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[
"Does rain dampen or increase the strength of smells?"
] |
[
false
] |
Tobacco for instance. Edit: Clarification: I meant if the smell is on something, not just wafting in the air. So for instance I went outside to smoke a cigarette and had to walk ~100ft through the rain to go inside. Did that rain dampen the smell or make it worse? Does this apply to all scents?
|
[
"I should've specified but I meant if the scent is on an object as opposed to wafting around in the air."
] |
[
"It's along the lines of what I thought, that both dampening and increasing the smell are possible outcomes."
] |
[
"That makes sense, thanks for the answer."
] |
[
"How long could the Earth last."
] |
[
false
] |
If the Sun were to remain at a constant temperature and never died how long could the Earth theoretically last to support life? How long will it take for Earth to become a dead planet like Mars?
|
[
"Quite a few billions of years.",
"The atmosphere is the most fragile part. Some planets lose atmosphere over time, as energetic gas molecules escape the planetary gravity and float off into space. But Earth's gravity is too high and its temperature too low, for this to happen significantly. If nothing changes, we could expect no significant atmospheric loss over ",
"at least a trillion years",
". I'll call that slow enough to be ignored.",
"The other significant change would be the magnetic field. That protects life on Earth from solar radiation, and it's generated by movement of the planet's molten core. At some distant point in the future, once the core cools down and solidifies, the magnetic field would be expected to weaken or cease. But the core is kept hot by the decay of long-lived radioactive atoms, with half-lives in the multiple billions of years. It's going to be a very long while before the core cools any significant amount.",
"In short: it's not going to happen this year, no matter what people say about the Mayan calendar."
] |
[
"Well the sun is a whole lot more active. It's an uncontrolled bomb that fuses something close to a billion tons of hydrogen every second. The Earth is just a big, slightly damp, slightly warm rock. :)"
] |
[
"If the Sun ",
" died/changed, there is no reason that the Earth's present state could not persist essentially forever. Over a very long time (many billions of years), there would be problems with atmospheric loss and on the next largest time scale, eventually the Earth would cool and plate tectonics come to a stop (perhaps 10s of billions of years?). "
] |
[
"Why does your head hurt when you aren't dehydrated?"
] |
[
false
] |
[deleted]
|
[
"There are several types of headaches. Tension headache, the most likely culprit of your current headache, are caused by the muscle wrapping around your head spasming (contracting spontaneously). This is perceived as a head ache.",
"Migraines are more serious type of headache. I believe these are caused by high blood pressure, and thus high intercranial pressure (I could be way off).",
"The last type of head ache is called a 'cluster headache'. This one is caused when your cells accidently release histamine. This hormone makes your blood vessels dilate, which puts pressure on a very sensitive nerve in your head, the Trigeminal never. The person's body accidently releases the histamine because of a disorder in the hypothalamus that is not fully understood. This type of headache affects .1% of the population."
] |
[
"uhhhh, sinus headache is my best guess. It could be from dehydration as well as simple fatigue, but when I think of a cold headache I think of a sinus headache.",
"A sinus is just a cavity...and we have a few in our skulls. One of these sinuses can be filled with fluid (90% sure snot). This is why you should never just breathe in when you have a running nose. Anyways, this fluid will fill up the sinus causes pressure. It is typically only one sinus that is affected, and the real hall mark (tell tale sign) of a sinus headache is a localized throbbing pain in your face, and spreads.",
"I forgot to mentioned something about migraines: they only affect one half of the head (or so I'm told). This makes differentiating between a migraine and a sinus headache difficult. (sinus headaches only affect a part of your head)"
] |
[
"Wait, you shouldn't \"suck in\" a running nose because the snot just collects more and more in your sinus?",
"I've been doing this for years out of laziness - I should really start blowing my nose...",
"I guess I do have a sinus headache then, considering I've had a running nose that I haven't blown out in days. ",
"Thanks Dimpl3s!"
] |
[
"Have there been recent progress in ancient Egyptian DNA sequencing?"
] |
[
false
] |
I keep seeing new results on neanderthals and even woolly mammoths... but the ancient Egyptians lived just a few thousands years ago. I understand there are issues with the hot climate (so DNA breaks down faster and in smaller strands) and contamination, but there are new sequencing technologies available that would work with <50bp strands, and the archeologists keep digging up new, hopefully less contaminated, mummies... why no news on that front (or maybe the media lost interest in reporting it?). What brought this on: just helped my 6th grader with the science project on Egypt, and this question came up. Thanks!
|
[
"Possibly because we've already sequenced the human genome and as you said, they were alive (are still alive, as Egyptians still exist) a few thousand years ago, and in that time frame there is no significant genetic mutations. It is likely that their genetic makeup would greatly resemble out own. "
] |
[
"One of those cases of not enough scientists or money to do everything. We (and our funding bodies) have to prioritise our research targets and if it doesn't look like there is much to gain, other things get prioritised. "
] |
[
"DNA is best preserved in arid environments like egypt ande east africa, it is damp tropical environments where it breaks down fastest."
] |
[
"If you could take all of the viruses out of your body during the peak of a bad flu, what volume would they fill?"
] |
[
false
] | null |
[
"Very little when wet, dried, even less.",
"Let me give you an example. In grad school, I worked on influenza. A couple times a year, we would do thousand egg harvests, innoculating a thousand eggs with the virus, and purifying the virus from the alantoic fluid. Out of about 6-7 liters of fluid, I'd end up with about two to four ml of viral suspension. "
] |
[
"You might. You might also throw up, it had the consistency of snot."
] |
[
"What would happen if I just straight drank that 2-4 ml of viral suspension? Would I just get the flu?"
] |
[
"Is it true that mad cow disease is caused by acts of cannibalism? If so, why is cow eating cow’s brain more dangerous than cow eating rat’s brain?"
] |
[
false
] | null |
[
"Mad cow disease (aka bovine spongiform encephalopathy) is caused by misfolded proteins called prions. There are two types of mad cow disease: classical and atypical. Atypical is rarer, and occurs spontaneously. Classical BSE occurs when cows eat feed contaminated with BSE-infected meat and bone meal. So yes, some types of BSE are transmitted by cannibalism.",
"Like many other pathogens, prions tend to be restricted to the natural host species that they infect. But just like many other pathogens, prions do, very rarely, cross species. The most well-known example would be variant Creutzfeldt-Jakob disease, which infects humans when they consume contaminated bovine meat."
] |
[
"Excellent comment. Wanted to point out that it's typically not bovine \"meat\" or skeletal muscle tissue that would be infectious but instead the tissues known as \"specified risk materials,\" which are Tonsils, Distal Ileum, Skull, Brain, Eyes, Spinal Cord, Trigeminal Ganglia, Dorsal Root Ganglia, and Vertebral Column."
] |
[
"You might be conflating a couple of things.",
"Prions that are responsible for a variety of related diseases affect the nervous system. Its possible to get a prion disease from eating the brains of an infected cow. Its also possible to get a prion disease from eating the brains of an infected person."
] |
[
"If gravity is curvature in spacetime, does that mean that when I throw a ball it is actually going straight in it's own space, but because of the earth that space is curved 'downward'?"
] |
[
false
] |
And if yes, can the force that is pulling me down right now be thought of as me going against the straightness of my movement? uh, so my body wants to go straight, and straight to it is down because of the curve. Am I in any way understandable? And after I've written this I see in the sidebar that disccussion should be 'Free of layman speculation', would this be one of those? and if so, where should i go with this?
|
[
"The short answer is yes, there is a whole branch of study of this in physics, the most relevant of these are geodesics. Standard procedure in GR is to use whatever geometry of spacetime due to the presence of mass or other parameters that we are interested in and reformulate the lagrangian, hamiltonian or other relevant formulation of mechanics to see how test particles will behave.",
"If you want to see more check out wiki or better yet search \"geodesics\" in the cornell journal archives:",
"http://arxiv.org/",
"Note: you may want to look up a spacetime your interested in since you will find a ton of papers if you just search \"geodesics\""
] |
[
"can the force that is pulling me down right now be thought of as me going against the straightness of my movement?",
"Here is a modified version of an answer I gave to a ",
"related question",
" a few days ago:",
"The critical thing to understand is that curved spacetime (gravity) is not a force.",
"Imagine sitting in a car. The car accelerates forward and you feel pressure on your back. This pressure comes from the force between your back and the chair in which you're sitting. You feel the force and you accelerate along with the car. This is what you expect from F = m a.",
"Summary: you feel force, you accelerate.",
"Now think about your butt. It's sitting on a chair. You feel pressure on your butt, but you don't seem to be accelerating.",
"Summary: You feel force, but you do not accelerate.",
"Woah, what happened?",
"Now suppose you jump off a cliff. You're in free fall. Gravity is pulling you downward and you seem to be accelerating downward... but you don't feel any force!.",
"Summary: You do not feel force, but you accelerate.",
"The reconciliation of all of this is that gravity is not a force. Free falling in gravity is actually the \"natural\" trajectory through space time. Any deviation from this trajectory is true acceleration. This is why you feel force on your butt when you're sitting in a chair: the chair is deflecting you from your natural free fall trajectory.",
"When you have a massive object, it just influences the shapes of the free fall trajectories. It's not a force in the usual sense because as we already saw, things in free fall don't feel any force. Another way to drive this point home is to realize that when you're in free fall, say in orbit around a planet, if you close your eyes you have absolutely no indication at all that you aren't just ",
" in space. Free fall in the presence of gravity and standing still in the absence of gravity feel exactly the same. There is absolutely no experiment you can do to tell the difference."
] |
[
"A few comments:",
"which will offset the fact that my timeline is angled a bit toward the mass.",
"The word you want to use here is ",
"\"worldline\"",
".",
"In that sense, a person sitting on a chair is a bit like an aircraft crabbing into a crosswind as it comes in to land.",
"That's a great metaphor, in my opinion. Even if it's not a perfect technical analogue it really gets the idea across.",
"If I were sitting on a chair at the event horizon of a black hole, I would be maintaining an instantaneous acceleration to the speed of light",
"Not sure what \"acceleration to the speed of light\" really means here. You would certainly have to be subject to a force in order to not fall into the black hole, but force/acceleration don't have the same dimensions of speed. Widipedia says that ",
"the force needed to remain stationary at an even horizon approaches infinite the closer you get to the horizon",
". I don't know the details of how to calculate that."
] |
[
"How close are we to cell phones/laptops that hold charge for a week or longer? Or better yet, wireless charging?"
] |
[
false
] | null |
[
"We already have wireless charging.",
"http://en.wikipedia.org/wiki/Inductive_charging"
] |
[
"Indeed, inductive charging has been around for a while.",
"As for the charge, that really is so dependent on usage and the phones draw at idle that it's hard to predict.",
"I have an old flip phone that when charged, if not used, will stay charged for easily 10+ days. I also have a modern smartphone that doesn't make it through the day with my level of usage.",
"I really have no idea what the answer is to that part of the question"
] |
[
"There are all kind of promises about batteries that will last 10x longer, by using nanomaterials. But so far nothing commercially available. ",
"http://en.wikipedia.org/wiki/Nanobatteries",
"There are two things that draw most of the power from a cellphone/laptop: The CPU and display. Some displays, like the Mirasol one uses much less electricity because there is no backlight needed if you have good ambient light. Unfortunately, that technology is not fully matured yet, so the display is not nearly as good as a classic LCD display.\nCPUs are getting more power efficient every year or so, as they become smaller. But in a few years, probably by the end of the decade they can't get any smaller due to physical limitations. Of course, new technology might allow for even smaller transistors, or optical processors, etc.",
"One other thing: As transistors become smaller, you can either increase the number of transistors (which will generally translate in faster CPUs) or you can decrease the power consumption. So I guess that even in 10 years from now the smartphones will still last for only a day or two, but will be much more powerful, maybe as powerful as current desktops."
] |
[
"Why can't we divide by zero?"
] |
[
false
] |
I mean, intuitively, 3/0 is 3 being divided by nothing...so why can't it be 3? I know I'm probably thinking about this all wrong, so can anyone clear this up?
|
[
"This also has to do with limits. If you're approaching it from the positive side, you'll get the above, while if you start from a negative number and work your way towards zero, you'll see that you get -infinity. The reason you cannot divide by zero is not so much that the result is infinity, but that it is both +infinity and -infinity (and hence an exact result cannot be defined)."
] |
[
"You can think of it this way:",
"3/1 = 3",
"3/0.5 = 6",
"3/0.25 = 12",
"3/0.01 = 300",
"3/0.001 = 3000",
"3/0.0001 = 30000",
"3/0.0000000001 = 30000000000",
"and so on. The closer you get to dividing by zero, the closer the answer gets to infinity. So, numerically, dividing by zero makes about as much sense as trying to make infinity into a number."
] |
[
"How can you put three things into zero boxes? Don't over think the problem."
] |
[
"Is there a repository of visible light pictures of space?"
] |
[
false
] |
I've been reading on ask science and saw that most pictures which are published are actually various spectrums of light, including ones that cannot be seen with the human eye. This makes for better looking pictures, but I was curious if there is anywhere I can see pictures of well known galaxies that only show light spectrums that are visible to the human eye.
|
[
"You can find a lot ",
"here",
", they are not sorted on filter, but they tell you in what spectrum the pic is taken once you click it. "
] |
[
"Thanks. I found this after posting. I was mainly curious if there was a good source that had the \"doctored\" pictures side by side with visible spectrum pictures. Same exact source data, but with different spectrums filtered out, etc."
] |
[
"Bear in mind that to get a pic as we see it, it needs to be made in R,G and B filters, which is not done very often, as a lot more information can be gained by adding infrared or other wavelengths. ",
"But as most of the things you see in these filters are quite distinct, you can see what belongs in what filter (with some prectise) \nThis site gives a good idea of how things look in all the filters: ",
"link"
] |
[
"Why does the pitch change when you zip a zipper faster/slower"
] |
[
false
] | null |
[
"Imagine yourself the zipper has a few points it will produce a sound on whenever you cross it. Each time you cross one of these marks it'll produce one sound wave.",
"Thus the frequency will be determined by how many marks you cross each second. Higher speed means more marks crossed per second equals more sound waves per second (higher frequency) which means higher pitch."
] |
[
"This is true, but that is the tuning fork vibrating at it's harmonic frequency.",
"If you start striking the pitchfork fast enough for the initial percussion to have an audible frequency it would make sounds of different pitch to your ears. This is what is happening with the zipper.",
"The harmonic frequency of the individual teeth and zipper do not change, but the initial percussion is fast enough for human ears. The initial percussion is a much louder sound and it easily covers the small sound of the plastic / metal harmonic vibration."
] |
[
"Would the speed at which it strikes each individual tooth in the zipper not change the pitch too?"
] |
[
"If you performed the double slit experiment with air as the medium and subject it to different sound frequencies, would you notice a change in the light pattern?"
] |
[
false
] | null |
[
"I not really sure what you're asking.",
"Are you saying: Can you use sound to make air into the 'double slit' and then send light through it?",
"If so, the answer is (sort-of) yes.",
"There are devices called Acousto-optical modulators that use sound waves to set up a periodic structure in a crystal, which is then used to diffract light. (",
"http://en.wikipedia.org/wiki/Acousto-optic_modulator",
")\nBy changing the frequencies you use, you can direct a beam of light where ever you want. ",
"If you were clever in picking the acoustic signal, you could make something like a double slit effect. One of the problems with this kind of set up is contrast. To get a clear diffraction pattern, you need big differences between the 'slits' and the bits between the slits. If the difference is small (the sounds signal has low power) then it is hard to see the the pattern over the background signal.",
"The problems with doing this in air are 1) the frequency required and 2) the power in the sound required.\nTo be the right spacing for optical light, the sound signal would need to be around 1 GHz (compare that to the highest sound a human can hear, around 20,000 Hz). And, to get good contrast there would need to be a huge amount of power in the sound. \nI don't know if either of those things are technologically possible."
] |
[
"Thanks for your answer. I didn't know what a AOM was until now. You are sort of on the right track as to what I was asking. The reason I asked this question stemmed from cymatics. So far, I've only seen the phenomenon in two dimensional planes such as sand on a glass pane. I was wondering if this sort of order could be possible in three dimensions. For example, if you were to fill a glass box with smoke and vibrate it at a given frequency, would the smoke order into a three dimensional pattern because the entire system is vibrating at a given frequency, or would nothing happen? So, say the laser and slits were all attached in a similar system with air, would the air organize and cause the light pattern to change due to the difference of refraction in the system? As I thought about it more, I was also curious what the result would be if you oscillated just the laser or just the slits. How might it affect the pattern? Or would it not because the speed of light is too fast to observe any difference caused by such slow oscillation?"
] |
[
"I guess that if you had nice loud standing waves in a foggy box you might see something; again, I'm not sure about the power required. Using audible sound would give nice features on the order of 10's of cm.",
"Another cool thing is that in humid air, low pressure areas would condense water into clouds. In theory, this could give you some nice visible contrast. (And if you had something else in the air, say soot or something else particulate, you would get fog mostly at the low pressure points and soot mostly at the high pressure points!) Once again, I'm a theorist in a different field, so I have no idea how feasible it is, but it's at least plausible.",
"What do you mean by oscillating the laser or the slits? Moving the beam back and forth over the slits? This wouldn't do anything really interesting: There is an oscillating part of the interference pattern that is determined by the direction and colour of the beam and position of the slits; and there is a brightness distribution (basically a Gaussian) over the top of this that will change as you move the beam around."
] |
[
"What are some counterintuitive non-quantum level phenomena?"
] |
[
false
] |
In the quantum world, nothing is intuitive (particle/wave duality, superposition, nothing happens with certainty, etc.) But in the "macro" world, are there examples of processes/events that are counterintuitive?
|
[
"When a human being moves from a low-altitude place to a higher altitude place, their body has to cope with lower oxygen levels. One of the ways a body can adapt is to make more hemoglobin, the protein in red blood cells that carries most of the oxygen we breathe to our tissues. Some athletes will train in a high-altitude environment to gain this adaptation and use it to their advantage when they return to the lower elevation where they normally play. So you'd expect that populations living at the highest possible elevations to have a lot more hemoglobin than people living near sea level.",
"Wrong. They actually have less. The reason is that more hemoglobin is better only up to a point, and then the blood becomes to viscous to flow properly. Instead, high-altitude populations have acquired mutations that enable their cells to use oxygen more efficiently."
] |
[
"The ",
"tennis racket theorem",
".",
"Babinet's principle in optics.",
"There are a lot of interesting effects in fluid mechanics, where the equations governing fluid flows can be very nonlinear.",
"This kind of involves quantum mechanics, but the differential cross section for scattering of pointlike charged particles in classical mechanics turns out to be exactly equal to the quantum result. Not just approximately equal in some limit; ",
" equal. You could interpret this as just dumb luck for the classical theory. There's no reason why classical scattering theory should get the exact answer for a quantum scattering process.",
"Relativity (special and general) is full of things which go against Newtonian intuitions, and don't really have anything to do with quantum mechanics."
] |
[
"Instead, high-altitude populations have acquired mutations that enable their cells to use oxygen more efficiently.",
"Per hemoglobin levels, this depends on the high-altitude population (Tibetan, Andes, or Ethiopian) ",
"http://www.pnas.org/content/99/26/17215.full"
] |
[
"Why are heart attack victims sometimes put into a medically induced coma?"
] |
[
false
] |
A friend collapsed from a heart attack a few days ago and was put into a medically induced coma. Why? What are the risks to this? Thanks.
|
[
"Well I can't speak specifically to your friends condition but can talk around general points.",
"The most likely scenario I could imagine would be in the setting of a cardiac arrest. A heart attack occurs when one of the coronary arteries that supplies the heart becomes blocked, and as a result the bit of heart muscle that artery was supplying with blood dies. There are many possible consequences from this, depending on how big a bit of muscle it was, and where in the heart it was, but one catastrophic consequence is that it can make the entire heart stop beating. This is what we call a cardiac arrest, and unless the patient gets prompt CPR they will die.",
"The aim of CPR is to get the heart beating again and to continue to get blood to vital organs while doing so. However, if we are successful at restarting the heart, that is only part of the story. If it takes too long to restart the heart, or there was a significant delay in starting the CPR then the vital organs will not have received enough blood and may be damaged. While any organs may be affected, the most vulnerable is the brain.",
"It is a not uncommon scenario to successfully resuscitate someone from a cardiac arrest only for them to have suffered devastating and irreversible brain damage. We are therefore very interested in anything that might protect the brain in patients who have been successfully resuscitated from cardiac arrests. In 2002 two independent studies were published in the New England Journal of Medicine ",
"link",
". These studies suggested that deeply sedating and cooling these patients to around 34 degrees may result in better neurological outcomes. This has now become pretty much standard of care, and in patients in whom the heart has been restarted it is a common practice."
] |
[
"Brain damage will start within several minutes after cardiac arrest if there is no CPR. It certainly doesn't always occur - people can make full recoveries after cardiac arrest, but the shorter the duration of CPR the better."
] |
[
"Curiously, do you feel there's much supporting evidence to agree that the amygdala is one of the first areas to see damage post arrest? I've argued this with a number of personnel, and we cannot come to a valid conclusion at this time. Anyone have good evidence for or against this?"
] |
[
"Is there a limit to how fast water can be pumped?"
] |
[
false
] |
If not, what sorts of variables affect how quickly water can be pumped? I watched and was interested in making my own and trying to improve upon it.
|
[
"More speed -> more power;",
"If turbulence is introduced or friction is significant,",
"More speed -> more energy.",
"If you're using a hand pump to pump some fluid some height differential, you absolutely cannot make a pump go as fast as you want, it would be limited by (among other things) how much power you can put out vs the difference in potential energy per unit time introduced by the pump. ",
"Btw, I don't understand the downvotes either, but w/e."
] |
[
"More speed -> more power;",
"If turbulence is introduced or friction is significant,",
"More speed -> more energy.",
"If you're using a hand pump to pump some fluid some height differential, you absolutely cannot make a pump go as fast as you want, it would be limited by (among other things) how much power you can put out vs the difference in potential energy per unit time introduced by the pump. ",
"Btw, I don't understand the downvotes either, but w/e."
] |
[
"The limit in terms of energy (or power) is of course the amount of work that needs to be done. So for example, if you're pumping water 1m higher, you need at least:",
"E~mg dh~m 10 1 = 10 Joules/kg [assumes uniform gravity]",
"If you're inflating a balloon from atmospheric pressure p0 to pressure P and volume V, you need more than:",
"E~P V (ln(P/p0 V)-ln(V)) = P ln(P/p0) Joules/cubic meter [assumes isothermal compression]",
"As for improving it, you need to look at losses that take you away from the limits above. In case of pumping water for example, the valves may be very narrow, causing a lot of turbulence in the water, dissipating your power as heat. Another definition of improving could be simply making it more powerful without making it more efficient -- e.g. by increasing the tubes diameter or making it more anatomical to use."
] |
[
"How hard was Dinosaur skin?"
] |
[
false
] |
All photos make it look like they had hard shells, is this just a dramatization? Wouldn't they be no more tough than a bear skin?
|
[
"You're forgetting the scales. Like many modern reptiles, many dinosaurs had scales on their skin. Think nonoverlapping scales like an alligator, not overlapping like a snake. Many other had feathers, or a combination of feathers and scales."
] |
[
"Depends on the dinosaur. The ones with feathers (probably most therapods) would have been not much different from modern birds. Ones with scales (the rest, based on skin imprints from a few different groups) would have been a bit tougher. Ones with armor (the ankylosaurs) may very well have been bulletproof, but at that point we're not really talking about skin anymore. But this all assumes they didn't have unusual properties that didn't fossilize."
] |
[
"We don't actually know what the skin of dinosaurs looked like or was made of. Because skin is an organic material it decomposes away, so humans have never seen dinosaur skin.",
"We can guestimate the properties of the skin based on environment, but the color of a dinosaurs skin is really up to the designer of the image. In fact, google image search the name of any dinosaur, and you will see a range of varying colors of skins."
] |
[
"So when we say the \"speed of light\" we are referring to a measurement that approximates an asymptotic value that cannot be physically measured?"
] |
[
false
] |
If a particle has mass, its velocity can never be the speed of light unless its Energy is infinite. Since light has mass, what is the deal? Light can't travel as fast than its own self? We are just approximating an asymptotic value we can't actually measure in the universe since everything has mass right?
|
[
"While light has mass-energy, it has no rest-mass...in a certain sense all of its energy is \"kinetic\" (although that's not exactly accurate).",
"Light does move at the speed of light. All photons--indeed all particles with zero rest mass--always move at the speed of light, never slower.",
"The fact that light moves \"slower\" inside materials is a macroscopic property of the material that has to do with photons constantly getting absorbed and reemitted. If you shoot a high energy gamma ray photon through a material and it goes straight through, it will move at the speed of light the whole time, even if the \"speed of light in the material\" is less than c. In general, the speed of light inside a material is a complicated function of the frequency of the light."
] |
[
"Light ",
" at a speed less than c. It hits a particle in the medium, then gets re-transmitted. This makes its overall speed a little slower. This is my understanding of it, at least."
] |
[
"Light ",
" at a speed less than c. It hits a particle in the medium, then gets re-transmitted. This makes its overall speed a little slower. This is my understanding of it, at least."
] |
[
"What happens to dead germs or bacteria?"
] |
[
false
] |
[deleted]
|
[
"Inside the body: macrophages eat them. (Sort of, dead bacteria, virus, fungus etc are destroyed by the immune system)",
"Outside the body: If you use hand sanitiser, germs will dry up and probably stick to the skin until it's rubbed off or you wash your hands. If you wash your hands with soap and water, the soap dissolves the outer layer of fat on your hands, and dirt, germs, some skincells and whatever else you have on your hands, is rinsed off. If you want clean, germ free hands, it's better to wash with soap and water and lather for about 30 sec (or something like that, I don't remember. More than just splash, once around, splash), but if you don't have a sink or the time, hand sanitiser is better than nothing."
] |
[
"Most will just dessicate or dry up. However this is also depended on what kind of bacteria we are talking about. Some bacteria will have a special capsule, allowing them to survive in very adverse conditions. ",
"But in your cause the rubbing alcohol would cause most of the water in the bacteria to migrate out leading to the bacteria drying up, and becoming dust."
] |
[
"I wasn't broken up over it or anything, but thanks for the explanation. I read Reddit from the front page, so I don't usually notice any sub-rules in the sub-reddits. I'll mind my manners in AskScience from here on out."
] |
[
"What are the funding agencies that fund \"risky\" research?"
] |
[
false
] |
I found to be very interesting, so I know that HHMI is the one that funds risky biomedical research But what about other organizations that fund research, in say, fields like the geosciences or astrophysics?
|
[
"Its just a front for the stargate program :P"
] |
[
"DARPA",
" actually funds a lot of weird stuff."
] |
[
"Scary bit: The Air Force runs a space program bigger than NASA. "
] |
[
"How does satelite radio differ from fm or am? I can easily build a radio at home for am/fm but whats stopping me from making something that picks up satelite?"
] |
[
false
] |
[deleted]
|
[
"There isn't a technical reason why you couldn't build a device that receives signals from satellite radio providers - it's typically broadcast in the S band range, like a number of common consumer devices like garage door openers and wifi routers.",
"However, AM/FM radio broadcasts are intended to be heard as broadly as possible, since they're supported primarily by advertisers who want to reach a broad market. Sirius makes its money from subscribers, so they need to add a security level - broadcasts are encrypted.",
"So you can build something that detects the signal, but won't be able to make sense of the information it contains since it can't decode the broadcast. "
] |
[
"Protecting broadcasts which are sent to large numbers of people is really hard. They all have to have copies of the decryption key buried somewhere inside their device. This means that breaking the mathematical part of the encryption is not necessary; all that's needed is to figure out how to extract the keys from the device.",
"In the past, satellite TV providers have had issues with ",
"people figuring out, and distributing, decryption keys and devices",
"."
] |
[
"If it was easy, then the encryption wouldn't be very good. Going into depth about it would be better served by its own question, but the gist is that encryption relies on the fact it can be very easy to transform numbers in one direction and very difficult in the other. Like say 11 * 13, you can do that in your head (to get 141). But try finding the prime factors of 141, that's more difficult. The trick with encryption is to come up with similar operations where the complexity is so immense that it would be unfeasible for a computer brute force the solution. "
] |
[
"AskScience AMA Series: I'm Will Armentrout, an astronomer at the Green Bank Observatory in the heart of the US National Radio Quiet Zone. Ask me anything!"
] |
[
false
] |
I'm Will Armentrout, an astronomer at the Green Bank Observatory ( ) in West Virginia. The Observatory is within the United States National Radio Quiet Zone, a 13,000 square mile area of the Appalachian mountains where radio transmissions are limited by federal and state law. These protections become more restrictive as you move closer to Green Bank, so since I live on observatory grounds, I go about my daily life with no cell phone, no microwave, no wifi, no wireless headphones... The Green Bank Telescope (GBT) is the largest movable structure anywhere on land, sitting at 485 feet tall and 17 million pounds. The radio telescope has a diameter of 100 meters (~300 feet) -- you could easily fit two football fields on the telescope's surface. The GBT is used to observe a huge variety of astrophysical phenomena, from active star forming regions, to pulsars and fast radio bursts, to galaxies billions of light years away, and more. My position involves a mix of my own scientific research and the chance to work with astronomers from across the world who want to use the GBT. I also coordinate our student research programs and observer training workshops. My scientific research focuses on how the Milky Way Galaxy conspires to produce high-mass star (masses greater than ~10 times that of our Sun). We use these high-mass star forming regions as probes for studying the structure of the Milky Way and how the environment around the Sun compares with other regions of our Galaxy. I'm particularly interested in an extremely distant spiral arm, known as the Outer Scutum-Centaurus Arms, which seems to be the outermost limit for high-mass star formation in our Galaxy about 20 kpc (or 70,000 light years) from the Earth. I'm originally from Ford City, Pennsylvania and went to Ford City High School. I graduated from Westminster College in 2012 with a BS in Physics and finished my PhD in Physics at West Virginia University in 2018. I started a postdoctoral position at the Green Bank Observatory right after graduate school, and was hired onto the permanent scientific staff earlier this year. Outside of work, I keep busy hiking in the Appalachians, keeping track of a small flock chickens, and renovating a huge century old building in my hometown with my siblings (any leads on old planetarium equipment?). I'll be on at 1 pm EDT (17 UT) on Wednesday, July 22nd, ask me anything! Username: Will_Armentrout
|
[
"I really think there will always be a place for large single-dish observatories, and the reason is that while interferometers can be fantastic instruments and get you exceptional resolution (the best resolution of any telescopes at any wavelength), there are things interferometers are not inherently good at.",
"For radio telescopes, the resolution you get goes as ~wavelength/diameter. The bigger the diameter, the smaller objects you're able to see. Interferometers simulate huge telescopes, effectively with diameters of many miles (or thousands of miles for the Very Long Baseline Array / VLB Interferometer). The problem for interferometers is that while you can have excellent resolution and see very tiny objects, you typically are not sensitive to large scale emission. Interferometers \"filter out\" diffuse emission, so if you're trying to observe large clouds in the Milky Way or the giant gas reservoirs surrounding nearby galaxies, you wouldn't be able to see that with interferometers. You would need a large single dish to see that large scale structure. This is called the \"zero spacing\" problem. ALMA in Chile has tried to get around this with an array of smaller antennae at the core of the main array, but the best option is a large single dish.",
"Large single dish telescopes also typically have good \"dynamic range\", so you're able to see both very bright and very faint objects at the same time with large single dishes. We're starting to make \"arrays\" of antennae that go on large single dishes like the GBT and Arecibo, so instead of just looking at one part of the sky, you can look at multiple nearby spots at once. The most ambitious project we currently have for the GBT is a 144 element receiver operating at our high frequency end (74-116 GHz). This will be a great complement for interferometers like the VLA and ALMA because we can map out large areas of the sky very quickly, compared to interferometers.",
"Another thing about large single dishes is that we tend to be good at detecting pulsars. At our low-frequency range, (~150 MHz to a few GHz), you can see a degree or so of the sky at one time. Since the telescope is so sensitive, its a good way to track down transient objects in space."
] |
[
"Any time I can see a clear view of the Milky Way strewn across the sky, I get a little misty eyed. Green Bank was picked as a place that would be good for a radio observatory (protected by the mountains from radio interference from nearby cities), but it would not be the best place for an optical observatory. Those are typically in deserts or high on mountain tops. That said, since there's a low population around Green Bank, there's not much light pollution, and you have some great, clear skies. Seeing the Milky Way isn't so much of a rarity here.",
"I also really love when I make the first observations of a new object. It makes you feel like a bit of a trailblazer or that you're increasing humanity's understanding of our tiny piece of the Universe."
] |
[
"Do you know how the size and restrictions of the National Radio Quiet Zone were determined? Do other observatories have areas of similar restriction?"
] |
[
"Really odd one, but can humans produce sounds that they cannot hear? So above the Hz that a human can hear but a cat, for example, could?"
] |
[
false
] | null |
[
"\"In 2012, Storms reclaimed the record for the Lowest Note Produced by a Human. The new record is G−7, or 0.189 Hz, eight octaves below the lowest G on the piano, or just over seven octaves below the piano.[5] The most recent published record is in the 2020 Guinness Book of World Records.\nStorms' record-setting sounds are so low as to be infrasonic, incapable of being perceived by the human ear.\"\n",
"Tim Storms Wikipedia"
] |
[
"That article says it would take about 5 seconds to complete one oscillation of the vocal cords at that lowest pitch. Which is, let’s say, really implausible."
] |
[
"A sound wave is a wave. It has an oscillating pattern and this one happens to take 5 seconds to complete an oscillation."
] |
[
"How common are viral & bacterial infections among aquatic organisms?"
] |
[
false
] |
Have there been any infectious diseases that have devastated entire populations/communities?
|
[
"Infections are common among all organisms. One good example is Vibrio cholerae, the bacteria that causes the disease cholera. It's natural habitat is shellfish. ",
"http://en.wikipedia.org/wiki/Vibrio_cholerae",
". This sort of behavior is a HUGE driving force for evolution. And for fun I leave a link about how koalas are being killed by the clap. ",
"http://en.wikipedia.org/wiki/Vibrio_cholerae",
".",
"AAAAAAND.... There are 10",
" stars in the observable universe and an estimated 10",
" bacteria alive on earth. Bacterial rule our world."
] |
[
"Thanks. We learned about infections in biology class, but we only went over land animals."
] |
[
"Another fun fact. There are 22000 genes in the human body. Recently scientists looked at the bacterial species in and on our bodies and found 8000000 different genes. Pretty crazy."
] |
[
"What happens to the 0.01% of bacteria that isnt killed by wipes/cleaners? Are they injured or disabled?"
] |
[
false
] |
|
[
"Ok, so I work in the industry of antimicrobial testing, and no, it's not a legal disclaimer, we test and see how much of a log reduction a product gets and we literally scrub the shit out of the device or surface or whatever, so no, it's not a CYA claim, it is based on actual FDA or EPA regulated testing on very specific strains of bacteria, fungi or viruses, or appropriate surrogates. The remaining bacteria or other microbes not killed may very well develop resistance and there are even concerns that some previously non-pathogenic strains of E. faecium and faecalis have evolved to be resistant to alcohol based sanitizers. And yes, sterilants can kill even super bad spore strains, but the contact times are like 20 minutes for even the best, trendiest ones used on devices. And those sterilants are pretty nasty. Basically, don't overuse any antibacterial substance, and know that manual scrubbing of contaminated surfaces with any cleanser or disinfectant goes a long way, a product just works better when you scrub and use at the proper contact time. "
] |
[
"There's also the ",
"minimum infective dose",
" to take into consideration. Let's say you're about to eat a sandwich and you've just washed your hands. If it takes 40 E. coli to infect you and washing your hands killed all but 10, you're likely to not be infected."
] |
[
"The 0.01% form spores or slime layers that are resistant to alcohols and detergents that are in the wipes. The purpose of the chemicals is to destroy bacterial cell walls. However, if the germ has a protective layer, it can remain on surfaces until it enters a more favorable environment. Not to mention, when the cleaners ",
" kill bacteria, the cell remains still remain on surfaces after being broken apart, so there is still a possibility of triggering immune systems even though the bacteria can't actively grow.",
"C. diff is one particular organism that is rampant in hospitals for this reason (that and the patients are already ",
" deprived of protective gut flora due to antibiotic therapy). That's why healthcare workers have to physically wash their hands by scrubbing for a period of time, and not just use hand sanitizers/cleaners."
] |
[
"Why does closing one eye help the pain when it's really bright out?"
] |
[
false
] |
Shouldn't it be equally bright in each eye?
|
[
"You \"feel\" bright light when the iris contracts and makes your pupils small. This is why photophobia is a common symptom of corneal abrasion and viral keratitis, and why browache results from pilocarpine drops that force the pupil to shrink.",
"When you cover one eye, you reduce the stimulus to pupil constriction. The pupils still constrict (even in the closed eye) but the stimulus isn't as intense, so the response is not as \"painful\"."
] |
[
"So, ",
"u/mckulty",
" is probably wrong, but it's OK, because this was a leading hypothesis for awhile, and there was no satisfactory explanation for photophobia until ~2006. The conceptually easiest way to show this is the following case report:",
"http://www.ncbi.nlm.nih.gov/pubmed/17121141",
" ",
"Wherein a patient had fixed, fully dilated pupils, but still felt photophobia. Since her pupls couldn't constrict, it mustn't be the constriction of the pupils that makes the eyes hurt. ",
"There are other subtle clues that photophobia isn't the pupil's fault. For instance, action spectra: Comparing different colors of visible light, and seeing how intense light of a certain color has to be before it causes pain, yields a different pattern for how intense it has to be to cause the pupil to constrict by a certain amount. Another one: Systemic drugs that cause pupillary constriction, like opiates, tend not to cause eye pain.",
"It's bothersome that people could have their rod and cone photoreceptors wiped out by retinitis pigmentosa, but still have photophobia, and still have some non-zero pupil reaction to light. This lead to a search for photoreception causing pupil size changes in the pupil itself (frogs have this) but none were found. Rather, there is a third kind of photoreceptor -- the intrinsically photosensitive retinal ganglion cell (ipRGC) discovred in mammals in 2000, that helps explain. These ipRGCs project to the posterior thalamus, as well as some hypothalamic nuclei (to help regulate circadian rhythm) and also play a small roll in pupil dilation. ",
"This ipRGC-to-thalamus pathway is probably the one detected in this paper:",
"http://www.ncbi.nlm.nih.gov/pubmed/21337474",
"Irritation at the trigeminal nerve (which does sensation of the face) causes photophobia. It also mediates sensation of the cornea -- which links photophobia to corneal damage -- and the meninges -- which links meningitis to photophobia. The first paper I linked to has a nice discussion section. Apparently, people have tried injecting saline solution into the frontalis muscle, and this causes photophobia. It's not related to innervation directly in and around the eye, as numbing the spheno-palatine ganglion (",
"http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1998572/",
") alleviates photophobia. ",
"Trigeminal nerve -mediated pain is via nerves projecting to the nucleus caudalis in the lower pons. We would have a good explanation for photophobia if this area was linked to the same part of the thalamus that our ipRGCs project to.",
"The same paper as above (",
"http://www.ncbi.nlm.nih.gov/pubmed/21337474",
") shows that anatomic pathway.",
"From a case report, we have MRI evidence that the trigeminal nucleus and posterior thalamus are preferentially activated in photophobia.",
"http://www.ncbi.nlm.nih.gov/pubmed/19674842",
"These are the same* areas that are shown to be anatomically linked in the previous paper (*same to the degree that the areas can be said to be the same given inter-individual variability in how the thalamus is organized)",
"Neuron labeling (anterograde and retrograde) in rats shows that the ipRCG-to-thamalus and nucleaus caudalis-to-thalamus come in very close contact ",
"http://www.nature.com/neuro/journal/v13/n2/abs/nn.2475.html",
"So, here's a data-driven model of how photophobia works:\n (1) ipRGCs from each eye form excitatory connections with the posterior thalamus (the rods and cones presumably do not, not even indirectly)\n (2) sensory nerves for the face, corneas, meninges -- part of cranial nerve V (Trigeminal) -- form excitatory connections with the nucleus caudalis (in the pons). Though not critical for this model, note that there's allowed to be a bit of spatial non-specificity here; and nucleus caudalis neurons receiving ",
" signals from the cornea may still receive a little signal from eyebrow area, or from the meninges. \n (3) the nucleus caudalis neurons form excitatory connections with the same part of the posterior thalamus\n (4) conscious perception of pain \"happens\" if that part of the thalamus gets enough excitatory input, to be bothered to forward the information to the cortex",
"So, let's just get a feel for this, albeit using made up numbers wherein a sum of 100 or more triggers pain, <100 is painless",
"you're in bright light without any irritation to your cornea, face, meninges, etc.\n Left eye light adds 30, right eye light adds 30, corneas add 5, meninges add 5, and face adds 1. \n76 points does not trigger photophobia.",
"So, you damage your left cornea, but lighting doesn't change. \n Left eye light adds 30, right eye light adds 30, corneas add 50, meninges add 5, and face adds 1. \n116 points ",
" trigger photophobia.",
"Since light hurts, you close one eye,\n Left eye light adds 32, right eye light adds 0, corneas add 50, meninges add 5, and face adds 1. \n88 points does not trigger photophobia.\n (left eye adds 32 instead of 30, because the pupil of one eye will dilate slightly if block light from hitting the other, as by closing one eye). ",
"Months later, your cornea is healed, but in a run of bad luck, you get meningitis,\n Left eye light adds 30, right eye light adds 30, corneas add 5, meninges add 50, and face adds 1. \n116 points ",
" trigger photophobia.",
"...so you head into a room that's mostly dark, and you feel better\n Left eye light adds 5, right eye light adds 5, corneas add 5, meninges add 50, and face adds 1. \n66 points does not trigger photophobia.",
"You recover fully from meningitis, and happen to step out from a dark movie theater to a bright sunny day; your pupils fully dilated and your retina adjusted to low light levels, your vision is whited out by the sudden blast of light, and it hurts\n Left eye light adds 50, right eye light adds 50, corneas add 5, meninges add 5, and face adds 1. \n116 points ",
" trigger photophobia.",
"By the time your pupils constrict, and you re-adjust to the light, or put sunglasses on, etc., \n Left eye light adds 40, right eye light adds 40, corneas add 5, meninges add 5, and face adds 1. \n91 points does not trigger photophobia.",
"but now, affronted by your choice of sunglasses style, a drunk punches you in the nose, \n Left eye light adds 40, right eye light adds 40, corneas add 5, meninges add 5, and face adds 11. \n101 points ",
" trigger photophobia.",
"Edit 1: I actually went through the trouble of looking this all up after I felt I couldn't give a full and satisfying answer to this question when it was posted ~4yr ago.",
"http://www.reddit.com/r/askscience/comments/hgzld/why_is_it_i_can_bear_the_sunlight_fine_with_one/",
"Edit 2: From Benarroch's article in the journal Neurology (2011) \"The melanopsin system: Phototransduction, projections, functions, and clinical implications\"\n \"Intrinsically photosensitive retinal ganglion cells. Melanopsin (also called opsin 4, Opn4) is a photopigment that was first identified in frog skin and was thereafter detected in a small subpopulation of retinal ganglion cells in vertebrates.8 The ipRGCs respond to light stimulation with depolarization in the absence of any synaptic input from\nrods and cones; hence their designation as intrinsically photosensitive.\"",
"(reference #8 here is a paper from 1998; this is fun, because for ~100 years, the only two photoreceptors were rods and cones, then ",
"! There's a third one!)",
"He continues, \n \"Migraine. Light exacerbates migraine headaches and several migraineurs have aversion to light (photophobia).\nThe preservation of these symptoms in blind individuals with light perception implies the potential involvement of the melanopsin system.1,7,35 Noseda et al.,35 using single-unit recording and neural tract tracing in the rat, identified dura-sensitive neurons that were modulated by light and projected extensively to the somatosensory,\nvisual, and associative cortices. These dura/light-sensitive neurons were apposed by axons from melanopsin-containing ipRGCs.35 These findings suggest a role of the melanopsin system in mediating migraine-related photophobia.\""
] |
[
"Ah.. the pupil isn't the only light control in human eyes. The retina itself is responsible for night vision; in dim light your retina gets more sensitive like raising the ISO on film or a digital camera. This would happen with one eye closed, or patched, no matter what happens in the other eye. ",
"Shining light in the right eye makes the left pupil constrict whether the left eye is open or not."
] |
[
"Is there a specific medical reason why 4 hours is the cutoff time to see a doctor after ED drug's effects won't go away?"
] |
[
false
] |
Or is there some arbitrariness to it?
|
[
"The reason being is the blood will clot and you might lose it.., the solution to this is 2 needles that are place on either side of the urtheral opening to drain the corpus cavernosum.",
"http://en.wikipedia.org/wiki/Corpus_cavernosum_penis",
"I have seen a few people come to the ER for it, each time it was resolved with a bag of ice after explaining the procedure."
] |
[
"Current scientific evidence demonstrates that when an erection lasts longer than 4 hours, it merits evaluation and possible treatment because of the potential detrimental effects of the erection on the viability and future function of the corporal tissue.",
"There is some \"arbitrariness\" to it, although starting at 4 hours you begin to see microscopic changes of severe and possibly irreversible injury.",
"More than you probably want to know..."
] |
[
"Greetings fellow science seekers! It's great if your friend's friend's uncle's cousin had some kind of issue with having an erection last longer than safe. However, this is a place for science instead of anecdotes. Unless you have relevant, expert knowledge on this subject, could you please keep it in your pants? Thanks!"
] |
[
"A thin girl from my hometown gained ~150 pounds in about 1 year. How is this possible?"
] |
[
false
] | null |
[
"It's difficult to answer questions about individual anecdotes without resorting to speculation which we try to avoid."
] |
[
"I was just wondering which medical conditions may result in rapid weight gain or if it's even possible to gain so much weight so quickly on her own accord. "
] |
[
"So a more general question like \"are there medical conditions that can cause a rapid amount of weight gain in a short period of time\" would be totally fine. But asking about a particular person is impossible to answer objectively over the internet. "
] |
[
"Why do infections not spread and kill us today, but seemingly killed often in the past?"
] |
[
false
] | null |
[
"Medicine"
] |
[
"Medicine"
] |
[
"Medicine like antibiotics, knowledge about cleaning wounds, hospital care if things get bad / fever persists."
] |
[
"Does Mercury experience any significant tidal forces from Sun?"
] |
[
false
] | null |
[
"Yes, though the tidal forces aren't strong enough to cause a full tidal lock. Instead Mercury is in a 3:2 orbital resonance with the Sun, meaning that three days on Mercury are equivalent to two full orbits around the Sun.",
"Solar tidal forces are relevant even on Earth: The solar tide is about half the magnitude of the lunar tide (but much longer period). The superposition of the lunar and solar tides is what leads to spring and neap tides."
] |
[
"The solar tide is about half the magnitude of the lunar tide (but much longer period)",
"The period is nearly the same, both are driven by the rotation of Earth. The time between the Sun at the same position in the sky is a bit shorter than the period between the Moon at the same position, but that difference is small (~1/30)."
] |
[
"The orbit is fairly regular. It is not closed - its perihelion precesses. 90% of this precession comes from the gravitational influence of other planets, which can be described with Newtonian mechanics. Only 10% is an effect of general relativity that doesn't exist in Newtonian mechanics."
] |
[
"Why are the wheels of NASA's Mars rover, Curiosity, wearing out?"
] |
[
false
] |
After reading an article from Pasadena News: ...I got to wondering why Curiosity's wheels are wearing out and what threat punctures are to a non-inflated solid aluminum wheel? I've never heard this discussion from any of the other rover camps. Is it because of Curiosity's greater mass? Harsh terrain of the area it's exploring? Different wheel design? I understand it's only travelled a little under 5km since landing in 2012. Is the surface of Mars really that rough? Thank you.
|
[
"Here are some photos in case anyone was wondering. ",
"http://mars.jpl.nasa.gov/msl-raw-images/msss/00490/mhli/0490MH0262000003E1_DXXX.jpg",
"http://mars.jpl.nasa.gov/msl-raw-images/msss/00490/mhli/0490MH0262000001E1_DXXX.jpg",
"http://mars.jpl.nasa.gov/msl-raw-images/msss/00494/mcam/0494ML1964004000E1_DXXX.jpg",
"http://mars.jpl.nasa.gov/msl-raw-images/msss/00411/mhli/0411MH0262001000C0_DXXX.jpg"
] |
[
"This topic has been discussed multiple times on other subs. That aluminum that's cracking is probably about the thickness of a cola can. This wear was expected and is largely cosmetic. "
] |
[
"This topic has been discussed multiple times on other subs. That aluminum that's cracking is probably about the thickness of a cola can. This wear was expected and is largely cosmetic. "
] |
[
"Why does a fan make me cooler instead of hotter?"
] |
[
false
] |
[deleted]
|
[
"In principle, you are correct. However, oxygen moves at something like 443m/s. The small amount of extra speed you are giving the atoms isn't particularly consequential. Really, the fan just ends up directing more of the molecules past you.",
"Overall, like was mentioned before, this has the effect of constantly sweeping newer, colder air towards you to sweep up heat and moisture(that brings heat with it as well)"
] |
[
"In principle, you are correct. However, oxygen moves at something like 443m/s. The small amount of extra speed you are giving the atoms isn't particularly consequential. Really, the fan just ends up directing more of the molecules past you.",
"Overall, like was mentioned before, this has the effect of constantly sweeping newer, colder air towards you to sweep up heat and moisture(that brings heat with it as well)"
] |
[
"Right. Taking a molecular view of things, the speed of air molecules due to Brownian motion is much greater than the speed they gain due to the fan, and so the fan doesn't increase the temperature of the air much at all. Since the air is cooler than you, when air molecules collide with your \"skin molecules\" the net transfer of energy is to the air molecules. Energy, in the form of heat, leaves your body and goes into the air."
] |
[
"Is air really invisible or have we evolved to not detect it's would-be colour?"
] |
[
false
] |
Does it simply not reflect light or have we evolved to not detect it since it would impede our vision. If it really doesn't have a colour, would it be possible for human's to evolve with visual organs that would adapt to another atmosphere that's more opaque?
|
[
"You can look at ",
"this chart",
" which shows the amount of light of various wavelengths.",
"The blackbody spectrum is the approximate colour of sunlight. By the time the light reaches sea level, you get the line shown by the red blocks. It seems substantial, but remember, the atmosphere is many kilometres thick so the energy reduction at the peak is about from 1.75 down to 1.3, or 28%. If you arbitrarily assume the atmosphere is 30 km thick, the absorbtion is only ~1% per km.",
"Our visual systems are optimised to work using the most abundant light (roughly 400 to 700 nm). Coincidentally, the air doesn't absorb much light in this range. ",
"See chart here.",
"So yes, our atmosphere is mostly colourless and invisible in our visual range (unless you are looking through a lot of air, such as standing at a high mountain and looking at the horizon).",
"Let's not talk about evolution. Lets just ask if can WE design an optical system to see in this environment.",
"If the atmosphere is gaseous, then the absorbtion will occur at certain wavelengths. You will need to design a sensor with a suitable sensitivity range to avoid the worst of the absorbtion, yet operate within the range with the most available light.",
"If the atmosphere is opaque due to particles in the atmosphere, it becomes much harder. Light of all wavelengths will get scattered and it will be like trying to see through a blizzard. You will need ",
" of a wavelength significantly different from the particle size. How about radar? Airplanes navigate through rain using radar."
] |
[
"Air does not interact significantly with any significantly sized band of light frequency. For example, if we had X-ray vision sight and there was ample X-ray light, we would see air still as transparent. However, as you probably know, X-rays are absorbed by very dense materials like bone and metal, but now flesh appears mostly transparent.",
"When we see infrared, we see new interactions from blackbody radiation, but similarly air doesn't absorb too much IR radiation. And again with radio waves, they can easily pass through the air and could also be seen by special eyes that see in microwave.",
"So then, why don't we have x-ray vision or microwave vision? The real question should be, what is so special about the visible light band? That is because of ",
"this unique phenomenon",
" in Earths atmosphere.",
"Lucky for humans, there is no large amount of gamma and x-ray illumination from space that makes it through our atmosphere, so if we did have X-ray sight, we would see very little. This is why X-ray machines have to emit their own illumination. Same case for gamma radiation.",
"As for IR, some species of life do indeed see in part of what we call the IR spectrum, and this is because hot objects emit their own light in the IR range due to black body radiation. If an object gets even hotter, we see it in the visible light band (like an incandescent light bulb). Why don't humans see in IR? Well, evolution is just a gradient, not a steady march towards perfection, and as far as I know we haven't had any ancestors who had such sight anyways. Same with UV light, which some animals can see.",
"Radio waves and lower frequencies are not commonly emitted by life forms, and (correct me if I am wrong) but life forms and many objects are transparent at those wavelengths. There would be little illumination, and you would see poorly as well.",
"TL;DR optical window"
] |
[
"Since human eyes are only developed to see visible light spectra Red to Violet this really impacts the question. Air up close is clear, but in a distance we see the mixture of gasses and particles as faint or brilliant colors. ",
"So the answer could possibly be that we haven't evolved, but there isn't a way that we could prove it, because we cannot see Ultraviolet/Microwave/Gamma Ray/X-Ray lights."
] |
[
"Why do Aurorae in the Northern Hemisphere seem more prevalent in the winter?"
] |
[
false
] |
EDIT: Answered! A simple matter of better observation opportunities. ...or is this just my perception? Does axial tilt affect aurora intensity? I do understand that we're just passing sunspot peak right now, but I've not seen much in my 45º latitude. I can, however, remember winter shows from years gone by that reached almost directly overhead.
|
[
"Northern latitudes get little sunlight in the winter. At the U.S./Canadian border (49°N) the nights are 16 hours long around the winter solstice. It is merely the perception because observers have significantly longer nights in winter than summer in those latitudes."
] |
[
"The aurora intensity actually peaks ",
"during the spring and fall",
". During the equinoxes the Earth's magnetic field links up with the interplanetary magnetic field, which can partially cancel Earth's magnetic field at the point of contact - triggering auroras.",
"However, since the auroras are a daily occurrence, and are relatively faint, weather and time of daylight also play a big part in aurora sightings. Winter in the northern hemisphere accompanies longer periods of darkness, and usually clearer weather. "
] |
[
"Aurora can only be seen at night. the resulting longer days of spring and summer simply limit the available opportunity to view the phenomenon. "
] |
[
"If you lived on a high-gravity planet would you develop super-strong bones and muscles? Would you be able to jump off tall Earth buildings without injury?"
] |
[
false
] | null |
[
"You would develop stronger muscles and bones, much like a weightlifter does, but nothing superhuman. You'd also wind up being a lot heavier, which would counteract much of your gain in strength. Top jumping athletes develop the muscles they need for jumping...you'd be developing all of your muscles.",
"In addition, you'd be more likely to develop joint and blood pressure problems, that could very well make you ability to jump worse.",
"You'd never be able to leap tall buildings in a single bound."
] |
[
"I don't see that question. I see a question about whether he could jump off a tall building, but not if he could jump high"
] |
[
"I don't see that question. I see a question about whether he could jump off a tall building, but not if he could jump high"
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"How does the most basic level of a computer's hardware/software relationship work -- How does a motherboard and CPU essentially consisting of a lot of binary switches and pathways between them actually run software?",
"I'm familiar with the concept of the motherboard having a machine language instruction set that's used to move things to/from memory, hard drives, peripherals, run calculations on the CPU, etc, but how the motherboard can actually remember what those instructions are and control its numerous circuits to run them while being basically made up of purely on/off switches is beyond me."
] |
[
"When a program is compiled, it is essentially compiled into a long list of instructions. Each instruction is just a sequence of bits, typically between 8 and 64 bits.",
"In the real world, a CPU distinguishes between registers and memory. You can think of registers as a very small but super-fast internal CPU memory. Usually, data has to be loaded into registers from memory with load instructions before it can be computed on, but for simplicity, let's assume we can compute on stuff directly in memory.",
"One example of an instruction would be: ADD, r1, r2.\nThis would add the number from memory location r2, to the number at\nmemory location r1, and store the result at memory location r1.",
"Now, recall that each instruction is encoded as a sequence of bits. Let's say that the add instruction is 40 bits long. Then some of the bits are encoding what the instruction actually is (in this case ADD), let's say the first 8 bits does this. Then we might have 16 bits encoding the memory location to load the first number from (r1), so this is basically a memory address, and another 16 bits for the second number.",
"Now, when the instruction is loaded from memory, you can basically imagine 40 wires lying next to each other (this is technically called a BUS), coming out from the memory, so that each wire has either a high voltage (if it carries a 1 bit) or a low voltage (if it carries a 0 bit). ",
"Now, the first 8 wires contain the numbers that encode ADD, so they will go into the CPU and \"flip\" some of these switches, so that what is loaded from memory will be directed into the part of the circuit that adds stuff (adding stuff is in turn just using the input numbers to flip some switches in a way, so that the result from adding these numbers comes out in the other end).",
"The next 16 bits will go into a circuit which takes memory addresses and loads whatever is at the address into the first input. Likewise for the next 16 bits.",
"The first 8 bits (the ones that coded for ADD) along with the first 16 bits, will then go into the circuit that decides where to store the result and flip some switches so that the result will be directed back to the r1 memory location.",
"All of this is very simplified of course, but this is roughly how it works."
] |
[
"Codecademy",
" is geared toward any level of competency. Pick a thing you want to be able to do (make a website, write code, whatever), and go for it."
] |
[
"Is there a limit to the number of planets that can plausibly form around star systems of two or more stars?"
] |
[
false
] | null |
[
"It depends on how closely the stars orbit each other. ",
"There are three types of possible orbits for planets in a binary star system: ",
"Planet orbits around Star A",
"Planet orbits around Star B",
"Planet orbits around the gravitational centre of Stars A and B",
"In cases 1 and 2, the upper limit for how many planets can have a stable orbit around each individual star will depend a great deal on the closest distance between stars A and B as they orbit each other. If the minimum distance is several hundred AU, then functionally it’s nearly the same as if the stars weren’t orbiting each other at all. If the minimum distance is within a few AU or less, then neither star is likely to have planets in stable orbits around them and only them.",
"In case 3, it depends on the maximum distance between the stars. If the stars are close to each other and have a relatively tight orbit with low eccentricity, then stable planetary orbits will be able to exist closer to the dual-star system, which in the end means more planets will be able to form and orbit around the two stars. If instead the stars have a highly elliptical orbit around each other, they may not have any planets orbiting around the dual system at all. ",
"As a nearby example, the Alpha Centauri system has three stars. A and B orbit around each other in an elliptical orbit. Their closest approach is distant enough for each star to have 3, maybe 4 planets each in stable orbits around each star, but no more than that. Any planets that orbit around the gravitational centre of the system would be many hundreds of AU distant and would have orbital periods of many thousands of years; these would all be uninhabitable frozen snowballs.",
"Proxima Centauri is extremely distant from the other two stars, so much so that their gravitational influence on it and its surroundings is negligible. So Proxima can have just as many planets around it as it could have if the other two stars weren’t even there."
] |
[
"Over the long term, probably not. Even slight perturbations in its orbit from either of the two stars, or another planet in the system, or even more moderate gravitational influences would inevitably destabilise an orbit like that, and its orbit would end up with a collision with one star or the other (or ejected from the system)."
] |
[
"Could there be a stable system where a planet orbits first star A and then star B in an ∞-like fashion?"
] |
[
"Audio Duration vs. Data Usage on CDs? Explanation?"
] |
[
false
] |
When burning a CD, why does is duration the only thing that matters instead of data used. I can burn a 72 minute FLAC audio file or a 72minute 128kbps MP3 file on the same CD, why is this?
|
[
"Because whatever your source file audio is, it gets converted to CD-Audio format to go on the CD, which is a fixed sample rate. So 72 minutes is 72 minutes however you slice it. "
] |
[
"Audio is stored on a CD in a fixed format, which varies in some important ways from the format that is used to store data on a CD. The typical format for audio CDs is referred to as ",
"Red Book",
", and fixes several parameters which control how large the data is on the CD. First, the audio is encoded as stereo 16-bit-per-sample 44.1kHz ",
"linear PCM",
". An error correcting code (called interleaved Read-Solomon coding) is then applied to the audio data, and finally it is modulated onto the physical disk using ",
"eight-fourteen modulation",
". The tightly defined audio standard was chosen to make it easy and cheap to implement players which play all CDs (remember how long ago this was). PCM encoded audio is the same size for all audio streams, no matter what type of compression was applied to it beforehand.",
"The CD-ROM format, originally called ",
"the yellow book",
", stores any arbitrary bitstream instead of an audio stream. Typically, the data stored on the disk is an ISO9660 filesystem containing files like the FLAC and MP3 files you talk about.",
"FLAC and MP3 files are different sizes because they contain different data. FLAC takes the PCM sound data (the same representation that is used on a CD) and uses clever coding trickery to reduce it's size without losing or changing any data. MP3, on the other hand, transforms the data in a way that can not be exactly recovered (but may be perceptually identical) in exchange for a much smaller file."
] |
[
"A friend of mine had an old car CD player with a switch that expanded either the left or right channel across both speakers. In exchange for mono sound (which doesn't matter in a car) he could record twice as much audio onto a CD as long as he remembered to change the switch to chose the 'side' of the CD."
] |
[
"Tobacco plants have been genetically altered and are now 40% more productive. How can such an old evolutionary process as photosynthesis be inefficient?"
] |
[
false
] |
If I understand this paper* correctly, it is said that photosynthesis in C3 plants is really inefficient. Specifically the photorespiration part where carbon is transformed in CO2 again. Scientists see this as a waste of energy, and it has now been improved by constructing "a metabolic pathway in transgenic tobacco plants that more efficiently recaptures the unproductive by-products of photosynthesis with less energy lost [...]. In field trials, these transgenic tobacco plants were ∼40% more productive than wild-type tobacco plants." How can we be so sure photorespiration is an inefficient process? Isn't it more logical that we don't fully grasp the complexity of the process yet? I mean it had billions year to evolve, it must have a benefit to do it this way right? (This is not my field of expertise, so if I'm saying things wrong, please correct / teach me.) * Edit: Ok, clear. Thank you both for your time and explanation :).
|
[
"Evolutionary processes do not arrive at the best solutions, only ones that work well enough to propagate. Perhaps there are other limiting factors that made more efficient photosynthesis less fit for survival, such as nutrient depletion. This is, in fact, a problem with modern engineered crops which require chemical fertilizer to reach maximum growth potential."
] |
[
"The only way to be sure that the process is inefficient is to prove that it can be significantly improved on. Biochemists can have the insight that it may be inefficient, but really, there's no other way to know than to effectively improve it. And then to prove that there's no catch with the improvement, and people will surely investigate potential side-effects in the next few years.",
"For such a basal process, though, I think we can be more hopeful that the improvement might be real, because the system in question is not as complex and dynamic as, say, ecological interactions, e.g. with the weather, soil chemistry or microbes and pathogens.",
"One important point that others have made, is that evolution only leads to local optimums. Its results must work—otherwise the thing would be dead—but they may be suboptimal from a general standpoint. And that's particularly true for systems (like the photorespiration pathway) that depend simultaneously on many pieces, because there's no natural way to change the entire system at once, nor to improve all the pieces at the same time."
] |
[
"Photosynthesis has one of the least efficient enzymes on earth, known as RuBisCo, and can only do several reactions a second, while many are able to carry out there processes 1000's of times per second. I'm betting this is the enzyme they tried to optimize. It also has a tendency to fix oxygen molecules instead of CO2 molecules, which wastes further energy. ",
"Why is this enzyme so terrible? We can't really know. It's likely a variety of factors that we will never know. For one reason or another, the inefficiency of this enzyme did not sufficiently reduce fitness for a heavy selection pressure on plants to improve upon it. "
] |
[
"Why can't we produce energy by fusion when we have working fusion bombs?"
] |
[
false
] | null |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):"
] |
[
"What is the flawed premise?"
] |
[
"We can produce energy from fusion in reactors, just not yet more than is put in to operate the reactor. And furthermore bombs and reactors (particularly magnetic confinement) are totally different physical problems, so being able to do one doesn't imply that we should be able to do the other."
] |
[
"Why does working memory have a limited capacity?"
] |
[
false
] |
Why can we only think of a few things at once?
|
[
"I don't think that's quite the same question. I think Noxzer answered appropriately. Capacity with working memory would be a matter of how much can be held at one time. Capacity with attention would be a matter of \"bandwidth\": how much information can be received at once. There's a subtle difference. But because of the link between the two (and particularly the model proposed by Noxzer) one can be answered in terms of the operations of the other.",
"That's not to say I can comment on the robustness of the model. There are many, many models for memory out right now. We have to appreciate the enormous complexity of the nervous system."
] |
[
"Good question, it actually has to do with attention.",
"There are a few working memory models out there, but one of the most widely used is the ",
"Time-Based Resource Sharing Model",
". Essentially what it says is that, in order to keep something in working memory, we need to keep refreshing the representation. If we don't, the representation decays and we lose it. This refreshing is controlled by attention, and our attention has limits in terms of the number of things we can actively attend to. Sometimes we can attend to multiple items (called \"chunking\") but generally adding more items increases cognitive load and eventually that load will accumulate towards capacity."
] |
[
"So you're simply changing the question to 'why does our attention have a limited capacity'. "
] |
[
"Heparin consists of a HUGE chain of molecules, so how can there be gel forms to treat swelling and hematoma? If it does, how exactly does it penetrate the skin. (Or if it doesn't penetrate the skin, but still works somehow)."
] |
[
false
] |
My other question would also be: In the professional field here in germany, Herparin is, besides swelling and sports injuries recommended to accelerate the healing of hematomas. But isn't it contraproductive to what the body is trying to do? I haven't found an explanation how it should work. But in germany something wouldn't get it's pharmaceutical license, if it doesn't work the way with no studies behind the main ingredient behind it (A friend of my who is a pharmacist actually told me that there are several licenced homeopathic remidies * (That was way misunderstood: See my post below: it's the undiluted base drug, mixed with other potencies and ignoring hahnemanns principles)*, which means they are effective, but just have to the label on it) What works are the other ingredients like 2-Propanol for the cooling effect and three different eatheric oils. Thank you guys! <3
|
[
"When you have a hematoma, the thing \"the body is trying to do\" is already over. ",
"A hematoma is just an area of blood that leaked out of a broken blood vessel. Once clotting occurs and the vessel has healed itself, you still have this blob of blood sitting there in the tissue. That's what a hematoma is. It doesn't have a purpose. It's wasted material, and the body will eventually break it down and resorb it.",
"I suppose heparin could somewhat speed up the process of breaking down that blood. However, I've never seen heparin given for a hematoma. I would think that its risks would usually outweigh the benefits. ",
"A superficial hematoma is a minor problem that doesn't need this heavy-duty drug. A hematoma in a critical area like the brain needs surgical intervention. Either way heparin would increase the risk of further bleeding without giving any very large benefit. "
] |
[
"Hey Guys! Friendly neighborhood mod here. This is a great question, but let's not focus on the whole \"Homeopathic remedies\" part of this question. We're not here to debate that. We're here to talk about heparin!",
"Cheers!"
] |
[
"I believe the heparin found in gel forms are usually low molecular weight forms so they should penetrate the skin more easily.",
"Heparin is capable of binding to histamine which sequesters it from triggering the inflammatory response. Among other things, histamine causes vasodilation and increases the permeability of capillaries near the site of injury. This leads to edema at the site which is the swelling that you would see. "
] |
[
"Since we measure nuclear warhead yields in terms of tonnes of TNT, would detonating an equivalent amount of TNT actually produce a similar explosion in terms of size, temperature, blast wave etc?"
] |
[
false
] |
Follow up question, how big would a Tzar Bomba size pile of TNT be? (50 megatons)
|
[
"Assuming a density >1 g/cc the volume of 50 megatons of TNT is on the order of 300x300x300 meters",
" \nThe initial conditions of the blast are quite different because the fusion event occurs in a much smaller volume and hence temperature and energy density are greater-initially. Thus the initial shockwave is faster and accompanied by UV, x-ray, and gamma radiation. ",
"In the case of a pile of TNT the detonation would propagate through the pile in several hundred ms and the initial fireball would be considerably cooler than the equivalent sized nuclear fireball.",
"That said, since a large fraction of the nuclear event is in the form of heat and radiation, the mechanical shockwave would be less powerful than that produced by a equivalent energy mass of TNT. In the latter case, the shock is the result of the sudden production of hot gas (Nitrogen, Carbon dioxide) at thousands of degrees in contrast to a smaller volume at tens to hundreds of thousands of degrees during a fusion event. So less energy is dissipated (initially)-as heat-in the chemical event, and more energy goes into the shockwave via gas expansion.",
"RAND has declassified documents that go into greater detail with graphs and tables. You can find some online.",
"Also, the US did tests with 1 kt (ish) piles of dynamite to simulate nuclear blasts. Videos can be found on the youtube."
] |
[
"This was super informative. Thanks!",
"Here are a couple quick youtube videos I found in case anyone else wants to see them.",
"https://www.youtube.com/watch?v=BGE9KSlHmO0",
"https://www.youtube.com/watch?v=arQMBGdxIfw"
] |
[
"It would release the same amount of ",
" (that's what tonnage equivalent means) but the devil is in the details. Conventional explosives release mostly mechanical energy and some heat; a nuke releases a bigger share of heat and a lot of ionizing radiation."
] |
[
"Does a rocket continue to accelerate if it has reached the velocity at which gas escapes its nozzle?"
] |
[
false
] |
[deleted]
|
[
"The exhaust gases move in a more or less constant velocity, with respect to its source, not the ground. A rocket with isp of 300 (exhaust velocity 2940m/s) will have exhaust of 2940m/s regardless of its speed, and as such, the force will be the same (but still dependant on throttle, air pressure, etc)."
] |
[
"Almost correct: it's not the speed that matters, but the ",
". The gases will accelerate from zero to exit velocity, and like you said this is relative to the source, not the ground. That means there's a net force on those gases in the direction of the nozzle. Newton's third law applies, so the rocket will undergo an equally strong force in the opposite direction."
] |
[
"Actually both comments are equivalent. There is a fixed distance from the combustion chamber to the nozzle's exit, so the exit velocity is determined by the acceleration.",
"In most equations about rockets only exhaust speed is taken into account, including the most famous (and probably the most useful) one, the Tsiolkovsky equation."
] |
[
"Exactly how does not finishing a course of antibiotics produce resistant bacteria? If a resistant population develops, wouldn't that population survive the entire course anyway?"
] |
[
false
] |
Always wondered exactly how this happens, even though I've learned THAT it happens in several classes.
|
[
"Resistance is not binary, i.e resistant/not resistant. If you do not kill all the bacteria, the ones hat are left are the ones that are a bit more resistant than the ones who died. Repeat that cycle enough times and you have a degree of resistance that makes it difficult to treat with normal doses of antibiotics.",
"Not finishing the antibiotics will also increase the risk for the infection coming back and then you have to use more antibiotics on bacteria that have already gotten a bit more resistant"
] |
[
"Bacteria reproduce very quickly, and mutate very often, and even swap genes amongst themselves. So they are constantly changing in tiny ways, which may effect how they react to antibiotics. ",
"Generally you do not get a bacteria that has mutated to be instantly immune to an antibiotic. Random mutations are not usually that kind, theres no reason for it to have evolved into that, and no environmental pressure for it to be immune. It would be nothing more than a matter of complete luck. And even if one DID do that somehow, it isnt necessarily going to become the dominant form of that kind of bacteria. Its just one of a couple hundred million others. ",
"Instead, of all the bacteria in your body causing the disease, some will be weak to antibiotics, others will be unremarkable, and a tiny handful will be more resistant. Just because of random mutations. Over the course of the treatment, most of those will die before the end anyway. They arent immune, theyre just slightly better equipped for surviving. But the mistake people make is by stopping the antibiotics when they feel better, rather than just carrying on.",
"But obviously you will 'feel better' if 90% of the bacteria causing your illness died. Doesnt mean they are all dead.",
"Now the remaining bacteria will repopulate, but only the ones who were able to survive thusfar can do so.All the bacteria have now been naturally selected to be a little resistant.",
"If you spread your disease to someone else, now they have slightly resistant bacteria. And if they go on a standard course of antibiotics to kill these bacteria, well they will likely survive.",
"Its not so much an 'all at once' thing, as it is a slowly increasing resistance. Eventually you end up where large chunks of the bacteria's population in humans have been naturally selected to be resistant, and a whole antibiotic is useless."
] |
[
"Additionally, even if there are a few strongly resistant individuals after completing the course, the immune system will have a much better chance of finishing them off if the last of the antibiotics nukes as many others as possible."
] |
[
"In string theory, what exactly is meant by the notion of \"other universes\"?"
] |
[
false
] |
I understand that in order for the mathematics of string theory to work out, it calls for 10 spatial dimensions, plus time. Why would the existence of additional spatial dimensions imply the existence of other/parallel "universes"? Or rather, what is really meant when that language is used? I see terms like "parallel universe" and "multiverse" used a lot, with no clear definition of what those mean. Is the implication that these "other" universes have different sets of physics/fundamental laws than "our" universe, or are variations of the same? Why is there emphasis on the idea of multiple n-dimensional universes instead of a single, 11-dimensional universe, which is what I would think string theory aims to describe? Do strings that vibrate in "our" four dimensions not exist in the other 7 (language about strings/branes/gravitons "traveling" between dimensions makes it seem so), or do they all exist in the same 11-dimensional universe and just variably not interact? And I suppose while I'm at it, what exactly is a Brane? Are they just abstract theoretical constructs? I see strings and particles described as sorts of Branes, but then I also see the entire universe described as a slice of a Brane, and Wikipedia says Branes have mass, and collide with each other, etc., which makes them seem very concrete. Perhaps this is too much to address at once, but I feel like I have a tenuous grasp of some basic aspects of string theory and the rest just gets too confusing. I desperately need some un-sensational clarification from an expert. I can't get out of my head a scene from "the Elegant Universe" that's a bunch of giant blue breadloafs swimming into each other, and this being described as "the multiverse". Maybe it's because I'm a Chemistry major and not a physicist, but the language used to describe M-theory usually just makes it sound so nonsensical. My sincere thanks to anyone who can respond.
|
[
"So there's a couple of things overlain here. ",
"First, string theory posits the idea of additional ",
" dimensions. This means the furthest you can travel along these dimensions is some very small distance (like 10",
" m or smaller) before you're back where you started. It's more about opening up different ways for the strings to have vibrational energy. ",
"Second, there's the idea that, well, these 3 space dimensions, maybe they're only a slice of some larger space. The particles we know and love are ",
" to these three dimensions. They are only free to move around in 3 ways. The strings would be free to vibrate in an additional 7 ways. But macroscopically, they can only move around in 3 dimensions. But maybe there are more dimensions \"up\" the scale that particles simply can't move around in. Our little slice is one membrane within that whole space.",
"And what if there are other membranes, or some other interactions. Maybe some of our particles ",
" leak off of our membrane. Particularly gravitons; maybe the particles describing how spacetime curves actually leave our 3 dimensional sheet and most of them are moving about in this larger dimensional space. And maybe that's why gravity is so weak. We only feel a small fraction of the overall gravitons produced.",
"And what if these other membranes, these other spaces can collide with our own? What if, every once in a while, they can exchange massive amounts of energy between them? Maybe that's what kicked off our own universe's expansion. Maybe our local universe got all its energy from a collision with some other brane. This is called the \"ekpyrotic model.\"",
"I say all this with the note that you should take the above with a huge grain of salt. It's some neat ideas. Not all of which bear out on data. We'll see if we can see polarization from early universe gravitational waves (BICEP2 thinks they might have seen them, but there may be other sources occluding them, like dust. Future experiments will help rule out the data). If we do detect such polarization more-or-less definitively, it will make an ekpyrotic model of the beginning of the universe far harder to reconcile with data. (The universe would, in such a case, have likely begun with inflationary big bang, rather than a collision providing energy).",
"Edit: forgot to answer your original question. In such a \"brane\" cosmology, you could call ",
" 3-brane \"the/'our' universe\" if you so choose. Since we're confined to this 3-brane, it's kind of the limits of what we can scientifically describe well. But we may be able to ",
" the existence of the higher extended dimensions, or other branes, even if we can't describe them directly.",
"Also, frankly, I think it's all probably not a particularly accurate description of reality. Just an idea that's interesting but that I doubt will be borne out by data. "
] |
[
"Yeah, it's not exactly a hierarchy, ",
". It's more like... the classic flatland example. Suppose you were a flatlander, confined to only 2 dimensions. there may be third dimensions and so on... but you, yourself, by the laws that govern you, are stuck where you are. ",
"And sometimes maybe a 3D thing casts a shadow on your world. Maybe a sphere passes through and you see a circle that grows from a point and then shrinks back down to nothing. ",
"so, like that, the laws of physics governing our physics... quantum field theory namely... maybe the particles only have a freedom to move in 3 dimensions only. and interact only with other things in those 3 dimensions.",
"More than that I don't know. As I say, I don't think the thing sounds realistic, so I haven't done in depth reading of it. It all sounds a bit magical-thinking to me, without any hard evidence, or even a suggestion of truth. "
] |
[
"Wow, thank you for the answer! ",
"So if I understand this correctly, string theory calls for these 10 spatial dimensions- 7 that only exist below Planck scale, and then 3 that we're familiar with that exist above that scale and in which particles move about and interact. Now this membrane theory assumes that above the scale of the fundamental particles we're familiar with, there may further exist higher operable dimensions? That is to say, just as those 7 dimensions only \"exist\" below a certain scale, our 3 dimensions would also only exist below even higher dimensions, and that's where all the gravitons run off to? ",
"I guess my new question is, why is this system described in terms of slices, rather than heirarchal? It sounds as though higher dimensions necessarily contain lower dimensions, but the image of colliding branes makes one imagine coequal sets of dimensions exchanging energy, rather than energy leaking (surging? Escaping?) from high to low. Is there an objective definition of a higher dimension? Is there a mathematical description of what a \"collision\" between separate dimensions looks like? Does this mean that there would be an indefinite number of spatial dimensions as you go up in scale?"
] |
[
"How do brain regions actually communicate together?"
] |
[
false
] |
This seems like it has a pretty obvious answer, but I couldn't really truly find any information on it without making my own guesses. To be clear, I mean 2 things by 'communicate'. First a synapse from the front region of the brain to the region at the back of the brain, just seems too expensive to be developing. Hence how do such brains regions show activity in synchronicity if they do not have such synapses? How does the above vary with the split between the left side of the brain and right side of the brain? A particular reason for asking this is because we can for example verbally communicate and do a visualization task with a lot less interference simultaneously.
|
[
"oh man... I'm still functionally a student, but this might be my first ever askscience question I have something to contribute to.",
"First, when you say 'a synapse from the front region to the back would be too expensive', you're meaning something else than what you're saying. A synapse is very, very small (20-40 nm, Kandel et al, 2000, p 176). The synapse is just the 'hop' from the end-terminal of one cell's axon into the receiving cell's receptors. The actual 'cable' where the signal propagates is called the 'axon', and axons can be very long. The longest can be over 1 meter long in the human body (!).",
"For your specific example... there's literally an exact system that does route information from the front of the brain to the back of the brain. For whatever insane reason, the human primary visual cortex is in the occipital lobe, in the back of your head. Your optic nerves (a fiber cord made up over over 1 million individual axons from the ganglion cells in your retina, themselves consolidating information from 126 million photo-receptive cells per eye) travel to the thalamus near the middle of your brain, route through the lateral geniculate nucleus in the thalamus, and then continue all the way straight back into the very back of your head... or rather, they route to the back of the head on the opposite side of your brain, so it even hops the middle too. You can see a crude map ",
"here",
".",
"In general, there's a huge white region under the neo-cortex, with an outer gray layer, called the 'white matter' and 'gray matter' respectively. The gray matter is the neural material containing cell bodies, the white matter is literally the cabling (axons) routing things where it belongs. You can see a cross-section of the brain showing what I'm talking about ",
"here",
". That's a cool video series if you'd like to know a little more about the physical structure of the brain by the way. Note HOW MUCH white there is though, an enormous amount of brain volume is apparently taken up by the axons. Those axons need extra cells to work too, Oligodendrocytes (in the central nervous system) and Schwann cells (in the peripheral) wrap the axons to help improve signal propagation speed and reduce noise, just like rubber insulation around an electrical wire, so you've got additional cells just to keep all that cabling running smoothly (with the exception of some short-range interneurons that work like the equivalent of raw electrical wire without any insulation). And yes, this is expensive. About 20% of the caloric intake in an adult human is spent by the brain.",
"There are some incredibly fascinating properties about how your brain wires itself from an information theory perspective, if you've got the willingness to brave a little math, I highly recommend James Stone's 'principles of neural information theory'. It's a little 150 page book not just exploring 'how' things work, but WHY they work. Starting from foundational information theory principles, there are some remarkably accurate predictions made about things like axonal diameter distributions in different regions and so on.",
"Anyway, the corpus callosum. There are many networks connecting the different regions of the brain. The corpus callossum is a major group of fibers connecting the left and right hemispheres, and weird stuff happens if it gets cut. Sperry et al explored this in the 1950's, and found all kinds of strange things that you can read about ",
"here",
".",
"Most of this can be found from Kandel's 'principles of neuro biology', 5th edition. it's a beastly 1,700 page textbook, but it's fascinating if for some reason you care to do a deep dive into the the basics of how the brain works."
] |
[
"This is an amazingly clear answer thanks. ",
"I will definitely check through the Kandel book and Stones neural information theory. I also looked at the links, its so very interesting. ",
"I also indeed meant more of a neural circuit or large scale brain network with my reference to synapse."
] |
[
"I agree, the brain is an incredibly fascinating topic. My actual area of research is artificial intelligence, and there are some incredible connections between the fields... I'm just self studying my way up into neural science, and it's really surprising where things are going, and how much we currently understand. The real magic I think won't be from just the physical understanding of how the brain's structured, so much as it'll be from computational neuro-biology, and an algorithmic understanding of how certain processes actually work. Jeff Hawkin's 'on intelligence' might be a book you'd be interested in. The book's a little old at this point (only a decade!) so a surprising amount of science-fiction hypotheticals in the book have already happened, or are on the very near horizon (computer programs that can recognize objects and 'see', self driving cars and so on) but the guts of the book is a conversation around how the human neo-cortex might work, made understandable enough that you can listen to it on a commute or whatever, vs Kandel and James Stone's book are college level textbooks, so I figured I'd throw something out there that's a little more accessible too."
] |
[
"Today, a brilliant white turkey vulture landed in my yard. Anybody care to expound on how rare this bird might be?"
] |
[
false
] |
Here's a few pictures I managed to get before it left: According to they are rare, but I believe they may be talking about albino birds. It looked a little ragged in person. It was a little wobbly and looked like it was having trouble flying and staying up. But what little I've read about albino birds is that they tend to have bad eyesight and live shorter lives.
|
[
"As I understand albinism, it is more common the more inbred something is. So if the area it came from has few breeding options, its commonality goes up per capita. If this species is in decline I would imagine it will become more and more common until it becomes extinct. "
] |
[
"If this species is in decline I would imagine it will become more and more common until it becomes extinct.",
"Turkey vultures are the pigeons of carrion-eaters. They're not dying out any time soon."
] |
[
"And ducks don't have 5ft wingspans."
] |
[
"Why don't we measure food energy in Joules?"
] |
[
false
] | null |
[
"Food energy ",
" measured in kilojoules in New Zealand where I live, occasionally also with calories in brackets. I suspect it's the same in all countries that use the metric system.",
"Fun fact: Calorie values given on food packaging are actually kilocalories. The kilo is dropped for some reason."
] |
[
"It's cultural. You can find many other instances where energy is measured in other units, and it's all cultural. One reason this happens so often is that energy is connected to so many different processes. In some cases, we're interested in the connection to thermal energy, and we've made units to reflect that. In other cases, we're interested in a mechanical connection. In other cases, we're apparently interested in the number of horses required to do the same job...",
"As chemical energy, we have a more natural connection of food calories to thermal energy. That's because we'll measure chemical energy through reactions and heat measurements in a lab (ostensibly at least). This is why people initially thought it made more sense to use the calorie. The unit is connected to the increase in temperature of water per some amount of energy.",
"So that's the ",
", and it is a historical human story. Scientifically any energy unit does the job."
] |
[
"The unit of energy in the International System of Units (SI) is the joule \n(J). This is the accepted standard unit of energy used in human energetics and it should also be used for the expression of energy in foods. Because nutritionists and food scientists are concerned with large amounts of energy, they generally use kiloJoules (kJ = 103J) or megaJoules (MJ = 106J). ",
"For many decades, food energy has been expressed in calories, which is not a coherent unit of thermochemical energy. Despite the recommendation of more than 30 years ago to use only joules, many scientists, non-scientists and consumers still find it difficult to abandon the use of calories. This is evident in that both joules (kJ) and calories (kcal) are used side by side in most regulatory frameworks, e.g. Codex Alimentarius (1991). ",
"FAO. Food energy - methods of analysis and conversion factors."
] |
[
"Demonstrations of natural frequencies"
] |
[
false
] |
Physics question, specifically about waves. I am afraid this will be incoherent because of my lack of related vocabulary but here it goes: I have seen various demonstrations of natural frequencies in videos and am looking for a way to recreate what I have seen. One of the methods I was shown demonstrated used a flattened cylinder with a grid of holes on one of the bases with a flammable gas being pumped out through the holes. The gas was lit and the height of the flame out of each individual hole was used to show the amplitude of the wave at various points. The frequency was changed and various wave patterns would appear in the grid of flames. Another method was a metal disc (called a resonating disc?) with a layer of fine sand on top. A violin bow was used to make the disc vibrate at various frequencies and patterns would appear in the fine sand based on the frequency. Is there anywhere I could find a resonating disc (if that is what it is called) and if not is there another similar method to illustrate waves I could recreate? Thank you for any feedback even it is to tell me this is not the place to ask. :)
|
[
"A pretty simple way to do something similar to what you are talking about is to use a speaker where you can control its frequency and put a dish of water on top of it. ",
"Video"
] |
[
"It's easy to experience a 3d version of this. Get some low frequency pure sine tones and play them back through a speaker in a medium to largish space. Walk slowly around the room and experience the sound go up and down in volume (in fact there will be places where you can't hear the sound at all and they will change based on frequency). The volume will change in the vertical plane as well, so move your head up and down. "
] |
[
"Maybe it's not so good visually, but if you have access to a guitar or other stretched string, you can play around with its natural frequencies."
] |
[
"Why the plume of steam when boiling water is removed from heat?"
] |
[
false
] |
Chemistry question- When a pot of boiling water is removed from a heat source (gas range burner), there is a plume of steam as the boiling subsides. What is the cause of this plume? Wouldn't the vaporization slow down/stop after being removed from heat as opposed to increasing temporarily?
|
[
"What you see is condensed water vapour - you can't easily see steam or gaseous water vapour. So what you're observing isn't the rate of vaporization - in fact, the vaporization doesn't increase. What changed when you moved the pot is the temperature of the air immediately above it - because it's cooler, more water vapour will condense, which is what you observe."
] |
[
"Steam is invisible. What you see is condensed water. The plume you see is condensate, coinciding with the removal of heat."
] |
[
"Thanks Rupert!"
] |
[
"Is it possible for any object to have no motion or momentum?"
] |
[
false
] | null |
[
"For each massive particle, there is a frame in which that particle is at rest."
] |
[
"Ok, now how does that work in practice.\nDoes that mean the massive particle is stationary in relation to the entire rest of the universe?"
] |
[
"Ok, now how does that work in practice.\nDoes that mean the massive particle is stationary in relation to the entire rest of the universe?"
] |
[
"What is the ringing noise you hear when it's very quiet?"
] |
[
false
] |
[deleted]
|
[
"/r/tinnitus"
] |
[
"While tinnitus is \"a ringing noise\", it's not necessarily \"the ringing noise when it's very quiet\". It really depends on how quiet OP is able to achieve. In a really quiet environment you can hear your own blood flow. With increase of blood pressure, the sound of blood flow will have a higher pitch, and, modulated by the hart-beat may, actually, be perceived as a ringing noise. "
] |
[
"Not a scientific source, but it is mentioned in John Cage's book ",
" that he asked the technician of a sensory deprivation tank what the source of a low hum and high-pitched whine were that became audible after several hours. The technician responded that the hum was his circulation, the whine his nervous system."
] |
[
"I heard Phytoplankton contributes more oxygen than trees themselves, is this true?"
] |
[
false
] |
I heard this from a friend and could hardly believe it, I was curious (not being a big science guy) that if this was a true fact or not.
|
[
"Remembering that 3/4 of the earth's surface is covered with water, you have a much greater potential area for photosynthesis. ",
"Bonus fact: While we often refer to crude oil as coming from dinosaurs, most of our oil is also from ancient phytoplankton."
] |
[
"That is what I said. We are in agreement. "
] |
[
"This is a misconception. The ocean only appears blue because that is the last wavelength of light to be filtered out. Phytoplankton are microscopic, so it would take an absolutely absurd number of them to turn the ocean green. In cases where this happens, it is usually an indicator of pollution, and it is not microalgae that you are seeing, but macroalgae. "
] |
[
"Besides the current monotremes, marsupials and placentals, have there ever been other different types of mammals?"
] |
[
false
] |
If the answer is yes, how many were there? Do we know how they reproduced? What made them different from the still extant ones?
|
[
"That depends on how you mean it. Were there other mechanisms of reproduction than egg-laying, marsupial or placental? No. Egg-laying is the ancestral trait, and everything that came before the marsupials laid eggs. ",
"Were there other types of mammals? Yes. We think of the monotremes as being the only egg-laying mammals, and that is true for extant mammals. But there were other types of mammals that were not monotremes that laid eggs but are now extinct. See here: ",
"http://www.tolweb.org/Mammalia/15040"
] |
[
"Thanks for the reply! ",
"What traits did those extinct mammals have that made them different from the current ones?"
] |
[
"I can't give you a really complete answer to that, but a big part of it is their teeth. "
] |
[
"Does a water/ethanol mixture in a pressure cooker release relatively more ethanol with steam release? Is the maximum pressure reduced?"
] |
[
false
] |
gave rise to the question how a reasonable mixture of ethanol and water (say 1:9) would behave if cooked in a pressure cooker. While ethanol boils at a lower temperature than water, a pressure cooker usually reaches a much higher temperature than both liquids' boiling point. On the other hand, ethanol has a higher vapour pressure, so it should reduce the maximum temperature that can be achieved before the valve opens. How would the mixture behave? Would it release mostly ethanol? Is there maybe an easy formula/rule of thumb with which the composition and release temperature of an (initial) ethanol/water mixture can be predicted (given a certain maximum pressure)? edit: Sigh, I misspoke in the title, it should read "Is the maximum temperature reduced?"
|
[
"Water and ethanol form an azeotrope that boils at a lower temperature than either pure water or pure ethanol. When you boil off any mixture of ethanol and water, the mass percentage in the vapor will tend to be closer to that azeotropic mixture than is the liquid you're boiling. That is how liquor is distilled, up to a maximum of about 95.5% Ethanol.",
"Here's a chart and description. ",
"https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equilibria/Physical_Equilibria/Fractional_Distillation_of_Non-ideal_Mixtures_(Azeotropes)",
"The pressure will raise the boiling point and I think distort the chart a bit, but I don't think it significantly effects the outcome; from ~10% ethanol, you'd start boiling off higher percentage but still far from pure Ethanol.",
"The effect on the cooker's operating temperature/pressure would depend on how the pressure cooker works. If it is regulated to a specific pressure, then it would operate at a lower temperature than when used with pure water. If it's regulated to a specific temperature, then it would operate at a higher pressure than when used with pure water."
] |
[
"When looking at this a few years ago, I had a hard time finding vapor pressure diagrams for ethanol/water solutions at pressures higher than atmospheric, but the takeaway I remember is that the azeotope comes at a lower percentage ethanol at higher pressures.",
"Pressure swing distillation takes advantage of the change in the azeotrope point with pressure. Done right, you can actually get beyond the azeotrope."
] |
[
"Same as if you'd just used water: some of the vapor will escape during heating and during cooling and some more when you open the cooker after the pressure drops but pressure cookers are designed to retain liquid so you don't lose much."
] |
[
"Is there a way to determine the color of something without using light?"
] |
[
true
] |
[deleted]
|
[
"Something similar has been ",
"asked before",
".",
"In short, yes it's possible to calculate via quantum mechanics, but it's really much easier to just find a way to take a colour photograph."
] |
[
"If you look at a single molecule, you can attempt to find its colour by calculating the absorption energies of its molecular orbitals. This is what dictates what wavelength of light a molecule absorbs light.",
"However, once we get into a ",
" of molecules, we get other effects. Quantum electrodynamics, for example, describes the interference patterns behind the phenomenon of ",
".",
"The main problem is that one requires ",
" of computational power in order to calculate the simplest of these problems. It's simply not practical (and in some cases, ",
" - for example, the analytical solution is only known for a few, ",
" configurations of electrons in atoms)."
] |
[
"If you look at a single molecule, you can attempt to find its colour by calculating the absorption energies of its molecular orbitals. This is what dictates what wavelength of light a molecule absorbs light.",
"However, once we get into a ",
" of molecules, we get other effects. Quantum electrodynamics, for example, describes the interference patterns behind the phenomenon of ",
".",
"The main problem is that one requires ",
" of computational power in order to calculate the simplest of these problems. It's simply not practical (and in some cases, ",
" - for example, the analytical solution is only known for a few, ",
" configurations of electrons in atoms)."
] |
[
"Where does the buoyant force come from if an object is at the bottom of a body of liquid? And does the buoyant force act more weakly on flatter objects?"
] |
[
false
] |
Suppose I take a block of wood and push it to the bottom of a bucket of water. When I let go of the block it will float to the top, clearly due to the buoyant force acting upon it. However, at the moment I let go of the block there are no water molecules beneath it to help push it upward. My intuition says that maybe it's due to the buoyant force acting on the sides of the object - i.e. water molecules are colliding against the two sides of the block, and the water molecules at a lower depth have greater kinetic energy - therefore although the horizontal components of their velocities cancel each other out, there is a net force upward. Is that correct? Come to think of it, it seems that in all cases (whether or not the object is at the bottom), does the buoyant force act more weakly on flat objects? It would seem that the flatter the object is, the less the pressure difference between the top and the bottom and hence flatter objects would tend to float upward more slowly than thicker objects. Is that actually true?
|
[
"If there is very little space between the block and the bottom of the bucket, you may notice a suction effect keeping the block of wood down there for a few parts of a second, or more. If there is truly no space between the block and the bucket bottom, it would stay stuck down got a long time, maybe indefinitely."
] |
[
"What des is getting at is that its not feasible to place the block on the bottom with no water underneath, and if it were it would indeed suction to the bottom. The sides have nothing to do with it (assuming they are parallel. ",
"And as for your third paragraph, the buoyant force relies soley on the volume of the object not its shape. If you had a flat object with equal volume to a cube, the difference in pressure on top/bottom will be less for the flat object BUT the pressure will be acting on a much larger surface. In both cases the Bouyant force is equal.",
"The flat object will rise more slowly however due its very inefficient shape. The cause for this is increased Drag in the water, not less bouyancy."
] |
[
"Indeed. This is how stricken submarines get trapped at the bottom of the ocean. They settle on the bottom, settle into the sediment, and even if they blow the tanks to make the submarine bouyant, it may not always be sufficient to overcome the suction."
] |
[
"Can a gas be more concentrated when dissolved in water than when it's in the atmosphere?"
] |
[
false
] |
The molarity of a gas at STP is 22.4 moles per liter. Are there any gases that can exceed 22.4M when aqueous? If not, can you raise temperature or [lower] pressure to make molarity greater than gaseous concentration before the solution evaporates?
|
[
"Not exactly the same thing, but a liter of gasoline has more hydrogen in it than a liter of liquid hydrogen. Liquid H2 has a very low density due to some interesting quantum effects, and the dense bonding of hydrogen to carbon actually stores more hydrogen than pure hydrogen!"
] |
[
"Okay, first things first you have this backwards: ",
"The molarity of a gas at STP is 22.4 moles per liter. ",
"This should, perhaps, with some thought, seem unreasonably large to you.",
"What you're thinking of is that 1 mol of a gas takes up 22.4 liters at STP. So the molarity is 1 mol/22.4 L = 0.045 M! Quite a different realm from 22.4 M...."
] |
[
"Henry's law can answer this; it is of the form \np = k x c, where k is the Henry's law constant of a specific solute, p is the partial pressure of the solute and c is the concentration in water. For c > p x 0,045 M x atm, p/k>p x 0,045M x atm <=> 1/k>0,045M x atm <=> k<22,2 l x atm/mol for a specific solute in a specific solvent.",
"For CO2 in water, k is ~29 l x atm/mol, meaning it's pretty close.\nfrom this ",
"http://www.henrys-law.org/",
", 1/k for different substances can be found; several obey the 1/k>0,045M x atm;\nHydroxyl radicals, ammonia, hydrogen chloride, molecular chlorine.... and there are 98 more pages of constants to search as well."
] |
[
"In biology how do ligands find their receptors physically? Do they just float around randomly and if they hit the receptor at the right angle they bind?"
] |
[
false
] |
For example, with antibodies, do they just float around the blood at a certain concentration and when they collide with the epitope of their corresponding antigen, they attach? I know its like a lock and key analogy, but textbooks just show a 2d image with an antibody falling ontop of an antigen. In actuality, is there anything attracting the two or is it just billions of antigens and billions of antibodies in an aqueous environment and just statistically likely to occur?
|
[
"That's correct, up until they're extremely close they're just diffusing around.",
"That might seem like it would take a while, but diffusion works with different speed on different scales. We can estimate the instantaneous velocity of a protein in water to be around 10 m/s, its thermal velocity. That doesn't sound very fast, but at the microscopic scale, that's an enormous velocity. In free flight, it would cover a cell in a microsecond, but of course it never gets that far before it bumps into something. So that antibody is bumping into sometimes literally a million times a second, it doesn't take long before it gets lucky and hits a receptor.",
"Diffusion only get you so far though, characteristically the average distance crudely goes as the square root of the timescale. To cross a cell, a protein would take only a few seconds, so for normal cellular processes, diffusion suffices. However, to travel a millimeter, you'd have to wait a few hours or more and for centimeters you're waiting weeks, at that point you need active transport to get places."
] |
[
"This really helped me visualize it. Before, I was imagining individual sand particles trying to fit into a groove that matches its geometric complementary shape"
] |
[
"Remember, everything inside your body is constantly surrounded by water. But at this scale, that really means that it is constantly being bashed into by baseballs thrown from every direction at hundreds of m/s. There's a ",
" of energy in room temperature water, and you can see this in the diffusion of macromolecules."
] |
[
"Why do video chat services, e.g. Skype, decrease in quality when the camera is moving?"
] |
[
false
] |
I have noticed when I chat on Skype, Facetime, or Gchat that the video quality significantly decreases when the camera is in motion. What about the video compression makes this such a tech hurdle?
|
[
"This is not my area, but as I understand it, instead of transmitting the entire frame 30 times per second (or whatever), the software basically says \"these pixels all stayed the same, and I'm sending you the new information for these other pixels\". When the camera moves, obviously you're having to update a lot more pixels than if it's holding still, as the background is changing rapidly from frame to frame. Thus the software has to send out a lot more information per frame."
] |
[
"/r/smeghead333",
" is correct, the compression algorithm generally sends \"key frames\" which are the entire camera area, and then following the keyframes only the delta (change) is sent, ie only the areas that are changing like your face talking.",
"When you move the camera around, it has to send more keyframes which are a lot bigger than just the changes, and in order to keep the motion smooth, it decreases the quality of the keyframes rather than sending them farther apart. "
] |
[
"To add on to what the others have said, it's less about movement than it is overall change, a movement changes the scene a lot making it harder for the algorithm to guess and place things, bring up the bitrate on a bd disc and you'll see this. But a movement isn't as harsh as something where the compressor just can't guess, a full change in image would be much harsher, try showing lots of different detailed images one after the other and watch it turn to mush on a low bitrate, the compressor just can't do anything to retain detail.",
"Edit: ",
"https://www.youtube.com/watch?v=kyztYavfFMs"
] |
[
"Is there a rule of thumb for maximizing the magnetic field when making a solenoid?"
] |
[
false
] |
As a physicist I'm a bit embarrassed asking this, but this is something I've never "gotten." I know all about how to calculate the B-field in a solenoid, but in a practical sense I'm not sure how I would go about designing one if I want the most bang for my voltage source. For example, suppose I have a 12 V car battery (so I can max out at ~100A without running out of juice too fast). So the parameters I'm working with are: 12V, and up to 100A. That's 1200W which is a lot of heat to dissipate, but let's just ignore that factor completely. My question is: what gauge wire and how many turns should I use to most judiciously use my 12 V to generate the B field? Of course I want both high current and number of turns, but higher gauge wire will give you lower current for a given length and higher turn density, and higher gauge wire will give you lower current for a given length and higher turn density. Sure, I could go ahead and work it all out, making some really complicated formulas involving wire diameter as a function of gauge, resistance as a function of gauge and wire length, wire length as a function of solenoid thickness and length, and so on, but shouldn't there be a "solenoid-maker's rule of thumb" somewhere? After all, isn't this like, the most common calculation anyone would ever want to do regarding solenoids, so as to not waste electricity and build materials in getting the desired B-field?
|
[
"Sure, I could go ahead and work it all out, making some really complicated formulas ",
"It shouldn't be that complicated. The resistance per length of the wire is R/L = ρ/A, where A is πR",
" . The length of wire being used is 2πR*N, where N is the number of loops, so the resistance of the solenoid will be R = 2ρN/πR. Since current is I = V/R, you get I = πRV/2ρN.",
"The turn density is directly proportional to the radius of the wire - you'll get 1/D turns per unit length (with diameter D = 2R measured in the same units). ",
"Since the magnetic field at the center of a solenoid is just B = µ_0 NI/",
", where ",
" is the length of the solenoid (not the length of the wire) we just have to put those pieces together, realizing that ",
" = N*D = 2NR:",
"B = µ_0 πV/(4ρN) ",
"Notice that the gauge completely cancels out! The higher current of a thicker wire balances out the reduction in # of turns, assuming the same resistivity of the wire and a constant voltage source. In practice, if you use too high gauge wire, it will probably melt with 100A running through it (or at least heat up, increasing its resistance), so I would say you're probably better off with a relatively thick wire that's still easy enough to work with.",
"I did this math pretty quickly and only typed out, and I am notoriously bad at doing calculations with a keyboard, so there may be some errors... But it's not actually a very difficult problem to solve, especially if we ignore details like the temperature dependence of resistivity."
] |
[
"Yes, it's a tradeoff between the two. That's why you pick a starting point that seems reasonable and iterate the design from there."
] |
[
"If we ignore the thermal wattage, then we've eliminated the whole problem!",
":)",
"Just design for 10KW, or 100KW, or whatever you want. If the field is too weak, then simply design for ",
"On the other hand, for real-world engineering, wattage is the primary variable, since we require that the solenoid not be destroyed.",
"In other words, ",
" Then design everything else for constant wattage. Doing so will produce an unusual effect: the strength of b-field becomes proportional to the kilograms of copper used. Unusual? Not really, since it's the same phenomenon as when 10HP electric motors weigh proportionally more than 0.1HP electric motors. Or, when the wattage-rating of a transformer ends up being proportional to its mass.",
"With fixed power, and if choosing a fixed KG of copper wire, we then can vary the wire sectional area and the wire length. Choosing a power supply voltage sets both values, given copper's resistivity.",
"Now, since we know the wire gauge, length, and supply volts, what volume of space do you wish to contain your maximum b-field? Do you want a pancake-coil with a disk-shaped region of maximum field? Or, a long narrow cylindrical coil? A classic Helmholtz coil-pair, which produces a low-gradient region between the two?",
"And of course you might want to add pole-pieces to greatly increase the field, using low-carbon steel (i.e. iron.) A classic configuration is a \"gap magnet\" with two E-shaped iron masses facing each other, with the middle of each \"E\" being shorter, and a pair of pancake-coils surrounding each middle iron leg.",
"Cheating: buy wire which has a square or rectangular section. This puts far more area of the flat faces in contact, so heat may more easily travel from the center of the windings to the outer surface. Normal round-section wire gives too much air-gap insulation between adjacent turns.",
"Heh, when I had to do this some years back, I didn't bother writing integrals, I just spreadsheeted the whole thing, with a couple hundred rows for the couple hundred layers of stepped radius."
] |
[
"Do animals besides humans have types of blood such as A, O-, etc.?"
] |
[
false
] |
[deleted]
|
[
"I think ",
"this",
" is what you are looking for"
] |
[
"Yes, in fact we have a pretty conservative blood type grouping of just 8 combinations (ABO and +/- combined) where as horses have 10, cattle have 11 and dogs have an impressive 13. Although in cattle the B group has 60 different antigens so I think they win the non-human blood group diversity prize."
] |
[
"Animals do have blood types, but the specific antigens differ. The blood type antigens are specific molecules on the surface of the red blood cells which determine \"blood type.\" When our body sees antigens it doesn't recognize, it attacks the blood cells. That's why we want a transfusion of blood with the same type of antigens: so our body doesn't recognize the blood as foreign and try to attack it.",
"Dogs, for example, have many possible RBC antigens, only two of which are clinically relevant, called dog erythrocyte antigens (DEA) 1.1 or 1.2. DEA 1.1 is what causes the most severe reactions and thus is the most relevant and most often tested for. Like a person can be A or B, a dog can be 1.1 positive, 1.2 positive, or negative for both. Cats, on the other hand, use the A, B, AB designation for their major antigens. (Different antigens than humans, I believe, they just used the same abbreviations)",
"If your pet has a blood transfusion, they may check his blood type first just like if you were getting a blood transfusion. However, unlike humans dogs don't naturally contain antibodies to either DEA 1.1 or 1.2 so even if they get blood of an incompatible type, the immune system doesn't realize right away and will take a while to do anything about it. Because of this, you don't actually have to do a crossmatch for a dog who has never been transfused. Cats, like humans, do have naturally-occurring antibodies to the blood antigens they don't have, however, so you must get a cat's blood type before transfusing.",
"EDIT: ",
"Source"
] |
[
"How long after clinical death, can someone be revived?"
] |
[
false
] |
How long without damage to the body (brain, heart, etc.)? And how long before being unable to keep yourself alive (breathing by yourself, without help)?
|
[
"The movies make it look like if the patient hasn't come back in 1 minute, then it's over.",
"Remember that most things in movies are unrealistic. The medical staff call it after 1 minute because a 20-minute-long scene of someone giving CPR would be very boring.",
"EDIT: punctuation"
] |
[
"It’s quite variable, but even with good CPR and return of spontaneous circulation after only a few minutes people can have quite significant hypoxic brain injuries. If you’ve been having CPR for more than 10-15 minutes your chances of survival are pretty slim.",
"There are certain cases where this doesn’t always hold true. Hypothermia is the classic one, because the low temperatures preserve the brain. It also depends on the quality of the CPR given. Also probably depends how healthy you are to start with.",
"I have to say that if I’m doing CPR for longer than 20 minutes I’m thinking about stopping 95% of the time.",
"The caveat to this question is that actually the time of death is 5 minutes after the last heartbeat, so you’re not even officially dead for the first 5 minutes. And if you started CPR after 5 minutes of no cardiac output your survival chances are even lower. So the question is probably flawed."
] |
[
"CPR for 20 minutes? The movies make it look like if the patient hasn't come back in 1 minute, then it's over. Can you explain why someone would need CPR for 20 mins? Rescue breathing for them too? I am very curious about this."
] |
[
"How does buoyancy work in zero gravity?"
] |
[
false
] |
And can it be used as a means of propulsion in space?
|
[
"Buoyancy is a force acting on a body as to oppose gravity when that body is immersed in a fluid. This force is proportional to the weight of the volume of fluid displaced. In zero gravity, the fluid has no weight and there is no direction in which buoyancy could act. Buoyancy requires gravity... or more generally a reference frame under acceleration. Example: If you spin a bucket of water on a string in outer space, a ball could be buoyant in the water. That would not be useful for propulsion though. "
] |
[
"I just took the liberty to animate your comment.",
" Yes, you ",
" make a ball float in outer space in a bucket with ",
". Now picture a still bucket (you somehow make the water stay in it).If you push a ball of lead, styrofoam, or any material into the water, it will just push the water away from it. "
] |
[
"Here's a good video answering your question. ",
"http://www.youtube.com/watch?v=bgC-ocnTTto",
"In it an astronaut places an alka-seltzer tablet into a spherical water drop. Without gravity the only major force affecting the bubbles is surface tension, which causes most of the bubbles to combine with each other and eventually form one large bubble in the middle of the water sphere.",
"There's also this video, ",
"http://www.youtube.com/watch?v=QPf5MJluhvo",
" in which an astronaut injects an air bubble into a water sphere, and then injects small water droplets into the bubble."
] |
[
"What prevents all dense stars from collapsing into black holes?"
] |
[
false
] |
I’m just starting to try and learn more about astronomy and physics, and black holes are super interesting to me. From my understanding, it seems that stars with large enough mass collapse under their own gravity when they die out as there isn’t enough energy to keep it stable, and as the mass crunches together from its own gravity it becomes ever more dense and thus, creating ever stronger gravity bringing it more mass until it results in a singularity. If I am not fundamentally misunderstanding this (which I probably am), why doesn’t every large star just collapse into a black hole? If gravity brings all of its mass down into the center, thus making it more dense and thus having a stronger gravity to bring in even more mass, wouldn’t anything with a sufficient enough starting mass collapse into singularity?
|
[
"At any given time, a star (or any celestial body, for that matter) is held up by some force opposing gravity. When stars are doing nuclear fusion, the outflow of radiation provides outward pressure which holds the star up against its own gravity.",
"When a star like our sun dies, it collapses down until it reaches something called \"electron degeneracy\". Basically, electrons don't want to be in the same places as one another. If they were, they would be degenerate. To avoid degeneracy, there is an outward pressure that works to prevent the material from collapsing more. For small stars, electron degeneracy pressure is strong enough to hold the remains of the star up against gravity. These electron-degenerate objects are called white dwarfs.",
"For larger stars, upon death, their gravity is strong enough to overcome the electron degeneracy pressure. As the star collapses, electrons and protons are forced together, and the entire material becomes neutrons. Neutrons will happily sit close to one another, but their degeneracy pressure is much stronger than electron degeneracy pressure. In this case, you get a small, dense object called a neutron star.",
"Only in the largest stars is the gravity strong enough to overcome neutron degeneracy pressure. If this is the case, the neutrons are forced together and the remaining mass collapses into a singularity, forming a black hole."
] |
[
"This explains it perfectly, thank you!"
] |
[
"Well using the sun as an example, the sun would need to be about 20 times more massive to end its life as a black hole. Stars that are born this size or larger can explode into a supernova at the end of their lifetimes before collapsing back into a black hole, an object with a gravitational pull so strong that nothing, not even light, can escape.",
"Now how about neutron stars? A neutron star is about 20 km in diameter and has the mass of about 1.4 times that of our Sun. This means that a neutron star is so dense that on Earth, one teaspoonful would weigh a billion tons! It collapses so much that protons and electrons combine to form neutrons.",
"So using a neutron star as an example, What prevents them from collapsing into a black hole is gravity. The gravity in the neutron star is balanced by an outward force due to neutron degeneracy. No light can escape from it due to its powerful gravitational field."
] |
[
"Do trees have a lifespan or are they immortal?"
] |
[
false
] | null |
[
"They definitely have lifespans. The right conditions can support them for long periods but time gets everything. ",
"Many palm trees have lifespans of about 100 years, which means a lot of the palms that give famous Los Angeles streets their look are almost about to die off."
] |
[
"Invididual trees have lifespans, which depends on the species. Some of them, including Great Basin bristlecone pine and Giant sequoia have been verified to live for thousands of years. But that seems to be the upper limit.",
"However, there are clonal trees. These are trees that form clones of themselves from a common root system. While no single tree lives for a very long time, the whole organism (which shares the same DNA) lives for a very very long time. ",
"Pando",
"), based on ",
"Quaking aspen",
" is thought to be the oldest clonal tree in the world, with an estimated age of at least 80000 years. There doesn't seem to be any upper limit on the lifespan of a clonal tree, other than environmental factors."
] |
[
"Some things have pretty good DNA repair mechanisms like the immortal jellyfish. I guess there are a couple of bristlecone pines that have been found to be about 5,000 years old which to me is pretty damn immortal. But I am pretty sure most species of tree will eventually die of old age regardless of conditions"
] |
[
"Does the speed at which a planet (or any other astral object in orbit) rotates affect the strength of its gravitational pull?"
] |
[
false
] |
I guess what I'm asking is this: The Earth rotates on its axis at a rate of 1 revolution every 24 hours, give or take a few seconds. If that rate changed, meaning it sped up or slowed down, would we feel a change in the strength of the Earth's gravity? If so, does a faster rotation speed mean a stronger pull or a weaker pull? I would also like to point out that I do NOT mean the speed of the Earth's rotation around the Sun, just the rotation on its own axis.
|
[
"Kind of, yes.",
"Although, the centrifugal force is not actually real but rather a pseudo force.",
"If you take a bucket on a rope, fill water in it and start swirling it around fast enough in a vertical circle, the water will not fall out, right?",
"Lets take a look at the moment the bucket is upside down, shell we?",
"From the perspective of the bucket, there is the gravitational force pulling the water (and the bucket itself) down, the rope, pulling down as well and the centrifugal force pushing the water upwards, against the bottom of the bucket.",
"From the perspective of someone standing on the ground watching you swing the bucket, however, there are only two forces effecting the bucket the gravitational force, and the pulling of the rope.",
"So why is the water not falling out?",
"The answer is, that the water of the bucket always want to go straight, and the force you apply always make them change direction, there seems to be an \"outward\" or \"centrifugal\" force \"pushing\" the contents against the side of the bucket. But it's an an illusion -- it's really just the momentum of the bucket and it's contents.",
"You have to use pseudo forces (Coriolis force and inertia) if you are in an accelerated frame of reference, like the rotating bucket or the rotating earth."
] |
[
"Yes and no. For an observer from space (the moon, let's say) the speed of earth's rotation doesn't affect gravity. If you're standing on the earth, then it does, depending on where you're standing. At the equator, gravity will feel reduced by 0.34% (not much) weaker than at the poles due to the earth spinning.",
"The force opposing gravity (at the equator) due to the planet spinning is proportional to the radius of the planet, and the square of the rotational frequency. As you get closer to the poles, the effect becomes nil."
] |
[
"The gravitational force would not be affected and depends only on the amount and locations of the planet and object's mass. However the net/total force on an object on the surface of the planet would be affected due to an increase in the centrifugal force."
] |
[
"How do parasites change a host creature's thought patterns?"
] |
[
false
] |
Like the Cordyceps fungus that forces ants and other creatures to climb to the top of a plant stem before the fungus fruits and releases spores. This kind of thing creeps me out but I would love to know how an invader can change the behavior of a much larger host. Cordyceps fungus video, see here:
|
[
"http://www.medicalnewstoday.com/articles/253802.php",
"http://www.theatlantic.com/magazine/archive/2012/03/how-your-cat-is-making-you-crazy/308873/",
"Toxoplasma is mentioned a lot. Apparently it is capable of altering the disposition of vertebrates, including ourselves. Is there anything to the hype?"
] |
[
"Will check those links out tomorrow, it's the night cycle where I am now."
] |
[
"Well a parasite like the liver fluke controls a cluster of nerves below the ant's oesophagus, which control various muscles, forcing the ant to climb a blade of grass at night. The exact method by which this occurs is, to my knowledge, still not fully understood."
] |
[
"Does /r/askscience believe travel beyond the solar system is impossible?"
] |
[
false
] |
[deleted]
|
[
"I don't believe it's impossible from a physics standpoint, seeing as the Voyager spacecraft is currently on it's way to interstellar space and that thing was built some time in the 70's. So it's clearly not impossible from a materials standpoint. Adding the human element would make the journey extremely difficult and much more dangerous, but nothing that is insurmountable.",
"So no, there's no scientific or mathematical reason space travel to Pluto or beyond would be impossible. It's all still wildly outside of anything we can hope to accomplish with modern technology though."
] |
[
"With current technology, yes it's impossible.",
"But with future technology and a whole lot of patience (multi-generational colony ships, for example), it's not impossible. Just really, really hard."
] |
[
"And it's important to remember, that regardless of technological advances, there is zero reason to believe it will ever get \"easy\". "
] |
[
"What is the feeling of \"freefall\"?"
] |
[
false
] |
I had this question arise the other day on the flight back from Colombia: What is the neurological origin of the gut and body feeling that one experiences with sudden drops (such as during plane turbulence or on a roller coaster)? And one more question: If this is related to a downward acceleration as a physical phenomenon- why do we not feel the same effect when accelerating foreward or backwards? [edit]: Thanks for the responses everyone! So it seems that the sensation is a combination of both the cochlear inability to detect position during free fall and the g forces on the abdominal organs.
|
[
"a basic answer ",
"here, in a previous comment",
".",
"to sum up, you have two otolith organs in each ear; they're sensitive to linear acceleration. the utricle senses linear acceleration in the horizontal/transverse plane around the head (left, right, forward, backward); the saccule senses vertical (top to bottom of the head) acceleration (up, down).",
"so long as you're upright, the saccule is sensing gravity, but the utricle might be silent (if you're upright and still). if you lie down, the saccule might stop signaling, but the utricle will start sensing gravity instead.",
"when you're in freefall, the utricle and the saccule are unable to sense gravity, since your entire body is accelerating in tandem. this is where the weird feeling comes from - it's your perception of the absence of gravity. the fact that you feel it in your body, or your 'gut', is interesting, but as far as we know it's a referred sensation, and a pretty reasonable one. there's no reason the brain would need to represent gravity as coming in through your ears..."
] |
[
"Thanks for the response! That's pretty interesting- I'll remember that in my anatomy class next year"
] |
[
"I'll respond to this part of your question: \"What is the neurological origin of the gut and body feeling that one experiences with sudden drops (such as during plane turbulence or on a roller coaster)?\"",
"This feeling is due to the change in the apparent gravity of our situation when engaged in circular movement. The body tries to maintain a normal condition of homeostasis, and for us that means that we adjust to g at it's normal value of 9.81 m/s",
" as that is the value that we experience here at the surface of the earth. Should that value change suddenly (as it does when we move in a circle due to the centripetal force), we \"feel\" the difference as our bodies try to adjust to the new value. ",
"This is the entire excitement behind roller coaster rides; what happens during the roller coaster ride is that the apparent gravity changes from 9.81 m/s",
" to higher values of g (on downward slopes) and then to lower values of g (when moving upward). As the value of the apparent gravity changes our body struggles to adjust to the new value of \"g\" and we sense this struggle and are \"thrilled\" or something.",
"A good website detailing the physics behind this phenomena can be found here:",
"http://www.ux1.eiu.edu/~cfadd/1350/06CirMtn/VertCircle.html"
] |
[
"What makes our bodies stay at 98.6 degrees?"
] |
[
false
] |
I may be asking a dumb question but, if we are constantly in air conditioned environments, at or around 74 degrees, why are we still at 98.6? I get like warm blood but what inside the body keeps us warm? Is blood just inherently warm or what.
|
[
"I don't know about the details of how the biological processes work, but I can provide some physics answers. Our bodies are hotter than the environment because they constantly produce heat as a result of our basic metabolic activities. The term \"heat\" here means thermal energy produced that can be moved around, but must end up somewhere. The energy that gets produced initially goes towards increasing the temperature of our bodies above that of the environment. The only way to drop the temperature back down is to transfer some of that heat to the environment. Exactly how that heat transfers to the environment is complex, but most of the time is dominated by convection transfer to the air around us, which naturally circulates around. Exactly how fast the heat transfers is another complex question, but depends roughly on the linear temperature difference between your skin/body and the air.",
"This all means that, as your body produces heat energy, its temperature increases, and with the temperature, the rate at which heat energy is transferred to the environment increases too. Your body temperature reaches an equilibrium when the rate of heat generation matches the rate at which it is transferred to the environment. HVAC (Heating, Ventilation, and Air Conditioning) systems need to take into account roughly how much heat human bodies generate in order to be sized properly for maintaining interior temperatures. There are ",
"various charts",
" and calculators out there to help engineers perform these calculations.",
"Where it gets tricky is that your body has a \"preferred\" temperature, at which it's processes work best, and includes various internal mechanisms to try to maintain that temperature no matter what's going on in your activity level and environment. You can sweat more or less, increase or decrease your activity level in various ways, and IIRC your body does things with your blood flow too in order to move heat out of your core faster or more slowly. Plus intentionally putting on or taking off layers of clothing. If it's too cold and you can't slow down heat leaving enough, then you eventually get hypothermia and die. If it's too hot and you can't move heat out fast enough, then you eventually get heat stroke and die."
] |
[
"Animals constantly regulate physiological processes. It’s also known as homeostasis, or a tendency towards a state of equilibrium. You can think of homeostasis and body temperature as a thermostat for your body. It can shift depending on conditions (at rest, active, hibernation, infection, etc.).",
"Many of these homeostatic processes in warm-blooded animals depend on an internal core temperature of 37 C, since enzymes act most efficiently at this temperature. At lower temps, these enzymes and reactions don’t operate as efficiently. Higher temperatures may cause reactions to operate more efficiently, but may cause proteins and enzymes to denature. It’s all about attaining a state of equilibrium.",
"How we achieve homeostasis is a bit more complex. There’s a litany of thermoregulatory neural and hormonal pathways at play. When we’re too hot, we sweat. We thirst. We seek shade. Other animals have distinct behavior (dogs pant). It all depends on our physiology.",
"When we’re too cold, we can generate heat in a process called thermogenesis. This can be through the catabolism of ATP, the conversion of chemical energy into kinetic energy and heat. ATP metabolism happens all the time, and it’s output depends on our energy requirements. In cold conditions, this can manifest as shivering (the kinetic aspect).",
"Alternatively, we can also generate heat through non-shivering thermogenesis. This is mediated through brown adipose tissue, which is usually found on the fat of visceral organs. Specifically, uncoupling protein 1 (UCP1) leverages the protein gradient in the mitochondria to drive this process. It’s especially important in babies; they’re more prone to heat loss since they have a higher surface area to volume ratio."
] |
[
"Others have explained the concept of homeostasis. I'll just explain one part of your question, where you asked how we maintain a body temp of 98.6 when comfortable room temp is 74. I'll be switching everything the Celsius though.",
"Air is a good insulator. Heat doesn't move through it easily, partly because of how far apart the molecules are in air. Body temp is 37 degrees and room temp is 21 degrees and that feels comfortable to us because the heat that's leaving our bodies is roughly equal to the heat that we are producing jut from everyday metabolic processes. Now lets say that you go jump in a pool. Well you've now surrounded yourself with a medium other than air. Water is very good at transferring heat. So much so that a temperature of 33 degrees feels comfortable to you, which is only 4 degrees off from what your body temp is.",
"Please note that I am resisting the urge to discuss the different methods for heat transfer, and how they are affected by different mediums other than by saying \"partially because of how far apart the air molecules are\"."
] |
[
"Freezing Water in a Cup"
] |
[
false
] |
I have a freezer at home and it's roughly -10 degrees celsius or so (14F), and I had about half a cup full with a block of ice. I added water to the cup of ice and left the block of ice sitting in the cup as I added the water and put it back in the freezer. I came back about 5-10 minutes later and the cup had no ice and just water in it. This may sound stupid but just wondering how this is possible. If the temperature is extremely relevant, I can have a look later at the exact temperature of the freezer
|
[
"Water is a much better conductor. Much like how you can get hypothermia in warm water fairly quickly while in the same temperature of air you would fair much better. The water you added was above freezing. This conducted warmer temperatures into the existing ice faster then the air could conduct colder temperatures into the water/ice combo. "
] |
[
"I like your answer, but I think you mean to say heat rather than temperature and that the water transferred heat to the ice faster than the air could transfer heat away from the water.",
"Cold isn't a physical property, only a description of relatively less heat than something else and it can't be conducted to anything."
] |
[
"here are the two things that are going on:",
"1) when you added the water the mixture of ice and water was already working on becoming a consistent temperature. meaning after a while the entire mixture of water and ice would be the same temperature. the only way it would be ice is if after the temperature is the same throughout the cup that the temperature is below 32 degrees F.",
"2) putting that cup into the freezer just cooled down the entire mixture a little more but apparently not enough to put it below 32 degrees F",
"the water you added to the cup was too warm to keep the overall temp below the freezing point"
] |
[
"Where does carbon 14 come from?"
] |
[
false
] |
[deleted]
|
[
"It's mostly created on Earth in the upper atmosphere due to bombardment of cosmic rays and nitrogen.",
"This is why it's such a good dating tool, stuff sealed from the atmosphere won't get exposed to any more and the amount of nitrogen and the cosmic bombardment rate is roughly fixed and insensitive to anything going on with Earth's weather or climate.",
" Some corrections are relevant and useful, but that's another story."
] |
[
"Thank you, this is exactly what I was looking for! Have a nice day! "
] |
[
"Have some gold"
] |
[
"Would water work as a Faraday Cage?"
] |
[
false
] |
Imagine if a big solar flare happened on the Sun. I have a mobile device which would get damaged by that and I want to save it. If I put my mobile device into waterproof box and then I put it under water. Would that water make a Faraday cage effect, which would save my mobile device from the solar wind actually damaging it?
|
[
"They are the same microwaves, frequency and wavelength. Just their pattern of re-radiation changes. The array of hole in the microwave oven window become a ",
"phased array antenna",
"."
] |
[
"First you have to understand a lot of what people call Faraday Cages are really a shielded enclosure. The original concept of the ",
"Faraday Cage",
" was for static electrical charges and not radio frequency signals. But the concept has morphed into that all shield enclosures are called Faraday Cages. ",
"As for the ",
"effectiveness of such an enclosure",
", it depends on mainly two things. One, the conductivity of the wall of the container and two, the size and number of holes through the walls. With water it would depend heavily on the salt concentration in the water. Sea water being much better than fresh water. ",
"As for holes in the enclosure, many people think that a hole smaller than a wavelength of the signal will block it. But signals will get through. The hole becomes a ",
"waveguide beyond cutoff",
" and will have to analyzed as such.",
"So there is no hard and fast rule on how effective a given enclosure will be. They all would have to be analyzed for the specific conditions."
] |
[
"As for holes in the enclosure, many people think that a hole smaller than a wavelength of the signal will block it. ",
"Wait, what does this tell me about microwave ovens? Isn't the mesh supposed to absorb all the microwave radiation?"
] |
[
"Are gas giant planets perfectly round?"
] |
[
false
] |
At some given radius, does Jupiter have the same density all the way around or does the density of gas vary throughout? If not, what causes the density variance?
|
[
"Jupiter, like all other planets, is not perfectly spherical, but instead is ellipsoid in shape, with a bulge around the equator. This is caused by the rotation of the planet around its axis pushing matter more outwards the closer to the equator it is.",
"If you measure the radius at the pole you'll find a figure roughly 7% lower than if you perform the same measurement at the equator (for reference, for Earth this difference is about 0.3%).",
"However, even if you ignore this effect, then the density is still not constant all around. Jupiter, like other planets with an atmosphere, has weather. Areas of higher density and of lower density develop in the gas, just like they do in Earths atmosphere. The famous \"great red spot\" on Jupiter is actually a very large storm in Jupiters atmosphere."
] |
[
"The famous \"great red spot\" on Jupiter is actually a very large storm in Jupiters atmosphere.",
"Well, sort of. It's certainly a vortex, but calling it a \"storm\" isn't quite right.",
"Storms on Earth are generally regions of low pressure. Curiously, though, the Great Red Spot (GRS) is actually a region of high pressure - on Earth, that's generally associated with clear air and calm conditions. Although there aren't clear skies and the perimeter has very high winds, the center of the GRS is actually quite calm. On the other hand, ",
"the turbulent low-pressure area",
" just to the immediate northwest of the GRS is very stormy, with extremely frequent lightning."
] |
[
"That's very interesting, thank you!"
] |
[
"What's particular about humans that we evolved advanced intelligence?"
] |
[
false
] | null |
[
"Anthropologists have chalked this up to the fact that our ancestors began cooking our food. This increased the amount of neurons in our brain to approximately 100 billion. (I've heard comparisons that animals around our size have 30 billion.)",
"So what does cooking food have to do with brains? When people eat raw food, it is not 'partially digested' like cooked food is. Eating raw food takes energy out of our bodies in order to digest, and even still, we can only extract somewhere around 30% of the calories out of it. However, when the food is cooked, we can extract nearly all the calories out of it.",
"Our brains require a lot of energy to function. We often think that our muscles require a lot of energy, but our brains require roughly 20% of the calories that our entire body requires.",
"So once our ancestors began cooking food, suddenly we had a lot more calories for our bodies to use which meant more brain development. It meant more neurons, and more neural synapses firing (You may have heard the expression neurons firing becomes the brain's wiring). Additionally, since we were absorbing more food than ever before, we didn't have to spend so much time hunting and gathering. Most animals are nearly constantly securing the most fundamental need in life: food. Once we began cooking our food, we had more time to sit back and think. We developed more advanced communication, tools, and the rest is history. "
] |
[
"Humans are A: Diurnal (active during the day), B: have opposable thumbs, C: have vocal apparatuses capable of making precise sounds.",
"Most meat eaters hunt during the night, but early primates hunted during the day. Now, the African sun is very hot, hot enough to make brain cells die much faster. So over time, primates evolved more brain cells for redundancy. ",
"I do not know why the thumb evolved, but it predates complex intelligence according to wikipedia, and its existence meant that smarter creatures could build better tools.",
"Lastly, vocal cords. Humans can swim. Humans have reflexive swimming abilities that even babies demonstrate (though I still wouldn't leave one unattended in a pool). This ability to swim meant that protein rich seafood (in particular clams) could be acquired and eaten readily for anyone living near water (See: most of humanity) and although written language began (As far as we can tell) between the Tigress and the Euphrates, the kind of intelligence humans have more likely evolved along the coast of Africa, and then moved inward.",
"Why do I bring up this? Well, the vocal cord began as a means to prevent water entering the lungs while we dive, but also enabled more complex speech sounds.",
"These three things come together as follows. Heat causes big brain. Thumbs cause big brain to develop tools. Speech allows information about tools to spread.",
"See, that last thing is what makes humans so superior. We can exchange information about tool building. But in order for that to happen, three traits had to occur in one organism."
] |
[
"So you're saying that the factor prohibiting other species from evolving greater intelligence is the energy cost? I don't really understand how the concept of marginal increases in intelligence would work, but for larger animals that already have huge caloric requirements, it seems the requirements of increased brain function would be marginal."
] |
[
"If we have a compressed spring and bring it to space, then release it. In what form does the energy leave?"
] |
[
false
] |
It can only be heat as far as I know. On earth it would be sound and kinetic too, but what about deep space? It can't all be heat?
|
[
"If there isn't any friction within the spring the energy will stay, shifting back and forth between kinetic energy and potential energy as the spring keeps oscillating until something stops it. With friction mechanical energy will dissipate to internal heat in the spring. The heat causes the spring to emit energy in the form of black-body radiation."
] |
[
"Thanks a lot for that answer! Makes some sense. :). So the spring will actually keep going \"up and down\" in space, or will it be vibrating? I'm just trying to visualize the oscillating. And this will slowly go over into radiation, and thus losing the spring energy?",
"If i got that right now, I would be happy. I think what you said it pretty damn cool."
] |
[
"The center of the spring will stay in place while the ends expand and contract in unison."
] |
[
"Question about photons, emission, absorption and time:"
] |
[
false
] |
I've been trying to follow some of the questions asked here recently and I apologize if I've missed some crucial tidbit that would make this all make sense to me without asking, but: If a photon's proper lifespan is zero, and it is emitted at the exact same instant it is absorbed, how can it be correct to say that empty space contains photons?
|
[
"\"Proper lifespan\" isn't what we want to say here. If we're going to talk about this, we want to do so in a rigorous and disciplined way, in order to maximize clarity of thought.",
"What we want to talk about here is ",
" The elapsed proper time along a trajectory is the integral over the curve parameter of the Minkowski inner product of the infinitesimal proper time element with itself, where the infinitesimal proper time element is defined as the square root of the Minkowski line element, with appropriate minus signs and factors of ",
" thrown in there wherever they're appropriate for your sign convention and choice of units.",
"That sounds like gibberish, I'm sure, but I spell it out like that to make an important point: This is not qualitative philosophical mumbo-jumbo we're talking about here. This is mathematics. And ",
" mathematics to boot. None of it's ambiguous or hard to interpret. So we can be ",
" clear about what it all means.",
"The proper time is the time that's measured by a moving clock. That's all. (Well, that's not all, it also has a geometric meaning, but that's its physical meaning.) If you were moving through spacetime along some trajectory — and hint hint, you are — proper time is what you'd measure with your wristwatch.",
"But because of the hyperbolic relationship between space and time, the infinitesimal proper time element ends up being a ",
" of terms. Timelike displacement on the one side, spacelike displacement on the other, minus sign in the middle. Which means it's possible for the trajectory to be such that, over each infinitesimally short bit of the trajectory, the timelike displacement and the spacelike displacement are exactly equal, making the total displacement zero. That's what a ",
" is; it's a trajectory which, at every point along the curve, the infinitesimal proper time element is exactly zero.",
"What does that mean? Does that mean that photons don't really exist, woo woo let's eat some drugs? No! It means that if photons had wristwatches, those wristwatches would never tick. And ",
"Light — any massless propagation of effect, really, but light is the most well known — exists right on the cusp between what we consider to be space and what we consider to be time. At one extreme we have coordinate distance, which is spacelike; it describes the directions in which you can ",
" With your ",
" Like ",
" At the other extreme we have coordinate time, which is timelike; it describes the order of events, one tick of the clock coming before the next coming before the next and so on. In between those two extremes we have null geodesics, which are trajectories through spacetime such that displacement in space is exactly equal to displacement in time — one meter of distance per meter of time, say — and the geometry of our universe is such that when those terms are equal, the proper time along the trajectory is zero.",
"Nothing magical, nothing mystical. Just geometry, a little bit of algebra and ",
" integral. Easy stuff, very straightforward.",
"EDIT: Whoops. There's a mistake in my second paragraph. I'm way too lazy to fix it. Consider finding it to be an exercise left for the reader."
] |
[
"quite well, thank you ;-)"
] |
[
"it is emitted at the exact same instant it is absorbed",
"Actually there's some delay, though I don't know the time scale here. But IIRC, it's why light propagates more slowly through materials.",
"can it be correct to say that empty space contains photons?",
"Because to all non-light speed observers, light does live for some length of time and travel some distance. It's only in the \"frame\" of light itself that the distance is contracted all the way to nothing, and takes no time to cross."
] |
[
"Why do we see meteor showers at roughly the same times each year?"
] |
[
false
] |
If the debris field is orbiting the sun too, why does the earth move through them with such regularity?
|
[
"Debris fields orbit the Sun on highly elliptical orbits because they are generated by comets, which also have highly elliptical orbits. There is debris strewn all along the elliptical path, so whenever we cross said path, we run into some of that debris.",
"This image",
" shows the debris field as the diagonal line stretching across the image, with the comet in the middle."
] |
[
"On scales as large as the Solar System, if a comet's orbit is inclined by even a degree with respect to the ecliptic (the plane that all the planets approximately orbit in), it will be significantly out of the plane. So it's not too surprising that the comets' orbits don't coincide with Earth's at more than one point (there are certainly debris fields which don't intersect the Earth's orbit)."
] |
[
"Do Earth's and the comet's orbits coincide at only one place? I guess I'd expect two or four. Are the elliptical orbits in the same plane as Earth's?"
] |
[
"What is a Lie group?"
] |
[
false
] |
What is its application? What field of math is it a part of? Why is it so complicated? And finally, what textbooks do I have to read to get to that level, I figure Linear Algebra is step 1? I only ask here because hours and hours on Wikipedia got me nowhere.
|
[
"You can get a basic idea of what a Lie group is fairly easily. It's just a set along with a binary operation, such that the operation obeys the group axioms (closure, associativity, and the existence of an identity and inverse), and the set describes a... well, smooth thingy is the best nonformal way to put it. A ball is a smooth thingy, while a pyramid is not a smooth thingy; the analogy is slightly misleading, because the thingy isn't required to have geometrical structure, but it gives you the basic idea.",
"It's so complicated because you need a complicated formal structure to get all of the details I glossed over right. For instance, it turns out that there is no way to make a Lie group out of a sphere; this isn't that surprising at all when you work out the formalities, but you would never be able to derive it from the informal description I just gave you.",
"Linear algebra is step 1. You'll also need some group theory, topology, and differential geometry. And then of course studying Lie groups is a subject in and of itself..."
] |
[
"What field of math is it a part of?",
"Its used a lot in mathematical physics. For example the angular momentum operators belong to SU(2). Its also used in studying fiber bundles.",
"It would help quite a bit in knowing what exactly your background is, are you a senior level physics student who has heard the term thrown around, or a math student who has just started learning algebra?"
] |
[
"A Lie group is a group and a (smooth?) manifold, such that the group operations are smooth/continuous. This makes it part of algebra (because of the groups) and differential geometry (because of the manifolds), although to be frank, I guess the majority of applications are found in the geometry field.",
"I don't find Lie groups to be very complicated. Group theory is \"straightforward\" (if anything in math is), and differential geometry is only complicated because it has to be to express some very simple ideas. Once you have worked enough with diff. geom. to intuitively understand what a manifold is, you will wonder why you ever thought it was hard. This goes for anything in math, but manifolds in particular.",
"In particular, the study of objects with more structure will often be simpler than the study of objects will little structure, in the sense that you have more tools at your disposal. Compare the study of Lie groups to the study of general groups or general manifolds.",
"You will want to read some group theory and then differential geometry (quite crucial). Once you have that, you're good to go. Group theory has few prerequisites, but indeed, you may want to brush up on linear algebra and basic functional analysis before diving into differential geometry, but you will typically want to do that before touching any higher mathematical field anyway."
] |
[
"Why is Hydromorphone not called Hydromorphine. Same for hydrocodone why is it not called hydrocodeine? Or are they just not related?"
] |
[
false
] | null |
[
"Morphine and codeine have allyl alcohols in their structures which are converted into ketones to make hydromorphone and hydrocodone respectively. Compounds with ketones in their structure typically end with the suffix -one. ",
"See the top half of this image. "
] |
[
"So its an organic chemistry nomenclature deal. When the -O bond become a ketone (=O) the ending changes to -one.",
"",
"https://pubchem.ncbi.nlm.nih.gov/compound/Morphine#section=2D-Structure",
"https://pubchem.ncbi.nlm.nih.gov/compound/Hydromorphone#section=2D-Structure",
"http://www.chem.uiuc.edu/GenChemReferences/nomenclature_rules.html",
"",
"Look at the different structures of morphine and hydromorphone and how the oxygen bond changes to a double bond."
] |
[
"Hydromorphone differs from morphine in that an alcohol group is replaced with a ketone group. Ketones are assigned names ending in “-one”.",
"If you compare the diagrams at ",
"https://en.wikipedia.org/wiki/Morphine",
" and ",
"https://en.wikipedia.org/wiki/Hydromorphone",
", the ketone group in the latter is in the bottom left corner.",
"The same applies to codeine and hydrocodone."
] |
[
"An accurate Helium thought experiment?"
] |
[
false
] |
[deleted]
|
[
"An \"ideal\" gas is one which doesn't really interact with other particles accept during collisions. So imagine a bunch of tiny little bouncy balls flying around in a vacuum so no wind resistance. Next you must remember that the bouncy balls on average don't lose any energy during collisions. So you've no got a room filled with bouncy balls flying all over the place completely random and if you change the size of the room they will just bounce further extending their range to whatever size of room you put them in. I will finish my explanation in about 20 minutes brb."
] |
[
"\"",
"\"",
"This is not correct. Helium is a gas, and will fill the container pretty much uniformly.",
"Also, a helium balloon floats in our atmosphere for exactly the same reason that a boat floats in water - they each weigh less per unit of volume than the fluid (water or atmosphere) that they are in. Therefore, the heavier substance tends to settle to the bottom, displacing the lighter substance."
] |
[
"Helium is a gas, and will fill the container pretty much uniformly.",
"This is mostly true, unless the container is very, very tall. ",
"As the column grows in size, atoms at the bottom of the container will compress from the weight of all the atoms above it. It's the same reason that atmospheric pressure decreases with height. ",
"Note that since helium is quite light, you'd need a container around 60 kilometers tall to have a pressure difference of 1/e (~37%) between top and bottom...which admittedly is probably out of the realm of what OP was asking."
] |
[
"What are the benefits and risks of \"inhaling alcohol?\""
] |
[
false
] |
Machines that vaporize alcohol and mix it with oxygen apparently exist as an alternative method of consuming alcohol. What are the benefits/dangers of this? Inspired by a current AskScience about bathing in alcohol:
|
[
"When you ingest alcohol, it's taken up into your bloodstream and the first places it goes is through the ",
"Portal Venous System",
" to the liver. It gets metabolized there in what's called the ",
"First Pass Metabolism",
" before it goes anywhere else in your body.",
"Basically, anything that you're eating goes to the liver before it goes anywhere else. This is a way to ensure that any toxins get removed from your bloodstream before they circulate to the rest of your body.",
"By inhaling alcohol, you're absorbing it through your lungs, rather than your stomach and bypassing this first pass metabolism. This means that you have unprocessed alcohol circulating throughout your bloodstream.",
"I'd recommend against it. It is an easy way to have a dangerous amount of alcohol in your blood stream in a relatively quick amount of time. There's a reason that these machines are being banned in so many places.",
"As a side note, the first pass metabolism is one reason that drugs are so hard to develop. Often up to 99% of a drug is eliminated in the liver before it even can take effect on the body. This is also the reason that injecting and smoking illicit drugs is usually much more effective than eating them. It's another way to bypass this mechanism. "
] |
[
"Its also important to note that you lose the ability to vomit as well, which increases the risks of alcohol poisoning. "
] |
[
"so how come when I take a shot of something really stiff I can feel drunk within seconds? is it just a placebo affect, some sort of muscle memory of being drunk other times?"
] |
[
"What are the downsides to a Molten Salt Thorium Reactor?"
] |
[
false
] |
Seems like its sort of an energy dream other than obtaining funding. Whats the fine print?
|
[
"not an expert but...",
"\"Molten salts can be highly corrosive, more so as temperatures rise. For the primary cooling loop of the MSR, a material is needed that can withstand corrosion at high temperatures and intense radiation. Experiments show that Hastelloy-N and similar alloys are quite suited to the tasks at operating temperatures up to about 700 °C. However, long-term experience with a production scale reactor has yet to be gained. Higher operating temperatures would be desirable, but at 850 °C thermo chemical production of hydrogen becomes possible, which creates serious engineering difficulties. Materials for this temperature range have not been validated, though carbon composites, molybdenum alloys (e.g. TZM), carbides, and refractory metal based or ODS alloys might be feasible.\"",
"\"Salts must be extremely pure initially, and would most likely be continuously cleaned in a large-scale molten salt reactor. Any water vapor in the salt will form hydrofluoric acid (HF) which is extremely corrosive. Other impurities can cause non-beneficial chemical reactions and would most likely have to be cleansed from the system. In conventional power plants where water is used as a coolant, great pains are taken to purify and deionize the water to reduce its corrosive properties.\"",
"In summary these types of salts can be chemically scary if shit were to go tits up but its hard to say what will happen in practice. Chemists deal with harsh chemicals all the time but the added nuclear element could make things complicated."
] |
[
"First of all, I suggest everyone read this:\n",
"http://energyfromthorium.com/pdf/MSadventure.pdf",
"Secondly, since this post gets referenced a lot:",
"Four problems with the MSR for those unaware",
"-Uses ultra expensive Hastelloy-N Alloy to house the salts. Its not even made anymore, but can be made.",
"-Fluoride salt corrodes cheaper metals, such as 316 SS.",
"-The vast expertise of MSRE is only on paper now (a lot of dudes are dead, a few remain), so we are literally duplicating equipment made from 1950-1960 and altering it to perform new tasks. Right now my thesis project is designing a batch purifier, which will make 52 kg of salt at a time. Alternative purification gases such as nitrogen trifluoride are being tested.",
"-Was designed under the premise that uranium was scarce, so that thorium breeding had to be done. That turned out not to be the case.",
"More minor problems",
"-Beryllium fluoride is not produced in batches high enough for a reactor. Took me 5+ months of search and back and forth with Materion to gain 100 kg of it. Its also some of the nastiest crap in hell.",
"-Seals are the biggest hassle ever with molten salt. Everything needs to be welded shut. Pipe connects have to be done with VCR, which still leak. For those not aware with how agonizing weld seals are let me explain: Imagine having to cut doors open every time you wanted to walk through, instead of turning a knob.",
"Edit 1/8/13:",
"Pros:",
"-China is apparently going to produce two molten salt reactors before 2020. They've been given a lot of money and personel. They also have help from us in the USA if they need it.",
"-China is going to need a ton of Hastelloy N, so Haynes Inc will probably be making a few forgings. Of what and when, they're not allowed to disclose to me.",
"-Materions new Pebble Bed Plant went online which use a lot of beryllium fluoride. They should be able to produce enough BeF2 for a reactor, I would assume.",
"-Three of the worlds top universities are on the job doing good work on the MSRE (Berkeley, MIT, and UW-Madison).",
"Cons:",
"-Enriched natural lithium (Li-7) is not produced in the US anymore and will have to be bought from china. The Y-12 plant at ORNL would have to be contracted for Li-7. This is a strategic resource. Will we be able to get enough Li-7 to run a reactor?"
] |
[
"It's an experimental design that has never been made as a full scale power generating plant.",
"No one has any idea whether it can be done economically and safely. It is an interesting concept that has never been proven to work well. It isn't as big a leap as fusion, but it's not much further along in development. ",
"This will probably be downvoted to hell but much of the positive buzz is due to marketing not engineering."
] |
[
"I just learned how cosmic rays are primarily (positively charged) protons and atomic nuclei. How is their charge balanced?"
] |
[
false
] |
If earth just sucked up positive particles it would accumulate a charge, so there must be some incoming negative charge to balance it? Are these just electrons, or other particles as well?
|
[
"We think ",
"cosmic rays are generated in supernovas",
" by shock waves. My understanding is that there are similar amounts of positive and negative particles generated initially, with similar velocities. But the electrons are screened out by ",
"inverse compton scattering",
". Basically, the electrons can bounce off the cosmic microwave background. The protons and other heavy elements have more momentum, so they plow through.",
"As far as the net charge of the earth goes, cosmic rays are not a large contribution since the solar wind sends a much bigger flux of charged particles our way. If cosmic rays did lead to a net positive charge, it would be self limiting since the charged surface would attract more electrons from the solar wind. The surface of the earth actually has a negative charge, with a positive charge in the atmosphere nearly balancing that out. ",
"This paper seems to sum up the messy details",
"."
] |
[
"It seems like you are assuming the net flux of cosmic rays to the earth is neutral, but in reality it is ",
"99% positive nuclei and 1% electrons",
". Also, they are generated by ",
"supernova shock waves",
", not from nuclear fusion per se."
] |
[
"You really need to read more about cosmic rays before you answer questions about them here. The wikipedia page would be a good place to start. The 1% vs 99% refers to the abundance of positive vs. negative particles. The proton-electron mass ratio is close to 2000, so if electrons were 1% of the mass of cosmic rays like you claim that would imply cosmic rays are mostly electrons by number. And while neutrons can be produced as secondary cosmic rays (i.e. the particles released when a primary cosmic ray collides with an atom in out atmosphere) they aren't a major component of primary cosmic rays. Finally, ",
"observation of pion decays confirmed the long held hypothesis that supernova produce most of the primary cosmic rays",
". Again, this is all stated on the wikipedia page if you want to check."
] |
[
"How can a system at an equilibrium have maximum entropy?"
] |
[
false
] |
I’m trying to understand the concept of entropy but I don’t understand why, if entropy is how chaotic a system is, a system at an equilibrium is considered to be at maximum entropy? Isn’t such a system at its most inactive state? I’m sorry for my use of simple words. Edit: I’m amazed by the quality of the replies I got. Thank you, you guys are great. Now I’ll need some time to digest this.
|
[
"I don’t understand why, if entropy is how chaotic a system is, ...",
"Ah ... this is the block in your understanding here: although historically entropy was ",
" as a measure of \"disorder\" in a system, and although it is still often ",
" as such, the truth of the matter is that entropy has virtually nothing to do with order or disorder/chaos.",
"Rather, entropy is a measure of the \"degeneracy of macrostates.\" Allow me to explain.",
"Thermodynamic systems can be described with both ",
" and ",
". Microstates are essentially the fundamental microscopic states of a system which govern the system's exact evolution over time, while macrostates are the emergent states which govern the system's average/approximate evolution.",
"For example, in a gas of particles, the position and momentum of every particle in the gas is part of the system's microstate. If you have a lot of gas, you have a lot of particles, and therefore the system's microstate is very complex and has a large number of independent variables.",
"However, if you want to have a qualitative idea of how the gas will behave, you do not need to know the values of all of these microstate variables. You only need to know a few variables, such as temperature and pressure. These variables are part of the system's ",
".",
"Every thermodynamic system has both a macrostate and a microstate at any given time. Every microstate that the system could possibly be in has a single corresponding macrostate (i.e. if you tell me what all the microscopic variables like the position and momenta of the particles are, I can tell you what the macroscopic variables like temperature and pressure must be). However, for every macrostate there could be ",
" corresponding microstates. This must be the case by the ",
"pigeonhole principle",
", since there are many more macrostates than microstates. They share a one-to-many relationship. If you tell me what the macroscopic variables are, I ",
" tell you what the microscopic variables must be.",
"Entropy, then, is a measure of ",
" microstates correspond to a given macrostate. The ",
" microstates there are for a given macrostate, the ",
" the entropy is.",
"A very simple example of this can be given in the form of an ordinary pair of throwing dice. The microstates are the individual die values after a throw, while the macrostates are the ",
" of the two dice. Typically, in a dice game, only the sum of the rolled dice matter: the macrostates are really what govern the game's evolution and determine who wins the game. But the microstates also \"matter\" insofar as they determine what the macrostate is. So for example, if I roll the two dice, I might have a microstate of [(3, 5)] while my macrostate might be [8].",
"If you sit down and count them, a pair of two dice have 36 possible microstates: [(1, 1), (1, 2), (2, 1), (1, 3) ... (6, 6)]. While it only has 11 possible macrostates: [2, 3, 4, ... 12].",
"However, the macrostates do not all have the same number of corresponding microstates. Some macrostates have more than the others. For example, there is only ",
" way to roll a [2] or a [12]: [(1, 1)] and [(6, 6)], respectively. However, there are ",
" ways to roll a [7]: [(1, 6), (2, 5), (3, 4), (4, 3), (5, 2), and (6, 1)].",
"So, we say that the macrostate of [7] has the highest entropy, while the macrostates of [2] and [12] have the lowest entropy. That is to say, if we were to choose a microstate at random (giving equal probability to choosing every possible microstate), we would expect to find ourselves in the macrostate of [7] with a higher probability than any other macrostate.",
"Now, when it comes to typical thermodynamic systems, it's like rolling a ",
" number of dice and then considering only the total sum of all dice. If we were to randomly mix up the individual die values, we would expect to ",
" be in a \"high entropy\" state: in a macrostate which has a high \"degeneracy\" (number of corresponding microstates).",
"And, if we started out in a low-entropy microstate, but then started changing die values by rolling dice (i.e. evolving the system in time according to the laws of physics), with a very high probability we could expect to quickly find ourselves in a higher-entropy microstate. At first, after just one or a few dice rolls, we would still be in a fairly low-entropy state but it would have higher entropy than our initial state. But as we roll many more dice, we would expect to find ourselves in higher- and higher-entropy states, eventually settling on the highest-entropy state, where we would tend to stay: in an equilibrium around that highest-entropy state. Any time a die roll takes us out of equilibrium (into a lower-entropy state), future die rolls would have a greater probability of putting us back into that highest-entropy state than they would of putting us into an even lower-entropy state, so we will tend to stay at or around the highest-entropy state.",
"So, that's basically what entropy is, and how entropy works. Hope that helps!"
] |
[
"if entropy is how chaotic a system is,",
"Entropy and chaos are unrelated concepts. Entropy is a mathematically well-defined quantity that can be calculated from the probability distribution of microscopic states of a statistical system. It's a concept that is useful not only in physics, but more generally in statistics and information theory. But we'll stick to physics for purposes of this question.",
"a system at an equilibrium is considered to be at maximum entropy?",
"Yes. At equilibrium, the entropy is maximized subject to whatever constraints are put on the system.",
"Isn’t such a system at its most inactive state?",
"Yes, equilibrium is \"the most inactive state\", by definition. Equilibrium is the state that a system reaches when you leave it to its own devices for a long time. It's the steady-state solution to the equation that governs the evolution of the distribution function. It's the most boring state there is; nothing happens. What's often more interesting is how a system out of equilibrium reaches equilibrium, and what equilibrium state it settles into. Once it's in equilibrium, we know exactly what it's going to do: stay that way."
] |
[
"An alternative but equivalent definition of entropy is ",
"Boltzmann's entropy",
", where Ω is the number of microstates of a given macrostate.",
"In the 100 coin flip example, the macrostate is \"50 heads, 50 tails\", or \"100 heads, 0 tails\". The microstates are all possible sequences of 100 flips. ",
"There's only one possible microstate corresponding to the macrostate \"100 heads, 0 tails\", it's HHHHHH... 100 times. The Boltzmann entropy in this case is k*ln(1) = 0, the same as what I derived above using the Gibbs definition.",
"However for \"50 heads, 50 tails\", there is a huge number of 100 flip sequences that will total to 50 heads and 50 tails. If you use combinatorics to properly calculate that number, it's something huge. And then the logarithm of a huge number is something big. So again, we see that the maximally \"ordered\" case had zero entropy and the maximally \"disordered\" case had positive entropy.",
"You can repeat this tedious exercise for every possible macrostate, and you'll find that the 50/50 split has the maximum entropy."
] |
[
"How can yogurts like Activia have \"active cultures\" but show no evidence of gas being produced in the container (the lids are not popped up, for example)?"
] |
[
false
] | null |
[
"Yogurt is made over a heat source at about 115 F and becomes too acidic for most bacteria to live due to fermentation products. It is then cooled down so the heat-loving bacteria that survived become mostly inactive. They're not dead but they're also not doing much.",
"Activia markets the presence of bacteria more heavily, and has trademarked a strain of bacteria and given it the extra-healthy-sounding name Bifidus Regularis. If there is any evidence of the benefits of \"Bifidus Regularis\" at all it is buried too deeply in their advertising literature for me to find..."
] |
[
"If there is any evidence of the benefits of \"Bifidus Regularis\"...",
"\"Bifidus Regularis\" is a scientific sounding name for ",
", an anaerobic Gram-positive rod that is found as a commensal bacterium in the mammalian intestinal tract. Of course, this is just one bacterium used as a probiotic and other common genera used include ",
" and ",
". ",
"There have been many clinical studies on probiotic bacteria with conflicting results. ",
"This article",
" reviews multiple clinical studies of probiotics on irritable bowel syndrome (IBS). I thought it would make sense to use IBS as an example since \"Regularis\" seems to imply probiotics should be great for these types of disorders. For many metrics such as reduction in bloating, probiotics are found to be better than placebo in just half of clinical trials. For others like abdominal pain probiotics seem to do a little better but it's still far from certain that they have a significant effect. ",
"EDIT: Typo."
] |
[
"Theyve been sued and had to pay money because of those false health benefit claims."
] |
[
"Were superconductors theorised first or discovered?"
] |
[
false
] |
The title say it all really. Were they mathematically predicted first or just discovered by accident or similar?
|
[
"In the early 1900s, there were competing theories about what would happen if a sufficiently pure metal were lowered towards absolute zero. Some thought that the trend of lower resistance would continue all the way down, others that electrons would become immobile and resistance would increase towards absolute zero. Heike Kammerling-Onnes tried to test this using mercury, which was easier to purify than solid metals. He found something totally unexpected, that the resistance didn't just smoothly decrease, but that there was an abrupt drop to zero at around 4 kelvin."
] |
[
"I expect people didn't believe him at first? The idea of exactly zero resistance sounds completely contrary to how most of physics works in the real world, so did other scientists doubt his measurement? Or was the testing mechanism sufficiently accurate or constructed in a way that removed all doubt?"
] |
[
"I am having trouble finding sources that answer your question, but he was awarded the Nobel prize in physics only two years later, mostly for his work on liquefying helium (which allowed him to do these experiments in the first place). "
] |
[
"Did the 1918 pandemic have asymptomatic carriers as the covid 19 pandemic does?"
] |
[
false
] | null |
[
"As far as we can tell, most if not all viruses have the potential for asymptomatic carriers. Do we know for sure that the 1918 Spanish Flu did? Not with direct evidence. That kind of testing just didn't exist back then. But we can say with a fairly high degree of confidence that yes it did."
] |
[
"Yes it did, the numbers will never be known though since the government had no testing capabilities like we have today.\nAsymptomatic infections happen because of the slight differences in the immune system from person to person that are caused by genetic variation.\nSome people are just bound to have a immune system that has a better handle on the disease than average. The same thing can be seen with most viral or bacterial infections, and has been observed even in people with HIV."
] |
[
"Does anyone have a citation that supports the idea that the mutations of Spanish Flu that we see every year have asymptomatic and pre-symptomatic carriers? My anecdotal experience suggests that may be the case."
] |
[
"Is it possible to create an electric jet engine?"
] |
[
false
] |
Jet planes make use of axial-flow compressors to compress air. They then mix the compressed air with fuel and burn both, resulting in gases escaping at large velocities through a nozzle. Is it possible to do away with the burning fuel part, and just compress the air and let it flow out through a nozzle? I understand the velocity of the air escaping would be lesser. But would it be so less that a plane simply cannot take off?
|
[
"A modern ",
"jet engine",
" is actually a compressor and turbine in one machine. The turbine harvests some of the energy from the burning fuel and uses it to power the compressor. The rest of the energy provides thrust or is lost as heat. If there is no energy input (fuel) then the turbine won't be able to generate enough energy to both run the compressor and provide thrust. ",
"Imagine the situation of 100% efficiency: all of the energy that gets put into the air by the compressor is regained by the turbine. In this case you have a do-nothing perpetual motion machine that will theoretically run forever but will provide no thrust. 100% efficiency is, of course, impossible.",
"If you're thinking of simply using electricity to compress air and then release it through a nozzle, then yes. It would work, but you would be far better off just using a propeller."
] |
[
"In a normal jet engine, the \"burning fuel\" part is what makes the back-end spin,,,, which is what turns the front part. If you eliminate the fuel-burning part, then you don't need the back end either, so all you have is a set of propellers on an electric motor. Which will certainly work (ducted fan) but isn't really a jet engine anymore. ",
"Also note that most typical [aircraft] jet engines don't produce \"reactive\" thrust much from their exhaust, but by the \"pull\" of the front compressor/fan stages. \nOne thrust diagram-\n",
"http://www.norcom2000.com/users/dcimper/assorted/inanities/general_wtf/jet/engine.html",
"\n-scanned from this book-\n",
"http://www.amazon.com/Development-Jet-Turbine-Aero-Engines/dp/1852605863/ref=tmm_hrd_title_0"
] |
[
"What prevents the pressurized air from escaping out the front?"
] |
[
"Diet Drinks, Dentistry Dissension"
] |
[
false
] |
Diet soda does contains sugars. They are simply sugars that the body cannot digest, so they pass through without calorie gain. Question One: can the bacteria that cause cavities feed on diet sugars? Restated, are there compounds in diet soda that can cause dental issues? I do have another diet soda related question, which is that everyone ever, when I say 'can I have a coke,' looks at me like I'm a monster. "Don't you know that diet soda actually causes you to gain weight/get cancer/get aids/turns into embalming fluid/etc.." Question Two: Has diet soda conclusively shown to be harmful in any way? Question Three: Does diet soda cause you to gain weight? I realize that #2 and 3 might have been answered on here before, and if so, feel free to tell me to use the search box and I will.
|
[
"The carbonic acid in diet soft drinks ",
" gradually dissolves the material that teeth are made of."
] |
[
"In addition to apartame (Nutrasweet) and sucralose (Splenda), some diet formulations contain ",
"ACE-K",
", a sweetner and sweet enhancer or sugar alcohols such as ",
"sorbitol",
". None of these have been conclusively shown to cause tooth decay, although there is some speculation that sugar alcohols can contribute to tooth decay."
] |
[
"Nutrisweet, which is in Diet Coke, isn't an inactive sugar, it's amino acids, which both you and bacteria can digest, but the amount is too small to have a significant caloric content for the beverage.",
"It's 100% bullshit that diet sodas have any association with weight gain or cancer.",
"There's another kind of artificial sweetener that contains sucralose, which is a non-digestable sugar, and it is also not digested by the bacteria in your mouth or gut. If it were, that could be considered caloric."
] |
[
"Why is the strength of my fingers so weak during the few minutes after waking up in the morning?"
] |
[
false
] | null |
[
"dentist here, most of my understanding of physiology pertains to the head and neck, but i have some understanding of extremities as well.",
"the further away you get from your heart (ie your fingers and toes) blood circulation relies less on your blood pressure and more on your muscles compressing and moving the blood through the blood vessels. you have one way valves in your veins so that blood can only move in one direction when your muscles are not active. ",
"most people have very little muscle movement in their extremities while sleeping. this decreases blood flow, which depletes the muscles of the nutrients and ions needed for muscle function. it is quickly restored (few minutes usually) as you get up and start moving around. ",
"you know that morning stretch that feels so good? it relates to this as well, as it is almost a \"blood flush\" of the various muscles in your extremities."
] |
[
"Thanks for the reply! This certainly makes sense. "
] |
[
"Thanks for the concern, but it's definitely not a medical issue. It doesn't happen every morning (presumably it's more likely after a night of deep, non-restless sleep now that I've read the comments). The few people I've asked about this before ",
"r/askscience",
" all said they knew exactly what I was asking about. Basically, you just can't make a fist of the same strength as the rest of the day first thing in the morning. Fingers still have their dexterity, feeling, etc."
] |
[
"I want to have a career in Astrophysics in the future; I'm 14 years old now. What can I do to better prepare myself?"
] |
[
false
] | null |
[
"I'm not im college yet but I plan on double majoring in particle physics and astronomy. I think astrophysics is similar. I've read lots of books, watched lots of shows on the Science Channel, and just stuff like that. Lots of websites can give you more information, I can give you some if you'd like. I can assure you, though, that to have a career in astrophysics or something like that, you HAVE to study a lot, obviously. To want to puruse a career in astrophysics, you sound very smart; I'm sure you study and everything anyway, you should be okay.",
"(This is personal advice--I'm no genius, as you can see my name isn't colored.)"
] |
[
"Thanks a lot for the reply! You were right, I have read multiple books on the subject but I still hunger for more. It would be fantastic if you could recommend any to me you found entertaining or informative."
] |
[
"I haven't read any books labeled \"astrophysics\" as the subject. But what I have read different ones about physics and astronomy; could you tell me which ones you prefer?"
] |
[
"Do other planets experience earthquakes?"
] |
[
false
] | null |
[
"They do.",
"The Apollo missions carried ",
"seismometers",
" that were deployed on the surface and measured ",
"moonquakes",
".",
"Currently, a mission called ",
"InSight",
" has deployed a seismometer on Mars to record the phenomenon and better understand the planet's interior."
] |
[
"Any process that can fracture rock or generate differential stress across a preexisting fracture is capable of generating a quake. A variety of different processes have been proposed for different populations of moonquakes, including ",
"meteorite impacts",
", ",
"tidal stresses",
", and ",
"expansion and contraction from diurnal temperature changes",
". For marsquakes, ",
"InSight",
" has detected a few deep marsquakes, but the cause remain uncertain (this data is super new, so as more events are collected from InSight over the mission duration, we'll hopefully get a better idea of what's going on)."
] |
[
"It was my understanding that a celestial body had to be geologically active to experience quakes? \nWhat are the causes of Moonquakes and Marsquakes?"
] |
[
"When astronomers refer to distances between galaxies, do they mean the distance as we observe them or as they are now?"
] |
[
false
] |
For example, if astronomers describe the distance between two galaxies in a supervoid that is a billion light-years away to be 150 million light-years. Is that distance representative of what we have observed (essentially an image from a billion years ago) or as it is now (accounting for the expansion of the universe)?
|
[
"It'd be distance at the observed time in the past. We sometimes use \"comoving units\" which do take into account the expansion of the universe. If two objects are a kiloparsec apart back when the universe was half its current size, then they are \"two comoving kiloparsecs apart\".",
"But additionally, galaxies are moving around and interacting with each other, so we typically can't just tack on the expansion of the universe factor and get the right present-day distance. We might see two galaxies on a collision course in the distant universe. By now, they would have merged and probably formed an elliptical galaxy, and maybe had other interactions too.",
"So we use the distance that's observed in the past because that's all that we can really know about."
] |
[
"Yes, they meant the distance from ",
" point to ",
" point."
] |
[
"Are there efforts made to create a map of what the universe probably looks like ",
"?",
"I'm not sure if that word \"now\" has a clear definition."
] |
[
"If the heart is a muscle, after running, will eating protein repair it and make it stronger like other muscles?"
] |
[
false
] | null |
[
"You mean like ",
"hypertrophic cardiomyopathy",
"? Actually, the article says \"Athletes are known to have enlarged hearts. It is the body’s way of adapting to intense exercise, and it is not a disease like hypertrophic cardiomyopathy.\""
] |
[
"Well, it wasn't necessarily a question about athletes, but the best way to improve cardiovascular performance for a layman who runs. So I know that after I work out, I should eat protein to help get stronger, and I was wondering if the same advice pertains to my heart after a cardio workout.",
"The article, it seems, focuses on the fact that this ",
" happen to athletes with intense training."
] |
[
"Fun fact, Sectarian the horse (won a bunch of races and) was found to have this condition (this was found after his death)"
] |
[
"Due to Climate Change, How Long Before Some Places Are Uninhabitable Due to Temperature?"
] |
[
false
] |
More specifically, high temperatures - I know that some places have recorded individual temperatures over 120, but I'm talking about over a prolonged period of time. Any ideas on how soon/where?
|
[
"There's no specific temperature at which a place becomes uninhabitable. Death Valley already exists--but it's a tourist attraction."
] |
[
"It's not so much straight temperature that's important, it's wet bulb temperature. This is temperature taking into account evaporative cooling- important because humans sweat and can survive higher temperatures through evaporative cooling. A human can survive very high temperatures in dry air, but a wet-bulb temperature of more than 95 degrees F is lethal after a few hours even for healthy, hydrated people in moving air. ",
"Currently no place on earth experiences this, because hot areas tend to be drier. But it's thought that we will start to see heatwaves passing this temperature in the Persian Gulf ",
"by 2100",
"."
] |
[
"Anywhere where humans currently reside, they could easily adapt to an increase of 1-5 degrees K/C. The problem is more about self sustaining, when local crops or ecosystems crumble, if they do. Any question regarding raise in temperature works on almost a global scale, what happens when we lose 5 % of our agriculture to swift temperature change? There are theories of areas dependent on the currents that might disappear due to loss of salt water, going cold, and frozen (like scandinavia if the gulf stream slows down). ",
"Most areas in which people live in today, that are exceedingly warm, have local agriculture (and also sufficient fresh water to support it) or import their food. The former could suffer, but if it did, then any areas depending on them for food would follow. "
] |
[
"[Chemistry/Physics] What is an effective way of separating carbon isotopes on a small scale in a lab?"
] |
[
false
] |
[deleted]
|
[
"Are you looking to get pure ",
" ",
"C? That'll be a challenge. You can buy highly enriched ",
"C containing compounds, but reducing them all the way down to pure elemental carbon on the lab scale will not be easy."
] |
[
"Extracting pure carbon from molecules with C13 only is way easier than doing isotope separation on your own.",
"@",
"u/grandmasteroftea",
":",
"on a small scale in a lab?",
"Forget it."
] |
[
"If you think about it, the easiest way to get ",
"C is some kind of distillation of a molecule containing a single carbon atom. Your choices are CO, CO2, methanol, formaldehyde, formic acid, maybe formamide or urea.",
"If I had to guess, I would imagine that the infrastructure already in place to generate pure CO2 can be co-opted to \"refine\" ",
"CO2 (certainly you can buy cylinders of ",
"CO2 for not too much money) and that feeding this ",
"CO2 into some kind of fermentation bioreactor is how the ",
"C-labelled glucose is generated.",
"The big challenge of what the OP is asking is (IMO) reducing whatever your ",
"C source is, down to elemental carbon. That is not at all easy to do on the lab scale. "
] |
[
"Can ice be compressed into water?"
] |
[
false
] |
I have wondered about this for some time. Since ice is not as dense as water and it forms a crystal structure, I was wondering if you applied enough pressure, could you break the structure and turn the ice back into water?
|
[
"Yes it can! The phase of water, whether solid, liquid, or gas, is a function of both temperature and pressure. ",
"Here",
" is the phase diagram for water. It will show that above ~100kbar (100,000 times normal atmospheric pressure), water will be solid, as in ice, no matter what temperature. ",
"EDIT: Oops, I misread the question, so here is a more specific answer. The answer is yes, increasing pressure can \"melt\" ice into water, but only in very specific circumstances. For example, if you were to keep water at the constant temperature of 260k. At low pressures, this will be in the gas form. If you were to increase pressure, the gas will become solid at ~0.001 bar, then at ~1500 bar it will change to liquid, and then back to solid at ~4000 bar"
] |
[
"Pressure, along with friction, is also part of the reason why ice skates work the way they do (or so we think). The blade has a very small surface area and a person is relatively heavy. Since pressure = force/area you can see the pressure exerted by the ice skate blades is very large. The pressure slightly compresses the ice underneath the skates, melting a bit of it to provide a slick surface for the blade to slide on.\nSource: ",
"http://en.wikipedia.org/wiki/Premelting#Ice_skating"
] |
[
"I suspect that the reason that snow melts when you pack it is that heat from your hand transfers to the snow. Unless the snow is sitting right at 0 C, you would have to impart an incredible pressure to compress it into water. This is clearly not what happens because even a well packed snowball contains a lot of air. If you were to push a snowball hard enough to turn it into water, this air would be forced out."
] |
[
"How loud is your pulse in decibels?"
] |
[
false
] |
If you you could link to an article or something, that'd be great. Also, some bonus questions that I have: How loud is your breathing? and How is our hearing absolute threshold measured?
|
[
"From what point? From inside your skull where if it's quiet enough you can hear your own blood flow and vibrations travel through your bones? Or from immediately next to the heart, in open air? Same goes for breathing. You hear it, but it would be extremely difficult to measure the vibrations going through your bones. The way I would do it is put a sensitive contact microphone and measure the signal in dBu. If I can get access to one in the next week, I'll PM you but I don't think I know anyone with one sensitive enough to measure something like that. ",
"Sidenote: To answer the \"absolute hearing threshold.\" If you go to an audiologist, they can perform a special hearing test on you. There are two components to the quality of a transducer like your ear, one being the dynamic range or difference in maximum and minimum pressure required to trigger it, and frequency response. One of the tests is to see how softly you can hear a single tone. When I went it was a lower mid range frequency, around 400 Hz but I'm ballparking. Audiologists, please step in to correct me. ",
"The \"absolute\" threshold of hearing is the bare minimum change in pressure it takes to move the hairs inside your ear. It's different in different people, in different ages and stages of deterioration. It's measured by playing very quiet tones, measuring the point where one can't hear them anymore, and using that data to draw an average. ",
"One thing I do not know but would like to is if it's different across the whole spectrum of hearing. I know that humans perceive loudness differently across the spectrum, meaning different frequencies at the same level won't sound like they're the same volume. I wonder whether it's due to the inner ear's frequency response or if it's from the brain's own interpretation of the signals from the ear. Or in audio terms, is it the microphone or the amplifier that's messing with perception?"
] |
[
"I'm an acoustical engineer, and I have studied psychoacoustics. So I can comment on some of this.",
"It's definitely possible to measure the vibration of a pulse, this is how stethoscopes work. The only difference here is we would be converting it to an electrical signal. The problem would be getting it into a meaningful measurement. You'd get different readings on different parts of the body. So which one is right?"
] |
[
"This is not an answer as to what the lower limit of audibility is, but I do have the answer to the ",
"range of human hearing",
"."
] |
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