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[
"Would a jar that had an absolute vacuum float or sink in water or air?"
] |
[
false
] |
[deleted]
|
[
"On water it would definitely float. Compared to the high density of water, there's not much difference between a vacuum and an air-filled jar.",
"Floating on air is much harder. In order to keep the jar from collapsing, its walls must be hard enough to resist external air pressure. And for that they need to be thick and heavy. Not likely to work. It's much easier to make a collapsible container (i.e. a balloon) and fill it with a gas that provides pressure from the inside but is much lighter than air, like hydrogen or helium. The former is flammable so it's usually avoided despite being lighter."
] |
[
"Archimedes Principle. The upward bouyancy force is equal to the weight of the gas/fluid displaced. So, it comes down to whether the \"average\" density of the jar is higher (sinks) or lower (floats) than the gas/fluid it's immersed in. What I mean by \"average\" density is that, even though the vacuum may not have any weight, the jar does. So the weight of the jar itself divided by the volume the jar takes up is the \"average\" density.",
"So really it depends on the volume of the jar, what it's made of and what you're immersing it in.",
"If we could assume the jar too was magically weightless than it would rise when immersed in anything (air, water, helium, whatever)."
] |
[
"It could float in air if your jar is light enough. A glass jar is so heavy that the mass of air in it at atmospheric pressure is negligible."
] |
[
"How much water is there under the earths surface? Will springs ever stop producing water?"
] |
[
false
] |
Curious as to whether or not it's possible we can run out of water?
|
[
"MS hydrogeology grad student here. I assume you’re asking about fresh groundwater that can be used by people (e.g. not sea water or salty brines). In answer to your first question, a recent study estimated the total groundwater volume with 2km of the earth’s surface (essentially this is the water that is accessible to people) at 22.6 million km",
" (Gleeson et al 2015). This is a huge amount of water, and is many times more than the total volume of fresh surface water (e.g. in lakes and rivers).\nAnswering your second question about springs and whether we will run out of water is more complicated. Many of the springs on earth are ephemeral, meaning that they can and do stop and resume flowing on a regular basis, usually in response to climate conditions (seasonally dry or wet periods, or longer term droughts or above average rainfall conditions). For the larger springs that flow perennially (year round), going dry is less likely but still possible, particularly in regions where human groundwater pumping from wells is removing significant volumes of water from aquifers feeding the springs. \nAs to whether or not it’s possible that we run out of water I would say it depends on the region in question and comes down to how much groundwater is being withdrawn by people versus how much is naturally recharging aquifers. In some regions such as the eastern US, recharge far exceeds withdrawals because annual rainfall is much higher in these regions and there is little threat of running out. In the western US the reverse is often true and groundwater is being withdrawn at a faster rate than it is being naturally replenished. An example of this can be found in California, where a historic drought and historically low snow fall in the Sierras has forced many farmers to feed their crops with groundwater instead of surface water. The result of this increased groundwater pumping has been significant drops in water levels and even land subsidence (in some cases as much as 1 ft). This doesn’t mean that California is in danger of running out of groundwater any time soon, just that currently they are withdrawing more than is being put back in. If this practice continues long enough, however, eventually the aquifer would be depleted.\nCitation: Gleeson et al. 2015: The global volume and distribution of modern groundwater, Nature geoscience: doi:10.1038/ngeo2590"
] |
[
"Springs are not areas where water is generated, they are outlets for underground reservoirs of water known as ",
"aquifers",
". Aquifers are fed by rainwater and snowmelt that drain into porous ground at higher elevations. Springs are just lower-elevation areas where the aquifer flows out of the ground, ",
"the diagrams on this page",
" and ",
"this page",
" might help you visualize what's going on."
] |
[
"I believe an aquitard is something which prevents (or significantly slows) the rate of water flow. An aquifer is what holds the groundwater. ",
" ",
"Fun fact: Artesian wells form when aquifers are confined by aquitards. The pressure of the water in the confined aquifer forces water upwards through the soil, creating the bubbling artesian well people are familiar with."
] |
[
"Will a magnet still attract molten metal?"
] |
[
false
] |
Lets say you have a pot of hot liquid metal, if you stick a magnet in it will the metal still stick to it magnetically? edit 1: Also, if it does stick, can you raise the temperature of the metal to the point where it WONT stick (assuming the magnet doesn't melt) edit 2: Got some really good answers guys thanks; I really liked the earths magnetic core discussion as well.
|
[
"Molten iron, for example, is not magnetic because the melting point of iron is 1538 ˚C and its ",
"Curie temperature",
" is 770 ˚C. The Curie temperature, essentially, is when a metal stops being magnetic. Since the melting point is greater than the Curie temperature, molten iron is not magnetic. The same can be said about molten cobalt and molten nickle."
] |
[
"then how does the earth maintain such a strong agnetic field with a core of molten iron and nickel?"
] |
[
"I thought that the inner core was a solid sphere of iron? ",
"http://en.wikipedia.org/wiki/Inner_core"
] |
[
"If white noise is a random audio signal, shouldn't we periodically hear tones? Or entire songs?"
] |
[
false
] |
I don't understand how white noise has its own sound if it's just a series of random data. In theory, couldn't said random notes eventually produce a tone? Additionally, if we had a million speakers playing a white noise signal in their own rooms for a million years, would one of them eventually play, say, Beethoven?
|
[
"Well, it is not just \"random data\", it has a specific characteristic. It contains equal power within a fixed bandwidth at any center frequency. A good analogy would be white light. ",
"White noise essentially contains a lot of notes, all at once. The mixture is fairly random, and constantly changing. If it were to just play a single note for any period of time, it would no longer be white noise during that time. ",
"I would say that the chances of a true white noise source behaving like you say, even over a million years, is similar to the chance of your light bulb filament flashing just green light for a moment then going back to being white again. "
] |
[
"I can't think of a reason why, given enough time, such a thing wouldn't eventually make music. I'm not going to try to do the math to figure out if a million years is long enough to get a song out of it. My gut tells me no, but my gut is unreliable at best. "
] |
[
"If we are not talking strictly about white noise anymore, this is essentially the same premise as the Infinite Monkey Theorem. And so the answer is almost surely yes, but there will not be nearly enough time before heat death of the universe for this to happen with any reasonable probability. "
] |
[
"Biology Are smaller animals/insects able to react to outside stimuli faster because their neural networks are smaller so the information travels a lesser distance?"
] |
[
false
] | null |
[
"The speed of action potential propagation isn't constant (like the speed of light is) across different organisms or even between two neurons in the same organism. ",
"This chart",
" can give you a good idea about the variation observed between neurons of different species (see conduction speed).",
"There is also a lot that goes on in the central nervous system between the perception of a stimulus and the reaction to it. All other things being equal, shorter axon lengths would result in a quicker reaction. But I don't know the speed of action potential propagation of neurons in insects, or the time it takes to process a visual stimulus for example in insects compared to larger animals. Maybe someone else does?"
] |
[
"Some information on response times. ",
"http://www.cals.ncsu.edu/course/ent425/tutorial/Ecology/defense.html",
" ",
"I suspect the fact that many insect responses are hardwired makes them speedier as there is no decision making involved."
] |
[
"Thanks for your input!"
] |
[
"What is Reynolds number?"
] |
[
false
] |
[deleted]
|
[
"Reynold's number is defined as the velocity * some characteristic length over the kinematic viscosity of a fluid. You can interpret this number as representing the ratio of inertial to viscous forces. This in turn can be interpreted as how much momentum of the bulk fluid is transferred to molecular interactions. That is, if you put in all this energy into moving some amount of fluid, how much of that energy gets tied up into molecules bumping into each other. ",
"In the end, it basically means that the larger the Reynold's number of a flow is, the more turbulent the flow is - and this relationship is not linear. For a given type of flow (for example, in a pipe, or in an open channel, or over a wing) there will be some critical values where the flow will drastically change behavoir."
] |
[
"Good, concise answer. I'll just add that in a practical sense, in addition to indicating general flow behaviour, it's most typically used as one of the methods of assessing the dynamic similitude between fluid flow systems."
] |
[
"No problem, I don't deal with fluid that much. I'm just looking over my old hydro notes here, and it seems you are right in normal circumstances. However, couldn't you just change gravity? Put the flume in a centrifuge?"
] |
[
"How to show that spin is a probabilistic property?"
] |
[
false
] |
For spatial coordinates we can do the double-slit experiment sending photons one by one and still getting interference pattern. What are the easiest to explain experiments one can do to check that spin is a probabilistic property? Reading wiki on the subject, it's usually just defined as such ("Spin can only have discrete values, thus if it has fixed value in one direction, it's projections on other directions are probabilistic"). Then maybe its better to ask, what are the simplest experiments to check that there's spin at all and that it's of the described nature? (Theoretically. It's probably impossible to do them at home anyway)
|
[
"Look up the Stern-Gerlach experiment.",
"The way it works is silver atoms come out of an oven in a stream. The structure of the silver atom is such that a single excess electron determines the spin of the entire atom. Passing the beam through a non-uniform magnetic field causes the stream to split into two (say, vertically).",
"Now the weirdness. Take one of those streams (say, the one that went up), so that those have definite spin. If you measure the spin again, they'll go up again. No brainer. But put it through a horizontal test, so that some go right and some go left. Now you're just measuring spin in the other direction. Now, if you do the vertical test again, they're mixed up and down. Somehow, having a definite value of spin \"right\" destroys the correlation we had in the \"up\" direction. "
] |
[
"Thanks a lot, will look into this."
] |
[
"Stern-Ger...DrJesusPhD said it already."
] |
[
"How do scientists actually know what material the Earth's core is made out of?"
] |
[
false
] |
I remember in school learning that the core of Earth is made from mostly iron and nickel. ...how did we get that particular information? I can wrap my mind around the idea of scientists figuring out what the inside of the Earth looks like using math and earthquake data but the actual composition of the center of the Earth? It confuses me. What process did we use to figure out the core is made out of iron and nickel without ever obtaining a sample of the Earth's core? EDIT: WOW this post got a lot of traction while I slept! Honestly can't wait to read thru all of this. This was a question I asked a couple of times during my childhood and no teacher ever gave me a satisfying answer. Thank you to everyone for taking the time to truly explain this to me. Adult me is happy! :) 2ND EDIT: I have personally given awards to the people who gave great responses. Thank you~! Also side note...rest in peace to all the mod deleted posts in the comment section. May your sins be forgotten with time. Also also I'm sorry mods for the extra work today.
|
[
"It’s super interesting geology stuff! Basically we map it out by measuring the speeds of seismic waves (earthquakes) and then compare the speeds (and deflect!) of that with other elements. Once we have a match, it’s safe to presume that’s the composition",
"Of course this is a really dumbed down answer, but be sure to read other comments as this is a really interesting question.",
"HERE",
" is a good article"
] |
[
"It was hypothesised that Earth had an iron core long before we could employ seismic measurements that deep because:",
"• Measurements of the Earth’s mass in the 1800s indicated that the Earth was on average quite a bit denser than the rocks we find at the surface and even the (slightly denser) rocks brought up from much deeper (in the mantle) that we ",
"occasionally find in volcanic rock.",
" There must be a region of something much denser inside the Earth just based on this.",
"• We have also known for a long time that the Earth has a magnetic field, and so something metallic is a good candidate for all that extra density down there. A formal publication on Earth’s magnetism was first ",
"made in 1600",
" proposing lodestone as the magnetic source, though this was before we had the mass measurements of the Earth and lodestone is still not dense enough, nor does it produce the right type of magnetism. It was not until 1919 that a self-exciting dynamo was proposed as an explanation for the Earth’s magnetic field. This forms the basis for our current geodynamo theory.",
"• The study of meteorites as rocks from space (rather than just superstitious stories or false assumptions of volcanic products) began in the early 1800s. It became known that some meteorites had a rock-like composition, while others were much denser, composed largely of iron. In 1897 E. Wiechert, (who subsequently became a renowned German seismologist), suggested that the interior of the Earth might consist of a dense metallic core, cloaked in a rocky outer cover. He called this cloak the “Mantel,” which later became anglicized to mantle. Metallic meteorites do in fact represent the cores of long gone planetoids, which managed to differentiate the heavier elements to their centre of mass before being smashed apart by collisions in the early Solar System.\nMeanwhile, the Milne seismograph had been invented in 1880, and subsequent refinements to seismic measurements meant we were able to put constraints on the density and composition of Earth’s interior further and further into the planet. By 1906, the first seismologic detection of the Earth’s fluid (outer) core was made by R. D. Oldham, who showed that P-waves have a significant slowing when travelling through the core. Oldham also predicted a P-wave shadow zone beyond 103° from the origin, ",
"shown here between 103° and 142°.",
"Around this time it was also found that no S-waves arrived at the other side of the Earth beyond the 103° mark, ie. they do not pass through the core at all, so that the S-wave shadow zone stretches between both the 103° points from either side of the origin. S-waves rely on shear strength of the medium in order to propagate and fluids have zero rigidity, so zero shear strength. This is how it was deduced that the core is fluid, which then led to that 1919 proposal for a self-exciting dynamo via the movement of conductive molten iron in the core.\nIt was not until 1936 when Inge Lehmann, a Danish seismologist, reported weak P-wave arrivals within the aforementioned P-wave shadow zone (103° - 142°) which she interpreted as an inner core with higher seismic velocity, possibly solid. The limitations and difficulty of interpreting weak seismic signals, and quite possibly the fact that Lehmann was a woman meant that this remained controversial for some time, but it is 100% true.\nNowadays, we can use seismic tomography to build up more detailed pictures of the Earth’s interior. This is the generation of many 2-D seismic slices through the Earth and then the stacking of them to produce a 3-D image, the same principle used for medical CAT scans. This is shedding light on the fact that the mantle is not particularly homogenous (it seems like the inner and outer cores are). The mantle has large (continent sized) structures of hotter rock within it, thought to be associated with the generation of mantle plumes. ",
"This is the sort of visualisation that can be generated from seismic tomography data."
] |
[
"It does! As well as density, phase (gas, liquid, solid), even things like crystal structure and alloying elements will make small adjustments to velocity, as will the relative velocity of moving material like magma blooms, which all must be accounted for to get the most precise answer. ",
"Researchers are constantly testing theories and seeing which most accurately reflects the observed data."
] |
[
"Is there a link between a person's learning of a programming language, and their ability to utilize their native spoken/written language?"
] |
[
false
] |
Here's my thinking, English as a language has a lot of exceptions to the rules. However programming languages seem to be more straight forward. Is there anything out there showing a strong correlation between the learning of a computer programming language, and improvements in the use of their native language. I ask this because my middle school students are learning Java as early as the 6th grade. In an unfortunate turn of events, I have a lot of students whose lexile scores are well below their grade level. While utilizing teaching methods that are more verbal and illustrative, I can get some good results from these students that typically perform poorly in writing and reading. The question is, will learning something like Java improve their ability to understand the mechanics of english language usage? Most studies point to better understanding of science and math, but I can't seem to find anything on written/verbal skills.
|
[
"It seems to me they think more in an \"object oriented\" speech pattern than do non programmers, in my subjective experience. That is, when they get to a certain point in the story, they make a \"function call\" to bring in more needed information relevant to the story",
"That would be \"functional\", not \"object-oriented\". An object-oriented discussion might be one where all the relevant characteristics of a person were described first and then each person was discussed relative to that description."
] |
[
"As both a professional linguist and hobbiest programmer, I'll say that the link is very simple: If you know the native language of the programming language (that is, English) then you'll have an easier time learning the programming language, but aside from that there's no real link.",
"After all, spoken language relies so strongly on context that it's almost rediculous: Think of the word \"right\", this word alone has a dozen distinct meanings, and there are many more like that. Programming languages, however, are much different because meaning is far more limited and discreet. "
] |
[
"I have a subjective experience with this, since I have a number of programmer friends. I have definitely noticed a tendency in certain individuals. When telling lengthy stories, it's apparent that programmers seem to have more digressions, bifurcations or 'branch points' and are easily able to return to the main story line precisely where they left off. It seems to me they think more in an \"object oriented\" speech pattern than do non programmers, in my subjective experience. That is, when they get to a certain point in the story, they make a \"function call\" to bring in more needed information relevant to the story, returning cleanly to the main thread. I don't know of any real study of this. It's more of a way of organizing thought into structures than it is a matter of syntax."
] |
[
"If I toss a coin 10 times and get heads each time..."
] |
[
false
] |
probability of getting a tails on the 11 time will still just be 50%. BUT isn't the probability of getting 10 tails on tossing the same coin 20 times 50% too? How can these both be true?
|
[
"Actually the probability of getting 10 tails for 20 tosses is 17.62%",
"Source: ",
"http://www.wolframalpha.com/input/?i=toss+20+coins"
] |
[
"Midway through the 20-flip experiment, if you've gotten 11 heads, the probability of getting 10 tails drops to 0."
] |
[
"To expand a tiny bit, 1/2 ^ 10 is 1/1024. This means if you did the \"flip 10 coins\" experiment a million times you would expect to see all heads about 1000 out of those million times. ",
"Also if you want to figure the probability of getting k heads in n coin tosses, use the ",
"binomial distribution",
" formula. "
] |
[
"We orbit the sun. What does the sun Orbit?"
] |
[
false
] |
The moons orbits us, we orbit the sun. What does the sun exactly Orbit? They say Voyager is about to leave the solar system, as far as I know this means it's on a escape trajectory from the Orbit of the sun. Now what will this spacecraft do next, follow a relatively similar path then our sun until some object pulls it into it's influence? And once this Voyager is in this limbo, do we know the forces that will be acting on it? Will we be able to plot this on where it will end up?
|
[
"Everything orbits centers of mass. The sun and the planets orbit their combined center of mass, which just happens to be very near the center of the sun. The sun orbits the center of mass of the Milky Way. At scales beyond this, galaxies don't orbit ",
", but can still be part of gravitationally-bound structures. The Milky Way is part of a gravitationally-bound structure called the Local Group, which is part of a gravitationally-bound structure called the Virgo Cluster. Galaxy clusters are believed to be the largest gravitationally-bound objects in the universe, although the Virgo Cluster is part of a larger (not gravitationally-bound) mass concentration called the Virgo Supercluster, which is itself a part of a larger supercluster called the Laniakea Supercluster. At these extremely large scales, the accelerating expansion of space dominates the relative gravitational attractions of galaxy clusters.",
"When Voyager is no longer dominated by the gravitational potential of a single star, it will continue to orbit the center of the Milky Way until its peculiar velocity brings it nearer to another mass concentration."
] |
[
"Our Sun is gravitationally locked with two other stars in our \"local group",
"What two stars? The Sun isn't gravitationally bound to any other stars. And there isn't really any local group of stars, just stars that happen to be close to us now, and won't be in the future."
] |
[
"Its also worth noting that the sun orbits at something like 220 kilometers per second, dragging all the stuff orbiting it such as Earth along with it too, and takes a couple hundred million years to make it all the way around."
] |
[
"Anyone aware of any oceanic wave phenomenon that generate slow moving straight waves?"
] |
[
false
] |
Years ago a saw a video that claimed there was an alignment of currents and the moon that generated slow moving linear waves. It looked pretty odd and for the life of me I can't remember what they called it. Anyone know what I'm talking about? From the original video, it was two linear waves intersecting in the ocean with people watching them. The waves were no more than 3-4 feet high each.
|
[
"Based on OP's description I assume \"linear\" means the large-scale spatial shape of the wave.",
"With a suitable geometry it should be possible to have two of them intersecting each other, to."
] |
[
"I think you may be thinking of a ",
"tidal bore"
] |
[
"Are you referring to a ",
"tidal bore",
"? There's a good and simple explanation for how they are formed in the Wikipedia article, but they're essentially formed when a high tidal range is forced into a relatively confined channel, generating waves. Tides themselves are waves caused by the gravitational gradient of the moon (and the sun) as it moves across the Earth as it rotates."
] |
[
"Are there any scientific studies that say beating your children is helpful or conducive to their mental and emotional maturity?"
] |
[
false
] | null |
[
"please tell me you are being ironic"
] |
[
"please tell me you are being ironic"
] |
[
"And thank Science that it is!"
] |
[
"Does a large-scale terrain irregularity database exist?"
] |
[
false
] |
Greetings. Considering that: The mountain/non-mountain distinction is subjective; "Land can have a degree of ruggedness whether or not it is described as a mountain. Moreover, land at low elevations can be more rugged than land at higher elevations." I'd like to know whether a database showing the proportion or index of large-scale terrain irregularities - i.e. of tens of miles or more - by country exists. The purpose is to infer the level of difficulty in the laying of infrastructure and to carry out cross-country comparisons. Ideally the database would allow to restrict the data to land with the exclusion of bodies of water such as lakes or rivers. Thanks. 1 "Consider the analogy of hills. Hills can be of varying degrees of steepness; the steeper the hill, the more exertion required to get to the top. Yet there is never any debate over whether an inclination is a hill. Indeed, public roads often display gradient ratios indicating precisely how steep a hill is: 1:10; 1:8, etc. Such quantifications make calculations of the energy required to traverse the hill possible (or, alternatively, which gear to put your car or bicycle in); a sign reading “Hill” or “Not a Hill” would not."
|
[
"I'm not 100% sure what you're looking for, but it seems like maps of gradients or local relief would work. There are any number of global (or near global) free data sets of ",
"DEMs",
", e.g. ",
"SRTM",
", ",
"ASTER",
", or ",
"ALOS",
". With a digital elevation dataset, it's then a trivial task with any ",
"GIS",
" program to calculate gradient (slope) or local relief (difference between minimum and maximum elevations within a specified radius) or any number of other ",
"metrics",
" that are used as some semi-quantitative measure of topographic ruggedness."
] |
[
"Excellent resources, especially the GIS blog. What GIS software and related manual would you recommend? The blog mentions ArcGIS, but the desktop base version requires an annual subscription of $800."
] |
[
"QGIS",
" is a pretty full featured, free, and open source GIS program."
] |
[
"How fast can the power output of a nuclear reactor be decreased in case of power spikes in the electrical grid? (Context inside)"
] |
[
false
] |
Due to nice weather and low electricity use my country had to sell electricity to neighbouring France to prevent a power spike. A politician came on saying it would be wise to close NPP's and replace them by gas-powered and biomass plants, as their power output can be decreased faster than it can in a NPP. I found this: "Most nuclear reactors are hence operated in a prompt subcritical, delayed critical condition: the prompt neutrons alone are not sufficient to sustain a chain reaction, but the delayed neutrons make up the small difference required to keep the reaction going. This has effects on how reactors are controlled: when a small amount of control rod is slid into or out of the reactor core, the power level changes at first very rapidly due to prompt subcritical multiplication and then more gradually, following the exponential growth or decay curve of the delayed critical reaction. Further, increases in reactor power can be performed at any desired rate simply by pulling out a sufficient length of control rod— " Can someone give more details about this limitation in speed? How fast can you decrease the power output by, say, 10%?
|
[
"Actually they can adjust much more quickly than you think.",
"http://en.wikipedia.org/wiki/Load_following_power_plant#Pressurized_water_reactors",
"\n",
"http://www.oecd-nea.org/nea-news/2011/29-2/nea-news-29-2-load-following-e.pdf"
] |
[
"I don't have your exact answer but a relevant fact: nuke plants are considered slow to start and stop, and are therefore treated as part of the baseload (left on for long periods of time), while other types of plants (such as natural gas, hydroelectric) are pretty quick to adjust and are used for most adjustments."
] |
[
"Thanks for the VERY relevant links!",
"The second one states that while load-following is ",
" possible in a nuclear reactor (more than I knew), it's harder on the equipment and the fuel. The first one seems to imply that even this difficulty does not apply in the French reactor design."
] |
[
"What's the most interesting scientific fact you know?"
] |
[
false
] |
There are many, many interesting things in science, but what are some of your favorite facts or studies?
|
[
"Most of our energy comes from a tiny little energy factory in our cells. This tiny little factory was essentially a small bacterium that our ancestral cells swallowed and they had a little microscopic Mexican stand-off. Eventually they got to know each other over the years and are now running the multi-billion cell industry that is our body."
] |
[
"Parity violation in the electro-weak sector is just bad-ass. What this tells us is that it makes a fundamental difference whether you construct your coordinate system right handed or left handed. Some say in a sort of sloppy way that this means that the universe can \"tell the difference\" between right and left...",
"To put this in a more layman friendly terms: Okay, I just wrote a long blob, but I think I was getting too mathy...let's try again....",
"If I give you a picture...it can be anything, let's say it is a picture of scientists working in the lab. If I show you two copies of the picture, one original, and one where I swapped right/left (ie a mirror image or parity transformation...remember in 2D you can only flip one coordinate, otherwise it is just a rotation, not a reflection). Now, I challenge you to figure out which is the original, and which is the mirror image.",
"You can easily come up with a bunch of different ways that you can tell the difference between the two (lettering on tshirts is mirrored, more left handers than right handers, etc.), but there is no physical law that would be violated by the mirrored image (ie: when I took the picture I could have gotten t-shirts screen printed whose characters that are mirrored/collected a whole bunch of lefties, etc.). So really, from a classical every day perspective there is no way you can tell the difference between a parity inverted world and the real world.",
"Now here comes the crazy ass weak force. If we look at beta decays of some atom (let's make it cobalt 60 for historical reasons). Cobalt's nucleus has some intrinsic angular momentum called spin (which is a pseudo-vector). It is found that in the lab the electrons are ejected preferentially anti-aligned with the spin of the nucleus. Because we see in the classical world things are parity invariant, this process should be parity invariant too. So we do a parity transformation on the decaying cobalt (show the mirror image) to see if we are right. Now under a parity transformation the vector direction of the emitted electrons will switch signs, but the spin \"vector\" (actually a pseudo vector for the following reason...) points in the same direction (you can think about spin sort of classically for a moment like angular momentum ",
" = ",
" x ",
". Under parity both ",
" and ",
" change sign, so you get two minus signs, which \"cancel\" and the angular momentum stays the same).",
"Now we have a problem. In the \"normal\" world we get that the electrons and the spin are anti-aligned and in a parity-inverted world, we get the EXACT opposite!! So, if instead of a picture of scientist working, I gave you pictures of some atomic processes -- one mirrored, the other not -- you too will now be able to tell which is the \"original\" and which I mirrored. bad-ass no?",
"Okay, that was reaaaaaally long winded...I hope that was of some use!"
] |
[
"Choice blindness is pretty interesting. ",
"Let's say you ask somebody to look at pictures of two different faces, and ask them to choose the one that they consider more attractive. You can then give them the picture that they ",
" choose, and ask them to justify why they chose that picture; most people will not only fail to realise they have been handed the wrong picture, but will also provide reasons ",
" they chose that picture.",
"Here's a ",
"link",
" to one of the relevant studies. PDF, as a warning."
] |
[
"when a boiler/furnace burns... does it expel both carbon monoxide AND carbon dioxide?"
] |
[
false
] |
or does it expel only carbon monoxide and a CO2 condensor changes the emissions into CO2?
|
[
"The boiler will emit both CO2 and CO, you can guestimate the amount using EPA emission factors - ",
"http://www.epa.gov/ttnchie1/ap42/",
" ."
] |
[
"Incomplete combustion results in CO as a product, while complete combustion gives CO2. Since you have both in a furnace, both are products.",
"Source"
] |
[
"thanks. that's exactly what i need to know. ",
"a boiler tuned properly should not emit CO. "
] |
[
"Would it be possible for two moons to orbit each other in the orbit of a planet?"
] |
[
false
] |
I mean in a stable orbit that could last at least a couple of thousand years.
|
[
"Yes. This is technically possible. In theory.",
"While we like to say things like \"the moon orbits the Earth\", the reality is that the moon and the Earth as a system are orbiting a shared point. It just so happens that the Earth is far more massive than the moon and therefore the center of that system is so close to the center of the Earth as to not matter that much in practice.",
"If you zoom out a bit, you could easily say that the common orbital center of the Earth-Moon system counts in relation to the Sun. Bam, three bodies! Or you can look at Pluto and Charon, whose orbital center is between the two bodies, and they orbit the sun as a system."
] |
[
"Moons by definition orbit a planet or asteroid. You can have a double asteroid in the Lagrange points 4 and 5 of a planet (orbiting the star in the same orbit, but 60 degrees ahead or behind), that can be stable for a very long time.",
"You can also have two objects orbiting each other while together orbiting the planet, but that would need very weird parameters to be stable over astronomical timescales. A few thousand years should be fine."
] |
[
"For SF planning purposes, the two moons are more likely to be stable over astronomical time periods if they are much closer to each other than to the planet. So viewed from the planet, if the moons look like two little dots circling each other, you're probably fine, but if you want two big Earth-sized moons together in the sky that's probably not a stable situation.",
"Stability would also be improved if the planetary system were far from its sun, so the sun were a small bright spark in the sky, and the planet might be quite cold.",
"Which might not be what you want. Unfortunately, in this case physics works in the opposite direction of science fiction awesomeness..."
] |
[
"Does air have a burning temperature?"
] |
[
false
] |
If I had a 1m cube filled with air and just kept increasing the temperature of the cube would the air inside set on fire at some point? If this is possible, could a theoretical temperature value be applied somewhere on Earth and then engulf the whole planet with fire until no air remained?
|
[
"Does air have a burning temperature?",
"No. In order for something to be combustible it must have some chemical potential energy that can be released by reacting that something with oxygen. In the case of air, everything is already stable, and it would actually require additional energy to pull it apart in order to bond it with oxygen. For example, diatomic nitrogen is the most abundant molecule in the atmosphere, weighing in at about 70%. Nitrogen-nitrogen bonds are extremely stable, so this doesn't want to react with oxygen... and that's a good thing, otherwise that reaction would have happened billions of years ago and left no oxygen behind. ",
"Carbon dioxide and water (H2O) are already a combustion products, so you can't burn that, it's just the ash of combusting hydrocarbons, like gas and coal. ",
"But you asked another question, which is a scary question.",
"If I had a 1m cube filled with air and just kept increasing the temperature of the cube would the air inside set on fire at some point?",
"If this is possible, could a theoretical temperature value be applied somewhere on Earth and then engulf the whole planet with fire until no air remained?",
"Please don't do this.",
"If you took a box of air and kept cranking up the temperature, eventually the gas will become an ionized plasma, as there is sufficient energy to break atomic bonds and free the electrons. Eventually, that plasma will be hot enough that nuclei can fuse. Like in the sun. If it's hot enough, nitrogen can fuse and release a tiny bit of energy. Could this perhaps start a self-sustaining fusion reaction that would burn the atmosphere like the sun? ",
"Fortunately not, Feynman and friends checked this before setting off the first atomic bomb. As the death-cloud expands, it will cool faster than it gains energy from fusion, so it shouldn't be possible.",
"Again, please don't try this, because it won't work. There are much better ways of ending the world."
] |
[
"Please don't do this.",
"Again, please don't try this, because it won't work. There are much better ways of ending the world.",
"I am laughing so hard at this, thank you for the great (and funny) answer."
] |
[
"There are much better ways of ending the world.",
"Please, expand?"
] |
[
"Is there any way to stop a star’s fusion reaction?"
] |
[
false
] |
Xenon-135 can poison a fission reaction in a nuclear reactor. Is there any analogous way of stopping a stellar fusion reaction, or would the only way to do it be to somehow blow up the star itself?
|
[
"If the star is not heavy enough, its gravitational collapse won't heat it to high enough temperatures to ignite any significant thermonuclear reactions. This is what brown dwarf stars are."
] |
[
"Understood- I am asking about what it would take to cause a star that ",
" massive enough - where fusion is already underway - and somehow stop the fusion from continuing to occur."
] |
[
"Disassemble it to reduce its mass.",
"https://en.wikipedia.org/wiki/Star_lifting"
] |
[
"Does electricity exist in 3 dimensions?"
] |
[
false
] |
I know that electrons are 3 dimensional objects, but one of their bi products, electricity (or other forms of radiation) I'm not so sure about. I get that electrons do have some mass, and move in more than 2 dimensions, but do the same rules apply to its more abstract products?
|
[
"It's not quite true that \"all particles are waves.\" They can ",
" like waves at times, and behave like particles at others."
] |
[
"Either you're referring to time, which I discounted by saying \"spatial\", or you're going with one of the umpteen theories that describe extra dimensions, of which none have been shown to be correct yet, as far as I know."
] |
[
"You can't discount them without discounting special relativity. ",
"Nothing in SR (or GR, for that matter) requires extra dimensions. As far as I know, the main theories talking about extra dimensions are all related to how we handle the fundamental forces and particles."
] |
[
"Why are flight times not affected by the Earths rotation?"
] |
[
false
] | null |
[
"First thing to think about: why are you not affected by the Earth's rotation?",
"Next, why, if you're inside a car, can you throw an object straight up and have it fall straight down?",
"Now think of the Earth as the car, and the plane as the object.",
"It's not a perfect analogy, as the Earth is a much larger and more complex atmospheric system, with winds and pressure waves and such. But the basic idea is the same. The Earth's atmosphere rotates more or less with the planet, otherwise you'd feel constant winds in one direction at absurd speeds as we rotates through the air. The momentum is essentially transferred from the planet to the air, and then from the air to the plane. Not perfectly transferred, but enough that for instance weather fronts are a bigger factor."
] |
[
"Since the troposphere (the lowest layer of the atmosphere) rotates at approximately the same speed as the Earth's surface, flying through it is analogous to driving on the surface. There is no advantage to driving or flying with or against the Earth's rotation.",
"Having said that, I will now contradict myself. There is an overall general tendency in the mid latitudes for flight level winds to blow in approximately west to east, relative to the ground. (These winds however are far slower than the rotation rate of the Earth) Nevertheless, for long flights, the time difference due to this pattern can amount to an hour or more (westbound flights taking longer)."
] |
[
"The strength and direction of the jet stream is driven by the rotation though, and that in turn affects air travel times."
] |
[
"What would the bottom of the crust and top of the mantle feel like?"
] |
[
false
] |
[deleted]
|
[
"This question actually gets at a fundamental debate within geology, or at least tectonics/geophysics. First, a few important points of terminology and clarification so that the explanation that follows make sense to everyone. 1) Their are two fundamentally different types of crust, ",
"oceanic crust",
", which is largely basalt and is relatively thin, usually on the order of ~10 km thick, and there is ",
"continental crust",
", which is much more variable in composition and thickness, but saying it's generally andesite and 30-50 km thick is a good first approximation. 2) As you stated, below the crust is the mantle, which is primarily ",
"peridotite",
", with the boundary between the crust and the mantle (the ",
"moho",
") representing a compositional change. 3) The top part of the mantle and the crust however are coupled to a certain degree and together form the ",
"lithosphere",
", which are basically the tectonic plates. And 4) the behavior and strengths of these various different earth materials in these different layers will depend on several factors, principally composition, temperature, pressure, and water content (addition of water drastically reduces the strength of materials).",
"Now that all of that is out of the way, to get to your question. For oceanic crust, the crust and mantle contact is likely just like solid rock, just hot. For a lot of this, it is useful to consider strength profiles, like ",
"this one",
". On these diagrams, the y-axis is depth and the x-axis is maximum ",
"differential stress",
", which for this discussion can be thought of as strength (higher max differential stress means more resistant to breaking or flowing). In the strength diagram, the left one is oceanic lithosphere, and we can see that the strength increases with depth passing from the crust into the mantle lithosphere and has its peak within the mantle lithosphere. This is because of the thinness of the oceanic crust and because of the materials involved. This means that in terms of your question, we wouldn't see much of a change in \"consistency\" across the crust mantle boundary, the mantle side would just be a little stronger and very much still solid. ",
"When we get to continental crust, it's a different story and that's where the debate begins. There are two broad ideas (with lines of evidence to support both) about the strength profile of the continental crust, which, in the grand tradition of food analogies, are referred to as the \"jelly sandwich\" and the \"creme brulee\" models. The jelly sandwich model argues that the upper continental crust is strong (top piece of bread), the lower crust is weak (jelly) and the upper mantle is strong (bottom piece of bread) and that in detail, a lot of the strength of the lithosphere as a whole resides in the mantle lithosphere (so maybe the bottom bread is stale). This jelly layer exists because of the materials involved, specifically quartz within the continental crust. Quartz begin to behave ductilley at higher temperatures (flow like a liquid on long time scales, but ",
") and this is basically the jelly in our sandwich. In the creme brulee model, the upper crust is strong (delicious caramelized sugar) and the lower crust and mantle are weak and behave plastically (delicious custard). To illustrate this, lets take a look at some ",
"strength profiles",
", which are taken from this ",
"paper (pdf)",
". The top right one is the traditional jelly sandwich, the bottom left is a modified version where the strength actually resides in the lower crust and the mantle is weak, and the bottom right is the creme brulee. What you can see from this diagram is this all really comes down to water. If the upper mantle is dry, it is strong (like in the jelly sandwich), but if it's wet, it's likely weak. The jelly sandwich is still the dominant model, but the debate still exists. If you have access to a library and enjoy long technical papers, ",
"this",
" is an excellent review of this debate.",
"So, at long last, if within continental crust, if the jelly sandwich model is correct, then the bottom of the crust would be \"gooey\" (flowing on long time scales) but still solid, where as the top of the mantle would be quite rigid and strong (i.e. a rock). If, however, the creme brulee model is real, then both would be \"gooey\", behaving like ductile/plastic solids."
] |
[
"That is exactly what some have argued, and indeed, the creme brulee model (as discussed in the link to the original article) was championed primarily on the basis of observations in a particular place (the Himalayan orogen). Most observations and what we know form rock deformation experiments suggest that the jelly sandwich is the most applicable, but that there are lots of variations depending on the exact thickness, temperature profile, composition, and water content within the area of lithosphere of interest, and that, yes, perhaps in some places the creme brulee model might work."
] |
[
"Is it possible that both models are right, in a sense. Like, if the jelly-sandwich model holds true in one area but the creme brulee model holds true elsewhere, dependent on a variety of factors, including the exact composition of the rock, water content and other factors?"
] |
[
"Why are some veins squiggly?"
] |
[
false
] | null |
[
"If all of our veins were just straight lines every time you out stretch your arm or turn your head or walk you'd be potentially stretching and ripping your interior vascular system - you need some slack in the body."
] |
[
"Ah yeah that makes perfect sense now"
] |
[
"Veins are very compliant vessels. This is so they can function as a reservoir for blood. They lack significant amounts of elastin fibers and smooth muscle around them. Arteries for example are typically very straight and circular. That’s due to their lack of compliance as a result of their increased elastin fibers and smooth muscle layers.",
"\nThis is by design. It means veins are trying to maximize their area and volume."
] |
[
"Does a blind person have balance issues if standing in a boat?"
] |
[
false
] |
[deleted]
|
[
"Sorry, I can only answer part of this question. Hopefully someone else can answer the other part.",
"Your body uses a few different systems to help it maintain balance, including vision, proprioception, and the vestibular system, which all work together to help your brain know where your different body parts are in space.",
"http://en.wikipedia.org/wiki/Proprioception",
"http://en.wikipedia.org/wiki/Vestibular_system",
"When a person with vision closes their eyes while standing still, the propioception sensory inputs and vestibular system are enough to keep a person standing upright without falling over.",
"I have no idea if a person who was born blind will be affected by their lack of vision being able to coordinate with the propioception and vestibular systems, or if their other systems become \"heightened\" to compensate."
] |
[
"Slightly offtopic but relevant and an easy answer. Blind people have difficulty in walking in a straight line and are not even better than blindfolded sighted people. (",
"Source",
")",
"More detailed scientific study",
" says:\nThe findings suggest that the controls of quiet stance and of\nbalancing on the mobile platform are unaffected by the\nlong-term absence of vision. The circuits subserving the\nstabilizing effect of vision seem to be hard-wired, leading to\nthe conclusion that any tactile, proprioceptive or vestibular\nfunction, enhanced by enduring brain plasticity starting\nearly in life, cannot replace normal vision. Conversely, it\nseems that blind subjects use a behavioural strategy leading\nto larger body oscillations, possibly a condition for\nincreasing the afferent information from the remaining\nsenses. It is not unlikely, however, that long-term repetition\nof the mobile platform balancing task could improve the\ncapacity of blind people to properly exploit other sensory\ninflow in order to compensate for loss of vision. This would\npossibly open rehabilitation perspectives, also in the light of\nproven improvement of static and dynamic balance\nperformances by practice with the moving platform in\npatients with vestibular disorders (Corna et al., 2003)."
] |
[
"The balance system is also known as the vestibular system.",
"In the inner ear, the balance system consists of three semicircular canals that contain fluid and “sensors” that detect rotational movement of the head. Each of the semicircular canals lies at a different angle and is situated at a right angle to each other. The semicircular canals deal with different movement: up-and-down, side-to-side, and tilting from one side to the other. All contain sensory hair cells that are activated by movement of inner ear fluid (endolymph). As the head moves, hair cells in the semicircular canals send nerve impulses to the brain by way of the acoustic nerve. The nerve impulses are processed in the brain to help us know where we are in space or if we are moving.",
"Located near the semicircular canals are the utricle and the saccule. The ends of the semicircular canals connect with the utricle, and the utricle connects with the saccule. The semicircular canals provide information about movement of the head. The sensory hair cells of the utricle and saccule provide information to the brain about head position when it is not moving. The utricle is sensitive to change in horizontal movement. The saccule is sensitive to the change in vertical acceleration (such as going up in an elevator). "
] |
[
"Why do we only have fingerprints on our hands and the soles of our feet?"
] |
[
false
] |
I couldn't find any information on this, so hopefully this isn't like grade 2 level stuff. But yea, why do the series of lines simply break off at the end of the palm? They seem to continue as "cracks" in the skin but do not have the classic "looping" style.
|
[
"Also, I think the ridges serve to better sense mechanical stimuli through touch. ",
"The fingerprinted skin on your hands and feet is a special skin (glabrous skin) in that it has different mechanoreceptors as normal hairy skin and is much more sensitive and finely tuned for various mechanical stimuli."
] |
[
"We don't need the extra grip for non-contact surfaces."
] |
[
"A large part of mechanoreception is actually sensing mechanical vibrations, e.g. perception of fine textures is a result of scanning the finger over the surface. Having these ridges amplifies these vibrations when you scan your finger. ",
"See ",
"here"
] |
[
"So I just got my house's water quality report, anything I should be concerned about?"
] |
[
false
] | null |
[
"So nallen is right, drinking water is very highly regulated and held to tight restrictions. Obviously, a high concentration of anything is not good. This is a problem you don't have.",
"Your Pb (Lead) content is very low (a good thing, because it can really mess you up). Ba (Barium) is also very low. This element mimics Ca (Calcium) in biological organisms and some Ba isotopes are radioactive, increasing the likelihood of cancer.",
"Trihalomethanes are common in industrial waste/refrigerants and are pretty carcinogenic. ",
"I am surprised, however, that they didn't look at the Hg (Mercury) content. Hg is a pretty nasty contaminant that messes you up similar to Pb. I'm in Iowa where there is a lot of Rn (Radon) that accumulates in basements and topsoil so it is monitored as well."
] |
[
"Maybe they decided there isn't sufficient quantities in this area? I am upstate New York (Albany basically) so perhaps we don't get too much of it in runoff and what not."
] |
[
"Yeah, that must be it. Hg tests are difficult (at best) so I'm going to assume they won't test for things that aren't even there to save money and time. I'm pretty sure Minnesota (where I'm originally from) tests for Hg because of the large number of lakes and the Mississippi river being natural sources of water runoff."
] |
[
"Is anti gravity technology possible?"
] |
[
false
] |
I just finished watching "PBS Telescope - Hunting the Edge of Space - The Ever Expanding Universe." It said that the galaxies are * expanding in defiance of gravity and this is thought to be due to dark energy. So I wondered, is anti gravity technology possible within the current understanding of the laws of physics? Or would a better understanding of dark matter be required to answer that question? Edit: * The space between the galaxies is expanding.
|
[
"Well... yes and no. It depends on what you mean, and on how much you think we know about gravity.",
"I assume by \"anti-gravity\" you mean a repulsive gravitational force. In the language of general relativity, gravity is a curvature of space-time. If the curvature caused by a massive object is \"positive\" then anti-gravity would be a negative curvature. This is not forbidden in GR, but it's never been observed, and it would lead to some really weird (but cool!) effects. Localized positive curvature is basically the same thing as mass, so localized negative curvature would be negative mass. It's been shown that this sort of negative curvature would be required to create things like ",
"wormholes",
" and ",
"warp fields",
".",
"Dark energy isn't negative curvature, but it is sort of like anti-gravity in that it contributes a uniform negative pressure that is sort of \"pushing the Universe apart.\"",
"Now from a quantum field theory perspective, if gravitons exist, and if, as predicted, they have spin-2, then gravity can only be an attractive force. What the heck does that mean? Basically, it just means, the theory of quantum gravity (which is still only hypothetical) says \"no anti-gravity.\"",
"But remember, we're talking about stuff that's still largely speculative at this point, and history has shown us that our speculations are usually wrong, and reality is much weirder and cooler than anyone could guess."
] |
[
"I guess I am too stupid to even ask the question properly."
] |
[
"That depends on a whole bunch of stuff. How are things arranged? What path are you taking and at what speed? Longer according to whom? "
] |
[
"Is there a reflex to wake you up if you are oxygen deprived during sleep?"
] |
[
false
] |
For example, if you were sleeping with your head completely covered with a thick blanket, would it be possible to get oxygen deprived and suffer health consequences like brain damage? Or would you reflexively have a reaction (e.g. moving) when oxygen deprived, even during sleep?
|
[
"Yes, although the arousal mechanism would likely originate first from an increase in carbon dioxide levels in your blood (as CO2 levels are the primary respiratory driver).",
"Although, if your body was exposed to hypercapnia(high C02) and hypoxia (low oxygen), you can experience a delay in arousal. ",
"Hypoxia impairs the arousal response to external resistive loading and airway occlusion during sleep.",
" This is especially dangerous in patients that have decreased respiratory drive due to commonly experiencing these conditions such as COPD or sleep apnea."
] |
[
"In a way it is. Carbon monoxide binds to hemoglobin, preventing the normal behavior of hemoglobin effectively causing hypoxia. As the primary respiratory drive is responsive to carbon dioxide levels, individuals can lose consciousness before the body detects any abnormalities. Thereby effectively dying of hypoxia."
] |
[
"The human body cannot detect a lack of oxygen. What it can detect is an abundance of carbon dioxide, which in most cases is roughly the same thing. If there is a high level of carbon dioxide in your blood, you will find yourself awake and panicking. "
] |
[
"How can you prove that quantum events are random?"
] |
[
false
] |
The question stems from this video: Here is the Wikipedia page on the topic but it's way over my head:
|
[
"At the moment, there is no known experiment which could determine if the the universe is deterministic or not. ",
"1",
" There are, in fact, a number of competing ideas about the ontology of the universe. Some are deterministic, many are probabilistic, some have testable consequences relative to current theory, and some do not. ",
"2",
" It is a major unanswered question in physics.",
"Quantum mechanics is often presented in the light of the Copenhagen Interpretation of quantum mechanics, which does treat the universe as probabilistic. This is mostly because it is difficult, if not impossible, to talk about quantum mechanics in a way that does not assume an ontology. Along with that is the fact that choice of ontology does not matter in terms of the actual consequences of the theory."
] |
[
"Only if the hidden variables are observable in some way. The Bohm-de Broglie interpretation can be compatible with relativity. There is a preferred frame of reference, but it is not observable. "
] |
[
"Bell's Theorem",
" tells us, that Quantum Mechanics is not governed by local hidden variables. A local hidden variable theory is one in which distant events are assumed to have no instantaneous (or at least faster-than-light) effect on local ones.",
"It says nothing about non-local hidden variables, though. Non-local hidden variables, however, ~~ will~~ might contradict the theory of relativity.",
"EDIT: thanks for the correction sfurbo "
] |
[
"What would happen if everyone on earth jumped at once"
] |
[
false
] | null |
[
"Almost nothing, except that everyone would be in the air briefly."
] |
[
"Would it burn enough calories to heat a village of 100 houses for a night?"
] |
[
"The Earth is about 12 orders of magnitude more massive than every person on it. Even jumping from the same location at the same time they wouldn't noticeably accelerate the Earth."
] |
[
"What is the biggest atom that our Sun can produce?"
] |
[
false
] |
[deleted]
|
[
"Fusion of elements within stars stop with Iron. As mynameiswillem points out, elements higher than Iron require a catalyst, like a supernova, to develop. As for the largest natural occurring element, Californium. The remaining elements are far too unstable to remain naturally."
] |
[
"This",
" is kind of long but essentially our sun will only be able to produce carbon.\nFusion after iron does happen. That is how we get everything heavier that iron. It just requires more energy than it puts out. Usually in the form of the gravitational collapse of a supernova. "
] |
[
"my very limited knowledge of astrophysics might be of help. iirc, the heavier elements were produced by super nova, not by the fusion alone that occurs in living stars. so, because our sun is nowhere near the size needed to super nova (is that a verb?), it wouldn't be able to create crazy heavy atoms."
] |
[
"What is the neurotransmitter for pain?"
] |
[
false
] |
We all know that the neurotransmitter for pleasure in the brain is dopamine but can someone explain what the neurotransmitter for pain is? Also, why don't we talk about the neurotransmitter for pain often?
|
[
"There are many chemicals involved in pain transmission. Initially, after damage to peripheral tissues, inflammatory substances (bradykinin and prostaglandin) are released. There are sensory neurons in the tissue which are specialized for pain, called nociceptors. They are activated by an influx of ions (calcium and sodium). These neurons release even more inflammatory substances (substance P and CRGP). The neurons transmit the painful stimulus to the spinal cord, using glutamate as the main neurotransmitter in the synapses. The signal then ascends to the brain, and eventually to the insula, which I believe is the primary pain center.",
"So based on this description, I'd say that glutamate and substance P are the main neurotransmitters of pain. Opioids (like morphine) work by reducing the activity of calcium channels, so it prevents those first nociceptive neurons from activating. Local anesthetics (like lidocaine) directly block the neuron sodium channels."
] |
[
"Interesting. Thanks for the info!"
] |
[
"Thalamus is a sensory relay station. All sensory input passes through the thalamus, except smell."
] |
[
"On r/TIL, someone posted that spacesuits, immediately after a spacewalk, smell like seared steak and/or hot metal. Can anyone explain this?"
] |
[
false
] |
Here is the link:
|
[
"According to astronaut Sunita Williams's ",
"blog",
", the general consensus among the crew is that the smell is caused by the ionization of the aluminum which comprises the ISS structure."
] |
[
"skip to 2:15 \nhe does a good job explaining it ",
"http://www.youtube.com/watch?v=eiAx2kqmUpQ"
] |
[
"Neat! So it (probably) isn't the smell of space itself, but instead of the space-",
"?"
] |
[
"Are neurotransmitters such as serotonin, dopamine, and GABA stored in the body like some vitamins and minerals are? Is it then possible to deplete them from chronic stress and/or bad diet? Furthermore is it possible to replenish them and cure things like anxiety and panic disorders?"
] |
[
false
] | null |
[
"This is sound science, but to elaborate and clarify, chemicals like dopamine , its not a matter of storage as it is how much is released during neural stimulation, and how they bind to their receptors. As mentioned there are receptors agonists and antagonists. I really do not know if on a cellular level certain things like long term depression cause less dopamine to be produced, but there is some evidence to support that there is less binding to its receptor in the neural cleft. Good Q."
] |
[
"This is sound science, but to elaborate and clarify, chemicals like dopamine , its not a matter of storage as it is how much is released during neural stimulation, and how they bind to their receptors. As mentioned there are receptors agonists and antagonists. I really do not know if on a cellular level certain things like long term depression cause less dopamine to be produced, but there is some evidence to support that there is less binding to its receptor in the neural cleft. Good Q."
] |
[
"Thank you for the response. May I respectfully ask for a paragraph break?"
] |
[
"Can an overactive immune-system benefit me in any ways I am not aware of?"
] |
[
false
] |
Here's my situation, I have been diagnosed with what has been described to me as an "autoimmune disorder", which has targeted my gastrointestinal system (pancreas/intestines primarily). Through some research and my doctors, I basically understand that my immune system is more or less over-active, attacking my body for no reason (that we know of). Since I'm not aware of the body having compartmentalized immune systems, could this "over-active" immune system benefit me in any overall ways I'm not aware of? edit- not asking for diagnosis or advice, I'm just curious as to the biology of the immune system and if what I ask if possible.
|
[
"It's possible, but not likely. Also, any benefit is probably going to be very, very minor (even trivial) compared to the problems it causes. But ultimately, it depends on what disorder you have.",
"Autoimmune disease doesn't really mean overactive immune system....your immune system is acting at a normal level, it's just doing it in the wrong way. Think of a hammer. The hammer impacts something...if that something is a nail, then that's good. If it's your windshield...not so good. Same force, same \"activity\", just dysregulated. It's not really \"overactive\" when it hits your windshield, it's doing what hammers do when they're doing stuff. If that makes sense.",
"Same with your immune system. It's acting like it should, attacking cells and killing them. If those cells were ",
", that would be awesome. But since those cells are your gut and pancreas, that sucks. ",
"Same force, same activity, just dysregulated. "
] |
[
"Thank you. That analogy really helped me understand what is going on."
] |
[
"It is really of no benefit. ",
"The power of your immune system revolves around variable regions in antibodies and some white blood cells. These variable regions are responsible for detecting the surface antigens (unique surface proteins of a cell) of \"invading\" cells.",
"During the creation process of these variable regions, you may end up accidentally acquiring a variable region which detect antigens for your own cells. During normal development, these cells should be destroyed. In rare cases these cells are not destroyed which creates an immune response for your own cells."
] |
[
"How many stars had to explode to create the heavier elements that make up our solar system? How much of a heavy element is created in a supernova? How many stars had to die to create Earth?"
] |
[
false
] |
[deleted]
|
[
"MrDanger is incorrect, you can't create heavier elements through the process of neutron bombardment. You can create lighter elements, like mercury(80) to gold(79). I suppose MrDanger is ",
" correct in that neutron bombardment is occurring within massive stars, but that isn't the process creating elements heavier than iron. ",
"As for your questions, I can't (with authority) answer them, but it is worth noting that the ",
"sun makes up an utterly overwhelming majority of the mass of the solar system.",
" and that our sun is nowhere near massive enough to create a supernova that forms many of the heavier elements. So while it maybe true that the \"atoms in your left hand came from a different star than the atoms in your right hand,\" a single supernova would likely produce far more the mass of heavier elements than is present in the planetary bodies in our solar system. "
] |
[
"Supernovas are extremely massive explosions of energy, beyond all human comprehension. It has been said that a supernova is to a nuclear bomb what a nuclear bomb is to a single flap of a mosquito wing. A huge amount of material is created in a typical supernova. According to NASA, a typical supernova creates enough dust for about 10000 Earths: ",
"http://www.universetoday.com/12273/supernova-generates-enough-dust-for-10000-earths/",
"Keep in mind, though, that most of the stuff the Earth is made of (Iron, nickel, and light elements like carbon and oxygen) are actually mostly made in the cores of active stars, not supernovas. The amount of material produced in this way is ",
" larger."
] |
[
"This is probably a question without an answer.",
"It can depend on these two factors:",
"Stellar nursery where the Sun was created.",
"How many Population I, II, and III stars had created the Nursery.(If was just one , Population III star, then there's your answer.)",
"What type of stars were created near the Sun, and whether or not they affected the amount of metals we have(So if a star took very little metals, we might have a surplus, if it took a lot, we'd have less than we would otherwise.)",
"While it definitely wasn't one star, since we'd need to go through at least two generations of stars to get the heavier elements we have, the best educated guess anyone could give would be around three or four stars. "
] |
[
"Does an empty refrigerator consume more power than a full one?"
] |
[
false
] |
My fridge is often nearly empty, so I got to wondering if filling it with a bunch of bottles of water would help keep it cool longer and thus increasing the time between cooling cycles, or if it simply doesn't matter what's in it.
|
[
"The power consumption is dependent on a number of things, but in this case, you're really only concerned with how much heat is lost to the environment.",
"Your suspicion is correct: If you open and close the refrigerator frequently, and it's empty, the cool air can quickly escape, making the fridge do more work to maintain its setpoint. In this case, it is beneficial to have more non-gaseous thermal mass in the fridge. Bottles of water or any liquid will help significantly. Even empty tupperware will serve to keep the cool air from escaping.",
"This will also help to extend the life of the compressor."
] |
[
"While correct, it might take a long time to pay off. Let's say a typical empty fridge has 400 liters of space in it and operates at 3°C in a 23°C room. Assume that opening it briefly causes half of the cold air inside (200 liters) to be replaced with warm room air. Approximating the density of air as 1.25 kg/m",
" and the heat capacity at 1 kJ/kg°K, this sets the fridge back about 5 kJ of energy that it has to pump out. Let's say we fill 90% of the space in the fridge with water bottles, reducing that energy loss by 90%, to 0.5 kJ.",
"So, having the bottles in the fridge saves 4.5 kJ each time it's opened. But what about the initial task of cooling down the water bottles? We've put 360 kg of water in the fridge, which has a heat capacity of about 4.2 kJ/kg°K, for a total of 30 MJ of heat that must be removed initially. You would have to open the fridge ",
" to recoup that investment. For someone who doesn't keep anything in their fridge, that might take you a while.",
"tl;dr: use balloons or water bottles full of air, not water."
] |
[
"Of course one would wonder why you would open and close an empty fridge very often."
] |
[
"Is there an evolutionary benefit to humans' complex sexual desires?"
] |
[
false
] |
[deleted]
|
[
"1) Don't look for adaptive consequences for every apparent \"trait\". Just because it's something humans do doesn't mean that they were shaped to do that by evolution because it improves their fitness.",
"2) See the ",
"bonobo chimp",
", our closest living relative, whose entire way of life is based on the freaky sex stuff, and whose sexual proclivity is probably far in excess of human sex. They use sex as social glue, not just a reproductive mechanism, so it's reasonable to suspect that the same might be true of humans."
] |
[
"Less of a \"reason\" and more of a consequence of having a large brain/complex society."
] |
[
"Just wanted to add that dolphins will engage in sex across species. They just enjoy sex. Evolution of a drive to have sex resulted in it being pleasurable. Leading to more frequent sex, which originally served to increase the number of offspring. This would seem at a glance to have no fitness benefit. However, sexual activity without a reproduction may benefit the individual by reducing stress. I think this is pretty common in more intelligent species. Masturbation would also be an example.",
"EDIT: *species"
] |
[
"Why does electricity always hum at a B-flat pitch?"
] |
[
false
] |
Whenever I pass a power plant or hear a lot of electricity running through my house, I always hear that pitch. Edit: To those asking, I am a musician.
|
[
"Electricity is run on an alternating current (AC) which reverses voltage in the pattern of a sine wave. In the US, the frequency of this alternating is 60 Hz, which is a B flat (more of a flat B or sharp B flat, really). Sometimes interactions with surroundings, especially at high voltages like in transformers, can cause a hum at the frequency the grid is run on. In most of Europe, as an example, it's run at 50 Hz not 60 Hz, so you would hear a G (a little sharp) instead of a B flat."
] |
[
"Good answer! To expand on this, in the industry we call it \"60 cycle hum\": Electrical current flow creates a magnetic field, and transformers have cores made of ferrous metal. So the changing alternating-current is causing the big metal cores to move a little bit in a way that matches the rate at which the current changes.",
"The fundamental frequency is 60Hz like our power frequency, but because of a phenomenon called ",
"\"magnetostriction\"",
" the transformer iron vibrates at twice that rate, or 120Hz.",
"If an electrical load on a piece of equipment screws up that normal 60Hz current we can absolutely hear it: Transformers that have a ton of current harmonics no longer produce a nice \"60 cycle hum\", but can have a much louder, sharper buzz that sounds very noticeably different."
] |
[
"In the US, alternating current (AC) oscillates at 60Hz and the buzzing you hear is generated by the second harmonic, so 120Hz. The nearest B-flat is at 116.54Hz, so it's pretty close! The next B is at 123.47Hz, so really you're hearing something that is very much in the middle of B and B-flat. If you were in Europe, where the standard is 50Hz, you'd be hearing something between G (98Hz) and G-sharp (103.83Hz).",
"Also, excellent ear, are you a musician?"
] |
[
"Is Wolff's law the reason that athletes usually have higher bone density, or is there another cause?"
] |
[
false
] |
So I've read somewhere that football players have stronger bones due to the nature of their sport. I've also heard a claim from various Muay Thai practitioners that Muay Thai can condition one's bones due to microfractures. The claim is that every time you do something like bumping your shin, a microfracture occurs. When the microfracture is healed, the bone is stronger(similar to muscle recovery). Is there any truth to this claim, and were there any studies done on this?
|
[
"Oooh goodie, a bone question! Finally, something that's my cup of tea.",
"It is absolutely true that loading bone makes it stronger. We tend to think of bones as inert and static things--basically giant hangers from which our muscles and organs hang. In fact, the truth is exactly the opposite--bones are very metabolically active.",
"Your bones are constantly being broken down and built back up by two cell types which work together. Osteoclasts are constantly breaking down old bone, and many osteoblasts follow the osteoclast through the bone, laying down new tissue. This new tissue is called osteoid, and it isn't nearly as mineralized as the rest of your bone. Every once in a while, an osteoblast gets stuck in it's osteoid, at which point it changes to osteocyte. Mineralization will progress around the osteocyte, and correspondingly over time, the surrounding osteoid will get progressively denser. This leads to a normal range of bone mineral density distribution (BMDD) (",
"http://www.ncbi.nlm.nih.gov/pubmed/22976646",
"). Figure 1 of that paper shows the normal range of BMDD in a rat mandible. ",
"Now, many things can alter this BMDD. Giving radiation or drugs (such as bisphosphonates or parathyroid hormone, both of which are used to treat osteoporosis) can alter a person's BMDD. So can their activities. Any activity that increases a load on a bone will trigger the bone to strengthen itself. But how does this work?",
"One possibility is microfractures. This absolutely a mechanism that will be occurring in top-level athletes. Their training regimens may, in fact, impart a level of damage to their bones to trigger fracture healing response mechanisms. But will this happen to you? Probably not.",
"Here's why: in any material, you have two types of \"damage\" you can do to the material: non-plastic deformation and plastic deformation. In non-plastic deformation, you are loading a material below it's yield point, meaning that when you remove the load, the ",
" Once you hit the yield point, plastic deformation occurs, and you will start producing micro- or macro-fractures. In plastic deformation, the material will ",
" go back to it's original shape, undamaged, which makes sense since we've fractured it. Here is an example stress-strain curve which shows what i'm talking about. ",
"http://images.tutorvista.com/content/solids-and-fluids/stress-strain-curve.gif",
" . As you can see, non-plastic comes first, and then once we have a fairly high level of displacement, we get plastic deformation. ",
"This might not make sense to you if you're still thinking about bones as giant blocks of calcium. They actually have a lot more to them than that. There is a ",
" of collagen in bones, which is a fairly stretchy material. In fact, gelatin (Jello) is a modified form of pig/cow collagen. Combining the strength of calcium with the ductility of collagen allows bone to be very strong, yet relatively robust against plastic deformation.",
"So if microfractures aren't how we're generally strengthening our bones, how does this process work? As it turns out, bone cells (ostecytes) can actually \"feel\" mechanical forces and respond to them. They do so through what are called \"mechanotransductive pathways\", which is a vague way of saying that they convert a mechanical stimulus or input into a biochemical or genetic effect. We know that this absolutely happens through nifty little contraptions like FlexCells ( ",
"http://www.flexcellint.com/",
" ) which allow us to mechanically load cell culture plates. We throw some osteoblasts on there, compare them to cells that aren't being loaded, and we see ",
" different gene expression profiles--so we know that the cells are responding directly to mechanical stimulus. This ( ",
"http://link.springer.com/article/10.1007/s12018-010-9079-x",
" ) is a fairly nice review on some of the more recent literature regarding osteocyte mechanotransduction, if you're interested in getting into gene names and whatnot."
] |
[
"Thank you so much for the detailed response. So what would be a real world comparison between the two ways bones strengthen(you mentioned that microfractures are not generally how bones strengthen).",
"As it turns out, bone cells (ostecytes) can actually \"feel\" mechanical forces and respond to them. They do so through what are called \"mechanotransductive pathways\", which is a vague way of saying that they convert a mechanical stimulus or input into a biochemical or genetic effect. We know that this absolutely happens through nifty little contraptions like FlexCells ( ",
"http://www.flexcellint.com/[3]",
" ) which allow us to mechanically load cell culture plates. We throw some osteoblasts on there, compare them to cells that aren't being loaded, and we see wildly different gene expression profiles--so we know that the cells are responding directly to mechanical stimulus. This ( ",
"http://link.springer.com/article/10.1007/s12018-010-9079-x[4]",
" ) is a fairly nice review on some of the more recent literature regarding osteocyte mechanotransduction, if you're interested in getting into gene names and whatnot.",
"Could I deduce that this would mean that most athletes have stronger bones due to heavy lifting, as opposed to constantly subjecting their skeletal structure to non-injurious blunt trauma? Also, how would you define \"top-level\" athletes?"
] |
[
"Could I deduce that this would mean that most athletes have stronger bones due to heavy lifting, as opposed to constantly subjecting their skeletal structure to non-injurious blunt trauma?",
"Well, be careful. Really, most athletes have stronger bones do to constantly subjecting their skeletal structure to high loads. This may or may not be a result of heavy lifting. It could also be a result of repetitive moderate lifting, high general activity, or whatever. ",
"Keep in mind that you need a basal level of loading to maintain a normal bone as well. A bone that doesn't see any load will wither. This is especially a problem for astronauts, who see extended periods of time with sub-physiological loading. If you're on bed rest for extended periods of time, you'll see bone atrophy as well. ( ",
"http://www.niams.nih.gov/Health_Info/Bone/Osteoporosis/Conditions_Behaviors/bed_rest.asp",
" )",
"Also, how would you define \"top-level\" athletes? ",
"I'm being deliberately vague here and using \"top-level\" athlete as a catch-all phrase to include those who might be routinely loading their bones near or to the yield point of that tissue. I can't imagine there are tons of people out there who fit into this category, though."
] |
[
"Why do nuclear bombs make mushroom clouds?"
] |
[
false
] |
Is the famous mushroom cloud that follows a nuclear detonation unique to nuclear explosions? Is it just the sheer size and power of nuclear bombs that makes the mushroom cloud so visible and defined whereas other explosion simply don't have the power necessary to create such a distinct cloud? In either case, why is the "mushroom" the shape that the cloud takes?
|
[
"This is not unique to nuclear weapons. Any sufficiently large explosion will produce a mushroom cloud. This is because the explosion pushes air out of the blast area, but after the explosion the air rushes back in. This is what causes the dust and smoke brought on by the explosion to form into the mushroom shape. Air rushes in at all angles, and as it collides in the center it rushes up (because the ground prevents down from being an option) this drags the particles in the air with it.",
"Nuclear blasts produce very prominent clouds not just because of their size but also because of the smoke they produce rapidly from the intense light of the blast. If I was not on my phone I would link to a few very good videos demonstrating the \"waves\" of a nuclear blast (intense light, explosion, rush of wind back into the explosions area). "
] |
[
"Fluid mechanics grad student here, to add a smidge.",
"Once the low pressure zone created by the hot gas equalizes (the void is \"filled\"), the upwelling stops. This is key to forming the mushroom. As the upwelling stops, a vortex ring is generated, whose strength is determined by the height of the plume. \nIf if didn't happen in a short burst, we'd get a boring old smoke trail, like that of a cigarette. ",
"This vortex ring is doughnut shaped circle of rotating gas. Therefore, as it spins, it pulls gas near the ground upward through its center. This inducted gas moves upward dragging particles like dirt along with it, thus contributing to the stem. These particles go up and over the top of the ring and fly outward creating the well defined bottom of the mushroom cap. Secondary rings can also form if the upwelling core is big enough to shed the first ring. That is the quintessential nuclear mushroom cloud image of the mushroom and secondary ring halfway up the stem. In reality, in sufficiently calm conditions any buoyant plume (or any abrupt but finite injection) will make a mushroom-like cloud. We only see them in the atmosphere when we have dominating effects (large explosion) and a particulate that gets entrained in the cloud and allows for visualization. ",
"For more info see keywords: buoyant plume, vortex ring"
] |
[
"At the center of the nuclear blast is a particularly hot fireball which rises much faster than conventional explosions as well, and that pulls the dust up, which lengthens the \"stem\" of the mushroom and draws more ground-level air towards the base of the \"stem.\" The initial blast produces super-hot X-rays which can't pass through much air without the air absorbing it, which heats them to the point that they absorb slightly cooler X-rays and that cascade continues until all the heat energy is absorbed or nothing gets hot enough to produce X-rays. So a whole lot of air gets superheated in the center, temperatures far hotter than the puny hundreds/thousands of degrees of a chemical explosive.",
"I've ",
" the fireball can rise at supersonic speeds, but I don't have a source for that claim. Does anyone?"
] |
[
"When you tag someone with a laser in a lasertag games, how does the gear knows who tag who ?"
] |
[
false
] |
I don’t understand quite well how you can manipulate a laser to transmit informations such as a username by shooting another player, knowing that there’s not a lot of parameters you can manipulate in a laser (amplitude, wavelength, etc) and that the lasergun is pretty cheap
|
[
"Generally the datastream is 8bit, RS232. ",
"RS232 is a physical layer which defines connectors, voltage levels, cable capacitance, etc. It does not specify the framing or formatting of the data stream. \"Asynchronous serial\" is the term for the general class of byte-oriented, start/stop-bit-framed clockless serial protocols that I think you're thinking of (although RS232 supports both synchronous and asynchronous communication)."
] |
[
"To elaborate on this answer, Frequency modulation(FM) or amplitude modulation(AM) can be done for any spectrum of electromagnetic radiation. Radio waves use this technology to transmit the data that you listen to in your car, but infrared and visible spectrum EM radiation can use this technique as well. Some radio waves transmit an analog signal that the radio simply interprets and displays. That being said, there are ways to interject even more information onto the waveform. Think about how the artist and song name get displayed on some radios as well as the song itself."
] |
[
"To elaborate on this answer, Frequency modulation(FM) or amplitude modulation(AM) can be done for any spectrum of electromagnetic radiation. Radio waves use this technology to transmit the data that you listen to in your car, but infrared and visible spectrum EM radiation can use this technique as well. Some radio waves transmit an analog signal that the radio simply interprets and displays. That being said, there are ways to interject even more information onto the waveform. Think about how the artist and song name get displayed on some radios as well as the song itself."
] |
[
"For satellites such as the James Webb, what are the benefits of observing infrared light versus visible light?"
] |
[
false
] | null |
[
"It's just a totally different slice of the universe. In general, you get a better picture of dust and gas, rather than of stars. This is important for completing the \"life-cycle\" of stars and galaxies, and seeing how stars and black holes are fuelled. It particularly focuses on \"warm\" dust and gas, rather than extremely ionised gas. This picks up stuff you would miss at higher frequencies. Myself, I work on large-scale outflows and inflows around supermassive black holes, and this is all gas and dust that is most visible at infrared and sub-millimetre wavelengths.",
"The dust can also be transparent in longer IR wavelengths, which means you can see stuff that's blocked by dust in optical light. So you can get more unbiased samples, and peak through the Milky Way disc a bit better.",
"It also helps for looking at very distant galaxies, where the optical light has been redshifted into infrared.",
"And it's also good for finding other cool-ish objects like planets.",
"But just to clarify: we don't want to use infrared ",
" other wavelengths. Ideally, we want to see everything in as many different wavelengths as possible, to get a full spectrum colour picture that tells us absolutely everything we could know about an object. Radio, sub-millimetre, infrared, optical, UV, x-rays, gamma rays, and even gravitational waves are all slightly different windows, and it's only when we combine them that we get the full picture. With something like a supermassive black hole, you have a big disc of molecular gas that emits in the sub-mm, you have an optical-UV accretion disc and an x-ray corona, you have a radio-emitting jet, and you have infrared emitting dusty gas being blown around by the SMBH too. You would miss this complex structure if you were stuck in just one waveband!",
"More practically: why is JWST an infrared telescope? Because Hubble still works, and because ground-based optical telescopes are actually really good. With \"adaptive optics\", you can actually cancel out a lot of the atmospheric issues. You can also build a ",
" telescope much more cheaply - and affordability is the difference between a telescope being built and not being built. Hubble has a 2.4m mirror, but 8m mirrors are fairly common on Earth, and the next class of 30m telescopes are on their way. But infrared telescopes are tricky to do on the ground, because things that are at room temperature emit a lot of infrared radiation. So you get a huge improvement by putting one in space with some top-quality insulation or active cooling. In terms of bang-per-buck, putting your money into a new infrared telescope in space gives you a bigger jump in visibility than putting up a bigger Hubble.",
"Edit: In case I missed anything, ",
"here",
" is the official NASA page on JWST science, highlighting what they think are the coolest things JWST will see."
] |
[
"One reason why James Webb is focussed on infra red is that with modern adaptive optics, we can do excellent visible-light and near infra-red work from the ground. But far infra-red doesn't make it through the atmosphere, so we need space telescopes for it."
] |
[
"The temperature of an object determines what wavelength of light it emits. If you are looking for visible light, you will only see objects that are 700K or hotter, so mostly stars. If you look for infrared light, you can see all objects warmer than 0K, which is everything."
] |
[
"Why is it so difficult for particle accelerators to increase in energy, seeing as you need about 10000000 Tev for ~one Joule?"
] |
[
false
] |
Couldn't we just pour an amount of energy measured in joules in, and see what happens?
|
[
"Couldn't we just pour an amount of energy measured in joules in, and see what happens?",
"Let me ask you the related question to illustrate the problem:",
"How?",
"How do you put one joule of energy into a particle? Do you have an answer? That's problem... neither does anyone else. The problem of energy transfer is a deep issue that pervades most of science and engineering, not just particle accelerators.",
"A chocolate bar has about half a million joules of energy in it. If you could transfer that power into a bullet, you could launch it at 10km... per ",
". At that speed you could flip over tanks.",
"Okay, let's do it! I'll stick my bullet into a chocolate bar and light it on fire and it should go at 10km/s right?... yeah no.",
"Right now, we don't have any mechanism of efficiently transferring the chocolate bar's chemical energy into the bullet's kinetic energy. We have very roundabout systems that can burn the chocolate bar, produce heat, maybe drive a compressor and then launch the bullet. But much of the energy is wasted. Even if it wasn't wasted there are engineering limits to how much acceleration can be applied.",
"Same thing with our particle accelerators. We can easily get terajoules from a nuclear reactor, but we have no way of directly applying that to the particles. Instead we go through a roundabout method of using magnetic and electric fields. You might be asking \"well why don't we increase those fields?\", we can certainly try but often times we're at the engineering limit. If we actually did increase those fields we would literally break the magnets. The stress they're under is too great. We can keep engineering better and better systems but that costs money. ",
"So going back to your question: ",
"Couldn't we just pour an amount of energy measured in joules in, and see what happens?",
"I'll tell you exactly what happens: the magnets would explode long before that energy is transferred to the particle. ",
"Do you think it's as simple as turning a knob on the LHC from one to eleven? The knob's already been maxed out. Turning it further would literally break the machine.",
"What we need is better machines. And that goes back to a fundamental problem we still haven't figured out:",
"How?",
"(EDIT: spelling and grammar)"
] |
[
"You're essentially asking about what limits the center of mass energy of colliders. In all colliders, particles are accelerated by an electric field. The problem is that the faster a particle goes, the least time it spends in the field, and so the least efficient the field is at accelerating. Colliders are therefore limited by length.",
"Circular colliders have an infinite length (just have the particles do as many turns as you want). However, curving the trajectory of a particle is done by magnetic fields, and these have to be higher the faster the particle is going to maintain the same amount of curvature.",
"This means that increasing collider energy implies either building bigger circular accelerators (which costs a lot of money, mainly because of excavation) or discovering ways to make better magnets. The LHC uses 8.3 T magnetic fields, which is among the strongest man-made ",
" magnetic fields.",
"For lighter particles, synchrotron radiation is also a problem in circular accelerators. A curving particle will radiate a quantity of energy that increases with a smaller mass and higher momentum."
] |
[
"\"Apart from all the other problems\" the effect of tides on CERN accelerators has been studied:",
"\"Effects of terrestrial tides on the LEP beam energy\" by L. Arnaudon et al., Nucl. Instr. Meth A 357, (1995) p 249.",
"http://dx.doi.org/10.1016/0168-9002(94)01526-0",
" (edit: doi links with parentheses break the reddit link mechanism) ",
"Abstract:",
"\"The circular e+e− collider LEP located near Geneva is used to investigate the properties of the Z boson. The measurements of the Z boson mass and resonance width are of fundamental importance for the standard model of the electroweak interactions. They require a knowledge of the LEP beam energy with a precision of ∼ 20 ppm, which is provided by a measurement of the electron spin precession frequency. To extrapolate beam energy calibrations over a longer period of time, effects causing energy changes have to be taken into account. Among these are the terrestrial tides due to the sun and moon which move the Earth surface up and down. ",
" We present results of measurements on the influence of terrestrial tides on the LEP beam energy that have been performed in 1992 and 1993.\""
] |
[
"How come earth is magnetic even though earth's core is above the Curie point (Temperature where nothing is magnetic) ?"
] |
[
false
] |
Does it have something to do with the pressure or something ?
|
[
"The Curie point refers to permanent magnetism, where half filled outer electron shells allow an atom to be magnetic. When the atoms in a substance are aligned such that their individual magnetic fields are in the same direction, the substance is magnetic (see ferromagnetism for more details). Above the Curie point, this breaks down, because the atoms won't stay aligned.",
"The earth's magnetic field, on the other hand, is created by dynamo action--that is, the flow of electrically conductive fluid (the outer core). This is driven largely by rotation and convection, which creates circulating electric currents, and thus, a magnetic field. The sun's magnetic field is created in a similar way, only with plasma instead of magma."
] |
[
"Are there any theories as to what it is about the rotation and convection that lead to the occasional flips in polarity?"
] |
[
"My understanding of the current theories on the subject is that because of the existent magnetic field, most of the currents will produce fields in the same orientation. Occasionally, however, there'll be small disturbances for one reason or another. There are many potential causes, such as impact events, the collision of the continental slabs on the tectonic plates, or massive volcanic eruption. These instabilities in the field usually dissipate, but occasionally (every 200,000 years or so, on average) they start to build up, which causes the pole to drift and the polarity's strength to decay, making it easier for more instabilities to occur. If it goes on long enough, the magnetic field will weaken significantly, and causes a runaway effect. These pole reversals take a long time to happen (on the order of 1,000-10,000 years), and in the meantime, the field is... messy.",
"Disclaimer: IANA geophysicist, so someone who ",
" can probably provide a more accurate, up-to-date, or comprehensive answer."
] |
[
"How did Tesla's tower work?"
] |
[
false
] |
It pulled electricity from the atmosphere correct? Is that even possible? If so, why has no one continued work on it?
|
[
"There are problems though. Earth-resonance falls off above 20KHz, and essentially becomes useless above about 100KHz. Yet Wardenclyffe coil is too small to operate below these frequencies. Tesla's records show two interesting facts: his original plans were for a tower 3X larger than the one he built. When cost estimates came in, he had to scale way back. So perhaps his original device would have operated below 20KHz. Second, one of his diagrams shows a spark gap placed in series with the main terminal. This would have the effect of pulsing the entire system at selectable low frequency. With an \"Extra Gap\" in line, the Earth itself becomes the main resonator, while the Wardenclyffe tower and it's Extra Gap is just a power supply. ",
"Brief testing",
" shows that this does work, although it's somewhat backwards from a normal Tesla coil where a 60Hz frequency power supply is used to generate hundreds of KHz output."
] |
[
"It wasn't meant as a power generator. ",
"Check this out"
] |
[
"I can answer this one!",
"Some people erroneously think it was just a simple high-voltage radio antenna. Basically a normal radio antenna but with power levels so high that a receiving antenna could generate useful power. You know how crystal radios can operate without a battery? Something like that, but scaled up.",
"That is, however, only part of the story. Tesla was much smarter than that. He reasoned that since the ground conducts electricity, the whole Earth must act like a giant capacitor. We now know that he was right.",
"Of course, the actual picture is a little more complicated, but Tesla realized that you could 'charge' the Earth system much like a giant battery. Resonant effects between distant transformers, coupled with the inherent capacitance of the Earth, would allow reasonably efficient wireless transfer of energy, with little escaping to space.",
"His initial experiments proved that this concept would work. He was able to transmit enough energy to power a light bulb over a distance of many miles.",
"However, no one knows the exact mathematical details of his approach; Tesla had a habit of being secretive and erratic and placing more emphasis on showing off than giving out concrete information (which is totally understandable given the technological atmosphere of the time and his rivalries with Edison). That is why there is so much mystique around this project.",
"At any rate, you can imagine that bathing the Earth in huge amounts of EM flux would be problematic. It would absolutely kill the idea of independent radio stations, for one thing. If I were to speculate, I'd say today's sensitive electronics would burn out in an instant if his World Wireless system had been implemented.",
"There's no doubt that he was a genius, of course. One of Tesla's inventions that I really love was his 'death-ray'. Aside from speculation and guesswork, though, it's hard to say what it really was. Some think it was an early version of the modern electron-beam welder: ",
"http://en.wikipedia.org/wiki/Electron_beam_welding",
" ."
] |
[
"What is the heaviest a single particle can be?"
] |
[
false
] | null |
[
"We don't know."
] |
[
"Wouldn't there be some sort of limit where it would collapse in on itself? "
] |
[
"There could be a limit, but we don't know what it would be."
] |
[
"Animals camouflage by mimicking their environment, but that’s in our visible spectrum. Does camouflage of certain creatures extend outside of our visible spectrum, and if so, how far?"
] |
[
false
] |
Follow up, are there camouflaged creatures that we don’t perceive as such, but are fully camouflaged in ultraviolet or infrared or even further?
|
[
"The question then would be, do predators rely on other forms of light, such as heat, to \"see\" prey? Snakes I believe can sense heat with their tongues. I'm sure most predators use smell to some extent to enhance their vison."
] |
[
"Snakes actually have a special organ that detects heat. Its called a pit organ."
] |
[
"Hence pit vipers?"
] |
[
"With mild temps and lack of snow this winter will there be an abnormal number of bugs in the spring?"
] |
[
false
] |
With the unseasonably warm temperatures and lack of snow in many places in the USA will that result in an abnormally high number of insects in the spring and summer?
|
[
"i dont know if harmony is the right word here. i would say that there is an equilibrium that nature is attempting to reach at all times. fluctuations in biological systems keep that balance slightly off which is actually good because it keeps the system running. think about it like a pendulum: if it is at equilibrium with gravity, then the clock does not tell time."
] |
[
"In general insects do best with stable winter temps. If the temperature fluctuates wildly during the season some insects may prematurely emerge from hibernation. Many insects have evolved protection against even the worst of winters. These protections (see: ",
"http://en.wikipedia.org/wiki/Insect_winter_ecology",
") are of little use if the fluctuating temperature rouses them early before stable food sources have emerged. Of course, many of their hibernating predators will also suffer so its difficult to simply answer with a straight up \"yes\" or \"no.\" (For the dangers of a warm winter, see: ",
"http://www.cbc.ca/news/technology/story/2007/01/05/hibernate.html",
")",
": It depends."
] |
[
"Does nature not have mechanisms to tune itself to create an overall harmony? For example, if there's a decline in the numbers of some species in one season (in this case, the one that prefers warmer winters), that creates comfortable environment for other species to thrive (like the lack of natural enemy or abundance of some type of food and so on). And in the next season(s) the situation turns around. I often notice there's - for instance - significantly less/more bees, while no flies or butterflies than the year before. I guess one factor contributing to it might be the temperatures in the winter but there's plenty of these factors I presume?",
"Edit: Everyone downvotes this question but nobody cares to say what's wrong with it? I might have used the wrong words but it was supposed to be a followup question using my current thought process, not layman speculation."
] |
[
"Why is Ebola so lethal? Does it have the potential to wipe out a significant population of the planet?"
] |
[
false
] |
Became curious of the disease, as Ebola is now spreading in Nigeria.
|
[
"In short, Ebola preferentially infects endothelial cells and is highly cytotoxic to those cells. So once it is in the bloodstream, it damages the endothelial cells that line blood vessels, causing circulatory system damage (or failure) causing the characteristic rashes, bruising and bleeding. As of now, Ebola is not easily spread. Most infected victims are family members, health care workers and others who have had close personal contact with the victims, such that they had contact with body fluids. However, now that the virus is spreading and is in contact with large population centers, it remains possible that natural selection will give rise to strains that can be transmitted a little more easily. It is not likely to ever become as easily transmitted as, say, influenza. Or if it does, it is likely to lose virulence. The bottom line: A deadly (Black Death-like)global Ebola pandemic is extremely unlikely."
] |
[
"Ebola is almost ",
" lethal to wipe out a significant part of the planet.",
"The epidemiological risk of an infection is determined by multiple factors - those most pertinent to Ebola are transmissibility and infective period.",
"Transmissibility is a composite of multiple different factors including vectors through which an infection can spread and the virulence of the infection, expressed in terms of R",
" - which is the number of subsequent cases each individual case generates. It follows then that where R",
" > 1, an epidemic is possible, and where R",
" < 1, the infection cannot sustain itself.",
"Specifically regarding Ebola, this historically has varied from 1.3 to 2.8 (",
"here",
" and ",
"here",
"), so historical (and the current) outbreak are indeed epidemics, but to becomes genuine pandemics they have to move beyond their immediate locality, and this is where Ebola becomes somewhat self defeating.",
"The incubation period of Ebola varies between 2 and 21 days, around 12 is most common. It's unknown at which stage during this period the infected individual becomes infectious themselves, but ",
"the risk of transmitting the disease before the onset of symptoms appears small",
".",
"Consider therefore that the onset of symptoms with Ebola is sudden and severe - with widespread pain, diarrhoea, dehydration and fever - all factors which mitigate against travel. Add to this the confirmed vectors for infection - direct contact with infected bodily fluids - and you begin to understand why it doesn't tear around the world in the same way a flu might.",
"TL:DR - People infected with the virus do not typically infect others until the onset of symptoms. The symptoms ",
" sufficiently severe to prevent people moving far afield. The virus can only spread by direct contact with infected material. Ebola appears and devastates a local community, but the disease pattern itself typically prevents its spreading further afield before it burns itself out."
] |
[
"In biology, one learns to never say absolute words like \"impossible\" or \"never\" or \"always\". However, evolution of airborne transmission of Ebola is extremely unlikely. While there are many enveloped viruses that infect humans (HIV, Hepatitis C, influenza, Ebola, West Nile and many more), efficient airborne transmission occurs only in a few such as influenza, and this because influenza has evolved specifically to infect the airways. I do research with enveloped viruses (not Ebola!). I am not at all concerned with airborne Ebola. It isn't going to happen (probably). "
] |
[
"I have an old AM/FM clock radio sitting on my office desk. Does it consume less energy when the radio is turned off compared to when it's left on with the volume all the way down?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"Devices powered on draw power",
"The answer can be found with a Google/Wiki search. Please start there and come back with a more specific question."
] |
[
"Sure, there's a difference. There's four major elements that draw power when you turn it on:",
"the power supply. Since no power supply is 100% efficient, it will leak some power, mostly in the form of heat. Usually accounts ~5-10% of power consumption (in losses).",
"the signal processing, all the way from the antenna to the amplifier, is another ~5-15%. Whether you use passive components (resistor, diodes, etc) or integrated circuits, they will also leak some power as heat besides the little power needed for processing.",
"the amplifier & output. The most power-hungry of the bunch, usually 50-80% of the total consumption, depending on the construction of your device. If you turn the volume to zero, a good design would have the amplifier not draw any power at all, but I don't know how rare this may be.",
"A typical alarm clock for your bedside without flashy features like WiFi etc. may be consuming ~2W of power in total."
] |
[
"No problem. You'll still find some more accurate information out there though."
] |
[
"Are the different regions of the brain physiologically different?"
] |
[
false
] |
[deleted]
|
[
"The answer would be \"both\": the cells are different, and the ways they are connected to each other are different.",
"Even in the cortex (you know, ",
"that wrinkled walnut-looking stuff",
" that you first imagine when you think about human brain): even in the cortex, although it looks pretty uniform at the first glance, cells in different regions are actually somewhat different. ",
"Look at this picture",
": motor cortex has to send signals down to the body, so it has lots of large cells that can grow long \"cables\" running down through the spinal cord. The visual cortex, on the contrary, receives information, and has to have lots of small cells to quickly process it. ",
"And if you go to other brain regions (you mentioned brain stem, for example), the differences only get greater. ",
"A cell in the cerebellum",
" - the part you use to learn and perform fine movements, would be very different from ",
"cells you use to recognize different smells",
". No wonder, right?",
"Also, on top of that, two cells that are similar in shape, can actually function pretty differently depending on their molecular machinery. They would react to different chemicals, release different chemicals, transmit electric signals differently... And indeed they would be different in different parts of the brain. Those cells in the brainstem that are responsible for your breathing have chemical sensors to detect that you haven't inhaled for a while, and it's about time to do it. Cells in a small nucleus in another part of the brain don't care about your breathing, but change their properties twice a day, there and back, controlling the way you get sleepy at night, and then get awake during the day. ",
"Yet at the same time, fundamentally, these are all neural cells, and they share lots of basic properties between them. In most cases, the most important thing is that they are connected differently. But then, on top of that, they are often fine-tuned to support different functions. Makes sense?"
] |
[
"There is huge anatomic variation between neurons, as discovered by Golgi in using a silver based stain which completely fills a random population of cells. Some may have small soma (10 microns) with few projections, while others may be have large cell bodies (50 microns) with highly branching dendritic arbor. Other neurons may send extremely long axons, potentially the length of the human body for dorsal root ganglion neurons. In addition the visible differences observed via microscopy, there are also huge differences between cells in the nature of the neurotransmitters that the cell is able to produce, among other molecular differences. There is also a lot of variation between the types of proteins that different cells possess. Because each of these cells serve a very specific purpose, the types of cell which make up a certain brain region could give some clues about the function of that region. ",
"Different parts of the brain may contain unique types of neurons. For example, the cerebellum, contains extremely large cells called the Purkinje cells, which send projections in a single plane. Also, organization of cells is one way to differentiate parts of the brain, as regions like the cortex and hippocampus organize cells neatly in layers or in a track, however the region of the brain called the striatum (implicated in movement disorders and addiction) is a jumble of a handful of different cell types with no clearly defined organization.",
"Many parts of the brain contain different parts of neurons, as well. The brain stem, as you mentioned, contains very few somata, but is basically a dense bundle of heavily myelinated axons - the parts of the neuron responsible for transmission of electrical signals. These tracts of myelinated axons, also called \"white matter,\" are found throughout the brain.",
"That being said, there are some similarities between neurons. All of them have a electrochemical gradient which separates ions between the inside and outside of the cell (even with this, however, there is variation between cells - some cells rest at -90mV, while others can rest at -40mV). Neurons are able to communicate with other neurons using either chemical signals or electrical signals, but this property is not unique to neurons - many cells release factors that transmit information between cells, and pacemaker cells in the heart communicate with other heart cells using electrical signals."
] |
[
"So is it individual cells performing functions or are they acting as a group and functioning altogether? Is there a very distinct line where one type of cells end and another type begins? "
] |
[
"Why do people have talents since birth?"
] |
[
false
] |
You know kids who have mad talent skills in art, singing, dancing, etc. Is talent transmitted somehow genetically?
|
[
"nobody has an answer i guess..."
] |
[
"These talents are not from birth, although i do understand the point your making, i believe these children that are really talented from a very young age have simply practiced these skills very regularly (usually due to parenting)\nI'm sure there is someone out there who could give you a better answer with some sources though"
] |
[
"yeah, that's what i'm saying... \nwhy some people can easily compose songs, while other can't, or draw paintings so easily, and so on.. i mean yeah, you can teach yourself, but you know this saying - \"i guess i just don't have the talent\"...\nso what's \"talent\"?"
] |
[
"Any doctors/medical students here? Why would just one leg feel tired for no apparent reason while laying in bed?"
] |
[
false
] |
I'm 25 and smoke a lot and never exercise but I'm starting to change that. My diet sucks but I'm not overweight (actually underweight). Anyway, I'm just now starting to exercise again after years of inactivity so that's not the reason it feels tired, it happened before I started again. I'll just be lying in bed and it will feel tired almost like I just exercised that leg (no burning or warmth, but close to that feeling). According to it doesn't sound at all like restless leg syndrome.
|
[
"That's pretty nonspecific...",
"How long has this been occurring?",
"Is it the whole leg, above the knee, below the knee, or just a specific portion?",
"You say \"tired\" or \"just exercised\"... Are talking as if it's totally spent, or is it more of a tightness/aching, or something else?",
"Basically, all the details you can give; \"weird leg feeling\" is about as helpful as \"some kind of pain but not really in my abdomen somewhere\" - it's like waving your hand at a globe and saying \"I live over there\"."
] |
[
"It's hard to explain. It's pretty much the entire leg. It feels almost totally spent, but not completely. No tightness or aching. No burning (like from lactic acid buildup after working out or whatever it is). Just like it's almost entirely spent and it's a little hard to move.",
"It doesn't feel heavy or anything. Just spent.",
"Most of the time it's my left leg, but I've had it happen to my right leg twice."
] |
[
"Are you describing weakness?"
] |
[
"With the billions of gallons of fossil fuel, can we glean any interesting paleontological knowledge from them? Or is it all too “gobbled up”?"
] |
[
false
] | null |
[
"Paleontology is more of a coal thing. If you look at coal under a microscope you can often still see the details of long-dead land plants and grains of pollen. Sometimes there are larger fossils, and sometimes animals. Many coal towns have fossils on display as trophies.",
"As a result of coal mining and coal research there's a lot of bizarrely specific and rich knowledge about the eras and places when significant amounts of coal was being laid down. Paleontologists have named this era the carboniferous, a time dominated by bizarre horsetail relative trees called lycopods that looked like they were designed by Dr. Seuss, alongside dragonflies the size of hawks and primitive tetrapods from before mammals and reptiles diverged.",
"There are biomarkers in oil, but it was mostly dead oceanic algae. Not much of the original microbes remain. Oil companies still give a few biologists jobs, but the microbes they're most financially interested in are oil-eating scavengers who came much later."
] |
[
"Wow... thanks so much! I learned a lot."
] |
[
"To add: if you happen to live in coal country, you can often find some really cool plant fossils in mine tailings. I'm most familiar with the Mazon Creek / Braidwood area southwest of Chicago, where there are organized tours and areas with public access."
] |
[
"Why does general anesthesia not stop the heart?"
] |
[
false
] |
I just recently learned (well, realized -- it makes sense, I just never thought about it) that people stop breathing when under general anesthesia. Why does the same procedure not stop the heart?
|
[
"I must correct you.",
"Patients do not all receive paralytic agents. They are only used when necessary for the surgery or for the method of ventilation. ",
"I see this stated quite often for some reason. ",
"Furthermore it is incorrect to state that the heart is unaffected. Most general anaesthetics depress cardiac function too - it's how much they depress them in a particular individual that is important. ",
"It is also incorrect to state that the heart does not receive signals from the brain in order to beat. Heart rate is controlled by a balance of the sympathetic and parasympathetic nervous systems and both of these receive their signals from the brain. "
] |
[
"The ",
"mechanism of general anesthesia",
" is pretty mysterious - it is known that centrally acting anesthetics inhibit neuron firing in certain parts of the brain. Some of these do have a respiratory depressing effect in the brain, but most of the reason why the patient cannot breathe under general is the use of paralytics. General anesthesia lowers consciousness, but you know that consciousness is not required for movement - this could be disastrous in a surgical scenario. So, patients are also given paralytics that act at the nictonic receptors of skeletal muscle to block nerves from telling muscle to contract. The muscles of respiration (i.e. diaphragm) have these receptors so your breathing is paralyzed as well as your other voluntary muscles - arms, legs, etc. ",
"The heart, however, is a different story. While it does receive outside innervation from the autonomic nervous system, it also has its own internal conduction system that is controlled by pacemaker cells in the sinoatrial node. Paralytics that stop respiration do not stop the heart because the heart does not rely upon signals from your brain to beat. "
] |
[
"Yes, this is exactly the case. It is important to remember that in true brain death the patient also cannot breathe for themselves - without a ventilator, the heart muscle will quickly die as the muscle is very sensitive to anaerobic conditions and then the patient will also be dead by cardiopulmonary criteria as well.",
"This is different from a ",
"persistent vegetative state",
" where there is no cortical activity (read: conscious thought, subjective experience, pain) but the brain stem is still functioning well enough to keep the patient breathing without a respirator. PVS is a matter of opinion, but to me it's also brain death as whatever part of your brain that makes you ",
" is no longer there. There might be breathing and a heartbeat but that's hardly all there is to life. Recovery of consciousness after 3 months is incredibly rare in these cases, and recovery of function (read: personality, communication, learning) is even rarer. (Edit: in case you're curious, fewer than .5% of people regained consciousness between 6-12 months after entering the PVS)"
] |
[
"Why are sexual side effects so common with antidepressants?"
] |
[
false
] |
My app won't let me submit without adding text, but see the title.
|
[
"Currently it isn't really known why",
"It also seems that the prevalence of these symptoms isn't very well known either. ",
"Initial studies found that such side effects were reported in less than 10% of patients. When doctors have specifically asked about treatment-emergent sexual difficulties, some have found that they are present in up to 60%[6] of patients.",
"This article talks about the sexual side-effects of certain antidepressants, though it seems clear more studies need to be done on these",
"http://apt.rcpsych.org/content/9/3/202.full"
] |
[
"This effect is multifactorial and not well understood. In general, it is not surprising that drugs which affect the way your neurons communicate could have sexual side effects given the complex interplay between your central and peripheral nervous system in arousal, erection, ejaculation/orgasm, etc., though this does seem particularly widespread in this group of medications. ",
"In general, the type of dysfunction and mechanism behind it is related to the class of medications we are talking about.",
"Tricyclic antidepressants act on peripheral (not in the brain or spine) signaling pathways. This includes having an anticholinergic effect (acetylcholine which is the cholinergic that is being anti'd is involved in sustaining an erection among other things). ",
"MAOIs are linked with orgasmic dysfunction but the mechanism behind this is poorly understood. ",
"SSRIs are associated with sexual dysfunction in ~50% of users. This is possibly as a result of the role serotonin plays in the spinal cord during the process of establishing an erection. It may also lower serum testosterone levels. ",
"It should be noted that these effects are not universal. Trazadone is associated with increased penile hardness at night and has even been implicated in a few cases of priapism (sustained erection, painful, bad). Buprion is also usually touted as having few sexual side effects. ",
"Animal models have been used to try to explain these side effects but many of the most relevant studies are still from the 80s and 90s, so progress seems slow. ",
"Additionally, people with psychologic disorders can be at a higher risk of sexual dysfunction independent of their medications.",
"I know that I have not adequately answered your question as to why in the most general sense, but I hope this provides a starting point for discussion."
] |
[
"Serotonin inhibits dopamine. Dopamine is the reward neurotransmitter, so an increase in serotonin will decrease almost every part of the sexual response cycle.",
"From Our Sexuality Eleventh Edition by Robert Crooks and Karla Baur",
"In contrast to the facilitator impact of dopamine on sexual behavior, the neurotransmitter serotonin appears to inhibit sexual activity. Male ejaculation causes a release of the serotonin in both the MPOA and the lateral hypothalamus, an area on the sides of the hypothalamus. This released serotonin temporarily reduces sex drive and behavior by inhibiting the release of dopamine.... Humans who suffer from depression are often provided antidepressant medications called selective serotonin reuptake inhibitors (SSRIs). These drugs, whose effect is to increase serotonin levels in the brain, often interfere with libido and sexual response."
] |
[
"There are reports of a tale of an Inuk making a knife out of shit and spit in deeply sub-zero temperatures and using it to butcher a dog, build a sleigh and flee. Is such a knife mechanically possible or is it a tall tale?"
] |
[
false
] |
link to the apocryphal tale here: Previous discussion of this story on TIL: I underline that the tale is from Inuit oral history, so it may have grown in the telling. Could such a knife hold an edge sufficient to kill, skin and butcher a dog? Could it be mechanically resilient enough to do the job the tale claims it did? Are the faeces necessary? Would not simply making a similar tool out of ice/snow and spit be just as effective (if true)?
|
[
"Shear rheological properties of fresh human faeces with different moisture content\n",
"http://www.scielo.org.za/pdf/wsa/v40n2/09.pdf"
] |
[
"Solidification of water that has been mixed with a fibrous component will create a ",
" (e.g., like fiberglass or concrete), with emergent material properties that differ from those of its constituents.",
"For example, ",
"Pykrete",
" is a mixture of ice and sawdust, which is much stronger (and more resistant to melting) than pure ice.",
"(edit:grammar)"
] |
[
"I was under the impression that he would have lived mainly off of seal meat, and blubber. Would that provide enough fiber to create a good composite, or would be more like frozen mud?"
] |
[
"When a wheel or anything circular spins really fast, why does it sometimes look like its spinning backwards and then spin forwards again?"
] |
[
false
] |
Video for reference edit: Thankyou Everyone for your responses, special shout out to for his link of a super helpful video with examples of what I'm trying to talk about
|
[
"This is known as the wagon-wheel effect. It is most commonly observed when viewing a video recording of a spinning wheel. In this case, it is a result of a strobe-like effect caused by the fact that a video is actually made up of a series of discrete frames.",
"It can also happen in real life viewing, though. In this case, it's not always clear what the cause might be. One known (and reproducible) cause is subtle vibration of the eyes. This is why the effect is most often noticed when viewing a rotating wheel from a moving vehicle, such as a car. The engine imparts a subtle vibration to a viewer inside the car, which then causes the effect when a rotating object outside of the vehicle is viewed.",
"It can also happen when perfectly stationary. In this case, the cause is unknown. There have been some proposals related to neural cyclic sympathy, but it's not conclusive. We know that the effect can happen after a rotating object is viewed continuously for a while, but the exact cause is still debated."
] |
[
"Is it possible that the frequency of AC street lamps cause us to view the wagon-wheel effect at night in a manner similar to how it's created in videos? I had always just assumed that was the case."
] |
[
"http://www.vinylengine.com/strobe-discs.shtml",
"Yes. Check out turntable strobe discs, a gadget from the days of vinyl.",
"The same effect can be very dangerous in workshops with rotating macinery. Lighting is typically powered from 2 or more phases of the electric supply, to minimize the effect. Circular saws (table saws) in particular can sometimes appear stationary under electric lights when still spinning."
] |
[
"Could you take a look at this link and tell me why he's wrong? (re: Darwinism and evolution)"
] |
[
false
] |
I'm an atheist, and I believe in evolution. However, because I'm not knowledgeable about the specifics of evolutionary biology, the fossil record, etc., I'm not good at evaluating or disputing claims by people on the fringe. I found this link by typing into Google, "Did humans have enough time to evolve." I was seeking a discussion on whether humans had enough time to evolve to such a high degree of sophistication, because intuitively, even millions upon millions of years just doesn't seem like enough time. However, I know that science isn't about intuition -- it's about facts. I'm not a troll or a secret supporter of this guy. I looked at another link of his and he's talking about alien intervention, kind of like that Discovery Channel show, so I realize he's on the fringe, and possibly has zero credibility. But regardless, are some of his points -- such as about the fossil record -- valid?
|
[
"False dichotomy.",
"Straw man.",
"Ditto. These aren't actually separate concepts in evolutionary biology, they're concepts made up by creationists who don't understand biology.",
"There's no 'missing link'",
"Did he just seriously claim that hominid fossils are actually bigfoot?",
"Yes he did.",
"He keeps putting \"prehuman\" in quotes despite the fact that it's not a term used in anthropology or biology.",
"I'm not sure what this guy's point is.",
"Seriously, nothing he writes is actually based on biology. He's just putting ",
" to make them look scary. You can't really confront something that isn't describing evolution with correct statements about evolution. It would be like trying to explain CPR to someone who starts off with \"And yet the ",
" insist on CPR despite the fact that our two hearts function well independently of each other.\"",
"edit: the numbers in my list might not match up with the numbers on the webpage. Blame reddit."
] |
[
"There's no 'missing link'",
"I like the graph, but I'm surprised to see the Successful Black Man meme pic :)"
] |
[
"I'd recommend reading an ",
" book on the subject. Dawkins has some good ones, like The Selfish Gene or The Greatest Show on Earth. Well, I've heard they're good. I haven't read them."
] |
[
"Why does Bismuth appear the way it does?"
] |
[
false
] |
Cross-post from , but why does bismuth look like ? I'm pretty sure it's gotta do with the structure of it and how light get's reflected/scattered, but what exactly would that structure "look like"?
|
[
"The colours you see are actually caused by an ",
"iridescent",
" oxide layer on the surface of the Bismuth. ",
"Edit: formatting "
] |
[
"Right. The very thin layer of oxide on the surface acts just like a thin layer of oil on a puddle. The thickness of the layer is about one-quarter of the wavelength of visible light, and that leads to interference of different colors depending on the exact thickness and angle you look at it."
] |
[
"I'm trying to use it in a painting/sculpture. I had a tiny piece of it and I was going to either embed it directly or take a tiny chisel to it or something. Unfortunately I cannot locate the bismuth, though I still have my other rocks I bought. I haven't a way to get back to that shop right noiw, so it's still on hold."
] |
[
"What is happening to the coke *soda*?"
] |
[
false
] |
What is happening to the coke after milk is being added to it? is the fat being bonded with the syrup? Or is the bilk bonding with the water and the other ingredients being heavier being pushed the the bottom. Kinda perplexed at the moment. hopefully we can get a chemist in here.
|
[
"What is happening is ,the fat in milk in in balls (casein)where the outside is hydrophillic and the inside is hydrophobic. Coke has a low pH level. When the milk is put in the low pH environment, the hydrophillic parts of the casein molecule get removed and dissolved, the hydrophobic fat molecules want to limit exposure to water so they clump together and then fall to the bottom. It is the concept of how cheese and yogurt is made. Bacteria convert lactose to lactic acid which causes coagulation. Then you add rennet to further coagulate to make cheese."
] |
[
"I don't know for sure, but I would guess that the artificial coloring bonds to the fat globs, pulling all the color to the bottom"
] |
[
"What is causing the clarifying effect in the soda though?"
] |
[
"Which transfers more heat to the mug, microwaving a 1/2 cup of water for a minute, or microwaving 1 cup for a minute?"
] |
[
false
] |
When I make coffee, I usually like to preheat the mug (to keep the coffee warm for longer) by filling it about halfway with water and microwaving it for a minute. This can usually raise the temperature of the water in the mug to about 85-90C, and the mug absorbs some of that heat. Would I be better off microwaving a full mug? The water's temperature would be far lower, which means a smaller heat gradient, but there would be more surface area for the heat transfer to occur.
|
[
"It is the other way around. The amount of heat your water in the mug receives, depends on your microwave's MHz radiation. The higher the radiation intensity is, the faster water heats up.",
"However, heat transfer rate remains constant with more or less water. Since a microwave's emissivity of electromagnetic waves (MHz) does not increase or decrease based on the volume of what's in, you will get the same thermal energy absorbed with less or more water.",
"But here is the trick, if you fill up the mug with water, the heat generated from your microwave will spread across water surface and temperature will not rise significantly due to the higher volume of water heat has to reach (emit to) and water to absorb. \nSo the the best way to heat up a mug as fast as possible is to splash water on both, inner and outer surfaces with little water filled in.",
"Read about Stefan-Boltzmann law of radiation. It states that ",
", which stands for emissivity, is a constant for both emissive and absorbent body. ",
"e = 1, emissive\ne = 0, absorbent \n",
"Which ever body generates heat (or simply has higher temperature than its counterpart) becomes emissive and the amount of energy transferred will remain the same as long as there is no change in either the type of material of either bodies or their surroundings.",
"A good read about this topic is the first law of Thermodynamics, specifically the third type of heat/heat transfer of energy through electromagnetic waves (radiation). ",
"First Law of Thermodynamics",
"Emissivity"
] |
[
"If you could get a full mug also to 80-90 degrees in the same time, then the mug would be hotter in that case. If instead the full mug only got to 60 degrees, the mug would be cooler.",
"Depends on your microwave power settings. In general, if you put more of the hot thing in the mug, the mug will heat up faster. But since you're heating the water inside the mug, it's more a question of the microwave's output.",
"Microwaves are designed specifically to heat water, not ceramic--so in general more volume of water means better heat capture from the microwave, but this can be offset by a larger thermal mass (more energy required to heat the water to the same temperature)."
] |
[
"This question really got me thinking about transfer of energy. In theory I would have thought the cup would heat up faster without the water because there are less particles in the cup than there would be with the cup and the water so the particles with just the cup would be absorbing all of the microwave energy whereas the cup and water would require more energy to be heated equally.",
"BUT I was also thinking about current state of matter of the water vs. the cup and how it takes less energy for the water to boil and then transfer the heat than it would for the cup since it's a solid. BUT then I thought that it might be the type of energy transfer taking place. ",
"Microwaves travel at a specific rate and maybe the water is more susceptible to capturing that energy where as the cup is less fluid, so it likely doesn't capture as much of the energy. All the energy is doing is vibrating the particles to create heat...it's possibly more difficult for the cup to capture the microwave energy because it (the cup) is less fluid and in a solid state.",
"It's the same principle as when you heat up food in the microwave, the portion of the dish that has food on it gets hot because of conduction. The energy is literally transferred from the food to the dish, but the other parts of the plate remain cool. ",
"TL:DR I don't know. But it's a great question and you really made me think about it, so thanks for that! "
] |
[
"Do humans emit X-rays from blackbody radiation?"
] |
[
false
] |
Infrared is the most well-known light emitted by humans, but what about the other frequencies of light? It seems by that there should be some–albeit a tiny amount–of every frequency emitted, but is this actually the case?
|
[
"I can't do the math right now, but you could calculate the energy emitted per second at your chosen frequency and then divide by the energy of a photon of that frequency; that should give an estimate of the rate at which photons are emitted.",
"Edit: I did the math. Taking the range of frequencies to be from 10",
" Hz to 1.1*10",
" Hz, I get 3*10",
" photons per square meter per second. To contrast, the age of the universe is a measly 10",
" seconds. I can say with absolute confidence that no living organism has ever emitted or will ever emit an x-ray photon."
] |
[
"Theoretically yes, but the intensity would be infinitessimally low. It would require a multiple order anti-Stokes shift where multiple atoms simultaneously combine their energy states and then release that energy as a single photon. The cross section of such an interaction is extremely tiny which leads to its extremely low probability of occuring."
] |
[
"No, I didn't, but it's not gonna matter. What is gonna be, 100 orders of magnitude? Schroeder talks in his thermo book about very large numbers: you can multiply them by ordinary numbers and they stay about the same."
] |
[
"When did people realize that a whip crack was breaking the sound barrier? What did people think was causing that sound before then?"
] |
[
false
] | null |
[
"It was hypothesised in 1905 and proven by work in 1927 and 1958, including using photographic techniques to reveal the shockwave in the air (a ",
" ). More recently high-speed photography has allowed the whip's speed to be directly measured.",
"http://mathfaculty.fullerton.edu/tmcmillen/papers/2002-PRL(whip).pdf",
"Before then, I think it was mostly presumed the noise was from parts of the whip impacting each other, but I'm not sure."
] |
[
"In 1677, Sir Francis North published ",
"A Philosophical Essay on Musick",
", where he hypothesized that sound is transmitted by vibration or force, and that a whipcrack was caused by air molecules rushing in to refill a vacuum. ",
"By this time, a rudimentary form of atomic theory was spreading in acceptance, and the first microscopes had proven much of the world existed beyond the immediate comprehension of our senses. North begins from the assumption the \"air we breath in to be a mixture of divers minute bodies which are of different sorts and sizes, though all of them are so small as to escape our senses.\" He notes the elasticity of air, and posits that sound moves through air as a cascade of these small colliding bodies. In short, he has a working theory of sound moving through air as an oscillation, and deal specifically with whips when speaking about a sudden pulse of sound ",
"when the Air is divided with any sudden force, as by the end of a Whip having all the motion of the Whip contract∣ed in it, and by a sudden turn throwing off the Air; by ascension, as in Thunder and Guns; or by any impression of force carrying it where other Air cannot so forcibly follow, as upon compressing of Air in a bladder till it breaks...",
"He goes further to state ",
"A Tone is the repetition of Cracks or Pulses in equal spaces of time so quick that the interstices or intervals are not perceptible to sense. The more quick the Pulses are, the more acute the ",
" is. Where the intervals are not equal, nor in musical proportion, the sound is not in ",
" but an irregular noise.",
"In 1687, North's contemporary Isaac Newton measured the speed of sound (although he was short by about 15 percent), but the first recorded attempt was made in 1630 by Marin Mersenne (who himself was about 15 percent high). "
] |
[
"We had detected sonic booms earlier in whips and rockets, but it became an actual problem when dive bombers shortly before and during WWII got fast enough for their props to break the sound barrier during steep dives.",
"Since the propeller tips are only briefly above the sound barrier, this creates a serious vibration problem where each tip creates a sonic boom as it reaches the \"fast\" side. At high RPMs, you're generating multiple shocks per second and the propellers were shattering."
] |
[
"How do we measure extremely low or extremely high temperatures?"
] |
[
false
] |
Normal thermometers are using the expansion of fluids but at extreme low temperatures, most fluids become solid and at extremely high temperatures, they will vaporize. Does it has anything to do with the different energy levels of the particles? And if so, how do we measure distant objects like the sun or the Pluto? Edit: Far objects are measured by their thermal radiation. Cold objects are explained . Thanks for the answers!
|
[
"Let me speak to how extremely cold temperatures are measured.\nI'm assuming you mean cold things like Bose-Einstein Condensates and things as cold as the ",
"current record",
" of 0.000 000 000 1 degrees above the absolute zero.",
" ",
"Temperature is a measure of the energy content of matter. The energy then relates to the motion of the atoms that constitute that matter. The lower the temperature, the lower the energy, the slower the atoms. Matter brought to very low temperatures are confined in a potential, meaning they are trapped in a small space by a central force. The spatial extent of the atoms in this centralized potential relates to their temperature.",
" ",
"Take for example the atmosphere on earth, which is about 10 km thick. Ten kilometers is how far atoms at the temperature distribution of our atmosphere can move against the confining gravitational force. If the temperature of the air were ten times smaller the atmosphere would be only 1 km thick.",
" ",
"This same principal is used to measure the temperature of ultra-cold systems in magnetic traps. The size of the chilled atomic cloud is determined by illuminating the cloud with laser light, which is strongly absorbed by the atoms, and they cast a shadow. With the help of several lenses, the shadow is imaged onto an electronic sensor similar to those in digital cameras. Since the magnetic fields are precisely known, the size of the cloud is an absolute measure for the atoms' energy and temperature. This of course encounters a quantum problem since measuring the temperature increases the temperature.",
" ",
"Another technique to determine ultra-cold temperature is to measure the kinetic energy of the atoms. For that, the magnetic trap is suddenly switched off by switching off the current through the magnet coils. In the absence of magnetic forces, the atoms simply fly away, and the cloud expands ballistically. The cloud size increases with time, and this increase is a direct observation of the velocity of the atoms and therefore their temperature. This approach has the benefit of inferring what the temperature was before you interacted with the matter.",
" ",
"You can read more and see pictures of atomic cloud shadows of Bose-Einstein Condensates that were used to measure their temperature ",
"here",
". Actually, if you just Google \"Bose-Einstein Condensates\" and look at the images, they are dominated by these types of cloud snapshots. Hopefully these images make intuitive sense now."
] |
[
"The basic problem encountered with measuring temperatures at both extreme low and extreme high limits is the requirement to link the measurement back to the unit definition of the kelvin. That means something has to be referenced to a measurement at the ",
"water triple point",
", or 273.16 K. In practice, the extreme temperatures are estimated by some fundamental equation that involves the energy factor kT , the product of temperature T with the ",
"Boltzmann constant k",
", which provides the link back to the definition of the kelvin. ",
"For the hottest temperatures like those of blue stars, optical measurements of the ",
"Black-body Radiation",
" spectrum, governed by the kT factor via ",
"Planck's Law",
", provides the means of estimating the temperature.",
"For the coldest laboratory temperatures, as in those achieved in laser-cooled atomic traps, ",
"u/phaseoptics",
"' post explains the concepts quite well. In that case the factor kT governs the distribution of energies in the Bose-Einstein (BE) condensate according to the ",
"BE statistical distribution",
". ",
"In the case of cold bulk matter or bulk systems of nuclear spins, such as the temperatures achieved by helium-3 dilution refrigeration or adiabatic demagnetization refrigeration, there are ",
"many techniques",
" that are combined over various temperature ranges. These include the use magnetic thermometers that are based on the ",
"Curie law of paramagnetic materials",
" via measurements of magnetic susceptibility, again governed by a Boltzmann factor of 1/kT ."
] |
[
"For objects a long way away (or objects so hot that no material could survive) I believe it's almost exclusively done by measuring thermal radiation, as already mentioned. You obviously already know about fluid-expansion thermometers. Some methods of temperature measurement include: ",
"resistance thermometers",
" (the resistance of a particular conductive material changes with temperature, and thus measuring the resistance can be used to measure the temperature), ",
"thermocouples",
" (when two different conductive materials are joined, a voltage is created that varies with temperature, and measuring this voltage can be used to measure temperature), ",
"pyrometers",
" (these are just specialized devices for measuring thermal radiation and converting it to a temperature measurement), and ",
"Langmuir probes",
" (electrodes used to determine characteristics of plasma, which can include the temperature of the plasma). "
] |
[
"Why do teeth have nerves?"
] |
[
false
] |
If they are only needed to help chew food, and we do not really feel anything through them, why then?
|
[
"You need teeth. Nerves preserve teeth. \n* If teeth had no nerves, you'd chomp on unchompable things -- \"me eat rock\" -- until your teeth wore down, broke, and fell out. Then you'd die and not have children whose teeth have no nerves.\n* If your teeth have nerves, you're a bit more careful about your teeth -- \"ow, me NO eat rock\" -- and you live a healthy life and get laid and have children whose teeth have nerves."
] |
[
"Take care of your teeth and you'll get laid. So many still don't understand this concept."
] |
[
"For the same reason we have nerves anywhere else in the body: to signal, through pain, when something is wrong (infection, trauma, etc.) It used to be thought that people with leprosy had super human strength. But one day a doctor who lived in a leper colony to care for them asked a patient to get a stuck sink valve unstuck. The patient succeeded but the doctor noticed the patient's hand was bleeding afterwards. He came to understand that the patient did not have superhuman strength. What the patient did have was a reduced ability to perceive pain, because the patient's nerves were damaged by the leprosy. So, a healthy person would have stopped trying to turn that stuck valve because the pressure of the metal on their skin would hurt. But a patient with leprosy would keep going because they couldn't feel the metal damaging the tissues in their hand. Similarly, diabetics with poor blood sugar control eventually lose sensory nerve function in their lower extremities, and can suffer damage to their knee joints and the soft tissues of their feet without even realizing it. ",
"Nerves offer us a feedback mechanism. Touch stove equals hot equals perceive pain equals pull hand away. If we lack this feedback mechanism, we damage ourselves. If we could not sense pressure and pain as we bite down, we would probably end up shattering our own teeth by biting down too hard, because there would be nothing signaling us to stop. Nerves are important! It's no fun when they signal the pain of a bad toothache, but ultimately they help protect us."
] |
[
"Why are felines/cats generally afraid of water?"
] |
[
false
] |
I find it interesting that despite having roughly the same physical attributes as a dog/fox/wolf etc, felines are afraid of water (whereas those I mentioned cant seem to get enough), despite having roughly the same body type. Why is this?
|
[
"Unfamiliarity.",
"Wild felines generally have no problem with swimming, and domestic cats can be accustomed to water and learn to enjoy it as well.",
"Evidence:",
"http://www.youtube.com/watch?v=RvgsrT8Z924",
" ",
"http://www.youtube.com/watch?v=_5EjgCHLBDA"
] |
[
"Is that genetic? If so, how were dogs familiar with it in their genetic past?"
] |
[
"I doubt it's genetic... what I meant by \"unfamiliarity\" is that domestic cats usually aren't exposed to water when young, and don't know that it won't hurt them or that they can swim."
] |
[
"Where do neutrons come from? If the whole universe started as hydrogen which is just a proton and an electron, where did the neutrons come from when they fused into heavier elements?"
] |
[
false
] | null |
[
"After the Big Bang, the universe eventually cooled enough for quarks to form bound hadrons. Protons and neutrons both would've been produced as a result.",
"Protons are stable (as far as we know), but free neutrons decay with a half-life on the order of ten minutes. So any neutrons produced during this process would not have lasted very long.",
"Luckily neutrons can be produced in stars as well. What happens is that two protons fuse together, forming a diproton resonance (helium-2, if you wish). Since the diproton is unbound, the vast majority of the time, it will immediately decay back into two protons. But some small fraction of the time, it can beta decay instead, forming a deuteron (hydrogen-2). The deuteron is a bound system consisting of a proton and a neutron."
] |
[
"At these temperatures the electrons are very detached. In plasma the electrons have been knocked off by the violence of the environment and are not bound to anything for now, although they are usually still nearby.",
"Also, the extra electron created in beta minus decay of a neutron into a proton will be moving away at relativistic speeds. So will the extra antielectron in beta plus decay of a diproton."
] |
[
"I misspoke. Diprotons undergo beta plus decay, not beta minus. Charge is conserved here."
] |
[
"What will be used as a substitute for helium?"
] |
[
false
] | null |
[
"Helium in the atmosphere is slowly leaking into space and it is not easy to recover. There is a lot of He still in natural gas deposits so I expect when He prices get driven way up we will see companies that extract natural gas start separating and selling He. The government may stockpile again, but it seems like an obvious opportunity for gas providers to make more money. ",
"Here is an article with more information."
] |
[
"As far as lighter than air gases, there aren't many that are lighter than air and are also safe to use like helium. ",
"At least that I can think of off the top of my head. "
] |
[
"The only reason the U.S. Government is selling off its helium reserves is because it's expensive to store. There's still plenty of helium in natural gas deposits; it's just not being extracted and sold because helium from the Government is still a lot cheaper. Once the government doesn't have any more helium, mining and extraction companies will start capturing the helium in the natural gas deposits and selling it, because that's when they'll start to profit from it. So we won't have to extract it from the atmosphere, and we won't have to find a replacement. We have another source."
] |
[
"Is there any evidence humans lived with Neanderthals or other species?"
] |
[
false
] |
Since modern humans have Neanderthal DNA did any human settlements have multiple species living together do we have evidence such as bones?
|
[
"I don't know of any sites where there were human and Neanderthal bones found together, but they probably exist somewhere given the genetic evidence. However, Neanderthals and Denisovans were found together, along with hybrid children. See: ",
"https://www.nature.com/articles/s41586-018-0455-x"
] |
[
"Yes, lots, since we have the entire Neanderthal genome. ",
"https://www.smithsonianmag.com/science-nature/neanderthal-and-human-matings-get-a-date-24217676/",
"https://www.smithsonianmag.com/smart-news/study-reveals-why-humans-dont-have-more-neanderthal-dna-180961047/"
] |
[
"Wow that is extremely interesting thank you"
] |
[
"What’s the science behind japanese oil hardener product?"
] |
[
false
] |
I’m currently using a product from japan to dispose used oil properly. I am curious on the science behind it and have googled but i don’t think it is a result of hydrogenation. I can’t seem to find the ingredients of the japanese oil hardener in english so i can’t really tell what made my used cooking oil solidified after putting in the powder.
|
[
"You may be able to find a safety data sheet for the product which will may tell you outright what is in it, or at least have some clues. ",
"Can you describe the end result? My guess is a brownish, soft and oily gel. ",
"I suspect it is something very similar to ordinary flour, possibly a mix of powdered starch, cellulose, and a preservative, processed in some way to prevent clumping. ",
"I base this guess on the ",
"website",
" of what appears to be a similar, product. Specifically: this product is a \"plant-based, non-toxic powder,\" it is relatively cheap, works with around a 10:1 ratio of oil to powder, and works at low cooking temperatures (recommends to add powder at around 77 ",
" C and it solidifies around 38 ",
" C). It is disposed of with ordinary garbage. This all is very similar to what happens when you just mix flour into oil or melted fat at moderate cooking temperature, for instance while making a roux."
] |
[
"Vegetable oil can under also harden under epoxidation, through oxidation and cross-linking. ",
"I imagine there are a view different ways to this, eg, peroxide and then some catalytic hardener to promote cross-linking, but I don’t know exactly what’s in yours. Can you give me a brand or something?"
] |
[
"Hah, even simpler than I thought. I bet it's just a powdered high melting point fat, that when mixed with a low melting point fat combines to make a moderate melting point fat. That's funny."
] |
[
"When studies are suggesting that the Pfizer vaccine's efficacy drops after six months, how do they measure this?"
] |
[
false
] |
Are they looking at infections/severe illness in vaccinated people on a population level, or are they measuring the amount of antibodies people have 6+ months after getting the vaccine? Could it be the case that, although antibodies decline, B and T cells can still offer long lasting protection?
|
[
"Neutralizing antibodies titers- there is a study out of Israel (published in NEJM) - they studied health care workers and had neutralizing antibodies checked before the recent wave. Lower detectable Titers of neutralizing antibodies predicted who was at risk for infection despite vaccination.",
"sauce"
] |
[
"I'd advise caution about this interpretation.",
"We expect antibody levels to drop to zero or background at some rate for any infection. Based on our knowledge of the immune system antibodies can only be a reasonable proxy in the short term at best.",
"Even then the Israel study is specifically saying there was a ",
" at six months, but you can't use that result to project forward. ",
"Based on the rate of decline for sars-cov-2, at 18 months you are going to have two people with similar levels of antibodies (maybe none) but vastly different responses to new infections, based on other factors."
] |
[
"You are correct. However, they found that titers were lower in those who got infected: in other words, as antibodies go down, risk of infection goes up. We don’t know what the B and T cells are doing, but at this point it looks like antibody levels are a decent proxy for overall immunity."
] |
[
"Why does tupperware get those weird white spots? Once the spots appear, is it still safe to use?"
] |
[
false
] |
I think everyone who's ever used tupperware knows what I'm talking about -- those that appear. Anecdotally, it seems to be related to washing or microwaving. So what causes them? Is this a physical change and/or a chemical change? And does anything about their appearance signal some kind of phenomenon that might make them unsafe for use?
|
[
"It is unlikely that it is a chemical change. Tupperware is made from mixtures of polyethylene and polypropylene, which inert to most conditions that you could make in your kitchen. However, you may know that if you heat Tupperware, that it becomes softer, and at highly elevated temperatures, may melt. What is most likely happening when you get these white spots on the Tupperware is that you have formed localized areas of elevated temperatures, and the polymers begin to shift relative to each other, and take a different conformation. This distortion just changes some of the physical properties of the plastic, such as making it opaque and rough to touch, but it is still completely safe to use; it just no longer looks aesthetically pleasing."
] |
[
"Its more then likley the plastics getting near its melting temp. Nothing you can do to fix it but it should still be safe to use. ",
"On a related note, Tupperware has a lifetime warnty, go to google find a local tupperware lady (or man) and ask to have them replaced. You shouldnt need a recipt. I know this isnt science but still may be helpful. "
] |
[
"i'm not a scientist but I've got an uncle who has a plastic forming company and a father who worked with the huge Mixing / Melting machines they use. here is their reason: tiny bubbles form during the mixing process that get worked out during the \"rolling process\". the process turns the shapeless goo into a sort of plate. this is done by passing it through rollers repeatedly with increasing pressure until the desired material density and shape are reached. the bubbles sometimes don't get pressed out but remain flattened along \nthe surface creating unstable layers. tiny invisible flaws. the plate next goes into a heat press which presses it into the desired shape. Tupperware in this case. if such an area takes damage it can give rise to a whole range of phenomenon like splotches and streaks. is it safe for use? no idea. is eating plastic flakes safe?"
] |
[
"Can a black hole be charged enough to overpower it's gravity?"
] |
[
false
] |
Like for example say you have a negatively charged object of some sort, could you have a black hole with a charge strong enough that it would allow that object to escape once already inside it's horizon? EDIT: tried to make the question a little clearer
|
[
"Sort of.",
"A charged black hole is indeed \"more repulsive\" than an uncharged one. The electromagnetic field of the hole acts sort of like dark energy in cosmology and modifies spacetime to be repulsive.",
"So it is not directly the Lorentz force that pushes you out (a simple force cannot really save you from a black hole) but rather the energy of the EM field that changes the structure of the hole itself.",
"The result is a Reissner-Nordström black hole. The black hole still has an external event horizon, but also an internal Cauchy horizon with a repulsive singularity; we will not discuss the interior region since it has unphysical properties and is likely unrealistic.",
"Let's now set G = 4 π ε = c = 1.",
"What I said applies to holes with Q < M, which are called subextremal. ",
"If Q = M the hole is extremal. The two horizons have degenerated into one surface. Extremal black hole are special because they don't impart any force on eachother. You can have a collection of extremal holes and even add the metrics together and they won't care.",
"Q > M is superextremal. In this case there are no horizons and you have a naked singularity. Naked means that the singularity is actually a place you can go visit, exchange light signals with, and then exit the hole and get back to the rest of the Universe. Informally we say that the repulsion has won over the attraction. Naked singularities are not thought to be possible and they are the subject of the cosmic censorship hypotheses. Even though superextremal black holes exist as solutions to the Einstein field equations, they cannot be built starting from realistic initial conditions.",
"Think about how you would make a subextremal black holes superextremal. You would pour electrons (which have Q>M) into it. It would turn out that as you near the extremal limit, the collective electromagnetic field of all the electrons carries itself energy that contributes to the mass M of the hole. Said otherwise, to get an electron close to another large like charge you need to give it potential energy, which increases the total energy of the black hole. Essentially Q would increase with M and you would only get asymptotically close to the extremal case. ",
"A superextremal black hole is therefore understood to be impossible in yet another way: for M to be less than Q you would need to pour negative mass to cancel at least the electromagnetic energy of the charge Q. Negative mass is impossible, so yeah.",
"This makes a lot of sense in black hole thermodynamics. The temperature of a black hole corresponds to its surface gravity. This vanishes for an extremal Reissner-Nordström hole, which is therefore at absolute zero. It's impossible to get to absolute zero with a finite amount of transformations.",
"Superextremal holes are inherently unstable and so they are not in thermal equilibrium and they have no temperature."
] |
[
"The information is already out. There is no need in EM to carry information about the total amount of charge at the speed of light. The field itself retains that information throughout space, in its shape.",
"Imagine charging a black hole by throwing electrons in it. An electron has field lines going out to infinity; the total flux of the electric field through a very large sphere at infinity gives the charge of the electron (Coulomb's law). Throwing the electron in, the field lines still connect it to infinity. As it overcomes the event horizon, the field lines still come from the black hole and go to infinity.",
"Again the flux of the field at infinity gives the charge of the electron, meaning that the black hole is charged."
] |
[
"How can a black hole be said to be charged? Isn't any EM field information unable to get out?"
] |
[
"Why do metals interfere with lower frequency (VHF) radio transmissions moreso than higher frequency (UHF) transmissions?"
] |
[
false
] |
To visualize photons riding transverse waves (the transmission) through a dense field of particles (the metal), and given a common amplitude and rate of propagation, makes it seem VHF transmissions would have fewer chances of intersecting a scattering particle (proton/neutron/electron) than UHF. So, why do UHF transmissions penetrate metals better than VHF? Does it have something to do with their higher energy imparting something analogous to inertia that makes them fundamentally harder to deflect?
|
[
"There's no need to invoke photons at all. The metal functions as a ",
"Faraday cage",
", and that is well-described by classical electrodynamics. Holes in the metal function as high-pass filters, as in order to prevent the propagation of light through a gap, that gap must be markedly smaller than the wavelength of the light.",
"Interestingly, the ",
"skin depth",
" of shorter wavelength light tends to be smaller, so were the metal very thin, we would expect the longer-wavelength light to propagate through it better, but so long as it is much thicker than the skin depth at both UHF and VHF, we should expect the effects to be strictly due to openings in the metal.",
"An easy way to both notice this effect (and to put an approximate bound on the wavelength) is to try listening to an AM radio station while driving through a metal truss bridge, then switch to an FM radio station. The latter should come through just fine, while the signal from the former is usually significantly decreased! AM radio is transmitted with wavelengths of a few hundred meters, while FM is a few meters.",
"Also, photons aren't \"riding\" the transverse EM waves. The waves are perturbations of the field and the field itself is quantized."
] |
[
"Ah, I see.",
"To a good approximation in most materials EM waves interact in a linear fashion. That is to say that doubling the amplitude of the wave is equivalent to simply doubling any of its effects. So if your signal before interaction with the metal was has amplitude A1 and after interaction A2, then we can expect that doubling the amplitude of A1 will lead to a simple doubling of the amplitude of A2. If A2 is just below your detection limits, then doubling its amplitude could make you go from no detection to detection, but this is just a simple multiplication, not really the wave penetrating the material any better (as the proportional decrease is unchanged).",
"As for the frequency effect: it’s hard for me to describe this without mathematics or getting a little ham-fisted myself, but to a very broad approximation you can treat the wavelength of the light as a fundamental size descriptor of the far-field wave and the wave can’t readily propagate through holes much smaller than that length scale.",
"A more detailed description depends a bit on your comfort and experience. To understand screening of fields by a conductor, a review of Gauss’ law is sufficient. For a more in-depth look at these sorts of interactions if you’re already comfortable with Maxwell’s equations, I recommend chapters 9 and 10 in Purcell’s Electricity and Magnetism. If you already have a undergraduate-level understanding of E&M and basics multivariate calculus, then Jackson is the gold standard. Chapter 9 gives greater mathematical detail on screening and radiation through a hole (also, a 2nd edition copy of Jackson’s Classical Electrodynamics is usually way cheaper than the 3rd edition, and I prefer the 2nd edition as it’s all in Gaussian units). People hate on Jackson, which you’ve probably heard if your at or close to the level where you’d encounter it, but I find the text very clear and pleasantly compact. It’s the problems at the end of the chapter that are impossible.",
"EDIT: I also realized I didn't quite answer your question:",
"I.e., what are the specific interactions that deflect/scatter the radio transmission?",
"other than to point you to Gauss' law. To a very good classical approximation, the conduction electrons (those that are free to move about the conductor) in a metal experience a force from the incoming EM wave which causes the electrons to be accelerated. That acceleration produces a radiated field itself, and that field is such that it is equal and opposite the incoming field inside the metal. So, when that induced field is added to the incoming field in the direction of propagation, the field is \"screened\" and there is no far-field radiation that passes through a sufficiently thick conductor. In the opposite direction, the induced field simply propagates away from the conductor, which is why metals are shiny. Resistance to the electrons moving in the metal converts some of the incoming energy to heat, which is why metals are, in general, not perfectly reflective and have finite skin depth.",
"This works so long as the electrons can \"keep up\" with the incoming field. Above a certain frequency, known as the \"plasma frequency\" of the metal, the electrons can no longer simply be accelerated along with the incoming field in a quasi-static sense, and the metals cease to be shiny at higher frequencies and their interactions are no longer well-described by this particular classical approximation."
] |
[
"Sincerely, that’s a great answer from a practical standpoint, and I thank you for it.",
"I also acknowledge that my description of photons “riding” waves of EM radiation was somewhat ham-fisted.",
"What I really was interested in, though, was an explanation of the physics. I.e., what are the specific interactions that deflect/scatter the radio transmission?",
"And now that you’ve mentioned it, I’m also curious why a Faraday cage would impede a transmission on account of its wavelength rather than its amplitude (unless those two are somehow linked, in which case I very much would like to know about that link ... and still how it matters to the size of the gaps in the cage)."
] |
[
"Honest question about the vaccine?"
] |
[
false
] | null |
[
"The question is removed because it’s off-topic. If you continue to try to override the moderators’ decisions you’ll be banned from ",
"r/askscience",
"."
] |
[
"Respectfully, I do not understand why it's off-topic. I'm asking for a scientific reason why we should all get vaccinated, as I'm unable to find an answer anywhere else.",
"I understand vaccination is good on a personal level for protection, but I'm asking ",
" why should I care if someone else does/doesn't get vaccinated."
] |
[
"All of your premises are wrong. The vaccines prevent transmission and infection. To the limited extent your question reflects reality it’s been asked and answered many times."
] |
[
"When it rains/snows - how comes the rain/snow does not fall out of the clouds all at the same time?"
] |
[
false
] |
as title says - Question asked by my work colleague. Thanks. Edit: followup question - would there be any circumstances where the rain could eventually just fall all at the same time? Edit 2: thank you guys for the answers.
|
[
"It does. It's called sleet. If snow falls from a cloud and enters warmer air as it falls, some of the snow will melt as it descends. Larger flakes will remain partially frozen. The effect at ground level is you get big, soppy flakes of snow with drops of water falling at the same time.",
"For your second question, the answer is: theoretically yes, but in practice no. Rain forms when a warm, humid air mass cools. As it cools some of the water vapour condenses into liquid water, which forms droplets. That forms a cloud. When the water droplets become large enough to fall, you get rain.",
"As water changes phase from vapour to solid, it releases heat energy, so the surrounding air warms up a tiny bit, which slows the formation of rain drops close to one that is already forming. The overall effect is that rain tends to fall fairly gently over time.",
"If raindrops form and are caught in an updraught, and potentially recycled up and down an active cloud many times, you can get a stratification where a fairly thin layer of the cloud has a very large concentration of raindrops. In the right conditions, this can all get dumped to the ground in a torrential burst, This sometimes happens in thunderstorms. You get rain, then heavy rain, then a torrential deafening downpur for a few seconds, then back to rain again. It's very impressive when it happens, but it's still only a tuny fraction of the total water in the cloud."
] |
[
"Rain isn't ",
" the clouds, the clouds ",
" rain!",
"When each individual water droplet gets too big for air currents to support it begins to fall. This happens over time, and a little bit differently for each drop. Basically, as the cloud continues to condense more water, it makes more rain. Its not a fixed quantity suddenly leaving, its more humid air being turned to liquid over time."
] |
[
"A raindrop falls when it weighs more than the force of the updraft on it. Since the drops grow randomly as they bump into each other and the updraft in any given location is also changing randomly, the moment when any given raindrop reaches “critical fall mass” (my made-up term) will also vary randomly, and so the drops will all fall at different times. ",
"This is also part of why storm rain has bigger heavier drops than, say, warm front all-day raindrops. Stronger updrafts == bigger, heavier raindrops. "
] |
[
"Is it possible to train your brain to have faster reaction times?"
] |
[
false
] | null |
[
"Call me out on this if I'm wrong, since I'm basing this on old information and fundamental neural mechanism.",
"At its core, reaction time can be broken down into a few components. Input to brain, processing and selection of response and finally signal that causes the response. For the first and the last, the timing is limited by a hard physiochemical limit, that is the nerve-nerve signaling and the action potential contained within the individual neuron itself. This, afaik, is relatively static, and unlikely to change with time.",
"The second is more simple, time to analyze and decide is highly experience based, and sufficient repetition is likely to increase such reaction times to a certain extent, though not beyond the fundamental limits imposed by the system."
] |
[
"This doesn't cover improvement (it might come down to genetics), but here is data for the fastest of the fast:",
"http://www.ncbi.nlm.nih.gov/pubmed/22739331"
] |
[
"Your reaction time to what? Regardless, yes, it's possible. One of the things to be aware of is that there's ultimately a trade-off between speed an accuracy, so past a certain point, your speed will improve, but you'll be false-alarming a lot as well. Video games are frequently used for this kind of training. Here's one of many such studies: ",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2896820/",
" "
] |
[
"Does ice get harder as it gets colder?"
] |
[
false
] |
Does water ice get harder as it gets colder? For example, an article said ice on Titan is "rock hard" because of the tempetature. Is this accurate?
|
[
"Here's where we pull out our handy ",
"deformation mechanism map for water ice",
" (Fig. 19.26 ",
"here",
"). This tells us---not surprisingly---the dominant deformation mechanism for an arbitrary temperature and stress, and also provides the deformation (i.e., creep) rate. The grain (crystallite) size for this map is 10 mm, but the trends I discuss below hold for other grain sizes.",
"Hardness is a measure of the stress required for plasticity, or permanent deformation. Let's choose the maximum deformation rate of 1/s (i.e., 1 radian of shear deformation per second). We see that the yield stress of ice is around 100 MPa (right axis), increasing slightly with decreasing temperature from 0°C toward absolute zero (top axis). The rate makes a bigger difference at higher temperatures because thermal energy allows solid to \"creep,\" or experience viscous flow over time. Closer to absolute zero, however, the creep rate is essentially zero and your only hope for deformation is fracture---failure of many, many atomic bonds essentially at once.",
"So the answer to your question is yes, assuming water ice, but the hardness increase is less than an order of magnitude compared to the ice in your freezer."
] |
[
"Yes, but I'm not sure how much.\nAssume a hydrogen bond takes a set amount of energy to break.\nAs you cool the ice further, you're removing vibrational energy from the water molecules, therefore putting less stress on the hydrogen bonds, therefore to meet the set energy required to break the bonds, you must apply more energy from a separate source."
] |
[
"Yes, somewhat. Temperature history certainly affects grain size. For ice, though, I don't see a huge dependence on gran size for the topics discussed here: ",
"check it out yourself",
"."
] |
[
"[Physics] What type of detector would be needed to verify or disprove the existence of the gravitational wave background?"
] |
[
false
] |
The gravitational wave background is conjectured to exist and is similar to the cosmic microwave background radiation, but instead of light, it is gravitational waves. As light from the first quarter million years of the universe could not penetrate the plasma soup at the time, the CMBR is limited to showing us the universe after that time - the gravitational wave background might enable us to probe earlier than that.
|
[
"Would we ever be able to measure it? If we're looking for a gravitational wave background that's similar stylistically to the CMB, it's earliest surface would be at nucleosynthesis right? I would think that anything from that time period would be redshifted into oblivion.",
"The start of BBN was about ~0.1s post BB and average temperature of 10 MeV, which would mean its it's corresponding temperature now would be ~1.4x10",
" eV, or 1.7x10",
" K if I scaled it properly (just started learned it this last school term, might not have). These were found assuming radiation domination until 47000 years post-bang, matter dom afterward, no dark matter.",
"If we use the end of BBN as the surface (100keV) this this becomes orders of magnitude smaller."
] |
[
"There was a group in 2014 that claimed to had found GWB only to learn a lesson in peer reviewing.",
"I believe you're referring to the BICEP2 resuls, but I feel I should point out that had nothing to do with peer review (in fact the paper passed peer review and was published in PRL): the problem was that the dust foreground was much stronger than any of the commonly used models or available experimental evidence predicted, and that fact (which was discovered by the Planck telescope) hadn't been released yet.",
"Anyways, back on topic. We're a long, ",
" was from detecting the primordial gravitational wave background directly (",
"this",
" page has a plot which shows what parts of parameter space various detectors operate in: none are even close, and LISA isn't even scheduled to come online till 2034). ",
" detection of the GWB, OTOH, is actually pretty close. BICEP3 came online last year or so, and the South Pole Telescope is installing an upgraded detector right about, well, now-ish. Both look for B-mode polarization in the CMB, which would be an indirect confirmation of primordial gravitational waves (less significant a discovery now that LIGO made it's detections, but still highly significant for cosmology)."
] |
[
"Please be civil. This is an educational subreddit. If you would like a source, please ask in a kind fashion. There are some great links in the sidebar on how to follow said suggestion. "
] |
[
"What drives the electric current in earth's core that is responsible for earth's magnetic field?"
] |
[
false
] |
I've searched high and low for a good paper or diagram that describes the current in the earth's core, but found nothing. We know it's there because it's necessary for a magnetic field, right? And unless the liquid core has a very positive or negative net charge, it is more than just the movement of the liquid itself. I hope I have the proper understanding, but please correct me if I'm wrong. If we know the magnetic field strengths at various places around the earth and at the same distance from the core, wouldn't it be possible to derive the location, structure and power of the electric current?
|
[
"Molten iron inside the earth is flowing. The flows are driven by convection (it's hotter at the center of the earth). This leads to the magnetic field.",
"More here ",
"http://www.usgs.gov/faq/?q=categories/9782/2738"
] |
[
"Rotation of the ferrous core in the surrounding magma."
] |
[
"Rotation of the ferrous core in the surrounding magma."
] |
[
"What dose the R [Random] in RAM [Randomly Accessible Memory] mean?"
] |
[
false
] |
Dose it mean, that it can be accesed at any [Random] moment, or that the any [Random] part can be accesed? Couldn't it have been AM [Accessible Memory] or FAM [Freely Accessible Memory]? What was the reason for the choice.
|
[
"The hard drive analogy is particular apt - before RAM, there was ",
"drum memory",
", which was a lot like a hard drive."
] |
[
"The hard drive analogy is particular apt - before RAM, there was ",
"drum memory",
", which was a lot like a hard drive."
] |
[
"The question has been answered already, but from a historical perspective a lot of the terminology we use today was coined in the age or punch and tape data storage. So, having a real random access was a pretty incredible thing. Being able to read memory by memory location instead of running through a long tape or shuffling punchcards or some other method was exceptional. ",
"Then things like the ",
"magnetic core memory",
" happened (Apollo mission used this) and, of course, the silicon chip (DRAM). More on this history of the magnetic core memory here: ",
"http://www.psych.usyd.edu.au/pdp-11/core.html",
"I'm not much of a historian, but I think this was the first effective and practical RAM. Decent timeline here:",
"http://inventors.about.com/od/rstartinventions/a/Ram.htm"
] |
[
"What interesting occurrence of memory in nature did we observe?"
] |
[
false
] |
. . Epigenetics can retain information across generations. The immune system stores information about pathogens. Those are two examples beyond the brain I can come up with that I would apply the concept of memory to. Do you know of more?
|
[
"I'm very stupid, but excuse me for that and indulge me: I'm not following your leap of logic. How would you characterize the relationship between epigenetics and shape-memory alloys?"
] |
[
"I don't have anything new, but since the context was fitting, I thought I'd share ",
"this research",
". ",
"tl;dr: Visit some wallabies isolated from predators for thousands of years, show them cut-outs of predators, watch wallabies get scared."
] |
[
"the prevailing hypothesis about molecular origins of life postulates that informational polymers like RNA (or PNA or others) began a cycle of self-catalyzing its own formation. These pre-biopolymers have been shown experimentally to adapt to their environment (Ill dig up a reference) but more importantly, attain the ability for their structures to be \"history dependent\" meaning not just mirroring the ambient conditions (state functions), but instead retaining structure from the path they took to get there. This was the beginning of evolution, and the beginning of chemical \"memory\" in the sense that you used in your question. These ideas have been demonstrated in the lab using model systems, although the actual historical chemical systems are as yet unknown."
] |
[
"How is it that if Earth exerts a force of gravity on you of 600N, then you also exert a force of gravity on Earth of 600N?"
] |
[
false
] | null |
[
"Could you elaborate on your question? That is, the question of \"how is this fact a fact\" is very difficult to answer with anything except \"well... that's the fact.\""
] |
[
"The gravitational force is proportional to the product of the two masses involved. So the larger the mass that's pulling on you is, the stronger you are attracted because there is more stuff to pull. But also the more mass you have, the stronger you are pulled because there is more mass to be pulled on.",
"So the Earth pulling on you is a whole lot of mass pulling on a little mass, but you pulling on the Earth is a little mass pulling on a whole lot of mass. "
] |
[
"I think what's confusing you here is a misinterpretation of the underlying meaning of Newton's third law. From a deep perspective, there aren't actually two independent forces involved. It isn't you pulling on the earth ",
" the earth pulling back. Rather, there is a single attractive force of 600N ",
" you and the earth."
] |
[
"Could a biologist/earth scientist please help me answer a question regarding plants asked by my ten-year old?"
] |
[
false
] |
Daughter: Dad - you said plants take water and air and transform it into plant matter? Smug dad: Quite right, little sunshine. Daughter: Well, that means the more plants there are, the less water there is, because they are using it up, turning it into something else... And so, one day, there cannot be any water left... right? Befuddled dad: Err, wait, that obviously cannot be right - hold that thought... (frantically tries to tackle the perceived paradox with common sense, finds he has none, but only half-truths, unfounded hypotheses, and more-than-half-forgotten high-school learning... Do plants return some water "when they are done"? Sweat/transpire? But some water would still be locked up in the new molecules of plant matter, no? Do the plants give it back after they die? Or is there so much water and so little plant material globally that it does not matter? Am I wrong and plants actually build themselves from air, using water only as a "catalyst"? And how do I dare to throw around big-boy words like "catalyst" when I cannot even answer a kiddie question about water?) Daughter: Dad? Dad: Don't worry, little buttercup, I'll ask the Internet, after the weekend... there is this cool forum, you know - ... Daughter: OK, let me know when you hear back from them! Dad (to himself): oooo, and I have a second question for those scientists as well.... Question 1: Plants, in my understanding, use up water and air to make more plant matter. Does this mean that their consumption of water is permanently removed from the water cycle? Question 2: In your view as scientists, how dangerous/problematic is it that "we" (i.e., parents with only a basic education in the natural sciences, but enough of useless other education to consider ourselves, vainly, "fairly educated") feed the next generation with our own falsehoods and misunderstandings from our privileged position of perceived authority figures? All this "teaching" about how the Earth and the ecosystems work, what atoms look like, how traits are inherited, how our bodies handle diseases... surely it is 60% wrong on a good day? I used to think how horrible it is that creationists teach their kids all these blatant falsehoods... but suddenly I am not so sure those parents who are accepting of science (but otherwise not well-versed in it) are any better. Thoughts?
|
[
"Plants also have to break down energy via respiration, which yields water as the final product."
] |
[
"Not only do plants have to undergo respiration, when animals metabolize sugars, we generate water as the by-product as well. That's how the water cycle is completed.",
"I think the most important lesson parents have to instill to their children is to ",
" if their answers are correct. Beyond giving the best answer you can provide, have them check back with you after they have collected their own findings - either through experimentation or research. As long as they can learn that, you should never be afraid of feeding them falsehood (obviously that should still be kept to a minimum...).",
"Then one day, when ",
" correct ",
", you can have the pride in having raised a child with the proper tools to discern truth from fiction. (Of course, you now have to deal with being constantly corrected...)"
] |
[
"The best thing any privileged authority figure ever did for me in teaching science was to lift the curtain and demystify what knowledge authority really is and isn't.",
"Science is often thought of as a large collection of useful facts, but in truth it's not (just that). Science is the attitude and technique that would allow someone completely ignorant of that large collection of facts to reproduce the whole thing given enough time (and funding).",
"Noting you and your daughter's confusion and seeking out further knowledge is exactly the right move. After all, it seems consequential that if plants really did consume water then there must have been much, much more water on the planet a long time ago. You could try looking that up to see if observations jive with your predictions."
] |
[
"How much virus is 10 TCID50?"
] |
[
false
] | null |
[
"Did you check this article: ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7973348/",
"? It has a lot of math, but the gist is that 1 TCID50 is the amount of virus needed to infect half of a tissue sample, so 10 TCID50 is 10 times that viral load"
] |
[
"The TCID50 is a way of measuring the amount of virus present in a sample, and 10 TCID50 means that if you take a sample and dilute it by a factor of 1,000,000,000 (10^10) only half of the cells that are exposed to the diluted sample will be infected. It's a laboratory measurement that's used to compare the infectivity of different virus strains or to determine the virus titer in a culture or vaccine. But it's hard to say how many viral particles are equivalent to 10 TCID50, it can vary depending on the virus and the method of measurement. But it's a relatively low viral dose, less than what you would get from a sneeze or a cough."
] |
[
"the amount of virus needed to infect 50% of the cells in tissue culture",
"Wait . . . I thought it was the amount needed to inoculate a flask of cells, in order to have a 50% chance of causing an infection (i.e. infecting at least one cell). Can you double check this?"
] |
[
"How does a permanent magnet attract ferromagnetic materials."
] |
[
false
] | null |
[
"Rat_poison answers the B and H question really well, so I'm going to answer your first question.",
"Ferromagnetic materials are magnets. a permanent magnet is a piece of ferromagnetic material that we have oriented all the domains (mostly) into the same direction. So all the individual magnet dipoles in the ferromagnet , which in the case of Iron Nickel and Cobalt and due to d-wave conduction electrons, add up to produce a large magnetic field. Now this is a slightly simplified explanation based on micro magnetics: One of the key energy components of a ferromagnetic material is that of the lowest possible magneto-static energy, which just means, as little field outside of the magnet as possible (stray magnetic field). Now it normally does this by random domains, but a forced single domain magnet can't (energy requirements etc). So if we put two magnets near each other they want to lessen that stray magnetic field between them as much as possible and so pull together. "
] |
[
"nth EDIT: Would the person who downvoted please explain the reason? I think I'm right and if I'm wrong I'd like to be corrected.",
"Magnetic monopoles have nothing to do with Maxwell's equations.\nTheir inexistence isn't something theory deduces. It's based on observation alone. In fact it works the other way around",
"(note: Capital letters are vectors)",
"BECAUSE we haven't observed magnetic monopoles we say that ∇B=0 (instead of saying ∇B=some",
"\"charge\")",
"The difference between B and H is the following:",
"H has to do with what kind of field a given current density produces. It is the magnetic effect of electical current. Think of a coil. Let us focus only on the area close to the axis of that coil. If the coil is large enough, you could say that current flowing through it creates a magnetic field, with parallel field lines. The more turns the coil has, and the more current flowing through it, the denser the field lines, the the larger the value of |H|.",
"What does B mean then?\nlet's say that we have a homogenous material of μ magnetic permeability. Within that material, B=μΗ\nThe more magnetic the material, the larger the μ.\nLet's use our previous example.\nClose to the axis of the coil, B=μ0",
"μ0*Η. μr is the relative index of the material. How many times more \"magnetic\" it is compared to empty space. Therefore, the electromagnet is getting stronger, but its overall shape doesn't really change.",
"In other words, the magnetic force is proportional to B. But B is the product of two factors:\n1.) It has a current density as cause. Think of it as \"how much current and how is it flowing in 3-D space\". This is H. Basically magnetic field tends to wrap itself around electrical current.\n2.) It is affected by the microscopic magnetic qualities of the medium. This is μ.",
"So, while in reality what we really care about is B, you can't produce it out of thin air. You have to create an H and then see what B it will produce."
] |
[
"Do you mean a paramagnetic material, where there are randomized, permanent dipoles? Ferro and ferrimagnetic materials do possess an overall magnetization vector. ",
"When a paramagnetic material is placed in an external magnetic field, because each unit does have a dipole, the crystal structures begin to orient themselves to the external magnetic field and thus form a vector.",
"B and H are sometimes used interchangeably, although B refers more to a magnetization vector and H refers to an external field strength. "
] |
[
"How is the observer effect consistent with quantum tunneling?"
] |
[
false
] |
The quantum observer effect has always been the part of QM that's hardest to wrap my head around. I was thinking about this and it raised the following. This is almost certainly a gap in my understanding of quantum mechanics, but I'll throw the question out there: if we can see macroscopic effects of quantum tunneling in say computer transistors, that seems like it'd be sufficient to count as observation of the electrons. But descriptions I've read of the observer effect seem to indicate that the wave-like properties of electrons should go away when they are observed, making quantum tunneling impossible. I'm sure I'm missing something, but what is it?
|
[
"An electron tunneling a new nanometers is not a macroscopic effect in itself. The result of it can have macroscopic effects, such as your electronics don't work. But those happen after the electron is measured on the other side of the barrier and tunneling has taken place. "
] |
[
"In basic quantum mechanics there are two major elements of the physics: (1) a ",
" part, where you have a wave function that evolves (according to a certain wave equation -- Schrödinger's Equation or the Dirac Equation or whatever) in a time-reversible way; and (2) a ",
" part, where the wave function \"collapses\" and resolves into a classical probability distribution function. ",
"Tunneling is an aspect of (1), the unitary part. It's not really affected by (2). In fact, the way you observe it is by collapsing the wavefunction and noticing that sometimes the collapsed particle resolves itself outside the classically allowed part of space. So the \"observation\" doesn't ruin the effect of tunneling -- far from it, it's how we observe that tunneling occurs in the first place!",
"(Incidentally, it's easier to see tunneling with photons than with electrons -- it was originally noticed in the context of the wave theory of light, as an \"evanescent wave\" in regions where the illumination can't normally reach -- for example just outside a prism where a beam of light is undergoing total internal reflection under Snell's Law. If you shoot a laser beam into one \"base\" of a 45° right-angle glass prism such that it ",
" be 100% internally reflected from the \"hypotenuse\" and exit from the opposite \"base\" 90° from the original direction, you can get the laser beam to go straight just by moving another 45° prism near the face where the reflection is going on. Some of the beam will \"leak\" through the air gap and go straight, if the two prisms are close enough. That's a macroscopic effect if ever there was one.)"
] |
[
"If a potential barrier is thin enough, an electron has a nonzero probability of being located on the \"other\" side. (By \"other\" we mean the side that is prohibited in classical mechanics.) Once we measure the electron to be on the \"other\" side, it actually is there.",
"It's not like how you are describing it (or how I think you are). It seems like you think that until we measure the electron's location, it can be anywhere, even on the \"other\" side, but we just don't know yet. But if we were to measure it, it should never appear on the \"other\" side. That is wrong. If it has a nonzero probability to be on the \"other\" side, then so be it. It is allowed to be there.",
"So maybe you could rephrase your question if I am not understand it correctly. I'm not entirely sure what you believe to be the relationship between quantum tunneling the observer effect, if you believe there to be any relationship at all."
] |
[
"Can humans make sounds that we cannot hear? What about other species?"
] |
[
false
] | null |
[
"I believe that he is asking is humans are able to create sounds that are outside this range. I would have to go with no on this as there would be no real need for humans to be able to make these sounds if we cannot hear them and so we have developed to a specific range. The typical human vocal range for males is 85-180 Hz and for females is 165-255 Hz. ",
"Source: ",
"http://en.wikipedia.org/wiki/Voice_frequency",
"Although to the second question I would say yes that there are animals that can make sounds outside of our range. Bats for instance use echolocation and these \"pings\" that they send out are range from 14,000-100,000 Hz well above human hearing levels. ",
"Source: ",
"http://en.wikipedia.org/wiki/Animal_echolocation#Bats"
] |
[
"on the second question, i think op means as it applies to that species. are there any species which can produce sounds that they cannot hear themselves"
] |
[
"Of course. Hold your arm out in front of you and waggle a finger around. This makes a sound. Can you hear it? No, because it's too quiet for you to hear. If you mean can we make a sound that is too low- or high-pitched to hear, then again, the answer is yes. Waggle your finger backwards and forwards once a second. This is a vibration of 1 Hz, which is too low to hear. If you were able to vibrate your finger much faster, say, at 500 times a second, you would hear this as a low buzz."
] |
[
"Was there any evolutionary advantage behind the widespread use of salt on cooked food? Or is it just because we got used to the taste?"
] |
[
false
] | null |
[
"Salt, drying, and freezing are the three food preservation methods that humans have had access to for thousands of years. Freezing isn't always available outside of cold climates, and drying can run the risk of other animals getting to the food before having the chance to eat it. ",
"Salt, however, is extremely useful for making foods deadly to many bacteria and other organisms that would otherwise live on the decaying matter. Humans are well adapted to eating foods with higher salt content than what is ordinarily found in nature. This is definitely an evolutionary advantage as it allows us to save portions of food for later consumption, without having to instead maintain stomach systems that can fight off the microorganisms which would be living on decaying matter. "
] |
[
"In addition to ignorant's comment...",
"Salt used to be very hard to come by for our ancestors, yet it is essential to be in our diet (mainly the Na/K pump and osmoregulation). Making it taste good got our ancestors to actively seek salt in their diet.",
"Monkeys still do this too. They have a diet of mainly fruits and vegetation. So they like to pick salt (not lice!) out of each others hairs."
] |
[
"Don't forget sugar, oil, and vinegar as natural preservatives in your list. "
] |
[
"How is data stored in huge data centres, like the Google Drive storages? Are they like the discs in hard drives but giant? Do they use discs at all?"
] |
[
false
] | null |
[
"Google has published statistics about hard drive failures",
" because they use so many of them.",
"In particle physics we use a mixture of hard drives (recent/frequently accessed data) and tapes (cheaper per terabyte, but accessing data can take hours or even days - for long-term storage), but we \"only\" have something like an exabyte (=1000 petabyte = 1 million terabyte) spread over several experiments. ",
"CERN is currently managing 600 petabytes",
". Raw data would be far more, but most of the events are not stored permanently, it's simply too much data to work with."
] |
[
"One of the better references here is Backblaze, because unlike Google etc, they are completely open about their large amount of storage.",
"https://www.backblaze.com/b2/storage-pod.html",
"It's worth noting their performance needs are much lower than, for example, any databases used by Google. Facebook has a lot of blogs on the software side:",
"https://engineering.fb.com/category/data-infrastructure/"
] |
[
"Rare events and analyses that need large data samples.",
"Raw events in ATLAS and CMS are of the order of 1 MB, it depends on what's happening in the event of course. There are collisions every ~30 ns during data-taking, if every collision would be stored we would get ~30 TB per second or ~200 exabyte per year and experiment. No one - not even Google - could work with that.",
"Most of that information never leaves the detector because the trigger systems immediately discard most of the boring events. Something like 1 kHz or 1 GB/s is written to disk for further analysis. LHCb has smaller events (~100 kB) but writes out more of them (~10 kHz), so they have a similar data rate. 3 GB/s * 3 months of runtime is 25 PB/year from these three experiments. ALICE collects a bit over 1 GB/s during heavy-ion collisions but that's a much shorter runtime, so it's probably a smaller contribution overall. Raw data isn't a nice format, so the software packages analyze them and reconstruct tracks, calorimeter clusters and so on and store that data in addition, that's very roughly doubling the size. Multiply by almost 10 years of running and we are already getting close (but keep in mind that all these numbers are just rough estimates, and all of them change from year to year). Add simulated events, files from further processing steps (e.g. users selecting samples with their specific process), smaller datasets from other experiments and much more and you end up with the 600 PB.",
"Belle II has ~100 kB for hadronic events that will happen at a rate of a few kHz at full luminosity, that's of the order of 0.5 GB/s, plus more but smaller events from other processes, so at its design luminosity it will probably have a similar data rate as ATLAS/CMS/LHCb today. That's not managed by CERN so it won't enter their data size numbers."
] |
[
"What is the physiological basis (and evolutionary significance) of itches, and why does scratching relieve them?"
] |
[
false
] |
[deleted]
|
[
"Wikipedia has a pretty reasonable article on itch.",
"The gist of it is that relatively recently, we found out, \"oh hey, there are actually specific receptive pathways for itch.\" For some reason, which never made sense to me personally, people had thought for a fair amount of time that itch was sensed by pain fibers... or fine touch fibers... IOW, that it was just a variation of another more familiar sensation, as opposed to it's own sub-sense of tactile sensation. ",
"There are a bunch of different types of sensory nerve fibers in your body. There are A fibers which are myelinated, meaning they send signals very quickly, which are subdivided into alpha and beta (both involved in sending signals to your brain about muscle load and stretch) and delta ('fast-pain' - send signals about cold among other things). ",
"There are also C fibers (we won't talk about B fibers) which are unmyelinated, so they conduct more slowly. There are a couple of different subtypes of C fibers, for example, one type senses temperature, one sense pain ('slow-pain' fibers).",
"And one type senses itch. ",
"Another way that you can group C-fibers is whether they respond to mechanical forces or not. You can group them into mechano-sensitive and mechano-insensitive. It turns out that the mechano-sensitive ones are the ones involved in pain, temperature, etc... and that the mechano-insensitive ones... well, they don't respone to mechanical forces, but they respond quite well to histamine.",
"So to summarize, itch is caused by histamine being detected by the peripheral nerve endings of specialized mechano-insensitive C-fibers (itch-fibers). ",
"Where did the histamine come from? Well, it has to be somewhere near where the endings of those itch fibers are, and those endings are in your skin. Another type of cell other than neurons hangs out in your skin - mast cells. Mast cells contain preformed packages of histamine and release them when they're told to.",
"Evolutionarily... the current thought is that itch originated as a defence against bugs and what not landing on you and transmitting parasites and other infections. Mosquito lands on you... histamine is released by mast cells, detected by itch fibers, and you feel the itch. Your response to to scratch to dislodge the mosquito from your skin.",
"Though this is all hypothetical as it's difficult to prove the evolutionary purpose of something... and this is a relatively new field."
] |
[
"Danharaj offered a dubious, extremely simplified explanation with no sources or credentials. Itching is most likely much more complex than that.",
"I wouldn't trust him on this. "
] |
[
"I can't speak to the evolutionary basis of itching, but ",
"this paper",
" came out a while ago, along with its ",
"sciencedaily commentary",
" if you can't access Nature Neuroscience.",
"tl;dr: There are sensory neurons in your skin that fire in response to histamine, which is released by inflammation at sites like, say, a mosquito bite. When you scratch, those neurons stop firing. They don't know why yet.",
"Also, it appears that ",
"scratching dampens activity",
" in the part of your brain responsible for aversive feelings. This scratching wasn't brought on by an itch, though, so it's hard to make out what that finding means."
] |
[
"When someone loses one of their five senses, does the brain actually change to make the others better or is it just a result of getting used to it?"
] |
[
false
] | null |
[
"I believe you are both right and wrong. Getting used to something means the brain has changed in some way.",
"It's common for brain areas that were previously associated with one of the senses (such as vision) to be used by other senses after the loss of that one. Blind patients often use the visual cortex to process sounds to a much larger extent than sighted people. I'm not sure about your specific examples, but none of them actually argue against a brain change."
] |
[
"I believe you are both right and wrong. Getting used to something means the brain has changed in some way.",
"It's common for brain areas that were previously associated with one of the senses (such as vision) to be used by other senses after the loss of that one. Blind patients often use the visual cortex to process sounds to a much larger extent than sighted people. I'm not sure about your specific examples, but none of them actually argue against a brain change."
] |
[
"I think, when discussing neuroscience, it's always important to emphasize that learning and other psychological changes are also neurological changes. There are people who don't really understand that or think about it that way. But, I also wanted to put out that the usage of different areas of the cortex in actuality DOES happen in people without the use of one of their senses. The fact that other people can mimic many of the behaviors doesn't actually mean their aren't adaptive brain changes in those that lost their senses to begin with to improve their functioning."
] |
[
"How much of a difference in DNA is there between the average first world person and a completely isolated tribesman in South America?"
] |
[
false
] |
Or is there a different, more significant biological difference?
|
[
"This is both wrong and a really unhelpful way to think about genetic differences between organisms.",
"Take chimps, who are much, much closer to us than rats. For the genes which we share there is about a 1% difference in the sequences of those. But humans have somewhere around 1500 more genes than Chimps which is about 5% more genes. Which is a marked and much more important difference. Alongside this we have a different number of chromosomes, several marked chromosome rearrangements and a very different pattern of chromosomal repeats important differences which are not captured by a simple percentage.",
"If you compare the rat and human genomes these differences are far greater."
] |
[
"This is both wrong and a really unhelpful way to think about genetic differences between organisms.",
"Take chimps, who are much, much closer to us than rats. For the genes which we share there is about a 1% difference in the sequences of those. But humans have somewhere around 1500 more genes than Chimps which is about 5% more genes. Which is a marked and much more important difference. Alongside this we have a different number of chromosomes, several marked chromosome rearrangements and a very different pattern of chromosomal repeats important differences which are not captured by a simple percentage.",
"If you compare the rat and human genomes these differences are far greater."
] |
[
"This is both wrong and a really unhelpful way to think about genetic differences between organisms.",
"Take chimps, who are much, much closer to us than rats. For the genes which we share there is about a 1% difference in the sequences of those. But humans have somewhere around 1500 more genes than Chimps which is about 5% more genes. Which is a marked and much more important difference. Alongside this we have a different number of chromosomes, several marked chromosome rearrangements and a very different pattern of chromosomal repeats important differences which are not captured by a simple percentage.",
"If you compare the rat and human genomes these differences are far greater."
] |
[
"What two species are the most distant relatives that can still produce an offspring?"
] |
[
false
] | null |
[
"I dunno if it's the ",
" distant, but the wholphin (a ",
" hybrid between a dolphin and a false killer whale) should at least get some mention. ",
"http://en.wikipedia.org/wiki/Wholphin"
] |
[
"Two different species of animal cannot, by definition, have fertile offspring.",
"Ursid hybrids (offspring of different species of bears)",
" are often fertile."
] |
[
"Wouldn't the fact that the offspring is fertile indicate that the dolphin and the whale are actually distant members of the same species? "
] |
[
"Do butterflies imitate the falling leaves?"
] |
[
false
] |
Today I saw a leaf spinning mid-air and the first thought was that it was a butterfly. Is it possible that butterflies evolved that way to imitate the falling leaves and escape the predators?
|
[
"As discussed in the research paper below, the fluttering pattern of butterfly wings does appear to be an adaption to avoid predatory birds since butterflies are active during the day. Likewise, fluttering by moths which are active at night would be adaptive to help escape bat predators. Some butterflies such as migratory monarchs do not flutter during their long migrations. However, there is no reason to associate butterfly and moth wing fluttering as an adaptation that mimics the flight pattern of falling leaves, which is a type of chaotic physical action explained by gravity and wind currents and not predatory behavior. ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2575472/"
] |
[
"I think that this sounds like a no on OP's question, though, which was whether flying butterflies mimic falling leaves. On the contrary, the authors of this study propose that butterflies have evolved to stand out against the background:",
"A bird, we suggest, could learn or inherently know that brightly colored airborne prey, discernable from afar, is not worth the chase. [...] Butterflies, we propose, are a mimetic assemblage in which showiness, in the sense of spectral contrast, is the shared aposematic trait. Implicit in our argument is that evasiveness, defined as “the ability to fly quickly, at varying speed and direction,” evolved early within the lepidopteran stock, providing the aversive trait that eventually was advertised by the butterflies' display of color.",
"In other words, butterflies mimic one another across species, but they don't mimic falling leaves.",
"There are plenty of butterflies that mimic dead leaves while perching, though. The comma is one example: ",
"https://commons.wikimedia.org/wiki/File:Polygonia_c-album-03_(xndr).jpg"
] |
[
"Interesting. Thanks!"
] |
[
"Are we the only species to use currency?"
] |
[
false
] | null |
[
"Hi DannyRoy4 thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
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" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"‘Anthropology’"
] |
[
"Anthropology "
] |
[
"Why do matter and anti-matter produce energy when they touch?"
] |
[
false
] | null |
[
"\"Why\" is a sort of generalized question. Do you mean \"what is the reason behind?\" or do you mean \"What is the processes by which it happens?\" ",
"From ",
"wikipedia's article titled Annihilation",
"Since energy and momentum must be conserved, the particles are simply transformed into new particles. They do not disappear from existence. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all quantum numbers of the original pair are zero. Hence, any set of particles may be produced whose total quantum numbers are also zero as long as conservation of energy and conservation of momentum are obeyed. When a particle and its antiparticle collide, their energy is converted into a force carrier particle, such as a gluon, W/Z force carrier particle, or a photon. These particles are afterwards transformed into other particles.",
"Here",
" is a good sort of overview that I really like. It's not an ",
" answer to your question, but it's a really good overview. "
] |
[
"Remember that energy is mass and energy is conserved. But a lot of other things are also conserved in physics like electric charge and various quantum numbers like baryon number, lepton number, etc. Normally you don't see particles undergoing reactions that involve changing to very different particles (such as, say, a proton turning into a photon or an electron turning into a neutron) because that would violate various conservation laws: energy, charge, etc.",
"However, when a particle of matter and its exact anti-matter counterpart react all of those other quantum numbers are zero, because matter and anti-matter have opposite quantum numbers, including charge. Which means that any quantum reaction which can occur with the given total amount of energy that also maintains the other conservation laws can occur.",
"Photons can carry away arbitrary amounts of energy, and they are chargeless etc. so just about any matter/anti-matter reaction can produce photons which we tend to regard as \"energy\". However, lots of other reactions are also possible, such as creation of other particle/anti-particle pairs with the same or lower energy. Typically, with a proton/anti-proton reaction, for example, the product is not photons but actually a cascade of various mesons such as pions or kaons, which can be charged or uncharged and will decay into not just photons but also neutrinos and leptons (electrons, positrons, etc.)"
] |
[
"They produce photons with kinetic energy, the energy was always there."
] |
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