between the flame itself and the surrounding atmosphere. This gradient has associated vorticity. As the flame moves upward, the vorticity entrains a growing region of the ambient fluid, eventually in a region wide enough that the annulus of the vortex pinches off the flame and the vortex is shed. This process has a characteristic frequency which depends on a number of factors including the density of the jet compared to the density of the ambient air, the vertical velocity of the jet, and the diameter of the jet.",
"A group of paraffin candles of the same or similar diameter will have very similar properties to each other in terms of the flame properties that are relevant to the oscillation of the flame, i.e. the flickering. ",
"This reference provides a good overview of the math behind the flicker.",
"https://arxiv.org/pdf/1803.10400"
] |
[
"Figure three in my link gives the flicker frequency as a function of sqrt(g/D) for pool flames. You can see there that observed frequencies range from ~0.2 to 20 Hz, so about two orders of magnitude. The flicker frequency is not super sensitive to flame temperature. However, it's certainly wrong to say as a blanket rule that fires flicker at 12 Hz because it's easy to find examples of steady flames which are by definition flickering at 0 Hz."
] |
[
"Tom Scott recently made a video about wildfires where he referenced the fact that wildfires (his wording was ‘fires’ so maybe all fire) also flicker at about 12 hertz. Maybe it isn’t just the burning medium."
] |
[
"What is meant by DNA Half-Life?"
] |
[
false
] |
I understand biological half-life (the amount of time it takes for 50% of a given sample of a drug to metabolize) and radioactive half-life (the amount of time it takes for 50% of a given sample of radioactive material to become... not radioactive), but as far as I know DNA is not inherently radioactive, so what doe the half-life mean in this context?
|
[
"Think of time as very slow metabolism, and you've got the idea. DNA degrades on standing - it's not the most robust molecule in the world, and in living cells it's surrounded by a complex repair and maintenance system. Heat, light, humidity, oxygen and other factors will gradually hydrolyze bonds and cause side reactions, to the point that the DNA sequence itself cannot be recovered."
] |
[
"Following the death of a cell containing DNA, enzymes such as nucleases begin to cleave the phosphodiester bonds holding the bases in DNA together, creating DNA fragments. In addition, microorganisms will digest the DNA as well.",
"However, once all the cellular material and microorganisms are long gone, intact DNA molecules may remain for some time. However, moisture (water molecules) alone are able to cleave these bonds and cause the DNA to fragment. ",
"The DNA half-life is the time it takes for 50% of a sample of intact DNA molecules to fragment.",
"For more info, take a look here: ",
"http://www.nature.com/news/dna-has-a-521-year-half-life-1.11555"
] |
[
"I'll simply state that the mechanisms of DNA decay in cellular contexts are fairly well-understood and they do not appear to hinge on the decay of any one isotope of any one atom."
] |
[
"What would an object traveling at speed greater than light appear considering doppler effect (and not considering relativistic effects)?"
] |
[
false
] | null |
[
"So, we're dealing with tachyons here and a few points are important. First, the existence of electrically charged tachyons would almost certainly result in a runaway pair-production process, so we have to assume the object isn't charged. Second, you couldn't use tachyons to convey information faster than the speed of light. A slightly technical exposition on why these are the case can be found ",
"here",
". Also, it should be noted that there is no physical reason to believe tachyons exist.",
"Now, to answer your question,",
"What would an object traveling at speed greater than light appear...",
"First, you would not see the object approaching you, as it will arrive before any light coming from it. Then, when it reaches you, you would see a double image: one blue-shifted image moving off in the direction of travel and one red-shifted image moving backward along the direction of approach (as the trailing light finally starts to reach your eyes)."
] |
[
"as we are learning, we are dealing with models and simplifications all the time. For example when dealing with planets and gravity and theit orbits, we ofter tend to simplify planet to mass points even when that means those mass points should have phisically impossible infinite density and this disregarding a few laws of physics. I believe that physical and mathematical simplifications are valid and that while my question doesn't make sense in \"real\" universe, it still poses an interesting thought."
] |
[
"Your planet analogy is a completely different thing. It's an approximation. ",
"Saying we can't go faster than the speed of light is not some kind of fudge factor approximation we make. It's a fundamental law of the universe. Your are correct when you say your question doesn't make sense."
] |
[
"Why did a semi-finished bottle of rum freeze solid in my fridge, but an unopened one didn't?"
] |
[
false
] |
I had two identical and unopened bottles of 40% abv rum in my deep freeze for several days. Both stayed liquid. I opened one and made myself a small cocktail. Removed maybe 1/6 of the entire bottle. Closed it and put it back in the deep freeze. Couple of days later I checked and noticed that the unopened bottle was still liquid, but most of the rum in the opened bottle had frozen solid. Why would it do that?
|
[
"My guess:",
"According to ",
"here",
" the freezing point of a 40% ethanol solution is -23 C, and 30% is -15C. Depending on your freezer, these temps are quite obtainable. I would guess that two things happened when you opened your rum: ",
"1) humidity from the air very slightly diluted the rum, raising the freezing point just enough to meet the temp of the freezer (probably a small contribution, since you didn't remove so much rum, and your humidity is only 40% inside)",
"2) humid air froze in the headspace of the bottle, making tiny crystals that touched the rum, acting as seeds for ice formation in the liquid. ",
"It is possible that the rum is well-filtered enough that it is unable to freeze despite the temperature being appropriately cold, because it has no nucleation points. The condensed humidity might provide that, allowing the opened bottle to freeze, while the sealed ones do not. ",
"You could test this by agitating your sealed rum and seeing if that makes it freeze (shake it vigorously, then put back in the freezer). This would introduce small air bubbles, which would serve the same purpose as the ice crystals, allowing the mixture to freeze. "
] |
[
"While I think you're right about the possibility that some of the water in the air diluted the rum, I'm inclined to think thats the smaller effect here. How important this is will entirely depend on the temperature of the freezer, though. If, somehow, the freezer temperature was perfectly in the middle of the freezing point between a 35% ethanol/water solution (unopened bottle) and a 34.9% ethanol/water solution (opened bottle) its possible.",
"I think your second point, about seeding of crystal growth, is more likely. I can't find any literature references to the nucleation rate of ethanol/water freezing that I can access at home but I think there is definitely abundant information for us to say that ethanol solutions do a poor job of freezing spontaneously in freezers. It puts us in the more likely scenario of both bottles being below their freezing points. Depending on what rum this is, for example if its not a 40% rum, this seems more likely than the above scenario. On the other hand, if its Bacardi 151 this explanation is rather unlikely.",
"One thing the OP mentioned though was that \"most\" of the rum in the open bottle was frozen. Maybe he accidentally performed ",
"fractional freezing",
"."
] |
[
"Maybe the alcohol in the open bottle evaporated?"
] |
[
"Why do some people's bruises readily appear while others hardly show?"
] |
[
false
] |
[deleted]
|
[
"Bruising (i.e. bleeding) is regulated by your body's ",
"haemostatic",
" systems, which maintain a fine balance between pro-clotting and pro-bleeding states. ",
"As a general overview, haemostasis can be thought of as being governed by three things: (i) blood vessels, (ii) ",
"platelets",
", and (iii) the ",
"coagulation cascade",
". Platelets and clotting proteins freely circulate in your blood, and in normal individuals, when vessels become damaged (e.g. a bruise), a cascade of reactions is initiated that causes platelets become activated and form a haemostatic plug over the site of damage and prevent bleeding. This plug is then reinforced by the actions of the clotting cascade. Thus, an individual's ability to clot properly is dependent on: the number of platelets in the blood, the correct functioning of those platelets, the number of clotting proteins in the blood, and the correct functioning of those proteins.",
"There are a number of congenital disorders that affect both platelet number/function and clotting protein abundance/function (e.g. ",
"haemophilia",
" and ",
"von Willebrand's disease",
"), and a number of acquired disorders (e.g. ",
"ITP",
"). Also, as platelets are made in the bone marrow and clotting factors are largely synthesised in the liver, diseases affecting these organs can also affect your ability to clot properly.",
"Thus, as there are so many factors involved, there's likely to be a large amount of heterogeneity between individuals in how quickly they can clot and thus how quickly bruises form/disappear. Furthermore, the yellow and green colours formed by bruises are caused by the breakdown products of haem (from haemoglobin in red blood cells) called bilirubin (yellow) and biliverdin (green). The further metabolism of these breakdown products is influenced by the function of your spleen and liver, and thus heterogeneity in these mechanisms will also [presumably, this is an educated guess] affect how quickly you can clear a bruise."
] |
[
"thanks for the complete response. A true champ here."
] |
[
"Vitamin K",
" is an essential co-factor for the synthesis of coagulation factors in the liver and is found primarily in the photosynthetic tissues of plants. As a result, regular dietary intake of vitamin K is important for the maintenance of a proper haemostatic equilibrium. Despite this, dietary vitamin K deficiency is [to my knowledge] relatively rare, and other physiological mechanisms are more likely to cause coagulopathies (problems with haemostasis)."
] |
[
"Where do files encrypted with password, like .rar files, store the password?"
] |
[
false
] |
[deleted]
|
[
"Right answer should be \"nowhere\".\nEncrypted file is just marked with specific flag. This flag is stored in the header of the file.\nInitial content is being encryped with the given password and written into encrypted file.\nPassword is not stored at all.\nTo decrypt file you have to know password. If it's right then file is decrypted successfully. If password is incorrect decription fails or provides unusable results."
] |
[
"Your operating doesn't know the password, if it just had a file with the password in it it wouldn't have to ask you for it. ",
"What happens is, in the first few bytes of the password protected file there is a marker that signals that the rest of the file is protected by a password. To read the rest, or at least to make sense of the rest, your computer needs to do some fancy math wit it. One of the variables for that formula is the password. ",
"So the password isn't so much preventing the computer from reading the file, but instead prevents it from being translated into something that makes sense to you."
] |
[
"All the program does is try your password on the encrypted archive file. It's like sticking a key into a keyhole. You can turn it, but if it's the wrong key it will just get stuck. For most encryption systems, if you put the wrong password in, you get gibberish out, or you get an explicit error. ",
"If it's gibberish, it will fail/look empty/etc."
] |
[
"why are the WHO flu vaccine recommended strains different for egg-based and cell/recombinant vaccines?"
] |
[
false
] |
For both quad- and tetra-valent vaccines, the first strain mentioned differs between egg-based and cell culture- or recombinant-based vaccines. Why is this? Thank you.
|
[
"When the WHO influenza vaccine group reviews potential viruses for ",
" vaccines, they have to ask ",
"When they look at ",
" vaccines, they ask",
"The second requirement is obviously different, and so they may find different candidates that work better for the different vaccines. ",
"(This is very simplified and there are other considerations besides simple growth, but the concept is the same - eggs and cells are different ways to grow the virus, and different strains may be more optimal for each.)"
] |
[
"Don’t confuse flu ",
" with flu ",
". Different subtypes (H1N1, H3N2, H2N2) come from new animal sources (birds, pigs). Once those subtypes are in humans, they evolve and mutate in response to population immunity, and form new ",
". ",
"Within those strains, there are of course trillions of individual viruses, many of which have slightly different sequences that don’t affect their antigenicity significantly, but that can change other characteristics of the virus. But those all arise from evolution in humans."
] |
[
"I've recently become aware that ",
"there are 12 different strains of HIV, and each might be an independent instance of cross-species spillover",
". Given that this flu strains difference involves the viruses growing better in different \"places\", could this imply that different flu strains involve spillovers from different animal sources?"
] |
[
"How does a spider pick where to put its web? Do they have the ability to 'sniff' out whether there's a lot of bugs in a certain location?"
] |
[
false
] | null |
[
"Air flow. If you see a web in your house, there is air flow in that area. Flying insects use air flow to move. Spiders eat flying insects, so they set up shop where the highway for their food is. "
] |
[
"None other than years as a weatherization contractor. When I seal up a house to make it more energy efficient, I always look for webs first. That's normally where I find the biggest leaks to the outside. Just put two and two together. "
] |
[
"That makes sense! Do you have a source? "
] |
[
"How are rivers and lakes affected by global warming?"
] |
[
false
] |
We've all seen the apocalyptic predictions of sea encroachment into areas like the American South and the European Low Countries. My limited understanding is both icecap melt and the change in ocean water volume are to blame. I am wondering what effects the predicted change in temperature has on inland bodies of water, such as streams, rivers, and lakes. Will rainfall be different? Evaporation?
|
[
"Current ",
"predictions",
" tell us that dry regions will become dryer and wet regions wetter. Summers are also expected to become dryer and winters wetter. Thus, in some areas rivers and lakes will dry out, and in others they will grow. Moreover, a warmer climate will influence the ecology of lakes. Lakes might, for example, not freeze over in winter or maintain a stronger thermocline. This will benefit some species and harm others. All-in-all, we know there will be huge changes, but we can only guess exactly will happen right now."
] |
[
"This turns out to be a remarkably difficult question to answer. For all that there's only so many places water can go, how it gets there depends on a lot of things that vary with climate change, and we don't necessarily know how much they'll vary and when. There are also a lot of human dimensions questions that come into play that make it complicated to predict. Rainfall and evaporation will absolutely be different, but how much and in what way varies widely by location and remains much more uncertain that estimates of air temperature. ",
"Take for instance the Great Lakes; my expertise is on Lake Michigan so that's what I'll quote here but I think the results are similar for other areas. ",
"Overall precipitation is expected in increase in the area, so that would tend to lead to higher water levels. But there's a ton of uncertainty in the estimates of how much increase we'll see, so it's hard to say how much higher. ",
"On the other hand, warmer temperatures, longer growing seasons, and reduced ice cover all contribute to increased evaporation (technically evapotranspiration, but don't worry about that), and thus lower waterlevels. ",
"How will those two opposing forces balance? There's no great agreement, but most agree that water levels are most likely to decline (e.g. ",
"). It's worth noting that a sustained decline in Lake Michigan waterlevels would have a devastating impact on local shipping - Not going to find the citation on this but I recall a foot of water level decline will close 50% of the ports on the lake; it's something on that order, anyway. ",
"Streams are similar but even more complex. Especially small, spring-fed streams are sensitive to total annual precipitation, but also the timing of that precipitation, and how it is partitioned into runoff and recharge (water that goes to the groundwater and feeds the springs). Stream temperature is an important ecological parameter for many of these streams, and is dependent on flow, land use, air temperature, and groundwater temperatures (though in general stream temperatures can be expected to rise). Flow into a stream may depend on the water levels of a lake it flows out of. ",
"Basically inland hydrology comprises a huge number of complex processes that are highly non-linear and closely linked, and it's hard to make a blanket statement that has much meaning. The work that's mostly going on in the field now is to build up an understanding of how the local systems interact with climatic variation, so we can be prepared to respond as things change, even if we can't know precisely how things will change ahead of time. "
] |
[
"It sounds like we could see widely varying effects by ecosystem, and even within a system. Thanks for the specifics on Lake Michigan. I was born in Wisconsin, so that's an example I can get my head around. "
] |
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